Abstract
Influenza viruses constantly evolve, reducing the overall protective effect of routine vaccination campaigns. Many different strategies are being explored to design universal influenza vaccines capable of protecting against evolutionary diverged viruses. The ectodomain of influenza A M2e protein (M2e) is among the most promising targets for universal vaccine design. Here, we generated two recombinant live attenuated influenza vaccines (LAIVs) expressing additional four M2e tandem repeats (4M2e) from the N-terminus of the viral hemagglutinin (HA) protein, in an attempt to enhance the M2e-mediated cross-protection. The recombinant H1N1+4M2e and H3N2+4M2e viruses retained growth characteristics attributable to traditional LAIV viruses and induced robust influenza-specific antibody responses in BALB/c mice, although M2e-specific antibodies were raised only after two-dose vaccination with LAIV+4M2e viruses. Mice immunized with either LAIV or LAIV+4M2e viruses were fully protected against a panel of heterologous influenza challenge viruses suggesting that antibody and cell-mediated immunity contributed to the protection. The protective role of the M2e-specific antibody was seen in passive serum transfer experiments, where enhancement in the survival rates between classical LAIV and chimeric H3N2+4M2e LAIV was demonstrated for H3N2 and H5N1 heterologous challenge viruses. Overall, the results of our study suggest that M2e-specific antibodies induced by recombinant LAIV+4M2e in addition to cellular immunity by LAIV play an important role in conferring protection against heterologous viruses.
Highlights
Influenza is a highly contagious pathogen possessing a serious threat to worldwide human population [1]
To confirm that the inserted four matrix 2 protein (M2e) tandem repeats are expressed on the surface of the recombinant live attenuated influenza vaccines (LAIVs)+4M2e viruses, we performed ELISA, where sucrose gradient-purified LAIV viruses were used as coating antigens and M2e-specific 14C2 was used as a primary antibody
Both H1N1 and H3N2 recombinant LAIV+4M2e viruses were able to bind 14C2 antibody, whereas their classical analogs did not react with this antibody, suggesting that the additional
Summary
Influenza is a highly contagious pathogen possessing a serious threat to worldwide human population [1]. The main obstacle for controlling influenza outbreaks is that the influenza virus tends to evolve and accumulate genetic changes to escape anti-influenza population immunity, generating novel epidemic and pandemic strains. Vaccines 2020, 8, 648 hemagglutinin (HA) and neuraminidase (NA) of influenza strains circulating in human population. Another evolutional mechanism, termed «antigenic shift», results in introduction of novel surface protein variants specific to non-human species, such as avian or swine, in human circulating influenza viruses. Current influenza virus vaccines are effective only when the predicted vaccine strains and circulating viruses are well-matched. The current strategy of influenza vaccination does not prevent the pandemic outbreaks, and protection efficacy is reduced or ineffective if mutant strains emerge
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