Isolation of Goose-origin scFv Antibodies Against Goose Parvovirus from Bacterial Display Antibody Libraries

Goose parvovirus(GPV)can cause a highly contagious and fatal gosling plague(GP)disease in goslings and muscoy ducklings.Here,three goose-origin neutralizing single chain variable fragment(scFv)antibodies against GPV SYG-61 were isolated.The genes of scFv antibodies were derived from goslings immunized with GPV SYG-61,and scFvs were subcloned into a pBSD vector for the construction of pBSD-scFv libraries.The pBSD-scFv libraries were screened following three rounds using VP2(protective antigen of GPV)as the bait by flow cytometry(FCM).After screening,the 15 clones with high mean fluorescence intensity(MFI)were isolated and sequenced.These 15 scFvs were expressed by pET-28a(+)in E.coli.The specificity and affinity of the 15 purified scFvs were successfully confirmed by ELISA.In the preliminary neutralization experiment on primary goose embryo fibroblast(GEF)in vitro,three of the 15 purified scFvs(named scFv-10,scFv-11 and scFv-50)showed significant neutralizing capacities.The study generated the first goose-origin neutralizing scFv against GPV and laid the foundation for the appearance of full-length goose-origin neutralizing monoclonal antibody against GPV.

Disulfide-stabilized single-chain antibody-targeted superantigen: Construction of a prokaryotic expression system and its functional analysis

AIM: To construct the expression vector of B3 (scdsFv)-SEA (D227A) and to identify its binding and cytotoxic ability to B3 antigen positive carcinoma cell lines.METHODS: This fusion protein was produced by a bacterial expression system in this study. It was expressed mainly in the inclusion body. The gene product was solubilized by guanidine hydrochloride, refolded by conventional dilution method, and purified using SP-sepharose cation chromatography.RESULTS: The expression vector B3 (scdsFv)-SEA-PETwas constructed, the expression product existed mainly in the inclusion body, the refolding product retained the binding ability of the single-chain antibody and had cytotoxic effect on HT-29 colon carcinoma cells. The stability assay showed that the resulting protein was stable at 37 ℃.CONCLUSION: This genetically engineered B3 (scdsFv)-SEA fusion protein has bifunction of tumor targeting and tumor cell killing and shows its promises as an effective reagent for tumor-targeted immunotherapy.

Screening and evaluation of human single-chain fragment variable antibody against hepatitis B virus surface antigen

BACKGROUND: Phage display technology has become a vital tool in studies aimed at identifying molecules binding to a specific target. It enables the rapid generation and selection of high affinity, fully human antibody product candidates to essentially any disease target appropriate for antibody therapy. In this study, we prepared the recombinant single-chain fragment variable ( ScFv) antibody to hepatitis B virus surface antigen (HBsAg) by the phage display technology for obtaining a virus-targeting mediator. METHODS: mRNA was isolated from B-lymphocytes from a healthy volunteer and converted into cDNA. The fragment variables of heavy and light chain were amplified separately and assembled into ScFv DNA with a specially constructed DNA linker by polymerase chain reaction. The ScFv DNA was ligated into the phagmid vector pCANT-AB5E and the ligated sample was transformed into competent E. coli TG1. The transformed cells were infected with M13K07 helper phage to form a human recombinant phage antibody library. The volume and recombinant rate of the library were evaluated by bacterial colony count and restriction analysis. After two rounds of panning with HBsAg. the phage clones displaying ScFv of the antibody were selected by enzyme-linked immunosorbant assay ( 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 anti-HBsAg ScFv. ELISA assay was used to detect the antigen binding affinity of the soluble anti-HBsAg ScFv. Finally, the relative molecular mass of soluble anti-HBsAg ScFv was measured by SDS-PAGE. RESULTS: The variable heavy ( VH ) and variable light (VL) and ScFv DNAs were about 340bp, 320bp and 750bp, respectively. The volume of the library was up to 2 × 106 and 8 of 10 random clones were recombinants. Two phage clones could strongly compete with the original HBsAb for binding to HBsAg. Within 2 strong positive phage clones, the soluble anti-HBsAg ScFv from one clone was found to have the binding activity with HBsAg. SDS-PAGE showed that the relative molecular weight of soluble anti-HBsAg ScFv was 32 kDa. CONCLUSION: The anti-HBsAg ScFv successfully produced by phage antibody technology may be useful for broadening the scope of application of the antibody.

