Recognition of prostate and breast tumor cells by helper T lymphocytes specific for a prostate and breast tumor-associated antigen, TARP

TARP as antigen in cancer immunotherapy

In recent decades, immunotherapy has become a pivotal element in cancer treatment. A remaining challenge is the identification of cancer-associated antigens suitable as targets for immunotherapeutics with potent on-target and few off-tumor effects. The T-cell receptor gamma (TCRγ) chain alternate reading frame protein (TARP) was first discovered in the human prostate and androgen-sensitive prostate cancer. Thereafter, TARP was also identified in breast and endometrial cancers, salivary gland tumors, and pediatric and adult acute myeloid leukemia. Interestingly, TARP promotes tumor cell proliferation and migration, which is reflected in an association with worse survival. TARP expression in malignant cells, its role in oncogenesis, and its limited expression in normal tissues raised interest in its potential utility as a therapeutic target, and led to development of immunotherapeutic targeting strategies. In this review, we provide an overview of TARP expression, its role in different cancer types, and currently investigated TARP-directed immunotherapeutic options.

Expression of placenta-specific 1 and its potential for eliciting anti-tumor helper T-cell responses in head and neck squamous cell carcinoma

Placenta-specific 1 (PLAC1) is expressed primarily in placental trophoblasts but not in normal tissues and is a targetable candidate for cancer immunotherapy because it is a cancer testis antigen known to be up-regulated in various tumors. Although peptide epitopes capable of stimulating CD8 T cells have been previously described, there have been no reports of PLAC1 CD4 helper T lymphocyte (HTL) epitopes and the expression of this antigen in head and neck squamous cell carcinoma (HNSCC). Here, we show that PLAC1 is highly expressed in 74.5% of oropharyngeal and 51.9% of oral cavity tumors from HNSCC patients and in several HNSCC established cell lines. We also identified an HTL peptide epitope (PLAC1_31-50) capable of eliciting effective antigen-specific and tumor-reactive T cell responses. Notably, this peptide behaves as a promiscuous epitope capable of stimulating T cells in the context of more than one human leukocyte antigen (HLA)-DR allele and induces PLAC1-specific CD4 T cells that kill PLAC1-positive HNSCC cell lines in an HLA-DR-restricted manner. Furthermore, T-cells reactive to PLAC1_31-50 peptide were detected in the peripheral blood of HNSCC patients. These findings suggest that PLAC1 represents a potential target antigen for HTL based immunotherapy in HNSCC.

Elevated TARP promotes proliferation and metastasis of salivary adenoid cystic carcinoma

OBJECTIVE

This study aims to analyze the expression of T-cell receptor γ chain alternate reading frame protein (TARP) in salivary adenoid cystic carcinoma (SACC) and its distant metastases and to investigate its influences on the development and progression of SACC.

STUDY DESIGN

TARP expression was analyzed in 50 primary SACCs, 13 specimens of metastatic adenoid cystic carcinoma of salivary gland origin, and 20 noncancerous tissues around SACC via immunohistochemistry. Cell Counting Kit-8 tests, wound healing assay, and Transwell experiments were performed to evaluate the effects of lentivirus-mediated TARP overexpression on the proliferation, migration, and invasion of SACC cells.

RESULTS

TARP expression was significantly increased in primary SACCs compared with adjacent noncancerous tissues, and this increase was further enhanced in metastases compared with primary SACCs. The expression level of TARP correlated significantly with tumor size, tumor-node-metastasis stage, perineural invasion, histologic type, and distant metastasis. Furthermore, TARP overexpression promoted the growth, migration, and invasion of SACC cells.

CONCLUSIONS

TARP plays an important role in and may be used as a marker to indicate the development and progression of SACC.

TARP vaccination is associated with slowing in PSA velocity and decreasing tumor growth rates in patients with Stage D0 prostate cancer

