Abstract
Abstract Background: Immune checkpoint inhibitors have minimal activity in unselected CRPC patients (pts). Combination regimens that generate a tumor-directed immune response (vaccine) and facilitate the resulting anti-tumor immune activity (checkpoint blockade, cytokines) have shown synergy in preclinical models. BNVax is a therapeutic poxviral vaccine targeting brachyury, a transcription factor involved in invasion and metastasis. BA is a bifunctional fusion protein: anti-PD-L1 monoclonal antibody fused to the TGFb-β-RII receptor extracellular domain (a TGF-β trap). N-803 is an IL-15 superagonist complex. Here we report an interim efficacy analysis of the QuEST1 study, aimed to rapidly interrogate safety and efficacy of immunotherapy combinations in CRPC. Methods: Asymptomatic/minimally symptomatic CRPC pts received BNVax + BA (Arm 2.1) or BNVax + BA + N-803 (Arm 2.2). BNVax is given as 2 prime doses followed by boosts. BA 1,200 mg intravenously and N-803 15 µg/kg subcutaneously are given every 2 weeks. Efficacy is defined as objective response by RECIST v1.1 or PSA decrease ≥ 30% sustained for ≥ 21 days. Safety was a secondary endpoint. Results: As of 10/11/20, 26 CRPC pts enrolled and had 1 to 23 months follow up. 1/13 pts (Arm 2.1) had a PSA response sustained for 13 months. 5/12 (41.6%) pts on treatment for at least 12 weeks (Arm 2.2) had sustained PSA responses, including 2 pts who progressed on enzalutamide. Of 3 patients with measurable disease, 2 had confirmed PR by RECIST. Grade 3 TRAEs: 1 pancreatitis (Arm 2.1), 1 secondary adrenal insufficiency (Arm 2.1), 1 tumor hemorrhage (Arm 2.1), 1 hyperglycemia due to new onset diabetes mellitus (Arm 2.2), 1 cystitis (Arm 2.2), 1 Rash with eosinophilia (Arm 2.2). One patient had grade 4 neutropenia that resolved with growth factor support and oral corticosteroids. Conclusions: BVax + BA + N-803 demonstrated a manageable safety profile and preliminary evidence of efficacy in CRPC. Addition of N-803 in Arm 2.2 was associated with more activity in this small sample. Arm 2.2 met the predetermined threshold for efficacy and will expand (n=25). Citation Format: James L. Gulley. The QuEST for an effective immunotherapy for prostate cancer [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2020 Oct 19-20. Philadelphia (PA): AACR; Cancer Immunol Res 2021;9(2 Suppl):Abstract nr IA07.
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