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Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, authorized	10,000,000	10,000,000
Preferred stock, issued	0	0
Preferred stock, outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, authorized	150,000,000	150,000,000
Common stock, issued	44,654,000	43,916,000
Common stock, outstanding	44,654,000	43,916,000

Common Stock

12 Months Ended

Dec. 31, 2023

Equity [Abstract]

Common Stock

8. Common Stock

As of December 31, 2023 and 2022, the authorized capital stock of the Company included 150,000,000 shares of common stock, $0.0001 par value, and 10,000,000 shares of undesignated preferred stock. As of December 31, 2023 and 2022, no undesignated shares of preferred stock were outstanding.

In accordance to the Fourth Amended and Restated Certificate of Incorporation, the holders of the common stock shall have the exclusive right to vote for the election of directors of the Company and on all other matters requiring stockholder action, each outstanding share entitling the holder thereof to one vote on each matter properly submitted to the stockholders of the Company for their vote; provided, however, that, except as otherwise required by law, holders of common stock, as such, shall not be entitled to vote on any amendment to any amendment to a certificate of designations of any series of undesignated preferred stock that alters or changes the powers, preferences, rights or other terms of one or more outstanding series of undesignated preferred stock if the holders of such affected series of undesignated preferred stock are entitled to vote, either separately or together with the holders of one or more other such series, on such amendment pursuant to a certificate of designations of any series of undesignated preferred stock.

Through December 31, 2023, no cash dividends have been declared or paid.

Public Offerings

In July 2019, the Company closed an underwritten public offering of 7,475,000 shares of its common stock at a public offering price of $18.50 per share (the “July 2019

Follow-on

Offering”), which included 975,000

shares of the Company’s common stock resulting from the full exercise of the underwriters’ option to purchase additional shares at the public offering price, less underwriting discounts and commissions. The net proceeds to the Company from the July 2019

Follow-on

Offering, after deducting underwriting discounts and commissions and other offering expenses payable by the Company, were $129,464.

In February 2020, the Company closed an underwritten public offering of 4,350,000 shares of its common stock at a public offering price of $23.00 per share (the “February 2020

Follow-on

Offering”). The net proceeds to the Company from the February 2020

Follow-on

Offering, after deducting underwriting discounts and commissions and other offering expenses payable by the Company, were $93,627.

In June 2020, the Company sold an aggregate of 384,140 shares of common stock under its 2019

“at-the-market”

facility (the “2019 ATM Facility”) for net proceeds, after deducting commissions and other offering expenses payable by the Company, of $8,130.

In November 2020, the Company closed an underwritten public offering of 5,000,000 shares of its common stock at a public offering price of $15.00 per share (the “November 2020

Follow-on

Offering”). The net proceeds to the Company from the November 2020

Follow-on

Offering, after deducting underwriting discounts and commissions and other offering expenses payable by the Company, were $70,221.

In May 2021, the Company sold an aggregate of 1,829,268 shares of common stock under the 2019 ATM Facility for net proceeds, after deducting commissions and other offering expenses payable by the Company, of $14,550.

There were no public offerings during the years ended December 31, 2023 and 2022.

Common Stock Reserved for Future Issuance

As of December 31, 2023 and 2022, the Company has reserved the following shares of common stock for future issuance:


	December 31,
	2023		2022
Shares reserved for exercise of outstanding stock options		5,142,272		9,423,271
Shares reserved for vesting of restricted stock units		936,358		940,392
Shares reserved for issuance under the 2018 Stock Option and Incentive Plan		7,978,667		5,005,295
Shares reserved for issuance under the 2018 Employee Stock Purchase Plan		1,771,748		1,467,026
Shares reserved for issuance under the 2019 Inducement Plan		1,407,211		786,656
Shares reserved for issuance under the 2020 Inducement Plan		1,700,000		1,637,000

Total shares of authorized common stock reserved for future issuance		18,936,256		19,259,640

- Definition

The entire disclosure for equity.

+ References

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+ Details

401(k) Savings Plan - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Retirement Benefits [Abstract]
Defined contribution plan, description	Currently, the Company makes matching contributions at a rate of 50% of the first 8% of employee contributions.
Employer matching contribution, percent of match	50.00%
Percent of employee contributions	8.00%
Defined contribution plan, expense	$ 388	$ 599

Net Income (Loss) per Share

12 Months Ended

Dec. 31, 2023

Earnings Per Share [Abstract]

Net Income (Loss) per Share

13. Net Income (Loss) per Share

The following table sets forth the computation of the Company’s basic and diluted net income (loss) per share for the years ended December 31, 2023 and 2022 (in thousands, except share and per share amounts):


	Year Ended December 31,
	2023		2022
Numerator:
Net income (loss) attributable to common stockholders—basic and diluted	$	12,157	$	(105,890	)

Denominator:
Weighted-average common shares outstanding—basic		44,327,204		43,738,739
Effect of dilutive securities:
Options to purchase common shares		119,677		—
Unvested restricted stock units		95,010		—
Employee stock purchase plan		26,027		—

Weighted-average common shares outstanding—diluted		44,567,918		43,738,739

Net income (loss) per share applicable to common stockholders—basic	$	0.27	$	(2.42	)
Net income (loss) per share applicable to common stockholders—diluted	$	0.27	$	(2.42	)

Diluted earnings per share includes the assumed exercise of dilutive options, the assumed issuance of unvested restricted stock units, and the assumed issuance of shares under the employee stock purchase plan using the treasury stock method unless the effect is anti-dilutive. The treasury stock method assumes that proceeds, including cash received from the exercise of employee stock options and the average unrecognized compensation expense for unvested share-based compensation awards, would be used to purchase the Company’s common stock at the average market price during the period.

For the year ended December 31, 2022, for purposes of the diluted net income (loss) per share calculation, stock options, unvested restricted stock units are considered to be common stock equivalents but have been

excluded from the calculation of diluted net loss per share, as their effect would be anti-dilutive for all periods presented. Therefore, the weighted-average number of common shares outstanding used to calculate both basic and diluted net income (loss) per share attributable to common stockholders is the same.

The following potentially dilutive common stock equivalents, presented based on amounts outstanding at each period end, were excluded from the computation of diluted net income (loss) per share attributable to common stockholders for the periods indicated:


	Year Ended December 31,
	2023		2022
Options to purchase common stock		3,765,482		9,423,271
Restricted stock units		662,103		940,392

Total anti-dilutive shares		4,427,585		10,363,663

Net Income (Loss) Per Share - Schedule of Dilutive Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	4,427,585	10,363,663
Options to Purchase Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	3,765,482	9,423,271
Restricted Stock Awards and Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	662,103	940,392

Stock-Based Compensation - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding [Roll Forward]
Number of options, Outstanding beginning balance	9,423,271
Number of options, Granted	123,501
Number of options, Exercised	(297,604)
Number of options, Cancelled or forfeited	(4,106,896)
Number of options, Outstanding ending balance	5,142,272	9,423,271
Number of options, Exercisable	3,670,053
Weighted average exercise price, Outstanding beginning balance	$ 7.26
Weighted average exercise price, Granted	1.09
Weighted average exercise price, Exercised	0.79
Weighted average exercise price, Cancelled or forfeited	7.44
Weighted average exercise price, Outstanding ending balance	7.33	$ 7.26
Weighted average exercise price, Exercisable	$ 8.84
Weighted average remaining contractual term, Outstanding balance	6 years 2 months 26 days	8 years 1 month 20 days
Weighted average remaining contractual term, Exercisable	5 years 5 months 8 days
Aggregate intrinsic value, Outstanding balance	$ 663	$ 22
Aggregate intrinsic value, Exercisable	$ 376

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Taxes [Line Items]
Deferred income tax expense (benefit)		$ 0
Deferred tax assets change in valuation allowance		23,802
Decreased deferred tax assets valuation allowance	$ 6,037
Current Income Tax Expense	377
Deferred tax assets, operating loss carryforwards, domestic	298,282	340,350
Payroll tax liability capped per year	250
Income tax reconciliation tax credit research	$ 250
Income tax credit carryforward expiration period	20 years
Percentage of cumulative changes in ownership interest subject to annual limitation	50.00%
Period of cumulative changes in ownership interest	3 years
U.S. federal [Member]
Income Taxes [Line Items]
Research and development tax credits carryforwards	$ 6,395	6,824
Orphan Drug Credit [Member] \| U.S. federal [Member]
Income Taxes [Line Items]
Research and development tax credits carryforwards	2,162
Expiration Through 2039 [Member]
Income Taxes [Line Items]
Deferred tax assets, operating loss carryforwards, state	277,626	316,668
Expiration Through 2033 [Member] \| State [Member]
Income Taxes [Line Items]
Research and development tax credits carryforwards	$ 2,482	$ 2,084

Restructuring - Additional Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($) Number	Oct. 31, 2023 Number	Jul. 12, 2023
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	$ 5,058
Accrued remaining payments	0
Company workforce reduction \| Number		11
Research and Development Expense [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	1,093
Board Of Director Chairman [Member]
Restructuring Cost and Reserve [Line Items]
Company workforce reduction			50.00%
Employee Severance and Other Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	479
Accrued remaining payments	0
July 2023 Workforce Reduction [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	3,015
July 2023 Workforce Reduction [Member] \| Research and Development Expense [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	1,800
July 2023 Workforce Reduction [Member] \| General and Administrative Expense [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	1,215
December Two Thousand Twenty Three Workforce Reduction [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	950
Expense related to future one-time employee benefits	86
Accrued remaining payments	$ 521
Company workforce reduction \| Number	8
December Two Thousand Twenty Three Workforce Reduction [Member] \| Research and Development Expense [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	$ 866
December Two Thousand Twenty Three Workforce Reduction [Member] \| General and Administrative Expense [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	$ 64

Note Payable (Tables)

12 Months Ended

Dec. 31, 2023

Debt Disclosure [Abstract]

Carrying Value of Note Payable

As of December 31, 2022 the carrying value of the note payable consists of the following:


	December 31, 2022
Note payable, including End of Term Charge	$	16,350
Debt discount, net of accretion		(1,074	)

Note payable, net of discount, long-term	$	15,276

Income Taxes - Schedule of Reconciliation of Income Tax Expense (Benefit) (Detail)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Federal income tax expense at statutory rate	21.00%	21.00%
State income taxes, net of federal benefit	3.70%	5.20%
Permanent differences	4.40%	(1.20%)
Foreign rate differential	(0.40%)	0.00%
Research and development tax credits	(4.30%)	0.80%
Change in valuation allowance	(48.20%)	(25.80%)
Stock based compensation	37.00%	0.00%
State rate changes	8.00%	0.00%
Deferred true ups	(2.20%)	0.00%
Provision to Return	0.00%	0.00%
Effective income tax rate	3.00%	0.00%

Nature of the Business - Additional Information (Detail) $ in Thousands			12 Months Ended
	Jun. 09, 2023 USD ($)	May 19, 2023 USD ($)	Dec. 31, 2023 USD ($)	Oct. 31, 2023 Number	Jul. 31, 2023	Dec. 31, 2022 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Accumulated deficit			$ (477,275)			$ (489,432)
Cash and cash equivalents			98,020			$ 92,563
Gain loss on recognize assets sales		$ 83,736	3,764
Reduction in workforce, percentage					50.00%
Company workforce reduction \| Number				11
Asset Purchase Agreement [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Cash payment of closing the transaction		$ 87,500
Gain loss on recognize assets sales	$ 83,736		$ 3,764
Company workforce reduction \| Number				8

- Definition

Amount of accumulated undistributed earnings (deficit).

+ References + Details

Net Income (Loss) per Share (Tables)

12 Months Ended

Dec. 31, 2023

Earnings Per Share [Abstract]

Components of Basic and Diluted Earnings Per Share


	Year Ended December 31,
	2023		2022
Numerator:
Net income (loss) attributable to common stockholders—basic and diluted	$	12,157	$	(105,890	)

Denominator:
Weighted-average common shares outstanding—basic		44,327,204		43,738,739
Effect of dilutive securities:
Options to purchase common shares		119,677		—
Unvested restricted stock units		95,010		—
Employee stock purchase plan		26,027		—

Weighted-average common shares outstanding—diluted		44,567,918		43,738,739

Net income (loss) per share applicable to common stockholders—basic	$	0.27	$	(2.42	)
Net income (loss) per share applicable to common stockholders—diluted	$	0.27	$	(2.42	)

Schedule of Dilutive Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Share


	Year Ended December 31,
	2023		2022
Options to purchase common stock		3,765,482		9,423,271
Restricted stock units		662,103		940,392

Total anti-dilutive shares		4,427,585		10,363,663

Supplemental Balance Sheet Information - Summary of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Supplemental Balance Sheet Information Disclosures [Abstract]
Prepaid research and development expenses	$ 572	$ 4,509
Prepaid insurance	816	999
Prepaid compensation benefits	0	327
Tax incentive refund, net of reserve	0	269
Other current assets	570	1,008
Prepaid expenses and other current assets	$ 1,958	$ 7,112

Income Taxes

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Income Taxes

12. Income Taxes

For the year ended December 31, 2023, the Company recorded $377 of current income tax expense as a result of the Asset Sale completed on June 9, 2023, and for the year ended December 31, 2022, the Company did not record a current income tax expense or (benefit) due to current and historical losses incurred by the Company. For the years ended December 31, 2023 and 2022 the Company did not record a deferred income tax expense or (benefit) due to current and historical losses incurred by the Company. The Company’s operations are predominantly based in the United States and the Company’s foreign subsidiaries generated

de minimis

losses for the years ended December 31, 2023 and 2022.

