Noninvasive Transdermal Administration of mRNA Vaccines Encoding Multivalent Neoantigens Effectively Inhibits Melanoma Growth

It is difficult to obtain specific tumor antigens, which is one of the main obstacles in the development of tumor vaccines. The vaccines containing multivalent antigens are thought to be more effective in antitumor therapy. In this study, a mRNA encoding three neoantigens of melanoma were prepared and encapsulated into the mannosylated chitosan-modified ethosomes (Eths^MC) to obtain a multivalent mRNA vaccine (MmRV) for transcutaneous immunization (TCI). MmRV can effectively induce maturation of dendritic cells, with a better performance than mRNA of a single neoantigen. TCI patches (TCIPs) loading MmRV or siRNA against PDL1 (siPDL1) were prepared and applied to the skin of melanoma-bearing mice. The results showed that TCIPs significantly increase the levels of TNF-α, IFN-γ, and IL-12 in both plasma and tumor tissues, inhibit tumor growth, as well as promote infiltration of CD⁴⁺ and CD⁸⁺ T cells in the tumor tissues. Furthermore, the combination of MmRV and siPDL1 showed much better antitumor effects than either monotherapy, suggesting a synergistic effect between the vaccine and PDL1 blocker. In addition, the treatment with the TCIPs did not cause damage to the skin, blood, and vital organs of the mice, showing good biosafety. To the best of our knowledge, this work is the first to construct a noninvasive TCI system containing MmRV and siPDL1, providing a convenient and promising approach for tumor treatment.