Dianthus Therapeutics (DNTH) 10-Q 6 Aug 20 2020 Q2 Quarterly report Financial data

Cover Page

Cover Page - shares	6 Months Ended
	Jun. 30, 2020	Jul. 31, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Jun. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Trading Symbol	MGTA
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	Accelerated Filer
Entity Ex Transition Period	false
Entity Emerging Growth Company	true
Entity Small Business	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		48,252,724
Title of 12(b) Security	Common Stock
Entity Interactive Data Current	Yes
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	100 Technology Square
Entity Address, City or Town	Cambridge
Entity Address, Postal Zip Code	02139
Entity Address, State or Province	MA
City Area Code	857
Entity File Number	001-38541
Entity Tax Identification Number	81-0724163
Local Phone Number	242-0170
Security Exchange Name	NASDAQ

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 136,287	$ 65,071
Marketable securities	40,214	80,658
Prepaid expenses and other current assets	3,376	4,114
Total current assets	179,877	149,843
Restricted cash	1,780	1,780
Property and equipment, net	9,070	9,891
Total assets	190,727	161,514
Current liabilities:
Accounts payable	2,650	2,812
Accrued expenses and other current liabilities	7,719	11,303
Total current liabilities	10,369	14,115
Deferred rent	6,444	6,206
Total liabilities	16,813	20,321
Commitments and contingencies (Note 6)
Stockholders' Equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized; no shares issued or outstanding
Common stock, $0.001 par value; 150,000,000 shares authorized; 48,309,457 shares and 39,466,254 shares issued and 48,241,212 shares and 39,260,532 shares outstanding as of June 30, 2020 and December 31, 2019, respectively	48	39
Additional paid-in capital	392,298	320,641
Accumulated other comprehensive income	153	8
Accumulated deficit	(218,585)	(179,495)
Total stockholders' equity	173,914	141,193
Total liabilities and stockholders' equity	$ 190,727	$ 161,514

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2020	Dec. 31, 2019
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	48,309,457	39,466,254
Common stock, Shares outstanding	48,241,212	39,260,532

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenue	$ 0	$ 0	$ 0	$ 0
Operating expenses:
Research and development	12,610	13,433	26,573	23,970
General and administrative	7,402	5,905	14,683	11,718
Total operating expenses	20,012	19,338	41,256	35,688
Loss from operations	(20,012)	(19,338)	(41,256)	(35,688)
Interest and other income, net	933	1,630	2,166	3,146
Net loss	$ (19,079)	$ (17,708)	$ (39,090)	$ (32,542)
Net loss per share, basic and diluted	$ (0.48)	$ (0.48)	$ (0.99)	$ (0.93)
Weighted average common shares outstanding, basic and diluted	39,611,837	36,662,562	39,488,137	35,051,371
Comprehensive loss:
Net loss	$ (19,079)	$ (17,708)	$ (39,090)	$ (32,542)
Other comprehensive income (loss):
Unrealized gains (losses) on marketable securities	(210)	98	145	147
Total other comprehensive income (loss)	(210)	98	145	147
Total comprehensive loss	$ (19,289)	$ (17,610)	$ (38,945)	$ (32,395)

