Effective production of single-chain variable fragment (scFv) antibody using recombinant Escherichia coli by DO-stat fed-batch culture

Investigating the influence of process parameters on the properties and refolding yield of single-chain variable fragment inclusion bodies

Ever since the potential of inclusion bodies (IBs) has been recognized, substantial advances have been made towards understanding IB processes and enabling efficient and controlled development strategies. Still, the influence of the chosen upstream processing (USP) strategy on the properties of inclusion bodies (IBs) and their refolding performance remains poorly understood. This work aims to target this challenge by investigating the influence of two chosen USP parameters, namely the specific substrate uptake rate and the temperature during induction, on IB titer, IB properties, namely IB purity, size and secondary protein structure of the IBs, as well as refolding yield of single-chain variable fragment M (scFvM) IBs. Contrary to findings in the literature, USP conditions neither had a statistically significant effect on the aforementioned IB properties nor on the refolding yield, but could clearly alter the IB titer. Our results provide detailed analytical insights on the independence of IB properties from USP conditions for this protein, while increasing the volumetric IB productivity proved feasible through variations in USP parameters. Therefore, titer maximization appears to be the sole optimization strategy for scFvM IBs and these findings may also apply to other target proteins with similar structural properties.

Development of a novel and broadly applicable sandwich ELISA assay based on rabbit single-chain variable fragments and a modified Ig-binding domain of protein L fused to a polystyrene-binding peptide

Most of currently available sandwich-type enzyme-linked immunosorbent assays (ELISA) require the use of full-length animal-derived antibodies which poses welfare criticisms and are often expensive to produce. There is therefore a strong demand for the development of more affordable and animal-free methods to produce antibodies for sandwich ELISA assay. To address these issues, we propose here the development of a new technology based on two complementary rabbit single-chain variable fragments (scFvs) and an Ig-binding domain of protein L (PpL1) fused to a polystyrene-binding peptide (PS-tag) that can be recombinantly produced in bacteria. Toward this goal, we developed a rabbit scFv capable to bind the antigen via its variable regions while engaging protein L through its constant framework domain. To enhance the density of captured scFv and enable a better solvent exposure, we generated multiple PpL1 variants bearing polystyrene-binding peptides (PS) tags fused to its ends. The tandem trimer of PpL1 variant bearing PS-tags located at the N-terminus (PpL1'-T-PSN) revealed increased antigen-binding signal when immobilized on hydrophilic polystyrene (phi-PS) plates. By CDR-grafting different antigen-binding specificities into our engineered protein L-binding scFv we validated our technology against a different antigen. Finally, to further enhance the sensitivity of our assay, we implemented a protein L-based pretreatment to remove potential inhibitory immunoglobulin often present in the blood samples. The ability to rapidly and cost-effectively generate animal-free recombinant antibody fragments that can be adsorbed and specifically oriented on plates while retaining their antigen-binding properties could lead to the development of innovative and widely applicable sandwich ELISA systems for the efficient, versatile and sensitive detection of different types of antigens.

Specific N-terminal amino acids potentiate the periplasmic expression of single-chain variable fragments in Escherichia coli

Single-chain variable fragments (ScFvs) are important in therapy, diagnosis and research because of their elevated antigen affinity and low immunogenicity. At present, high-yield scFv expression in Escherichia coli is limited by insoluble aggregation in the reducing environment of the cytoplasm or low yields in the periplasm. Here we achieved increased expression of scFvs in the periplasm by inserting optimal amino acids between the signal peptide and scFv. We constructed an expression library with three random amino acids at the scFv N-terminus, screened this library with a single-step colony assay and identified the specific sequences that boosted periplasmic expression of scFvs.