RAPT Therapeutics and Shanghai Jeyou Pharmaceutical Announce Positive Topline Data from Phase 2 Trial of RPT904 (JYB1904) in Chronic Spontaneous Urticaria

Rhea-AI Summary

RAPT (Nasdaq: RAPT) and Shanghai Jeyou announced positive topline Phase 2 results for RPT904 (JYB1904) in chronic spontaneous urticaria (CSU) on Oct 20, 2025. In a randomized, double-blind 137-patient study, RPT904 dosed every 8 weeks (Q8W) or 12 weeks (Q12W) produced numerically greater UAS7 reductions and higher proportions of patients with UAS7=0 at Weeks 8, 12 and 16 versus omalizumab dosed Q4W. RPT904 showed durability to Week 16 after a single dose and was well tolerated with no serious adverse events related to study drug. Jeyou will advance RPT904 to Phase 3 in China; RAPT will discuss a Phase 3 path with the FDA and host a conference call on Oct 20, 2025.

Positive

• Numerically larger UAS7 reductions vs omalizumab at Weeks 8–16
• Higher proportion with UAS7=0 at Weeks 8, 12, 16
• Durable response to a single 300 mg dose out to Week 16
• No serious adverse events related to study drug reported
• Jeyou advancing RPT904 to Phase 3 in China

Negative

• Study was not a formal non-inferiority trial and had no statistical hypothesis testing
• Primary data limited to the initial 16-week treatment period (short follow-up)

Insights

Clinical Development Strategist

Phase 2 topline shows durable efficacy and clean safety, supporting progression to registrational study.

RPT904 produced larger mean reductions in UAS7 versus omalizumab across Week 8, Week 12 and Week 16 (e.g., RPT904 Q8W: -20.51 at Week 8 vs omalizumab -17.00), and higher proportions achieving UAS7=0 at those timepoints (RPT904 Q8W 32.61% at Week 8 to 45.65% at Week 16 vs omalizumab 31.11% to 33.33%). These numerical advantages plus absence of serious drug‑related adverse events support a Phase 3 move from an efficacy and tolerability standpoint.

Risks and dependencies include the study not being a formal non‑inferiority trial and no hypothesis testing performed, so Phase 3 will need pre‑specified statistical margins and larger sample sizes to confirm benefit. Key near‑term items to watch are the planned discussion with the FDA and the design choices for a pivotal program (endpoint selection, non‑inferiority vs superiority margin, sample size) over the next 3–12 months.

Regulatory & Commercial Analyst

Data provide a pathway to Phase 3 in China and regulatory engagement in the U.S.; commercial positioning looks promising if replicated.

Jeyou plans to advance RPT904 to Phase 3 in China and RAPT intends to discuss a Phase 3 path with the FDA after reporting positive topline results on October 20, 2025. The single‑dose durability to Week 16 and less frequent Q8W/Q12W dosing versus standard Q4W dosing could translate into a differentiated patient convenience profile if confirmed in pivotal trials.

Regulatory and commercial triggers include successful protocol agreement with regulators and confirmatory Phase 3 outcomes; expect formal Phase 3 plans and regulatory interactions to emerge within 12 months. Monitor the exact statistical plan agreed with FDA and any Phase 3 safety signals across larger populations as the primary near‑term checkpoints.

-  RPT904 at both Q8W and Q12W dosing showed comparable efficacy and safety to omalizumab at Q4W dosing
-  Efficacy sustained at Week 16 after a single dose of RPT904
-  Well tolerated with no serious adverse events related to study drug
-  Jeyou to advance RPT904 to Phase 3 development in China
-  RAPT to discuss Phase 3 development path with FDA
-  RAPT to host conference call at 8:30 am ET today

SOUTH SAN FRANCISCO, Calif. and SHANGHAI, Oct. 20, 2025 (GLOBE NEWSWIRE) -- RAPT Therapeutics, Inc. (Nasdaq: RAPT), a clinical-stage immunology-based biopharmaceutical company focused on discovering, developing and commercializing novel therapies for patients living with inflammatory and immunological diseases, and Shanghai Jeyou Pharmaceutical Co., Ltd. (Jeyou), formerly called Shanghai Jemincare Pharmaceutical Co., Ltd., a leading pharmaceutical company in China, today announced positive topline data from Jeyou’s Phase 2 trial of RPT904 (JYB1904) as monotherapy in chronic spontaneous urticaria (CSU). The trial, which was conducted in China, was designed to evaluate the safety and efficacy of RPT904 at dosing intervals of 8 weeks (Q8W) and 12 weeks (Q12W) compared to omalizumab dosed every 4 weeks (Q4W). The study was not a formal non-inferiority study and no statistical hypothesis was tested. The results from this study indicate that RPT904 dosed Q8W or Q12W has comparable efficacy and safety to omalizumab dosed Q4W, and the companies believe these results warrant advancing RPT904 to Phase 3 development.

