RAS Pathway–Mutated Chronic Myelomonocytic Leukemia at the Single Cell Level

RAS pathway mutations, which are present in 30% of patients with chronic myelomonocytic leukemia (CMML) at diagnosis, confer a high risk of resistance to and progression after hypomethylating agent (HMA) therapy, the current standard of care for the disease. Using single-cell, multi-omics technologies, we sought to dissect the biological mechanisms underlying the initiation and progression of RAS pathway–mutated CMML. We found that RAS pathway mutations induced the transcriptional reprogramming of hematopoietic stem and progenitor cells (HSPCs), which underwent proliferation and monocytic differentiation in response to cell-intrinsic and -extrinsic inflammatory signaling that also impaired immune cells' functions. HSPCs expanded at disease progression and relied on the NF-KB pathway effector MCL1 to maintain their survival, which explains why patients with RAS pathway–mutated CMML do not benefit from BCL2 inhibitors such as venetoclax. Our study has implications for developing therapies to improve the survival of patients with RAS pathway–mutated CMML. Overall design: Single cell RNA and ATAC sequencing in Lin-CD34+ stem and progenitor cells and mononuclear cells isolated from patients with CMML and RAS pathway mutations at the time of diagnosis or after failure of hypomethylation agent therapy or venetoclax-based therapy