Screening of a ScFv Antibody With High Affinity for Application in Human IFN-γ Immunoassay

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.

CRISPR/Cas12a-based fluorescence aptasensor integrated with two-dimensional cobalt oxyhydroxide nanosheets for IFN-γ detection

Cytokine storm (CS) is a risky immune overreaction accompanied by significant elevations of pro-inflammatory cytokines including interferon-γ (IFN-γ), interleukin and tumor necrosis factor. Sensitive detection of cytokine is conducive to studying CS progress and diagnosing infectious diseases. In this study, we developed a tandem system combining aptamer, strand displacement amplification (SDA), CRISPR/Cas12a, and cobalt oxyhydroxide nanosheets (termed Apt-SCN tandem system) as a signal-amplified platform for IFN-γ detection. Owing to the stronger affinity, target IFN-γ bound specifically to the aptamer from aptamer-complementary DNA (Apt-cDNA) duplex. The cDNA released from the Apt-cDNA duplex initiated SDA, resulting in the generation of double-stranded DNA products that could activate the trans-cleavage activity of CRISPR/Cas12a. The activated CRISPR/Cas12a further cleaved FAM-labeled single-stranded DNA probe, preventing it from adhering to the cobalt oxyhydroxide nanosheets and recovering the fluorescence signal. Sensitive fluorometric analysis of IFN-γ was successfully performed with detection limit as low as 0.37 nM. Unlike traditional protein analysis methods, Apt-SCN tandem system incorporates multiple signal amplification techniques and may also be applicable for other cytokines assay. This study was the initial study to utilize SDA and CRISPR/Cas12a to detect IFN-γ, showing great potential for cytokines clinical assay and CS prevention.

Human-murine chimeric autoantibodies with high affinity and specificity for systemic sclerosis

Scleroderma 70 (Scl-70) is commonly used in the clinic for aiding systemic sclerosis (SSc) diagnosis due to its recognition as autoantibodies in the serum of SSc patients. However, obtaining sera positive for anti-Scl-70 antibody can be challenging; therefore, there is an urgent need to develop a specific, sensitive, and easily available reference for SSc diagnosis. In this study, murine-sourced scFv library were screened by phage display technology against human Scl-70, and the scFvs with high affinity were constructed into humanized antibodies for clinical application. Finally, ten high-affinity scFv fragments were obtained. Three fragments (2A, 2AB, and 2HD) were select for humanization. The physicochemical properties of the amino acid sequence, three-dimensional structural basis, and electrostatic potential distribution of the protein surface of different scFv fragments revealed differences in the electrostatic potential of their CDR regions determined their affinity for Scl-70 and expression. Notably, the specificity test showed the half-maximal effective concentration values of the three humanized antibodies were lower than that of positive patient serum. Moreover, these humanized antibodies showed high specificity for Scl-70 in diagnostic immunoassays for ANA. Among these three antibodies, 2A exhibited most positive electrostatic potential on the surface of the CDRs and highest affinity and specificity for Scl-70 but with least expression level; thus, it may provide new foundations for developing enhanced diagnostic strategies for SSc.

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.

Structural and molecular rationale for the diversification of resistance mediated by the Antibiotic_NAT family

The environmental microbiome harbors a vast repertoire of antibiotic resistance genes (ARGs) which can serve as evolutionary predecessors for ARGs found in pathogenic bacteria, or can be directly mobilized to pathogens in the presence of selection pressures. Thus, ARGs from benign environmental bacteria are an important resource for understanding clinically relevant resistance. Here, we conduct a comprehensive functional analysis of the Antibiotic_NAT family of aminoglycoside acetyltransferases. We determined a pan-family antibiogram of 21 Antibiotic_NAT enzymes, including 8 derived from clinical isolates and 13 from environmental metagenomic samples. We find that environment-derived representatives confer high-level, broad-spectrum resistance, including against the atypical aminoglycoside apramycin, and that a metagenome-derived gene likely is ancestral to an aac(3) gene found in clinical isolates. Through crystallographic analysis, we rationalize the molecular basis for diversification of substrate specificity across the family. This work provides critical data on the molecular mechanism underpinning resistance to established and emergent aminoglycoside antibiotics and broadens our understanding of ARGs in the environment.

