Vaccination with a Human High Molecular Weight Melanoma-Associated Antigen Mimotope Induces a Humoral Response Inhibiting Melanoma Cell Growth In Vitro

Chondroitin sulfate proteoglycan 4: An attractive target for antibody-based immunotherapy

Multifunctional molecules involved in tumor progression and metastasis have been identified as valuable targets for immunotherapy. Among these, chondroitin sulfate proteoglycan 4 (CSPG4), a significant tumor cell membrane-bound proteoglycan, has emerged as a promising target, especially in light of advances in chimeric antigen receptor (CAR) T-cell therapy. The profound bioactivity of CSPG4 and its role in pivotal processes such as tumor proliferation, migration, and neoangiogenesis underline its therapeutic potential. We reviewed the molecular intricacies of CSPG4, its functional attributes within tumor cells, and the latest clinical-translational advances targeting it. Strategies such as blocking monoclonal antibodies, conjugate therapies, bispecific antibodies, small-molecule inhibitors, CAR T-cell therapies, trispecific killer engagers, and ribonucleic acid vaccines against CSPG4 were assessed. CSPG4 overexpression in diverse tumors and its correlation with adverse prognostic outcomes emphasize its significance in cancer biology. These findings suggest that targeting CSPG4 offers a promising avenue for future cancer therapy, with potential synergistic effects when combined with existing treatments.

Immunohistochemical detection of the chondroitin sulfate proteoglycan 4 protein in primary and metastatic melanoma

Treatment of malignant melanoma, the most aggressive form of skin cancer, continues to be a major challenge for clinicians. New targeted therapies with kinase inhibitors or drugs which modify the immune response are often accompanied by the development of resistance or severe side effects. In this context, chondroitin sulfate proteoglycan 4 (CSPG4), a highly immunogenic melanoma tumor antigen, could be a potential target for alternative therapeutic approaches. The aim of the present study was to identify differences in the levels of CSPG4 protein expression in primary and metastatic melanomas as well as to analyze correlations between CSPG4 expression and histopathological data and patient characteristics. A total of 189 melanoma tissue samples from Lower Austria, including primary melanomas and melanoma metastases, were immunohistochemically stained for the expression of CSPG4 and statistical analyses were performed. A total of 65.6% of melanoma tissue samples stained positive for the expression of CSPG4. Primary nodular and primary superficial spreading melanomas demonstrated a significantly higher number of positively stained tissue samples for CSPG4 compared with primary lentigo maligna melanomas. No significant differences in the expression of CSPG4 were demonstrated between primary melanomas and melanoma metastases. The present study supports the advancement of the understanding of CSPG4 tissue expression patterns in melanoma patients and provides additional information for further investigation of CSPG4 as a potential therapeutic target.

Identification of heptapeptides targeting a lethal bacterial strain in septic mice through an integrative approach

Effectively killing pathogenic bacteria is key for the treatment of sepsis. Although various anti-infective drugs have been used for the treatment of sepsis, the therapeutic effect is largely limited by the lack of a specific bacterium-targeting delivery system. This study aimed to develop antibacterial peptides that specifically target pathogenic bacteria for the treatment of sepsis. The lethal bacterial strain Escherichia coli MSI001 was isolated from mice of a cecal ligation and puncture (CLP) model and was used as a target to screen bacterial binding heptapeptides through an integrative bioinformatics approach based on phage display technology and high-throughput sequencing (HTS). Heptapeptides binding to E. coli MSI001 with high affinity were acquired after normalization by the heptapeptide frequency of the library. A representative heptapeptide VTKLGSL (VTK) was selected for fusion with the antibacterial peptide LL-37 to construct the specific-targeting antibacterial peptide VTK-LL37. We found that, in comparison with LL37, VTK-LL37 showed prominent bacteriostatic activity and an inhibitive effect on biofilm formation in vitro. In vivo experiments demonstrated that VTK-LL37 significantly inhibited bacterial growth, reduced HMGB1 expression, alleviated lesions of vital organs and improved the survival of mice subjected to CLP modeling. Furthermore, membrane DEGP and DEGQ were identified as VTK-binding proteins by proteomic methods. This study provides a novel strategy for targeted pathogen killing, which is helpful for the treatment of sepsis in the era of precise medicine.

The phage display of Bacillus subtilis Lipase A significantly enhances catalytic activity due to altered nanoscale distribution in colloidal solution

Screening libraries of mutant proteins by phage display is now relatively common. However, one unknown factor is how the bacteriophage scaffold itself influences the properties of the displayed protein. This communication evaluates the effect of solution parameters on the catalytic activity of phage displayed Bacillus subtilis Lipase A (BSLA), compared to the free enzyme in solution. While the pH- and temperature-activity profiles of BSLA were not intrinsically affected by phage display, the nanoscale distribution of BSLA within the micellar assay buffer was. This lead to a pronounced increase of activity of phage-BSLA relative to the free enzyme, owing to the accumulation of phage-BSLA at the substrate-rich micelles. Considering this result obtained for BSLA, caution is warranted and similar effects should be considered when selecting other enzymes/proteins by phage display, as the activity of the displayed protein may differ from that of the free protein.

The development of inovirus-associated vector vaccines using phage-display technologies

Introduction: Inovirus-associated vectors (IAVs) are derived from bacterial filamentous viruses (phages). As vaccine carriers, they have elicited both cellular and humoral responses against a variety of pathogens causing infectious diseases and other non-infectious diseases. By displaying specific antigen epitopes or proteins on their coat proteins, IAVs have merited much study, as their unique abilities are exploited for widespread vaccine development. Areas covered: The architectural traits of filamentous viruses and their derivatives, IAVs, facilitate the display of specific antigenic peptides which induce antibody production to prevent or curtail infection. Inoviruses provide a foundation for cost-efficient large-scale specific phage display. In this paper, the development of different applications of inovirus-based phage display vaccines across a broad range of pathogens and hosts is reviewed. The references cited in this review were selected from established databases based on the authors' knowledge of the study subject. Expert commentary: The importance of phage-display technology has been recently highlighted by the Nobel Prize in Chemistry 2018 awarded to George P. Smith and Sir Gregory P. Winter. Furthermore, the symbiotic nature of filamentous viruses infecting intestinal F+E. coli strains offers an attractive platform for the development of novel vaccines that stimulate mucosal immunity.

