Interactions between purified human cord blood haemopoietic progenitor cells and accessory cells

Summary. The role of accessory cells in haemopoiesis remains confused. This appears in large part to reflect the use of impure populations of accessory cells and progenitor cells in previous studies. In this study, cell sorter purified populations of both accessory cells and haemopoietic progenitor cells were used to examine interactions between these cell types. We used a double culture protocol in which purified CD34+ cells were cultured with purified NK, T or monocytic cells in the first liquid culture phase after which the cells were transferred to secondary agar cultures to determine the number of colony forming cells (CFC). NK cells co-cultured with CD34+ cells resulted in an increased number of erythroid progenitors with no effect on the number of non-erythroid progenitors. In contrast, there were increased numbers of erythroid and non-erythroid CFC when the CD34+ cells were co-cultured with either purified T cells or monocytes. CD34+ cells cultured with cell-conditioned media derived from NK cells, T cells or monocytes in transwells where the CD34+ cells and the accessory cells were separated by a 0·2 μm membrane, showed no enhancement in CFC. These results suggest that intimate cell–cell contact is required for these events.