Recombinant human monoclonal antibodies against different conformational epitopes of the E2 envelope glycoprotein of hepatitis C virus that inhibit its interaction with CD81

The antibody response to the envelope proteins of hepatitis C virus (HCV) m ay play an important role in controlling the infection. To allow molecular analyses of protective antibodies, we isolated human monoclonal antibodies to the E2 envelope glycoprotein of HCV from a combinatorial Fab library est ablished from bone marrow of a chronically HCV-infected patient. Anti-E2 re active clones were selected using recombinant E2 protein. The bone marrow d onor carried HCV genotype 2b, and E2 used for selection wars of genotype la . The antibody clones were expressed as Fab fragments in E. coil, and as Fa b fragments and IgG1 in CHO cells. Seven different antibody clones were cha racterized, and shown to have high affinity for E2, genotype la, Three clon es also had high affinity for E2 of genotype 1b. They all bind to conformat ion-dependent epitopes, Five clones compete for the same or overlapping bin ding sites, while two bind to one or two other epitopes of E2, Four clones corresponding to the different epitopes were tested as purified IgG1 far bl ocking the CD81-E2 interaction in vitro; all four were positive at 0.3-0.5 mu g/ml. Thus, the present results suggest the existence of at le;Pst two c onserved epitopes in E2 that mediate inhibition of the E2-CD81 interaction, of which one appeared immunodominant in this donor.