Preparation of Monoclonal Antibody Against PthA-NLS and Cloning of the Relative ScFv Gene

The present study aimed at the preparation of monoclonal antibody against the recombinant PthA-NLS and the isolation of the relative ScFv （single chain variable fragment） genes, providing the possibility to better understand the pathogenesis mechanism via PthA, and developing proper construct for future experimentation to obtain citrus plants resistant to canker disease by transformation and plant antibody techniques. The recombinant polypeptide PthA-NLS was injected into Balb/c mice to produce monoclonal antibody. Total RNA was isolated from the hybridoma cell line 3D10H2 which secreted anti- PthA-NLS McAb, and the variable region genes were amplified with specific primers by RT-PCR and SOE-PCR （splicing by overlap extension）, and then the ScFv gene was isolated. The recombinant ScFv gene was cloned into pGEM-T and pET32a（＋） vector. The later plasmid was transferred into E. coli BL21 （DE3） and the expression of the recombinant protein was induced. Three cell lines producing monoclonal antibody against PthA-NLS were acquired and named 1C8H1, 2D12B6, and 3D8A10. The recombinant ScFv gene of about 750 bp was constructed. The sequencing results showed that the ScFv gene consists of a 360 bp heavy chain, a 342 bp light chain, and a 45 bp linker region. The recombinant fusion ScFv protein was expressed by IPTG induction, and a 44.5 kDa of recombinant fusion protein was obtained. In conclusion, we obtained three cell lines stably producing monoclonal antibody specifically bound to PthA-NLS, and the relative ScFv gene was constructed and successfully expressed in E. coli. These results may play an important role in further understanding the pathogenesis mechanism and in the development of possible citrus resistant to canker disease by genetic transformation and plant antibiobody.

Bioinformatics-led design of single-chain antibody molecules targeting DNA sequences for retinoblastoma

The development of single-chain Fv antibody (scFv) by recombinant gene expression is an important milestone for cancer therapy. Single-chain antibodies are reconstructed for cancer-targeted therapy to provide good penetration into tumor tissue and to improve their pharmacokinetics in vivo, offering a clinically valuable application. The relationship needs to be analyzed that there may be some variations between the structure and function of the fusion proteins, and the relationship between the structure and function of protein molecules was obtained through analyzing relevant literature at home and abroad as well as modeling analysis. Through our analysis of the interaction region between antibody and antigen, and of the binding sites for molecular conformation, it is clear that existing antibodies need to be modified at the DNA sequence level, enhancing the biological activity of the antibodies. Based on the view that bio-molecular computer models are closely integrated with biological experiments, a bio-molecular structure-activity relationship model can be established in terms of molecular conformation, physical and chemical properties and the biological activity of single-chain antibodies. Two enlightenments are obtained from our analysis. On one hand, the structure-activity relationship is clear for new immune molecules at the gene expression level. On the other hand, a single-chain antibody molecule can be designed and optimized for the cancer-oriented treatment. In this article, we provided the theoretical and experimental basis for the development of single-chain antibodies appropriate for retinoblastoma therapy.

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.

