Human recombinant single-chain antibody fragments, specific for the hypervariable region 1 of hepatitis C virus, from immune phage-display libraries

Reduction of enterotoxin induced fluid accumulation in ileal loops of neonatal calves with anti-F5 fimbriae recombinant antibody

Neonatal calf colibacillosis caused by enterotoxigenic Escherichia coli (ETEC) is an economically significant problem in most parts of the world. The most common ETEC found in calves express the F5 (K99) fimbriae, which are necessary for the attachment of the bacteria to the ganglioside receptors on enterocytes. It is known that prevention of ETEC F5(+) adhesion to its ganglioside receptors with specific antibodies protects calves from colibacillosis. Previously we have described the development and characterization of a mouse recombinant antibody fragment (moRAb) that prevents F5 fimbrial protein induced agglutination of horse red blood cells (HRBC), which exhibit the same gangloside receptor for F5 fimbriae. Here we demonstrate that this recombinant antibody fragment inhibits in vitro the attachment of ETEC F5(+) bacteria to HRBC as well as isolated calf enterocytes, and in vivo it decreases fluid accumulation in intestinal loops of calves. Thus, correct oral administration of this anti-F5 moRAb may serve as an immunoprophylactic for cost effective control of colibacillosis in calves.

Chimeric monoclonal antibodies to hypervariable region 1 of hepatitis C virus

Two chimeric monoclonal antibodies (cAbs), 2P24 and 15H4, to hypervariable region 1 (HVR1) of hepatitis C virus (HCV) were constructed by grafting the variable regions of murine monoclonal antibodies (mAbs) 2P24 and 15H4 to a human IgG1 kappa constant region. Two cAb-producing cell lines were adapted to serum-free media. Both cAb 2P24 and cAb 15H4 cell lines produced 3-5 microg antibodies ml(-1) after 3-5 days culture. cAbs retained binding characteristics similar to those observed in the original mAbs. There was no clear difference in affinity between binding of cAbs and mAbs to seven HVR1 peptides. Mixtures of biotinylated cAbs or mAbs reacted with 32 (86 %) and 31 (84 %) of 37 HVR1 peptides, respectively, but not with non-HVR1 control peptides. HCV from 16 out of 18 (89 %) random HCV-containing plasmas was captured by the mixture of biotinylated cAbs. The capture from IgG-depleted plasmas suggested that cAbs captured mainly free rather than complexed HCV, irrespective of genotype. A mixture of the two cAbs inhibited HCV binding to Molt-4 cells in a dose-dependent manner. These cAbs may be useful for prevention of nosocomial HCV infection and passive immunization to prevent HCV reinfection after liver transplantation.

Piezoelectric biosensors for real-time monitoring of hybridization and detection of hepatitis C virus

The piezoelectric quartz crystal resonators modified with oligonucleotide probes were used for detection of hepatitis C virus (HCV) in serum. The gold electrodes on either rough or smooth surface crystals were modified with a self-assembled monolayer of cystamine. After activation with glutaraldehyde, either avidin or streptavidin were immobilized and used for attachment of biotinylated DNA probes (four different sequences). Piezoelectric biosensors were used in a flow-through setup for direct monitoring of DNA resulting from the reverse transcriptase-linked polymerase chain reaction (RT-PCR) amplification of the original viral RNA. The samples of patients with hepatitis C were analyzed and the results were compared with the standard RT-PCR procedure (Amplicor test kit of Roche, microwell format with spectrophotometric evaluation). The piezoelectric hybridization assay was completed in 10 min and the same sensing surface was suitable for repeated use.

Broadly cross-reactive mimotope of hypervariable region 1 of hepatitis C virus derived from DNA shuffling and screened by phage display library

The hypervariable region 1 (HVR1) is the target of neutralizing antibodies but with isolate specificity. The aim of this study was to obtain immunogenic mimotopes of HVR1, which can react broadly with different HVR1 antibodies and could be one of the candidate immunogens in an effective vaccine against HCV. Thirty-one HVR1 cDNA fragments were digested by DNase I into a pool of random fragments and reassembled by repeated cycles of annealing in the presence of DNA polymerase to their original size. The shuffled HVR1 was then inserted into the gene III phagemid vector pCANTAB-5E and displayed on the surface of the phage. Eight individual phages were selected after four rounds of biopanning against anti-HVR1. ELISA was carried out on immobilized purified phages, respectively, to detect their reactivity with a panel of sera. DNA sequences of the inserts were analyzed and compared with the consensus sequences defined by Puntoriero et al. [(1998) EMBO J 17:3521-3533]. The reactivity of the eight selected clones to the 30 sera were from 53.3 to 80%. Among these, phage 13 (ETYVSGGSAARNAYGLTSLFTVGPAQK, aa 384-410) reacted most broadly. None of the selected sequences encoded for peptides corresponded to known HVR1 from original viral isolates. The two high reactive phages had the similar amino acid sequences with the consensus, which might play a particular role in determining the frequency of reactivity. In conclusion, this study has used effectively DNA shuffling combined with phage display technology to identify broadly cross-reactive mimotopes recognized by human polyclonal antibodies. Mimotope 13 and 23 appeared to be most reactive immunologically and could be candidate immunogens. Efforts are now underway to identify their neutralizing antibodies by immunization of animals.

