Generation, Characterization, and Applications of Influenza A Reporter Viruses

Bacterial Artificial Chromosome Reverse Genetics Approaches for SARS-CoV-2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a new member of the Coronaviridae family responsible for the coronavirus disease 19 (COVID-19) pandemic. To date, SARS-CoV-2 has been accountable for over 624 million infection cases and more than 6.5 million human deaths. The development and implementation of SARS-CoV-2 reverse genetics approaches have allowed researchers to genetically engineer infectious recombinant (r)SARS-CoV-2 to answer important questions in the biology of SARS-CoV-2 infection. Reverse genetics techniques have also facilitated the generation of rSARS-CoV-2 expressing reporter genes to expedite the identification of compounds with antiviral activity in vivo and in vitro. Likewise, reverse genetics has been used to generate attenuated forms of the virus for their potential implementation as live-attenuated vaccines (LAV) for the prevention of SARS-CoV-2 infection. Here we describe the experimental procedures for the generation of rSARS-CoV-2 using a well-established and robust bacterial artificial chromosome (BAC)-based reverse genetics system. The protocol allows to produce wild-type and mutant rSARS-CoV-2 that can be used to understand the contribution of viral proteins and/or amino acid residues in viral replication and transcription, pathogenesis and transmission, and interaction with cellular host factors.

Highly Cross-Reactive and Protective Influenza A Virus H3N2 Hemagglutinin- and Neuraminidase-Specific Human Monoclonal Antibodies

Due to antigenic drift and shift of influenza A viruses (IAV) and the tendency to elicit predominantly strain-specific antibodies, humanity remains susceptible to new strains of seasonal IAV and is at risk from viruses with pandemic potential for which limited or no immunity may exist. The genetic drift of H3N2 IAV is specifically pronounced, resulting in two distinct clades since 2014. Here, we demonstrate that immunization with a seasonal inactivated influenza vaccine (IIV) results in increased levels of H3N2 IAV-specific serum antibodies against hemagglutinin (HA) and neuraminidase (NA). Detailed analysis of the H3N2 B cell response indicated expansion of H3N2-specific peripheral blood plasmablasts 7 days after IIV immunization which expressed monoclonal antibodies (MAbs) with broad and potent antiviral activity against many H3N2 IAV strains as well as prophylactic and therapeutic activity in mice. These H3N2-specific B cell clonal lineages persisted in CD138+ long-lived bone marrow plasma cells. These results demonstrate that IIV-induced H3N2 human MAbs can protect and treat influenza virus infection in vivo and suggest that IIV can induce a subset of IAV H3N2-specific B cells with broad protective potential, a feature that warrants further study for universal influenza vaccine development. IMPORTANCE Influenza A virus (IAV) infections continue to cause substantial morbidity and mortality despite the availability of seasonal vaccines. The extensive genetic variability in seasonal and potentially pandemic influenza strains necessitates new vaccine strategies that can induce universal protection by focusing the immune response on generating protective antibodies against conserved targets within the influenza virus hemagglutinin and neuraminidase proteins. We have demonstrated that seasonal immunization with inactivated influenza vaccine (IIV) stimulates H3N2-specific monoclonal antibodies in humans that are broad and potent in their neutralization of virus in vitro. These antibodies also provide protection from H3N2 IAV in a mouse model of infection. Furthermore, they persist in the bone marrow, where they are expressed by long-lived antibody-producing plasma cells. This significantly demonstrates that seasonal IIV can induce a subset of H3N2-specific B cells with broad protective potential, a process that if further studied and enhanced could aid in the development of a universal influenza vaccine.