A reconciliation of income tax expense (benefit) computed at the statutory federal income tax rate to the Company’s effective tax rate as reflected in the consolidated financial statements is as follows:


	Year Ended December 31,
	2023			2022
Federal income tax expense at statutory rate		21.0	%		21.0	%
State income taxes, net of federal benefit		3.7			5.2
Permanent differences		4.4			(1.2	)
Foreign rate differential		(0.4	)		—
Research and development tax credits		(4.3	)		0.8
Change in valuation allowance		(48.2	)		(25.8	)
Stock based compensation		37.0			—
State rate changes		(8.0	)		—
Deferred true ups		(2.2	)		—
Provision to return		—			—

Effective income tax rate		3.0	%		—	%

Deferred taxes are recognized for temporary differences between the basis of assets and liabilities for financial statement and income tax purposes. The significant components of the Company’s deferred tax assets and liabilities are comprised of the following:


	December 31,
	2023			2022
Deferred tax assets:
U.S., foreign and state net operating loss carryforwards	$	80,185		$	91,416
Research and development credits		8,356			8,471
Capitalized start up and organizational costs		21			23
Equity based compensation		313			3,610
Licensing agreements		3,710			3,929
Section 174 R&D capitalization		25,045			16,307
Lease liability		240			227
Accruals and other		906			1,032

Total deferred tax assets		118,776			125,015
Valuation allowance		(118,658	)		(124,695	)

Net deferred tax assets	$	118		$	320

Deferred tax liabilities:
Property and equipment	$	—		$	(102	)
ROU Asset		(118	)		(218	)

Total deferred tax liabilities		(118	)		(320	)

Net deferred tax liabilities	$	—		$	—

The Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets. As of December 31, 2023 and 2022 based on the Company’s history of operating losses, the Company has concluded that it is not more likely than not that the benefit of its deferred tax assets will be realized. Accordingly, the Company has provided a full valuation allowance for deferred tax assets as of December 31, 2023 and 2022. The valuation allowance decreased by $6,037 during the year ended December 31, 2023, due primarily to net operating income, and increased by $23,802 during the year ended December 31, 2022, due primarily to net operating losses generated.

As of December 31, 2023 and 2022, the Company had U.S. federal net operating loss carryforwards of $298,282 and $340,350, respectively, that may be available to offset future income tax liabilities. All of the U.S. federal tax operating losses can be carried forward indefinitely. As of December 31, 2023 and 2022, the Company also had U.S. state net operating loss carryforwards of $277,626 and $316,668, respectively, which may be available to offset future taxable income. These losses expire at various dates beginning in 2041.

As of December 31, 2023 and 2022, the Company had federal research and development tax credit carryforwards of $6,395 and $6,824, respectively. Included in the $6,395 of federal tax credit carryforwards are $2,162 of orphan drug credits. Through the year ended December 31, 2020 the Company qualifies for, and has elected to, apply part of its federal research credits against its payroll tax liability in accordance with certain provisions of the Internal Revenue Code. The amount applied towards the Company’s payroll tax liability is capped at $250 per year. The federal research credits generated in excess of the $250 cap are able to be carried forward for 20 years. As of December 31, 2023 and 2022, the Company had state research and development tax credit carryforwards of approximately $2,482 and $2,084, respectively, available to reduce future tax liabilities which expire at various dates beginning in 2035. For all years through December 31, 2023, the Company generated research credits but has not conducted a study to document the qualified activities. This study may result in an adjustment to the Company’s research and development credit carryforwards.

Under the provisions of the Internal Revenue Code, the net operating loss and tax credit carryforwards are subject to review and possible adjustment by the Internal Revenue Service and state tax authorities. Net operating loss and tax credit carryforwards may become subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant shareholders over a three-year period in excess of 50 percentage points, as defined under Sections 382 and 383 of the Internal Revenue Code, respectively, as well as similar state provisions. This could limit the amount of tax attributes that can be utilized annually to offset future tax liabilities. The amount of the annual limitation is determined based on the value of the Company immediately prior to the ownership change. The Company performed an analysis to determine if an ownership change and subsequent limitation of its attributes had occurred. Subsequent ownership changes may further affect the limitation in future years. The Company has completed numerous financings since its inception, which may have resulted in a change in control as defined by Sections 382 and 383 of the Internal Revenue Code, or could result in a change in control in the future and may result in a limitation in future years.

The Company files income tax returns in the United States, Australia and Canada, and in several states. The foreign, federal and state income tax returns are generally subject to tax examinations for the tax years ended December 31, 2020 through December 31, 2023. To the extent the Company has tax attribute carryforwards, the tax years in which the attribute was generated may still be adjusted upon examination by foreign tax authorities, the Internal Revenue Service, or state tax authorities to the extent utilized in a future period.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//740/tableOfContent

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-14

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 21
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-21

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 270
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482526/740-270-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 17
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-17

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I.5.Q1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-2

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482603/740-30-50-2

+ Details

Restructuring - Schedule of Restructuring Activities (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	$ 5,058
Employee Severance And Other Benefit [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	479
Cash Payments	(4,058)
Liability included in accrued expenses and other current liabilities at December 31, 2023	$ 521

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References + Details

Consolidated Statements Of Operations And Comprehensive Income (Loss) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Operating expenses:
Research and development	$ 47,700	$ 72,186
General and administrative	23,967	33,248
Total operating expenses	71,667	105,434
Gain on asset sale	83,736	0
Loss on impairment	(1,877)	0
Income (loss) from operations	10,192	(105,434)
Other income (expense):
Interest income (expense), net	2,420	(299)
Other expense, net	(78)	(157)
Total other income (expense), net	2,342	(456)
Income (loss) before income taxes	12,534	(105,890)
Provision for income tax expense	377	0
Net income (loss) and comprehensive income (loss) attributable to common stockholders-basic and diluted	$ 12,157	$ (105,890)
Net income (loss) per share applicable to common stockholders-basic	$ 0.27	$ (2.42)
Net income (loss) per share applicable to common stockholders diluted	$ 0.27	$ (2.42)
Weighted-average common shares outstanding basic	44,327	43,739
Weighted-average common shares outstanding-diluted	44,568	43,739

Supplemental Balance Sheet Information - Summary of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	$ 6,706	$ 6,698
Less: Accumulated depreciation and amortization	(4,421)	(3,804)
Impairment	(937)	0
Sale of assets	(1,348)	0
Property and equipment, net	0	2,894
Laboratory and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	5,973	5,967
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	629	629
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	$ 104	$ 102

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Jan. 01, 2024	Dec. 31, 2023	Dec. 31, 2022	Apr. 16, 2020
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Common stock reserved for issuance		18,936,256	19,259,640
Number of options granted		123,501
Aggregate intrinsic value of options exercised		$ 123	$ 50
Options Granted, Weighted-average grant-date fair value		$ 0.79	$ 0.99
Total fair value of restricted stock awards and restricted stock units vested		$ 1,449	$ 9
Unrecognized stock-based compensation expenses		$ 4,221
Unrecognized stock-based compensation expense, period for recognition		1 year 7 months 6 days
Restricted Stock [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Unvested restricted stock awards		0
2018 Stock Option and Incentive Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Number of common shares that may be issued under the plan		616,300
Common shares available for future grant		7,978,667
Number of shares of common stock outstanding, increase, percentage		4.00%
Common stock reserved for issuance		7,978,667	5,005,295	3,300,000
Number of options granted		123,501	5,369,650
Allocate additional shares	0
2015 Stock Option and Grant Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Number of common shares that may be issued under the plan		2,008,564
Common shares available for future grant		0
Option vesting period		4 years
2018 Employee Stock Purchase Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Common shares available for future grant		1,771,748
Employee Stock Purchase Plan, description		The ESPP provides that the number of shares reserved and available for issuance will automatically increase each January 1, beginning on January 1, 2019 and each January 1 thereafter through January 1, 2028, by the least of (i) 1% of the outstanding number of shares of our common stock on the immediately preceding December 31; (ii) 1,115,700 shares or (iii) such number of shares as determined by the ESPP administrator (the “ESPP Evergreen”)
Number of common shares issued		134,439	120,947
2018 Employee Stock Purchase Plan [Member] \| Maximum [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Number of common shares that may be issued under the plan		223,200
Number of shares of common stock outstanding, increase, percentage		1.00%
Number of common shares that may increase under the plan		1,115,700
2019 Inducement Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Number of common shares that may be issued under the plan		1,800,000
Common shares available for future grant		1,407,211
2020 Inducement Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Number of common shares that may be issued under the plan		1,700,000
Common shares available for future grant		1,700,000

Stock-Based Compensation

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Stock-Based Compensation

9. Stock-Based Compensation

Amended and Restated 2015 Stock Option and Grant Plan

The Company’s Amended and Restated 2015 Stock Option and Grant Plan, (the “2015 Plan”) provides for the Company to issue restricted stock awards and restricted stock units, or to grant incentive stock options or

non-statutory

stock options. Incentive stock options may be granted only to the Company’s employees including officers and members of the Board who are also employees. Restricted stock awards and restricted stock units and

non-statutory

stock options may be granted to employees, members of the Board, outside advisors, and consultants of the Company.

The total number of common shares that may be issued under the 2015 Plan was 2,008,564 shares. Following the IPO, no further grants have been made under 2015 plan.

Shares that expire, are terminated, surrendered or cancelled under the 2015 Plan without having been fully exercised will be available for future awards under the 2018 Plan (as defined below). In addition, shares of common stock that are tendered to the Company by a participant to exercise an award are added to the number of shares of common stock available for future awards.

The 2015 Plan is administered by the Board. Equity awards granted to employees and members of the Board typically vest over four years.

2018 Stock Option and Incentive Plan

The Company’s 2018 Stock Option and Incentive Plan (the “2018 Plan”) was adopted by the Board on June 1, 2018 and approved by stockholders on June 7, 2018 and became effective upon the effectiveness of the Company’s Registration Statement on Form

S-1.

The 2018 Plan replaced the 2015 Plan as the Board determined not to make additional awards under the 2015 Plan following the pricing of the Company’s IPO. The 2018 Plan allows the Board, compensation committee or other designated committee to make equity-based and cash-based incentive awards to its officers, employees, directors and other key persons (including consultants).

The Company initially reserved 616,300 shares of its common stock for the issuance of awards under the 2018 Plan. The 2018 Plan provides that the number of shares reserved and available for issuance under the plan will automatically increase each January 1, beginning on January 1, 2019, by 4% of the outstanding number of shares of our common stock on the immediately preceding December 31, or such lesser number of shares as determined by its Board or compensation committee (the “Plan Evergreen”). This number is subject to adjustment in the event of a stock split, stock dividend or other change in its capitalization.

On April 16, 2020, the Board adopted an amendment to the 2018 Plan (the “Amendment”), to (i) increase the number of shares of common stock currently reserved for issuance under the 2018 Plan by 3,300,000 shares and (ii) automatically terminate the 2018 Plan’s annual increase (or “evergreen”) provision after January 2022. The Amendment was approved by the Board on June 4, 2020 and the Company’s stockholders on June 4, 2020.

The number of shares of common stock available for future grant under the 2018 Plan was 7,978,667 as of December 31, 2023, which does not include the shares added to the 2018 Plan reserve on January 1, 2024 as a result of the Plan Evergreen for the year ended December 31, 2023.

During the years ended December 31, 2023 and 2022, the Company granted options to purchase 123,501 and, 5,369,650 shares, respectively, of common stock to employees, nonemployees and members of the Board.

2018 Employee Stock Purchase Plan

The Company’s 2018 Employee Stock Purchase Plan (the “ESPP”) was adopted by the Board on June 1, 2018 and approved by stockholders on June 7, 2018 and became effective upon the effectiveness of the Company’s Registration Statement on Form

S-1.

The ESPP is intended to qualify as an “employee stock purchase plan” within the meaning of Section 423(b) of the Code. The ESPP initially reserves and authorizes the issuance of up to a total of 223,200 shares of common stock to participating employees.

The ESPP provides that the number of shares reserved and available for issuance will automatically increase each January 1, beginning

on January 1, 2019 and each January 1 thereafter through January 1, 2028, by the least of (i) 1% of the outstanding number of shares of our common stock on the immediately preceding December 31; (ii) 1,115,700 shares or (iii) such number of shares as determined by the ESPP administrator (the “ESPP Evergreen”). With respect to the January 1, 2024 ESPP Evergreen, the Company’s Compensation Committee opted to allocate zero additional shares to the ESPP share reserve. The number of shares reserved under the ESPP is subject to adjustment in the event of a stock split, stock dividend or other change in the Company’s capitalization.

During the years ended December 31, 2023 and 2022, the Company issued 134,439 and 120,947 shares, respectively of common stock. The total number of shares of common stock available for future grant was 1,771,748 as of December 31, 2023.

2019 Inducement Plan

The Company’s 2019 Inducement Plan (the “2019 Plan”) was adopted by the Board on December 11, 2019. The purpose of the 2019 Plan is to allow the Company to grant equity awards to new employees as inducements material to such new employee’s acceptance of employment with the Company. The Company intends that the shares underlying the 2019 Plan be reserved for persons to whom the Company may issue securities without stockholder approval as an inducement pursuant to Rule 5635(c)(4) of the Nasdaq marketplace rules.

The Company initially reserved 1,800,000 shares of its common stock for the issuance of awards under the 2019 Plan.

The number of shares of common stock available for future grant under the 2019 Plan was 1,407,211 as of December 31, 2023.

2020 Inducement Plan

The Company’s 2020 Inducement Plan (the “2020 Plan”) was adopted by the Board on December 9, 2020. The purpose of the 2020 Plan is to allow the Company to grant equity awards to new employees as inducements material to such new employee’s acceptance of employment with the Company. The Company intends that the shares underlying the 2020 Plan be reserved for persons to whom the Company may issue securities without stockholder approval as an inducement pursuant to Rule 5635(c)(4) of the Nasdaq marketplace rules.

The Company initially reserved 1,700,000 shares of its common stock for the issuance of awards under the 2020 Plan.

The number of shares of common stock available for future grant under the 2020 Plan was 1,700,000 as of December 31, 2023.

