Phage Display Technique as a Tool for Diagnosis and Antibody Selection for Coronaviruses

Abstract

Phage display is one of the important and effective molecular biology techniques and has remained indispensable for research community since its discovery in the year 1985. As a large number of nucleotide fragments may be cloned into the phage genome, a phage library may harbour millions or sometimes billions of unique and distinctive displayed peptide ligands. The ligand-receptor interactions forming the basis of phage display have been well utilized in epitope mapping and antigen presentation on the surface of bacteriophages for screening novel vaccine candidates by using affinity selection-based strategy called biopanning. This versatile technique has been modified tremendously over last three decades, leading to generation of different platforms for combinatorial peptide display. The translation of new diagnostic tools thus developed has been used in situations arising due to pathogenic microbes, including bacteria and deadly viruses, such as Zika, Ebola, Hendra, Nipah, Hanta, MERS and SARS. In the current situation of pandemic of Coronavirus disease (COVID-19), a search for neutralizing antibodies is motivating the researchers to find therapeutic candidates against novel SARS-CoV-2. As phage display is an important technique for antibody selection, this review presents a concise summary of the very recent applications of phage display technique with a special reference to progress in diagnostics and therapeutics for coronavirus diseases. Hopefully, this technique can complement studies on host-pathogen interactions and assist novel strategies of drug discovery for coronaviruses.

Fig. 1

Schematic representation of M13-based phage display of POI expressed as fusion protein with structural coat proteins. The copy number of POI is related to the fusion partner. Fusion partner:Copies per virion—pIII:5, pVI:5, pVII:5, pVIII:2700, pIX:5

Fig. 2

Different antibody formats used for phage display. Conventional IgG structurally comprising two heavy (H) chains (composed of V_H and C_H domains) and two light (L) chains (composed of V_L and C_L domains) and carrying two antigen-binding sites constituted by V_H and V_L domains. Heavy-chain antibodies of family Camelidae lack both constant and variable light chains (C_L and V_L) and the antigen-binding site is formed only by the heavy-chain variable domain (VHH/nanobody). The new antigen receptor (IgNAR) antibodies from sharks are constituted of two protein chains, each containing one variable (V_NAR) and five constant domains (C_H). The phage antibody display format may include as follows: Antigen binding fragment (Fab) of conventional immunoglobulins consisting of V_H, C_H1, V_L and C_L domains where C_H1 and C_L domains are joined by a disulphide bond, Single-chain fragment antigen binding (scFab) consisting of V_H, C_H1, V_L and C_L domains where C_H1 and V_L are joined via linker, fragment variable (F_V) consisting of variable regions of heavy-chain (V_H) and light-chain (V_L), single-chain fragment variable (scFv) consisting of variable regions, i.e. V_H and V_L joined through a linker, variable domain of human antibodies (VH) or VHH

Fig. 3

Structural characteristics of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2)

Fig. 4

An illustration of phage display technique for epitope characterization of monoclonal antibodies binding to spike protein of MERS-CoV using phage display technique. The whole RNA can be extracted and cDNA amplified. Spike protein encoding gene can be amplified by PCR. The gene segments can be obtained by fragmentation using restriction enzymes and segments cloned in phagemid vector. Transformation of phagemids in E. coli and infection with helper phage can lead to production of phages displaying protein encoded by cloned genomic segment. The phage library thus formed can be screened using Anti-S-mABs by ELISA and phages binding specifically can be selected by repeated rounds of biopanning (elution, amplification, binding and washing). DNA sequencing of bound phages leads to epitope mapping