Identification and epitope mapping of anti-p72 single-chain antibody against African swine fever virus based on phage display antibody library

African swine fever virus(ASFV)is a lethal pathogen that causes severe threats to the global swine industry and it has already had catastrophic socio-economic effects.To date,no licensed prophylactic vaccine exists.Limited knowledge exists about the major immunogens of ASFV and the epitope mapping of the key antigens.As such,there is a considerable requirement to understand the functional monoclonal antibodies(mAbs)and the epitope mapping may be of utmost importance in our understanding of immune responses and designing improved vaccines,therapeutics,and diagnostics.In this study,we generated an ASFV antibody phage-display library from ASFV convalescent swine PBMCs,further screened a specific ASFV major capsid protein(p72)single-chain antibody and fused with an IgG Fc fragment(scFv-83-Fc),which is a specific recognition antibody against ASFV Pig/HLJ/2018 strain.Using the scFv-83-Fc mAb,we selected a conserved epitope peptide(221MTGYKH226)of p72 retrieved from a phage-displayed random peptide library.Moreover,flow cytometry and cell uptake experiments demonstrated that the epitope peptide can significantly promote BMDCs maturation in vitro and could be effectively uptaken by DCs,which indicated its potential application in vaccine and diagnostic reagent development.Overall,this study provided a valuable platform for identifying targets for ASFV vaccine development,as well as to facilitate the optimization design of subunit vaccine and diagnostic reagents.

Generation and selection of immunized Fab phage display library against human B cell lymphoma

The approval of using monoclonal antibodies as a targeted therapy in the management of patients with B cell lymphoma has led to new treatment options for this group of patients. Production ofmonoclonal antibodies by the traditional hybridoma technology is costly, and the resulting murine antibodies often have the disadvantage of triggering human anti-mouse antibody （HAMA） response. Therefore recombinant Fab antibodies generated by the phage display technology can be a suitable alternative in managing B cell lymphoma. In this study, we extracted total RNA from spleen cells of BALB/c mice immunized with human B lymphoma cells, and used RT-PCR to amplify cDNAs coding for the κ light chains and Fd fragments of heavy chains. After appropriate restriction digests, these cDNA fragments were successively inserted into the phagemid vector pComb3H-SS to construct an immunized Fab phage display library. The diversity of the constructed library was approximately 1.94× 10^7. Following five rounds of biopanning, soluble Fab antibodies were produced from positive clones identified by ELISA. From eight positive clones, FabC06, FabC21, FabC43 and FabC59 were selected for sequence analysis. At the level of amino acid sequences, the variable heavy domains （VH） and variable light domains （VL） were found to share 88-92% and 89-94% homology with sequences coded by the corresponding murine germline genes respectively. Furthermore, reactivity with membrane proteins of the B cell lymphoma was demonstrated by immunohistochemistry and western blotting. These immunized Fab antibodies may provide a valuable tool for further study of B cell lymphoma and could also contribute to the improvement of disease therapy.

Phage display selection on whole cells yields a small peptide specific for HCV receptor human CD81

The human CD81(hCD81),the most recently proposed receptor of hepatitis C virus(HCV),can especifically bind to HCV envelope glycoprotein 2(E2).In this study,hCD81-expressing murine NIH/3T3 cells were used to select hCD81-binding peptides from a phage displayed nonapeptide library(PVIII9aaCys).Eighteen of the 75clones selected from the library showed specific binding to the hCD81-expressing NIH/3T3 cells by enzyme linked immunosorbent assay(ELISA)and competitive inhibition test.Twelve out of the 18 clones shared the amino acid motif SPQYWTGPA.Sequence comparison of the motif showed no amino acid homology with the native HCV E2.The motif-containing phages could competitively inhibit the ability of HCV E2 binding to native hCD81-expressing MOLT-4 cells,and induce HCV E2 specific immune response in vivo.These results suggest that the selected motif SPQYWTGPA should be a mimotope of HCV E2 to bind to hCD81 molecules.Our findings cast new light on developing HCV receptor antagonists.