Stock Option Valuation

The assumptions that the Company used to determine the grant-date fair value of stock options granted to employees and members of the Board were as follows, presented on a weighted-average basis:


	Year Ended December 31,
	2023			2022
Expected option life (years)		6.00			5.98
Risk-free interest rate		3.82	%		2.47	%
Expected volatility		83.36	%		80.43	%
Expected dividend yield		—	%		—	%

The following table summarizes the Company’s stock option activity for the year ended December 31, 2023:


	Number of Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
Outstanding as of December 31, 2022		9,423,271		$	7.26		8.14	$	22
Granted		123,501		$	1.09
Exercised		(297,604	)	$	0.79
Cancelled or forfeited		(4,106,896	)	$	7.44

Outstanding as of December 31, 2023		5,142,272		$	7.33		6.24	$	663

Exercisable as of December 31, 2023		3,670,053		$	8.84		5.44	$	376

The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the underlying stock options and the estimated fair value of the Company’s common stock for those stock options that had exercise prices lower than the estimated fair value of the Company’s common stock.

The aggregate intrinsic value of options exercised during the years ended December 31, 2023 and 2022 was $123 and $50, respectively.

The weighted-average grant-date fair value of the Company’s stock options granted during the years ended December 31, 2023 and 2022 was $0.79 and $0.99, respectively.

Restricted Common Stock

The Company has granted restricted common stock (or restricted stock awards) with time-based vesting conditions to certain employees of the Company.

The purchase price of the restricted stock awards are determined by the Board. Unvested shares of restricted stock awards may not be sold or transferred by the holder. These restrictions lapse according to the time- based vesting conditions of each award. The Company has the option to repurchase the restricted stock awards at the original purchase price if the grantee terminates its working relationship with the Company prior to the vesting date. There were no unvested restricted stock awards as of December 31, 2023.

Restricted Stock Units

Restricted stock units represent an unsecured promise to grant at no cost a set number of shares of common stock upon vesting. With respect to restricted stock units, recipients are not entitled to cash dividends and have no voting rights during the vesting period.

The following table summarizes the Company’s restricted stock award and restricted stock unit activity for the year ended December 31, 2023:


	Number of Shares			Weighted- Average Grant Date Fair Value
Issued and unvested as of December 31, 2022		940,392		$	3.62
Granted		1,548,117			1.65
Vested		(305,502	)		4.74
Forfeited, cancelled or expired		(1,246,649	)		2.02

Issued and unvested as of December 31, 2023		936,358		$	2.13

The total fair value of restricted stock awards and restricted stock units vested during the years ended December 31, 2023 and 2022 was $1,449 and $9, respectively.

Stock-Based Compensation

Stock-based compensation expense was allocated as follows:


	Year Ended December 31,
	2023		2022
Research and development	$	1,927	$	2,785
General and administrative		4,964		8,737

Total stock-based compensation expense	$	6,891	$	11,522

As of December 31, 2023, total unrecognized compensation cost related to unvested stock-based awards was $4,221, which is expected to be recognized over a weighted-average period of 1.6 years.

License and Purchase Agreements - Additional Information (Detail) £ in Thousands, $ in Thousands						1 Months Ended	3 Months Ended	12 Months Ended
	Sep. 08, 2023 GBP (£)	May 19, 2023 USD ($)	Oct. 02, 2017 USD ($)	Jan. 27, 2016 USD ($) shares	Jan. 27, 2016 CAD ($)	Aug. 31, 2017 USD ($) shares	Sep. 30, 2020 USD ($)	Dec. 31, 2023 USD ($) shares	Dec. 31, 2023 GBP (£) shares	Dec. 31, 2022 USD ($) shares	Dec. 31, 2020 USD ($)	Jan. 04, 2024 CAD ($)	Nov. 17, 2016 USD ($)	Jan. 27, 2016 CAD ($) shares
License Agreement [Line Items]
Gain loss on recognize assets sales		$ 83,736,000						$ 3,764,000
Collaborative agreement expenses								$ 1,610,000		$ 2,346,000
Common stock, issued \| shares								44,654,000	44,654,000	43,916,000
Research and development								$ 47,700,000		$ 72,186,000
Preferred stock issued \| shares								0	0	0
MPSII License Agreement [Member]
License Agreement [Line Items]
Upfront license fee											$ 8,000,000
Sale of Cystinosis Program [Member]
License Agreement [Line Items]
Cash payment of closing the transaction		$ 87,500,000
University of Manchester Agreement [Member] \| MPSII License Agreement [Member]
License Agreement [Line Items]
Milestone payments payable							$ 80,000,000
Milestone payment paid							$ 2,000,000
Research and development expense \| £	£ 3,900								£ 9,900
UHN Agreement [Member]
License Agreement [Line Items]
Research and development expense								$ 93,000		$ 161,000
Milestone fees								0		0
UHN Agreement [Member] \| Fabry License Agreement [Member]
License Agreement [Line Items]
Upfront license fee				$ 75,000
Milestone payments payable				2,450,000
Option fee				$ 20,000
Cash payment of closing the transaction												$ 194
UHN Agreement [Member] \| Interleukin 12 License Agreement [Member]
License Agreement [Line Items]
Upfront license fee					$ 264
Milestone payments payable														$ 19,275
Milestone fees								0		0
Annual maintenance fees					$ 50
Common stock, issued \| shares				1,161,665										1,161,665
Fair value of shares issued				$ 480,000
Payments upon closing of an initial public offering				$ 2,000,000
Research and development								37,000		39,000
BioMarin Pharmaceutical Inc [Member]
License Agreement [Line Items]
Upfront license fee						$ 500,000
Preferred stock issued \| shares						233,765
Milestone payments										13,000,000
Expenses related to license								0		0
GenStem Therapeutics Inc [Member]
License Agreement [Line Items]
Upfront license fee			$ 1,000,000
Milestone payments payable			$ 16,000,000
Expenses related to license								0		0
Lund University Rights Holders Agreement [Member]
License Agreement [Line Items]
Milestone payments payable													$ 550,000
Expenses related to license								$ 0		$ 0

Nature of the Business	12 Months Ended
Nature of the Business	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of the Business	1. Nature of the Business AVROBIO, Inc. (the “Company” or “AVROBIO”) is a gene therapy company which has been focused on developing potentially curative hematopoietic stem cell, or HSC, gene therapies to treat rare diseases following a single dose treatment regimen. On July 12, 2023, following a comprehensive review of the Company’s business by its Board of Directors (the “Board”), the Company announced its intention to halt development of its programs and explore strategic alternatives focused on maximizing stockholder value, which may include, but are not limited to, an acquisition, a merger, business combination or divestiture. The decision was not related to any safety or medical issues or negative regulatory feedback related to the Company’s programs. See Note 15 for further discussion. On January 30, 2024, the Company entered into the Merger Agreement with Tectonic Therapeutic, Inc. (“Tectonic”) pursuant to which a wholly-owned subsidiary of the Company will merge with and into Tectonic, with Tectonic surviving as a wholly-owned subsidiary of the Company (the “Merger”). See Note 16 for further discussion. The Company is subject to risks and uncertainties including, should it resume development of its product candidates, risks and uncertainties common to early-stage companies in the biotechnology industry, including but not limited to, risks associated with completing preclinical studies and clinical trials, receiving regulatory approvals for product candidates, development by competitors of new biopharmaceutical products, dependence on key personnel, protection of proprietary technology, compliance with government regulations and the ability to secure additional capital to fund operations. Should the Company resume development of its product candidates, significant additional research and development efforts, including preclinical and clinical testing and regulatory approval, prior to commercialization, would be required. These efforts would require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s product development efforts are successful, should the Company resume development of its product candidates, it is uncertain when, if ever, the Company would realize revenue from product sales. In accordance with the Financial Accounting Standards Board (“FASB”) Accounting Standards Update (“ASU”) 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern (Subtopic 205-40), the Company has evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date that the consolidated financial statements are issued. The Company has devoted substantially all of its efforts to research and development, business planning, acquiring operating assets, seeking protection for its technology and product candidates, and raising capital. Since inception, the Company has had recurring losses and has funded its operations through sales of preferred stock and common stock, a term loan facility and the sale of the Company’s cystinosis gene therapy program (designated AVR-RD-04) and all other assets of the Company specifically related to this program. As of December 31, 2023, the Company had an accumulated deficit of $477,275. The Company expects that its cash and cash equivalents of $98,020 as of December 31, 2023 will be sufficient to fund current planned operations and capital expenditure requirements for at least the next twelve months from the filing date of this Annual Report on Form 10-K with the Securities and Exchange Commission (“SEC”). On May 19, 2023, the Company entered into an Asset Purchase Agreement (the “Asset Purchase Agreement”) with Novartis Pharma AG and Novartis Pharmaceuticals Corporation (collectively, “Novartis”), providing for the sale of the Company’s cystinosis gene therapy program (designated AVR-RD-04) and all other assets of the Company specifically related to this program. The aggregate consideration to the Company consisted of a cash payment of $87,500 upon closing of the transaction. The Company completed the Asset Sale (as defined below) on June 9, 2023 and recognized $83,736 as a gain on asset sale, net of $3,764 transaction costs, in the consolidated statement of operations and comprehensive income (loss). See Note 3 for further discussion. In July 2023, the Board approved a reduction in the Company’s workforce by approximately 50% across different areas and functions in the Company (the “July 2023 Workforce Reduction”). The July 2023 Workforce Reduction was substantially completed by the end of July 2023. The Company informed affected employees in the July 2023 Workforce Reduction on July 12, 2023. Since the date of the July 2023 Workforce Reduction, the Company’s remaining employees have primarily focused on activities relating to halting further development of the Company’s programs, the pursuit of strategic alternatives, and the provision of services under the previously disclosed Separation Services Agreement between the Company and Novartis in connection with the sale to Novartis of the Company’s cystinosis gene therapy program. The Company’s remaining workforce was further reduced by 11 employees in a workforce reduction implemented effective as of October 31, 2023 (the “October 2023 Workforce Reduction”). The Company’s workforce was further reduced by 8 employees in the December 2023 Workforce Reduction effective as of December 31, 2023 (the “December 2023 Workforce Reduction”). Affected employees in the July 2023 Workforce Reduction, October 2023 Workforce Reduction, and December 2023 Workforce Reduction were offered separation benefits, including severance payments. See Note 15 for further discussion.

Leases - Summary of Future Minimum Lease Payments Due Under Operating Leases (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($)
Leases [Abstract]
2024	$ 896
2025	0
2026	0
2027	0
Thereafter	0
Total lease payments	896
Less: interest	(18)
Present value of lease liabilities	$ 878

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2023
Subsequent Events [Abstract]
Subsequent Events	16. Subsequent Events On January 30, 2024, following a comprehensive review of strategic alternatives, the Company entered into the Merger Agreement with Tectonic pursuant to which a wholly-owned subsidiary of the Company will merge with and into Tectonic, with Tectonic surviving as a wholly-owned subsidiary of the Company. The Merger was unanimously approved by the Company’s Board, and the Company’s Board resolved to recommend approval of the Merger Agreement to the Company’s stockholders. The closing of the Merger is subject to approval by the Company’s and Tectonic’s stockholders as well as other customary closing conditions, including the effectiveness of a registration statement on Form S-4 filed with the SEC in connection with the transaction and Nasdaq’s approval of the listing of the shares of the Company’s common stock to be issued in connection with the Merger. If the Company is unable to satisfy certain closing conditions or if other mutual closing conditions are not satisfied, Tectonic will not be obligated to complete the Merger. The Merger Agreement contains certain termination rights of each of the Company and Tectonic. Under certain circumstances detailed in the Merger Agreement, the Company could be required to pay Tectonic a termination fee of approximately $2,713 or Tectonic could be required to pay the Company a termination fee of approximately $4,900. In addition, in certain circumstances upon the termination of the Merger Agreement, the Company could be required to pay the costs and expenses of Tectonic in an amount not to exceed $650. If the Merger is completed, the business of Tectonic will continue as the business of the combined company.

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Summary of Assumptions that Used to Determine Grant-Date Fair Value of Stock Options Granted to Employees and Members of Board

The assumptions that the Company used to determine the grant-date fair value of stock options granted to employees and members of the Board were as follows, presented on a weighted-average basis:


	Year Ended December 31,
	2023			2022
Expected option life (years)		6.00			5.98
Risk-free interest rate		3.82	%		2.47	%
Expected volatility		83.36	%		80.43	%
Expected dividend yield		—	%		—	%

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity for the year ended December 31, 2023:


	Number of Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
Outstanding as of December 31, 2022		9,423,271		$	7.26		8.14	$	22
Granted		123,501		$	1.09
Exercised		(297,604	)	$	0.79
Cancelled or forfeited		(4,106,896	)	$	7.44

Outstanding as of December 31, 2023		5,142,272		$	7.33		6.24	$	663

Exercisable as of December 31, 2023		3,670,053		$	8.84		5.44	$	376

Summary of Restricted Stock Award and Restricted Stock Unit Activity

The following table summarizes the Company’s restricted stock award and restricted stock unit activity for the year ended December 31, 2023:


	Number of Shares			Weighted- Average Grant Date Fair Value
Issued and unvested as of December 31, 2022		940,392		$	3.62
Granted		1,548,117			1.65
Vested		(305,502	)		4.74
Forfeited, cancelled or expired		(1,246,649	)		2.02

Issued and unvested as of December 31, 2023		936,358		$	2.13

Schedule of Stock-based Compensation Expense

Stock-based compensation expense was allocated as follows:


	Year Ended December 31,
	2023		2022
Research and development	$	1,927	$	2,785
General and administrative		4,964		8,737

Total stock-based compensation expense	$	6,891	$	11,522

Related Party Transactions	12 Months Ended
Related Party Transactions	Dec. 31, 2023
Related Party Transactions [Abstract]
Related Party Transactions	14. Related Party Transactions UHN In connection with the Company’s entry into a license agreement with UHN on January 27, 2016, the Company issued UHN 1,161,665 shares of its common stock. Upon the closing of the IPO in 2018, as UHN’s fully-diluted percentage ownership of the Company was reduced within a range of specified percentages, the Company was obligated to pay UHN an amount of $2,000, which was paid in July 2018. For the years ended December 31, 2023 and 2022, the Company recognized $130 and $200, respectively, of research and development expense related to the license agreements with UHN. Refer to Note 3 “License and Purchase Agreements” for additional information regarding the UHN license agreements. Others For the years ended December 31, 2023 and 2022, the Company recorded expenses of $934 and $3,200, respectively, related to a sublease to rent lab space, provided by an entity affiliated with a member of the board.

