Tectonic Therapeutic (TECX) S-4 13 Feb 24 Registration of securities issued in business combination transactions Financial data

Cover

Cover	9 Months Ended
	Sep. 30, 2023
Document Information [Line Items]
Document Type	S-4
Amendment Flag	false
Entity Registrant Name	AVROBIO, INC.
Entity Central Index Key	0001681087
Entity Incorporation, State or Country Code	DE
Entity Primary SIC Number	2836
Entity Tax Identification Number	81-0710585
Entity 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
City Area Code	617
Local Phone Number	914-8420
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Business Contact [Member]
Document Information [Line Items]
Contact Personnel Name	Erik Ostrowski
Entity Address, Address Line One	100 Technology Square
Entity Address, Address Line Two	Sixth Floor
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02139
City Area Code	617
Local Phone Number	914-8420

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 105,842	$ 92,563	$ 189,567
Restricted cash	283	283	0
Prepaid expenses and other current assets	2,860	7,112	9,578
Held for sale assets	185	0
Total current assets	109,170	99,958	199,145
Operating lease assets	912	1,057	0
Property and equipment, net	0	2,894	4,126
Restricted cash, net of current portion	400	0	492
Other assets	40	40	74
Total assets	110,522	103,949	203,837
Current liabilities:
Accounts payable	910	384	3,486
Accrued expenses and other current liabilities	5,002	11,732	15,638
Operating lease liabilities	1,647	999	0
Deferred rent		0	262
Total current liabilities	7,559	13,115	19,386
Note payable, net of discount	0	15,276	14,945
Operating lease liabilities, net of current portion	105	188	0
Deferred rent, net of current portion		0	30
Total liabilities	7,664	28,579	34,361
Commitments and contingencies
Stockholders' equity:
Preferred stock, $0.0001 par value; 10,000 shares authorized and no shares issued or outstanding as of December 31, 2022 and 2021		0	0
Common stock	4	4	4
Additional paid-in capital	571,344	564,798	553,014
Accumulated deficit	(468,490)	(489,432)	(383,542)
Total stockholders' equity	102,858	75,370	169,476
Total liabilities and stockholders' equity	$ 110,522	$ 103,949	$ 203,837

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Statement of Financial Position [Abstract]
Preferred stock, par value		$ 0.0001	$ 0.0001
Preferred stock, authorized		10,000,000	10,000,000
Preferred stock, issued		0	0
Preferred stock, outstanding		0	0
Common stock, par value	$ 0.0001	$ 0.0001	$ 0.0001
Common stock, authorized	150,000,000	150,000,000	150,000,000
Common stock, issued	44,558,000	43,916,000	43,652,000
Common stock, outstanding	44,558,000	43,916,000	43,652,000

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Operating expenses:
Research and development	$ 14,829	$ 15,919	$ 43,310	$ 54,049	$ 72,186	$ 83,114
General and administrative	6,262	7,066	18,730	26,128	33,248	35,727
Total operating expenses	21,091	22,985	62,040	80,177	105,434	118,841
Gain on asset sale	0	0	83,736	0
Loss on impairment	(1,842)	0	(1,842)	0
(Loss) Income from operations	(22,933)	(22,985)	19,854	(80,177)	(105,434)	(118,841)
Other (expense) income:
Interest income (expense), net	1,407	111	1,160	(544)	(299)	(224)
Other expense, net	(51)	(95)	(72)	(135)	(157)	(61)
Total other income (expense), net	1,356	16	1,088	(679)	(456)	(285)
Net income (loss) and comprehensive income (loss) attributable to common stockholders - basic and diluted	$ (21,577)	$ (22,969)	$ 20,942	$ (80,856)	$ (105,890)	$ (119,126)
Net income (loss) per share applicable to common stockholders basic	$ (0.48)	$ (0.52)	$ 0.47	$ (1.85)	$ (2.42)	$ (2.78)
Net income (loss) per share applicable to common stockholders diluted	$ (0.48)	$ (0.52)	$ 0.47	$ (1.85)	$ (2.42)	$ (2.78)
Weighted-average common shares outstanding basic	44,527,997	43,772,990	44,234,936	43,722,129	43,739,000	42,854,000
Weighted-average common shares outstanding-diluted	44,527,997	43,772,990	44,425,531	43,722,129	43,739,000	42,854,000

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	ATM Facility [Member]	Common Stock [Member]	Common Stock [Member] ATM Facility [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] ATM Facility [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2020	$ 254,344		$ 4		$ 518,756		$ (264,416)
Beginning balance, shares at Dec. 31, 2020			41,569,000
Vesting of restricted stock awards and units, shares			1,000
Exercise of stock options	920				920
Exercise of stock options, shares			226,000
Issuance of common stock, net of offering costs		$ 14,550				$ 14,550
Issuance of common stock upon public offering, net of offering costs, shares				1,829,000
Issuance of common stock under the 2018 employee stock purchase plan	209				209
Issuance of common stock under the 2018 employee stock purchase plan, shares			27,000
Stock-based compensation expense	18,579				18,579
Net Income (Loss)	(119,126)						(119,126)
Ending balance at Dec. 31, 2021	$ 169,476		$ 4		553,014		(383,542)
Ending balance, shares at Dec. 31, 2021			43,652,000
Exercise of stock options, shares	0
Issuance of common stock under the 2018 employee stock purchase plan	$ 203				203
Issuance of common stock under the 2018 employee stock purchase plan, shares			121,000
Stock-based compensation expense	9,267				9,267
Net Income (Loss)	(80,856)						(80,856)
Ending balance at Sep. 30, 2022	98,090		$ 4		562,484		(464,398)
Ending balance, shares at Sep. 30, 2022			43,773,000
Beginning balance at Dec. 31, 2021	169,476		$ 4		553,014		(383,542)
Beginning balance, shares at Dec. 31, 2021			43,652,000
Vesting of restricted stock awards and units, shares			1,000
Exercise of stock options	$ 58				58
Exercise of stock options, shares	142,013		142,000
Issuance of common stock under the 2018 employee stock purchase plan	$ 204				204
Issuance of common stock under the 2018 employee stock purchase plan, shares			121,000
Stock-based compensation expense	11,522				11,522
Net Income (Loss)	(105,890)						(105,890)
Ending balance at Dec. 31, 2022	75,370		$ 4		564,798		(489,432)
Ending balance, shares at Dec. 31, 2022			43,916,000
Beginning balance at Jun. 30, 2022	118,343		$ 4		559,768		(441,429)
Beginning balance, shares at Jun. 30, 2022			43,696,000
Issuance of common stock under the 2018 employee stock purchase plan	60				60
Issuance of common stock under the 2018 employee stock purchase plan, shares			77,000
Stock-based compensation expense	2,656				2,656
Net Income (Loss)	(22,969)						(22,969)
Ending balance at Sep. 30, 2022	98,090		$ 4		562,484		(464,398)
Ending balance, shares at Sep. 30, 2022			43,773,000
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 awards and units, shares			284,000
Exercise of stock options	$ 176				176
Exercise of stock options, shares	223,273		224,000
Issuance of common stock under the 2018 employee stock purchase plan	$ 86				86
Issuance of common stock under the 2018 employee stock purchase plan, shares			134,000
Stock-based compensation expense	6,284				6,284
Net Income (Loss)	20,942						20,942
Ending balance at Sep. 30, 2023	102,858		$ 4		571,344		(468,490)
Ending balance, shares at Sep. 30, 2023			44,558,000
Beginning balance at Jun. 30, 2023	122,037		$ 4		568,946		(446,913)
Beginning balance, shares at Jun. 30, 2023			44,308,000
Vesting of restricted stock awards and units, shares			30,000
Exercise of stock options	106				106
Exercise of stock options, shares			107,000
Issuance of common stock under the 2018 employee stock purchase plan	73				73
Issuance of common stock under the 2018 employee stock purchase plan, shares			113,000
Stock-based compensation expense	2,219				2,219
Net Income (Loss)	(21,577)						(21,577)
Ending balance at Sep. 30, 2023	$ 102,858		$ 4		$ 571,344		$ (468,490)
Ending balance, shares at Sep. 30, 2023			44,558,000

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Stockholders' Equity (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($)
ATM Facility [Member]
Issuance of common stock upon public offering, offering costs	$ 47

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Cash flows from operating activities:
Net income (loss)	$ 20,942	$ (80,856)	$ (105,890)	$ (119,126)
Adjustments to reconcile net loss to net cash used in operating activities:
Gain on asset sale	(83,736)	0
Stock-based compensation expense	6,284	9,267	11,522	18,579
Depreciation and amortization expense	617	1,105	1,440	1,399
Non-cash asset impairment charges	1,842	0
Non-cash interest expense	1,074	260	331	0
Loss on disposal of property and equipment	0	59	59	0
Deferred rent expense	0	(231)	0	(223)
Non-cash lease expense	1,597	0	2,726	0
(Gain)/loss on impairment of leasehold improvements			86	0
(Gain)/loss on extinguishment of operating lease			(81)	0
Other			0	49
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	4,252	(195)	2,466	(2,018)
Other assets	0	(33)	34	362
Accounts payable	526	(1,672)	(3,102)	804
Current and non-current operating lease liabilities	(1,827)	0	(2,893)	0
Accrued expenses and other current liabilities	(6,730)	(1,305)	(3,906)	2,149
Net cash used in operating activities	(55,159)	(73,535)	(97,208)	(98,025)
Cash flows from investing activities:
Proceeds from asset sale, net	83,736	0
Purchases of property and equipment	(8)	(267)	(267)	(2,461)
Proceeds from the sale of property, plant, and equipment	1,198	0
Net cash provided by (used in) investing activities	84,926	(267)	(267)	(2,461)
Cash flows from financing activities:
Repayment of note payable, including end of term charge	(16,350)	0
Proceeds from long-term debt			0	15,000
Payments of issuance cost related to long-term debt			0	(103)
Proceeds from exercise of stock options	176	0	58	920
Proceeds from issuance of ESPP shares	86	203
Net cash (used in) provided by financing activities	(16,088)	203	262	30,371
Net increase (decrease) in cash, cash equivalents and restricted cash	13,679	(73,599)	(97,213)	(70,115)
Cash, cash equivalents and restricted cash at beginning of period	92,846	190,059	190,059	260,174
Cash, cash equivalents and restricted cash, end of period	106,525	116,460	92,846	190,059
Supplemental disclosure of non-cash investing and financing activities:
Interest paid	831	1,002	1,425	98
Purchases of property and equipment included in accounts payable and accrued expenses	0	0
Right of use asset obtained in exchange for operating lease liabilities			4,319	0
Reconciliation of cash, cash equivalents and restricted cash reported within the condensed consolidated balance sheets:
Cash and cash equivalents, end of period	105,842	115,968	92,563	189,567
Restricted cash	683	492	283	492
Cash, cash equivalents and restricted cash, end of period	$ 106,525	$ 116,460	92,846	190,059
2018 Employee Stock Purchase Plan [Member]
Cash flows from financing activities:
Proceeds from issuance of ESPP shares			204	209
Public Offering [Member]
Cash flows from financing activities:
Proceeds from issuance of ESPP shares			0	(205)
ATM Facility [Member]
Cash flows from financing activities:
Proceeds from issuance of ESPP shares			$ 0	$ 14,550

