Affinity for the cognate monoclonal antibody of synthetic peptides derived from selection by phage display. Role of sequences flanking thebinding motif

Humoral immune responses against gonadotropin releasing hormone elicited by immunization with phage-peptide constructs obtained via phage display

Phage display is based on genetic engineering of phage coat proteins resulting in fusion peptides displayed on the surface of phage particles. The technology is widely used for generation of phages with novel characteristics for numerous applications in biomedicine and far beyond. The focus of this study was on development of phage-peptide constructs that stimulate production of antibodies against gonadotropin releasing hormone (GnRH). Phage-peptide constructs that elicit production of neutralizing GnRH antibodies can be used for anti-fertility and anti-cancer applications. Phage-GnRH constructs were generated via selection from a phage display library using several types of GnRH antibodies as selection targets. Such phage constructs were characterized for sequence similarities to GnRH peptide and frequency of their occurrence in the selection rounds. Five of the constructs with suitable characteristics were tested in mice as a single dose 5×10(11) virions (vir) vaccine and were found to be able to stimulate production of GnRH-specific antibodies, but not to suppress testosterone (indirect indicator of GnRH antibody neutralizing properties). Next, one of the constructs was tested at a higher dose of 2×10(12) vir per mouse in combination with a poly(lactide-co-glycolide) (PLGA)-based adjuvant. This resulted in multifold increase in GnRH antibody production and significant reduction of serum testosterone, indicating that antibodies produced in response to the phage-GnRH immunization possess neutralizing properties. To achieve optimal immune responses for desired applications, phage-GnRH constructs can be modified with respect to flanking sequences of GnRH-like peptides displayed on phage. Anticipated therapeutic effects also might be attained using optimized phage doses, a combination of several constructs in a single treatment, or application of adjuvants and advanced phage delivery systems.

Use of Phage Display technology in development of canine visceral leishmaniasis vaccine using synthetic peptide trapped in sphingomyelin/cholesterol liposomes

Background

Leishmania parasites can cause visceral or cutaneous disease and are found in subtropical and tropical regions of the Old and New World. The pathology of the infection is determined by both host immune factors and species/strain differences of the parasite. Dogs represent the major reservoir of Leishmania infantum (syn. L. chagasi) and vaccines are considered the most cost-effective control tools for canine disease.

Methods

Selection of immunodominant peptides was performed by Phage Display to identify sequences recognized by L. infantum naturally infected animals. Sera from Leishmania infected animals were used in the biopanning to selection of specific peptides. Serum samples from T. cruzi infected and healthy animals were used as control. After selection, synthetic peptides were produced in membrane (spot-synthesis) in soluble form and blotting and ELISA were performed for validation of serum reactivity. Selected peptide was formulated with aluminum hydroxide and liposomes and immunization was performed in BALB/c mice. Protection was determined by qPCR after challenge infection with virulent L. infantum.

Results

We reported the selection of Peptide 5 through Phage Display technique and demonstrate its ability to promote a state of immunity against L. infantum infection in murine model after immunization using liposomes as vaccine carrier. Our results demonstrate that immunization with Peptide 5 when formulated with aluminum hydroxide and liposomes is immunogenic and elicited significant protection associated with the induction of mixed Th1/Th2 immune response against L. infantum infection.

Conclusion

Peptide 5 is a promising vaccine candidate and the findings obtained in the present study encourage canine trials to confirm the effectiveness of a vaccine against CVL.