- Definition

The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-5

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-6

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
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-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
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-Section 50
-Paragraph 1
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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-Publisher FASB
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
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-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(e))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//850/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-6

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

+ Details

License and Purchase Agreements	12 Months Ended
License and Purchase Agreements	Dec. 31, 2023
License Agreements [Abstract]
License and Purchase Agreements	3. License and Purchase Agreements Agreement with The University of Manchester On September 30, 2020, the Company entered into an agreement (“MPSII License Agreement”) with The University of Manchester, England (“UoM”), whereby UoM granted to the Company an exclusive worldwide license under certain patent and other intellectual property rights, subject to certain retained rights, to develop, commercialize and sell an ex vivo lentiviral gene therapy for use in the treatment of Hunter syndrome, or mucopolysaccharidosis type II (“MPSII”). As consideration for the MPSII License Agreement, the Company agreed to pay UoM an upfront, one-time fee of $8,000, which was recognized as research and development expense during the year ended December 31, 2020. As part of the agreement, the Company was obligated to make milestone payments of up to an aggregate of $80,000 upon the achievement of specified development and regulatory milestones, to pay royalties, on a product-by-product and country-by-country basis, of a mid-single digit percentage based on net sales of products licensed under the agreement and to pay a low double-digit percentage of any sublicense fees received by the Company. During the third quarter of 2022, a $2,000 milestone payment under the MPSII License Agreement became due following the date of regulatory approval of the CTA for the investigator-sponsored Phase 1/2 clinical trial sponsored by UoM. Concurrently with the MPSII License Agreement, the Company entered into a collaborative research funding agreement with UoM (“CRFA”). Under the CRFA, the Company has agreed to fund the budgeted costs of an investigator-sponsored Phase 1/2 clinical trial to be sponsored by UoM in connection with the development activities under the MPSII License Agreement, which were estimated to equal approximately £9,900 in the aggregate. On September 8, 2023 the Company and UoM terminated the MPSII License Agreement and the CFRA, and in connection with such termination, the Company paid UoM £3,900. Following the termination of the MPSII License Agreement and the CFRA, the Company does not have any remaining financial obligations to UoM. For the years ended December 31, 2023 and 2022, the Company recognized $1,610 and $2,346, respectively, of costs related to the CRFA, excluding the payment made in connection with the termination. Agreements with University Health Network (“UHN”) Fabry License Agreement— On January 27, 2016, the Company entered into an agreement with UHN, pursuant to which UHN granted the Company an option to enter into an exclusive license under the UHN intellectual property related to Fabry disease in accordance with the pre-negotiated licensing terms. On November 4, 2016, the Company exercised its option and entered into a license agreement with UHN, pursuant to which UHN granted the Company an exclusive worldwide license under certain intellectual property rights and a non-exclusive worldwide license under certain know-how, in each case subject to certain retained rights, to develop, commercialize and sell products for use in the treatment of Fabry disease. In addition, for three years following the execution of the agreement, UHN granted the Company an exclusive option to obtain a license under certain improvements to the licensed intellectual property rights as well as an option to negotiate a license under certain other improvements. Under this agreement, the Company paid an option fee of CAD$20, an upfront license fee of CAD$75, plus the annual license maintenance fee for the first year. Thereafter, the Company was also required to pay UHN future annual license maintenance fees until the first sale of a licensed product in certain markets. The Company was also obligated to make future milestone payments in an aggregate amount of up to CAD$2,450 upon the achievement of specified milestones as well as royalties on a country-by-country basis of a low to mid-single-digit percentage of annual net sales of licensed products and a lower single-digit royalty percentage in certain circumstances. Additionally, the Company had agreed to pay a low double-digit royalty percentage of all sublicensing revenue. The agreement required the Company to meet certain performance milestones within specified timeframes. UHN could terminate the agreement if the Company failed to meet these performance milestones despite using commercially reasonable efforts and the Company is unable to reach agreement with UHN on revised timeframes. The Company’s royalty obligation was to expire on a licensed product-by-licensed product and country-by-country basis upon the latest to occur of the expiration or termination of the last valid claim under the licensed intellectual property rights in such country, the tenth anniversary of the first commercial sale of such licensed product in such country and the expiration of any applicable regulatory exclusivity in such country. Unless terminated earlier, the agreement was to expire upon the expiration of the Company’s royalty obligation for all licensed products. UHN could terminate the agreement if the Company failed to make any payments within a specified period after receiving written notice of such failure, or in the event that the Company fails to obtain or maintain insurance. Either the Company or UHN could terminate the license agreement in the event of a material breach by the other party and failure to cure such breach within a certain period of time. The Company could voluntarily terminate the agreement with prior notice to UHN. Effective January 4, 2024, AVROBIO terminated the Fabry license agreement with UHN, and in connection with such termination, the Company paid UHN CAD$194. Following the termination of the agreement, AVROBIO does not have any remaining financial obligations to UHN pursuant to the Fabry license agreement. For the years ended December 31, 2023 and 2022, the Company recorded research and development expense related to this agreement with UHN of $93 and $161, respectively, which consists of reimbursable funded study trial costs and license maintenance fees. No milestone fees were incurred related to the Fabry license agreement in the years ended December 31, 2023 and 2022. Interleukin 12 License Agreement— On January 27, 2016, the Company entered into an exclusive license agreement with UHN, pursuant to which UHN granted the Company a license to certain patent rights for the commercial development, manufacture, distribution and use of any products or processes resulting from development of those patent rights related to Interleukin 12. Upon execution of this agreement, the Company paid an upfront license fee of CAD $264. In addition, as part of the initial consideration for the license, the Company issued to UHN 1,161,665 shares of the Company’s common stock and agreed to pay UHN up to $2,000 upon the closing of an IPO if certain criteria are met. The fair value of the shares issued to UHN of $480 and the upfront fee was expensed upon the execution of the agreement. Upon the closing of the Company’s initial public offering (the “IPO”) in 2018, as the criteria were met, the Company paid UHN $2,000. The Company was also required to pay UHN future annual license maintenance fees of CAD $50 on each anniversary of the effective date of the license agreement prior to expiration or termination and potential future milestone payments of up to CAD $19,275 upon the achievement of specified clinical and regulatory milestones. The Company also agreed to pay UHN royalties of a low single-digit percentage of net sales of licensed products sold by the Company. If the Company granted any sublicense rights under the license agreement, the Company agreed to pay UHN a low double-digit royalty percentage of any sublicense income received by the Company. The agreement also required the Company to meet certain diligence requirements based upon specified milestones. Effective as of August 24, 2023, the Company and UHN agreed to terminate the Interleukin 12 License Agreement, and in connection with such termination there were no payments made to UHN. Following the termination of the agreement, the Company does not have any remaining financial obligations to UHN pursuant to the Interleukin 12 License Agreement. For the years ended December 31, 2023 and 2022, the Company recorded research and development expense related to this agreement with UHN of $37 and $39, respectively, which consists of license maintenance fees. No milestone fees were incurred related to the Interleukin 12 license agreement in the years ended December 31, 2023 and 2022. Agreement with BioMarin Pharmaceutical Inc. (“BioMarin”) On August 31, 2017, the Company entered into a license agreement with BioMarin, pursuant to which BioMarin granted the Company an exclusive worldwide license under certain intellectual property rights owned or controlled by BioMarin to develop, commercialize and sell products for use in the treatment of Pompe disease. The license agreement was amended in February 2018 and again in January 2020 to, among things, provide that BioMarin would supply the Company with certain technology materials. As consideration for this agreement, the Company paid an upfront license fee of $500 in cash and issued 233,765 shares of Series B Preferred Stock to BioMarin at the time of the Company’s Series B Preferred Stock financing in January 2018. The Company is also obligated to make future milestone payments of up to $13,000 upon the achievement of certain specified milestones and agreed to pay BioMarin royalties of a low single-digit percentage of net sales of licensed products sold by the Company or its affiliates covered by patent rights in a relevant country. No expenses related to the license were recorded for the years ended December 31, 2023 and 2022. Unless terminated earlier, the agreement expires upon the expiration of the Company’s royalty obligation for all licensed products throughout the world. BioMarin and the Company can terminate the agreement in the event of a material breach by the other party and failure to cure such breach within a certain period of time. The Company may terminate the agreement at will upon written notice to BioMarin. BioMarin has the right to terminate the agreement upon the Company’s bankruptcy or insolvency, or in the event of any challenge or opposition to the licensed patent rights or related actions brought by the Company or its affiliates or sublicensees, or if the Company, its affiliates or sublicensees knowingly assist a third-party in challenging or otherwise opposing the licensed patent rights, except as required under a court order or subpoena. Agreement with Papillon Therapeutics, Inc. (previously GenStem Therapeutics, Inc.) On October 2, 2017, the Company entered into a license agreement with GenStem, pursuant to which GenStem granted the Company an exclusive worldwide license, subject to certain retained rights, under certain intellectual property rights owned or controlled by GenStem to develop, commercialize and sell products for use in the treatment of cystinosis. Under this agreement, the Company paid an upfront license fee of $1,000 and is required to make payments upon completion of certain milestones up to an aggregate of $16,000. The Company also agreed to pay GenStem a tiered mid to high single-digit royalty percentage on annual net sales of licensed products as well as a low double-digit percentage of sublicense income received from certain third-party licensees. The Company’s royalty obligation expires on a licensed product-by-licensed product and country-by-country basis on the eleventh anniversary of the first commercial sale of such licensed product in such country or the expiration of the last valid claim under the licensed patent rights covering such licensed product in such country, whichever is later. Unless terminated earlier, the agreement expires upon the expiration of the Company’s royalty obligation for all licensed products throughout the world. GenStem and the Company can terminate the agreement in the event of a material breach by the other party and failure to cure such breach within a certain period of time. The Company may terminate the agreement at will upon the specified prior written notice to GenStem. In October 2021, the Company received notice that the license agreement with GenStem had been assigned to Papillon. The license agreement with Papillon was assigned to Novartis on May 19, 2023 in conjunction with the Company’s Asset Purchase Agreement with Novartis which provided for the sale of the Company’s cystinosis gene therapy program and all other assets of the Company specifically related to this program (see “Sale of Cystinosis Program” below). No expenses related to the license were recorded for the years ended December 31, 2023 and 2022. Agreement with Lund University Rights Holders On November 17, 2016, the Company entered into a license agreement with affiliates of Lund University, along with certain other relevant rights holders that may be added from time to time, pursuant to which such rights holders granted to the Company an exclusive worldwide license, subject to certain retained rights, under certain intellectual property rights to develop, commercialize and sell products in any and all uses relevant to Gaucher disease. As consideration for the license, the Company is required to make payments in connection with the achievement of certain milestones up to an aggregate of $550. The agreement expires on the latest of (i) the twentieth anniversary of the end of a certain research project the Company is funding pursuant to an agreement with Lund University, (ii) the expiration of the term of any patent filed on the licensed rights that covers a licensed product, (iii) the expiration of any applicable marketing exclusivity right and (iv) such time that neither the Company nor any sublicensees, partners or contractors are commercializing a licensed product. Either the Company or the rights holders acting together may terminate the license agreement if the other such party commits a material breach and fails to cure such breach within a certain period of time, or if the other party enters into liquidation, becomes insolvent, or enters into composition or statutory reorganization proceedings. No expenses related to the license were recorded for the years ended December 31, 2023 and 2022. Sale of Cystinosis Program On May 19, 2023, the Company entered into the Asset Purchase Agreement with Novartis, providing for the sale of the Company’s cystinosis gene therapy program (designated AVR-RD-04) and all other assets of the Company specifically related to this program. In addition, pursuant to the Asset Purchase Agreement, the Company has granted an exclusive license to Novartis to use certain intellectual property of the Company, which consists of certain proprietary elements of the Company’s plato ® gene therapy platform technology specifically within the field of cystinosis. The foregoing transactions contemplated by the Asset Purchase Agreement are referred to as the “Asset Sale.” The Company has also agreed not to assert claims against Novartis for violations of certain other Company intellectual property rights in connection with Novartis’s exercise of the exclusive license granted to it under the Asset Purchase Agreement, and for violations of the licensed intellectual property, except in connection with activities by Novartis in the fields of Gaucher disease, Pompe disease, Hunter syndrome and Fabry disease, or indemnification claims under the Asset Purchase Agreement. The aggregate consideration to the Company consisted of a cash payment of $87,500 upon closing of the transaction. The Company recognized $83,736 as a gain on asset sale, net of $3,764 in transaction costs, in the consolidated statement of operations and comprehensive income (loss).

401(k) Savings Plan	12 Months Ended
401(k) Savings Plan	Dec. 31, 2023
Retirement Benefits [Abstract]
401(k) Savings Plan	10. 401(k) Savings Plan The Company established a defined contribution savings plan under Section 401(k) of the Internal Revenue Code. Eligible employees may make pretax contributions to the 401(k) Plan up to statutory limits. At the election of the Board, the Company may elect to match employee contributions. Currently, the Company makes matching contributions at a rate of 50% of the first 8% of employee contributions. The Company recorded $388 and $599 of expenses related to its 401(k) match for the years ended December 31, 2023 and 2022, respectively.

- Definition

The entire disclosure for retirement benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 70
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480794/715-70-50-1

Reference 2: http://www.xbrl.org/2003/role/exampleRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
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Reference 14: http://www.xbrl.org/2003/role/disclosureRef
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480266/715-60-50-3

+ Details

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Basis of Presentation

The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification (“ASC”) and ASU of FASB.

Principles of Consolidation

The accompanying consolidated financial statements include the accounts of AVROBIO, Inc. and its wholly owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation.