CD20-Mimotope Peptides: A Model to Define the Molecular Basis of Epitope Spreading

Antigen-mimicking peptide (mimotope)-based vaccines are one of the most promising forms of active-immunotherapy. The main drawback of this approach is that it induces antibodies that react poorly with the nominal antigen. The aim of this study was to investigate the molecular basis underlying the weak antibody response induced against the naïve protein after peptide vaccination. For this purpose, we analyzed the fine specificity of monoclonal antibodies (mAb) elicited with a 13-mer linear peptide, complementary to theantigen-combining site of the anti-CD20 mAb, Rituximab, in BALB/c mice. Anti-peptide mAb competed with Rituximab for peptide binding. Even so, they recognized a different antigenic motif from the one recognized by Rituximab. This explains their lack of reactivity with membrane (naïve) CD20. These data indicate that even on a short peptide the immunogenic and antigenic motifs may be different. These findings highlight an additional mechanism for epitope spreading and should be taken into account when designing peptides for vaccine purposes.

Chondroitin Sulfate Proteoglycan 4 and Its Potential As an Antibody Immunotherapy Target across Different Tumor Types

Overexpression of the chondroitin sulfate proteoglycan 4 (CSPG4) has been associated with the pathology of multiple types of such as melanoma, breast cancer, squamous cell carcinoma, mesothelioma, neuroblastoma, adult and pediatric sarcomas, and some hematological cancers. CSPG4 has been reported to exhibit a role in the growth and survival as well as in the spreading and metastasis of tumor cells. CSPG4 is overexpressed in several malignant diseases, while it is thought to have restricted and low expression in normal tissues. Thus, CSPG4 has become the target of numerous anticancer treatment approaches, including monoclonal antibody-based therapies. This study reviews key potential anti-CSPG4 antibody and immune-based therapies and examines their direct antiproliferative/metastatic and immune activating mechanisms of action.

Human recombinant Fab fragment from combinatorial libraries of a B-cell lymphoma patient recognizes core protein of chondroitin sulphate proteoglycan 4

CD antigens are well known as therapeutic targets of B-cell lymphoma. To isolate therapeutic antibodies that recognize novel targets other than CD antigens, we constructed a phage display combinatorial antibody Fab library from bone marrow lymphocytes of B-cell lymphoma patient. To eliminate antibodies reactive with known B-cell lymphoma antigen, non-hematopoietic and patient's sera reactive HeLaS3 cells was selected as a target of whole cell panning. Five rounds of panning against live HeLaS3 cells retrieved single Fab clone, termed AHSA (Antibody to HeLa Surface Antigen). Using phage display random peptide library, LSYLEP was identified as an epitope sequence of AHSA. LC-MS/MS analysis of AHSA-precipitated HeLaS3 cell lysates detected several fragments corresponding to the sequence of chondroitin sulphate proteoglycan 4 (CSPG4) core protein. Since LSYLEP sequence was at the position of 313-318 of CSPG4, we considered that CSPG4 was AHSA-associated antigen. Double staining of CSPG4-postive MDA-MB-435S cells with AHSA and anti-CSPG4 rabbit antibody showed identical staining position, and reduced AHSA reactivity was observed in CSPG4-siRNA treated MDA-MB-435S cells. In conclusion, we retrieved a human Fab from antibody library of B-cell lymphoma patient, and identified CSPG4 as a recognizing antigen. AHSA may have potential benefits for development of CSPG4-targeting theranostics for B-cell lymphoma.

CSPG4: a prototype oncoantigen for translational immunotherapy studies

Thanks to striking progress in both the understanding of anti-tumor immune response and the characterization of several tumor associated antigens (TAA), a more rational design and more sophisticated strategies for anti-tumor vaccination have been possible. However, the effectiveness of cancer vaccines in clinical trial is still partial, indicating that additional studies are needed to optimize their design and their pre-clinical testing. Indeed, anti-tumor vaccination success relies on the choice of the best TAA to be targeted and on the translational power of the pre-clinical model used to assess its efficacy. The chondroitin sulfate proteoglycan-4 (CSPG4) is a cell surface proteoglycan overexpressed in a huge range of human and canine neoplastic lesions by tumor cells, tumor microenvironment and cancer initiating cells. CSPG4 plays a central role in the oncogenic pathways required for malignant progression and metastatization. Thanks to these features and to its poor expression in adult healthy tissues, CSPG4 represents an ideal oncoantigen and thus an attractive target for anti-tumor immunotherapy. In this review we explore the potential of CSPG4 immune-targeting. Moreover, since it has been clearly demonstrated that spontaneous canine tumors mimic the progression of human malignancies better than any other pre-clinical model available so far, we reported also our results indicating that CSPG4 DNA vaccination is safe and effective in significantly increasing the survival of canine melanoma patients. Therefore, anti-CSPG4 vaccination strategy could have a substantial impact for the treatment of the wider population of spontaneous CSPG4-positive tumor affected dogs with a priceless translational value and a revolutionary implication for human oncological patients.

Application of phage peptide display technology for the study of food allergen epitopes

Phage peptide display technology has been used to identify IgE-binding mimotopes (mimics of natural epitopes) that mimic conformational epitopes. This approach is effective in the characterization of those epitopes that are important for eliciting IgE-mediated allergic responses by food allergens and those that are responsible for cross-reactivity among allergenic food proteins. Application of this technology will increase our understanding of the mechanisms whereby food allergens elicit allergic reactions, will facilitate the discovery of diagnostic reagents and may lead to mimotope-based immunotherapy.

