OBJECTIVETo isolate single chain antibody fragments (scFv) against cell surface molecules by pathfinder selection from an anti-KG1a cell scFv phage library.

METHODSThe anti-KG1a scFv library was enriched by KGla cell panning for three rounds, or unenriched, then processed for pathfinder selection respectively using anti-CD34 monoclonal antibody as pathfinder molecule. ScFv phage clones were randomly picked and identified by binding KG1a cells using immunofluorescein and flow cytometry. The KG1a+ clones were further identified by KG1a, HL60, U937, and CEM cell lines and ELISA. Their antigenic molecules on cell surface were digested by chymopapain and analyzed by flow cytometry. DNAs from ten positive clones were sequenced. The scFv clones with different primary structure were used to analyze the molecular weight of their antigens by Western blot.

RESULTSOne hundred and two KG1a+ scFv phage clones were isolated from 144 enriched and 96 unenriched scFv phage library respectively, among which 47 bound KG1a, HL60, U937, and CEM cells, 55 bound KG1a cells exclusively. None of 28 KG1a+, HL60-, U937-, and CEM- scFv clones bound to the CD34 antigen, as confirmed by ELISA, although most of their antigens were sensitive to chymopapain digestion. DNA sequences from ten positive clones showed that they were from four different clones. They bound antigens with different molecular weight.

CONCLUSIONSOne hundred and two scFv phage clones specific for hematopoietic stem and progenitor cells have been isolated from an anti-KG1a cell scFv phage library. The pathfinder selection has showed advantages to improve the screening efficacy of scFv phage clones against antigens, which present at very low densities on the cell surface.

Antibodies, Anti-Idiotypic ; immunology ; Antibodies, Monoclonal ; genetics ; Antibody Specificity ; Bacteriophages ; genetics ; Cloning, Molecular ; Hematopoietic Stem Cells ; immunology ; Humans ; Immunoglobulin Fc Fragments ; biosynthesis ; genetics ; immunology ; Immunoglobulin Fragments ; genetics ; immunology ; Immunoglobulin Variable Region ; genetics ; immunology ; Peptide Library ; Single-Chain Antibodies

Single chain antibody fragment (scFv) is a small molecule composed of a variable region of heavy chain (VH) and a variable region of light chain (VL) of an antibody, and these two chains are connected by a flexible short peptide. scFv is the smallest functional fragment with complete antigen-binding activity, which contains both the antibody-recognizing site and the antigen-binding site. Compared with other antibodies, scFv has the advantages of small molecular weight, strong penetration, low immunogenicity, and easy expression. Currently, the most commonly used display systems for scFv mainly include the phage display system, ribosome display system, mRNA display system, yeast cell surface display system and mammalian cell display system. In recent years, with the development of scFv in the field of medicine, biology, and food safety, they have also attracted much attention in the sectors of biosynthesis and applied research. This review summarizes the advances of scFv display systems in recent years in order to facilitate scFv screening and application.
Animals ; Immunoglobulin Variable Region/genetics* ; Immunoglobulin Fragments/metabolism* ; Single-Chain Antibodies/metabolism* ; Peptide Library ; Mammals/genetics*

OBJECTIVETo screen and characterize the variable region gene about prostate specific membrane antigen (PSMA) of the Chinese Fab fragment, and to establish a new approach to researches on PSMA and prostate gene therapy.

METHODSWe used purified PSMA protein as antigen, stuck it on the ELISA plate and scanned the phage Fab fragment antibody library by phage display technology. After five cycles of "absorbing-elution-amplification", we got the Fab fragment phage antibody of PSMA with high antigen binding ability and specificity, and tested it with immunodetection and sequencing.

RESULTSThe sequence of Fd fragment was 696 base pairs encoding 232 amino-acid residues, with 98% homological similarity to the human immunoglobulin gamma chain, while the light chain was constructed by 630 base pairs encoding 210 amino-acid residues, with 93% homological similarity to kappa chain.

