Messenger RNA electroporation of human monocytes, followed by rapid in vitro differentiation, leads to highly stimulatory antigen-loaded mature dendritic cells.

Dendritic cells (DC) are professional Ag-capturing and -presenting cells of the immune system. Because of their exceptional capability of activating tumor-specific T cells, cancer vaccination research is now shifting toward the formulation of a clinical human DC vaccine. We developed a short term and serum-free culture protocol for rapid generation of fully mature, viable, and highly stimulatory CD83(+) DC. Human monocytes were cultured for 24 h in serum-free AIM-V medium, followed by 24-h maturation by polyriboinosinic polyribocytidylic acid (polyI:C). Short term cultured, polyI:C-maturated DC, far more than immature DC, showed typical mature DC markers and high allogeneic stimulatory capacity and had high autologous stimulatory capacity in an influenza model system using peptide-pulsed DC. Electroporation of mRNA as an Ag-loading strategy in these cells was optimized using mRNA encoding the enhanced green fluorescent protein (EGFP). Monocytes electroporated with EGFP mRNA, followed by short term, serum-free differentiation to mature DC, had a phenotype of DC, and all showed positive EGFP fluorescence. Influenza matrix protein mRNA-electroporated monocytes cultured serum-free and maturated with polyI:C showed high stimulatory capacity in autologous T cell activation experiments. In conclusion, the present short term and serum-free ex vivo DC culture protocol in combination with mRNA electroporation at the monocyte stage imply an important reduction in time and consumables for preparation of Ag-loaded mature DC compared with classical DC culture protocols and might find application in clinical immunotherapy settings.