An overview on application of phage display technique in immunological studies

Phage display is very strong technique in drug discovery and development. Phage display has many applications in improving the immunological studies. Development of monoclonal antibody, peptides, peptidomimetics and epitope mapping are main application of phage display. Selection of monoclonal antibody or peptides that are displayed on the surface of the phages can be occurred through biopanning process. In biopanning process phage library is incubated with antigen and particular phages can be identified and isolated. Increasing the stringency in the biopanning rounds can be help to select phages with high affinity and specificity. Here, we describe an overview of phage display application with focusing on monoclonal antibody production and epitope mapping.

Human scFv antibody fragments specific for hepatocellular carcinoma selected from a phage display library

AIM:To identify the scFv antibody fragments specific for hepatocellular carcinoma by biopanning from a large human naive scFv phage display library. METHODS: A large human naive scFv phage library was used to search for the specific targets by biopanning with the hepatocellular carcinoma cell line HepG2 for the positive-selecting and the normal liver cell line L02 for the counter-selecting. After three rounds of biopanning, individual scFv phages binding selectively to HepG2 cells were picked out. PCR was carried out for identification of the clones containing scFv gene sequence. The specific scFv phages were selected by ELISA and flow cytometry. DMA sequences of positive clones were analyzed by using Applied Biosystem Automated DNA sequencers 3 730. The expression proteins of the specific scFv antibody fragments in F.coli HB2151 were purified by the affinity chromatography and detected by SDS-PAGE, Western blot and ELISA. The biological effect of the soluble antibody fragments on the HepG2 cells was investigated by observing the cell proliferation. RESULTS: Two different positive clones were obtained and the functional variable sequences were identified. Their DNA sequences of the scFv antibody fragments were submitted to GenBank (accession nos: AY686498 and AY686499). The soluble scFv antibody fragments were successfully expressed in E.coli HB2151. The relative molecular mass of the expression products was about 36 ku, according to its predicted M, value. The two soluble scFv antibody fragments also had specific binding activity and obvious growth inhibition properties to HepG2 cells. CONCLUSION: The phage library biopanning permits identification of specific antibody fragments for hepatocellular carcinoma and affords experiment evidence for its immunotherapy study.

Phage display: development of nanocarriers for targeted drug delivery to the brain

The blood brain barrier represents a formidable obstacle for the transport of most systemati- cally administered neurodiagnostics and neurotherapeutics to the brain. Phage display is a high throughput screening strategy that can be used for the construction of nanomaterial peptide libraries. These libraries can be screened for finding brain targeting peptide ligands. Surface functionalization of a variety of nanocarriers with these brain homing peptides is a sophisticated way to develop nanobiotechnology-based drug delivery platforms that are able to cross the blood brain barrier. These efficient drug delivery systems raise our hopes for the diagnosis and treatment of various brain disorders in the future.

Phage display creates innovative applications to combat hepatitis B virus

Hepatitis B virus (HBV) has killed countless lives in human history. The invention of HBV vaccines in the 20th century has reduced significantly the rate of the viral infection. However, currently there is no effective treatment for chronic HBV carriers. Newly emerging vaccine escape mutants and drug resistant strains have complicated the viral eradication program. The entire world is now facing a new threat of HBV and human immunodeficiency virus co-infection. Could phage display provide solutions to these life-threatening problems? This article reviews critically and comprehensively the innovative and potential applications of phage display in the development of vaccines, therapeutic agents, diagnostic reagents, as well as gene and drug delivery systems to combat HBV. The application of phage display in epitope mapping of HBV antigens is also discussed in detail. Although this review mainly focuses on HBV, the innovative applications of phage display could also be extended to other infectious diseases.

PSMA mimotope isolated from phage displayed peptidelibrary can induce PSMA specific immune response

Prostate-specific membrane antigen (PSMA) is a cellsurface glycoprotein expressed predominantly in prostatesecretory acinar epithelium and prostate cancer cells aswell as in several extraprostatic tissues. Mouse monoclonal antibody 4G5 specific to the extracellular domainof PSMA was used to screen two phage displayed peptide libraries (9aa linear and 9aa cys library). Three 4G5reactive phagotopes were identified. Sequence analysis ofisolated clones demonstrated that the interaction motif'VDPA/SK' has high homology to 719-725aa on PSMA.Immunohistochemical staming of the prostate cancer sam ple with the PSMA-mimic phagotope (mimotope) immunized serum antibodies demonstrate that the mimotopeisolated from the phage displayed peptide libraries can induce PSMA specific immune response in vivo.