Segment Information

Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker, or decision-making group, in making decisions on how to allocate resources and assess performance. The Company’s chief operating decision maker is the chief executive officer (“CEO”). The Company and the CEO view the Company’s operations and manage its business as one operating segment. All material long-lived assets of the Company reside in the United States.

Use of Estimates

The preparation of financial statements in conformity with GAAP requires that the Company make estimates and judgments that may affect the reported amounts of assets, liabilities and expenses and the related disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting periods. On an

on-going

basis, the Company evaluates its estimates, judgments and methodologies. The Company bases its estimates on historical experience and on various other assumptions that are believed to be reasonable, the results of which form the basis for making judgments about the carrying values of assets and liabilities. Actual results may differ from these estimates. Changes in estimates are reflected in reported results in the period in which they become known.

Cash and Cash Equivalents

The Company considers all highly liquid investments purchased with original maturities of three months or less at acquisition to be cash equivalents. As of December 31, 2023 and 2022, cash and cash equivalents were primarily held in interest-bearing money market funds.

Concentrations of Credit Risk

The Company has no significant

off-balance

sheet risk, such as foreign exchange contracts, option contracts, or other foreign hedging arrangements. Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents and restricted cash. Periodically, the Company maintains deposits in accredited financial institutions in excess of federally insured limits. The Company deposits its cash and cash equivalents in financial institutions that it believes have high credit quality and has not experienced any losses on such accounts and does not believe it is exposed to any unusual credit risk beyond the normal credit risk associated with commercial banking relationships.

Fair Value Measurements

Certain assets and liabilities of the Company are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable:

•

Level 1— Fair values are determined utilizing prices (unadjusted) in active markets for identical assets or liabilities that the Company has the ability to access.

•

Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data.

•

Level 3—Unobservable inputs that are supported by little or no market activity that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques.

The carrying amounts of the Company’s financial instruments, which include cash equivalents, accounts payable, and accrued expenses, approximated their fair values as of December 31, 2023 and 2022 due to the

short-term

nature of these instruments.

The Company has evaluated the estimated fair value of financial instruments using available market information. The use of different market assumptions, estimation methodologies, or both, could have a significant effect on the estimated fair value amounts. See Note 4

“Fair Value of Financial Assets and Liabilities”

for further discussion.

Property and Equipment

Property and equipment are recorded at cost. Depreciation and amortization is calculated using the straight-line method over the following estimated useful lives of the assets:


		Estimated Useful Life
Laboratory and office equipment		5 years
Computer equipment		2 years
Leasehold improvements		Lesser of lease term or 10 years

Impairment of Long-Lived Assets

Long-lived assets consist of property and equipment. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset group for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset group to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset group are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset group over its fair value, determined based on discounted cash flows. During the year ended December 31, 2023 the Company recognized a $937 loss on impairment of property, plant, and equipment as a result of the reclassification of these assets to held for sale. The Company did not record any impairment loss during the year ended December 31, 2022.

Leases

Prior to January 1, 2022, the Company accounted for leases in accordance with FASB ASC 840, Leases. At lease inception, the Company determined if an arrangement was an operating or capital lease. For operating leases, the Company recognized rent expense, inclusive of rent escalations, on a straight-line basis over the lease term.

Effective on January 1, 2022, the Company accounts for leases in accordance with ASC Topic 842, Leases (“ASC 842”). Upon transition, the Company applied the package of practical expedients permitted under ASC 842 transition guidance to its entire lease portfolio at January 1, 2022. As a result, the Company was not required to reassess (i) whether any expired or existing contracts are or contain leases, (ii) the classification of any expired or existing leases, and (iii) initial direct costs for any existing leases. Furthermore, as a lessee the Company elected to combine lease and

non-lease

components together for the majority of its leases. As a result, for these applicable classes of underlying assets, the Company accounted for each separate lease component and the

non-lease

components associated with that lease component as a single lease component.

In accordance with ASC 842, the Company determines whether an arrangement is or contains a lease at inception. A contract is or contains a lease if the contract conveys the right to control the use of an identified asset for a period of time in exchange for consideration. The Company records leases at the lease commencement date, when control of the underlying asset is transferred from the lessor to the lessee, as operating or finance leases and records a

right-of-use

(“ROU”) asset and a lease liability on the consolidated balance sheet for all leases with a lease term of greater than twelve months. The Company has elected to not recognize leases with a lease term of twelve months or less on the balance sheet and will recognize lease payments for such short-term leases as an expense on a straight-line basis.

The Company enters into contracts that contain both lease and

non-lease

components.

Non-lease

components may include items such as maintenance, utilities, or other operating costs. For leases of real estate, the Company combines the lease and associated

non-lease

components in its lease arrangements as a single lease component. Variable costs, such as utilities or maintenance costs, are not included in the measurement of

right-of-use

assets and lease liabilities, but rather are expensed when the event determining the amount of variable consideration to be paid occurs.

Operating lease assets and liabilities are recognized at the lease commencement date based on the present value of the lease payments over the lease term using the discount rate implicit in the lease if readily determinable. If the rate implicit is not readily determinable, the Company utilizes its incremental borrowing rate based upon the available information at the lease commencement date. ROU assets are further adjusted for items

such as initial direct costs, prepaid rent, or lease incentives. Operating lease payments are expensed using the straight-line method as an operating expense over the lease term. The Company’s lease terms may include options to extend the lease when it is reasonably certain that the Company will exercise that option. Finance lease assets are amortized to depreciation expense using the straight-line method over the shorter of the useful life of the related asset or the lease term. Finance lease payments are bifurcated into (i) a portion that is recorded as interest expense and (ii) a portion that reduces the finance lease liability associated with the lease.

During the year ended December 31, 2023 the Company recognized a $940 loss on impairment of ROU assets as a result of the discontinued use of lab space in Cambridge, Massachusetts, United States. The Company did not record any impairment loss during the year ended December 31, 2022.

Comprehensive Income (Loss)

Comprehensive income (loss) is defined as the change in stockholders’ equity of a business enterprise during a period from transactions and other events and circumstances from

non-owner

sources. Comprehensive income (loss) includes net income (loss) as well as other changes in stockholders’ equity (deficit) which includes certain changes in equity that are excluded from net income (loss). Comprehensive loss has been disclosed in the accompanying consolidated statements of operations and comprehensive loss and equals the Company’s net loss for all periods presented.

Foreign Currency Translation

The functional currency of the Company’s international operations in Canada and Australia is the U.S. dollar. Accordingly, all operating assets and liabilities of these international subsidiaries are remeasured into U.S. dollars using the exchange rates in effect at the balance sheet date or historical rates, as appropriate, while expenses are remeasured into U.S. dollars at the average rates in effect during the period. Any differences resulting from the remeasurement of assets, liabilities, and operations of the Canadian and Australian subsidiaries are recorded within other (expense) income, net in the consolidated statements of operations and comprehensive loss. During the years ended December 31, 2023 and 2022, the Company recorded foreign exchange losses of $122 and $92, respectively, in other expense in the consolidated statements of operations and comprehensive loss.

Research and Development Expenses

Research and development costs are expensed as incurred. Research and development expenses consist of costs incurred in performing research and development activities, including salaries, stock-based compensation and benefits, facilities costs, depreciation, third-party license fees, and external costs of outside vendors engaged to conduct preclinical development activities and clinical trials as well as to manufacture research and development materials.

Non-refundable

prepayments for goods or services that will be used or rendered for future research and development activities are deferred and capitalized. Such amounts are recognized as an expense as the goods are delivered or the related services are performed or until it is no longer expected that the goods will be delivered or the services rendered.

The Company has entered into various research and development related contracts with parties both inside and outside of the United States. The payments related to these agreements are recorded as research and development expenses as incurred. The Company records accrued liabilities for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies or clinical trials, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs.

Stock-Based Compensation

For stock-based awards issued to employees and members of the Company’s Board for their services on the Board, the Company measures the estimated fair value of the stock-based award on the date of grant and recognizes compensation expense for those awards over the requisite service period, which is generally the vesting period of the respective award. The Company issues stock-based awards with only service-based vesting conditions and records the expense for these awards using the straight-line method. The Company has not issued any stock-based awards with performance- or market-based vesting conditions. The Company accounts for forfeitures as they occur.

The measurement date for

non-employee

awards is the later of the adoption date of ASU

2018-07,

or the date of grant. For stock-based awards granted to nonemployees subject to graded vesting that only contain service conditions, the Company has elected to recognize stock-based compensation expense using the straight-line recognition method.

The Company classifies stock-based compensation expense in its consolidated statements of operations and comprehensive loss in the same manner in which the award recipient’s cash compensation costs are classified.

The fair value of each stock option award is estimated on the date of grant using the Black-Scholes option pricing model. As there was no public market for its common stock prior to June 21, 2018, which was the first day of trading, and as the trading history of the Company’s common stock was limited through December 31, 2022, the Company determined the volatility for awards granted based on an analysis of reported data for a group of guideline companies that issued options with substantially similar terms. The expected volatility has been determined using a weighted-average of the historical volatility measures of this group of guideline companies. The Company expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. The expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. The Company has not paid, and does not anticipate paying, cash dividends on its common stock; therefore, the expected dividend yield is assumed to be zero.

Income Taxes

Deferred tax assets and liabilities are determined on the basis of the differences between the consolidated financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established.

The Company accounts for uncertain tax positions recognized in the consolidated financial statements by prescribing a

more-likely-than-not

threshold for financial statement recognition and measurement of a tax position taken or expected to be taken in a tax return. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties.

Net Income (Loss) per Share

Basic net loss per share is computed by dividing net loss by the weighted-average number of shares of common stock outstanding during the period, without consideration of potential dilutive securities. Diluted net loss per share is computed by adjusting the weighted-average shares outstanding for the potential dilutive effects

of common stock equivalents outstanding during the period calculated in accordance with the treasury stock method. For purposes of the diluted net loss per share calculation, stock options and restricted stock units are considered to be common stock equivalents but have been excluded from the calculation of diluted net loss per share, as their effect would be anti-dilutive for all periods presented. Therefore, basic and diluted net loss per share were the same for all periods presented.

Subsequent Event Considerations

The Company considers events or transactions that occur after the balance sheet date but prior to the issuance of the consolidated financial statements to provide additional evidence for certain estimates or to identify matters that require additional disclosure. Subsequent events have been evaluated as required. See Note 16.

Recently Adopted Accounting Pronouncements

Recently Issued Accounting Pronouncements

In December 2023, the FASB issued Accounting Standard Update ASU

2023-09

“Income Taxes (Topic 740): Improvements to Income Tax Disclosures.” This guidance is intended to enhance the transparency and decision-usefulness of income tax disclosures. The amendments in ASU

2023-09

address investor requests for enhanced income tax information primarily through changes to disclosure regarding rate reconciliation and income taxes paid both in the United States and in foreign jurisdictions. ASU

2023-09

is effective for fiscal years beginning after December 15, 2024 on a prospective basis, with the option to apply the standard retrospectively. Early adoption is permitted. The Company is currently evaluating this guidance to determine the impact it may have on its consolidated financial statement disclosures.

In October 2023, the FASB issued ASU

2023-06

“Disclosure Improvements: Codification Amendments in Response to the SEC’s Disclosure Update and Simplification Initiative.” which incorporates certain SEC disclosure requirements into the FASB Accounting Standards Codification (“Codification”). The amendments in the ASU are expected to clarify or improve disclosure and presentation requirements of a variety Codification topics, allow investors to more easily compare entities subject to the SEC’s existing disclosures with those entities that were not previously subject to the requirements, and align the requirements in the Codification with the SEC’s regulations. The effective date for each amendment will be the date on which the SEC’s removal of that related disclosure from Regulation

S-X

or Regulation

S-K

becomes effective, with early adoption prohibited. The amendments in this ASU should be applied prospectively. The Company is currently evaluating this guidance to determine the impact it may have on its consolidated financial statement disclosures.

Stock-Based Compensation - Summary of Restricted Stock Award and Restricted Stock Unit Activity (Detail) - Restricted Stock Units [Member]	12 Months Ended
	Dec. 31, 2023 $ / shares shares
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Number of shares, Issued and unvested beginning balance \| shares	940,392
Number of shares, Granted \| shares	1,548,117
Number of shares, Vested \| shares	(305,502)
Number of shares, Forfeited, cancelled or expired \| shares	(1,246,649)
Number of shares, Issued and unvested ending balance \| shares	936,358
Weighted average grant date fair value, Issued and unvested, beginning balance \| $ / shares	$ 3.62
Weighted average grant date fair value, Granted \| $ / shares	1.65
Weighted average grant date fair value, Vested \| $ / shares	4.74
Weighted average grant date fair value, Forfeited, cancelled or expired \| $ / shares	2.02
Weighted average grant date fair value, Issued and unvested, ending balance \| $ / shares	$ 2.13

Subsequent Events - Additional Information (Details) - USD ($) $ in Thousands		12 Months Ended
	Jan. 30, 2024	Dec. 31, 2023	Dec. 31, 2022
Subsequent Event [Line Items]
Costs and expenses		$ 2,118	$ 2,971
Subsequent Event [Member]
Subsequent Event [Line Items]
Termination Fee	$ 4,900
Termination Fee To Be Paid	2,713
Costs and expenses	$ 650

Leases

12 Months Ended

Dec. 31, 2023

Leases [Abstract]

Leases

6. Leases

On August 31, 2018, the Company entered into a sublease agreement for lab space located in Cambridge Massachusetts, United States, which was set to expire in October 2020. On June 9, 2020, the Company amended the terms of the sublease, which was set to expire in April 2022. Effective January 1, 2022, the Company amended the terms of the sublease, to extend the term through April 2023. In July 2022, the company moved its corporate headquarters to our subleased space in this location. Effective January 24, 2023, the Company amended the terms of the sublease, which is now set to expire in April 2024. The annual lease payments are subject to a 5% increase each year. In accordance with the lease agreement, the Company is required to maintain a security deposit of $283, which was recorded in restricted cash as of December 31, 2023 and 2022.