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity (Deficit) - 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, 2018	$ 145,648	$ 33	$ 248,349	$ (8)	$ (102,726)
Beginning balance, shares at Dec. 31, 2018		33,305,033
Issuance of common stock upon public offering net of underwriting discounts, commissions and offering costs	60,276	$ 5	60,271
Issuance of common stock upon public offering net of underwriting discounts, commissions and offering costs		4,887,500
Vesting of restricted stock		$ 1	(1)
Vesting of restricted stock, shares		395,279
Issuance of common stock upon exercise of stock options	850		850
Issuance of common stock upon exercise of stock options, shares		123,046
Stock-based compensation expense	5,177		5,177
Unrealized gains on marketable securities	147			147
Net loss	(32,542)				(32,542)
Ending balance at Jun. 30, 2019	179,556	$ 39	314,646	139	(135,268)
Ending balance, shares at Jun. 30, 2019		38,710,858
Beginning balance at Dec. 31, 2018	145,648	$ 33	248,349	(8)	(102,726)
Beginning balance, shares at Dec. 31, 2018		33,305,033
Net loss	(76,800)
Ending balance at Dec. 31, 2019	141,193	$ 39	320,641	8	(179,495)
Ending balance, shares at Dec. 31, 2019		39,260,532
Beginning balance at Mar. 31, 2019	134,003	$ 34	251,488	41	(117,560)
Beginning balance, shares at Mar. 31, 2019		33,581,975
Issuance of common stock upon public offering net of underwriting discounts, commissions and offering costs	60,276	$ 5	60,271
Issuance of common stock upon public offering net of underwriting discounts, commissions and offering costs		4,887,500
Vesting of restricted stock, shares		197,564
Issuance of common stock upon exercise of stock options	287		287
Issuance of common stock upon exercise of stock options, shares		43,819
Stock-based compensation expense	2,600		2,600
Unrealized gains on marketable securities	98			98
Net loss	(17,708)				(17,708)
Ending balance at Jun. 30, 2019	179,556	$ 39	314,646	139	(135,268)
Ending balance, shares at Jun. 30, 2019		38,710,858
Beginning balance at Dec. 31, 2019	141,193	$ 39	320,641	8	(179,495)
Beginning balance, shares at Dec. 31, 2019		39,260,532
Issuance of common stock upon public offering net of underwriting discounts, commissions and offering costs	64,563	$ 9	64,554
Issuance of common stock upon public offering net of underwriting discounts, commissions and offering costs		8,625,000
Vesting of restricted stock, shares		125,673
Issuance of common stock upon exercise of stock options	1,817		1,817
Issuance of common stock upon exercise of stock options, shares		224,354
Stock-based compensation expense	5,244		5,244
Unrealized gains on marketable securities	145			145
Issuance of common stock under Employee Stock Purchase Plan, shares		5,653
Issuance of common stock under Employee Stock Purchase Plan	42		42
Net loss	(39,090)				(39,090)
Ending balance at Jun. 30, 2020	173,914	$ 48	392,298	153	(218,585)
Ending balance, shares at Jun. 30, 2020		48,241,212
Beginning balance at Mar. 31, 2020	125,401	$ 39	324,505	363	(199,506)
Beginning balance, shares at Mar. 31, 2020		39,454,635
Issuance of common stock upon public offering net of underwriting discounts, commissions and offering costs	64,563	$ 9	64,554
Issuance of common stock upon public offering net of underwriting discounts, commissions and offering costs		8,625,000
Vesting of restricted stock, shares		61,047
Issuance of common stock upon exercise of stock options	693		693
Issuance of common stock upon exercise of stock options, shares		94,877
Stock-based compensation expense	2,504		2,504
Unrealized gains on marketable securities	(210)			(210)
Issuance of common stock under Employee Stock Purchase Plan, shares		5,653
Issuance of common stock under Employee Stock Purchase Plan	42		42
Net loss	(19,079)				(19,079)
Ending balance at Jun. 30, 2020	$ 173,914	$ 48	$ 392,298	$ 153	$ (218,585)
Ending balance, shares at Jun. 30, 2020		48,241,212

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities:
Net loss	$ (39,090)	$ (32,542)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	5,244	5,177
Depreciation and amortization expense	988	875
Net amortization (accretion) of premiums (discounts) on marketable securities	63	(614)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	738	(7,989)
Accounts payable	(238)	(430)
Accrued expenses and other current liabilities	(3,805)	855
Deferred rent	238	4,699
Net cash used in operating activities	(35,862)	(29,969)
Cash flows from investing activities:
Purchases of property and equipment	(167)	(2,377)
Purchases of marketable securities	(4,974)	(94,176)
Maturities of marketable securities	45,500	40,000
Net cash provided by (used in) investing activities	40,359	(56,553)
Cash flows from financing activities:
Proceeds from public offerings, net of underwriting discounts and commissions	64,860	60,874
Payments of public offering costs	0	(436)
Proceeds from exercise of common stock options	1,817	850
Proceeds from issuance of common stock under Employee Stock Purchase Plan	42	0
Net cash provided by financing activities	66,719	61,288
Net increase (decrease) in cash, cash equivalents and restricted cash	71,216	(25,234)
Cash, cash equivalents and restricted cash at beginning of period	66,851	60,125
Cash, cash equivalents and restricted cash at end of period	138,067	34,891
Supplemental disclosure of non-cash investing and financing activities:
Purchase of property and equipment included in accounts payable and accrued expenses	0	472
Offering costs included in accounts payable and accrued expenses	$ 297	$ 162

