Vaccination with three tandem repeats of M2 extracellular domain fused to Leismania major HSP70 protects mice against influenza A virus challenge.

Influenza viruses are globally important respiratory pathogens with high degree of morbidity and mortality during annual epidemics. Influenza A vaccination has been challenged due to genetic evolution. M2 protein is the surface antigen of the virus and facilitates virus entry into the host cells. N-terminal 24 amino acid residues that constitute the extracellular domain of M2 protein (M2e) show remarkable conservation among all subtypes of influenza A viruses. The aim of the present study was to investigate the effects of using HSP70 as an adjuvant fused to three tandem repeats of M2e (3M2e) to enhance the immune responses against influenza A challenge. The mice were immunized three times by intradermal inoculations of 3M2e alone or in combination with Alum adjuvant or in fused form to HSP70. The specific immune responses were evaluated by measuring the serum antibody titers, lymphocyte proliferation, as well as Th1 and Th2 cytokines. The results showed that, although 3M2e with no adjuvant could induce secretion of specific antibodies, significantly higher humoral immune responses were stimulated in combination with Alum adjuvant (p < 0.05). Moreover, analysis of specific immune responses revealed that the 3M2e-HSP70 chimer protein mainly stimulated IgG2a and IFN-γ responses indicating aTh1 bias which shows the ability of HSP as a powerful adjuvant for activation of cellular immune responses. This was supported by a higher IgG2a/IgG1 ratio, significantly increased IL-4 production and lymphocyte proliferation (P ˂ 0.001) compared with mice vaccinated with 3M2e alone or supplemented with Alum, suggesting a mixture of Th1 and Th2 type cellular immune response with a Th1 bias. The findings of this study indicated that 3M2e-HSP70 enhances humoral and cellular immune responses and improves immune protection against influenza challenge in mice. Thus, it has the potential to be used as a promising vaccine candidate.