T-cell receptor alternate reading frame protein (TARP) is a 58-residue protein over-expressed in prostate and breast cancer. We investigated TARP peptide vaccination's impact on the rise in PSA (expressed as Slope Log(PSA) or PSA Doubling Time (PSADT)), validated tumor growth measures, and tumor growth rate in men with Stage D0 prostate cancer. HLA-A*0201 positive men were randomized to receive epitope-enhanced (29-37-9V) and wild-type (27-35) TARP peptides administered as a Montanide/GM-CSF peptide emulsion or as an autologous peptide-pulsed dendritic cell vaccine every 3 weeks for a total of five vaccinations with an optional 6th dose of vaccine at 36 weeks based on immune response or PSADT criteria with a booster dose of vaccine for all patients at 48 and 96 weeks. 41 patients enrolled with median on-study duration of 75 weeks at the time of this analysis. Seventy-two percent of patients reaching 24 weeks and 74% reaching 48 weeks had a decreased Slope Log(PSA) compared to their pre-vaccination baseline (p = 0.0012 and p = 0.0004 for comparison of overall changes in Slope Log(PSA), respectively). TARP vaccination also resulted in a 50% decrease in median tumor growth rate (g): pre-vaccine g = 0.0042/day, post-vaccine g = 0.0021/day (p = 0.003). 80% of subjects exhibited new vaccine-induced TARP-specific IFNγ ELISPOT responses but they did not correlate with decreases in Slope Log(PSA). Thus, vaccination with TARP peptides resulted in significant slowing in PSA velocity and reduction in tumor growth rate in a majority of patients with PSA biochemical recurrence.

Peptide vaccines in breast cancer: The immunological basis for clinical response

This review discusses peptide-based vaccines in breast cancer, immune responses and clinical outcomes, which include studies on animal models and phase I, phase I/II, phase II and phase III clinical trials. Peptide-based vaccines are powerful neoadjuvant immunotherapies that can directly target proteins expressed in tumor cells, mainly tumor-associated antigens (TAAs). The most common breast cancer TAA epitopes are derived from MUC1, HER2/neu and CEA proteins. Peptides derived from TAAs could be successfully used to elicit CD8 and CD4 T cell-specific responses. Thus, choosing peptides that adapt to natural variations of human leukocyte antigen (HLA) genes is critical. The most attractive advantage is that the target response is more specific and less toxic than for other therapies and vaccines. Prominent studies on NeuVax - E75 (epitope for HER2/neu and GM-CSF) in breast cancer and DPX-0907 (HLA-A2-TAAs) expressed in breast cancer, ovarian and prostate cancer have shown the efficacy of peptide-based vaccines as neoadjuvant immunotherapy against cancer. Future peptide vaccine strategies, although a challenge to be applied in a broad range of breast cancers, point to the development of degenerate multi-epitope immunogens against multiple targets.

Molecular characterization of the feline T-cell receptor γ alternate reading frame protein (TARP) ortholog

T-cell receptor γ alternate reading frame protein (TARP) is expressed by human prostate epithelial, prostate cancer, and mammary cancer cells, but is not found in normal mammary tissue. To date, this protein has only been described in humans. Additionally, no animal model has been established to investigate the potential merits of TARP as tumor marker or a target for adoptive tumor immunotherapy. In this study conducted to characterize feline T-cell receptor γ sequences, constructs very similar to human TARP transcripts were obtained by RACE from the spleen and prostate gland of cats. Transcription of TARP in normal, hyperplastic, and neoplastic feline mammary tissues was evaluated by conventional RT-PCR. In felines similarly to the situation reported in humans, a C-region encoding two open reading frames is spliced to a J-region gene. In contrast to humans, the feline J-region gene was found to be a pseudogene containing a deletion within its recombination signal sequence. Our findings demonstrated that the feline TARP ortholog is transcribed in the prostate gland and mammary tumors but not normal mammary tissues as is the case with human TARP.

T cells engineered with a T cell receptor against the prostate antigen TARP specifically kill HLA-A2+ prostate and breast cancer cells

To produce genetically engineered T cells directed against prostate and breast cancer cells, we have cloned the T-cell receptor recognizing the HLA-A2-restricted T-cell receptor γ-chain alternate reading-frame protein (TARP)(4-13) epitope. TARP is a protein exclusively expressed in normal prostate epithelium and in adenocarcinomas of the prostate and breast. Peripheral blood T cells transduced with a lentiviral vector encoding the TARP-TCR proliferated well when exposed to peptide-specific stimuli. These cells exerted peptide-specific IFN-γ production and cytotoxic activity. Importantly, HLA-A2(+) prostate and breast cancer cells expressing TARP were also killed, demonstrating that the TARP(4-13) epitope is a physiologically relevant target for T-cell therapy of prostate and breast cancer. In conclusion, we present the cloning of a T cell receptor (TCR) directed against a physiologically relevant HLA-A2 epitope of TARP. To our knowledge this report on engineering of T cells with a TCR directed against an antigen specifically expressed by prostate cells is unique.

