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The fundamental event in prion disease is thought to be the posttranslational conversion of the cellular prion protein (PrPC) into a pathogenic isoform (PrPSc). The occurrence of PrPC on the cell surface and PrPSc in amyloid plaques in situ or in aggregates following purification complicates the study of the molecular events that underlie the disease process. Monoclonal antibodies are highly sensitive probes of protein conformation which can be used under these conditions. Here, we report the rescue of a diverse panel of 19 PrP-specific recombinant monoclonal antibodies from phage display libraries prepared from PrP deficient (Prnp0/0) mice immunized with infectious prions either in the form of rods or PrP 27-30 dispersed into liposomes. The antibodies recognize a number of distinct linear and discontinuous epitopes that are presented to a varying degree on different PrP preparations. The epitope reactivity of the recombinant PrP(90-231) molecule was almost indistinguishable from that of PrPC on the cell surface, validating the importance of detailed structural studies on the recombinant molecule. Only one epitope region at the C terminus of PrP was well presented on both PrPC and PrPSc, while epitopes associated with most of the antibodies in the panel were present on PrPCbut absent from PrPSc.

We report the characterization of a type-common human recombinant monoclonal antibody previously isolated by antigen selection from a phage-displayed combinatorial antibody library established from a herpes simplex virus (HSV)-seropositive individual. Competition with well-characterized murine monoclonal antibodies and immunodetection of gD truncations revealed that this antibody recognizes the group Ib antigenic site of glycoprotein D, a highly conserved and protective type-common determinant. To our knowledge, this is the first human group Ib monoclonal antibody ever described. The antibody also displayed first-order neutralization kinetics and a high neutralization rate constant, was capable of completely inhibiting syncytium formation by a fusogenic strain of HSV type 1, and efficiently neutralized low-passage clinical isolates of both HSV serotypes. Taken together with our earlier observations of the in vivo antiviral activities of this human recombinant antibody in animal models of HSV infection, the present results support the high therapeutic potential of this antibody.

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