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	6 Months Ended
	Jun. 30, 2020
Nature of the Business and Basis of Presentation	1. Nature of the Business and Basis of Presentation Magenta Therapeutics, Inc. (the “Company”) is a clinical-stage biotechnology company developing novel medicines to bring the curative power of immune reset to more patients with autoimmune diseases, blood cancers and genetic diseases. 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 its initial public offering. The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations , the continuing impact of the COVID-19 coronavirus and the ability to secure additional capital to fund operations. Product candidates currently under development will require significant additional 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’s development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales. In June 2020, the Company issued and sold 8,625,000 shares of its common stock, including the underwriters’ exercise in full of their option to purchase additional shares of common stock, in a follow-on s In May 2019, the Company issued and sold 4,887,500 shares of its common stock, including the underwriters’ exercise in full of their option to purchase additional shares of common stock, in a follow-on s The Company has a shelf registration statement on Form S-3 Commission (the “SEC”), which covers the offering, issuance and sale of up to an aggregate of $ million of common stock, preferred stock, debt securities, warrants and/or units of any combination thereof. The Company simultaneously entered into a sales agreement with Cowen and Company, LLC, as sales agent, to provide for the issuance and sale by the Company of up to $ million of common stock from time to time in “at-the-market” offerings under the Shelf (the “ATM Program”). The Shelf was declared effective by the SEC on August , . As of June , , no sales have been made pursuant to the ATM Program. The Company has incurred recurring losses since inception, including net losses of $39.1 million and $76.8 million for the six months ended June 30, 2020 and the year ended December 31, 2019, respectively. As of June 30, 2020, the Company had an accumulated deficit of $218.6 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 its ability to raise additional capital to fund its operations. The Company expects its expenses to increase substantially in connection with ongoing activities, particularly as the Company advances its preclinical activities and clinical trials for its product candidates in development. Accordingly, the Company will need to obtain substantial additional funding in connection with continuing operations. 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. Although management continues to pursue these plans, 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”).

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2020
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies 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, 2019 was derived from audited financial statements but does not include all disclosures required by GAAP. The accompanying unaudited consolidated financial statements as of June 30, 2020 and for the three and six months ended June 30, 2020 and 2019 have been prepared by the Company pursuant to the rules and regulations of the 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, 2019 included in the Company’s Annual Report on Form 10-K, 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 than-not 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 and six months ended June 30, 2020 and 2019, 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 affect is anti-dilutive. The Company reported a net loss for the three and six months ended June 30, 2020 and 2019. 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: June 30, 2020 2019 Stock options to purchase common stock 5,809,118 4,913,620 Unvested restricted common stock 68,245 627,242 Shares of common stock issuable under Employee Stock Purchase Plan 8,213 — 5,885,576 5,540,862 Recently Adopted Accounting Pronouncements In December 2019, the Financing Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“ASU”) No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes 2019-12”). 2019-12 2019-12 Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases 2016-02”). 2016-02 right-of-use guidance was effective for annual reporting periods beginning after December 15, 2018 and for interim periods within those fiscal years. For nonpublic entities and emerging growth companies that choose to take advantage of the extended transition period, the guidance was effective for annual reporting periods beginning after December 15, 2019. In June 2020, the FASB issued ASU No. 2020-05, 2016-02 2018-11, Leases (Topic 842) Targeted Improvements 2016-02 right-of-use In June 2016, the FASB issued ASU No. 2016-13, Financial No. 2019-10,

