Senecavirus A (SVA) is a major viral pathogen causing disease in pigs, and effective monitoring of SVA infection is critical for disease control. In this study, we aimed to develop a reliable ELISA method for rapidly detecting neutralizing antibodies against SVA. We used HEK293F cells to express an SVA-specific porcine Fab antibody and verified the biological activity of the Fab antibody by indirect ELISA, immunofluorescence assay, virus neutralization test, and Western blotting. The Fab antibody was biotinylated and used as a competitive antibody to establish a competitive ELISA (C-ELISA) for detecting neutralizing antibodies against SVA. We then evaluated the C-ELISA in terms of sensitivity, specificity, repeatability, and result agreement rate with the VNT. The results showed that we successfully prepared an SVA-specific porcine Fab antibody, which showed high affinity for SVA. We named this antibody 1M33Fab and designated it as Bio-1M33Fab after biotin labeling. The assay conditions were optimized as follows: the coating concentration of SVA particles being 1 μg/mL, the working concentration of Bio-1M33Fab being 0.5 μg/mL, the optimal serum dilution of 1:10, and the optimal dilution of enzyme-labeled avidin being 1:30 000. At a percent inhibition (PI) of 47%, the assay demonstrated the highest sensitivity (96.88%) and specificity (100%), with no cross-reactivity observed with the positive sera of major porcine viral diseases. The intra-assay coefficient of variation ranged from 1.12% to 7.34%, while the inter-assay coefficient of variation ranged from 1.10% to 8.97%, indicating good repeatability. In the detection of 224 clinical pig serum samples, C-ELISA and VNT showed a result agreement rate of 93.75%. In conclusion, we successfully develop a C-ELISA method for detecting neutralizing antibodies against SVA by using a porcine-derived Fab antibody, which lays a foundation for the development of detection kits.
Animals ; Swine ; Antibodies, Neutralizing/immunology* ; Enzyme-Linked Immunosorbent Assay/methods* ; Immunoglobulin Fab Fragments/immunology* ; Antibodies, Viral/immunology* ; Picornaviridae/immunology* ; Humans ; HEK293 Cells ; Swine Diseases/diagnosis* ; Picornaviridae Infections/diagnosis*

Entero virus 71 (EV71) causes hand, foot, and mouth disease (HFMD) and occasionally leads to severe neurological complications and even death. Scavenger receptor class B member 2 (SCARB2) is a functional receptor for EV71, that mediates viral attachment, internalization, and uncoating. However, the exact binding site of EV71 on SCARB2 is unknown. In this study, we generated a monoclonal antibody (mAb) that binds to human but not mouse SCARB2. It is named JL2, and it can effectively inhibit EV71 infection of target cells. Using a set of chimeras of human and mouse SCARB2, we identified that the region containing residues 77-113 of human SCARB2 contributes significantly to JL2 binding. The structure of the SCARB2-JL2 complex revealed that JL2 binds to the apical region of SCARB2 involving α-helices 2, 5, and 14. Our results provide new insights into the potential binding sites for EV71 on SCARB2 and the molecular mechanism of EV71 entry.
Amino Acid Sequence ; Animals ; Antibodies, Monoclonal ; chemistry ; genetics ; metabolism ; Binding Sites ; Cell Line ; Crystallography, X-Ray ; Enterovirus A, Human ; drug effects ; genetics ; growth & development ; immunology ; Fibroblasts ; drug effects ; virology ; Gene Expression ; HEK293 Cells ; Humans ; Immunoglobulin Fab Fragments ; chemistry ; genetics ; metabolism ; Lysosome-Associated Membrane Glycoproteins ; chemistry ; genetics ; immunology ; Mice ; Models, Molecular ; Protein Binding ; Protein Conformation, alpha-Helical ; Protein Conformation, beta-Strand ; Protein Interaction Domains and Motifs ; Receptors, Scavenger ; chemistry ; genetics ; immunology ; Receptors, Virus ; chemistry ; genetics ; immunology ; Recombinant Fusion Proteins ; chemistry ; genetics ; immunology ; Sequence Alignment ; Sequence Homology, Amino Acid ; Sf9 Cells ; Spodoptera ; Thermodynamics

