ARTIFICIAL ANTIBODIES FOR AFFINITY-CHROMATOGRAPHY OF HOMOLOGOUS PROTEINS - APPLICATION TO BLOOD-CLOTTING PROTEINS

A method to readily isolate antibodies that bind to only one member of a family of homologous proteins is described. A library of different single chain antibody fragments can be displayed on the surface of a b acteriophage vector. Individual antibodies from this library recognizi ng a particular protein from a family of homologous proteins can be re adily isolated by a two-step affinity screening process. In the first step antibodies which bind specifically to the undesired proteins or t o homologous regions of the proteins are removed. In the second step, those antibodies specifically recognizing the desired protein are then isolated. Using this procedure and starting with a naive antibody lib rary, a single chain antibody fragment specific to the blood clotting protein, Protein C, which did not recognize either of the homologous p roteins, Factor IX or Factor X, was isolated. Similarly an antibody sp ecific to Factor IX, but not Factor X or Protein C, was also isolated. The isolated antibodies can be readily produced, purified, and affixe d to sepharose beads for affinity chromatography of the blood clotting factors. One of the key advantages to this procedure over conventiona l monoclonal antibody isolation is that the antibodies are isolated an d produced in vitro so a broad range of related proteins, toxins, viru ses, or other products can be targeted.