Efficient presentation of tumor idiotype to autologous T cells by CD83+ dendritic cells derived from highly purified circulating CD14+ monocytes in multiple myeloma patients

Objectives To generate mature and fully functional CD83+ dendritic cells derived from circulating CD14+ cells highly purified from the leukapheresis products of multiple myeloma patients. Materials and Methods CD14+ monocytes were selected by high-gradient magnetic separation and differentiated to immature dendritic cells with granulocyte-macrophage colony-stimulating factor and interleukin-4 for 6–7 days and then induced to terminal maturation by the addition of tumor necrosis factor-α or stimulation with CD40 ligand. Dendritic cells were characterized by immunophenotyping, evaluation of soluble antigens uptake, cytokine secretion, capacity of stimulating allogeneic T cells, and ability of presenting nominal antigens, including tumor idiotype, to autologous T lymphocytes. Results Phenotypic analysis showed that 90% ± 6% of cells recovered after granulocyte-macrophage colony-stimulating factor and interleukin-4 stimulation expressed all surface markers typical of immature dendritic cells and demonstrated a high capacity of uptaking soluble antigens as shown by the FITC-dextran assay. Subsequent exposure to maturation stimuli induced the downregulation of CD1a and upregulation of CD83, HLA-DR, costimulatory molecules and induced the secretion of large amounts of interleukin-12. Mature CD83+ cells showed a diminished ability of antigen uptake whereas they proved to be potent stimulators of allogeneic T cells in a mixed lymphocyte reaction. Monocyte-derived dendritic cells, pulsed before the addition of maturation stimuli, were capable of presenting soluble proteins such as keyhole limpet hemocyanin and tetanus toxoid to autologous T cells for primary and secondary immune response, respectively. Conversely, pulsing of mature (CD83+) dendritic cells was less efficient for the induction of T-cell proliferation. More importantly, CD14+ cells-derived dendritic cells stimulated autologous T-cell proliferation in response to a tumor antigen such as the patient-specific idiotype. Moreover, idiotype-pulsed dendritic cells induced the secretion of interleukin-2 and γ-interferon by purified CD4+ cells. T-cell activation was better achieved when Fab immunoglobulin fragments were used as compared with the whole protein. When dendritic cells derived from CD14+ cells from healthy volunteers were analyzed, we did not find any difference with samples from myeloma patients as for cell yield, phenotypic profile, and functional characteristics. Conclusion These studies demonstrate that mobilized purified CD14+ cells represent the optimal source for the production of a homogeneous cell population of mature CD83+ dendritic cells suitable for clinical trials in multiple myeloma.