DYSFUNCTIONAL T CELLS IN MULTIPLE MYELOMA ARE ANTIGEN-SELECTED AND RESPOND TO MYELOMA IMMUNOGLOBULIN NEOANTIGENS

?vidence suggests that the T-cell repertoire in multiple myeloma (MM) is shaped by antigen selection. However, the molecular underpinnings of this observation are not fully understood, particularly concerning T-cell receptor (TR) gene repertoire profiles. Moreover, most information derives from the analysis of a single tissue compartment [i.e. peripheral blood (PB) or bone marrow (BM)], thus hindering the paired assessment of T-cell profiles. We performed a combined immunophenotypic and immunogenetic characterization of T cells in MM and MGUS and explored the possibility that the myeloma paraprotein contains peptide sequences that can serve as neoantigens for T cells. Flow cytometry revealed increased effector T-cell subsets in the BM and high expression levels of exhaustion markers (PD-1, CTLA-4) on BM T cells in MM compared to MGUS and, especially, healthy donors. RNA-seq revealed significant differences for both CD4+ and CD8+ T cells in MM and MGUS versus healthy donors in processes such as T-cell exhaustion, differentiation, and regulation of cell migration, apoptosis, senescence and cell death. NGS documented oligoclonal expansions of CD4+ and, particularly, CD8+ T cells in MM and MGUS that were more pronounced in the BM, arguing for selection by BM-biased antigens. A significant number of putative class I/II T cell neoepitopes were identified, contained in the MM paraprotein, whose immunogenicity was confirmed by ex vivo experiments. Overall, oligoclonally expanded T cells are present in MM, even at early ontogenetic stages, displaying an exhausted phenotype likely due to prolonged exposure to antigen(s), including tumor-specific antigens derived from the MM paraprotein.