Tumor-associated antigens for specific immunotherapy of prostate cancer

Prostate cancer (PCa) is the most common noncutaneous cancer diagnosis and the second leading cause of cancer-related deaths among men in the United States. Effective treatment modalities for advanced metastatic PCa are limited. Immunotherapeutic strategies based on T cells and antibodies represent interesting approaches to prevent progression from localized to advanced PCa and to improve survival outcomes for patients with advanced disease. CD8⁺ cytotoxic T lymphocytes (CTLs) efficiently recognize and destroy tumor cells. CD4⁺ T cells augment the antigen-presenting capacity of dendritic cells and promote the expansion of tumor-reactive CTLs. Antibodies mediate their antitumor effects via antibody-dependent cellular cytotoxicity, activation of the complement system, improving the uptake of coated tumor cells by phagocytes, and the functional interference of biological pathways essential for tumor growth. Consequently, several tumor-associated antigens (TAAs) have been identified that represent promising targets for T cell- or antibody-based immunotherapy. These TAAs comprise proteins preferentially expressed in normal and malignant prostate tissues and molecules which are not predominantly restricted to the prostate, but are overexpressed in various tumor entities including PCa. Clinical trials provide evidence that specific immunotherapeutic strategies using such TAAs represent safe and feasible concepts for the induction of immunological and clinical responses in PCa patients. However, further improvement of the current approaches is required which may be achieved by combining T cell- and/or antibody-based strategies with radio-, hormone-, chemo- or antiangiogenic therapy.

Current vaccination strategies for prostate cancer

CONTEXT

The first therapeutic cancer vaccine demonstrating effectiveness in a phase 3 study was approved by the US Food and Drug Administration on 29 April 2010. The pivotal trial demonstrated overall survival (OS) benefit in patients treated with antigen-loaded leukapheresis cells compared with a control infusion. Results of other prostate cancer (PCa) vaccination strategies are awaited, as this approach may herald a new era in the care for patients with advanced PCa.

OBJECTIVE

Consider effectiveness and safety of vaccination strategies in the treatment of PCa.

EVIDENCE ACQUISITION

We searched three bibliographic databases (January 1995 through October 2010) for randomised phase 2 and 3 studies of vaccination strategies for PCa based on predetermined relevant Medical Subject Heading terms and free text terms.

EVIDENCE SYNTHESIS

Data from 3 randomised phase 3 and 10 randomised phase 2 vaccination trials are discussed with respect to clinical outcome in terms of progression-free survival and OS, toxicity, prostate-specific antigen (PSA) response, and immunologic response. Three phase 3 trials (D9901, D9902A, and D9902B) that enrolled a total of 737 patients, all controlled and double-blinded, tested the efficacy of sipuleucel-T. The largest of these three trials, called Immunotherapy for Prostate Adenocarcinoma Treatment (IMPACT), has demonstrated safety and effectiveness of sipuleucel-T (now marketed as Provenge) as measured by prolonged survival of 512 asymptomatic patients with metastatic castration-resistant PCa (mCRPC). The study showed a 4.1-mo median survival benefit in the sipuleucel-T vaccine-treated group compared with the control group (25.8 vs 21.7 mo; hazard ratio [HR]: 0.78; 95% confidence interval [CI], 0.62-0.98; p=0.032) and extended 3-yr survival (31.7% vs 23.0%). In contrast, two phase 3 vaccination trials with a whole-tumour-cell mixture of two PCa cell lines (GVAX) and testing GVAX either alone or in combination with chemotherapy versus chemotherapy alone (VITAL1 and 2) were terminated prematurely based on futility and increased deaths. Other phase 2 vaccination trials testing different types of vaccines in castration-resistant PCa patients have been reported with variable outcomes. Notably, a controlled, double-blind, randomised phase 2 vaccine trial of PROSTVAC-VF, a recombinant viral vector containing complementary DNA encoding PSA, in 125 patients with chemotherapy-naïve, minimally symptomatic mCRPC also demonstrated safety but no significant effect on the time to disease progression. In comparison with controls (n=40), PROSTVAC-VF-treated patients (n=82) experienced longer median survival of 8.5 mo (25.1 vs 16.6 mo; HR: 0.56; 95% CI, 0.37-0.85; p=0.0061) and extended 3-yr survival (30% vs 17%). In general, PCa vaccines are perceived to have less toxicity compared with current cytotoxic or targeted therapies. Evaluation of clinical efficacy of different vaccination strategies (eg, protein-, peptide- and DNA-based vaccines) in the context of properly designed and controlled phase 3 studies is warranted.

