The Company’s lease portfolio is primarily comprised of operating leases for office, laboratory, and non-GMP pilot plant manufacturing space located in Seattle, WA, Cambridge, MA, and South San Francisco, CA. Operating leases have contractual periods expiring between April 2024 and April 2030. These leases contain various rent abatement periods, after which they require monthly lease payments that may be subject to annual increases throughout the lease term. The Seattle and South San Francisco lease agreements provide the Company with the option to renew for an additional period of five years. The Company is not reasonably certain it will renew these leases, and therefore the renewal options are not considered in the remaining lease term. Certain leases provide the Company the right to make tenant improvements, including the addition of laboratory space, and include a lease incentive allowance.

The following table contains additional information related to our operating leases:

Location	Approximate Square Footage	Commencement Dates	Expiration Dates
Seattle, WA	48,086	March 2019 to September 2020	December 2026 to April 2028
Cambridge, MA	56,859	March 2019 to May 2020	November 2025 to February 2028
South San Francisco, CA	66,075	December 2019 to October 2020	April 2024 to April 2030

Throughout the term of the lease agreements, the Company is responsible for paying certain operating costs, in addition to rent, such as common area maintenance, taxes, utilities, and insurance. These additional charges are considered variable lease costs and are recognized in the period in which the costs are incurred.

	Three Months Ended March 31,
	2021		2020
	(in thousands)
Operating lease cost	$	2,898	$	2,444
Shot-term lease cost		512		470
Variable lease cost		1,087		621
Total lease cost	$	4,497	$	3,535

As of March 31, 2021, the weighted-average remaining lease term was 7.3 years and the weighted-average incremental borrowing rate was 10.72%.

The following table reconciles the Company’s undiscounted operating lease cash flows by fiscal year, to the present value of the operating lease liabilities as of March 31, 2021 (in thousands):

2021 (remaining 9 months)	$	10,300
2022		15,535
2023		15,989
2024		15,663
2025		15,621
2026 and thereafter		42,616
Total undiscounted lease payments		115,724
Less: imputed interest		(36,950	)
Less: tenant improvement allowances		(8,515	)
Present value of operating lease liabilities	$	70,259