Abstract CT112: An off-the-shelf multivalent vaccine containing cancer’s dark matter, DPV-001, combined with PD-1 +/- GITR in head & neck cancer: safety, efficacy, and immunodynamics from the phase 1 GITRVax trial

Abstract

Abstract Background: Immune responses to shared cancer antigens have correlated with durable clinical responses. DPV-001 is a novel microvesicle vaccine that contains >300 proteins for genes commonly overexpressed by cancer and is enriched for short-lived proteins (SLiPs), and defective ribosomal products (DRiPs), including non-canonical peptides, representing potential shared non-mutated alternative cancer neoantigens (dark matter). Preclinical studies identified increased therapeutic efficacy when this vaccine strategy was combined with anti-PD-1 and anti-GITR, leading to this clinical trial for patients with advanced or metastatic HNSCC. Methods: Following safety run-in, eligible pts were randomly assigned 1:1 to receive DPV-001 +/- GITR agonist mAb (INCAGN-1949; q2wks). All received sequenced PD-1 mAb (retifanlimab; q4wks) starting D15. Safety was evaluated as the primary endpoint and efficacy was evaluated as a secondary endpoint. Tumor biopsies were taken pre-treatment, Wk 2 and 8, and assessed by CITE-seq, scRNA-seq, BCR-seq, and TCR-seq. Multiplex immunofluoresence was performed on biopsies. Blood samples were taken pre-treatment and at multiple timepoints and analyzed by flow cytometry and seromics. Results: 18 pts received backbone therapy of DPV-001 + sequenced PD-1; of these, 9 pts also received GITR starting D1 (Arm 2). G3 irAE's included: hypothyroidism & mucositis (Arm 1, same pt); pneumonitis and adrenal insufficiency (Arm 2, separate pts). No G4 toxicity was observed. Combining both arms, the response rate (RR) for PD-1 naïve pts was 55% (5/9), and 33% (3/9) for PD-1 experienced pts. Two CR's have been observed in Arm 2. Durability of response (DOR) and progression-free survival (PFS) will be reported at the meeting. DPV-001 induced increased Ki67+ CD4 EM (p<0.042) by D15, prior to first dose of PD-1. Addition of GITR at D1 further increased Ki67+ CD4 (p=0.008) & CD8 EM cells (P=0.0006) by D15. Activated or proliferating CD4 and CD8 EM were significantly increased in both arms by D30 (p<0.025). Across above specified analyses, pts receiving GITR had the greatest increase. Evaluable pts had significantly (all p<0.032) increased numbers of TIL expressing IFN-γ and/or GZMB, LAG-3, and TIM3 in on-treatment biopsies. TCR, BCR, and seromic analyses, as well as studies to identify targets of anti-cancer immunity, are ongoing. Conclusions: This 18 pt trial of DPV-001 and sequenced PD-1 +/- GITR shows a promising RR and evidence of increased activation and expansion of effector T cells in PBL and tumor. Upregulation of LAG-3 and TIM3 by T cells that infiltrate the tumor and have increased in number, provide a rationale for including inhibitors for both in this treatment strategy. Current efforts include evaluating whether immune responses target shared non-canonical alternative neoantigens, or Dark Matter, contained in DPV-001, and whether synchronized antibody and cellular response is evidenced. Acknowledgements: Incyte, Providence Portland Medical Foundation, Steve and Cindy Harder, Trial Registry: NCT04470024, Ethics Approval: PSJH IRB# 2020000480 Citation Format: Rom S. Leidner, Christopher Paustian, Shawn M. Jensen, Tarsem Moudgil, Yoshinobu Koguchi, Noah Simons, Venkatesh Rajamanickam, Ryan Meng, Marcus A. Couey, Quyen Vu, Matthew H. Taylor, Anne Long, Abigail J. Staeck, Lakhvir Kaur, Tijana Jovanovic, Brady Bernard, Tanisha Christie, Noriko Iwamoto, Yuriko Minegishi, Koji Ueda, William Redmond, Lessli M. Rushforth, Takashi Shimada, Patrick Rethwisch, Ashish Patel, Richard B. Bell, Carlo B. Bifulco, Traci L. Hilton, Hong-Ming Hu, Brian Piening, Walter J. Urba, Bernard A. Fox. An off-the-shelf multivalent vaccine containing cancer’s dark matter, DPV-001, combined with PD-1 +/- GITR in head & neck cancer: safety, efficacy, and immunodynamics from the phase 1 GITRVax trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT112.