Identification Of Tumor-associated Antigens Research Articles

Identification and Characterization of T Cell Epitopes Deduced from RGS5, a Novel Broadly Expressed Tumor Antigen.

Identification of tumor-associated antigens (TAA) has resulted in the development of therapeutic vaccines for the treatment of cancer. We applied an integrated functional genomics approach to identify TAA in malignant tissues of patients with renal cell carcinoma (RCC). A comparative DNA chip analysis of tumor and the corresponding non-malignant tissue from patients with RCC followed by sequencing of peptides bound to the HLA-class I molecules by mass spectrometry was applied to identify novel TAA in RCC. To confirm the immunogenicity of identified epitopes cytotoxic T lymphocytes (CTL) were generated using dendritic cells (DC). Utilizing this approach, two peptides derived from RGS5 binding to either HLA-A*02 or 03 were identified. The key function of regulators of G protein-signalling (RGS) is to bind to G protein α subunits and to stimulate their intrinsic GTPase activity. The hydrolysis of guanosine triphosphate (GTP) to guanosine diphosphate (GDP) thereby is accelerated and the inactive heterotrimer more rapidly restored. Thus, RGS proteins inhibit the biological activity of G proteins. Interestingly, it was recently shown that RGS5 is overexpressed in pericytes of newly developing tumor vessels, indicating that RGS5 plays an important role during tumor angiogenesis.Using RT-PCR analysis we found that RGS5 is expressed on a broad variety of tumor cells including RCC, colorectal, breast and ovarian cancer, malignant melanoma and multiple myeloma as well as in acute and chronic leukemias making this protein an interesting candidate for the development of vaccination strategies to target the tumor cells and the tumor vessels. CTL that were induced using the RGS5 peptides lysed autologous DC pulsed with the cognate peptide or transfected with in vitro transcribed RGS5 RNA as well as HLA-matched tumor cell lines. The specificity and HLA restriction was confirmed using blocking monoclonal antibodies and in cold-target inhibition assays. We next utilized DC transfected with RGS5 RNA to generate specific CTL. Using this approach we confirmed the processing and presentation of the identified peptides by malignant cells. These CTL lysed tumor cells in an antigen specific manner while sparing non-malignant cells. To analyze the induction of RGS5 specific CTL in an autologous setting in patients with malignant diseases, we used blood samples from a patient with acute myeloid leukemia (AML) in complete remission after chemotherapy and were able to generate specific CTL capable of recognizing autologous AML blasts while sparing non-malignant cells.Our results demonstrate that RGS5 is a novel tumor rejection antigen expressed in a wide range of malignancies that can be applied to target malignant cells and tumor angiogenesis.

Clinical applications of virosomes in cancer immunotherapy

Cancer immunotherapy is increasingly accepted as a treatment option for advanced stage disease. The identification of tumour-associated antigens in 1991 has prompted the development of antigen-specific immunotherapeutic strategies for a variety of cancers. Many of them result in some immunological responses in cancer patients; however, clinical results were not observed concomitantly with immunological responses; therefore, further improvements in the field of immunotherapy are urgently needed. Virosomes are lipidic envelopes devoid of genetic information, but which retain the antigenic profile and fusogenic properties from their viral origin. Virosomes are versatile antigen carriers and can be engineered to perform various tasks in cancer immunotherapy. Preclinical data have fostered the development of innovative clinical protocols. Hence, immunopotentiating reconstituted influenza virosomes will be assessed in breast and melanoma immunotherapy, and may contribute to the development of clinically effective cancer vaccines and ultimately improve patient outcomes. The objective of this review is to provide an overview of the potential clinical applications of virosomes as innovative and potentially effective reagents in active specific cancer immunotherapy.

