Selection of Internalizing Antibodies for Drug Delivery

Large non-immune (na�ve) antibody gene diversity libraries displayed on filamentous phage have proven to be a reliable source of antibodies to any purified protein antigen (1 –3 ). In some instances, it is possible to directly select peptides and antibody fragments that bind cell-surface receptors from filamentous phage libraries by incubation of phage libraries with a target cell line (4 –8 ). This has led to a marked increase in the number of potential cell-targeting molecules. However, the isolation of cell type-specific antibodies from na�ve libraries has been difficult because selections often result in crossreactive antibodies that bind to common cell-surface antigens (9 ).