Nature of the Business

Nature of the Business	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
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 ex vivo lentiviral gene therapies to treat rare diseases following a single dose treatment regimen. On July 12, 2023, following a comprehensive review of the Company’s business by its Board of Directors (the “Board”), the Company announced its intention to halt development of its programs and explore strategic alternatives focused on maximizing stockholder value, which may include, but are not limited to, an acquisition, a merger, business combination or divestiture. The decision was not related to any safety or medical issues or negative regulatory feedback related to the Company’s programs. See Note 13 for further discussion. The Company is subject to risks and uncertainties including, should it resume development of its product candidates, risks and uncertainties common to early-stage companies in the biotechnology industry, including but not limited to, risks associated with completing preclinical studies and clinical trials, receiving regulatory approvals for product candidates, development by competitors of new biopharmaceutical products, dependence on key personnel, protection of proprietary technology, compliance with government regulations and the ability to secure additional capital to fund operations. Should the Company resume development of its product candidates, significant additional research and development efforts, including preclinical and clinical testing and regulatory approval, prior to commercialization, would be required. These efforts would require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s product development efforts are successful, should the Company resume development of its product candidates, it is uncertain when, if ever, the Company would realize revenue from product sales. In accordance with the Financial Accounting Standards Board (“FASB”) Accounting Standards Update (“ASU”) 2014-15, 205-40), 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) 10-Q 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) 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”). Affected employees in the July 2023 Workforce Reduction and October 2023 Workforce Reduction were offered separation benefits, including severance payments. See Note 13 for further discussion.	1. Nature of the Business AVROBIO, Inc. (the “Company” or “AVROBIO”) is a clinical-stage gene therapy company focused on developing potentially curative ex vivo The Company is subject to 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. Product candidates currently under development will require significant additional research and development efforts, including preclinical and clinical testing and regulatory approval, prior to commercialization. These efforts 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, it is uncertain when, if ever, the Company will 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 205-40), 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 and a term loan facility. As of December 31, 2022, the Company had an accumulated deficit of $489,432. The Company expects that its cash and cash equivalents of $92,563 as of December 31, 2022 may not be sufficient to fund operations for at least the next twelve months from the date of issuance of these consolidated financial statements which raises substantial doubt about the Company’s ability to continue as a going concern, and the Company will need to obtain additional funding. The Company expects to finance its operations through potential public or private equity financings, debt financings, collaboration agreements or other capital sources. The future viability of the Company is dependent on its ability to raise additional capital to finance its operations. The Company’s inability to raise capital as and when needed could have a negative impact on its financial condition and ability to pursue its business strategies. There can be no assurance that the current operating plan will be achieved or that additional funding will be available on terms acceptable to the Company, or at all. The accompanying consolidated financial statements have been prepared on a going concern basis, which contemplates the realization of assets and satisfaction of liabilities in the ordinary course of business. The consolidated financial statements do not include any adjustments relating to the recoverability and classification of recorded asset amounts or the amounts and classification of liabilities that might result from the outcome of this uncertainty.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
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 Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“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, 2022, 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 September 30, 2023, and the results of its operations for the three and nine months ended September 30, 2023 and 2022, its statements of stockholders’ equity for the three and nine months ended September 30, 2023 and 2022 and its statement of cash flows for the nine months ended September 30, 2023 and 2022. The results for the three and nine months ended September 30, 2023 are not necessarily indicative of the results to be expected for the year ending December 31, 2022, 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, 2022, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K 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 September 30, 2023, there have been no changes to the Company’s significant accounting policies as described in the Company’s Annual Report on Form 10-K 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 Accounting Standards Update (“ASU”) No. 2018-07, Compensation-Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting non-employee 2018-07, non-employee 2018-07, The Company classifies stock-based compensation expense in its consolidated statements of operations and comprehensive income (loss) in the same manner in which the award recipient’s cash compensation costs are classified. Emerging Growth Company Status The Company is an “emerging growth company,” as defined in the Jumpstart Our Business Startups Act, or JOBS Act, and may take advantage of certain exemptions from various reporting requirements that are applicable to other public companies that are not emerging growth companies. The Company may take advantage of these exemptions until the Company is no longer an “emerging growth company.” Section 107 of the JOBS Act provides that an “emerging growth company” can take advantage of the extended transition period afforded by the JOBS Act for the implementation of new or revised accounting standards. The Company has elected to use the extended transition period for complying with new or revised accounting standards and as a result of this election, its consolidated financial statements may not be comparable to companies that comply with public company effective dates. The Company may take advantage of these exemptions up until the last day of the fiscal year following the fifth anniversary of its IPO or such earlier time that it is no longer an “emerging growth company.” 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 2016-13. 2016-13 available-for-sale In November 2019, the FASB issued ASU 2019-11, Codification Improvements to Topic 326, Financial Instruments – Credit Losses 2019-11. 2019-11 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”). Principles of Consolidation The accompanying consolidated financial statements include the accounts of AVROBIO, Inc. and its wholly owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation. Segment Information Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker, or decision-making group, in making decisions on how to allocate resources and assess performance. The Company’s chief operating decision maker is the chief executive officer (“CEO”). The Company and the CEO view the Company’s operations and manage its business as one operating segment. All material long-lived assets of the Company reside in the United States. Use of Estimates The preparation of financial statements in conformity with GAAP requires that the Company make estimates and judgments that may affect the reported amounts of assets, liabilities and expenses and the related disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting periods. On an on-going Cash and Cash Equivalents The Company considers all highly liquid investments purchased with original maturities of three months or less at acquisition to be cash equivalents. As of December 31, 2022 and 2021, cash and cash equivalents were primarily held in interest-bearing money market funds. Concentrations of Credit Risk The Company has no significant off-balance Fair Value Measurements Certain assets and liabilities of the Company are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: • Level 1— Fair values are determined utilizing prices (unadjusted) in active markets for identical assets or liabilities that the Company has the ability to access. • Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3—Unobservable inputs that are supported by little or no market activity that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The carrying amounts of the Company’s financial instruments, which include cash equivalents, accounts payable, and accrued expenses, approximated their fair values as of December 31, 2022 and 2021 due to the short-term The Company has evaluated the estimated fair value of financial instruments using available market information. The use of different market assumptions, estimation methodologies, or both, could have a significant effect on the estimated fair value amounts. See Note 4 “Fair Value of Financial Assets and Liabilities” Property and Equipment Property and equipment are recorded at cost. Depreciation and amortization is calculated using the straight-line method over the following estimated useful lives of the assets: Estimated Useful Life Laboratory and office equipment 5 years Computer equipment 2 years Leasehold improvements Lesser of lease term or 10 years Impairment of Long-Lived Assets Long-lived assets consist of property and equipment. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset group for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset group to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset group are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset group over its fair value, determined based on discounted cash flows. The Company did not record any impairment loss during the years ended December 31, 2022 and 2021. Leases Prior to January 1, 2022, the Company accounted for leases in accordance with FASB ASC 840, Leases. At lease inception, the Company determined if an arrangement was an operating or capital lease. For operating leases, the Company recognized rent expense, inclusive of rent escalations, on a straight-line basis over the lease term. Effective on January 1, 2022, the Company accounts for leases in accordance with ASC Topic 842, Leases (“ASC 842”). Upon transition, the Company applied the package of practical expedients permitted under ASC 842 transition guidance to its entire lease portfolio at January 1, 2022. As a result, the Company was not required to reassess (i) whether any expired or existing contracts are or contain leases, (ii) the classification of any expired or existing leases, and (iii) initial direct costs for any existing leases. Furthermore, as a lessee the Company elected to combine lease and non-lease non-lease In accordance with ASC 842, the Company determines whether an arrangement is or contains a lease at inception. A contract is or contains a lease if the contract conveys the right to control the use of an identified asset for a period of time in exchange for consideration. The Company records leases at the lease commencement date, when control of the underlying asset is transferred from the lessor to the lessee, as operating or finance leases and records a right-of-use The Company enters into contracts that contain both lease and non-lease Non-lease non-lease right-of-use Operating lease assets and liabilities are recognized at the lease commencement date based on the present value of the lease payments over the lease term using the discount rate implicit in the lease if readily determinable. If the rate implicit is not readily determinable, the Company utilizes its incremental borrowing rate based upon the available information at the lease commencement date. ROU assets are further adjusted for items such as initial direct costs, prepaid rent, or lease incentives. Operating lease payments are expensed using the straight-line method as an operating expense over the lease term. The Company’s lease terms may include options to extend the lease when it is reasonably certain that the Company will exercise that option. Finance lease assets are amortized to depreciation expense using the straight-line method over the shorter of the useful life of the related asset or the lease term. Finance lease payments are bifurcated into (i) a portion that is recorded as interest expense and (ii) a portion that reduces the finance lease liability associated with the lease. Comprehensive Income (Loss) Comprehensive income (loss) is defined as the change in stockholders’ equity of a business enterprise during a period from transactions and other events and circumstances from non-owner Foreign Currency Translation The functional currency of the Company’s international operations in Canada and Australia is the U.S. dollar. Accordingly, all operating assets and liabilities of these international subsidiaries are remeasured into U.S. dollars using the exchange rates in effect at the balance sheet date or historical rates, as appropriate, while expenses are remeasured into U.S. dollars at the average rates in effect during the period. Any differences resulting from the remeasurement of assets, liabilities, and operations of the Canadian and Australian subsidiaries are recorded within other (expense) income, net in the consolidated statements of operations and comprehensive loss. During the years ended December 31, 2022 and 2021, the Company recorded foreign exchange losses of $92 and $61, respectively, in other expense in the consolidated statements of operations and comprehensive loss. Research and Development Expenses Research and development costs are expensed as incurred. Research and development Non-refundable The Company has entered into various research and development related contracts with parties both inside and outside of the United States. The payments related to these agreements are recorded as research and development expenses as incurred. The Company records accrued liabilities for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies or clinical trials, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs. Stock-Based Compensation For stock-based awards issued to employees and members of the Company’s board of directors (the “Board”) for their services on the Board, the Company measures the estimated fair value of the stock-based award on the date of grant and recognizes compensation expense for those awards over the requisite service period, which is generally the vesting period of the respective award. The Company issues stock-based awards with only service-based vesting conditions and records the expense for these awards using the straight-line method. The Company has not issued any stock-based awards with performance-or market-based vesting conditions. The Company accounts for forfeitures as they occur. The measurement date for non-employee 2018-07, The Company classifies stock-based compensation expense in its consolidated statements of operations and comprehensive loss in the same manner in which the award recipient’s cash compensation costs are classified. The fair value of each stock option award is estimated on the date of grant using the Black-Scholes option pricing model. As there was no public market for its common stock prior to June 21, 2018, which was the first day of trading, and as the trading history of the Company’s common stock was limited through December 31, 2022, the Company determined the volatility for awards granted based on an analysis of reported data for a group of guideline companies that issued options with substantially similar terms. The expected volatility has been determined using a weighted-average of the historical volatility measures of this group of guideline companies. The Company expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. The expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. The Company has not paid, and does not anticipate paying, cash dividends on its common stock; therefore, the expected dividend yield is assumed to be zero. Income Taxes Deferred tax assets and liabilities are determined on the basis of the differences between the consolidated financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established. The Company accounts for uncertain tax positions recognized in the consolidated financial statements by prescribing a more-likely-than-not Net Loss per Share Basic net loss per share is computed by dividing net loss by the weighted-average number of shares of common stock outstanding during the period, without consideration of potential dilutive securities. Diluted net loss per share is computed by adjusting the weighted-average shares outstanding for the potential dilutive effects of common stock equivalents outstanding during the period calculated in accordance with the treasury stock method. For purposes of the diluted net loss per share calculation, stock options and restricted stock units are considered to be common stock equivalents but have been excluded from the calculation of diluted net loss per share, as their effect would be anti-dilutive for all periods presented. Therefore, basic and diluted net loss per share were the same for all periods presented. Subsequent Event Considerations The Company considers events or transactions that occur after the balance sheet date but prior to the issuance of the consolidated financial statements to provide additional evidence for certain estimates or to identify matters that require additional disclosure. Subsequent events have been evaluated as required. See Note 16. Emerging Growth Company Status The Company is an “emerging growth company,” as defined in the Jumpstart Our Business Startups Act, or JOBS Act, and may take advantage of certain exemptions from various reporting requirements that are applicable to other public companies that are not emerging growth companies. The Company may take advantage of these exemptions until the Company is no longer an “emerging growth company.” Section 107 of the JOBS Act provides that an “emerging growth company” can take advantage of the extended transition period afforded by the JOBS Act for the implementation of new or revised accounting standards. The Company has elected to use the extended transition period for complying with new or revised accounting standards and as a result of this election, its consolidated financial statements may not be comparable to companies that comply with public company effective dates. The Company may take advantage of these exemptions up until the last day of the fiscal year following the fifth anniversary of an offering or such earlier time that it is no longer an “emerging growth company.” Recently Adopted Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases As previously noted, the Company adopted ASC 842 with an effective date of January 1, 2022, using the modified retrospective transition approach which uses the effective date as the date of initial application. As a result, prior periods are presented in accordance with the previous guidance in ASC 840. The Company has elected to apply the package of practical expedients requiring no reassessment of whether any expired or existing contracts are or contain leases, the lease classification of any expired or existing leases, or the capitalization of initial direct costs for any existing leases. Upon its adoption of ASC 842 on January 1, 2022, the Company recognized operating lease right-of-use In December 2019, the FASB issued ASU No. 2019-12, Simplifying the Accounting for Income Taxes 2019-12. 2019-12 Recently Issued Accounting Pronouncements In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses 2016-13. 2016-13 available-for-sale 2016-13 non-emerging 2016-13 In November 2019, the FASB issued ASU 2019-11, Codification Improvements to Topic 326, Financial Instruments – Credit Losses 2019-11. 2019-11 2016-13, 2016-13 2019-11 2016-13 2019-11 2016-13 2019-11

License Agreements

License Agreements	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
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 one-time 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 country-by-country mid-single 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 September 30, 2023, the Company did not incur costs related to the CRFA, excluding the payment made in connection with the termination. For the three months ended September 30, 2022, the Company incurred $590 related to the CRFA. For the nine months ended September 30, 2023 and 2022, the Company incurred $1,610 and $1,970 related to the CRFA, respectively, excluding the payment made in connection with the termination. Agreements with University Health Network (“UHN”) Fabry License Agreement—  On January 27, 2016, the Company entered into an agreement with UHN, pursuant to which UHN granted the Company an option to enter into an exclusive license under the UHN intellectual property related to Fabry disease in accordance with the pre-negotiated non-exclusive know-how, 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 mid-single-digit 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 country-by-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. On October 3, 2023 the Company provided a notice of termination to UHN with respect to the Fabry License Agreement, specifying an effective date of termination of January 4, 2024. For the three months ended September 30, 2023, the Company recorded research and development expense related to this agreement with UHN of $25. For the three months ended September 30, 2022 the Company did not incur any research and development expense related to this agreement with UHN for reimbursable funded study trial costs. For the nine months ended September 30, 2023 and 2022, the Company recorded research and development expense related to this agreement with UHN of $59 and $106, respectively, which consists of reimbursable funded study trial costs. No milestone or maintenance fees were incurred related to this agreement in the three and nine months ended September 30, 2023 and 2022. Interleukin 12 License Agreement— On January 27, 2016, the Company entered into an exclusive license agreement with UHN, pursuant to which UHN granted the Company a license to certain patent rights for the commercial development, manufacture, distribution and use of any products or processes resulting from development of those patent rights related to Interleukin 12. Upon execution of this agreement, the Company paid an upfront license fee of CAD $264. In addition, as part of the initial consideration for the license, the Company issued to UHN 1,161,665 shares of the Company’s common stock and agreed to pay UHN up to $2,000 upon the closing of an IPO if certain criteria are met. The fair value of the shares issued to UHN of $480 and the upfront fee was expensed upon the execution of the agreement. Upon the closing of the 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. 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 September 30, 2023 the Company did not incur any costs related to this agreement with UHN. For the three months ended September 30, 2022, the Company recorded research and development expense related to this agreement with UHN of $39. For the nine months ended September 30, 2023 and 2022, the Company recorded research and development expense related to this agreement with UHN of $37 and $39, respectively. No milestone fees were incurred related to this agreement in the three and nine months ended September 30, 2023 and 2022. Agreement with BioMarin Pharmaceutical Inc. (“BioMarin”) On August 31, 2017, the Company entered into a license agreement with BioMarin, pursuant to which BioMarin granted the Company an exclusive worldwide license under certain intellectual property rights owned or controlled by BioMarin to develop, commercialize and sell products for use in the treatment of Pompe disease. The license agreement was amended in February 2018 and again in January 2020 to, among things, provide that BioMarin would supply the Company with certain technology materials. As consideration for this agreement, the Company paid an upfront license fee of $500 in cash and issued 233,765 shares of Series B Preferred Stock to BioMarin at the time of the Company’s Series B Preferred Stock financing in January 2018. The Company 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 and nine months ended September 30, 2023 and 2022. Unless terminated earlier, the agreement expires upon the expiration of the Company’s royalty obligation for all licensed products throughout the world. BioMarin and the Company can terminate the agreement in the event of a material breach by the other party and failure to cure such breach within a certain period of time. The Company may terminate the agreement at will upon written notice to BioMarin. BioMarin has the right to terminate the agreement upon the Company’s bankruptcy or insolvency, or in the event of any challenge or opposition to the licensed patent rights or related actions brought by the Company or its affiliates or sublicensees, or if the Company, its affiliates or sublicensees knowingly assist a third-party in challenging or otherwise opposing the licensed patent rights, except as required under a court order or subpoena. Agreement with Papillon Therapeutics, Inc. (previously GenStem Therapeutics, Inc.) On October 2, 2017, the Company entered into a license agreement with GenStem, pursuant to which GenStem granted the Company an exclusive worldwide license, subject to certain retained rights, under certain intellectual property rights owned or controlled by GenStem to develop, commercialize and sell products for use in the treatment of cystinosis. Under this agreement, the Company paid an upfront license fee of $1,000 and is required to make payments upon completion of certain milestones up to an aggregate of $16,000. The Company also agreed to pay GenStem a tiered mid to high single-digit royalty percentage on annual net sales of licensed products as well as a low double-digit percentage of sublicense income received from certain third-party licensees. The Company’s royalty obligation expires on a licensed product-by-licensed country-by-country The Company has recognized no expenses related to this agreement for the three and nine months ended September 30, 2023 and 2022. Agreement with Lund University Rights Holders On November 17, 2016, the Company entered into a license agreement with affiliates of Lund University, along with certain other relevant rights holders that may be added from time to time, pursuant to which such rights holders granted to the Company an exclusive worldwide license, subject to certain retained rights, under certain intellectual property rights to develop, commercialize and sell products in any and all uses relevant to Gaucher disease. As consideration for the license, the Company is required to make payments in connection with the achievement of certain milestones up to an aggregate of $550. The agreement expires on the latest of (i) the twentieth anniversary of the end of a certain research project the Company is funding pursuant to an agreement with Lund University, (ii) the expiration of the term of any patent filed on the licensed rights that covers a licensed product, (iii) the expiration of any applicable marketing exclusivity right and (iv) such time that neither the Company nor any sublicensees, partners or contractors are commercializing a licensed product. Either the Company or the rights holders acting together may terminate the license agreement if the other such party commits a material breach and fails to cure such breach within a certain period of time, or if the other party enters into liquidation, becomes insolvent, or enters into composition or statutory reorganization proceedings. The Company has recognized no expenses related to this agreement for the three and nine months ended September 30, 2023 and 2022. Sale of Cystinosis Program On May 19, 2023, the Company entered into the Asset Purchase Agreement with Novartis, providing for the sale of the Company’s cystinosis gene therapy program (designated AVR-RD-04) ® referred to as the “Asset Sale.” The Company has also agreed not to assert claims against Novartis for violations of certain other Company intellectual property rights in connection with Novartis’s exercise of the exclusive license granted to it under the Asset Purchase Agreement, and for violations of the licensed intellectual property, except in connection with activities by Novartis in the fields of Gaucher disease, Pompe disease, Hunter syndrome and Fabry disease, or indemnification claims under the Asset Purchase Agreement. The aggregate consideration to the Company consisted of a cash payment of $87,500 upon closing of the transaction. The Asset Purchase Agreement contains certain customary representations, warranties and covenants. The Asset Purchase Agreement also contains customary indemnification provisions pursuant to which the parties agree to indemnify each other for certain matters, including, among other things, breaches of certain representations, warranties and covenants in connection with the Asset Sale, subject to specified caps and limitations. The Company has also agreed to a covenant that would prohibit the Company from engaging in specified activities that would compete with the cystinosis business, for a period of 5 years, subject to certain limitations and exceptions. The Company completed the Asset Sale on June 9, 2023. For the three and nine months ended September 30, 2023 the Company recognized $83,736 as a gain on asset sale, net of $3,764 transaction costs, related to legal, accounting, and financial advisory services and transferred prepaid assets.	3. License 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 one-time As part of the agreement, the Company is 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 country-by-country mid-single Unless terminated earlier, the agreement expires upon the later of 15 years from the effective date or the expiration of the last valid claim of the licensed patents, subject to certain surviving rights and obligations. UoM and the Company can each terminate the agreement in the event of the bankruptcy or insolvency of the other party, or a material breach by the other party and failure to cure such breach within a certain period of time. UoM has the right to terminate the agreement in the event of certain actions relating to challenge or opposition to the licensed intellectual property brought by the Company or its affiliates or sublicensees. Concurrently with the MPSII License Agreement, the Company entered into a collaborative research funding agreement with UoM (“CRFA”). Under the CRFA, the Company has agreed to fund the budgeted costs of an investigator-sponsored Phase 1/2 clinical trial to be sponsored by UoM in connection with the development activities under the MPSII License Agreement, which are currently estimated to equal approximately £9,900 in the aggregate. For the years ended December 31, 2022 and 2021, the Company recognized $2,346 and $1,437, respectively, of costs 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 non-exclusive know-how, 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 mid-single-digit 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 country-by-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. For the years ended December 31, 2022 and 2021, the Company recorded research and development expense related to this agreement with UHN of $161 and $209, respectively, which consists of reimbursable funded study trial costs and license maintenance fees. No milestone fees were incurred related to the Fabry license agreement in the years ended December 31, 2022 and 2021. 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 is 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 grants any sublicense rights under the license agreement, the Company has agreed to pay UHN a low double-digit royalty percentage of any sublicense income received by the Company. The agreement requires the Company to meet certain diligence requirements based upon specified milestones. The agreement expires on the later of the date the last patent rights expire in the last country or ten years from the date of first sale. 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. The Company can voluntarily terminate the agreement with prior notice to UHN. 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. For the years ended December 31, 2022 and 2021, the Company recorded research and development expense related to this agreement with UHN of $39 for both periods, which consists of license maintenance fees. No milestone fees were incurred related to the Interleukin 12 license agreement in the years ended December 31, 2022 and 2021. Agreement with BioMarin Pharmaceutical Inc. (“BioMarin”) On August 31, 2017, the Company entered into a license agreement with BioMarin, pursuant to which BioMarin granted the Company an exclusive worldwide license under certain intellectual property rights owned or controlled by BioMarin to develop, commercialize and sell products for use in the treatment of Pompe disease. The license agreement was amended in February 2018 and again in January 2020 to, among things, provide that BioMarin would supply the Company with certain technology materials. As consideration for this agreement, the Company paid an upfront license fee of $500 in cash and issued 233,765 shares of Series B Preferred Stock to BioMarin at the time of the Company’s Series B Preferred Stock financing in January 2018. The Company is also obligated to make future milestone payments of up to $13,000 upon the achievement of certain specified milestones and agreed to pay BioMarin royalties of a low single-digit percentage of net sales of licensed products sold by the Company or its affiliates covered by patent rights in a relevant country. No expenses related to the license were recorded for the years ended December 31, 2022 and 2021. 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 country-by-country No expenses related to the license were recorded for the years ended December 31, 2022 and 2021. Agreement with Lund University Rights Holders On November 17, 2016, the Company entered into a license agreement with affiliates of Lund University, along with certain other relevant rights holders that may be added from time to time, pursuant to which such rights holders granted to the Company an exclusive worldwide license, subject to certain retained rights, under certain intellectual property rights to develop, commercialize and sell products in any and all uses relevant to Gaucher disease. As consideration for the license, the Company is required to make payments in connection with the achievement of certain milestones up to an aggregate of $550. The agreement expires on the latest of (i) the twentieth anniversary of the end of a certain research project the Company is funding pursuant to an agreement with Lund University, (ii) the expiration of the term of any patent filed on the licensed rights that covers a licensed product, (iii) the expiration of any applicable marketing exclusivity right and (iv) such time that neither the Company nor any sublicensees, partners or contractors are commercializing a licensed product. Either the Company or the rights holders acting together may terminate the license agreement if the other such party commits a material breach and fails to cure such breach within a certain period of time, or if the other party enters into liquidation, becomes insolvent, or enters into composition or statutory reorganization proceedings. No expenses related to the license were recorded for the years ended December 31, 2022 and 2021.

