Monoclonal Phage ELISA Research Articles

Isolation and characterization of a novel single-chain variable fragment (scFv) against Lymphocyte function-associated antigen-1 (LFA-1) using phage display method.

Lymphocyte function-associated antigene-1 (LFA-1) is a well-described integrin found on lymphocytes and other leukocytes, which is known to be overexpressed in leukemias and lymphomas. This receptor plays a significant role in immune responses such as T-cell activation, leukocyte cell-cell interactions, and trafficking of leukocyte populations. Subsequently, binders of LFA-1 emerge as potential candidates for cancer and autoimmune therapy. This study used the phage display technique to construct and characterize a high-affinity single-chain fragment variable (scFv) antibody against LFA-1. After expression, purification, dialysis, and concentration of the recombinant LFA-1 protein, four female BALB/c mice were immunized, splenocyte's mRNA was extracted, and cDNA was synthesized. A scFv library was constructed by linking the amplified VH/Vκ fragments through a 72-bp linker using SOEing PCR. Next, the scFv gene fragments were cloned into the pComb-3XSS phagemid vector; thus, the phage library was developed. The selection process involved three rounds of phage-bio-panning, polyclonal, and monoclonal phage ELISA. AF17 was chosen and characterized among the positive clones through SDS-PAGE, Western blotting, indirect ELISA, and in-silico analyses. The results of the study showed the successful construction of a high-affinity scFv library against LFA-1. The accuracy of the AF17 production and its ability to bind to the LFA-1 were confirmed through SDS-PAGE, Western blot, and ELISA. This study highlights the potential application of the high-affinity AF17 against LFA-1 for targeting T lymphocytes for therapeutic purposes.

The specific biopanning of single-domain antibody against haptens based on a functionalized cryogel.

Phage display technology is commonly applied for high-throughput screening of single-domain antibodies (sdAbs), and the problem of non-specific adsorption caused by carrier proteins seriously affects the biopanning of single-domain antibodies specific to haptens. In this paper, enrofloxacin (ENR)-functionalized cryogels were prepared by the ethylenediamine (EDA) and carbodiimide methods for application in the biopanning of ENR-specific phages. To improve the efficiency of biopanning, double blocking, a wash solution flow rate of 1 mL/min, and phage pre-incubation were applied to the biopanning process through single-factor experiments. Results of flat colony counting showed that the phage output of AG-ENR cryogels was 15 times higher than that of AG cryogels for the same input amount. And seven complete sequences of ENR-specific shark sdAbs were obtained by monoclonal phage ELISA and sequence alignment. All these results indicate that functionalized cryogels could be used as a novel and efficient method for phage biopanning for single-domain antibodies to haptens.

Inhibition of avian influenza virus H9N2 infection by antiviral hexapeptides that target viral attachment to epithelial cells

The H9N2 subtype of influenza A virus circulates frequently among poultry in Asian and North African countries causing economic loss in the poultry sector. The antigenic variations of the H9N2 virus were at the origin of its genetic evolution through the emergence of viral strains transmissible to humans and resistant to chemical antivirals, which require a strengthening of the fight means against this virus. In this study, we used a random linear hexapeptide library fused to the gene III protein of M13 filamentous bacteriophage to select new antiviral peptides that inhibit the infectivity of H9N2 virus. After three rounds of stringent selection and amplification, polyclonal phage-peptides directed against H9N2 virus were assessed by ELISA, and the optimal phage-peptides were grown individually and characterized for binding to H9N2 virus by monoclonal phage ELISA. The DNA of 27 phage-peptides clones was amplified by PCR, sequenced, and their amino acid sequences were deduced. Sixteen different phage-peptides were able to bind specifically the H9N2 virus, among them, 13 phage-peptides interacted with the hemagglutinin H9. Two selected peptides, P1 (LSRMPK) and P2 (FAPRWR) have shown antiviral activity in ovo and P1 was more protective in vivo then P2 when co-administered with the H9N2 virus. Mechanistically, these peptides prevent infection by inhibiting the attachment of the H9N2 virus to the cellular receptor. Molecular docking revealed that the peptides LSRMPK and FAPRWR bind to hemagglutinin protein H9, but interact differently with the receptor binding site (RBS). The present study demonstrated that the peptide P1 (LSRMPK) could be used as a new inhibitory molecule directed against the H9N2 virus.