PASD1, a DLBCL-associated cancer testis antigen and candidate for lymphoma immunotherapy

Despite advances in defining clinically relevant subtypes of diffuse large B-cell lymphoma (DLBCL), identifying high-risk patients and improved therapeutic options remains a priority. One approach is through the identification of tumor-associated antigens (TAAs), of which cancer testis antigens (CTAs) are of particular interest. Their restricted normal tissue expression, commonly widespread expression in tumors and immunogenicity makes them attractive therapeutic targets and markers for early diagnosis of cancer.1

Analyzing T cell responses

This book represents the first comprehensive description and evaluation of the most important assays utilized to monitor immune responses against tumor associated antigens. Each chapter, prepared by leading investigators in tumor immunology and immunotherapy, details a specific immune topic or analytical method. Specifically tailored to the needs of clinical researchers, basic science investigators, and biotechnology innovators, this book provides information that is both sufficiently detailed and eloquently succinct. All discussions are substantiated with a comprehensive literature review. The categorization and organization of these sections is such that one can either pursue the entire book or quickly find necessary information on a specific assay or concept of interest. An in-depth description of the methods utilized in the identification of tumor associated antigens is complemented by extensive lists of HLA class I and class II restricted antigens. This book also addresses the essential topic of tumor cells’ ability to evade immune recognition and destruction. The potential mechanisms regarding the disparity between the patients’ immunological and clinical response following immunization are reviewed. Importantly, potential therapeutic strategies to overcome the immune escape mechanisms have been discussed. Having described an appropriate amount of background information in order to establish a fundamental understanding of the antigen-specific immune responses, the book then moves to specifically address the particular assays utilized by the tumor immunologists in the following chapters: Cytotoxicity Assays focuses on evaluating the cellular immune responses to tumors and the monitoring of killer lymphocytes in cancer patients. In addition, the killing mechanisms utilized by the effector lymphocytes and the different types of CTL-inducing cancer vaccines are discussed. Monitoring T Cell Proliferation highlights the importance of proliferation as a significant indicator of lymphocyte activation. Specifically, important regulators and principles of T cell proliferation are reviewed. A variety of monitoring techniques and methods for data analysis are also discussed. ELISPOT Assay concentrates on the principle, performance, result interpretation and limitations of this important and widely used method for monitoring the immune status of patients receiving cancer vaccines. A very helpful section on the assay’s problems and suggested solutions is also included. Modified ELISPOT describes some modifications of this assay specifically developed for T cell monitoring in cancer vaccine trials. These modifications, Granzyme B ELISPOT and Autologous Tumor IFN-γ ELISPOT, allow better assessment of low frequency tumor-specific CTL and their functions in cancer vaccine trials. Intracellular Cytokine Staining focuses on the technique of this sensitive assay for analysis of T cell responses. In addition, monitoring of spontaneous tumor immunity and vaccination studies in patients with cancer are also discussed. Cytometric Cytokine Secretion Assay provides a detailed description of this innovative method for the analysis and enrichment of viable cells according to the secreted cytokines. The cytokine secretion assay has proven to be especially useful for the detection and isolation of viable antigen-specific T cells after a short restimulation with specific antigen in vitro to induce secretion of cytokines. This chapter provides comprehensive background information and very useful practical considerations on the detection and isolation of cytokine-secreting, antigenspecific T cells. Cancer Metastasis Rev (2006) 25:501–502 DOI 10.1007/s10555-006-9015-1

Identification of RGS5 as a tumor-associated antigen expressed in a broad range of human malignancies and recognized by antigen specific cytotoxic T cells

2569 Background: Identification of tumor-associated antigens (TAA) have resulted in the development of therapeutic vaccines for the treatment of cancer. We applied an integrated functional genomics approach to identify TAA in malignant tissues of patients with renal cell carcinoma (RCC). Methods: A comparative DNA chip analysis of tumor and the corresponding non-malignant tissue from patients with RCC followed by sequencing of peptides bound to the HLA-class I molecules by mass spectrometry was applied to identify novel TAA in RCC. To confirm the immunogenicity of identified epitopes cytotoxic T lymphocytes (CTL) were generated using dendritic cells (DC). Results: RGS5 was found to be overexpressed in 16 of 29 analyzed RCC (5.7–29.9 fold) as compared to non-malignant renal tissue. Two peptides derived from RGS5 binding to either HLA-A*02 or 03 were identified. RGS5 was previously shown to be expressed in pericytes and promote tumor angiogenesis. Using RT-PCR analysis we found that RGS5 is expressed on a broad variety of tumor cells including RCC, colorectal, breast and ovarian cancer, malignant melanoma and multiple myeloma as well as in acute and chronic leukemias making this protein an interesting candidate for the development of vaccination strategies to target the tumor cells and the tumor vessels. CTL that were induced using the RGS5 peptides lysed autologous DC pulsed with the cognate peptide or transfected with in vitro transcribed RGS5 RNA as well as HLA-matched tumor cell lines. The specificity and HLA restriction was confirmed using blocking monoclonal antibodies and in cold-target inhibition assays. We next utilized DC transfected with RGS5 RNA to generate specific CTL. Using this approach we confirmed the processing and presentation of the identified peptides by malignant cells. These CTL lysed tumor cells in antigen specific manner while sparing non-malignant cells. In an ongoing vaccine trial RGS5 peptides could safely be given to RCC patients resulting in the induction of peptide specific CTL responses. Conclusions: Our results demonstrate that RGS5 is a novel tumor rejection antigen expressed in a wide range of malignancies that can be applied to target malignant cells and tumor angiogenesis. [Table: see text]