CONCLUSIONS

Cancer vaccines represent a new paradigm in the treatment of PCa. The IMPACT trial showed improved survival but no difference in time to disease progression in mCRPC patients with minimal tumour burden. Observations in phase 2 and 3 trials pave the way for other vaccination approaches for this disease, raise questions regarding the most appropriate clinical trial designs, and underscore the importance of identifying biomarkers for antitumour effect to better implement such therapies.

Developing an effective breast cancer vaccine

BACKGROUND

Harnessing the immune response in treating breast cancer would potentially offer a less toxic, more targeted approach to eradicating residual disease. Breast cancer vaccines are being developed to effectively train cytotoxic T cells to recognize and kill transformed cells while sparing normal ones. However, achieving this goal has been problematic due to the ability of established cancers to suppress and evade the immune response.

METHODS

A review of the literature on vaccines and breast cancer treatment was conducted, specifically addressing strategies currently available, as well as appropriate settings, paradigms for vaccine development and response monitoring, and challenges with immunosuppression.

RESULTS

Multiple issues need to be addressed in order to optimize the benefits offered by breast cancer vaccines. Primary issues include the following: (1) cancer vaccines will likely work better in a minimal residual disease state, (2) clinical trial design for immunotherapy should incorporate recommendations from expert groups such as the Cancer Vaccine Working Group and use standardized immune response measurements, (3) the presently available cancer vaccine approaches, including dendritic cell-based, tumor-associated antigen peptide-based, and whole cell-based, have various pros and cons, (4) to date, no one approach has been shown to be superior to another, and (5) vaccines will need to be combined with immunoregulatory agents to overcome tumor-related immunosuppression.

CONCLUSIONS

Combining a properly optimized cancer vaccine with novel immunomodulating agents that overcome tumor-related immunosuppression in a well-designed clinical trial offers the best hope for developing an effective breast cancer vaccine strategy.

Antibody responses to galectin-8, TARP and TRAP1 in prostate cancer patients treated with a GM-CSF-secreting cellular immunotherapy

A critical factor in clinical development of cancer immunotherapies is the identification of tumor-associated antigens that may be related to immunotherapy potency. In this study, protein microarrays containing >8,000 human proteins were screened with serum from prostate cancer patients (N = 13) before and after treatment with a granulocyte-macrophage colony-stimulating factor (GM-CSF)-secreting whole cell immunotherapy. Thirty-three proteins were identified that displayed significantly elevated (P Collapse

Key Words

• immunotherapy
• tumor antigen
• autoantibody
• protein microarray
• prostate cancer
• biomarker

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MESH Headings

• Antibodies/blood
• Antibodies/immunology
• Biomarkers, Pharmacological
• Biomarkers, Tumor/immunology
• Clinical Trials as Topic
• Disease Progression
• Galectins/immunology
• Granulocyte-Macrophage Colony-Stimulating Factor/therapeutic use
• HSP90 Heat-Shock Proteins/biosynthesis
• HSP90 Heat-Shock Proteins/genetics
• HSP90 Heat-Shock Proteins/immunology
• High-Throughput Screening Assays
• Humans
• Immunotherapy, Adoptive
• Male
• Neoplasm Metastasis
• Nuclear Proteins/biosynthesis
• Nuclear Proteins/genetics
• Nuclear Proteins/immunology
• Prognosis
• Prostatic Neoplasms/diagnosis
• Prostatic Neoplasms/immunology
• Prostatic Neoplasms/mortality
• Prostatic Neoplasms/pathology
• Prostatic Neoplasms/therapy
• Protein Array Analysis
• Retrospective Studies
• Survival Analysis
• Treatment Outcome

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Grants Collapse

Affiliation(s)

Minh C. Nguyen Cell Genesys Inc., 500 Forbes Blvd, South San Francisco, CA 94080 USA
Guang Huan Tu Cell Genesys Inc., 500 Forbes Blvd, South San Francisco, CA 94080 USA
Kathryn E. Koprivnikar Cell Genesys Inc., 500 Forbes Blvd, South San Francisco, CA 94080 USA
Melissa Gonzalez-Edick Cell Genesys Inc., 500 Forbes Blvd, South San Francisco, CA 94080 USA
Karin U. Jooss Cell Genesys Inc., 500 Forbes Blvd, South San Francisco, CA 94080 USA
Thomas C. Harding Cell Genesys Inc., 500 Forbes Blvd, South San Francisco, CA 94080 USA Five Prime Therapeutics, Inc., 1650 Owens Street Suite 200, San Francisco, CA 94158 USA

