Selection of a single chain variable fragment antibody against ivermectin from a phage displayed library

Bioengineering and computational analysis of programmed cell death ligand-1 monoclonal antibody

The trans-membrane proteins of the B7 family programmed cell death ligand-1 (PD-L1) and programmed death-1 (PD-1) play important roles in inhibiting immune responses and enhancing self-tolerance via T-cell modulation. Several therapeutic antibodies are used to promote T-cell proliferation by preventing interactions between PD-1/PD-L1. Recombinant technology appears to be quite useful in the production of such potent antibodies. In this study, we constructed recombinant molecules by cloning variable regions of the PD-L1 molecule into pMH3 vectors and transferring them into mammalian cell lines for expression. G418 supplementation was used to screen the recombinant clones, which were then maintained on serum-free medium. The full-length antibody was isolated and purified from the medium supernatant at a concentration of 0.5-0.8 mg/ml. Antibody binding affinity was investigated using ELISA and immunofluorescence methods. The protein-protein interactions (PPI) were determined using a docking approach. The SWISS model was utilized for homology modeling, while ZDOCK, Chimera, and PyMOL were used to validate 3D models. The Ramachandran plots were constructed using the SWISS model, which revealed that high-quality structures had a value of more than 90%. Current technologies allow for the accurate determination of antigen-antibody interactions.

Efficient development and expression of scFv recombinant proteins against PD-L1 surface domain and potency in cancer therapy

PD-L1 is a 40 kDa trans-membrane protein of B7 family and an important T cell regulator. Binding of PD-L1 and PD-1 inhibits proliferation and activation of T cell results cell exhaustion. This phenomenon can be reversed by blocking PD-L1/PD-1 interactions with single chain variables fragment (scFv) fusion proteins and by direct inhibition of tumor cells with drug conjugates. The human phage-displayed scFv library was utilized to generate scFv against the PD-L1 antigen by affinity bio-panning. The positive clones were selected by continuous transfection of bacterial cells and sequence analysis. The binding affinity and specificity of the scFv and antibody fragments were determined by using surface plasmon resonance biosensor, western blot analysis, and immunofluorescence assay. After three rounds of panning selection, about 30% of clones have a binding affinity with targeted PD-L1 antigen. Eight positive clones with accurate sequences were isolated and analyzed for binding affinity with PD-L1 antigen. Three of those with accurate sequences and binding affinity were selected for the recombinant formation and soluble expression by Escherichia coli host machinery. The highly positive recombinant clones with the exact orientation of FR and CDR domains were developed and can be used as a drug carrier tools in ADC formation or direct inhibition of immune checkpoint in cancer immunotherapy. The conjugate achieved its initial potency and need efficient improvement to enhance direct tumor suppression and bio-therapeutics strategies enrichment.

Rapid isolation of single-chain antibodies from a human synthetic phage display library for detection of Bacillus thuringiensis (Bt) Cry1B toxin

Single chain variable fragment antibody (scFv) is capable of binding its target antigens and is one of the most popular recombinant antibodies format for many applications. In this study, a large human synthetic phage displayed library (Tomlinson J) was employed to generate scFvs against Cry1B toxin by affinity panning. After four rounds of panning, six monoclonal phage particles capable of binding with the Cry1B were isolated, sequenced and characterized by Enzyme-Linked Immunosorbent Assay (ELISA). Two of the identified novel anti-Cry1B scFvs, namely H9 and B12, were expressed in Escherichia coli HB2151 and purified by Ni metal ion affinity chromatography. Sodium dodecyl sulfate polyacrylamine gel electrophoresis (SDS-PAGE) indicated that the relative molecular mass of scFv was estimated at 30 kDa. The purified scFv-H9 was used to develop an indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) for Cry1B toxin. The linear range of detection for standards in this ic-ELISA was approximately 0.19-1.1 μg mL⁻¹ and 50% inhibition of control (IC₅₀) was 0.84 μg mL⁻¹ for Cry1B. The affinity of scfv-H9 was (1.95±0.12) × 10⁷ M⁻¹ and showed cross-reactivity with Cry1Ab toxin and Cry1Ac toxin (8.53% and 7.58%, respectively), higher cross-reactivity (12.8%) with Cry1C toxin. The average recoveries of Cry1B toxin from spiked leaf and rice samples were in the range 89.5-96.4%, and 88.5-95.6%, respectively, with a coefficient of variation (C.V) less than 6.0%. These results showed promising applications of scfv-H9 for detecting Cry1B toxin in agricultural and environmental samples.

A monoclonal antibody-based ELISA for multiresidue determination of avermectins in milk

Due to the widespread use and potential toxicity of avermectins (AVMs), multi-residue monitoring of AVMs in edible tissues, especially in milk, has become increasingly important. With the aim of developing a broad-selective immunoassay for AVMs, a broad-specific monoclonal antibody (Mab) was raised. Based on this Mab, a homologous indirect enzyme-linked immunosorbent assay (ELISA) for the rapid detection of AVMs in milk was developed. Under the optimized conditions, the IC₅₀ values in assay buffer were estimated to be 3.05 ng/mL for abamectin, 13.10 ng/mL for ivermectin, 38.96 ng/mL for eprinomectin, 61.00 ng/mL for doramectin, 14.38 ng/mL for emamectin benzoate. Detection capability (CCβ) of the ELISA was less than 5 ng/mL and 2 ng/mL in milk samples prepared by simple dilution and solvent extraction, respectively. The optimized ELISA was used to quantify AVMs in milk samples spiked at different amounts. The mean recovery and coefficient of variation (CV) were 95.90% and 15.42%, respectively. The Mab-based ELISA achieved a great improvement in AVMs detection. Results proved this broad-selective ELISA would be useful for the multi-residue determination of AVMs in milk without purification process.