Fair Value Measurement

Fair Value Measurement	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Fair Value Measurement	4. Fair Value Measurement 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 September 30, 2023 and December 31, 2022: Fair Value Measurements as of September 30, 2023 Level 1 Level 2 Level 3 Total Assets: Cash equivalents — money market funds $ 104,541 $ —  $ —  $ 104,541 $ 104,541 $ —  $ —  $ 104,541 Fair Value Measurements as of December 31, 2022 Level 1 Level 2 Level 3 Total Assets: Cash equivalents — money market funds $ 91,095 $ —  $ —  $ 91,095 $ 91,095 $ —  $ —  $ 91,095 The fair value of cash equivalents was determined through quoted prices by third-party pricing services. During the nine months ended September 30, 2023, there were no transfers between levels.	4. Fair Value of Financial Assets and Liabilities The Fair Value Measurements as of Level 1 Level 2 Level 3 Total Assets: Cash equivalents—money market funds $ 91,095 $ —  $ —  $ 91,095 $ 91,095 $ —  $ —  $ 91,095 Fair Value Measurements as of Level 1 Level 2 Level 3 Total Assets: Cash equivalents—money market funds $ 189,332 $ —  $ —  $ 189,332 $ 189,332 $ —  $ —  $ 189,332 During the years ended December 31, 2022 and 2021, there were no transfers between levels.

Supplemental Balance Sheet Info

Supplemental Balance Sheet Information	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
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: September 30, December 31, Prepaid research and development expenses $ 828 $ 4,509 Prepaid insurance 1,221 999 Other current assets 805 1,008 Prepaid compensation benefits 6 327 Tax incentive refund — 269 Prepaid expenses and other current assets $ 2,860 $ 7,112 Property and equipment, net Property and equipment, net consisted of the following: September 30, December 31, Laboratory and office equipment $ 5,973 $ 5,967 Leasehold improvements 629 629 Computer equipment 104 102 6,706 6,698 Less: Accumulated depreciation and amortization (4,421 ) (3,804 ) Reclassified to held for sale (2,285 ) —  Property and equipment, net $ —  $ 2,894 Reclassified to held for sale $ 2,285 $ —  Less: Loss on impairment (902 ) —  Less: Sales (1,198 ) —  Held for Sale $ 185 $ —  As of September 30, 2023, the Company had $185 of property and equipment classified as held for sale, and the Company’s intention is to complete the sale of these assets within the fourth quarter of 2023. During the three and nine months ended September 30, 2023, $2,285 of assets were reclassified as held for sale and $1,198 were sold. For the three and nine months ended September 30, 2023, the Company recognized $902 as a loss on impairment on assets. No depreciation or amortization expense was recognized for the three months ended September 30, 2023. Depreciation and amortization expense was $617 for the nine months ended September 30, 2023. Depreciation and amortization expense was $336 and $1,105, respectively, for the three and nine months ended September 30, 2022. Restricted cash As of September 30, 2023 and December 31, 2022, 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. The cash will be restricted until the termination or modification of the lease arrangement. September 30, December 31, Restricted cash $ 283 $ 283 Restricted cash, net of current portion 400 —  Accrued expenses and other current liabilities Accrued expenses and other current liabilities consisted of the following: September 30, December 31, Research and development expenses $ 1,479 $ 6,122 Compensation and benefit costs 2,402 4,175 Consulting and professional fees 1,120 1,224 Other liabilities 1 211 Accrued expenses and other current liabilities $ 5,002 $ 11,732	5. Supplemental Balance Sheet Information Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets consisted of the following: December 31, 2022 2021 Prepaid research and development expenses $ 4,509 $ 4,496 Tax incentive refund, net of reserve 269 2,697 Prepaid insurance 999 112 Prepaid compensation benefits 327 575 Other current assets 1,008 1,698 Prepaid expenses and other current assets $ 7,112 $ 9,578 Property and Equipment, Net Property and equipment, net consisted of the following: December 31, 2022 2021 Laboratory and office equipment $ 5,967 $ 6,162 Leasehold improvements 629 1,635 Computer equipment 102 149 6,698 7,946 Less: Accumulated depreciation and amortization (3,804 ) (3,820 ) Property and equipment, net $ 2,894 $ 4,126 Depreciation and amortization expense for the years ended December 31, 2022 and 2021 was $1,440 and $1,399, respectively. Restricted Cash As of December 31, 2022 and 2021, 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. The cash will be restricted until the termination or modification of the lease arrangement. December 31, 2022 2021 Restricted cash $ 283 $ —  Restricted cash, net of current portion —  492 Accrued Expenses Accrued expenses consisted of the following: December 31, 2022 2021 Research and development expenses $ 6,122 $ 8,882 Compensation and benefit costs 4,175 5,579 Consulting and professional fees 1,224 999 Other liabilities 211 178 $ 11,732 $ 15,638

Leases

Leases	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
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 was set to expire in October 2020. On June 9, 2020, the Company amended the terms of the sublease, which was set to expire in April 2022. Effective January 1, 2022, the Company amended the terms of the sublease, to extend the term through April 2023. In July 2022, the Company moved its corporate headquarters to its subleased space in this location. Effective January 24, 2023, the Company amended the terms of the sublease, which is now set to expire in April 2024. The annual lease payments are subject to a 5% increase each year. In accordance with the lease agreement, the Company is required to maintain a security deposit of $283, which was recorded in restricted cash as of September 30, 2023 and December 31, 2022. 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. On June 1, 2020, the Company entered into a lease agreement for office space located in Toronto, Ontario, Canada, which is set to expire in June 2025. The annual lease payments are fixed for years 1 and 2, and then subject to a 6.67% increase for years 3 through 5. In accordance with the lease agreement, the Company is required to maintain a security deposit of CAD$27, which was recorded in other long-term assets as of September 30, 2023 and December 31, 2022. In October 2022, the Company entered into a sublease agreement to sublease this space. The term of the sublease agreement commenced on October 1, 2022 and expires on June 29, 2025. AVROBIO, INC. NOTES TO UNAUDITED CONDENSED CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED) (in thousands, except share and per share data) The following table summarizes the effect of lease costs in the Company’s consolidated statement of operations and comprehensive income (loss): Three Months Ended 2023 Operating lease costs $ 483 Sublease income (23 ) Total lease costs $ 460 During the three months ended September 30, 2023 and 2022, the Company made cash payments for operating leases of $706 and $831, respectively. During the nine months ended September 30, 2023 and 2022, the Company made cash payments for operating leases of $2,088 and $2,493, respectively. As of September 30, 2023, future minimum payments of operating lease liabilities are as follows (in thousands): September 30, 2023 $ 706 2024 1,033 2025 69 2026 — 2027 — Thereafter — Total lease payments $ 1,808 Less: interest (82 ) Plus: FX gain/loss 26 Present value of lease liabilities $ 1,752 As of September 30, 2023, the weighted average remaining lease term was 0.8 years and the weighted average incremental borrowing rate used to determine the operating lease liability was 15.59%. As of September 30, 2022, the weighted average remaining lease term was 1.0 year and the weighted average incremental borrowing rate used to determine the operating lease liability was 10.51%.	6. Leases On January 12, 2018, the Company entered into a lease agreement for office space located in Cambridge, Massachusetts. The lease agreement was set to expire in January 2023 and was terminated early in September 2022. The annual lease payments were subject to a 3% increase each year. The Company received a tenant incentive allowance of $842 in 2018. In accordance with the lease agreement, the Company was required to maintain a security deposit of $209, which was recorded in restricted cash as of December 31, 2021. On August 31, 2018, the Company entered into a sublease agreement for lab space located in Cambridge Massachusetts, United States, which was set to expire in October 2020. On June 9, 2020, the Company amended the terms of the sublease, which was set to expire in April 2022. Effective January 1, 2022, the Company amended the terms of the sublease, to extend the term through April 2023. In July 2022, the company moved our corporate headquarters to our subleased space in this location. Effective January 24, 2023, the Company amended the terms of the sublease, which is now set to expire in April 2024. The annual lease payments are subject to a 5% increase each year. In accordance with the lease agreement, the Company is required to maintain a security deposit of $283, which was recorded in restricted cash as of December 31, 2022 and 2021. On June 1, 2020, the Company entered into a lease agreement for office space located in Toronto, Ontario, Canada, which is set to expire in June 2025. The annual lease payments are fixed for years 1 and 2, and then subject to a 6.67% increase for years 3 through 5. In accordance with the lease agreement, the Company is required to maintain a security deposit of CAD$27, which was recorded in other long-term assets as of December 31, 2022 and 2021. In October 2022, the Company entered into a sublease agreement to sublease this space. The term of the sublease agreement commenced on October 1, 2022 and expires on June 29, 2025. The following table summarizes the effect of lease costs in the Company’s consolidated statement of operations and comprehensive loss: Year ended Operating lease costs $ 2,994 Sublease income (23 ) Total lease costs $ 2,971 During the year ended December 31, 2022 the Company made cash payments for operating leases of $3,167. As of December 31, 2022, future minimum payments of operating lease liabilities are as follows (in thousands): As of 2023 $ 1,007 2024 138 2025 69 2026 —  2027 —  Thereafter —  Total lease payments $ 1,214 Less: interest (53 ) Plus: FX gain/loss 26 Present value of lease liabilities $ 1,187 As of December 31, 2022, the weighted average remaining lease term was 0.9 years and the weighted average incremental borrowing rate used to determine the operating lease liability was 10.58%. Future minimum payments required under the leases as of December 31, 2021 presented in accordance with ASC 840, the relevant accounting standard at that time (in thousands): Year Ending December 31, 2022 $ 1,297 2023 208 2024 147 2025 73 Total $ 1,725 Rent expense during the year ended December 31, 2021 was $2,648.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
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 nine months ended September 30, 2023 and 2022 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 September 30, 2023 and December 31, 2022, 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 September 30, 2023. 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.	11. Commitments and Contingencies Lease Agreements Refer to Note 6 “Leases” for discussion of the commitments associated with the Company’s lease portfolio. Other Funding Commitments As of December 31, 2022, the Company had several ongoing clinical and non-clinical Guarantees The Company enters into certain agreements with other parties in the ordinary course of business that contain indemnification provisions. These typically include agreements with directors and officers, business partners, contractors, landlords and clinical sites. Under these provisions, the Company generally indemnifies and holds harmless the indemnified party for losses suffered or incurred by the indemnified party as a result of the Company’s activities. These indemnification provisions generally survive termination of the underlying agreement. The maximum potential amount of future payments the Company could be required to make under these indemnification provisions is unlimited. However, to date the Company has not incurred material costs to defend lawsuits or settle claims related to these indemnification provisions. As a result, the estimated fair value of these obligations is minimal. Litigation The Company, from time to time, may be party to litigation arising in the ordinary course of business. The Company was not subject to any material legal proceedings during the years ended December 31, 2022 and 2021, and to the best of its knowledge, no material legal proceedings are currently pending or threatened. Other The Company is also party to various agreements, principally relating to licensed technology, that require future payments relating to milestones not met as of December 31, 2022 and 2021, or royalties on future sales of specified products. No milestone or royalty payments under these agreements are expected to be payable in the immediate future. See Note 3 “Licenses Agreements” The Company enters into standard indemnification agreements in the ordinary course of business. Pursuant to the agreements, the Company agrees to indemnify, hold harmless, and to reimburse the indemnified party for losses suffered or incurred by the indemnified party, generally the Company’s business partners, in connection with any U.S. patent or any copyright or other intellectual property infringement claim by any third-party with respect to the Company’s products. The term of these indemnification agreements is generally perpetual any time after execution of the agreement. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is unlimited. The Company has never incurred costs to defend lawsuits or settle claims related to these indemnification agreements.

401(k) Savings Plan

401(k) Savings Plan	9 Months Ended
	Sep. 30, 2023
Retirement Benefits [Abstract]
401(k) Savings Plan	10. 401(k) Savings Plan The Company established a defined contribution savings plan under Section 401(k) of the Internal Revenue Code. Eligible employees may make pretax contributions to the 401(k) Plan up to statutory limits. At the election of the Board, the Company may elect to match employee contributions. Currently, the Company makes matching contributions at a rate of 50% of the first 8% of employee contributions. The Company recorded $599 and $593 of expenses related to its 401(k) match for the years ended December 31, 2022 and 2021, respectively.

