Peptide mimotopes as surrogate antigens of carbohydrates in vaccine discovery

Peptide mimotopes to emulate carbohydrates

Glycoconjugates on animal cell surfaces are involved in numerous biological functions and diseases, especially the adhesion/metastasis of cancer cells, infection, and the onset of glycan-related diseases. In addition to glycoantigen detection, the regulation of glycan (carbohydrate)-protein interactions is needed to develop therapeutic strategies for glycan-related diseases. Preparation of a diverse range of glycan derivatives requires a massive effort, but the preparation and identification of alternative glycan-mimetic peptide mimotopes may provide a solution to this issue. Peptide mimotopes are recognized by glycan-binding proteins, such as lectins, enzymes, and antibodies, alternative to glycan ligands. Phage-display technology is the first choice in the selection of "glycan (carbohydrate)-mimetic peptide mimotopes" from a large repertoire of library sequences. This tutorial review describes the advantages of peptide mimotopes in comparison to glycan ligands, as well as their structural and functional mimicry. The detailed library design is followed by a description of the strategy used to improve affinity, and finally, an outline of the vaccine application of glycan-mimetic peptides is provided.

In-vitro Detection of Phytopathogenic Fungal Cell Wall by Polyclonal Sera Raised Against Trimethyl Chitosan Nanoparticles

Purpose

The objective of this research was to generate a tool for the first-line detection of fungal infection in plants. Chitin is one of the unique fungal cell wall polysaccharide which is naturally deacetylated to chitosan upon infection. It is said to be involved in the fungal cell wall modulation and plant-pathogen communication. Therefore, detection of chitosan could be potentially helpful in the detection of fungal contamination.

Methods

Five different phytopathogenic fungi strains were used for the study. Polyclonal sera were raised in the mice against Trimethylchitosan nanoparticles to generate an enhanced humoral immune response and generate a rich and heterogeneous repertoire of antibodies. The binding affinity of the sera with fungal cell wall was analyzed by ELISA, Langmuir isotherm, confocal microscopy and ITC (Isothermal Calorimetry).

Results

The raised polyclonal sera could detect chitosan in the fungal cell wall, as analyzed with the different techniques. However, the detection specificity varied among the strains in proportion to the chitin content of their cell wall. Fusarium oxysporum was detected with the highest affinity while Trichoderma reesei was detected with the least affinity by ELISA. Adsorption isotherm, as well as ITC, revealed the specific and high binding capacity. Confocal microscopy also confirmed the detection of all strains used in the study.

Conclusion

This novel technique employing TMC nanoparticulate system could be potentially used as a source to raise sera against chitosan in an inexpensive and less laborious manner. Rapid detection of fungal contamination by the polyclonal antibodies could help in devising a quick solution. The polyclonal sera are expected to detect a span of epitopes and provide precise detection. The detection system could be advanced for future applications such as food quality control, crop protection, and human fungal infection detection and treatment.

Glycointeractions in bacterial pathogenesis

Many important interactions between bacterial pathogens and their hosts are highly specific binding events that involve host or pathogen carbohydrate structures (glycans). Glycan interactions can mediate adhesion, invasion and immune evasion and can act as receptors for toxins. Several bacterial pathogens can also enzymatically alter host glycans to reveal binding targets, degrade the host cell glycans or alter the function of host glycoproteins. In recent years, high-throughput screening technologies, such as lectin, glycan and mucin microarrays, have transformed the field by identifying new bacterial-host glycointeractions, which are crucial for colonization, persistence and disease. In this Review, we discuss interactions involving both host and bacterial glycans that have a role in bacterial pathogenesis. We also highlight recent technological advances that have illuminated the glycoscience of microbial pathogenesis.

Identification of Peptide Mimotope Ligands for Natalizumab

Mimotope peptides selected from combinatorial peptide libraries can be used as capture reagents for immunoassay detection of therapeutic monoclonal antibodies (mAbs). We report the use of phage display libraries to identify peptide ligands (Veritopes^TM) that bind natalizumab, a therapeutic mAb indicated for use in multiple sclerosis. PKNPSKF is identified as a novel natalizumab-binding motif, and peptides containing this motif demonstrated utility as capture reagents in enzyme-linked immunosorbent assays (ELISAs). A peptide containing the identified motif was shown to be competitive with the natural ligand (α4-integrin) and a neutralizing anti-idiotype antibody for natalizumab binding, indicating that Veritopes^TM act as surrogate ligands that bind the antigen binding site of natalizumab. Affinity maturation further confirmed the motif sequence and yielded peptides with greater apparent affinity by ELISA. Veritopes^TM are promising assay reagents for therapeutic drug level monitoring.

Identification of Peptide Mimics of a Glycan Epitope on the Surface of Parasitic Nematode Larvae

Phage display was used to identify peptide mimics of an immunologically protective nematode glycan (CarLA) by screening a constrained C7C peptide library for ligands that bound to an anti-CarLA mAb (PAB1). Characterisation of these peptide mimotopes revealed functional similarities with an epitope that is defined by PAB1. Mimotope vaccinations of mice with three selected individual phage clones facilitated the induction of antibody responses that recognised the purified, native CarLA molecule which was obtained from Trichostrongylus colubriformis. Furthermore, these mimotopes are specifically recognised by antibodies in the saliva of animals that were immune to natural polygeneric nematode challenge. This shows that antibodies to the PAB1 epitope form part of the mucosal polyclonal anti-CarLA antibody response of nematode immune host animals. This demonstrates that the selected peptide mimotopes are of biological relevance. These peptides are the first to mimic the PAB1 epitope of CarLA, a defined larval glycan epitope which is conserved between many nematode species.

Antibodies: At The Nexus of Antigens and Cancer Vaccines

This review describes the development of monoclonal antibodies and the inception of their use in cancer therapy, their impact on defining cancer biomarkers, and their structural utility in new cancer vaccine development.

