Human tumor-rejection antigens and peptides from genes to clinical research

One of the most significant advances in the field of modern tumor immunology is the identification of genes encoding tumor-rejection antigens that are recognized by human leukocyte antigen (HLA) class I-restricted and tumor-specific cytotoxic T lymphocytes (CTLs). Several peptides encoded by these genes are now under clinical trial as cancer vaccines, and major tumor regression has been observed in some melanoma patients. These results indicate that identification of the peptides capable of inducing CTLs may provide a new modality of cancer therapy. We investigated tumor-rejection antigens from epithelial cancers, and reported 7 genes encoding tumor-rejection antigens and peptides available for specific immunotherapy of HLA-A26 or -A24 patients with epithelial cancers. Furthermore, we identified more than 10 genes encoding tumor-rejection antigens and peptides available for specific immunotherapy of HLA-A2 patients with epithelial cancers. Therefore these new antigens and peptides could be applicable to the treatment of numerous epithelial cancer patients worldwide. Phase I clinical trials of cancer vaccine with these peptides for epithelial cancer patients are in progress at our university. Basic and clinical research will provide new insights for a better understanding of the molecular basis of T cell-mediated recognition of cancer cells and be important for the development of cancer vaccines.     

Expression of tumor-associated antigens in breast cancer subtypes

ObjectivesTumor-associated antigens (TAAs) are frequently overexpressed in several cancer types. The aim of this study was to investigate the expression of TAAs in breast cancer.Material and methodsA total of 250 selected invasive breast cancers including 50 estrogen receptor (ER)-positive (Luminal B like), 50 triple-negative (TN), 50 ER-positive lobular type, 50 ER- and progesterone receptor (PgR)-positive (Luminal A like) and 50 cerbB2-positive breast cancers, were assessed for New York esophageal squamous cell carcinoma-1 (NY-ESO-1), Wilms tumor antigen (WT-1) and PReferentially expressed Antigen of MElanoma (PRAME) antigen expression by immunohistochemistry (IHC).ResultsA significantly higher expression of cancer testis (CT)-antigens NY-ESO-1 and WT-1 antigen was detected in TN breast cancers compared with ER-positive tumors. NY-ESO-1 overexpression (score 2 + and 3+) assessed by monoclonal and polyclonal antibodies was detected in 9 (18%) TN cancers as compared to 2 (4%) ER-positive tumors (p = 0.002). WT1 over-expression (score 2 + and 3+) was confirmed in 27 (54%) TN tumor samples as compared to 6 (12%) ER-positive (p < 0.0001). PRAME over-expression (score 2 + and 3+) was detected in 8 (16%) HER2 positive tumor samples as compared to no TN and ER-positive cancers (p = 0.0021).ConclusionsNY-ESO-1 and WT1 antigens are overexpressed in TN breast cancers. Because of the limited therapeutic options for this patient subgroup, CT antigen-based vaccines might prove to be useful for patients with this phenotype of breast cancer.     

Update: Immunological Strategies for Prostate Cancer

Prostate cancer is the second most common cause of cancer-related death in US men. Along with initial therapy using surgery, radiotherapy, or cryotherapy, hormonal therapy is the mainstay of treatment. For men with advanced (metastatic) disease, docetaxel-based chemotherapy is US Food and Drug Administration (FDA)-approved, and provides a significant survival advantage. This relative paucity of treatment options drives an ongoing quest for additional treatment modalities; among these is immunotherapy. The concept that prostate cancer is a malignancy that can be targeted by the immune system may seem counterintuitive; certainly kidney cancer and melanoma are more traditionally thought of as immune responsive cancers. However, prostate cancer arises in a relatively unique organ and may express a number of proteins (antigens) against which an immune response can be generated. More importantly, several of these agents have now demonstrated a significant survival benefit in randomized controlled clinical trials, and one agent in particular (Sipuleucel-T, Dendreon Corporation, Seattle, WA) could be FDA-approved in 2010. This update summarizes recent clinical developments in the field of prostate cancer immunotherapy, with a focus on dendritic cell vaccines, virus-based vaccines, DNA-based vaccines, and cell-based vaccines. In addition, the notion of agents that target immune checkpoints is introduced. Enthusiasm for prostate cancer immunotherapy is founded upon its potential to mediate targeted, specific, tumor cell destruction without significant systemic toxicity; however, this has yet to be fully realized in the clinical arena.     

