Transcutaneous immunization with CD40 ligation boosts cytotoxic T lymphocyte mediated antitumor immunity independent of CD4 helper cells in mice.

Transcutaneous immunization (TCI) is a novel vaccination strategy that utilizes skin-associated lymphatic tissue to induce immune responses. Employing T-cell epitopes and the TLR7 agonist imiquimod onto intact skin mounts strong primary, but limited memory CTL responses. To overcome this limitation, we developed a novel imiquimod-containing vaccination platform (IMI-Sol) rendering superior primary CD8+ and CD4+ T-cell responses. However, it has been unclear whether IMI-Sol per se is restricted in terms of memory formation and tumor protection. In our present work, we demonstrate that the combined administration of IMI-Sol and CD40 ligation unleashes fullblown specific T-cell responses in the priming and memory phase, strongly enhancing antitumor protection in mice. Interestingly, these effects were entirely CD4+ T cell independent, bypassing the necessity of helper T cells. Moreover, blockade of CD70 in vivo abrogated the boosting effect of CD40 ligation, indicating that the adjuvant effect of CD40 in TCI is mediated via CD70 on professional APCs. Furthermore, this work highlights the so far underappreciated importance of the CD70/CD27 interaction as a promising adjuvant target in TCI. Summing up, we demonstrate that the novel formulation IMI-Sol represents a powerful vaccination platform when applied in combination with sufficient adjuvant thereby overcoming current limitations of TCI.

Combined immunotherapy: CTLA-4 blockade potentiates anti-tumor response induced by transcutaneous immunization.

BACKGROUND: The epidermal application of the Toll Like Receptor 7 agonist imiquimod and a T-cell peptide epitope (transcutaneous immunization, TCI) mediates systemic peptide-specific cytotoxic T-cell (CTL) responses and leads to tumor protection in a prophylactic tumor setting. However, it does not accomplish memory formation or permanent defiance of tumors in a therapeutic set-up. As a distinct immunologic approach, CTLA-4 blockade augments systemic immune responses and has shown long-lasting effects in preclinical experiments as well as in clinical trials. OBJECTIVE: The study investigates the vaccination capacity of TCI in combination with the checkpoint inhibitor CTLA-4 in matters of primary response, memory formation and tumor protection and characterizes the role of regulatory T cells (Tregs). METHODS: After performing TCI with IMI-Sol (containing 5% Imiquimod) and the model epitope SIINFEKL, 6-8 week old C57BL/6 mice received anti-CTLA-4 antibody either s.c or i.p. The CTL responses and frequency of peptide specific CD8+ T-cells were then evaluated on day 8. To determine anti-tumor effects, a therapeutic tumor challenge with B16 OVA melanoma was performed. RESULTS: The combination of s.c. anti-CTLA-4 antibody and TCI leads to an enhanced systemic cytotoxic response, to memory formation and allows significantly improved survival in a tumor setting with B16 OVA melanoma. Towards the mechanism, we show that in this vaccination protocol the CTLA-4 antibody acts mainly Treg-independent. CONCLUSION: We demonstrate that the combination of TCI with IMI-Sol and anti-CTLA-4 can confer potent immune responses and tumor-protection. These results might contribute to the development of advanced vaccination approaches targeting tumors or persistent infectious diseases.