LEASES

12 Months Ended

Dec. 31, 2023

Overview of Significant Leases

We lease three facilities for office and laboratory space in Cambridge, Massachusetts that represent substantially all of our significant lease obligations. An overview of these significant leases are as follows:

675 West Kendall Street

We lease office and laboratory space located at 675 West Kendall Street, Cambridge, Massachusetts for our corporate headquarters from BMR-675 West Kendall Street, LLC, or BMR, under a non-cancelable real property lease. The lease commenced on May 1, 2018 and monthly rent payments became due commencing on February 1, 2019 upon substantial completion of the building improvements, and continue for 15 years, with options to renew for two five-year terms each. Exercise of these options was not determined to be reasonably certain and thus was not included in the operating lease liability on the consolidated balance sheet as of December 31, 2023.

300 Third Street

We lease office and laboratory space located at 300 Third Street, Cambridge, Massachusetts under a non-cancelable real property lease agreement by and between us and ARE-MA Region No. 28, LLC, or ARE-MA, dated as of September 26, 2003, as amended. The term of the lease expires on January 31, 2034 with options to renew for two five-year terms each. Exercise of these options was not determined to be reasonably certain and thus was not included in the operating lease liability on the consolidated balance sheet as of December 31, 2023.

101 Main Street

We lease office space on several floors at 101 Main Street, Cambridge, Massachusetts under non-cancelable real property lease agreements by and between us and RREEF America REIT II CORP. PPP, or RREEF, entered into in 2015. In 2020, we amended our lease agreement, pursuant to which the term of the lease with respect to two floors was extended for an additional five years, through June 2026, with an option to renew for one five-year term. Exercise of this option was not determined to be reasonably certain and thus was not included in the operating lease liability on the consolidated balance sheet as of December 31, 2023. In addition, we have a separate lease agreement for an additional floor at 101 Main Street, which expires in March 2024 and will not be extended.

Other Lease Disclosures

Our facility leases described above generally contain customary provisions allowing the landlords to terminate the leases if we fail to remedy a breach of any of our obligations under any such lease within specified time periods, or upon our bankruptcy or insolvency. The leases do not include any restrictions or covenants that had to be accounted for under the lease guidance.

Total rent expense, including operating expenses, under all of our real property leases was $61.6 million, $58.6 million and $59.5 million for the years ended December 31, 2023, 2022 and 2021, respectively.

The following table summarizes our costs included in operating expenses related to right of use lease assets we have entered into through December 31, 2023:


	Year Ended December 31,
(In thousands)	2023		2022		2021
Operating lease cost	$	46,367	$	45,789	$	45,359
Variable lease cost	20,278		17,614		18,271
Total	$	66,645	$	63,403	$	63,630

Short-term lease costs were not material for the years ended December 31, 2023 and 2022.

Net cash paid for the amounts included in the measurement of the operating lease liability in our consolidated balance sheet and included in change in operating lease liability within operating activities in our consolidated statement of cash flow was $46.5 million and $43.1 million for the years ended December 31, 2023 and 2022, respectively. The weighted-average remaining lease term and weighted-average discount rate for all leases as of December 31, 2023 was 9 years and 8%, respectively, and as of December 31, 2022 was 10 years and 8%, respectively.

Future lease payments for non-cancellable operating leases and a reconciliation to the carrying amount of the operating lease liability presented in the consolidated balance sheet as of December 31, 2023 were as follows, in thousands:


Year Ending December 31
2024	$	43,587
2025	46,369
2026	40,648
2027	39,006
2028	38,358
2029 and thereafter	210,073
Total undiscounted lease liability	418,041
Less imputed interest	(133,430)
Total discounted lease liability	$	284,611

Current operating lease liability	$	41,510
Non-current operating lease liability	243,101
Total	$	284,611