0000950170-23-022192 | 10-Q | XBRL Viewer

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Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Summary Of Significant Accounting Policies [Line Items]
Operating Lease, Right-of-Use Asset	$ 0	$ 23,168

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2021	$ 172,672	$ 59	$ 498,210	$ (30)	$ (325,567)
Beginning balance, shares at Dec. 31, 2021		58,799,157
Stock-based compensation expense	1,905		1,905
Unrealized gains (losses) on marketable securities	(439)			(439)
Net loss	(22,950)				(22,950)
Ending balance at Mar. 31, 2022	151,188	$ 59	500,115	(469)	(348,517)
Ending balance, shares at Mar. 31, 2022		58,799,157
Beginning balance at Dec. 31, 2021	172,672	$ 59	498,210	(30)	(325,567)
Beginning balance, shares at Dec. 31, 2021		58,799,157
Net loss	(76,500)
Ending balance at Dec. 31, 2022	105,958	$ 61	508,107	(181)	(402,029)
Ending balance, shares at Dec. 31, 2022		60,639,909
Vesting of restricted stock, shares		8,912
Stock-based compensation expense	506		506
Unrealized gains (losses) on marketable securities	165			165
Net loss	(29,170)				(29,170)
Ending balance at Mar. 31, 2023	$ 77,459	$ 61	$ 508,613	$ (16)	$ (431,199)
Ending balance, shares at Mar. 31, 2023		60,648,821

- Definition

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

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+ Details

- Definition

Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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+ Details

Related Parties - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
NMDP Be The Match
Related Party Transaction [Line Items]
Expenses paid to related party		$ 100,000
Amounts owed to related party	$ 0
Maximum [Member] \| ImmunoGen
Related Party Transaction [Line Items]
Expenses paid to related party	100,000
Amounts owed to related party	100,000		$ 100,000
Maximum [Member] \| NMDP Be The Match
Related Party Transaction [Line Items]
Expenses paid to related party	$ 100,000
Accounts Payable, Accrued Expenses and Other Current Liabilities [Member] \| NMDP Be The Match
Related Party Transaction [Line Items]
Amounts owed to related party			$ 100,000

- Definition

Carrying amount as of the balance sheet date of obligations due all related parties. For classified balance sheets, represents the current portion of such liabilities (due within one year or within the normal operating cycle if longer).

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+ Details

Fair Value of Financial Assets (Tables)

3 Months Ended

Mar. 31, 2023

Schedule of Marketable Securities by Security Type

As of March 31, 2023, marketable securities by security type consisted of (in thousands):


			Gross		Gross					Estimated
	Amortized		Unrealized		Unrealized			Credit		Fair
	Cost		Gains		Losses			Losses		Value
U.S. treasury notes (due within one year)	$	29,699	$	1	$	(17	)	$	—	$	29,683
Total	$	29,699	$	1	$	(17	)	$	—	$	29,683

As of December 31, 2022 marketable securities by security type consisted of (in thousands):


			Gross		Gross			Estimated
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
U.S. treasury notes (due within one year)	$	54,596	$	2	$	(183	)	$	54,415
Total	$	54,596	$	2	$	(183	)	$	54,415

Schedule of Financial Assets Measured at Fair Value on Recurring Basis

The following tables present information about the Company’s financial assets measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values (in thousands):


	Fair Value Measurements at March 31, 2023 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	47,508	$	—	$	—	$	47,508
Marketable securities:
U.S. treasury notes		—		29,683		—		29,683
Total	$	47,508	$	29,683	$	—	$	77,191


	Fair Value Measurements at December 31, 2022 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	56,663	$	—	$	—	$	56,663
Marketable securities:
U.S. treasury notes		—		54,415		—		54,415
Total	$	56,663	$	54,415	$	—	$	111,078

Accrued Expenses and Other Current Liabilities (Tables)

3 Months Ended

Mar. 31, 2023

Schedule of Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following (in thousands):


	March 31, 2023		December 31, 2022
Accrued payroll and related expenses	$	1,622	$	4,162
Accrued external research and development expenses		1,390		3,091
Accrued professional fees		1,666		654
Accrued other		224		364
	$	4,902	$	8,271

Fair Value of Financial Assets - Schedule of Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	$ 29,683	$ 54,415
Fair Value on Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	77,191	111,078
Level 1 [Member] \| Fair Value on Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	47,508	56,663
Level 2 [Member] \| Fair Value on Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	29,683	54,415
Money Market Funds [Member] \| Fair Value on Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	47,508	56,663
Money Market Funds [Member] \| Level 1 [Member] \| Fair Value on Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	47,508	56,663
US Treasury Notes [Member] \| Fair Value on Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	29,683	54,415
US Treasury Notes [Member] \| Level 1 [Member] \| Fair Value on Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	0	0
US Treasury Notes [Member] \| Level 2 [Member] \| Fair Value on Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	$ 29,683	$ 54,415

Restructuring and Other Charges - Summary of Restructuring Liability included in Accrued Payroll and Related Expenses (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2023 USD ($)
Restructuring Cost and Reserve [Line Items]
Accrued restructuring, Beginning Balance	$ 4,162
Accrued restructuring, Ending Balance	1,622
Employee-Related Costs [Member]
Restructuring Cost and Reserve [Line Items]
Accrued restructuring, Beginning Balance	0
Expense incurred	6,319
Payments	(4,752)
Accrued restructuring, Ending Balance	$ 1,567

Restructuring and Other Charges (Additional Information) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Restructuring Cost and Reserve [Line Items]
Reduction in workforce, Percent	84.00%
Retention amount paid	$ 700
Loss on lease termination	(8,059)	$ 0
Loss on disposal of property and equipment	3,400
Impairment charge of lab equipment	300
Maximum [Member]
Restructuring Cost and Reserve [Line Items]
Employee retention amount	3,900
Severance and Related Costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring charge related to severance cost	$ 5,600

Leases (Tables)

3 Months Ended

Mar. 31, 2023

Leases [Abstract]

Schedule of Components of the Company's Lease Expense


	Three months ended March 31,
	2023		2022
Operating lease cost	$	1,602	$	1,602
Short-term lease cost		—		—
Variable lease cost		491		506
	$	2,093	$	2,108

Schedule of Supplemental Disclosure Of Cash Flow Information Related To The Lease

Supplemental disclosure of cash flow information related to the lease was as follows (in thousands):


	Three months ended March 31,
	2023		2022
Cash paid for amounts included in the measurement of operating lease liabilities	$	16,455	$	1,595
Operating lease liabilities arising from obtaining right-of-use asset	$	—	$	—

Fair Value of Financial Assets - Schedule of Marketable Securities by Security Type (Detail) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Marketable Securities [Line Items]
Amortized Cost	$ 29,699	$ 54,596
Gross Unrealized Gains	1	2
Gross Unrealized Losses	(17)	(183)
Estimated Fair Value	29,683	54,415
US Treasury Notes [Member] \| Due With In One Year [Member]
Marketable Securities [Line Items]
Amortized Cost	29,699	54,596
Gross Unrealized Gains	1	2
Gross Unrealized Losses	(17)	(183)
Estimated Fair Value	$ 29,683	$ 54,415