Advances in specific immunotherapy for prostate cancer

OBJECTIVES: The absence of effective therapies for advanced prostate cancer has entailed an intensive search for novel treatments. This review presents an overview of specific immunotherapeutic strategies for prostate cancer. METHODS: Current literature was reviewed regarding the identification of tumor antigens and the design of T-cell- and antibody-based immunotherapy for prostate cancer. The PubMed database was searched using the key words antibodies, clinical trials, dendritic cells, immunotherapy, prostate cancer, and T cells. RESULTS: T cells and antibodies are powerful components of the specific antitumor immune response. CD8+ cytotoxic T lymphocytes (CTLs) efficiently destroy tumor cells. CD4+ T cells improve the antigen-presenting capacity of dendritic cells (DCs) and support the stimulation of tumor-reactive CTLs. Monoclonal antibodies exhibit their antitumor effects via antibody-dependent cellular cytotoxicity and complement activation. Consequently, much attention has been given to the identification of tumor antigens that represent attractive targets for specific immunotherapy. Several prostate cancer-related antigens were described and used in clinical trials. Such studies were based on the administration of peptides, proteins, or DNA. Furthermore, men with prostate cancer were vaccinated with peptide-, protein-, or RNA-loaded DCs, which display an extraordinary capacity to induce tumor-reactive T cells. Monoclonal antibodies directed against surface antigens were also used. Clinical trials revealed that immunotherapeutic strategies represent safe and feasible concepts for the induction of immunologic and clinical responses in men with prostate cancer. CONCLUSIONS: Specific immunotherapy represents a promising treatment modality for prostate cancer. Further improvement of the current approaches is required and may be achieved by combining T-cell- and antibody-based vaccination strategies with radio-, hormone-, chemo-, or antiangiogenic therapy.     

Active Antigen-specific Immunotherapy of Melanoma: from Basic Science to Clinical Investigation

Advanced-stage melanoma here dismal prognosis, and novel therapeutic approaches are urgently required. The possibility of taking advantage of the immune response of patients for its treatment has been an appealing concept for almost a century. Only during the last decade, however, has the molecular identification of tumor-associated antigens (TAAs) offered the possibility of vaccinating patients (e.g., active induction of TAA-specific immune responses). Active antigen-specific immunotherapy (AASIT) is currently being investigated in a number of clinical centers as a treatment option for advanced-stage melanoma. A large number of melanoma TAAs have been molecularly characterized and are being used in vaccination trials in various molecular forms and according to various immunization protocols. Here we provide a short overview on melanoma TAAs, the technologies currently in use to induce specific cytotoxic T-lymphocyte (CTL) responses in vivo, and their monitoring. We also propose a tentative AASIT agenda for the next few years, aiming at improving the capacity to induce and monitor TAA-specific immune responses and to verify their clinical effectiveness.This work was partially funded by grants from the Swiss Bridge Foundation and by the Swiss Science Foundation.     

