Single Chain Variable Fragments Produced in Escherichia coli against Heat-Labile and Heat-Stable Toxins from Enterotoxigenic E. coli

Recombinant monoclonal antibody production in yeasts: Challenges and considerations

Monoclonal antibodies (mAbs) are laboratory-based engineered protein molecules with a monovalent affinity or multivalent avidity towards a specific target or antigen, which can mimic natural antibodies that are produced in the human immune systems to fight against detrimental pathogens. The recombinant mAb is one of the most effective classes of biopharmaceuticals produced in vitro by cloning and expressing synthetic antibody genes in a suitable host. Yeast is one of the potential hosts among others for the successful production of recombinant mAbs. However, there are very few yeast-derived mAbs that got the approval of the regulatory agencies for direct use for treatment purposes. Certain challenges encountered by yeasts for recombinant antibody productions need to be overcome and a few considerations related to antibody structure, host engineering, and culturing strategies should be followed for the improved production of mAbs in yeasts. In this review, the drawbacks related to the metabolic burden of the host, culturing conditions including induction mechanism and secretion efficiency, solubility and stability, downstream processing, and the pharmacokinetic behavior of the antibody are discussed, which will help in developing the yeast hosts for the efficient production of recombinant mAbs.

Production and Characterization of Biotinylated Anti-fenitrothion Nanobodies and Development of Sensitive Fluoroimmunoassay

A simple and sensitive fluoroimmunoassay (FIA) based on a heavy-chain antibody (VHH) for rapid detection of fenitrothion was developed. A VHH library was constructed from an immunized alpaca, and one clone recognizing fenitrothion (namely, VHHjd8) was achieved after careful biopanning. It was biotinylated by fusing with the Avi tag and biotin ligase to obtain a fusion protein (VHHjd8-BT), showing both binding capacity to fenitrothion and the streptavidin poly-horseradish peroxidase conjugate (SA-polyHRP). Based on a competitive assay format, the absorbance spectrum of oxidized 3,3',5,5'-tetramethylbenzidine generated by SA-polyHRP overlapped the emission spectrum of carbon dots, which resulted in quenching of signals due to the inner-filter effect. The developed FIA showed an IC₅₀ value of 1.4 ng/mL and a limit of detection of 0.03 ng/mL, which exhibited 15-fold improvement compared with conventional enzyme-linked immunosorbent assay. The recovery test of FIA was validated by standard GC-MS/MS, and the results showed good consistency, indicating that the assay is an ideal tool for rapid screening of fenitrothion in bulk food samples.

Antibody therapy against antibiotic-resistant diarrheagenic Escherichia coli: a systematic review

Over four billion episodes of diarrhea occur annually in developing countries with diarrheagenic Escherichia coli (DEC) outbreaks also being reported, until now bacterial diarrhea is conventionally addressed by the antibiotic treatment regimes. In recent decades, the emergence of antimicrobial-resistant strains has become a major obstacle in diarrheal treatment; hence, novel and ideal therapeutics are needed. Notably, 80% of DEC is resistant to first-class antibiotics. Among the existing strategies, passive immunization is considered as an alternative to combat drug-resistant bacteria. Antibodies specific to an antigen can be used for prophylactic and therapeutic purposes. In this review, we have systematically discussed the effect of passive immunotherapy to combat DEC and explored the types and advancements in antibodies used against antibiotic-resistant DEC.

Heat-Labile Toxin from Enterotoxigenic Escherichia coli Causes Systemic Impairment in Zebrafish Model

