The TLR3 agonist poly(I:C) targets CD8+T cells and augments their antigen-specific responses upon their adoptive transfer into naive recipient mice

We have recently reported that the toll-like receptor 3 (TLR3) agonist poly(1:Q induces adjuvant effects to post vaccination CD8+ T cells responses through rapid induction of innate mediators, including NK cells, macrophages, dendritic cells (DCs), and inflammatory cytokines. However, whether this TLR3 agonist directly targets CD8+ T cells needs to be carefully investigated. In this study, we found that optimal post vaccination CD8+ T cell responses to ex vivo DC-based vaccination requires triggering of TLR3 signaling pathway in DCs in vitro as well as in the recipient host, indicating a role for other cell types. Real-time PCR analysis revealed that TLRs (TLP1-TLR13) are expressed ill Purified (>99% pure) CD4+ and CD8+ T cells from C57BL/6 and BALB/c mice, where the magnitude of the expression was strain and cell type dependent. In Vitro, treatment of these purified T cells with poly(l:C) modulated the expression of TLRs including TLR3. Furthermore, non-specific and antigen-specific Stimulation of CD8+ T cells by phorbol myristate acetate and MHC class 1 peptide-pulsed splenocytes, respectively, modulated TLR expression in purified CD4+ and CD8+ T cells. Importantly, brief conditioning Of Purified naive TCR transgenic OT-1 (CD8+) T cells in vitro with poly(1:Q induced activation of these cells in absence of antigen stimulation. Interestingly, when these in vitro poly(I:C)-conditioned OT-1 cells were adoptively transferred into naive recipient followed by peptide vaccination, they showed superior expansion and activation to their naive counterparts. These results suggest that CD8+ T cells can be activated by triggering their TLR3. Furthermore, the data support the notion of direct involvement of TLRs in adaptive immune responses. (C) 2008 Elsevier Ltd. All rights reserved.