Carbohydrate-mimetic peptides for pan anti-tumor responses

Molecular mimicry is fundamental to biology and transcends to many disciplines ranging from immune pathology to drug design. Structural characterization of molecular partners has provided insight into the origins and relative importance of complementarity in mimicry. Chemical complementarity is easy to understand; amino acid sequence similarity between peptides, for example, can lead to cross-reactivity triggering similar reactivity from their cognate receptors. However, conformational complementarity is difficult to decipher. Molecular mimicry of carbohydrates by peptides is often considered one of those. Extensive studies of innate and adaptive immune responses suggests the existence of carbohydrate mimicry, but the structural basis for this mimicry yields confounding details; peptides mimicking carbohydrates in some cases fail to exhibit both chemical and conformational mimicry. Deconvolution of these two types of complementarity in mimicry and its relationship to biological function can nevertheless lead to new therapeutics. Here, we discuss our experience examining the immunological aspects and implications of carbohydrate-peptide mimicry. Emphasis is placed on the rationale, the lessons learned from the methodologies to identify mimics, a perspective on the limitations of structural analysis, the biological consequences of mimicking tumor-associated carbohydrate antigens, and the notion of reverse engineering to develop carbohydrate-mimetic peptides in vaccine design strategies to induce responses to glycan antigens expressed on cancer cells.

Recent advances toward the development of inhibitors to attenuate tumor metastasis via the interruption of lectin-ligand interactions

Aberrant glycosylation is a well-recognized phenomenon that occurs on the surface of tumor cells, and the overexpression of a number of ligands (such as TF, sialyl Tn, and sialyl Lewis X) has been correlated to a worse prognosis for the patient. These unique carbohydrate structures play an integral role in cell-cell communication and have also been associated with more metastatic cancer phenotypes, which can result from binding to lectins present on cell surfaces. The most well studied metastasis-associated lectins are the galectins and selectins, which have been correlated to adhesion, neoangiogenesis, and immune-cell evasion processes. In order to slow the rate of metastatic lesion formation, a number of approaches have been successfully developed which involve interfering with the tumor lectin-substrate binding event. Through the generation of inhibitors, or by attenuating lectin and/or carbohydrate expression, promising results have been observed both in vitro and in vivo. This article briefly summarizes the involvement of lectins in the metastatic process and also describes different approaches used to prevent these undesirable carbohydrate-lectin binding events, which should ultimately lead to improvement in current cancer therapies.

Identification of a Peptide Mimic of Bioactive Gibberellins with Affinity to GA 2-Oxidase

Previously we reported the first example of peptide mimics of a small hydrophobic molecule, a phytohormone gibberellin. The second peptide mimic of gibberellin has been identified from random peptide libraries by its affinity to a type of catalyzing enzyme of gibberellins, which specifically recognizes bioactive gibberellins. These results suggest that even hydrophobic compounds can be mimicked by peptides.

Tumor-Associated Glycans and Immune Surveillance

Changes in cell surface glycosylation are a hallmark of the transition from normal to inflamed and neoplastic tissue. Tumor-associated carbohydrate antigens (TACAs) challenge our understanding of immune tolerance, while functioning as immune targets that bridge innate immune surveillance and adaptive antitumor immunity in clinical applications. T-cells, being a part of the adaptive immune response, are the most popular component of the immune system considered for targeting tumor cells. However, for TACAs, T-cells take a back seat to antibodies and natural killer cells as first-line innate defense mechanisms. Here, we briefly highlight the rationale associated with the relative importance of the immune surveillance machinery that might be applicable for developing therapeutics.

Development of a lipopolysaccharide-targeted peptide mimic vaccine against Q fever

Coxiella burnetii is a Gram-negative bacterium that causes acute and chronic Q fever in humans. Creation of a safe and effective new generation vaccine to prevent Q fever remains an important public health goal. Previous studies suggested that Ab-mediated immunity to C. burnetii phase I LPS (PI-LPS) is protective. To identify the potential peptides that can mimic the protective epitopes on PI-LPS, a PI-LPS-specific mAb 1E4 was generated, characterized, and used to screen a phage display library. Interestingly, our results indicate that 1E4 was able to inhibit C. burnetii infection in vivo, suggesting that 1E4 is a protective mAb. After three rounds of biopanning by 1E4 from the phage display library, a mimetic peptide, m1E41920, was identified, chemically synthesized, and conjugated to keyhole limpet hemocyanin (KLH) for examining its immunogenicity. The results indicate that the synthetic peptide m1E41920 was able to inhibit the binding of 1E4 to PI Ag, suggesting m1E41920 shares the same binding site of 1E4 with the epitopes of PI Ag. In addition, m1E41920-KLH elicited a specific IgG response to PI Ag, and immune sera from m1E41920-KLH-immunized mice was able to inhibit C. burnetii infection in vivo, suggesting that m1E41920 may specifically mimic the protective epitope of PI-LPS. Furthermore, m1E41920-KLH was able to confer significant protection against C. burnetii challenge. Thus, m1E41920-KLH is a protective Ag and may be useful for developing a safe and effective vaccine against Q fever. This study demonstrates the feasibility of developing a peptide mimic vaccine against Q fever.

Peptide mimotopes of malondialdehyde epitopes for clinical applications in cardiovascular disease

Autoantibodies specific for malondialdehyde-modified LDL (MDA-LDL) represent potential biomarkers to predict cardiovascular risk. However, MDA-LDL is a high variability antigen with limited reproducibility. To identify peptide mimotopes of MDA-LDL, phage display libraries were screened with the MDA-LDL-specific IgM monoclonal Ab LRO4, and the specificity and antigenic properties of MDA mimotopes were assessed in vitro and in vivo. We identified one 12-mer linear (P1) and one 7-mer cyclic (P2) peptide carrying a consensus sequence, which bound specifically to murine and human anti-MDA monoclonal Abs. Furthermore, MDA mimotopes were found to mimic MDA epitopes on the surface of apoptotic cells. Immunization of mice with P2 resulted in the induction of MDA-LDL-specific Abs, which strongly immunostained human atherosclerotic lesions. We detected IgG and IgM autoAbs to both MDA mimotopes in sera of healthy subjects and patients with myocardial infarction and stable angina pectoris undergoing percutaneous coronary intervention, and the titers of autoAbs correlated significantly with respective Ab titers against MDA-LDL. In conclusion, we identified specific peptides that are immunological mimotopes of MDA. These mimotopes can serve as standardized and reproducible antigens that will be useful for diagnostic and therapeutic applications in cardiovascular disease.

