No escape mutants and decreased variability of viral quasispecies after immunization against long alpha helix of pandemic H1N1 in a mouse model study

[Keine Fluchtmutanten und verminderte Variabilität der viralen
Quasispezies nach Impfung gegen die lange Alpha-Helix von
pandemischem H1N1 im Mausversuch]
For an increase in pandemic preparedness and to overcome yearly efforts and costs for the production of seasonal influenza vaccines, new approaches for the induction of broadly protective and long-lasting immune responses have been developed during the past decade. It is critical to understand the evolution of influenza viruses in response to Universal Influenza Vaccines. Antibody pressure on conserved domains may increase their variability and lead to the rise of escape mutants. Here we used a mouse challenge model with a vaccine construct targeting the long alpha helix of hemagglutinin stalk to identify alterations in quasispecies composition. The viral ribonucleic acid from lungs of vaccinated and non-vaccinated mice was extracted and analyzed using a next generation sequencing approach. The viral ribonucleic acid in the supernatant of infected Madin Darby Canine kidney cells was used as comparison. The vaccine used elicited significant seroconversion and protection against homologous and heterologous influenza virus strains in mice. The vaccine not only significantly reduced lung viral titers, but also induced a well-known bottleneck effect by decreasing virus diversity. In contrast to the classical bottleneck effect, here we showed a significant increase in the frequency of viruses with amino acid sequences identical to that of vaccine targeting the long alpha helix domain. No emergence of escape mutants in significant quantity was detected after vaccination. These findings support the potential of targeting the conserved long alpha helix domains and add to the hope of having a potent and safe Universal Influenza Vaccine in the near future.