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Therapeutic vaccines in metastatic castration-resistant prostate cancer: principles in clinical trial design

Although docetaxel was approved for the treatment of metastatic castration-resistant prostate cancer in 2004, additional therapies are still required. Prostate cancer is often slow-growing and expresses many tumor-associated antigens, making it a feasible target for immunotherapy. Several therapeutic cancer vaccines have been developed for prostate cancer, including antigen-presenting-cell-based, vector-based, and whole tumor cell vaccines. Initial trials demonstrated that vaccine approaches have limited toxicity. Clinical trials of targeted biologic therapies have demonstrated that patient selection is vital, and there is preliminary evidence that clinical parameters can be used to encompass metastatic prostate cancer patients who will more probably respond to vaccine treatment. In addition to appropriate patient selection, a successful clinical trial must have an appropriate primary endpoint as well. Three randomized, 'placebo'-controlled studies in metastatic castration-resistant prostate cancer have suggested a clinically significant survival advantage in spite of a lack of improvement in time to progression, implying that overall survival is the ideal endpoint for such trials. Careful examination of data from completed immunotherapy clinical trials in prostate cancer has identified appropriate patient populations and endpoints. Those principles need to be applied to future trial design to properly evaluate prostate cancer vaccines.

Genome-wide high-resolution screening in Dupuytren's disease reveals common regions of DNA copy number alterations

PURPOSE

Dupuytren's disease (DD) is a familial disorder with a high genetic susceptibility in white people; however, its etiopathogenesis remains unknown. Previous comparative genomic hybridization studies using lower-resolution, 44-k oligonucleotide-based arrays revealed no copy number variation (CNV) changes in DD. In this study, we used a higher-resolution genome-wide screening (next-generation microarrays) comprising 963,331 human sequences (3 kb spacing between probes) for whole genome DNA variation analysis. The objective was to detect cryptic chromosomal imbalances in DD.

METHODS

Agilent SurePrint G3 microarrays, one million format (Agilent Technologies, Santa Clara, CA), were used to detect CNV regions (CNVRs) in DNA extracted from nodules of 4 white men with DD (age, 69 +/- 4 y). Reference samples were from the DNA of 10 men who served as control patients. Copy number variations that were common to greater than 3 assessed DD individuals (p < .05) were selected as candidate loci for DD etiology. In addition, quantitative polymerase chain reactions (qPCR) assays were designed for selected CNVRs on DNA from 13 DD patients and 11 control patients. Independent t-tests and Fisher's exact tests were carried out for statistical analysis.

RESULTS

Three novel CNVs previously unreported in the phenotypically normal population were detected in 3 DD cases, located at 10q22, 16p12.1, and 17p12. Nine polymorphic CNVRs potentially associated with DD were determined using our strategic selection criteria, locating to chromosomes 1q31, 6p21, 7p14, 8p11, 12p13, 14q11, 17q21 and 20p13. More than 3 of the DD cases tested had a CNVR located to a small region on 6p21 and 4 CNVRs within 6p21-22 of the human leukocyte antigen (HLA) genes.

CONCLUSIONS

Three novel copy number alterations were observed in 3 unrelated patients with sporadic (no known family history) DD. Nine polymorphic CNVRs were found to be common among the DD cases. These variants might contain genes involved in DD formation, indicating that important gene networks expressed within the palmar fascia might contribute to genetic susceptibility of DD.

Peptide epitope identification for tumor-reactive CD4 T cells

Because T lymphocytes have the capacity to recognize tumor cells, significant efforts are being devoted towards the development of T cell-based immunotherapy for cancer. Most of this work has centered in the induction of anti-tumor CD8 T cells, which exhibit cytolytic activity towards tumor cells expressing tumor-specific or tumor associated antigens. Unfortunately to this day, T cell-based immunotherapy for cancer remains suboptimal. One of the possible explanations is that these immunotherapies have ignored the role that CD4 T helper lymphocytes play in the generation and persistence of CD8 T cell responses. Thus, we believe that in order to obtain clinical benefits T cell-based immunotherapy must stimulate both CD8 and CD4 tumor-reactive T cell responses. During the past seven years our group has focused on the identification of CD4 T cell epitopes from tumor-associated and tumor-specific antigens that could be used to complement the already identified CD8 T cell epitopes to produce effective vaccination strategies against numerous tumor types. We will describe here the strategy we used that resulted in the identification and characterization of numerous CD4 T cell epitopes that are applicable to developing therapies against hematological malignancies and solid tumors.