Note Payable

Note Payable	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Debt Disclosure [Abstract]
Note Payable	8. Note Payable On November 2, 2021 (the “Closing Date”), the Company entered into a Loan and Security Agreement (the “Loan Agreement”) with Silicon Valley Bank (“SVB”) pursuant to which a term loan in an aggregate principal amount of up to $50,000 (the “Term Loan Facility”) was available to the Company in three tranches, subject to certain terms and conditions. The first tranche of $15,000 was advanced to the Company on the Closing Date. Subject to the terms and conditions of the Loan Agreement, the first tranche allowed the Company to borrow an additional $15,000 through October 31, 2023. Upon satisfaction of certain milestones, the second and third tranches were available under the Term Loan Facility which allowed the Company to borrow an additional amount up to $10,000 in each tranche through October 31, 2023. Additionally, the Company could seek to borrow up to an additional $15,000 at the sole discretion of the lender through the term of the Loan Agreement. The Loan Agreement provided for an October 1, 2026 maturity date (the “Maturity Date”). The Company was required to pay an end of term fee (“End of Term Charge”) equal to 9.00% of the aggregate principal amount of the Term Loan advances upon repayment. Advances under the Term Loan Facility bore interest at a rate equal to the greater of either (i) the Prime Rate (as reported in The Wall Street Journal) plus 4.85%, and (ii) 8.10%. The Company was obligated to make interest only payments through November 1, 2024. Following the interest only period, the Company was to repay the principal balance and interest of the advances in equal monthly installments through October 1, 2026. The Company could prepay advances under the Loan Agreement, in whole or in part, at any time subject to a prepayment charge (the “Prepayment Premium”) equal to: (a) 1.50% of amounts so prepaid, if such prepayment occurred during the first year following the Closing Date; (b) 1.00% of the amount so prepaid, if such prepayment occurred during the second year following the Closing Date; and (c) 0.00% of the amount so prepaid, if such prepayment occurred after the second year following the Closing Date. Upon prepayment or repayment of all or any of the term loans under the Term Loan Facility, the Company was required to pay (in addition to any Prepayment Premium) an end of term charge of 9.0% of the aggregate funded amount under the Term Loan Facility. The Term Loan Facility was secured by substantially all of the Company’s assets, other than the Company’s intellectual property. The Company agreed to not pledge or secure its intellectual property to others. The End of Term Charge is recorded as a debt discount with an initial carrying balance of $1,350. During the year ended December 31, 2021 the Company recognized $103 of debt issuance costs related to legal expenses that has been included in the debt discount balance. The debt discount costs are being accreted to the principal amount of debt and being amortized from the date of issuance through the Maturity Date to interest expense using the effective-interest rate method. The effective interest rate of the outstanding debt under the Loan Agreement was approximately 16.29%. On June 9, 2023, upon the closing of the Asset Sale, all outstanding amounts due and owed, including principal, interest, and other charges, under the Term Loan Facility, dated as of November 2, 2021, by and among the Company, Silicon Valley Bank, a division of First-Citizens Bank & Trust and the other parties thereto, were repaid in full and the Term Loan Facility was terminated. Upon repayment, the obligations of the Company under the Term Loan Facility were satisfied in full, the Term Loan Facility and all related loan documents were terminated and all liens and security interests granted thereunder were released and terminated (excluding certain indemnification obligations that expressly survive termination of the Term Loan Facility). During the three months ended September 30, 2023 the Company did not recognize any interest expense related to the Loan Agreement, and during the three months ended September 30, 2022 the Company recognized $482 of interest expense related to the Loan Agreement which is reflected in other (expense) income, net on the consolidated statements of operations and comprehensive income (loss), respectively. During the nine months ended September 30, 2023 and 2022, the Company recognized $1,917 and $1,280 of interest expense related to the Loan Agreement which is reflected in other (expense) income, net on the consolidated statements of operations and comprehensive income (loss), respectively. Of the $1,917 recognized during the nine months ended September 30, 2023, $939 is related to the loss on the extinguishment of debt due to the write off of the debt discount balance.	7. Note Payable On November 2, 2021 (the “Closing Date”), the Company entered into a Loan and Security Agreement (the “Loan Agreement”) with Silicon Valley Bank pursuant to which a term loan in an aggregate principal amount of up to $50,000 (the “Term Loan Facility”) is available to the Company in three tranches, subject to certain terms and conditions. The first tranche of $15,000 was advanced to the Company on the Closing Date. Subject to the terms and conditions of the Loan Agreement, the first tranche allows the Company to borrow an additional $15,000 through October 31, 2023. Upon satisfaction of certain milestones, the second and third tranches are available under the Term Loan Facility which allows the Company to borrow an additional amount up to $10,000 in each tranche through October 31, 2023. Additionally, the Company may seek to borrow up to an additional $15,000 at the sole discretion of the lender through the term of the Loan Agreement. The Loan Agreement matures on October 1, 2026 (the “Maturity Date”). The Company is required to pay an end of term fee (“End of Term Charge”) equal to 9.00% of the aggregate principal amount of the Term Loan advances upon repayment. Advances under the Term Loan Facility will bear interest at a rate equal to the greater of either (i) the Prime Rate (as reported in The Wall Street Journal) plus 4.85%, and (ii) 8.10%. The Company will make interest only payments through November 1, 2024. Following the interest only period, the Company will repay the principal balance and interest of the advances in equal monthly installments through October 1, 2026. The Company may prepay advances under the Loan Agreement, in whole or in part, at any time subject to a prepayment charge (the “Prepayment Premium”) equal to: (a) 1.50% of amounts so prepaid, if such prepayment occurs during the first year following the Closing Date; (b) 1.00% of the amount so prepaid, if such prepayment occurs during the second year following the Closing Date, and (c) 0.00% of the amount so prepaid, if such prepayment occurs after the second year following the Closing Date. Upon prepayment or repayment of all or any of the term loans under the Term Loan Facility, the Company will pay (in addition to any Prepayment Premium) an end of term charge of 9.0% of the aggregate funded amount under the Term Loan Facility. The Term Loan Facility is secured by substantially all of the Company’s assets, other than the Company’s intellectual property. The Company has agreed to not pledge or secure its intellectual property to others. The Term Loan Facility is subject to certain terms and conditions that would be considered an Event of Default, including any material adverse change to the Company. The End of Term Charge is recorded as a debt discount with an initial carrying balance of $1,350. During the year ended December 31, 2021 the Company recognized $103 of debt issuance costs related to legal expenses that has been included in the debt discount balance. The debt discount costs are being accreted to the principal amount of debt and being amortized from the date of issuance through the Maturity Date to interest expense using the effective-interest rate method. The effective interest rate of the outstanding debt under the Loan Agreement is approximately 15.00%. As of December 31, 2022 and 2021 the carrying value of the note payable consists of the following: December 31, 2022 2021 Note payable, including End of Term Charge $ 16,350 $ 16,350 Debt discount, net of accretion (1,074 ) (1,405 ) Note payable, net of discount, long-term $ 15,276 $ 14,945 As of December 31, 2022, the future principal payments due under the arrangement, excluding interest and the end of term charge, are as follows: Year Ending December 31, Principle 2023 $ —  2024 1,875 2025 7,500 2026 5,625 Total $ 15,000 During the year ended December 31, 2022, the Company recognized $1,808 of interest expense related to the Loan Agreement, which is reflected in other (expense) income, net on the consolidated statements of operations and comprehensive loss. During year ended December 31, 2021, the Company recognized $203 of interest expense related to the Loan Agreement.

Stockholders' Equity

Stockholders' Equity	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Equity [Abstract]
Stockholders' Equity	9. Stockholders’ Equity C ommon Stock As of September 30, 2023 and December 31, 2022, the authorized capital stock of the Company included 150,000,000 shares of common stock, $0.0001 par value and 10,000,000 shares of undesignated preferred stock. As of September 30, 2023 and December 31, 2022, no undesignated preferred stock was outstanding. As of September 30, 2023, no cash dividends have been declared or paid. Common Stock Reserved for Future Issuance As of September 30, 2023 and December 31, 2022, the Company has reserved the following shares of common stock for future issuance: September 30, December 31, Shares reserved for exercise of outstanding stock options 5,922,447 9,423,271 Shares reserved for vesting of restricted stock units 1,224,997 940,392 Shares reserved for issuance under the 2018 Stock Option and Grant Plan 7,287,262 5,005,295 Shares reserved for issuance under the 2018 Employee Stock Purchase Plan 1,332,587 1,467,026 Shares reserved for issuance under the 2019 Inducement Plan 1,137,800 786,656 Shares reserved for issuance under the 2020 Inducement Plan 1,700,000 1,637,000 Total shares of authorized common stock reserved for future issuance 18,605,093 19,259,640	8. Common Stock As of December 31, 2022 and 2021, the authorized capital stock of the Company included 150,000,000 shares of common stock, $0.0001 par value, and 10,000,000 shares of undesignated preferred stock. As of December 31, 2022 and 2021, no undesignated shares of preferred stock were outstanding.  In accordance to the Fourth Amended and Restated Certificate of Incorporation, the holders of the common stock shall have the exclusive right to vote for the election of directors of the Company and on all other matters requiring stockholder action, each outstanding share entitling the holder thereof to one vote on each matter properly submitted to the stockholders of the Company for their vote; provided, however, that, except as otherwise required by law, holders of common stock, as such, shall not be entitled to vote on any amendment to any amendment to a certificate of designations of any series of undesignated preferred stock that alters or changes the powers, preferences, rights or other terms of one or more outstanding series of undesignated preferred stock if the holders of such affected series of undesignated preferred stock are entitled to vote, either separately or together with the holders of one or more other such series, on such amendment pursuant to a certificate of designations of any series of undesignated preferred stock. Through December 31, 2022, no cash dividends have been declared or paid. Public Offerings In July 2019, the Company closed an underwritten public offering of 7,475,000 shares of its common stock at a public offering price of $18.50 per share (the “July 2019 Follow-on Follow-on In February 2020, the Company closed an underwritten public offering of 4,350,000 shares of its common stock at a public offering price of $23.00 per share (the “February 2020 Follow-on Follow-on In June 2020, the Company sold an aggregate of 384,140 shares of common stock under its 2019 “at-the-market” In November 2020, the Company closed an underwritten public offering of 5,000,000 shares of its common stock at a public offering price of $15.00 per share (the “November 2020 Follow-on Follow-on In May 2021, the Company sold an aggregate of 1,829,268 shares of common stock under the 2019 ATM Facility for net proceeds, after deducting commissions and other offering expenses payable by the Company, of $14,550. As of December 31, 2022, approximately $26,549 of common stock remained available for future issuance under the 2019 ATM Facility. Common Stock Reserved for Future Issuance As of December 31, 2022 and 2021, the Company has reserved the following shares of common stock for future issuance: December 31, 2022 2021 Shares reserved for exercise of outstanding stock options 9,423,271 7,423,777 Shares reserved for vesting of restricted stock units 940,392 599,850 Shares reserved for issuance under the 2018 Stock Option and Incentive Plan 5,005,295 2,583,736 Shares reserved for issuance under the 2018 Employee Stock Purchase Plan 1,467,026 1,151,010 Shares reserved for issuance under the 2019 Inducement Plan 786,656 412,686 Shares reserved for issuance under the 2020 Inducement Plan 1,637,000 1,637,000 Total shares of authorized common stock reserved for future issuance 19,259,640 13,808,059

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Share-Based Payment Arrangement [Abstract]
Stock-Based Compensation	10. Stock-based Compensation Stock Option Valuation The assumptions that the Company used to determine the grant-date fair value of stock options granted to employees and members of the Board were as follows, presented on a weighted-average basis: Nine Months Ended 2023 2022 Expected option life (years) 6.00 5.96 Risk-free interest rate 3.82 % 1.80 % Expected volatility 83.36 % 80.22 % Expected dividend yield — % — % The following table summarizes the Company’s stock option activity for the nine months ended September 30, 2023: Number of Weighted- Weighted- Aggregate Outstanding as of December 31, 2022 9,423,271 $ 7.26 8.14 $ 22 Granted 123,501 $ 1.09 Exercised (223,273 ) $ 0.79 Cancelled or forfeited (3,401,052 ) $ 7.15 Outstanding as of September 30, 2023 5,922,447 $ 7.43 6.32 $ 1,068 Exercisable as of September 30, 2023 3,606,590 $ 10.16 4.82 $ 217 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 nine months ended September 30, 2023 was $85. No options were exercised during the nine months ended September 30, 2022. The weighted-average grant-date fair value of the Company’s stock options granted during the nine months ended September 30, 2023 and 2022 was $0.79 and $1.23, respectively. Restricted Stock Units The following table summarizes the Company’s restricted common stock units for the nine months ended September 30, 2023: Number Weighted- Issued and unvested as of December 31, 2022 940,392 $ 3.62 Granted 1,548,117 $ 1.65 Vested (283,835 ) $ 4.98 Forfeited, cancelled or expired (979,677 ) $ 2.02 Issued and unvested as of September 30, 2023 1,224,997 $ 2.10 The total fair value of restricted stock units vested during the nine months ended September 30, 2023 and 2022 was $1,367 and $7, respectively. Stock-Based Compensation Stock-based compensation expense was allocated as follows: Three Months Nine Months Ended 2023 2022 2023 2022 Research and development $ 415 $ 448 $ 1,705 $ 2,169 General and administrative 1,804 2,208 4,579 7,098 Total stock-based compensation expense $ 2,219 $ 2,656 $ 6,284 $ 9,267 As of September 30, 2023, total unrecognized compensation cost related to the unvested stock-based awards was $6,282, which is expected to be recognized over a weighted-average period of 2.10 years.	9. Stock-Based Compensation Amended and Restated 2015 Stock Option and Grant Plan The Company’s Amended and Restated 2015 Stock Option and Grant Plan, (the “2015 Plan”) provides for the Company to issue restricted stock awards and restricted stock units, or to grant incentive stock options or non-statutory non- The total number of common shares that may be issued under the 2015 Plan was 2,008,564 shares. Following the IPO, no further grants have been made under 2015 plan. Shares that expire, are terminated, surrendered or cancelled under the 2015 Plan without having been fully exercised will be available for future awards under the 2018 Plan (as defined below). In addition, shares of common stock that are tendered to the Company by a participant to exercise an award are added to the number of shares of common stock available for future awards. The 2015 Plan is administered by the Board. Equity awards granted to employees and members of the Board typically vest over four years. 2018 Stock Option and Incentive Plan The Company’s 2018 Stock Option and Incentive Plan (the “2018 Plan”) was adopted by the Board on June 1, 2018 and approved by stockholders on June 7, 2018 and became effective upon the effectiveness of the Company’s Registration Statement on Form S-1. The Company initially reserved 616,300 shares of its common stock for the issuance of awards under the 2018 Plan. The 2018 Plan provides that the number of shares reserved and available for issuance under the plan will automatically increase each January 1, beginning on January 1, 2019, by 4% of the outstanding number of shares of our common stock on the immediately preceding December 31, or such lesser number of shares as determined by its Board or compensation committee (the “Plan Evergreen”). This number is subject to adjustment in the event of a stock split, stock dividend or other change in its capitalization. On April 16, 2020, the Board adopted an amendment to the 2018 Plan (the “Amendment”), to (i) increase the number of shares of common stock currently reserved for issuance under the 2018 Plan by 3,300,000 shares and (ii) automatically terminate the 2018 Plan’s annual increase (or “evergreen”) provision after January 2022. The Amendment was approved by the Board on June 4, 2020 and the Company’s stockholders on June 4, 2020. The number of shares of common stock available for future grant under the 2018 Plan was 5,005,295 as of December 31, 2022, which does not include the shares added to the 2018 Plan reserve on January 1, 2022 as a result of the Plan Evergreen for the year ended December 31, 2022. During the years ended December 31, 2022 and 2021, the Company granted options to purchase 5,369,650 and, 4,253,232 shares, respectively, of common stock to employees, nonemployees and members of the Board. 2018 Employee Stock Purchase Plan The Company’s 2018 Employee Stock Purchase Plan (the “ESPP”) was adopted by the Board on June 1, 2018 and approved by stockholders on June 7, 2018 and became effective upon the effectiveness of the Company’s Registration Statement on Form S-1. shares or (iii) such number of shares as determined by the ESPP administrator (the “ESPP Evergreen”). The number of shares reserved under the ESPP is subject to adjustment in the event of a stock split, stock dividend or other change in our capitalization. During the years ended December 31, 2022 and 2021, the Company issued 120,947 and 27,580 shares, respectively of common stock. The total number of shares of common stock available for future grant was 1,467,026 as of December 31, 2022, which does not include the shares added to the ESPP reserve on January 1, 2023 as a result of the ESPP Evergreen for the year ended December 31, 2022. 2019 Inducement Plan The Company’s 2019 Inducement Plan (the “2019 Plan”) was adopted by the Board on December 11, 2019. The purpose of the 2019 Plan is to allow the Company to grant equity awards to new employees as inducements material to such new employee’s acceptance of employment with the Company. The Company intends that the shares underlying the 2019 Plan be reserved for persons to whom the Company may issue securities without stockholder approval as an inducement pursuant to Rule 5635(c)(4) of the Nasdaq marketplace rules. The Company initially reserved 1,800,000 shares of its common stock for the issuance of awards under the 2019 Plan. The number of shares of common stock available for future grant under the 2019 Plan was 786,656 as of December 31, 2022. 2020 Inducement Plan The Company’s 2020 Inducement Plan (the “2020 Plan”) was adopted by the Board on December 9, 2020. The purpose of the 2020 Plan is to allow the Company to grant equity awards to new employees as inducements material to such new employee’s acceptance of employment with the Company. The Company intends that the shares underlying the 2020 Plan be reserved for persons to whom the Company may issue securities without stockholder approval as an inducement pursuant to Rule 5635(c)(4) of the Nasdaq marketplace rules. The Company initially reserved 1,700,000 shares of its common stock for the issuance of awards under the 2020 Plan. The number of shares of common stock available for future grant under the 2020 Plan was 1,637,000 as of December 31, 2022. Stock Option Valuation The assumptions that the Company used to determine the grant-date fair value of stock options granted to employees and members of the Board were as follows, presented on a weighted-average basis: Year Ended 2022 2021 Expected option life (years) 5.98 6.06 Risk-free interest rate 2.47 % 0.80 % Expected volatility 80.43 % 81.22 % Expected dividend yield —  % —  % The following table summarizes the Company’s stock option activity for the year ended December 31, 2022: Number of Weighted- Weighted- Aggregate Outstanding as of December 31, 2021 7,423,777 $ 13.54 6.79 $ 1,469 Granted 5,369,650 $ 1.43 Exercised (142,013 ) $ 0.41 Cancelled or forfeited (3,228,143 ) $ 12.31 Outstanding as of December 31, 2022 9,423,271 $ 7.26 8.14 $ 22 Exercisable as of December 31, 2022 3,068,082 $ 13.11 6.15 $ 22 The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the underlying stock options and the estimated fair value of the Company’s common stock for those stock options that had exercise prices lower than the estimated fair value of the Company’s common stock. The aggregate intrinsic value of options exercised during the years ended December 31, 2022 and 2021 was $50 and $1,826, respectively. The weighted-average grant-date fair value of the Company’s stock options granted during the years ended December 31, 2022 and 2021 was $0.99 and $8.70, respectively. Restricted Common Stock The Company has granted restricted common stock (or restricted stock awards) with time-based vesting conditions to certain employees of the Company. Restricted stock units Restricted stock units represent an unsecured promise to grant at no cost a set number of shares of common stock upon vesting. With respect to restricted stock units, recipients are not entitled to cash dividends and have no voting rights during the vesting period. The following table summarizes the Company’s restricted stock award and restricted stock unit activity for the year ended December 31, 2022: Number Weighted- Issued and unvested as of December 31, 2021 599,850 $ 9.64 Granted 920,168 1.56 Vested (575 ) 15.65 Forfeited, cancelled or expired (579,051 ) 6.56 Issued and unvested as of December 31, 2022 940,392 $ 3.62 The total fair value of restricted stock awards and restricted stock units vested during the years ended December 31, 2022 and 2021 was $9 and $5, respectively. Stock-Based Compensation Stock-based compensation expense was allocated as follows: Year Ended 2022 2021 Research and development $ 2,785 $ 6,996 General and administrative 8,737 11,583 Total stock-based compensation expense $ 11,522 $ 18,579 As of December 31, 2022, total unrecognized compensation cost related to unvested stock-based awards was $18,719, which is expected to be recognized over a weighted-average period of 2.3 years.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Income Taxes	12. Income Taxes For the years ended December 31, 2022 and 2021, the Company did not record a current or deferred income tax expense or (benefit) due to current and historical losses incurred by the Company. The Company’s operations are predominantly based in the United States and the Company’s foreign subsidiaries generated de minimis A reconciliation of income tax expense (benefit) computed at the statutory federal income tax rate to the Company’s effective tax rate as reflected in the consolidated financial statements is as follows: Year Ended 2022 2021 Federal income tax expense at statutory rate 21.0 % 21.0 % State income taxes, net of federal benefit 5.2 % 6.0 % Permanent differences -1.2 % -1.2 % Foreign rate differential 0.0 % 0.1 % Research and development tax credits 0.8 % 2.0 % Change in valuation allowance -25.8 % -27.9 % Provision to Return 0.0 % 0.0 % Effective income tax rate 0.0 % 0.0 % Deferred taxes are recognized for temporary differences between the basis of assets and liabilities for financial statement and income tax purposes. The significant components of the Company’s deferred tax assets and liabilities are comprised of the following: December 31, 2022 2021 Deferred tax assets: U.S., foreign and state net operating loss carryforwards $ 91,416 $ 84,102 Research and development credits 8,471 7,821 Capitalized start up and organizational costs 23 26 Equity based compensation 3,610 3,926 Licensing agreements 3,929 3,749 Section 174 R&D Capitalization 16,307 —  Lease Liability 227 —  Accruals and other 1,032 1,376 Total deferred tax assets 125,015 101,000 Valuation allowance (124,695 ) (100,893 ) Net deferred tax assets $ 320 $ 107 Deferred tax liabilities: Property and equipment $ (102 ) $ (107 ) ROU Asset (218 ) —  Total deferred tax liabilities $ —  $ —  The Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets. As of December 31, 2022 and 2021 based on the Company’s history of operating losses, the Company has concluded that it is not more likely than not that the benefit of its deferred tax assets will be realized. Accordingly, the Company has provided a full valuation allowance for deferred tax assets as of December 31, 2022 and 2021. The valuation allowance increased by $23,802 and $30,401 during the years ended December 31, 2022 and 2021, respectively, due primarily to net operating losses generated. As of December 31, 2022 and 2021, the Company had U.S. federal net operating loss carryforwards of $340,350 and $312,967, respectively, that may be available to offset future income tax liabilities. The U.S. federal tax operating loss carryforwards of approximately $17,743 will expire at various dates through 2037. Approximately $322,607 of the U.S. federal tax operating losses can be carried forward indefinitely. As of December 31, 2022 and 2021, the Company also had U.S. state net operating loss carryforwards of $316,668 and $290,500, respectively, which may be available to offset future taxable income. These losses expire at various dates beginning in 2041. As of December 31, 2022 and 2021, the Company had federal research and development tax credit carryforwards of $6,824 and $6,234, respectively. Included in the $6,824 of federal tax credit carryforwards are $2,027 of orphan drug credits. Through the year ended December 31, 2020 the Company qualifies for, and has elected to, apply part of its federal research credits against its payroll tax liability in accordance with certain provisions of the Internal Revenue Code. The amount applied towards the Company’s payroll tax liability is capped at $250 per year. The federal research credits generated in excess of the $250 cap are able to be carried forward for 20 years. As of December 31, 2022 and 2021, the Company had state research and development tax credit carryforwards of approximately $2,084 and $1,959, respectively, available to reduce future tax liabilities which expire at various dates beginning in 2037. For all years through December 31, 2022, the Company generated research credits but has not conducted a study to document the qualified activities. This study may result in an adjustment to the Company’s research and development credit carryforwards. Under the provisions of the Internal Revenue Code, the net operating loss and tax credit carryforwards are subject to review and possible adjustment by the Internal Revenue Service and state tax authorities. Net operating loss and tax credit carryforwards may become subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant shareholders over a three-year period in excess of 50 percentage points, as defined under Sections 382 and 383 of the Internal Revenue Code, respectively, as well as similar state provisions. This could limit the amount of tax attributes that can be utilized annually to offset future tax liabilities. The amount of the annual limitation is determined based on the value of the Company immediately prior to the ownership change. Subsequent ownership changes may further affect the limitation in future years. The Company has completed numerous financings since its inception, which may have resulted in a change in control as defined by Sections 382 and 383 of the Internal Revenue Code, or could result in a change in control in the future. The Company files income tax returns in the United States, Australia and Canada, and in several states. The foreign, federal and state income tax returns are generally subject to tax examinations for the tax years ended December 31, 2016 through December 31, 2020. To the extent the Company has tax attribute carryforwards, the tax years in which the attribute was generated may still be adjusted upon examination by foreign tax authorities, the Internal Revenue Service, or state tax authorities to the extent utilized in a future period.

