Abstract
The development of an influenza vaccine with broad protection and durability remains an attractive idea due to the high mutation rate of the influenza virus. An extracellular domain of Matrix 2 protein (M2e) is among the most attractive target for the universal influenza vaccine owing to its high conservancy rate. Here, we generated two recombinant live attenuated influenza vaccine (LAIV) candidates encoding four M2e epitopes representing consensus sequences of human, avian and swine influenza viruses, and studied them in a preclinical ferret model. Both LAIV+4M2e viruses induced higher levels of M2e-specific antibodies compared to the control LAIV strain, with the LAIV/HA+4M2e candidate being significantly more immunogenic than the LAIV/NS+4M2e counterpart. A high-dose heterosubtypic influenza virus challenge revealed the highest degree of protection after immunization with LAIV/HA+4M2e strain, followed by the NS-modified LAIV and the classical LAIV virus. Furthermore, only the immune sera from the LAIV/HA+4M2e-immunized ferrets protected mice from a panel of lethal influenza viruses encoding M genes of various origins. These data suggest that the improved cross-protection of the LAIV/HA+4M2e universal influenza vaccine candidate was mediated by the M2e-targeted antibodies. Taking into account the safety profile and improved cross-protective potential, the LAIV/HA+4M2e vaccine warrants its further evaluation in a phase I clinical trial.
Highlights
Influenza viruses cause acute respiratory tract infections that occur periodically in the form of epidemics and pandemics and remain a major unresolved public health problem worldwide
Mouse studies confirmed that these modified live attenuated influenza vaccine (LAIV) were capable of inducing higher levels of matrix 2 protein (M2e)-specific antibodies compared to classical LAIVs, and these antibodies were associated with enhanced protection against a panel of heterologous and heterosubtypic influenza viruses [6,7]
In an early proof-of-concept study we demonstrated the feasibility of an approach to enhance M2e-specific antibody responses after vaccination
Summary
Influenza viruses cause acute respiratory tract infections that occur periodically in the form of epidemics and pandemics and remain a major unresolved public health problem worldwide. Mouse studies confirmed that these modified LAIVs were capable of inducing higher levels of M2e-specific antibodies compared to classical LAIVs, and these antibodies were associated with enhanced protection against a panel of heterologous and heterosubtypic influenza viruses [6,7] To further optimize these vaccine candidates, we adjusted the consensus amino acid sequences of the M2e epitopes according to our comprehensive analysis of all influenza A viruses circulating in human and animal reservoirs [5]. The new 4M2e construct consisted of four 23 amino acids-long M2e epitopes separated by flexible linkers, including consensus human (classical human, hM2e), swine (M2 of classical swine lineage, sM2e), avian/swine (M2 of swine influenza viruses derived from Eurasian avian H1N1, a/sM2e), and human/swine (M2 of pandemic H1N1, h/sM2e) M2 lineages This construct was inserted in full-length HA or truncated NS1 genes of an H3N2 LAIV virus and two recombinant LAIV+4M2e viruses were assessed in a pre-clinical ferret model. Ferrets are considered the best test system for studying influenza in humans, as they are most susceptible to infection with virulent strains of influenza virus when administered intranasally and their infection proceeds as in humans with similar clinical symptoms [8]
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