Commitments and Contingencies - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended
	Feb. 28, 2023	Mar. 31, 2023	Mar. 31, 2022	Nov. 30, 2022	Mar. 31, 2018	Nov. 30, 2016
Other Commitments [Line Items]
Research and development expense		$ 7,995,000	$ 16,547,000
Wedbush Member
Other Commitments [Line Items]
Minimum success fee	$ 1,500,000
Percentage of success fee of transaction value	1.00%
Collaborative Arrangement [Member] \| Technology and Research Fees and Support [Member]
Other Commitments [Line Items]
Research and development expense		400,000	400,000
Collaborative Arrangement [Member] \| Development, Regulatory and Commercial Milestone [Member] \| Per Target [Member] \| Maximum [Member]
Other Commitments [Line Items]
Potential milestone payments due					$ 83,500,000
Collaborative Arrangement [Member] \| Achievement of Development Milestone [Member]
Other Commitments [Line Items]
Research and development expense		0	2,000,000.0
License Agreement With Harvard [Member] \| Maintenance [Member] \| Annual [Member]
Other Commitments [Line Items]
Payment obligation						$ 100,000
License Agreement With Harvard [Member] \| Achievement of Development and Regulatory Milestones [Member]
Other Commitments [Line Items]
Research and development expense		0	$ 0
License Agreement With Harvard [Member] \| Achievement of Development and Regulatory Milestones [Member] \| Maximum [Member]
Other Commitments [Line Items]
Potential milestone payments due						$ 7,400,000
License Agreement with ImmunoGen [Member]
Other Commitments [Line Items]
Upfront nonrefundable payment				$ 4,400,000
License Agreement with ImmunoGen [Member] \| Achievement of Development and Regulatory Milestones [Member]
Other Commitments [Line Items]
Research and development expense		$ 0
License Agreement with ImmunoGen [Member] \| Achievement of Development and Regulatory Milestones [Member] \| Maximum [Member]
Other Commitments [Line Items]
Potential milestone payments due				$ 125,000,000.0

Stock-Based Awards - Schedule of Stock Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock based compensation expense	$ 506	$ 1,905
Research and Development Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock based compensation expense	15	527
General and Administrative Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock based compensation expense	$ 491	$ 1,378

Subsequent Events

3 Months Ended

Mar. 31, 2023

Subsequent Events [Abstract]

Subsequent Events

13. Subsequent Events

Asset Sales

On April 7, 2023, the Company entered into an asset purchase agreement related to MGTA-45, one of the Company’s conditioning product candidates, for cash consideration of $0.8 million, reimbursement of up to $0.5 million for certain expenses and a potential $10.0 million milestone payment contingent upon the achievement of a certain regulatory milestone. During the exclusivity period prior to executing a definitive purchase agreement, the buyer agreed to reimburse the Company for certain research and development expenses incurred under current vendor agreements. During the three months ended March 31, 2023, the Company recorded $1.1 million in other income in connection with this reimbursement.

On April 20, 2023, the Company entered into an asset purchase agreement related to MGTA-145, the Company’s mobilization product candidate, for cash consideration of $1.0 million and a potential $5.0 million milestone payment contingent upon the achievement of a certain clinical milestone.

On April 21, 2023, the Company entered into an asset purchase agreement related to the CD117 antibodies used with MGTA-117, one of the Company’s conditioning product candidates, for cash consideration of $1.5 million and a potential $5.0 million milestone payment contingent upon the achievement of a certain clinical milestone.

Merger Agreement

On May 2, 2023, following a comprehensive review of strategic alternatives, the Company entered into the Merger Agreement with Dianthus pursuant to which a wholly-owned subsidiary of the Company will merge with and into Dianthus, with Dianthus surviving as a wholly-owned subsidiary of the Company. The Merger was unanimously approved by the Company’s board of directors, and the Company’s board of directors resolved to recommend approval of the Merger Agreement to the Company’s stockholders. The closing of the Merger is subject to approval by the Company’s and Dianthus’ stockholders as well as other customary closing conditions, including the effectiveness of a registration statement filed with the SEC in connection with the transaction and Nasdaq’s approval of the listing of the shares of the Company’s common stock to be issued in connection with the transaction. If the Company is unable to satisfy certain closing conditions or if other mutual closing conditions are not satisfied, Dianthus will not be obligated to complete the Merger. The Merger Agreement contains certain termination rights of each of the Company and Dianthus. Under certain circumstances detailed in the Merger Agreement, the Company could be required to pay Dianthus a termination fee of $13.3 million or Dianthus could be required to pay the Company a termination fee of $13.3 million. In addition, in certain circumstances upon the termination of the Merger Agreement, the Company could be required to pay the costs and expenses of Dianthus in an amount not to exceed $1.5 million, or Dianthus could be required to pay the Company’s costs and expenses in an amount not to exceed $1.5 million. If the Merger is completed, the business of Dianthus will continue as the business of the combined company.

At or prior to the effective time of the Merger, the Company will enter into a Contingent Value Rights Agreement (the “CVR Agreement”) with a rights agent (“Rights Agent”) pursuant to which the Company’s pre-Merger common stockholders will receive one contingent value right (each, a “CVR”) for each outstanding share of common stock held by such stockholder on such date. Each CVR will represent the contractual right to receive certain net proceeds, if any, derived from any consideration that is paid to the Company as a result of the disposition of the Company’s pre-Merger legacy assets by December 31, 2023, net of any indemnity obligations, transaction costs and certain other expenses, during the period that is three years after the closing of the Merger. The contingent payments under the CVR Agreement, if they become payable, will become payable to the Rights Agent for subsequent distribution to the holders of the CVRs subject to certain withholdings for expenses and potential indemnity claims. In the event that no such proceeds are received, holders of the CVRs will not receive any payment pursuant to the CVR Agreement.

Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 48,523	$ 57,626
Marketable securities	29,683	54,415
Prepaid expenses and other current assets	2,914	3,561
Assets held for sale	541	0
Restricted Cash, Current	1,780	0
Total current assets	83,441	115,602
Restricted cash	0	1,780
Operating lease, right-of-use asset	0	23,168
Property and equipment, net	0	6,095
Total assets	83,441	146,645
Current liabilities:
Accounts payable	1,080	2,454
Accrued expenses and other current liabilities	4,902	8,271
Operating lease liability, current portion	0	3,824
Total current liabilities	5,982	14,549
Operating lease liability, net of current portion	0	26,138
Total liabilities	5,982	40,687
Commitments and contingencies (Note 10)
Stockholders' Equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized; no shares issued or outstanding	0	0
Common stock, $0.001 par value; 150,000,000 shares authorized; 60,648,821 and 60,639,909 shares issued and outstanding as of March 31, 2023 and December 31, 2022, respectively	61	61
Additional paid-in capital	508,613	508,107
Accumulated other comprehensive loss	(16)	(181)
Accumulated deficit	(431,199)	(402,029)
Total stockholders' equity	77,459	105,958
Total liabilities and stockholders' equity	$ 83,441	$ 146,645

