Abstract B045: Tumor- and T-cell-centric parameters shape the immunogenicity of cancer neoantigens and determine productive antitumor CD8+ T cell responses

Abstract Cancer arises from the accumulation of genetic alterations, leading to the production of mutant proteins processed and presented as neoantigens on the surface of malignant cells. These can be derived from missense mutations or large insertions, deletions or translocations that produce indels and/or gene fusions. A major hurdle in developing cell-based therapies that engage the immune system against targets preferentially expressed on tumor cells is our inability to prioritize neoantigens due to insufficient knowledge of what drives immunogenicity. Accumulating evidence suggests CD8+ T cells recognize and mount effective responses against neoepitopes across various cancers, and both immune- and tumor-centric parameters play a role in this. However, it isn’t known how the TCR repertoire drives antitumor responses, whether different patients with the same cancer type and similar HLAs generate comparable responses, or if differences in TCR specificity against conserved neoepitopes can be exploited to generate effective TCR-T cell-based therapies. To address these shortcomings and provide additional therapeutic options for patients with cancer, the goal of this research was to comprehensively assess the factors contributing to differences in tumor immunogenicity across different classes of antigens and define the principles of CD8+ T cell immune recognition that shape these responses. We hypothesized that different classes of antigens would have different peptide affinities and stabilities and in turn, affect the diversity of the naïve TCR repertoire. Furthermore, TCRs whose cognate antigen is highly dissimilar to self would have a higher probability of generation (Pgen). To test this, we performed peptide exchange assays using antigen presenting beads expressing HLA-A*02:01 to measure peptide-HLA (pHLA) affinity and stability. Naïve CD8+ T cells were then isolated from healthy donor PBMCs expressing HLA-A*02:01 and co-cultured with matched monoallelic K562 cells or autologous dendritic cells pulsed with viral and cancer antigens for a two-week period. On day 14, scRNA-seq and scTCR-seq were performed to characterize CD8+ transcriptional profiles, TCR diversity, and Pgen. Interestingly, our initial studies indicated that gene fusions, which display a greater distance from self than SNVs, have greater exchange rates, affinity, and stability compared to SNVs, but similar to viral antigens. While all antigens were able to induce CD8+ T cell expansion in co-culture assays, gene fusions and viral antigens generated the greatest frequency of antigen-specific CD8+ T cells and these TCRs tended to have a higher Pgen suggesting there may be an evolutionarily conserved mechanism in how specific TCR clonotypes are generated against evolutionarily encountered antigens and/or antigens with a high dissimilarity to self. Surprisingly, the number and diversity of the neoantigen-specific responses were heterogeneous and, in some cases, unique to the donor, which suggests there is a difference in donors’ ability to generate private vs public TCRs. Citation Format: Jessica L. Schmeling, Anthony E. Zamora. Tumor- and T-cell-centric parameters shape the immunogenicity of cancer neoantigens and determine productive antitumor CD8+ T cell responses [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor Immunology and Immunotherapy; 2024 Oct 18-21; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2024;12(10 Suppl):Abstract nr B045.