Sensitization of malignant glioma to chemotherapy through dendritic cell vaccination

Drug resistance represents a major cause of chemotherapy failure in patients with cancer. The characterization of the molecular pathways involved in drug resistance has provided new targets to circumvent or reverse chemotherapy resistance. Many of these target proteins are often overexpressed in human glioma and have been identified as tumor antigens, which implicate the development of immunotherapy as a therapeutic strategy. Dendritic cells (DCs) are the most potent antigen-presenting cells of the immune system and have been demonstrated to stimulate antibody and cell-mediated immune responses against tumor-associated antigens. Ex vivo-generated and tumor antigen-loaded DCs have been successfully introduced to clinical vaccination protocols, which have proven to be feasible and effective in some glioma patients. Most importantly, immunotherapy followed by chemotherapy could significantly increase 2-year survival in malignant glioma patients, which obviously demonstrates that DC vaccination could increase the sensitivity of tumor cells to chemotherapy. This review focuses on recent advances in the identification of tumor-associated antigen in glioma, as well as novel insights into their biological function related to drug resistance. These insights may provide the rationale for a novel strategy of a DC cancer vaccine that sensitizes tumor cells to chemotherapy. In addition, the current research status and the future direction of a DC-based vaccine to treat glioma in animal models and clinical trials will also be discussed.

Viral Vectors for Cancer Immunotherapy

Over the last decade, immunotherapy approaches for the treatment of cancer have been investigated with renewed vigour, perhaps catalyzed by the clinical successes seen with monoclonal antibody and cytokine based therapies. The identification of tumor-associated antigens (TAAs) in multiple cancer types has enabled the development of targeted immunotherapies and allayed some of the safety concerns associated with the induction of deleterious autoimmune reactions. In addition to the TAA or therapeutic gene, the antigen delivery system is equally as important for the development of a successful cancer vaccine. One approach to induce a potent and targeted antitumor response is to use viruses to deliver the TAA to cells of the immune system. A diverse array of oncolytic viruses and recombinant viral vectors encoding numerous therapeutic genes or TAAs have been tested in pre-clinical studies and produced results which, in some cases, justify their clinical development as potential cancer immunotherapies. Within the last 5-10 years, many such recombinant vectors have made the transition from pre-clinical research to clinical development and it is these, which are given most weight in this review.

HPtaa database-potential target genes for clinical diagnosis and immunotherapy of human carcinoma

Tumor-associated antigens (TAAs) have been the most actively employed targets in the clinical diagnosis and treatment of human carcinoma, such as PSA in the diagnosis of prostate cancer and NY-ESO-1 in the immunotherapy of melanoma and other cancers. However, identification of TAAs has often been hampered by the complicated and laborsome laboratory procedures. In order to accelerate the process of tumor antigen discovery, and thereby improve diagnosis and treatment of human carcinoma, we have made an effort to establish a publicly available Human Potential Tumor Associated Antigen database (HPtaa) with potential TAAs identified by in silico computing (). Tumor specificity was chosen as the core of tumor antigen evaluation, together with other relevant clues. Various platforms of gene expression, including microarray, expressed sequence tag and SAGE data, were processed and integrated by several penalty algorithms. A total of 3518 potential TAAs have been included in the database, which is freely available to academic users. As far as we know, this database is the first one addressing human potential TAAs, and the first one integrating various kinds of expression platforms for one purpose.

