Report of the National Institutes of Health SARS-CoV-2 Antiviral Therapeutics Summit.

The NIH Virtual SARS-CoV-2 Antiviral Summit, held on 6 November 2020, was organized to provide an overview on the status and challenges in developing antiviral therapeutics for coronavirus disease 2019 (COVID-19), including combinations of antivirals. Scientific experts from the public and private sectors convened virtually during a live videocast to discuss severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) targets for drug discovery as well as the preclinical tools needed to develop and evaluate effective small-molecule antivirals. The goals of the Summit were to review the current state of the science, identify unmet research needs, share insights and lessons learned from treating other infectious diseases, identify opportunities for public-private partnerships, and assist the research community in designing and developing antiviral therapeutics. This report includes an overview of therapeutic approaches, individual panel summaries, and a summary of the discussions and perspectives on the challenges ahead for antiviral development.

Complement-mediated enhancement of antibody function for neutralization of pseudotype virus containing hepatitis C virus E2 chimeric glycoprotein.

We previously reported a number of features of hepatitis C virus (HCV) chimeric glycoproteins related to pseudotype virus entry into mammalian cells. In this study, pseudotype virus was neutralized by HCV E2 glycoprotein-specific antibodies and infected human sera. Neutralization (50% reduction of pseudotype virus plaque formation) was observed with two human immunoglobulin G1 monoclonal antibodies (MAbs) at concentrations of between 2.5 and 10 microg/ml. A hyperimmune rabbit antiserum to an E2 hypervariable region 1 (HVR1) mimotope also exhibited an HCV E2 pseudotype virus neutralization titer of approximately 1/50. An E1 pseudotype virus used as a negative control was not neutralized to a significant level (<1/10) by these MAbs or rabbit antiserum to E2 HVR1. Since HCV probably has a lipid envelope, the role of complement in antibody-mediated virus neutralization was examined. Significant increases in the neutralization titers of the human MAbs (approximately 60- to 160-fold higher) and rabbit antiserum to HVR1 mimotopes (approximately 10-fold higher) were observed upon addition of guinea pig complement. Further, these studies suggested that complement activation occurred primarily by the classical pathway, since a deficiency in the C4 component led to a significant decrease in the level of virus neutralization. This same decrease was not observed with factor B-deficient complement. We also determined that 9 of 56 HCV-infected patient sera (16%) had detectable pseudotype virus neutralization activity at serum dilutions of between 1/20 and 1/50 and that complement addition enhanced the neutralization activity of some of the HCV-infected human sera. Taken together, these results suggest that during infection, HCV E2 glycoprotein induces a weak neutralizing antibody response, that those antibodies can be measured in vitro by the surrogate pseudotype virus plaque reduction assay, and that neutralization function can be augmented by complement.