Synapsin I is an oligomannose-carrying glycoprotein, acts as an oligomannose-binding lectin, and promotes neurite outgrowth and neuronal survival when released via glia-derived exosomes

Oligomannosidic glycans play important roles in nervous system development and function. By performing a phage display screening with oligomannose-specific antibodies, we identified an oligomannose-mimicking peptide that was functionally active in modulating neurite outgrowth and neuron-astrocyte adhesion. Using the oligomannose-mimicking peptide in crosslinking experiments, synapsin I was identified as a novel oligomannose-binding protein in mouse brain. Further analyses not only verified that synapsin I is an oligomannose-binding lectin, but also indicated that it is a glycoprotein carrying oligomannose and Lewis(x). We also found that synapsin I is expressed in glia-enriched cultures and is released from glial cells via exosomes. Incubation of glial-derived exosomes in the presence of high KCl concentrations or subjecting glial cell cultures to either oxygen/glucose deprivation or hydrogen peroxide resulted in release of synapsin I from exosomes. Application of synapsin I promoted neurite outgrowth from hippocampal neurons and increased survival of cortical neurons upon hydrogen peroxide treatment or oxygen/glucose deprivation. Coculture experiments using wild-type hippocampal neurons and wild-type or synapsin-deficient glial cells showed enhanced neurite outgrowth when synapsin was expressed by glial cells. Synapsin-induced neurite outgrowth was dependent on oligomannose on synapsin I and the neural cell adhesion molecule NCAM at the neuronal cell surface. The data indicate that, under conditions of high neuronal activity and/or oxidative stress, synapsin can be released from glial-derived exosomes and promotes neurite outgrowth and neuronal survival by modulating the interactions between glia and neurons.

Enhancement of the immunogenicity of synthetic carbohydrate vaccines by chemical modifications of STn antigen

The abnormal glycans expressed on the surface of tumor cells, known as tumor-associated carbohydrate antigens, increase the chance to develop carbohydrate-based anticancer vaccines. However, carbohydrate antigens pose certain difficulties, and the major drawback is their weak immunogenicity. To tackle this problem, numerous structurally modified STn antigens were designed and synthesized in this work. These synthetic antigens were screened in vitro by using competitive ELISA method, and the antigens with positive response were conjugated to the protein carrier for vaccination. The vaccination results on mice showed that some fluorine-containing modifications on the STn antigen can significantly increase the anti-STn IgG titers and improve the ratios of anti-STn IgG/IgM. The antisera can recognize the tumor cells expressing the native STn antigen.

The discovery of small-molecule mimicking peptides through phage display

Using peptides to achieve the functional and structural mimicry of small-molecules, especially those with biological activity or clear biotechnological applications, has great potential in overcoming difficulties associated with synthesis, or unfavorable physical properties. Combinatorial techniques like phage display can aid in the discovery of these peptides even if their mechanism of mimicry is not rationally obvious.The major focus of this field has been limited to developing biotin and sugar mimetics. However, the full "mimicry" of these peptides has not yet been fully established as some bind to the target with a different mechanism than that of the natural ligand and some do not share all of the natural ligand's binding partners. In this article, mimicry of small-molecules by phage display-discovered peptides is reviewed and their potential in biochemical and medical applications is analyzed.

The modulation of adaptive immune responses by bacterial zwitterionic polysaccharides

The detection of pathogen-derived molecules as foreign particles by adaptive immune cells triggers T and B lymphocytes to mount protective cellular and humoral responses, respectively. Recent immunological advances elucidated that proteins and some lipids are the principle biological molecules that induce protective T cell responses during microbial infections. Polysaccharides are important components of microbial pathogens and many vaccines. However, research concerning the activation of the adaptive immune system by polysaccharides gained interest only recently. Traditionally, polysaccharides were considered to be T cell-independent antigens that did not directly activate T cells or induce protective immune responses. Here, we review several recent advances in “carbohydrate immunobiology”. A group of bacterial polysaccharides that are known as “zwitterionic polysaccharides (ZPSs)” were recently identified as potent immune modulators. The immunomodulatory effect of ZPSs required antigen processing and presentation by antigen presenting cells, the activation of CD4 T cells and subpopulations of CD8 T cells and the modulation of host cytokine responses. In this review, we also discuss the potential use of these unique immunomodulatory ZPSs in new vaccination strategies against chronic inflammatory conditions, autoimmunity, infectious diseases, allergies and asthmatic conditions.

Vaccination with peptide mimotopes produces antibodies recognizing bacterial capsular polysaccharides

A phage display peptide library was screened using a panel of antibodies to the capsular polysaccharides of Streptococcus agalactiae and Neisseria meningitidis. Mimotopes NPDHPRVPTFMA (2-8), LIPFHKHPHHRG (3-2) and EQEIFTNITDRV (G3) showing the highest binding capacity and strongest ELISA reaction were selected for immunization experiments. These mimotopes were either synthesised as oligodeoxynucleotides for DNA immunization or MAP (multiple antigen peptide) for peptide immunization. Mimotope-DNA vaccination, particularly for G3, induced antibodies recognizing a number of target bacteria. This response was seen after the second boost injection and was significantly enhanced by the 3rd boost injection with a Th1-associated profile, which was dominated by IgG2a, followed by IgG1. Mimotope-MAP immunization also produced strong humoral immune responses to the bacteria. Antibodies from G3 DNA immunization reacted with the surface molecules of S. agalactiae, N. meningitidis and Escherichia coli K5 shown by indirect immunofluorescence staining, indicating a possible localization to the bacterial capsule. Antibodies produced both from DNA/MAP immunization reacted with purified bacterial capsular polysaccharides by ELISA and were of high avidity. We have further characterized peptide G3 by a 'tiling path' study to examine the effect of changing individual residues in the peptide in raising antibodies, which showed that the EIFTN motif in G3 was important in generating antibodies to several capsulated bacteria. We conclude that mimotope immunization with DNA or MAP potentially induces strong antibody responses against encapsulated bacteria. It is suggested that the antibody targets are polysaccharides, and these antibodies may cross react at least among closely related species of bacteria.

Bridging innate and adaptive antitumor immunity targeting glycans

Effective immunotherapy for cancer depends on cellular responses to tumor antigens. The role of major histocompatibility complex (MHC) in T-cell recognition and T-cell receptor repertoire selection has become a central tenet in immunology. Structurally, this does not contradict earlier findings that T-cells can differentiate between small hapten structures like simple glycans. Understanding T-cell recognition of antigens as defined genetically by MHC and combinatorially by T cell receptors led to the “altered self” hypothesis. This notion reflects a more fundamental principle underlying immune surveillance and integrating evolutionarily and mechanistically diverse elements of the immune system. Danger associated molecular patterns, including those generated by glycan remodeling, represent an instance of altered self. A prominent example is the modification of the tumor-associated antigen MUC1. Similar examples emphasize glycan reactivity patterns of antigen receptors as a phenomenon bridging innate and adaptive but also humoral and cellular immunity and providing templates for immunotherapies.