Heat-labile toxin I (LT-I), produced by strains of enterotoxigenic Escherichia coli (ETEC), causes profuse watery diarrhea in humans. Different in vitro and in vivo models have already elucidated the mechanism of action of this toxin; however, their use does not always allow for more specific studies on how the LT-I toxin acts in systemic tracts and intestinal cell lines. In the present work, zebrafish (Danio rerio) and human intestinal cells (Caco-2) were used as models to study the toxin LT-I. Caco-2 cells were used, in the 62nd passage, at different cell concentrations. LT-I was conjugated to FITC to visualize its transport in cells, as well as microinjected into the caudal vein of zebrafish larvae, in order to investigate its effects on survival, systemic traffic, and morphological formation. The internalization of LT-I was visualized in 3 × 104 Caco-2 cells, being associated with the cell membrane and nucleus. The systemic traffic of LT-I in zebrafish larvae showed its presence in the cardiac cavity, yolk, and regions of the intestine, as demonstrated by cardiac edema (100%), the absence of a swimming bladder (100%), and yolk edema (80%), in addition to growth limitation in the larvae, compared to the control group. There was a reduction in heart rate during the assessment of larval survival kinetics, demonstrating the cardiotoxic effect of LT-I. Thus, in this study, we provide essential new depictions of the features of LT-I.

TCR-pMHC bond conformation controls TCR ligand discrimination

A major unanswered question is how a TCR discriminates between foreign and self-peptides presented on the APC surface. Here, we used in situ fluorescence resonance energy transfer (FRET) to measure the distances of single TCR–pMHC bonds and the conformations of individual TCR–CD3ζ receptors at the membranes of live primary T cells. We found that a TCR discriminates between closely related peptides by forming single TCR–pMHC bonds with different conformations, and the most potent pMHC forms the shortest bond. The bond conformation is an intrinsic property that is independent of the binding affinity and kinetics, TCR microcluster formation, and CD4 binding. The bond conformation dictates the degree of CD3ζ dissociation from the inner leaflet of the plasma membrane via a positive calcium signaling feedback loop to precisely control the accessibility of CD3ζ ITAMs for phosphorylation. Our data revealed the mechanism by which a TCR deciphers the structural differences among peptides via the TCR–pMHC bond conformation.

Molecular evolution of single chain fragment variable (scFv) for diagnosis of lymphatic filariasis

Endemic countries with lymphatic filariasis are striving towards the Global Program to Eliminate Lymphatic Filariasis (GPELF) by 2020. Efficient and cost-effective diagnostic tools to assess active filarial infection are critical to eradicate lymphatic filariasis. Detection of circulating filarial antigens in sera is one of the precise methods to identify this infection. Monoclonal antibodies and single chain fragment variable (scFv) against Wuchereria bancrofti antigen SXP1 have been developed for antigen detection. Molecular cloning of scFv for recombinant expression has laid a platform for developing novel genetic constructs with enhanced reactivity. In this study, a simple procedure is developed to create diverse libraries of scFv based on a single DNA framework with all the requisites for an in vitro protein synthesis and ribosomal display. Error Prone-PCR was performed to incorporate random mutations and screened by ribosome display technique to isolate evolved scFv. Evolved scFv with six mutations showed tenfold increase in affinity compared to wild-type scFv for rWbSXP1. In silico studies showed that four mutations introduced unique molecular interactions between the evolved scFv and SXP1. Reactivity with asserted clinical samples of endemic normals (EN), microfilariaemic (MF), chronic pathology (CP) and non-endemic normals (NEN) showed significant augment (59.69%, p < 0.0001) in reactivity to MF samples with evolved scFv in comparison to wild-type scFv. Sensitivity of scFv was increased from 15.62 ng to 195 pg by evolved scFv in serum samples. This evolutionary method coupled with ribosome display has facilitated us to improve the reactivity of the ScFv without diminishing the specificity.

Development and Validation of Shiga Toxin-Producing Escherichia coli Immunodiagnostic Assay

Shiga toxin (Stx)-producing Escherichia coli (STEC) and its subgroup enterohemorrhagic E. coli are important pathogens involved in diarrhea, which may be complicated by hemorrhagic colitis and hemolytic uremic syndrome, the leading cause of acute renal failure in children. Early diagnosis is essential for clinical management, as an antibiotic treatment in STEC infections is not recommended. Previously obtained antibodies against Stx1 and Stx2 toxins were employed to evaluate the sensitivity and specificity of the latex Agglutination test (LAT), lateral flow assay (LFA), and capture ELISA (cEIA) for STEC detection. The LAT (mAb Stx1 plus mAb stx2) showed 99% sensitivity and 97% specificity. Individually, Stx1 antibodies showed 95.5% and 94% sensitivity and a specificity of 97% and 99% in the cEIA and LFA assay, respectively. Stx2 antibodies showed a sensitivity of 92% in both assays and a specificity of 100% and 98% in the cEIA and LFA assay, respectively. These results allow us to conclude that we have robust tools for the diagnosis of STEC infections.

