A novel autocrine pathway of tumor escape from immune recognition: melanoma cell lines produce a soluble protein that diminishes expression of the gene encoding the melanocyte lineage melan-A/MART-1 antigen through down-modulation of its promoter

Assembly of Biologically Functional Structures by Nucleic Acid Templating: Implementation of a Strategy to Overcome Inhibition by Template Excess

Delivery of therapeutic molecules to pathogenic cells is often hampered by unintended toxicity to normal cells. In principle, this problem can be circumvented if the therapeutic effector molecule is split into two inactive components, and only assembled on or within the target cell itself. Such an in situ process can be realized by exploiting target-specific molecules as templates to direct proximity-enhanced assembly. Modified nucleic acids carrying inert precursor fragments can be designed to co-hybridize on a target-specific template nucleic acid, such that the enforced proximity accelerates assembly of a functional molecule for antibody recognition. We demonstrate the in vitro feasibility of this adaptation of nucleic acid-templated synthesis (NATS) using oligonucleotides bearing modified peptides (“haplomers”), for templated assembly of a mimotope recognized by the therapeutic antibody trastuzumab. Enforced proximity promotes mimotope assembly via traceless native chemical ligation. Nevertheless, titration of participating haplomers through template excess is a potential limitation of trimolecular NATS. In order to overcome this problem, we devised a strategy where haplomer hybridization can only occur in the presence of target, without being subject to titration effects. This generalizable NATS modification may find future applications in enabling directed targeting of pathological cells.

T cell receptor therapy against melanoma-Immunotherapy for the future?

Malignant melanoma has seen monumental changes in treatment options the last decade from the very poor results of dacarbazine treatment to the modern-day use of targeted therapies and immune checkpoint inhibitors. Melanoma has a high mutational burden making it more capable of evoking immune responses than many other tumours. Even when considering double immune checkpoint blockade with anti-CTLA-4 and anti-PD-1, we still have far to go in melanoma treatment as 50% of patients with metastatic disease do not respond to current treatment. Alternative immunotherapy should therefore be considered. Since melanoma has a high mutational burden, it is considered more immunogenic than many other tumours. T cell receptor (TCR) therapy could be a possible way forward, either alone or in combination, to improve the response rates of this deadly disease. Melanoma is one of the cancers where TCR therapy has been frequently applied. However, the number of antigens targeted remains fairly limited, although advanced personalized therapies aim at also targeting private mutations. In this review, we look at possible aspects of targeting TCR therapy towards melanoma and provide an implication of its use in the future.

HERV-K activation is strictly required to sustain CD133+ melanoma cells with stemness features

BACKGROUND

Melanoma is a heterogeneous tumor in which phenotype-switching and CD133 marker have been associated with metastasis promotion and chemotherapy resistance. CD133 positive (CD133+) subpopulation has also been suggested as putative cancer stem cell (CSC) of melanoma tumor. Human endogenous retrovirus type K (HERV-K) has been described to be aberrantly activated during melanoma progression and implicated in the etiopathogenesis of disease. Earlier, we reported that stress-induced HERV-K activation promotes cell malignant transformation and reduces the immunogenicity of melanoma cells. Herein, we investigated the correlation between HERV-K and the CD133+ melanoma cells during microenvironmental modifications.

METHODS

TVM-A12 cell line, isolated in our laboratory from a primary human melanoma lesion, and other commercial melanoma cell lines (G-361, WM-115, WM-266-4 and A375) were grown and maintained in the standard and stem cell media. RNA interference, Real-time PCR, flow cytometry analysis, self-renewal and migration/invasion assays were performed to characterize cell behavior and HERV-K expression.

RESULTS

Melanoma cells, exposed to stem cell media, undergo phenotype-switching and expansion of CD133+ melanoma cells, concomitantly promoted by HERV-K activation. Notably, the sorted CD133+ subpopulation showed stemness features, characterized by higher self-renewal ability, embryonic genes expression, migration and invasion capacities compared to the parental cell line. RNA interference-mediated downregulation experiments showed that HERV-K has a decisive role to expand and maintain the CD133+ melanoma subpopulation during microenvironmental modifications. Similarly, non nucleoside reverse transcriptase inhibitors (NNRTIs) efavirenz and nevirapine were effective to restrain the activation of HERV-K in melanoma cells, to antagonize CD133+ subpopulation expansion and to induce selective high level apoptosis in CD133+ cells.

