0000950170-24-057091 | 10-Q | XBRL Viewer

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Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2024	Dec. 31, 2023
Statement of Financial Position [Abstract]
Preferred Stock, Per Share	$ 0.0001	$ 0.0001
Preferred Stock, Shares Authorized	10,000	10,000
Preferred Stock, Shares Issued	0	0
Preferred Stock, Shares Outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, authorized	150,000,000	150,000,000
Common stock, issued	44,882,000	44,654,000
Common stock, outstanding	44,882,000	44,654,000

Leases

3 Months Ended

Mar. 31, 2024

Leases [Abstract]

Leases

6. Leases

On August 31, 2018, the Company entered into a sublease agreement for office and lab space located in Cambridge Massachusetts, United States, which originally was set to expire in October 2020 but was subsequently amended and expired on April 30, 2024. In July 2022, the Company moved its corporate headquarters to this subleased location. Effective January 24, 2023, the Company amended the terms of the sublease, which expired on April 30, 2024. In accordance with the sublease agreement, the Company was required to maintain a security deposit of $283, which was recorded in restricted cash as of March 31, 2024 and December 31, 2023. In July 2023, the Company ceased use of the lab space. This resulted in an impairment of the right of use asset of $940, recognized in the third quarter of 2023. Effective as of April 22, 2024, the Company moved its corporate headquarters to its current location at One Broadway, 14th Floor, Cambridge, Massachusetts 02142.

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. In accordance with the lease agreement, the Company was required to maintain a security deposit of CAD$27. 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 was set to expire 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:


	Three Months Ended March 31,		Three Months Ended March 31,
	2024		2023
Operating lease costs	$	339	$	670
Sublease income		—		(23	)
Total lease costs	$	339	$	647

During the three months ended March 31, 2024 and 2023, the Company made cash payments for operating leases of $672 and $687, respectively.

As of March 31, 2024, future minimum payments of operating lease liabilities are as follows:


	March 31, 2024
2024	$	224
2025		—
2026		—
2027		—
Thereafter		—
Total lease payments	$	224
Less: interest		—
Present value of lease liabilities	$	224

As of March 31, 2024, the weighted average remaining lease term was 0.1 years and the weighted average incremental borrowing rate used to determine the operating lease liability was 16.15%. As of March 31, 2023, the weighted average remaining lease term was 1.2 years and the weighted average incremental borrowing rate used to determine the operating lease liability was 15.67%.

Related Party Transactions	3 Months Ended
Mar. 31, 2024
Related Party Transactions [Abstract]
Related Party Transactions	11. Related Party Transactions UHN For the three months ended March 31, 2024, the Company did not recognize research and development expense related to the license agreements with UHN. For the three months ended March 31, 2023, the Company recognized $71 of research and development expense related to the license agreements with UHN. Refer to Note 3 “License Agreements” for additional information regarding the UHN license agreements. Others In the first quarter of 2023, the sublease for space that was previously provided by an entity affiliated with a member of the Company’s Board was assigned to Novartis. Therefore, for the three months ended March 31, 2024 the Company did not record expense related to a sublease to rent office and lab space provided by an entity affiliated with a member of the Company’s Board. For the three months ended March 31, 2023 the Company recorded $652 related to the sublease to rent office and lab space previously provided by an entity affiliated with a member of the Company’s Board.

Related Party Transactions

3 Months Ended

Mar. 31, 2024

Related Party Transactions

11. Related Party Transactions

UHN

For the three months ended March 31, 2024, the Company did not recognize research and development expense related to the license agreements with UHN. For the three months ended March 31, 2023, the Company recognized $71 of research and development expense related to the license agreements with UHN. Refer to Note 3 “License Agreements” for additional information regarding the UHN license agreements.

Others

In the first quarter of 2023, the sublease for space that was previously provided by an entity affiliated with a member of the Company’s Board was assigned to Novartis. Therefore, for the three months ended March 31, 2024 the Company did not record expense related to a sublease to rent office and lab space provided by an entity affiliated with a member of the Company’s Board. For

the three months ended March 31, 2023 the Company recorded $652 related to the sublease to rent office and lab space previously provided by an entity affiliated with a member of the Company’s 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.

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+ Details

Restructuring Activities (Tables)

3 Months Ended

Mar. 31, 2024

Restructuring and Related Activities [Abstract]

Schedule of Restructuring Activities


	Three Months Ended March 31,
	2024
Restructuring expenses	$	5,299
Cash payments		(4,820	)
Non-cash expenses		(479	)
Liability included in accrued expenses and other current liabilities at March 31, 2024	$	—

Supplemental Balance Sheet Information - Summary of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Supplemental Balance Sheet Information Disclosures [Abstract]
Other current assets	$ 626	$ 570
Prepaid insurance	411	816
Prepaid research and development expenses	37	572
Prepaid expenses and other current assets	$ 1,074	$ 1,958

