Inflammatory CD4/CD8 double positive human T cells arise from reactive CD8 T cells and are sufficient to mediate GVHD pathology

An important paradigm in allogeneic hematopoietic cell transplantations (allo-HCTs) is the prevention of graft-vs-host disease (GVHD) while preserving the graft-vs-leukemia (GVL) activity of donor T cells. From an observational clinical study of adult allo-HCT recipients, we identified a CD4+/CD8+ double positive T cell (DPT) population, not present in starting grafts, whose presence was predictive of [≥] grade 2 GVHD. Using an established xenogeneic transplant model, we reveal that the DPT population develop from antigen stimulated CD8 T cells which become transcriptionally, metabolically and phenotypically distinct from single-positive CD4 and CD8 T cells. Isolated DPTs were sufficient to mediate xeno-GVHD pathology when re-transplanted into naive mice but provided no survival benefit when mice were challenged with a human B-ALL cell line. Overall, this study reveals human DPTs as a T cell population directly involved with GVHD pathology. One Sentence SummaryHuman CD4+/CD8+ double positive T cells (DPTs) mediate xenogeneic GVHD but possess limited GVL activity.