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. On August 13, 2018, the Company entered into a sublease agreement for the entire leased premises, with a related party. 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 in addition to passthrough of operating expenses and real estate taxes charged by the landlord. The Company did not record a loss on the sublease as future payments to its landlord were not materially different from future rent payments expected from the subtenant over the term of the sublease.

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 is $39.50 per square foot and will increase 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.

Future minimum lease payments, net of anticipated sublease payments, as of September 30, 2019 are as follows:

For the Years Ending December 31,	Amount (in thousands)
2019	$	697
2020		2,810
2021		2,815
2022		2,987
2023		3,077
Thereafter		10,366
Total future minimum lease payments	$	22,752

The lease agreement entered into in December 2017 allowed for a tenant improvement allowance not to exceed $10.9 million to be applied to the total cost of tenant improvements to the leased premises. The total tenant improvement allowance of $10.9 million was recorded as deferred rent incentives on the Company’s condensed consolidated balance sheets and is being recognized as a reduction to rent expense over the term of the lease. As of September 30, 2019, the remaining balance of deferred rent incentives totaled $8.6 million.

Rent expense, net of amortization of the deferred rent incentives, for the three and nine months ended September 30, 2019 was $0.4 million and $1.0 million, respectively, as compared to $0.5 million and $2.3 million for the three and nine months ended September 30, 2018. The Company maintains letters of credit, secured by restricted cash, for security deposits totaling $1.3 million and $1.8 million as of September 30, 2019 and December 31, 2018, respectively, in conjunction with its current leases.