Construction of Human ScFv Phage Display Library against Ovarian Tumor

In order to construct a single chain fragment variable （ScFv） phage display library against ovarian tumor, by using RT-PCR, the human heavy chain variable region genes （VH） and light chain variable region genes （VL） were amplified from lymphocytes of ovarian tumor patients and subsequently assembled into ScFv genes by SOE. The resulting ScFv genes were electrotransformed into E. coli TG1 and amplified with the co-infection of helper phage M13KO7 to obtain phage display library. The capacity and titer of the resulting library were detected. The phage antibody library with a capacity of approximately 3 × 10^9 cfu/μg was obtained. After amplification with helper phage, the titer of antibody library reached 5 μ 10^12 cfu/mL. Human ScFv library against ovarian tumor was constructed successfully, which laid a foundation for the screening of ovarian tumor specific ScFv for the radioimmunoimaging diagnosis of ovarian tumor.

Screening and Identification of a Novel Hepatocellular Carcinoma Cell Binding Peptide by Using a Phage Display Library

The purpose of this study was to screen peptides that can specifically bind to human hepatocellular carcinoma （hHCC） cells using phage display of random peptide library in order to develope a peptide-based carrier for the diagnosis or therapy of hHCC. A peptide 12-mer phage display library was employed and 4 rounds of subtractive panning were performed using the hHCC cell line HepG2 as the target. After panning, the phages that specifically bound to and internalized in hHCC cells were selected. The selected phages demonstrated highly specific affinity to HepG2 cells analyzed by ELISA and immunofluorescence analysis. 57.3% of the selected phage clones displayed repeated sequence FLLEPHLMDTSM, and 4 amino acid residues, FLEP were extremely conservative. Based on the sequencing results, a 16-mer peptide （WH-16） was synthesized. The competitive EL1SA showed that the binding of the phage clones displayed sequence FLLEPHLMDTSM to HepG2 cells was efficiently inhibited by WH-16. Our findings indicate that cellular binding of phage is mediated via its displayed peptide and the synthesized 16-mer peptide may have the potential to be a delivery carrier in target diagnosis or therapy for hHCC.

Rapid Selection of Phage Se-scFv with GPX Activity via Combination of Phage Display Antibody Library with Chemical Modification

Glutathione peroxidase（GPX） plays an important role in scavenging reactive oxygen species. A series of catalytic antibodies with GPX activity have been generated by the authors of＇ this study. To obtain humanized catalytic antibodies, the phage-displayed human antibody library was used to select novel antibodies by repetitive screening, Phage antibodies, scFv-B8 and scFv-H6 with the GSH-binding site, were obtained from the library by enzyme-linked immu- nosorbent assay（ELISA） analysis with 4 rounds of scelection against their respective haptens, S-2,4-dinitriphenyl t-butyl ester（GStI-s-DNP-Bu） and S-2,4-dinit,-iphenyl t-hexyl ester（GSH-s-I）NP-He）. Nevertheless, several studies need to be condueted to determine whether scFv-B8 and seFv-tI6 possess GPX activity. 1＇o enhance the speed of the selection, selenocysteine（Sec, the catalytic group of GPX） was incorporated directly into the phages, scFv-B8 and seFv-H6, by chemical mutation to form the phages Se-scFv-B8 and Se-scFv-H6. The GPX activities were found to be 3012 units/μmol and 2102 units/μmol, respectively. To improve the GPX activity of the phage Se-scFv-B8, DNA shuffling was used to construct a secondary library and another positive phage antibody scFv-B9 was screened out by another panning against GSH-s-DNP-Bu. When Sec was incorporated via chemical mutation into the phage antibody scFv-B9, its GPX activity reached 3560 units/μmol, which is 1.17-fold higher than the phage antibody Se-scFv-B8 and almost approached the order of magnitude of native GPX. The rapid selection is the prerequisite for generating humanized Se-seFv with GPX activity.