Selection of human single domain antibodies (sdAb) against thymidine kinase 1 and their incorporation into sdAb-Fc antibody constructs for potential use in cancer therapy.

Thymidine Kinase 1 (TK1) is primarily known as a cancer biomarker with good prognostic capabilities for both hematological and solid malignancies. However, recent studies targeting TK1 at protein and mRNA levels have shown that TK1 may be useful as a therapeutic target. In order to examine the use of TK1 as a therapeutic target, it is necessary to develop therapeutics specific for it. Single domain antibodies (sdAbs), represent an exciting approach for the development of immunotherapeutics due to their cost-effective production and higher tumor penetration than conventional antibodies. In this study, we isolated sdAb fragments specific to human TK1 from a human sdAb library. A total of 400 sdAbs were screened through 5 rounds of selection by monoclonal phage ELISA. The most sensitive sdAb fragments were selected as candidates for preclinical testing. The sdAb fragments showed specificity for human TK1 in phage ELISA, Western blot analysis and had an estimated limit of detection of 3.9 ng/ml for the antibody fragments 4-H-TK1_A1 and 4-H-TK1_D1. The antibody fragments were successfully expressed and used for detection of membrane associated TK1 (mTK1) through flow cytometry on cancer cells [lung (~95%), colon (~87%), breast (~53%)] and healthy human mononuclear cells (MNC). The most sensitive antibody fragments, 4-H-TK1_A1 and 4-H-TK1_D1 were fused to an engineered IgG1 Fc fragment. When added to cancer cells expressing mTK1 co-cultured with human MNCs, the anti-TK1-sdAb-IgG1_A1 and D1 were able to elicit a significant antibody-dependent cell-mediated cytotoxicity (ADCC) response against lung cancer cells compared to isotype controls (P<0.0267 and P<0.0265, respectively). To our knowledge this is the first time that the isolation and evaluation of human anti-TK1 single domain antibodies using phage display technology has been reported. The antibody fragments isolated here may represent a valuable resource for the detection and the targeting of TK1 on tumor cells.

Isolation and characterizations of a novel recombinant scFv antibody against exotoxin A of Pseudomonas aeruginosa

BackgroundPseudomonas aeruginosa is the leading cause of nosocomial infections, especially in people with a compromised immune system. Targeting virulence factors by neutralizing antibodies is a novel paradigm for the treatment of antibiotic-resistant pseudomonas infections. In this respect, exotoxin A is one of the most potent virulence factors in P. aeruginosa. The present study was carried out to identify a novel human scFv antibody against the P. aeruginosa exotoxin A domain I (ExoA-DI) from a human scFv phage library.MethodsThe recombinant ExoA-DI of P. aeruginosa was expressed in E. coli, purified by Ni-NTA column, and used for screening of human antibody phage library. A novel screening procedure was conducted to prevent the elimination of rare specific clones. The phage clone with high reactivity was evaluated by ELISA and western blot.ResultsBased on the results of polyclonal phage ELISA, the fifth round of biopanning leads to the isolation of several ExoA-DI reactive clones. One positive clone with high affinity was selected by monoclonal phage ELISA and used for antibody expression. The purified scFv showed high reactivity with the recombinant domain I and full-length native exotoxin A.ConclusionsThe purified anti-exotoxin A scFv displayed high specificity against exotoxin A. The human scFv identified in this study could be the groundwork for developing a novel therapeutic agent to control P. aeruginosa infections.

Development of monoclonal antibodies against recombinant LipL21 protein of pathogenic Leptospira through phage display technology

Leptospirosis is a potentially fatal zoonosis that is caused by spirochete Leptospira. The signs and symptoms of leptospirosis are usually varied, allowing it to be mistaken for other causes of acute febrile syndromes. Thus, early diagnosis and identification of a specific agent in clinical samples is crucial for effective treatment. This study was aimed to develop specific monoclonal antibodies against LipL21 antigen for future use in leptospirosis rapid and accurate immunoassay. A recombinant LipL21 (rLipL21) antigen was optimized for expression and evaluated for immunogenicity. Then, a naïve phage antibody library was utilized to identify single chain fragment variable (scFv) clones against the rLipL21 antigen. A total of 47 clones were analysed through monoclonal phage ELISA. However, after taking into consideration the background OD405 values, only 4 clones were sent for sequencing to determine human germline sequences. The sequence analysis showed that all 4 clones are identical. The in silico analysis of scFv-lip-1 complex indicated that the charged residues of scFv CDRs are responsible for the recognition with rLipL21 epitopes. The generated monoclonal antibody against rLipL21 will be evaluated as a detection reagent for the diagnosis of human leptospirosis in a future study.