To obtain human antibodies against the Gn protein of Severe fever with thrombocytopenia syndrome virus (SFTSV) with phage display technology, this study aimed to screen anti-Gn protein antibodies from an anti-SFTSV Fab human phage display library. Antibody genes were identified by sequence analysis and the specificity of antibodies was confirmed by ELISA. The Fab antibody genes were cloned into the HL51-14 vector and expressed in a mammalian cell expression system. IgG antibodies were then purified by protein A affinity chromatography,and the results were further confirmed by ELISA,IFA,western blotting assays and micro-neutralization tests. The results showed that, after three rounds of panning, there were 390 human Fab antibodies against SFTSV particles, of which 364 were specific for nucleoprotein. Coated with the Gn protein, eight different Fab antibodies specific for Gn protein were obtained after the determination of the subtype and subclass of antibodies by gene sequencing; five of these antibodies were from the Lambda library and three were from the Kappa library. The eight IgG antibodies could specifically bind to Gn protein according to the ELISA, IFA and Western blotting assays. The micro-neutralization test showed that these eight antibodies had no neutralizing activity,but they could still provide a reference for research in human monoclonal antibodies against SFTSV.
Antibodies ; genetics ; immunology ; Bunyaviridae Infections ; genetics ; immunology ; virology ; Cell Line ; Cloning, Molecular ; Humans ; Immunoglobulin Fab Fragments ; genetics ; immunology ; Immunoglobulin G ; genetics ; immunology ; Neutralization Tests ; Phlebovirus ; genetics ; immunology ; Viral Proteins ; genetics ; immunology

To identify human monoclonal HIV-l-neutralizing antibodies from an HIV-1 CRF07BC specific phage display antibody library by cell-based screening. 293T cells were transfected by pCH064. 2-Env plas mid and then used to biopan the phage antibody library. The positive phage clones were screened by cell based ELISA and sequenced for the variable region of heavy (VH) and light (VL) chains. The expressed Fabs were purified by Ni(+2) -NTA column and analyzed by SDS-PAGE. The cell- and gp120 protein-based ELISA as well as flow cytometry were used to measure Fab's binding activity. The neutralizing activity of Fabs was assessed by HIV-1 pseudoviruses. After 4-round biopanning, the binding phages to transfected cells were enriched about 650-folds. A total of 28 positive clones were screened out by cell ELISA and sequence analysis identified 5 different Fabs possessing unique VH and VL (2801, 2837, 2863, 2870 and 2920). Interestingly, these Fabs reacted with the Env-transfected 293T cells but not soluble gp120 proteins, suggesting that they might target conformation-dependent epitopes presenting on viral Env complex. We found that three Fabs (2801, 2863, 2870) exhibited potent neutralizing activity against CRF07_BC isolate CH120. 6 with IC50 of 2.24, 0.89 and 3.09 microg/mL respectively, and that 2801 and 2863 cross-neutral ized the subtype B isolate SF162 at IC50 of 0.69 and 3.52 microg/mL respectively. In conclusion, the HIV-1 Env-transfected 293T cells can be used to efficiently enrich and screen the phage antibody library and isolate human monoclonal HIV-1-neutralizing Fabs that target the Env complex-dependent conformational epitopes. Therefore, our studies provide a powerful platform for exploring the mechanism of HIV-1 neu tralizing response and for designing AIDS vaccines.
Antibodies, Monoclonal ; genetics ; immunology ; Antibodies, Neutralizing ; genetics ; immunology ; Enzyme-Linked Immunosorbent Assay ; methods ; HEK293 Cells ; HIV Antibodies ; genetics ; immunology ; HIV Envelope Protein gp120 ; genetics ; immunology ; HIV Infections ; immunology ; virology ; HIV-1 ; genetics ; immunology ; isolation & purification ; Humans ; Immunoglobulin Fab Fragments ; genetics ; immunology ; Neutralization Tests ; Peptide Library ; Transfection

