Isolation of single-chain variable fragment (scFv) antibodies for detection of Chickpea chlorotic dwarf virus (CpCDV) by phage display

Development of novel neutralizing single-chain fragment variable antibodies against S100A8

S100A8 plays a critical role in the pathogenesis of several inflammatory diseases and multiple types of cancer. Therefore, targeting the S100A8 function may alleviate the pathogenic process in various diseases. Here, specific single-chain variable fragment (scFv) antibodies targeting recombinant S100A8 (rS100A8) were selected by phage display technique and characterized using cDNA sequencing, immunoassay tests, and molecular docking. The neutralizing activity of scFvs was examined by a cell viability assay in rS100A8-treated macrophages. Furthermore, the modulatory effects of scFvs on the expression of inflammatory markers and apoptosis-related genes in macrophages and human colorectal carcinoma HT-29 cells treated with rS100A8 or dextran sulfate sodium (DSS) were assessed by RT-qPCR and flow cytometry. Based on our results, four scFvs were identified to be capable of detecting rS100A8 in the immunoassay tests. Among the selected scFvs, two clones (SA8-E6 and SA8-E12), alone or in combination, exhibited the highest blocking activity on rS100A8 and potently inhibited S100A8-induced cytotoxicity in macrophages. The use of a SA8-E6 and SA8-E12 (SA8-E6-12) cocktail inhibited the upregulation of TLR4 and RAGE, as well as inflammation and apoptosis-related genes in macrophages and HT-29 cells stimulated with rS100A8. Additionally, SA8-E6-12 exerted a significant inhibitory effect on inflammation and apoptosis induced by the S100A8/A9 complex in DSS-stimulated macrophages. We also demonstrated by molecular docking that the interaction of S100A8 with SA8-E6-12 was mainly restricted to the binding domain involved in the connection of S100A8 to TLR4. Further studies are required to explore the efficacy of these anti-S100A8 scFvs as potential therapeutic agents using in vivo models of S100A8-driven inflammatory diseases.

Transient expression of anti-HrpE scFv antibody reduces the hypersensitive response in non-host plant against bacterial phytopathogen Xanthomonas citri subsp. citri

Citrus canker is a bacterial disease caused by Xanthomonas citri subsp. citri (Xcc) that affects the citrus industry worldwide. Hrp pili subunits (HrpE), an essential component of Type III secretion system (T3SS) bacteria, play a crucial role in the pathogenesis of Xcc by transporting effector proteins into the host cell and causing canker symptoms. Therefore, development of antibodies that block HrpE can suppress disease progression. In this study, a specific scFv detecting HrpE was developed using phage display technique and characterized using sequencing, ELISA, Western blotting, and molecular docking. In addition, a plant expression vector of pCAMBIA-scFvH6 was constructed and agroinfiltrated into Nicotiana tabacum cv. Samson leaves. The hypersensitive response (HR) in the leaves of transformed and non-transformed plants was evaluated by inoculating leaves with Xcc. After three rounds of biopanning of the phage library, a specific human scFv antibody, named scFvH6, was identified that showed high binding activity against HrpE in ELISA and Western blotting. Molecular docking results showed that five intermolecular hydrogen bonds are involved in HrpE-scFvH6 interaction, confirming the specificity and high binding activity of scFvH6. Successful transient expression of pCAMBIA-scFvH6 in tobacco leaves was verified using immunoassay tests. The binding activity of plant-produced scFvH6 to detect HrpE in Western blotting and ELISA was similar to that of bacterial-produced scFvH6 antibody. Interestingly, tobacco plants expressing scFvH6 showed a remarkable reduction in HR induced by Xcc compared with control plants, so that incidence of necrotic lesions was significantly higher in non-transformed controls (≥ 1.5 lesions/cm2) than in the plants producing scFvH6 (≤ 0.5 lesions/cm2) after infiltration with Xcc inoculum. Our results revealed that the expression of scFvH6 in tobacco leaves can confer resistance to Xcc, indicating that this approach could be considered to provide resistance to citrus bacterial canker disease.

Development and characterization of phage display-derived anti-toxin antibodies neutralizing TcdA and TcdB of Clostridioides difficile

