An efficient method to make human monoclonal antibodies from memory B cells: potent neutralization of SARS coronavirus

Abstract

Passive serotherapy can confer immediate protection against microbial infection, but methods to rapidly generate human neutralizing monoclonal antibodies are not yet available. We have developed an improved method for Epstein-Barr virus transformation of human B cells. We used this method to analyze the memory repertoire of a patient who recovered from severe acute respiratory syndrome coronavirus (SARS-CoV) infection and to isolate monoclonal antibodies specific for different viral proteins, including 35 antibodies with in vitro neutralizing activity ranging from 10(-8)M to 10(-11)M. One such antibody confers protection in vivo in a mouse model of SARS-CoV infection. These results show that it is possible to interrogate the memory repertoire of immune donors to rapidly and efficiently isolate neutralizing antibodies that have been selected in the course of natural infection.

Figure 1. Characterization of the SARS-CoV neutralizing S3.1 monoclonal antibody.

(a) Staining of BHK cells transfected with SARS-CoV spike mRNA by purified S3.1 antibody (circles) and by the 6 months convalescent serum (squares). The filled symbols indicate the antibody concentration at which complete neutralization was observed. (b,c) Staining of SARS-CoV detected by immunoelectron microscopy. Top left, negative control; top right three panels, convalescent serum; bottom left, supernatant of a non-neutralizing B cell clone; bottom right three panels, S3.1 monoclonal antibody. Bar, 100 nm.

Figure 2. Binding and neutralization capacity of monoclonal antibodies specific for SARS-CoV spike.

Shown is the staining of BHK cells transfected with SARS-CoV spike mRNA by serial dilutions of ten neutralizing monoclonal antibodies. The symbols indicate the neutralizing titer: that is, the antibody dilution added in the neutralization assay that gave complete viral neutralization.