There have been conflicting reports on the role of CD161+ and CCR6+ lymphocyte subsets, not formally defined as containing MAIT cells, in graft‐versus‐host disease (GVHD) following bone marrow or haematopoetic stem cell transplantation preceded by myeloablative conditioning [interestingly, MAIT cells do not re‐emerge post‐transplant following non‐myeloablative conditioning with anti‐CD52 therapy [39] (L. J. Walker, unpublished data) ]. This evidence concerns the gene CCR6 and graft versus host disease.