Display of Antibody Chains on Filamentous Bacteriophage

The construction of very large combinatorial libraries whereby antigen-binding functional domains of antibodies (Abs) are cloned and displayed on the surface of bacteriophage is proving to be a powerful technology in providing reagents for immunotherapy. Combinations of randomly assembled pairs of immunoglobulin heavy (H) and light (L) chain genes are cloned and expressed as fusions of bacteriophage coat proteins, allowing the bacteriophage expressing them to be selected by methods analogous to affinity chromatography. Purified phage can then be used for the production of large amounts of the pure antibody in a soluble form. Although phage-derived antibodies lack the effector functions of the parent antibodies since they have no Fc regions, these can subsequently be engineered into place or substituted with others, such as a toxin, with relative ease if required. Various antigen-recognition regions of the Ab can be cloned and selected, including:

1.	Fv fragments that are noncovalently associated heterodimers of the heavy variable (VH) and light variable (VL) domains
2.	Single-chain Fv fragments (scFv) consisting of VH and VL regions linked by a flexible peptide
3.	Fabs that are noncovalently associated VH-CH and VL-CL pairings of Ab chains.