Summary of Significant Accounting Policies - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Detail) - shares	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount	7,190,312	8,071,638
Employee Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount	0	36,012
Stock Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount	6,907,815	7,580,453
Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount	282,497	455,173

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Cash flows from operating activities:
Net loss	$ (29,170)	$ (22,950)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	506	1,905
Depreciation and amortization expense	421	511
Loss on disposal of property and equipment	3,355	0
Impairment of assets held for sale	270	0
Noncash lease expense	786	699
Loss on lease termination	8,059	0
Net amortization (accretion) of premiums (discounts) on marketable securities	(336)	115
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	647	132
Accounts payable	(1,159)	1,398
Accrued expenses and other current liabilities	(3,339)	(859)
Operating lease liabilities	(15,639)	(692)
Net cash used in operating activities	(35,599)	(19,741)
Cash flows from investing activities:
Purchases of property and equipment	(245)	(27)
Proceeds from sale of property and equipment	1,508	0
Purchases of marketable securities	(9,767)	(40,117)
Maturities of marketable securities	35,000	0
Net cash provided by (used in) investing activities	26,496	(40,144)
Cash flows from financing activities:
Net cash provided by financing activities	0	0
Net decrease in cash, cash equivalents and restricted cash	(9,103)	(59,885)
Cash, cash equivalents and restricted cash at beginning of period	59,406	133,430
Cash, cash equivalents and restricted cash at end of period	50,303	73,545
Supplemental disclosure of non-cash activities:
Decrease in right-of-use asset and operating lease liabilities due to lease termination	$ 14,323	$ 0

Assets Held For Sale

3 Months Ended

Mar. 31, 2023

Property, Plant and Equipment Assets Held-for-sale Disclosure [Abstract]

Assets Held For Sale

4. Assets Held For Sale

In March 2023, the Company committed to a plan to sell its remaining lab equipment and therefore has classified the amount as assets held for sale on the consolidated balance sheet as of March 31, 2023. The assets held for sale were reported at the lower of the carrying amount or fair value, less costs to sell. Accordingly, during the three months ended March 31, 2023, the Company recorded

an impairment charge, which was included in restructuring and other charges, of $0.3 million related to the lab equipment classified as assets held for sale.

Leases - Schedule of Components of the Company's Lease Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Lease, Cost [Abstract]
Operating lease cost	$ 1,602	$ 1,602
Short-term lease cost	0	0
Variable lease cost	491	506
Lease cost	$ 2,093	$ 2,108

Cover Page - shares	3 Months Ended
Cover Page - shares	Mar. 31, 2023	Apr. 30, 2023
Document Type	10-Q
Amendment Flag	false
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Mar. 31, 2023
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q1
Entity Registrant Name	Magenta Therapeutics, Inc.
Entity Central Index Key	0001690585
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Ex Transition Period	false
Entity Emerging Growth Company	true
Entity Small Business	true
Entity Shell Company	false
Entity Tax Identification Number	81-0724163
Entity Interactive Data Current	Yes
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	300 Technology Square, 8th Floor
Entity Address, City or Town	Cambridge
Entity Address, Postal Zip Code	02139
Entity Address, State or Province	MA
Entity File Number	001-38541
City Area Code	857
Local Phone Number	242-0170
Entity Common Stock, Shares Outstanding		60,648,883
Common Stock [Member]
Trading Symbol	MGTA
Title of 12(b) Security	Common Stock
Security Exchange Name	NASDAQ
Preferred Stock [Member]
No Trading Symbol Flag	true
Title of 12(b) Security	Preferred Stock
Security Exchange Name	NASDAQ

Commitments and Contingencies

3 Months Ended

Mar. 31, 2023

Commitments and Contingencies

10. Commitments and Contingencies

Leases

The Company’s commitments under its leases are described in Note 9.

Collaboration Agreement

In March 2018, the Company entered into a collaboration agreement with Heidelberg Pharma Research GmbH (“HDPR”) whereby the parties agreed to combine the Company’s stem cell platform with proprietary antibodies across up to four exclusive targets with HDPR’s proprietary Antibody Targeted Amanitin Conjugates platform. Under the agreement, the Company could pay upfront technology access fees, research exclusivity fees and payment for research support. Additionally, upon the exercise of certain license rights, the Company may have been obligated to pay HDPR development, regulatory and commercial milestone payments of up to $83.5 million per target as well as royalties on net sales of products licensed under the agreement. During each of the three months ended March 31, 2023 and 2022, the Company recorded $0.4 million of research and development expense related to this agreement for upfront technology access fees, research exclusivity fees and research support. During the three months ended March 31, 2023, the Company did not incur any expense related to the achievement of these milestones. During the three months ended March 31, 2022, the Company recorded $2.0 million of research and development expense related to the achievement of a development milestone. In April 2023, this collaboration agreement was terminated.

Intellectual Property Licenses

The Company had a license agreement with the President and Fellows of Harvard College (“Harvard”), entered into in November 2016, for an exclusive, worldwide, royalty-bearing license for certain technologies related to conditioning and mobilization. Under the agreement, the Company was obligated to pay Harvard maintenance fees of $0.1 million annually and to reimburse qualified expenses related to the patents. The Company was also obligated to pay milestone payments of up to $7.4 million for the first two licensed products upon the achievement of certain development and regulatory milestones and to pay royalties on a product-by-product and country-by-country basis on net sales of products licensed under the agreement. During the three months ended March 31, 2023 and 2022, the Company did not incur any expense related to the achievement of these milestones. In April 2023, this agreement was amended and restated and a portion of the license agreement related to certain conditioning technology was assigned to a third party in connection with the sale of certain conditioning assets of the Company (see Note 13).

In November 2022, the Company entered into a license agreement with ImmunoGen, Inc. (“ImmunoGen”), for an exclusive, worldwide, royalty-bearing license for certain technology related to one of the Company’s conditioning programs. Upon execution of the agreement, the Company made a nonrefundable payment of $4.4 million in partial consideration for the license. Under the agreement, the Company was also obligated to pay milestone payments of up to $125.0 million in the aggregate upon the achievement of certain development, regulatory and sales-based milestones and to pay single-digit royalties on a product-by-product and country-by-country basis on net sales of products licensed under the agreement. During the three months ended March 31, 2023, the Company did not incur any expense related to the achievement of these milestones. Effective December 29, 2022, Michael Vasconcelles, a member of the Company’s board of directors, joined ImmunoGen as Executive Vice President of Research, Development, and Medical Affairs (see Note 12). In April 2023, this license agreement was assigned to a third party in connection with the sale of certain conditioning assets of the Company (see Note 13).

Strategic Financial Advisor

In February 2023, the Company entered into an agreement with an advisor to act as the Company’s exclusive strategic financial advisor in connection with a potential strategic transaction including but not limited to an acquisition, merger, business combination or other transaction. Upon the consummation of any such transaction, the Company has agreed to pay the advisor a success fee of 1% of the transaction value with a minimum fee of $1.5 million. During the three months ended March 31, 2023, the Company did not record any expense related to this agreement.

Indemnification Agreements

In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and senior management that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company is not aware of any claims under indemnification arrangements, and it has not accrued any liabilities related to such obligations in its consolidated financial statements as of March 31, 2023.