This study is to investigate the tumor invasion and metastasis inhibition effects of the immunoconjugate composed of lidamycin and anti-type IV collagenase monoclonal antibody Fab' fragment. Boyden chamber assay was used to evaluate the influence of Fab'-LDM on HT-1080 cells invasion ability, gelatinase spectrum was used to measure the change of invasion factor MMP-2 and MMP-9's secretion, and RT-PCR was adopted to determine TIMP-1 mRNA expression level. The immunoconjugate inhibition of tumor in situ metastasis was also tested in nude mice. The Fab'-LDM conjugates had dose-dependent inhibition effect on HT-1080 cells' invasion. At the concentrations of 5 and 10 nmol L(-1), the Fab'-LDM inhibited the invasion by (60 +/- 12) % and (79 +/- 11) % respectively. At the concentration of 5 and 10 nmol L(-1), the Fab'-LDM inhibited the secretion of MMP-2 by (42 +/- 8) % and (54 +/- 6) % and that of MMP-9 by (57 +/- 3) % and (87 +/- 1) %, respectively. RT-PCR indicated that conjugates increased the anti-invasion factor TIMP-1 level. The in vivo experiment showed that, compared with the control group, the tumor inhibition rate in Fab', Fab'-LDM, and LDM group equaled to (30 +/- 13) %, (86 +/- 26) %, (74 +/- 22) % respectively. In conclusion, Fab'-LDM could inhibit the invasion and metastasis of tumor and it might be a new tumor biotherapy agent.
Aminoglycosides ; pharmacology ; Animals ; Antibiotics, Antineoplastic ; pharmacology ; Antibodies, Monoclonal ; immunology ; Cell Line, Tumor ; Enediynes ; pharmacology ; Fibrosarcoma ; metabolism ; pathology ; Humans ; Immunoconjugates ; pharmacology ; Immunoglobulin Fab Fragments ; pharmacology ; Matrix Metalloproteinase 2 ; immunology ; secretion ; Matrix Metalloproteinase 9 ; immunology ; secretion ; Mice ; Mice, Inbred BALB C ; Mice, Nude ; Neoplasm Invasiveness ; Neoplasm Metastasis ; Neoplasm Transplantation ; RNA, Messenger ; metabolism ; Tissue Inhibitor of Metalloproteinase-1 ; genetics ; metabolism ; Tumor Burden ; drug effects

A combinatorial human Fab library to the rabies virus was constructed using antibody genes derived from the blood of vaccinated donors. The library were panned and selected on purified rabies virus particles of aG or CTN strain with phage display. Eleven unique human Fab antibodies specific for the rabies virus glycoprotein were obtained by ELISA, IFA and DNA sequences analysis of these antibodies. Among these Fab antibodies, five human Fab antibodies were converted to full-length human IgG antibodies with recombinant baculovirus system. The five full-length human IgG antibodies were tested in vitro for rabies virus neutralization, resulting in all specificities to neutralize the virus. The obtained human anti-rabies antibodies lay the basis for the production of cocktail of anti-rabies monoclonal antibody with chinese intellectual property.
Amino Acid Sequence ; Animals ; Antibodies, Neutralizing ; immunology ; Antibodies, Viral ; immunology ; Cell Line ; Cricetinae ; Humans ; Immunoglobulin Fab Fragments ; genetics ; immunology ; Immunoglobulin G ; genetics ; immunology ; Molecular Sequence Data ; Neutralization Tests ; Rabies ; immunology ; virology ; Rabies virus ; genetics ; immunology

