Isolation and Characterization of Targeting-HBsAg VNAR Single Domain Antibodies from Whitespotted Bamboo Sharks (Chiloscyllium plagiosum).

Immunoglobulin new antigen receptor (IgNAR) is a naturally occurring antibody that consists of only two heavy chains with two independent variable domains. The variable binding domain of IgNAR, called variable new antigen receptor (VNAR), is attractive due to its solubility, thermal stability, and small size. Hepatitis B surface antigen (HBsAg) is a viral capsid protein found on the surface of the Hepatitis B virus (HBV). It appears in the blood of an individual infected with HBV and is widely used as a diagnostic marker for HBV infection. In this study, the whitespotted bamboo sharks (Chiloscyllium plagiosum) were immunized with the recombinant HBsAg protein. Peripheral blood leukocytes (PBLs) of immunized bamboo sharks were further isolated and used to construct a VNAR-targeted HBsAg phage display library. The 20 specific VNARs against HBsAg were then isolated by bio-panning and phage ELISA. The 50% of maximal effect (EC50) of three nanobodies, including HB14, HB17, and HB18, were 4.864 nM, 4.260 nM, and 8.979 nM, respectively. The Sandwich ELISA assay further showed that these three nanobodies interacted with different epitopes of HBsAg protein. When taken together, our results provide a new possibility for the application of VNAR in HBV diagnosis and also demonstrate the feasibility of using VNAR for medical testing.

Characterization and humanization of VNARs targeting human serum albumin from the whitespotted bamboo shark (Chiloscyllium plagiosum).

The Shark-derived immunoglobulin new antigen receptors (IgNARs) have gained increasing attention for their high solubility, exceptional thermal stability, and intricate sequence variation. In this study, we immunized whitespotted bamboo shark (Chiloscyllium plagiosum) to create phage display library of variable domains of IgNAR (VNARs) for screening against Human Serum Albumin (HSA), a versatile vehicle in circulation due to its long in vivo half-life. We identified two HSA-binding VNAR clones, 2G5 and 2G6, and enhanced their expression in E. coli with the FKPA chaperone. 2G6 exhibited a strong binding affinity of 13 nM with HSA and an EC50 of 1 nM. In vivo study with a murine model further provided initial validation of 2G6's ability to prolong circulation time by binding to HSA. Additionally, we employed computational molecular docking to predict the binding affinities of both 2G6 and its humanized derivative, H2G6, to HSA. Our analysis unveiled that the complementarity-determining regions (CDR1 and CDR3) are pivotal in the antigen recognition process. Therefore, our study has advanced the understanding of the potential applications of VNARs in biomedical research aimed at extending drug half-life, holding promise for future therapeutic and diagnostic progressions.