Construction and characterization of an intracellular single-chain human antibody to hepatitis C virus non-structural 3 protein

BACKGROUND/AIMS

We developed a single-chain antibody fragment (scFv) to the non-structural 3 protein (NS3) of hepatitis C virus (HCV) and tested its ability to interfere with the HCV replication cycle in infected hepatocytes.

METHODS

The variable regions of the human monoclonal antibody CM3.B6 that recognizes a conformational epitope within the helicase domain of NS3 were introduced into adenoviral vectors for expression in mammalian hepatocytes. Expression and binding properties of the scFv were analyzed by immunological assays. Effects of intracellular expression of the scFv on HCV replication were assessed in primary hepatocytes isolated from explanted livers of patients with chronic HCV infection by reverse transcription-polymerase chain reaction.

RESULTS

Transduction of HepG2 cells by the recombinant adenoviruses resulted in stable, efficient expression of scFv in the cytoplasm that was non-toxic to the cells. The scFv specifically bound to its cognate antigen. Significantly, intracellular expression of scFv resulted in a decrease in HCV genomic RNA in HCV infected hepatocytes.

CONCLUSIONS

These results indicate that specific binding of a scFv to NS3 may inhibit one or more functions of this essential viral protein thus interfering with the HCV replication cycle.

Expression and bioactivity identification of soluble MG7 scFv

AIM

To examine the molecular mass and identify the bioactivity of MG7 scFv for its application as a targeting mediator in gene therapy of gastric cancer.

METHODS

Two strongly positive recombinant phage clones screened from MG7 recombinant phage antibody library were separately transfected into E.coli TG1. Plasmid was isolated from the transfected E.coli TG1 and digested by EcoR I and Hind III to examine the length of exogenous scFv gene. Then, the positive recombinant phage clones were individually transfected into E.coli HB2151. The transfectant was cultured and induced by IPTG. Perplasmic extracts was prepared from the induced transfectant by osmotic shock. ELISA was used to examine the antigen-binding affinity of the soluble MG7 scFv. Immunodotting assay was adopted to evaluate the yield of soluble MG7 scFv produced by transfected E.coli HB2151. Western blot was used to examine the molecular mass of MG7 scFv. Finally, the nucleotide sequence of MG7 scFv was examined by DNA sequencing.

RESULTS

Two positive recombinant phage clones were found to contain the exogenous scFv gene. ELISA showed that MG7 scFv had strong antigen-binding affinity. Immuodotting assay showed that transfected E.coli HB2151 could successfully produce the soluble MG7 scFv with high yield via induction by IPTG. The molecular mass of MG7 scFv was 30 kDa by western blot. DNA sequencing demonstrated that the VH and VL genes of MG7 scFv were 363 bp and 321 bp,respectively.

CONCLUSION

We have successfully developed the soluble MG7 scFv which possessed strong antigen-binding affinity.

Production and characterization of monoclonal antibodies specific for a conserved epitope within hepatitis C virus hypervariable region 1

Frequent mutations in hypervariable region 1 (HVR1) of the main envelope protein of hepatitis C virus (HCV) is a major mechanism of persistence by escaping the host immune recognition. HVR1 contains an epitope eliciting neutralizing antibodies. This study was aimed to prepare broadly cross-reacting, high-affinity, monoclonal antibodies (MAb) to the HVR1 C terminus of HCV with potential therapeutic neutralizing capacity. A conserved amino residue group of glycine (G) at position 23 and glutamic acid (Q) at position 26 in HVR1 was confirmed as a key epitope against which two MAbs were selected and characterized. MAbs 2P24 and 15H4 were immunoglobulin G1 kappa chain [IgG1(kappa)], cross-reacted with 32 and 30 of 39 random C-terminal HVR1 peptides, respectively, and did not react with other HCV peptides. The V(H) of 2P24 and 15H4 heavy chains originated from Igh germ line v gene family 1 and 8, respectively. In contrast, the V(L) kappa sequences were highly homologous. The affinity (K(d)) of 2P24 and 15H4 (10(-9) or 10(-8) M with two immunizing peptides and 10(-8) M with two nonimmunizing HVR1 peptides) paralleled the reactivity obtained with peptide enzyme immunoassay. MAbs 2P24 and 15H4 captured 25 of 31 (81%) HCV in unselected patients' plasmas. These antibodies also blocked HCV binding to Molt-4 cells in a dose-dependent fashion. The data presented suggest that broadly cross-reactive MAbs to a conserved epitope within HCV HVR1 can be produced. Clinical application for passive immunization in HCV-related chronic liver disease and after liver transplantation is considered.

