The Company has operating leases for its corporate office, laboratory space and dedicated space in a vivarium in South San Francisco, California. Rent expense, which is recognized on a straight-line basis over the term of each lease, were $0.6 million and $0.4 million for the three months ended March 31, 2021 and 2020, respectively. The total cash paid for operating leases included in the operating cash flows were $0.4 million and $0.4 million for the three months ended March 31, 2021 and 2020, respectively. The weighted-average remaining lease term was 7.6 years for the corporate office and laboratory space leases as of March 31, 2021. The weighted-average discount rate was 9% as of March 31, 2021.

In May 2020, the Company signed an amendment to its office and laboratory facilities lease. The amended lease provides for an eight-year non-cancelable lease of additional office and laboratory space in the same building. The lease for additional office and laboratory space provides for abatement of rent during the first three months of the lease and contains rent escalations during the term of the lease. The lease for this additional space commenced in January 2021 and expires in January 2029. The lease amendment also includes an extension of the lease term for the existing office and laboratory space beginning on May 1, 2020 and expiring in January 2029. The lease agreement includes an option to extend the lease for an additional seven-year term.

In January 2021, the Company signed a third amendment to its corporate office and laboratory facilities lease which provides for lease of additional space in the same building. The lease of this additional space commenced in April 2021 and expires in March 2024. The other terms of the existing lease remain unchanged.

Maturities of operating lease liabilities under existing operating leases as of March 31, 2021 were as follows (in thousands):

Year ending December 31,	Amount
2021 (remaining nine months)	$	1,674
2022		2,064
2023		2,053
2024		2,125
2025		2,200
2026 and thereafter		7,322
Total future minimum lease payments		17,438
Less imputed interest		(5,013	)
Present value of net minimum lease payments	$	12,425
Operating lease liabilities:
Current		2,151
Non-current		10,274
Total lease liability	$	12,425

Total minimum lease payments of $0.7 million related to the lease of additional space under the amendment were excluded from the table above as the lease agreement had not yet commenced as of March 31, 2021.