Legal Proceedings

The Company is not currently a party to any material legal proceedings. At each reporting date, the Company evaluates whether or not a potential loss amount or a potential range of loss is probable and reasonably estimable under the provisions of the authoritative guidance that addresses accounting for contingencies. The Company expenses the costs related to its legal proceedings as they are incurred.

401(k) Savings Plan

3 Months Ended

Mar. 31, 2023

401(k) Savings Plan

. 401(k) Savings Plan

The Company has a 401(k) available for participating employees who meet certain eligibility requirements. Eligible employees may defer a portion of their salary as defined by the plan. Company contributions to the plan may be made at the discretion of the board of directors of the Company. The Company makes matching contributions of up to 2% of eligible wages. During the three months ended March 31, 2023 and 2022, the Company recorded less than $0.1 million and $0.1 million, respectively, of expense related to this matching contribution.

- Definition

The entire disclosure for retirement benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
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-Name Accounting Standards Codification
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-Section 55
-Paragraph 17
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2023	Dec. 31, 2022
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, Shares authorized	10,000,000	10,000,000
Preferred stock, Shares issued	0	0
Preferred stock, Shares outstanding	0	0
Common stock, Par value	$ 0.001	$ 0.001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, Shares issued	60,648,821	60,639,909
Common stock, Shares outstanding	60,648,821	60,639,909

Restructuring and Other Charges

3 Months Ended

Mar. 31, 2023

Restructuring and Related Activities [Abstract]

Restructuring and Other Charges

6. Restructuring and Other Charges

The Company also announced a corporate restructuring that resulted in a reduction in its workforce by 84% that was substantially completed in the first quarter of 2023. In connection with the corporate restructuring, the Company recorded a restructuring charge for severance and related costs of $5.6 million during the three months ended March 31, 2023. The Company also approved up to $3.9 million of retention amounts to employees, subject to remaining actively employed with the Company through specified dates. The retention amounts are being expensed as the services are performed. During the three months ended March 31, 2023, the Company recorded retention costs of $0.7 million.

Restructuring and other charges also includes loss on lease termination of $8.1 million (see Note 9), loss on disposal of property and equipment of $3.4 million, primarily related to leasehold improvements in connection with the lease termination, and impairment of lab equipment of $0.3 million (see Note 4).

The Company’s restructuring liability, which was included in accrued payroll and related expenses, consisted of the following (in thousands):


	Employee-Related Costs
Accrued restructuring balance at January 1, 2023	$	—
Expense incurred		6,319
Payments		(4,752	)
Accrued restructuring balance at March 31, 2023	$	1,567

Leases

3 Months Ended

Mar. 31, 2023

Leases [Abstract]

Leases

9. Leases

The Company had a sublease, as amended, for up to approximately 69,000 square feet of office and laboratory space in Cambridge, Massachusetts. The sublease was subject and subordinate to a prime lease between the sublandlord and the prime landlord. The term of the sublease commenced in June 2018 and was set to expire in February 2028. In connection with the corporate restructuring, on March 31, 2023 (the “Termination Date”), the Company, entered into a Sublease Termination and Release Agreement (the “Termination Agreement”) with the sublandlord which, effective immediately, terminated the sublease. In exchange for the early termination of the sublease pursuant to the Termination Agreement, the Company made a termination payment of $14.8 million and recorded a loss on lease termination of $8.1 million (see Note 6).

In connection with this sublease, the Company was required to maintain a cash balance of $1.8 million to secure a letter of credit associated with the sublease. This amount was classified in the consolidated balance sheets as current restricted cash at March 31, 2023 and noncurrent restricted cash at December 31, 2022. This amount was released to the Company in May 2023.

Prior to the lease termination, the components of the Company’s lease expense under ASC 842 were as follows (in thousands):


	Three months ended March 31,
	2023		2022
Operating lease cost	$	1,602	$	1,602
Short-term lease cost		—		—
Variable lease cost		491		506
	$	2,093	$	2,108

Supplemental disclosure of cash flow information related to the lease was as follows (in thousands):


	Three months ended March 31,
	2023		2022
Cash paid for amounts included in the measurement of operating lease liabilities	$	16,455	$	1,595
Operating lease liabilities arising from obtaining right-of-use asset	$	—	$	—

In addition, the Company had a sub-sublease, as amended, for 26,114 square feet of office and laboratory space in Cambridge, Massachusetts which was set to expire in April 2024. In connection with the Termination Agreement, this sub-sublease was assigned to the sublandlord on the Termination Date. The Company recorded other income of $0.8 million during each of the three months ended March 31, 2023 and 2022, respectively, related to this sub-sublease.

Subsequent Events - Additional Information - (Details) - USD ($) $ in Millions					3 Months Ended
	May 02, 2023	Apr. 21, 2023	Apr. 20, 2023	Apr. 07, 2023	Mar. 31, 2023
MGTA-45 [Member]
Subsequent Event [Line Items]
Other Income					$ 1.1
Subsequent Event [Member] \| MGTA-45 [Member]
Subsequent Event [Line Items]
Cash Consideration				$ 0.8
Milestone Payment				10.0
Subsequent Event [Member] \| MGTA-145 [Member]
Subsequent Event [Line Items]
Cash Consideration			$ 1.0
Milestone Payment			$ 5.0
Subsequent Event [Member] \| MGTA-117 [Member]
Subsequent Event [Line Items]
Cash Consideration		$ 1.5
Milestone Payment		$ 5.0
Subsequent Event [Member] \| Dianthus [Member]
Subsequent Event [Line Items]
Business Combination, Contingent Consideration Arrangements, Description	At or prior to the effective time of the Merger, the Company will enter into a Contingent Value Rights Agreement (the “CVR Agreement”) with a rights agent (“Rights Agent”) pursuant to which the Company’s pre-Merger common stockholders will receive one contingent value right (each, a “CVR”) for each outstanding share of common stock held by such stockholder on such date. Each CVR will represent the contractual right to receive certain net proceeds, if any, derived from any consideration that is paid to the Company as a result of the disposition of the Company’s pre-Merger legacy assets by December 31, 2023, net of any indemnity obligations, transaction costs and certain other expenses, during the period that is three years after the closing of the Merger. The contingent payments under the CVR Agreement, if they become payable, will become payable to the Rights Agent for subsequent distribution to the holders of the CVRs subject to certain withholdings for expenses and potential indemnity claims. In the event that no such proceeds are received, holders of the CVRs will not receive any payment pursuant to the CVR Agreement.
Merger Agreement Potential Termination Fee Payable	$ 13.3
Merger Agreement Potential Termination Fee Receivable	13.3
Subsequent Event [Member] \| Maximum [Member] \| MGTA-45 [Member]
Subsequent Event [Line Items]
Reimbursement Payment				$ 0.5
Subsequent Event [Member] \| Maximum [Member] \| Dianthus [Member]
Subsequent Event [Line Items]
Merger Agreement Potential Costs And Expenses Payable Upon Termination	1.5
Merger Agreement Potential Costs And Expenses Receivable Upon Termination	$ 1.5