Identification of an HLA-A*0201-restricted T-cell epitope derived from the prostate cancer-associated protein trp-p8

BACKGROUND: New concepts for the immunotherapy of prostate carcinoma (PCa) largely depend on the identification of suitable target antigens that are present in a high percentage of prostate tumors. Their expression in normal tissues should be restricted to the prostate and they should be immunogenic in vivo. The number of antigens displaying these properties is still limited. Here, we identify for the first time an immunogenic peptide derived from the prostate-specific protein transient receptor potential-p8 (trp-p8) that is recognized by cytotoxic T lymphocytes (CTLs) from PCa patients. METHODS: To determine the abundance of trp-p8 in prostate tumors, the expression level of trp-p8 mRNA was quantitatively analyzed in a panel of prostate cancer tissues. Trp-p8-derived human leukocyte antigen (HLA)-A*0201-restricted peptides were selected and tested for the in vitro activation of CTLs when loaded on autologous dendritic cells (DCs). RESULTS: Trp-p8 mRNA was found to be expressed in all prostate tumors and in the corresponding normal prostate tissue. Of five selected trp-p8-derived peptides, only peptide GLMKYIGEV was shown to activate specific CTLs, which effectively lysed PCa cells confirming the endogenous generation and presentation of this peptide by tumor cells. CONCLUSIONS: Our results suggest this antigen as a suitable target for the T-cell-based immunotherapy of PCa.     

Immunotherapy of malignant melanoma

Several areas of immunotherapeutic research may ultimately improve the effectiveness of active specific immunotherapy for melanoma and other malignancies. Identification of the most relevant tumor antigens will continue to be a vital component of vaccine design. Optimizing delivery of these antigens by use of adjuvants, dendritic cells, or heat shock proteins will enhance the immunogenicity of vaccines. The use of DNA vaccines to deliver nucleotides that encode relevant antigens and immunologic molecules, such as costimulatory molecules, and the use of targeted therapy with immunocytokines have yielded promising results in animal studies. Finally, cutting-edge techniques such as quantitative polymerase chain reaction and gene/protein microarrays will be used to monitor the response to a vaccine and thereby guide management decisions. Although IFN-alpha 2b is the only FDA-approved adjuvant treatment for AJCC stage IIB/III melanoma, recent data failed to show a benefit in overall survival. For patients with AJCC stage IV melanoma, chemotherapy with dacarbazine is currently the standard of care, with modest response rates of 15% to 20%. The encouraging response rates and low toxicities that were reported in phase I/III trials suggest that active immunotherapy may prove to be the most effective adjuvant therapy. At present, there are no FDA-approved cancer vaccines for malignant melanoma, and the results of ongoing randomized phase III clinical trials are greatly anticipated.     

Ovarian cancer-associated lymphocyte recognition of folate binding protein peptides

Background: Tumor-associated lymphocytes (TAL) isolated from ovarian cancer patients contain cytotoxic T lymphocytes (CTL) capable of recognizing specific HLA/peptide complexes on tumor cells leading to tumor cell lysis. Currently, HER2/neu, overexpressed in only 30% of breast and ovarian cancers, is the only known source of CTL-recognized peptides in epithelial cancers. Therefore, we have investigated peptides derived from folate binding protein (FBP), which is over-expressed in more than 90% of ovarian cancers and in the majority of other epithelial tumors. Methods: TAL were isolated from the malignant ascites of four consecutive HLA-A2⁺ ovarian cancer patients and incubated in IL-2. Initial chromium-release assays were performed within 1 week. T2 cells, incubated with peptide, were used to reconstitute T cell epitopes. The FBP sequence was interrogated for HLA-A2 binding peptides, and five were synthesized (E37–41). Results: Freshly cultured, unstimulated ovarian TAL recognize peptides derived from FBP. These peptides are presented in the context of HLA-A2, and are specifically recognized in a HLA class I-restricted fashion. TAL recognition of these reconstituted T cell epitopes is concentration dependent. Furthermore, the FBP peptides are shown by cold target inhibition studies to be naturally processed and presented antigens. Conclusions: FBP peptides are recognized by freshly isolated TAL from ovarian cancer patients, suggesting in vivo expression and sensitization. Because FBP is over-expressed 20-fold in most adenocarcinomas, these peptides may be used in a widely applicable peptide-based vaccine for epithelial tumors.Presented at the 51st Annual Cancer Symposium of The Society of Surgical Oncology, San Diego, California, March 26–29, 1998.     