Fair Value of Financial Assets

Fair Value of Financial Assets	6 Months Ended
	Jun. 30, 2020
Fair Value of Financial Assets	3. Fair Value of Financial Assets As of June 30, 2020, marketable securities by security type consisted of (in thousands): Amortized Gross Gross Estimated United States Treasury Notes (due within one year) $ 40,061 $ 153 $ — $ 40,214 Total $ 40,061 $ 153 $ — $ 40,214 As of December 31, 2019, marketable securities by security type consisted of (in thousands): Amortized Gross Gross Estimated United States Treasury Notes (due within one year) $ 78,656 $ 25 $ (21 ) $ 78,660 Agency Bonds (due within one year) 1,994 4 — 1,998 Total $ 80,650 $ 29 $ (21 ) $ 80,658 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 June 30, 2020 Using: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 136,357 $ — $ — $ 136,357 Marketable securities: United States Treasury Notes — 40,214 — 40,214 Total $ 136,357 $ 40,214 $ — $ 176,571 Fair Value Measurements at December 31, 2019 Using: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 64,796 $ — $ — $ 64,796 Marketable securities: United States Treasury Notes — 78,660 — 78,660 Agency Bonds — 1,998 — 1,998 Total $ 64,796 $ 80,658 $ — $ 145,454 During the three and six months ended June 30, 2020 and 2019, there were no transfers between Level 1, Level 2 and Level 3.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	6 Months Ended
	Jun. 30, 2020
Accrued Expenses and Other Current Liabilities	4. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consisted of the following (in thousands): June 30, 2020 December 31, 2019 Accrued external research and development expenses $ 4,052 $ 6,516 Accrued payroll and related expenses 1,938 3,247 Deferred rent, current portion 601 601 Accrued professional fees 819 660 Accrued other 309 279 $ 7,719 $ 11,303

Stock-Based Awards

Stock-Based Awards	6 Months Ended
	Jun. 30, 2020
Stock-Based Awards	5. 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”) , 2019 Employee Stock Purchase Plan The Magenta Therapeutics, Inc. 2019 Employee Stock Purchase Plan (the “ESPP”) became effective in June 2019. The offering periods begin in December and June of each year. The initial offering period commenced on December 1, 2019 and ended on May 29, 2020. 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. During the six months ended June 30, 2020, 5,653 shares of common stock were purchased under the ESPP at a purchase price per share of $7.51. As of June 30, 2020, 160,872 shares remained available for issuance under the ESPP. Grant of Stock Options During the six months ended June 30, 2020, the Company granted options to certain employees, directors and consultants with service-based vesting conditions for the purchase of 1,759,596 shares of common stock with a weighted average grant date fair value of $8.04 per share. Stock-Based Compensation Stock-based compensation expense was classified in the statements of operations and comprehensive loss as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Research and development expenses $ 780 $ 1,268 $ 1,802 $ 2,524 General and administrative expenses 1,724 1,332 3,442 2,653 $ 2,504 $ 2,600 $ 5,244 $ 5,177 As of June 30, 2020, total unrecognized compensation cost related to unvested share-based awards was $22.0 million, which is expected to be recognized over a weighted average period of 2.5 years.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2020
Commitments and Contingencies	6. Commitments and Contingencies Leases In May 2018, the Company entered into a sublease for up to approximately 69,000 square feet of office and laboratory space in Cambridge, Massachusetts. The sublease was amended effective March 2019 to increase the lease payments over the lease term and to increase the sublandlord-funded tenant improvements. The sublease is subject and subordinate to a prime lease between the sublandlord and the prime landlord. The term of the sublease commenced in June 2018 and expires in February 2028. The sublandlord has the right to terminate the sublease after five years. The Company is also obligated to pay real estate taxes and other costs related to the premises, including costs of operations and management of the leased premises. In connection with the sublease, as amended, the sublandlord agreed to fund up to $5.5 million in tenant improvements to the leased facility, of which $5.2 million has been paid as of June 30, 2020. The Company is required to maintain a cash balance of $1.8 million to secure a letter of credit associated with the sublease. This amount was classified as noncurrent restricted cash in the consolidated balance sheets at June 30, 2020 and December 31, 2019. As of June 30, 2020 and December 31, 2019, the Company had long-term deferred rent of $6.4 million and $6.2 million, respectively, related to lease incentives and payment escalations. As of June 30, 2020 and December 31, 2019, the short-term portion of deferred rent of $0.6 million for each period was included in accrued expenses and other current liabilities. The Company recorded rent expense of $1.6 million during each of the three months ended June 30, 2020 and 2019 and $3.1 million during each of the six months ended June 30, 2020 and 2019. As of June 30, 2020, the future minimum lease payments due under the noncancelable operating lease is as follows (in thousands): Remainder of 2020 (six months) $ 2,950 2021 6,072 2022 6,375 2023 6,734 2024 7,100 Thereafter 24,899 $ 54,130 In the fourth quarter of 2018, the Company entered into two two sub-subleases sub-subleases sub-subleases. 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 may pay upfront technology access fees, research exclusivity fees and payment for research support. Additionally, upon the exercise of certain license rights, the Company may be 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 June 30, 2020 and 2019, the Company recorded less than $0.1 million of research and development expense related to this agreement for upfront technology access fees, research exclusivity fees and research support. During the six months ended June 30, 2020 and 2019, the Company recorded less than $0.1 million and $0.4 million, respectively, of research and development expense related to this agreement for upfront technology access fees, research exclusivity fees and research support. Intellectual Property Licenses The Company has 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. The Company is obligated to pay Harvard maintenance fees of $0.1 million annually to reimburse qualified expenses related to the patents. The Company is 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 country-by-country The Company has a license agreement with Novartis International Pharmaceutical Ltd. (“Novartis”), entered into in April 2017, to use and develop certain patent rights (the “Novartis License”). Under the Novartis License, the Company was granted an exclusive, worldwide, sublicensable license to research, develop and commercialize certain licensed products that contain Novartis compounds for the expansion of cord blood derived non-gene-edited/-modified product-by-product country-by-country The Company has agreements with third parties in the normal course of business, under which it can license certain developed technologies. If the Company exercises its rights to license the respective technologies, it may be subject to additional fees and milestone payments. During the three and six months ended June 30, 2020 and 2019, the Company did not exercise its rights to the license of certain developed technologies under these agreements. 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 as of June 30, 2020. 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

