Establishment of Neutralizing Monoclonal Antibodies Against Severe Acute Respiratory Syndrome Coronavirus 2 by the Screening with Exosomes Expressing the Viral Spike Protein

Monoclonal antibodies (mAbs) against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes COVID-19, are the important tools both for the diagnosis and therapeutics of this infectious disease. The high-performance antibody against spike protein of SARS-CoV-2 is expected to inhibit the binding of viruses to their receptors on the surface of their target cells. In this study, we propose the novel screening method for mAbs against the pathogenic infectious virus using exosome. By this method, the exosome that artificially expresses SARS-CoV-2 spike protein was purified and used as a virus-like vesicle, which could bind to the viral receptor, angiotensin-converting enzyme 2 (ACE2). As a result, seven mAbs that could bind to the spike protein were obtained and six of these clones could strongly inhibit the binding to ACE2 of both the protein corresponding to the receptor binding domain (RBD) and the exosome expressing the spike protein. Interestingly, some of these antibodies seemed to share their epitopes in RBD, suggesting that highly antigenic sites exist in the spike protein. In view of the neutralizing activities on infection, five clones of these antibodies could inhibit the internalization of vesicular stomatitis virus-based pseudo viruses expressing various types of spike proteins derived from SARS-CoV-2 variants. In addition, these antibodies inhibited the infection of SARS-CoV-2 to cultured mammalian cells. These antibodies are expected to be utilized for both diagnosis and therapeutics of COVID-19.

Comparative In Vitro and In Vivo Analysis of H1N1 and H1N2 Variant Influenza Viruses Isolated from Humans between 2011 and 2016

Influenza A virus pandemics are rare events caused by novel viruses which have the ability to spread in susceptible human populations. With respect to H1 subtype viruses, swine H1N1 and H1N2 viruses occasionally cross the species barrier to cause human infection. Recently isolated from humans (termed variants), swine viruses were shown to display great genetic and antigenic diversity, hence posing considerable public health risk. Here, we utilized in vitro and in vivo approaches to provide characterization of H1 subtype variant viruses isolated since the 2009 pandemic and discuss the findings in context with previously studied H1 subtype human isolates. The variant viruses were well adapted to replicate in the human respiratory cell line Calu-3 and the respiratory tracts of mice and ferrets. However, with respect to hemagglutinin (HA) activation pH, the variant viruses had fusion pH thresholds closer to that of most classical swine and triple-reassortant H1 isolates rather than viruses that had adapted to humans. Consistent with previous observations for swine isolates, the tested variant viruses were capable of efficient transmission between cohoused ferrets but could transmit via respiratory droplets to differing degrees. Overall, this investigation demonstrates that swine H1 viruses that infected humans possess adaptations required for robust replication and, in some cases, efficient respiratory droplet transmission in a mammalian model and therefore need to be closely monitored for additional molecular changes that could facilitate transmission among humans. This work highlights the need for risk assessments of emerging H1 viruses as they continue to evolve and cause human infections.IMPORTANCE Influenza A virus is a continuously evolving respiratory pathogen. Endemic in swine, H1 and H3 subtype viruses sporadically cause human infections. As each zoonotic infection represents an opportunity for human adaptation, the emergence of a transmissible influenza virus to which there is little or no preexisting immunity is an ongoing threat to public health. Recently isolated variant H1 subtype viruses were shown to display extensive genetic diversity and in many instances were antigenically distinct from seasonal vaccine strains. In this study, we provide characterization of representative H1N1v and H1N2v viruses isolated since the 2009 pandemic. Our results show that although recent variant H1 viruses possess some adaptation markers of concern, these viruses have not fully adapted to humans and require further adaptation to present a pandemic threat. This investigation highlights the need for close monitoring of emerging variant influenza viruses for molecular changes that could facilitate efficient transmission among humans.