Abstract CT570: KISIMA-01: A first-in-human trial of the heterologous prime-boost vaccine ATP128/VSV-GP128 with ezabenlimab (BI 754091) in patients with stage IV colorectal cancer

Abstract

Abstract Background: Most microsatellite stable/mismatch repair proficient (MSS/MMRp) stage IV colorectal cancers (CRC) do not respond to PD-1 inhibition. ATP128, based on the KISIMA platform, is a single chimeric fusion protein, composed of 3 elements essential to generate potent antitumoral cellular immunity: a proprietary cell-penetrating peptide (CPP) for antigen delivery, a proprietary Toll-like receptor (TLR)-peptide agonist with self-adjuvant properties and a modulable multi-antigenic domain (Mad), where the Mad for CRC includes 3 antigens: carcinoembryonic antigen (CEA), Survivin, Achaete-scute complex homolog 2 (ASCL2). VSV-GP128 is a recombinant vesicular stomatitis virus (VSV) carrying the glycoprotein (GP) of a non-neurotropic strain of lymphocytic choriomeningitis virus (LCMV) instead of the native VSV-GP. The GP of the LCMV abrogates neurotoxicity. As viral vector, VSV-GP128 expresses a Mad with identical sequence to ATP128 integrated in a linear, negative-sense, single-stranded RNA genome. Preclinical data have shown that priming with KISIMA vaccine followed by VSV-GP boost induced a large pool of polyfunctional and persistent antigen-specific cytotoxic T cells in the periphery as well as within the tumor in several tumor models. Combining heterologous vaccination with a PD-1 inhibitor further improved its therapeutic efficacy (Das et al., Nature Communication 2021). Methods: KISIMA-01 (NCT04046445) is an open-label, multi-center Phase 1b umbrella trial to investigate the safety, tolerability and immunogenicity of the heterologous prime-boost vaccine AT128/VSV-GP128 in combination with the anti-PD1 ezabenlimab in patients with stage IV MSS CRC. Two different patient cohorts are investigated: 1) maintenance setting (during a chemotherapy free period) after a minimum of 4 months of 1st line standard chemotherapy with clinical benefit (defined as PR or SD) (n=30); 2) resectable liver-limited disease (n=15). ATP128 is given subcutaneously on day 1 (prime); VSV-GP128 is administered intravenously on day 15 as the heterologous boost. ATP128 is again administered on day 29 (injection 3) and then every 4 weeks for the last 3 immunizations. Ezabenlimab is administered every 3 weeks starting with the first ATP128 administration. Blood and tissue samples are collected before, during and after ATP128/VSV-GP128 treatment to monitor the induction of a tumor associated antigen-specific immune response and immune-related changes. Immunogenicity will be analyzed in the peripheral blood using ELISpot, and in the tumor microenvironment by immunohistochemical assessment of tumor-infiltrating lymphocytes (TILs). Clearance of ctDNA is analyzed as an exploratory endpoint. The heterologous prime-boost cohorts (ATP128/VSV-GP128) of the KISIMA-01 trial are recruiting in the US, Switzerland and Belgium. Citation Format: Heinz-Josef Lenz, Thibaud Koessler, Paul Oberstein, Eric Van Cutsem, Sunnie Kim, Ralph Fritsch, Hans Prenen, Michael Morse, Delphine Gani, Madiha Derouazi, Thomas Bogenrieder, Scott Kopetz. KISIMA-01: A first-in-human trial of the heterologous prime-boost vaccine ATP128/VSV-GP128 with ezabenlimab (BI 754091) in patients with stage IV colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr CT570.