Diagnostic and therapeutic potential of shark variable new antigen receptor (VNAR) single domain antibody

Abstract

Conventional monoclonal antibodies (mAbs) have been widely used in research and diagnostic applications due to their high affinity and specificity. However, multiple limitations, such as large size, complex structure and sensitivity to extreme ambient temperature potentially weaken the performance of mAbs in certain applications. To address this problem, the exploration of new antigen binders is extensively required in relation to improve the quality of current diagnostic platforms. In recent years, a new immunoglobulin-based protein, namely variable domain of new antigen receptor (VNAR) was discovered in sharks. Unlike conventional mAbs, several advantages of VNARs, include small size, better thermostability and peculiar paratope structure have attracted interest of researchers to further explore on it. This article aims to first present an overview of the shark VNARs and outline the characteristics as an outstanding new reagent for diagnostic and therapeutic applications.

Shark New Antigen Receptor (IgNAR): Structure, Characteristics and Potential Biomedical Applications

“…In addition to these canonical cysteines, CDRs may have non-canonical/extra cysteine residues that form additional disulfide bonds within the variable domain [ 22 ]. These features differentiate VH from the VHH and VNAR domains ( Figure 2 ), and to date are used as a means of classifying VNAR based on the presence or absence of these extra cysteine residues within the hypervariable region [ 5 , 11 , 12 , 14 , 15 , 18 , 23 ]. VNAR is classified into four types (I, II, III, and IV), the subtypes are further divided based on the number of additional cysteines contained [ 18 ].…”

“…The type I variable domains of IgNAR had been reported only in nurse sharks (Gin-glymostoma cirratum) [ 12 , 14 ], but have now been also identified in the wobbegong shark (Orectolobus ornatus) [ 18 ]. VNAR type 1 has non-canonical cysteine residues in FR2 and FR4, and two paired residues in CDR3 [ 14 ].…”

“…The variable domain of camelids and sharks identified with molecular weights of approximately 15 kDa and 12 kDa that are referred to as VHH and VNAR, respectively ( Figure 1 C); the antigen-binding site is formed in only one single domain of the heavy chain [ 1 ]. Inter-chain disulfide bonds joint the structure of VHH and VNAR domain [ 11 , 12 , 13 ]. The camelid antibody consists of the constant domain two (C2) and constant domain three (C3) with a hinge region between the variable region and the constant domain two (C2), and constant domain one (C1) is absent due to a donor splice site mutation [ 1 ] ( Figure 1 B).…”

Brain Delivery of Single-Domain Antibodies: A Focus on VHH and VNAR

“…The main difference of their variable domain is the absence of complementary-determining region 2 (CDR2) leading to only two CDRs. Even though VNAR are lacking one CDR, they can still recognize numerous antigens thanks to a higher variability in CDR1 and a longer CDR3 [ 35 ]. These characteristics make them the smallest antibodies with a molecular weight of only 12 kDa.…”

Neutralizing Human Antibodies against Severe Acute Respiratory Syndrome Coronavirus 2 Isolated from a Human Synthetic Fab Phage Display Library

“…Monoclonal antibodies (mAbs) have been recognized as significant biologics in therapeutic fields and are now rapidly taking a position as an alternative treatment that complements vaccines in working against newly emerging pathogenic viruses, such as SARS-CoV-2 [ 22 , 23 , 24 , 25 ]. Since viral neutralization by targeting the S protein has previously been shown to correlate with therapeutic efficacy in animal models [ 26 ], tremendous efforts have been made, based on the structural information of the S protein and its critical role in viral entry, to discover neutralizing mAbs that block the RBD of the S1 subunit through a variety of approaches, such as phage display library selection [ 27 , 28 , 29 , 30 ]; antibody selection through immunization of animals, such as humanized mice, dromedary camels, or sharks [ 31 , 32 , 33 , 34 ]; and antibody isolation from memory or plasma B cells of naturally infected human donors [ 31 , 35 , 36 , 37 , 38 , 39 ]. At the time of writing, 198 antibodies programs are in discovery and development phases globally, among which 66 are going through clinical trials (phase 1/2/3).…”