Fair Value Measurement - Summary of Financial Assets Measured at Fair Value on Recurring Basis (Detail) - Fair Value on Recurring Basis [Member] - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Assets Fair Value Disclosure
Assets Fair Value Disclosure	$ 89,229	$ 96,707
Money Market Funds [Member] \| Cash Equivalents [Member]
Assets Fair Value Disclosure
Assets Fair Value Disclosure	89,229	96,707
Level 1 [Member]
Assets Fair Value Disclosure
Assets Fair Value Disclosure	89,229	96,707
Level 1 [Member] \| Money Market Funds [Member] \| Cash Equivalents [Member]
Assets Fair Value Disclosure
Assets Fair Value Disclosure	89,229	96,707
Level 2 [Member]
Assets Fair Value Disclosure
Assets Fair Value Disclosure	0	0
Level 2 [Member] \| Money Market Funds [Member] \| Cash Equivalents [Member]
Assets Fair Value Disclosure
Assets Fair Value Disclosure	0	0
Level 3 [Member]
Assets Fair Value Disclosure
Assets Fair Value Disclosure	0	0
Level 3 [Member] \| Money Market Funds [Member] \| Cash Equivalents [Member]
Assets Fair Value Disclosure
Assets Fair Value Disclosure	$ 0	$ 0

Leases - Summary of Future Minimum Payments of Operating Lease Liabilities (Details) $ in Thousands	Mar. 31, 2024 USD ($)
Leases [Abstract]
2024	$ 224
2025	0
2026	0
2027	0
Thereafter	0
Total lease payments	224
Less: interest	0
Present value of lease liabilities	$ 224

Net Income (Loss) Per Share

3 Months Ended

Mar. 31, 2024

Earnings Per Share [Abstract]

Net Income (Loss) Per Share

10. Net Income (Loss) Per Share

For purposes of the diluted net loss per share calculation, stock options and unvested restricted stock 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 loss per share 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 loss per share for the periods indicated:


	Three Months Ended March 31,
	2024		2023
Options to purchase common stock		4,812,817		9,154,769
Restricted stock units		677,785		2,026,338

Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Operating expenses:
Research and development	$ 683	$ 17,333
General and administrative	7,258	7,887
Total operating expenses	7,941	25,220
Loss from operations	(7,941)	(25,220)
Other income:
Interest income, net	1,146	248
Other (expense) income, net	(13)	15
Total other income, net	1,133	263
Net loss and comprehensive loss attributable to common stockholders-basic and diluted	$ (6,808)	$ (24,957)
Net loss per share - basic	$ (0.15)	$ (0.57)
Net loss per share - diluted	$ (0.15)	$ (0.57)
Weighted-average common shares outstanding - basic	44,791	44,037
Weighted-average common shares outstanding - diluted	44,791	44,037

Stockholders' Equity - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Equity [Abstract]
Common stock, authorized	150,000,000	150,000,000
Common stock, par value	$ 0.0001	$ 0.0001
Undesignated preferred stock	10,000,000	10,000,000
Undesignated shares of preferred stock outstanding	0	0
Cash dividends	$ 0

Subsequent Events (Additional Information) (Details)	Mar. 31, 2024 Number
Subsequent Event [Line Items]
Company workforce reduction	11

Commitments and Contingencies

3 Months Ended

Mar. 31, 2024

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

7. Commitments and Contingencies

Legal Proceedings

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 three months ended March 31, 2024 and 2023 and to the best of the Company’s 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 at March 31, 2024 and December 31, 2023, or royalties on future sales. No milestone or royalty payments under these agreements are expected to be payable in the immediate future, except as disclosed in Note 3 “License Agreements.”

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. Further, the Company indemnifies its directors and officers who are, or were, serving at the Company’s request in such capacities. The Company’s maximum exposure under these arrangements is unknown as of March 31, 2024. The Company does not anticipate recognizing any significant losses relating to these arrangements. 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.

Supplemental Balance Sheet Information - Summary of Accrued Expenses (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Accrued Liabilities, Current [Abstract]
Consulting and professional fees	$ 1,630	$ 892
Compensation and benefit costs	686	3,463
Research and development expenses	396	711
Other liabilities	330	383
Accrued expenses and other current liabilities	$ 3,042	$ 5,449

Pay vs Performance Disclosure - USD ($) $ in Thousands	3 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Mar. 31, 2024	Mar. 31, 2023
Pay vs Performance Disclosure
Net Income (Loss)	$ (6,808)	$ (24,957)

- Definition

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

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+ Details

Net Income (Loss) Per Share - Components of Basic and Diluted Earnings Per Share (Details) - $ / shares shares in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Denominator:
Weighted-average common shares outstanding - basic	44,791	44,037
Weighted-average number of common shares outstanding - diluted	44,791	44,037
Net loss per share - basic	$ (0.15)	$ (0.57)
Net income (loss) per share applicable to common stockholders diluted	$ (0.15)	$ (0.57)

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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- Definition

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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+ Details

Fair Value Measurement (Tables)

3 Months Ended

Mar. 31, 2024

Fair Value Disclosures [Abstract]

Summary of Financial Assets Measured at Fair Value on Recurring Basis

The following table presents information about the Company’s financial assets 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 March 31, 2024 and December 31, 2023:


	Fair Value Measurements as of March 31, 2024
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents — money market funds	$	89,229	$	—	$	—	$	89,229
	$	89,229	$	—	$	—	$	89,229


	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

Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2024 USD ($) Segment	Dec. 31, 2023 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Number of operating segment \| Segment	1
Operating lease assets	$ 110	$ 432
Operating lease liabilities	$ 224

Restructuring Activities

3 Months Ended

Mar. 31, 2024

Restructuring and Related Activities [Abstract]

Restructuring Activities

12. Restructuring Activities

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). For the three months ended March 31, 2024 and 2023, no related expense was recognized. 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 as of March 31, 2024.

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). For the three months ended March 31, 2024 and 2023, no related expense was recognized. 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 as of March 31, 2024.