CONCLUSIONS

HERV-K activation promotes melanoma cells phenotype-switching and is strictly required to expand and maintain the CD133+ melanoma cells with stemness features in response to microenvironmental modifications.

Heat shock protein-90 inhibitors enhance antigen expression on melanomas and increase T cell recognition of tumor cells

In an effort to enhance antigen-specific T cell recognition of cancer cells, we have examined numerous modulators of antigen-expression. In this report we demonstrate that twelve different Hsp90 inhibitors (iHsp90) share the ability to increase the expression of differentiation antigens and MHC Class I antigens. These iHsp90 are active in several molecular and cellular assays on a series of tumor cell lines, including eleven human melanomas, a murine B16 melanoma, and two human glioma-derived cell lines. Intra-cytoplasmic antibody staining showed that all of the tested iHsp90 increased expression of the melanocyte differentiation antigens Melan-A/MART-1, gp100, and TRP-2, as well as MHC Class I. The gliomas showed enhanced gp100 and MHC staining. Quantitative analysis of mRNA levels showed a parallel increase in message transcription, and a reporter assay shows induction of promoter activity for Melan-A/MART-1 gene. In addition, iHsp90 increased recognition of tumor cells by T cells specific for Melan-A/MART-1. In contrast to direct Hsp90 client proteins, the increased levels of full-length differentiation antigens that result from iHsp90 treatment are most likely the result of transcriptional activation of their encoding genes. In combination, these results suggest that iHsp90 improve recognition of tumor cells by T cells specific for a melanoma-associated antigen as a result of increasing the expressed intracellular antigen pool available for processing and presentation by MHC Class I, along with increased levels of MHC Class I itself. As these Hsp90 inhibitors do not interfere with T cell function, they could have potential for use in immunotherapy of cancer.

Tumor-infiltrating lymphocytes and their significance in melanoma prognosis

The role of the tumor-infiltrating lymphocyte (TIL) and its relationship to prognosis has been most extensively studied in malignant melanoma. The purpose of this chapter is to discuss in depth the immunobiology and molecular aspects of lymphocyte function in general and particularly TIL function in the context of antimelanoma immunity. Emphasis is placed upon the role of these inflammatory mediators in the enhancement and impairment of progression of this often fatal human cancer. In addition, the analysis of TILs in melanoma and their direct relationship to prognosis as well as their effect on the positivity of the sentinel lymph node will be discussed. Furthermore, details of lymph node responses to metastatic melanomas and their prognostic significance will be clarified. Finally, the importance of TILs for the evaluation of therapeutic response and how TIL immunobiology could critically inform the design of novel melanoma immunotherapeutic protocols will be elucidated.

Immune-mediated adverse events associated with ipilimumab ctla-4 blockade therapy: the underlying mechanisms and clinical management

Immunomodulation with the anti-CTLA-4 monoclonal antibody ipilimumab has been shown to extend overall survival (OS) in previously treated and treatment-naive patients with unresectable stage III or IV melanoma. Blockade of CTLA-4 signaling with ipilimumab prolongs T-cell activation and restores T-cell proliferation, thus amplifying T-cell-mediated immunity and the patient's capacity to mount an effective antitumor immune response. While this immunostimulation has unprecedented OS benefits in the melanoma setting, it can also result in immune-mediated effects on various organ systems, leading to immune-related adverse events (irAEs). Ipilimumab-associated irAEs are common and typically low grade and manageable, but can also be serious and life threatening. The skin and gastrointestinal tract are most frequently affected, while hepatic, endocrine, and neurologic events are less common. With proper management, most irAEs resolve within a relatively short time, with a predictable resolution pattern. Prompt and appropriate management of these irAEs is essential and treatment guidelines have been developed to assist oncologists and their teams. Implementation of these irAE management algorithms will help ensure that patients are able to benefit from ipilimumab therapy with adequate control of toxicities.

The RNA-binding E3 ubiquitin ligase MEX-3C links ubiquitination with MHC-I mRNA degradation

The novel RNA-binding E3 ubiquitin ligase MEX-3C targets the mRNA of MHC-I gene HLA-A2 for degradation in a RING-dependent manner. Depletion of MEX-3C in NK cells leads to reduced killing of target cells.

