Commitments and Contingencies Operating Leases Our administrative offices and research facilities are located in San Diego, California. We lease an aggregate of approximately 80,000 square feet of office and research space in five buildings. The leases commenced in June 2011, November 2013 and June 2018 and continue through January 2023 . The leases are subject to approximately 3.0% annual increases throughout the terms of the leases. We also pay a pro rata share of operating costs, insurance costs, utilities and real property taxes. We received incentives under the leases, including tenant improvement allowances and reduced or free rent, for which the unamortized deferred rent balances associated with these incentives was $1.7 million and $0.3 million as of December 31, 2018 and 2017, respectively. We lease approximately 10,000 square feet of office space for a satellite office located in South San Francisco, California. The lease commenced in November 2015 and continues through January 2021 . The lease is subject to approximately 3.0% annual increases throughout the term of the lease. We also pay a pro rata share of operating costs, insurance costs, utilities and real property taxes. We received incentives under the lease, including tenant improvement allowances and reduced or free rent, for which the unamortized deferred rent balances associated with these incentives was $0.2 million and $0.3 million as of December 31, 2018 and 2017, respectively. Additionally, we lease certain office equipment under operating leases. Total rent expense was approximately $2.5 million , $2.3 million and $2.2 million for the years ended December 31, 2018, 2017 and 2016 , respectively. Approximate annual future minimum operating lease payments as of December 31, 2018 are as follows (in thousands): Year: Operating Leases 2019 $ 2,953 2020 2,995 2021 2,557 2022 2,506 2023 112 Total minimum lease payments $ 11,123 Other Commitments We have existing supply agreements with contract manufacturing organizations Avid Bioservices, Inc. (Avid) and Catalent Indiana LLC (formerly Cook Pharmica LLC) (Catalent) to produce supplies of bulk rHuPH20. Under the terms of the agreements, we are committed to certain minimum annual purchases of bulk rHuPH20. At December 31, 2018 , we had a $14.6 million minimum purchase obligation in connection with these agreements. In June 2011, we entered into a services agreement with Patheon for the technology transfer and manufacture of Hylenex recombinant. At December 31, 2018 , we had a $0.3 million minimum purchase obligation in connection with this agreement. Contingencies We have entered into an in-licensing agreement with a research organization, which is cancelable at our option with 90 days written notice. Under the terms of this agreement, we have received a license to the know-how and technology claimed, in certain patents or patent applications. We are required to pay fees, milestones and/or royalties on future sales of products employing the technology or falling under claims of a patent, and some of the agreements require minimum royalty payments. We continually reassess the value of the license agreement. If the in-licensed and research candidate is successfully developed, we may be required to pay milestone payments of approximately $8.0 million over the life of this agreement in addition to royalties on sales of the affected products. Due to the uncertainties of the development process, the timing and probability of the remaining milestone and royalty payments cannot be accurately estimated. Legal Contingencies From time to time, we may be involved in disputes, including litigation, relating to claims arising out of operations in the normal course of our business. Any of these claims could subject us to costly legal expenses and, while we generally believe that we have adequate insurance to cover many different types of liabilities, our insurance carriers may deny coverage or our policy limits may be inadequate to fully satisfy any damage awards or settlements. If this were to happen, the payment of any such awards could have a material adverse effect on our consolidated results of operations and financial position. Additionally, any such claims, whether or not successful, could damage our reputation and business. We currently are not a party to any legal proceedings, the adverse outcome of which, in managements opinion, individually or in the aggregate, would have a material adverse effect on our consolidated results of operations or financial position.