Screening of TACE Peptide Inhibitors from Phage Display PeptideLibrary

Summary： To obtain the recombinant tumor necrosis factor-α converting enzyme （TACE） ectodomain and use it as a selective molecule for the screening of TACE peptide inhibitors, the cDNA coding catalytic domain （TS00） and full-length ectodomain （T1300） of TACE were amplified by RT-PCR, and the expres.sion plasmids were constructed by inserting T800 and T1300 into plasmid pET-28a and pET-28c respectively. The recombinant TS00 and T1300 were induced by IPTG, and SDS-PAGE and Western blotting analysis results revealed that TS00 and T1300 were highly expressed in the form of inclusion body. After Ni^2＋-NTA resin affinity chromatography, the recombinant proreins were used in the screening of TACE-binding peptides from phage display peptide library respectively. After 4 rounds of biopanning, the positive phage clones were analyzed by ELISA, competitive inhibition assay and DNA sequencing. A common amino acid sequence （TRWLVYFSRPYLVAT） was found and synthesized. The synthetic peptide could inhibit the TNF-α release from LPS-stimulated human peripheral blood mononuclear cells （PBMC） up to 60.3%. FACS analysis revealed that the peptide mediated the accumulation of TNF-α on the cell surface. These results demonstrate that the TACE binding peptide is an effective antagonist of TACE.

Construction of white spot syndrome virus (WSSV) whole genome phage display library

A rebuilt vector pCANTAB 5 EE was obtained by inserting a 34 bp double-stranded oligonucleotide which contained a EcoRV recognition sequence into pCANTAB 5 E. White spot syndrome virus （WSSV） genome DNA was fragmented by sonication to isolate fragments mainly in the range of 0.8 ～2.0 kb, then the fragments were blunt-ended with T4 DNA polymerase and cloned into the EcoRV site of pCANTAB 5 EE. The primary recombinant clone of the library was 3.0 × 10^5.Colony PCR of random selected recombinants showed that the size of the inserts was 0.12 ～ 1.77 kb. After the whole library recombinant phages infected Escherichia coli HB2151 cells, the extracellular and periplasmic extracts were dropped on PVDF membranes to perform dot blot, using polyclonal mouse anti-VP24 serum,anti-WSV026 serum,anti-WSV063 serum,anti-WSV069 serum,anti-WSV112 serum, anti WSV238 serum,anti-WSV303 serum and anti-VP26 serum as the primary antibody, respectively. The results showed that the display library could express the viral proteins.

Screening and Identification of a Targeting Peptide to nGLP-1R from Phage Display Peptide Library

In order to provide the structure information for designing new exendin-4 analogues, a phage display peptide library was screened by targeting the N-terminal extracellular domain of GLP-1R（nGLP-1R）. After four rounds of selection, nine sequences were obtained, four of them have higher affinity for nGLP-1R than the others. We chose two of them named X and Y peptides. Islet β-cell proliferation assay suggested that X and Y peptides didn＇t have any activity to increase islet β-cell proliferation. In other words, X and Y peptides were not agonists to GLP-1R. However, the conservative motifs of X and Y peptides provided us useful information to design new exendin-4 analogues.

SELECTION OF NEW EPITOPES FROM MONOVALENT DISPLAYED PHAGE OCTAPEPTIDE LIBRARY

A library of 2 ×107 random octapeptides was constructed by use of phagemid-based monovalent phage display system. The randomly synthesized degenerated oligodeoxyribonucleotides (oligos ) were fused to the truncated g Ⅲ (p230-p403). Sequence analysis of 11 randomly chosen clones suggested that the degenerated inserts and its deduced amino acid (aa) sequences are randomly distributed. The library was used to select binding peptides to the monoclonal antibody (mAb) 9E10, which recognizes a continuous decapeptide epi- tope of denatured human c-myc protein. After four to five rounds of panning, most of the eluted clones could bind to 9E10. Sequence analysis of the selected positive clones indicated that the binding sequences could fall into two classes, one class (clone 1) shares a consensus motif, ISE x x L, with c-myc decapeptide; and the sequences of the other class are entirely different. The binding of both classes to 9E10 could be specifically inhibited by free c-myc decapeptide. The immunogenicity of the phage peptide was further investigated by construction of multivalent displayed phage peptides and immunization of animals with or without adjuvant. ELISA and competitive ELISA showed that anti-serum from both mice and rabbit immunized with either clone could bind to the original antigen, c-myc decapeptide. These results denote that in spite of the dissimilarity of the selected peptides with c-myc decapeptide, they are capable of inducing similar immune respones in vivo, thus actually mimicking the antigen epitope.

