Operating Leases—In September 2016, the Company entered into a noncancelable operating lease beginning in November 2016 for office, laboratory and manufacturing space in Bedford, Massachusetts, that expires in October 2021, with an option for an additional three-year term. In 2018, the Company entered into a sublease agreement for the entire leased premises. The rent commencement date of the sublease was December 2018, and the sublease will terminate on the scheduled termination date of the original lease. Under the terms of the sublease, the subtenant is obligated to pay the Company aggregate base rent of approximately $2.7 million over the term of the sublease, based on the same level of rent the Company is obligated to pay the landlord, in addition to a passthrough of operating expenses and real estate taxes charged by the landlord.

In December 2017, the Company entered into a noncancelable operating lease for approximately 67,000 square feet of research and development, manufacturing and general office space in Bedford, Massachusetts. The lease expires in February 2027 with an option for an additional five-year term. Rent became due under the lease in two phases; rent on the first 46,000 square feet started in September 2018 and rent on the remaining 21,000 square feet started in March 2019. The initial annual base rent was $39.50 per square foot and increases by three percent annually. The Company is obligated to pay, on a pro-rata

basis, real estate taxes and operating costs related to the premises. The lease agreement entered into in December 2017 allowed for a tenant improvement allowance not to exceed $10.9 million, which the Company received in full, to be applied to the total cost of tenant improvements to the leased premises. The unamortized balance of the tenant improvement allowance was included in deferred rent incentives and has been recorded as a reduction to operating right-of-use asset upon adoption of the new leasing standards.

The Company maintains letters of credit, secured by restricted cash, for security deposits totaling $1.3 million as of December 31, 2020 and 2019, respectively, in conjunction with its current leases.

The following table summarizes operating lease costs and variable lease costs, as well as sublease income for the year ended December 31, 2020:

Year ended December 31, 2020	Amount (in thousands)
Operating lease costs	$	2,492
Variable lease costs		2,355
Sublease income		(913	)
Net lease cost	$	3,934

The maturities of our operating lease liabilities as of December 31, 2020 were as follows:

	Amount
For the Years Ending December 31,	(in thousands)

2021	$	3,834
2022		2,987
2023		3,077
2024		3,169
Thereafter		7,197
Total undiscounted lease payments	$	20,264
Less: imputed interest		(4,822	)
Present value of operating lease liabilities	$	15,442

The following table summarizes the lease term and discount rate as of December 31, 2020:

	As of December 31, 2020
Weighted-average remaining lease term (years)
Operating leases		5.9
Weighted-average discount rate
Operating leases		9.9	%

The following table summarizes the supplemental cash flow information related to the Company's operating leases for the year ended December 31, 2020.

Year ended

December 31, 2020

(in thousands)

Cash paid for amounts included in the measurement of lease liabilities

3,804