Identification by phage display and characterization of two neutralizing chimpanzee monoclonal antibodies to the hepatitis E virus capsid protein

Two monoclonal antibodies (MAbs) against the ORF2 protein of the SAR-55 str ain of hepatitis E virus (HEV) were isolated by phage display from a cDNA l ibrary of chimpanzee (Pan troglodytes) gamma 1/kappa antibody genes. Both M Abs, HEV#4 and HEV#31, bound to reduced, denatured open reading frame 2 (OR F2) protein in a Western blot, suggesting that they recognize linear epitop es, The affinities (equilibrium dissociation constants, K-d) for the SAR-55 ORF2 protein were 1.7 nM for HEV#4 and 5.4 nM for HEV#31, The two MAbs als o reacted in an enzyme-linked immunosorbent assay,vith recombinant ORF2 pro tein from a heterologous HEV, the Meng strain. Each MAb blocked the subsequ ent binding of the other MAb to homologous ORF2 protein in indirect competi tion assays, suggesting that they recognize the same or overlapping epitope s, Radioimmunoprecipitation assays suggested that at least part of the line ar epitope(s) recognized by the two MAbs is located between amino acids 578 and 607. MAbs were mixed with homologous HEV in vitro and then inoculated into rhesus monkeys (Macaca mulatta) to determine their neutralizing abilit y. Whereas all control animals developed hepatitis (elevated liver enzyme l evels in serum) and seroconverted to HEV, those receiving an inoculum incub ated with either HEV#4 or HEV#31 were not infected. Therefore, each MAb neu tralized the SAR-55 strain of HEV in vitro.