Expression of secreted human single-chain fragment variable antibody against human amyloid beta peptide in Pichia pastoris

BACKGROUND：Studies have shown that monoclonal or polyclonal antibody injections of amyloid β peptide are effective in removing amyloid β peptide overload in the brain. OBJECTIVE： Based on successful screening of a human single-chain fragment variable antibody specific to amyloidβpeptide, this paper aimed to express recombinant human single-chain variable antibody against amyloid β peptide. DESIGN, TIME AND SETTING： A single sample experiment was performed at the Department of Nuclear Medicine, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences and Peking Union Hospital （Beijing, China） from January to July 2006. MATERIALS： Human single-chain fragment variable antibody gene against amyloid β peptide was screened from a human phage-display antibody library. METHODS： Human single-chain fragment variable antibody gene was mutated to eliminate a BamHI restriction site and cloned into a T easy plasmid for pT-scFvAβ construction, which was identified by PCR amplification and endonuclease digestion. Plasmid pT-scFvAβ was cut by EcoRI and NotI endonucleases, and the antibody gene was cloned into pPIC9K plasmid to construct pPIC9K-scFvAβ expression vector, which was confirmed by gene sequencing. Linearized pPIC9K-scFvAβ was used to transform a Pichia pastoris GS115 cell line, and the recombinant was induced by 0.5% methanol to express human single-chain fragment variable antibody specific to amyloid β peptide. MAIN OUTCOME MEASURES： Protein electrophoresis was used to identify PCR products, gene sequencing was used to verify the pPIC9K-scFvA sequence, and SDS-PAGE was used to detect recombinant expression of human single-chain fragment variable antibody specific to amyloid β peptide in Pichia pastoris. RESULTS： Gene sequencing confirmed pPIC9K-scFvAβ orientation. Recombinants were obtained by linearized pPIC9K-scFvAβ transformation. After induction with 0.5% methanol, the recombinant yeast cells secreted proteins of 33-ku size. CONCLUSION： The expression vector pPIC9K-scFvAβ was successfully constructed. Human single-chain fragment variable antibody specific to amyloid β peptide was recombinantly expressed in Pichia pastoris.

KGla细胞免疫小鼠脾细胞scFv噬菌体展示文库的构建及其表达

目的 :用噬菌体展示技术构建KGla免疫小鼠的脾细胞scFv表达文库。方法 :用人髓系白血病细胞系KGla细胞免疫小鼠 ,取其脾细胞 ,RT PCR扩增VH和Vκ基因并克隆入噬菌体展示表达载体 ,构建scFv文库 ,并测定文库的库容量和BstN1酶切单个克隆分析文库的多样性。用KGla作为固相抗原 ,进行四轮吸附 洗脱 富集的筛选 ,SDS PAGE检验筛选后文库scFv的呈示表达。结果 :文库的库容为 3× 10 6cfu ,单个克隆的BstN1Ⅰ酶切图谱显示多样 ,提示文库的容量和多样性均能满足进一步筛选分离目的基因的需要 ,筛选后的文库能很好地表达外源scFv。结论

抗黄曲霉毒素B1单链抗体(scFv)库的建立和筛选

从抗黄曲霉毒素B1单克隆抗体细胞系中扩增到重链可变区(VH)和轻链可变区(VL),经PCR将VH、Linker和VL连接成单链抗体(scFv),并克隆到载体pCANTAB-5E,经电转化大肠杆菌TG1,构建了库容量为1×108的单链抗体库。通过辅助噬菌体M13KO7感染后,使单链抗体展示在噬菌体衣壳蛋白pIII的N端,得到客容量为1×108的噬菌体展示的抗体库。将抗体库用于"淘洗-富集-扩增"4轮以后,得到针对AFB1特异性的噬菌体抗体。进一步以噬菌体感染大肠杆菌HB2151,在细菌细胞周质中可溶性大量表达,最终经竞争ELISA分析表明获得了3株可以稳定分泌抗黄曲霉毒素B1 scFv菌株,分别命名为3C3、3B3和4A2。