RNA-binding E3 ubiquitin ligases were recently identified, though their function remains unclear. While studying the regulation of the MHC class I (MHC-I) pathway, we here characterize a novel role for ubiquitin in mRNA degradation. MHC-I molecules provide ligands for both cytotoxic T-lymphocytes as well as natural killer (NK) cells, and play a central role in innate and adaptive immunity. MHC-I cell-surface expression is closely monitored by NK cells, whose killer immunoglobulin-like receptors encode MHC-I-specific activatory and inhibitory receptors, implying that MHC-I expression needs to be tightly regulated. In a functional siRNA ubiquitome screen we identified MEX-3C, a novel RNA-binding ubiquitin E3 ligase, as responsible for the post-transcriptional, allotype-specific regulation of MHC-I. MEX-3C binds the 3′UTR of HLA-A2 mRNA, inducing its RING-dependent degradation. The RING domain of MEX-3C is not required for HLA-A2 cell-surface downregulation, but regulates the degradation of HLA-A2 mRNA. We have therefore uncovered a novel post-transcriptional pathway for regulation of HLA-A allotypes and provide a link between ubiquitination and mRNA degradation.

Proteasome inhibition blocks NF-κB and ERK1/2 pathways, restores antigen expression, and sensitizes resistant human melanoma to TCR-engineered CTLs

Adoptive cell transfer (ACT) of ex vivo engineered autologous lymphocytes encoding high-affinity MART-1/HLA-A*0201-specific T-cell receptor (TCR)α/β chains (F5 CTL), densely infiltrate into sites of metastatic disease, mediating dramatic but partial clinical responses in patients with melanoma. We hypothesized that MART-1 downmodulation in addition to aberrant apoptotic/survival signaling could confer resistance to death signals delivered by transgenic CTLs. To explore this hypothesis, we established an in vitro model of resistant (R) lines from MART-1(+)/HLA-A*0201(+) F5 CTL-sensitive parental (P) lines under serial F5 CTL-selective pressure. We have recently reported that several melanoma R lines, while retaining MART-1 expression, exhibited constitutive NF-κB activation and overexpression of NF-κB-dependent resistance factors. Another established melanoma cell line M244, otherwise sensitive to F5 CTL, yielded R lines after serial F5 CTL-selective pressure, which had both reduced MART-1 expression levels, thus, could not be recognized, and were resistant to CTL-delivered apoptotic death signals. The proteasome inhibitor bortezomib blocked NF-κB activity, decreased phospho-ERK1/2, increased phospho-c-jun-NH(2)-kinase (p-JNK) levels, reduced expression of resistance factors, restored MART-1 expression to sufficient levels, which in combination allowed M244R lines be sensitized to F5 CTL killing. These findings suggest that proteasome inhibition in immune resistant tumors can restore proapoptotic signaling and improve tumor antigen expression.

"Stealth" melanoma cells in histology-negative sentinel lymph nodes

A proportion of patients who develop regional and distant recurrences of melanoma after a pathologically negative sentinel lymph node (SN) biopsy are reported to have enhanced signals for melanoma-associated messenger ribonucleic acid (mRNA) when sensitive molecular approaches such as reverse transcriptase polymerase chain reaction (RT-PCR) are used to evaluate their SN tissue. The significance of these findings remains controversial, because the cellular source of the augmented signals cannot be known as the nodal tissue is destroyed during preparation for RT-PCR. Nevertheless, it is claimed that the source of the augmented signal is covert metastatic melanoma cells. To determine whether there are histologically occult metastases in SN and whether there are sources of augmentable melanoma-associated mRNA other than melanoma cells, we applied reverse transcriptase in situ polymerase chain reaction (RT in situ PCR) to formalin-fixed paraffin-embedded nodal tissue. This approach amplifies small amounts of melanoma-associated mRNA and permits identification of cells that express that mRNA. Cells containing MART-1 mRNA were detected in 6 of 21 SNs (29%) and 2 of 16 nonsentinel lymph node (NSNs) (13%) that were tumor negative on hematoxylin and eosin and on immunohistochemical assessment for S-100, MART-1, and HMB-45. In patients with microscopic evidence of melanoma in their SN, MART-1 mRNA-positive cells were identified in 2 of 7 NSNs (29%) that were histologically tumor free. MART-1 mRNA-positive cells were also detected in tumor-negative SN sections from 6 of 7 (86%) nodes that had tumor present in areas of the node not represented in the studied sections. Some cells that expressed MART-1 mRNA that was diffusely distributed in the cytoplasm appeared to be melanoma cells, whereas others resembled macrophages. The latter cells expressed augmented mRNA on granules that were intermixed with melanin granules. In other cases, MART-1 mRNA-positive macrophage-like cells contained nuclei and nucleoli more typical of melanoma cells and may represent the macrophage-melanoma hybrids that have been previously reported. Combination of RT in situ PCR for MART-1 mRNA and immunohistochemistry for CD68 revealed that CD68 was colocalized in some cells that expressed MART-1 mRNA. Some lymph nodes that are tumor negative by histology and immunohistochemistry contain cells that express mRNA for MART-1. Some of these cells may be interpreted as "stealth" melanoma cells in which, despite the presence of MART-1 mRNA, there is an absence of immunohistochemically detectable MART-1 protein. Other cells that contain MART-1 mRNA are clearly not melanoma cells or may represent melanoma hybrids. These findings should be taken into account when interpreting and applying the results of RT-PCR analysis of nodal (and other) tissues.

