Short-term stimulation of mouse CD8 + T cells in vitro with the TLR9 agonist CpG enhances their antigen-specific expansion in vivo after administration of the TLR3 agonist Poly(I:C)

Abstract

Recent preclinical studies, including ours, have shown that the conditioning of CD8 + T cells in vitro with certain cytokines, in particular IL-2, IL-7, IL-12, and IL-15, can significantly enhance anti-cancer adoptive T cell therapy. Given the pleiotropic effect of toll-like receptor ligands (TLRLs) on innate and adaptive immune cells as compared to a single cytokine, we aimed in this study to use TLR3L (Poly (I: C)) and TLR9L (CpG) to condition T cells in vitro as compared to IL-12. Splenocytes were harvested from pmel-1 TCR transgenic mice, in which CD8+ T cells are engineered to recognize MHC class-1 melanoma peptide. Cultured splenocytes for 24 h in vitro with media or with MHC class-1 melanoma peptide plus or minus IL-12, TLR3L or TLR9L for assessment of their activation, proliferation and cytokine production or adoptively transferred to syngeneic B6 mice which followed by peptide vaccination with TLR3L or TLR9L. Interestingly, the enhanced antigen-specific proliferation of CD8+ T cells by TLR3L and TLR9L was associated with antigen-independent proliferation of non-CD8+ T cells in the spleen. More interestingly, the differences in vitro and in vivo combination of TLR3L and TR9L showed that the best antigen-specific expansion of adoptively transferred CD8+ T cells was seen when CD8+ T cells were stimulated in vitro with TLR9L and TLR3L in vivo. In conclusion, our results indicate that conditioning of CD8+ T cells in vitro and in vivo with certain TLRLs can markedly enhance their antigen-specific responses upon their adoptive transfer mediated by the bystander effect of B cells.