Spatial and functional relationships between human hemopoietic and marrow stromal cells in vitro

The aims of the present study were to determine which stromal elements are important for the proliferation of human hemopoietic precursor cells in vitro and to develop a model for human bone marrow transplantation. First, we incubated bone marrow mononuclear cells in liquid culture under different conditions to obtain different proportions of fibroblasts, fat cells, and macrophages. We also looked for persistent hemopoiesis in association with these stromal cells. Second, we seeded nonadherent bone marrow mononuclear cells onto established stromal monolayers by incubating them together for 2 h and then washed off the unattached cells. The cells remaining on the monolayer were then stimulated by granulocyte-macrophage colony-stimulating activity (GM-CSA). We found that persistent hemopoiesis was maintained only in the presence of fibroblasts, fat cells, and macrophages. We also found that hemopoietic precursor cells attached to monolayers containing fibroblasts and fat cells, but not to monolayers containing fibroblasts or macrophages alone. Therefore, fibroblasts, fat cells, and macrophages appear to be necessary for the maintenance of human hemopoiesis in vitro, and fat cells may permit repopulation of marrow stroma by transplanted hemopoietic stem cells. This in vitro model might reflect features of human bone marrow transplantation in vivo.