New Brunswick, New Jersey, USA, November 8, 2026
Johnson & Johnson has announced encouraging Phase 1 clinical trial results for its investigational immunotherapy combination of pasritamig and JNJ-9401 in patients with advanced prostate cancer. The combination demonstrated substantial reductions in prostate-specific antigen (PSA), a biomarker commonly used to monitor prostate cancer activity, among patients with metastatic castration-resistant prostate cancer (mCRPC). At the recommended treatment regimen, 73% of patients (11 out of 15) achieved PSA reductions of at least 50%, while 47% (7 out of 15) experienced reductions of at least 90%. Additionally, four patients achieved undetectable PSA levels. The findings were presented during a late-breaking oral presentation at the Society for Immunotherapy of Cancer (SITC) 2026 Annual Meeting on November 8, 2026. The investigational combination represents an innovative approach to prostate cancer treatment because it targets two different prostate cancer-associated proteins through complementary immune activation mechanisms. According to Johnson & Johnson, the findings provide encouraging early evidence supporting further investigation of this dual-antigen-targeted immunotherapy strategy. The results are particularly relevant for patients with advanced prostate cancer who have already received multiple systemic treatments and may have limited therapeutic options.
Dual-Bispecific Antibody Combination Targets KLK2 and PSMA
The investigational combination brings together two bispecific antibodies designed to stimulate and strengthen the body’s immune response against prostate cancer cells. Pasritamig, a first-in-class KLK2xCD3 bispecific antibody, is designed to direct T cells toward cancer cells expressing kallikrein-related peptidase 2 (KLK2). By bringing immune cells into close contact with cancer cells, pasritamig aims to initiate an immune response against the tumor. The second component, JNJ-9401, is a PSMAxCD28 costimulatory bispecific antibody designed to provide an additional signal that enhances T-cell activation and function. It targets prostate-specific membrane antigen (PSMA), another protein associated with prostate cancer cells. Together, these investigational therapies are designed to deliver complementary immune signals through two different tumor-associated targets. This dual-targeting strategy aims to improve the strength and sustainability of immune activity against advanced prostate cancer. The approach may be particularly important in metastatic castration-resistant prostate cancer, a challenging stage of the disease in which cancer continues to progress despite treatments targeting androgen signaling pathways. By exploring complementary T-cell activation mechanisms, Johnson & Johnson aims to expand the potential role of immunotherapy in prostate cancer treatment.
Deep PSA Reductions and Encouraging Safety Findings
The ongoing, open-label, multicenter Phase 1 study evaluated the safety, tolerability and preliminary clinical activity of pasritamig combined with JNJ-9401. As of June 15, 2026, a total of 144 patients had enrolled in the study. Patients receiving the recommended regimen had undergone extensive previous treatment, with a median of four prior lines of systemic therapy. Among the 15 patients evaluated at this recommended regimen, seven achieved PSA reductions of at least 90%. Importantly, all seven remained on treatment for more than six months without disease progression at the time of the reported analysis. The safety findings were also encouraging. No Grade 3 or higher treatment-related adverse events, dose-limiting toxicities or treatment-related adverse events leading to treatment discontinuation or death were reported at the recommended regimen. Cytokine release syndrome (CRS), an inflammatory reaction that can occur following immune cell activation, was observed in three patients (20%), with all cases classified as mild Grade 1 events. No cases of immune effector cell-associated neurotoxicity syndrome (ICANS) were reported. The recommended regimen combines pasritamig 300 mg administered intravenously with JNJ-9401 200 mg administered subcutaneously every six weeks, following two initial weekly step-up doses of pasritamig. The dosing schedule may offer the potential for outpatient administration.
Advertisement
Johnson & Johnson Advances Combination Into Phase 3
Building on the encouraging early findings, Johnson & Johnson is advancing the pasritamig and JNJ-9401 combination into Phase 3 clinical development. The combination is being evaluated in the ongoing KLK2-comPAS Phase 3 study (NCT07164443), which aims to determine whether adding JNJ-9401 to pasritamig can improve treatment outcomes in patients with metastatic castration-resistant prostate cancer. The company is also investigating pasritamig in other treatment combinations and clinical settings, including its combination with docetaxel in another Phase 3 development program. These research initiatives reflect Johnson & Johnson’s broader commitment to developing innovative oncology treatments and expanding therapeutic options for patients with advanced prostate cancer. However, the reported 73% PSA response rate represents preliminary findings from only 15 patients receiving the recommended regimen and does not establish a definitive survival benefit or confirm long-term clinical efficacy. Larger clinical studies will be necessary to determine whether the observed biomarker responses translate into meaningful improvements in patient outcomes. Overall, the Phase 1 findings represent an important development milestone for Johnson & Johnson’s prostate cancer immunotherapy program, supporting continued evaluation of dual-bispecific antibody approaches in advanced prostate cancer.
Source: Johnson & Johnson press release
