Clonal hematopoiesis is clonally unrelated to multiple myeloma and associates with specific microenvironmental changes

Background: Multiple myeloma (MM) initiation and progression depends on genomic events of a post-germinal center B-cell and on changes in the tumor microenvironment (TME). Clonal hematopoiesis of indeterminate potential (CHIP) refers to hematopoietic stem cells’ (HSC) clonal expansion supported by somatic mutations in leukemia-driver genes in otherwise healthy individuals, and results in inflammatory changes of myeloid cells. Methods: To determine the potential interrelationships between MM and CHIP, we assessed by targeted DNA NGS the prevalence and clinical correlates of CHIP in peripheral blood (PB) of 106 newly diagnosed MM patients, 27 of whom serially sampled after first-line treatment. To assess a possible link between the clonality in the myeloid compartment and MM, HSCs and plasma cells (PCs) from bone marrow (BM) aspirates of 8 CHIP-pos patients were sorted and analyzed by NGS for myeloid and lymphoid clonality. To evaluate possible CHIP-induced changes in TME, transcriptomic profile and interaction with the neoplastic clone, we performed scRNA-seq in 132,752 BM cells from 8 CHIP-pos and 8 CHIP-neg cases. Results: We detected 36 CHIP mutations in 23 patients (21.7%) at diagnosis. The most frequently mutated genes were TET2, DNMT3A, and ASXL1. 6/27 patients with serial samples had CHIP at diagnosis. Of those, 4 showed sub clonal evolution, mostly through changes in clonal sizes and in one case with branching evolution to a different clone. One patient treated with DRd developed a TP53-mutant clone that was not present at diagnosis. CHIP associated with advanced R-ISS stage, higher age, and a non-significant trend toward lower median hemoglobin. CHIP mutations were found in flow-sorted BM HSCs but not in PCs, arguing against a clonal hierarchy between CHIP and MM. We next investigated a possible interaction between CHIP and MM via cell-extrinsic mechanisms analyzing by scRNA-seq 78,431 non-malignant BM cells from 16 cases. CHIP carriers showed reduced level of naïve T-cells and increased expression of CD8 T-cell exhaustion markers (e.g., LAG3, TIGIT, EOMES). Pathway analysis indicated increased activation of IFNα/γ responses, as well as pro-inflammatory cytokine signaling pathways in CHIP-pos monocytes and T cells. GO analysis showed decreased antigen-presenting function in CHIP-pos dendritic cells. MultinicheNET showed that in CHIP-pos BM inferred cell-cell interactions between TME subpopulations and malignant PC (54,321) promoted survival and proliferation (e.g., TNFSF13B-TNFRSF17, CCL5-SDC1, CD40LG-CD40). Additionally, tumor cells seemed to evade immune recognition by hijacking immune-inhibitory ligand-receptor predicted interactions (e.g., CD48-CD244 in CD8 T, B2M-KLRC1 in NK, BST2-LILRA4 in DC). Conclusion: Our study showed that CHIP is frequently co-existing with MM at diagnosis and can change during treatment, despite having only a minor impact on baseline clinical and laboratory variables. Our main finding is that the TME is significantly disrupted at single-cell transcriptomic level in MM cases harboring CHIP. In particular, the immune TME shows changes usually seen in more advanced disease. These observations might impact response to immunotherapy and warrant further investigations.