The randomized, double-blind Phase 2 study enrolled 137 adult patients with CSU inadequately controlled by H1 antihistamines for a 16-week treatment period with patients randomized 1:1:1 across three arms. Patients randomized to the RPT904 Q8W arm received 300 mg subcutaneously (SC) at Week 0 and Week 8, while patients randomized to the RPT904 Q12W arm received a single 300 mg dose SC at Week 0 (to represent a dosing interval of at least every 12 weeks). Patients randomized to the omalizumab Q4W arm received 300 mg SC at Weeks 0, 4, 8 and 12. The primary endpoint was change from baseline in the seven-day urticaria activity score (UAS7) at Weeks 8, 12 and 16, and a key secondary endpoint was the proportion of patients with UAS7=0 at Weeks 8, 12 and 16. After the initial 16-week treatment period, patients were followed for an additional 16 weeks without additional treatment. The data reported today are from the initial 16-week treatment period.

The data from both the RPT904 Q8W and Q12W treatment arms showed numerically greater improvements on the UAS7 endpoint and numerically higher proportion of patients with UAS7=0 at all timepoints (Weeks 8, 12 and 16) compared to omalizumab Q4W.

The mean baseline UAS7 scores (±SD) in the RPT904 Q8W, Q12W and omalizumab Q4W arms were 28.7 (±7.2), 28.9 (±6.6) and 28.8 (±7.9), respectively. The least squares mean change from baseline in UAS7 (and 95% confidence interval) at the three time points were:

	RPT904 Q8W (N=46)	RPT904 Q12W (N=46)	omalizumab Q4W (N=45)
Week 8	-20.51 (-23.88, -17.13)	-21.05 (-24.42, -17.67)	-17.00 (-20.39, -13.61)
Week 12	-22.14 (-25.46, -18.82)	-21.73 (-25.04, -18.43)	-18.51 (-21.83, -15.18)
Week 16	-23.20 (-26.49, -19.91)	-22.16 (-25.43, -18.89)	-19.14 (-22.43, -15.86)

The proportion of patients (as a percentage) with UAS7=0 (and 95% confidence interval) at the three time points were:

	RPT904 Q8W (N=46)	RPT904 Q12W (N=46)	omalizumab Q4W (N=45)
Week 8	32.61 (19.53, 48.02)	32.61 (19.53, 48.02)	31.11 (18.17, 46.65)
Week 12	36.96 (23.21, 52.45)	39.13 (25.09, 54.63)	24.44 (12.88, 39.54)
Week 16	45.65 (30.90, 60.99)	43.48 (28.93, 58.89)	33.33 (20.00, 48.95)

RPT904 was well tolerated with no serious adverse events related to study drug and no treatment-related adverse events resulting in treatment discontinuation.

“Based on these positive results, we are preparing to advance JYB1904 to Phase 3,” remarked Mr. Ting Li, President of Jeyou. “We are excited about JYB1904 and our goal is to seek approval as soon as we can with the hope of bringing this important therapy to the many CSU patients in China.”

Ana Maria Giménez-Arnau, M.D., Ph.D., Professor of Dermatology at Hospital del Mar Research Institute, Universitat Pompeu Fabra in Barcelona, remarked, “While omalizumab is the current standard of care for CSU patients, there remains an unmet need for improved therapies. I am particularly intrigued by the data showing RPT904’s deep and durable effect with a single dose. This suggests patients could have the option to go from a treatment that requires monthly dosing to one that can be administered quarterly, which would benefit patients and represent a significant advance in the CSU treatment paradigm.”

Brian Wong, M.D., Ph.D., President and CEO of RAPT, added, “These data exceeded our expectations by not only showing comparable efficacy and safety to omalizumab at Q12W dosing, but also showing durability after a single dose out to Week 16. We believe these data support moving to a pivotal Phase 3 trial in CSU and we plan to discuss our next steps with the FDA and other regulatory authorities. With these encouraging data reported today, we also look forward to initiating our Phase 2b trial in food allergies before the end of the year.”

Webcast Conference Call
RAPT will host a webcast conference call accompanied by a slide presentation today, October 20, 2025 at 8:30 a.m. ET. To join the conference call via phone and participate in the live Q&A session, please pre-register online here to receive a telephone number and unique passcode required to enter the call. The live webcast and audio archive of the presentation may be accessed on the RAPT Therapeutics website at https://investors.rapt.com/events-and-presentations.

About Chronic Spontaneous Urticaria (CSU)
Chronic spontaneous urticaria is a mast cell-driven disorder characterized by the sudden onset of debilitating hives and intense itch. While H1 antihistamines provide symptomatic relief for some, they fail to address the underlying IgE-autoantibody pathology. Consequently, there is a need for therapies that target the upstream IgE-mast cell axis for patients whose CSU is uncontrolled by antihistamines.

