Recombinant human antibody fragment against tetanus toxoid produced by phage display

Neutralizing anti-diphtheria toxin scFv produced by phage display

BACKGROUND

Diphtheria can be prevented by vaccination, but some epidemics occur in several places, and diphtheria's threat is considerable. Administration of diphtheria antitoxin (DAT) produced from hyperimmunized animals is the most common treatment. Recombinant human antibody fragments such as single-chain variable fragments (scFv) produced by phage display library may introduce an interesting approach to overcome the limitations of the traditional antibody therapy. In the present study, B cells of immunized volunteers were used to construct a human single-chain fragment (HuscFv) library.

MATERIALS AND METHODS

The library was constructed with the maximum combination of heavy and light chains. As an antigen, Diphtheria toxoid (DTd) was used in four-round phage bio-panning to select phage clones that display DTd bound HuscFv from the library. After panning, individual scFv clones were selected. Clones that were able to detect DTd in an initial screening assay were transferred to Escherichia coli HB2151 to express the scFvs and purification was followed by Ni metal ion affinity chromatography. Toxin neutralization test was performed on Vero cells. The reactivity of the soluble scFv with diphtheria toxin were done and affinity calculation based on Beatty method was calculated.

RESULTS

The size of the constructed scFv library was calculated to be 1.3 × 106 members. Following four rounds of selection, 40 antibody clones were isolated which showed positive reactivity with DTd in an ELISA assay. Five clones were able to neutralize DTd in Vero cell assay. These neutralizing clones were used for soluble expression and purification of scFv fragments. Some of these soluble scFv fragments show neutralizing activity ranging from 0.6 to 1.2 µg against twofold cytotoxic dose of diphtheria toxin. The affinity constant of the selected scFv antibody was determined almost 107 M-1.

CONCLUSION

This study describes the prosperous construction and isolation of scFv from the immune library, which specifically neutralizes diphtheria toxin. The HuscFv produced in this study can be a potential candidate to substitute the animal antibody for treating diphtheria and detecting toxins.

Phage display technology for fabricating a recombinant monoclonal ScFv antibody against tetanus toxin

Tetanus is a specific infectious disease, often associated with lower immunization in developing countries and catastrophic events (such as earthquakes). Millions of people, especially children, die every year from tetanus disease. Therefore, it is necessary to devise a rapid and sensitive detection method for tetanus toxin to ensure an early diagnosis and clinical treatment of tetanus. The current study looks at developing a novel, high specific, low-cost, and sensitive ScFv antibody. It is capable of tetanus detection immunoassays in clinical diagnosis, suspicious foods, and water monitoring. For this regard, a high-quality phage display antibody library (8.7 × 107 PFU/ml) was constructed. Tetanus-specific antibodies with high affinity retrieved from libraries. After phage rescue and four rounds of biopanning, clone screening was performed by phage ELISA. Recombinant antibodies expressed from the AC8 clone showed the highest affinity for tetanus. SDS-PAGE and western blotting confirmed the presence of a high-quality, pure ScFv band at 32 kDa. ELISA was used to determine the affinity value, estimated to be around 10-8 M. The results suggest that the proposed detection method by ScFv antibodies is an alternative diagnostic tool enabling rapid and specific detection of the tetanus toxin.

Developing Recombinant Antibodies by Phage Display Against Infectious Diseases and Toxins for Diagnostics and Therapy

Antibodies are essential molecules for diagnosis and treatment of diseases caused by pathogens and their toxins. Antibodies were integrated in our medical repertoire against infectious diseases more than hundred years ago by using animal sera to treat tetanus and diphtheria. In these days, most developed therapeutic antibodies target cancer or autoimmune diseases. The COVID-19 pandemic was a reminder about the importance of antibodies for therapy against infectious diseases. While monoclonal antibodies could be generated by hybridoma technology since the 70ies of the former century, nowadays antibody phage display, among other display technologies, is robustly established to discover new human monoclonal antibodies. Phage display is an in vitro technology which confers the potential for generating antibodies from universal libraries against any conceivable molecule of sufficient size and omits the limitations of the immune systems. If convalescent patients or immunized/infected animals are available, it is possible to construct immune phage display libraries to select in vivo affinity-matured antibodies. A further advantage is the availability of the DNA sequence encoding the phage displayed antibody fragment, which is packaged in the phage particles. Therefore, the selected antibody fragments can be rapidly further engineered in any needed antibody format according to the requirements of the final application. In this review, we present an overview of phage display derived recombinant antibodies against bacterial, viral and eukaryotic pathogens, as well as microbial toxins, intended for diagnostic and therapeutic applications.

