Abstract 4538: T-cell immunogenicity and biomarker profiling in advanced melanoma patients receiving the personalized vaccine EVX-01 in combination with pembrolizumab

Abstract Patients with advanced melanoma were treated with a personalized neoantigen vaccine, EVX-01, in combination with pembrolizumab in a phase 2 clinical study (NCT05309421). The peptide-based EVX-01 vaccine consists of multiple tumor-specific neoantigens (neoAg) identified by Evaxion Biotech’s target discovery AI-Immunology™ platform. As reported in September 2024 at the one-year follow-up, the treatment was well tolerated, neoAg specific T-cell responses were observed, and the objective response rate was 11/16 (68.8%) in the overall cohort.To investigate potential markers associated with the immunogenic and therapeutic effect, several biomarker analysis technologies were applied. Baseline tumor biopsies as well as longitudinal blood samples before, during and after treatment were collected. Vaccine-specific T-cell responses were analyzed by ELISpot of peripheral blood mononuclear cells (PBMCs). Treatment-induced changes of circulating immune cell subsets were characterized using spectral flow cytometry.Baseline tumor samples were analyzed by genomic and transcriptomic analyses, immunohistochemistry (IHC), and AI-assisted digital pathology to understand the characteristics of the tumor and the immunological landscape of the tumor microenvironment (TME).Longitudinal plasma and serum samples were assessed for treatment-induced changes of circulating markers using the Olink proteomics technology and Nordic Bioscience's ProteinFingerPrint Technology™. Immunogenicity analysis demonstrated vaccine-specific T-cells in all patients after EVX-01 priming (n=15) and repeated booster immunizations lead to sustained magnitude and broadness of T-cell responses. Overall, the analysis showed that 78% of the AI-Immunology™ selected neoAgs were immunogenic and 93% of the immunogenic peptides induced de novo responses.Quantification of functionally diverse immune cell subsets in patient PBMCs will further increase our understanding of the immunological changes induced by EVX-01. Immunohistochemistry analysis of baseline tumor biopsies showed PD-L1 expression and T-cell infiltration in 66% and 75% of tumor specimens, respectively. Additional analyses are being conducted to evaluate relevant features of TME, such as fibrosis and spatial distribution of different cell types in the TME. Olink proteomic analysis and ECM turnover marker analysis of serum samples will provide further insights into tumor- and immune-related interactions during EVX-01 treatment. The immune and biomarker analyses enhance our understanding of the complex interactions between the immune and tumor compartments, while also shedding light on treatment induced adaptations. This new understanding can aid in refining therapeutic strategies and identifying predictive biomarkers that may guide treatment decisions in the future. Citation Format: Mads Lausen, Michail A. Pavlidis, Rasmus Ohrt Andersen, Thomas Trolle, Nikolas Thuesen, Christian Garde, Nicholas Willumsen, Morten Asser Karsdal, Nadia Viborg, Adnan Khattak, Georgina V. Long, Paolo A. Ascierto, Carolina Cimminiello, Michael J. Chisamore, Stine Friis Thorsen, Birgitte Rønø, Daniela Kleine-Kohlbrecher. T-cell immunogenicity and biomarker profiling in advanced melanoma patients receiving the personalized vaccine EVX-01 in combination with pembrolizumab [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4538.