TcdA and TcdB are known as the major virulence attributes of Clostridioides difficile. Hence, neutralizing the TcdA and TcdB activities can be considered as an efficient therapeutic approach against C. difficile infection (CDI). In this work, we utilized phage display technique to select single-chain fragment variable (scFv) fragments as recombinant antibodies displayed on the surface of phages, which specifically target native TcdA, or TcdB (nTcdA and nTcdB), and their recombinant C-terminal combined repetitive oligopeptide (CROP) domains (rTcdA and rTcdB). After three rounds of biopanning, abundance of phage clones displaying high reactivity with TcdA or TcdB was quantified through enzyme-linked immunosorbent assay (ELISA). Furthermore, selected scFvs were characterized by cell viability and neutralization assays. The gene expression of immunological markers, IL-8 and TNF-α, was examined in treated Caco-2 cells by RT-qPCR. The epitopes of neutralizing scFvs were also identified by molecular docking. Totally, 18 scFv antibodies (seven for TcdA and 11 for TcdB) were identified by ELISA. Among selected scFvs, two clones for TcdA (rA-C2, A-C9) and three clones for TcdB (rB-B4, B-F5, B-F11) exhibited the highest neutralizing activity in Caco-2 and Vero cells. Moreover, the cocktail of anti-TcdA and anti-TcdB antibodies notably decreased the mRNA expression of TNF-α and IL-8 in Caco-2 cells. Molecular docking revealed that the interaction between scFv and toxin was mostly restricted to CROP domain of TcdA or TcdB. Our results collectively provided more insights for the development of neutralizing scFvs against C. difficile toxins using phage display. Further research is needed to meticulously evaluate the potential of scFvs as an alternative treatment for CDI using animal models and clinical trials.IMPORTANCETargeting the major toxins of Clostridioides difficile by neutralizing antibodies is a novel therapeutic approach for CDI. Here, we report a panel of new anti-TcdA (rA-C2, A-C9) and anti-TcdB (rB-B4, B-F5, and B-F11) recombinant antibody fragments (scFvs) isolated from Tomlinson I and J libraries using phage display technique. These scFv antibodies were capable of neutralizing their respective toxin and showed promise as potential therapeutics against TcdA and TcdB of C. difficile in different in vitro models. In addition, in silico analysis showed that at least two neutralization mechanisms, including inhibiting cell surface binding of toxins and inhibiting toxin internalization can be proposed for the isolated scFvs in this work. These findings provide more insights for the applicability of specific scFvs toward C. difficile toxins at in vitro level. However, further research is required to evaluate the potential application of these scFvs as therapeutic agents for CDI treatment in clinical setting.

Rapid-format recombinant antibody-based methods for the diagnosis of Clostridioides difficile infection: Recent advances and perspectives

Clostridioides difficile, the most common cause of nosocomial diarrhea, has been continuously reported as a worldwide problem in healthcare settings. Additionally, the emergence of hypervirulent strains of C. difficile has always been a critical concern and led to continuous efforts to develop more accurate diagnostic methods for detection of this recalcitrant pathogen. Currently, the diagnosis of C. difficile infection (CDI) is based on clinical manifestations and laboratory tests for detecting the bacterium and/or its toxins, which exhibit varied sensitivity and specificity. In this regard, development of rapid diagnostic techniques based on antibodies has demonstrated promising results in both research and clinical environments. Recently, application of recombinant antibody (rAb) technologies like phage display has provided a faster and more cost-effective approach for antibody production. The application of rAbs for developing ultrasensitive diagnostic tools ranging from immunoassays to immunosensors, has allowed the researchers to introduce new platforms with high sensitivity and specificity. Additionally, DNA encoding antibodies are directly accessible in these approaches, which enables the application of antibody engineering to increase their sensitivity and specificity. Here, we review the latest studies about the antibody-based ultrasensitive diagnostic platforms for detection of C. difficile bacteria, with an emphasis on rAb technologies.

Identification of New Chickpea Virus and Control of Chickpea Virus Disease

Objective. The objective of the study was to discuss the classification, virus characteristics, detection methods, and control measures of chickpea virus, with an aim to provide a theoretical basis for identification of new chickpea virus and control of chickpea virus disease. Methods. The domestic and foreign studies were reviewed, and the virus coat protein or nucleic acid sequence was identified by immunological and molecular diagnostic techniques. Results. There were 14 main types of chickpea viruses attacking, and seven Luteoviridae viruses were reported, namely, chickpea chlorotic stunt virus (CpCSV), bean leafroll virus (BLRV), beet western yellows virus (BWYV), soybean dwarf virus (SbDV), cotton leafroll dwarf virus (CLRDV), cucurbit aphid-borne yellows virus (CABYV), and phasey bean mild yellows virus (PhBMYV). The family Geminiviridae includes chickpea chlorotic dwarf virus (CpCDV), chickpea chlorosis virus (CpCV), chickpea redleaf virus (CpRLV), chickpea yellows virus (CpYV), and mastrevirus. The family Nanoviridae is dominated by the faba bean necrotic yellows virus (FBNYV). The family Bromoviridae includes cucumber mosaic virus (CMV) and alfalfa mosaic virus (AMV). Conclusion. At present, there are mainly 12 types of viruses infecting chickpeas, which are transmitted by leafhoppers or aphids and are associated with symptoms such as yellowing, chlorosis, and stunted pod development, resulting in serious yield loss. Correct use of various molecular diagnostic tools to detect and identify chickpea virus can accurately assess chickpea virus infection and provide a basis for the prevention and treatment of chickpea virus disease.