Hypoxia increases the heterogeneity of melanoma cell populations and affects the response to vemurafenib

A hypoxic microenvironment is one of the predominant reasons for incomplete response to melanoma treatment. Vemurafenib, which targets the mutated BRAF-V600 kinase, improves melanoma patient survival, however, resistance invariably develops. The present study evaluated the effect of hypoxia on three BRAF-V600E mutant melanoma cell lines, M14, A375 and 518A2, treated with vemurafenib. Compared with the other two cell lines, hypoxic vemurafenib-treated A375 cells exhibited an enhanced cell proliferation rate and migratory capacity compared with normoxic vemurafenib-treated A375 cells. Immunoblotting analyses revealed that the expression levels of hypoxia inducible factor (HIF)1α and carbonic anhydrase IX were reduced in vemurafenib‑treated M14 and 518A2 cells, however, not in A375 cells. The expression levels of the mitogen‑activated protein kinase, Janus kinase-signal transducer and activator of transcription, and phosphatidylinositol-4,5-bisphosphate 3‑kinase signaling pathway proteins revealed a cell‑type specific response to vemurafenib and hypoxia. Knockdown experiments of HIF1α performed in hypoxic A375 cells decreased the expression of phosphorylated (p‑)protein kinase B, which was restored following vemurafenib treatment, and increased the expression of p‑extracellular‑signal‑regulated kinases. Therefore, three melanoma cell lines responded to vemurafenib under hypoxia in a cell type‑specific manner, suggesting that a subset of cells provides a treatment-resistant pool, from which disease relapse may originate. These data confirmed that vemurafenib may be successful in treating the proliferating cells, whereas the non‑proliferating subpopulation must be addressed by a combination of vemurafenib with other treatment strategies.

Phage-fused epitopes fromLeishmania infantumused as immunogenic vaccines confer partial protection againstLeishmania amazonensisinfection

Two mimotopes ofLeishmania infantumidentified by phage display were evaluated as vaccine candidates in BALB/c mice againstLeishmania amazonensisinfection. The epitope-based immunogens, namely B10 and C01, presented as phage-fused peptides; were used without association of a Th1 adjuvant, and they were administered isolated or in combination into animals. Both clones showed a specific production of interferon-gamma (IFN-γ), interleukin-12 (IL-12) and granulocyte/macrophage colony-stimulating factor (GM-CSF) afterin vitrospleen cells stimulation, and they were able to induce a partial protection against infection. Significant reductions of parasite load in the infected footpads, liver, spleen, bone marrow and paws’ draining lymph nodes were observed in the immunized mice, in comparison with the control groups (saline, saponin, wild-type and non-relevant clones). Protection was associated with an IL-12-dependent production of IFN-γ, mediated mainly by CD8+T cells, against parasite proteins. Protected mice also presented low levels of IL-4 and IL-10, as well as increased levels of parasite-specific IgG2a antibodies. The association of both clones resulted in an improved protection in relation to their individual use. More importantly, the absence of adjuvant did not diminish the cross-protective efficacy againstLeishmaniaspp. infection. This study describes for the first time two epitope-based immunogens selected by phage display technology againstL. infantuminfected dogs sera, which induced a partial protection in BALB/c mice infected withL. amazonensis.

Anti-chondroitin sulfate proteoglycan 4-specific antibodies modify the effects of vemurafenib on melanoma cells differentially in normoxia and hypoxia

Chondroitin sulfate proteoglycan 4 (CSPG4), a highly immunogenic melanoma tumor antigen, is a potential target for antibody-based immunotherapy. The mechanism by which CSPG4 affects melanoma progression is only partly understood, in particular the involvement of other receptor tyrosine kinases and the tumor microenvironment. We have previously reported on a mimotope-based vaccine against CSPG4 in a human melanoma xenograft model that resulted in reduction of tumor growth. Herein we describe the influence of hypoxia on the response to polyclonal anti-CSPG4-antibodies induced by this vaccine in combination with the BRAF inhibitor vemurafenib to enhance therapeutic efficacy by simultaneously targeting multiple signaling pathways. Melanoma cells were treated with polyclonal anti-CSPG4-antibodies and vemurafenib. Proliferation, migration and invasion were evaluated in a real-time setting in the impedance-based x-CELLigence® system. Western blotting and quantitative PCR arrays were used to determine protein and mRNA expression of hypoxia inducible factor 1α (HIF1α), carbonic anhydrase IX (CAIX) and signaling pathway proteins. A melanoma xenograft model was used to detect HIF1α and CAIX expression in vivo. Hypoxia enhanced the antiproliferative response to vemurafenib. The migration and invasion capacities of vemurafenib-treated melanoma cells were increased, in spite of vemurafenib-decreased expression of HIF1α and CAIX. Polyclonal anti-CSPG4-antibodies reduced the Transwell migration of vemurafenib-treated, BRAF V600E-mutant and CSPG4-expressing melanoma cells in hypoxia. This was associated with the downregulation of phosphorylated AKT, a kinase contributing to tumor cell migration. Our results highlight CSPG4 as a potential target for modulating treatment resistance to vemurafenib induced by the hypoxic microenvironment.

Theranostic impact of NG2/CSPG4 proteoglycan in cancer

NG2/CSPG4 is an unusual cell-membrane integral proteoglycan widely recognized to be a prognostic factor, a valuable tool for ex vivo and non-invasive molecular diagnostics and, by virtue of its tight association with malignancy, a tantalizing therapeutic target in several tumour types. Although the biology behind its involvement in cancer progression needs to be better understood, implementation of NG2/CSPG4 in the routine clinical practice is attainable and has the potential to contribute to an improved individualized management of cancer patients. In this context, its polymorphic nature seems to be particularly valuable in the effort to standardize informative diagnostic procedures and consolidate forcible immunotherapeutic treatment strategies. We discuss here the underpinnings for this potential and highlight the benefits of taking advantage of the intra-tumour and inter-patient variability in the regulation of NG2/CSPG4 expression. We envision that NG2/CSPG4 may effectively be exploited in therapeutic interventions aimed at averting resistance to target therapy agents and at interfering with secondary lesion formation and/or tumour recurrence.