Current concepts in immunotherapy for the treatment of colorectal cancer

Immunotherapy could have a role in the therapy of colorectal cancer as there is now convincing evidence that the immune system can specifically recognize and destroy malignant cells. The MAb 17-1A has been used in advanced and primary disease, along with newer agents such as anti-epidermal growth factor receptor (EGFR) antibody. Immunotherapy with autologous tumour cell vaccine, genetic modification of immunostimulatory cytokines, suicide genes and TAAs as discussed. The multiplicity of peptide and carbohydrate antigens which can be potential targets for immunotherapy are also discussed. These include MUC1, Thomsen-Friedenreich and Sialosyl-Tn antigens and HER2 / neu. Active specific immunotherapy with the anti-idiotypic antibodies CEAVac and 105AD7, along with DC vaccines, is being currently used in adjuvant clinical trials. 105AD7 has been shown to cause significantly greater apoptosis of tumour cells in colorectal cancer patients, while CEAVac generated T cell proliferative anti-CEA responses. Dendritic cells pulsed with tumour mRNA or TAAs currently are being assessed in clinical trials. The role of HSPs in the anti-tumour immune response is discussed. Non-specific immunotherapeutic agents used in clinical trials with chemotherapeutic regimens have not shown any definitive benefit. Tumour progression may occur as result of escape from the host anti-cancer immune response. Better understanding of mechanisms of tumour evasion could explain why immunotherapy trials in patients have not shown better results. These include down-regulation of immune responses by the tumour, altered expression of MHC and/or TAAs by tumour cells, altered expression of adhesion molecules by tumour and/or DCs and usurpation of the immune response to the advantage of the cancer.     

Tumor vaccines in renal cell carcinoma

Introduction Although most vaccines target foreign infectious agents, therapeutic cancer vaccines target both well-established and metastatic tumor cells expressing tumor antigens. Active immunotherapy is intended to enhance or activate the immunosurveillance of an individual through a therapeutic vaccine. Renal cell carcinoma (RCC) is one of the most immunoresponsive cancers in humans, which in turn makes it an ideal candidate for immune based therapies. Method Several types of therapeutic vaccines have been tested and applied in the clinical setting and can be divided into cell-based vaccines including direct application of inactivated autologous tumor cells, gene modified tumor cell-based, dendritic cell-based (expressing RCC derived tumor antigens), and non-cell-based vaccines. This review will examine the current status of cell-based vaccine immunotherapy and focuses on non-cell-based vaccine strategies. Conclusion Recent advances in molecular targeting therapy have introduced a battery receptor tyrosine kinase (RTK) and mTOR inhibitors that provide promising treatment options, however, the tolerability of tumor vaccines and the success of clinical effectiveness in selected populations combined with recent advances in cellular therapies warrant the continued exploration of novel methods of tumor vaccine therapies in the clinical setting.     

Local secretion of IL-12 augments the therapeutic impact of dendritic cell–tumor cell fusion vaccination

Background

The development of dendritic cell (DC)–tumor fusion vaccines is a promising approach in cancer immunotherapy. Using fusion vaccines allows a broad spectrum of known and unidentified tumor-associated antigens to be presented in the context of MHC class I and class II molecules, with potent co-stimulation provided by the DCs. Although DC–tumor fusion cells are immunogenic, murine studies have shown that effective immunotherapy requires a third signal, which can be provided by exogenous interleukin 12 (IL-12). Unfortunately, systemic administration of IL-12 induces severe toxicity in cancer patients, potentially precluding clinical use of this cytokine to augment fusion vaccine efficacy. To overcome this limitation, we developed a novel approach in which DC–tumor fusion cells locally secrete IL-12, then evaluated the effectiveness of this approach in a murine B16 melanoma model.

Materials and methods

Tumor cells were stably transduced to secrete murine IL-12p70. These tumor cells were then electrofused to DC to form DC–tumor heterokaryons. These cells were used to treat established B16 pulmonary metastases. Enumeration of these metastases was performed and compared between experimental groups using Wilcoxon rank sum test. Interferon γ enzyme-linked immunosorbent spot assay was performed on splenocytes from treated mice.