Development, characterization, and immunotherapeutic use of peptide mimics of the Thomsen-Friedenreich carbohydrate antigen

The tumor-associated carbohydrate Thomsen-Friedenreich antigen (TF-Ag; Galbeta1-3GalNAcalpha-O-Ser/Thr) is overexpressed on the cell surface of several types of tumor cells, contributing to cancer cell adhesion and metastasis to sites containing TF-Ag-binding lectins. A highly specific immunoglobulin G(3) monoclonal antibody (Ab) developed to TF-Ag (JAA-F11) impedes TF-Ag binding to vascular endothelium, blocking a primary metastatic step and providing a survival advantage. In addition, in patients, even low levels of antibodies to TF-Ag seem to improve prognosis; thus, it is expected that vaccines generating antibodies toward TF-Ag would be clinically valuable. Unfortunately, vaccinations with protein conjugates of carbohydrate tumor-associated Ags have induced clinically inadequate immune responses. However, immunization using peptides that mimic carbohydrate Ags such as Lewis has resulted in both Ab and T-cell responses. Here, we tested the hypothesis that vaccinations with unique TF-Ag peptide mimics may generate immune responses to TF-Ag epitopes on tumor cells, useful for active immunotherapy against relevant cancers. Peptide mimics of TF-Ag were selected by phage display biopanning using JAA-F11 and rabbit anti-TF-Ag Ab and were analyzed in vitro to confirm TF-Ag peptide mimicry. In vitro, TF-Ag peptide mimics bound to TF-Ag-specific peanut agglutinin and blocked TF-Ag-mediated rolling and stable adhesion of cancer cells to vascular endothelium. In vivo, the immunization with TF-Ag-mimicking multiple antigenic peptides induced TF-Ag-reactive Ab production. We propose that this novel active immunotherapy approach could decrease tumor burden in cancer patients by specifically targeting TF-Ag-positive cancer cells and blocking metastasis.

Peptides mimicking GD2 ganglioside elicit cellular, humoral and tumor-protective immune responses in mice

INTRODUCTION

Because of its restricted distribution in normal tissues and its high expression on tumors of neuroectodermal origin, GD2 ganglioside is an excellent target for active specific immunotherapy. However, GD2 usually elicits low-titered IgM and no IgG or cellular immune responses, limiting its usefulness as a vaccine for cancer patients. We have previously shown that anti-idiotypic monoclonal antibody mimics of GD2 can induce antigen-specific humoral and cellular immunity in mice, but inhibition of tumor growth by the mimics could not be detected.

METHODS AND RESULTS

Here, we isolated two peptides from phage display peptide libraries by panning with GD2-specific mAb ME361. The peptides inhibited binding of the mAb to GD2. When coupled to keyhole limpet hemocyanin (KLH) or presented as multiantigenic peptides in QS21 adjuvant, the peptides induced in mice antibodies binding specifically to GD2 and delayed-type hypersensitive lymphocytes reactive specifically with GD2-positive D142.34 mouse melanoma cells. Induction of delayed-type hypersensitivity (DTH) reaction was dependent on CD4-positive lymphocytes. The immunity elicited by the peptides significantly inhibited growth of GD2-positive melanoma cells in mice.

CONCLUSION

Our study suggests that immunization with peptides mimicking GD2 ganglioside inhibits tumor growth through antibody and/or CD4-positive T cell-mediated mechanisms. Cytolytic T lymphocytes most likely do not play a role. Our results provide the basis for structural analysis of carbohydrate mimicry by peptides.

Immunotherapy of hepatocellular carcinoma with a vaccine based on xenogeneic homologous alpha fetoprotein in mice

alpha-Fetoprotein (AFP) is a diagnostic marker for the presence of hepatocellular carcinoma, and a potential target for immunotherapy. Unfortunately, the immunity to AFP is presumably difficult to elicit because of immune tolerance acquired during the development of immune system. In the present study, we used AFP as a model antigen to explore the feasibility of the immunotherapy of AFP-positive liver cancer by the breaking of immune tolerance against AFP in a cross-reaction between the xenogeneic homologues and self molecules. Recombinant rat AFP was prepared as a vaccine, and mouse AFP was prepared as a control. Immunized with rat AFP was effective at protective and therapeutic antitumor immunity in hepatocellular carcinoma model in mice. Both humoral and cellular immune responses may be responsible for the antitumor activity against AFP-positive tumor cells, and no marked side effects were observed in the immunized mice. Thus, our study may provide an effective vaccine strategy for the treatment of AFP-positive hepatocellular carcinoma, and may be of importance to further exploration of the breaking of immune tolerance to self molecules.

Glycopeptide dendrimers, part III: a review. Use of glycopeptide dendrimers in immunotherapy and diagnosis of cancer and viral diseases

Glycopeptide dendrimers containing different types of tumor associated-carbohydrate antigens (T(N), TF, sialyl-T(N), sialyl-TF, sialyl-Le(x), sialyl-Le(a) etc.) were used in diagnosis and therapy of different sorts of cancer. These dendrimeric structures with incorporated T-cell epitopes and adjuvants can be used as antitumor vaccines. Best results were obtained with multiantigenic vaccines, containing, e.g. five or six different TAAs. The topic of TAAs and their dendrimeric forms at molecular level are reviewed, including structure, syntheses, and biological activities. Use of glycopeptide dendrimers as antiviral vaccines against HIV and influenza is also described. Their syntheses, physico-chemical properties, and biological activities are given with many examples.

Immunological evidence for functional rather than structural mimicry by a Shigella flexneri Y polysaccharide-mimetic peptide

An approach to vaccine design is the use of molecules that mimic the immunogenic element of interest. In this context, the interaction of MDWNMHAA, a peptide mimic of the Shigella flexneri Y O polysaccharide (PS), with an anti-carbohydrate monoclonal antibody, as studied previously by X-ray crystallography, suggested the presence of functional rather than structural mimicry and a bound peptide conformation that was not represented significantly in the free-ligand ensemble. The antibody response elicited by an MDWNMHAA-carrier protein (tetanus toxoid [TT]) conjugate has now been investigated in BALB/c mice. The mice were immunized following a homologous prime/boost strategy using MDWNMHAA-TT as the immunogen. The mice showed anti-peptide antibody (immunoglobulin G [IgG]) titers that increased after being boosted. High anti-lipopolysaccharide (LPS) (IgG) titers were observed after the last boost. A faster immune response, with cross-reactive titers, was observed with a peptide conjugate with 30% more copies of the peptide. The binding of anti-peptide polyclonal antibodies to LPS could be inhibited by LPS, PS, MDWNMHAA, and MDWNMHAA-bovine serum albumin, as assessed by inhibition enzyme-linked immunosorbent assay. Conversely, mice immunized with PS-TT showed IgG anti-peptide titers. These data demonstrate the cross-reactivity of the antibody response and support the hypothesis that functional, as opposed to structural, mimicry of the S. flexneri Y O PS by MDWNMHAA or the underrepresentation of the bound ligand conformation in the free-ligand ensemble does not compromise immunological cross-reactivity. Prime/boost strategies were performed with a heterologous boost of PS-TT or MDWNMHAA-TT. They led to high anti-LPS titers after only three injections, suggesting alternatives to improve the immunogenicity of the carbohydrate-mimetic peptide and confirming the antigenic mimicry.

