Rubius Therapeutics (RUBY) 10-Q 14 Nov 19 2019 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2019	Oct. 31, 2019
Document and Entity Information
Document Type	10-Q
Document Period End Date	Sep. 30, 2019
Entity Registrant Name	RUBIUS THERAPEUTICS, INC.
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		79,800,858
Entity Central Index Key	0001709401
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Amendment Flag	false

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 109,611	$ 307,064
Investments	215,078	96,987
Prepaid expenses and other current assets	5,073	9,737
Restricted cash		622
Total current assets	329,762	414,410
Operating lease, right-of-use-asset	47,911
Property, plant and equipment, net	52,478	62,796
Restricted cash	1,735	1,735
Other assets	386	168
Total assets	432,272	479,109
Current liabilities:
Accounts payable	11,679	7,886
Accrued expenses and other current liabilities	14,866	7,616
Operating lease liabilities	6,998	4,502
Total current liabilities	33,543	20,004
Long-term debt, net of discount	49,509	24,347
Other long-term liabilities	438	309
Operating lease liabilities, net of current portion	41,439	41,441
Total liabilities	124,929	86,101
Commitments and contingencies (see Note 11)
Stockholders' equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized at September 30, 2019 and December 31, 2018; no shares issued or outstanding at September 30, 2019 and December 31, 2018
Common stock, $0.001 par value; 150,000,000 shares authorized at September 30, 2019 and December 31, 2018; 79,777,733 and 79,234,853 shares issued and outstanding at September 30, 2019 and December 31, 2018, respectively	80	79
Additional paid-in capital	575,365	543,040
Accumulated other comprehensive income (loss)	166	(29)
Accumulated deficit	(268,268)	(150,082)
Total stockholders' equity	307,343	393,008
Total liabilities and stockholders' equity	$ 432,272	$ 479,109

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Sep. 30, 2019	Dec. 31, 2018
CONDENSED CONSOLIDATED BALANCE SHEETS
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, share authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, share authorized (in shares)	150,000,000	150,000,000
Common stock, shares issued (in shares)	79,777,733	79,234,853
Common stock, shares outstanding (in shares)	79,777,733	79,234,853

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Operating expenses:
Research and development	$ 33,530	$ 14,363	$ 81,919	$ 35,230
General and administrative	14,952	13,191	42,254	27,311
Total operating expenses	48,482	27,554	124,173	62,541
Loss from operations	(48,482)	(27,554)	(124,173)	(62,541)
Other income (expense):
Change in fair value of preferred stock warrant liability		(426)		(2,187)
Interest expense	(835)	(87)	(1,957)	(259)
Interest income and other income, net	2,302	1,705	7,144	2,975
Total other income, net	1,467	1,192	5,187	529
Net loss	$ (47,015)	$ (26,362)	$ (118,986)	$ (62,012)
Net loss per share, basic and diluted	$ (0.59)	$ (0.42)	$ (1.52)	$ (2.33)
Weighted average common shares outstanding, basic and diluted	79,115,305	62,311,111	78,357,791	26,662,233
Comprehensive loss:
Net loss	$ (47,015)	$ (26,362)	$ (118,986)	$ (62,012)
Other comprehensive income (loss):
Unrealized gains (losses) on investments, net of tax of $0	(124)	8	195	(19)
Comprehensive loss	$ (47,139)	$ (26,354)	$ (118,791)	$ (62,031)

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS
Unrealized gains (losses) on investments, tax	$ 0	$ 0	$ 0	$ 0

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Cash flows from operating activities:
Net loss		$ (118,986)	$ (62,012)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense		30,440	18,402
Depreciation and amortization expense		2,294	879
Change in fair value of preferred stock warrant liability	$ 426		2,187
Accretion of discount on investments		(1,939)	(198)
Loss on disposal of property and equipment		119
Non-cash interest expense		201	26
Changes in operating assets and liabilities:
Prepaid expenses and other current assets		(2,129)	(2,792)
Operating lease, right-of-use-asset		3,336
Other assets		(293)
Accounts payable		3,184	2,402
Accrued expenses and other current liabilities		3,725	2,472
Deferred rent			(14)
Operating lease liabilities		(1,411)
Net cash used in operating activities		(81,459)	(38,648)
Cash flows from investing activities:
Purchases of property, plant and equipment		(27,381)	(11,671)
Purchases of investments		(259,231)	(87,369)
Sales and maturities of investments		143,275	33,460
Net cash used in investing activities		(143,337)	(65,580)
Cash flows from financing activities:
Proceeds from issuance of convertible preferred stock, net of issuance costs			100,986
Proceeds from initial public offering of common stock, net of commissions and underwriting discounts			257,866
Payments of initial public offering costs			(3,449)
Proceeds from repayment of promissory note			245
Repurchase of unvested restricted common stock		(122)
Proceeds from borrowings under loan and security agreement		25,000
Proceeds from issuance of common stock upon exercise of stock options		1,843	18
Net cash provided by financing activities		26,721	355,666
Net increase (decrease) in cash, cash equivalents and restricted cash		(198,075)	251,438
Cash, cash equivalents and restricted cash at beginning of period		309,421	104,572	$ 104,572
Cash, cash equivalents and restricted cash at end of period	$ 356,010	111,346	356,010	$ 309,421
Supplemental cash flow information:
Cash paid for interest, net of interest capitalized		1,706
Cash paid for leases		3,194
Supplemental disclosure of non-cash investing and financing information:
Lease assets obtained in exchange for new operating lease liabilities		49,496
Purchases of property, plant and equipment included in accounts payable or accrued expenses		6,073	1,353
Amounts capitalized under build-to-suit lease transaction			24,657
Deferred offering costs and issuance costs included in accounts payable or accrued expenses		$ 11
Offering costs and issuance costs included in accounts payable and accrued expenses			99
Reclassification of warrant liability to additional paid-in capital			3,053
Conversion of preferred stock to common stock upon closing of the initial public offering			$ 240,776

CONDENSED CONSOLIDATED STATEM_4

CONDENSED CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ EQUITY (DEFICIT) - USD ($) $ in Thousands	Common stock	Additional paid-in capital	Accumulated other comprehensive loss	Accumulated deficit	Convertible preferred stock	Total
Balances at Beginning of period (in shares) at Dec. 31, 2017	14,977,317				43,933,006
Balances at Beginning of period at Dec. 31, 2017	$ 15	$ 17,277		$ (60,979)	$ 139,790	$ (43,687)
Issuance of common stock upon exercise of stock options (in shares)	19,750
Issuance of common stock upon exercise of stock options		4				4
Stock-based compensation expense		2,613				2,613
Unrealized gains (losses) on investments			$ (45)			(45)
Net loss				(14,411)		(14,411)
Balances at End of period (in shares) at Mar. 31, 2018	14,997,067				51,845,438
Balances at End of period at Mar. 31, 2018	$ 15	19,802	(45)	(75,298)	$ 240,776	(55,526)
Convertible preferred stock
Issuance of stock, net of issuance costs (in shares)					7,912,432
Issuance of stock, net of issuance costs					$ 100,986
Balances at Beginning of period (in shares) at Dec. 31, 2017	14,977,317				43,933,006
Balances at Beginning of period at Dec. 31, 2017	$ 15	17,277		(60,979)	$ 139,790	(43,687)
Net loss						(62,012)
Balances at End of period (in shares) at Sep. 30, 2018	79,042,603
Balances at End of period at Sep. 30, 2018	$ 79	533,846	(19)	(122,899)		411,007
Cumulative effect adjustment for adoption | ASU 2018-07		(92)		92
Balances at Beginning of period (in shares) at Mar. 31, 2018	14,997,067				51,845,438
Balances at Beginning of period at Mar. 31, 2018	$ 15	19,802	(45)	(75,298)	$ 240,776	(55,526)
Issuance of common stock upon exercise of stock options (in shares)	12,750
Issuance of common stock upon exercise of stock options		14				14
Stock-based compensation expense		5,902				5,902
Vesting of restricted common stock		122				122
Unrealized gains (losses) on investments			18			18
Net loss				(21,239)		(21,239)
Balances at End of period (in shares) at Jun. 30, 2018	15,009,817				51,845,438
Balances at End of period at Jun. 30, 2018	$ 15	25,840	(27)	(96,537)	$ 240,776	(70,709)
Shares issued	12,055,450
Issuance of common stock, initial public offering, net of issuance cost $3,548	$ 12	254,306				254,318
Cashless exercise of warrants	131,273
Issuance of common stock upon exercise of stock options (in shares)	625
Stock-based compensation expense		9,887				9,887
Vesting of restricted common stock		36				36
Conversion of preferred stock warrant to common stock warrant upon closing of initial public offering		3,053				3,053
Conversion of redeemable convertible preferred stock to common stock (in shares)	51,845,438				(51,845,438)
Conversion of redeemable convertible preferred stock to common stock	$ 52	240,724			$ (240,776)	240,776
Unrealized gains (losses) on investments			8			8
Net loss				(26,362)		(26,362)
Balances at End of period (in shares) at Sep. 30, 2018	79,042,603
Balances at End of period at Sep. 30, 2018	$ 79	533,846	(19)	(122,899)		411,007
Balances at Beginning of period (in shares) at Dec. 31, 2018	79,234,853
Balances at Beginning of period at Dec. 31, 2018	$ 79	543,040	(29)	(150,082)		393,008
Issuance of common stock upon exercise of stock options (in shares)	619,342
Issuance of common stock upon exercise of stock options	$ 1	798				799
Stock-based compensation expense		9,478				9,478
Vesting of restricted common stock		22				22
Unrealized gains (losses) on investments			110			110
Net loss				(32,581)		(32,581)
Balances at End of period (in shares) at Mar. 31, 2019	79,854,195
Balances at End of period at Mar. 31, 2019	$ 80	553,338	81	(181,863)		$ 371,636
Balances at Beginning of period (in shares) at Dec. 31, 2018						0
Balances at Beginning of period (in shares) at Dec. 31, 2018	79,234,853
Balances at Beginning of period at Dec. 31, 2018	$ 79	543,040	(29)	(150,082)		$ 393,008
Net loss						(118,986)
Balances at End of period (in shares) at Sep. 30, 2019	79,777,733
Balances at End of period at Sep. 30, 2019	$ 80	575,365	166	(268,268)		$ 307,343
Balances at Beginning of period (in shares) at Dec. 31, 2018						0
Balances at End of period (in shares) at Sep. 30, 2019						0
Cumulative effect adjustment for adoption | ASU 2016-02				800		$ 800
Balances at Beginning of period (in shares) at Mar. 31, 2019	79,854,195
Balances at Beginning of period at Mar. 31, 2019	$ 80	553,338	81	(181,863)		371,636
Issuance of common stock upon exercise of stock options (in shares)	223,484
Issuance of common stock upon exercise of stock options		572				572
Stock-based compensation expense		10,604				10,604
Vesting of restricted common stock		13				13
Unrealized gains (losses) on investments			209			209
Net loss				(39,390)		(39,390)
Balances at End of period (in shares) at Jun. 30, 2019	80,077,679
Balances at End of period at Jun. 30, 2019	$ 80	564,527	290	(221,253)		343,644
Issuance of common stock upon exercise of stock options (in shares)	367,971
Issuance of common stock upon exercise of stock options	$ 1	471				472
Stock-based compensation expense		10,358				10,358
Repurchase of unvested restricted common stock (in shares)	(667,917)
Repurchase of unvested restricted common stock	$ (1)					(1)
Vesting of restricted common stock		9				9
Unrealized gains (losses) on investments			(124)			(124)
Net loss				(47,015)		(47,015)
Balances at End of period (in shares) at Sep. 30, 2019	79,777,733
Balances at End of period at Sep. 30, 2019	$ 80	$ 575,365	$ 166	$ (268,268)		$ 307,343
Balances at End of period (in shares) at Sep. 30, 2019						0