Anti-ROR1 scFv-EndoG as a Novel Anti-Cancer Therapeutic Drug

Aim: Immunotoxins are proteins that consist of an antibody fragment linked to a toxin, used as agents for targeted therapy of cancers. Although the most potent immunotoxins are made from bacterial and plant toxins, obstacles which contribute to poor responses are immunogenicity in patients and rapid development of neutralizing antibodies. In the present study we proposed a new therapeutic immunotoxin for targeted cancer therapy of ROR1 expressing cancers: an anti ROR1 single chain fragment variable antibody (scFv)-endonuclease G (anti ROR1 scFv-EndoG). Methods: The three-dimensional structure of anti ROR1 scFv-EndoG protein was modeled and structure validation tools were employed to confirm the accuracy and reliability of the developed model. In addition, stability and integrity of the model were assessed by molecular dynamic (MD) simulation. Results: All results suggested the protein model to be acceptable and of good quality. Conclusions: Anti-ROR1 scFv-EndoG would be expected to bind to the ROR1 extracellular domain by its scFv portion and selectively deliver non-immunogenic human endonuclease G enzyme as an end-stage apoptosis molecule into ROR1-expressing cancer cells and lead rapidly to apoptosis. We believe that anti ROR1 and other anti-tumor antigen scFv-EndoG forms may be helpful for cancer therapy.

Presence and characterization of Escherichia coli virulence genes isolated from diseased pigs in the central region of Argentina

Background:

The main pathogen of neonatal and post weaning diarrhea and edema disease (ED) is Escherichia coli and pathotypes involved are enterotoxigenic, enteropathogenic, and shiga toxigenic (ETEC, EPEC, and STEC, respectively). Those diseases cause economic loss in pig production.

Aim:

The aim of this work was to evaluate the presence of strains expressing virulence markers genes and the antibiotic susceptibility profiles of E. coli from clinical cases of post weaning diarrhea and ED in farms in the central area of Argentina.

Materials and Methods:

Intensive pig farms from the central region of Argentina were sampled. Intestinal mucosa swabs from pigs with diarrhea were taken, seeded on MacConkey agar plates, biochemically typified and tested by polymerase chain reaction (PCR). Antibiograms were made by disk-diffusion method.

Results:

A total of 54 strains from clinical cases studied showed PCR findings: 88.88% (48/54) expressed at least one gene coding for a virulence factor. Colonization factors found were: 39.58% of strains had F18, 33.33% were F4 and 31.25% adhesin involved in diffuse adherence-I; 29.17%, 25%, and 2.1% expressed LT, STb, and STa, respectively. 25% were STx and 16.67% were eae positive. Only 2.1% were STx2. The most active antibiotics against most strains were gentamicin and ceftiofur, but resistance profiles against many antibiotics were found.

Conclusion:

High circulation of pathogens strains of E. coli among pigs with diarrhea with an extended antibiotic resistance profile.

Diarrheagenic Escherichia coli

Most Escherichia coli strains live harmlessly in the intestines and rarely cause disease in healthy individuals. Nonetheless, a number of pathogenic strains can cause diarrhea or extraintestinal diseases both in healthy and immunocompromised individuals. Diarrheal illnesses are a severe public health problem and a major cause of morbidity and mortality in infants and young children, especially in developing countries. E. coli strains that cause diarrhea have evolved by acquiring, through horizontal gene transfer, a particular set of characteristics that have successfully persisted in the host. According to the group of virulence determinants acquired, specific combinations were formed determining the currently known E. coli pathotypes, which are collectively known as diarrheagenic E. coli. In this review, we have gathered information on current definitions, serotypes, lineages, virulence mechanisms, epidemiology, and diagnosis of the major diarrheagenic E. coli pathotypes.