Incorporation of polyinosine-polycytidylic acid enhances cytotoxic T cell activity and antitumor effects by octaarginine-modified liposomes encapsulating antigen, but not by octaarginine-modified antigen complex.

In a previous study, we reported on the efficient delivery of an antigen to the cytosol and a specific-antigen presentation on MHC class I in dendritic cells by rationally controlling the intracellular trafficking of ovalbumin (OVA), a model antigen, with stearylated octaarginine-modified liposomes (R8-Lip/OVA). However, no significant difference in antitumor effects against E.G7-OVA, OVA expressed lymphoma, was observed between R8-Lip/OVA and an electrostatic complex of R8 and OVA (R8/OVA-Com). In this study, we hypothesized that use of adjuvants clarified the difference in immune responses between R8-Lip/OVA and R8/OVA-Com, and selected polyinosine-polycytidylic acid (polyI:C) as an adjuvant. Cytotoxic T lymphocyte (CTL) activity of the polyI:C and OVA encapsulated R8-Lip (R8-Lip/PIC/OVA) was drastically enhanced compared to R8-Lip/OVA and complete Freund's adjuvant with OVA. Moreover, the incorporation of polyI:C clearly was critical for the difference in antitumor effects and CTL activities between R8-Lip/OVA and R8/OVA-Com. These findings suggest that the carriers that are incorporated polyI:C has a great influence on the induction of cellular immunity in vivo.