抗Pgp基因工程抗体ScFv的构建、表达及其活性测定

目的 :构建表达抗PgpScFv,进行体外活性的测定。方法 :利用RT PCR方法 ,克隆抗Pgp杂交瘤细胞PHMAO2的重链可变区基因 (VH) ,轻链可变区基因 (VL) ,拼接为单链抗体 (ScFv) ,再克隆到具有强启动子的PET2 8a(+)载体上进行表达 ,并进行了表达产物体外活性的测定。结果 :构建了表达质粒PET2 8a(+) ScFvPGP。表达产物可与表达Pgp抗原的K5 6 2 A0 2细胞特异性结合 ,并不抑制Pgp外排泵的功能。结论 :构建表达的抗PgpScFv只有针对Pgp抗原的识别功能 ,并无抑制作用 ,因此应用于人体后不会干扰正常细胞的排泄分泌功能 ,无论是作为靶向诊断治疗的载体还是作为双功能抗体的一臂 ,均具有广泛的应用前景。

高亲和力抗Met人源基因工程抗体scFv的筛选与特性分析

目的应用噬菌体展示技术制备抗HGF受体Met特异性、高亲和力的全人抗体scFv片段。方法以从天然抗体库中筛选出的Fab基因可变区VH和VL为模板,分别在CDR区引入有限突变和随机突变,扩增出scFv基因库,克隆于pComb3XSS中,构建scFv次级突变抗体库,筛选高亲和力克隆。结果经5轮细胞筛选和2轮抗原固相筛选,选取60个克隆进行ELISA检测,选择较高亲和力的噬菌体抗体,克隆于原核表达载体pBAD-gIII/A中,经诱导表达、SDS-PAGE和Westernblotting分析,在相对分子质量30000处出现预期大小的蛋白条带。单链抗体经表达、变性与复性和IMAC亲和纯化后,用于流式细胞术、免疫沉淀分析,结果表明,scFv能够与S114细胞表达Met的胞外区特异性结合,其亲和常数Kd值为4.76×10-8mol/L,与突变前抗体的亲和力(Kd值为5.24×10-6mol/L)相比,抗体的亲和力提高约100倍。竞争ELISA结果显示,亲和力成熟后抗体的抗原结合表位未变。结论经过CDR突变和抗体库筛选,有效提高了抗体的亲和力,该抗体有望成为临床肿瘤诊断或治疗的候选分子。

基于流式细胞术的scFv抗体库筛选技术的建立

目的利用NlpA前导肽诱导抗体锚定细菌内膜建立筛选scFv抗体库的展示技术,为高亲和力抗体的筛选奠定基础。方法从pNAD质粒中克隆出NlpA前导肽基因序列,酶切后将该序列克隆进pHEN1表达载体中。以PEAI质粒为模板,利用PCR的方法克隆得到抗-hIL-1β抗体的重链可变区和轻链可变区基因,然后利用重叠PCR的方法构建得到抗-hIL-1βscFv抗体。将scFv抗体插入到NlpA leader-pHEN1表达载体中构建成展示scFv的重组质粒pBSD-scFv。将pBSD-scFv转入到E.coli DH5α中诱导表达,原生质球制备后,采用梯度浓度的抗原进行孵育,最后经流式细胞术(FCM)检测抗体展示情况并且分选阳性群体,利用质粒提取的方法来替代PCR方法拯救阳性基因,转化E.coli DH5α,利用FCM再次检测该群体展示的抗体与抗原结合情况。结果所展示的抗-hIL-1βscFv抗体依次与抗原和FITC标记的抗原特异性抗体孵育后,用FCM实时检测,结果显示出很强的荧光信号并且表现出抗原浓度依赖性。拯救出的pBSD-scFv-原生质球的FCM检测结果与首次展示的FCM结果一致,该系统能够稳定的展示抗体。结论经过该细菌展示系统展示的scFv抗体能够有效的折叠,与相应的抗原具有很好的特异结合能力。