CONDENSED CONSOLIDATED STATEM_5

CONDENSED CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ EQUITY (DEFICIT (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2018	Mar. 31, 2018
Net of issuance cost	$ 3,548
Series C convertible preferred stock
Net of issuance cost		$ 214

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	9 Months Ended
	Sep. 30, 2019
Nature of the Business and Basis of Presentation
Nature of the Business and Basis of Presentation	1. Nature of the Business and Basis of Presentation Rubius Therapeutics, Inc. (“Rubius” or the “Company”) is a therapeutics company focused on using its platform to develop red cell therapeutics for the treatment of patients with severe diseases. Rubius was incorporated in April 2013 as VL26, Inc. under the laws of the State of Delaware. In January 2015, the Company changed its name to Rubius Therapeutics, Inc. 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 ability to establish clinical- and commercial-scale manufacturing processes and the ability to secure additional capital to fund operations. In addition, the Company is subject to uncertainty regarding the performance and safety of red cell therapeutics in humans. 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 drug development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales. On July 20, 2018, the Company completed its initial public offering (“IPO”), pursuant to which it issued and sold 12,055,450 shares of common stock, inclusive of 1,572,450 shares sold by the Company pursuant to the full exercise of the underwriters’ option to purchase additional shares. The aggregate net proceeds received by the Company from the IPO were $254.3 million, after deducting underwriting discounts and commissions and other offering costs. Upon the closing of the IPO, all of the shares of the Company’s outstanding convertible preferred stock then outstanding automatically converted into 51,845,438 shares of common stock (see Note 7). The accompanying condensed consolidated financial statements have been prepared on the basis of continuity of operations, realization of assets and the satisfaction of liabilities and commitments in the ordinary course of business. The Company has incurred recurring losses since inception, including net losses of $119.0 million for the nine months ended September 30, 2019 and $89.2 million for the year ended December 31, 2018. As of September 30, 2019, the Company had an accumulated deficit of $268.3 million. The Company expects to continue to generate operating losses in the foreseeable future. As of November 14, 2019, the issuance date of the interim condensed consolidated financial statements, the Company expects that its cash, cash equivalents and investments will be sufficient to fund its operating expenses and capital expenditure requirements for at least 12 months from the issuance date of the interim condensed consolidated financial statements. The Company may seek additional funding through private or public equity financings, debt financings, collaborations, strategic alliances and marketing, distribution or licensing arrangements. The Company may not be able to obtain financing on acceptable terms, or at all, and the Company may not be able to enter into collaborations or other arrangements. The terms of any financing may adversely affect the holdings or the rights of the Company's stockholders. If the Company is unable to obtain funding, the Company could be forced to delay, reduce or eliminate some or all of its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects. 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 Company’s condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly owned subsidiary. All intercompany accounts and transactions have been eliminated in consolidation. Certain prior period amounts have been reclassified to conform to the current year presentation.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2019
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Unaudited Interim Financial Information The condensed consolidated balance sheet at December 31, 2018 was derived from audited financial statements but does not include all disclosures required by GAAP. The accompanying unaudited condensed consolidated financial statements as of September 30, 2019 and for the three and nine months ended September 30, 2019 and 2018 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 the financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. These condensed consolidated financial statements should be read in conjunction with the Company’s audited condensed consolidated financial statements and the notes thereto for the year ended December 31, 2018 included in the Company’s Annual Report on Form 10-K for the year-ended December 31, 2018, 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 condensed consolidated financial position as of September 30, 2019 and condensed consolidated results of operations for the three and nine months ended September 30, 2019 and 2018 and the condensed consolidated cash flows for the nine months ended September 30, 2019 and 2018 have been made. The Company’s condensed consolidated results of operations for the three and nine months ended September 30, 2019 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2019. 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 revenue and expenses during the reporting periods. Significant estimates and assumptions reflected in these condensed consolidated financial statements include, but are not limited to, the accrual of research and development expenses, the valuation of common stock and the preferred stock warrant liability prior to the IPO and the valuation of stock-based awards. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates as there are changes in circumstances, facts and experience. Actual results may differ from those estimates or assumptions. Concentrations of Credit Risk and of Significant Suppliers Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents and investments. The Company’s cash, cash equivalents and investments, as of September 30, 2019, consisted of U.S. government money market funds, U.S. government treasury bills, U.S. government agency bonds and U.S. government treasury notes. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. The Company relies, and expects to continue to rely, on a small number of vendors to manufacture supplies and raw materials for its development programs. These programs could be adversely affected by a significant interruption in these manufacturing services or the availability of raw materials. Cash Equivalents The Company considers all highly liquid investments with original maturities of three months or less at the date of purchase to be cash equivalents. Restricted Cash The Company maintained letters of credit totaling $1.7 million and $1.8 million for the benefit of the landlords of its leased properties , as of September 30, 2019 and December 31, 2018, respectively. As of December 31, 2018, the Company also maintained restricted cash of $0.5 million to collateralize its corporate credit card. The Company was required to maintain separate cash balances of these amounts to secure the letters of credit. Related to these separate cash balances, the Company classified $1.7 million as restricted cash (non-current) in its condensed consolidated balance sheet as of both September 30, 2019 and December 31, 2018, and classified $0.6 million as restricted cash (current) in its condensed consolidated balance sheet as of December 31, 2018. The Company did not have any restricted cash (current) as of September 30, 2019. 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 investments 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 liabilities. The carrying value of the Company’s long-term debt approximates its fair value due to its variable interest rate, which approximates a market interest rate. Investments The Company’s investments 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 (deficit). Realized gains and losses and declines in value determined to be other than temporary are based on the specific identification method and are included as a component of other income (expense), net in the condensed consolidated statements of operations and comprehensive loss. The Company classifies its investments with maturities beyond one year as short-term, based on their highly liquid nature and because such investments are available for current operations. The Company evaluates its investments with unrealized losses for other-than-temporary impairment. When assessing investments for other-than-temporary declines in value, the Company considers such factors as, among other things, how significant the decline in value is as a percentage of the original cost, how long the market value of the investment has been less than its original cost, the Company’s ability and intent to retain the investment for a period of time sufficient to allow for any anticipated recovery in fair value and market conditions in general. If any adjustment to fair value reflects a decline in the value of the investment that the Company considers to be “other than temporary,” the Company reduces the investment to fair value through a charge to the statement of operations and comprehensive loss. No such adjustments were necessary during the periods presented. Leases In February 2016, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“ASU”) No. 2016-02, Leases (Topic 842) (“ASU 2016-02”), which was codified as Accounting Standards Codification (“ASC”), 842, Leases, to enhance the transparency and comparability of financial reporting related to leasing arrangements. The Company adopted the standard effective January 1, 2019 using the modified retrospective transition method. The prior period results continue to be presented under ASC 840 based on the accounting standards originally in effect for such periods. The adoption of the new standard resulted in the recognition of a cumulative effect adjustment of $0.8 million to accumulated deficit due to the derecognition of the Company’s build-to-suit lease. At the inception of an arrangement as lessee or lessor, the Company determines whether the arrangement is or contains a lease. Operating lease cost is recognized over the lease term on a straight-line basis. Variable lease cost and short-term leases (lease terms less than 12 months) are recognized as incurred. When determining the lease term, the Company includes options to extend or terminate the lease when it is reasonably certain that it will exercise that option. For lessee arrangements, operating lease liabilities and their corresponding right-of-use assets are recorded based on the present value of lease payments over the expected lease term. The interest rate implicit in lease contracts is typically not readily determinable. As such, the Company utilizes its incremental borrowing rate, which is the rate incurred to borrow on a collateralized basis over a similar term an amount equal to the lease payments in a similar economic environment. Certain adjustments to the right-of-use asset may be required for items such as initial direct costs paid or incentives received. Operating leases are recognized on the balance sheet as right-of-use assets, operating lease liabilities current and operating lease liabilities non-current. The Company has elected to adopt the following lease policies in conjunction with the adoption of ASU 2016-02: (1) for lessee and lessor arrangements within all asset classes, combine lease and non-lease components as a single component, with the lease expense recognized over the expected term on a straight-line basis and (2) for lessee arrangements, apply short-term lease exemption for all leases that qualify, where a right-of-use asset or lease liability will not be recognized for leases with terms of one year or less. Recently Adopted Accounting Pronouncements ASU No. 2018-07, Compensation — Stock Compensation In June 2018, the FASB issued ASU No. 2018-07, Compensation — Stock Compensation (Topic 718), Improvements to Non-Employee Share-Based Payment Accounting (“ASU 2018-07”). This ASU is intended to simplify aspects of share-based compensation issued to non-employees by making the guidance consistent with the accounting for employee share-based compensation. For public entities, ASU 2018-07 is required to be adopted for annual periods beginning after December 15, 2018, including interim periods within those fiscal years. For non-public entities, ASU 2018-07 is effective for annual periods beginning after December 15, 2019. Early adoption was permitted for all entities but no earlier than the Company’s adoption of ASU 2014-09. During the third quarter of 2018, the Company adopted ASU 2018-07 with an effective date of January 1, 2018 by remeasuring outstanding equity-classified awards issued to non-employees for which a measurement date had not been established through a cumulative-effect adjustment to accumulated deficit as of January 1, 2018. The Company has elected to estimate the expected term of options utilizing the “simplified” method for both employee and non-employee options that qualify as “plain-vanilla” options. The Company has elected to account for forfeitures for non-employee options as they occur rather than apply an estimated forfeiture rate to stock-based compensation expense . The following table summarizes the cumulative effect to the Company’s condensed consolidated balance sheet upon the adoption of ASU 2018-07 on January 1, 2018 (in thousands): Balance at Balance at December 31, 2017 Adjustments January 1, 2018 Additional paid-in capital $ 17,277 $ (92) $ 17,185 Accumulated deficit (60,979) 92 (60,887) The $0.1 million adjustment is the result of the change in fair value of the unvested awards, representing awards for which a measurement date had not been established, using an expected term rather than the contractual term of the awards. As of the adoption date of January 1, 2018, the Company had 330,917 outstanding options to non-employees for which a measurement date had not been established. As of the adoption date of January 1, 2018, the Company had 4,767,014 shares of restricted common stock held by non-employees that were being accounted for as stock options for which a measurement date had not been established. The weighted average fair value of these awards was $5.88 per share as of January 1, 2018. The following table presents, on a weighted average basis, the assumptions used in the Black-Scholes option-pricing model to determine the fair value of outstanding awards granted to non-employees for which a measurement date had not been established as of the adoption date of January 1, 2018: Risk-free interest rate 2.3 % Expected volatility 74 % Expected dividend yield — Expected term (in years) 6.1 Common stock value $ 6.28 ASU No. 2016-02, Leases In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) (“ASU 2016-02”), which sets out the principles for the recognition, measurement, presentation and disclosure of leases for both parties to a contract (i.e., lessees and lessors). The new standard requires lessees to classify leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the lessee. This classification determines whether lease expense is recognized over the lease term based on an effective interest method for financing leases or on a straight-line basis for operating leases. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than 12 months regardless of their classification. Leases with a term of 12 months or less may be accounted for similar to previous guidance for operating leases under ASC 840. For public entities, the guidance was effective for annual reporting periods beginning after December 15, 2018 and for interim periods within those fiscal years. ASU 2016-02 initially required adoption using a modified retrospective approach, under which all years presented in the financial statements would be prepared under the revised guidance. In July 2018, the FASB issued ASU 2018-11, Leases (Topic 842) , which added an optional transition method under which financial statements may be prepared under the revised guidance for the year of adoption, but not for prior years. Under the latter method, entities will recognize a cumulative catch-up adjustment to the opening balance of retained earnings in the period of adoption. The Company adopted ASC 842 using the modified retrospective approach with an effective date of January 1, 2019 for leases that existed on that date. Prior period results continue to be presented under ASC 840 based on the accounting standards originally in effect for such periods. This standard provides a number of optional practical expedients in transition. The Company applied the package of practical expedients to leases that commenced prior to the effective date, whereby it elected not to reassess the following: (i) whether any expired or existing contracts contain leases; (ii) the lease classification for any expired or existing leases; and (iii) initial direct costs for any existing leases. The Company elected the short-term lease recognition exemption for all leases that qualify, where a right-of-use asset or lease liability will not be recognized for short term leases that have terms of one year or less. The most significant effects of adoption were the recognition of material new right-of-use assets and corresponding liabilities on its condensed consolidated balance sheet related to its existing facility operating leases (see Note 12). In addition, the Company has a material lease where the Company was deemed the owner during the construction period and for which the construction was not complete as of January 1, 2019. The Company took control of the leased space during the first quarter of 2019 at which time the lease commenced. Under ASC 842, as the commencement date of this material lease had not occurred, the new right-of-use assets and corresponding liabilities related to this lease were not recognized on the condensed consolidated balance sheet as of date of adoption, January 1, 2019, however, were recognized upon the commencement date of January 28, 2019. The adoption of this standard has had a material impact on the Company’s financial position but is not expected to significantly affect the Company’s results of operations. The following table summarizes the financial impact on the Company’s condensed consolidated balance sheet upon the adoption of ASU 2016-02 and the cumulative effect adjustment on January 1, 2019 (in thousands): Balance at Balance at December 31, 2018 Adjustments January 1, 2019 Operating lease, right-of-use-asset $ — $ 1,751 $ 1,751 Property, plant and equipment, net 62,796 (45,142) 17,654 Deferred rent 143 (143) — Accrued expenses and other current liabilities 12,118 (4,451) 7,667 Lease liability, net of current portion 41,441 (41,441) — Operating lease liabilities — 616 616 Operating lease liabilities, net of current portion — 1,226 1,226 Accumulated deficit (150,082) 800 (149,282) ASU No. 2018-15, Intangibles–Goodwill and Other–Internal-Use Software In August 2018, the FASB issued ASU No. 2018-15, Intangibles–Goodwill and Other–Internal-Use Software (Topic 350): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That is a Service Contract. This new guidance aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. For public entities, the guidance is effective for annual reporting periods beginning after December 15, 2019 and for interim periods within those fiscal years. Early adoption is permitted. The Company early-adopted this standard on January 1, 2019 on a prospective basis. The adoption did not have a material impact on the Company’s condensed consolidated financial statements. Recently Issued Accounting Pronouncements In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement (“ASU 2018-13”), which modifies the disclosure requirements for fair value measurements. For all entities, this guidance is required to be adopted for annual periods beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted. The Company currently is evaluating the impact the adoption of ASU 2018-13 may have on its disclosures.

