On April 1, 2019, the Company entered into the Head Lease, a direct operating lease for its former headquarters located at 301 Binney Street, Cambridge, MA originally consisting of approximately 114,000 rentable square feet of office and laboratory space on the first and second floors. The Head Lease had a term of 123 months with two five-year extension options and certain expansion rights. The Head Lease also included a letter of credit of $7.7 million, posted with the landlord as a security deposit, which was collateralized by a money market account recorded as restricted cash on the Company’s consolidated balance sheets. The Company had also entered into customary non-disturbance arrangements with the building landlord’s mortgagee and with the property ground lessor recognizing Company’s leasehold interest in this property.

On February 28, 2020, the Company amended the Head Lease. The Lease Amendment partially terminated the Company’s rights and obligations with respect to an approximately 40,000 rentable square feet. The Company continued to lease the remaining space of approximately 74,000 square feet including the area covered by the subleased premise, discussed below. In connection with this Lease Amendment, the Company reduced its remaining lease payments through June 2029 by approximately $41.9 million and paid a $6.3 million termination fee and $0.2 million related to other initial direct costs, which were deferred and recognized over the remaining lease term. The Company’s security deposit was also reduced by approximately $2.7 million to approximately $5.0 million.

The Lease Amendment was determined to be a lease modification that qualified as a change of accounting on the existing lease and not a separate contract. As such, the Right-of-Use (“ROU”) assets and operating lease liabilities were remeasured using an incremental borrowing rate at the date of modification of 9.7%, which resulted in a reduction of the ROU asset of $21.4 million and a reduction in the operating lease liabilities of $23.5 million. The Company recorded the resulting gain of approximately $2.1 million as a component of operating expenses in the condensed consolidated statement of operations and comprehensive loss for the year ended December 31, 2020.

On September 15, 2020, the Company entered into the Second Lease Amendment to its Head Lease. The Second Lease Amendment partially terminated the Company’s rights and obligations with respect to approximately 17,000 rentable square feet (the “Surrender Space”), including 15,700 rentable square feet subleased by the Company to a subtenant. The Company continues to lease approximately 57,000 square feet of space, under terms of the Second Lease Amendment. The Company reduced its remaining lease payments through June 2029 by approximately $16.9 million. The Company paid no termination or other initial direct costs related to the execution of the Second Lease Amendment. The Company’s security deposit was reduced by approximately $1.2 million to approximately $3.8 million,

The Second Lease Amendment was determined to be a lease modification that qualified as a change of accounting on the existing lease and not a separate contract. As such, the ROU assets and operating lease liabilities were remeasured using an incremental borrowing rate at the date of modification of 6.1%, which resulted in a reduction of the ROU asset of $5.9 million and a reduction in the operating lease liabilities of $5.5 million. The Company recorded the resulting loss of approximately $0.4 million as a component of operating expenses in the condensed consolidated statement of operations and comprehensive loss for the year ended December 31, 2020.

On April 30, 2021, the Company entered into a Termination Agreement for its Head Lease as initially amended on February 28, 2020, and further amended on September 15, 2020. Pursuant to the Termination Agreement, the Company surrendered the leased space of approximately 57,000 square feet to the building’s landlord. The Company did not pay any termination fees in connection with the Termination Agreement. As a result of the termination of the Head Lease, the related right-of-use asset was written off, the lease liability was derecognized, and the $3.8 million security deposit was returned to the Company and recorded as part of our cash balance. In total, the Company recognized a loss on the termination of the Head Lease of $0.9 million during the three months ended June 30, 2021. The loss is included in “General and administrative” expenses on our condensed consolidated statement of operations and comprehensive loss.

The Company had an operating lease ROU asset of approximately $43.4 million related to the amended Head Lease recorded in its condensed consolidated balance sheets as of December 31, 2020. The Company had current and non-current operating lease liabilities of approximately $3.3 million and $38.9 million, respectively, related to the amended Head Lease recorded in its consolidated balance sheets as of December 31, 2020.

Lease cost is recognized on a straight-line basis over the lease term. For the three and six months ended June 30, 2021, the Company recognized a total of approximately $0.6 million and $2.2 million, respectively, of total lease costs. Variable lease costs not subject to an index or rate are recognized as incurred. For the three and six months ended June 30, 2021, the Company recognized a total of approximately $0.2 million and $0.7 million, respectively, of variable lease costs related to the Head Lease, as amended.

