Hollow microneedle-mediated micro-injections of a liposomal HPV E7 43-63 synthetic long peptide vaccine for efficient induction of cytotoxic and T-helper responses.

Recent studies have shown that intradermal vaccination has great potential for T cell-mediated cancer immunotherapy. However, classical intradermal immunization with a hypodermic needle and syringe has several drawbacks. Therefore, in the present study a digitally controlled hollow microneedle injection system (DC-hMN-iSystem) with an ultra-low dead volume was developed to perform micro-injections (0.25-10μL) into skin in an automated manner. A synthetic long peptide derived from human papilloma virus formulated in cationic liposomes, which was used as a therapeutic cancer vaccine, was administered intradermally by using the DC-hMN-iSystem. Fused silica hollow microneedles with an inner diameter of 50μm and a bevel length of 66±26μm were successfully fabricated via hydrofluoric acid etching. Upon piercing these microneedles into the skin using a protrusion length of 400μm, microneedles were inserted at a depth of 350±55μm. Micro-injections of 1-10μL had an accuracy between 97 and 113% with a relative standard deviation (RSD) of 9%, and lower volumes (0.25 and 0.5μL) had an accuracy of 86-103% with a RSD of 29% in ex vivo human skin. Intradermal administration of the therapeutic cancer vaccine via micro-injections induced strong functional cytotoxic and T-helper responses in mice, while requiring much lower volumes as compared to classical intradermal immunization. In conclusion, by using the newly developed DC-hMN-iSystem, very low vaccine volumes can be precisely injected into skin in an automated manner. Thereby, this system shows potential for minimally-invasive and potentially pain-free therapeutic cancer vaccination.