Preparation of single chain variable fragment of MG7 mAb by phage display technology

AIM: To develop the single chain variable fragment of MG₇ murine anti-human gastric cancer monoclonal antibody using the phage display technology for obtaining a tumor-targeting mediator.

METHODS: mRNA was isolated from MG₇ producing murine hybridoma cell line and converted into cDNA. The variable fragments of heavy and light chain were amplified separately and assembled into ScFv with a specially constructed DNA linker by PCR. The ScFvs DNA was ligated into the phagmid vector pCANTAB5E and the ligated sample was transformed into competent E. Coli TG1. The transformed cells were infected with M13K07 helper phage to form MG₇ recombinant phage antibody library. The volume and recombinant rate of the library were evaluated by means of bacterial colony count and restriction analysis. After two rounds of panning with gastric cancer cell line KATOIII of highly expressing MG₇-binding antigen, the phage clones displaying ScFv of the antibody were selected by ELISA from the enriched phage clones. The antigen binding affinity of the positive clone was detected by competition ELISA. HB2151 E.coli was transfected with the positive phage clone demonstrated by competition ELISA for production of a soluble form of the MG₇ ScFv. ELISA assay was used to detect the antigen-binding affinity of the soluble MG₇ ScFv. Finally, the relative molecular mass of soluble MG₇ ScFv was measured by SDS-PAGE.

RESULTS: The V-H, V-L and ScFv DNAs were about 340 bp, 320 bp and 750 bp, respectively. The volume of the library was up to 2 × 10⁶ and 8 of 11 random clones were recombinants. Two phage clones could strongly compete with the original MG₇ antibody for binding to the antigen expressed on KATOIII cells. Within 2 strong positive phage clones, the soluble MG₇ ScFv from one clone was found to have the binding activity with KATOIII cells. SDS-PAGE showed that the relative molecular weight of soluble MG₇ ScFv was 32.

CONCLUSION: The MG₇ ScFv was successfully produced by phage antibody technology, which may be useful for broadening the scope of application of the antibody.

Pharmacokinetics study of a novel chimeric single-chain variable fragment antibody against western equine encephalitis virus

A novel recombinant single-chain fragment variable (scFv) antibody against western equine encephalitis (WEE) virus has been previously constructed and partially characterized. The RS10B5huFc antibody was made by fusing an anti-WEE scFv to a human heavy-chain IgG1 constant region. The RS10B5huFc antibody was functional in binding to WEE virus in enzyme-linked immunosorbent assays (ELISAs), and the Fc domain of the antibody was capable of effector functions, such as binding to protein G and human complement. In this study, the RS10B5huFc antibody was further characterized by BIAcore analyses and was found to possess a binding affinity to a WEE virus epitope (K[D] = 9.14 x 10(-6) M), 4.5-fold lower than its parental mouse monoclonal antibody (MAb) 10B5 E7E2 (K[D] = 2 x 10(-6) M). No cross-reactivity was found between the RS10B5huFc antibody and three other alphaviruses (Sindbis virus [SIN], Venezuelan equine encephalitis [VEE] virus, and eastern equine encephalitis [EEE] virus). Pharmacokinetics studies showed that the RS10B5huFc antibody (free and encapsulated) was found to be retained in the lungs of mice for greater than 48 h when administered intranasally. In contrast, when administered intramuscularly to mice, the RS10B5huFc antibody was not detected in the lungs and only found in the liver and kidneys.

Identification of a human epitope in hepatitis C virus (HCV) core protein using a molecularly cloned antibody repertoire from a non-symptomatic, anti-HCV-positive patient

Healthy carriers of hepatitis C virus (HCV) infection exhibit a specific antibody response against all HCV antigens, which could play a role in disease control. Generation of panels of human antibodies may permit a thorough characterization of this response and further identify particular antibodies with potential clinical value. To this effect, we have established a human phage-display antibody library from a patient exhibiting a high antibody response against HCV antigens and no clinical symptoms of disease. This library was screened against a recombinant core antigen [amino acids (aa) 1-119] produced in E. coli. Two recombinant Fab-carrying phages (rFabCs) were isolated and characterized. Both rFabC3 and rFabC14 recognize aa 1-48 on core antigen, but rFabC14 is competed out by a synthetic peptide, C(2-20) (aa 1-20), at much lower concentrations than rFabC3. In order to identify more precisely the recognition sites of these antibodies, we produced soluble forms of the rFabs (sFabs), and used them to pan a random phage-display peptide library. A single peptide sequence, QLITKPL, was identified with sFabC3, while two equally represented sequences, HAFPHLH and SAPSSKN, were isolated using sFabC14. The QLITKPL sequence was partially localized between aa 8 and 14 of core protein, but no clear homology was found for the two sFabC14 peptides. However, we confirmed the specificity of these peptides by competition experiments with sFabC14.