On June 1, 2020, the Company entered into a lease agreement for office space located in Toronto, Ontario, Canada, which was set to expire in June 2025. On October 31, 2023, the lease agreement was terminated. The annual lease payments were fixed for years 1 and 2, and then subject to a 6.67% increase for years 3 through 5. In accordance with the lease agreement, the Company was required to maintain a security deposit of CAD$27, which was recorded in other long-term assets as of December 31, 2022. In October 2022, the Company entered into a sublease agreement to sublease this space. The term of the sublease agreement commenced on October 1, 2022 and expires on June 29, 2025. The sublease was also terminated on October 31, 2023.

The following table summarizes the effect of lease costs in the Company’s consolidated statement of operations and comprehensive loss:


	Year Ended December 31,
	2023			2022
Operating lease costs	$	2,195		$	2,994
Sublease income		(77	)		(23	)

Total lease costs	$	2,118		$	2,971

During the years ended December 31, 2023 and 2022 the Company made cash payments for operating leases of $2,771 and $3,167, respectively.

As of December 31, 2023, future minimum payments of operating lease liabilities are as follows (in thousands):


	As of December 31, 2023
2024		896
2025		—
2026		—
2027		—
Thereafter		—

Total lease payments	$	896
Less: interest		(18	)

Present value of lease liabilities	$	878

As of December 31, 2023, the weighted average remaining lease term was 0.3 years and the weighted average incremental borrowing rate used to determine the operating lease liability was 16.15%. As of December 31, 2022, the weighted average remaining lease term was 0.9 years and the weighted average incremental borrowing rate used to determine the operating lease liability was 10.58%.

Supplemental Balance Sheet Information - Summary of Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Accrued Liabilities, Current [Abstract]
Research and development expenses	$ 711	$ 6,122
Compensation and benefit costs	3,463	4,175
Consulting and professional fees	892	1,224
Other liabilities	383	211
Accrued expenses	$ 5,449	$ 11,732

Stock-Based Compensation - Schedule of Stock-based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 6,891	$ 11,522
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	1,927	2,785
General and Administrative Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 4,964	$ 8,737

Fair Value of Financial Assets and Liabilities - Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - Fair Value on Recurring Basis [Member] - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Assets Fair Value Disclosure
Assets Fair Value Disclosure	$ 96,707	$ 91,095
Money Market Funds [Member] \| Cash Equivalents [Member]
Assets Fair Value Disclosure
Assets Fair Value Disclosure	96,707	91,095
Level 1 [Member]
Assets Fair Value Disclosure
Assets Fair Value Disclosure	96,707	91,095
Level 1 [Member] \| Money Market Funds [Member] \| Cash Equivalents [Member]
Assets Fair Value Disclosure
Assets Fair Value Disclosure	$ 96,707	$ 91,095

Leases - Schedule of effective lease cost comprehensive income loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Leases [Abstract]
Operating lease costs	$ 2,195	$ 2,994
Sublease income	(77)	(23)
Total lease costs	$ 2,118	$ 2,971

Common Stock (Tables)

12 Months Ended

Dec. 31, 2023

Equity [Abstract]

Summary of Common Stock Reserved for Future Issuance

As of December 31, 2023 and 2022, the Company has reserved the following shares of common stock for future issuance:


	December 31,
	2023		2022
Shares reserved for exercise of outstanding stock options		5,142,272		9,423,271
Shares reserved for vesting of restricted stock units		936,358		940,392
Shares reserved for issuance under the 2018 Stock Option and Incentive Plan		7,978,667		5,005,295
Shares reserved for issuance under the 2018 Employee Stock Purchase Plan		1,771,748		1,467,026
Shares reserved for issuance under the 2019 Inducement Plan		1,407,211		786,656
Shares reserved for issuance under the 2020 Inducement Plan		1,700,000		1,637,000

Total shares of authorized common stock reserved for future issuance		18,936,256		19,259,640

- Definition

Tabular disclosure of an entity's stock, including par or stated value per share, number and dollar amount of share subscriptions, shares authorized, shares issued, shares outstanding, number and dollar amount of shares held in an employee trust, dividend per share, total dividends, share conversion features, par value plus additional paid in capital, the value of treasury stock and other information necessary to a fair presentation, and EPS information. Stock by class includes common, convertible, and preferred stocks which are not redeemable or redeemable solely at the option of the issuer. Includes preferred stock with redemption features that are solely within the control of the issuer and mandatorily redeemable stock if redemption is required to occur only upon liquidation or termination of the reporting entity. If more than one issue is outstanding, state the title of each issue and the corresponding dollar amount; dollar amount of any shares subscribed but unissued and the deduction of subscriptions receivable there from; number of shares authorized, issued, and outstanding.

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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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+ Details

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Schedule of Property and Equipment Estimated Useful Life

Property and equipment are recorded at cost. Depreciation and amortization is calculated using the straight-line method over the following estimated useful lives of the assets:


		Estimated Useful Life
Laboratory and office equipment		5 years
Computer equipment		2 years
Leasehold improvements		Lesser of lease term or 10 years

Restructuring

12 Months Ended

Dec. 31, 2023

Restructuring and Related Activities [Abstract]

Restructuring

15. Restructuring

In July 2023, the Board approved a reduction in the Company’s workforce by approximately 50% across different areas and functions in the Company’s July 2023 Workforce Reduction. The July 2023 Workforce Reduction was substantially completed by the end of July 2023. The Company informed affected employees in the July 2023 Workforce Reduction on July 12, 2023. Since the date of the July 2023 Workforce Reduction, the Company’s remaining employees have primarily focused on activities relating to halting further development of the Company’s programs, the pursuit of strategic alternatives, and the provision of services under the previously disclosed Separation Services Agreement between the Company and Novartis in connection with the sale to Novartis of the Company’s cystinosis gene therapy program. Under the July 2023 Workforce Reduction, the Company recognized total restructuring expenses of $3,015 for the year ended December 31, 2023, recognized as $1,800 and $1,215 of research and development and general and administrative expense, respectively, in the consolidated statement of operations and comprehensive income (loss). These

one-time

employee termination benefits are related to affected employees, who were offered separation benefits, including severance payments. Approximately $479 of these expenses were related to

non-cash

stock-based compensation expense and there are no remaining accrued payments at December 31, 2023.

The Company’s workforce was reduced by 11 employees in the October 2023 Workforce Reduction effective as of October 31, 2023. Under the October 2023 Workforce Reduction, the Company recognized total restructuring expenses of $1,093 for the year ended December 31, 2023 recognized as research and development expense in the consolidated statement of operations and comprehensive income (loss). These

one-time

employee termination benefits are related to affected employees, who were offered separation benefits, including severance payments. There are no remaining accrued payments at December 31, 2023.

The Company’s workforce was reduced by 8 employees in the December 2023 Workforce Reduction effective as of December 31, 2023. Under the December 2023 Workforce Reduction, the Company recognized total restructuring expenses of $950 for the year ended December 31, 2023 recognized as $866 and $64 of research and development and general and administrative expense, respectively, in the consolidated statement of operations and comprehensive income (loss). The Company estimates an additional $86 of expense related to future

one-time

employee benefits. These

one-time

employee termination benefits are related to affected employees, who were offered separation benefits, including severance payments. As of December 31, 2023, the Company had $521 in accrued payments. The Company expects that payments of these costs will substantially be made through the end of the first quarter of 2024.


	Employee Severance and Other Benefits
Restructuring expenses	$	5,058
Cash payments		(4,058	)
Non-cash expenses		(479	)

Liability included in accrued expenses and other current liabilities at December 31, 2023	$	521

Related Party Transactions - Additional Information (Detail) - USD ($) $ in Thousands		1 Months Ended	12 Months Ended
	Jan. 27, 2016	Jul. 31, 2018	Dec. 31, 2023	Dec. 31, 2022
Related Party Transaction [Line Items]
Research and development expense			$ 47,700	$ 72,186
Operating lease costs			2,195	2,994
License Agreement [Member]
Related Party Transaction [Line Items]
Provision for maximum cash payment		$ 2,000
Research and development expense			130	200
License Agreement [Member] \| Stock Purchase Agreement [Member]
Related Party Transaction [Line Items]
Common stock issued for initial consideration for license	1,161,665
Sub-lease Agreement [Member] \| Officers and Board Members [Member]
Related Party Transaction [Line Items]
Operating lease costs			$ 934	$ 3,200

Note Payable

12 Months Ended

Dec. 31, 2023

Debt Disclosure [Abstract]

Note Payable

7. Note Payable

On November 2, 2021 (the “Closing Date”), the Company entered into a Loan and Security Agreement (the “Loan Agreement”) with Silicon Valley Bank pursuant to which a term loan in an aggregate principal amount of up to $50,000 (the “Term Loan Facility”) was available to the Company in three tranches, subject to certain terms and conditions. The first tranche of $15,000 was advanced to the Company on the Closing Date. Subject to the terms and conditions of the Loan Agreement, the first tranche allowed the Company to borrow an additional $15,000 through October 31, 2023. Upon satisfaction of certain milestones, the second and third tranches were available under the Term Loan Facility which allowed the Company to borrow an additional amount up to $10,000 in each tranche through October 31, 2023. Additionally, the Company could seek to borrow up to an additional $15,000 at the sole discretion of the lender through the term of the Loan Agreement. The Loan Agreement provided for an October 1, 2026 maturity date (the “Maturity Date”). The Company was required to pay an end of term fee (“End of Term Charge”) equal to 9.00% of the aggregate principal amount of the Term Loan advances upon repayment.

Advances under the Term Loan Facility bore interest at a rate equal to the greater of either (i) the Prime Rate (as reported in The Wall Street Journal) plus 4.85%, and (ii) 8.10%. The Company was obligated to make interest only payments through November 1, 2024. Following the interest only period, the Company was to repay the principal balance and interest of the advances in equal monthly installments through October 1, 2026.

The Company could prepay advances under the Loan Agreement, in whole or in part, at any time subject to a prepayment charge (the “Prepayment Premium”) equal to: (a) 1.50% of amounts so prepaid, if such prepayment occurred during the first year following the Closing Date; (b) 1.00% of the amount so prepaid, if such prepayment occurred during the second year following the Closing Date, and (c) 0.00% of the amount so prepaid, if such prepayment occurred after the second year following the Closing Date.

Upon prepayment or repayment of all or any of the term loans under the Term Loan Facility, the Company was required to pay (in addition to any Prepayment Premium) an end of term charge of 9.0% of the aggregate funded amount under the Term Loan Facility.

The Term Loan Facility was secured by substantially all of the Company’s assets, other than the Company’s intellectual property. The Company agreed to not pledge or secure its intellectual property to others.

The End of Term Charge is recorded as a debt discount with an initial carrying balance of $1,350. During the year ended December 31, 2021 the Company recognized $103 of debt issuance costs related to legal expenses that has been included in the debt discount balance. The debt discount costs are being accreted to the principal amount of debt and being amortized from the date of issuance through the Maturity Date to interest expense using the effective-interest rate method. The effective interest rate of the outstanding debt under the Loan Agreement was approximately 16.29%.

On June 9, 2023, upon the closing of the Asset Sale, all outstanding amounts due and owed, including principal, interest, and other charges, under the Term Loan Facility, dated as of November 2, 2021, by and among the Company, Silicon Valley Bank, a division of First-Citizens Bank & Trust and the other parties thereto, were repaid in full and the Term Loan Facility was terminated. Upon repayment, the obligations of the Company under the Term Loan Facility were satisfied in full, the Term Loan Facility and all related loan documents were terminated and all liens and security interests granted thereunder were released and terminated (excluding certain indemnification obligations that expressly survive termination of the Term Loan Facility).

As of December 31, 2022 the carrying value of the note payable consists of the following:


	December 31, 2022
Note payable, including End of Term Charge	$	16,350
Debt discount, net of accretion		(1,074	)

Note payable, net of discount, long-term	$	15,276

During the year ended December 31, 2023, the Company recognized $1,917 of interest expense related to the Loan Agreement, of which $939 is related to the loss on the extinguishment of debt due to the write off of the debt discount balance, which is reflected in other expense, net on the consolidated statements of operations and comprehensive loss. During year ended December 31, 2022, the Company recognized $1,808 of interest expense related to the Loan Agreement.

- Definition

The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(c))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 470
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//470/tableOfContent

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1C

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1C

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1C
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1C

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1E

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1I

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1I

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1I

+ Details

Supplemental Balance Sheet Information - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Impairment Effects on Earnings Per Share [Line Items]
Depreciation and amortization expense	$ 617	$ 1,440

Restructuring (Tables)

12 Months Ended

Dec. 31, 2023

Restructuring and Related Activities [Abstract]

Schedule of Restructuring Activities


	Employee Severance and Other Benefits
Restructuring expenses	$	5,058
Cash payments		(4,058	)
Non-cash expenses		(479	)

Liability included in accrued expenses and other current liabilities at December 31, 2023	$	521

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation

Principles of Consolidation

Segment Information

Use of Estimates

on-going

Cash and Cash Equivalents

Concentrations of Credit Risk

The Company has no significant

off-balance

Fair Value Measurements

•

Level 1— Fair values are determined utilizing prices (unadjusted) in active markets for identical assets or liabilities that the Company has the ability to access.

•

short-term

nature of these instruments.

“Fair Value of Financial Assets and Liabilities”

for further discussion.

Property and Equipment

Property and equipment are recorded at cost. Depreciation and amortization is calculated using the straight-line method over the following estimated useful lives of the assets:


		Estimated Useful Life
Laboratory and office equipment		5 years
Computer equipment		2 years
Leasehold improvements		Lesser of lease term or 10 years

Impairment of Long-Lived Assets

Leases

non-lease

components together for the majority of its leases. As a result, for these applicable classes of underlying assets, the Company accounted for each separate lease component and the

non-lease

components associated with that lease component as a single lease component.

right-of-use

The Company enters into contracts that contain both lease and

non-lease

components.