About RPT904
RPT904 is a novel, half-life extended anti-IgE bio-better monoclonal antibody (mAb) targeting the same epitope as omalizumab for the treatment of patients with food allergy, chronic spontaneous urticaria and other allergic inflammatory diseases. RPT904 is designed to inhibit free and cell-bound human immunoglobulin E (IgE), a key driver of allergic diseases, and in early clinical studies has demonstrated extended pharmacokinetics and pharmacodynamic properties compared to omalizumab, a first generation anti-IgE mAb.

About RAPT Therapeutics, Inc.
RAPT is a clinical-stage immunology-based biopharmaceutical company focused on discovering, developing and commercializing novel therapies for patients living with inflammatory and immunological diseases. Utilizing our deep and proprietary expertise in immunology, we develop novel therapies that are designed to modulate the critical immune responses underlying these diseases.

About Shanghai Jeyou Pharmaceutical Co., Ltd.
Shanghai Jeyou Pharmaceutical Co., Ltd., originally the R&D center of Jiangxi Jemincare Group Co., Ltd., has now been spun off as an independent entity. Jeyou has built a strong scientific team with comprehensive end-to-end capabilities in drug discovery and development. To date, more than 10 programs have progressed to the clinical stage from Jeyou’s in-house pipeline.

Jiangxi Jemincare Group Co., Ltd. is a leading pharmaceutical company from China. Founded in 1999, Jemincare focuses on the development, manufacturing and commercialization of therapeutics across key strategic fields including oncology, nephrology, cerebro-cardiovascular, analgesic and respiratory health. For more information, please visit www.jemincare.com.

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 “anticipate,” “estimates,” “expects,” “look forward,” “planned,” “potential” “will” and similar expressions (as well as other words or expressions referencing future events, conditions or circumstances) are intended to identify forward-looking statements. These statements relate to future events and involve known and unknown risks, uncertainties and other factors that may cause actual results, performance or achievements to be materially different from any future performances or achievements expressed or implied by the forward-looking statements. Each of these statements is based only on current information, assumptions and expectations that are inherently subject to change and involve a number of risks and uncertainties. Forward-looking statements include, but are not limited to, statements about the efficacy and safety of RPT904, the clinical development of RPT904, including timing of clinical trials and expectations of RAPT and Jeyou to advance RPT904 to phase 3, plans for regulatory interactions, the therapeutic and commercial potential of RPT904, and other statements that are not historical fact. Many factors may cause differences between current expectations and actual results, including unexpected or unfavorable safety or efficacy data observed during clinical studies, preliminary data and trends that may not be predictive of future data or results or that may not demonstrate safety or efficacy or lead to regulatory approval, RAPT’s reliance on its partners and other third parties, clinical trial site activation or enrollment rates that are lower than expected, unanticipated or greater than anticipated impacts or delays due to macroeconomic and geopolitical conditions (including the long-term impacts of ongoing overseas conflicts, tariffs and trade tensions, fluctuations in inflation and interest rates and other economic uncertainty), changes in expected or existing competition, changes in the regulatory environment, the uncertainties and timing of the regulatory approval process and the sufficiency of RAPT’s cash resources. Detailed information regarding risk factors that may cause actual results to differ materially from the results expressed or implied by statements in this press release may be found in RAPT’s Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission (SEC) on August 7, 2025 and subsequent filings made by RAPT with the SEC. These forward-looking statements speak only as of the date hereof. RAPT disclaims any obligation to update these forward-looking statements, except as required by law.

RAPT Investor Contact:
Sylvia Wheeler
swheeler@wheelhouselsa.com

RAPT Media Contact:
Aljanae Reynolds
areynolds@wheelhouselsa.com

FAQ

What did RAPT report on Oct 20, 2025 about RPT904 (RAPT) in CSU?

RAPT and Jeyou reported positive Phase 2 topline data showing RPT904 Q8W and Q12W had numerically greater UAS7 improvement and higher UAS7=0 rates versus omalizumab Q4W through Week 16.

How did RPT904 (JYB1904) perform versus omalizumab in the Phase 2 trial?

RPT904 arms showed numerically larger least-squares mean UAS7 reductions and higher percentages of patients with UAS7=0 at Weeks 8, 12 and 16 versus omalizumab Q4W.

Were there safety concerns in the RPT904 Phase 2 study announced Oct 20, 2025?

No treatment-related serious adverse events were reported and no treatment-related discontinuations occurred during the initial 16-week treatment period.

What are next steps after the Oct 20, 2025 RPT904 Phase 2 results for RAPT (RAPT)?

Jeyou will advance RPT904 to Phase 3 in China and RAPT will discuss a Phase 3 development path with the FDA.

How many patients were enrolled in the RPT904 Phase 2 CSU trial (RAPT)?

The randomized, double-blind Phase 2 study enrolled 137 adult CSU patients randomized 1:1:1 across three arms.

Does the Phase 2 RPT904 data include formal statistical proof of non-inferiority to omalizumab?

No; the study was not a formal non-inferiority trial and did not test a statistical hypothesis.