Stock-Based Awards - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Common Stock [Member] \| Employee Service Based Vesting [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, options, grants in period, gross	3,750
Weighted average fair value of stock options granted	$ 0.41
Share based compensation arrangement , requisite service period	4 years
Performance Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized stock-based compensation expense related to unvested share-based awards	$ 1.6
Restricted Stock Units (RSUs) [Member] \| Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant of restricted stock	123,125
Grant weighted average grant date fair value per share	$ 0.55
Restricted Stock Units (RSUs) [Member] \| Minimum [Member] \| Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation arrangement , requisite service period	18 months
Restricted Stock Units (RSUs) [Member] \| Maximum [Member] \| Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation arrangement , requisite service period	4 years
Service Based Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized stock-based compensation expense related to unvested share-based awards	$ 4.3
Period for recognition of unrecognized expense	2 years
2018 Stock Option and Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for issuance	7,231,663
2019 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for issuance	593,239
Percentage of purchase price of common stock under the ESPP	85.00%
Common stock purchased	0	0

Nature of the Business and Basis of Presentation

3 Months Ended

Mar. 31, 2023

Nature of the Business and Basis of Presentation

1. Nature of the Business and Basis of Presentation

Magenta Therapeutics, Inc. (the “Company”) is a biotechnology company previously focused on improving stem cell transplantation. The Company was incorporated under the laws of the State of Delaware in June 2015 as HSCTCo Therapeutics, Inc. In February 2016, the Company changed its name to Magenta Therapeutics, Inc. and in June 2018 the Company completed an initial public offering of its common stock.

In February 2023, after a review of the Company’s business, programs, resources and capabilities, including anticipated costs and timelines, the Company announced the decision to halt further development of its programs and to conduct a comprehensive review of strategic alternatives. The Company also announced a corporate restructuring that resulted in a reduction in its workforce by 84% that was substantially completed in the first quarter of 2023 (see Note 6).

As part of the strategic review process, the Company explored potential strategic alternatives that included, without limitation, an acquisition, merger, business combination or other transactions. The Company has and is continuing to explore strategic alternatives related to its product candidates and related assets, including, without limitation, licensing transactions and asset sales.

In April 2023, the Company sold certain assets, including intellectual property, related to its product candidates MGTA-117, MGTA-45 and MGTA-145 (see Note 13).

On May 2, 2023, following a comprehensive review of strategic alternatives, the Company entered into an Agreement and Plan of Merger (the “Merger Agreement”) with Dianthus Therapeutics, Inc. (“Dianthus”) pursuant to which a wholly-owned subsidiary of the Company will merge with and into Dianthus, with Dianthus surviving as a wholly-owned subsidiary of the Company (the “Merger”). In connection with the Merger, the Company will distribute to the Company’s pre-Merger common stockholders contingent value rights (“CVRs”), representing the contractual right to receive payments from the post-closing combined company upon receipt of certain proceeds, if any, derived from consideration paid as a result of the disposition of the Company’s pre-Merger legacy assets, net of any indemnity obligations, transaction costs and certain other expenses, during the period that is three years after the closing of the Merger. The Merger was unanimously approved by Company’s board of directors, and the Company’s board of directors resolved to recommend approval of the Merger Agreement to the Company’s stockholders. The closing of the Merger is subject to approval by the Company’s and Dianthus’ stockholders, as well as other customary closing conditions. If the Merger is completed, the business of Dianthus will continue as the business of the combined company (see Note 13).

The Company’s future operations are highly dependent on the success of the Merger and there can be no assurances that the Merger will be successfully consummated. In the event that the Company does not complete the Merger, the Company may explore strategic alternatives, including, without limitation, another strategic transaction and/or pursue a dissolution and liquidation of the Company.

In January 2023, the Company received a written notice from the staff of Nasdaq’s Listing Qualifications Department, notifying the Company that, for the 30 consecutive business day period between December 15, 2022 through January 30, 2023, the bid price for its common stock had closed below the $1.00 per share minimum bid price requirement for continued listing on Nasdaq pursuant to Nasdaq Listing Rule 5450(a)(1), (the “Minimum Bid Price Requirement”). In accordance with Nasdaq Listing Rule 5810(c)(3)(A), the Company has 180 calendar days, or until July 31, 2023, to regain compliance with the Minimum Bid Price Requirement. If the Company fails to satisfy the continued listing requirements of Nasdaq, such as the Minimum Bid Price Requirement, Nasdaq may take steps to delist its common stock.

In addition, the Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, our ability to successfully complete clinical trials, obtain marketing approvals, manufacture a commercial-scale medicine or arrange for a third party to do so on our behalf, conduct sales and marketing activities necessary for successful commercialization of product candidates, dependence on key personnel, protection of proprietary technology, compliance with government regulations, the continuing impact of the coronavirus (“COVID-19”) pandemic and the ability to secure additional capital to fund operations. The development of any product candidates may require significant research and development efforts, including extensive 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 resumed development efforts and were successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales.

The Company has incurred recurring losses since inception, including net losses of $29.2 million for the three months ended March 31, 2023 and $76.5 million for the year ended December 31, 2022. As of March 31, 2023, the Company had an accumulated deficit of $431.2 million. The Company expects to continue to generate operating losses for the foreseeable future. The Company expects that its cash, cash equivalents and marketable securities will be sufficient to fund its operating expenses and capital expenditure requirements through at least 12 months from the issuance date of these consolidated financial statements. The future viability of the Company beyond that point is dependent on the results of the strategic review process and its ability to raise additional capital to fund its operations.

The Company expects to continue to incur costs and expenditures in connection with the process of evaluating strategic alternatives. There can be no assurance, however, that the Company will be able to successfully consummate any particular strategic transaction. The process of continuing to evaluate these strategic options may be very costly, time-consuming and complex and the Company has incurred, and may in the future incur, significant costs related to this continued evaluation, such as legal, accounting and advisory fees and expenses and other related charges. Should the Company resume the development of product candidates, it will need to obtain substantial additional funding in connection with continuing operations, particularly as the Company advances its preclinical activities and clinical trials for its product candidates in development. If the Company is unable to raise capital when needed, or on attractive terms, it could be forced to delay, reduce or eliminate its research or drug development programs or any future commercialization efforts. There is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations, if at all.

The consolidated financial statements include the accounts of the Company and its wholly owned subsidiary. All intercompany balances and transactions have been eliminated. The consolidated financial statements have been prepared in accordance 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 GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”).