Investments and Fair Value of F

Investments and Fair Value of Financial Assets and Liabilities	9 Months Ended
	Sep. 30, 2019
Investments and Fair Value of Financial Assets and Liabilities
Investments and Fair Value of Financial Assets and Liabilities	3. Investments and Fair Value of Financial Assets and Liabilities Investments by security type consisted of the following (in thousands): September 30, 2019 Amortized Cost Gross Gross Fair Value U.S. treasury bills and notes (due within one year) $ 201,045 $ 165 $ (8) $ 201,202 U.S. government agency bonds (due within one year) 13,867 9 — 13,876 $ 214,912 $ 174 $ (8) $ 215,078 December 31, 2018 Amortized Cost Gross Gross Fair Value U.S. treasury notes (due within one year) $ 79,312 $ — $ (26) $ 79,286 U.S. government agency bonds (due within one year) 17,704 — (3) 17,701 $ 97,016 $ — $ (29) $ 96,987 The following tables present the Company’s fair value hierarchy for its assets and liabilities, which are measured at fair value on a recurring basis (in thousands): Fair value measurements at September 30, 2019 using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 109,611 $ — $ — $ 109,611 Investments: U.S. government agency bonds — 13,876 — 13,876 U.S. treasury bills and notes — 201,202 — 201,202 $ 109,611 $ 215,078 $ — $ 324,689 Fair value measurements at December 31, 2018 using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 282,160 $ — $ — $ 282,160 U.S. treasury bills — 24,904 — 24,904 Investments: U.S. government agency bonds — 17,701 — 17,701 U.S. treasury notes — 79,286 — 79,286 $ 282,160 $ 121,891 $ — $ 404,051 U.S. government money market funds were valued by the Company based on quoted market prices, which represent a Level 1 measurement within the fair value hierarchy. U.S. treasury notes and U.S. government agency bonds were valued by the Company using quoted prices in active markets for similar securities, which represent a Level 2 measurement within the fair value hierarchy. There have been no changes to the valuation methods during the nine months ended September 30, 2019. The Company evaluates transfers between levels at the end of each reporting period. There were no transfers between Level 1, Level 2 or Level 3 during the nine months ended September 30, 2019.

Property, Plant and Equipment,

Property, Plant and Equipment, Net	9 Months Ended
	Sep. 30, 2019
Property, Plant and Equipment, Net.
Property, Plant and Equipment, Net	4. Property, Plant and Equipment, Net Property, plant and equipment, net consisted of the following (in thousands): September 30, 2019 December 31, 2018 Laboratory equipment $ 14,763 $ 7,122 Land 1,300 1,300 Leasehold improvements 446 117 Computer equipment 1,001 276 Furniture and fixtures 1,214 — Construction-in-progress 37,727 55,828 56,451 64,643 Less: Accumulated depreciation and amortization (3,973) (1,847) $ 52,478 $ 62,796 Upon adoption of ASU 2016-02 (Topic 842), the existing construction-in-progress balance within property and equipment, and the corresponding build-to-suit facility lease financing obligation balance were derecognized, resulting in a reduction to construction-in-progress of $45.1 million (see Note 2). Manufacturing Facility On July 31, 2018, the Company completed its purchase of a 135,000 square foot manufacturing facility located in Smithfield, Rhode Island for a purchase price of $8.0 million. In August 2018, the Company began renovations to customize this facility to manufacture clinical supply of its product candidates. Of the total purchase price, $1.3 million was allocated to the value of land acquired based on the value of comparable assets, and $6.7 million was allocated to construction in progress, as the building was not ready for its intended use. During the nine months ended September 30, 2019, the Company capitalized approximately $15.3 million in construction-in-progress for design, demolition and construction costs related to the renovation project. Construction-in-progress capitalized to date totaled $17.3 million. During the nine months ended September 30, 2019, the Company capitalized $11.5 million in construction-in-progress for manufacturing equipment to be used in the facility. In addition, the Company capitalized interest of $0.3 million and personnel-related costs of $1.3 million during the nine months ended September 30, 2019 and to date during the construction period.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	9 Months Ended
	Sep. 30, 2019
Accrued Expenses and Other Current Liabilities
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): September 30, 2019 December 31, 2018 Accrued employee compensation and benefits $ 4,797 $ 3,377 Accrued external research and development expenses 3,265 2,252 Accrued manufacturing facility expenses 4,949 — Accrued general and administrative expenses 1,539 1,676 Other 316 311 $ 14,866 $ 7,616

Debt

Debt	9 Months Ended
	Sep. 30, 2019
Debt
Debt	6. Debt The Company was party to a loan and security agreement, as amended (the “2015 Credit Facility”), under which the Company had borrowed an aggregate of $5.5 million. Until May 2018, borrowings under the 2015 Credit Facility bore interest at an annual rate equal to the bank’s prime rate plus 1.25%, subject to a floor of 4.5%, and were repayable in monthly interest-only payments through May 2018 and in equal monthly payments of principal plus accrued interest from June 2018 until the maturity date in November 2019. In May 2018, the Company further amended the 2015 Credit Facility to modify the interest rate and extend the interest-only payment period and the maturity date. Subsequent to this amendment, outstanding borrowings under the 2015 Credit Facility bore interest at an annual rate equal to the bank’s prime rate plus 0.75%, subject to a floor of 5.5%, and were repayable in monthly interest-only payments through May 2019 and in equal monthly payments of principal plus accrued interest from June 2019 until the scheduled maturity date in November 2020. In December 2018, the Company repaid all borrowings under the 2015 Credit Facility. The aggregate principal amount of the loan outstanding at the time of repayment was $5.5 million and the Company did not incur any penalties as a result of the repayment. The Company recognized a loss on the extinguishment of the 2015 Credit Facility of less than $0.1 million related to the unamortized debt discount at the time of repayment. The loss on extinguishment was recorded as additional interest expense. 2018 Credit Facility On December 21, 2018 (the “Closing Date”), the Company entered into a loan and security agreement (the “Loan Agreement”) with Solar Capital Ltd. as collateral agent for the lenders party thereto for an aggregate principal amount of $75.0 million. The aggregate principal amount will be funded in three tranches of term loans of $25.0 million each. On the Closing Date, the Company made an initial borrowing of $25.0 million. In June 2019, the Company made a second borrowing of $25.0 million. The third tranche will be available to the Company through June 30, 2020, subject to the satisfaction of certain financial covenants. Interest on the outstanding loan balance will accrue at a rate of the one-month U.S. LIBOR rate plus 5.50%. Monthly principal payments will commence 36 months after the Closing Date and will be amortized over the following 24 months. Certain backend fees are due to the lender at the time of final repayment based on the total funded term loans. The Company accrues the backend fees that will be due at final repayment to outstanding debt by charges to interest expense over the term of the loans using the effective-interest method. The term loans are subject to a prepayment fee of 1.00% in the first year, 0.50% in the second year and 0.25% in the third year. In conjunction with 2018 Credit Facility, the Company incurred issuance costs of $0.8 million. The Loan Agreement contains financial covenants that require the Company to maintain either a certain minimum cash balance or a minimum market capitalization threshold. The Company was in compliance with all such covenants as of September 30, 2019. The Loan Agreement contains customary representations, warranties and covenants and also includes customary events of default, including payment defaults, breaches of covenants, change of control and a material adverse change default. Upon the occurrence of an event of default, a default interest rate of an additional 4.00% per annum may be applied to the outstanding loan balances, and the lenders may declare all outstanding obligations immediately due and payable. Borrowings under the Loan Agreement are collateralized by substantially all of the Company’s assets, other than its intellectual property. As of September 30, 2019, the estimated future principal payments due were as follows (in thousands): Year ending December 31, 2019 (three months ending December 31) $ — 2020 — 2021 — 2022 25,000 Thereafter 25,000 $ 50,000

Convertible Preferred Stock

Convertible Preferred Stock	9 Months Ended
	Sep. 30, 2019
Convertible Preferred Stock.
Convertible Preferred Stock	7. Convertible Preferred Stock The Company had issued Series A redeemable convertible preferred stock (the “Series A Preferred Stock”), Series B convertible preferred stock (the “Series B Preferred Stock”) and Series C convertible preferred stock (the “Series C Preferred Stock”). In February 2018, the Company issued and sold 7,912,432 shares of Series C Preferred Stock at a price of $12.79 per share for gross proceeds of $101.2 million. The Company incurred issuance costs in connection with the Series C Preferred Stock of $0.2 million. Upon the closing of the IPO in July 2018, all 51,845,438 shares of the Company’s outstanding convertible preferred stock automatically converted into shares of common stock and, therefore, there was no outstanding preferred stock at September 30, 2019 and December 31, 2018, respectively.