Identification of tumor associated antigens recognized by IgG from tumor‐infiltrating B cells of lung cancer: Correlation between Ab titer of the patient's sera and the clinical course

We previously demonstrated that TIB recognize tumor antigens and produce antibodies against them. In the present study, we identified three tumor antigens recognized by TIB in lung cancer and evaluated whether changes in the antibody titer against these antigens correlated with the patient's clinical course. A lung cancer cell line, G603L, was established from a primary lung tumor of a patient, G603. Seven months later, adrenal metastasis was detected and surgically resected. The latter tumor was mildly infiltrated with B cells and xenotransplanted into SCID mice to obtain human IgG. A cDNA library was constructed from G603L and SEREX was carried out using TIB-derived IgG. The sero-reactive clones were sequenced and one of these antigens was revealed to be MAGE-B2 whereas the others were novel antigens. In the immuno-monitoring of the patient's sera, high antibody titer against MAGE-B2 was observed before operation and the titer decreased after resection of the primary tumor. It was elevated again at the time of adrenal metastasis, but then decreased after resection. The change in antibody titer against the second antigen was similar to MAGE-B2, and the antibody titer against the third antigen was low before the primary operation but increased at the time of recurrence. Our results suggest that TIB recognized tumor antigens and the antibody titers against these antigens were changed along with the patient's clinical course. Therefore, these antibodies could be used as tumor markers for the patient.

Manipulating the Local Tumor Microenvironment with Poxviruses Expressing Costimulatory Molecules

The identification of tumor-associated antigens and new insights into the molecular and cellular basis of tumor immunology have generated a variety of vaccine strategies. Although promising in animal models, data from early-phase clinical trials have not been encouraging. These studies have documented the ability of vaccines to prime T cells, but these responses have not correlated with therapeutic effectiveness. Because the location of T-cell activation and effector activity may impact T-cell function significantly, attention has been placed on the tumor microenvironment. There is now evidence that T-cell responses may be altered in the setting of established tumor growth. To alter the balance between local immune responses and tumor growth, a vaccine regimen using direct intratumoral delivery of poxvirus vaccines expressing costimulatory molecules was developed. An initial series of clinical trials has documented the safety profile of this approach and has suggested that local and systemic immunity can be induced. Herein, we review the general rationale for this approach, discuss the results of ongoing clinical trials, and highlight critical questions that can be addressed in well-designed preclinical and clinical studies.

Identification of BCOX1, a novel gene overexpressed in breast cancer

The identification of tumor-associated antigens, which are specifically expressed in cancer tissues, is of utmost important for immunotherapy of breast cancer. We have combined in silico screening and experimental expression analysis to identify genes that are differentially expressed in breast carcinomas compared with their corresponding normal tissues. Using these approaches, we identified a novel gene, BCOX1, with overexpression in breast carcinoma. BCOX1 was highly homologous to KIAA0100, a hypothetical gene located on chromosome 17q11.2. RNA in situ hybridization shows that BCOX1 mRNA signal is mainly located in the cytoplasm of breast carcinoma epithelial cells, but not in those of normal epithelial cells, stroma cells and lymphocytes. Furthermore, mRNA expression of BCOX1 was moderately elevated in ductal in situ carcinoma (DCIS), peaked in invasive breast carcinoma (IBC) and metastatic breast carcinoma cells (MET) whereas absent in benign ductal epithelial cells. The predicted BCOX1 open reading frame of 666 bp encodes a putative protein of 222 amino acid residues with a calculated molecular weight of 24920 Da and a PI of 5.86. Computational analyses predict that the putative BCOX1 protein is a cytoplasmic protein. The functional relevance of this novel gene is yet to be determined. This study warrants further investigations to explore the molecular functions of BCOX1, and to determine its potential diagnostic and therapeutic applications for breast cancer.