Induction of EBV-latent membrane protein 1-specific MHC class II-restricted T-cell responses against natural killer lymphoma cells

EBV-encoded latent membrane protein 1 (LMP1) has oncogenic potential and is expressed in many EBV-associated malignancies. Although LMP1 is regarded as a potential tumor-associated antigen for immunotherapy and several LMP1-specific MHC class I-restricted CTL epitopes have been reported, little is known regarding MHC class II-restricted CD4 helper T-lymphocyte (HTL) epitopes for LMP1. The goal of the present studies was to determine whether MHC class II-restricted CD4 T-cell responses could be induced against the LMP1 antigen and to evaluate the antitumor effect of these responses. We have combined the use of a predictive MHC class II binding peptide algorithm with in vitro vaccination of CD4 T cells using candidate peptides to identify naturally processed epitopes derived from LMP1 that elicit immune responses against EBV-expressing tumor cells. Peptide LMP1(159-175) was effective in inducing HTL responses that were restricted by HLA-DR9, HLA-DR53, or HLA-DR15, indicating that this peptide behaves as a promiscuous T-cell epitope. Moreover, LMP1(159-175)-reactive HTL clones directly recognized EBV lymphoblastoid B cells, EBV-infected natural killer (NK)/T-lymphoma cells and naturally processed antigen in the form of LMP1+ tumor cell lysates presented by autologous dendritic cells. Because the newly identified epitope LMP1(159-175) overlaps with an HLA-A2-restricted CTL epitope (LMP1(159-167)), this peptide might have the ability to induce simultaneous CTL and HTL responses against LMP1. Overall, our data should be relevant for the design and optimization of T-cell epitope-based immunotherapy against various EBV-associated malignancies, including NK/T cell lymphomas.

HLA class II antigen presentation by prostate cancer cells

Prostate cancer is the second most commonly diagnosed cancer in men. Recent evidence suggests that reduced expression of target protein antigens and human leukocyte antigen (HLA) molecules is the predominant immune escape mechanism of malignant prostate tumor cells. The purpose of this study was to investigate the prospect of antigen specific immunotherapy against prostate cancer via the HLA class II pathway of immune recognition. Here, we show for the first time that prostate cancer cells express HLA class II proteins that are recognized by CD4+ T cells. Prostate tumor cells transduced with class II molecules efficiently presented tumor-associated antigens/peptides to CD4+ T cells. This data suggests that malignant prostate tumors can be targeted via the HLA class II pathway, and that class II-positive tumors could be employed for direct antigen presentation, and CD4+ T-cell mediated tumor immunotherapy.Prostate Cancer and Prostatic Diseases (2008) 11, 334-341; doi:10.1038/sj.pcan.4501021; published online 16 October 2007.

Targeting tumours by adoptive transfer of immune cells

1. Surgery, radiotherapy and chemotherapy are the most widely used and well-established modalities for treating malignant diseases. Surgery is used to excise solid tumours and radiotherapy/chemotherapy are used for the treatment of liquid tumours and for solid tumours where there is a risk of micrometastases. A major drawback for both radiotherapy and chemotherapy is their lack of specificity for tumour cells. Both these treatments can destroy normal bone marrow cells and result in severe side-effects. 2. The impairment of haemapoiesis due to bone marrow destruction combined with the use of toxins in chemotherapy that inhibit the proliferation of immune cells leaves many patients immunocompromised. This complicates the development of prophylactic (vaccine) strategies for tumours where patients are undergoing conventional therapy. 3. An alternative approach is to expand and activate tumour-specific immune cells in vitro that can then be adoptively transferred back in large numbers. This is defined as adoptive immunotherapy and has the advantage of potentially bypassing the immuno-inhibitory effects of conventional therapies. 4. Transferred immune cells have been shown to mediate tumour regression in patients by both direct and indirect mechanisms. The immune cells used include tumour reactive T lymphocytes and dendritic cells, which elicit tumour specific responses. 5. Many novel cell-based immunotherapeutic strategies developed in murine tumour models are now being applied in human clinical trials. The malignancies targeted include melanoma, chronic myelogenous leukaemia and breast, ovarian, colon and kidney cancers. In the present review, we discuss these novel cell-based strategies and the implications they have for the future treatment of human malignancies.

