The Versatility of Framework Regions of Chicken V(H) and V(L) to Mutations

To identify the interchangeability of V(H) and V(L) framework region (FR) residues, we artificially introduced random mutations at all residue positions in a chicken monoclonal antibody, which has only one functional V(H) and Vλ gene. When we classified the amino acids into 5 groups by their physicochemical properties, all FR residues could be replaced by another group except L23 (C), H36 (W), H86 (D), H104 (G), and H106 (G). Eighty-two (50.9%), 48 (29.8%), 17 (10.6%), and 9 FR residues (5.6%) could be replaced by 4, 3, 2, and 1 group(s), individually, without significant loss of reactivity. We also confirmed a similar level of versatility with 2 different chicken antibodies. This high level of versatility on FR residues has not been predicted because it has not been observed in the 150 chicken antibodies that we previously generated or in the 1,269 naïve chicken V(H) sequences publically available. In conclusion, chicken antibody FR residues are highly interchangeable and this property can be applied for improving the physicochemical property of antibody including thermal stability, solubility and viscosity.

Next-generation sequencing enables the discovery of more diverse positive clones from a phage-displayed antibody library

Phage display technology provides a powerful tool to screen a library for a binding molecule via an enrichment process. It has been adopted as a critical technology in the development of therapeutic antibodies. However, a major drawback of phage display technology is that because the degree of the enrichment cannot be controlled during the bio-panning process, it frequently results in a limited number of clones. In this study, we applied next-generation sequencing (NGS) to screen clones from a library and determine whether a greater number of clones can be identified using NGS than using conventional methods. Three chicken immune single-chain variable fragment (scFv) libraries were subjected to bio-panning on prostate-specific antigen (PSA). Phagemid DNA prepared from the original libraries as well as from the Escherichia coli pool after each round of bio-panning was analyzed using NGS, and the heavy chain complementarity-determining region 3 (HCDR3) sequences of the scFv clones were determined. Subsequently, through two-step linker PCR and cloning, the entire scFv gene was retrieved and analyzed for its reactivity to PSA in a phage enzyme immunoassay. After four rounds of bio-panning, the conventional colony screening method was performed for comparison. The scFv clones retrieved from NGS analysis included all clones identified by the conventional colony screening method as well as many additional clones. The enrichment of the HCDR3 sequence throughout the bio-panning process was a positive predictive factor for the selection of PSA-reactive scFv clones.

Ig-like domain 6 of VCAM-1 is a potential therapeutic target in TNFα-induced angiogenesis

Tumor necrosis factor alpha (TNFα)-induced angiogenesis plays important roles in the progression of various diseases, including cancer, wet age-related macular degeneration, and rheumatoid arthritis. However, the relevance and role of vascular cell adhesion molecule-1 (VCAM-1) in angiogenesis have not yet been clearly elucidated. In this study, VCAM-1 knockdown shows VCAM-1 involvement in TNFα-induced angiogenesis. Through competitive blocking experiments with VCAM-1 Ig-like domain 6 (VCAM-1-D6) protein, we identified VCAM-1-D6 as a key domain regulating TNFα-induced vascular tube formation. We demonstrated that a monoclonal antibody specific to VCAM-1-D6 suppressed TNFα-induced endothelial cell migration and tube formation and TNFα-induced vessel sprouting in rat aortas. We also found that the antibody insignificantly affected endothelial cell viability, morphology and activation. Finally, the antibody specifically blocked VCAM-1-mediated cell–cell contacts by directly inhibiting VCAM-1-D6-mediated interaction between VCAM-1 molecules. These findings suggest that VCAM-1-D6 may be a potential novel therapeutic target in TNFα-induced angiogenesis and that antibody-based modulation of VCAM-1-D6 may be an effective strategy to suppress TNFα-induced angiogenesis.

A phosphorylation pattern-recognizing antibody specifically reacts to RNA polymerase II bound to exons

The C-terminal domain of RNA polymerase II is an unusual series of repeated residues appended to the C-terminus of the largest subunit and serves as a flexible binding scaffold for numerous nuclear factors. The binding of these factors is determined by the phosphorylation patterns on the repeats in the domain. In this study, we generated a synthetic antibody library by replacing the third heavy chain complementarity-determining region of an anti-HER2 (human epidermal growth factor receptor 2) antibody (trastuzumab) with artificial sequences of 7–18 amino-acid residues. From this library, antibodies were selected that were specific to serine phosphopeptides that represent typical phosphorylation patterns on the functional unit (YSPTSPS)₂ of the RNA polymerase II C-terminal domain (CTD). Antibody clones pCTD-1stS2 and pCTD-2ndS2 showed specificity for peptides with phosphoserine at the second residues of the first or second heptamer repeat, respectively. Additional clones specifically reacted to peptides with phosphoserine at the fifth serine of the first repeat (pCTD-1stS5), the seventh residue of the first repeat and fifth residue of the second repeat (pCTD-S7S5) or the seventh residue of either the first or second repeat (pCTD-S7). All of these antibody clones successfully reacted to RNA polymerase II in immunoblot analysis. Interestingly, pCTD-2ndS2 precipitated predominately RNA polymerase II from the exonic regions of genes in genome-wide chromatin immunoprecipitation sequencing analysis, which suggests that the phosphoserine at the second residue of the second repeat of the functional unit (YSPTSPS)2 is a mediator of exon definition.