Commitments and contingencies Operating leases The Company leases office space in South Plainfield, New Jersey for its principal office under three noncancelable operating leases through May 2022, August 2024 and October 2024 in addition to office space in various countries for international employees primarily through workspace providers. Rent expense was approximately $2.7 million , $2.2 million , and $2.2 million for the years ended December 31, 2018 , 2017 , and 2016 , respectively. The Company also leases certain office equipment under operating leases. Future minimum lease payments as of December 31, 2018 are as follows: 2019 $ 3,216 2020 2,900 2021 2,409 2022 2,082 2023 and thereafter 3,321 Total $ 13,928 Other contingencies Under various agreements, the Company will be required to pay royalties and milestone payments upon the successful development and commercialization of products. The Company has entered into funding agreements with The Wellcome Trust Limited (Wellcome Trust) for the research and development of small molecule compounds in connection with its oncology and antibacterial programs. As the Company has discontinued development under its antibacterial program, it no longer expects that milestone and royalty payments from the Company to Wellcome Trust will apply under that agreement, resulting in a change to the total amount of development and regulatory milestone payments the Company may become obligated to pay for this program. Under the oncology program funding agreement, to the extent that the Company develops and commercializes program intellectual property on a for-profit basis itself or in collaboration with a partner (provided the Company retains overall control of worldwide commercialization), the Company may become obligated to pay to Wellcome Trust development and regulatory milestone payments and single-digit royalties on sales of any research program product. The Companys obligation to pay such royalties would continue on a country-by-country basis until the longer of the expiration of the last patent in the program intellectual property in such country covering the research program product and the expiration of market exclusivity of such product in such country. The Company made the first development milestone payment of $0.8 million to Wellcome Trust under the oncology program funding agreement during the second quarter of 2016. Additional milestone payments up to an aggregate of $22.4 million may become payable by the Company to Wellcome Trust under this agreement. The Company has also entered into a collaboration agreement with the SMA Foundation. The Company may become obligated to pay the SMA Foundation single- digit royalties on worldwide net product sales of any collaboration product that is successfully developed and subsequently commercialized or, if the Company outlicenses rights to a collaboration product, a specified percentage of certain payments the Company receives from its licensee. The Company is not obligated to make such payments unless and until annual sales of a collaboration product exceed a designated threshold. The Companys obligation to make such payments would end upon its payment to the SMA Foundation of a specified amount. Pursuant to the Merger Agreement with Agilis, the Company is required to pay $40.0 million of development milestone payments no later than the second anniversary of the closing of the Merger, regardless of whether the applicable milestones have been achieved. The Company may also be obligated to pay additional development, regulatory approval, and net sales milestones and net sales royalties. Refer to Note 3 for further details. The Company also has a Collaboration and License Agreement with Akcea for the commercialization of Tegsedi and Waylivra, and products containing those compounds in countries in Latin America and the Caribbean. Pursuant to the agreement, the Company paid Akcea an upfront licensing fee, which included an initial payment of $12.0 million . An additional $6.0 million is payable within 30 days after receipt of regulatory approval of Waylivra from the FDA or the EMA, whichever occurs earlier. In addition, Akcea is eligible to receive milestone payments, on a Product-by-Product basis, of $4.0 million upon receipt of regulatory approval for a product from ANVISA, the Brazilian Health Regulatory Authority, subject to a maximum aggregate amount of $8.0 million for all such products. Akcea is also entitled to receive royalty payments subject to certain terms set forth in the Akcea Collaboration and License Agreement. The Company has employment agreements with certain employees which require the funding of a specific level of payments, if certain events, such as a change in control or termination without cause, occur. Additionally, the Company has royalty payments associated with Translarna and Emflaza product net sales, payable quarterly or annually in accordance with the terms of the related agreements. From time to time in the ordinary course of our business, we are subject to claims, legal proceedings and disputes, including as a result of patients seeking to participate in our clinical trials or otherwise gain access to our product candidates. We are not currently aware of any material legal proceedings against us.