Recognition of prostate and melanoma tumor cells by six-transmembrane epithelial antigen of prostate-specific helper T lymphocytes in a human leukocyte antigen class II-restricted manner

The six-transmembrane epithelial antigen of prostate (STEAP) protein is an attractive candidate for T cell-based immunotherapy because it is overexpressed in prostate cancer and various other tumor types. Several peptide epitopes capable of stimulating CTLs that killed STEAP-expressing tumor cells have been described. Our goal was the identification of helper T lymphocyte (HTL) epitopes of STEAP for the optimization of T cell-based immunotherapies against STEAP-expressing malignancies. Candidate HTL epitopes for STEAP were predicted using in silico algorithms for HLA class II-binding peptides and were tested for their ability to elicit HTL responses by in vitro peptide vaccination of CD4 T lymphocytes from healthy individuals and prostate cancer patients. Two peptides (STEAP(102-116) and STEAP(192-206)) were effective in stimulating in vitro antitumor HTL responses in both normal individuals and prostate cancer patients. Notably, both STEAP HTL peptides behaved as promiscuous T-cell epitopes because they stimulated T cells in the context of more than one MHC class II allele. These newly described STEAP HTL epitopes could be of value for the design and optimization of T cell-based immunotherapy against STEAP-expressing tumors.

Vaccination therapy in prostate cancer

Radical prostatectomy and radiation therapy provide excellent localized prostate cancer (PC) control. Although the majority of prostate carcinoma is nowadays diagnosed at early stages with favourable risk features, in patients up to 30-40% it recurs within 10 years. Furthermore, the lack of effective therapies, once prostate carcinoma becomes refractory to androgen deprivation, mandates the development of alternative therapeutic options. There is a growing interest in harnessing the potency and specificity of anti-tumour immunity through the generation of fully competent dendritic cells and tumour reactive effector lymphocytes. Several strategies to treat or prevent the development of metastatic PC have been explored in clinical trials and are summarized in this review, considering also the feasibility and safety of these approaches. In some cases clinical responses were achieved showing that vaccine-primed T cells induced anti-tumour activity in vivo. The present findings and perspectives of the immunologic interventions in PC patients will be discussed.

Alternative translational products and cryptic T cell epitopes: expecting the unexpected

Although CD8 T cell epitopes have been studied extensively, often overlooked are unconventional cryptic epitopes generated from nontraditional sources of peptides/proteins and/or mechanisms of translation. In this review, we discuss alternative reading frame epitopes, both mechanistically and also in terms of their physiologic importance in the induction of antiviral and antitumor CTL responses. Issues of the influence of cryptic translational products on foreign and self-Ag diversity, thymic selection, and the T cell repertoire; disease pathogenesis; and approaches to vaccine design are discussed in context of the potentially large impact of unconventional epitopes on T cell immunity.

Functional Analysis of Birch Pollen Allergen Bet v 1-Specific Regulatory T Cells

Allergen-specific immunotherapy using peptides is an efficient treatment for allergic diseases. Recent studies suggest that the induction of CD4+ regulatory T (Treg) cells might be associated with the suppression of allergic responses in patients after allergen-specific immunotherapy. Our aim was to identify MHC class II promiscuous T cell epitopes for the birch pollen allergen Bet v 1 capable of stimulating Treg cells with the purpose of inhibiting allergic responses. Ag-reactive CD4+ T cell clones were generated from patients with birch pollen allergy and healthy volunteers by in vitro vaccination of PBMC using Bet v 1 synthetic peptides. Several CD4+ T cell clones were induced by using 2 synthetic peptides (Bet v 1(141-156) and Bet v 1(51-68)). Peptide-reactive CD4+ T cells recognized recombinant Bet v 1 protein, indicating that these peptides are produced by the MHC class II Ag processing pathway. Peptide Bet v 1(141-156) appears to be a highly MHC promiscuous epitope since T cell responses restricted by numerous MHC class II molecules (DR4, DR9, DR11, DR15, and DR53) were observed. Two of these clones functioned as typical Treg cells (expressed CD25, GITR, and Foxp3 and suppressed the proliferation and IL-2 secretion of other CD4+ T cells). Notably, the suppressive activity of these Treg cells required cell-cell contact and was not mediated through soluble IL-10 or TGF-beta. The identified promiscuous MHC class II epitope capable of inducing suppressive Treg responses may have important implication for the development of peptide-based Ag-specific immunotherapy to birch pollen allergy.

