PANNING PHAGE ANTIBODY LIBRARIES ON CELLS - ISOLATION OF HUMAN FAB FRAGMENTS AGAINST OVARIAN-CARCINOMA USING GUIDED SELECTION

The display of repertoires of human antibody (Ab) fragments on filamen tous phages and selection by binding of the phage to antigen (Ag) have provided a ready means of deriving human Ab against purified Ag. Howe ver, it has been more difficult to obtain phage Ab against an individu al Ag of a complex mixture, such as cell surface Ag. Using the techniq ue of ''guided selection,'' we generated human Ab against the high-aff inity folate-binding protein (FBP), a cell surface Ag that is overexpr essed in many human ovarian carcinomas, The guiding Ab template was pr ovided by the light chain of mouse monoclonal Ab Mov19 (K-aff, 10(8) M -1) directed against FBP; this was paired with repertoires of human he avy chains displayed on phages, and the hybrid Ab fragments were selec ted by binding to an ovarian carcinoma cell line (OVCAR3), The selecte d human heavy chains were then paired with repertoires of human light chains. Further panning led to the isolation of a human Fab fragment, C4, with a binding affinity of 0.2 x 10(8) M-1. This was highly specif ic for FBP, as demonstrated by ELISA and flow cytometry data and by im munoprecipitation of the relevant molecule from the cell surface of ov arian carcinoma cells, Moreover, C4 targeted the same or a closely rel ated epitope of the Ag, as did the template rodent monoclonal Ab Mov19 . These results suggest the usefulness of guided selection as a simple means to deriving human Ab against cell surface Ag for which a rodent Ab is available.