1009 – BAD ALLIES: COEXISTING MUTANT CLONES REWIRE THE MARROW MICROENVIRONMENT TO PROMOTE EXPANSION

Abstract

The progression of clonal hematopoiesis (CH) is shaped not only by cell-intrinsic mutational effects but also by cooperative signaling interactions among coexisting mutant clones that collectively remodel the bone marrow niche, alter cytokine landscapes, and reshape competitive fitness hierarchies in ways that fundamentally influence disease trajectory. Although clone size predicts clinical risk and DNMT3A and TET2 mutations account for the majority of CH cases, the mechanisms by which coexisting clones interact to drive expansion remain poorly defined. Through the development of nonirradiated competitive transplant chimeras incorporating Dnmt3a-mutant and Tet2-deficient bone marrow under homeostatic conditions, introduced individually and in combination, three interconnected findings were identified: Dnmt3a-mutant clones exhibit modest, lineage-neutral expansion in isolation; Tet2-deficient clones expand robustly and promote myeloid output without increasing HSC frequency; and coexistence of both populations accelerates Dnmt3a-mutant clone expansion and induces distinct stem and myeloid phenotypes not observed when either clone competes alone. Mechanistically, single-cell transcriptomic analyses and bulk chromatin accessibility profiling reveal mutation-specific remodeling of cytokine-responsive transcriptional states and pathways governing stem cell persistence, consistent with Tet2-mutant cells reshaping the local signaling environment to lower response thresholds and potentiate expansion programs in neighboring Dnmt3a-mutant populations. These findings are being extended through analysis of multi-mutation CH cohorts to define how clonal composition influences inflammatory signaling and disease progression in human disease. It is proposed that CH evolution is governed less by the presence of individual mutations than by cooperative, niche-mediated crosstalk among coexisting clones, thereby establishing a framework in which clonal competition drives CH progression and identifying shared signaling dependencies as candidate targets to limit expansion and reduce transformation risk.

The progression of clonal hematopoiesis (CH) is shaped not only by cell-intrinsic mutational effects but also by cooperative signaling interactions among coexisting mutant clones that collectively remodel the bone marrow niche, alter cytokine landscapes, and reshape competitive fitness hierarchies in ways that fundamentally influence disease trajectory. Although clone size predicts clinical risk and DNMT3A and TET2 mutations account for the majority of CH cases, the mechanisms by which coexisting clones interact to drive expansion remain poorly defined. Through the development of nonirradiated competitive transplant chimeras incorporating Dnmt3a-mutant and Tet2-deficient bone marrow under homeostatic conditions, introduced individually and in combination, three interconnected findings were identified: Dnmt3a-mutant clones exhibit modest, lineage-neutral expansion in isolation; Tet2-deficient clones expand robustly and promote myeloid output without increasing HSC frequency; and coexistence of both populations accelerates Dnmt3a-mutant clone expansion and induces distinct stem and myeloid phenotypes not observed when either clone competes alone. Mechanistically, single-cell transcriptomic analyses and bulk chromatin accessibility profiling reveal mutation-specific remodeling of cytokine-responsive transcriptional states and pathways governing stem cell persistence, consistent with Tet2-mutant cells reshaping the local signaling environment to lower response thresholds and potentiate expansion programs in neighboring Dnmt3a-mutant populations. These findings are being extended through analysis of multi-mutation CH cohorts to define how clonal composition influences inflammatory signaling and disease progression in human disease. It is proposed that CH evolution is governed less by the presence of individual mutations than by cooperative, niche-mediated crosstalk among coexisting clones, thereby establishing a framework in which clonal competition drives CH progression and identifying shared signaling dependencies as candidate targets to limit expansion and reduce transformation risk.