Warrants to Purchase Convertibl

Warrants to Purchase Convertible Preferred Stock	9 Months Ended
	Sep. 30, 2019
Warrants to Purchase Convertible Preferred Stock.
Warrants to Purchase Convertible Preferred Stock	8. Warrants to Purchase Convertible Preferred Stock During 2015 and 2017, the Company issued warrants to purchase up to 133,333 shares of Series A Preferred Stock and 2,234 shares of Series B Preferred Stock, respectively, in connection with the 2015 Credit Facility and an amendment to the 2015 Credit Facility (see Note 6). The warrants were exercisable at a price of $0.60 per share and $8.39 per share for the 2015 and 2017 issuances, respectively, and had a contractual term of ten years from issuance. The fair value of the warrants on the issuance date was recorded as a debt discount and as a preferred stock warrant liability. The Company remeasured the fair value of the liability for these preferred stock warrants at each reporting date and recorded any adjustments as other income (expense). The warrants outstanding at each reporting date were remeasured using the Black-Scholes option-pricing model, and the resulting change in fair value was recorded in other income (expense) in the Company’s condensed consolidated statements of operations and comprehensive loss. For the year ended December 31, 2018, the Company recorded other expense of $2.2 million to reflect the change in fair value of these preferred stock warrants. Upon the closing of the IPO in July 2018, the Company’s outstanding warrants to purchase preferred stock automatically became warrants to purchase an aggregate of 135,567 shares of common stock. In July 2018, the holders of such warrants completed a cashless exercise of the warrants, resulting in the Company’s issuance of 131,273 shares of common stock, whereby 4,294 shares of common stock were withheld by the Company to pay for the exercise price of the warrants.

Equity

Equity	9 Months Ended
	Sep. 30, 2019
Equity
Equity	9. Equity Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. Common stockholders are not entitled to receive dividends, unless declared by the board of directors. In February 2018, the Company increased the number of authorized shares of common stock from 65,000,000 shares to 75,000,000 shares. In April 2018, the Company increased the number of authorized shares of common stock from 75,000,000 shares to 78,800,000 shares. In June 2018, the Company increased the number of authorized shares of common stock from 78,800,000 shares to 79,000,000 shares. On July 20, 2018, the Company filed a restated certificate of incorporation in the State of Delaware, which, among other things, restated the number of shares of all classes of stock that the Company has authority to issue to 160,000,000 shares, consisting of (i) 150,000,000 shares of common stock, $0.001 par value per share, and (ii) 10,000,000 shares of preferred stock, $0.001 par value per share. The shares of preferred stock are currently undesignated. Also on July 20, 2018, the Company completed its IPO, pursuant to which it issued and sold 12,055,450 shares of common stock, inclusive of 1,572,450 shares sold by the Company pursuant to the full exercise of the underwriters’ option to purchase additional shares. The aggregate net proceeds received by the Company from the IPO were $254.3 million, after deducting underwriting discounts and commissions and other offering costs. Upon the closing of the IPO, all of the shares of the Company’s outstanding convertible preferred stock then outstanding automatically converted into 51,845,438 shares of common stock (see Note 7). On August 1, 2019, the Company entered into a Distribution Agreement (the “Distribution Agreement”) with J.P. Morgan Securities LLC, Jefferies LLC and SVB Leerink LLC (the “Sales Agents”), pursuant to which the Company may issue and sell, from time to time, shares of its common stock having an aggregate offering price of up to $100.0 million through the Sales Agents. The Company’s registration statement on Form S-3 filed on August 1, 2019 was declared effective on August 21, 2019. The Sales Agents may sell common stock by any method permitted by law deemed to be an “at the market offering” as defined in Rule 415(a)(4) of the Securities Act of 1933, as amended, including sales made directly on or through the Nasdaq Global Select Market or any other existing trade market for the common stock, in negotiated transactions at market prices prevailing at the time of sale or at prices related to prevailing market prices, or any other method permitted by law. The Sales Agents will be entitled to receive 3.0% of the gross sales price per share of common stock sold pursuant to the Distribution Agreement. As of September 30, 2019, no shares of common stock have been issued and sold pursuant to the Distribution Agreement.

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2019
Stock-Based Compensation
Stock-Based Compensation	10. Stock-Based Compensation Service-Based Stock Options During the nine months ended September 30, 2019, the Company granted options with service-based vesting conditions for the purchase of 2,519,604 shares of common stock with a weighted average exercise price of $13.65 per share and a weighted average grant-date fair value of $9.25 per share. Stock-Based Compensation The Company recorded stock-based compensation expense in the following expense categories of its condensed consolidated statements of operations and comprehensive loss (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Research and development expenses $ 2,195 $ 1,347 $ 6,798 $ 2,331 General and administrative expenses 8,163 8,540 23,642 16,071 $ 10,358 $ 9,887 $ 30,440 $ 18,402 As of September 30, 2019, total unrecognized compensation cost related to the unvested stock-based awards was $76.9 million, which is expected to be recognized over a weighted average period of 2.3 years.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2019
Commitments and Contingencies
Commitments and Contingencies	11. Commitments and Contingencies License Agreement with the Whitehead Institute for Biomedical Research The Company has a license agreement with the Whitehead Institute for Biomedical Research (“WIBR”), as amended, under which the Company has been granted an exclusive, sublicensable, nontransferable license under certain patent families related to the development of the Company’s red cell therapies (the “WIBR License”). The Company is obligated to pay WIBR annual license maintenance fees of less than $0.1 million, as well as patent-related costs, including legal fees, and low single-digit royalties based on annual net sales of licensed products and licensed services by the Company and its sublicensees. Based on the progress the Company makes in the advancement of products covered by the licensed patent rights, the Company is required to make aggregate milestone payments of up to $1.6 million upon the achievement of specified preclinical, clinical and regulatory milestones. In addition, the Company is required to pay to WIBR a percentage of the non-royalty payments that it receives from sublicensees of the patent rights licensed by WIBR. This percentage varies from low single-digit to low double-digit percentages and will be based upon the clinical stage of the product that is the subject of the sublicense. Royalties shall be paid by the Company on a licensed product-by-licensed product and country-by-country basis, beginning on the first commercial sale of such licensed product in such country until expiration of the last valid patent claim covering such licensed product in such country. The Company has the right to terminate the WIBR License in its entirety, on a patent-by-patent or country-by-country basis, at will upon three months’ notice to WIBR. WIBR may terminate the agreement upon breach of contract or in the event of the Company’s bankruptcy, liquidation, insolvency or cessation of business related to the license. 401(k) Plan In January 2018, the Company established a defined-contribution plan under Section 401(k) of the Internal Revenue Code (the “401(k) Plan”). The 401(k) Plan covers all employees who meet defined minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pre-tax basis. The Company will make matching contributions at a rate of 50% of each employee’s contribution up to a maximum employee contribution of 6% of eligible plan compensation. For the three and nine months ended September 30, 2019, the Company made matching contributions of $0.2 million and $0.4 million, respectively. Indemnification Agreements In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, contract research organizations, 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 executive officers 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. The Company has not incurred any material costs as a result of such indemnifications and is not currently aware of any indemnification claims. Legal Proceedings The Company is not currently 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 as incurred the costs related to such legal proceedings.

