Enhanced dendritic cell antigen presentation in RNA-based immunotherapy

Background. Dendritic cells pulsed with mRNA provide a unique approach to tumor immunotherapy. We hypothesized that increased mRNA transfection efficiency and dendritic cell maturation would improve antigen processing and presentation as well as T-cell costimulation, resulting in enhanced induction of antimelanoma immune responses. Methods. Immature monocyte-derived dendritic cells were transfected with mRNA by passive pulsing, lipofection, or electroporation. Dendritic cells were either left untreated or matured using the double-stranded RNA poly(I:C). T-Cell cultures were generated by stimulation of naïve T-cells with each set of dendritic cells. Specific antigen presentation and specific effector T-cell generation were analyzed by an IFN-γ release Elispot assay. Results. Greatest intracellular green fluorescent protein was observed by flow cytometry following dendritic cell electroporation with green fluorescent protein mRNA. DC presentation of Mart-1/Melan A peptide, as measured by Elispot assay using a specific T-cell clone, was greatest following transfection with Mart-1/Melan A mRNA by electroporation. Maturation of dendritic cells further improved antigen presentation regardless of transfection technique. Specific Mart-1/Melan A effector T cells were produced after culture of naïve T cells with dendritic cells that were electroporated with Mart-1/Melan A mRNA and then matured, but not for dendritic cells that remained immature. Conclusions. Efficient mRNA transfection by electroporation as well as dendritic cell maturation results in increased levels of Mart-1/Melan A antigen presentation and enhanced production of antigen-specific effector T cells. This combination of strategies may be used to enhance immune responses to RNA-based dendritic cell vaccines.