Identification of neutralizing human monoclonal antibodies from Italian Covid-19 convalescent patients

In the absence of approved drugs or vaccines, there is a pressing need to develop tools for the therapy and prevention of Covid-19. Human monoclonal antibodies have very good probability of being safe and effective tools for the therapy and prevention of SARS-CoV-2 infection and disease. Here we describe the screening of PBMCs from seven people that survived Covid-19 infection to isolate human monoclonal antibodies against SARS-CoV-2. Over 1100 memory B cells were single cell sorted using the stabilized prefusion form of the spike protein and incubated for two weeks to allow natural production of antibodies. Supernatants from each cell were tested by ELISA for spike protein binding, and positive antibodies were further tested for neutralization of spike binding to the ACE2 receptor on Vero E6 cells and for virus neutralization in vitro. From the 1167 memory B specific for SARS-CoV-2, we recovered 265 B lymphocytes expressing human monoclonals recognizing the spike protein and 10 of these were able to inhibit the binding of the spike protein to the receptor. Finally, 17 mAbs were able to neutralize the virus when assessed for neutralization in vitro. Lead drug candidates will be selected from the panel of potent neutralizing antibodies identified with the procedure described in this study.