CD8+TCR+ and CD8+TCR- cells in whole bone marrow facilitate the engraftment of hematopoietic stem cells across allogeneic barriers

Although purified hematopoietic stem cells (HSC) are sufficient to engraft irradiated allogeneic recipients, bone marrow (BM) contains other cells that facilitate engraftment. Here, several candidate facilitators were tested by cotransplantation with HSC. Both TCR+ and TCR(-)CD8 alpha(+) BM subpopulations have facilitative potential. CD8(+)TCR(+) cells are typical T lymphocytes. CD8(+)TCR(-) facilitators are CD3(-), not CD3(+), have a granular morphology, and are CD8 beta(-) and CD11c(+); they share phenotypic characteristics with CD8 alpha alpha lymphoid dendritic cells and veto cells. We also demonstrate that lytic function is not necessary for facilitation and that the CD8 alpha molecule is either important for facilitation or in the development of facilitators.