Architectural insight into inovirus-associated vectors (IAVs) and development of IAV-based vaccines inducing humoral and cellular responses: implications in HIV-1 vaccines

Inovirus-associated vectors (IAVs) are engineered, non-lytic, filamentous bacteriophages that are assembled primarily from thousands of copies of the major coat protein gp8 and just five copies of each of the four minor coat proteins gp3, gp6, gp7 and gp9. Inovirus display studies have shown that the architecture of inoviruses makes all coat proteins of the inoviral particle accessible to the outside. This particular feature of IAVs allows foreign antigenic peptides to be displayed on the outer surface of the virion fused to its coat proteins and for more than two decades has been exploited in many applications including antibody or peptide display libraries, drug design, and vaccine development against infectious and non-infectious diseases. As vaccine carriers, IAVs have been shown to elicit both a cellular and humoral response against various pathogens through the display of antibody epitopes on their coat proteins. Despite their high immunogenicity, the goal of developing an effective vaccine against HIV-1 has not yet materialized. One possible limitation of previous efforts was the use of broadly neutralizing antibodies, which exhibited autoreactivity properties. In the past five years, however, new, more potent broadly neutralizing antibodies that do not exhibit autoreactivity properties have been isolated from HIV-1 infected individuals, suggesting that vaccination strategies aimed at producing such broadly neutralizing antibodies may confer protection against infection. The utilization of these new, broadly neutralizing antibodies in combination with the architectural traits of IAVs have driven the current developments in the design of an inovirus-based vaccine against HIV-1. This article reviews the applications of IAVs in vaccine development, with particular emphasis on the design of inoviral-based vaccines against HIV-1.

Mimotope-based vaccines of Leishmania infantum antigens and their protective efficacy against visceral leishmaniasis

BACKGROUND

The development of cost-effective prophylactic strategies to prevent leishmaniasis has become a high-priority. The present study has used the phage display technology to identify new immunogens, which were evaluated as vaccines in the murine model of visceral leishmaniasis (VL). Epitope-based immunogens, represented by phage-fused peptides that mimic Leishmania infantum antigens, were selected according to their affinity to antibodies from asymptomatic and symptomatic VL dogs' sera.

METHODOLOGY/MAIN FINDINGS

Twenty phage clones were selected after three selection cycles, and were evaluated by means of in vitro assays of the immune stimulation of spleen cells derived from naive and chronically infected with L. infantum BALB/c mice. Clones that were able to induce specific Th1 immune response, represented by high levels of IFN-γ and low levels of IL-4 were selected, and based on their selectivity and specificity, two clones, namely B10 and C01, were further employed in the vaccination protocols. BALB/c mice vaccinated with clones plus saponin showed both a high and specific production of IFN-γ, IL-12, and GM-CSF after in vitro stimulation with individual clones or L. infantum extracts. Additionally, these animals, when compared to control groups (saline, saponin, wild-type phage plus saponin, or non-relevant phage clone plus saponin), showed significant reductions in the parasite burden in the liver, spleen, bone marrow, and paws' draining lymph nodes. Protection was associated with an IL-12-dependent production of IFN-γ, mainly by CD8+ T cells, against parasite proteins. These animals also presented decreased parasite-mediated IL-4 and IL-10 responses, and increased levels of parasite-specific IgG2a antibodies.

CONCLUSIONS/SIGNIFICANCE

This study describes two phage clones that mimic L. infantum antigens, which were directly used as immunogens in vaccines and presented Th1-type immune responses, and that significantly reduced the parasite burden. This is the first study that describes phage-displayed peptides as successful immunogens in vaccine formulations against VL.

Epitope mapping of epidermal growth factor receptor (EGFR) monoclonal antibody and induction of growth-inhibitory polyclonal antibodies by vaccination with EGFR mimotope

One of the proposed approaches in cancer therapy is to induce and direct the patient's own immune system against cancer cells. In this study, we determined the epitope mapping of the rat anti-human epidermal growth factor receptor (EGFR) monoclonal antibody ICR-62 using a phage display of random peptide library and identified a 12 amino acids peptide, which was recognized as a mimotope. The peptide was synthesized and conjugated to bovine serum albumin (BSA) as carrier protein (P-BSA). We have shown that ICR-62 can react specifically with P-BSA as well as native EGFR. Two rabbits were immunized either by BSA or P-BSA and the rabbits IgGs were purified and examined for binding to the antigens, mimotope and the EGFR protein purified from the EGFR overexpressing A431 cell line. We showed that the rabbit IgG generated against the mimotope is capable of inhibiting the growth of A431 cells by 15%, but does not have any effect on the growth of EGFR-negative MDA-MB-453 cell line in vitro. Our results support the need for further investigations on the potential of vaccination with either mimotope of the EGFR or epitope displayed on the surface of phage particles for use in active immunotherapy of cancer.

Bacteriophage vehicles for phage display: biology, mechanism, and application

The phage display technique is a powerful tool for selection of various biological agents. This technique allows construction of large libraries from the antibody repertoire of different hosts and provides a fast and high-throughput selection method. Specific antibodies can be isolated based on distinctive characteristics from a library consisting of millions of members. These features made phage display technology preferred method for antibody selection and engineering. There are several phage display methods available and each has its unique merits and application. Selection of appropriate display technique requires basic knowledge of available methods and their mechanism. In this review, we describe different phage display techniques, available bacteriophage vehicles, and their mechanism.

Phage display--a powerful technique for immunotherapy: 2. Vaccine delivery

Phage display is a powerful technique in medical and health biotechnology. This technology has led to formation of antibody libraries and has provided techniques for fast and efficient search of these libraries. The phage display technique has been used in studying the protein-protein or protein-ligand interactions, constructing of the antibody and antibody fragments and improving the affinity of proteins to receptors. Recently phage display has been widely used to study immunization process, develop novel vaccines and investigate allergen-antibody interactions. This technology can provide new tools for protection against viral, fungal and bacterial infections. It may become a valuable tool in cancer therapies, abuse and allergies treatment. This review presents the recent advancements in diagnostic and therapeutic applications of phage display. In particular the applicability of this technology to study the immunization process, construction of new vaccines and development of safer and more efficient delivery strategies has been described.

Antithetic roles of proteoglycans in cancer

Proteoglycans (PGs), a family of complex post-translationally sculptured macromolecules, are fundamental regulators of most normal and aberrant cellular functions. The unparalleled structural-functional diversity of PGs endows them with the ability to serve as critical mediators of the tumor cells' interaction with the host microenvironment, while directly contributing to the organization and dynamic remodeling of this milieu. Despite their indisputable importance during embryonic development and in the adult organism, and their frequent dysregulation in tumor lesions, their precise involvement in tumorigenesis awaits a more decisive demonstration. Particularly challenging is to ascertain to what extent selected PGs may catalyze tumor progression and to what extent they may inhibit it, implying antithetic functions of individual PGs. Integrated efforts are needed to consolidate the routine use of PGs in the clinical monitoring of cancer patients and to broaden the exploitation of these macromolecules as therapeutic targets. Several PGs have the required attributes to be contemplated as effective antigens for immunotherapeutic approaches, while the tangible results obtained in recent clinical trials targeting the NG2/CSPG4 transmembrane PG urge further development of PG-based cancer treatment modalities.

