In October 2014, the Company entered into an agreement to lease office and laboratory space in Cambridge, Massachusetts under an operating lease agreement with a term through January 2020, with an option to extend the term of the lease for an additional five-year period which the Company plans to execute. Upon the execution of the original lease, the Company provided a $0.3 million security deposit. The Company has recorded this security deposit in other assets on the consolidated balance sheets. In January 2016, the Company entered into a ten-year agreement to lease office and laboratory space in Cambridge, Massachusetts under an operating lease agreement, with an option to terminate the lease at the end of the sixth year and an option to extend the term of the lease for an additional three years. Upon the execution of this lease, the Company provided a $2.2 million security deposit, which has been recorded in other assets on the consolidated balance sheets. In addition, the Company had prepaid $2.2 million in lease payments as of December 31, 2018 under the terms of this lease.

The Company recognizes rent expense, inclusive of escalation charges, on a straight-line basis over the initial term of the lease agreements. The Company recorded rent expense of $6.2 million, $6.0 million and $2.7 million during the years ended December 31, 2018, 2017 and 2016, respectively.

Future minimum lease payments under the Company’s property leases as of December 31, 2018 are as follows:

Year Ending December 31,	(In thousands)
2019	$	5,616
2020		4,963
2021		5,507
2022		3,861
Thereafter		-
	$	19,947

In connection with a July 2014 IP license with Caribou Biosciences, Inc. (“Caribou”), a stockholder who held 5.5 percent of the Company’s common stock at December 31, 2018, the Company gained access to sublicensed IP from various academic and professional institutions. Under these sublicenses, the Company may be obligated to pay development and regulatory milestones of up to $6.4 million, sales-based milestones of up to $20.0 million and up to mid-single-digit royalties on net sales of any products covered by issued patents to these entities in certain circumstances.