New Brunswick, N.J. – November 08, 2026 -- Johnson & Johnson reported that 73% of patients (11 of 15) treated with its pasritamig and JNJ-9401 bispecific antibody combination achieved PSA reductions of at least 50% in a first-in-human Phase 1 study in metastatic castration-resistant prostate cancer (mCRPC). Seven of the 15 patients (47%) reached reductions of at least 90%. The data were presented in a late-breaking oral session at the Society for Immunotherapy of Cancer (SITC) 2026 Annual Meeting (Abstract #1175).
Dual-antigen regimen targets KLK2 and PSMA with complementary T-cell signals
The combination is the first dual-tumor-antigen-targeted bispecific regimen clinically evaluated in prostate cancer. Pasritamig, a first-in-class KLK2xCD3 bispecific, directs T cells toward prostate cancer cells. JNJ-9401, a PSMAxCD28 costimulatory bispecific, adds a second signal meant to strengthen and sustain T-cell activity.
The target population has few options. Median overall survival in metastatic prostate cancer resistant to androgen pathway modulation ranges from about 13.5 to 31.6 months, depending on the site of metastasis. Immune checkpoint inhibitors have shown minimal clinical benefit in the disease.
Seven patients with deep PSA responses stayed progression-free beyond six months
As of June 15, 2026, 144 patients had enrolled in the open-label, multicenter study. The 15 patients at the recommended regimen were heavily pretreated, with a median of four prior systemic therapy lines (range, two to six). Four achieved undetectable PSA levels. All seven patients with reductions of at least 90% remained on treatment for more than six months without disease progression.
Laura Graham, M.D., of the University of Colorado School of Medicine, called the activity "particularly interesting" given prostate cancer's history of resistance to immunotherapy. She said the findings warrant evaluation in a larger Phase 3 study.
No Grade 3 or higher treatment-related events reported at the recommended dose
At the recommended regimen, investigators reported no Grade 3 or higher treatment-related adverse events, dose-limiting toxicities, or treatment-related events leading to discontinuation or death. Cytokine release syndrome occurred in three patients (20%). All cases were Grade 1, presented as temporary fever, and none required tocilizumab. No cases of immune effector cell-associated neurotoxicity syndrome were reported.
The recommended regimen is JNJ-9401 200 mg subcutaneously plus pasritamig 300 mg intravenously, both every six weeks, after two weekly pasritamig step-up doses. The company said the profile points to potential outpatient administration.
Johnson & Johnson cautioned that the results rest on a small number of patients at the recommended regimen. Larger populations are needed to determine clinical benefit and safety.
Phase 3 KLK2-comPAS trial tests pasritamig with and without JNJ-9401 in mCRPC
The combination is already in the Phase 3 KLK2-comPAS study (NCT07164443), which tests whether adding JNJ-9401 to pasritamig improves outcomes in mCRPC. Pasritamig is also in the Phase 3 KLK2-PASenger study, combined with docetaxel in first-line mCRPC.
Yusri Elsayed, M.D., Global Therapeutic Area Head, Oncology at Johnson & Johnson, described pasritamig as a foundational component of the company's prostate cancer pipeline. The Phase 1 study (NCT06095089) also includes a frontline mCRPC dose-expansion cohort at the recommended regimen.