483 Initial safety results and immune responses induced by a novel human papillomavirus (HPV)-specific gorilla adenovirus immunotherapy vaccine, PRGN-2009, in patients with advanced HPV-associated cancers

Background PRGN-2009 is a novel gorilla adenovirus vaccine containing 35 non-HLA-restricted epitopes of HPV 16 and 18 which is being tested in an open-label, NCI-sponsored, single-center Phase I/II study alone and combined with the bifunctional TGF-β ”trap”/anti-PD-L1 fusion protein bintrafusp alfa (BA) (NCT04432597). Methods For the Phase I of the trial, eligible patients are adults with previously treated (checkpoint blockade allowed) recurrent/metastatic HPV-associated cancers. Objectives are to assess the safety and determine the recommended phase 2 dose (RP2D) of PRGN-2009 alone and combined with BA. Treatment followed a single-agent 3+3 dose escalation at two dose levels of PRGN-2009 (dose level 1: 1x1011 viral particle units (VPU), dose level 2: 5x1011 VPU) subcutaneously Q2W for 3 times, then Q4W for up to one year in total. After determination of RP2D, a combination cohort of 10 patients treated with PRGN-2009 at the RP2D combined with BA (1200 mg IV Q2W for 52 weeks) opened. Peripheral blood mononuclear cells collected from patients before and after vaccination with PRGN-2009 were stimulated with overlapping peptide pools and assessed by intracellular cytokine staining to identify HPV-16 and HPV-18 specific T-cells, as well as T-cells targeting cascade antigens not encoded by the vaccine. Results Six patients were enrolled in the single-agent PRGN-2009 dose-escalation phase (3 with cervical cancer, 2 with anal cancer, 1 with vaginal cancer). Observed adverse events were Grade 1-2 flu-like syndrome (headache, body aches), injection site reactions (erythema, pruritus, soreness, localized edema), fatigue, and rash. There were no dose limiting toxicities, and 5x1011 VPU was selected as RP2D. Four patients had stable disease as best response, (one ongoing, 10 months on treatment).T-cells targeting HPV-16 and/or HPV-18 were increased after vaccination in 100% of patients, with 3/6 (50%) developing HPV-16 T cells and 5/6 (83%) developing HPV-18 T cells. In some patients, the magnitude and breadth of HPV-16 and HPV-18 specific T cells were notably increased after repeated vaccination. T cells that target the cascade antigens brachyury and MUC1 were also increased in all patients evaluated. Multifunctional T-cell responses against all these antigens were also developed after vaccination in the majority of patients. No differences in immunogenicity were noted between the two dose levels. Enrollment is underway in combination with BA. Updated data will be presented. Conclusions The Phase 1 results demonstrate the safety of single-agent PRGN-2009 and induction of anti-HPV T-cell immune responses, supporting the hypothesis that PRGN-2009 could potentially induce anti-tumor effects in HPV-associated cancers. Acknowledgements This research was supported in part by the Intramural Research Program of the NIH, NCI. Trial Registration NCT04432597 Ethics Approval Approved by the NIH IRB (Ref No 543876). All participants have given informed consent before taking part in the study.