Background: Monocytapheresis has been established to collect a sufficient number of monocytes (MO) for differentiation to dendritic cells (DC) as a cancer vaccine. Platelets (Plt) are invariably found as a contaminant in the final monocytapheresis product. The aim of this study was to investigate DC differentiation under the influence of Plt with regard to their function and phenotype.
Methods: MO were isolated and co-cultured with autologous Plt at different MO:Plt ratios (1:1.7, 1:5, 1:15, 1:45 and 1:135) in the presence of interleukin-4 (IL-4) and granulocyte-macrophage colony-stimulating factor (GM-CSF). IL-12p70 release after ligation of CD40L was determined in the supernatant by enzyme-linked immunosorbent assay (ELISA). For T-cell stimulation, tetanus toxoid was added to immature DC and maturation was induced by adding cytokines (IL-1beta, IL-6, tumor necrosis factor-alpha and prostaglandin E(2)). Stimulated T cells were analyzed for activation and proliferation as well as for intracellular cytokines by flow cytometry.
Results: All DC cultures were strongly positive for CD83. At a contaminating concentration of 5 Plt/MO, matured DC showed the highest expression of HLA-DR, CD80 and CD86, inducing a strong T-cell proliferation with high production of IL-4 and interferon-gamma. The highest level of IL-12p70 production was observed by the same DC group.
Discussion: Plt did not negatively influence DC maturation but enhanced the expression of co-stimulatory molecules and the release of IL-12. Functionally this was reflected by a strong T-cell response that involved T-helper 1 (Th1)- as well as Th2-biased T cells. Our findings show that controlling the Plt concentration may provide important advantages for the generation of DC for use in immunotherapy.