Non-lease

components may include items such as maintenance, utilities, or other operating costs. For leases of real estate, the Company combines the lease and associated

non-lease

components in its lease arrangements as a single lease component. Variable costs, such as utilities or maintenance costs, are not included in the measurement of

right-of-use

assets and lease liabilities, but rather are expensed when the event determining the amount of variable consideration to be paid occurs.

Comprehensive Income (Loss)

Comprehensive income (loss) is defined as the change in stockholders’ equity of a business enterprise during a period from transactions and other events and circumstances from

non-owner

Foreign Currency Translation

Research and Development Expenses

Non-refundable

Stock-Based Compensation

The measurement date for

non-employee

awards is the later of the adoption date of ASU

2018-07,

Income Taxes

The Company accounts for uncertain tax positions recognized in the consolidated financial statements by prescribing a

more-likely-than-not

Net Income (Loss) per Share

Subsequent Event Considerations

Recently Adopted Accounting Pronouncements

In June 2016, the FASB issued ASU

No. 2016-13,

Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, or ASU

2016-13.

ASU

2016-13

requires that credit losses be reported as an allowance using an expected losses model, representing the entity’s current estimate of credit losses expected to be incurred. For

available-for-sale

debt securities with unrealized

losses

, this standard now requires allowances to be recorded instead of reducing the amortized cost of the investment. On January 1, 2023 the Company adopted this standard, which had no impact on its financial position or results of operations.

In November 2019, the FASB issued ASU

2019-11,

“Codification Improvements to Topic 326, Financial Instruments – Credit Losses,” or ASU

2019-11.

ASU

2019-11

is an accounting pronouncement that amends ASU

2016-13,

“Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments.” The amendments update guidance on reporting credit losses for financial assets. These amendments affect loans, debt securities, trade receivables, net investments in leases, off balance sheet credit exposures, reinsurance receivables, and any other financial assets not excluded from the scope that have the contractual right to receive cash. On January 1, 2023 the Company adopted this standard, which had no impact on its financial position or results of operations.

Recently Issued Accounting Pronouncements

In December 2023, the FASB issued Accounting Standard Update ASU

2023-09

“Income Taxes (Topic 740): Improvements to Income Tax Disclosures.” This guidance is intended to enhance the transparency and decision-usefulness of income tax disclosures. The amendments in ASU

2023-09

In October 2023, the FASB issued ASU

2023-06

S-X

or Regulation

S-K

Supplemental Balance Sheet Information

12 Months Ended

Dec. 31, 2023

Balance Sheet Related Disclosures [Abstract]

Supplemental Balance Sheet Information

5. Supplemental Balance Sheet Information

Prepaid Expenses and Other Current Assets

Prepaid expenses and other current assets consisted of the following:


	December 31,
	2023		2022
Prepaid research and development expenses	$	572	$	4,509
Prepaid insurance		816		999
Prepaid compensation benefits		—		327
Tax incentive refund, net of reserve		—		269
Other current assets		570		1,008

Prepaid expenses and other current assets	$	1,958	$	7,112

Property and Equipment, Net

Property and equipment, net consisted of the following:


	December 31,
	2023			2022
Laboratory and office equipment	$	5,973		$	5,967
Leasehold improvements		629			629
Computer equipment		104			102

		6,706			6,698
Less: Accumulated depreciation and amortization		(4,421	)		(3,804	)
Impairment		(937	)		—
Sale of assets		(1,348	)		—

Property and equipment, net	$	—		$	2,894

Depreciation and amortization expense for the years ended December 31, 2023 and 2022 was $617 and $1,440, respectively.

Restricted Cash

As of December 31, 2023 and 2022, the Company had restricted cash as presented in the table below, which consists of cash used to secure a letter of credit for the benefit of the landlord in connection with the Company’s lease agreement as well as restricted cash related to the Company’s corporate credit card program. The cash will be restricted until the termination or modification of the lease arrangement and corporate credit card program, respectively.


	December 31,
	2023		2022
Restricted cash	$	283	$	283
Restricted cash, net of current portion		400		—

Accrued Expenses

Accrued expenses consisted of the following:


	December 31,
	2023		2022
Research and development expenses	$	711	$	6,122
Compensation and benefit costs		3,463		4,175
Consulting and professional fees		892		1,224
Other liabilities		383		211

	$	5,449	$	11,732

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Cash flows from operating activities:
Net income (loss)	$ 12,157	$ (105,890)
Adjustments to reconcile net loss to net cash used in operating activities:
Gain on asset sale	(83,736)	0
Stock-based compensation expense	6,891	11,522
Depreciation and amortization expense	617	1,440
Non-cash asset impairment charges	1,877	0
Loss on disposal of property and equipment	0	59
Non-cash interest expense	1,074	331
Non-cash income tax expense	377	0
(Gain)/loss on impairment of leasehold improvements	0	86
(Gain)/loss on extinguishment of operating lease	(72)	(81)
Non-cash lease expense	1,912	2,726
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	5,154	2,466
Other assets	40	34
Accounts payable	(357)	(3,102)
Current and non-current operating lease liabilities	(2,464)	(2,893)
Accrued expenses and other current liabilities	(6,660)	(3,906)
Net cash used in operating activities	(63,190)	(97,208)
Cash flows from investing activities:
Proceeds from asset sale, net	83,736	0
Proceeds from the sale of property, plant, and equipment	1,348	0
Purchases of property and equipment	(8)	(267)
Net cash provided by (used in) investing activities	85,076	(267)
Cash flows from financing activities:
Repayment of note payable, including end of term charge	(16,350)	0
Exercise of stock options	235	58
Proceeds from issuance of common stock under 2018 employee stock purchase plan	86	204
Net cash (used in) provided by financing activities	(16,029)	262
Net increase (decrease) in cash, cash equivalents and restricted cash	5,857	(97,213)
Cash, cash equivalents and restricted cash at beginning of period	92,846	190,059
Cash, cash equivalents and restricted cash, end of period	98,703	92,846
Supplemental Cash:
Interest paid	831	1,425
Supplemental disclosure of non-cash investing and financing activities:
Right of use asset obtained in exchange for operating lease liabilities	2,392	4,319
Reconciliation of cash, cash equivalents and restricted cash reported within the consolidated balance sheets:
Cash and cash equivalents, end of period	98,020	92,563
Restricted cash	683	283
Cash, cash equivalents and restricted cash, end of period	$ 98,703	$ 92,846

Supplemental Balance Sheet Information (Tables)

12 Months Ended

Dec. 31, 2023

Balance Sheet Related Disclosures [Abstract]

Summary of Prepaid Expenses and Other Current Assets

Prepaid expenses and other current assets consisted of the following:


	December 31,
	2023		2022
Prepaid research and development expenses	$	572	$	4,509
Prepaid insurance		816		999
Prepaid compensation benefits		—		327
Tax incentive refund, net of reserve		—		269
Other current assets		570		1,008

Prepaid expenses and other current assets	$	1,958	$	7,112

Summary of Property and Equipment, Net

Property and equipment, net consisted of the following:


	December 31,
	2023			2022
Laboratory and office equipment	$	5,973		$	5,967
Leasehold improvements		629			629
Computer equipment		104			102

		6,706			6,698
Less: Accumulated depreciation and amortization		(4,421	)		(3,804	)
Impairment		(937	)		—
Sale of assets		(1,348	)		—

Property and equipment, net	$	—		$	2,894

Summary of Restricted Cash


	December 31,
	2023		2022
Restricted cash	$	283	$	283
Restricted cash, net of current portion		400		—

Summary of Accrued Expenses

Accrued expenses consisted of the following:


	December 31,
	2023		2022
Research and development expenses	$	711	$	6,122
Compensation and benefit costs		3,463		4,175
Consulting and professional fees		892		1,224
Other liabilities		383		211

	$	5,449	$	11,732

Leases (Tables)

12 Months Ended

Dec. 31, 2023

Leases [Abstract]

Schedule of effective lease cost comprehensive income loss

The following table summarizes the effect of lease costs in the Company’s consolidated statement of operations and comprehensive loss:


	Year Ended December 31,
	2023			2022
Operating lease costs	$	2,195		$	2,994
Sublease income		(77	)		(23	)

Total lease costs	$	2,118		$	2,971

Summary of Future Minimum Lease Payments Due Under Operating Leases

As of December 31, 2023, future minimum payments of operating lease liabilities are as follows (in thousands):


	As of December 31, 2023
2024		896
2025		—
2026		—
2027		—
Thereafter		—

Total lease payments	$	896
Less: interest		(18	)

Present value of lease liabilities	$	878

Summary of Significant Accounting Policies - Schedule of Property and Equipment Estimated Useful Life (Detail)	12 Months Ended
	Dec. 31, 2023
Laboratory and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment estimated useful life	5 years
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment estimated useful life	2 years
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment estimated useful life	10 years
Property and equipment estimated useful life	Lesser of lease term

Fair Value of Financial Assets and Liabilities - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Fair value input transfer between levels	$ 0	$ 0

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2021	$ 169,476	$ 4	$ 553,014	$ (383,542)
Beginning balance, shares at Dec. 31, 2021		43,652,000
Vesting of restricted stock awards and units, shares		1,000
Exercise of stock options	58		58
Exercise of stock options, shares		142,000
Issuance of common stock under 2018 employee stock purchase plan	$ 204
Issuance of common stock under 2018 employee stock purchase plan, shares	121
Stock-based compensation expense	$ 11,522		11,522
Net Income (Loss)	(105,890)			(105,890)
Ending balance at Dec. 31, 2022	75,370	$ 4	564,798	(489,432)
Ending balance, shares at Dec. 31, 2022		43,916,000
Vesting of restricted stock awards and units, shares		306,000
Exercise of stock options	$ 235		235
Exercise of stock options, shares	297,604	298,000
Issuance of common stock under 2018 employee stock purchase plan	$ 86		86
Issuance of common stock under 2018 employee stock purchase plan, shares		134,000
Stock-based compensation expense	6,891		6,891
Net Income (Loss)	12,157			12,157
Ending balance at Dec. 31, 2023	$ 94,739	$ 4	$ 572,010	$ (477,275)
Ending balance, shares at Dec. 31, 2023		44,654,000

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(g)(1)(ii))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 323
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481687/323-10-50-3

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 28
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482907/825-10-50-28

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482765/220-10-50-6

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-3

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 65
-Paragraph 1
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480175/815-40-65-1

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-8

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-9

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-11

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-11

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-4

Reference 13: http://www.xbrl.org/2003/role/exampleRef
-Topic 946
-SubTopic 830
-Name Accounting Standards Codification
-Section 55
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480167/946-830-55-10

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section 45
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483581/946-220-45-7

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
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-Name Accounting Standards Codification
-Section S99
-Paragraph 1
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Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-22

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
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-Name Accounting Standards Codification
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-Paragraph 1
-Subparagraph (SX 210.6-07(9))
-Publisher FASB
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Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
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-Paragraph 3
-Subparagraph (SX 210.6-09(1)(d))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-3

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(i))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1A

Reference 20: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
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+ Details

- Definition

Amount of equity (deficit) attributable to parent. Excludes temporary equity and equity attributable to noncontrolling interest.

+ References

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+ Details

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Schedule of Reconciliation of Income Tax Expense (Benefit)


	Year Ended December 31,
	2023			2022
Federal income tax expense at statutory rate		21.0	%		21.0	%
State income taxes, net of federal benefit		3.7			5.2
Permanent differences		4.4			(1.2	)
Foreign rate differential		(0.4	)		—
Research and development tax credits		(4.3	)		0.8
Change in valuation allowance		(48.2	)		(25.8	)
Stock based compensation		37.0			—
State rate changes		(8.0	)		—
Deferred true ups		(2.2	)		—
Provision to return		—			—

Effective income tax rate		3.0	%		—	%

Schedule of Deferred Tax Assets and Liabilities


	December 31,
	2023			2022
Deferred tax assets:
U.S., foreign and state net operating loss carryforwards	$	80,185		$	91,416
Research and development credits		8,356			8,471
Capitalized start up and organizational costs		21			23
Equity based compensation		313			3,610
Licensing agreements		3,710			3,929
Section 174 R&D capitalization		25,045			16,307
Lease liability		240			227
Accruals and other		906			1,032

Total deferred tax assets		118,776			125,015
Valuation allowance		(118,658	)		(124,695	)

Net deferred tax assets	$	118		$	320

Deferred tax liabilities:
Property and equipment	$	—		$	(102	)
ROU Asset		(118	)		(218	)

Total deferred tax liabilities		(118	)		(320	)

Net deferred tax liabilities	$	—		$	—

Commitments and Contingencies	12 Months Ended
Commitments and Contingencies	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	11. Commitments and Contingencies Lease Agreements Refer to Note 6 “ Leases ” for discussion of the commitments associated with the Company’s lease portfolio. Other Funding Commitments The Company enters into contracts in the normal course of business with contract research organizations and clinical sites for the conduct of clinical trials, professional consultants for expert advice and other vendors for clinical supply manufacturing or other services. These contracts are generally cancellable, with notice, at the Company’s option and do not have significant cancellation penalties. Guarantees The Company enters into certain agreements with other parties in the ordinary course of business that contain indemnification provisions. These typically include agreements with directors and officers, business partners, contractors, landlords and clinical sites. Under these provisions, the Company generally indemnifies and holds harmless the indemnified party for losses suffered or incurred by the indemnified party as a result of the Company’s activities. These indemnification provisions generally survive termination of the underlying agreement. The maximum potential amount of future payments the Company could be required to make under these indemnification provisions is unlimited. However, to date the Company has not incurred material costs to defend lawsuits or settle claims related to these indemnification provisions. As a result, the estimated fair value of these obligations is minimal. Litigation The Company, from time to time, may be party to litigation arising in the ordinary course of business. The Company was not subject to any material legal proceedings during the years ended December 31, 2023 and 2022, and to the best of its knowledge, no material legal proceedings are currently pending or threatened. Other The Company is also party to various agreements, principally relating to licensed technology, that require future payments relating to milestones not met as of December 31, 2023 and 2022, or royalties on future sales of specified products. No milestone or royalty payments under these agreements are expected to be payable in the immediate future. See Note 3 “Licenses Agreements” for discussion of these arrangements. The Company enters into standard indemnification agreements in the ordinary course of business. Pursuant to the agreements, the Company agrees to indemnify, hold harmless, and to reimburse the indemnified party for losses suffered or incurred by the indemnified party, generally the Company’s business partners, in connection with any U.S. patent or any copyright or other intellectual property infringement claim by any third-party with respect to the Company’s products. The term of these indemnification agreements is generally perpetual any time after execution of the agreement. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is unlimited. The Company has never incurred costs to defend lawsuits or settle claims related to these indemnification agreements.

