Baboon Marrow Transplants : Cell Separation and Engraftment Data Day posttransplant

The CD34 antigen is present on 1-4% of human marrow cells including virtually all hematopoietic progenitors detected by in vitro assays. Since the anti-CD34 monoclonal antibody 12-8 reacts with a similar marrow population in baboons, it was possible to test whether this antigen is expressed by stem cells responsible for hematopoietic reconstitution in vivo. CD34+ cells were enriched from marrows of five baboons using avidin-biotin immunoadsorption. After lethal irradiation, the five animals were given 15-27 X 106 autologous marrow cells (3.2-4.4 X 106 cells/kg) containing 65-91% CD34+ cells. All animals achieved granulocyte counts > 1,000/mm3 and platelet counts > 20 X 103/mm3 by 13-24 d posttransplant and subsequently developed normal peripheral blood counts. Two additional animals received 184 and 285 X 106 marrow cells/ kg depleted ofCD34+ cells. One animal died at day 29 without engraftment, while the other had pancytopenia for > 100 d posttransplant. The data suggest that stem cells responsible for hematopoietic reconstitution are CD34+.