The Silver locus product Pmel17/gp100/Silv/ME20: controversial in name and in function

Mouse coat color mutants have led to the identification of more than 120 genes that encode proteins involved in all aspects of pigmentation, from the regulation of melanocyte development and differentiation to the transcriptional activation of pigment genes, from the enzymatic formation of pigment to the control of melanosome biogenesis and movement [Bennett and Lamoreux (2003) Pigment Cell Res. 16, 333]. One of the more perplexing of the identified mouse pigment genes is encoded at the Silver locus, first identified by Dunn and Thigpen [(1930) J. Heredity 21, 495] as responsible for a recessive coat color dilution that worsened with age on black backgrounds. The product of the Silver gene has since been discovered numerous times in different contexts, including the initial search for the tyrosinase gene, the characterization of major melanosome constituents in various species, and the identification of tumor-associated antigens from melanoma patients. Each discoverer provided a distinct name: Pmel17, gp100, gp95, gp85, ME20, RPE1, SILV and MMP115 among others. Although all its functions are unlikely to have yet been fully described, the protein clearly plays a central role in the biogenesis of the early stages of the pigment organelle, the melanosome, in birds, and mammals. As such, we will refer to the protein in this review simply as pre-melanosomal protein (Pmel). This review will summarize the structural and functional aspects of Pmel and its role in melanosome biogenesis.

Clinical applications of recombinant virus-based cancer immunotherapy

Cancer immunotherapy looks back over one century of clinical applications. In spite of major advances in the comprehension of oncogenesis and treatment of cancer, malignant tumours remain a leading cause of disability and death worldwide. Since 1991, a breakthrough in immunology allowed the identification of tumour-associated antigens, opening the era of specific immunotherapy. On the other hand, recombinant virus are powerful vectors that are able to express various gene products in vivo, including cytokines and tumour antigens. Therefore, many groups have implemented clinical trials of active specific tumour immunotherapy. Phase I trials have demonstrated favourable safety profiles. However, major tumour responses remain anecdotal in heavily metastatic patients. This review will critically present and discuss the clinical achievements of recombinant virus-based cancer immunotherapy. This paper will attempt to shed some light on the perspectives opened by advanced cancer immunotherapy protocols, review the drawbacks of this approach and the reasons why it is believed that recombinant virus-based cancer immunotherapy may be of relevance in the treatment of human malignancies.

ABCE1, a member of ATP-binding cassette transporter gene, encodes peptides capable of inducing HLA-A2-restricted and tumor-reactive cytotoxic T lymphocytes in colon cancer patients

To provide a scientific basis for specific immunotherapy of colon cancer, this study focused on the identification of tumor-associated antigens recognized by HLA-A2-restricted and cancer-reactive cytotoxic T lymphocytes (CTLs) from tumor-infiltrating lymphocytes (TIL) of a colon cancer patient. We identified a gene coding a member of the ATP-binding cassette transporter (ABCE1), which is known as an inhibitor to the 2-5A/RNase L system, a central pathway of interferon action, and its gene expression is amplified in drug-resistant cells. The ABCE1 mRNA was ubiquitously expressed in tumor cell lines, as well as normal cells or tissues. Among 21 peptides with the HLA-A2 binding motifs, 2 ABCE1-derived peptides were recognized by the colon cancer-reactive CTLs in a dose-dependent manner. CTL precursors reactive to these 2 ABCE1 peptides were detected in the peripheral blood mononuclear cells (PBMCs) of the colon cancer patient, from whom the TILs had been obtained. In addition, these ABCE1 peptides had the potential to generate HLA-A2-restricted and colon cancer-reactive CTLs from the PBMCs of colon cancer patients, but not from those of healthy donors. Their cytotoxicity against colon cancer was mainly ascribed to peptide-specific and CD8+ CTLs. No definite cytotoxicity was observed against normal T cell blasts, irrespective of the expression of the ABCE1 mRNA. These results indicate that the ABCE1 and its peptides could be target molecules in specific immunotherapy for HLA-A2(+) colon cancer patients.

