Phage display technology has played a key role in the discovery and optimisation of antibodies for a wide range of clinical or research applications, with its greatest impact seen in the development of antibody-based drugs. Innovations in bioengineering and selection strategies are now overcoming historic limitations of phage display – enhancing library diversity, expression and folding, and ultimately streamlining development workflow to expedite therapeutic antibody discovery processes.
Phage display technology enables the identification of fully human therapeutic monoclonal antibodies (mAbs) from extensive repertoires of antibody fragments presented on the surface of bacteriophages. Broadly, these fragments, often in the form of heavy-chain variable domains (VHH), single-chain variable fragments (scFv), or antigen-binding fragments (Fab), are genetically fused to the phage genome (often the minor coat protein pIII) through a smaller plasmid derivative known as a phagemid. This approach results in the formation of functional phage particles displaying pIII-antibody fusions, facilitating the creation of a diverse collection of antibody fragments, known as a phage display library.
Phage display is the most widely adopted method for antibody selection, distinguished by its robustness, simplicity, and capacity to accommodate large libraries. The selection process, known as “biopanning” or “panning” screens Fab phage display libraries to identify lead candidates with desirable properties (Figure 1).1 During this process, immobilised target antigens bind phages displaying antibodies that specifically recognise them. Non-binding phages are then removed through rigorous washing steps, while antigen-specific phages are recovered and amplified in vitro, often in E. coli hosts. Washing steps, using blocking agents such as bovine serum albumin (BSA), are critical for eliminating nonspecific binders and controlling binding properties by adjusting buffer components and stringency. For example, prolonged wash times can isolate clones with slow dissociation rates, while varying pH and salt concentrations can influence binding specificity. As a result, high-affinity phage clones are enriched through iterative rounds of biopanning, and antigen-specific antibody fragments are subsequently isolated, characterised, sequenced, and expressed as recombinant proteins.