Leases - Additional Information (Detail) $ in Thousands	3 Months Ended
Leases - Additional Information (Detail) $ in Thousands	Mar. 31, 2023 USD ($) ft²	Mar. 31, 2022 USD ($)	Dec. 31, 2022 USD ($)
Leases [Line Items]
Restricted Cash, Noncurrent	$ 0		$ 1,780
Restricted Cash, Current	$ 1,780		0
Property sublease, description	The Company had a sublease, as amended, for up to approximately 69,000 square feet of office and laboratory space in Cambridge, Massachusetts. The sublease was subject and subordinate to a prime lease between the sublandlord and the prime landlord. The term of the sublease commenced in June 2018 and was set to expire in February 2028
Decrease in operating lease liability	$ (15,639)	$ (692)
Gain Loss On Termination Of Lease	$ (8,059)	0
Sub Sublease [Member]
Leases [Line Items]
Square feet of property subject to sublease \| ft²	26,114
Other income from sub-sublease	$ 800	$ 800
Office and Lab Sublease [Member]
Leases [Line Items]
Operating lease termination payment	14,800
Office and Lab Sublease [Member] \| Letter of Credit [Member]
Leases [Line Items]
Restricted Cash, Noncurrent			$ 1,800
Restricted Cash, Current	$ 1,800

Stock-Based Awards

3 Months Ended

Mar. 31, 2023

Stock-Based Awards

8. Stock-Based Awards

2018 Stock Option and Incentive Plan

The Company grants stock-based awards under the Magenta Therapeutics, Inc. 2018 Stock Option and Incentive Plan (the “2018 Plan”). The Company also has outstanding stock options under the Magenta Therapeutics, Inc. 2016 Stock Option and Grant Plan, as amended (the “2016 Plan”), but is no longer granting awards under the 2016 Plan. As of March 31, 2023, 7,231,663 shares of common stock were available for issuance under the 2018 Plan.

Grant of Stock Options

During the three months ended March 31, 2023, the Company granted options to certain employees with service-based vesting conditions for the purchase of 3,750 shares of common stock with a weighted average grant date fair value of $0.41 per share. Stock-based compensation expense is being recognized over the requisite service period of four years.

Grant of Restricted Stock Units

During the three months ended March 31, 2023, the Company granted 123,125 restricted stock units to certain employees with a weighted average grant date fair value of $0.55 per share. Stock-based compensation expense is being recognized over the requisite service periods of 18 months to four years.

2019 Employee Stock Purchase Plan

Employees may elect to participate in The Magenta Therapeutics, Inc. 2019 Employee Stock Purchase Plan (the “ESPP”). The purchase price of common stock under the ESPP is equal to 85% of the lower of the fair market value of the common stock on the

offering date or the exercise date. The six-month offering periods begin in December and June of each year. During the three months ended March 31, 2023 and 2022, there were no shares of common stock purchased under the ESPP. As of March 31, 2023, 593,239 shares remained available for issuance under the ESPP.

Stock-Based Compensation

Stock-based compensation expense was classified in the statements of operations and comprehensive loss as follows (in thousands):


	Three months ended March 31,
	2023		2022
Research and development expenses	$	15	$	527
General and administrative expenses		491		1,378
	$	506	$	1,905

As of March 31, 2023, unrecognized compensation expense related to unvested share-based awards with service-based vesting conditions was $4.3 million, which is expected to be recognized over a weighted average period of 2.0 years. Additionally, the Company had unrecognized compensation cost of $1.6 million related to the unvested performance restricted stock units for which the performance conditions were not considered probable of achievement as of March 31, 2023.

Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022	Jan. 30, 2023
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Entity incorporation date	Jun. 01, 2015
Entity incorporation state code	DE
Reduction in workforce, Percent	84.00%
Net loss	$ (29,170)	$ (22,950)	$ (76,500)
Accumulated deficit	$ (431,199)		$ (402,029)
Common Stock [Member] \| Maximum [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Share Price				$ 1.00

- Definition

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

+ References

+ Details

Leases - Schedule of Supplemental Disclosure Of Cash Flow Information Related To The Lease (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Leases [Abstract]
Cash paid for amounts included in the measurement of operating lease liabilities	$ 16,455	$ 1,595
Operating lease liabilities arising from obtaining right-of-use asset	$ 0	$ 0

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Operating expenses:
Research and development	$ 7,995	$ 16,547
General and administrative	6,132	7,287
Restructuring and other charges	18,003	0
Total operating expenses	32,130	23,834
Loss from operations	(32,130)	(23,834)
Interest and other income, net	2,960	884
Net loss	$ (29,170)	$ (22,950)
Net loss per share, basic	$ (0.48)	$ (0.39)
Net loss per share, diluted	$ (0.48)	$ (0.39)
Weighted average common shares outstanding, basic	60,645,652	58,799,157
Weighted average common shares outstanding, diluted	60,645,652	58,799,157
Comprehensive loss:
Net loss	$ (29,170)	$ (22,950)
Other comprehensive gain (loss):
Unrealized gains (losses) on marketable securities	165	(439)
Total other comprehensive gain (loss)	165	(439)
Total comprehensive loss	$ (29,005)	$ (23,389)

Restructuring and Other Charges (Tables)

3 Months Ended

Mar. 31, 2023

Restructuring and Related Activities [Abstract]

Summary of Restructuring Liability included in Accrued Payroll and Related Expenses

The Company’s restructuring liability, which was included in accrued payroll and related expenses, consisted of the following (in thousands):


	Employee-Related Costs
Accrued restructuring balance at January 1, 2023	$	—
Expense incurred		6,319
Payments		(4,752	)
Accrued restructuring balance at March 31, 2023	$	1,567

Accrued Expenses and Other Current Liabilities

3 Months Ended

Mar. 31, 2023

Accrued Expenses and Other Current Liabilities

5. Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following (in thousands):


	March 31, 2023		December 31, 2022
Accrued payroll and related expenses	$	1,622	$	4,162
Accrued external research and development expenses		1,390		3,091
Accrued professional fees		1,666		654
Accrued other		224		364
	$	4,902	$	8,271

Summary of Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2023

Use of Estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting periods. Significant estimates and assumptions reflected in these financial statements include, but are not limited to, the accrual for research and development expenses and the valuation of stock-based awards. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from those estimates.

Unaudited Interim Financial Information

The consolidated balance sheet at December 31, 2022 was derived from audited financial statements but does not include all disclosures required by GAAP. The accompanying unaudited consolidated financial statements as of March 31, 2023 and for the three months ended March 31, 2023 and 2022 have been prepared by the Company pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”) for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. The Company believes, however, that the disclosures are adequate to make the information presented not misleading. These consolidated financial statements should be read in conjunction with the Company’s audited financial statements for the year ended December 31, 2022 included in the Company’s most recent Annual Report on Form 10-K on file with the SEC. In the opinion of management, all adjustments, consisting only of normal recurring adjustments necessary for a fair statement of the Company’s consolidated financial position as of March 31, 2023 and consolidated results of operations for the three months ended March 31, 2023 and 2022 and consolidated cash flows for the three months ended March 31, 2023 and 2022 have been made. The results of operations for the three months ended March 31, 2023 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2023 or any other interim period.

Marketable Securities

The Company’s marketable securities are classified as available-for-sale and are carried at fair value with the unrealized gains and losses reported as a component of accumulated other comprehensive income (loss) in stockholders’ equity. Realized gains and losses are included as a component of interest and other income, net based on the specific identification method. The Company classifies its marketable securities with maturities beyond one year as short-term, based on their highly liquid nature and because such marketable securities are available for current operations.