Leases

Leases	9 Months Ended
	Sep. 30, 2019
Leases
Leases	12. Leases Operating Leases The Company leases its office and laboratory facilities in Cambridge, Massachusetts under two noncancelable operating leases. The first lease expires in September 2021. The second lease is subject to two expiration dates based on two distinct leased spaces, expiring in January 2027 and August 2028. The lease agreements include lease incentives, payment escalations and rent holidays. In January 2018, the Company entered into a lease for office and laboratory space in Cambridge, Massachusetts (the “Initial Space”). The lease term commenced on January 28, 2019 and expires eight years from the commencement date. The Company is entitled to one five-year option to extend, which is not included in the lease term. The initial annual base rent is approximately $3.8 million, and such amount will increase during the initial term by 3% annually on the anniversary of the commencement date. The Company is obligated to pay its portion of real estate taxes and costs related to the premises, including costs of operations, maintenance, repair, replacement and management of the new leased premises. In connection with the lease, the Company maintains a letter of credit for the benefit of the landlord in the amount of $0.9 million, which is collateralized by a cash deposit of the same amount. The lease agreement allows for a landlord-provided tenant improvement allowance of $9.4 million to be applied to the costs of the construction of the leasehold improvements, of which $0.5 million is repayable to the landlord over the term of the lease. In November 2018, the Company entered into a lease amendment for office and laboratory space in the same building (the “Expansion Space”). The lease term for the Expansion Space commenced on August 8, 2019 and expires approximately nine years from the commencement date. The initial annual base rent for the Expansion Space is approximately $2.5 million and such amount will increase by 3% annually on the anniversary of the commencement date. The Company is obligated to pay its portion of real estate taxes and costs related to the Expansion Space, including costs of operations, maintenance, repair, replacement and property management. In connection with the lease amendment, the Company increased the letter of credit held for the benefit of the landlord by $0.6 million, which is collateralized by a cash deposit of the same amount. The lease amendment increased the landlord-provided tenant improvement allowance by $9.2 million, of which $2.0 million is repayable to the landlord over the term of the lease. During 2018, in accordance with ASC 840, Leases, the Company was deemed to be the owner of the lease for the Initial and Expansion Space during the construction period due to certain indemnification provisions within the lease agreement. As a result, as of December 31, 2018, the Company capitalized approximately $45.1 million (equal to the estimated fair value of its leased portion of the premises) as construction-in-progress within property, plant and equipment and recorded a corresponding build-to-suit facility lease financing obligation. Under ASC 842, the Company is no longer considered the accounting owner due to (1) the Company not having the right to obtain or control the leased premises during the construction period, (2) the lessor having no right of payment for the partially constructed assets, and the leased premises are not of a specialized nature and, thus, could be potentially leased to another tenant, and (3) the Company not legally owning or controlling the land on which the property improvements will be constructed. As such, upon adoption of ASU 2016-02 (Topic 842), the existing construction-in-progress balance within property and equipment, and the corresponding build-to-suit facility lease financing obligation balance were derecognized. Subsequently, the Company took control of the Initial Space on January 28, 2019 at which time the lease commenced and the Company assessed and determined the accounting treatment for the asset and corresponding liability under ASC 842. The Company evaluated its vendor contracts to identify embedded leases, if any, and noted that an agreement with a contract manufacturing supplier constituted a lease under ASC 842 as the Company has the right to substantially all the economic benefits from the use of the asset and can direct the use of the asset. The Company entered into the agreement during the first quarter of 2019. The lease commenced during March 2019 and expires 22 months from commencement date with no stated option to extend the term. As the Company’s leases do not provide an implicit rate, the Company utilized its incremental borrowing rate based on information available at the lease commencement date, which represents an internally developed rate that would be incurred to borrow, on a collateralized basis, over a similar term, an amount equal to the lease payments in a similar economic environment. The Company has elected to account for each lease component and its associated non-lease components as a single lease component and, therefore, has allocated all the contract consideration across lease components only. This may result in the initial and subsequent measurement of the balances of the right-of-use asset and lease liability for leases being greater than if the policy election was not applied. Assets under operating lease at September 30, 2019 were $47.9 million. The leases do not include any restrictions or covenants that had to be accounted for under the lease guidance. As of September 30, 2019, minimum lease payments under the Company’s operating leases are as follows (in thousands): Year Ending December 31, 2019 (three months ending December 31) $ 3,284 2020 9,224 2021 7,551 2022 7,186 2023 7,390 2024 7,601 Thereafter 22,058 64,294 Less: imputed interest (15,857) $ 48,437 As of December 31, 2018, minimum commitments under the Company’s operating leases, as required under prior lease guidance in ASC 840, were as follows (in thousands): Year Ending December 31, 2019 $ 5,458 2020 7,141 2021 7,168 2022 6,820 2023 7,024 Thereafter 27,777 $ 61,388 The Company has not entered any material financing leases as of September 30, 2019. Sublease In February 2019, the Company entered into a sublease agreement with a related party to sublease all office and laboratory space under one of the Company’s operating leases in Cambridge, Massachusetts (see Note 14). The term of the sublease agreement commenced in February 2019 and expires at the end of the Company’s lease agreement with the landlord in September 2021, with no option to extend. The annual rent for the subleased premises is equal to the annual rent owed by the Company to the landlord for the leased premises. The sublessee is obligated to pay all real estate taxes and costs related to the subleased premises, including cost of operations, maintenance, repair, replacement and property management. The Company concluded that the sublease is an operating lease. Consistent with the Company’s policy election for lessor operating leases, each lease component and its associated non-lease components is accounted for as a single lease component. As of September 30, 2019, future undiscounted cash inflows under the sublease are as follows (in thousands): Year Ending December 31, 2019 (three months ending December 31) $ 182 2020 735 2021 541 $ 1,458 Lease Portfolio The components of lease cost and supplemental balance sheet information for the Company’s lease portfolio were as follows (in thousands, except term and discount rate amounts): Three Months Ended September 30, Nine Months Ended September 30, 2019 2019 Lease Cost Operating lease cost $ 2,136 $ 4,769 Short-term lease cost 20 116 Variable lease cost 624 1,554 Sublease income (270) (639) Total lease cost $ 2,510 $ 5,800 Operating Leases Operating lease, right-of-use-asset $ 47,911 Operating lease liabilities $ 6,998 Operating lease liabilities, net of current portion $ 41,439 Other information: Weighted average remaining lease term - operating leases 7.70 years Weighted-average discount rate - operating leases

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2019
Net Loss Per Share
Net Loss Per Share	13. Net Loss per Share Basic and diluted net loss per share was calculated as follows (in thousands, except share and per share amounts): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Numerator: Net Loss $ (47,015) $ (26,362) $ (118,986) $ (62,012) Denominator: Weighted average common shares outstanding, basic and diluted 79,115,305 62,311,111 78,357,791 26,662,233 Net loss per share, basic and diluted $ (0.59) $ (0.42) $ (1.52) $ (2.33) The Company’s potential dilutive securities have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share is the same. The Company excluded the following potential common shares from the periods in the table above, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect: September 30, 2019 2018 Restricted common stock 397,252 2,644,423 Stock options to purchase common stock 15,849,584 14,701,283 16,246,836 17,345,706