Immunodiagnosis of canine visceral leishmaniasis using mimotope peptides selected from phage displayed combinatorial libraries

ELISA and RIFI are currently used for serodiagnosis of canine visceral leishmaniasis (CVL). The accuracy of these tests is controversial in endemic areas where canine infections by Trypanosoma cruzi may occur. We evaluated the usefulness of synthetic peptides that were selected through phage display technique in the serodiagnosis of CVL. Peptides were chosen based on their ability to bind to IgGs purified from infected dogs pooled sera. We selected three phage clones that reacted only with those IgGs. Peptides were synthesized, polymerized with glutaraldehyde, and used as antigens in ELISA assays. Each individual peptide or a mix of them was reactive with infected dogs serum. The assay was highly sensitive and specific when compared to soluble Leishmania antigen that showed cross-reactivity with anti-T. cruzi IgGs. Our results demonstrate that phage display technique is useful for selection of peptides that may represent valuable synthetic antigens for an improved serodiagnosis of CVL.

Immunodiagnosis of human neurocysticercosis using a synthetic peptide selected by phage-display

The usefulness of a synthetic peptide in the serodiagnosis of Taenia solium human neurocysticercosis (NC) has been evaluated. Phage-displayed peptides were screened with human antibodies to scolex protein antigen from cysticercus cellulosae (SPACc). One clone was found to interact specifically with anti-SPACc IgGs. The corresponding synthetic peptide was found to be recognized in ELISA by NC patient's sera. The study was carried out with sera from 28 confirmed NC patients, 13 control sera and 73 sera from patients suffering from other infectious diseases. A 93% sensibility and a 94.3% specificity was achieved. Figures of 89% and 31.4% of sensibility and specificity were obtained in a SPACc-based ELISA. Immunoblotting of SPACc with anti-peptide antibodies revealed a single band of approximately 45 kDa in 1D and four 45 kDa isoforms in 2D-gel electrophoresis. A strong and specific immunostaining in the fibers beneath the suckers, at the base of the rostellum, and in the tissue surrounding the scolex of cysticerci was observed by immunomicroscopy. Our results show that a peptide-based immunodiagnostic of neurocisticercosis can be envisioned.

An FcgammaRIIa-binding peptide that mimics the interaction between FcgammaRIIa and IgG

A disulphide-constrained peptide that binds to the low affinity Fc receptor, FcgammaRIIa (CD32) has been identified and its structure solved by NMR. Linear (7-mer and 12-mer) and disulphide-constrained (7-mer) phage display peptide libraries were panned on recombinant soluble FcgammaRIIa genetically fused to HSA (HSA-FcgammaRIIa). Peptides were isolated only from the constrained peptide library and these contained the consensus sequence, CWPGWxxC. Phage clones displaying variants of the peptide consensus sequence bound to FcgammaRIIa and the strongest binding clone C7C1 (CWPGWDLNC) competed with IgG for binding to FcgammaRIIa and was inhibited from binding to FcgammaRIIa by the FcgammaRIIa-blocking antibody, IV.3, suggesting that C7C1 and IgG share related binding sites on FcgammaRIIa. A synthetic disulphide-constrained peptide, pep-C7C1 bound to FcgammaRIIa by biosensor analysis, albeit with low affinity (KD approximately 100microM). It was significant that the FcgammaRIIa consensus peptide sequence contained a Proline (Pro3), which when substituted with alanine abrogated FcgammaRIIa binding, consistent with Pro3 contributing to receptor binding. Upon binding of IgG and IgE to their respective Fc receptors (FcgammaRs and FcepsilonRI) Pro329 in the Fc makes a critical interaction with two highly conserved Trp residues (Trp90 and Trp113) of the FcRs. The NMR structure of pep-C7C1 revealed a stabilizing type II beta-turn between Trp2 and Trp5, with Pro3 solvent exposed. Modelling of the pep-C7C1 structure in complex with FcgammaRIIa suggests that Pro3 of C7C1 binds to FcgammaRIIa by inserting between Trp90 and Trp113 of FcgammaRIIa thereby mimicking the molecular interaction made between FcgammaRIIa and IgG.

