General and administrative (G&A) expenses for the second quarter ended June 30, 2019 were $3.0 million, compared to $0.6 million for the same period in 2018. For the six months ended June 30, 2019, G&A expenses were $5.4 million, compared to $1.0 million for the same period in 2018. The increase in G&A expenses was primarily attributable to increased personnel and related costs as the company expanded its G&A team to support operations, including additional non-cash stock-based compensation cost of $0.6 million and $0.8 million for the three and six months ended June 30, 2019, as compared to the same periods in 2018. Furthermore, the company incurred additional costs in 2019 that were not incurred during the same period in 2018 as Synthorx now operates as a public company, including additional insurance, legal and accounting fees.

About Synthorx
Synthorx, Inc. is a clinical-stage biotechnology company focused on prolonging and improving the lives of people with cancer and autoimmune disorders. Synthorx' proprietary, first-of-its-kind Expanded Genetic Alphabet platform technology expands the genetic code by adding a new DNA base pair and is designed to create optimized biologics, referred to as Synthorins. A Synthorin is a protein optimized through incorporation of novel amino acids encoded by the new DNA base pair that enables site-specific modifications, which enhance the pharmacological properties of these therapeutics. The company's lead product candidate, THOR-707, a variant of interleukin-2 (IL-2), is in development in multiple tumor types as a single agent and in combination with an immune checkpoint inhibitor. The company was founded based on important discoveries at The Scripps Research Institute. Synthorx is headquartered in La Jolla, Calif. For more information, visit www.synthorx.com.

Forward-Looking Statements
Statements in this press release that are not strictly historical in nature are "forward-looking statements" within the meaning of the Private Securities Litigation Reform Act of 1995. These statements include, but are not limited to, statements related to: plans underlying THOR-707 clinical trials and development; preclinical data or plans underlying any of our other development programs; references to the development of our product candidates; the potential safety and efficacy of THOR-707 and our other product candidates; and the potential advantages of these drug programs. Because such statements are subject to risks and uncertainties, actual results may differ materially from those expressed or implied by such forward-looking statements. Words such as "believes," "anticipates," "plans," "expects," "intends," "will," "goal," "potential" and similar expressions are intended to identify forward-looking statements. These forward-looking statements are based upon the Synthorx's current expectations and involve assumptions that may never materialize or may prove to be incorrect. Actual results and the timing of events could differ materially from those anticipated in such forward-looking statements as a result of various risks and uncertainties, which include, without limitation, risks associated with the process of discovering, developing and commercializing drugs that are safe and effective for use as human therapeutics and operating as a development stage company; Synthorx's ability to develop, initiate or complete preclinical studies and clinical trials for, obtain approvals for and commercialize any of its product candidates; changes in Synthorx's plans to develop and commercialize its product candidates; the potential for clinical trials of THOR-707 or any future clinical trials of other product candidates to differ from preliminary or expected results; Synthorx's ability to raise any additional funding it will need to continue to pursue its business and product development plans; regulatory developments in the United States and foreign countries; Synthorx's reliance on key third parties, including contract manufacturers and contract research organizations; Synthorx's ability to obtain and maintain intellectual property protection for its product candidates; the loss of key scientific or management personnel; competition in the industry in which Synthorx operates; and market conditions. For a more detailed discussion of these and other factors, please refer to Synthorx's filings with the Securities and Exchange Commission. You are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date hereof. All forward-looking statements are qualified in their entirety by this cautionary statement and Synthorx undertakes no obligation to revise or update this press release to reflect events or circumstances after the date hereof, except as required by law.