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). For the three months ended March 31, 2024 the Company recognized $74 and $9 of research and development and general and administrative expense, respectively, in the consolidated statement of operations and comprehensive loss. For the three months ended March 31, 2023, no related expense was recognized. 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 as of March 31, 2024.

The Company’s workforce was reduced by 2 employees in the February 2024 Workforce Reduction effective as of February 29, 2024. Under the February 2024 Workforce Reduction, the Company recognized total restructuring expenses of $241 for the three months ended March 31, 2024 recognized as $146 and $96 of research and development and general and administrative expense, respectively, in the consolidated statement of operations and comprehensive loss. For the three months ended March 31, 2023, no related expense was recognized. 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 as of March 31, 2024.


	Three Months Ended March 31,
	2024
Restructuring expenses	$	5,299
Cash payments		(4,820	)
Non-cash expenses		(479	)
Liability included in accrued expenses and other current liabilities at March 31, 2024	$	—

Nature of the Business

3 Months Ended

Mar. 31, 2024

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. On January 30, 2024, the Company entered into the Agreement and Plan of Merger and Reorganization (the “Merger Agreement”), with Alpine Merger Subsidiary, Inc. (“Merger Sub”), a direct, wholly owned subsidiary of the Company, and Tectonic Therapeutic, Inc. (“Tectonic”) pursuant to which Merger Sub will merge with and into Tectonic, with Tectonic surviving as a wholly-owned subsidiary of the Company (the “Merger”).

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 March 31, 2024, the Company had an accumulated deficit of $484,083. The Company expects that its cash and cash equivalents of $90,481 as of March 31, 2024 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 Quarterly Report on Form 10-Q 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 on June 9, 2023 and recognized $83,736 as a gain on asset sale, net of $3,764 transaction costs, in the condensed consolidated statement of operations and comprehensive income (loss) for the three months ended March 31, 2024. 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, December 2023 Workforce Reduction, and February 2024 Workforce Reduction were offered separation benefits, including severance payments. See Note 12 for further discussion.

Stockholders' Equity

3 Months Ended

Mar. 31, 2024

Equity [Abstract]

Stockholders' Equity

8. Stockholders’ Equity

Common Stock

As of March 31, 2024 and December 31, 2023, 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 March 31, 2024 and December 31, 2023, no undesignated preferred stock was outstanding.

Through March 31, 2024, no cash dividends have been declared or paid.

Common Stock Reserved for Future Issuance

As of March 31, 2024 and December 31, 2023, the Company has reserved the following shares of common stock for future issuance:


	March 31, 2024		December 31, 2023
Shares reserved for exercise of outstanding stock options		4,812,817		5,142,272
Shares reserved for vesting of restricted stock units		677,785		936,358
Shares reserved for issuance under the 2018 Stock Option and Grant Plan		8,299,245		7,978,667
Shares reserved for issuance under the 2018 Employee Stock Purchase Plan		1,771,748		1,771,748
Shares reserved for issuance under the 2019 Inducement Plan		1,511,183		1,407,211
Shares reserved for issuance under the 2020 Inducement Plan		1,700,000		1,700,000
Total shares of authorized common stock reserved for future issuance		18,772,778		18,936,256

- Definition

The entire disclosure for equity.

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+ Details

Supplemental Balance Sheet Information (Tables)

3 Months Ended

Mar. 31, 2024

Balance Sheet Related Disclosures [Abstract]

Summary of Prepaid Expenses and Other Current Assets

Prepaid expenses and other current assets consisted of the following:


	March 31, 2024		December 31, 2023
Other current assets	$	626	$	570
Prepaid insurance		411		816
Prepaid research and development expenses		37		572
Prepaid expenses and other current assets	$	1,074	$	1,958

Summary of Restricted Cash

As of March 31, 2024 and December 31, 2023, the Company had restricted cash as presented in the table below, which consists of cash used to secure letters of credit for the benefit of the landlord in connection with the Company’s lease agreements 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.


	March 31, 2024		December 31, 2023
Restricted cash	$	283	$	283
Restricted cash, net of current portion		400		400

Summary of Accrued Expenses

Accrued expenses and other current liabilities consisted of the following:


	March 31, 2024		December 31, 2023
Consulting and professional fees	$	1,630	$	892
Compensation and benefit costs		686		3,463
Research and development expenses		396		711
Other liabilities		330		383
Accrued expenses and other current liabilities	$	3,042	$	5,449

Fair Value Measurement

3 Months Ended

Mar. 31, 2024

Fair Value Disclosures [Abstract]

Fair Value Measurement

4. Fair Value Measurement


	Fair Value Measurements as of March 31, 2024
	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents — money market funds	$	89,229	$	—	$	—	$	89,229
	$	89,229	$	—	$	—	$	89,229


	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

The fair value of cash equivalents was determined through quoted prices by third-party pricing services.