Related Parties

Related Parties	9 Months Ended
	Sep. 30, 2019
Related Parties
Related Parties	14. Related Parties In April 2013, the Company entered into a services agreement with Flagship Ventures Management, Inc. (“Flagship”), an affiliate of one of its principal stockholders, to provide general and administrative services to the Company, including certain consulting services and the provision of employee health and dental benefit plans for the Company’s employees. The Company recorded general and administrative expense for services received under this agreement of $0.3 million and $0.8 million during the three and nine months ended September 30, 2018, respectively. The Company made cash payments of $0.4 million and $0.8 million for the three and nine months ended September 30, 2018, respectively, related to these services. The Company did not receive services under this agreement during the three and nine months ended September 30, 2019. As of September 30, 2019, the Company had no amounts payable to Flagship for costs related to the services agreement. In February 2019, the Company entered into a sublease agreement with a related party to sublease all office and laboratory space under one of the Company’s operating leases in Cambridge, Massachusetts. The term of the sublease agreement commenced in February 2019 and expires at the end of the Company’s lease agreement with the landlord in September 2021, with no option to extend (see Note 12). Under this agreement, the Company recorded other income of $0.3 million and $0.6 million during the three and nine months ended September 30, 2019, respectively. The Company received cash payments of $0.1 million and $0.4 million during the three and nine months ended September 30, 2019. As of September 30, 2019, the Company recorded accounts receivable of $0.1 million under this agreement.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2019
Summary of Significant Accounting Policies
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 revenue and expenses during the reporting periods. Significant estimates and assumptions reflected in these condensed consolidated financial statements include, but are not limited to, the accrual of research and development expenses, the valuation of common stock and the preferred stock warrant liability prior to the IPO and the valuation of stock-based awards. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates as there are changes in circumstances, facts and experience. Actual results may differ from those estimates or assumptions.
Concentrations of Credit Risk and of Significant Suppliers	Concentrations of Credit Risk and of Significant Suppliers Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents and investments. The Company’s cash, cash equivalents and investments, as of September 30, 2019, consisted of U.S. government money market funds, U.S. government treasury bills, U.S. government agency bonds and U.S. government treasury notes. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. The Company relies, and expects to continue to rely, on a small number of vendors to manufacture supplies and raw materials for its development programs. These programs could be adversely affected by a significant interruption in these manufacturing services or the availability of raw materials.
Cash Equivalents	Cash Equivalents The Company considers all highly liquid investments with original maturities of three months or less at the date of purchase to be cash equivalents.
Restricted Cash	Restricted Cash The Company maintained letters of credit totaling $1.7 million and $1.8 million for the benefit of the landlords of its leased properties , as of September 30, 2019 and December 31, 2018, respectively. As of December 31, 2018, the Company also maintained restricted cash of $0.5 million to collateralize its corporate credit card. The Company was required to maintain separate cash balances of these amounts to secure the letters of credit. Related to these separate cash balances, the Company classified $1.7 million as restricted cash (non-current) in its condensed consolidated balance sheet as of both September 30, 2019 and December 31, 2018, and classified $0.6 million as restricted cash (current) in its condensed consolidated balance sheet as of December 31, 2018. The Company did not have any restricted cash (current) as of September 30, 2019.
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 investments 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 liabilities. The carrying value of the Company’s long-term debt approximates its fair value due to its variable interest rate, which approximates a market interest rate.
Investments	Investments The Company’s investments 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 (deficit). Realized gains and losses and declines in value determined to be other than temporary are based on the specific identification method and are included as a component of other income (expense), net in the condensed consolidated statements of operations and comprehensive loss. The Company classifies its investments with maturities beyond one year as short-term, based on their highly liquid nature and because such investments are available for current operations. The Company evaluates its investments with unrealized losses for other-than-temporary impairment. When assessing investments for other-than-temporary declines in value, the Company considers such factors as, among other things, how significant the decline in value is as a percentage of the original cost, how long the market value of the investment has been less than its original cost, the Company’s ability and intent to retain the investment for a period of time sufficient to allow for any anticipated recovery in fair value and market conditions in general. If any adjustment to fair value reflects a decline in the value of the investment that the Company considers to be “other than temporary,” the Company reduces the investment to fair value through a charge to the statement of operations and comprehensive loss. No such adjustments were necessary during the periods presented.
Leases	Leases In February 2016, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“ASU”) No. 2016-02, Leases (Topic 842) (“ASU 2016-02”), which was codified as Accounting Standards Codification (“ASC”), 842, Leases, to enhance the transparency and comparability of financial reporting related to leasing arrangements. The Company adopted the standard effective January 1, 2019 using the modified retrospective transition method. The prior period results continue to be presented under ASC 840 based on the accounting standards originally in effect for such periods. The adoption of the new standard resulted in the recognition of a cumulative effect adjustment of $0.8 million to accumulated deficit due to the derecognition of the Company’s build-to-suit lease. At the inception of an arrangement as lessee or lessor, the Company determines whether the arrangement is or contains a lease. Operating lease cost is recognized over the lease term on a straight-line basis. Variable lease cost and short-term leases (lease terms less than 12 months) are recognized as incurred. When determining the lease term, the Company includes options to extend or terminate the lease when it is reasonably certain that it will exercise that option. For lessee arrangements, operating lease liabilities and their corresponding right-of-use assets are recorded based on the present value of lease payments over the expected lease term. The interest rate implicit in lease contracts is typically not readily determinable. As such, the Company utilizes its incremental borrowing rate, which is the rate incurred to borrow on a collateralized basis over a similar term an amount equal to the lease payments in a similar economic environment. Certain adjustments to the right-of-use asset may be required for items such as initial direct costs paid or incentives received. Operating leases are recognized on the balance sheet as right-of-use assets, operating lease liabilities current and operating lease liabilities non-current. The Company has elected to adopt the following lease policies in conjunction with the adoption of ASU 2016-02: (1) for lessee and lessor arrangements within all asset classes, combine lease and non-lease components as a single component, with the lease expense recognized over the expected term on a straight-line basis and (2) for lessee arrangements, apply short-term lease exemption for all leases that qualify, where a right-of-use asset or lease liability will not be recognized for leases with terms of one year or less.
Recently Adopted Accounting Pronouncements and Recently Issued Accounting Pronouncements	Recently Adopted Accounting Pronouncements ASU No. 2018-07, Compensation — Stock Compensation In June 2018, the FASB issued ASU No. 2018-07, Compensation — Stock Compensation (Topic 718), Improvements to Non-Employee Share-Based Payment Accounting (“ASU 2018-07”). This ASU is intended to simplify aspects of share-based compensation issued to non-employees by making the guidance consistent with the accounting for employee share-based compensation. For public entities, ASU 2018-07 is required to be adopted for annual periods beginning after December 15, 2018, including interim periods within those fiscal years. For non-public entities, ASU 2018-07 is effective for annual periods beginning after December 15, 2019. Early adoption was permitted for all entities but no earlier than the Company’s adoption of ASU 2014-09. During the third quarter of 2018, the Company adopted ASU 2018-07 with an effective date of January 1, 2018 by remeasuring outstanding equity-classified awards issued to non-employees for which a measurement date had not been established through a cumulative-effect adjustment to accumulated deficit as of January 1, 2018. The Company has elected to estimate the expected term of options utilizing the “simplified” method for both employee and non-employee options that qualify as “plain-vanilla” options. The Company has elected to account for forfeitures for non-employee options as they occur rather than apply an estimated forfeiture rate to stock-based compensation expense . The following table summarizes the cumulative effect to the Company’s condensed consolidated balance sheet upon the adoption of ASU 2018-07 on January 1, 2018 (in thousands): Balance at Balance at December 31, 2017 Adjustments January 1, 2018 Additional paid-in capital $ 17,277 $ (92) $ 17,185 Accumulated deficit (60,979) 92 (60,887) The $0.1 million adjustment is the result of the change in fair value of the unvested awards, representing awards for which a measurement date had not been established, using an expected term rather than the contractual term of the awards. As of the adoption date of January 1, 2018, the Company had 330,917 outstanding options to non-employees for which a measurement date had not been established. As of the adoption date of January 1, 2018, the Company had 4,767,014 shares of restricted common stock held by non-employees that were being accounted for as stock options for which a measurement date had not been established. The weighted average fair value of these awards was $5.88 per share as of January 1, 2018. The following table presents, on a weighted average basis, the assumptions used in the Black-Scholes option-pricing model to determine the fair value of outstanding awards granted to non-employees for which a measurement date had not been established as of the adoption date of January 1, 2018: Risk-free interest rate 2.3 % Expected volatility 74 % Expected dividend yield — Expected term (in years) 6.1 Common stock value $ 6.28 ASU No. 2016-02, Leases In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) (“ASU 2016-02”), which sets out the principles for the recognition, measurement, presentation and disclosure of leases for both parties to a contract (i.e., lessees and lessors). The new standard requires lessees to classify leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the lessee. This classification determines whether lease expense is recognized over the lease term based on an effective interest method for financing leases or on a straight-line basis for operating leases. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than 12 months regardless of their classification. Leases with a term of 12 months or less may be accounted for similar to previous guidance for operating leases under ASC 840. For public entities, the guidance was effective for annual reporting periods beginning after December 15, 2018 and for interim periods within those fiscal years. ASU 2016-02 initially required adoption using a modified retrospective approach, under which all years presented in the financial statements would be prepared under the revised guidance. In July 2018, the FASB issued ASU 2018-11, Leases (Topic 842) , which added an optional transition method under which financial statements may be prepared under the revised guidance for the year of adoption, but not for prior years. Under the latter method, entities will recognize a cumulative catch-up adjustment to the opening balance of retained earnings in the period of adoption. The Company adopted ASC 842 using the modified retrospective approach with an effective date of January 1, 2019 for leases that existed on that date. Prior period results continue to be presented under ASC 840 based on the accounting standards originally in effect for such periods. This standard provides a number of optional practical expedients in transition. The Company applied the package of practical expedients to leases that commenced prior to the effective date, whereby it elected not to reassess the following: (i) whether any expired or existing contracts contain leases; (ii) the lease classification for any expired or existing leases; and (iii) initial direct costs for any existing leases. The Company elected the short-term lease recognition exemption for all leases that qualify, where a right-of-use asset or lease liability will not be recognized for short term leases that have terms of one year or less. The most significant effects of adoption were the recognition of material new right-of-use assets and corresponding liabilities on its condensed consolidated balance sheet related to its existing facility operating leases (see Note 12). In addition, the Company has a material lease where the Company was deemed the owner during the construction period and for which the construction was not complete as of January 1, 2019. The Company took control of the leased space during the first quarter of 2019 at which time the lease commenced. Under ASC 842, as the commencement date of this material lease had not occurred, the new right-of-use assets and corresponding liabilities related to this lease were not recognized on the condensed consolidated balance sheet as of date of adoption, January 1, 2019, however, were recognized upon the commencement date of January 28, 2019. The adoption of this standard has had a material impact on the Company’s financial position but is not expected to significantly affect the Company’s results of operations. The following table summarizes the financial impact on the Company’s condensed consolidated balance sheet upon the adoption of ASU 2016-02 and the cumulative effect adjustment on January 1, 2019 (in thousands): Balance at Balance at December 31, 2018 Adjustments January 1, 2019 Operating lease, right-of-use-asset $ — $ 1,751 $ 1,751 Property, plant and equipment, net 62,796 (45,142) 17,654 Deferred rent 143 (143) — Accrued expenses and other current liabilities 12,118 (4,451) 7,667 Lease liability, net of current portion 41,441 (41,441) — Operating lease liabilities — 616 616 Operating lease liabilities, net of current portion — 1,226 1,226 Accumulated deficit (150,082) 800 (149,282) ASU No. 2018-15, Intangibles–Goodwill and Other–Internal-Use Software In August 2018, the FASB issued ASU No. 2018-15, Intangibles–Goodwill and Other–Internal-Use Software (Topic 350): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That is a Service Contract. This new guidance aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. For public entities, the guidance is effective for annual reporting periods beginning after December 15, 2019 and for interim periods within those fiscal years. Early adoption is permitted. The Company early-adopted this standard on January 1, 2019 on a prospective basis. The adoption did not have a material impact on the Company’s condensed consolidated financial statements. Recently Issued Accounting Pronouncements In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement (“ASU 2018-13”), which modifies the disclosure requirements for fair value measurements. For all entities, this guidance is required to be adopted for annual periods beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted. The Company currently is evaluating the impact the adoption of ASU 2018-13 may have on its disclosures.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2019
Non-employees
Recently Adopted Accounting Pronouncements
Schedule of assumptions used to determine the fair value of stock awards granted	Risk-free interest rate 2.3 % Expected volatility 74 % Expected dividend yield — Expected term (in years) 6.1 Common stock value $ 6.28
ASU 2018-07
Recently Adopted Accounting Pronouncements
Summary of impact of accounting standard adoption	The following table summarizes the cumulative effect to the Company’s condensed consolidated balance sheet upon the adoption of ASU 2018-07 on January 1, 2018 (in thousands): Balance at Balance at December 31, 2017 Adjustments January 1, 2018 Additional paid-in capital $ 17,277 $ (92) $ 17,185 Accumulated deficit (60,979) 92 (60,887)
ASU 2016-02
Recently Adopted Accounting Pronouncements
Summary of impact of accounting standard adoption	The following table summarizes the financial impact on the Company’s condensed consolidated balance sheet upon the adoption of ASU 2016-02 and the cumulative effect adjustment on January 1, 2019 (in thousands): Balance at Balance at December 31, 2018 Adjustments January 1, 2019 Operating lease, right-of-use-asset $ — $ 1,751 $ 1,751 Property, plant and equipment, net 62,796 (45,142) 17,654 Deferred rent 143 (143) — Accrued expenses and other current liabilities 12,118 (4,451) 7,667 Lease liability, net of current portion 41,441 (41,441) — Operating lease liabilities — 616 616 Operating lease liabilities, net of current portion — 1,226 1,226 Accumulated deficit (150,082) 800 (149,282)

Investments and Fair Value of_2

Investments and Fair Value of Financial Assets and Liabilities (Tables)	9 Months Ended
	Sep. 30, 2019
Investments and Fair Value of Financial Assets and Liabilities
Schedule of investments by security type	Investments by security type consisted of the following (in thousands): September 30, 2019 Amortized Cost Gross Gross Fair Value U.S. treasury bills and notes (due within one year) $ 201,045 $ 165 $ (8) $ 201,202 U.S. government agency bonds (due within one year) 13,867 9 — 13,876 $ 214,912 $ 174 $ (8) $ 215,078 December 31, 2018 Amortized Cost Gross Gross Fair Value U.S. treasury notes (due within one year) $ 79,312 $ — $ (26) $ 79,286 U.S. government agency bonds (due within one year) 17,704 — (3) 17,701 $ 97,016 $ — $ (29) $ 96,987
Schedule of financial assets and liabilities measured at fair value on a recurring basis	The following tables present the Company’s fair value hierarchy for its assets and liabilities, which are measured at fair value on a recurring basis (in thousands): Fair value measurements at September 30, 2019 using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 109,611 $ — $ — $ 109,611 Investments: U.S. government agency bonds — 13,876 — 13,876 U.S. treasury bills and notes — 201,202 — 201,202 $ 109,611 $ 215,078 $ — $ 324,689 Fair value measurements at December 31, 2018 using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 282,160 $ — $ — $ 282,160 U.S. treasury bills — 24,904 — 24,904 Investments: U.S. government agency bonds — 17,701 — 17,701 U.S. treasury notes — 79,286 — 79,286 $ 282,160 $ 121,891 $ — $ 404,051

Property, Plant and Equipment_2

Property, Plant and Equipment, Net (Tables)	9 Months Ended
	Sep. 30, 2019
Property, Plant and Equipment, Net.
Schedule of property, plant and equipment, Net	Property, plant and equipment, net consisted of the following (in thousands): September 30, 2019 December 31, 2018 Laboratory equipment $ 14,763 $ 7,122 Land 1,300 1,300 Leasehold improvements 446 117 Computer equipment 1,001 276 Furniture and fixtures 1,214 — Construction-in-progress 37,727 55,828 56,451 64,643 Less: Accumulated depreciation and amortization (3,973) (1,847) $ 52,478 $ 62,796

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	9 Months Ended
	Sep. 30, 2019
Accrued Expenses and Other Current Liabilities
Schedule of accrued expenses and other current liabilities	Accrued expenses and other current liabilities consisted of the following (in thousands): September 30, 2019 December 31, 2018 Accrued employee compensation and benefits $ 4,797 $ 3,377 Accrued external research and development expenses 3,265 2,252 Accrued manufacturing facility expenses 4,949 — Accrued general and administrative expenses 1,539 1,676 Other 316 311 $ 14,866 $ 7,616

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2019
Debt
Schedule of estimated future principal payments due	As of September 30, 2019, the estimated future principal payments due were as follows (in thousands): Year ending December 31, 2019 (three months ending December 31) $ — 2020 — 2021 — 2022 25,000 Thereafter 25,000 $ 50,000

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2019
Stock-Based Compensation
Schedule of allocation of share based compensation	The Company recorded stock-based compensation expense in the following expense categories of its condensed consolidated statements of operations and comprehensive loss (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Research and development expenses $ 2,195 $ 1,347 $ 6,798 $ 2,331 General and administrative expenses 8,163 8,540 23,642 16,071 $ 10,358 $ 9,887 $ 30,440 $ 18,402