In vitro peptide immunization of target tax protein human T-cell leukemia virus type 1-specific CD4+ helper T lymphocytes

PURPOSE

Adult T-cell leukemia/lymphoma induced by human T-cell leukemia virus type 1 (HTLV-1) is usually a fatal lymphoproliferative malignant disease. HTLV-1 Tax protein plays a critical role in HTLV-1-associated leukemogenesis and is an attractive target for vaccine development. Although HTLV-1 Tax is the most dominant antigen for HTLV-1-specific CD8(+) CTLs in HTLV-1-infected individuals, few epitopes recognized by CD4(+) helper T lymphocytes in HTLV-1 Tax protein have been described. The aim of the present study was to study T-helper-cell responses to HTLV-1 Tax and to identify naturally processed MHC class II-restricted epitopes that could be used for vaccine development.

EXPERIMENTAL DESIGN

An MHC class II binding peptide algorithm was used to predict potential T-helper cell epitope peptides from HTLV-1 Tax. We assessed the ability of the corresponding peptides to elicit helper T-cell responses by in vitro vaccination of purified CD4(+) T lymphocytes.

RESULTS

Peptides Tax(191-205) and Tax(305-319) were effective in inducing T-helper-cell responses. Although Tax(191-205) was restricted by the HLA-DR1 and DR9 alleles, responses to Tax(305-319) were restricted by either DR15 or DQ9. Both these epitopes were found to be naturally processed by HTLV-1(+) T-cell lymphoma cells and by autologous antigen-presenting cells that were pulsed with HTLV-1 Tax(+) tumor lysates. Notably, the two newly identified helper T-cell epitopes are found to lie proximal to known CTL epitopes, which will facilitate the development of prophylactic peptide-based vaccine capable of inducing simultaneous CTL and T-helper responses.

CONCLUSION

Our data suggest that HTLV-1 Tax protein could serve as tumor-associated antigen for CD4(+) helper T cells and that the present epitopes might be used for T-cell-based immunotherapy against tumors expressing HTLV-1.

Defining MHC class II T helper epitopes for WT1 tumor antigen

The product of Wilms' tumor gene 1 (WT1) is overexpressed in diverse human tumors, including leukemia, lung and breast cancer, and is often recognized by antibodies in the sera of patients with leukemia. Since WT1 encodes MHC class I-restricted peptides recognized by cytotoxic T lymphocytes (CTL), WT1 has been considered as a promising tumor-associated antigen (TAA) for developing anticancer immunotherapy. In order to carry out an effective peptide-based cancer immunotherapy, MHC class II-restricted epitope peptides that elicit anti-tumor CD4(+) helper T lymphocytes (HTL) will be needed. In this study, we analyzed HTL responses against WT1 antigen using HTL lines elicited by in vitro immunization of human lymphocytes with synthetic peptides predicted to serve as HTL epitopes derived from the sequence of WT1. Two peptides, WT1(124-138) and WT1(247-261), were shown to induce peptide-specific HTL, which were restricted by frequently expressed HLA class II alleles. Here, we also demonstrate that both peptides-reactive HTL lines were capable of recognizing naturally processed antigens presented by dendritic cells pulsed with tumor lysates or directly by WT1+ tumor cells that express MHC class II molecules. Interestingly, the two WT1 HTL epitopes described here are closely situated to known MHC class I-restricted CTL epitopes, raising the possibility of stimulating CTL and HTL responses using a relatively small synthetic peptide vaccine. Because HTL responses to TAA are known to be important for promoting long-lasting anti-tumor CTL responses, the newly described WT1 T-helper epitopes could provide a useful tool for designing powerful vaccines against WT1-expressing tumors.

The immunotherapy of prostate and bladder cancer

The role of the immune system in controlling the growth of tumour cells is highly complex and has been extensively debated. It is well documented that the immune system controls virally induced cancers, and there is evidence for a role of specific immunity in other types of tumours. The greater understanding of the regulation and optimization of adoptive, specific immune responses, and the better characterization of tumour-associated antigens indicate the way for active specific vaccination and cell therapy in urological tumours. Currently, bacille Calmette Guerin immunotherapy is established for localized bladder cancer and many experimental immunotherapies are under evaluation. Here we review some timely aspects of tumour immunology, and describe the current status and development of immunotherapy in prostate and bladder cancer.