Five Prime Therapeutics Presents Initial Safety Data from the Phase 1 Trial of FPT155 at the Society for Immunotherapy of Cancer Annual Meeting

Five Prime Therapeutics, Inc. (NASDAQ: FPRX), a clinical-stage biotechnology company focused on developing immune modulators and precision therapies for solid tumor cancers, today presented initial safety data from the Phase 1 clinical trial of FPT155 in patients with advanced solid tumors in a poster presentation at the Society for Immunotherapy of Cancer (SITC) 34th Annual Meeting in National Harbor, Maryland. The poster can be found on the Publications Page of the Five Prime Therapeutics website.

"FPT155 is a first-in-class CD80 fusion protein with potential dual mechanisms to activate T cells," said Helen Collins, M.D., Executive Vice President and Chief Medical Officer of Five Prime Therapeutics. "Importantly, the initial safety results for FPT155 suggest that it may not cause the same safety issues seen with a prior molecule targeting CD28. This allows us to continue enrolling patients to study additional dose escalation cohorts and identify a dose for future studies."

The FPT155 data presented at SITC included initial safety results from the Phase 1a dose escalation portion of the trial, which is designed to characterize the safety and pharmacokinetic (PK)/pharmacodynamic (PD) profile of FPT155 and identify a recommended dose for the Phase 1b portion of the trial. This included data from 15 patients with solid tumors that were treated with FPT155 at doses of 0.07 mg, 0.21 mg, 0.7 mg, 2.1 mg, 7 mg, 21 mg, and 42 mg. The key highlights from the presentation include:

• FPT155 was well tolerated at all dose levels, with no dose-limiting toxicities and no grade 4 or higher adverse events.
• There is no evidence of clinical or laboratory cytokine release syndrome, an adverse event associated with a prior therapy targeting CD28.
• Dose escalation with FPT155 is ongoing with the study currently enrolling patients at the 70 mg dose level.

The Phase 1a/1b open-label, multicenter, dose escalation, dose exploration and dose expansion study will evaluate the safety and tolerability of FPT155 in patients with advanced solid tumors. The Phase 1a dose escalation portion of the trial will characterize the safety and PK/PD profile of FPT155 and will identify a recommended dose for the Phase 1b portion of the trial. The Phase 1b portion of the trial is intended to further characterize the safety, PK/PD profile, and preliminary efficacy of FPT155.

About FPT155

FPT155 is a first-in-class CD80 fusion protein that (i) directly engages CD28 to enhance its co-stimulatory T-cell activation activity without inducing super agonism, and (ii) blocks CTLA-4 from competing for endogenous CD80, allowing CD28 signaling to prevail in T-cell activation in the tumor microenvironment. FPT155 has also demonstrated its ability to retain anti-tumor activity independent of its engagement with CTLA-4, suggesting a differentiated mechanism of action from CTLA-4-blocking antibodies. Studies in preclinical models suggest FPT155 has the potential to be a potent T-cell co-stimulator with strong monotherapy anti-tumor activity.

About Five Prime Therapeutics

Five Prime Therapeutics, Inc. develops innovative protein therapeutics to improve the lives of patients with cancer. The company focuses on developing immune modulators and precision therapies for solid tumor cancers paired with companion diagnostics to identify patients who are most likely to benefit from treatment with Five Prime's product candidates. The company's product candidates have innovative mechanisms of action and address patient populations in need of better therapies. Five Prime has entered into strategic collaborations with leading global pharmaceutical companies and has promising product candidates in clinical and preclinical development. For more information, please visit www.fiveprime.com.

Cautionary Note on Forward-looking Statements

This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Words such as "may," "will," "expect," "plan," "anticipate," "estimate," "intend" and similar expressions (as well as other words or expressions referencing future events, conditions or circumstances) are intended to identify forward-looking statements. These forward-looking statements are based on Five Prime's expectations and assumptions as of the date of this press release. Each of these forward-looking statements involves risks and uncertainties. Actual results may differ materially from these forward-looking statements. Factors that may cause actual results to differ from those expressed or implied in the forward-looking statements in this press release are discussed in Five Prime's filings with the U.S. Securities and Exchange Commission, including the "Risk Factors" contained therein. Except as required by law, Five Prime assumes no obligation to update any forward-looking statements contained herein to reflect any change in expectations, even as new information becomes available.

Source: Five Prime Therapeutics, Inc.