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2019
Leases
Schedule of minimum lease payments under the Company’s operating leases	As of September 30, 2019, minimum lease payments under the Company’s operating leases are as follows (in thousands): Year Ending December 31, 2019 (three months ending December 31) $ 3,284 2020 9,224 2021 7,551 2022 7,186 2023 7,390 2024 7,601 Thereafter 22,058 64,294 Less: imputed interest (15,857) $ 48,437 As of December 31, 2018, minimum commitments under the Company’s operating leases, as required under prior lease guidance in ASC 840, were as follows (in thousands): Year Ending December 31, 2019 $ 5,458 2020 7,141 2021 7,168 2022 6,820 2023 7,024 Thereafter 27,777 $ 61,388
Schedule of future undiscounted cash inflows under the sublease	As of September 30, 2019, future undiscounted cash inflows under the sublease are as follows (in thousands): Year Ending December 31, 2019 (three months ending December 31) $ 182 2020 735 2021 541 $ 1,458
Schedule of lease cost and lease liabilities for the Company’s lease portfolio	The components of lease cost and supplemental balance sheet information for the Company’s lease portfolio were as follows (in thousands, except term and discount rate amounts): Three Months Ended September 30, Nine Months Ended September 30, 2019 2019 Lease Cost Operating lease cost $ 2,136 $ 4,769 Short-term lease cost 20 116 Variable lease cost 624 1,554 Sublease income (270) (639) Total lease cost $ 2,510 $ 5,800 Operating Leases Operating lease, right-of-use-asset $ 47,911 Operating lease liabilities $ 6,998 Operating lease liabilities, net of current portion $ 41,439 Other information: Weighted average remaining lease term - operating leases 7.70 years Weighted-average discount rate - operating leases

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2019
Net Loss Per Share
Schedule of calculation of basic and diluted net loss per share attributable to common stockholders	Basic and diluted net loss per share was calculated as follows (in thousands, except share and per share amounts): Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Numerator: Net Loss $ (47,015) $ (26,362) $ (118,986) $ (62,012) Denominator: Weighted average common shares outstanding, basic and diluted 79,115,305 62,311,111 78,357,791 26,662,233 Net loss per share, basic and diluted $ (0.59) $ (0.42) $ (1.52) $ (2.33)
Schedule of dilutive securities excluded from computations of diluted weighted average shares outstanding	September 30, 2019 2018 Restricted common stock 397,252 2,644,423 Stock options to purchase common stock 15,849,584 14,701,283 16,246,836 17,345,706

Nature of the Business and Ba_2

Nature of the Business and Basis of Presentation (Details) - USD ($) $ in Thousands	Jul. 20, 2018	Jul. 31, 2018	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Jan. 01, 2019	Dec. 31, 2018	Dec. 31, 2017
Sale of Equity
Net proceeds after deducting underwriting discounts and commissions and other offering costs										$ 257,866
Net loss			$ (47,015)	$ (39,390)	$ (32,581)	$ (26,362)	$ (21,239)	$ (14,411)	$ (118,986)	$ (62,012)
Accumulated deficit			$ (268,268)						$ (268,268)		$ (149,282)	$ (150,082)	$ (60,979)
Common stock
Sale of Equity
Shares issued (in shares)						12,055,450
Conversion of redeemable convertible preferred stock to common stock (in shares)	51,845,438	51,845,438				51,845,438
IPO
Sale of Equity
Shares issued (in shares)	12,055,450
Net proceeds after deducting underwriting discounts and commissions and other offering costs	$ 254,300
Conversion of redeemable convertible preferred stock to common stock (in shares)		131,273
IPO | Common stock
Sale of Equity
Shares issued (in shares)	12,055,450
Overallotment
Sale of Equity
Shares issued (in shares)	1,572,450

Summary of Significant Accoun_4

Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Jan. 01, 2018
Restricted cash for the benefit of the landlords of leased properties	$ 1,700			$ 1,800
Restricted cash to collateralize corporate credit card				500
Restricted cash (non-current)	$ 1,735			1,735
Restricted cash (current)				$ 622
Change in fair value of the unvested awards					$ 100
ASU 2016-02
Change in fair value of the unvested awards		$ 800
Accumulated deficit | ASU 2016-02
Change in fair value of the unvested awards		$ 800	$ 800

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Recently Adopted Accounting Pronouncements (Details) - USD ($)	Jan. 01, 2018	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Recently Adopted Accounting Pronouncements
Additional paid-in capital		$ 575,365,000				$ 543,040,000				$ 17,277,000
Accumulated deficit		(268,268,000)			$ (149,282,000)	(150,082,000)				(60,979,000)
Change in fair value of the unvested awards	$ 100,000
Financial impact on the Company’s condensed consolidated balance sheet upon the adoption of ASUs and the cumulative effect adjustment
Operating lease, right-of-use-asset		47,911,000			1,751,000
Property, plant and equipment, net		52,478,000			17,654,000	62,796,000
Deferred rent						143,000
Accrued expenses and other current liabilities					7,667,000	12,118,000
Lease liability, net of current portion						41,441,000
Operating lease liabilities, current portion		6,998,000			616,000	4,502,000
Operating lease liabilities, net of current portion		41,439,000			1,226,000	41,441,000
Stockholders Equity		$ 307,343,000	$ 343,644,000	$ 371,636,000		$ 393,008,000	$ 411,007,000	$ (70,709,000)	$ (55,526,000)	$ (43,687,000)
Non-employees
Assumptions used to determine the fair value of outstanding awards granted
Weighted average grant-date fair value (per share)	$ 5.88
Risk-free interest rate	2.30%
Expected volatility	74.00%
Expected term (in years)	6 years 1 month 6 days
Common stock value	$ 6.28
Restricted Common Stock | Non-employees
Assumptions used to determine the fair value of outstanding awards granted
Number of outstanding options	4,767,014
Stock options | Non-employees
Assumptions used to determine the fair value of outstanding awards granted
Number of outstanding options	330,917
ASU 2018-07
Recently Adopted Accounting Pronouncements
Additional paid-in capital	$ 17,185,000
Accumulated deficit	(60,887,000)
ASU 2016-02
Recently Adopted Accounting Pronouncements
Change in fair value of the unvested awards				$ 800,000
ASU 2016-02 | Adjustments
Recently Adopted Accounting Pronouncements
Accumulated deficit					800,000
Financial impact on the Company’s condensed consolidated balance sheet upon the adoption of ASUs and the cumulative effect adjustment
Operating lease, right-of-use-asset					1,751,000
Property, plant and equipment, net					(45,142,000)
Deferred rent					(143,000)
Accrued expenses and other current liabilities					(4,451,000)
Lease liability, net of current portion					(41,441,000)
Operating lease liabilities, current portion					616,000
Operating lease liabilities, net of current portion					$ 1,226,000
Adjustments for New Accounting Principle, Early Adoption | ASU 2018-07
Recently Adopted Accounting Pronouncements
Additional paid-in capital	(92,000)
Accumulated deficit	$ 92,000

Investments and Fair Value of_3

Investments and Fair Value of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Marketable securities
Amortized Cost	$ 214,912	$ 97,016
Gross Unrealized Gains	174
Gross Unrealized Losses	(8)	(29)
Fair Value	215,078	96,987
Assets:
Investments	215,078	96,987
Transfers between Level 1, Level 2 or Level 3
Transfer from Level 1 to Level 2, assets	0
Transfer from Level 2 to Level 1, assets	0
Transfers into Level 3, assets	0
Transfer out of Level 3, assets	0
Transfer from Level 1 to Level 2, liabilities	0
Transfer from Level 2 to Level 1, liabilities	0
Transfers into Level 3, liabilities	0
Transfer out of Level 3, liabilities	0
U.S. treasury bills and notes
Marketable securities
Amortized Cost	201,045
Gross Unrealized Gains	165
Gross Unrealized Losses	(8)
Fair Value	201,202
Assets:
Investments	201,202
U.S. government agency bonds
Marketable securities
Amortized Cost	13,867	17,704
Gross Unrealized Gains	9
Gross Unrealized Losses		(3)
Fair Value	13,876	17,701
Assets:
Investments	13,876	17,701
U.S. treasury notes
Marketable securities
Amortized Cost		79,312
Gross Unrealized Losses		(26)
Fair Value		79,286
Assets:
Investments		79,286
Recurring
Assets:
Assets	324,689	404,051
Recurring | Money market funds
Assets:
Cash equivalents	109,611	282,160
Recurring | U.S. treasury bills and notes
Marketable securities
Fair Value	201,202
Assets:
Investments	201,202
Recurring | U.S. treasury bills
Assets:
Cash equivalents		24,904
Recurring | U.S. government agency bonds
Marketable securities
Fair Value	13,876	17,701
Assets:
Investments	13,876	17,701
Recurring | U.S. treasury notes
Marketable securities
Fair Value		79,286
Assets:
Investments		79,286
Recurring | Level 1
Assets:
Assets	109,611	282,160
Recurring | Level 1 | Money market funds
Assets:
Cash equivalents	109,611	282,160
Recurring | Level 2
Assets:
Assets	215,078	121,891
Recurring | Level 2 | U.S. treasury bills and notes
Marketable securities
Fair Value	201,202
Assets:
Investments	201,202
Recurring | Level 2 | U.S. treasury bills
Assets:
Cash equivalents		24,904
Recurring | Level 2 | U.S. government agency bonds
Marketable securities
Fair Value	13,876	17,701
Assets:
Investments	$ 13,876	17,701
Recurring | Level 2 | U.S. treasury notes
Marketable securities
Fair Value		79,286
Assets:
Investments		$ 79,286

Property, Plant and Equipment_3

Property, Plant and Equipment, Net (Details) $ in Thousands	Jul. 31, 2018USD ($)ft²	Sep. 30, 2019USD ($)	Sep. 30, 2019USD ($)	Jan. 01, 2019USD ($)	Dec. 31, 2018USD ($)
Property, Plant and Equipment, Net
Property, Plant and Equipment, Gross		$ 56,451	$ 56,451		$ 64,643
Less: Accumulated depreciation and amortization		(3,973)	(3,973)		(1,847)
Property, plant and equipment, net		52,478	52,478	$ 17,654	62,796
Personnel related cost capitalized		1,300
Maximum
Property, Plant and Equipment, Net
Capitalized interest cost		300
Laboratory equipment
Property, Plant and Equipment, Net
Property, Plant and Equipment, Gross		14,763	14,763		7,122
Land
Property, Plant and Equipment, Net
Property, Plant and Equipment, Gross		1,300	1,300		1,300
Purchases and additions	$ 1,300
Leasehold improvements
Property, Plant and Equipment, Net
Property, Plant and Equipment, Gross		446	446		117
Computers and software
Property, Plant and Equipment, Net
Property, Plant and Equipment, Gross		1,001	1,001		276
Furniture and fixtures
Property, Plant and Equipment, Net
Property, Plant and Equipment, Gross		1,214	1,214
Construction-in-progress
Property, Plant and Equipment, Net
Property, Plant and Equipment, Gross		37,727	37,727		$ 55,828
Purchases and additions	$ 6,700	11,500
Build-to-suit lease
Property, Plant and Equipment, Net
Derecognition of property and equipment		45,100	45,100
Manufacturing facility
Property, Plant and Equipment, Net
Square footing of facility acquired | ft²	135,000
Purchases and additions	$ 8,000
Technology Service | Construction-in-progress
Property, Plant and Equipment, Net
Purchases and additions		$ 15,300	$ 17,300

