Modulation of Regulatory T Cell Function by Monocyte-Derived Dendritic Cells Matured through Electroporation with mRNA Encoding CD40 Ligand, Constitutively Active TLR4, and CD70

Regulatory T cells (T-regs) counteract anticancer immune responses through a number of mechanisms, limiting dendritic cell (DC)-based anticancer immunotherapy. In this study, we investigated the influence of various DC activation stimuli on the T-reg functionality. We compared DCs activated by electroporation with mRNA encoding constitutively active TLR4 (caTLR4) and CD40 ligand (DiMix-DCs), or these factors together with mRNA encoding the costimulatory molecule CD70 (TriMix-DCs) with DCs maturated in the presence of a mixture of inflammatory cytokines (DCs maturated with a combination of the cytokines IL-1 beta, IL-6, TNF-alpha, and PGE(2)) for their ability to counteract T-regs on different levels. We first demonstrated that there was no difference in the extent of T-reg induction starting from CD4(+)CD252(-) T cells under the influence of the different DC maturation stimuli. Second, we showed that both DiMix- and TriMix-DCs could partly alleviate T-reg inhibition of CD8(+) T cells. Third, we observed that CD8(+) T cells that had been precultured with DiMix-DCs or TriMix-DCs were partially protected against subsequent T-reg suppression. Finally, we showed that T-regs cocultured in the presence of TriMix-DCs, but not DiMix-DCs, partially lost their suppressive capacity. This was accompanied by a decrease in CD27 and CD25 expression on T-regs, as well as an increase in the expression of T-bet and secretion of IFN-gamma, TNF-alpha, and IL-10, suggesting a shift of the T-reg phenotype toward a Th1 phenotype. In conclusion, these data suggest that TriMix-DCs are not only able to suppress T-reg functions, but moreover could be able to reprogram T-regs to Th1 cells under certain circumstances.