401(k) Savings Plan	6 Months Ended
	Jun. 30, 2020
401(k) Savings Plan	7. 401(k) Savings Plan The Company has a 401(k) available for participating employees who meet certain eligibility requirements

Related Parties

Related Parties	6 Months Ended
	Jun. 30, 2020
Related Parties	8. Related Parties National Marrow Donor Program (as successor in interest to Be The Match BioTherapies, LLC) Effective March 2018, the 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 Be The Match/National Marrow Donor Program organization in June 2020. The Company has collaboration agreements with the National Marrow Donor Program (as successor in interest to Be The Match BioTherapies, LLC) and a research agreement with an affiliated organization, Center for International Blood and Marrow Transplant Research. For each of the three months ended June 30, 2020 and 2019, the Company recorded expense of less than $0.1 million related to these agreements. For the six months ended June 30, 2020 and 2019, the Company recorded expense of $0.2 million and $0.1 million, respectively, related to these agreements. As of June 30, 2020 and December 31, 2019, amounts on the balance sheet related to these agreements were less than $0.1 million and $0.2 million, respectively, which amounts were included in accounts payable and accrued expenses and other current liabilities and less than $0.1 million as of June 30, 2020 and December 31, 2019, which amounts were included in prepaid expenses and other current assets.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2020
Use of Estimates	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	Unaudited Interim Financial Information The consolidated balance sheet at December 31, 2019 was derived from audited financial statements but does not include all disclosures required by GAAP. The accompanying unaudited consolidated financial statements as of June 30, 2020 and for the three and six months ended June 30, 2020 and 2019 have been prepared by the Company pursuant to the rules and regulations of the 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, 2019 included in the Company’s Annual Report on Form 10-K,
Fair Value Measurements	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	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 than-not
Comprehensive Loss	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 and six months ended June 30, 2020 and 2019, the Company’s only element of other comprehensive income (loss) was unrealized gains (losses) on marketable securities.
Net Loss per Share	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 affect is anti-dilutive. The Company reported a net loss for the three and six months ended June 30, 2020 and 2019. 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: June 30, 2020 2019 Stock options to purchase common stock 5,809,118 4,913,620 Unvested restricted common stock 68,245 627,242 Shares of common stock issuable under Employee Stock Purchase Plan 8,213 — 5,885,576 5,540,862
Recently Adopted Accounting Pronouncements and Recently Issued Accounting Pronouncements	Recently Adopted Accounting Pronouncements In December 2019, the Financing Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“ASU”) No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes 2019-12”). 2019-12 2019-12 Recently Issued Accounting Pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases 2016-02”). 2016-02 right-of-use guidance was effective for annual reporting periods beginning after December 15, 2018 and for interim periods within those fiscal years. For nonpublic entities and emerging growth companies that choose to take advantage of the extended transition period, the guidance was effective for annual reporting periods beginning after December 15, 2019. In June 2020, the FASB issued ASU No. 2020-05, 2016-02 2018-11, Leases (Topic 842) Targeted Improvements 2016-02 right-of-use In June 2016, the FASB issued ASU No. 2016-13, Financial No. 2019-10,

