6. Commitments and Contingencies Leases In February 2015, the Company entered into a sublease with a Massachusetts limited liability company (the  sublandlord ) for 15,981 square feet of office space in Boston, Massachusetts. The sublease is subject and subordinate to a prime lease, dated October 5, 2010, between the sublandlord and the prime landlord. The term of the sublease commenced on April 1, 2015 and expires on December 31, 2016. If the term of the prime lease is terminated for any reason prior to the expiration or earlier termination of the sublease, the sublease will terminate immediately and the Company will have no recourse against the sublandlord for such termination. The Company is obligated to make monthly payments under the sublease totaling $408 and $555 for the years ending December 31, 2015 and 2016, respectively, aggregating $963 in total minimum lease payments. In June 2015, the Company entered into a lease for the existing space with the prime landlord (the  landlord ) which effectively extends the term of the lease of the existing space until July 2018. The Company is obligated to make monthly payments under the new lease totaling $839 and $489 for the years ending December 31, 2017 and 2018, respectively, aggregating $1,328 in total minimum lease payments. Total minimum lease payments under both of these operating leases aggregate $2,291 over their full term. Payment escalations specified in the lease agreements are accrued such that rent expense per square foot is recognized on a straight-line basis over the terms of occupancy. Prior to April 2015, the Company leased office space in Cambridge, Massachusetts, and obtained certain office-related services on a month-to-month basis under a 30-day cancelable operating service agreement. The Company recorded exit costs of $133 included in rent expense in the six months ended June 30, 2015 in connection with the termination of the Cambridge lease. During the three months ended June 30, 2015 and 2014, the Company recognized $181 and $103, respecti