Specificity of mimotope-induced anti-high molecular weight-melanoma associated antigen (HMW-MAA) antibodies does not ensure biological activity

Vaccines based on peptide mimics (mimotopes) of conformational tumor antigen epitopes have been investigated for a variety of human tumors including breast cancer, tumors expressing the carcinoembryonic antigen, B cell lymphoma, neuroblastoma, and melanoma. In our previous work, we designed a vaccine based on a mimotope of the high molecular weight-melanoma associated antigen (HMW-MAA) that elicited HMW-MAA-specific antibodies (Abs) with anti-tumor activity in vitro and in vivo. In this study, we aimed to identify mimotopes of additional distinct HMW-MAA epitopes, since they could be used to construct a polymimotope melanoma vaccine. For this purpose, random peptide phage libraries were screened with the anti-HMW-MAA monoclonal antibodies (mAbs) VT80.12 and VF1-TP43 yielding one peptide ligand for each mAb. Both peptides inhibited the binding of the corresponding mAb to the HMW-MAA. Furthermore, when coupled to the carrier protein keyhole limpet hemocyanin (KLH), both HMW-MAA mimotopes elicited peptide-specific Abs in rabbits or BALB/c mice, but only the mimotope isolated with the mAb VT80.12 elicited HMW-MAA-specific Abs and only in mice. However, the latter Abs had no detectable effect on HMW-MAA expressing human melanoma cells in vitro. These results describe limitations related to the phage display technique and emphasize the need to characterize the functional properties of the mAb utilized to isolate mimotopes of the corresponding epitopes.

Functional and clinical relevance of chondroitin sulfate proteoglycan 4

The lack of effective conventional therapies for the treatment of advanced stage melanoma has stimulated interest in the development of novel strategies for the management of patients with malignant melanoma. Among them, immunotherapy has attracted much attention because of the potential role played by immunological events in the clinical course of melanoma. For many years, T cell-based immunotherapy has been emphasized in part because of the disappointing results of the monoclonal antibody (mAb)-based clinical trials conducted in the early 1980s and in part because of the postulated major role played by T cells in tumor growth control. More recently, mAb-based therapies have gained in popularity given their clinical and commercial success for a variety of malignant diseases. As a result, there has been increased interest in identifying and characterizing antibody-defined melanoma antigens. Among them, the chondroitin sulfate proteoglycan 4 (CSPG4), also known as high molecular weight-melanoma associated antigen (HMW-MAA) or melanoma chondroitin sulfate proteoglycan (MCSP), has attracted much attention in recent years because of the growing experimental evidence that it fulfills two requirements for immunotherapy to be therapeutically effective: (1) targeting of cancer stem cells (CSC) and (2) development of combinatorial therapies to counteract the escape mechanisms driven by the genetic instability of tumor cells. With this in mind, in this chapter, we have reviewed recent information related to the distribution of CSPG4 on various types of tumors, including CSC, its expression on pericytes in the tumor microenvironment, its recognition by T cells, its role in cell biology as well as the potential mechanisms underlying the ability of CSPG4-specific immunity to control malignant cell growth.

Modulatory effects of tumor-derived heat shock protein in DNA vaccination against nasopharyngeal carcinoma

Use of anti-idiotype antibody vaccines is a promising strategy against tumor, however, their immunogenicity still need to be improved. Heat shock proteins (HSPs) have been shown to act as adjuvants when coadministered with peptides or given as fusion proteins and enhance the vaccination efficiency. To evaluate the enhancement of the potency of anti-idiotype antibody immunogenicity by heat shock protein gp96, C57BL/6 mice were immunized with three intramuscular inoculations of the G22 DNA and/or gp96 DNA vaccine. Control was inoculated with empty plasmid pcDNA3.1. The levels of G22-specific antibody and lymphocyte phenotype were measured by ELISA, fluorescence activated cell sorter (FACS) analysis, respectively. In the tumor protection experiment, the immunized mice were then challenged with CMT-93-G22 cells. The tumor size and the survival time of the animals were compared among these groups. The results showed that the efficacy of G22 DNA vaccine could be enhanced by coadministrating with gp96 DNA which might be relevant with activating CD8(+)T cells. Furthermore, co-injection of G22 DNA with gp96 DNA could prolong the survival time and lessen the tumor size of the CMT-93-G22-bearing mice. Our study demonstrates for the first time that G22+gp96 DNA vaccine can induce comparable G22-specific CD8(+)T cell response and is a promising candidate DNA vaccine for nasopharyngeal carcinoma.

Purification of bacteriophage M13 by anion exchange chromatography

M13 is a non-lytic filamentous bacteriophage (phage). It has been used widely in phage display technology for displaying foreign peptides, and also for studying macromolecule structures and interactions. Traditionally, this phage has been purified by cesium chloride (CsCl) density gradient ultracentrifugation which is highly laborious and time consuming. In the present study, a simple, rapid and efficient method for the purification of M13 based on anion exchange chromatography was established. A pre-packed SepFast Super Q column connected to a fast protein liquid chromatography (FPLC) system was employed to capture released phages in clarified Escherichia coli fermented broth. An average yield of 74% was obtained from a packed bed mode elution using citrate buffer (pH 4), containing 1.5 M NaCl at 1 ml/min flow rate. The purification process was shortened substantially to less than 2 h from 18 h in the conventional ultracentrifugation method. SDS-PAGE revealed that the purity of particles was comparable to that of CsCl gradient density ultracentrifugation method. Plaque forming assay showed that the purified phages were still infectious.

Mimotope vaccination--from allergy to cancer

BACKGROUND

Mimotopes are peptides mimicking protein, carbohydrates or lipid epitopes and can be generated by phage display technology. When selected by antibodies, they represent exclusively B-cell epitopes and are devoid of antigen/allergen-specific T-cell epitopes. Coupled to carriers or presented in a multiple antigenic peptide form mimotopes achieve immunogenicity and induce epitope-specific antibody responses upon vaccination.

