Novel Adjuvant Based on the Pore-Forming Protein Sticholysin II Encapsulated into Liposomes Effectively Enhances the Antigen-Specific CTL-Mediated Immune Response

Vaccine strategies to enhance CD8(+) CTL responses remain a current challenge because they should overcome the plasmatic and endosomal membranes for favoring exogenous Ag access to the cytosol of APCs. As a way to avoid this hurdle, sticholysin (St) II, a pore-forming protein from the Caribbean Sea anemone Stichodactyla helianthus, was encapsulated with OVA into liposomes (Lp/OVA/StII) to assess their efficacy to induce a CTL response. OVA-specific CD8(+) T cells transferred to mice immunized with Lp/OVA/StII experienced a greater expansion than when the recipients were injected with the vesicles without St, mostly exhibiting a memory phenotype. Consequently, Lp/OVA/StII induced a more potent effector function, as shown by CTLs, in vivo assays. Furthermore, treatment of E.G7-OVA tumor-bearing mice with Lp/OVA/StII significantly reduced tumor growth being more noticeable in the preventive assay. The contribution of CD4(+) and CD8(+) T cells to CTL and antitumor activity, respectively, was elucidated. Interestingly, the irreversibly inactive variant of the StI mutant StI W111C, encapsulated with OVA into Lp, elicited a similar OVA-specific CTL response to that observed with Lp/OVA/StII or vesicles encapsulating recombinant StI or the reversibly inactive StI W111C dimer. These findings suggest the relative independence between StII pore-forming activity and its immunomodulatory properties. In addition, StII-induced in vitro maturation of dendritic cells might be supporting these properties. These results are the first evidence, to our knowledge, that StII, a pore-forming protein from a marine eukaryotic organism, encapsulated into Lp functions as an adjuvant to induce a robust specific CTL response.Center of Molecular ImmunologyInternational Foundation for ScienceCAPES-MESUniv Havana, Ctr Prot Studies, Fac Biol, Calle 25 Entre J & I,455,Plaza Revoluc, Havana 10400, CubaCtr Mol Immunol, Immunobiol Div, Havana 11600, CubaUniv Fed Sao Paulo, Paulista Med Sch, Dept Microbiol Immunol & Parasitol, Discipline Immunol, BR-04023900 Sao Paulo, BrazilHarvard Med Sch, Dept Microbiol & Immunobiol, Boston, MA 02115 USAMcGill Univ, Goodman Canc Res Ctr, Montreal, PQ, CanadaMcGill Univ, Dept Biochem, Montreal, PQ, CanadaUniv Fed Sao Paulo, Paulista Med Sch, Dept Microbiol Immunol & Parasitol, Discipline Immunol, BR-04023900 Sao Paulo, BrazilCAPES-MES: 111/11Web of Scienc