Mature T cells are part of adherent cells in human long-term bone marrow cultures

We determined the proportion of lymphocytes in nonadherent and adherent fractions of human bone marrow cells cultured by a Dexter-type continuous marrow culture method. T-lymphocytes, B-lymphocytes, and common alloantigen (CALLA)-positive cells (cells with receptors for CALLA) were sequentially enumerated using commercially available appropriate monoclonal antibodies. Nonadherent cells from weeks 2-5 of culture contained relatively fixed proportions of OKT3-positive (4%-10.4%) and CALLA-positive (5%-6.6%) cells. The adherent cells during the culture period between weeks 6 and 18 contained an average of 34% OKT3-positive cells with a range from 6% to 68.5%, despite a high hydrocortisone concentration of 5 X 10(-5) M added to the growth medium. The T cells retrieved from the adherent layers and resuspended in steroid-free medium responded to PHA stimulation and to mixed leukocyte culture in the same manner as did freshly drawn peripheral blood leukocytes. These results indicate that adherent cell populations include mature T-lymphocytes in human long-term bone marrow cultures. In view of well-documented interactions of nonlymphoid hematopoietic progenitors with T-lymphocytes in the clonogenic culture system, it can be speculated that the adherent T cells also may play a role in proliferation and differentiation of granulocyte-macrophage and erythroid progenitors in this long-term culture system.