Shark IgNAR antibody mimotopes target a murine immunoglobulin through extended CDR3 loop structures

Mimotopes mimic the three-dimensional topology of an antigen epitope, and are frequently recognized by antibodies with affinities comparable to those obtained for the original antibody-antigen interaction. Peptides and anti-idiotypic antibodies are two classes of protein mimotopes that mimic the topology (but not necessarily the sequence) of the parental antigen. In this study, we combine these two classes by selecting mimotopes based on single domain IgNAR antibodies, which display exceptionally long CDR3 loop regions (analogous to a constrained peptide library) presented in the context of an immunoglobulin framework with adjacent and supporting CDR1 loops. By screening an in vitro phage-display library of IgNAR variable domains (V(NAR)s) against the target antigen monoclonal antibody MAb5G8, we obtained four potential mimotopes. MAb5G8 targets a linear tripeptide epitope (AYP) in the flexible signal sequence of the Plasmodium falciparum Apical Membrane Antigen-1 (AMA1), and this or similar motifs were detected in the CDR loops of all four V(NAR)s. The V(NAR)s, 1-A-2, -7, -11, and -14, were demonstrated to bind specifically to this paratope by competition studies with an artificial peptide and all showed enhanced affinities (3-46 nM) compared to the parental antigen (175 nM). Crystallographic studies of recombinant proteins 1-A-7 and 1-A-11 showed that the SYP motifs on these V(NAR)s presented at the tip of the exposed CDR3 loops, ideally positioned within bulge-like structures to make contact with the MAb5G8 antibody. These loops, in particular in 1-A-11, were further stabilized by inter- and intra- loop disulphide bridges, hydrogen bonds, electrostatic interactions, and aromatic residue packing. We rationalize the higher affinity of the V(NAR)s compared to the parental antigen by suggesting that adjacent CDR1 and framework residues contribute to binding affinity, through interactions with other CDR regions on the antibody, though of course definitive support of this hypothesis will rely on co-crystallographic studies. Alternatively, the selection of mimotopes from a large (<4 x 10(8)) constrained library may have allowed selection of variants with even more favorable epitope topologies than present in the original antigenic structure, illustrating the power of in vivo selection of mimotopes from phage-displayed molecular libraries.

Development of peptide mimics of a protective epitope of Vibrio cholerae Ogawa O-antigen and investigation of the structural basis of peptide mimicry

As an alternative approach toward the development of a cholera vaccine, the potential of peptide mimics of Vibrio cholerae lipopolysaccharide (LPS) to elicit cross-reactive immune responses against LPS was investigated. Two closely related protective monoclonal antibodies, S-20-4 and A-20-6, which are specific for Ogawa O-antigen (O-specific polysaccharide; O-SP) of V. cholerae O1, were used as the target antibodies (Abs) to pan phage display libraries under different elution conditions. Six phage clones identified from S-20-4 panning showed significant binding to both S-20-4 and A-20-6. Thus, it is likely that these phage-displayed peptides mimic an important conformational epitope of Ogawa antigens and are not simply functionally recognized by S-20-4. Each of the six phage clones that could bind to both monoclonal antibodies also competed with LPS for binding to S-20-4, suggesting that the peptides bind close to the paratope of the Ab. In order to predict how these peptide mimics interact with S-20-4 compared with its carbohydrate counterpart, one peptide mimic, 4P-8, which is one of the highest affinity binders and shares motifs with several other peptide mimics, was selected for further studies using computer modeling methods and site-directed mutagenesis. These studies suggest that 4P-8 is recognized as a hairpin structure that mimics some O-SP interactions with S-20-4 and also makes unique ligand interactions with S-20-4. In addition, 4P-8-KLH was able to elicit anti-LPS Abs in mice, but the immune response was not vibriocidal or protective. However, boosting with 4P-8-KLH after immunizing with LPS prolonged the LPS-reactive IgG and IgM Ab responses as well as vibriocidal titers and provided a much greater degree of protection than priming with LPS alone.

[Innovative strategies to diagnose and monitor tuberculosis patients]

Mycobacterium tuberculosis is the single most deadly microorganism worldwide. A third of the world population is thought to have latent tuberculosis and approximately 2 million people die of the disease each year. Short and closely supervised treatment regimens are needed, but it is also essential to develop new strategies to ensure prompt diagnosis of the disease. In particular, cheap methods are needed to tackle tuberculosis from a population perspective. The present article reviews the advances in immunology and molecular strategies for epidemiological diagnosis and monitoring of tuberculosis patients.

Paratope plasticity in diverse modes facilitates molecular mimicry in antibody response

The immune response against methyl-alpha-D-mannopyranoside mimicking 12-mer peptide (DVFYPYPYASGS) was analyzed at the molecular level towards understanding the equivalence of these otherwise disparate Ags. The Ab 7C4 recognized the immunizing peptide and its mimicking carbohydrate Ag with comparable affinities. Thermodynamic analyses of the binding interactions of both molecules suggested that the mAb 7C4 paratope lacks substantial conformational flexibility, an obvious possibility for facilitating binding to chemically dissimilar Ags. Favorable changes in entropy during binding indicated the importance of hydrophobic interactions in recognition of the mimicking carbohydrate Ag. Indeed, the topology of the Ag-combining site was dominated by a cluster of aromatic residues, contributed primarily by the specificity defining CDR H3. Epitope-mapping analysis demonstrated the critical role of three aromatic residues of the 12-mer in binding to the Ab. Our studies delineate a mechanism by which mimicry is manifested in the absence of either structural similarity of the epitopes or conformational flexibility in the paratope. An alternate mode of recognition of dissimilar yet mimicking Ags by the anti-peptide Ab involves plasticity associated with aromatic/hydrophobic and van der Waals interactions. Thus, antigenic mimicry may be a consequence of paratope-specific modulations rather than being dependent only on the properties of the epitope. Such modulations may have evolved toward minimizing the consequences of antigenic variation by invading pathogens.

