POISONING OF HEALTHY HEMATOPOIESIS IS AN UNANTICIPATED MECHANISM DRIVING CLONAL DOMINANCE IN VEXAS SYNDROME [scRNA-seq]

Clonal dominance characterizes hematopoiesis during aging and increases susceptibility to blood cancers and common non-malignant disorders. VEXAS syndrome is a recently discovered adult-onset autoinflammatory disease burdened by a high mortality rate and caused by dominant hematopoietic clones bearing somatic mutations in the UBA1 gene. However, pathogenic mechanisms fueling clonal dominance are unknown. Moreover, the lack of disease models hampers the development of disease-modifying therapies. Here, we performed immunophenotypic dissection of hematopoiesis and single-cell transcriptomics in a VEXAS patient cohort revealing pervasive inflammation across all lineages. Hematopoietic stem/progenitor cells (HSPCs) in VEXAS patients proliferate less, are mostly committed toward myelopoiesis, and prone to egress from the bone marrow. Humanized xenograft models of VEXAS syndrome, generated by inserting the causative mutation in healthy HSPCs through base editing, fully recapitulated patients’ hematologic and inflammatory hallmarks. Competitive transplants of VEXAS-like and normal HSPCs showed that while mutant cells are resilient to the inflammatory milieu, wild-type ones are poisoned and progressively overwhelmed by VEXAS clones, becoming unable to support functional multilineage hematopoiesis. Our study unveils an unanticipated mechanism of clonal dominance, provides new models for preclinical investigation of therapeutic strategies, and has relevant implications for clinical management of VEXAS patients.