Function and expression of checkpoint inhibitors and immune agonists on immune cells in monoclonal gammopathy of undetermined significance (MGUS), smoldering multiple myeloma (SMM) and MM and tumor-specific T lymphocytes.

Abstract

11577 Background: Characterization of expression and function of immune regulatory molecules in tumor microenvironment will provide the framework for developing novel therapeutic strategies. Methods: We evaluated the expression and functional impact of various immuno-regulatory molecules, PD-1, PDL-1, PDL-2, LAG3, TIM3, OX40 and GITR, on the CD138+ tumor cells, myeloid derived suppressor cells (MDSC), and T cell subsets from patients with MGUS, SMM and active MM (newly diagnosed, relapsed, relapsed/refractory), and the myeloma-specific cytotoxic T lymphocytes (CTL) induced with XBP1/CD138/CS1 peptides. Results: PDL-1/PDL-2 was more highly expressed on CD138+ myeloma cells in active MM than SMM or MGUS. G-type MDSC (CD11b+CD33+HLA-DRlowCD15+). Treg cells (CD3+CD4+/CD25+FOXP3+) numbers were increased and expressed higher levels of PD1/PD-L1 in active MM than in MGUS, SMM or healthy donors. Among the checkpoint molecules (PD-1, PDL-1, PDL-2, LAG3, OX40, GITR) evaluated, PD-1 showed the highest expression on CD3+CD4+ and CD3+CD8+T cells in BMMC and PBMC from patients with active MM. Functionally, T cells from MM patients showed increased proliferation upon treatment with an individual immune agonist ( > 150%) or checkpoint inhibitor ( > 100%). Interestingly, each individual anti-checkpoint molecule induced proliferation of T cells expressing other checkpoint molecules. In addition, the blockade of PD1, LAG3 or TIM3 enhanced MM antigen-specific cytotoxicity, assessed by parameters including CD107a, granzyme B and IFN-g production, which was most prominent within the memory CTL subset of MM antigen-specific T cells. Conclusions: These results demonstrate an increased frequency of immune regulatory cells, which highly express checkpoint inhibitors in active MM. Direct stimulation with an immune agonist or blockade of a checkpoint inhibitor increased MM patients’ T cell proliferation and myeloma-specific CTL function, supporting development of combination immune regulatory therapies to improve patient outcome in MM.