For the three and six months ended June 30, 2020, the Company recognized a total of approximately $2.2 million and $4.9 million, respectively, of total lease costs and $0.5 million and $1.5 million, respectively, of variable lease costs, related to the Head Lease, as amended.

Supplemental cash flow information related to leases for the six months ended June 30, 2021 is as follows:

	Six Months Ended June 30,
	2021		2020
Decrease in right-of-use assets related to lease modifications and termination	$	42,058	$	21,386
Decrease in operating lease liabilities due to lease modifications and termination	$	41,177	$	23,499
Cash paid for amounts included in the measurement of lease liabilities (in thousands)	$	1,887	$	4,249
Weighted-average remaining lease term of operating leases (in years)		—		9.0
Weighted-average discount rate of operating leases		—		9.7	%

On October 18, 2019, the Company entered into an agreement with a third party to sublease 15,700 rentable square feet of its lease premises under the Head Lease. The sublease was scheduled to expire on June 30, 2029, unless earlier terminated in accordance with the sublease agreement, and had no extension options. The sublease provided for annual base rent of approximately $1.5 million in the first year, which increased on a yearly basis by 3.0% (subject to an abatement of base rent of approximately $0.7 million for the first six months of the sublease). As part of the consideration for the sublease, the sublessee agreed to provide licensed rooms and services within the sublease premises to the Company over the sublease term free of charge. In addition, the sublessee was responsible for its pro rata share of certain costs, taxes and operating expenses related to the subleased space, the consideration for which is variable and is based on the actual operating costs of the lessor. The Company allocated the total consideration in the sublease agreement between the lease and non-lease components in the contract based on their relative standalone prices. The Company determined that the variable consideration related exclusively to non-lease components and would be recognized as incurred. The sublease included an initial security deposit of $0.5 million, which was provided by the sublessee in the form of a letter of credit, and an additional security deposit of $0.4 million within nine months of the sublease commencement.

For the six months ended June 30, 2020, gross sublease income of $0.5 million was recorded related to the sublease. Net sublease income of approximately $0.1 million was recorded in interest and other income in the condensed consolidated statements of operations and comprehensive loss for the six months ended June 30, 2020.

On September 15, 2020, concurrent with execution of the Second Lease Amendment, the Company entered into the Sublease Termination Agreement to terminate its sublease of 15,700 rentable square feet. Under the terms of the Sublease Termination Agreement, the subtenant was relieved of its obligation to provide future cash rental payments to the Company. The agreements requiring the former subtenant to provide licensed rooms and services to the Company free of charge through the original sublease term survived the sublease termination. The Company expects to receive the benefit of the licensed rooms and services beginning in the third quarter of 2021. The letter of credit security deposit related to the sublease was released.

The Company determined that the Sublease Termination Agreement constitutes a non-monetary exchange under ASC 845 Nonmonetary Transactions (“ASC 845”) where, in return for the free rooms and the services, the Company agreed to terminate its rights and obligations under the sublease agreement. In accordance with ASC 845, the Company determined that the accounting for the transaction should be based on the fair value of assets or services involved. The Company estimated the fair value of the rooms and services to be approximately $1.5 million and $2.9 million, respectively. Accordingly, prepaid rooms and services of $4.4 million were recorded upon the sublease termination, of which $1.8 million is recorded in other current assets and $2.6 million is recorded in other assets in the condensed consolidated balance sheets as of June 30, 2021. Termination fee income of $3.1 million was recognized related to the rooms and services, after considering the rent receivable balance of $1.3 million outstanding from the subtenant. The remaining unamortized direct costs of $0.2 million were written off.

The Company determined that the licensed rooms represent a lease under ASC 842. Once the Company obtains control of the rooms, the prepaid rooms balance will be reclassified from other assets to a ROU asset, and the related lease expense will be recorded on a straight-line basis over the lease term. The Company determined that the licensed services represent a non-lease component, which will be recognized separately from the lease component for this asset class. The expense related to the licensed services will be recognized on a straight-line

basis over the period the services are received. Both the lease expense and services expense will be recognized as a component of research and development costs in the consolidated statements of operations and comprehensive loss.