A probe for capture and Fe3+-induced conformational change of lactoferrin selected from phage displayed peptide libraries

Linear pentadecamer and cyclic hexamer peptide phage libraries were used to isolate phage clones with binding affinity toward lactoferrins purified from human and bovine milk. Phage clones with high specificity toward lactoferrin were selected with different binding strengths depending on the sequence of the peptide displayed by the phage. Phages coated to a microtiterplate were able to capture lactoferrin from crude milk samples without prior treatment. One of the selected sequences, EGKQRR, failed to bind to lactoferrin. In contrast, a branched tree-peptide bearing 4 EGKQRR sequences did bind to lactoferrin (Kd approximately 29 microM) and was also capable of inhibiting the binding of the phage to lactoferrin (IC(50) approximately 17 microM), indicating that avidity was important. Unexpectedly, the affinity of the phage for lactoferrin was influenced by the amount of bound Fe(3+), with a much lower affinity when lactoferrin was saturated with Fe(3+) as compared with the iron-depleted or partially saturated (natural) lactoferrin. As the phage does not bind to the Fe(3+)-binding site, the difference in binding affinity is due to differences in conformation of lactoferrin induced by Fe(3+). These results demonstrate that avidity or multipoint attachment and Fe(3+)-induced conformational changes play an important role in the binding of the selected phage to lactoferrin. Thus, we could demonstrate that, by the use of selected phage clones, we are able not only to detect lactoferrin, but also to capture lactoferrin from crude milk samples. Furthermore, the extent of phage binding provides additional information about the iron content and the concomitant conformation of lactoferrin.

Phage display for epitope determination: a paradigm for identifying receptor-ligand interactions

Antibodies that react with many different molecular species of protein and non-protein nature are widely studied in biology and have particular utilities, but the precise epitopes recognized are seldom well defined. The definition of epitopes by X-ray crystallography of the antigen-antibody complex, the gold standard procedure, has shown that most antibody epitopes are conformational and specified by interactions with topographic determinants on the surface of the antigenic molecule. Techniques available for the definition of such epitopes are limited. Phage display using either gene-specific libraries, or random peptide libraries, provides a powerful technique for an approach to epitope identification. The technique can identify amino acids on protein antigens that are critical for antibody binding and, further, the isolation of peptide motifs that are both structural and functional mimotopes of both protein and non-protein antigens. This review discusses techniques used to isolate such mimotopes, to confirm their specificity, and to characterize peptide epitopes. Moreover there are direct practical applications to deriving epitopes or mimotopes by sequence, notably the development of new diagnostic reagents, or therapeutic agonist or antagonist molecules. The techniques developed for mapping of antibody epitopes are applicable to probing the origins of autoimmune diseases and certain cancers by identifying "immunofootprints" of unknown initiating agents, as we discuss herein, and are directly applicable to examination of a wider range of receptor-ligand interactions.

A vascular endothelial growth factor high affinity receptor 1-specific peptide with antiangiogenic activity identified using a phage display peptide library

Vascular endothelial growth factor (VEGF) is known to play a predominant role in tumor angiogenesis and metastasis formation that is mediated by its interactions with two tyrosine kinase receptors, VEGFRI (Flt-1) and VEGFRII (KDR). Inhibition of VEGF-dependent events in tumor tissues is known to enhance apoptosis and to suppress tumor growth. A novel peptide, SP5.2, which selectively binds Flt-1 and inhibits a broad range of VEGF-mediated events, was identified using a phage-display library screening. The fluorescein-labeled SP5.2 specifically bound to VEGF-stimulated primary human cerebral endothelial cells (HCECs), whereas non-stimulated HCECs, as well as human neuroblastoma cells (ShyY) did not show any interaction with the peptide. SP5.2 prevented proliferation of cultured primary human umbilical vein endothelial cells induced by recombinant human VEGF165 with an IC50 of 5 microm. SP5.2 was also shown to antagonize VEGF- and PLGF-induced, but not basic fibroblast growth factor-induced proliferation of HCECs. In contrast to "scrambled" peptide, SP5.2 was also found to selectively inhibit VEGF-stimulated migration of HCECs. The in vitro analysis of antiangiogenic activity of SP5.2 using a capillary-like tube formation assay showed that VEGF-induced angiogenesis of HCECs grown on Matrigel was completely inhibited in the presence of 10 microm SP5.2. Further studies demonstrated that SP5.2 prevented VEGF-induced permeability increase in HCECs monolayers. To explore whether SP5.2 can be used as a targeting agent, chemical and recombinant conjugates of SP5.2 with reporter proteins (peroxidase and beta-galactosidase) were produced. The resulting products showed significant increases (200-fold for SP5.2-beta-gal and 400-fold for SP5.2-peroxidase) in binding affinity to recombinant Flt-1 compared with the original synthetic SP5.2, suggesting that conjugate with therapeutic activity in nanomolar range could potentially be developed based on SP5.2 structure.

