CAR19 Tregs treat murine chronic Graft-Versus-Host Disease through immune suppression in absence of measurable B-cell cytolysis.

Abstract

Chronic Graft-Versus-Host disease (cGVHD) remains a major cause of morbidity and mortality after allogeneic hematopoietic transplantation. CGVHD pathophysiology involves cooperation between Tfollicular helper cells (TFH) and germinal center B-cells (GCB), allo- and auto-antibody depositions in cGVHD tissues, and fibrosis. We evaluated human CD19-directed chimeric antigen receptor (CAR19) T-cell therapy in a clinically relevant murine cGVHD model with bronchiolitis obliterans syndrome (BOS). Although CD8 CAR19 T-cells effectively reduced peripheral B-cell and GCB frequencies, pulmonary function was unimproved. In contrast, a single CAR19 CD4 regulatory T-cells (Treg) infusion mitigated ongoing pulmonary disease and modulated germinal centers (GC) associated with reduced TFH frequencies compared to control Tregs but without measurable B-cell depletion. Compared to EGFR Treg infusion, mice receiving CAR19 Tregs exhibited enhanced suppression of B-cell activation, preserved splenic architecture, and provided greater opportunities for interaction with CD19+ B-cells at the B-cell follicle boundary zones. Taken together with the absence of detectable B-cell cytolysis, these findings are most consistent with GC suppression rather than B-cell depletion as the dominant mechanism. Overall, our findings suggest that CAR19 Tregs represent a promising and safe cGVHD/BOS therapeutic strategy, offering immunosuppressive benefits and improved disease outcomes that may be more limited with CD8 CAR19 T-cell treatment.