Net Income (Loss) Per Share

Net Income (Loss) Per Share	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Earnings Per Share [Abstract]
Net Loss Per Share	11. Net Income (Loss) Per Share The following table sets forth the computation of the Company’s basic and diluted net income (loss) per share for the three and nine months ended September 30, 2023 and 2022 (in thousands, except share and per share amounts): Three Months Ended Nine Months Ended 2023 2022 2023 2022 Numerator: Net income (loss) attributable to common stockholders—basic and diluted $ (21,577 ) $ (22,969 ) $ 20,942 $ (80,856 ) Denominator: Weighted-average common shares outstanding—basic 44,527,997 43,772,990 44,234,936 43,722,129 Weighted-average common shares outstanding—diluted 44,527,997 43,772,990 44,425,531 43,722,129 Net income (loss) per share applicable to common stockholders—basic $ (0.48 ) $ (0.52 ) $ 0.47 $ (1.85 ) Net income (loss) per share applicable to common stockholders—diluted $ (0.48 ) $ (0.52 ) $ 0.47 $ (1.85 ) The Company excluded the following potential common shares from the computation of diluted net income (loss) per share attributable to common stockholders for the three and nine months ended September 30, 2023 and 2022 because including them would have had an anti-dilutive effect: Three Months Ended Nine Months Ended 2023 2022 2023 2022 Options to purchase common stock 4,827,316 8,083,363 7,683,446 8,083,363 Restricted stock units 276,008 870,536 1,414,256 870,536 Employee stock purchase plan —  —  4,976 —	13. Net Loss per Share For purposes of the diluted net loss per share calculation, stock options, unvested restricted stock awards and unvested restricted stock units are considered to be common stock equivalents but have been excluded from the calculation of diluted net loss per share, as their effect would be anti-dilutive for all periods presented. Therefore, the weighted-average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The following potentially dilutive common stock equivalents, presented based on amounts outstanding at each period end, were excluded from the computation of diluted net loss per share attributable to common stockholders for the periods indicated: Year Ended December 31, 2022 2021 Options to purchase common stock 9,423,271 7,423,777 Restricted stock awards and units 940,392 599,850

Related Party Transactions

Related Party Transactions	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Related Party Transactions [Abstract]
Related Party Transactions	12. Related Party Transactions UHN For the three months ended September 30, 2023 and 2022, the Company recognized $25 and $82, respectively, of research and development expense related to the license agreements with UHN. For the nine months ended September 30, 2023 and 2022, the Company recognized $97 and $145, respectively, of research and development expense related to the license agreements with UHN. Refer to Note 3 “ 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 September 30, 2023 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 September 30, 2022 the Company recorded $795 related to the sublease to rent office and lab space previously provided by an entity affiliated with a member of the Company’s Board. For the nine months ended September 30, 2023 and 2022, the Company recorded expenses of $754 and $2,381, respectively, related to the sublease to rent office and lab space previously provided by an entity affiliated with a member of the Company’s Board.	14. Related Party Transactions UHN In connection with the Company’s entry into a license agreement with UHN on January 27, 2016, the Company issued UHN 1,161,665 shares of its common stock. Upon the closing of the IPO in 2018, as UHN’s fully-diluted percentage ownership of the Company was reduced within a range of specified percentages, the Company was obligated to pay UHN an amount of $2,000, which was paid in July 2018. For the years ended December 31, 2022 and 2021, the Company recognized $200 and $248, respectively, of research and development expense related to the license agreements with UHN. Refer to Note 3 “License Agreements” Others For the years ended December 31, 2022 and 2021, the Company recorded expenses of $3,200 and $1,523, respectively, related to a sublease to rent lab space, provided by an entity affiliated with a member of the board.

Restructuring Activities

Restructuring Activities	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Restructuring and Related Activities [Abstract]
Restructuring Activities	13. 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 $3,685 for the three and nine months ended September 30, 2023. These one-time the three months ended September 30, 2023, $903 of these expenses were related to non-cash Employee Severance Restructuring expenses $ 3,685 Cash payments (2,782 ) Non-cash (903 ) Liability included in accrued expenses and other current liabilities at September 30, 2023 $ —	15. Restructuring In January 2022, the Company announced the deprioritization of AVR-RD-01, AVR-RD-01 FAB-GT FAB-GT In connection with the deprioritization of AVR-RD-01 Under the Workforce Reduction, the Company recognized total restructuring expenses for the year ended December 31, 2022 of $1,369, which are included within Research and development and General and administrative expenses. No restructuring expenses were incurred for the year ended December 31, 2021. These one-time

Subsequent Events

Subsequent Events	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Subsequent Events [Abstract]
Subsequent Events	14. Subsequent Events The Company’s workforce was reduced by 11 employees in the October 2023 Workforce Reduction effective as of October 31, 2023. Affected employees in the October 2023 Workforce Reduction were offered separation benefits, including severance payments. The Company estimates that the severance and termination-related costs will total approximately $1.2 million in the aggregate and expects to primarily record these charges in the fourth quarter of 2023. The Company expects that payments of these costs will substantially be made through the end of the fourth quarter of 2023.	16. Subsequent Events On March 10, 2023, Silicon Valley Bank, based in Santa Clara, California, was closed by the California Department of Financial Protection and Innovation, which appointed the Federal Deposit Insurance Corporation (“FDIC”) as receiver. On March 12, 2023, the U.S. Treasury, Federal Reserve, and FDIC announced that depositors with Silicon Valley Bank or its successor bridge bank (collectively, “SVB”) will have access to all of their money starting March 13, 2023. Our agreement with SVB currently requires substantially all of our cash and cash equivalents to be deposited with SVB, and we historically have relied primarily on SVB for commercial banking services. We are pursuing actions to make alternative banking arrangements, including opening deposit accounts at one or more other financial institutions. SVB has agreed to waive covenants related to maintaining our deposits at SVB for a period of 30 days, during which time we have agreed to obtain an Account Control Agreement (“ACA”) for all accounts held outside of SVB. The Company has concluded that it is probable that it will obtain the ACA for all accounts held outside of SVB prior to the expiration of the 30-day