Effective January 1, 2023, when the fair value is below the amortized cost of a marketable security, an estimate of expected credit losses is made. The credit-related impairment amount is recognized in the consolidated statements of operations and comprehensive loss. Credit losses are recognized through the use of an allowance for credit losses account in the consolidated balance sheet and subsequent improvements in expected credit losses are recognized as a reversal of an amount in the allowance account. If the Company has the intent to sell the security or it is more likely than not that the Company will be required to sell the security prior to recovery of its amortized cost basis, then the allowance for the credit loss is written-off and the excess of the amortized cost basis of the asset over its fair value is recorded in the consolidated statements of operations and comprehensive loss. There were no credit losses recorded during the three months ended March 31, 2023.

Fair Value Measurements

Certain assets and liabilities 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—Quoted prices in active markets for identical assets or liabilities.

•

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 and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques.

The Company’s cash equivalents and marketable securities are carried at fair value, determined according to the fair value hierarchy described above (see Note 3). The carrying values of the Company’s accounts payable and accrued expenses approximate their fair values due to the short-term nature of these assets and liabilities.

Income Taxes

The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the consolidated financial statements or in the Company’s tax returns. Deferred taxes are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect in the years 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 deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies.

The Company accounts for uncertainty in income taxes recognized in its consolidated financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the consolidated financial

statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties.

Comprehensive Loss

Comprehensive loss includes net loss as well as other changes in stockholders’ equity that result from transactions and economic events other than those with stockholders. For the three months ended March 31, 2023 and 2022, the Company’s only element of other comprehensive income (loss) was unrealized gains (losses) on marketable securities.

Net Loss per Share

Basic net income (loss) per share is computed by dividing the net income (loss) by the weighted average number of shares of common stock outstanding for the period. Diluted net income (loss) per share is computed by dividing net income (loss) by the weighted average number of common shares outstanding for the period, including potential dilutive common shares assuming the dilutive effect of outstanding stock options. For periods in which the Company has reported net losses, diluted net loss per common share is the same as basic net loss per common share, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive.

The Company reported a net loss for the three months ended March 31, 2023 and 2022. The following potential dilutive securities, presented based on amounts outstanding at each period end, have been excluded from the calculation of diluted net loss per share because including them would have had an anti-dilutive impact:


	As of March 31,
	2023		2022
Stock options to purchase common stock		6,907,815		7,580,453
Unvested restricted common stock units		282,497		455,173
Shares of common stock issuable under Employee Stock Purchase Plan		—		36,012
		7,190,312		8,071,638

Recently Issued Accounting Pronouncements

Recently Adopted Accounting Pronouncements Effective January 1, 2023, the Company adopted ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments for the year ended December 31, 2023. The new standard adjusts the accounting for assets held at amortized cost basis, including marketable securities accounted for as available for sale, and trade receivables. The standard eliminates the probable initial recognition threshold and requires an entity to reflect its current estimate ofall expected credit losses. The allowance for credit losses is a valuation account that is deducted from the amortized cost basis of the financial assets to present the net amount expected to be collected. The adoption of this standard did not have a material impact on the Company’s consolidated financial statements and related disclosures.

Recently Issued Accounting Pronouncements

Other accounting standards that have been issued or proposed by the FASB or other standards-setting bodies that do not require adoption until a future date are not expected to have a material impact on the Company’s consolidated financial statements upon adoption.

- Definition

Disclosure of accounting policy for income taxes, which may include its accounting policies for recognizing and measuring deferred tax assets and liabilities and related valuation allowances, recognizing investment tax credits, operating loss carryforwards, tax credit carryforwards, and other carryforwards, methodologies for determining its effective income tax rate and the characterization of interest and penalties in the financial statements.

+ References + Details

Stockholders' Equity

3 Months Ended

Mar. 31, 2023

Equity [Abstract]

Stockholders' Equity

7. Stockholders' Equity

Adoption of Stockholder Rights Plan

On March 31, 2023, the Company’s board of directors unanimously adopted a limited duration stockholder rights plan (the “Rights Plan”) which expires at the close of business on March 30, 2024.

Pursuant to the Rights Plan, the Company declared a dividend distribution of one preferred stock purchase right for each outstanding share of the Company’s common stock to stockholders of record as of the close of business on April 11, 2023 (the “Record Date”). In addition, one right will automatically attach to each share of common stock issued between the Record Date and the earlier of the distribution date and the expiration date of the rights. Each right entitles the registered holder thereof to purchase

from the Company a unit consisting of one ten-thousandth of a share (a “Unit”) of Series A Junior Participating Cumulative Preferred Stock, par value $0.001 per share, of the Company at a cash exercise price of $3.75 per Unit, subject to adjustment, under certain conditions specified in the Rights Plan.

The rights will become exercisable if an entity, person or group acquires beneficial ownership of 10% or more of the Company’s outstanding common stock. In the event that the rights become exercisable due to the triggering ownership threshold being crossed, each right will entitle its holder (other than the person, entity or group triggering the Rights Plan, whose rights will become void and will not be exercisable) to receive shares of common stock having a market value equal to two times the exercise price of the right. In the event of a merger or similar change of control of the Company, each right will entitle its holder (other than the person, entity or group triggering the Rights Plan, whose rights will become void and will not be exercisable) to receive shares of common stock of the acquiring company having a market value equal to two times the exercise price of the right.

Under the Rights Plan, any person, entity or group that currently owns more than the triggering percentage may continue to own its shares of common stock but may not acquire any additional shares of common stock or form a group with another owner of common stock, without triggering the Rights Plan.

In connection with the adoption of the Rights Plan, the Company’s board of directors approved a Certificate of Designations of Series A Junior Participating Cumulative Preferred Stock which designates the rights, preferences and privileges of 15,000 shares of preferred stock. The Certificate of Designations was filed with the Secretary of State of Delaware and became effective on March 31, 2023.

On May 2, 2023, the Company’s board of directors approved an amendment No. 1 to the Rights Plan (the “Amendment No. 1”), effective as of May 2, 2023. Amendment No. 1 prevents the approval, execution, delivery or performance of the Merger Agreement, or the consummation prior to the termination of the Merger Agreement of the Merger or any of the other transactions contemplated by the Merger Agreement in accordance with its terms, from, among other things, (i) resulting in a Stock Acquisition Date or Distribution Date (each as defined in the Rights Plan) or permitting the rights to be exercised or exchanged, (ii) constituting a Section 11(a)(ii) Event or a Section 13 Event (each as defined in the Rights Plan) and (iii) causing the Company, the wholly-owned subsidiary of the Company in the Merger, or their respective affiliates to be deemed an Acquiring Person (as defined in the Rights Plan) for any purpose under the Rights Plan.

- Definition

The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-URI https://asc.fasb.org/topic&trid=2208762

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496158-112644

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 13
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496158-112644

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 14
-Subparagraph (c)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496171-112644

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 14
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126973232&loc=SL123496171-112644

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI https://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Payables and Accruals [Abstract]
Accrued payroll and related expenses	$ 1,622	$ 4,162
Accrued external research and development expenses	1,390	3,091
Accrued professional fees	1,666	654
Accrued other	224	364
Total	$ 4,902	$ 8,271

Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2023

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Use of Estimates

Unaudited Interim Financial Information

Marketable Securities

Fair Value Measurements

•

Level 1—Quoted prices in active markets for identical assets or liabilities.

