Laser-Assisted Intradermal Delivery of Adjuvant-Free Vaccines Targeting XCR1+ Dendritic Cells Induces Potent Antitumoral Responses

The development of vaccines inducing efficient CD8(+) T cell responses is the focus of intense research. Dendritic cells (DCs) expressing the XCR1 chemokine receptor, also known as CD103(+) or CD8α(+) DCs, excel in the presentation of extracellular Ags to CD8(+) T cells. Because of its high numbers of DCs, including XCR1(+) DCs, the skin dermis is an attractive site for vaccine administration. By creating laser-generated micropores through the epidermis, we targeted a model protein Ag fused to XCL1, the ligand of XCR1, to dermal XCR1(+) DCs and induced Ag-specific CD8(+) and CD4(+) T cell responses. Efficient immunization required the emigration of XCR1(+) dermal DCs to draining lymph nodes and occurred irrespective of TLR signaling. Moreover, a single intradermal immunization protected mice against melanoma tumor growth in prophylactic and therapeutic settings, in the absence of exogenous adjuvant. The mild inflammatory milieu created in the dermis by skin laser microporation itself most likely favored the development of potent T cell responses in the absence of exogenous adjuvants. The existence of functionally equivalent XCR1(+) dermal DCs in humans should permit the translation of laser-assisted intradermal delivery of a tumor-specific vaccine targeting XCR1(+) DCs to human cancer immunotherapy. Moreover, considering that the use of adjuvants in vaccines is often associated with safety issues, the possibility of inducing protective responses against melanoma tumor growth independently of the administration of exogenous adjuvants should facilitate the development of safer vaccines.