CONCLUSIONUsing phage display technology, we obtained the gene sequence of Fab antibody fragment specific to PSMA, and the antibody gene has the classic structural features of immunoglobulin light chain and heavy chain. The coding output of the antibody gene has the specificity and immunological competence to PSMA.

Cloning, Molecular ; Enzyme-Linked Immunosorbent Assay ; Genetic Code ; Humans ; Immunoglobulin Fab Fragments ; genetics ; Immunoglobulin Variable Region ; genetics ; Male ; Peptide Library ; Prostate-Specific Antigen ; immunology

To rapidly select potent anti-VSTM1-v2 scFv (single-chain antibody fragment) by construction and screening of a humanized scFv library in which a murine VH-CDR3 library was grafted onto a human scFv framework. A murine VH-CDR3 library was amplified from anti-VSTM1-v2 murine cDNA and grafted on human scFv (VH3-VK1) framework. Anti-VSTM1-v2 scFv templates were selected and enriched through ribosome display, TA-cloned into expression vector, and transformed into BL21 (DE3) for soluble expression of target scFv. A total of 1000 clones were randomly picked. Positive ones were first identified using colony PCR, indirect ELISA, Western blotting and then verified with sequencing and dose response ELISA. At last an anti-VSTM1-v2 humanized scFv with good binding affinity (EC50 = 21.35 nmol x L(-1)) was selected from the humanized library of 10(12) members generated in this study. This scFv antibody might have potential applications. This study provides a new approach for rapid screening of humanized antibodies.
Animals ; Complementarity Determining Regions ; genetics ; immunology ; Cytokines ; immunology ; Humans ; Immunoglobulin Fragments ; genetics ; immunology ; Immunoglobulin Heavy Chains ; genetics ; immunology ; Mice ; Peptide Library ; Protein Binding ; Receptors, Immunologic ; immunology ; Single-Chain Antibodies ; genetics ; immunology ; isolation & purification

AIMTo construct recombinant retroviruses expressing anti-CD20 scFv/CD80/CD28/zeta gene and detect its expression in Jurkat cells.

METHODCD28-zetacDNA were amplified from plasmids pBULLET and inserted into pLNCX vector that contained anti-CD20 scFv/CD80 gene. The recombinant plasmids were transfected into PA 317 cells. Retroviruses were harvested from culture medium of PA 317 cells. Then NIH 3T3 were transfected with retroviruses. Objective gene expression was determined by PCR and FACS. Jurkat cells were transfected with high titer of retroviruses and resistant clones were obtained by G418 selection. Objective mRNA was determined by RT- PCR.

RESULTSThe recombinant eukaryotic vector was constructed successfully by PCR and enzyme digestion analysis and objective gene was amplified from NIH 3T3 cells transfected with retroviruses by PCR; FACS showed that objective protein could be expressed in NIH 3T3 cells. Objective gene was amplified from Jurkat cells transfected with retroviruses by RT-PCR.

CONCLUSIONRecombinant retrovirus expressing anti-CD20 scFv/CD80/CD28/zeta gene was successfully constructed and objective protein could be expressed in Jurkat cells.

Antigens, CD20 ; genetics ; metabolism ; B7-1 Antigen ; genetics ; metabolism ; CD28 Antigens ; genetics ; metabolism ; Genetic Vectors ; Humans ; Immunoglobulin Fab Fragments ; genetics ; metabolism ; Immunoglobulin Variable Region ; genetics ; metabolism ; Jurkat Cells ; Recombinant Fusion Proteins ; genetics ; metabolism ; Retroviridae ; genetics ; T-Lymphocytes ; metabolism ; Transfection

OBJECTIVETo screen anti-c-Met Fab from a phage antibody library and identify its binding activity.

METHODSThe expression of c-Met of HCC lines was identified by Western blot and immunofluorescence. Antibodies against c-Met were screened with immobilized antigen. After five rounds of panning, 30 randomly selected clones were identified by phage ELISA to select specific clones with high affinity. The positive clones were selected for Fab soluble expression in TOP10F and the binding activities were analysed in HCC lines.