重组抗HER2 ScFv/FDT/caspase-6基因的构建、表达及其活性鉴定

目的:构建重组抗HER2 ScFv/FDT/caspase-6基因的表达载体,转染SGC7901胃癌细胞后观察其促凋亡作用.方法:采用重组PCR法,将抗HER2的单链抗体(e23sFv)通过白喉毒素的Furin识别位点的编码序列(FDT)与人重构型caspase-6(RC6)基因重组,构建融合蛋白表达基因e23sFv-FDT-RC6.将所获得的重组基因克隆入真核表达载体pCMV,以脂质体法瞬时转染HER2阳性的SGC7901细胞和HER2阴性的HeLa细胞.MTT法检测目的基因转染后细胞的增殖情况.间接免疫荧光染色观察目的基因的表达对SGC7901细胞的促凋亡作用.结果:把e23sFv-RC6,e23sFv-FDT-RC6基因克隆入真核表达载体pCMV,酶切鉴定和基因测序证明目的基因序列正确.转染SGC7901和HeLa细胞后,Western Blot检测到目的蛋白的表达.MTT实验观察到转染pCMV-e23sFv-FDT-RC6的SGC7901细胞的增殖被明显抑制,间接免疫荧光染色可以观察到表达e23sFv-FDT-RC6融合蛋白的SGC7901细胞形态发生改变,部分细胞呈现典型凋亡特征.结论:重组抗HER2 ScFv/FDT/caspase-6基因的表达可促进HER2阳性SGC7901胃癌细胞的凋亡.

全人源抗狂犬病病毒scFv-Fc融合抗体的制备及活性分析

目的:制备全人源抗狂犬病病毒scFv-Fc融合抗体,并分析其结合活性。方法:构建全人源抗狂犬病病毒scFv-Fc融合抗体原核表达载体,优化表达并纯化全人源抗狂犬病病毒scFv-Fc融合抗体。以纯化的灭活狂犬病病毒包板,对纯化的抗体进行结合活性分析。结果:构建全人源抗狂犬病病毒scFv-Fc-pColdⅡ原核表达载体,经测序分析正确后,转入大肠杆菌BL21(DE3)进行表达,在加入浓度为0.5 mmol/L IPTG时,scFv-Fc融合抗体的表达较高,其分子量大小为57 000。纯化后的scFv-Fc融合抗体在1∶512的条件下仍可以较好地结合狂犬病病毒。结论:构建全人源抗狂犬病病毒scFv-Fc-pColdⅡ原核表达载体,表达并纯化了scFv-Fc融合抗体,为研发狂犬病暴露后预防治疗性抗体药物奠定了基础。

小鼠ScFv基因片段的构建

目的 利用分子重组技术构建小鼠单链抗体片段 (ScFv)。方法 采用PCR反应从小鼠脾细胞扩增鼠免疫球蛋白的重链和轻链可变区 ,利用连结引物将重链和轻链DNA组装成单链抗体 (ScFv)片段。结果 克隆出VH,VL 基因 ,用Linker将VH,VL 连接起来后的ScFv构建成功 ,其分子量为 75 0bp。结论 ScFv分子小 ,异源性低 ,可以结合与噬菌体载体中形成融合蛋白表达 ,该技术是抗体制备的一种简便、可靠的方法。

重组抗HER2 ScFv/tbid基因的表达及其对乳腺癌SKBr-3细胞的促凋亡作用

目的:观察构建的重组抗HER2ScFv/tbid基因在SKBr-3细胞中的表达及其对转染的SKBr-3细胞的作用.方法:用限制性内切酶双酶切已构建的pcDNA-bid质粒,获得带有PE转膜结构域和tbid的重组基因,将所获基因插入到真核表达载体pCMV单链抗体基因ScFv23e的下游,转染SKBr-3细胞.间接免疫荧光法检测目的蛋白的表达,MTT法检测目的基因转染后细胞的增殖情况.结果:转染SKBr-3细胞后,检测出目的蛋白的表达.MTT实验发现细胞的增殖被明显抑制.间接免疫荧光双标记染色检测tBid的表达,并可观察到Cytc在细胞质中存在,SKBr-3细胞出现凋亡.结论:重组抗HER2ScFv/tBid分子可以在转染的SKBr-3细胞中表达,并且可抑制转染细胞的生长,诱导细胞发生凋亡.