During the three months ended March 31, 2024, 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

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Share-Based Payment Arrangement [Abstract]
Aggregate intrinsic value of options exercised	$ 16	$ 1
Total fair value of restricted stock units vested	326	$ 194
Unrecognized stock-based compensation expenses	$ 2,911
Unrecognized stock-based compensation expense, period for recognition	1 year 10 months 28 days

Leases - Summary of Effective Lease Cost Comprehensive Income Loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Leases [Abstract]
Operating lease costs	$ 339	$ 670
Sublease income	0	(23)
Total lease costs	$ 339	$ 647

Stock-Based Compensation - Schedule of Stock-based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 878	$ 2,530
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	170	622
General and Administrative Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 708	$ 1,908

Nature of the Business - Additional Information (Detail) $ in Thousands		3 Months Ended	12 Months Ended
	Jun. 09, 2023 USD ($)	Mar. 31, 2024 USD ($) Number	Dec. 31, 2023 USD ($)	Jul. 31, 2023	May 19, 2023 USD ($)	Mar. 31, 2023 USD ($)
Accumulated deficit		$ (484,083)	$ (477,275)
Cash payment of closing the transaction					$ 87,500
Cash and cash equivalents		90,481	98,020			$ 72,326
Gain loss on recognize assets sales	$ 83,736	$ 3,764	$ 83,736
Reduction in workforce, percentage				50.00%
Reduction in workforce, number \| Number		11
Asset Purchase Agreement [Member]
Reduction in workforce, number \| Number		8

- Definition

Amount of accumulated undistributed earnings (deficit).

+ References + Details

Leases (Tables)

3 Months Ended

Mar. 31, 2024

Leases [Abstract]

Schedule of Effect of Lease Costs in the Company's Consolidated Statement of Operations and Comprehensive Loss

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


	Three Months Ended March 31,		Three Months Ended March 31,
	2024		2023
Operating lease costs	$	339	$	670
Sublease income		—		(23	)
Total lease costs	$	339	$	647

Schedule of Future Minimum Payments of Operating Lease Liabilities

As of March 31, 2024, future minimum payments of operating lease liabilities are as follows:


	March 31, 2024
2024	$	224
2025		—
2026		—
2027		—
Thereafter		—
Total lease payments	$	224
Less: interest		—
Present value of lease liabilities	$	224

Summary of Significant Accounting Policies (Policies)	3 Months Ended
Summary of Significant Accounting Policies (Policies)	Mar. 31, 2024
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed consolidated financial statements (the “unaudited condensed 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 the FASB. The unaudited condensed consolidated financial statements have been prepared on the same basis as the audited annual consolidated financial statements as of and for the year ended December 31, 2023, and, in the opinion of management, reflect all adjustments, consisting of normal recurring adjustments, necessary for the fair presentation of the Company’s financial position as of March 31, 2024, and the results of its operations for the three months ended March 31, 2024 and 2023, its statements of stockholders’ equity for the three months ended March 31, 2024 and 2023 and its statement of cash flows for the three months ended March 31, 2024 and 2023. The results for the three months ended March 31, 2024 are not necessarily indicative of the results to be expected for the year ending December 31, 2024, any other interim periods, or any future year or period. These interim financial statements should be read in conjunction with the audited financial statements as of and for the year ended December 31, 2023, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2023, filed with the SEC on March 14, 2024. The unaudited condensed consolidated financial statements reflect the application of certain significant accounting policies as described below and elsewhere in these notes to the unaudited condensed consolidated financial statements. As of March 31, 2024, there have been no changes to the Company’s significant accounting policies as described in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2023.
Segment Information	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	Use of Estimates The preparation of the unaudited condensed consolidated 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 ongoing 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. Significant estimates relied upon in preparing the unaudited condensed consolidated financial statements include the determination of the fair value of share-based awards issued and the estimation of accrued research and development expenses.
Stock-Based Compensation	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. Prior to the adoption of ASU No. 2018-07, Compensation-Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting, the measurement date for non-employee awards was generally the date the services are completed, resulting in financial reporting period adjustments to stock-based compensation during the vesting terms for changes in the fair value of the awards. After adoption of ASU 2018-07, the measurement date for non-employee awards is the later of the adoption date of ASU 2018-07, or the date of grant, without change in the fair value of the award. 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.
Subsequent Event Considerations	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.
Recently Issued Accounting Pronouncements	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 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.

- Definition

Disclosure of accounting policy for segment reporting.

+ References + Details

Supplemental Balance Sheet Information

3 Months Ended

Mar. 31, 2024

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:


	March 31, 2024		December 31, 2023
Other current assets	$	626	$	570
Prepaid insurance		411		816
Prepaid research and development expenses		37		572
Prepaid expenses and other current assets	$	1,074	$	1,958

Restricted cash


	March 31, 2024		December 31, 2023
Restricted cash	$	283	$	283
Restricted cash, net of current portion		400		400

Accrued expenses and other current liabilities

Accrued expenses and other current liabilities consisted of the following:


	March 31, 2024		December 31, 2023
Consulting and professional fees	$	1,630	$	892
Compensation and benefit costs		686		3,463
Research and development expenses		396		711
Other liabilities		330		383
Accrued expenses and other current liabilities	$	3,042	$	5,449

Stockholders' Equity - Summary of Common Stock Reserved for Future Issuance (Detail) - shares	Mar. 31, 2024	Dec. 31, 2023
Class Of Stock [Line Items]
Total shares of authorized common stock reserved for future issuance	18,772,778	18,936,256
Employee Stock Option
Class Of Stock [Line Items]
Total shares of authorized common stock reserved for future issuance	4,812,817	5,142,272
Restricted Stock Units
Class Of Stock [Line Items]
Total shares of authorized common stock reserved for future issuance	677,785	936,358
2018 Stock Option and Incentive Plan
Class Of Stock [Line Items]
Total shares of authorized common stock reserved for future issuance	8,299,245	7,978,667
2018 Employee Stock Purchase Plan
Class Of Stock [Line Items]
Total shares of authorized common stock reserved for future issuance	1,771,748	1,771,748
2019 Inducement Plan
Class Of Stock [Line Items]
Total shares of authorized common stock reserved for future issuance	1,511,183	1,407,211
2020 Inducement Plan
Class Of Stock [Line Items]
Total shares of authorized common stock reserved for future issuance	1,700,000	1,700,000