OBJECTIVE/METHODS

In allergy IgG antibodies may block IgE binding to allergens, whereas other IgG antibody specificities enhance this and support the anaphylactic reaction. In cancer, inhibitory antibody specificities prevent growth signals derived from overexpressed oncogenes, whereas growth-promoting specificities enhance signalling and proliferation. Therefore, the mimotope concept is applicable to both fields for epitope-specific vaccination and analysis of conformational B-cell epitopes for the allergen/antigen.

RESULTS/CONCLUSIONS

Mimotope technology is a relatively young theme in allergology and oncology. Still, proof of concept studies testing allergen and tumour mimotope vaccines suggest that mimotopes are ready for clinical trials.

Two structurally different rituximab-specific CD20 mimotope peptides reveal that rituximab recognizes two different CD20-associated epitopes

Peptide mimotopes of the CD20 epitope recognized by rituximab are useful tools for studying this therapeutic mAb's functional properties. We previously identified two structurally different peptides that are both effective mimotopes: a 7-mer cyclic peptide (Rp15-C) bearing the antigenic motif (a/sNPS) that matches 170(ANPS)173 of the extracellular loop of CD20, and a 12-mer linear peptide (Rp5-L) containing the antigenic motif (WPxWLE) lacking sequence homology to CD20. In this study, we investigated whether the different structures of Rp15-C and Rp5-L reflect the mimicry of the same or different CD20 epitopes recognized by rituximab. Using immunochemical methods, we found that, like Rp15-C, Rp5-L mimics the raft-associated form of CD20 (by inhibiting rituximab binding to CD20 in vitro). Rp5-L and Rp15-C elicit, in immunized mice, anti-CD20 Abs that stain CD20+ cells with a punctate pattern similar to that of rituximab. However, only anti-Rp5-L Abs recognize denatured CD20. When phage-display peptide libraries were panned with anti-Rp5-L, phage clones were enriched that expressed the consensus qWPxwL, similar to the antigenic motif (WPxWLE), but not matching (a/sNPS). Finally, (WPxWLE) and (ANPS) share some, but not all, contact sites within the rituximab Ag-combining site, indicating that (WPxWLE) is not an exact replica of Rp15-C (or CD20) (ANPS). Altogether, these results indicate that the two structurally different peptides are also conformationally different, and suggest that rituximab recognizes two different CD20-associated epitopes.

Reduction of human melanoma tumor growth in severe combined immunodeficient mice by passive transfer of antibodies induced by a high molecular weight melanoma-associated antigen mimotope vaccine

PURPOSE

The high molecular weight melanoma-associated antigen (HMW-MAA) is an attractive target for immunotherapy of malignant melanoma. We have recently generated a vaccine based on the HMW-MAA mimotope 225D9.2+ that was able to induce anti-HMW-MAA antibodies with antitumor activity in vitro. Here, we investigated the antitumor activity of these antibodies in a human melanoma xenotransplant severe combined immunodeficient (SCID) mouse model.

EXPERIMENTAL DESIGN

Tumors were established by injecting the human melanoma 518A2 cells into C.B.17 SCID/SCID mice. In tumor prevention experiments, 200 microg purified total IgG antibodies were injected intravenously the same day or on day 5 in therapeutic experiments. Antibody administration was repeated every fourth day and tumor volumes were measured. Antibody specificity and tumor infiltration by macrophages were investigated by immunohistochemistry.

RESULTS

Within 35 days after cell inoculation, antibody treatment reduced tumor growth up to 40% in the therapeutic and up to 62% in the tumor prevention experiments compared with the control mice. In tumors of all groups, a similar distribution of the HMW-MAA and no differences in infiltration of macrophages were detected by immunohistochemistry.

CONCLUSIONS

Here, we showed that antibodies induced by the 225D9.2+ mimotope effectively inhibited melanoma tumor growth. Additional mechanisms besides antibody-dependent cell cytotoxicity like disruption of interactions of melanoma cells mediated by extracellular matrix components seem to be involved in tumor growth inhibition. Based on our findings, we suggest that active immunization with this mimotope might be a promising strategy for treatment of melanoma.

Overview of mimotopes and related strategies in tumor vaccine development

Tumor vaccine has been studied extensively as an alternative or adjuvant therapy in the treatment of malignant tumors in the hope of prolonging the overall survival rates of cancer patients. The efficacy largely relies on the specificity of the target. In the last decade, many antibody epitopes, called mimotopes, have been revealed as candidates through phage-display technology. These mimotopes do not necessarily consist of amino acid sequences that are identical to the native antigen but they do mimic their structure. Tumor vaccines based on these mimotopes have been proposed as an important developing strategy. Some peptide mimotopes have produced encouraging clinical outcomes. Although most studies are still in the preclinical phase, these findings will possibly pave the way for the development of novel mimotope-based tumor vaccines.

Targeting 11q23 positive acute leukemia cells with high molecular weight-melanoma associated antigen-specific monoclonal antibodies

BACKGROUND

Acute leukemia with 11q23 aberrations is associated with a poor outcome with therapy. The lack of efficacy of conventional therapy has stimulated interest in developing novel strategies. Recent studies have shown that 11q23-positive acute leukemia cells express the high molecular weight-melanoma associated antigen (HMW-MAA). This tumor antigen represents a useful target to control growth of human melanoma tumors in patients and in severe combined immunodeficient (SCID) mice, utilizing antibody-based immunotherapy. This effect appears to be mediated by inhibition of the HMW-MAA function such as triggering of the focal adhesion kinase/proline-rich tyrosine kinase 2 (Pyk2) pathways. Therefore, in this study we tested whether HMW-MAA-specific monoclonal antibodies (mAb) could inhibit growth of 11q23-positive leukemia cells in SCID mice.

METHODS

HMW-MAA-specific mAb were tested for their ability to inhibit the in vitro proliferation of an 11q23-positive acute myeloid leukemia (AML) cell line and blasts from four patients with 11q23 aberrations and their in vivo growth in subcutaneous and disseminated xenograft models.

