Positive Topline, Phase 2 Data Announced for RPT904 Monotherapy in CSU

New phase 2 data highlight the potential of RPT904 (JYB1904) to serve as a less frequent dosing alternative to omalizumab for patients with chronic spontaneous urticaria (CSU).1

These findings were announced by RAPT Therapeutics, Inc., and Shanghai Jeyou Pharmaceutical Co., Ltd. RPT904 was designed as a next-generation, half-life–extended anti-IgE monoclonal antibody (mAb) that targets the same epitope as omalizumab.

“While omalizumab is the current standard of care for CSU patients, there remains an unmet need for improved therapies," Ana Maria Giménez-Arnau, MD, PhD, professor of Dermatology at Hospital del Mar Research Institute, Universitat Pompeu Fabra in Barcelona, said in a statement.1 "I am particularly intrigued by the data showing RPT904’s deep and durable effect with a single dose."

The medication was designed to neutralize both free and cell-bound immunoglobulin E (IgE), a central mediator of allergic inflammation. RPT904 may help to provide longer-lasting pharmacokinetic and pharmacodynamic effects compared to omalizumab. It is also being developed for the treatment of food allergies and other allergic inflammatory diseases outside of CSU.

In this phase 2 analysis, conducted in China, investigators looked into the safety and efficacy of RPT904. Participants were randomized (1:1:1) to be treated every 8 weeks (Q8W), every 12 weeks (Q12W), or with omalizumab every 4 weeks (Q4W). The randomized, double-blind study involved 137 adult subjects with CSU inadequately controlled by H1 antihistamines.

The research team's primary endpoint was the change from the point of baseline in the 7-day Urticaria Activity Score (UAS7) at the 8, 12, and 16-week marks. Additionally, a key secondary endpoint was the proportion of subjects attaining UAS7=0 (complete resolution of symptoms) at the same timepoints. After the 16-week treatment phase, those involved were then observed for an additional 16 weeks without further dosing.

At baseline, the team found the mean (±SD) UAS7 scores were 28.7 (±7.2) for the RPT904 Q8W cohort, 28.9 (±6.6) for the Q12W cohort, and 28.8 (±7.9) for the omalizumab Q4W cohort. Across all of the assessment points, participants receiving RPT904 Q8W or Q12W had numerically greater reductions in UAS7 scores and higher rates of UAS7=0 compared with omalizumab. RPT904 was well tolerated overall, and the investigators did not identify any serious adverse events attributed to the study drug. No treatment-related discontinuations were reported.

While this research was not powered for non-inferiority and no formal statistical hypothesis testing was conducted by the investigators, the data suggest that RPT904 dosed at Q8W or Q12W demonstrated comparable efficacy and safety to omalizumab Q4W. Based on these findings, both companies indicated plans to advance RPT904 into phase 3 development.

“Based on these positive results, we are preparing to advance JYB1904 to Phase 3,” Ting Li, president of Jeyou, said in a statement.1 “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.”

References

1. RAPT Therapeutics and Shanghai Jeyou Pharmaceutical Announce Positive Topline Data from Phase 2 Trial of RPT904 (JYB1904) in Chronic Spontaneous Urticaria. RAPT Therapeutics, Inc. October 20, 2025. https://www.globenewswire.com/news-release/2025/10/20/3169321/0/en/RAPT-Therapeutics-and-Shanghai-Jeyou-Pharmaceutical-Announce-Positive-Topline-Data-from-Phase-2-Trial-of-RPT904-JYB1904-in-Chronic-Spontaneous-Urticaria.html.

2. Kolkhir P, Bonnekoh H, Maurer M, et al. Chronic Spontaneous Urticaria: A Review. JAMA. 2024 Nov 5;332(17):1464-1477. doi: 10.1001/jama.2024.15568. PMID: 39325444.