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
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 Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“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, 2022, 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 September 30, 2023, and the results of its operations for the three and nine months ended September 30, 2023 and 2022, its statements of stockholders’ equity for the three and nine months ended September 30, 2023 and 2022 and its statement of cash flows for the nine months ended September 30, 2023 and 2022. The results for the three and nine months ended September 30, 2023 are not necessarily indicative of the results to be expected for the year ending December 31, 2022, 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, 2022, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K 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 September 30, 2023, there have been no changes to the Company’s significant accounting policies as described in the Company’s Annual Report on Form 10-K	Basis of Presentation The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”).
Principles of Consolidation		Principles of Consolidation The accompanying consolidated financial statements include the accounts of AVROBIO, Inc. and its wholly owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation.
Segment Information	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.	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.	Use of Estimates The preparation of financial statements in conformity with GAAP requires that the Company make estimates and judgments that may affect the reported amounts of assets, liabilities and expenses and the related disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting periods. On an on-going
Cash and Cash Equivalents		Cash and Cash Equivalents The Company considers all highly liquid investments purchased with original maturities of three months or less at acquisition to be cash equivalents. As of December 31, 2022 and 2021, cash and cash equivalents were primarily held in interest-bearing money market funds.
Concentrations of Credit Risk		Concentrations of Credit Risk The Company has no significant off-balance
Fair Value Measurements		Fair Value Measurements Certain assets and liabilities of the Company are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable: • Level 1— Fair values are determined utilizing prices (unadjusted) in active markets for identical assets or liabilities that the Company has the ability to access. • Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3—Unobservable inputs that are supported by little or no market activity that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The carrying amounts of the Company’s financial instruments, which include cash equivalents, accounts payable, and accrued expenses, approximated their fair values as of December 31, 2022 and 2021 due to the short-term The Company has evaluated the estimated fair value of financial instruments using available market information. The use of different market assumptions, estimation methodologies, or both, could have a significant effect on the estimated fair value amounts. See Note 4 “Fair Value of Financial Assets and Liabilities”
Property and Equipment		Property and Equipment Property and equipment are recorded at cost. Depreciation and amortization is calculated using the straight-line method over the following estimated useful lives of the assets: Estimated Useful Life Laboratory and office equipment 5 years Computer equipment 2 years Leasehold improvements Lesser of lease term or 10 years
Impairment of Long-Lived Assets		Impairment of Long-Lived Assets Long-lived assets consist of property and equipment. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset group for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset group to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset group are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset group over its fair value, determined based on discounted cash flows. The Company did not record any impairment loss during the years ended December 31, 2022 and 2021.
Leases		Leases Prior to January 1, 2022, the Company accounted for leases in accordance with FASB ASC 840, Leases. At lease inception, the Company determined if an arrangement was an operating or capital lease. For operating leases, the Company recognized rent expense, inclusive of rent escalations, on a straight-line basis over the lease term. Effective on January 1, 2022, the Company accounts for leases in accordance with ASC Topic 842, Leases (“ASC 842”). Upon transition, the Company applied the package of practical expedients permitted under ASC 842 transition guidance to its entire lease portfolio at January 1, 2022. As a result, the Company was not required to reassess (i) whether any expired or existing contracts are or contain leases, (ii) the classification of any expired or existing leases, and (iii) initial direct costs for any existing leases. Furthermore, as a lessee the Company elected to combine lease and non-lease non-lease In accordance with ASC 842, the Company determines whether an arrangement is or contains a lease at inception. A contract is or contains a lease if the contract conveys the right to control the use of an identified asset for a period of time in exchange for consideration. The Company records leases at the lease commencement date, when control of the underlying asset is transferred from the lessor to the lessee, as operating or finance leases and records a right-of-use The Company enters into contracts that contain both lease and non-lease Non-lease non-lease right-of-use Operating lease assets and liabilities are recognized at the lease commencement date based on the present value of the lease payments over the lease term using the discount rate implicit in the lease if readily determinable. If the rate implicit is not readily determinable, the Company utilizes its incremental borrowing rate based upon the available information at the lease commencement date. ROU assets are further adjusted for items such as initial direct costs, prepaid rent, or lease incentives. Operating lease payments are expensed using the straight-line method as an operating expense over the lease term. The Company’s lease terms may include options to extend the lease when it is reasonably certain that the Company will exercise that option. Finance lease assets are amortized to depreciation expense using the straight-line method over the shorter of the useful life of the related asset or the lease term. Finance lease payments are bifurcated into (i) a portion that is recorded as interest expense and (ii) a portion that reduces the finance lease liability associated with the lease.
Comprehensive Income (Loss)		Comprehensive Income (Loss) Comprehensive income (loss) is defined as the change in stockholders’ equity of a business enterprise during a period from transactions and other events and circumstances from non-owner
Foreign Currency Translation		Foreign Currency Translation The functional currency of the Company’s international operations in Canada and Australia is the U.S. dollar. Accordingly, all operating assets and liabilities of these international subsidiaries are remeasured into U.S. dollars using the exchange rates in effect at the balance sheet date or historical rates, as appropriate, while expenses are remeasured into U.S. dollars at the average rates in effect during the period. Any differences resulting from the remeasurement of assets, liabilities, and operations of the Canadian and Australian subsidiaries are recorded within other (expense) income, net in the consolidated statements of operations and comprehensive loss. During the years ended December 31, 2022 and 2021, the Company recorded foreign exchange losses of $92 and $61, respectively, in other expense in the consolidated statements of operations and comprehensive loss.
Research and Development Expenses		Research and Development Expenses Research and development costs are expensed as incurred. Research and development Non-refundable The Company has entered into various research and development related contracts with parties both inside and outside of the United States. The payments related to these agreements are recorded as research and development expenses as incurred. The Company records accrued liabilities for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies or clinical trials, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs.
Stock-Based Compensation	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 Accounting Standards Update (“ASU”) No. 2018-07, Compensation-Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting non-employee 2018-07, non-employee 2018-07, The Company classifies stock-based compensation expense in its consolidated statements of operations and comprehensive income (loss) in the same manner in which the award recipient’s cash compensation costs are classified.	Stock-Based Compensation For stock-based awards issued to employees and members of the Company’s board of directors (the “Board”) for their services on the Board, the Company measures the estimated fair value of the stock-based award on the date of grant and recognizes compensation expense for those awards over the requisite service period, which is generally the vesting period of the respective award. The Company issues stock-based awards with only service-based vesting conditions and records the expense for these awards using the straight-line method. The Company has not issued any stock-based awards with performance-or market-based vesting conditions. The Company accounts for forfeitures as they occur. The measurement date for non-employee 2018-07, The Company classifies stock-based compensation expense in its consolidated statements of operations and comprehensive loss in the same manner in which the award recipient’s cash compensation costs are classified. The fair value of each stock option award is estimated on the date of grant using the Black-Scholes option pricing model. As there was no public market for its common stock prior to June 21, 2018, which was the first day of trading, and as the trading history of the Company’s common stock was limited through December 31, 2022, the Company determined the volatility for awards granted based on an analysis of reported data for a group of guideline companies that issued options with substantially similar terms. The expected volatility has been determined using a weighted-average of the historical volatility measures of this group of guideline companies. The Company expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. The expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. The Company has not paid, and does not anticipate paying, cash dividends on its common stock; therefore, the expected dividend yield is assumed to be zero.
Income Taxes		Income Taxes Deferred tax assets and liabilities are determined on the basis of the differences between the consolidated financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established. The Company accounts for uncertain tax positions recognized in the consolidated financial statements by prescribing a more-likely-than-not
Net Loss per Share		Net Loss per Share Basic net loss per share is computed by dividing net loss by the weighted-average number of shares of common stock outstanding during the period, without consideration of potential dilutive securities. Diluted net loss per share is computed by adjusting the weighted-average shares outstanding for the potential dilutive effects of common stock equivalents outstanding during the period calculated in accordance with the treasury stock method. For purposes of the diluted net loss per share calculation, stock options and restricted stock units are considered to be common stock equivalents but have been excluded from the calculation of diluted net loss per share, as their effect would be anti-dilutive for all periods presented. Therefore, basic and diluted net loss per share were the same for all periods presented.
Subsequent Event Considerations	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.	Subsequent Event Considerations The Company considers events or transactions that occur after the balance sheet date but prior to the issuance of the consolidated financial statements to provide additional evidence for certain estimates or to identify matters that require additional disclosure. Subsequent events have been evaluated as required. See Note 16.
Emerging Growth Company Status	Emerging Growth Company Status The Company is an “emerging growth company,” as defined in the Jumpstart Our Business Startups Act, or JOBS Act, and may take advantage of certain exemptions from various reporting requirements that are applicable to other public companies that are not emerging growth companies. The Company may take advantage of these exemptions until the Company is no longer an “emerging growth company.” Section 107 of the JOBS Act provides that an “emerging growth company” can take advantage of the extended transition period afforded by the JOBS Act for the implementation of new or revised accounting standards. The Company has elected to use the extended transition period for complying with new or revised accounting standards and as a result of this election, its consolidated financial statements may not be comparable to companies that comply with public company effective dates. The Company may take advantage of these exemptions up until the last day of the fiscal year following the fifth anniversary of its IPO or such earlier time that it is no longer an “emerging growth company.”	Emerging Growth Company Status The Company is an “emerging growth company,” as defined in the Jumpstart Our Business Startups Act, or JOBS Act, and may take advantage of certain exemptions from various reporting requirements that are applicable to other public companies that are not emerging growth companies. The Company may take advantage of these exemptions until the Company is no longer an “emerging growth company.” Section 107 of the JOBS Act provides that an “emerging growth company” can take advantage of the extended transition period afforded by the JOBS Act for the implementation of new or revised accounting standards. The Company has elected to use the extended transition period for complying with new or revised accounting standards and as a result of this election, its consolidated financial statements may not be comparable to companies that comply with public company effective dates. The Company may take advantage of these exemptions up until the last day of the fiscal year following the fifth anniversary of an offering or such earlier time that it is no longer an “emerging growth company.”
Recently Adopted 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 2016-13. 2016-13 available-for-sale In November 2019, the FASB issued ASU 2019-11, Codification Improvements to Topic 326, Financial Instruments – Credit Losses 2019-11. 2019-11 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments	Recently Adopted Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases As previously noted, the Company adopted ASC 842 with an effective date of January 1, 2022, using the modified retrospective transition approach which uses the effective date as the date of initial application. As a result, prior periods are presented in accordance with the previous guidance in ASC 840. The Company has elected to apply the package of practical expedients requiring no reassessment of whether any expired or existing contracts are or contain leases, the lease classification of any expired or existing leases, or the capitalization of initial direct costs for any existing leases. Upon its adoption of ASC 842 on January 1, 2022, the Company recognized operating lease right-of-use In December 2019, the FASB issued ASU No. 2019-12, Simplifying the Accounting for Income Taxes 2019-12. 2019-12
Recently Issued Accounting Pronouncements		Recently Issued Accounting Pronouncements In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses 2016-13. 2016-13 available-for-sale 2016-13 non-emerging 2016-13 In November 2019, the FASB issued ASU 2019-11, Codification Improvements to Topic 326, Financial Instruments – Credit Losses 2019-11. 2019-11 2016-13, 2016-13 2019-11 2016-13 2019-11 2016-13 2019-11

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2023
Accounting Policies [Abstract]
Schedule of Property and Equipment Estimated Useful Life	Property and equipment are recorded at cost. Depreciation and amortization is calculated using the straight-line method over the following estimated useful lives of the assets: Estimated Useful Life Laboratory and office equipment 5 years Computer equipment 2 years Leasehold improvements Lesser of lease term or 10 years

Fair Value Measurement (Tables)

Fair Value Measurement (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
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 September 30, 2023 and December 31, 2022: Fair Value Measurements as of September 30, 2023 Level 1 Level 2 Level 3 Total Assets: Cash equivalents — money market funds $ 104,541 $ —  $ —  $ 104,541 $ 104,541 $ —  $ —  $ 104,541 Fair Value Measurements as of December 31, 2022 Level 1 Level 2 Level 3 Total Assets: Cash equivalents — money market funds $ 91,095 $ —  $ —  $ 91,095 $ 91,095 $ —  $ —  $ 91,095	The Fair Value Measurements as of Level 1 Level 2 Level 3 Total Assets: Cash equivalents—money market funds $ 91,095 $ —  $ —  $ 91,095 $ 91,095 $ —  $ —  $ 91,095 Fair Value Measurements as of Level 1 Level 2 Level 3 Total Assets: Cash equivalents—money market funds $ 189,332 $ —  $ —  $ 189,332 $ 189,332 $ —  $ —  $ 189,332

Supplemental Balance Sheet In_2

Supplemental Balance Sheet Information (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Balance Sheet Related Disclosures [Abstract]
Summary of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consisted of the following: September 30, December 31, Prepaid research and development expenses $ 828 $ 4,509 Prepaid insurance 1,221 999 Other current assets 805 1,008 Prepaid compensation benefits 6 327 Tax incentive refund — 269 Prepaid expenses and other current assets $ 2,860 $ 7,112	Prepaid expenses and other current assets consisted of the following: December 31, 2022 2021 Prepaid research and development expenses $ 4,509 $ 4,496 Tax incentive refund, net of reserve 269 2,697 Prepaid insurance 999 112 Prepaid compensation benefits 327 575 Other current assets 1,008 1,698 Prepaid expenses and other current assets $ 7,112 $ 9,578
Summary of Property and Equipment, Net	Property and equipment, net consisted of the following: September 30, December 31, Laboratory and office equipment $ 5,973 $ 5,967 Leasehold improvements 629 629 Computer equipment 104 102 6,706 6,698 Less: Accumulated depreciation and amortization (4,421 ) (3,804 ) Reclassified to held for sale (2,285 ) —  Property and equipment, net $ —  $ 2,894 Reclassified to held for sale $ 2,285 $ —  Less: Loss on impairment (902 ) —  Less: Sales (1,198 ) —  Held for Sale $ 185 $ —  As of September 30, 2023, the Company had $185 of property and equipment classified as held for sale, and the Company’s intention is to complete the sale of these assets within the fourth quarter of 2023. During the three and nine months ended September 30, 2023, $2,285 of assets were reclassified as held for sale and $1,198 were sold. For the three and nine months ended September 30, 2023, the Company recognized $902 as a loss on impairment on assets. No depreciation or amortization expense was recognized for the three months ended September 30, 2023. Depreciation and amortization expense was $617 for the nine months ended September 30, 2023. Depreciation and amortization expense was $336 and $1,105, respectively, for the three and nine months ended September 30, 2022.	Property and equipment, net consisted of the following: December 31, 2022 2021 Laboratory and office equipment $ 5,967 $ 6,162 Leasehold improvements 629 1,635 Computer equipment 102 149 6,698 7,946 Less: Accumulated depreciation and amortization (3,804 ) (3,820 ) Property and equipment, net $ 2,894 $ 4,126
Summary of Restricted Cash	Restricted cash As of September 30, 2023 and December 31, 2022, 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. The cash will be restricted until the termination or modification of the lease arrangement. September 30, December 31, Restricted cash $ 283 $ 283 Restricted cash, net of current portion 400 —	Restricted Cash As of December 31, 2022 and 2021, 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. The cash will be restricted until the termination or modification of the lease arrangement. December 31, 2022 2021 Restricted cash $ 283 $ —  Restricted cash, net of current portion —  492
Summary of Accrued Expenses	Accrued expenses consisted of the following: December 31, 2022 2021 Research and development expenses $ 6,122 $ 8,882 Compensation and benefit costs 4,175 5,579 Consulting and professional fees 1,224 999 Other liabilities 211 178 $ 11,732 $ 15,638	Accrued expenses and other current liabilities Accrued expenses and other current liabilities consisted of the following: September 30, December 31, Research and development expenses $ 1,479 $ 6,122 Compensation and benefit costs 2,402 4,175 Consulting and professional fees 1,120 1,224 Other liabilities 1 211 Accrued expenses and other current liabilities $ 5,002 $ 11,732

Leases (Tables)

Leases (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Leases [Abstract]
Schedule of effective lease cost comprehensive income loss	The following table summarizes the effect of lease costs in the Company’s consolidated statement of operations and comprehensive income (loss): Three Months Ended 2023 Operating lease costs $ 483 Sublease income (23 ) Total lease costs $ 460	The following table summarizes the effect of lease costs in the Company’s consolidated statement of operations and comprehensive loss: Year ended Operating lease costs $ 2,994 Sublease income (23 ) Total lease costs $ 2,971
Schedule of Future Minimum Payments of Operating Lease Liabilities	As of September 30, 2023, future minimum payments of operating lease liabilities are as follows (in thousands): September 30, 2023 $ 706 2024 1,033 2025 69 2026 — 2027 — Thereafter — Total lease payments $ 1,808 Less: interest (82 ) Plus: FX gain/loss 26 Present value of lease liabilities $ 1,752	As of December 31, 2022, future minimum payments of operating lease liabilities are as follows (in thousands): As of 2023 $ 1,007 2024 138 2025 69 2026 —  2027 —  Thereafter —  Total lease payments $ 1,214 Less: interest (53 ) Plus: FX gain/loss 26 Present value of lease liabilities $ 1,187
Schedule of future minimum lease payments for capital leases relevant accounting standard		Future minimum payments required under the leases as of December 31, 2021 presented in accordance with ASC 840, the relevant accounting standard at that time (in thousands): Year Ending December 31, 2022 $ 1,297 2023 208 2024 147 2025 73 Total $ 1,725

Note Payable (Tables)

Note Payable (Tables)	12 Months Ended
	Dec. 31, 2022
Debt Disclosure [Abstract]
Carrying Value of Note Payable	As of December 31, 2022 and 2021 the carrying value of the note payable consists of the following: December 31, 2022 2021 Note payable, including End of Term Charge $ 16,350 $ 16,350 Debt discount, net of accretion (1,074 ) (1,405 ) Note payable, net of discount, long-term $ 15,276 $ 14,945
Future Principal Payments	As of December 31, 2022, the future principal payments due under the arrangement, excluding interest and the end of term charge, are as follows: Year Ending December 31, Principle 2023 $ —  2024 1,875 2025 7,500 2026 5,625 Total $ 15,000

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Equity [Abstract]
Summary of Common Stock Reserved for Future Issuance	As of September 30, 2023 and December 31, 2022, the Company has reserved the following shares of common stock for future issuance: September 30, December 31, Shares reserved for exercise of outstanding stock options 5,922,447 9,423,271 Shares reserved for vesting of restricted stock units 1,224,997 940,392 Shares reserved for issuance under the 2018 Stock Option and Grant Plan 7,287,262 5,005,295 Shares reserved for issuance under the 2018 Employee Stock Purchase Plan 1,332,587 1,467,026 Shares reserved for issuance under the 2019 Inducement Plan 1,137,800 786,656 Shares reserved for issuance under the 2020 Inducement Plan 1,700,000 1,637,000 Total shares of authorized common stock reserved for future issuance 18,605,093 19,259,640	As of December 31, 2022 and 2021, the Company has reserved the following shares of common stock for future issuance: December 31, 2022 2021 Shares reserved for exercise of outstanding stock options 9,423,271 7,423,777 Shares reserved for vesting of restricted stock units 940,392 599,850 Shares reserved for issuance under the 2018 Stock Option and Incentive Plan 5,005,295 2,583,736 Shares reserved for issuance under the 2018 Employee Stock Purchase Plan 1,467,026 1,151,010 Shares reserved for issuance under the 2019 Inducement Plan 786,656 412,686 Shares reserved for issuance under the 2020 Inducement Plan 1,637,000 1,637,000 Total shares of authorized common stock reserved for future issuance 19,259,640 13,808,059

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Share-Based Payment Arrangement [Abstract]
Summary of Assumptions that Used to Determine Grant-Date Fair Value of Stock Options Granted to Employees and Members of Board of Directors	The assumptions that the Company used to determine the grant-date fair value of stock options granted to employees and members of the Board were as follows, presented on a weighted-average basis: Nine Months Ended 2023 2022 Expected option life (years) 6.00 5.96 Risk-free interest rate 3.82 % 1.80 % Expected volatility 83.36 % 80.22 % Expected dividend yield — % — %	The assumptions that the Company used to determine the grant-date fair value of stock options granted to employees and members of the Board were as follows, presented on a weighted-average basis: Year Ended 2022 2021 Expected option life (years) 5.98 6.06 Risk-free interest rate 2.47 % 0.80 % Expected volatility 80.43 % 81.22 % Expected dividend yield —  % —  %
Summary of Stock Option Activity	The following table summarizes the Company’s stock option activity for the nine months ended September 30, 2023: Number of Weighted- Weighted- Aggregate Outstanding as of December 31, 2022 9,423,271 $ 7.26 8.14 $ 22 Granted 123,501 $ 1.09 Exercised (223,273 ) $ 0.79 Cancelled or forfeited (3,401,052 ) $ 7.15 Outstanding as of September 30, 2023 5,922,447 $ 7.43 6.32 $ 1,068 Exercisable as of September 30, 2023 3,606,590 $ 10.16 4.82 $ 217	The following table summarizes the Company’s stock option activity for the year ended December 31, 2022: Number of Weighted- Weighted- Aggregate Outstanding as of December 31, 2021 7,423,777 $ 13.54 6.79 $ 1,469 Granted 5,369,650 $ 1.43 Exercised (142,013 ) $ 0.41 Cancelled or forfeited (3,228,143 ) $ 12.31 Outstanding as of December 31, 2022 9,423,271 $ 7.26 8.14 $ 22 Exercisable as of December 31, 2022 3,068,082 $ 13.11 6.15 $ 22
Summary of Restricted Common Stock Units	The following table summarizes the Company’s restricted common stock units for the nine months ended September 30, 2023: Number Weighted- Issued and unvested as of December 31, 2022 940,392 $ 3.62 Granted 1,548,117 $ 1.65 Vested (283,835 ) $ 4.98 Forfeited, cancelled or expired (979,677 ) $ 2.02 Issued and unvested as of September 30, 2023 1,224,997 $ 2.10	The following table summarizes the Company’s restricted stock award and restricted stock unit activity for the year ended December 31, 2022: Number Weighted- Issued and unvested as of December 31, 2021 599,850 $ 9.64 Granted 920,168 1.56 Vested (575 ) 15.65 Forfeited, cancelled or expired (579,051 ) 6.56 Issued and unvested as of December 31, 2022 940,392 $ 3.62
Schedule of Stock-based Compensation Expense	Stock-based compensation expense was allocated as follows: Three Months Nine Months Ended 2023 2022 2023 2022 Research and development $ 415 $ 448 $ 1,705 $ 2,169 General and administrative 1,804 2,208 4,579 7,098 Total stock-based compensation expense $ 2,219 $ 2,656 $ 6,284 $ 9,267	Stock-based compensation expense was allocated as follows: Year Ended 2022 2021 Research and development $ 2,785 $ 6,996 General and administrative 8,737 11,583 Total stock-based compensation expense $ 11,522 $ 18,579

