Subcutaneous co-administration of the STING agonist, c-di-AMP, to the recombinant influenza nucleoprotein leads to an enhanced immune response and provides broad protection

SANCHEZ, MARIA VICTORIA; EBENSEN, THOMAS; SCHULZE, KAI; CARGNELUTTI, DIEGO ESTEBAN; IBAÑEZ, ITATI; SCODELLER, EDUARDO; GUZMAN, CARLOS

Alberta

Simposio; Keystone Symposium J5 Emerging Technologies in Vaccine Discovery and Development conference; 2018

Bill and Melinda Gates Foundation

Seasonal influenza vaccines mediate the protection trough the induction of strain-specific antibodies which neutralize only viruses contained in the vaccine. Occasionally, antigenic mismatches between vaccine strains and the circulating virus lead to a suboptimal vaccine efficacy. This situation becomes more problematic in case of the emergence of new pandemic strains, for which the world´s population have scarce immunological protection. Cellular immune responses have been reported to be very effective to reduce influenza morbidity and mortality in human and animal models. However, the current vaccines fail to induce significant cellular responses.An interesting approach to induce robust cellular immune responses could be achieved by the use of conserved antigens and an appropriate adjuvant in the vaccine formulation. The nucleoprotein is a very good candidate to be used in universal influenza vaccines since this one induces strong T-cell mediated immune responses able to provide cross-protection against highly virulent strains. The STING agonists ( cyclic di-nucleotides) have received much attention recently for their excellent properties to improve immune responses co-administered with antigens, mainly by mucosal route. However, the properties of these adjuvants by the parenteral route have not been deeply studied.Here, we have developed a vaccine formulated with the recombinant viral nucleoprotein (rNP) in combination with a STING agonist, the c-di-AMP adjuvant. The vaccine was administered in mice by subcutaneous route in a two-dose regimen (on day 1 and on day 21). Humoral and cellular immune responses induced by the adjuvanted and non-adjuvanted vaccinations were evaluated, as well as the efficacy of cross-protection against two different influenza strains.We found that the adjuvanted formulation induced significant NP-specific titers of IgG, and IgG1 and IgG2a subclasses, compared to non-adjuvanted formulation. The cellular immune response of mice immunized with the adjuvanted formulation showed mainly Th1 and lower Th2 bias-response. ELISPOT assays of these animals showed high numbers of spleen cells secreting IFN-γ and IL-2, and lower number of spleen cells secreting IL-4. Cytotoxicity assay in vivo with CFSE showed that mice vaccinated with the adjuvanted formulation induced significant cell-mediated cytotoxicity, compared to non-adjuvanted vaccination.