RESULTSc-Met expressed in HCC membrane was confirmed by Western blot and immunofluorescence. A Fab fragment named AM2-26 with fine activity to c-Met was selected. AM2-26 binding specificity was confirmed by IP, FACS and immunofluorescence.

CONCLUSIONThe anti-c-Met Fab binding to c-Met in HCC provides a promising candidate for the biotherapy of hepatoma.

Antibodies ; immunology ; isolation & purification ; Cell Line, Tumor ; Cloning, Molecular ; Gene Library ; Humans ; Immunoglobulin Fab Fragments ; immunology ; Immunoglobulin Variable Region ; immunology ; Peptide Library ; Proto-Oncogene Proteins c-met ; immunology ; Recombinant Fusion Proteins ; immunology

OBJECTIVETo investigate the efficacy of anti-idiotype antibody 3F6 and its single-chain variable fragment (3F6 ScFv) to induce humoral and cellular immune responses against small-cell-lung cancer (SCLC).

METHODS3F6 and 3F6 ScFv (Ab2) were used to immunize BALB/c mice. The reaction of antibodies (Ab3) with specific antigen on NCI-H128 cells was tested by ELISA and Western blot, and the antibody binding inhibition assays were performed by competitive Western blot. Cellular immunity against SCLC induced by Ab2 was detected by a delayed-type hypersensitivity response and mouse lymphocyte proliferation assay.

RESULTSThe sera immunized with Ab2 showed significant reaction (P < 0.001, as compared to control sera) with SCLC-specific antigen on NCI-H128 cells and specifically competed the binding of 2F7 (Ab1) to the specific antigen. DTH responses challenged with NCI-H128 cells were significantly (P < 0.001) stronger in mice immunized with Ab2 as compared to mice immunized with normal mouse IgG. T cell proliferation was significantly higher in Ab2-immunized mice (P < 0.05) than in control mice.

CONCLUSIONThe two kinds of anti-idiotypic antibodies successfully mimic the SCLC-specific antigen on NCI-H128 cell and induce strong humoral and cellular immune responses to SCLC-specific antigen in syngeneic mice. They may become novel vaccines against human small-cell-lung cancer and worthy of further investigation.

Animals ; Antibodies, Anti-Idiotypic ; immunology ; Antibodies, Neoplasm ; immunology ; Antigens, Neoplasm ; immunology ; Cancer Vaccines ; immunology ; Carcinoma, Small Cell ; immunology ; Cytotoxicity, Immunologic ; drug effects ; Immunoglobulin Fab Fragments ; immunology ; Immunoglobulin Fragments ; immunology ; Immunoglobulin Variable Region ; immunology ; Lung Neoplasms ; immunology ; Mice ; Mice, Inbred BALB C

OBJECTIVESequences analysis of Ig variable regions from the peripheral blood mononuclear cells (PBMC) of patients with chronic B lymphocytic leukemia.

METHODSTotal RNA was isolated from PBMC of patients with chronic B lymphocytic leukemia, oligo-dT-primed cDNA was synthesized from RNA. The cDNA was amplified by Taq DNA polymerase with a set of specific 5' primers corresponding to Ig FR1 and 3' primers corresponding to CH1 (C micro /C) or CL (Ckappa/Clambda), the PCR products of variable regions of Ig heavy (IgH) and light (IgL) chains were sequenced by ABI PRISM Dye terminator cycle sequencing ready reaction kit and ABI PRISM 310 Genetic Analyzer. The gene homology of variable regions of IgH and IgL chains was compared by using DNA tools 5.1 system and "the international immunogenetics database".

RESULTSFour light chains and 3 heavy chains were amplified from 4 and 3 patients respectively. Homology analysis of the sequences of 4 light chains and 3 heavy chains were performed by DNA tools system. The sequences of light chains are high homologous. And the sequences of heavy chains are quite different. The homologous analysis of the sequences of variable region by using "the international immunogenetics database" showed that the sequences were higher homologous to idiotype gene of some B lymphocytic leukemia. Four VL genes belong to human Ig Vkappa subgroup I, 2 of 3 VH genes belong to VH3 family and 1 belongs to VH5 family.