- 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

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+ Details

Fair Value Measurement - Additional Information (Detail) $ in Thousands	Mar. 31, 2024 USD ($)
Fair Value Disclosures [Abstract]
Fair value input transfer between levels	$ 0

Insider Trading Arrangements	3 Months Ended
Insider Trading Arrangements	Mar. 31, 2024
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

License Agreements

3 Months Ended

Mar. 31, 2024

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 had 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 expected 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 three months ended March 31, 2024, the Company did not incur costs related to the CRFA. For the three months ended March 31, 2023, the Company incurred $1,610 related to the CRFA.

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 is also required to pay UHN future annual license maintenance fees until

the first sale of a licensed product in certain markets. The Company is 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 has agreed to pay a low double-digit royalty percentage of all sublicensing revenue.

The agreement requires the Company to meet certain performance milestones within specified timeframes. UHN may terminate the agreement if the Company fails 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 expires 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 expires upon the expiration of the Company’s royalty obligation for all licensed products. UHN can terminate the agreement if the Company fails 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 may 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 can 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 three months ended March 31, 2024, the Company did not incur research and development expense related to this agreement with UHN. For the three months ended March 31, 2023 the Company recorded research and development expense related to this agreement with UHN of $34, which consists of reimbursable funded study trial costs. No milestone or maintenance fees were incurred related to this agreement in the three months ended March 31, 2024 and 2023.

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 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 three months ended March 31, 2024, the Company did not incur research and development expense related to this agreement with UHN. For the three months ended March 31, 2023 the Company recorded research and development expense related to this agreement with UHN of $37. No milestone fees were incurred related to this agreement in the three months ended March 31, 2024 and 2023.

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 has 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 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.

The Company has recognized no expenses related to the license for the three months ended March 31, 2024 and 2023.

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 Therapeutics, Inc. (“Papillon”). On June 9, 2023, in connection with the close of the Asset Purchase Agreement, discussed and defined above, the Company transferred this agreement to Novartis.

The Company has recognized no expenses related to this agreement for the three months ended March 31, 2024 and 2023.

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.

The Company has recognized no expenses related to this agreement for the three months ended March 31, 2024 and 2023.

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. During the year ended December 31, 2023, 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).

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Cash flows from operating activities:
Net loss	$ (6,808)	$ (24,957)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	878	2,530
Depreciation and amortization expense	0	328
Non-cash interest expense	0	80
Non-cash lease expense	322	592
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	884	2,187
Accounts payable	216	207
Current and non-current operating lease liabilities	(654)	(600)
Accrued expenses and other current liabilities	(2,407)	(651)
Net cash used in operating activities	(7,569)	(20,284)
Cash flows from investing activities:
Purchases of property and equipment	0	(8)
Net cash used in investing activities	0	(8)
Cash flows from financing activities:
Proceeds from exercise of stock options	26	42
Proceeds from issuance of ESPP shares	4	13
Net cash provided by financing activities	30	55
Net decrease in cash, cash equivalents and restricted cash	(7,539)	(20,237)
Cash, cash equivalents and restricted cash at beginning of period	98,703	92,846
Cash, cash equivalents and restricted cash, end of period	91,164	72,609
Supplemental disclosure of non-cash investing and financing activities:
Interest paid	0	463
Lease liability arising from obtaining right-of-use assets	0	2,392
Reconciliation of cash, cash equivalents and restricted cash reported within the condensed consolidated balance sheets:
Cash and cash equivalents, end of period	90,481	72,326
Restricted cash	683	283
Cash, cash equivalents and restricted cash, end of period	$ 91,164	$ 72,609

Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2024

Share-Based Payment Arrangement [Abstract]

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity for the three months ended March 31, 2024:


	Number of Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
Outstanding as of December 31, 2023		5,142,272		$	7.33		6.24	$	663
Granted		—		$	—
Exercised		(32,756	)	$	0.79
Cancelled or forfeited		(296,699	)	$	9.71
Outstanding as of March 31, 2024		4,812,817		$	7.23		6.09	$	519
Exercisable as of March 31, 2024		3,639,245		$	8.45		5.46	$	346

Summary of Restricted Common Stock Units

The following table summarizes the Company’s restricted common stock units for the three months ended March 31, 2024:


	Number of Shares			Weighted- Average Grant Date Fair Value
Issued and unvested as of December 31, 2023		936,358		$	2.13
Granted		60,251		$	1.31
Vested		(190,973	)	$	1.71
Forfeited, cancelled or expired		(127,851	)	$	2.49
Issued and unvested as of March 31, 2024		677,785		$	2.11

Schedule of Stock-based Compensation Expense

Stock-based compensation expense was allocated as follows:


	Three Months Ended March 31,
	2024		2023
Research and development	$	170	$	622
General and administrative		708		1,908
Total stock-based compensation expense	$	878	$	2,530

Net Income (Loss) Per Share (Tables)

3 Months Ended

Mar. 31, 2024

Earnings Per Share [Abstract]

Schedule of Dilutive Common Stock Equivalents Excluded from Computation of Diluted Net Income (Loss) Per Share