Therapeutic monoclonal antibodies in oncology

The mainstay of systemic therapy for solid and haematological malignancies in the 20th century was chemotherapy. This approach has the drawbacks of toxicity to normal tissue, drug resistance and lack of efficacy. The demand for more effective and tolerable treatments has led to the development of novel therapeutic agents that specifically target the malignant cell. The hallmarks of malignant disease are self sufficiency in growth signals, insensitivity to growth inhibition, evasion of apoptosis, acquisition of limitless replicative potential, induction of angiogenesis and invasion and metastasis.1 All these processes are ultimately due to genetic defects which subsequently lead to the abrogation of normal cellular processes. Key to the development of targeted therapies is the ability to define the growth factors, transcription factors or receptors that phenotypically distinguish, in some way, the tumour from its normal counterpart. One class of novel agents that can specifically target and disrupt molecular pathways underlying tumorigenesis are the therapeutic monoclonal antibodies. Monoclonal antibodies are produced by a single clone of B-cells, and are monospecific and homogeneous. Since the original report on production of such antibodies, by Kohler and Milstein2 in 1975, a vast number have become available. Early developments in the cancer sphere were made in the academic sector, with the identification of tumour-associated antigens and immunization with tumours to produce novel monoclonal antibodies. Initially, the antibodies were created by fusing B cells from immunized mice with human lymphoma cells, thus creating murine monoclonal antibodies. A big disadvantage of these preparations was that human recipients developed antimouse antibodies, which led to allergic reactions and reduced the efficacy.3 However, application of recombinant DNA technology led to the development first of chimeric antibodies, then of partially humanized antibodies,4,5 and ultimately of fully humanized antibodies.6 Box 1 outlines the features of the different types in this progression. Radiochemistry and antibody engineering research were initially driven by the academic sector, followed by start-up biotech companies and subsequently larger pharmaceutical conglomerates. Whilst many of the antibodies were tested in the clinical setting—either unconjugated or more commonly as radioimmunoconjugates—very few (anti-CD20 being the first major exception) went on to be commercially developed. Box 1 Types of monoclonal antibody that have been developed Type of antibody Chimeric Chimeric antibodies are 65–90% human and consist of the constant or effector domain of the human antibody molecule combined with the murine variable regions (which bring about antigen recognition) by transgenic fusion of the immunoglobulin gene Partially humanized Partially humanized antibodies are about 95% human and consist of the complementarity determining regions of the murine antibody (which determine antibody specificity) and a limited number of structural aminoacids grafted onto a CDR-depleted human antibody backbone by recombinant technology Deimmunized Deimmunized antibodies have the immunogenic epitopes in the murine variable domains replaced with benign aminoacid sequences, resulting in a deimmunized variable domain. The deimmunized variable domains are linked genetically to human antibody constant domains Primatized Primatized antibodies have a chimeric antibody structure of human and monkey that is close to an exact copy of a human antibody Fully humanized Fully human antibodies have been developed by use of genetically engineered transgenic mice and advances in the generation of synthetic human antibody libraries At present, therapeutic monoclonal antibodies are being used in haematological and solid malignancies including non-Hodgkin's lymphoma, breast cancer and colorectal cancer. The mechanism of their antitumour effect is not precisely known but is thought to include complement-dependent cytotoxicity, antibody-dependent cellular cytotoxicity and blocking or steric hindrance of the function of the target antigen. This review focuses on current use in oncology but Table 1 lists some of the antibodies in clinical development. Table 1 A summary of monoclonal antibodies used in cancer medicine or in development

Cellular immunotherapy for cancer: current concepts and clinical perspectives scientific basis and approaches for therapeutic cancer vaccines. Part I.

Tumour immunotherapy is not a new concept. Since the original (and partially successful) attempts at using bacterial products to treat sarcomas by William Coley 100 years ago, the number of immunologically based anticancer therapies has increased almost exponentially. This pathway has not been smooth and uniform, and the most basic concepts continue to be challenged. In particular, the role of the immune system in the development and eradication of malignant disease, the so-called ‘immune surveillance’, remains controversial [1,2]. Nevertheless, the recent resurgence of interest in this field has resulted in a large portfolio of clinical trials, some of which are now at the phase III stage. This remarkable progress has only been made possible by advances in key areas, including the development of monoclonal antibody technology, the identification of tumour-associated antigens (TAA), the insights into the molecular basis of antigen presentation and T-cell activation, the development of gene transfer technology, and the identification, large-scale culture and manipulation of powerful antigen-presenting dendritic cells. In this review, we will discuss the scientific basis for cellular cancer immunotherapy and recent developments in the identification of TAA and their interactions with T cells. The various approaches to cancer immunotherapy will be described, along with the new techniques being used to evaluate the immune response (the so-called ‘immunological readouts’). Finally, we present an overview of important ongoing or completed clinical trials of cellular immunotherapy for cancer.

