Human CD34⁺ HLA-DR^- bone marrow cells contain progenitor cells capable of self-renewal, multilineage differentiation, and long-term in vitro hematopoiesis

Human bone marrow cells expressing CD34 but not HLA-DR were isolated by immunofluorescence flow cytrometric cell sorting. These cells contained a hematopoietic cell (CFU-B1) capable of producing, in an in vitro semisolid culture system, blast-cell-containing colonies, which possessed the capacity for self-renewal and commitment to multipotential hematopoietic differentiation. In addition, CD34⁺ HLA-DR^- marrow cells contained primitive megakaryocyte progenitor cells, the burst-forming unit-megakaryocyte (BFU-MK). A subset of CD34⁺ HLA-DR^- marrow cells lacking the expression of CD15 and CD71 was obtained by flow cytometric cell sorting and was capable of sustaining in vitro hematopoiesis in suspension culture for up to 8 weeks in the absence of a preestablished adherent marrow cell layer. The combinations of IL-3 + IL-1α and IL-3 + IL-6 sustained proliferation of these cells for 8 weeks, induced maximal cellular expansion, and increased the numbers of assayable progenitor cells. These studies demonstrate that human CD34⁺ HLA-DR^- marrow cells and their subsets contain primitive multipotential hematopoietic cells capable of self-renewal and of differentiation into multiple hematopoietic lineages.