Screening of scFvs against cTnI from Phage Display Antibody Library and Their Expression in E.coli Rosetta

The single chain variable fragments of antibodies(scFvs) against cTnI were screened from the phage display antibody library by using cTnI as the target antigen. After four rounds of panning, four clones(H2, G5, A9, B9) from the phage display antibody library were verified to show higher binding affinity for cTnI by ELISA and to contain the variable region genes of the light and heavy chains of scFvs by sequencing. The variable region genes of scFvs H2 and G5 were successfully amplified by polymerase chain reactions(PCR) and cloned into expression vector pPELB and expressed as a soluble protein in E.coli Rosetta, whose expression yield was about 2% of total proteins. The expressed proteins were purified by nickel(Ni) affinity chromatography and a single band is shown in the position of 28 kDa on SDS-PAGE. The western blot analysis result verifies that the expressed scFv proteins are capable of binding with monoclonal antibodies against hexa-histidine, indicating that they are hexa-histidin-tagged aim proteins. The immunoassay demonstrates that the expressed scFv proteins are able to specifically react with cTnI molecules. The association constant(K_A) values range from 1.2×10 4 to 1.7 ×10 5 L/mol that are correspondent to the affinities of polyclonal antibodies against cTnI from rabbits. These antibodies can be valuable reagents for the immunoassay of cTnI.

Application of phage display technology in targeted therapy of breast cancer

Phage display is a technology of gene expression and screening, it is widely used in the fields of defining antigen epitopes, signal transduction, genetic treatment, parasites research and tumor targeted therapy. Breast cancer is the most common cancer in women, we can obtain peptides specially associated with breast cancer by using phage display technology, and this method has great potential in early diagnosis of breast cancer and development new targeted drugs.

Identification and Characterization of Peptides Binding AgEG1 from a Phage Display Library

Endoglucanases are the main cellulolytic enzymes digestion as well as its good kinetic properties make it an attractive of Anoplophora glabripennis. Their high activities in cellulose target for development of cellulase inhibitors. In this study, random pepfide phage display technology was employed to identify peptides that bound the AgEG1, a member of endoglucanase isozymes. Phage clones with peptide LPPNPTK and XPP （X is residue T, L, A or H） motif frequently occurred in the selected phage population and showed a higher phage recovery than other clones. Peptide LPPNPTK was chemically synthesized and characterized tor its binding activities to AgEG1. The synthetic peptide exhibited high specificity for AgEG1. The peptide LPPNPTK has the potential to be developed into inhibitors of the endoglucanase of A. glabripennis.

Construction of a Multipurpose M13KE Phage Display System

In this study, a multipurpose M13KE phage display vector was constructed from wild-type M13KE phage for long peptide or protein display libraries without helper phage to expand the scope of targeted high-throughput screening. Based on the relationship between the structure and function of minor coat protein of wild-type MI3KE （wt-plII）, a truncated gene III （tglll） encoding minor coat protein from M13KE phage was cloned. A fusion gene fragment harboring a hw/tac promoter, signal peptide and C-terminal region sequence of gill was assembled with SOEing-PCR （splice-overlapping-extension polymerase chain reaction） method and inserted into M13KE vector. SDS-PAGE and Western blot analysis with anti-M13 pIII moneclonal antibody were employed to detect the expression of re- combinant protein, c-Myc and HA tag sequences were fused into the recombinant protein. The results showed that tglll was inserted into an unessential region of M13KE. According to the results of SDS-PAGE and Western blot with anti-M13 pIII antibody, pIII was expressed by wt-gIII and tgIII, glII harboring two tags ex- pressed both c-Myc and HA peptides using SDS-PAGE and Western blot with the corresponding monoclonal antibodies. In this study, a multipurpose M13KE phage display system was successfully constructed, which could express both short and long peptide libraries without helper phage. In future, the obtained M13KE phage display system may be used for targeted high-throughput screening of long peptide libraries without helper phage.

Construction of Large Human Single-chain Antibody Phage Display Library

A large human naive single chain antibody (scFv) library is constructed from 60 healthy donors via phage display technique. During the period, some methods are employed to optimize the diversity, such as multi donors, different annealing temperature, half nest PCR, and assembly by two way fusion PCR. In this study, 78 electroporations resulted in 1010 library, diversity of which is assayed by enzyme fingerprint. The efficiency and diversity are all better than other researches.