A rAb screening method for improving the probability of identifying peptide mimotopes of carbohydrate antigens

Peptide mimotopes have been investigated as surrogate antigens of carbohydrate (CHO) targets on pathogen and tumor cells in vaccine and therapeutic discovery. One of the main bottlenecks in peptide mimotope discovery is the inability of initial screening regimes to differentiate between true mimotopes and non-mimotopes. As a result, subsequent in vivo analysis of putative peptide mimotopes is often inefficient requiring the use of experimental animals during a lengthy in vivo immunization process. Here, we demonstrate a rapid preliminary screening method to identify putative mimotopes using a recombinant antibody (rAb) library, which may increase the probability of identifying peptides that will elicit a CHO-cross-reactive response in vivo. A human naïve rAb library was screened against both an established peptide mimotope and a non-mimotope of the Group B Streptococcus (GBS) type III polysaccharide to determine if selected antibodies cross-reacted with the original GBS polysaccharide. We were able to differentiate between these two peptides because peptide-binding Abs that cross-reacted to GBS was isolated only with the peptide mimotope. We discuss the feasibility of using this method to significantly increase the breadth of screening and reduce the discovery time for peptide mimotopes.

A Monoclonal Antibody to Lewis Y/Lewis b Revealing Mimicry of the Histone H1 to Carbohydrate Structures

Antibodies to either peptide or carbohydrate tumour antigens are established tools for diagnostics and therapy. We here describe an antibody (A70-A/A9) recognizing a carbohydrate epitope common to the tumour-associated Lewis Y and Lewis b antigens (Fucalpha1-2Galbeta1-4/3[Fucalpha1-3/4]GlcNAcbeta-). Its specificity was established without doubt with a panel of 86 synthetic mono- and oligosaccharidic structures. This antibody was found to cross-react with the nuclear protein histone H1. Binding to H1 was specific, periodate-insensitive (non-carbohydrate) and saturable. Histone H1 was able to inhibit Lewis Y binding very effectively in a concentration-dependent manner. We conclude that it represents an example of natural peptide mimicry of a carbohydrate epitope. It may explain the observed occurrence of 'anti-histone autoantibodies' in cancer patients.

Galectins - potential targets for cancer therapy

Galectins are a family of galactose binding lectins that have become the focus of attention of cancer biologists due to their numerous regulatory roles in normal cellular metabolism and also because of their altered levels in various cancers. They are reportedly similar to several prominent and established modulators of apoptosis. In this review, we present a brief outline of the advancements in the methodology used to detect and identify them and their therapeutic applications in cancer. Their possible interactions with other glycoconjugates are also discussed and a vision for their future use in diagnosis and therapeutics is provided.

Towards a vaccine for Cryptococcus neoformans: principles and caveats

In the Damage-response framework of microbial pathogenesis, infectious diseases are one outcome of a host-microorganism interaction in a susceptible host. In cryptococcal disease, damage to the host is caused by Cryptococcus neoformans virulence determinants, the nature of the host response, or both. Further, the disease may be acute or reactivated from a latent state. Hence, a vaccine for C. neoformans would need to prevent disease resulting from either acute or reactivated infection. The evidence to support the development of a vaccine for C. neoformans that induces antibody-mediated immunity is discussed herein.

Anti-tick vaccines

There is now abundant evidence that vaccination with defined protein antigens is able to induce significant immunity to tick infestation. In a limited number of cases, this immunity has been duplicated by vaccination with recombinant antigens, a critical step on the pathway to commercial vaccine production. The existence of two commercial vaccines has allowed a number of field studies showing that the existing products can make an important contribution to an integrated approach to the control of ticks in the field. Under most circumstances however, the use of a tick vaccine as the single, stand alone control technology is likely to require more efficacious vaccines than those currently available. Increases in efficacy are most likely to come through the discovery of additional, effective vaccine antigens. The number of antigens with demonstrated effect is increasing, though only slowly, while the number of potential antigens that remain to be evaluated is increasing more quickly. There is limited, though convincing, evidence that some of these antigens will show effective cross-species protection, though in a poorly understood and unpredictable way. The groundwork has been laid; the potential of the field is still to be effectively exploited.

Induction of IgG antibodies against the GD2 carbohydrate tumor antigen by vaccination with peptide mimotopes

The disialoganglioside GD2, a carbohydrate antigen, is expressed on all tumors of neuroectodermal origin, including melanoma, neuroblastoma, sarcoma and small cell lung cancer. Due to its specific expression on tumor surfaces, GD2 is an attractive target for immunotherapies. The mouse/human chimeric anti-GD2 mAb ch14.18 is already applied in melanoma and neuroblastoma trials as a passive immunotherapy. To establish an active immunotherapy alternative, we aimed to replace the poorly immunogenic ganglioside with immunogenic peptides. Previously, we used the ch14.18 antibody to select GD2 peptide mimics from a phage display library. In the present study, two mimics of the ch14.18 epitope were coupled to keyhole limpet hemocyanin and used for immunizing BALB/c mice. Induction of a specific humoral immune response towards the original antigen GD2, both purified and expressed on neuroblastoma and melanoma cells, could be demonstrated in ELISA, Western blot, and immunofluorohistochemistry. As the elicited antibodies were of the IgG isotype, the mimotope conjugates were capable of recruiting T cell help and inducing memory phenomena. In conclusion, we show that an epitope of the carbohydrate antigen GD2 can successfully be translated into immunogenic peptide mimotopes. Our immunization experiments indicate that GD2 mimotopes are suitable for active immunotherapy of GD2-expressing tumors.

Inhibition and Detection of Galectins

More and more studies report on the roles that galectins play in numerous types of cancer. These roles can be varied, as has been shown particularly for galectin-3. These studies have created the need for inhibitors that can block unwanted effects, and the need to detect galectins in tissues, in order to better understand their role, and aid in diagnosis and prognosis. Since galectins bind beta-galactosides, monovalent galactose-derived inhibitors have been prepared but also peptidic ones have appeared. Since galectins often induce crosslinking and partake in aggregation phenomena, multivalency has been a successful design element in inhibitor development. Currently, there are no cheap and convenient solutions available for the detection of, ideally multiple, galectins in tissue samples, although antibody-based methods such as ELISA and Western blot analysis are being used. Besides these, a chemical probe-based method also shows potential as an alternative.

