Crosstalk Between Donor T Cells and Recipient IL-33+ Target Tissue Stroma Controls Alloimmune Responses Causing Graft-versus-Host Disease 2260079

Abstract Introduction Graft-versus-host disease (GVHD) remains a major complication of allogeneic hematopoietic cell transplantation (AlloHCT). Conditioning with chemotherapy and radiation enables donor engraftment but causes tissue injury that upregulates the alarmin interleukin-33 (IL-33) in fibroblastic reticular cells (FRCs) in secondary lymphoid organs (SLO) and tissue stromal cells. While mechanisms releasing IL-33 from nuclear sequestration remain elusive, free IL-33 directly activates donor CD4+ T cells to promote Th1 differentiation and expansion. Early IL-33 blockade limits GVHD initiation, yet the role of local IL-33 in sustaining alloimmunity remains unclear. We used preclinical models to define how IL-33 signaling to donor T cells within SLO versus the gastrointestinal tract (GIT) stroma controls active GVHD and graft-versus-lymphoma (GVL) responses. Methods BALB/c recipients received B6 T cell—depleted bone marrow, A20 lymphomas, and T cells from donors with inducible ST2 (IL-33R) deletion to control IL-33 signaling during GVHD and GVL. To identify stromal functions, B6 recipients lacking IL-33 in FRCs (CCL19-Cre×Il33fl/fl) or gut epithelium (Vil-Cre×Il33fl/fl) were transplanted with BALB/c T cells and bone marrow. T cell—dependent IL-33 release was tested using GzmB⁻/⁻, St2+/+, and St2⁻/⁻ T cells. Results Late ST2 deletion resolved GVHD without compromising GVL. IL-33 signaling increased Foxp3 levels and reduced T-bet expression in donor CD4+ T cells, while sustaining TCF-1. Unexpectedly, loss of FRC-derived IL-33 exacerbated GVHD, whereas gut epithelial IL-33 deletion was protective. IL-33 induced GzmB, and GzmB⁻/⁻ T cells displayed impaired activation and expansion. Conclusion Early SLO-derived IL-33 establishes effector programming that influences later tissue responses. IL-33+ stroma—T-cell crosstalk programs donor CD4+ T-cell fate and shapes local alloimmunity during GVHD. IL-33—stroma feedback is a key signal to alloreactive T cells during GVHD. Funding Source NIH/NIAID F30AI147437, NIH T32 CA082084, NIH/NHLBI R01HL122489, NIH/NIAID R21AI121981, NIH/NIAID R56AI13927 Topic Categories Transplantation Immunology (TRAN)