	Three Months Ended March 31,
	2024		2023
Options to purchase common stock		4,812,817		9,154,769
Restricted stock units		677,785		2,026,338

Supplemental Balance Sheet Information - Summary of Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Restricted Cash and Investments [Abstract]
Restricted cash	$ 283	$ 283
Restricted cash, net of current portion	$ 400	$ 400

Leases (Additional Information) (Details) $ in Thousands, $ in Thousands			3 Months Ended
	Jun. 01, 2020	Aug. 31, 2018	Mar. 31, 2024 USD ($)	Sep. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Mar. 31, 2024 CAD ($)	Mar. 31, 2024 USD ($)	Dec. 31, 2023 CAD ($)	Dec. 31, 2023 USD ($)
Lessee, Lease, Description [Line Items]
Lease agreement expiration month and year	2025-06	2020-10
Impairment of right of use assets				$ 940
Cash payments for pperating leases			$ 672		$ 687
Weighted average remaining lease term					1 year 2 months 12 days	1 month 6 days	1 month 6 days
Weighted average incremental borrowing rate					15.67%	16.15%	16.15%
Restricted Cash [Member]
Lessee, Lease, Description [Line Items]
Security deposit in connection with lease							$ 283		$ 283
Other Noncurrent Assets [Member]
Lessee, Lease, Description [Line Items]
Security deposit in connection with lease						$ 27		$ 27

Condensed 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, 2022	$ 75,370	$ 4	$ 564,798	$ (489,432)
Beginning balance, shares at Dec. 31, 2022		43,916,000
Vesting of restricted stock units, shares		105,000
Exercise of stock options	42		42
Exercise of stock options, shares		46,000
Issuance of common stock under the 2018 employee stock purchase plan	13		13
Issuance of common stock under 2018 employee stock purchase plan, shares		21,000
Stock-based compensation expense	2,530		2,530
Net Income (Loss)	(24,957)			(24,957)
Ending balance at Mar. 31, 2023	52,998	$ 4	567,383	(514,389)
Ending balance, shares at Mar. 31, 2023		44,088,000
Beginning balance at Dec. 31, 2023	94,739	$ 4	572,010	(477,275)
Beginning balance, shares at Dec. 31, 2023		44,654,000
Vesting of restricted stock units, shares		191,000
Exercise of stock options	$ 26		26
Exercise of stock options, shares	32,756	33,000
Issuance of common stock under the 2018 employee stock purchase plan	$ 4		4
Issuance of common stock under 2018 employee stock purchase plan, shares		4,000
Stock-based compensation expense	878		878
Net Income (Loss)	(6,808)			(6,808)
Ending balance at Mar. 31, 2024	$ 88,839	$ 4	$ 572,918	$ (484,083)
Ending balance, shares at Mar. 31, 2024		44,882,000

- Definition

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

+ References

+ Details

- Definition

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

+ References

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+ Details

License Agreements - Additional Information (Detail) £ in Thousands, $ in Thousands, $ in Thousands							1 Months Ended	3 Months Ended			12 Months Ended
	Sep. 08, 2023 GBP (£)	Jun. 09, 2023 USD ($)	Sep. 30, 2020 USD ($)	Oct. 02, 2017 USD ($)	Jan. 27, 2016 CAD ($) shares	Jan. 27, 2016 USD ($)	Aug. 31, 2017 USD ($) shares	Mar. 31, 2024 GBP (£) shares	Mar. 31, 2024 USD ($) shares	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($) shares	Dec. 31, 2020 USD ($)	Jan. 04, 2024 CAD ($)	May 19, 2023 USD ($)	Nov. 17, 2016 USD ($)
License Agreement [Line Items]
Collaborative agreement expenses									$ 0	$ 1,610
Common stock, issued \| shares								44,882,000	44,882,000		44,654,000
Research and development									$ 683	17,333
Preferred stock issued \| shares								0	0		0
Cash payment of closing the transaction														$ 87,500
Gain loss on recognize assets sales		$ 83,736							$ 3,764		$ 83,736
Net of transaction costs											$ 3,764
Sale of Cystinosis Program [Member]
License Agreement [Line Items]
Cash payment of closing the transaction														$ 87,500
University of Manchester Agreement [Member] \| MPSII License Agreement [Member]
License Agreement [Line Items]
Upfront license fee												$ 8,000
Milestone payments payable			$ 80,000
Milestone payment paid			$ 2,000
Research and development expense \| £	£ 3,900							£ 9,900
UHN Agreement [Member]
License Agreement [Line Items]
Research and development expense									0	34
Milestone fees									0	0
UHN Agreement [Member] \| Fabry License Agreement [Member]
License Agreement [Line Items]
Upfront license fee					$ 75
Milestone payments payable					2,450
Option fee					20
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
Fair value of shares issued						$ 480
Payments upon closing of an initial public offering						$ 2,000
Research and development									0	37
BioMarin Pharmaceutical Inc [Member]
License Agreement [Line Items]
Upfront license fee							$ 500
Preferred stock issued \| shares							233,765
Milestone payments									13,000
Expenses related to license									0	0
GenStem Therapeutics Inc [Member]
License Agreement [Line Items]
Upfront license fee				$ 1,000
Milestone payments payable				$ 16,000
Expenses related to license									0	0
Lund University Rights Holders Agreement [Member]
License Agreement [Line Items]
Milestone payments payable															$ 550
Expenses related to license									$ 0	$ 0