Results

We show that vaccination with DCs fused to syngeneic melanoma cells that stably express murine IL-12p70 significantly reduces counts of established lung metastases in treated animals when compared with DC–tumor alone (P = 0.029). Interferon γ enzyme-linked immunosorbent spot assays suggest that this antitumor response is mediated by CD4⁺ T cells, in the absence of a tumor-specific CD8⁺ T cell response, and that the concomitant induction of antitumor CD4⁺ and CD8⁺ T cell responses required exogenous IL-12.

Conclusions

This study is, to the best of our knowledge, the first report that investigates the impact of local secretion of IL-12 on antitumor immunity induced by a DC–tumor fusion cell vaccine in a melanoma model and may aid the rational design of future clinical trials.     

Lung cancer-associated tumor antigens and the present status of immunotherapy against non-small-cell lung cancer

Despite recent advances in surgery, irradiation, and chemotherapy, the prognosis of patients with lung cancer is still poor. Therefore, the development and application of new therapeutic strategies are essential for improving the prognosis of this disease. Significant progress in our understanding of tumor immunology and molecular biology has allowed us to identify the tumor-associated antigens recognized by cytotoxic T lymphocytes. Immune responses and tumor-associated antigens against not only malignant melanoma but also lung cancer have been elucidated at the molecular level. In a theoretical sense, tumor eradication is considered possible through antigen-based immunotherapy against such diseases. However, many clinical trials of cancer vaccination with defined tumor antigens have resulted in objective clinical responses in only a small number of patients. Tumor escape mechanisms from host immune surveillance remain a major obstacle for cancer immunotherapy. A better understanding of the immune escape mechanisms employed by tumor cells is necessary before we can develop a more effective immunotherapeutic approach to lung cancer. We review recent studies regarding the identification of tumor antigens in lung cancer, tumor immune escape mechanisms, and clinical vaccine trials in lung cancer.     

Characterization of cell surface antigens expressed in the HMA-1 breast cancer cell line

This report describes the characterization of an estrogen receptor-positive breast cancer cell line, HMA-1, established from a breast cancer patient, based on the expression of tumor-associated antigens (TAAs), the HLA-DR antigen, and the c-erbB-2 proto-oncogene product. In flow cytometric and immunohistochemical analyses, HMA-1 was found to express increased levels of several TAAs including MUC1, TAG-72 (sialyl Tn), Tn, T, sialyl Le^a, Le^x, and Le^y, HMA-1 also expressed enhanced levels of the HLA-DR antigen and c-erbB-2 protein. These results indicate that HMA-1 is a unique cell line with abundant TAAs which may serve as an appropriate breast cancer cell line for application in the multidisciplinary research of breast cancer.     

Identification of an immunodominant H-2D(b)-restricted CTL epitope of human PSA

BACKGROUND: Human prostate specific antigen (PSA) is expressed selectively in prostate epithelium and is a potential target for the immunotherapy against prostate cancer. Various PSA-based vaccines have been reported to induce cytotoxic T lymphocyte (CTL) responses in animal models. Here, we present the identification and validation of an immunodominant CTL epitope of PSA in C57Bl/6 mice (H-2(b)). METHODS: PSA-specific CTLs were induced by immunization with a plasmid expressing PSA. Epitope specificity of the CTLs was determined by their reactivity against a panel of C-terminus truncated or mutated PSA proteins and use of bioinformatical prediction with the SYFPEITHI algorithm. RESULTS: The majority of PSA-specific CTLs were directed against a single H-2D(b) restricted epitope corresponding to the amino acid residues 65-74 (HCIRNKSVIL) of the protein. The CTLs had similar functional avidity against two putative H-2D(b) binding peptides: a 9-aa-long psa65-73 (HCIRNKSVI) and a 10-aa-long psa65-74 (HCIRNKSVIL). CONCLUSIONS: We demonstrate that the psa65-73 peptide can be used for reactivation of PSA-specific CTLs in vitro and ex vivo, and H-2D(b) pentamers assembled with this peptide are an efficient tool for monitoring of PSA-specific CTL responses after DNA vaccination.     

