Cutting edge: A major fraction of human bone marrow lymphocytes are Th2-like CD1d-reactive T cells that can suppress mixed lymphocyte responses

Murine bone marrow (BM) NK T cells can suppress graft-vs-host disease, tran splant rejection, and MLRs. Human BM contains T cells with similar potentia l. Human BM was enriched for NK T cells, similar to 50% of which recognized the nonpolymorphic CD1d molecule. In contrast to the well-characterized bl ood-derived CD1d-reactive invariant NK T cells, the majority of human BM CD 1d-reactive T cells used diverse TCR. Healthy donor invariant NK T cells ra pidly produce large amounts of IL-4 and IFN-gamma and can influence Th1/Th2 decision-making. Healthy donor BM CD1d-reactive T cells were Th2-biased an d suppressed NMR and, unlike the former, responded preferentially to CD1d() lymphoid cells. These results identify a novel population of human T cell s which may contribute to B cell development and/or maintain Th2 bias again st autoimmune T cell responses against new B cell Ag receptors. Distinct CD 1d-reactive T cell populations have the potential to suppress graft-vs-host disease and stimulate antitumor responses.