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Schedule of Reconciliation of Income Tax Expense (Benefit)	A reconciliation of income tax expense (benefit) computed at the statutory federal income tax rate to the Company’s effective tax rate as reflected in the consolidated financial statements is as follows: Year Ended 2022 2021 Federal income tax expense at statutory rate 21.0 % 21.0 % State income taxes, net of federal benefit 5.2 % 6.0 % Permanent differences -1.2 % -1.2 % Foreign rate differential 0.0 % 0.1 % Research and development tax credits 0.8 % 2.0 % Change in valuation allowance -25.8 % -27.9 % Provision to Return 0.0 % 0.0 % Effective income tax rate 0.0 % 0.0 %
Schedule of Deferred Tax Assets and Liabilities	Deferred taxes are recognized for temporary differences between the basis of assets and liabilities for financial statement and income tax purposes. The significant components of the Company’s deferred tax assets and liabilities are comprised of the following: December 31, 2022 2021 Deferred tax assets: U.S., foreign and state net operating loss carryforwards $ 91,416 $ 84,102 Research and development credits 8,471 7,821 Capitalized start up and organizational costs 23 26 Equity based compensation 3,610 3,926 Licensing agreements 3,929 3,749 Section 174 R&D Capitalization 16,307 —  Lease Liability 227 —  Accruals and other 1,032 1,376 Total deferred tax assets 125,015 101,000 Valuation allowance (124,695 ) (100,893 ) Net deferred tax assets $ 320 $ 107 Deferred tax liabilities: Property and equipment $ (102 ) $ (107 ) ROU Asset (218 ) —  Total deferred tax liabilities $ —  $ —

Net Income (Loss) Per Share (Ta

Net Income (Loss) Per Share (Tables)	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Earnings Per Share [Abstract]
Components of Basic and Diluted Earnings Per Share	The following table sets forth the computation of the Company’s basic and diluted net income (loss) per share for the three and nine months ended September 30, 2023 and 2022 (in thousands, except share and per share amounts): Three Months Ended Nine Months Ended 2023 2022 2023 2022 Numerator: Net income (loss) attributable to common stockholders—basic and diluted $ (21,577 ) $ (22,969 ) $ 20,942 $ (80,856 ) Denominator: Weighted-average common shares outstanding—basic 44,527,997 43,772,990 44,234,936 43,722,129 Weighted-average common shares outstanding—diluted 44,527,997 43,772,990 44,425,531 43,722,129 Net income (loss) per share applicable to common stockholders—basic $ (0.48 ) $ (0.52 ) $ 0.47 $ (1.85 ) Net income (loss) per share applicable to common stockholders—diluted $ (0.48 ) $ (0.52 ) $ 0.47 $ (1.85 )
Schedule of Dilutive Common Stock Equivalents Excluded from Computation of Diluted Net Loss per Share	The Company excluded the following potential common shares from the computation of diluted net income (loss) per share attributable to common stockholders for the three and nine months ended September 30, 2023 and 2022 because including them would have had an anti-dilutive effect: Three Months Ended Nine Months Ended 2023 2022 2023 2022 Options to purchase common stock 4,827,316 8,083,363 7,683,446 8,083,363 Restricted stock units 276,008 870,536 1,414,256 870,536 Employee stock purchase plan —  —  4,976 —	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 attributable to common stockholders for the periods indicated: Year Ended December 31, 2022 2021 Options to purchase common stock 9,423,271 7,423,777 Restricted stock awards and units 940,392 599,850

Restructuring Activities (Table

Restructuring Activities (Tables)	9 Months Ended
	Sep. 30, 2023
Restructuring and Related Activities [Abstract]
Schedule of Restructuring Activities	Employee Severance Restructuring expenses $ 3,685 Cash payments (2,782 ) Non-cash (903 ) Liability included in accrued expenses and other current liabilities at September 30, 2023 $ —

Nature of the Business - Additi

Nature of the Business - Additional Information (Detail) $ in Thousands		3 Months Ended	9 Months Ended
	Jun. 09, 2023 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2023 USD ($)	Oct. 31, 2023 Number	Jul. 12, 2023	May 19, 2023 USD ($)	Dec. 31, 2022 USD ($)	Sep. 30, 2022 USD ($)	Dec. 31, 2021 USD ($)
Accumulated deficit		$ (468,490)	$ (468,490)				$ (489,432)		$ (383,542)
Cash and cash equivalents		105,842	105,842				$ 92,563	$ 115,968	$ 189,567
Cash payment of closing the transaction						$ 87,500
Gain loss on recognize assets sales	$ 83,736	$ 83,736	$ 3,764
Reduction in workforce, percentage					50%
Subsequent Event [Member]
Reduction in workforce, number | Number				11

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2023 USD ($)	Sep. 30, 2023 USD ($) SEGMENT	Dec. 31, 2022 USD ($) SEGMENT	Dec. 31, 2021 USD ($)	Jan. 01, 2022 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Number of operating segment | SEGMENT		1	1
Impairment loss of long-lived assets	$ 940,000		$ 0	$ 0
Foreign exchange losses			92,000	61,000
Operating lease assets	912,000	$ 912,000	1,057,000	$ 0	$ 1,301,000
Operating lease liabilities	$ 1,752,000	$ 1,752,000	$ 1,187,000		1,593,000
Deferred rent liabilities					$ 292,000
Expected Dividend Yield [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Expected cash dividend yield			0

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Schedule of Property and Equipment Estimated Useful Life (Detail)	9 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Laboratory and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment estimated useful life		5 years
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment estimated useful life		2 years
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment estimated useful life		10 years
Property and equipment estimated useful life	Lesser of lease term

License Agreements - Additional

License Agreements - Additional Information (Detail) £ in Thousands, $ in Thousands, $ in Thousands							1 Months Ended	3 Months Ended			9 Months Ended			12 Months Ended
	Sep. 08, 2023 GBP (£)	Jun. 09, 2023 USD ($)	Sep. 30, 2020 USD ($)	Oct. 02, 2017 USD ($)	Jan. 27, 2016 USD ($)	Jan. 27, 2016 CAD ($) shares	Aug. 31, 2017 USD ($) shares	Sep. 30, 2023 USD ($) shares	Sep. 30, 2022 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2023 USD ($) shares	Sep. 30, 2023 GBP (£) shares	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($) shares	Dec. 31, 2021 USD ($) shares	Dec. 31, 2020 USD ($)	Dec. 31, 2018 USD ($)	May 19, 2023 USD ($)	Nov. 17, 2016 USD ($)
License Agreement [Line Items]
Collaborative agreement expenses								$ 0	$ 590		$ 1,610		$ 1,970	$ 2,346	$ 1,437
Common stock, issued | shares								44,558,000			44,558,000	44,558,000		43,916,000	43,652,000
Research and development								$ 14,829	15,919		$ 43,310		54,049	$ 72,186	$ 83,114
Preferred stock issued | shares														0	0
Cash payment of closing the transaction																		$ 87,500
Gain loss on recognize assets sales		$ 83,736						83,736			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							$ 80,000
Milestone payment paid			$ 2,000							2,000
Milestone payment due										$ 4,000
Agreement Expiration Period														15 years
Agreement Expiration Description														upon the later of 15 years from the effective date or the expiration of the last valid claim of the licensed patents
Research and development expense	£ 3,900											£ 9,900		$ 9,900
UHN Agreement [Member]
License Agreement [Line Items]
Research and development expense								25	0		59		106	161	$ 209
Milestone fees								0	0		0		0	0	0
Research and development								0
UHN Agreement [Member] | Fabry License Agreement [Member]
License Agreement [Line Items]
Upfront license fee						$ 75
Milestone payments payable						2,450
Option fee						20
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		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												$ 2,000
Research and development									39		37		39	39	39
BioMarin Pharmaceutical Inc [Member]
License Agreement [Line Items]
Upfront license fee							$ 500
Preferred stock issued | shares							233,765
Milestone payments											13,000			13,000
Expenses related to license								0	0		0		0	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		0		0
Lund University Rights Holders Agreement [Member]
License Agreement [Line Items]
Milestone payments payable																			$ 550
Expenses related to license								$ 0	$ 0		$ 0		$ 0	$ 0	$ 0

Fair Value Measurement - Summar

Fair Value Measurement - Summary of Financial Assets Measured at Fair Value on Recurring Basis (Detail) - Fair Value on Recurring Basis [Member] - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Assets Fair Value Disclosure
Assets Fair Value Disclosure		$ 91,095	$ 189,332
Money Market Funds [Member] | Cash Equivalents [Member]
Assets Fair Value Disclosure
Assets Fair Value Disclosure		91,095	189,332
Level 1 [Member]
Assets Fair Value Disclosure
Assets Fair Value Disclosure	$ 104,541	91,095	189,332
Level 1 [Member] | Money Market Funds [Member] | Cash Equivalents [Member]
Assets Fair Value Disclosure
Assets Fair Value Disclosure	$ 104,541	$ 91,095	$ 189,332

Supplemental Balance Sheet In_3

Supplemental Balance Sheet Information - Summary of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Supplemental Balance Sheet Information Disclosures [Abstract]
Prepaid research and development expenses	$ 828	$ 4,509	$ 4,496
Tax incentive refund, net of reserve	0	269	2,697
Prepaid insurance	1,221	999	112
Prepaid compensation benefits	6	327	575
Other current assets	805	1,008	1,698
Prepaid expenses and other current assets	$ 2,860	$ 7,112	$ 9,578

Supplemental Balance Sheet In_4

Supplemental Balance Sheet Information - Summary of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	$ 6,706	$ 6,698	$ 7,946
Less: Accumulated depreciation and amortization	(4,421)	(3,804)	(3,820)
Property and equipment, net	0	2,894	4,126
Reclassified to held for sale	2,285	0
Less: Loss on impairment	(902)	0
Less: Sales	(1,198)	0
Held for Sale	185	0
Laboratory and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	5,973	5,967	6,162
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	629	629	1,635
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	$ 104	$ 102	$ 149

Supplemental Balance Sheet In_5

Supplemental Balance Sheet Information - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Impairment Effects on Earnings Per Share [Line Items]
Depreciation and amortization expense			$ 617	$ 1,105	$ 1,440	$ 1,399
Property, plant, and equipment that is held for sale			1,198
Held for Sale			185		$ 0
loss on impairment on assets	$ 0	$ 0	83,736	0
Property, Plant and Equipment [Member]
Impairment Effects on Earnings Per Share [Line Items]
Property, plant, and equipment that is held for sale			185
Held for Sale	2,285		2,285
loss on impairment on assets	902		902
depreciation or amortization expense	$ 0	$ 336	$ 617	$ 1,105

Supplemental Balance Sheet In_6

Supplemental Balance Sheet Information - Summary of Restricted Cash (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Restricted Cash and Investments [Abstract]
Restricted cash	$ 283	$ 283	$ 0
Restricted cash, net of current portion	$ 400	$ 0	$ 492

Supplemental Balance Sheet In_7

Supplemental Balance Sheet Information - Summary of Accrued Expenses (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Accrued Liabilities, Current [Abstract]
Compensation and benefit costs	$ 2,402	$ 4,175	$ 5,579
Research and development expenses	1,479	6,122	8,882
Consulting and professional fees	1,120	1,224	999
Other liabilities	1	211	178
Accrued expenses and other current liabilities	$ 5,002	$ 11,732	$ 15,638

Leases - Additional Information

Leases - Additional Information (Detail) $ in Thousands						3 Months Ended		9 Months Ended		12 Months Ended
	Jan. 01, 2022	Jun. 09, 2020	Jun. 01, 2020	Aug. 31, 2018	Jan. 12, 2018 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Sep. 30, 2023 CAD ($)	Dec. 31, 2022 CAD ($)	Dec. 31, 2021 CAD ($)
Lessee, Lease, Description [Line Items]
Lease Expiration Month And Year	2023-04	2022-04	2025-06	2020-10
Percentage of annual increase in rent	5%		6.67%		3%
Tenant incentive allowance					$ 842,000
Lease Expiration Date			Jun. 29, 2025
Annual Lease Payments Description								The annual lease payments are fixed for years 1 and 2, and then subject to a 6.67% increase for years 3 through 5		The annual lease payments are fixed for years 1 and 2, and then subject to a 6.67% increase for years 3 through 5
Operating leases and Rent expenses						$ 706,000	$ 831,000	$ 2,088,000	$ 2,493,000	$ 3,167	$ 2,648,000
Weighted average remaining lease						9 months 18 days	1 year	9 months 18 days	1 year	10 months 24 days		9 months 18 days	10 months 24 days
Weighted average incremental borrowing rate						15.59%	10.51%	15.59%	10.51%	10.58%		15.59%	10.58%
Impairment of right of use assets						$ 940,000				$ 0	0
Restricted Cash [Member]
Lessee, Lease, Description [Line Items]
Security Deposit						$ 283,000		$ 283,000		283,000	283,000
Other Noncurrent Assets [Member]
Lessee, Lease, Description [Line Items]
Security Deposit												$ 27	$ 27	$ 27
Cambridge, Massachusetts
Lessee, Lease, Description [Line Items]
Lease Expiration Month And Year					2023-01
Cambridge, Massachusetts | Restricted Cash [Member]
Lessee, Lease, Description [Line Items]
Security Deposit										$ 209,000	$ 209,000

Leases - Summary of effective l

Leases - Summary of effective lease cost comprehensive income loss (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Leases [Abstract]
Operating lease costs	$ 483	$ 2,994
Sublease income	(23)	(23)
Total lease costs	$ 460	$ 2,971

Leases - Summary of Future Mini

Leases - Summary of Future Minimum Payments of Operating Lease Liabilities (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022	Jan. 01, 2022
Leases [Abstract]
2023	$ 706
2024	1,033	$ 1,007
2025	69	138
2026	0	69
2027	0	0
2027		0
Thereafter	0	0
Total lease payments	1,808	1,214
Less: interest	(82)	(53)
Plus: FX gain/loss	26	26
Present value of lease liabilities	$ 1,752	$ 1,187	$ 1,593

Lease - Schedule of Future Mini

Lease - Schedule of Future Minimum Lease Payments for Capital Leases Relevant Accounting Standard (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
2022	$ 1,033	$ 1,007
2023	69	138
2024	0	69
2025	0	0
Total lease payments	$ 1,808	$ 1,214
Accounting Standards Update 840 Member
2022			$ 1,297
2023			208
2024			147
2025			73
Total lease payments			$ 1,725