Vaccination strategies for solid tumors--fundamentals, limitations, and recent results

Recent studies clearly prove the existence of cancer immunosurveillance and justify renewed hope for the development of effective vaccination therapies for solid tumors. The identification of tumor-associated antigens has provided researchers with promising targets for T cell-based immunotherapies. New monitoring techniques will facilitate the correlation of immunological effectiveness of vaccination strategies with clinical results. In order to acchieve greater immunological effectiveness, a tumor vaccine should incorporate both CD4+ and CD8+ epitopes. Adjuvants should be systematically tested for their potential to break immunological tolerance and mechanisms that enable cancer cells to escape from immunosurveillance should be further investigated. This approach will open new perspectives in the development of tumor vaccines for solid tumors. At the same time, future vaccination studies should include patients in earlier stages of their disease or in the adjuvant setting in order to avoid on overwhelming effect of mechanisms that help tumors to evade immunosurveillance.

Identification of tumor-associated antigens in human thyroid papillar carcinoma

Identification of tumor-associated antigens in human thyroid papillar carcinoma

Antigen-specific immunotherapy and cancer vaccines.

The specific activation of the immune system to control cancer growth in vivo has been a long-standing goal in cancer immunology and medical oncology. The identification of tumor-associated antigens has provided the basis for new concepts in antigen-specific immunotherapy. The first clinical trials on cancer vaccines were designed to evaluate the toxicity and objectively measurable immunologic effects in relation to clinical developments mostly in patients with metastatic disease. MHC class I- and II-restricted peptide epitopes, antigenic proteins, viral constructs, mini-genes and whole tumor cells have been used either alone or combined with different cytokines (i.e., IL-2, IL-12, GM-CSF), adjuvants (incomplete Freund's adjuvant, montanide, QS21) or with dendritic cells to induce specific immune responses in vivo. Standardized assay systems to evaluate the immunologic effects of cancer vaccines have been established. Clinical developments during and after vaccination were followed in relation to vaccine-induced immune responses. Prognostic tumor features, i.e., homogeneity of tumor antigen and MHC class I/II expression and intratumoral cellular infiltrates, have been identified that may help to select patients who are more likely to benefit from antigen-specific cancer vaccines in the future.

The Golgi Protein RCAS1 Controls Cell Surface Expression of Tumor-associated O-Linked Glycan Antigens

Tumor immunology has received a large impetus from the identification of tumor-associated antigens. Among them, a monoclonal antibody, 22.1.1, was instrumental in defining a novel tumor-associated antigen that was termed "receptor binding cancer antigen expressed on SiSo cells" (RCAS1). RCAS1 was proposed to induce growth arrest and apoptosis on activated immune cells, mediated by a putative death receptor. Structurally, RCAS1 was predicted to exist as a type II transmembrane protein and in a soluble form. Here, we analyzed occurrence, membrane topology, and subcellular localization of the RCAS1-encoded gene product. RCAS1 was shown to be a ubiquitously expressed type III transmembrane protein with a Golgi-predominant localization. Monoclonal antibody 22.1.1 failed to recognize RCAS1, as demonstrated by confocal microscopy. Instead, we showed that the cognate 22.1.1 epitope is identical with the tumor-associated O-linked glycan Tn (N-acetyl-d-galactosamine, GalNAc). Overexpression of RCAS1 in cell lines that are negative for 22.1.1 surface staining led to the generation of Tn and the closely related TF (Thomsen-Friedenreich, Galbeta1-3GalNAc) antigen, thus providing a functional link to the generation of the 22.1.1 epitope. We suggest that RCAS1 modulates surface expression of tumor-associated, normally cryptic O-linked glycan structures and contributes indirectly to the antigenicity of tumor cells.