To investigate the antitumor activities of the immunoconjugates composed of anti-type IV collagenase monoclonal antibody Fab' fragment and lidamycin (LDM) prepared with different linkers. The immunoconjugates were prepared by linking Fab' to lysine-69 of LDM apoprotein by SPDP, LCSPDP, SMBS or SSMPB as the intermediate drug linkers. Immunoreactivities of the conjugates were determined by ELISA. The cytotoxicities of the conjugates were examined by clonogenic assay. In vivo antitumor effects of the conjugates were evaluated in nude mice bearing subcutaneously implanted HT-1080 tumor. ELISA assay showed that the conjugates retained part of the immunoreactivity of 3G11 against the antigen. The cytotoxicities of the Fab'-SMBS-LDM and Fab'-SSMPB-LDM to HT-1080 cells were significantly potent, compared with Fab'-SPDP-LDM, Fab'-LCSPDP-LDM and free LDM. In animal models at the same condition, free LDM, Fab'-SPDP-LDM and Fab'-LCSPDP-LDM inhibited the growth of HT-1080 tumor by 70.9%, 74.8% and 72.3%, while Fab'-SMBS-LDM and Fab'-SSMPB-LDM reached 78.0% and 87.7%, respectively. The median survival time of the mice treated with free LDM, Fab'-SPDP-LDM and Fab'-LCSPDP-LDM were prolonged by 71.9%, 82.2% and 107.5%, respectively, compared with that of untreated group. Whereas, the median survival time of Fab'-SMBS-LDM and Fab'-SSMPB-LDM were prolonged by 145.2% and 165.8%, respectively, indicating that Fab'-SSMPB-LDM was more effective than Fab'-SMBS-LDM in tumor suppression and life span prolongation. Fab'-SSMPB-LDM has more marked selective antitumor efficacy and lower toxicity, and might be a novel candidate for cancer therapy.
Aminoglycosides ; pharmacology ; Animals ; Antibiotics, Antineoplastic ; pharmacology ; Antibodies, Monoclonal ; immunology ; Cell Line, Tumor ; drug effects ; Cell Proliferation ; drug effects ; Collagenases ; immunology ; Enediynes ; pharmacology ; Fibrosarcoma ; pathology ; Humans ; Immunoconjugates ; pharmacology ; Immunoglobulin Fab Fragments ; immunology ; Matrix Metalloproteinase Inhibitors ; Mice ; Mice, Inbred BALB C ; Mice, Nude ; Neoplasm Transplantation ; Tumor Burden ; drug effects

OBJECTIVETo evaluate the feasibility and efficacy of radioimmunotherapy with 131 I-labeled humanized anti-HBsAg Fab (131 I-anti-HBsAg Fab) combined with 131 I-labeled anti-nucleus antigen monoclonal antibody chTNT (131 I-chTNT) in nude mice bearing human hepatocellular carcinoma.

METHODSNude mice bearing subcutaneous human hepatocellular carcinoma xenografts were treated by intratumoral injection of 131 I-anti-HBsAg Fab and/or 131 I-chTNT, and the changes in the tumor size and alterations in the radioactivity concentration in the tumor and non-tumor tissues were observed.

RESULTSThe tumor inhibition rate in mice treated with 131 I-anti-HBsAg Fab combined with 131 I-chTNT (73.09%) was significantly higher than that in mice treated with 131 I-anti-HBsAg Fab (47.8%) or 131 I-chTNT (54.26%) alone. Combined treatment also resulted in significantly higher tumor-to-normal radioactivity concentration ratios than the treatment with the single agents.

CONCLUSIONIntratumoral injection with 131 I-labeled monoclonal antibodies can increase the radioactivity concentration in the tumor and enhance the efficacy of the radioimmunotherapy in nude mice bearing human hepatocellular carcinoma.

Animals ; Antibodies, Antinuclear ; immunology ; Antibodies, Monoclonal ; therapeutic use ; Carcinoma, Hepatocellular ; pathology ; radiotherapy ; Cell Line, Tumor ; Hepatitis B Surface Antigens ; immunology ; Humans ; Immunoconjugates ; therapeutic use ; Immunoglobulin Fab Fragments ; immunology ; Iodine Radioisotopes ; therapeutic use ; Liver Neoplasms, Experimental ; pathology ; radiotherapy ; Mice ; Mice, Nude ; Radioimmunotherapy ; methods ; Treatment Outcome ; Xenograft Model Antitumor Assays

OBJECTIVETo construct a human phage display antibody library, which will help to develop new drugs and vaccines against respiratory syncytial virus (RSV) and solve many of the issues that have limited the progression and application of murine monoclonal antibodies (McAbs) in the clinic. This can provide a platform for human antibody preparation and diagnosis, prophylaxis and therapy of RSV infection in children.

