Oligomerization of bacterially expressed H1N1 recombinant hemagglutinin contributes to protection against viral challenge.

Vaccination is the most effective intervention to prevent influenza and control the spread of the virus. Alternatives are needed to the traditional egg-based vaccine strategy for a more rapid response to new outbreaks. Two different hemagglutinin (HA) fragments (rHA1 and rHA1) derived from influenza A virus subtype H1N1 were expressed in Escherichia coli and characterized by immunoblot, gel filtration, hemagglutination, and competitive binding assays. rHA1 included neutralizing epitopes and the trimerization domain, whereas rHA1 included only the head of HA with the neutralizing epitopes. Mice were immunized with rHA1 or rHA1, and sera were tested for the presence of neutralizing antibodies. Mice were then challenged with H1N1 and infection severity was monitored. rHA1 trimerized, whereas rHA1 was unable to form oligomers. Both rHA1 and rHA1 elicited the production of neutralizing antibodies, but only oligomerized rHA1 protected against live virus challenges in mice. This study demonstrated that bacterially expressed HA was capable of folding properly and eliciting the production of neutralizing antibodies, and that HA oligomerization contributed to protection against viral challenge. Therefore, prokaryotic-derived vaccine platforms can provide antigenic and structural requirements for viral protection, as well as allow for the rapid and cost-effective incorporation of multiple antigens for broader protection.