Net Income (Loss) Per Share - Components of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Net Income (Loss) Attributable to Parent [Abstract]
Net income (loss) attributable to common stockholder basic	$ 12,157	$ (105,890)
Net income (loss) attributable to common stockholders diluted	$ 12,157	$ (105,890)
Options to purchase common shares	119,677
Unvested restricted stock awards and units	95,010
Employee stock purchase program	26,027
Weighted average common shares outstanding basic	44,327,204	43,738,739
Weighted average common share outstanding diluted	44,567,918	43,738,739
Net income (loss) per share applicable to common stockholders-basic	$ 0.27	$ (2.42)
Net income (loss) per share applicable to common stockholders diluted	$ 0.27	$ (2.42)

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets:
U.S., foreign and state net operating loss carryforwards	$ 80,185	$ 91,416
Research and development credits	8,356	8,471
Capitalized start up and organizational costs	21	23
Equity based compensation	313	3,610
Licensing agreements	3,710	3,929
Section 174 R&D Capitalization	25,045	16,307
Lease Liability	240	227
Accruals and other	906	1,032
Total deferred tax assets	118,776	125,015
Valuation allowance	(118,658)	(124,695)
Net deferred tax assets	118	320
Deferred tax liabilities:
Property and equipment	0	(102)
ROU Asset	(118)	(218)
Total deferred tax liabilities	118	320
Net Deferred Tax Liabilities	$ 0	$ 0

Supplemental Balance Sheet Information - Summary of Restricted Cash (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Restricted Cash and Investments [Abstract]
Restricted cash	$ 283	$ 283
Restricted cash, net of current portion	$ 400	$ 0

Fair Value of Financial Assets and Liabilities

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Fair Value of Financial Assets and Liabilities

4. Fair Value of Financial Assets and Liabilities

The following table presents information about the Company’s financial assets and liabilities measured at fair value on a recurring basis and indicates the level of the fair value hierarchy utilized to determine such fair values as of December 31, 2023 and 2022:


	Fair Value Measurements as of December 31, 2023
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents—money market funds	$	96,707	$	—	$	—	$	96,707

	$	96,707	$	—	$	—	$	96,707


	Fair Value Measurements as of December 31, 2022
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents—money market funds	$	91,095	$	—	$	—	$	91,095

	$	91,095	$	—	$	—	$	91,095

During the years ended December 31, 2023 and 2022, there were no transfers between levels.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Fair Value of Financial Assets and Liabilities (Tables)

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis


	Fair Value Measurements as of December 31, 2023
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents—money market funds	$	96,707	$	—	$	—	$	96,707

	$	96,707	$	—	$	—	$	96,707


	Fair Value Measurements as of December 31, 2022
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents—money market funds	$	91,095	$	—	$	—	$	91,095

	$	91,095	$	—	$	—	$	91,095

Cover Page	12 Months Ended
Cover Page	Dec. 31, 2023
Document Information [Line Items]
Document Type	S-4/A
Amendment Flag	false
Entity Registrant Name	AVROBIO, INC.
Entity Central Index Key	0001681087
Entity Incorporation, State or Country Code	DE
Entity Primary SIC Number	2836
Entity Tax Identification Number	81-0710585
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Address, Address Line One	100 Technology Square
Entity Address, Address Line Two	Sixth Floor
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02139
Entity Small Business	true
Business Contact [Member]
Document Information [Line Items]
Contact Personnel Name	Erik Ostrowski
Entity Address, Address Line One	100 Technology Square
Entity Address, Address Line Two	Sixth Floor
Entity Address, City or Town	Cambridge
Entity Address, Postal Zip Code	02139
City Area Code	617
Local Phone Number	914-8420

Note Payable - Carrying Value of Note Payable (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Debt Disclosure [Abstract]
Note payable, including End of Term Charge		$ 16,350
Debt discount, net of accretion		(1,074)
Note payable, net of discount, long-term	$ 0	$ 15,276

Common Stock - Additional Information (Detail) - USD ($)	1 Months Ended					12 Months Ended
	May 31, 2021	Nov. 30, 2020	Jun. 30, 2020	Feb. 29, 2020	Jul. 31, 2019	Dec. 31, 2023	Dec. 31, 2022
Class of Stock [Line Items]
Common stock, shares authorized						150,000,000	150,000,000
Common stock, par value						$ 0.0001	$ 0.0001
Undesignated preferred stock						10,000,000
Undesignated shares of preferred stock outstanding						0	0
Cash dividends						$ 0
Proceeds from issuance of common stock under 2018 employee stock purchase plan						$ 86,000	$ 204,000
July 2019 Follow-on Offering [Member]
Class of Stock [Line Items]
Proceeds from issuance of common stock under 2018 employee stock purchase plan					$ 129,464,000
July 2019 Follow-on Offering [Member] \| Common Stock [Member]
Class of Stock [Line Items]
Common stock, shares issued and sold					7,475,000
Issuance price per shares					$ 18.5
Over-Allotment Option [Member] \| Common Stock [Member]
Class of Stock [Line Items]
Common stock, shares issued and sold					975,000
February 2020 Follow-on Offering [Member]
Class of Stock [Line Items]
Proceeds from issuance of common stock under 2018 employee stock purchase plan				$ 93,627,000
February 2020 Follow-on Offering [Member] \| Common Stock [Member]
Class of Stock [Line Items]
Common stock, shares issued and sold				4,350,000
Issuance price per shares				$ 23
ATM Facility [Member]
Class of Stock [Line Items]
Common stock, shares issued and sold	1,829,268		384,140
Proceeds from issuance of common stock under 2018 employee stock purchase plan	$ 14,550,000		$ 8,130,000
November 2020 Follow-on Offering [Member]
Class of Stock [Line Items]
Proceeds from issuance of common stock under 2018 employee stock purchase plan		$ 70,221,000
November 2020 Follow-on Offering [Member] \| Common Stock [Member]
Class of Stock [Line Items]
Common stock, shares issued and sold		5,000,000
Issuance price per shares		$ 15

Stock-Based Compensation - Summary of Assumptions that Used to Determine Grant-Date Fair Value of Stock Options Granted to Employees and Members of Board (Detail)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Expected option life (years)	6 years	5 years 11 months 23 days
Risk-free interest rate	3.82%	2.47%
Expected volatility	83.36%	80.43%

Note Payable - Additional Information (Details) $ in Thousands		12 Months Ended
	Nov. 02, 2021 USD ($) Tranche	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Debt Disclosure [Line Items]
Debt Issuance Costs, Net			$ 1,074
Interest expense recognized		$ 1,917	$ 1,808
Loss on the extinguishment		$ 939
Term Loan Facility [Member] \| Silicon Valley Bank [Member]
Debt Disclosure [Line Items]
Loan maturity date	Oct. 01, 2026
End of term charge as percentage on principal amount	9.00%
Loan, interest rate	8.10%
Term Loan Facility [Member] \| Silicon Valley Bank [Member] \| Prime Rate [Member]
Debt Disclosure [Line Items]
Loan, interest rate	4.85%
Term Loan Prepayment During First Year [Member] \| Silicon Valley Bank [Member]
Debt Disclosure [Line Items]
Line of credit facility prepayment of premium percentage	1.50%
Term Loan Prepayment During Second Year [Member] \| Silicon Valley Bank [Member]
Debt Disclosure [Line Items]
Line of credit facility prepayment of premium percentage	1.00%
Term Loan Prepayment After Second Year [Member] \| Silicon Valley Bank [Member]
Debt Disclosure [Line Items]
Line of credit facility prepayment of premium percentage	0.00%
Loan Agreement [Member] \| Silicon Valley Bank [Member]
Debt Disclosure [Line Items]
Loan, interest rate	16.29%
Debt discount	$ 1,350
Loan Agreement [Member] \| Silicon Valley Bank [Member] \| Legal Expenses [Member]
Debt Disclosure [Line Items]
Debt Issuance Costs, Net				$ 103
Loan Agreement [Member] \| Term Loan Facility [Member] \| Silicon Valley Bank [Member]
Debt Disclosure [Line Items]
Borrowing amount	$ 50,000
Debt instrument number of tranches \| Tranche	3
Proceeds from loan agreement	$ 15,000
Additional borrowing amount	15,000
Line of credit facility additional discretionary	$ 15,000
Loan maturity date	Oct. 01, 2026
End of term charge as percentage on principal amount	9.00%
Loan Agreement [Member] \| Term Loan Facility [Member] \| Silicon Valley Bank [Member] \| Regulatory Milestone [Member]
Debt Disclosure [Line Items]
Additional borrowing amount	$ 10,000

Leases - Additional Information (Detail) $ in Thousands, $ in Thousands					12 Months Ended
	Jan. 01, 2022	Jun. 09, 2020	Jun. 01, 2020	Aug. 31, 2018	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2022 CAD ($)
Lease agreement expiration month and year	2023-04	2022-04	2025-06	2020-10
Percentage of annual increase in rent	5.00%		6.67%
Lease expiration date			Jun. 29, 2025
Sublease termination date			October 31, 2023
Annual lease payments, description					The annual lease payments were fixed for years 1 and 2, and then subject to a 6.67% increase for years 3 through 5
Operating leases and Rent expenses					$ 2,771	$ 3,167
Weighted average remaining lease					3 months 18 days	10 months 24 days	10 months 24 days
weighted average incremental borrowing rate					16.15%	10.58%	10.58%
Restricted Cash [Member]
Security deposit in connection with lease					$ 283	$ 283
Other Long-term Assets [Member]
Security deposit in connection with lease							$ 27

Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($) Segment	Dec. 31, 2022 USD ($)
Significant Of Accounting Policies [Line Items]
Number of operating segment \| Segment	1
Impairment loss	$ 940	$ 0
Impairment of Long-Lived Assets		(937)
Foreign exchange losses	$ 122	$ 92
Expected Dividend Yield [Member]
Significant Of Accounting Policies [Line Items]
Expected cash dividend yield	0

Common Stock - Summary of Common Stock Reserved for Future Issuance (Detail) - shares	Dec. 31, 2023	Dec. 31, 2022	Apr. 16, 2020
Class of Stock [Line Items]
Total shares of authorized common stock reserved for future issuance	18,936,256	19,259,640
Employee Stock Option
Class of Stock [Line Items]
Total shares of authorized common stock reserved for future issuance	5,142,272	9,423,271
Restricted Stock Units [Member]
Class of Stock [Line Items]
Total shares of authorized common stock reserved for future issuance	936,358	940,392
2018 Stock Option and Incentive Plan [Member]
Class of Stock [Line Items]
Total shares of authorized common stock reserved for future issuance	7,978,667	5,005,295	3,300,000
2018 Employee Stock Purchase Plan [Member]
Class of Stock [Line Items]
Total shares of authorized common stock reserved for future issuance	1,771,748	1,467,026
2019 Inducement Plan [Member]
Class of Stock [Line Items]
Total shares of authorized common stock reserved for future issuance	1,407,211	786,656
2020 Inducement Plan [Member]
Class of Stock [Line Items]
Total shares of authorized common stock reserved for future issuance	1,700,000	1,637,000

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 2: http://www.xbrl.org/2003/role/recommendedDisclosureRef
-Topic 272
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-Name Accounting Standards Codification
-Section 45
-Paragraph 3
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-URI https://asc.fasb.org//1943274/2147483014/272-10-45-3

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 272
-SubTopic 10
-Name Accounting Standards Codification
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482987/272-10-50-1

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(d))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
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-Section 50
-Paragraph 13
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Section 50
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Subparagraph (b)
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-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Name Accounting Standards Codification
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-URI https://asc.fasb.org//1943274/2147481112/505-10-50-2

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
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Reference 15: http://www.xbrl.org/2003/role/disclosureRef
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Reference 17: http://www.xbrl.org/2003/role/disclosureRef
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Reference 18: http://www.xbrl.org/2003/role/disclosureRef
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479886/946-10-S99-3

+ Details

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 98,020	$ 92,563
Restricted cash	283	283
Prepaid expenses and other current assets	1,958	7,112
Total current assets	100,261	99,958
Operating lease assets	432	1,057
Property and equipment, net	0	2,894
Restricted cash, net of current portion	400	0
Other assets	0	40
Total assets	101,093	103,949
Current liabilities:
Accounts payable	27	384
Accrued expenses and other current liabilities	5,449	11,732
Operating lease liabilities	878	999
Total current liabilities	6,354	13,115
Note payable, net of discount	0	15,276
Operating lease liabilities, net of current portion	0	188
Total liabilities	6,354	28,579
Commitments and contingencies (Note 11)
Stockholders' equity:
Preferred stock, $0.0001 par value; 10,000 shares authorized and no shares issued or outstanding as of December 31, 2023 and 2022	0	0
Common stock, $0.0001 par value; 150,000 shares authorized as of December 31, 2023 and 2022; 44,654 and 43,916 shares issued and outstanding as of December 31, 2023 and 2022, respectively	4	4
Additional paid-in capital	572,010	564,798
Accumulated deficit	(477,275)	(489,432)
Total stockholders' equity	94,739	75,370
Total liabilities and stockholders' equity	$ 101,093	$ 103,949