What are the commonalities governing the behavior of humoral immune recognitive repertoires?

The humoral repertoire of immune systems is large, random and somatically selected. It is derived from a germline selected repertoire by a variety of diversification mechanisms, complementation of subunits, mutation and gene conversion. However derived, the end-product must be able to recognize and rid a vast variety of pathogens. This is accomplished by viewing antigens as combinatorials of epitopes, an astuce that permits a small repertoire to respond sufficiently rapidly to a vast antigenic universe. A somatically generated repertoire, however, requires a solution to two problems. First, a somatic mechanism for a self-nonself discrimination has to be put in place. Second, the repertoire has to be coupled to the effector mechanisms in a coherent fashion. The rules governing these two mechanisms are species-independent and delineate the parameters of all immune repertoires, whatever the somatic mechanism used to generate them.

Effect of oriented or random PEGylation on bioactivity of a factor VIII inhibitor blocking peptide

Peptides as therapeutic substances are efficient agents in the treatment of several diseases. However, they often have to be chemically modified in order to be suited as therapeutic agent. Conjugation to large carrier molecules is often required. A critical step is the identification of available sites for chemical reaction, without influencing bioactivity. Peptide 238/S1 with the sequence NH(2)-PYWKWQYKYD-COOH previously selected from a combinatorial decapeptide library, has the ability to block inhibitory antibodies against blood clotting factor VIII (FVIII) and therefore, it constitutes a lead for developing a drug to treat patients suffering from development of such antibodies. The aims of this study were (i) to identify sites of the peptide, which are suited for modification without losing bioactivity and (ii) to find out the influence of molecular size of polyethylene glycol (PEG) for bioactivity of the peptide. The contribution of each amino acid residue to biological functionality was investigated by mutational analysis. This method confirmed that the N-terminus is crucial for activity, whereas both lysine residues could be exchanged by other L-amino acids. Using mutational analysis it was possible to identify peptides with higher reactivity compared to the wild type 238/S1. PEGylation experiments demonstrated that conjugation of the peptide to PEG 20,000 resulted in a loss of reactivity, while PEG 5,000 could maintain the bioactivity when conjugated in a site directed manner. The peptide lost its neutralization properties when PEG was coupled to the N-terminus, again indicating that this part of the peptide is important for functionality.

Peptides mimicking Vibrio cholerae O139 capsular polysaccharide elicit protective antibody response

Vibrio cholerae is the etiological agent of cholera. V. cholerae serogroup O1 had been, until 1992, the only serogroup responsible for large epidemics and pandemics of cholera. In 1992, a new serotype of V. cholerae emerged in South-East Asia that caused a massive outbreak of cholera in India and neighboring countries. The new serotype was named V. cholerae O139. The main differences between V. cholerae O139 and O1 are that the former possesses a capsular polysaccharide and different lipopolysaccharide. Capsular polysaccharides are, in general, T-independent antigens giving rise to poor immune responses lacking immunological memory. In order to overcome this, monoclonal antibodies against the capsular polysaccharide of V. cholerae O139 were used to screen different phage-displayed random peptide libraries. Eight different phage clones were selected and characterized using enzyme immunoassay with the monoclonal antibodies, and then tested for specificity by competition with V. cholerae O139 capsular polysaccharide. Selected peptides were sequenced, synthesized and conjugated to bovine serum albumin (BSA) and keyhole limpet hemocyanin (KLH). The conjugated peptides were used to immunize mice. It is evident that the anti-peptide mouse antibodies bind to the V. cholerae O139 capsular polysaccharide. In addition, the anti-peptide antibodies are protective in a suckling mouse model. The protective efficacy is both specific and dose-dependent. A PCT (PCT/IT2003/000489) with the publication number WO 2004/056851 has been filed for the sequences of the eight peptides.

Toward a better understanding of the basis of the molecular mimicry of polysaccharide antigens by peptides: the example of Shigella flexneri 5a

Protein conjugates of oligosaccharides or peptides that mimic complex bacterial polysaccharide antigens represent alternatives to the classical polysaccharide-based conjugate vaccines developed so far. Hence, a better understanding of the molecular basis ensuring appropriate mimicry is required in order to design efficient carbohydrate mimic-based vaccines. This study focuses on the following two unrelated sets of mimics of the Shigella flexneri 5a O-specific polysaccharide (O-SP): (i) a synthetic branched pentasaccharide known to mimic the average solution conformation of S. flexneri 5a O-SP, and (ii) three nonapeptides selected upon screening of phage-displayed peptide libraries with two protective murine monoclonal antibodies (mAbs) of the A isotype specific for S. flexneri 5a O-SP. By inducing anti-O-SP antibodies upon immunization in mice when appropriately presented to the immune system, the pentasaccharide and peptides p100c and p115, but not peptide p22, were qualified as mimotopes of the native antigen. NMR studies based on transferred NOE (trNOE) experiments revealed that both kinds of mimotopes had an average conformation when bound to the mAbs that was close to that of their free form. Most interestingly, saturation transfer difference (STD) experiments showed that the characteristic turn conformations adopted by the major conformers of p100c and p115, as well as of p22, are clearly involved in mAb binding. These latter experiments also showed that the branched glucose residue of the pentasaccharide was a key part of the determinant recognized by the protective mAbs. Finally, by using NMR-derived pentasaccharide and peptide conformations coupled to STD information, models of antigen-antibody interaction were obtained. Most interestingly, only one model was found compatible with experimental data when large O-SP fragments were docked into one of the mIgA-binding sites. This newly made available system provides a new contribution to the understanding of the molecular mimicry of complex polysaccharides by peptides and short oligosaccharides.

Peptide mimotopes of Mycobacterium tuberculosis carbohydrate immunodeterminants

Cell-surface saccharides of Mycobacterium tuberculosis appear to be crucial factors in tuberculosis pathogenicity and could be useful antigens in tuberculosis immunodiagnosis. In the present study, we report the successful antigenic and immunogenic mimicry of mannose-containing cell-wall compounds of M. tuberculosis by dodecamer peptides identified by phage-display technology. Using a rabbit antiserum raised against M. tuberculosis cell-surface saccharides as a target for biopanning, peptides with three different consensus sequences were identified. Phage-displayed and chemically synthesized peptides bound to the anticarbohydrate antiserum. Rabbit antibodies elicited against the peptide QEPLMGTVPIRAGGGS recognize the mannosylated M. tuberculosis cell-wall antigens arabinomannan and lipoarabinomannan, and the glycosylated recombinant protein alanine/proline-rich antigen. Furthermore, antibodies were also able to react with mannan from Saccharomyces cerevisiae, but not with phosphatidylinositol dimannosides or arabinogalactan from mycobacteria. These results suggest that the immunogenic peptide mimics oligomannosidic epitopes. Interestingly, this report provides evidence that, in contrast with previously known carbohydrate mimotopes, no aromatic residues are necessary in a peptide sequence for mimicking unusual glycoconjugates synthesized by mycobacteria. The possible usefulness of the identified peptide mimotopes as surrogate reagents for immunodiagnosis and for the study of functional roles of the native non-peptide epitopes is discussed.

