Clonal selection and amplification of phage displayed antibodies by linking antigen recognition and phage replication.

The immune response generates a tremendous array of antibody specificities by VDJ-gene rearrangements. A similar diversity can be obtained by expressing entire V-gene repertoires on the surface of filamentous bacteriophages creating large antibody libraries. Here we describe how the clonal selection mechanisms of the humoral immune response can also be mimicked in the phage display system by linking antigen-recognition and phage replication. We have achieved this by displaying antibody libraries on engineered, non-infectious phage with gene 3 deletions. Individual, antigen-specific phage are made replication competent by allowing a fusion protein, consisting of the antigen and phage coat protein 3, to bind the displayed antibody fragment. This fusion protein bridges the phage and F-pili of the bacteria and allows infection to be initiated and the phage to be clonally amplified with specific enrichment factors of approximately 10(10) after only two rounds.