METHODSPeripheral blood lymphocytes were isolated from 52 children with RSV infection. cDNA was synthesized from the total RNA of lymphocytes. The light and heavy chain Fd (VH-CH1) fragments of immunoglobulin gene were amplified by RT-PCR. The amplified products were cloned into phagemid vector pComb3x and the clone samples were electrotransformed into competent E.coli XL1-Blue. The transformed cells were then infected with M13K07 helper phage to yield recombinant phage antibody of Fabs. The plasmids extracted from amplified E.coli were digested with restriction endonucleases Sac I, Xba I, Spe I and Xho I to monitor the insertion of the light or heavy chain Fd genes. RSV virions were utilized as antigens to screen Fab antibodies.

RESULTSBy recombination of light and heavy chain genes, an immune Fab phage display antibody library against RSV containing 2.08x10(7) different clones was constructed, in which 70% clones had light chains and heavy chain Fd genes. The capacity of Fab phage antibody gene library was 1.46x10(7) and the titre of the original Fab antibody library was about 1.06x10(12) pfu/mL. The antibody library gained an enrichment in different degrees after the preliminary panning.

CONCLUSIONSUtilizing the technology of phage display, an immune Fab phage display antibody library against RSV was successfully constructed in this study, which laid a valuable experimental foundation for further study and created favorable conditions for preparing human McAbs. This may also contribute to the improvement in the diagnosis, therapy and prophylaxis of RSV infection in children.

Antibodies, Viral ; genetics ; Bacteriophages ; genetics ; Child ; Humans ; Immunoglobulin Fab Fragments ; genetics ; Immunoglobulin Heavy Chains ; genetics ; Immunoglobulin Light Chains ; genetics ; Peptide Library ; Respiratory Syncytial Viruses ; immunology

Several studies have demonstrated the role of 4-1BBL in T cell activation. Furthermore, enhanced 4-1BB/4-1BBL interaction has been shown to amplify T-cell-mediated antitumor immunity in several mouse models. However, when applied in humans, it was difficult to generate sufficient T cells ex vivo and whole cell vaccines to transfer back into patients. To overcome this difficulty, we have focused on producing the human 4-1BBL extracellular domain/anti-CD20 Fab' fusion protein. In this report, PCR and overlap PCR were used to construct the human 4-1BBL extracellular domain/anti-CD20 Fab' expression vector. DNA sequence was analyzed by the Terminus of Dideoxy Nucleotide. The product was purified by affinity chromatography and analyzed by SDS-PAGE and HPLC; its antigen binding activity was examined by rosetting assay. The data of DNA sequence showed that the human 4-1BBL extracellular domain/anti-CD20 Fab' fusion protein was corrected. The fusion protein was recovered in high yield (up to 200 microg/mL) after E-taq purification. The fusion protein was capable of simultaneous binding to stimulated Jurkat cells and Raji cells as shown by cellular rosetting. In conclusion, the human 4-1BBL extracellular domain/anti-CD20 Fab' fusion protein was induced to express in E. coli 16C9. The results of some biological activity experiments indicated that the fusion protein could bind to stimulated Jurkat cells and Raji cells. Furthermore, 4-1BBL-negative tumors can be converted into 4-1BBL-positive tumors by the fusion protein without the need for 4-1BBL gene transfer to the malignant cells.
4-1BB Ligand ; biosynthesis ; genetics ; Antibodies, Bispecific ; immunology ; Antigens, CD20 ; immunology ; Humans ; Immunoglobulin Fab Fragments ; biosynthesis ; genetics ; Immunotherapy ; methods ; Lymphoma, Non-Hodgkin ; therapy ; Recombinant Fusion Proteins ; biosynthesis ; genetics ; immunology