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2020
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: June 30, 2020 2019 Stock options to purchase common stock 5,809,118 4,913,620 Unvested restricted common stock 68,245 627,242 Shares of common stock issuable under Employee Stock Purchase Plan 8,213 — 5,885,576 5,540,862

Fair Value of Financial Assets

Fair Value of Financial Assets (Tables)	6 Months Ended
	Jun. 30, 2020
Schedule of Marketable Securities by Security Type	As of June 30, 2020, marketable securities by security type consisted of (in thousands): Amortized Gross Gross Estimated United States Treasury Notes (due within one year) $ 40,061 $ 153 $ — $ 40,214 Total $ 40,061 $ 153 $ — $ 40,214 As of December 31, 2019, marketable securities by security type consisted of (in thousands): Amortized Gross Gross Estimated United States Treasury Notes (due within one year) $ 78,656 $ 25 $ (21 ) $ 78,660 Agency Bonds (due within one year) 1,994 4 — 1,998 Total $ 80,650 $ 29 $ (21 ) $ 80,658 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):
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 June 30, 2020 Using: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 136,357 $ — $ — $ 136,357 Marketable securities: United States Treasury Notes — 40,214 — 40,214 Total $ 136,357 $ 40,214 $ — $ 176,571 Fair Value Measurements at December 31, 2019 Using: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 64,796 $ — $ — $ 64,796 Marketable securities: United States Treasury Notes — 78,660 — 78,660 Agency Bonds — 1,998 — 1,998 Total $ 64,796 $ 80,658 $ — $ 145,454 During the three and six months ended June 30, 2020 and 2019, there were no transfers between Level 1, Level 2 and Level 3.

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	6 Months Ended
	Jun. 30, 2020
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following (in thousands): June 30, 2020 December 31, 2019 Accrued external research and development expenses $ 4,052 $ 6,516 Accrued payroll and related expenses 1,938 3,247 Deferred rent, current portion 601 601 Accrued professional fees 819 660 Accrued other 309 279 $ 7,719 $ 11,303

Stock-Based Awards (Tables)

Stock-Based Awards (Tables)	6 Months Ended
	Jun. 30, 2020
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 June 30, Six Months Ended June 30, 2020 2019 2020 2019 Research and development expenses $ 780 $ 1,268 $ 1,802 $ 2,524 General and administrative expenses 1,724 1,332 3,442 2,653 $ 2,504 $ 2,600 $ 5,244 $ 5,177

Commitments and Contingencies (

Commitments and Contingencies (Tables)	6 Months Ended
	Jun. 30, 2020
Schedule of Future Minimum Lease Payments Due Under Noncancelable Operating Lease	As of June 30, 2020, the future minimum lease payments due under the noncancelable operating lease is as follows (in thousands): Remainder of 2020 (six months) $ 2,950 2021 6,072 2022 6,375 2023 6,734 2024 7,100 Thereafter 24,899 $ 54,130

Nature of the Business and Ba_2

Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Jun. 30, 2020	Aug. 08, 2019	May 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Entity incorporation date						Jun. 30, 2015
Entity incorporation state code						DE
Net loss				$ (19,079)	$ (17,708)	$ (39,090)	$ (32,542)	$ (76,800)
Accumulated deficit	$ (218,585)			$ (218,585)		(218,585)		$ (179,495)
Net proceeds from common stock			$ 60,300			$ 64,860	$ 60,874
Maximum [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Shelf offering value		$ 350,000
Common Stock [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Stock issued, shares	8,625,000		4,887,500	8,625,000	4,887,500	8,625,000	4,887,500
Stock issued, price per shares	$ 8		$ 13.25	$ 8		$ 8
Net proceeds from common stock	$ 64,600
Cowen and Company LLC [Member] | Maximum [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
ATM offering value		$ 100,000