RESULTS

The HMW-MAA-specific mAb did not affect in vitro proliferation although they down-regulated phosphorylated (P) Pyk2 expression. Furthermore, the mAb enhanced the in vitro anti-proliferative effect of cytarabine. In vivo the mAb inhibited the growth of leukemic cells in a dose-dependent fashion. However, the difference did not reach statistical significance. No effect was detected on P-Pyk2 expression. Furthermore, HMW-MAA-specific mAb in combination with cytarabine did not improve tumor inhibition. Lastly, the combination of two mAb which recognize distinct HMW-MAA determinants had no detectable effect on survival in a disseminated xenograft model.

CONCLUSIONS

HMW-MAA-specific mAb down-regulated P-Pyk2 expression and enhanced the anti-proliferative effect of cytarabine in vitro, but had no detectable effect on survival or growth of leukemia cells in vivo. Whether the HMW-MAA-specific mAb can be used as carriers of toxins or chemotherapeutic agents against 11q23-acute leukemia remains to be determined.

Identification of an antigenic and immunogenic motif expressed by two 7-mer rituximab-specific cyclic peptide mimotopes: implication for peptide-based active immunotherapy

Two 7-mer cyclic peptides-Rp15-C and Rp13-C-which bear the antigenic motif recognized by the anti-CD20 mAb rituximab, but have different motif-surrounding amino acids, show a comparable avidity for rituximab and inhibit the binding of rituximab to raft-associated CD20 and rituximab-induced membrane ceramide on human lymphoid Daudi cells. Their immunogenic profiles differed: Abs recognizing CD20 were induced in two and five of five BALB/c mice immunized with Rp15-C and Rp13-C, respectively. Analysis of immunogenic motif, performed by panning a 7-mer phage-display peptide library with purified anti-peptide IgGs, showed that the motif defined by anti-Rp15-C mostly included amino acids surrounding the rituximab-specific antigenic motif <aNPS>, whereas that defined by anti-Rp13-C was <NPS>. These data indicate that their motif-surrounding amino acids can markedly influence the specificity of Abs, even when elicited with a short 7-mer peptide. Because these anti-peptide Abs are of IgG isotype, their specificity is likely to reflect how peptides are processed at the T cell level and suggest that, within a short peptide, the motifs defined by T cells during the initial phase and upon their stimulation may be different. Our findings may account for the failure of most forms of peptide-based immunotherapy in cancer and autoimmune diseases in which anti-mimotope Abs are expected to play a relevant therapeutic effect. They also suggest strategies to implement the specificity of peptide-induced Abs against the target Ag.

A cell surface 230 kDa protein from murine melanoma involved with tumor malignancy

Because melanoma incidence has increased at a dramatic rate, it is relevant to identify novel melanoma antigens for diagnosis and develop monoclonal antibodies recognizing such molecules. Some monoclonal antibodies (mAbs), raised against murine melanoma, identify molecules correlated with carcinogenesis. Herein, we describe a murine melanoma-associated 230 kDa molecule, expressed only in tumorigenic cell lines. Moreover, its expression is higher in more metastatic than less metastatic cells. G12F2 mAb, produced against this antigen, inhibited in vitro proliferation of both murine and human melanoma cells and enhanced in vitro complement activity. It also affected in vivo tumor growth and lung metastases formation. This 230kDa molecule represents an important target for experimental melanoma studies and may become a potential diagnostic marker for malignancy as well as a useful tool for immunotherapeutic approaches.

Mimotope vaccines: epitope mimics induce anti-cancer antibodies

Mimotopes are epitope-mimicking structures. When applied for immunizations they induce desired antibody specificities exclusively based on the principle of molecular mimicry. This is important as antibodies directed against tumor-associated antigens may harbor diverse biological effects depending on their epitope specificity. Thus they may inhibit or promote tumor growth. This review gives an update on different vaccination strategies based on the mimotope concept.

Maintenance of antigen-specific immunological memory through variable regions of heavy and light chains of anti-idiotypic antibody

Immunological memory is characterized by a quick and enhanced immune response after re-exposure to the same antigen. To explain the mechanism involved in generation and maintenance of immunological memory, we had earlier proposed a hypothesis involving the relay of memory by idiotypic and anti-idiotypic B cells. The peptidomimic present in the hypervariable region of anti-idiotypic antibody was hypothesized to carry forward immunological memory. In the present work, we provide evidence supporting a role for the anti-idiotypic antibody in eliciting antigen-specific B-cell and T-cell responses. Employing the idiotypic monoclonal antibody (Ab(1)) specific for haemagglutinin (H) protein of rinderpest virus, Ab(2beta) was generated, which possesses an internal image of the H protein in the region between amino acids 527 and 556. We demonstrate that antigen-specific memory is perpetuated by immunization with Ab(2), as shown by maintenance of antigen-specific T-cell responses upon restimulation in vitro of Ab(2) immune splenocytes by antigen-presenting cells expressing H protein or pulsed with H-protein-derived peptides. We have also shown that boosting with antigen-specific anti-idiotypic B cells generates a memory response in antigen-primed mice. Evidence has been provided for the existence of an antigen-specific B-cell idiotypic network in the body that supports the perpetuation of immunological memory as proposed in the relay hypothesis.

Delayed tumor onset and reduced tumor growth progression after immunization with a Her-2/neu multi-peptide vaccine and IL-12 in c-neu transgenic mice

Passive immunotherapy with monoclonal antibodies is a routinely performed but cost intensive treatment against certain cancers. Induction of humoral anti-tumor responses by active peptide immunization has therefore become a favorable treatment concept. We have recently identified three peptides representing B-cell epitopes of the extracellular domain of Her-2/neu each of them inducing Her-2/neu specific immune responses with anti-tumor activity in vitro. The present study was performed to evaluate the in vivo protective capacity of a combined vaccination with these three peptides in FVB/N transgenic mice spontaneously developing c-neu overexpressing breast cancers. The three Her-2/neu peptides coupled to tetanus toxoid were administered with or without addition of recombinant IL-12. At the time all untreated mice had developed tumors about 40% of peptide-immunized mice and nearly 60% of mice immunized with the peptide vaccine co-applied with IL-12 remained tumor free. Moreover, co-administration of IL-12 had a significant impact on the retardation of tumor progression. The enhanced anti-tumor efficacy of the vaccine by IL-12 was associated with a Th1 biased immune response as demonstrated by an increased IFN-gamma production in vitro and elevated Her-2-specific IgG levels. Our findings clearly demonstrate that this multi-peptide vaccine is effective in tumor prevention and support its use against minimal disease, drug-resistant tumors or even for prophylaxis against cancers overexpressing Her-2/neu.

