Poisoning of Healthy Hematopoiesis Is an Unanticipated Mechanism Driving Clonal Dominance in Vexas Syndrome

• Published in: Blood 2024-11, Vol.144, p.4050-4050
• Main Authors: Fiumara, Martina, Molteni, Raffaella, Campochiaro, Corrado, Alfieri, Roberta, Pacini, Guido, Tomelleri, Alessandro, Diral, Elisa, Varesi, Angelica, Weber, Alessandra, Quaranta, Pamela, Albano, Luisa, Gaddoni, Chiara, Basso-Ricci, Luca, Stefanoni, Davide, Bergonzi, Gregorio Maria, Annoni, Andrea, Panigada, Maddalena, Cantoni, Eleonora, Canarutto, Daniele, Xie, Stephanie Z, D'Alessandro, Angelo, Di Micco, Raffaella, Aiuti, Alessandro, Ciceri, Fabio, De Luca, Giacomo, Dagna, Lorenzo, Matucci-Cerinic, Marco, Merelli, Ivan, Cenci, Simone, Scala, Serena, Cavalli, Giulio, Naldini, Luigi, Ferrari, Samuele
• Format: Article
• Language: English
• ISSN: 0006-4971
• DOI: 10.1182/blood-2024-207200

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 develop humanized models of VEXAS syndrome through base editing technology and capitalize on granular omic datasets from patients and the model itself to unravel cell state perturbations and biologic mechanisms driving clonal dominance in VEXAS syndrome. Immunophenotypic dissection of hematopoiesis in VEXAS patients (n=9) compared to controls highlighted myeloid bias, impaired lympho/erythro/megakaryo-poiesis, increased mobilization to the bloodstream, and lower primitiveness of HSPCs as major phenotypic markers in patients. Moreover, patients' HSPCs had impaired reconstitution capacity in immunodeficient mice, hampering their use for further studies. We thus leveraged base editing to develop in vitro and in vivo models of VEXAS syndrome by genetically converting human wildtype HSPCs (UBA1wt) into UBA1 mutant (UBA1mut) with >90% efficiency. Clonogenic and multilineage differentiation assays revealed an exclusive myeloid and NK output of UBA1mut HSPCs. Concordantly, xenotransplantation of >80% UBA1mut HSPCs resulted in a 10-50-fold lower human cell output in vivo compared to controls (100% UBA1wt) due to dramatic shrinkage of the lymphoid compartment. Conversely, NK and myeloid ones were more preserved. HSPCs from bone marrow of UBA1mut mice were lower in number and mostly myeloid-biased. Of note, myeloid cells and HSPCs were mostly UBA1mut, while the few differentiated lymphoid cells were UBA1wt. Single-cell RNA-sequencing (scRNA-seq) on human UBA1mut grafts showed pervasive upregulation of inflammatory and apoptotic transcriptional responses, and lower propensity to engage cell cycle, across all hematopoietic subpopulations. Primitive HSCs from UBA1mut mice early activate inflammatory responses, are prematurely aged, and transcriptionally imprinted toward myelopoiesis. Notably, the immunophenotype, lineage repopulation patterns, and transcriptomic programs across all human hematopoietic subpopulations strikingly mirrored those observed in VEXAS patients from our cohort, validating the reliability of the model. We then leveraged our humanized model to study how different degrees of mosaicism a