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Detail) - shares	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount	5,885,576	5,540,862
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	5,809,118	4,913,620
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	68,245	627,242
Shares of common stock issuable under the ESPP [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share, amount	8,213

Fair Value of Financial Asset_2

Fair Value of Financial Assets - Schedule of Marketable Securities by Security Type (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Marketable Securities [Line Items]
Amortized Cost	$ 40,061	$ 80,650
Gross Unrealized Gains	153	29
Gross Unrealized Losses	0	(21)
Estimated Fair Value	40,214	80,658
United States Treasury Notes [Member]
Marketable Securities [Line Items]
Amortized Cost	40,061	78,656
Gross Unrealized Gains	153	25
Gross Unrealized Losses	0	(21)
Estimated Fair Value	$ 40,214	78,660
Agency Bonds [Member]
Marketable Securities [Line Items]
Amortized Cost		1,994
Gross Unrealized Gains		4
Gross Unrealized Losses		0
Estimated Fair Value		$ 1,998

Fair Value of Financial Asset_3

Fair Value of Financial Assets - Schedule of Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	$ 40,214	$ 80,658
Fair Value on Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	176,571	145,454
Level 1 [Member] | Fair Value on Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	136,357	64,796
Level 2 [Member] | Fair Value on Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	40,214	80,658
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	136,357	64,796
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	136,357	64,796
United States Treasury Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	40,214	78,660
United States Treasury Notes [Member] | Fair Value on Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	40,214	78,660
United States 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	$ 40,214	78,660
Agency Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities		1,998
Agency Bonds [Member] | Fair Value on Recurring Basis [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities		1,998
Agency Bonds [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		$ 1,998

Fair Value of Financial Asset_4

Fair Value of Financial Assets - Additional Information (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, assets, level 1 to level 2 transfers, amount	$ 0	$ 0
Fair value, assets, level 2 to level 1 transfers, amount	0	0
Fair value, measurement with unobservable inputs reconciliation, recurring basis, asset transfers into level 3	0	0
Fair value, measurement with unobservable inputs reconciliation, recurring basis, asset, transfers out of level 3	$ 0	$ 0

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Accrued external research and development expenses	$ 4,052	$ 6,516
Accrued payroll and related expenses	1,938	3,247
Deferred rent, current portion	601	601
Accrued professional fees	819	660
Accrued other	309	279
Total	$ 7,719	$ 11,303

Stock-Based Awards - Additional

Stock-Based Awards - Additional Information (Detail) $ / shares in Units, $ in Millions	6 Months Ended
	Jun. 30, 2020USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized stock-based compensation expense | $	$ 22
Period for recognition of unrecognized expense	2 months 15 days
Employees [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	1,759,596
Weighted average fair value of stock options granted | $ / shares	$ 8.04
2018 Stock Option and Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock available for issuance under ESPP	2,833,512
2019 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock available for issuance under ESPP	160,872
Percentage of purchase price of common stock under the ESPP	85.00%
Common stock purchased	5,653
Stock issued, price per shares | $ / shares	$ 7.51

Stock-Based Awards - Schedule o

Stock-Based Awards - Schedule of Stock Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock based compensation expense	$ 2,504	$ 2,600	$ 5,244	$ 5,177
Research and Development Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock based compensation expense	780	1,268	1,802	2,524
General and Administrative Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock based compensation expense	$ 1,724	$ 1,332	$ 3,442	$ 2,653