•

Income Taxes

Comprehensive Loss

Net Loss per Share


	As of March 31,
	2023		2022
Stock options to purchase common stock		6,907,815		7,580,453
Unvested restricted common stock units		282,497		455,173
Shares of common stock issuable under Employee Stock Purchase Plan		—		36,012
		7,190,312		8,071,638

Recently Adopted Accounting Pronouncements

Effective January 1, 2023, the Company adopted ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments for the year ended December 31, 2023. The new standard adjusts the accounting for assets held at amortized cost basis, including marketable securities accounted for as available for sale, and trade receivables. The standard eliminates the probable initial recognition threshold and requires an entity to reflect its current estimate of all expected credit losses. The allowance for credit losses is a valuation account that is deducted from the amortized cost basis of the financial assets to present the net amount expected to be collected. The adoption of this standard did not have a material impact on the Company’s consolidated financial statements and related disclosures.

Recently Issued Accounting Pronouncements

Assets Held For Sale (Additional Information) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2023 USD ($)
Property, Plant and Equipment [Abstract]
Impairment charge of lab equipment	$ 0.3

Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2023

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share

The following potential dilutive securities, presented based on amounts outstanding at each period end, have been excluded from the calculation of diluted net loss per share because including them would have had an anti-dilutive impact:


	As of March 31,
	2023		2022
Stock options to purchase common stock		6,907,815		7,580,453
Unvested restricted common stock units		282,497		455,173
Shares of common stock issuable under Employee Stock Purchase Plan		—		36,012
		7,190,312		8,071,638

Fair Value of Financial Assets

3 Months Ended

Mar. 31, 2023

Fair Value of Financial Assets

3. Fair Value of Financial Assets

As of March 31, 2023, marketable securities by security type consisted of (in thousands):


			Gross		Gross					Estimated
	Amortized		Unrealized		Unrealized			Credit		Fair
	Cost		Gains		Losses			Losses		Value
U.S. treasury notes (due within one year)	$	29,699	$	1	$	(17	)	$	—	$	29,683
Total	$	29,699	$	1	$	(17	)	$	—	$	29,683

As of December 31, 2022 marketable securities by security type consisted of (in thousands):


			Gross		Gross			Estimated
	Amortized		Unrealized		Unrealized			Fair
	Cost		Gains		Losses			Value
U.S. treasury notes (due within one year)	$	54,596	$	2	$	(183	)	$	54,415
Total	$	54,596	$	2	$	(183	)	$	54,415


	Fair Value Measurements at March 31, 2023 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	47,508	$	—	$	—	$	47,508
Marketable securities:
U.S. treasury notes		—		29,683		—		29,683
Total	$	47,508	$	29,683	$	—	$	77,191


	Fair Value Measurements at December 31, 2022 Using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	56,663	$	—	$	—	$	56,663
Marketable securities:
U.S. treasury notes		—		54,415		—		54,415
Total	$	56,663	$	54,415	$	—	$	111,078

- Definition

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

+ References + Details

Related Parties

3 Months Ended

Mar. 31, 2023

Related Parties

12. Related Parties

Effective December 29, 2022, Michael Vasconcelles, a member of the Company’s board of directors, joined ImmunoGen as Executive Vice President of Research, Development, and Medical Affairs. The Company and ImmunoGen entered into a license agreement in November 2022 (see Note 10) and a Material Transfer and Evaluation Agreement, as amended, in August 2020. During the three months ended March 31, 2023, the Company recorded expense of less than $0.1 million related to these agreements. As of March 31, 2023 and December 31, 2022, amounts on the consolidated balance sheet related to these agreements was less than $0.1 million which was included in accounts payable and accrued expenses.

Effective March 2018, Amy Lynn Ronneberg, the then serving President of Be The Match BioTherapies, LLC, became a member of the Company’s board of directors and subsequently was appointed Chief Executive Officer of the National Marrow Donor Program/Be The Match (“NMDP/Be The Match”) organization in June 2020. The Company had collaboration agreements with the National Marrow Donor Program (as successor in interest to Be The Match BioTherapies Collection Services, LLC (formerly known as Be The Match BioTherapies, LLC)) which expired in December 2022, and research agreements in 2018 and 2020 with an affiliated organization, Center for International Blood and Marrow Transplant Research for work that has been completed. In addition, in June 2020, the Company entered into a clinical collaboration agreement with NMDP/Be The Match to evaluate the potential utility of MGTA-145 for mobilizing and collecting hematopoietic stem cells from donors in a single day and then using them for allogeneic transplant in patients. Under the terms of this agreement, the Company was obligated to fund up to fifty percent of NMDP/Be The Match clinical trial costs and provide the trial drugs to be included in research and development expense. The clinical collaboration was discontinued in the first quarter of 2023. During the three months ended March 31, 2023 and 2022, the Company recorded expense of less than $0.1 million and $0.1 million, respectively, related to these agreements. As of March 31, 2023, there were no amounts on the consolidated balance sheet related to these agreements. As of December 31, 2022, amounts on the consolidated balance sheet related to these agreements was $0.1 million, which was included in accounts payable and accrued expenses and other current liabilities.

Stockholders' Equity (Additional Information) (Details) - shares	3 Months Ended
	Mar. 31, 2023	Dec. 31, 2022
Class of Stock [Line Items]
Business close date	Mar. 30, 2024
Preferred stock, Shares authorized	10,000,000	10,000,000
Stockholder Rights Plan [Member]
Class of Stock [Line Items]
Dividend distribution	one preferred stock purchase right for each outstanding share of the Company’s common stock to stockholders of record as of the close of business on April 11, 2023 (the “Record Date”)
Preferred stock purchase rights	Each right entitles the registered holder thereof to purchase from the Company a unit consisting of one ten-thousandth of a share (a “Unit”) of Series A Junior Participating Cumulative Preferred Stock, par value $0.001 per share, of the Company at a cash exercise price of $3.75 per Unit, subject to adjustment, under certain conditions specified in the Rights Plan
Equity ownership threshold rights exercisable	10.00%
Conversion description	In the event that the rights become exercisable due to the triggering ownership threshold being crossed, each right will entitle its holder (other than the person, entity or group triggering the Rights Plan, whose rights will become void and will not be exercisable) to receive shares of common stock having a market value equal to two times the exercise price of the right. In the event of a merger or similar change of control of the Company, each right will entitle its holder (other than the person, entity or group triggering the Rights Plan, whose rights will become void and will not be exercisable) to receive shares of common stock of the acquiring company having a market value equal to two times the exercise price of the right
Stockholder Rights Plan [Member] \| Series A Junior Participating Cumulative Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, Shares authorized	15,000

Stock-Based Awards (Tables)

3 Months Ended

Mar. 31, 2023

Schedule of Stock Based Compensation Expense

Stock-based compensation expense was classified in the statements of operations and comprehensive loss as follows (in thousands):


	Three months ended March 31,
	2023		2022
Research and development expenses	$	15	$	527
General and administrative expenses		491		1,378
	$	506	$	1,905

401(k) Savings Plan - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, Employer matching contribution, percent of employees' gross pay	2.00%
Defined Contribution Plan, Employer Discretionary Contribution Amount		$ 0.1
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 0.1