Isolation and characterization of nanobodies against epithelial cell adhesion molecule as novel theranostic agents for cancer therapy

Epithelial cell adhesion molecule (EpCAM) plays an important role in tumorigenesis. Camelids produce functional antibodies composed of heavy chains only that bind to their antigens via a single domain variable fragment known as nanobody. Nanobodies show multiple advantages over traditional monoclonal antibodies. Isolation of functional anti-EpCAM nanobodies (Nbs) was the main aim of this study. An immune nanobody library containing 108 members was constructed previously. Anti -EpCAM nanobodies were isolated from camel immune library using phage display. Four consecutive rounds of biopanning were performed on immobilized EpCAM. Four nanobodies (Nb4, Nb5, Nb22, and Nb23) with highest signal intensity in monoclonal phage ELISA were selected. Affinity of these selected nanobodies for EpCAM was in the nanomolar range. Selected nanobodies significantly inhibited proliferation of MCF-7 cells. The in vivo study revealed that a significant reduction in tumor size occurred when treated with nanobodies Nb4 and Nb5, after 14 days monitoring. Our data revealed that nanobodies Nb4 and Nb5 could be considered as attractive theranostic agents for EpCAM overexpressing cancers.

Abstract 519: Exploring the potential of human nanobodies against thymidine kinase 1 for the targeting of lung cancer cells

Abstract Single domain antibodies or nanobodies (Nbs) have positively proved effective for the targeting of multiple tumor targets. This study describes the isolation of human Nbs against the tumor proliferation biomarker thymidine kinase 1 (TK1). The anti-TK1 Nbs were used to target membrane associated TK1 in the non-small cell lung carcinoma cell lines NCI-H460 and A549 cells. TK1 is a pyrimidine salvage enzyme that is upregulated in malignant tissues. Recently, we have reported the presence of a TK1 form that is associated to the cell membrane in breast, lung and colon tumors as well as leukemia. Our findings suggest that targeting of TK1 in proliferating cancer cells may be an alternative approach for the treatment of cancer. Using phage display technology, we isolated a total of 237 nanobodies from the Daniel Christ DAb library. After 2-4 rounds of selection the affinity of the nanobodies to TK1 was tested with monoclonal phage ELISA using human recombinant TK1. Ten of the most sensitive anti-TK1 Nbs were then selected and evaluated with dose response curves as possible candidates for preclinical testing. The dose response curves showed R squares values ranging from 0.9738-0.9980 fitting a sigmoidal curve. Thus, indicating a strong antibody dose response relationship specific for TK1. In addition, the specificity of the TK1 antibodies was tested by screening against unrelated proteins and cell lysate from an siRNA TK1 knockdown using monoclonal phage ELISA. Nanobodies showed negligible binding when screened against TK1 non related proteins. Validation of the anti-TK1 Nbs with TK1 siRNA knockdown showed a significant reduction on the Nbs binding compared to wild type. The sensitivity of the anti-TK1 Nbs to detect TK1 was within the nanomolar range (between 100-20 ng/ml) and had thermostable standing temperatures between 50-75 °C. The anti-TK1 Nbs were used to detect membrane associated TK1 in the non-small cell lung carcinoma cell lines NCI-H460 and A549. The phage nanobodies showed binding capacity to TK1 on cancer cells with 30- 60% of positive cells for NCI-H460 and 25 to 40% for A549 cells. Human Nbs represent a valuable resource for the detection and the targeting of TK1 in proliferating tumor cells. Further work is required to enable the exploration of the therapeutic uses of anti-TK1 Nb-based therapies and their incorporation to cell adoptive therapies such as chimeric antigen receptor (CAR) therapies. Citation Format: Edwin J. Velazquez, Jordan D. Cress, Kathryn R. Smith, David M. Bellini, Jonathan R. Skidmore, Zachary D. Ewell, Richard A. Robison, Kim L. O'Neill. Exploring the potential of human nanobodies against thymidine kinase 1 for the targeting of lung cancer cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 519.

