Transcutaneous immunization with imiquimod is amplified by CD40 ligation and results in sustained cytotoxic T-lymphocyte activation and tumor protection

Transcutaneous immunization (TCI) using ligands of Toll-like receptors (TLRs) and cytotoxic T-lymphocyte (CTL) epitopes lead to the induction of potent T-cell responses. To characterize the efficacy of TCI-mediated CTL activation, we monitored the frequency and functional activity of specific CTL induced with TCI using the ovalbumin-derived epitope SIINFEKL composed in creme containing the synthetic TLR7 ligand R-837. We found that the frequency and activity decayed rapidly 10 d post-TCI. Consistently, no significant memory T-cell formation was detectable. In a prophylactic vaccination setting, TCI was protective against a lethal challenge with ovalbumin expressing EG.7 thymoma cells when the tumor cells were inoculated 5 d later. However, only a delay of tumor growth was observed when the tumor challenge was performed 55 d after immunization. Conversely, a single combined treatment with TCI and an agonist anti-CD40 (FGK-45) monoclonal antibody greatly enhanced the primary response, with up to 30% of peptide-specific CTL and the effective induction of memory cells. Consequently, mice treated with TCI/anti-CD40 were completely protected against a lethal tumor challenge with EG.7 tumor cells after 55 d.