Identification and characterization of shark VNARs targeting the Helicobacter pylori adhesin HpaA

Helicobacter pylori (H. pylori) is recognized as a pathogen associated with several gastrointestinal diseases. The current treatments exhibit numerous drawbacks, including antibiotic resistance. H. pylori can adhere to and colonize the gastric mucosa through H. pylori adhesin A (HpaA), and antibodies against HpaA may be an effective therapeutic approach. The variable domain of immunoglobulin new antigen receptor (VNAR) is a novel type of single-domain antibody with a small size, good stability, and easy manufacturability. This study isolated VNARs against HpaA from an immune shark VNAR phage display library. The VNARs can bind both recombinant and native HpaA proteins. The VNARs, 2A2 and 3D6, showed high binding affinities to HpaA with different epitopes. Furthermore, homodimeric bivalent VNARs, biNb-2A2 and biNb-3D6, were constructed to enhance the binding affinity. The biNb-2A2 and biNb-3D6 had excellent stability at gastrointestinal pH conditions. Finally, a sandwich ELISA assay was developed to quantify the HpaA protein using BiNb-2A2 as the capture antibody and BiNb-3D6 as the detection antibody. This study provides a potential foundation for novel alternative approaches to treatment or diagnostics applications of H. pylori infection.