Discovery of Novel Peptidomimetics for Brain-Derived Neurotrophic Factor using Phage Display Technology

Brain-Derived Neurotrophic Factor (BDNF) is a neuroprotectant candidate for neurodegenerative diseases. However, there are several clinical concerns about its therapeutic applications. In the current study, we selected BDNF-mimicking small peptides from phage-displayed peptide library as alternative molecules to the clinical challenges. The peptide library was screened against BDNF receptor (Neurotrophic Tyrosine Kinase Receptor Type 2, NTRK2) and evaluated by ELISA. Polyclonal phage ELISA indicated that target populations were enriched round by round and the panning process was truly effective. The results of monoclonal phage-ELISA showed that all clones had principally bound to NTRK2 but fifteen best clones were sequenced, which twelve of them have SGVYKVAYDWQH (peptide 1) sequence, two pairs were GLHTSATNLYLH (peptide 2), and TVLSHPSTATLI (peptide 3) and one sequence was QQRPYVQDLRLI (peptide 4). Alignment of these peptides and BDNF sequence showed that the resulting peptides conformationally mimicked loop 2 (E40-KVPVSKGQLK-Q51) of BDNF. This region of BDNF is responsible for specific receptor binding and biological activity. According to the similarity of these peptides with BDNF, they could be considered as novel peptidomimetics with therapeutic properties. In addition, modeled peptides were submitted to Protein Model Data Base (peptides 1, 2, 3 and 4 as PMDB ID: PM0081104, PM0081105, PM0081106, PM0081107, respectively).

Identification of a novel single chain fragment variable antibody targeting CD24-expressing cancer cells

CD24 is a heavy glycosylated protein that is overexpressed in numerous cancer and cancer stem cells. It is involved in the development, invasion, and metastasis of the cancer cells. CD24 can be considered in targeted cancer therapy as a new target. Here, phage display technology was used for the identification of novel scFv antibodies against CD24. To do so, the CD24 protein was expressed and purified from a stable transgenic CHO cell line. The cells were developed by using a CD24 encoding construct, which targets the 18S rRNA gene. The recombinant CD24 was used in the biopanning process. Four rounds of biopanning were performed with the Tomlinson J library. The polyclonal phage ELISA and DNA sequencing of the selected colonies confirmed that specific binders have been enriched during the biopanning process. Based on the DNA sequencing results, three phage-displaying scFv were obtained and their specificity to CD24 was verified in the monoclonal phage ELISA. The results showed that clone 3 (called Jd3) has the highest affinity to CD24 and also is the most abundant clone (80%) among the three clones. Therefore, Jd3 was selected for further analyses. In order to produce soluble Jd3-scFv, the phage was transfected to E. coli BL21 pLysS. Soluble Jd3 scFv was expressed and purified successfully. The soluble Jd3 scFv showed appropriate affinity to recombinant CD24 in the ELISA analysis. Also, the immunocytochemistry experiment showed that the purified Jd3 scFv can bind to the CD24 expressing A549 cells. So, the scFv may be useful in the targeted delivery of drugs or diagnostic nanoparticles to the CD24 expressing cancer cells. To the best of our knowledge, this study is the first report to identify an scFv antibody against CD24, using the phage display method.

Development of a Novel Human Single Chain Antibody Against EGFRVIII Antigen by Phage Display Technology.

Purpose: EGFRvIII as the most common mutant variant of the epidermal growth factor receptor is resulting from deletion of exons 2-7 in the coding sequence and junction of exons 1 and 8 through a novel glycine residue. EGFRvIII is highly expressed in glioblastoma, carcinoma of the breast, ovary, and lung but not in normal cells. The aim of the present study was identification of a novel single chain antibody against EGFRvIII as a promising target for cancer therapy. Methods: In this study, a synthetic peptide corresponding to EGFRvIII protein was used for screening a naive human scFv phage library. A novel five-round selection strategy was used for enrichment of rare specific clones. Results: After five rounds of screening, six positive scFv clones against EGFRvIII were selected using monoclonal phage ELISA, among them, only three clones had expected size in PCR reaction. The specific interaction of two of the scFv clones with EGFRvIII was confirmed by indirect ELISA. One phage clone with higher affinity in scFv ELISA was purified for further analysis. The purity of the produced scFv antibody was confirmed using SDS-PAGE and Western blotting analyses. Conclusion: In the present study, a human anti- EGFRvIII scFv with high affinity was first identified from a scFv phage library. This study can be the groundwork for developing more effective diagnostic and therapeutic agents against EGFRvIII expressing cancers.