Protective immunity induced by phage displayed mitochondrial related peptides of Schistosoma japonicum

New antigens and strategies are necessary for vaccine development against schistosomiasis japonica. Using a pool of 43 high titred anti-SWA sera from individuals residing in an Schistosoma japonicum endemic area of China, we have cloned a S. japonicum gene by cDNA library screening. The recombinant Sj338 protein has 44-46% identity to a mitochondrial precursor receptor protein of humans and rats. Immunization of mice with the recombinant Sj338 conferred 27-32% (p<0.01) reduction in worm burdens following cercarial challenge. In an effort to identify protective epitopes in Sj338 and increase the level of protection, we screened a random 12-mer peptide library constructed in M13 using a polyspecific anti-Sj338 rabbit serum. After five rounds of biopanning, we identified 30 reactive clones consisting of 11 distinct peptide sequences. These clones shared limited primary sequence homology with the recombinant Sj338 protein. Anti-sera raised against these phage clones recognized recombinant Sj338 and SWAP by Western blot. In murine vaccination experiments using whole recombinant phage without adjuvant, four of these clones demonstrated worm reductions of 11.6-25.1% (p=ns - 0.05) compared to M13 vaccinated animals. Animals vaccinated with all four of these phage demonstrated 34.2% (p<0.01) worm reduction compared to controls vaccinated with M13 clone. These data suggest that mimotope peptides are potential vaccine candidates for S. japonicum.

NG2-expressing cells in the nervous system: role of the proteoglycan in migration and glial-neuron interaction

The NG2 glycoprotein is a type I membrane protein expressed in the developing and adult central nervous system (CNS) by subpopulations of glia including oligodendroglial precursor cells (OPCs), and in the developing CNS additionally by pericytes. In the mouse CNS, expression of NG2 protein is already observed at embryonic day 13 and peaks between postnatal days 8 and 12. NG2+ cells persist in grey and white matter in adult mouse brain: cells in the developing and adult brain show clear differences in migration, cell-cycle length and lineage restriction. Several groups have provided evidence that subpopulations of NG2+ cells can generate neurons in vivo. Neuronal stimulation in the developing and adult hippocampus leads to Ca2+ signals in apposing NG2+ glia, suggesting that these cells may modulate synaptic activity, and NG2+ cells often ensheath synapses. The structure of the protein with two N-terminal LamininG/Neurexin/Sex-hormone-binding globulin domains suggests a role in adhesion. The C-terminal PSD-95/DiscsLarge/Zona Occludens-1 (PDZ)-binding motif has been found to associate with several PDZ proteins including the Glutamate Receptor Interacting Protein GRIP: NG2 may thus act to position AMPA receptors on glia towards sites of neuronal glutamate release. Furthermore, the NG2 proteoglycan plays a role in cell migration and spreading and associates with actin-containing cytoskeletal structures.

Targeting Melanoma Cells with Human High Molecular Weight-Melanoma Associated Antigen-Specific Antibodies Elicited by a Peptide Mimotope: Functional Effects

Human high molecular weight-melanoma associated Ag (HMW-MAA) mimics have been shown to elicit HMW-MAA-specific humoral immune responses that appear to be clinically beneficial. This finding has stimulated interest in characterizing the mechanism(s) underlying the ability of the elicited Abs to exert an anti-tumor effect. To address this question, in the present study, we have generated HMW-MAA-specific Abs by sequentially immunizing rabbits with the peptide P763.74, which mimics the HMW-MAA determinant recognized by mAb 763.74, and with HMW-MAA(+) melanoma cells. HMW-MAA-specific Abs isolated from immunized rabbits mediated cell-dependent cytotoxicity but did not mediate complement-dependent cytotoxicity of HMW-MAA(+) melanoma cells. These Abs also effectively inhibited spreading, migration and Matrigel invasion of HMW-MAA(+) melanoma cells. Besides contributing to our understanding of the role of HMW-MAA in the biology of melanoma cells, these results suggest that both immunological and nonimmunological mechanisms underlie the beneficial clinical effects associated with the induction of HMW-MAA-specific Abs in melanoma patients immunized with a HMW-MAA mimic.

Generation of biologically active linear and cyclic peptides has revealed a unique fine specificity of rituximab and its possible cross-reactivity with acid sphingomyelinase-like phosphodiesterase 3b precursor

Heterogeneity of the effector functions displayed by rituximab and other anti-CD20 monoclonal antibodies (mAbs) apparently recognizing the same CD20 epitope suggests that additional mechanisms, probably related to mAb fine specificity, are responsible for B-cell depletion. To improve our understanding of rituximab's function, its fine specificity was investigated by means of phage display peptide library (PDPL)-expressing 7-mer cyclic (c7c) or 7-/12-mer linear peptides. Rituximab-specific c7c PDPL-derived clone insert sequences expressed the motif A(S)NPS overlapping the human CD20 170ANPS173. P172 was the most critical for rituximab binding, since its replacement with S172 (of mouse CD20) abolished the reactivity. The WPXWLE motif expressed by the linear PDPL-derived clone insert sequences could only be aligned to the reverse-oriented 161WPXWLE156 of acid sphingomyelinase-like phosphodiesterase 3b precursor (ASMLPD), though linear peptides bearing WPXWLE competed with cyclic ones for rituximab-paratope binding. Anti-CD20 mAb 1F5 only displayed a reactivity profile similar to that of rituximab, which also reacted with ASMLPD-derived peptides. Peptides induced antibodies with specificity and effector functions similar to those of rituximab. Our results show a unique fine specificity of rituximab, define the molecular basis for the lack of rituximab reactivity with mouse CD20 (mCD20), and the potential of targeting CD20 in an active immunotherapy setting. A possible rituximab interaction with ASMLPD is suggested.