Epitope selection from an uncensored peptide library displayed on avian leukosis virus

Phage display libraries have provided an extraordinarily versatile technology to facilitate the isolation of peptides, growth factors, single chain antibodies, and enzymes with desired binding specificities or enzymatic activities. The overall diversity of peptides in phage display libraries can be significantly limited by Escherichia coli protein folding and processing machinery, which result in sequence censorship. To achieve an optimal diversity of displayed eukaryotic peptides, the library should be produced in the endoplasmic reticulum of eukaryotic cells using a eukaryotic display platform. In the accompanying article, we presented experiments that demonstrate that polypeptides of various sizes could be efficiently displayed on the envelope glycoproteins of a eukaryotic virus, avian leukosis virus (ALV), and the displayed polypeptides could efficiently attach to cognate receptors without interfering with viral attachment and entry into susceptible cells. In this study, methods were developed to construct a model library of randomized eight amino acid peptides using the ALV eukaryotic display platform and screen the library for specific epitopes using immobilized antibodies. A virus library with approximately 2 x 10(6) different members was generated from a plasmid library of approximately 5 x 10(6) diversity. The sequences of the randomized 24 nucleotide/eight amino acid regions of representatives of the plasmid and virus libraries were analyzed. No significant sequence censorship was observed in producing the virus display library from the plasmid library. Different populations of peptide epitopes were selected from the virus library when different monoclonal antibodies were used as the target. The results of these two studies clearly demonstrate the potential of ALV as a eukaryotic platform for the display and selection of eukaryotic polypeptides libraries.

Peptide decoys selected by phage display block in vitro and in vivo activity of a human anti-FVIII inhibitor

Hemophilia A is a life-threatening, hemorrhagic, X-linked recessive disorder resulting in deficient factor VIII (FVIII) activity. After the infusion of therapeutic FVIII, 25% of patients develop anti-FVIII antibodies that inhibit FVIII procoagulant activity, thus precluding further administration of FVIII. Here we report a novel approach aimed at neutralizing the activity of FVIII inhibitors by peptide epitope surrogates. To illustrate our concept, we chose the human anti-FVIII monoclonal antibody, Bo2C11, as a representative of anti-FVIII antibodies and a phage-displayed peptide library approach to obtain surrogate peptides. We selected a series of constrained dodecapeptides with the core sequence W-NR, which specifically interacts with the combining site of Bo2C11. The peptides mimic the epitope recognized by Bo2C11 and are able to inhibit specifically and in a dose-dependent manner the binding of Bo2C11 to FVIII. Peptide 107, in particular, neutralized the activity of Bo2C11 in vitro and restored normal hemostasis in hemophilic mice. Thus, the use of peptide decoys may be a promising new approach for the neutralization of pathologic antibodies.