Transient expression of an scFvG8 antibody in plants and characterization of its effects on the virulence factor pthA of Xanthomonas citri subsp. citri

Citrus bacterial canker, caused by Xanthomonas citri subsp. citri (Xcc), is a major disease of citrus plants, causing a significant loss in the citrus industry. The pthA is a bacterial effector protein mediates protein-protein and protein-DNA interactions and modulates host transcription. Injection of pthA effector protein into the host cell induces the expression of the susceptibility gene CsLOB1 which is required for citrus canker disease development. In this study, we described in planta expression of a specific anti-pthA single-chain variable fragment (scFv) recombinant antibody, scFvG8, and assessed its function using molecular docking, immunoblotting, and indirect enzyme-linked immunosorbent assay (ELISA). Based on the results, homology-based molecular docking suggested that at least eight intermolecular hydrogen bonds are involved in pthA-scFvG8 interactions. Immunoblotting and indirect ELISA results reconfirmed specific binding of scFvG8 to pthA protein. Moreover, gene fragment encoding scFvG8 was cloned into plant expression vector and transiently expressed in leaves of Nicotiana tabacum cv. Samson by agroinfiltration method. Transient expression of scFvG8 (at the expected size of 35 kDa) in N. tabacum leaves was confirmed by western blotting. Also, immunoblotting and indirect ELISA showed that the plant-derived scFvG8 had similar activity to purified scFvG8 antibody in detecting pthA. Additionally, in scFvG8-expressing tobacco leaves challenged with Xcc, a reduction (for up to 70%) of hypersensitive response (HR) possibly via direct interaction with pthA, was observed in the necrotic leaf area compared to control plants infected with empty vector. The results obtained in this study confirm that scFvG8 can suppress the function of pthA effector protein within plant cells, thus the induction of stable expression of scFvG8 in lime trees can be considered as an appropriate approach to confer resistance to Xcc.

A new single-chain variable fragment (scFv) antibody provides sensitive and specific detection of citrus tristeza virus

Citrus tristeza virus (CTV) is the most economically important virus disease of citrus worldwide. To develop a specific serological assay for CTV, a Tomlinson phage display antibody library of single chain variable fragments (scFv) was screened with a recombinant CTV coat protein (CTV-CP) heterologously expressed in Escherichia coli. The phage clones were checked by ELISA to identify clones with high specificity for CTV-CP. Eight clones were strongly reactive with CTV-CP. Nucleotide sequencing of these clones revealed that all of them contained the same sequence. Thus, the phage-displayed scFv antibody was termed scFvF10. Evaluation of scFvF10 binding to CTV-CP by plate-trapped antigen ELISA (PTA-ELISA) and immunoblotting, showed that it was specific and allowed sensitive detection of CTV-CP. Homology-based molecular modeling and docking analysis confirmed that the interaction between CTV-CP and scFvF10, with a binding energy of -738 kj mol-1, occurred mainly by 12 intermolecular hydrogen bonds. Moreover, triple-antibody sandwich (TAS)-ELISA using scFvF10 as second antibody showed high sensitivity in the detection of CTV infected samples. The CTV detection limit of scFvF10 by PTA-ELISA and TAS-ELISA were 0.05 and 0.01 μg CP/mL, respectively. Our results with different diagnostic assays demonstrated that scFvF10 has the potential to be used as an efficient tool for CTV-infected plant diagnosis.

Selection and Characterization of a Single-Chain Variable Fragment against Porcine Circovirus Type 2 Capsid and Impedimetric Immunosensor Development

Porcine circovirus type 2 (PCV2) is the primary causative agent of porcine circovirus-associated disease (PCVAD) that causes huge global economic losses for the swine industry. Effective strategies or rapid detection of PCV2 in pig are essential to control PCVAD. Here, single-chain variable fragments (scFvs) were selected and characterized against the PCV2 capsid using phage display technology. Phage scFv clones were selected from the human scFv phagemid library (Tomlinson I + J) for direct panning against the PCV2 capsid. Eighty-four monoclonal phage scFvs were individually tested for binding to the PCV2 capsid by ELISA. Eight scFv clones showed significant binding to the PCV2 capsid and only three clones (clone nos. 13, 37, and 81) contained both VHCDRs and VLCDRs in the sequence. Clone scFv no. 81 had the highest reactivity to the PCV2 capsid and was constructed in the pET22b (+) expression vector. The recombinant was transformed to Escherichia coli BL21(DE3) for expression and purification. The scFv showed appropriate affinity to the PCV2 capsid by western blot analysis. Kinetics of scFv and the PCV2 capsid were determined using surface plasmon resonance and showed binding affinity in the nanomolar range (K D = 57.2 nM). Our scFv was first applied in the development of an impedimetric immunosensor for PCV2 capsid detection, and results showed that impedance increased with increasing PCV2 capsid expression with limit of detection = 114 nM. Findings demonstrated that our scFv has potential for use as a receptor for biosensor devices.