On August 30, 2019, Synthorx, Inc. entered into a Sub-Sublease (the Sublease) with Avelas Biosciences, Inc. for office and laboratory space located at 11099 North Torrey Pines Road, California (the Premises). The purpose of the Sublease is to provide the Company with additional office and laboratory space in the same building as the Company's existing principal office is located. Under the terms of the Sublease, commencing on or around September 1, 2019 (the Commencement Date), the Company will sublease approximately 7,109 square feet in the Premises (the Rented Area) at the rate of $24,858.23 per month (the Base Rate), with no Base Rate payable for the first six months following the Commencement Date. The Base Rate is scheduled to increase to $25,603.97 per month beginning on March 1, 2021, and the Company is also responsible for certain operating expenses throughout the life of the Sublease. The Sublease will continue until February 29, 2022. The Company has the option to extend the Sublease for one successive one-year term for which the Base Rate would be increased to $26,372.09 per month.