Whole IgG surface display on mammalian cells: Application to isolation of neutralizing chicken monoclonal anti-IL-12 antibodies

We have developed a mammalian cell surface display vector, suitable for directly isolating IgG molecules based on their antigen-binding affinity and biological activity. Using an Epstein-Barr virus-derived episomal vector, antibody libraries are displayed as whole IgG molecules on the cell surface and screened for specific antigen binding by a combination of magnetic beads and fluorescence-activated cell sorting. Plasmids encoding antibodies with desired binding characteristics are recovered from sorted cells and are converted to the form for production of soluble IgG. Transiently expressed soluble IgG antibodies are individually tested for binding to target antigens, as well as for biological activities, such as neutralization. This vector system was used to generate antibody display libraries derived from spleen cDNA of chickens immunized with human and mouse IL-12. Chicken–human chimeric IgG1 antibodies that neutralize human and mouse IL-12 were successfully isolated from the library. The mammalian surface display vector developed in this work facilitates the isolation of monoclonal antibodies from essentially any species.