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) $ in Thousands	1 Months Ended	3 Months Ended			6 Months Ended
	Apr. 30, 2017USD ($)	Jun. 30, 2020USD ($)	Jun. 30, 2019USD ($)	Dec. 31, 2018ft²Sublease	Jun. 30, 2020USD ($)Milestone	Jun. 30, 2019USD ($)	Dec. 31, 2019USD ($)	May 31, 2018USD ($)ft²	Nov. 30, 2016USD ($)
Other Commitments [Line Items]
Sublease commencement period					2018-06
Sublease expiration period					2028-02
Property sublease, description					In May 2018, the Company entered into a sublease for up to approximately 69,000 square feet of office and laboratory space in Cambridge, Massachusetts. The sublease was amended effective March 2019 to increase the lease payments over the lease term and to increase the sublandlord-funded tenant improvements. The sublease is subject and subordinate to a prime lease between the sublandlord and the prime landlord. The term of the sublease commenced in June 2018 and expires in February 2028. The sublandlord has the right to terminate the sublease after five years.
Sublease termination period					5 years
Long-term deferred rent		$ 6,444			$ 6,444		$ 6,206
Deferred rent, current portion		601			601		601
Rent expense		1,600	$ 1,600		3,100	$ 3,100
Rental payments receivable		800			800
Research and development expense		12,610	13,433		26,573	23,970
Research and Development Expenses [Member]
Other Commitments [Line Items]
Research and development expense					0	100
Office and Lab Sublease [Member]
Other Commitments [Line Items]
Tenant improvement lease allowance					5,200
Long Term Deferred Rent [Member]
Other Commitments [Line Items]
Long-term deferred rent		6,400			6,400		6,200
Short Term Deferred Rent [Member]
Other Commitments [Line Items]
Deferred rent, current portion		600			600		$ 600
Maximum [Member] | Office and Lab Sublease [Member]
Other Commitments [Line Items]
Square feet of property subject to sublease | ft²								69,000
Tenant improvement allowance								$ 5,500
Sub-Sublease [Member]
Other Commitments [Line Items]
Square feet of property subject to sublease | ft²				27,000
Lease agreement maturity period				2 years
Number of Sub-sublease | Sublease				2
Other income from sub-sublease		700	700		$ 1,400	1,400
License Agreement with Novartis International Pharmaceutical Ltd. [Member]
Other Commitments [Line Items]
Number of milestones met | Milestone					0
License Agreement with Novartis International Pharmaceutical Ltd. [Member] | Maximum [Member]
Other Commitments [Line Items]
License agreement royalty percentage	20.00%
License Agreement with Novartis International Pharmaceutical Ltd. [Member] | Achievement of Clinical and Regulatory Milestones [Member] | Maximum [Member]
Other Commitments [Line Items]
Payment obligation	$ 177,000
License Agreement with Novartis International Pharmaceutical Ltd. [Member] | Development and Regulatory Milestones [Member] | Maximum [Member]
Other Commitments [Line Items]
Payment obligation	$ 125,000
Collaboration Agreement [Member] | Maximum [Member]
Other Commitments [Line Items]
Research and development expense		100	$ 100		$ 100	400
Collaboration Agreement [Member] | Development, Regulatory and Commercial Milestone [Member] | Per Target [Member] | Maximum [Member]
Other Commitments [Line Items]
Payment obligation		$ 83,500			83,500
License Agreement With Harvard [Member] | Maintenance [Member] | Annually Through 2019 [Member] | Maximum [Member]
Other Commitments [Line Items]
Payment obligation									$ 100
License Agreement With Harvard [Member] | Achievement of Development and Regulatory Milestones [Member] | Maximum [Member]
Other Commitments [Line Items]
Payment obligation									$ 7,400
License Agreement With Third Parties [Member] | License [Member]
Other Commitments [Line Items]
Research and development expense					$ 0	$ 0
Letter of Credit [Member] | Office and Lab Sublease [Member]
Other Commitments [Line Items]
Cash balance to secure letter of credit associated with sublease								$ 1,800

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Future Minimum Lease Payments Due Under Noncancelable Operating Lease (Detail) $ in Thousands	Jun. 30, 2020USD ($)
Operating Leased Assets [Line Items]
Remainder of 2020 (six months)	$ 2,950
2021	6,072
2022	6,375
2023	6,734
2024	7,100
Thereafter	24,899
Operating leases future minimum payments due	$ 54,130

Related Parties - Additional In

Related Parties - Additional Information (Detail) - Match Bio Therapies [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Related Party Transaction [Line Items]
Expenses paid to related party	$ 0.1	$ 0.1	$ 0.2	$ 0.1
Accounts Payable, Accrued Expenses and Other Current Liabilities [Member]
Related Party Transaction [Line Items]
Amounts owed to related party	0.1		0.1		$ 0.2
Prepaid Expenses and Other Current Assets [Member]
Related Party Transaction [Line Items]
Amounts owed to related party	$ 0.1		$ 0.1		$ 0.1