Cell-based vaccines for renal cell carcinoma: genetically-engineered tumor cells and monocyte-derived dendritic cells

Initial vaccine developments for renal cell carcinoma (RCC) have concentrated on cell-based approaches in which tumor cells themselves provide mixtures of unknown tumor-associated antigens as immunizing agents. Antigens derived from autologous tumors can direct responses to molecular composites characteristic of individual tumors, whereas antigens derived from allogeneic tumor cells must be commonly shared by RCC. Three types of cell-based vaccine for RCC have been investigated: isolated tumor cell suspensions, gene modified tumor cells and dendritic cells (DCs) expressing RCC-associated antigens. Approaches using genetic modification of autologous RCC have included ex vivo modification of tumor cells or modification of tumors in vivo. We have used gene-modification of allogeneic tumor cell lines to create generic RCC vaccines. More recently, emphasis has shifted to the use of DCs as cell-based vaccines for RCC. DCs have moved to a position of central interest because of their excellent stimulatory capacity, combined with their ability to process and present antigens to both naive CD4 and CD8 cells. The long impasse in identifying molecular targets for specific immunotherapy of RCC is now rapidly being overcome through the use of tools and information emerging from human genome research. Identification of candidate molecules expressed by RCC using cDNA arrays, combined with protein arrays and identification of peptides presented by MHC molecules, allow specific vaccines to be tailored to the antigenic profile of individual tumors, providing the basis for development of patient-specific vaccines.B. Frankenberger and S. Regn made equal contributions to these studies     

Immunotherapy for esophageal carcinoma

Recent progress in gene technology has clarified the existence of some cancer-rejection genes and peptides such as MAGE, MART, etc. Many clinical trials with cancer vaccines have been performed. Since the clinical efficacy of HLA class I-restricted peptide vaccines is still poor, many researchers are mainly administering dendritic cell therapies. However, there have been few clinicals trials of cancer-specific immunotherapy for esophageal carcinomas. We have performed cancer vaccine therapy with SART-1 peptide and locoregional adoptive immunotherapy with activated autologous lymphocytes for patients with advanced esophageal carcinoma in a phase I and a phase I/II trial, respectively. The clinical responses were poor in the vaccine trial because of the rapid growth of esophageal cancers and the requirement for more than 2 months to activate and increase killer T cells after in vivo vaccination, while locoregional adoptive immunotherapy was effective for the treatment of esophageal cancers even in advanced stages with organ metastases. Based on these results, we think that a combination immunotherapy with adoptive immunotherapy and vaccine therapy is needed for the treatment of advanced esophageal carcinomas.     

Talimogene Laherparepvec in Non-Melanoma Cancers

BackgroundTalimogene laherparepvec (T-VEC) is the first oncolytic virus therapy approved by the United States Food and Drug Administration (in 2015) for the treatment of advanced-stage melanoma. Despite a paucity of Phase III trials for T-VEC as a therapy for non-melanoma cancers, successful off-label use of T-VEC for this purpose has been reported in the literature.ObjectiveWe sought to review the literature describing T-VEC as a treatment for non-melanoma cancer.MethodsSystematic searches of the PubMed literature database and ClinicalTrials.gov website were performed in July 2020, focusing on T-VEC in combination with non-melanoma cancer, including squamous cell carcinoma, Merkel cell carcinoma, sarcoma, cutaneous B-cell lymphoma, and cutaneous T-cell lymphoma. Articles were screened based on their title and abstract.ResultsNine articles with 87 patients were included. Relevant articles included case reports, case series, and Phase I and Phase II trials. The majority of patients in the studies had refractory cancers or had been heavily pretreated. Overall, T-VEC demonstrated efficacy for non-melanoma cancer, both independently and in combination with biologics.ConclusionT-VEC has demonstrated efficacy for non-melanoma cancers. Phase III trials of T-VEC for this indication are warranted to expand its clinical utility.     