Stock-Based Compensation

3 Months Ended

Mar. 31, 2024

Share-Based Payment Arrangement [Abstract]

Stock-Based Compensation

9. Stock-based Compensation

Stock Option Valuation

The following table summarizes the Company’s stock option activity for the three months ended March 31, 2024:


	Number of Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
Outstanding as of December 31, 2023		5,142,272		$	7.33		6.24	$	663
Granted		—		$	—
Exercised		(32,756	)	$	0.79
Cancelled or forfeited		(296,699	)	$	9.71
Outstanding as of March 31, 2024		4,812,817		$	7.23		6.09	$	519
Exercisable as of March 31, 2024		3,639,245		$	8.45		5.46	$	346

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 three months ended March 31, 2024 and 2023 was $16 and $1, respectively.

Restricted Stock Units

The following table summarizes the Company’s restricted common stock units for the three months ended March 31, 2024:


	Number of Shares			Weighted- Average Grant Date Fair Value
Issued and unvested as of December 31, 2023		936,358		$	2.13
Granted		60,251		$	1.31
Vested		(190,973	)	$	1.71
Forfeited, cancelled or expired		(127,851	)	$	2.49
Issued and unvested as of March 31, 2024		677,785		$	2.11

The total fair value of restricted stock units vested during the three months ended March 31, 2024 and 2023 was $326 and $194, respectively.

Stock-Based Compensation

Stock-based compensation expense was allocated as follows:


	Three Months Ended March 31,
	2024		2023
Research and development	$	170	$	622
General and administrative		708		1,908
Total stock-based compensation expense	$	878	$	2,530

As of March 31, 2024, total unrecognized compensation cost related to the unvested stock-based awards was $2,911, which is expected to be recognized over a weighted-average period of 1.91 years.

Stock-Based Compensation - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding [Roll Forward]
Number of options, Outstanding beginning balance	5,142,272
Number of options, Granted	0
Number of options, Exercised	(32,756)
Number of options, Cancelled or forfeited	(296,699)
Number of options, Outstanding ending balance	4,812,817	5,142,272
Number of options, Exercisable	3,639,245
Weighted average exercise price, Outstanding beginning balance	$ 7.33
Weighted average exercise price, Granted	0
Weighted average exercise price, Exercised	0.79
Weighted average exercise price, Cancelled or forfeited	9.71
Weighted average exercise price, Outstanding ending balance	7.23	$ 7.33
Weighted average exercise price, Exercisable	$ 8.45
Weighted average remaining contractual term, Outstanding balance	6 years 1 month 2 days	6 years 2 months 26 days
Weighted average remaining contractual term, Exercisable	5 years 5 months 15 days
Aggregate intrinsic value, Outstanding balance	$ 519	$ 663
Aggregate intrinsic value, Exercisable	$ 346

Summary of Significant Accounting Policies	3 Months Ended
Summary of Significant Accounting Policies	Mar. 31, 2024
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying condensed consolidated financial statements (the “unaudited condensed 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 the FASB. The unaudited condensed consolidated financial statements have been prepared on the same basis as the audited annual consolidated financial statements as of and for the year ended December 31, 2023, and, in the opinion of management, reflect all adjustments, consisting of normal recurring adjustments, necessary for the fair presentation of the Company’s financial position as of March 31, 2024, and the results of its operations for the three months ended March 31, 2024 and 2023, its statements of stockholders’ equity for the three months ended March 31, 2024 and 2023 and its statement of cash flows for the three months ended March 31, 2024 and 2023. The results for the three months ended March 31, 2024 are not necessarily indicative of the results to be expected for the year ending December 31, 2024, any other interim periods, or any future year or period. These interim financial statements should be read in conjunction with the audited financial statements as of and for the year ended December 31, 2023, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2023, filed with the SEC on March 14, 2024. The unaudited condensed consolidated financial statements reflect the application of certain significant accounting policies as described below and elsewhere in these notes to the unaudited condensed consolidated financial statements. As of March 31, 2024, there have been no changes to the Company’s significant accounting policies as described in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2023. 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 the unaudited condensed consolidated 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 ongoing 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. Significant estimates relied upon in preparing the unaudited condensed consolidated financial statements include the determination of the fair value of share-based awards issued and the estimation of accrued research and development expenses. 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. Prior to the adoption of ASU No. 2018-07, Compensation-Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting, the measurement date for non-employee awards was generally the date the services are completed, resulting in financial reporting period adjustments to stock-based compensation during the vesting terms for changes in the fair value of the awards. After adoption of ASU 2018-07, the measurement date for non-employee awards is the later of the adoption date of ASU 2018-07, or the date of grant, without change in the fair value of the award. 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. 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. 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 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.

Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2024

Equity [Abstract]

Summary of Common Stock Reserved for Future Issuance

As of March 31, 2024 and December 31, 2023, the Company has reserved the following shares of common stock for future issuance:


	March 31, 2024		December 31, 2023
Shares reserved for exercise of outstanding stock options		4,812,817		5,142,272
Shares reserved for vesting of restricted stock units		677,785		936,358
Shares reserved for issuance under the 2018 Stock Option and Grant Plan		8,299,245		7,978,667
Shares reserved for issuance under the 2018 Employee Stock Purchase Plan		1,771,748		1,771,748
Shares reserved for issuance under the 2019 Inducement Plan		1,511,183		1,407,211
Shares reserved for issuance under the 2020 Inducement Plan		1,700,000		1,700,000
Total shares of authorized common stock reserved for future issuance		18,772,778		18,936,256

- 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.

