Purification and characterization of human bone marrow lymphocyte subpopulations: evidence for the existence of an alloreactive immature T cell.

This study was conducted in order to clarify further the role of bone marrow lymphocyte (BML) subsets in graft-versus-host disease (GVHD) after clinical BM transplantation. Human BML separated by velocity sedimentation through a continuous sucrose gradient were found to consist of 38% T, 21% B and 41% null cells. T cells were purified from BML or peripheral blood lymphocytes (PBL) by rosette formation with sheep red blood cells (SRBC) and subsequent gradient centrifugation. Mitogenic stimulation of BML, PBL and the respective T cell subsets revealed the well-known reactivity of mature T lymphocytes, whereas non-T lymphocytes comprising T cell precursors showed only a weak response. In allogeneic stimulation kinetics, however, non-T-BML disclosed a delayed but marked responsiveness as compared to BML and T-BML suggesting that a T cell precursor matures under culture conditions. This cell type could be involved in GVHD in addition to mature T cells after clinical bone marrow transplantation.