[Graft-versus-host disease: new insights into disease pathogenesis]

Graft-versus-host disease (GVHD) is a potentially life-threatening complication associated with allogeneic hematopoietic stem cell transplantation (allo-SCT). Although prophylaxis and GVHD treatment using immunosuppressants are essential for a successful allo-SCT, profound immunosuppression could lead to an infection and/or the recurrence of malignant diseases. Recently, the concept of tissue tolerance has emerged. This concept has been identified as a means to suppress GVHD by relying on tissue-intrinsic mechanisms that are independent from those underlying immune tolerance. Thus, GVHD prophylaxis and treatments targeting the mechanisms that promote tissue tolerance could help suppress GVHD and maintain leukocyte-mediated immune responses against tumors and infectious pathogens. Epithelial regeneration from LGR5-positive intestinal stem cells and epithelial maintenance mediated by metabolites from the intestinal microbiota are representative mechanisms that promote tissue tolerance in the gut. However, these protective mechanisms are weakened by GVHD and conditioning regimens. This review focuses on the pathophysiology of acute GVHD and tissue-intrinsic mechanisms that promote tissue tolerance.