Isolation and characterization of a novel human scFv inhibiting EGFR vIII expressing cancers

EGFRvIII, a mutant form of epidermal growth factor receptor is highly expressed in glioblastoma, carcinoma of the breast, ovary, and lung but not in normal cells. This tumor specific antigen has emerged as a promising candidate for antibody based therapy of several cancers. The aim of the present study was isolation and characterization of a human single chain antibody against EGFRvIII as a promising target for cancer therapy. For this, a synthetic peptide corresponding to EGFRvIII protein was used for screening the naive human scFv phage library. Selection was performed using a novel screening strategy for enrichment of rare specific clones. After five rounds of screening, six positive scFv clones against EGFRvIII were selected using monoclonal phage ELISA, among them, a clone with an amber mutation in VH CDR2 coding sequence showed higher reactivity. The mutation was corrected through site directed mutagenesis and then scFv fragment was expressed after subcloning into the bacterial expression vector. Expression in BL21 pLysS resulted in a highly soluble scFv appeared in soluble fraction of E. coli lysate. Bioinformatic in silico analysis between scFv and EGFRvIII sequences confirmed specific binding of desired scFv to EGFRvIII in CDR regions. The specific reactivity of the purified scFv with native EGFRvIII was confirmed by cell based ELISA and western blot. In conclusion, human anti- EGFRvIII scFv isolated from a scFv phage library displayed high reactivity with EGFRvIII. The scFv isolated in this study can be the groundwork for developing more effective diagnostic and therapeutic agents against EGFRvIII expressing cancers.

Antiproliferative and apoptotic effects of a specific anti-insulin-like growth factor I receptor single chain antibody on breast cancer cells.

Insulin-like growth factor I receptor (IGF-IR) is expressed on breast cancer cells and involves in metastasis, survival, and proliferation. Currently, application of IGF-IR-targeting monoclonal antibodies (mAbs), alone or in combination with other drugs, is a promising strategy for breast cancer therapy. Single-chain fragment variable (scFv) antibodies have been introduced as appropriate tools for tumor-targeting purposes because of their advantages over whole antibodies. In the present study, we employed a naïve phage library and isolated scFvs against a specific epitope from extracellular domain of IGF-IR by panning process. The selected scFvs were further characterized using polyclonal and monoclonal phage ELISA, soluble monoclonal ELISA, and colony PCR and sequencing. Antiproliferative and apoptotic effects of selected scFv antibodies on breast cancer cell lines were also evaluated by MTT and Annexin V/PI assays. The results of ELISA indicated specific reactions of the isolated scFvs against the IGF-IR peptide, and analyses of PCR product and sequencing confirmed the presence of full length VH and Vκ inserts. Treatment of MCF7 and SKBR3 cells with anti-IGF-IR scFv led to a significant growth inhibition. The results also showed that scFv treatment significantly augmented trastuzumab growth inhibitory effects on SKBR3 cells. The percentage of the apoptotic MCF7 and SKBR3 cells after 24-h treatment with scFv was 39 and 30.70 %, respectively. Twenty-four-hour treatment with scFv in combination with trastuzumab resulted in 44.75 % apoptosis of SKBR3 cells. Taken together, our results demonstrate that the targeting of IGF-IR by scFv can be an effective strategy in the treatment of breast cancer and provide further evidence for effectiveness of dual targeting of HER2 and IGF-IR in breast cancer therapy.

Invert biopanning: A novel method for efficient and rapid isolation of scFvs by phage display technology

Phage display is a prominent screening technique for development of novel high affinity antibodies against almost any antigen. However, removing false positive clones in screening process remains a challenge. The aim of this study was to develop an efficient and rapid method for isolation of high affinity scFvs by removing NSBs without losing rare specific clones. Therefore, a novel two rounds strategy called invert biopanning was developed for isolating high affinity scFvs against EGFRvIII antigen from human scFv library. The efficiency of invert biopanning method (procedure III) was analyzed by comparing with results of conventional biopanning methods (procedures I and II). According to the results of polyclonal ELISA, the second round of procedure III displayed highest binding affinity against EGFRvIII peptide accompanied by lowest NSB comparing to other two procedures. Several positive clones were identified among output phages of procedure III by monoclonal phage ELISA which displayed high affinity to EGFRvIII antigen. In conclusion, results of our study indicate that invert biopanning is an efficient method for avoiding NSBs and conservation of rare specific clones during screening of a scFv phage library. Novel anti EGFRvIII scFv isolated could be a promising candidate for potential use in treatment of EGFRvIII expressing cancers.