Structure, epitope mapping, and docking simulation of a gibberellin mimic peptide as a peptidyl mimotope for a hydrophobic ligand

Using NMR spectroscopy and simulated annealing calculations, we determined the solution structure of the disulfide-linked cyclized decapeptide ACLPWSDGPC (SD), which is bound to an anti-(gibberellin A(4)) mAb 4-B8(8)/E9 and was found to be the first peptidyl mimotope for a hydrophobic ligand. The resulting structure of the peptide showed a beta-turn-like conformation in residues three to seven and the region converges well (average rmsd 0.54 A). The binding activity and the epitopes of the peptide to the antibody were assessed using saturation transfer difference (STD)-NMR experiments. We also conducted docking simulations between the peptide and the mAb to determine how the peptide is bound to the mAb. Resonances around the beta-turn-like conformation of peptide SD (residues 3-5) showed strong STD enhancement, which agreed well with results from docking simulation between peptide SD and the mAb. Together with the commonality of amino acid residues of the mAb involved in interactions with gibberellin A(4) (GA(4)) and peptide SD, we concluded that peptide SD is bound to the antigen-binding site of mAb 4-B8(8)/E9 as a GA(4) mimic, confirming evidence for the existence of peptide mimics even for hydrophobic ligands.

Reduction of spontaneous metastases through induction of carbohydrate cross-reactive apoptotic antibodies

The selective targeting of tumor-associated carbohydrate Ags by the induction of serum Abs that trigger apoptosis of tumor cells as a means to reduce circulating tumor cells and micrometastases would be an advantage in cancer vaccine development. Some plant lectins like Griffonia simplicifolia lectin I and wheat germ agglutinin mediate the apoptosis of tumor cells. We investigated the possibility of using these lectins as templates to select peptide mimotopes of tumor-associated carbohydrate Ags as immunogens to generate cross-reactive Abs capable of mediating apoptosis of tumor cells. In this study, we show that immunization with a mimotope selected based on its reactivity with Griffonia simplicifolia lectin I and wheat germ agglutinin induced serum IgM Abs in mice that mediated the apoptosis of murine 4T1 and human MCF7 cell lines in vitro, paralleling the apoptotic activity of the lectins. Vaccine-induced anti-carbohydrate Abs reduced the outgrowth of micrometastases in the 4T1 spontaneous tumor model, significantly increasing survival time of tumor-bearing animals. This finding parallels suggestions that carbohydrate-reactive IgM with apoptotic activity may have merit in the adjuvant setting if the right carbohydrate-associated targets are identified.

Carbohydrate moieties as vaccine candidates

Carbohydrate epitopes or glycotopes are structurally diverse, occur in a variety of chemical contexts, and are present on the surfaces of cells in the body and on the surfaces of pathogens. These various structures and modes of presentation affect how they are perceived and processed by the body and dictate the outcome of the immune response directed against them. This review focuses on mechanisms of carbohydrate immunity, with an emphasis on carbohydrate vaccines that have been or are being developed for protection against encapsulated bacterial pathogens. We discuss the cellular basis of carbohydrate immunity, newly identified glycotope processing pathways and recognition capabilities, and the synthetic and microarray technologies that are being developed that will permit new experimental approaches to carbohydrate vaccine development and the exploration of the interaction of the immune system with self and nonself glycans.

Peptide mimotopes of phomopsins: identification, characterization and application in an immunoassay

Peptide mimotopes of plant-associated toxins offer the potential for improving analytical and diagnostic methodologies as well as providing candidates for potential protective vaccines against plant poisoning diseases. Monoclonal antibody (mAb) C3C11, which recognizes the antimicrotubule phomopsin mycotoxins, was used to isolate peptide mimics of phomopsin A from a random 15-mer phage display peptide library. A total of 46 clones were isolated that showed specific reactivity with the mAb. Amino acid sequence analysis revealed four different types of mimotope sequences, all of which contained a common motif V-A-L/V-C. Of the 46 clones isolated, 44 contained the motif V-A-L-C while 2 contained the V-A-V-C motif. All four types of phage clones inhibited the reactivity of the mAb with phomopsin A in a competition ELISA. The clone with the mimotope sequence CTVALCNMYFGAKLD demonstrated the strongest binding. It was further shown that synthetic peptides containing these mimotope amino acid sequences were able to inhibit the mAb-phomopsin A interaction, indicating that the peptide mimotopes were responsible for the specific binding, independent of the phage framework. The results also suggest that the mimotope peptides bind to mAb C3C11 at the same site as phomopsin A. The application of recombinant phage particles carrying phomopsin mimotopes in immunoassay was evaluated and the results demonstrated approximately 100-fold increase in sensitivity in comparison with a conventional immunoassay using a chemically linked phomopsin-horseradish peroxidase conjugate.

Identification of peptide ligands for malignancy- and growth-regulating galectins using random phage-display and designed combinatorial peptide libraries

Members of the galectin family of endogenous lectins are involved in tumor growth regulation and in establishing characteristics of the malignant phenotype via protein-carbohydrate and protein-protein interactions. To identify peptide ligands with the potential to modulate these tumor-relevant interactions beneficially, complementary screening methods were employed, that is, both phage-display and a combinatorial pentapeptide library with the key YXY tripeptide core. Three representative prototype galectins were selected. The search for high-affinity ligands among phage-displayed random heptamers yielded enrichment after five selection cycles of the nonglycomimetic CQSPSARSC peptide in the case of the chicken homologue of galectin-1 but not the human protein, an indication for specificity. The most active glycomimetic from the combinatorial library of 5832 pentamers was WYKYW. Identification of peptide ligands for galectins with and without glycomimetic properties is thus possible. Our study documents the potential to combine the two library-based approaches for structural optimization of lead peptides.