Polyguanine-conjugated antigens target scavenger receptors in dendritic cells and induce antitumor immunity against melanoma

Abstract

Abstract We have developed a vaccine design involving the conjugation of polyguanine (Poly(dG)) to protein or peptide antigens for the specific targeting of scavenger receptors in dendritic cells with intrinsic adjuvant capabilities. We have shown that Poly(dG) conjugation to ovalbumin generates stable particle conjugates (Poly(dG)-OVA) that induce greater T cell (helper, cytotoxic, and memory) and antibody responses. In this study, we show that Poly(dG)-OVA treatment of DCs in vitro induces greater antigen internalization and expression of activation markers CD86, MHC II, and CCR7. In vivo, intradermal injection of Poly(dG)-OVA resulted in the formation of an antigen depot in the skin lasting for several days and an increase in recruited immune infiltrates. Increased association of Poly(dG)-OVA is observed with MHC II- and CD11c-expressing cells in the skin compared to OVA. This is accompanied by the expression of pro-inflammatory CCL2 and IL-6 in the skin. Poly(dG)-OVA was also able to internalize more in skin migrating DCs and was transported more efficiently to draining lymph nodes. Poly(dG)-OVA immunization of B16-OVA-bearing mice contributed to delayed tumor progression and improved survival. We also developed Poly(dG)-Mgp10025–33 and Poly(dG)-TRP2180–188 to study melanoma-specific responses. Immunization with the these conjugates led to significant peptide-specific in vivo cytotoxic T cell responses compared to unconjugated peptides. Mice with B16 tumors immunized with combined Poly(dG)-Mgp100 Poly(dG)-TRP2 had delayed tumor progression and improved survival. Our results show that Poly(dG) conjugation of antigens is an effective strategy for the development of antitumor vaccines with improved immune responses.