History of Live, Attenuated Influenza Vaccine

Exploiting membrane vesicles derived from avian pathogenic Escherichia coli as a cross-protective subunit vaccine candidate against avian colibacillosis

Avian pathogenic Escherichia coli (APEC) is a notable pathogen that frequently leads to avian colibacillosis, posing a substantial risk to both the poultry industry and public health. The commercial vaccines against avian colibacillosis are primarily inactivated vaccines, but their effectiveness is limited to specific serotypes. Recent advances have highlighted bacterial membrane vesicles (MV) as a promising candidate in vaccine research. How to produce bacterial MVs vaccines on a large scale is a significant challenge for the industrialization of MVs. The msbB gene encodes an acyltransferase and has been implicated in altering the acylation pattern of lipid A, leading to a decrease in lipid A content in lipopolysaccharides (LPS). Here, we evaluated the immunoprotective efficacy of MVs derived from the LPS low-expressed APEC strain FY26ΔmsbB, which was an APEC mutant strain with a deletion of the msbB gene. The nitrogen cavitation technique was employed to extract APEC MVs, with results indicating a significant increase in MVs yield compared to that obtained under natural culture. The immunization effectiveness was assessed, revealing that FY26ΔmsbB MVs elicited an antibody response of laying hens and facilitated bacterial clearance. Protective efficacy studies demonstrated that immunization with FY26ΔmsbB MVs conferred the immune protection in chickens challenged with the wild-type APEC strain FY26. Notably, LPS low-carried MVs recovered from the mutant FY26ΔmsbB also displayed cross-protective capabilities, and effectively safeguarding against infections caused by O1, O7, O45, O78, and O101 serotypes virulent APEC strains. These findings suggest that MVs generated from the LPS low-expressed APEC strain FY26ΔmsbB represent a novel and empirically validated subunit vaccine for the prevention and control of infections by various APEC serotypes.

Influenza Vaccine Effectiveness and Progress Towards a Universal Influenza Vaccine

At various times in recent decades, surges have occurred in optimism about the potential for universal influenza vaccines that provide strong, broad, and long-lasting protection and could substantially reduce the disease burden associated with seasonal influenza epidemics as well as the threat posed by pandemic influenza. Each year more than 500 million doses of seasonal influenza vaccine are administered around the world, with most doses being egg-grown inactivated subunit or split-virion vaccines. These vaccines tend to have moderate effectiveness against medically attended influenza for influenza A(H1N1) and influenza B, and somewhat lower for influenza A(H3N2) where differences between vaccine strains and circulating strains can occur more frequently due to antigenic drift and egg adaptations in the vaccine strains. Several enhanced influenza vaccine platforms have been developed including cell-grown antigen, the inclusion of adjuvants, or higher antigen doses, to improve immunogenicity and protection. During the COVID-19 pandemic there was unprecedented speed in development and roll-out of relatively new vaccine platforms, including mRNA vaccines and viral vector vaccines. These new platforms present opportunities to improve protection for influenza beyond existing products. Other approaches continue to be explored. Incremental improvements in influenza vaccine performance should be achievable in the short to medium term.

Naturally occurring PAE206K point mutation in 2009 H1N1 pandemic influenza viruses impairs viral replication at high temperatures

The emergence of influenza virus A pandemic H1N1 in April 2009 marked the first pandemic of the 21st century. In this study, we observed significant differences in the polymerase activities of two clinical 2009 H1N1 influenza A virus isolates from Chinese and Japanese patients. Sequence comparison of the three main protein subunits (PB2, PB1, and PA) of the viral RNA-dependent RNA polymerase complex and subsequent mutational analysis revealed that a single amino acid substitution (E206K) was responsible for the observed impaired replication phenotype. Further in vitro experiments showed that presence of PAE206K decreased the replication of influenza A/WSN/33 virus in mammalian cells and a reduction in the virus's pathogenicity in vivo. Mechanistic studies revealed that PAE206K is a temperature-sensitive mutant associated with the inability to transport PB1-PA complex to the nucleus at high temperature (39.5 ​°C). Hence, this naturally occurring variant in the PA protein represents an ideal candidate mutation for the development of live attenuated influenza vaccines.

Next generation live-attenuated influenza vaccine platforms

INTRODUCTION

Influenza virus is a major cause of seasonal epidemics and intermittent pandemics. Despite the current molecular biology and vaccine development, influenza virus infection is a significant burden. Vaccines are considered an essential countermeasure for effective control and prevention of influenza virus infection. Even though current influenza virus vaccines provide efficient protection against seasonal influenza outbreaks, the efficacy of these vaccines is not suitable due to antigenic changes of the viruses.

AREAS COVERED

This review focuses on different live-attenuated platforms for influenza virus vaccine development and proposes essential considerations for a rational universal influenza virus vaccine design.

EXPERT OPINION

Despite the recent efforts for universal influenza virus vaccines, there is a lack of broadly reactive antibodies' induction that can confer broad and long-lasting protection. Various strategies using live-attenuated influenza virus vaccines (LAIVs) are investigated to induce broadly reactive, durable, and cross-protective immune responses. LAIVs based on NS segment truncation prevent influenza virus infection and have shown to be effective vaccine candidates among other vaccine platforms. Although many approaches have been used for LAIVs generation, there is still a need to focus on the LAIVs development platforms to generate a universal influenza virus vaccine candidate.