Targeting Leishmania major parasite with peptides derived from a combinatorial phage display library

Cutaneous leishmaniasis (CL) is a global problem caused by intracellular protozoan pathogens of the genus Leishmania for which there are no suitable vaccine or chemotherapy options. Thus, de novo identification of small molecules binding to the Leishmania parasites by direct screening is a promising and appropriate alternative strategy for the development of new drugs. In this study, we used a random linear hexapeptide library fused to the gene III protein of M13 filamentous bacteriophage to select binding peptides to metacyclic promastigotes from a highly virulent strain of Leishmania major (Zymodeme MON-25; MHOM/TN/94/GLC94). After four rounds of stringent selection and amplification, polyclonal and monoclonal phage-peptides directed against L. major metacyclic promastigotes were assessed by ELISA, and the optimal phage-peptides were grown individually and characterized for binding to L. major by monoclonal phage ELISA. The DNA of 42 phage-peptides clones was amplified by PCR, sequenced, and their amino acid sequences deduced. Six different peptide sequences were obtained with frequencies of occurrence ranging from 2.3% to 85.7%. The biological effect of the peptides was assessed in vitro on human monocytes infected with L. major metacyclic promastigotes, and in vivo on susceptible parasite-infected BALB/c mice. The development of cutaneous lesions in the right hind footpads of infected mice after 13 weeks post-infection showed a protection rate of 81.94% with the injected peptide P2. Moreover, Western blots revealed that the P2 peptide interacted with the major surface protease gp63, a protein of 63kDa molecular weight. Moreover, bioinformatics were used to predict the interaction between peptides and the major surface molecule of the L. major. The molecular docking showed that the P2 peptide has the minimum interaction energy and maximum shape complimentarity with the L. major gp63 active site. Our study demonstrated that the P2 peptide occurs at high frequency during the screening procedure, best inhibits L. major growth kinetics in vitro, and reduces cutaneous lesions in BALB/c mice, thus showing great promise in the development of new therapeutic molecules.

Development of protective agent against Hottentotta saulcyi venom using camelid single-domain antibody.

Hottentotta saulcyi, medically important scorpion species, causes some of harmful toxic exposure in Iran. Administrated, conventional antivenom-based immunotherapy is still limited and hardly meet ideal characteristic of effective treatment for scorpion envenomation. In this study we aimed to develop a neutralizing agent directed against scorpion venom based on VHH, variable domain of the Camelidae heavy chain antibody or Nanobody. This promising biomolecule is well-established as an advantageous tool for therapeutic purposes due to its small size, stability, monomeric performance and less immunogenicity. In this study, a large Nb library was constructed and phage displayed after successful camel immunization using H. saulcyi scorpion crude venom. After a series of biopanning rounds on Sephadex G50 purified venom fraction and screening by monoclonal phage ELISA, the best reactive Nb was retrieved and designated Nb12. The selected Nb was then expressed as soluble protein in Escherichia coli, purified and confirmed by SDS-PAGE analysis and western blotting. The lead candidate Nb12 bound scorpion venom with Kaff value of 5×10(7)M(-1). Nb12 was shown to be capable of neutralizing 2 LD50 of whole venom of scorpion toxin when injected in the ratio of the Nb/toxin of 1.4:1 into C57BL/6 mice. In challenge experiment, Nb succeeded to rescue all i.p. lethal dose injected mice even when administrated i.v., 20min after envenoming. These results with ease of production and superior neutralizing activity make Nb a suitable anti-toxin candidate for treatment of scorpion envenoming.

Production of Novel VHH Nanobody Inhibiting Angiogenesis by Targeting Binding Site of VEGF.