Functional fine-mapping and molecular modeling of a conserved loop epitope of the measles virus hemagglutinin protein

Neutralizing and protective monoclonal antibodies (mAbs) were used to fine-map the highly conserved hemagglutinin noose epitope (H379-410, HNE) of the measles virus. Short peptides mimicking this epitope were previously shown to induce virus-neutralizing antibodies [El Kasmi et al. (2000) J. Gen. Virol.81, 729-735]. The epitope contains three cysteine residues, two of which (Cys386 and Cys394) form a disulfide bridge critical for antibody binding. Substitution and truncation analogues revealed four residues critical for binding (Lys387, Gly388, Gln391 and Glu395) and suggested the binding motif X7C[KR]GX[AINQ]QX2CEX5 for three distinct protective mAbs. This motif was found in more than 90% of the wild-type viruses. An independent molecular model of the core epitope predicted an amphiphilic loop displaying a remarkably stable and rigid loop conformation. The three hydrophilic contact residues Lys387, Gln391 and Glu395 pointed on the virus towards the solvent-exposed side of the planar loop and the permissive hydrophobic residues Ile390, Ala392 and Leu393 towards the solvent-hidden side of the loop, precluding antibody binding. The high affinity (Kd = 7.60 nm) of the mAb BH216 for the peptide suggests a high structural resemblance of the peptide with the natural epitope and indicates that most interactions with the protein are also contributed by the peptide. Improved peptides designed on the basis of these findings induced sera that crossreacted with the native measles virus hemagglutinin protein, providing important information about a lead structure for the design of more stable antigens of a synthetic or recombinant subunit vaccine.

Localization of the discontinuous immunodominant region recognized by human anti-thyroperoxidase autoantibodies in autoimmune thyroid diseases

The discontinuous immunodominant region (IDR) recognized by autoantibodies directed against the thyroperoxidase (TPO) molecule, a major autoantigen in autoimmune thyroid diseases, has not yet been completely localized. By using peptide phage-displayed technology, we identified three critical motifs, LXPEXD, QSYP, and EX(E/D)PPV, within selected mimotopes which interacted with the human recombinant anti-TPO autoantibody (aAb) T13, derived from an antibody phage-displayed library obtained from thyroid-infiltrating TPO-selected B cells of Graves' disease patients. Mimotope sequence alignment on the TPO molecule, together with the binding analysis of the T13 aAb on TPO mutants expressed by Chinese hamster ovary cells, demonstrated that regions 353-363, 377-386, and 713-720 from the myeloperoxidase-like domain and region 766-775 from the complement control protein-like domain are a part of the IDR recognized by the recombinant aAb T13. Furthermore, we demonstrated that these regions were involved in the binding to TPO of sera containing TPO-specific autoantibodies from patients suffering from Hashimoto's and Graves' autoimmune diseases. Identification of the IDR could lead to improved diagnosis of thyroid autoimmune diseases by engineering "mini-TPO" as a target autoantigen or designing therapeutic peptides able to block undesired autoimmune responses.

Peptides derived from the two regulatory domains of p53 are recognized by two p53-activating antibodies

The C-terminus of the transcription factor p53 seems to play an important role by controlling the specific DNA-binding activity, which is directly associated with sensing damaged DNA. Another region located in the N-terminus of the protein has also been shown to regulate the DNA-binding activity of the protein. This activity can be promoted by peptides derived from these two negative regulatory regions or by binding of antibodies directed against the C-terminus of the p53 protein. Using both phage display peptide and multiple peptide synthesis technologies, we demonstrated that mAbs HR231 and Pab421, two p53-activating antibodies, recognize peptides derived from the C-terminus of p53, as previously described, but also peptides from the N-terminus of the protein, suggesting that these peptides are part of a conformational epitope. Furthermore, the sequences of these peptides are located in the two negative regulatory regions identified on the p53 protein, which is consistent with the biological activity of mAbs HR231 and Pab421.

