Selection and characterization of cell binding and internalizing phage antibodies

Many therapeutic targets are cell surface receptors, which can be challenging antigens for antibody generation. For many therapeutic applications, one needs antibodies that not only bind the cell surface receptor but also are internalized into the cell. This allows use of the antibody to deliver various payloads into the cell to achieve a therapeutic effect. Phage antibody technology has proven a powerful tool for the generation and optimization of human antibodies to any antigen. While applied to the generation of antibodies to purified proteins, it is possible to directly select cell binding and internalizing antibodies on cells. Potential advantages of this approach include: cell surface receptors are in native conformation on intact cells while this might not be so for recombinant proteins; antibodies can be selected for both cell binding and internalization properties; the antibodies can be used to identify their tumor associated antigens; and such antibodies can be used for human treatment directly since they are human in sequence. This review will discuss the factors that impact the successful selection of cell binding and internalizing antibodies. These factors include the cell types used for selection, the impact of different phage antibody library formats, and the specific selection protocols used.