Tetanus Neurotoxin Neutralizing Antibodies Screened from a Human Immune scFv Antibody Phage Display Library

Tetanus neurotoxin (TeNT) produced by Clostridiumtetani is one of the most poisonous protein substances. Neutralizing antibodies against TeNT can effectively prevent and cure toxicosis. Using purified Hc fragments of TeNT (TeNT-Hc) as an antigen, three specific neutralizing antibody clones recognizing different epitopes were selected from a human immune scFv antibody phage display library. The three antibodies (2-7G, 2-2D, and S-4-7H) can effectively inhibit the binding between TeNT-Hc and differentiated PC-12 cells in vitro. Moreover, 2-7G inhibited TeNT-Hc binding to the receptor via carbohydrate-binding sites of the W pocket while 2-2D and S-4-7H inhibited binding of the R pocket. Although no single mAb completely protected mice from the toxin, they could both prolong survival when challenged with 20 LD₅₀s (50% of the lethal dose) of TeNT. When used together, the mAbs completely neutralized 1000 LD₅₀s/mg Ab, indicating their high neutralizing potency in vivo. Antibodies recognizing different carbohydrate-binding pockets could have higher synergistic toxin neutralization activities than those that recognize the same pockets. These results could lead to further production of neutralizing antibody drugs against TeNT and indicate that using TeNT-Hc as an antigen for screening human antibodies for TeNT intoxication therapy from human immune antibody library was convenient and effective.

Phage and Yeast Display

Despite the availability of antimicrobial drugs, the continued development of microbial resistance--established through escape mutations and the emergence of resistant strains--limits their clinical utility. The discovery of novel, therapeutic, monoclonal antibodies (mAbs) offers viable clinical alternatives in the treatment and prophylaxis of infectious diseases. Human mAb-based therapies are typically nontoxic in patients and demonstrate high specificity for the intended microbial target. This specificity prevents negative impacts on the patient microbiome and avoids driving the resistance of nontarget species. The in vitro selection of human antibody fragment libraries displayed on phage or yeast surfaces represents a group of well-established technologies capable of generating human mAbs. The advantage of these forms of microbial display is the large repertoire of human antibody fragments present during a single selection campaign. Furthermore, the in vitro selection environments of microbial surface display allow for the rapid isolation of antibodies--and their encoding genes--against infectious pathogens and their toxins that are impractical within in vivo systems, such as murine hybridomas. This article focuses on the technologies of phage display and yeast display, as these strategies relate to the discovery of human mAbs for the treatment and vaccine development of infectious diseases.

Delivery of Constitutively Active Mutant MKK6(E) With TAT-OSBP Induces Apoptosis in Human Ovarian Carcinoma HO8910 Cells

Biologically active peptides and proteins are novel agents that show promise in the development of anticancer drugs. Their relatively low cell permeability and poor tumor selectivity, however, impede their widespread applicability. In this study, we evaluated the tumor selectivity, cellular internalization, and biological activity of a cell-permeable ovarian cancer cell-specific therapeutic protein consisting of TAT-OSBP and constitutively active MKK6(E), an upstream kinase of the p38 signaling pathway that mediates cellular apoptosis. OSBP, a 7-amino-acid peptide with high affinity for human ovarian cancer HO8910 cells, was conjugated to the cell-penetrating peptide (TAT) to form a tumor-selective peptide (TAT-OSBP), which was further conjugated with EGFP or MKK6(E). Flow cytometry and fluorescent microscopy were performed to evaluate the tumor-targeted penetration of TAT-OSBP-EGFP. The inhibitory effects of TAT-OSBP-MKK6(E) were determined by cell proliferation and apoptosis assays. The internalization efficiency of TAT-OSBP-EGFP was significantly higher than that of TAT-EGFP. TAT-OSBP-EGFP selectively penetrated HO8910 cells. TAT-OSBP-MKK6(E) fusion protein inhibited cancer cell growth to varying degrees, with the highest level of inhibition in HO8910 cells. Moreover, TAT-OSBP-MKK6(E) significantly induced apoptosis of HO8910 cells. However, there was no significant difference in apoptosis in the normal ovarian epithelial cells treated with either TAT-OSBP-MKK6(E) or TAT-MKK6(E). Our results demonstrate that TAT-OSBP-MKK6(E) is a novel artificially designed molecule, which induces apoptosis and selectively targets human ovarian carcinoma HO8910 cells. Our study provides novel insights that may aid in the development of a new generation of anticancer drugs.

Methods for the Creation of Cyclic Peptide Libraries for Use in Lead Discovery

The identification of initial hits is a crucial stage in the drug discovery process. Although many projects adopt high-throughput screening of small-molecule libraries at this stage, there is significant potential for screening libraries of macromolecules created using chemical biology approaches. Not only can the production of the library be directly interfaced with a cell-based assay, but these libraries also require significantly fewer resources to generate and maintain. In this context, cyclic peptides are increasingly viewed as ideal scaffolds and have proven capability against challenging targets such as protein-protein interactions. Here we discuss a range of methods used for the creation of cyclic peptide libraries and detail examples of their successful implementation.