A human SARS-CoV neutralizing antibody against epitope on S2 protein

An immune antibody phage-display library was constructed from B cells of SARS convalescent patients. More than 80 clones were selected from the library by using the whole inactivated SARS-CoV virions as target. One human scFv, B1, was characterized extensively. The B1 recognized SARS pseudovirus in vivo and competed with SARS sera for binding to SARS-CoV with high affinity (equilibrium dissociation constant, K(d) = 105 nM). The B1 also has potent neutralizing activities against infection by pseudovirus expressing SARS-CoV S protein in vitro. Finally, we found that the B1 recognized an epitope on S2 protein, especially within amino acids 1023-1189 of S2 protein. This study not only first made a human neutralizing antibody, which recognized an epitope on S2 protein like natural antibody in sera, but also may help us to better understand the immunological characteristics of SARS protein and SARS vaccine design.