+ References

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+ Details

Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2024	May 02, 2024
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Mar. 31, 2024
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q1
Entity Registrant Name	AVROBIO, INC.
Entity Central Index Key	0001681087
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	true
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	true
Securities Act File Number	001-38537
Entity Tax Identification Number	81-0710585
Entity Address, Address Line One	One Broadway
Entity Address, Address Line Two	Fourteenth Floor
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02142
City Area Code	617
Local Phone Number	914-8420
Entity Incorporation, State or Country Code	DE
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Trading Symbol	AVRO
Security Exchange Name	NASDAQ
Entity Common Stock, Shares Outstanding		44,893,750
Former Address [Member]
Document Information [Line Items]
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

Related Party Transactions - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Related Party Transaction [Line Items]
Research and development expense	$ 683	$ 17,333
Operating lease costs	339	670
License Agreement [Member]
Related Party Transaction [Line Items]
Research and development expense	0	71
Sub-lease Agreement [Member] \| Officers and Board Members [Member]
Related Party Transaction [Line Items]
Operating lease costs	$ 0	$ 652

Restructuring Activities (Additional Information) (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024 USD ($) Number	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($) Number	Feb. 29, 2024 Number	Oct. 31, 2023 Number	Jul. 12, 2023
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	$ 5,299
Reduction in workforce, number \| Number	11
Board Of Directors [Member]
Restructuring Cost and Reserve [Line Items]
Company workforce reduction						50.00%
Employee Severance and Other Benefits
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	$ 479
Cash Payments	4,820
July 2023 Workforce Reduction [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	0	$ 0	$ 3,015
Accrued Remaining Payments	0
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
October 2023 Workforce Reduction [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	0	0
Accrued Remaining Payments	0
Reduction in workforce, number \| Number					11
October 2023 Workforce Reduction [Member] \| Research and Development Expense [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring expenses			1,093
December 2023 Workforce Reduction [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring expenses		0	$ 950
Accrued Remaining Payments	0
Reduction in workforce, number \| Number			8
December 2023 Workforce Reduction [Member] \| Research and Development Expense [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	74		$ 866
December 2023 Workforce Reduction [Member] \| General and Administrative Expense [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	9		$ 64
February 2024 Workforce Reduction [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	241
Expense related to one-time employee benefits		$ 0
Accrued Remaining Payments	0
Reduction in workforce, number \| Number				2
February 2024 Workforce Reduction [Member] \| Research and Development Expense [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	146
February 2024 Workforce Reduction [Member] \| General and Administrative Expense [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	$ 96

Net Income (Loss) Per Share - Schedule of Dilutive Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Share (Detail) - shares	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
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	4,812,817	9,154,769
Restricted Stock Awards and Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	677,785	2,026,338

Stock-Based Compensation - Summary of Restricted Common Stock Units (Detail) - Restricted Stock Units	3 Months Ended
	Mar. 31, 2024 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares, Issued and unvested beginning balance \| shares	936,358
Number of shares, Granted \| shares	60,251
Number of shares, Vested \| shares	(190,973)
Number of shares, Forfeited, cancelled or expired \| shares	(127,851)
Number of shares, Issued and unvested ending balance \| shares	677,785
Weighted average grant date fair value, Issued and unvested, beginning balance \| $ / shares	$ 2.13
Weighted average grant date fair value, Granted \| $ / shares	1.31
Weighted average grant date fair value, Vested \| $ / shares	1.71
Weighted average grant date fair value, Forfeited, cancelled or expired \| $ / shares	2.49
Weighted average grant date fair value, Issued and unvested, ending balance \| $ / shares	$ 2.11

Supplemental Balance Sheet Information - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Impairment Effects on Earnings Per Share [Line Items]
Depreciation and amortization expense	$ 0	$ 328

Restructuring Activities - Summary of Restructuring Activities (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2024 USD ($)
Restructuring Cost and Reserve [Line Items]
Non-cash expenses	$ (5,299)
Employee Severance and Other Benefits
Restructuring Cost and Reserve [Line Items]
Cash Payments	(4,820)
Non-cash expenses	(479)
Liability included in accrued expenses and other current liabilities at March 31, 2024	$ 0

- 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

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 90,481	$ 98,020
Restricted cash	283	283
Prepaid expenses and other current assets	1,074	1,958
Total current assets	91,838	100,261
Operating lease assets	110	432
Restricted cash, net of current portion	400	400
Total assets	92,348	101,093
Current liabilities:
Accounts payable	243	27
Accrued expenses and other current liabilities	3,042	5,449
Operating lease liabilities	224	878
Total current liabilities	3,509	6,354
Total liabilities	3,509	6,354
Commitments and contingencies (Note 7)
Stockholders’ equity:
Preferred stock, $0.0001 par value; 10,000 shares authorized and no shares issued or outstanding as of March 31, 2024 and December 31, 2023	0	0
Common stock, $0.0001 par value; 150,000 shares authorized; 44,882 and 44,654 shares issued and outstanding as of March 31, 2024 and December 31, 2023, respectively	4	4
Additional paid-in capital	572,918	572,010
Accumulated deficit	(484,083)	(477,275)
Total stockholders’ equity	88,839	94,739
Total liabilities and stockholders’ equity	$ 92,348	$ 101,093