Allogeneic transplantation of blood stem cells concentrated by density gradients.

Discontinuous albumin density gradients were used to physically separate hemopoietic cells from immunocompetent lymphocytes in peripheral blood mononuclear cells of dogs. Transplantation of these stem cell concentrates into lethally irradiated allogeneic recipients restored hemopoiesis in nine of 12 animals. Tolerance and long-term survival, however, were achieved only in pairs matched for major histocompatibility antigens. These animals showed stable chimerism in bone marrow cells but transiently regenerated autochthonous cells demonstrable only in the peripheral blood. As compared with earlier studies using grafts of unseparated peripheral blood mononuclear cells, the numbers of CFUc transplanted were similar; the number of mononuclear cells, however, was reduced by a factor of 60. It thus appears that the granulocyte-macrophage colony-forming assay (GM-CFUc) is able to predict within limits the hemopoietic potential of a graft. Although very low numbers of blood-derived CFUc were effective (33,000-42,000/kg body weight), the superiority of blood stem cells over bone marrow grafts remains to be established.