Low molecular weight peptides restore the procoagulant activity of factor VIII in the presence of the potent inhibitor antibody ESH8

Following repeated administration of factor VIII (FVIII), a significant number of hemophilia A patients develop antibodies (Abs), inhibiting the procoagulant activity of infused FVIII. We have designed an approach based on the blocking of the deleterious activity of these Abs by peptide decoys mimicking the anti-FVIII Ab epitopes. Here, the well characterized inhibitory monoclonal Ab ESH8 served as a model. Several phage peptide libraries were screened for specific binding to ESH8. Seven constrained dodecapeptide sequences were obtained. Six sequences carried the consensus motif, hydrophobic-(Y/F)GKTXL. This motif showed a certain similarity with the (2231)QVDFQKTMKV(2240) sequence of the C(2) domain. In the seventh sequence, YCNPSIGDKNCR, the residues GDKN are similar to the sequence (2267)DGHQ(2270). Upon inspection of the C(2) domain crystallographic structure, the two stretches QVDFQKTMKV and DGHQ appeared close together in space and might constitute a discontinuous epitope. Corresponding synthetic peptides were able to inhibit the binding of ESH8 to FVIII in a specific and dose-dependent manner. Moreover, the ability of the selected peptides to neutralize the inhibitory activity of ESH8 was demonstrated in functional tests as well as in vivo in a murine model of hemophilia A. This study demonstrates the potential of this approach to neutralize the activity of potent inhibitory Abs.

Comparative properties of two peptide-antibody interactions as deduced from epitope delineation

The linear epitope recognized by three closely related antibodies specific for the E6 oncoprotein of papillomavirus type 16 was delineated by phage display, spot peptide synthesis on cellulose membranes, and kinetic measurements with antigenic variants using a BIACORE. The same approaches, recently applied to an antibody specific for tobacco mosaic virus protein, led to the clear-cut delineation of a functional epitope comprising four key positions with well defined physico-chemical properties. In contrast, the E6 system is characterized by a non-essential contribution to binding of various factors, so that combinations of alternative properties are compatible with measurable binding activity.

Survey of the year 2000 commercial optical biosensor literature

We have compiled a comprehensive list of the articles published in the year 2000 that describe work employing commercial optical biosensors. Selected reviews of interest for the general biosensor user are highlighted. Emerging applications in areas of drug discovery, clinical support, food and environment monitoring, and cell membrane biology are emphasized. In addition, the experimental design and data processing steps necessary to achieve high-quality biosensor data are described and examples of well-performed kinetic analysis are provided.

Anti-peptide antibody blocks peptide binding to MHC class I molecules in the endoplasmic reticulum

The finding that MHC class I molecules are physically associated with the TAP transporter has suggested that peptides may be directly transported into the binding groove of the class I molecules rather than into the lumen of the endoplasmic reticulum (ER) where they subsequently would encounter class I molecules by diffusion. Such a mechanism would protect peptides from peptidases in the ER and/or escaping back into the cytoplasm. However, we find that an anti-peptide Ab that is cotranslationally transported into the ER prevents TAP-transported peptides from being presented on class I molecules. The Ab only blocks the binding of its cognate peptide (SIINFEKL) but not other peptides (KVVRFKDL, ASNENMETM, and FAPGNYPAL). Therefore, most TAP-transported peptides must diffuse through the lumen of the ER before binding stably to MHC class I molecules.

Delineation of a linear epitope by multiple peptide synthesis and phage display

Two different approaches, the phage display technique and the Spot peptide synthesis on cellulose membranes, were used to identify sequences recognized by Fab 57P, specific for tobacco mosaic virus protein (TMVP), and define the preferred chemical composition of a functional epitope. Kinetic measurements of the interaction between peptide variants and the antibody fragment were used to further refine the molecular basis of binding activity. Our results show that the functional epitope of Fab 57P requires precise physico-chemical properties at a limited number of positions, and that residues flanking these key residues can influence binding affinity. The phage display and Spot synthesis methods allowed the straightforward localization of the binding region and the identification of residues that are essential for recognition. However, these methods yielded slightly different views of accessory factors that are able to influence antibody binding. The influence on binding activity of these factors can only be assessed through quantitative affinity measurements.