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Accrued Expenses and Other Current Liabilities
Accrued employee compensation and benefits	$ 4,797	$ 3,377
Accrued external research and development expenses	3,265	2,252
Accrued manufacturing facility expenses	4,949
Accrued general and administrative expenses	1,539	1,676
Other	316	311
Accrued expenses and other current liabilities	$ 14,866	$ 7,616

Debt (Details)

Debt (Details) $ in Thousands	Dec. 21, 2018USD ($)tranche	Jun. 30, 2019USD ($)	May 31, 2018	May 31, 2017	Dec. 31, 2018USD ($)	Sep. 30, 2019USD ($)
Estimated future principal payments due
2022						$ 25,000
Thereafter						25,000
Total debt						$ 50,000
2015 Credit Facility
Debt
Principal amount					$ 5,500
Floor rate			5.50%	4.50%
Repayment					5,500
2015 Credit Facility | Maximum
Debt
Loss on extinguishment					$ (100)
2015 Credit Facility | Prime rate
Debt
Variable interest rate			0.75%	1.25%
2018 Credit Facility
Debt
Maximum amount outstanding	$ 75,000
Number of tranche | tranche	3
Borrowing	$ 25,000	$ 25,000
Period for commencing monthly principal payments	36 months
Amortization period	24 months
Prepayment fee in first year	1.00%
Prepayment fee in second year	0.50%
Prepayment fee in third year	0.25%
Issuance costs	$ 800
Debt default interest rate addition (as a percent)	4
2018 Credit Facility | One-month U.S. LIBOR
Debt
Variable interest rate	5.50%
2018 Credit Facility | Term loan
Debt
Borrowing	$ 25,000

Convertible Preferred Stock (De

Convertible Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	Jul. 20, 2018	Jul. 31, 2018	Feb. 28, 2018	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2019	Dec. 31, 2018
Convertible Preferred Stock
Proceeds from issuance of convertible preferred stock					$ 100,986
Payments of initial public offering costs					$ 3,449
Preferred stock outstanding						0	0
Series C convertible preferred stock
Convertible Preferred Stock
Preferred stock issued			7,912,432
Convertible preferred stock issue price (dollars per share)			$ 12.79
Proceeds from issuance of convertible preferred stock			$ 101,200
Payments of initial public offering costs			$ 200
Common stock
Convertible Preferred Stock
Number of common stock issued on conversion	51,845,438	51,845,438		51,845,438

Warrants to Purchase Converti_2

Warrants to Purchase Convertible Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	12 Months Ended
	Jul. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2015
Warrants to purchase convertible preferred stock
Warrants contractual term (in years)			10 years
Other expenses		$ 2.2
IPO
Warrants to purchase convertible preferred stock
Warrants to purchase aggregate	135,567
Issuance of warrants exercise	131,273
Shares withheld to pay exercise price	4,294
Series A redeemable convertible preferred stock
Warrants to purchase convertible preferred stock
Maximum number of preferred shares can purchase from outstanding warrants				133,333
Warrants exercisable price				$ 0.60
Warrants contractual term (in years)				10 years
Series B convertible preferred stock
Warrants to purchase convertible preferred stock
Maximum number of preferred shares can purchase from outstanding warrants			2,234
Warrants exercisable price			$ 8.39

Equity (Details)

Equity (Details) $ / shares in Units, $ in Thousands	Sep. 30, 2019$ / sharesshares	Jul. 20, 2018USD ($)$ / sharesshares	Jul. 31, 2018shares	Sep. 30, 2018shares	Sep. 30, 2019Vote$ / sharesshares	Sep. 30, 2018USD ($)	Aug. 01, 2019USD ($)	Dec. 31, 2018$ / sharesshares	Jun. 30, 2018shares	Apr. 30, 2018shares	Feb. 28, 2018shares	Jan. 31, 2018shares
Equity
Number of votes per share | Vote					1
Common stock, authorized (in shares)	150,000,000	150,000,000			150,000,000			150,000,000	79,000,000	78,800,000	75,000,000	65,000,000
Shares authorized		160,000,000
Common stock, par value (in dollars per share) | $ / shares	$ 0.001	$ 0.001			$ 0.001			$ 0.001
Preferred stock, share authorized (in shares)	10,000,000	10,000,000			10,000,000			10,000,000
Preferred stock, par value (in dollars per share) | $ / shares	$ 0.001	$ 0.001			$ 0.001			$ 0.001
Net proceeds after deducting underwriting discounts and commissions and other offering costs | $						$ 257,866
Common stock
Equity
Shares issued (in shares)				12,055,450
Conversion of redeemable convertible preferred stock to common stock (in shares)		51,845,438	51,845,438	51,845,438
IPO
Equity
Shares issued (in shares)		12,055,450
Net proceeds after deducting underwriting discounts and commissions and other offering costs | $		$ 254,300
Conversion of redeemable convertible preferred stock to common stock (in shares)			131,273
IPO | Common stock
Equity
Shares issued (in shares)		12,055,450
Overallotment
Equity
Shares issued (in shares)		1,572,450
At the market offering
Equity
Shares issued (in shares)	0
Percentage of commission							3.00%
Aggregate offering price | $							$ 100,000

Stock-Based Compensation - Perf

Stock-Based Compensation - Performance based stock options (Details) - Service Based Stock Options - Vesting based on service period	9 Months Ended
	Sep. 30, 2019$ / sharesshares
Stock-Based Compensation
Options granted | shares	2,519,604
Options exercise price	$ 13.65
Weighted average grant-date fair value (per share)	$ 9.25

Stock-Based Compensation - Comp

Stock-Based Compensation - Compensation expense (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Stock-based compensation expense
Stock-based compensation expense		$ 10,358	$ 9,887	$ 30,440	$ 18,402
Unrecognized compensation cost	$ 76,900	76,900		76,900
Unrecognized compensation cost expected to be recognized over a weighted average period	2 years 3 months 18 days
Research and development expenses
Stock-based compensation expense
Stock-based compensation expense		2,195	1,347	6,798	2,331
General and administrative expenses
Stock-based compensation expense
Stock-based compensation expense		$ 8,163	$ 8,540	$ 23,642	$ 16,071

Commitments and Contingencies -

Commitments and Contingencies - Collaborative Arrangements And Non-collaborative Arrangement (Details) - WIBR - Maximum $ in Millions	9 Months Ended
	Sep. 30, 2019USD ($)
Collaborative Arrangements and Non-collaborative Arrangement
Aggregate milestone payments	$ 1.6
License maintenance fees
Collaborative Arrangements and Non-collaborative Arrangement
License costs	$ 0.1

Commitments and Contingencies_2

Commitments and Contingencies - Defined Contribution Plan (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended	9 Months Ended
	Jan. 31, 2018	Sep. 30, 2019	Sep. 30, 2019
Other Commitments [Line Items]
Employer matching contribution (as a percent)	50.00%
Company matching contribution		$ 0.2	$ 0.4
Maximum
Other Commitments [Line Items]
Maximum employee contribution	6.00%

Leases (Details)

Leases (Details) $ in Thousands	1 Months Ended		9 Months Ended
	Nov. 30, 2018USD ($)	Jan. 31, 2018USD ($)Options	Sep. 30, 2019USD ($)leasepropertyitem	Aug. 08, 2019	Jan. 01, 2019USD ($)	Dec. 31, 2018USD ($)
Leases
Number of leases | lease			2
Number of expiration period | item			2
Number of leased properties | property			2
Lease term		8 years		9 years
Extended lease term		5 years
Number of options to renew lease | Options		1
Lessee, Operating Lease, Existence of Option to Extend [true false]		true
Initial annual base rent	$ 2,500	$ 3,800
Base rent incremental (as a percentage)	3.00%	3.00%
Benefit of the landlord secured by cash deposit	$ 600	$ 900
Tenant improvement allowance	9,200	9,400
Tenant improvement repayable to landlord	$ 2,000	$ 500
Construction-in-progress within property and equipment						$ 45,100
Operating lease, right-of-use-asset			$ 47,911		$ 1,751
Embedded lease contracts
Leases
Lease term			22 months
Lessee, Operating Lease, Existence of Option to Extend [true false]			false

Leases - Minimum lease payments

Leases - Minimum lease payments (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Minimum lease payments
2019 (three months ending December 31)	$ 3,284
2020	9,224
2021	7,551
2022	7,186
2023	7,390
2024	7,601
Thereafter	22,058
Payments due	64,294
Less: imputed interest	(15,857)
Operating lease liability	$ 48,437
Operating Leases, Future Minimum Payments, Due Thereafter		$ 27,777
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2019		5,458
2020		7,141
2021		7,168
2022		6,820
2023		7,024
Thereafter		27,777
Total		$ 61,388

Leases - Sublease (Details)

Leases - Sublease (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2019USD ($)
Sublease
Lessee, Operating Sublease, Existence of Option to Extend [true false]	false
Future undiscounted cash inflows under the sublease
2019 (three months ending December 31)	$ 182
2020	735
2021	541
Total	$ 1,458

Leases - Lease Portfolio (Detai

Leases - Lease Portfolio (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Lease Cost
Operating lease cost	$ 2,136	$ 4,769
Short-term lease cost	20	116
Variable lease cost	624	1,554
Sublease income	(270)	(639)
Total lease cost	2,510	5,800
Operating Leases
Operating lease, right-of-use-asset	47,911	47,911	$ 1,751
Operating lease liabilities	6,998	6,998	616	$ 4,502
Operating lease liabilities, net of current portion	$ 41,439	$ 41,439	$ 1,226	$ 41,441
Weighted average remaining lease term - operating leases	7 years 8 months 12 days	7 years 8 months 12 days
Weighted-average discount rate - operating leases	7.58%	7.58%

Net Loss Per Share - Weighted A

Net Loss Per Share - Weighted Average Shares (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator:
Net Loss	$ (47,015)	$ (39,390)	$ (32,581)	$ (26,362)	$ (21,239)	$ (14,411)	$ (118,986)	$ (62,012)
Denominator:
Weighted average common shares outstanding, basic and diluted	79,115,305			62,311,111			78,357,791	26,662,233
Net loss per share, basic and diluted	$ (0.59)			$ (0.42)			$ (1.52)	$ (2.33)

Net Loss Per Share - Antidiluti

Net Loss Per Share - Antidilutive Securities (Details) - shares	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Diluted net loss per share attributable to common stockholders
Antidilutive securities excluded from computation of of diluted weighted average shares outstanding	16,246,836	17,345,706
Restricted Common Stock
Diluted net loss per share attributable to common stockholders
Antidilutive securities excluded from computation of of diluted weighted average shares outstanding	397,252	2,644,423
Stock options
Diluted net loss per share attributable to common stockholders
Antidilutive securities excluded from computation of of diluted weighted average shares outstanding	15,849,584	14,701,283

Related Parties (Details)

Related Parties (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Related Parties
Cash payments	$ 0.1		$ 0.4
Accounts Receivable	0.1		$ 0.1
Option to extend			false
Other income	0.3		$ 0.6
Flagship
Related Parties
Payment of general and administrative expenses		$ 0.3		$ 0.8
Cash payments		$ 0.4		$ 0.8
Amount due to related party	$ 0		$ 0