The immune response to tumors as a tool toward immunotherapy

Until recently cancer medical therapy was limited to chemotherapy that could not differentiate cancer cells from normal cells. More recently with the remarkable mushroom of immunology, newer tools became available, resulting in the novel possibility to attack cancer with the specificity of the immune system. Herein we will review some of the recent achievement of immunotherapy in such aggressive cancers as melanoma, prostatic cancer, colorectal carcinoma, and hematologic malignancies. Immunotherapy of tumors has developed several techniques: immune cell transfer, vaccines, immunobiological molecules such as monoclonal antibodies that improve the immune responses to tumors. This can be achieved by blocking pathways limiting the immune response, such as CTLA-4 or Tregs. Immunotherapy may also use cytokines especially proinflammatory cytokines to enhance the activity of cytotoxic T cells (CTLs) derived from tumor infiltrating lymphocytes (TILs). The role of newly discovered cytokines remains to be investigated. Alternatively, an other mechanism consists in enhancing the expression of TAAs on tumor cells. Finally, monoclonal antibodies may be used to target oncogenes.

A screening assay to identify agents that enhance T-cell recognition of human melanomas

Although a series of melanoma differentiation antigens for immunotherapeutic targeting has been described, heterogeneous expression of antigens such as Melan-A/MART-1 and gp100 results from a loss of antigenic expression in many late stage tumors. Antigen loss can represent a means for tumor escape from immune recognition, and a barrier to immunotherapy. However, since antigen-negative tumor phenotypes frequently result from reversible gene regulatory events, antigen enhancement represents a potential therapeutic opportunity. Accordingly, we have developed a cell-based assay to screen for compounds with the ability to enhance T-cell recognition of melanoma cells. This assay is dependent on augmentation of MelanA/MART-1 antigen presentation by a melanoma cell line (MU89). T-cell recognition is detected as interleukin-2 production by a Jurkat T cell transduced to express a T-cell receptor specific for an HLA-A2 restricted epitope of the Melan-A/MART-1 protein. This cellular assay was used to perform a pilot screen by using 480 compounds of known biological activity. From the initial proof-of-principle primary screen, eight compounds were identified as positive hits. A panel of secondary screens, including orthogonal assays, was used to validate the primary hits and eliminate false positives, and also to measure the comparative efficacy of the identified compounds. This cell-based assay, thus, yields consistent results applicable to the screening of larger libraries of compounds that can potentially reveal novel molecules which allow better recognition of treated tumors by T cells.

Melanoma vaccines: developments over the past 10 years

Decades of preclinical evaluation and clinical trials into melanoma vaccines have yielded spectacular progress in our understanding of melanoma antigens and the immune mechanisms of tumor rejection. Key insights and the results of their clinical evaluation are reviewed in this article. Unfortunately, durable clinical benefit following vaccination remains uncommon. Two recent clinical advances that will impact on melanoma vaccine development are trials with inhibitors of CTLA-4 and oncogenic BRAF. Long-term therapeutic control of melanoma will require integration of specific active immunotherapy with these emerging successful therapies from the disparate fields of immune regulation and signal transduction.

