Repeated administration of cytokines improve the ex-vivo generation of human dendritic cells

The in vitro generation of dendritic cells (DCs) enables us to practice antitumor immune therapy. Peripheral monocytes can differentiate to DCs in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin 4 (IL-4) in vitro. To generate a large number of DCs, we compared the number of DCs generated from leukapheresis products to those from conventional blood samplings in healthy volunteers. The induction rates of the DCs were equal for these two blood samplings, and 10(7) DCs were obtainable from one leukapheresis product. In contrast, the number of DCs varied significantly depending on the individual (30-50% in good responders vs. less than 10% in poor responders). DCs appeared as aggregates of indented cells during culture in good responders, while large cells were floating sparsely in poor responders. Repeated administration of GM-CSF and IL-4 improved the yields of DCs and induced proliferation of autologous lymphocytes in poor responders. As a prototype of cell therapy, the generation of DCs will require a titration of differentiation processes, depending on each individual's responsiveness to cytokines.