Identification and Functional Characterization of Self-Reactive Memory-Phenotype CD8+ T Cells Infiltrating Murine Tumors

Conventional CD8⁺ T cells that can recognize tumor-derived antigens are key mediators of the anti-tumor immune response at baseline and in the context of immunotherapy. However, the antigen specificity of a significant proportion of tumor-infiltrating CD8⁺ T cells (CD8-TILs) remains undetermined. Recent research has demonstrated that memory phenotype CD8⁺ T cells (CD8-MP cells), a unique, thymically derived, self-peptide antigen-specific CD8⁺ T cell population, recurrently infiltrate tumors in a prostate cancer model. In this work, we utilized comparative bulk RNA-sequencing, single-cell RNA-sequencing with paired TCR-sequencing, and in-depth phenotypic and functional characterization of CD8-MP T cell clones to interrogate the contribution of self-peptide-specific CD8-MP cells to the anti-tumor immune response. These studies revealed that tumor-infiltrating CD8-MP cells are a heterogeneous population of cells that are detected in several distinct murine tumor models. Additional experiments suggest that CD8-MP infiltration into tumors is driven by recognition of self-antigens presented by either immune cells infiltrating the tumor or the tumor cells themselves. Functionally, CD8-MP origin cells isolated from tumors demonstrated pro-inflammatory properties, including cytokine secretion and degranulation, suggesting they may play a previously underappreciated role in the anti-tumor immune response.