Item

Abstract

Myeloblasts are associated with adverse outcomes and define transformation to acute myeloid leukemia in all chronic myeloid neoplasms. Myeloblasts represent hematopoietic stem and progenitor cells (HSPCs) that express CD34, but are never resolved into stem and progenitor subpopulations during clinical evaluation. Therefore, how expansion of myeloblasts reshapes the HSPC compartment and its impact on clinical outcomes remains undefined. To address this important feature of disease progression, we transcriptionally and immunophenotypically mapped CD34 + HSPCs at single cell resolution for 66 samples from 45 patients with CMML. Single cell-RNA sequencing was performed on 137,578 CD34 + enriched HSPCs from 39 CMML samples and integrated with 63,672 publicly available CD34 + normal HSPCs (Fig A). We overlaid each CMML sample on a pseudotime projection of differentiation trajectories from normal samples to establish sample-specific aberrancies in HSPC states. This mapping classified samples into HSPC-biased groups of monocyte (mono)-bias, megakaryocyte erythroid (ME)-bias, and normal-like, respectively enriched for GMP, MEP, and HSC transcriptional signatures (Fig B). These groups were associated with distinct clinical genomic characteristics and were congruent with patient-specific bulk sequencing. For example, ME biased cases had statistically higher hemoglobin and mono-bias cases were associated with adverse survival, inflammatory clinical correlates, and RAS pathway mutations (Fig C). Importantly, we identified significant depletion of HSC across CMML that was most pronounced in the mono-bias group. This was validated by flow cytometry in 26 CD34 + enriched samples, which showed HSC numbers decreased as myeloblasts expanded and disease progressed (Fig D,E).