Detection of αB-Conotoxin VxXXIVA (αB-CTX) by ic-ELISA Based on an Epitope-Specific Monoclonal Antibody

In view of the toxicological hazard and important applications in analgesics and cancer chemotherapeutics of αB-CTX, it is urgent to develop an accurate, effective and feasible immunoassay for the determination and analysis of αB-CTX in real samples. In this study, MBP-αB-CTX4 tandem fusion protein was used as an immunogen to elicit a strong immune response, and a hybridoma cell 5E4 secreting IgG2b against αB-CTX was successfully screened by hybridoma technology. The affinity of the purified 5E4 monoclonal antibody (mAb) was 1.02 × 108 L/mol, which showed high affinity and specificity to αB-CTX. Epitope 1 of αB-CTX is the major binding region for 5E4 mAb recongnization, and two amino acid residues (14L and 15F) in αB-CTX were critical sites for the interaction between αB-CTX and 5E4 mAb. Indirect competitive ELISA (ic-ELISA) based on 5E4 mAb was developed to detect and analyze αB-CTX in real samples, and the linear range of ic-ELISA to αB-CTX was 117–3798 ng/mL, with a limit of detection (LOD) of 81 ng/mL. All the above results indicated that the developed ic-ELISA had high accuracy and repeatability, and it could be applied for αB-CTX detection and drug analysis in real samples.

A comprehensive comparison between camelid nanobodies and single chain variable fragments

By the emergence of recombinant DNA technology, many antibody fragments have been developed devoid of undesired properties of natural immunoglobulins. Among them, camelid heavy-chain variable domains (VHHs) and single-chain variable fragments (scFvs) are the most favored ones. While scFv is used widely in various applications, camelid antibodies (VHHs) can serve as an alternative because of their superior chemical and physical properties such as higher solubility, stability, smaller size, and lower production cost. Here, these two counterparts are compared in structure and properties to identify which one is more suitable for each of their various therapeutic, diagnosis, and research applications.

Sensitive immunoassays based on specific monoclonal IgG for determination of bovine lactoferrin in cow milk samples

Lactoferrin (LF), a bioactive multifunctional protein of the transferrin family, is found mainly in the secretions of all mammals, especially in milk. In the present study, a hybridoma cell (LF8) secreting IgG against bovine LF was screened, and the purified LF8 mAb showed high specificity and affinity to bovine LF. The linear range of ic-ELISA to detect LF was 9.76 ~ 625 ng/mL, with a limit of detection (LOD) of 0.01 ng/mL. The average recovery of intra- and inter-assay were (104.45 ± 4.12)% and (107.13 ± 4.72)%, respectively. The LOD of colloidal gold- and AuNFs-based strip by naked eye were 9.7 and 2.4 ng/mL, respectively, and the detection time was less than 10 min without any samples pretreatment and expensive equipment. The developed ELISA and lateral flow immunosensors based on specific IgG could be used directly for rapid detection of the bovine LF content in cow milk samples.

Evolution of Escherichia coli Expression System in Producing Antibody Recombinant Fragments

Antibodies and antibody-derived molecules are continuously developed as both therapeutic agents and key reagents for advanced diagnostic investigations. Their application in these fields has indeed greatly expanded the demand of these molecules and the need for their production in high yield and purity. While full-length antibodies require mammalian expression systems due to the occurrence of functionally and structurally important glycosylations, most antibody fragments and antibody-like molecules are non-glycosylated and can be more conveniently prepared in E. coli-based expression platforms. We propose here an updated survey of the most effective and appropriate methods of preparation of antibody fragments that exploit E. coli as an expression background and review the pros and cons of the different platforms available today. Around 250 references accompany and complete the review together with some lists of the most important new antibody-like molecules that are on the market or are being developed as new biotherapeutics or diagnostic agents.

A functionally neutral single chain antibody to measure beta-1 integrin uptake and recycling

Integrin‐mediated cell adhesion and signaling are critical for many physiological processes. The dynamic turnover of integrins and their associated adhesion complexes through endocytic and recycling pathways has emerged as an important mechanism for controlling cell migration and invasion in cancer. Thus, the regulation of integrin trafficking and how this may be altered by disease‐specific molecular mechanisms has generated considerable interest. However, current tools available to study integrin trafficking may cause artifacts and/or do not provide adequate kinetic information. Here, we report the generation of a functionally neutral and monovalent single chain antibody to quantitatively and qualitatively measure β1 integrin trafficking in cells. Our novel probe can be used in a variety of assays and allows for the biochemical characterization of rapid recycling of endogenous integrins. We also demonstrate its potential utility in live cell imaging, providing proof of principle to guide future integrin probe design.