Identification of HLA-DRB1*1501-restricted T-cell epitopes from human prostatic acid phosphatase

BACKGROUND: The crucial role of CD4 T-cells in anti-tumor immune response is widely recognized, yet the identification of HLA class II-restricted epitopes derived from tumor antigens has lagged behind compared to class I epitopes. This is particularly true for prostate cancer. Based on the hypothesis that successful cancer immunotherapy will likely resemble autoimmunity, we searched for the CD4 T-cell epitopes derived from prostatic proteins that are restricted by human leukocyte antigen (HLA)-DRB1*1501, an allele associated with granulomatous prostatitis (GP), a disease that may have an autoimmune etiology. One of the antigens implicated in the development of autoimmunity in the prostate is prostatic acid phosphatase (PAP), which is also considered a promising target for prostate cancer immunotherapy. METHODS: We immunized transgenic (tg) mice engineered to express HLA-DRB1*1501 with human PAP. A library of overlapping 20-mer peptides spanning the entire human PAP sequence was screened in vitro for T-cell recognition by proliferative and interferon (IFN)-gamma enzyme-linked immunosorbent spot (ELISPOT) assays. RESULTS: We identified two 20-mer peptides, PAP (133-152), and PAP (173-192), that were immunogenic and naturally processed from whole PAP in HLA-DRB1*1501 tg mice. These peptides were also capable of stimulating CD4 T lymphocytes from HLA-DRB1*1501-positive patients with GP and normal donors. CONCLUSIONS: These peptides can be used for the design of a new generation of peptide-based vaccines against prostate cancer. The study can also be helpful in understanding the role of autoimmunity in the development of some forms of chronic prostatitis.     

Mechanisms of action of bacillus Calmette-Guérin in the treatment of superficial bladder cancer

Summary Local immunotherapy with bacillus Calmette-Guérin (BCG) is an effective treatment to prevent recurrence and progression of superficial bladder cancer, but the antitumor mechanism of action of BCG remains unclear. There are some experimental and clinical data suggesting that BCG antigens are processed not only by immunocompetent cells but also by urothelial cells and tumor cells. The foreign antigen may be presented at the cell curface by major histocompatibility complex (MHC) class II molecules and recognized by CD4 cells. The cytotoxic effect could result from the direct activity of CD4 cells or from the cytotoxic effect of released cytokines and the activation of other cytotoxic cells [cytolytic T-lymphocytes CTLs; CD8 cells), macrophages, natural killer (NK) or lymphokine-activated killer (LAK) cells]. These mechanisms are also involved in tumorrejection, and the identification of some specific tumor rejection antigens presented to specific CTLs could provide new therapeutic approaches.     

IMMUNOTHERAPY,INCLUDING GENE THERAPY,FOR METASTATIC MELANOMA

Current standard therapy for distant metastatic melanoma is ineffective and often compromises the quality of a patient's life. Immunotherapy is briefly reviewed in relation to its many forms: from local non-specific to the more recent specific vaccines, including those using specific melanoma peptides (e.g. from the proteins encoded by melanoma-associated gene (MAGE)) and those involving genetically transduced autologous melanoma cells using retroviral vectors in vitro. The mode of action of genetically transduced melanoma cells incorporating the granulocyte macrophage colony stimulating factor (GM-CSF) gene (GVAX) is presented as a paradigm for cytokine-mediated strategies. Trials of GVAX and other cytokine gene strategies are under way in Brisbane, Boston and Amsterdam, and some interim perspectives on the clinical outcomes and immunological mechanisms involved are sketched. Some of the compounding problems in immunotherapeutic strategies for cancer are identified, and possible adjunct manoeuvres for overcoming them are discussed.