Novel strategy for selection of monoclonal antibodies against highly conserved antigens: phage library panning against ephrin-B2 displayed on yeast

A Novel Specific Single-Chain Variable Fragment Diagnostic System for Viral Hemorrhagic Septicemia Virus

Viral hemorrhagic septicemia virus (VHSV), one of the most important viral marine pathogens worldwide, has a broad range of hosts, such as members of the families Salmonidae and Paralichthyidae. In addition to being highly contagious, VHSV causes high lethality. The transmission of VHSV can be both vertical and horizontal. In fish, the resolution of VHSV infection is challenging. Thus, early diagnosis of VHSV infections is critical, especially in fish farms that have a high population of juvenile fish. Serological methods are commonly used to detect viral antigens. However, limited serological methods are available for marine viruses. In this study, a VHSV-specific single-chain variable fragment (scFv), E5, was selected using the yeast surface display and phage display systems. scFv, a type of recombinant antibody, comprises a variable heavy chain ([Formula: see text]) and a variable light chain ([Formula: see text]) connected by a polypeptide linker. An scFv clone was selected from the VHSV glycoprotein-expressing yeast cells using the bio-panning method. The scFv-encoding gene was subcloned and expressed in the Escherichia coli expression system. The binding affinity of the expressed and purified scFv protein was determined using an enzyme-linked immunosorbent assay and western blotting. Thus, this study reported a method to identify VHSV-specific scFv using bio-panning that can be utilized to develop a diagnostic system for other viruses.

Fully human recombinant antibodies against EphA2 from a multi-tumor patient immune library suitable for tumor-targeted therapy

Enhanced EphA2 expression is observed in a variety of epithelial-derived malignancies and is an important target for anti-tumor therapy. Currently, Therapeutic monoclonal antibodies against immune checkpoints have shown good efficacy for tumor treatment. In this study, we constructed an immune single-chain fragment variable (scFv) library using peripheral blood mononuclear cells (PBMCs) from 200 patients with a variety of malignant tumors. High affinity scFvs against EphA2 can be easily screened from the immune library using phage display technology. Anti-EphA2 scFvs can be modified into any form of recombinant antibody, including scFv-Fc and full-length IgG1 antibodies, and the recombinant antibody affinity was improved following modification. Among the modified anti-EphA2 antibodies the affinity of 77-IgG1 was significantly increased, reaching a pmol affinity level (10⁻¹²). We further demonstrated the binding activity of recombinant antibodies to the EphA2 protein, tumor cells, and tumor tissues using macromolecular interaction techniques, flow cytometry and immunohistochemistry. Most importantly, both the constructed scFvs-Fc, as well as the IgG1 antibodies against EphA2 were able to inhibit the growth of tumor cells to some extent. These results suggest that the immune libraries from patients with malignant tumors are more likely to screen for antibodies with high affinity and therapeutic effect. The constructed fully human scFv immune library has broad application prospects for specific antibody screening. The screened scFv-Fc and IgG1 antibodies against EphA2 can be used for the further study of tumor immunotherapy.

Development of novel detection system for sweet potato leaf curl virus using recombinant scFv

Sweet potato leaf curl virus (SPLCV) causes yield losses in sweet potato cultivation. Diagnostic techniques such as serological detection have been developed because these plant viruses are difficult to treat. Serological assays have been used extensively with recombinant antibodies such as whole immunoglobulin or single-chain variable fragments (scFv). An scFv consists of variable heavy (V_H) and variable light (V_L) chains joined with a short, flexible peptide linker. An scFv can serve as a diagnostic application using various combinations of variable chains. Two SPLCV-specific scFv clones, F7 and G7, were screened by bio-panning process with a yeast cell which expressed coat protein (CP) of SPLCV. The scFv genes were subcloned and expressed in Escherichia coli. The binding affinity and characteristics of the expressed proteins were confirmed by enzyme-linked immunosorbent assay using SPLCV-infected plant leaves. Virus-specific scFv selection by a combination of yeast-surface display and scFv-phage display can be applied to detection of any virus.

Discovering aptamers by cell-SELEX against human soluble growth factors ectopically expressed on yeast cell surface

SELEX, the process of selecting aptamers, is often hampered by the difficulty of preparing target molecules in their native forms and by a lack of a simple yet quantitative assay for monitoring enrichment and affinity of reactive aptamers. In this study, we sought to discover DNA aptamers against human serum markers for potential therapeutic and diagnostic applications. To circumvent soluble expression and immobilization for performing SELEX, we ectopically expressed soluble growth factors on the surface of yeast cells to enable cell-SELEX and devised a flow cytometry-based method to quantitatively monitor progressive enrichment of specific aptamers. High-throughput sequencing of selected pools revealed that the emergence of highly enriched sequences concurred with the increase in the percentage of reactive aptamers shown by flow cytometry. Particularly, selected DNA aptamers against VEGF were specific and of high affinity (K(D)  = ∼ 1 nM) and demonstrated a potent inhibition of capillary tube formation of endothelial cells, comparable to the effect of a clinically approved anti-VEGF antibody drug, bevacizumab. Considering the fact that many mammalian secretory proteins have been functionally expressed in yeast, the strategy of implementing cell-SELEX and quantitative binding assay can be extended to discover aptamers against a broad array of soluble antigens.