Note Payable - Additional Infor

Note Payable - Additional Information (Detail) $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
	Nov. 02, 2021 USD ($) Tranche	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Debt Disclosure [Line Items]
Debt Issuance Costs, Net						$ 1,074	$ 1,405
Interest expense recognized		$ 0	$ 482	$ 1,917	$ 1,280	$ 1,808	203
Term Loan Facility [Member] | Silicon Valley Bank [Member]
Debt Disclosure [Line Items]
Loan maturity date	Oct. 01, 2026
End of term charge as percentage on principal amount	9%
Loan, interest rate	8.10%
Term Loan Facility [Member] | Silicon Valley Bank [Member] | Prime Rate [Member]
Debt Disclosure [Line Items]
Loan, interest rate	4.85%
Term Loan Prepayment During First Year [Member] | Silicon Valley Bank [Member]
Debt Disclosure [Line Items]
Line of credit facility prepayment of premium percentage	1.50%
Term Loan Prepayment During Second Year [Member] | Silicon Valley Bank [Member]
Debt Disclosure [Line Items]
Line of credit facility prepayment of premium percentage	1%
Term Loan Prepayment After Second Year [Member] | Silicon Valley Bank [Member]
Debt Disclosure [Line Items]
Line of credit facility prepayment of premium percentage	0%
Loan Agreement [Member]
Debt Disclosure [Line Items]
Loan, interest rate	15%
Gain (Loss) on Extinguishment of Debt, before Debt Issuance Cost Writeoff				1,917
Deferred Debt Issuance Cost, Writeoff				$ 939
Loan Agreement [Member] | Silicon Valley Bank [Member]
Debt Disclosure [Line Items]
Loan, interest rate	16.29%
Debt discount	$ 1,350
Loan Agreement [Member] | Silicon Valley Bank [Member] | Legal Expenses [Member]
Debt Disclosure [Line Items]
Debt Issuance Costs, Net	103						$ 103
Loan Agreement [Member] | Term Loan Facility [Member] | Silicon Valley Bank [Member]
Debt Disclosure [Line Items]
Borrowing amount	$ 50,000
Debt instrument number of tranches | Tranche	3
Proceeds from loan agreement	$ 15,000
Additional borrowing amount	15,000
Line of credit facility additional discretionary	$ 15,000
Loan maturity date	Oct. 01, 2026
End of term charge as percentage on principal amount	9%
Loan Agreement [Member] | Term Loan Facility [Member] | Silicon Valley Bank [Member] | Regulatory Milestone [Member]
Debt Disclosure [Line Items]
Additional borrowing amount	$ 10,000

Note Payable - Carrying Value o

Note Payable - Carrying Value of Note Payable (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Debt Disclosure [Abstract]
Note payable, including End of Term Charge		$ 16,350	$ 16,350
Debt discount, net of accretion		(1,074)	(1,405)
Note payable, net of discount, long-term	$ 0	$ 15,276	$ 14,945

Note Payable - Future Principal

Note Payable - Future Principal Payments (Detail) $ in Thousands	Dec. 31, 2022 USD ($)
Debt Disclosure [Abstract]
2023	$ 0
2024	1,875
2025	7,500
2026	5,625
Total	$ 15,000

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($)	1 Months Ended					9 Months Ended		12 Months Ended
	May 31, 2021	Nov. 30, 2020	Jun. 30, 2020	Feb. 29, 2020	Jul. 31, 2019	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Class of Stock [Line Items]
Common stock, authorized						150,000,000		150,000,000	150,000,000
Common stock, par value						$ 0.0001		$ 0.0001	$ 0.0001
Undesignated preferred stock						10,000,000		10,000,000	10,000,000
Undesignated shares of preferred stock outstanding						0		0	0
Cash dividends						$ 0		$ 0
Proceeds from issuance of common stock, net of offering costs						$ 86,000	$ 203,000
July 2019 Follow-on Offering [Member]
Class of Stock [Line Items]
Proceeds from issuance of common stock, net of offering costs					$ 129,464,000
July 2019 Follow-on Offering [Member] | Common Stock [Member]
Class of Stock [Line Items]
Common stock, shares issued and sold					7,475,000
Issuance price per shares					$ 18.5
Over-Allotment Option [Member] | Common Stock [Member]
Class of Stock [Line Items]
Common stock, shares issued and sold					975,000
February 2020 Follow-on Offering [Member]
Class of Stock [Line Items]
Proceeds from issuance of common stock, net of offering costs				$ 93,627,000
February 2020 Follow-on Offering [Member] | Common Stock [Member]
Class of Stock [Line Items]
Common stock, shares issued and sold				4,350,000
Issuance price per shares				$ 23
ATM Facility [Member]
Class of Stock [Line Items]
Common stock, shares issued and sold	1,829,268		384,140
Proceeds from issuance of common stock, net of offering costs	$ 14,550,000		$ 8,130,000					0	$ 14,550,000
Common stock remained available for future issuance								$ 26,549,000
ATM Facility [Member] | Common Stock [Member]
Class of Stock [Line Items]
Common stock, shares issued and sold									1,829,000
November 2020 Follow-on Offering [Member]
Class of Stock [Line Items]
Proceeds from issuance of common stock, net of offering costs		$ 70,221,000
November 2020 Follow-on Offering [Member] | Common Stock [Member]
Class of Stock [Line Items]
Common stock, shares issued and sold		5,000,000
Issuance price per shares		$ 15

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Common Stock Reserved for Future Issuance (Detail) - shares	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021	Apr. 16, 2020
Class of Stock [Line Items]
Total shares of authorized common stock reserved for future issuance	18,605,093	19,259,640	13,808,059
Employee Stock Option [Member]
Class of Stock [Line Items]
Total shares of authorized common stock reserved for future issuance	5,922,447	9,423,271	7,423,777
Restricted Stock Units
Class of Stock [Line Items]
Total shares of authorized common stock reserved for future issuance	1,224,997	940,392	599,850
2018 Stock Option and Incentive Plan
Class of Stock [Line Items]
Total shares of authorized common stock reserved for future issuance	7,287,262	5,005,295	2,583,736	3,300,000
2018 Employee Stock Purchase Plan
Class of Stock [Line Items]
Total shares of authorized common stock reserved for future issuance	1,332,587	1,467,026	1,151,010
2019 Inducement Plan
Class of Stock [Line Items]
Total shares of authorized common stock reserved for future issuance	1,137,800	786,656	412,686
2020 Inducement Plan
Class of Stock [Line Items]
Total shares of authorized common stock reserved for future issuance	1,700,000	1,637,000	1,637,000

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Assumptions that Used to Determine Grant-Date Fair Value of Stock Options Granted to Employees and Members of Board of Directors (Detail)	9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Expected option life (years)	6 years	5 years 11 months 15 days	5 years 11 months 23 days	6 years 21 days
Risk-free interest rate	3.82%	1.80%	2.47%	0.80%
Expected volatility	83.36%	80.22%	80.43%	81.22%
Expected dividend yield	0%	0%

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding [Roll Forward]
Number of options, Outstanding beginning balance	9,423,271	7,423,777	7,423,777
Number of options, Granted	123,501		5,369,650
Number of options, Exercised	(223,273)	0	(142,013)
Number of options, Cancelled or forfeited	(3,401,052)		(3,228,143)
Number of options, Outstanding ending balance	5,922,447		9,423,271	7,423,777
Number of options, Exercisable	3,606,590		3,068,082
Weighted average exercise price, Outstanding beginning balance	$ 7.26	$ 13.54	$ 13.54
Weighted average exercise price, Granted	1.09		1.43
Weighted average exercise price, Exercised	0.79		0.41
Weighted average exercise price, Cancelled or forfeited	7.15		12.31
Weighted average exercise price, Outstanding ending balance	7.43		7.26	$ 13.54
Weighted average exercise price, Exercisable	$ 10.16		$ 13.11
Weighted average remaining contractual term, Outstanding balance	6 years 3 months 25 days		8 years 1 month 20 days	6 years 9 months 14 days
Weighted average remaining contractual term, Exercisable	4 years 9 months 25 days		6 years 1 month 24 days
Aggregate intrinsic value, Outstanding balance	$ 1,068		$ 22	$ 1,469
Aggregate intrinsic value, Exercisable	$ 217		$ 22

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021	Apr. 16, 2020
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Common stock reserved for issuance	18,605,093		19,259,640	13,808,059
Number of options granted	123,501		5,369,650
Aggregate intrinsic value of options exercised	$ 85		$ 50	$ 1,826
Options Granted, Weighted-average grant-date fair value	$ 0.79	$ 1.23	$ 0.99	$ 8.7
Total fair value of restricted stock units vested	$ 1,367	$ 7	$ 9	$ 5
Unrecognized stock-based compensation expenses	$ 6,282		$ 18,719
Unrecognized stock-based compensation expense, period for recognition	2 years 1 month 6 days		2 years 3 months 18 days
Exercise of stock options, shares	223,273	0	142,013
Restricted Stock [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Unvested restricted stock awards			0
2018 Stock Option and Incentive Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Number of common shares that may be issued under the plan			616,300
Common shares available for future grant			5,005,295
Number of shares of common stock outstanding, increase, percentage			4%
Common stock reserved for issuance	7,287,262		5,005,295	2,583,736	3,300,000
Number of options granted			5,369,650	4,253,232
2015 Stock Option and Grant Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Number of common shares that may be issued under the plan			2,008,564
Common shares available for future grant			0
Option vesting period			4 years
2018 Employee Stock Purchase Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Common shares available for future grant			1,467,026
Employee Stock Purchase Plan, description			The ESPP provides that the number of shares reserved and available for issuance will automatically increase each January 1, beginning on January 1, 2019 and each January 1 thereafter through January 1, 2028, by the least of (i) 1% of the outstanding number of shares of our common stock on the immediately preceding December 31; (ii) 1,115,700 shares or (iii) such number of shares as determined by the ESPP administrator (the “ESPP Evergreen”)
Number of common shares issued			120,947	27,580
2018 Employee Stock Purchase Plan [Member] | Maximum [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Number of common shares that may be issued under the plan			223,200
Number of shares of common stock outstanding, increase, percentage			1%
Number of common shares that may increase under the plan			1,115,700
2019 Inducement Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Number of common shares that may be issued under the plan			1,800,000
Common shares available for future grant			786,656
2020 Inducement Plan [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Number of common shares that may be issued under the plan			1,700,000
Common shares available for future grant			1,637,000

Stock-Based Compensation - Su_3

Stock-Based Compensation - Summary of Restricted Common Stock Units (Detail) - Restricted Stock Units - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares, Issued and unvested beginning balance	940,392	599,850
Number of shares, Granted	1,548,117	920,168
Number of shares, Vested	(283,835)	(575)
Number of shares, Forfeited, cancelled or expired	(979,677)	(579,051)
Number of shares, Issued and unvested ending balance	1,224,997	940,392
Weighted average grant date fair value, Issued and unvested, beginning balance	$ 3.62	$ 9.64
Weighted average grant date fair value, Granted	1.65	1.56
Weighted average grant date fair value, Vested	4.98	15.65
Weighted average grant date fair value, Forfeited, cancelled or expired	2.02	6.56
Weighted average grant date fair value, Issued and unvested, ending balance	$ 2.1	$ 3.62

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Stock-based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 2,219	$ 2,656	$ 6,284	$ 9,267	$ 11,522	$ 18,579
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	415	448	1,705	2,169	2,785	6,996
General and Administrative Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 1,804	$ 2,208	$ 4,579	$ 7,098	$ 8,737	$ 11,583

401(k) Savings Plan - Additiona

401(k) Savings Plan - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Retirement Benefits [Abstract]
Defined contribution plan, description	Currently, the Company makes matching contributions at a rate of 50% of the first 8% of employee contributions.
Employer matching contribution, percent of match	50%
Percent of employee contributions	8%
Defined contribution plan, expense	$ 599	$ 593

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Income Taxes [Line Items]
Deferred income tax expense (benefit)	$ 0	$ 0
Deferred tax assets change in valuation allowance	23,802	30,401
Deferred tax assets, operating loss carryforwards, domestic	340,350	312,967
Deferred tax assets, operating loss carryforwards, not subject to expiration	322,607
Payroll tax liability capped per year	250
Income tax reconciliation tax credit research	$ 250
Income tax credit carryforward expiration period	20 years
Percentage of cumulative changes in ownership interest subject to annual limitation	50%
Period of cumulative changes in ownership interest	3 years
U.S. federal [Member]
Income Taxes [Line Items]
Research and development tax credits carryforwards	$ 6,824	6,234
Orphan Drug Credit [Member] | U.S. federal [Member]
Income Taxes [Line Items]
Research and development tax credits carryforwards	2,027
Expiration Through 2037 [Member]
Income Taxes [Line Items]
Deferred tax assets, operating loss carryforwards, subject to expiration	17,743
Expiration Through 2039 [Member]
Income Taxes [Line Items]
Deferred tax assets, operating loss carryforwards, state	316,668	290,500
Expiration Through 2033 [Member] | State [Member]
Income Taxes [Line Items]
Research and development tax credits carryforwards	$ 2,084	$ 1,959

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of Income Tax Expense (Benefit) (Detail)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Federal income tax expense at statutory rate	21%	21%
State income taxes, net of federal benefit	5.20%	6%
Permanent differences	1.20%	1.20%
Foreign rate differential	0%	0.10%
Research and development tax credits	0.80%	2%
Change in valuation allowance	25.80%	27.90%
Provision to Return	0%	0%
Effective income tax rate	0%	0%

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Deferred tax assets:
U.S., foreign and state net operating loss carryforwards	$ 91,416	$ 84,102
Research and development credits	8,471	7,821
Capitalized start up and organizational costs	23	26
Equity based compensation	3,610	3,926
Licensing agreements	3,929	3,749
Section 174 R&D Capitalization	16,307	0
Lease Liability	227	0
Accruals and other	1,032	1,376
Total deferred tax assets	125,015	101,000
Valuation allowance	(124,695)	(100,893)
Net deferred tax assets	320	107
Deferred tax liabilities:
Property and equipment	(102)	(107)
ROU Asset	(218)	0
Total deferred tax liabilities	$ 0	$ 0

Net Income (Loss) Per Share - C

Net Income (Loss) Per Share - Components of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Numerator:
Net income (loss) attributable to common stockholder basic	$ (21,577)	$ (22,969)	$ 20,942	$ (80,856)
Net income (loss) attributable to common stockholders diluted	$ (21,577)	$ (22,969)	$ 20,942	$ (80,856)
Denominator:
Weighted-average common shares outstanding basic	44,527,997	43,772,990	44,234,936	43,722,129	43,739,000	42,854,000
Weighted-average number of common shares outstanding - diluted	44,527,997	43,772,990	44,425,531	43,722,129	43,739,000	42,854,000
Net income (loss) per share applicable to common stockholders basic	$ (0.48)	$ (0.52)	$ 0.47	$ (1.85)	$ (2.42)	$ (2.78)
Net income (loss) per share applicable to common stockholders diluted	$ (0.48)	$ (0.52)	$ 0.47	$ (1.85)	$ (2.42)	$ (2.78)

Net Income (Loss) Per Share - S

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		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
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	4,827,316	8,083,363	7,683,446	8,083,363	9,423,271	7,423,777
Restricted Stock Awards and Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share amount					940,392	599,850
Restricted Stock Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	276,008	870,536	1,414,256	870,536
Employee stock purchase plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	0	0	4,976	0

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Detail) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Jan. 27, 2016	Jul. 31, 2018	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Related Party Transaction [Line Items]
Research and development expense			$ 14,829	$ 15,919	$ 43,310	$ 54,049	$ 72,186	$ 83,114
Expense related to related party			483				2,994
License Agreement [Member]
Related Party Transaction [Line Items]
Provision for maximum cash payment		$ 2,000
Research and development expense			25	82	97	145	200	248
License Agreement [Member] | Stock Purchase Agreement [Member]
Related Party Transaction [Line Items]
Common stock issued for initial consideration for license	1,161,665
Sub-lease Agreement [Member] | Officers and Board Members [Member] | Related Party [Member]
Related Party Transaction [Line Items]
Expense related to related party			$ 0	$ 795	$ 754	$ 2,381	$ 3,200	$ 1,523

Restructuring Activities (Addit

Restructuring Activities (Additional Information) (Details) - USD ($)	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021	Jul. 12, 2023
Restructuring Cost and Reserve [Line Items]
Expected Workforce Reduction Rate			23%
Restructuring expenses		$ 3,685,000
Board Of Directors [Member]
Restructuring Cost and Reserve [Line Items]
Company workforce reduction					50%
Employee Severance and Other Benefits
Restructuring Cost and Reserve [Line Items]
Restructuring expenses		(903,000)	$ 1,369,000	$ 0
Cash Payments	$ 2,782,000	2,782,000	1,369,000
Accrued Remaining Payments	0	0	$ 0
July 2023 Workforce Reduction [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring expenses	$ 3,685,000	$ 3,685,000

Restructuring Activities - Summ

Restructuring Activities - Summary of Restructuring Activities (Detail) - USD ($)	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2023	Dec. 31, 2022	Dec. 31, 2021
Restructuring Cost and Reserve [Line Items]
Restructuring expenses		$ 3,685,000
Employee Severance and Other Benefits
Restructuring Cost and Reserve [Line Items]
Cash Payments	$ (2,782,000)	(2,782,000)	$ (1,369,000)
Restructuring expenses		(903,000)	$ 1,369,000	$ 0
Liability included in accrued expenses and other current liabilities at September 30, 2023	$ 0	$ 0

Subsequent Events (Additional I

Subsequent Events (Additional Information) (Details) - Subsequent Event [Member] $ in Millions	3 Months Ended
	Dec. 31, 2023 USD ($)	Oct. 31, 2023 Number
Subsequent Event [Line Items]
Severance and termination related costs | $	$ 1.2
Company workforce reduction | Number		11