Phage display screening is a well-established technique to identify antibody fragments and other binding molecules against any targets of interest. Phage display involves foreign proteins expressed as fusions to the coat protein III of a bacteriophage M13. Libraries of phage-displayed peptides or proteins are thereby physically linked to their encoding nucleic acid, allowing selection of binding partners for myriad target types by iterative rounds of in vitro panning and amplification, followed by DNA sequencing. Libraries of over a billion members can be screened in a matter of days, offering an efficient alternative to more traditional methods of epitope mapping, receptor ligand identification, or protein evolution.

Phage Display Screening Procedures

Depending on the available functional format of the antigen, the phage display can be performed under different conditions. Solid-phase screening is the most straightforward screening method that coats antigens directly on a solid surface. An alternative method is liquid-phase screening in which biotinylated antigens bind to the phage in solution. Compared with solid-phase screening, the antigen concentration can be controlled and the possible conformational changes can be avoided. Then the complexes of phage bound to the antigen can be captured. Next, the antigen-bound phage is eluted off via pH change or protease digestion and reinfected into E. coli. After 3-4 rounds of screening, the target-specific clones can be obtained. Compared with immune libraries, selections with naïve or synthetic sdAb libraries are performed similarly but need 1 or 2 more selection rounds as these libraries are not target-specific.

插图1 噬菌体筛选流程图

Advantages of Phage Display Screening

• The sdAb generation can be biased towards desired regions of the target via the control of screening conditions.

• Available for antigen presented on the surface of whole cells or tissue.

Project Study ：Discovery of anti-Claudin18.2 VHHs using phage display technology