CONCLUSIONIg genes have idiotype and same disease may have same idiotype.

Base Sequence ; Cloning, Molecular ; DNA, Complementary ; chemistry ; Gene Rearrangement ; Genes, Immunoglobulin ; Humans ; Immunoglobulin Fab Fragments ; genetics ; Immunoglobulin Heavy Chains ; genetics ; Immunoglobulin Light Chains ; genetics ; Immunoglobulin Variable Region ; genetics ; Leukemia, Lymphocytic, Chronic, B-Cell ; genetics ; immunology ; Molecular Sequence Data ; Polymerase Chain Reaction

To evaluate the efficiency of three in vitro refolding methods for a humanized single-chain Fv antibody against human CTLA4(CD152) expressed in E. coli, the denatured and purified inclusion bodies (IBS) were refolded by dilution, dialysis and in situ refolding via Immobilized Metal-Ion-Affinity Chromatography (IMAC), respectively. The concentration of refolded scFvs was examined by Bradford method. And the antigen binding activity of the refolded scFvs was analyzed by indirect cell-ELISA. The highest and lowest refolding yields could be obtained by dialysis and in situ refolding via IMAC, respectively. The binding activity of the refolded scFv by dialysis was 1.95-fold higher than that by dilution, 4.13-fold higher than that by in situ refolding via IMAC (GSH/GSSH excluded) and 3.63-fold higher than that by in situ refolding via IMAC (GSH/GSSH included), respectively. In conclusion, a high refolding yield and binding activity of scFv with natural conformation could be obtained by dialysis in the condition of 0. 15 mol/L sodium chloride, 50 mmol/L Tirs-HCl, pH 8. 0 buffer containing 3 mmol/L reduced glutathione and 1 mmol/L oxidized glutathione for 48 hours at 4 degrees C.
Antigens, CD ; biosynthesis ; genetics ; immunology ; Antigens, Differentiation ; biosynthesis ; genetics ; immunology ; CTLA-4 Antigen ; Cloning, Molecular ; Escherichia coli ; genetics ; metabolism ; Humans ; Immunoglobulin Fc Fragments ; biosynthesis ; genetics ; immunology ; Immunoglobulin Variable Region ; biosynthesis ; genetics ; immunology ; Recombinant Fusion Proteins ; biosynthesis ; genetics ; immunology

We studied the aggregation of a recombinant engineering antibody (chA21). Anti-ErbB2 antibody chA21 was produced by fusing single-chain Fv (scFv) with human IgG1 Fc fragment, and it was proved to be a drug candidate for cancer therapy. We characterized the aggregation of chA21 by high performance sized-exclusive chromatography (HPSEC), dynamic light scattering (DLS), SDS-PAGE, indirect ELISA assay, and compared the influence of temperature and additive on the level of aggregation and binding activity. Conformation changes of different levels of aggregation were also analyzed via circular dichroism (CD). Finally, we analyzed which part of chA21 was involved in aggregation by cleaving it into scFv and Fc fragments. The results showed that chA21 could form aggregates in the storage solution. The aggregates interacted through non-covalent bonds and remained binding activity. Temperature and additive could slightly affect the level of aggregation and binding activity, while the conformations of chA21 were stable. Aggregation propensity of scFv fragment was almost same as chA21, indicating that scFv may be the major part to form the aggregates. The research on aggregation may be helpful to develop a suitable formulation for chA21 clinical application as well as provide direction for future antibody design and reconstruction.
Antibodies ; chemistry ; metabolism ; Humans ; Immunoglobulin Fc Fragments ; chemistry ; metabolism ; Immunoglobulin Variable Region ; chemistry ; metabolism ; Protein Conformation ; Protein Engineering ; methods ; Receptor Aggregation ; immunology ; Receptor, ErbB-2 ; chemistry ; immunology ; Recombinant Proteins ; biosynthesis ; chemistry ; genetics ; immunology