Genomic and Immunologic Analysis of Cmaf and Hypermutated Multiple Myeloma: Implications for Immunologic Therapy

The advent of therapeutic monoclonal antibodies (elotuzumab, daratumumab) for multiple myeloma (MM) heralded a new era of immunologic therapy for this disease. Laboratory and clinical data suggest that immune checkpoint inhibitors (ICI) targeting the PD-1/PD-L1 axis are a promising novel strategy, as PD-L1 is commonly expressed on MM cells and a phase 2 clinical trial demonstrated encouraging responses to pembrolizumab (anti-PD-1) in combination with pomalidomide and dexamethasone. However, two late stage MM clinical trials of ICI combined with either lenalidomide or pomalidomide were halted due to safety concerns and lack of efficacy, although subgroup analysis suggested that the overall response rate in subjects with immune related adverse events was higher in subjects who received pembrolizumab + pomalidomide and dexamethasone vs the control group. As a result, further investigation of ICI in MM has largely discontinued. This discrepancy with the positive findings in the early phase trial suggests that genetic or immunologic features of the tumors or immune microenvironment of the patients may influence outcome to ICI, but these factors are as yet undefined. In solid tumors, high mutation burden as assessed by microsatellite sequence instability-high (MSI-high) or mismatch repair genes deficiency (dMMR) was correlated to response to anti-PD-1 ICI, and is now an indication for these agents. Newly diagnosed MM is considered an intermediate-low mutation burden disease (<10 muts/Mb), but a subset of newly diagnosed subjects, often characterized by overexpression of cMAF, have two-to-ten-fold higher average mutation burden. In addition, clonal evolution, characterized by accumulation of somatic mutations, is a common feature of MM and increases the mutation burden through its natural history. We hypothesized that cMAF/hyper-mutated (HM) MM patients may be more likely to have a tumor microenvironment (TME) that is amenable to ICI therapy, analogous to MSI-high/dMMR solid tumor patients. To investigate this, we identified cMAF/HM (n=25) and standard mutation burden (n=20) subjects from the CoMMPass database of newly-diagnosed MM patients. We performed bulk RNA sequencing and mass cytometry (CyTOF) analysis of CD138- bone marrow mononuclear cells, representing the TME, and proteomic (O-link) and grand serology (ELISA-based) analysis of peripheral blood plasma. CyTOF analysis of the TME demonstrated that cMAF/HM subjects had relatively decreased cycling myeloid cells and increased CD4+, CD73^low T cells compared to standard. cMAF/HM subjects had significantly higher frequencies of antibody titers against the MM-associated autologous antigens SOX2 and NY-ESO-1. These results suggest that cMAF/HM patients are more likely to feature immune activation in the TME and generate adaptive immune responses to MM-associated antigens, but these responses are not sufficient to control the disease, possibly due to inhibition by checkpoint ligands such as PD-L1. These results support further investigation of ICI-based combination therapies in cMAF/HM MM patients.