8. Commitments and Contingencies Operating Leases In 2014, the Company entered into an operating lease and subsequent amendments to lease approximately 46,167 square feet of office and research space in Newton, Massachusetts with a term through September 30, 2022. The lease provided the Company with an allowance for improvements of $1,616 which was incurred in the first quarter of 2015. In February 2018, the lease was amended to extend the term of the lease to September 30, 2025 and expand the leased premises to approximately 62,143 square feet. In June 2018, the lease was further amended to expand the premise to a total of approximately 98,502 square feet with no change to the lease term. The 2018 lease amendments provided the Company with an allowance for improvements of $2,131, which was fully incurred during the year ended December 31, 2018. The Company evaluated the lease amendments and determined that the classification of the lease as an operating lease had not changed, and that the amendments did not constitute a new lease. As such, the unamortized balances of the existing deferred rent and tenant improvement allowances, along with the additions to deferred rent and tenant improvement allowances, are being amortized through September 30, 2025. All improvements were deemed normal tenant improvements, were recorded as leasehold improvements and deferred rent and are being recorded as a reduction to rent expense ratably over the lease term. The Company is recording rent expense on a straight-line basis through the end of the lease term, inclusive of the period in which there are no scheduled rent payments. The Company has recorded deferred rent on the consolidated balance sheets at December 31, 2018 and December 31, 2017, accordingly. Finally, the Company has provided a security deposit in the form of a cash-collateralized letter of credit in the amount of $550. The amount is classified within non-current restricted cash on the consolidated balance sheet. The Company is also party to immaterial operating leases in both Munich, Germany and Tel Aviv, Israel with lease periods through January 2020 and June 2019, respectively. Monthly rent is approximately $8 under the Munich, Germany lease and $11 monthly under the Tel Aviv, Israel lease using December 31, 2018 exchange rates. As of December 31, 2018, the minimum future rent payments under the lease agreements are as follows (in thousands): 2019 $ 3,046 2020 3,208 2021 3,277 2022 3,447 2023 3,718 Thereafter 6,735 Total future minimum lease payments $ 23,431 The Company recorded rent expense totaling $2,480, $1,198 and $1,150 for the years ended December 31, 2018, 2017, and 2016, respectively. Research Agreements In July 2011 and September 2013, the Company entered into research agreements in which the Company received payments upon the achievement of certain milestones. The agreements require the Company to pay royalties on product sales and on a portion of any other sublicense income. The Company made payments of $540 and $2,221 in connection with these agreements in the years ended December 31, 2018 and 2017, respectively, and recorded these amounts to research and development expense. No royalty payments on product sales have been made to date. Litigation From time to time the Company may face legal claims or actions in the normal course of business. The Company is not currently a party to any material litigation and, accordingly, does not have amounts recorded for any litigation-related matters.