鸡源Bursin-ScFv噬菌体展示文库的构建及初步筛选

本研究利用抗三肽囊素(Bursin)单克隆抗体免疫SPF来航鸡,获得产生抗独特型抗体的脾细胞,从中提取总RNA,经反转录合成cDNA第一链。以cDNA第一链为模板,根据来航鸡IgG抗体重链(VH)、轻链(VL)可变区基因FR设计引物,进行PCR扩增。在体外扩增出该抗体的可变区VH和VL基因(大小分别约为370和320 bp)。通过重叠延伸反应(SOE),以(Gly4Ser)3为连接肽,将VH和VL基因连接成为VH-Linker-VLScFv,将ScFv DNA与噬菌粒载体pHEN1的连接产物转化于大肠杆菌TG1,经辅助噬菌体M13K07感染后,获得重组的鸡源抗三肽囊素独特型抗体全套单链噬菌体抗体库。并测得该库容量约为5×105,噬菌体中ScFv基因的插入率为80%,用辅助噬菌体援救后,得到滴度为1011PFU/mL的初级噬菌体抗体库。用抗Bursin单克隆抗体(2F9-4/HU2)进行4轮"吸附-洗脱-扩增"的淘筛,出现特异性富集。经ELISA、动物试验表明所筛选的5个阳性克隆可与抗Bursin单克隆抗体(2F9-4/HU2)特异性结合,并能促进抗体的生产。

三肽囊素抗独特型ScFv噬菌体展示文库的构建

利用在体外构建的三肽囊素抗独特型抗体可变区VH和VL基因,通过重叠延伸反应(SOE),以(Gly4Ser)3为连接肽,将VH和VL基因连接成为VH-Linker-VLScFv,且ScFvDNA与噬菌粒载体pHEN1的连接产物转化于大肠杆菌TG1,经辅助噬菌体M13K07感染后,获得重组的鸡源抗三肽囊素抗独特型抗体全套单链噬菌体抗体库,并将该抗体库展示在噬菌体表面,以利用噬菌体展示技术的强大筛选能力筛选出与三肽囊素同功能单链抗体(Bursin-ScFv)。

抗胃癌鼠单抗3H11 scFv的包含体表达及柱上在位复性

目的：在大肠杆菌高效表达抗胃癌单抗３Ｈ１１的ｓｃＦｖ。方法：利用ＰＣＲ技术将３Ｈ１１ｓｃＦｖ基因从分泌型表达载体转移至高效表达载体，获得３Ｈ１１ｓｃＦｖ包含体的表达，经超声裂解、洗涤、变性后，尝试透析复性和凝胶过滤色谱柱上在位复性，结果：透析复性未能得到有活性的３Ｈ１１ｓｃＦｖ，而柱上在位复性效果良好，获得有功能性的３Ｈ１１ｓｃＦｖ。结论：成功进行了３Ｈ１１ｓｃＦｖ的柱上复性，不同ｓｃＦｖ在表达和复性中显示出明显差异，在基因工程抗体研制中值得注意。

IgM型单克隆抗体之scFv库的建立与筛选

从一个抗脂磷酸聚糖IgM型单克隆抗体细胞的mRNA中经RT-PCR克隆重链可变区(VH)和轻链可变区(VL),然后将VH、Linker和VL连接成scFv,并克隆到载体pCANTAB-5E,转Escherichia coliTG1感受态细胞,构建了单链抗体库。通过辅助噬菌体M13KO7感染后,使单链抗体展示在噬菌体衣壳蛋白pIII的N端,得到噬菌体展示的抗体库。将抗体库用于"淘洗—富集—扩增"3轮以后,得到针对脂磷酸聚糖特异性的噬菌体抗体。测序结果表明,该scFv的VH基因序列全长390 bp,编码127个氨基酸;VL基因序列全长341 bp,编码113个氨基酸。二者均符合小鼠免疫球蛋白可变区基因特征,含有4个框架区(FR)、3个抗原互补决定区(CDR)及抗体特征性的2个半胱氨酸残基。