Efficiency of human HLA-mismatched CD34⁺ cells from unrelated donors in establishing in vitro hematopoiesis in allogeneic long-term marrow cultures

We have examined the capacity of highly purified human CD34⁺ marrow cell isolates from unrelated HLA-mismatched donors to establish in vitro hematopoiesis on recipient marrow stromal cells in 2-stage hematopoietic long-term marrow cultures (H-LTMC). HLA-typing of both peripheral blood mononuclear cells and CD34⁺ marrow cells was performed for both HLA class I and HLA class II antigens for eight healthy individuals. Significant antigenic mismatches for these molecules ranged from three to six antigens for each recipient-donor pair. Comparison of MHC antigen expression by peripheral blood cells and CD34⁺ marrow cell isolates confirmed the presence of identical HLA-A, -B, and -C, and -DR specificities on the surface of these cells. Typing of -DQ specificities, however, was not consistently reactive on CD34⁺ cells. The ≤20% plating efficiency of purified CD34⁺ cells for BFU-E, CFU-GM, and CPU-MIX allowed us to use inoculum doses of 10³, 10⁴, and 10⁵ cells to determine the efficiency of allogeneic CD34⁺ cells in achieving in vitro engraftment and the establishment of hematopoiesis in H-LTMC. Engraftment of adherent BFU-E, CFU-GM, and CFU-MIX was equally efficient for autologous and allogeneic CD34⁺ cells. In vitro hematopoiesis reflected by the cumulative recoveries of progenitor cells over time was also equivalent for allogeneic and autologous CD34⁺ cells. These results demonstrate that highly purified, HLA-mismatched CD34⁺ marrow cells proliferate and establish in vitro hematopoiesis as efficiently as autologous cells in marrow derived stromal cell cultures and confirm that interactions between stromal cells and highly purified CD34⁺, DR-, and CD34⁺, DR⁺ marrow cell isolates are not MHC-restricted.