Selection and characterization of human serum albumin-specific porcine scFv antibodies using a phage display library

VNAR development through antigen immunization of Japanese topeshark (Hemitriakis japanica)

The VNAR (Variable New Antigen Receptor) is the smallest single-domain antibody derived from the variable domain of IgNAR of cartilaginous fishes. Despite its biomedical and diagnostic potential, research on VNAR has been limited due to the difficulties in obtaining and maintaining immune animals and the lack of research tools. In this study, we investigated the Japanese topeshark as a promising immune animal for the development of VNAR. This shark is an underutilized fishery resource readily available in East Asia coastal waters and can be safely handled without sharp teeth or venomous stingers. The administration of Venus fluorescent protein to Japanese topesharks markedly increased antigen-specific IgM and IgNAR antibodies in the blood. Both the phage-display library and the yeast-display library were constructed using RNA from immunized shark splenocytes. Each library was enriched by biopanning, and multiple antigen-specific VNARs were acquired. The obtained antibodies had affinities of 1 × 10-8 M order and showed high plasticity, retaining their binding activity even after high-temperature or reducing-agent treatment. The dissociation rate of a low-affinity VNAR was significantly improved via dimerization. These results demonstrate the potential utility of the Japanese topeshark for the development of VNAR. Furthermore, we conducted deep sequencing analysis to reveal the quantitative changes in the CDR3-coding sequences, revealing distinct enrichment bias between libraries. VNARs that were primarily enriched in the phage display had CDR3 coding sequences with fewer E. coli rare codons, suggesting translation machinery on the selection and enrichment process during biopanning.

Generation of porcine monoclonal antibodies based on single cell technologies

The development of a rapid and efficient system to generate porcine monoclonal antibodies (mAbs) is an important step toward the discovery of critical neutralizing targets for designing rational vaccines against porcine viruses. In this study, we established a platform for producing porcine mAbs based on single cell technologies. First, we singled out an optimal donor from 507 pigs based on serum antibody neutralizing activity against porcine reproductive and respiratory syndrome virus (PRRSV). After identifying the contribution of IgG to the neutralizing activity, single CD45R⁺IgG⁺Ag⁺ B cells were sorted from peripheral blood mononuclear cells (PBMCs). Single B cell RT-PCR was performed using primers designed to cover the germline repertoire of the porcine VH/VL gene segments. Paired VH/VLs were cloned into a eukaryotic expression vector and transfected into 293T cells. We demonstrate that full-length porcine mAbs were produced, and antigen-specific mAbs were obtained after further validation. The approach reported in this study can be applied to generate porcine mAbs against any given antigen and may help with the screening of neutralizing antibodies against porcine pathogens.

Development of a Rapid Identification Method for a Variety of Antibody Candidates Using High-throughput Sequencing

As an alternative to hybridoma technology, the antibody phage library system can also be used for antibody selection. This method enables the isolation of antigen-specific binders through an in vitro selection process known as biopanning. While it has several advantages, such as an avoidance of animal immunization, the phage cloning and screening steps of biopanning are time-consuming and problematic. Here, we introduce a novel biopanning method combined with high-throughput sequencing (HTS) using a next-generation sequencer (NGS) to save time and effort in antibody selection, and to increase the diversity of acquired antibody sequences. Biopannings against a target antigen were performed using a human single chain Fv (scFv) antibody phage library. VH genes in pooled phages at each round of biopanning were analyzed by HTS on a NGS. The obtained data were trimmed, merged, and translated into amino acid sequences. The frequencies (%) of the respective VH sequences at each biopanning step were calculated, and the amplification factor (change of frequency through biopanning) was obtained to estimate the potential for antigen binding. A phylogenetic tree was drawn using the top 50 VH sequences with high amplification factors. Representative VH sequences forming the cluster were then picked up and used to reconstruct scFv genes harboring these VHs. Their derived scFv-Fc fusion proteins showed clear antigen binding activity. These results indicate that a combination of biopanning and HTS enables the rapid and comprehensive identification of specific binders from antibody phage libraries.

An Anti-Human Lutheran Glycoprotein Phage Antibody Inhibits Cell Migration on Laminin-511: Epitope Mapping of the Antibody

The Lutheran glycoprotein (Lu), also known as basal cell adhesion molecule (B-CAM), is an Ig superfamily (IgSF) transmembrane receptor for laminin α5. Although Lu is not present in normal hepatocytes, its expression is significantly increased in hepatocellular carcinoma (HCC). In this study, we isolated thirteen phage antibodies to Lu from a phage library of peripheral blood from HCC patients, suggesting that these patients produced autoantibodies against endogenous Lu. To characterize the phage antibodies, we determined the Lu domains they recognize. The extracellular domain of Lu contains five IgSF domains, D1-D2-D3-D4-D5. The epitope of one phage antibody (A7) was localized to the D5 domain. The other phage antibodies recognized the D2 domain, which is also recognized by a function blocking mouse monoclonal antibody. One of the antibodies to D2 (C7) inhibited the binding of Lu to ligand, and it also prevented tumor cell migration on laminin-511 (LM-511). However, the C7 scFv purified from the periplasm fraction of bacteria did not exhibit the inhibitory effects, indicating that the scFv form could not sterically inhibit the binding of Lu to LM-511. We also identified the amino acid residues that form the epitope recognized by the C7 phage antibody. Mutagenesis studies showed that Arg²⁴⁷ is necessary for forming the epitope. The C7 phage antibody and its epitope may be useful for developing drugs to prevent HCC progression and/or metastasis.

High-efficiency antibody discovery achieved with multiplexed microscopy

The analysis of secreted antibody from large and diverse populations of B cells in parallel at the clonal level can reveal desirable antibodies for diagnostic or therapeutic applications. By immobilizing B cells in microdroplets with particulate reporters, decoding and isolating them in a microscopy environment, we have recovered panels of antibodies with rare attributes to therapeutically relevant targets. The ability to screen up to 100 million cells in a single experiment can be fully leveraged by accessing primary B-cell populations from evolutionarily divergent species such as chickens.