Heamagglutinin Conserved Domain (HA2) Prepared in Prokaryotic System is Immunogenic in Mice but not Protective against Lethal Influenza Challenge

Influenza vaccine production process is time-consuming with little-to-no cross-protection which requires annual adjustment. The construction of a universal vaccine to deal with the pandemics and epidemics which occasionally threat human population is the aim of many researches worldwide. Today, influenza vaccines are mostly against two major antigenic proteins, hemagglutinin and neuraminidase. As compared to high variable globular head, the hemagglutinin stalk domain is more conserved among different subtypes of influenza A viruses which could be a good candidate to develop a cross-protective vaccine. In this study, recombinant HA2 protein comprising fusion peptide was expressed in E.coli, purified using Ni-TED columns, refolded and desalted by dialysis. BALB/c mice in different groups were immunized with HA2 alone or supplemented with Alum or Alum/CPG. Vaccinated mice sera were examined for anti-HA2 specific IgG responses. Finally, mice were challenged with one LD90 of mouse-adapted A/PR8 virus. The results showed that HA2 recombinant protein could provoke immunogenicity in BALA/c mice and this immune response could be elevated with Alum and Alum/CpG. Despite promising immune responses, there was insignificant protection of HA2-immunized mice when challenged with the mouse-adapted strain A/PR8. Therefore, HA2 protein alongside with other influenza virus conserved proteins should be studied to achieve a suitable vaccine formulation for broad spectrum cross-reactive immune responses.