Abstract
Conserved epitopes are targets commonly researched to be part of universal vaccine candidates against influenza viruses (IV). These conserved epitopes need to be cross-protecting against distinct IV subtypes and to have a strong immunogenic potential. Nevertheless, subunit vaccines generally require a strong adjuvant to enhance their immunological effects. Herewith, we compare four different adjuvants differing in their immunological signatures that may enhance efficacy of a conserved hemagglutinin (HA)-epitope from IV, the NG-34, to define the most efficient combination of antigen/adjuvant to combat IV infections. Soluble NG-34 was mixed with adjuvants like aluminium hydroxide (AH) and AddaVax, known to induce Th2 and humoral responses; CAF01 which displays a biased Th1/Th17 profile and Diluvac Forte which augments the humoral response. Combinations were tested in different groups of mice which were subjected to immunological analyses. CAF01 + NG-34 induced a complete immune response with the highest IgG1, IgG2c titers and percentages of activated CD4 T cell promoting IFN-γ, IL-2 and TNF-α producing cells. Furthermore, in NG-34 stimulated mice splenocytes, cytokine levels of IFN-γ, IL-1β, IL-6, IL-10, IL-17 and TNF-α were also the highest in the CAF01 + NG-34 mouse group. This complete induced immune response covering the humoral and the cellular arms of the adaptive immunity promoted by CAF01 + NG-34 group suggests that CAF01 could be a good candidate as an adjuvant to combine with NG-34 for an efficacious vaccine against IV. However, more studies performed in IV hosts as well as studies with a challenge model are further required.