The dynamic turnover of integrins through endocytic trafficking pathways has emerged as a key mechanism for cell migration and invasion. Lakoduk et al. report the generation of a functionally neutral and monovalent antibody‐based probe to track and measure endogenous beta‐1 integrin uptake and fast recycling in multiple cell types. Their tool, scFv^K20, serves as proof of principle inspiration for future integrin probe design.

Development of an ic-ELISA and immunochromatographic strip based on IgG antibody for detection of ω-conotoxin MVIIA

ω-conotoxin MVIIA(ω-CTX MVIIA) is a peptide consisting of 25 amino acid residues secreted mainly by Conus magus. In view of the toxin threat to humans and animals and defined application in analgesic therapy, it is necessary to develop a rapid, effective and accuracy method for the quantification and analysis of ω-CTX MVIIA in real samples. In the present study, a hybridoma cell named 2E5 stable secreting IgG antibody against ω-CTX MVIIA was selected successfully, and the subtype of Mab 2E5 was IgG1. The purified monoclonal antibody(Mab) 2E5 has high affinity (about 2.79 × 10⁹ L/mol), and shows high specificity to ω-CTX MVIIA antigen. The linear range of ic-ELISA to detect ω-CTX MVIIA was 0.20˜7.22 μg/mL, with a lower detection limit (LOD) of 0.14 ng/mL. The average recovery of intra- and inter-assay were (85.45 ± 2.28)% and (88.03 ± 4.80)% respectively, with a coefficient of variation from 2.59% to 5.42%. The LOD of colloidal strip by naked eye was 1 μg/mL, and the detection time was less than 10 min without any equipment. The developed ELISA and colloidal test strips based on this IgG antibody could be used to detect ω-CTX MVIIA residue in real Conus samples.

Design and Production of Bispecific Antibodies

With the current biotherapeutic market dominated by antibody molecules, bispecific antibodies represent a key component of the next-generation of antibody therapy. Bispecific antibodies can target two different antigens at the same time, such as simultaneously binding tumor cell receptors and recruiting cytotoxic immune cells. Structural diversity has been fast-growing in the bispecific antibody field, creating a plethora of novel bispecific antibody scaffolds, which provide great functional variety. Two common formats of bispecific antibodies on the market are the single-chain variable fragment (scFv)-based (no Fc fragment) antibody and the full-length IgG-like asymmetric antibody. Unlike the conventional monoclonal antibodies, great production challenges with respect to the quantity, quality, and stability of bispecific antibodies have hampered their wider clinical application and acceptance. In this review, we focus on these two major bispecific types and describe recent advances in the design, production, and quality of these molecules, which will enable this important class of biologics to reach their therapeutic potential.

Competitive and noncompetitive immunoassays for the detection of benzothiostrobin using magnetic nanoparticles and fluorescein isothiocyanate-labeled peptides

Phage-displayed peptides have been proven to be powerful reagents for competitive and noncompetitive immunoassays. However, they are unconventional reagents, which greatly limit their analytical commercial applications and require additional reagents for detection. In this work, the peptides that specifically bind with anti-benzothiostrobin monoclonal antibody (mAb) or benzothiostrobin-mAb immunocomplex were synthesized and conjugated with fluorescein isothiocyanate (FITC) as substitutes of the phage-displayed peptides to avoid their shortcomings and extend their applications. Competitive and noncompetitive fluorescence immunoassays (FIAs) for benzothiostrobin were developed by mAb coupling with magnetic nanoparticles as concentration elements and peptides conjugated with FITC as tracers. Compared with enzyme-linked immunosorbent assays, the FIAs reduced the number of steps from 6 to 2 and analysis time from more than 5 to 1.2 h. The competitive FIA showed the half-maximal inhibition concentration (IC₅₀) of 16.8 ng mL^-1 and detection range (IC₁₀-IC₉₀) of 1.0-759.9 ng mL^-1, while the concentration of analyte producing 50% saturation of the signal (SC₅₀) and detection range (SC₁₀-SC₉₀) of noncompetitive FIA were 93.4 and 5.9-788.2 ng mL^-1, respectively. The average spiked recoveries were 68.33-98.50% and 73.33-96.67% for competitive and noncompetitive FIAs, respectively. The FIAs showed good correlation with high-performance liquid chromatography for the detection of benzothiostrobin in authentic samples. Graphical abstract Development of competitive and noncompetitive fluorescence immunoassays for benzothiostrobin by using monoclonal antibody coupling with magnetic nanoparticles as concentration elements and peptides conjugated with fluorescein isothiocyanate as tracers.