Vascular endothelial growth factor (VEGF) is one of the key players in angiogenesis and is considered as one of the major targets in cancer therapy. VEGF is secreted by the cancerous cells to form new vessels that carry oxygen and nutrients to the tumor, allowing it to grow beyond 1-2 mm. Cancerous cells spread using these veins and cause malignancy. Therefore, neutralization of VEGF could prevent tumor growth and malignancy, and nowadays, antibodies are widely used for such purpose. Among antibody fragments, nanobodies possess unique characteristics which make them appropriate tools for cancer therapy. In this study, the receptor-binding region of VEGF was used to produce a nanobody using phage display technology. A camel was immunized with the recombinant VEGF, and VHH fragments were amplified using nested PCR on lymphocyte complementary DNA (cDNA). The highest binding affinity was achieved after three rounds of panning. Twenty-four clones were tested by monoclonal phage ELISA, and the clone with the highest affinity (VA12) was selected for soluble expression of nanobody. VA12 was tested under various physicochemical conditions and showed considerable stability in extreme temperatures, pH, and various urea concentrations. Stability of VA12 under such conditions is considered as an advantage over the prevailing antibodies.

Immunoreaction of a recombinant nanobody from camelid single domain antibody fragment with Acinetobacter baumannii

Acinetobacter baumannii, an important nosocominal pathogen, causes various human infections like meningitis, bacteremia and pneumonia. The aim of this study was to produce nanobodies derived from camel heavy chain antibodies (HcAb) against a conserved region of the biofilm associated protein (Bap) of A. baumannii, by phage display technique. A camel was immunized with the purified recombinant protein expressed from the conserved region of Bap and polyclonal antibody production was confirmed by ELISA. After RNA extraction from peripheral lymphocytes, cDNA was prepared and a phagemid library was constructed. Phage particles encoding nanobodies were produced by infecting transformed cells with a M13K07 helper phage. A total of six panning rounds were performed to select high affinity clones. Screening of high affinity monoclonal nanobodies was performed using phage-ELISA. A clone with the highest absorption in monoclonal phage-ELISA was selected for soluble expression of the desired nanobody. This is the first report on the expression and production of nanobodies against Bap. Increasing trends of drug resistance have shifted the focus to the role of antibodies in diagnosis and treatment of human diseases. Similarities of the produced VHH to human VH, makes the role of this nanobody promising in immunotherapy.

Isolation of specific humanized anti-D-dimer scFv fragments from scFv phage libraries

Objective To isolate specific humanized anti-D-dimer scFv(single chain Fv) antibody from scFv phage libraries. Methods Isolate anti-D-dimer positive clones from Tomlinson I + J phage libraries by three rounds of panuing, then sequence monoclonal genes by bideoxy-mediated chain termination and express soluble scFv antibody; Pick out anti-D-dimer antibodies with high specificity and affinity by ELISA.Results After three rounds of selection from human scFv phage libraries Tomlinson I and J, 38 monclonal specific anti-D-dimer scFv fragments were selected. By polyclonal and monoclonal phage ELISA and gene sequencing, 20 different full-length monoclonal scFv phages were identified, the result of soluble scFv ELISA showed that 20 full-length monoclonal scFv were expressed smoothly. According to the result of soluble scFv ELISA, in 5 scFv antibodies with high value of A450 selected, 3 scFv antibody fragments showed high specific and affinity. Conclusion Antibody phage display was an effective, rapid method to isolate anti-D-dimer antibodies with high specificity and affinity. Key words: Screening; Anti-D-dimer antibody; Phage display

Phage ESCape: An emulsion-based approach for the selection of recombinant phage display antibodies

Antibody phage display technology is a well established method for selecting specific antibodies against desired targets. Although phage display is the most widely used method of generating synthetic antibodies, it is laborious to perform multiple selections with different antigens simultaneously using conventional manual methods. We have developed a novel approach to the identification and isolation of cells secreting phage encoding desirable antibodies that utilizes compartmentalization and Fluorescence Activated Cell Sorting (FACS). This method, termed Phage Emulsion, Secretion, and Capture (ESCape), allows us to individually query each phage against the antigen. Here, we demonstrate the ability of Phage ESCape to identify novel scFvs against a phosphopeptide epitope of the Her2 kinase from a phage display library containing approximately 108 synthetically diversified antibodies. Clones were analyzed by monoclonal phage ELISA against the Her2 phosphopeptide, and positive binders were identified as those showing a signal greater than 3-fold higher than the background signal against an irrelevant antigen. We isolated antibodies recognizing the phosphopeptide in a single round of selection by Phage ESCape, but the strength and specificity of the hits was substantially improved when the library was pre-enriched by a single round of biopanning. By minimizing the selection rounds required for phage display and using a FACS machine as a ‘colony picker’ equivalent, Phage ESCape has the potential to dramatically increase the throughput of in vitro screening methods.