Simple biophysical model of tumor evasion from immune system control

The competitive nonlinear interplay between a tumor and the host's immune system is not only very complex but is also time-changing. A fundamental aspect of this issue is the ability of the tumor to slowly carry out processes that gradually allow it to become less harmed and less susceptible to recognition by the immune system effectors. Here we propose a simple epigenetic escape mechanism that adaptively depends on the interactions per time unit between cells of the two systems. From a biological point of view, our model is based on the concept that a tumor cell that has survived an encounter with a cytotoxic T-lymphocyte (CTL) has an information gain that it transmits to the other cells of the neoplasm. The consequence of this information increase is a decrease in both the probabilities of being killed and of being recognized by a CTL. We show that the mathematical model of this mechanism is formally equal to an evolutionary imitation game dynamics. Numerical simulations of transitory phases complement the theoretical analysis. Implications of the interplay between the above mechanisms and the delivery of immunotherapies are also illustrated.

Cytotoxic T lymphocyte responses against melanocytes and melanoma

Background

Vitiligo is a common toxicity associated with immunotherapy for melanoma. Cytotoxic T lymphocytes (CTLs) against melanoma commonly target melanoma-associated antigens (MAAs) which are also expressed by melanocytes. To uncouple vitiligo from melanoma destruction, it is important to understand if CTLs can respond against melanoma and melanocytes at different levels.

Methods

To understand the dichotomous role of MAA-specific CTL, we characterized the functional reactivities of established CTL clones directed to MAAs against melanoma and melanocyte cell lines.

Results

CTL clones generated from melanoma patients were capable of eliciting MHC-restricted, MAA-specific lysis against melanocyte cell lines as well as melanoma cells. Among the tested HLA-A*0201-restricted CTL clones, melanocytes evoked equal to slightly higher degranulation and cytolytic responses as compared to melanoma cells. Moreover, MAA-specific T cells from vaccinated patients responded directly ex vivo to melanoma and melanocytes. Melanoma cells express slightly higher levels of MART-1 and gp100 than melanocytes as measured by quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR) and immunohistochemistry.

Conclusions

Our data suggest that CTLs respond to melanoma and melanocytes equally in vitro and directly ex vivo.

Phase I/II trial of a dendritic cell vaccine transfected with DNA encoding melan A and gp100 for patients with metastatic melanoma

This trial tested a dendritic cell (DC) therapeutic cancer vaccine in which antigen is loaded using a novel non-viral transfection method enabling the uptake of plasmid DNA condensed with a cationic peptide. Proof of principle required the demonstration of diverse T lymphocyte responses following vaccination, including multiple reactivities restricted through both major histocompatibility complex (MHC) class I and II. Patients with advanced melanoma were offered four cycles of vaccination with autologous DC expressing melan A and gp100. Disease response was measured using Response Evaluation Criteria in Solid Tumours. Circulating MHC class I- and II-restricted responses were measured against peptide and whole antigen targets using interferon-γ ELIspot and enzyme-linked immunosorbent assay assays, respectively. Responses were analyzed across the trial population and presented descriptively for some individuals. Twenty-five patients received at least one cycle. Vaccination was well tolerated. Three patients had reduction in disease volume. Across the trial population, vaccination resulted in an expansion of effector responses to both antigens, to the human leukocyte antigen A2-restricted modified epitope, melan A ELAGIGILTV, and to a panel of MHC class I- and II-restricted epitopes. Vaccination with mature DC non-virally transfected with DNA encoding antigen had biological effect causing tumour regression and inducing diverse T lymphocyte responses.

AAV2-mediated in vivo immune gene therapy of solid tumours

Background

Many strategies have been adopted to unleash the potential of gene therapy for cancer, involving a wide range of therapeutic genes delivered by various methods. Immune therapy has become one of the major strategies adopted for cancer gene therapy and seeks to stimulate the immune system to target tumour antigens. In this study, the feasibility of AAV2 mediated immunotherapy of growing tumours was examined, in isolation and combined with anti-angiogenic therapy.

Methods

Immune-competent Balb/C or C57 mice bearing subcutaneous JBS fibrosarcoma or Lewis Lung Carcinoma (LLC) tumour xenografts respectively were treated by intra-tumoural administration of AAV2 vector encoding the immune up-regulating cytokine granulocyte macrophage-colony stimulating factor (GM-CSF) and the co-stimulatory molecule B7-1 to subcutaneous tumours, either alone or in combination with intra-muscular (IM) delivery of AAV2 vector encoding Nk4 14 days prior to tumour induction. Tumour growth and survival was monitored for all animals. Cured animals were re-challenged with tumourigenic doses of the original tumour type. In vivo cytotoxicity assays were used to investigate establishment of cell-mediated responses in treated animals.

Results

AAV2-mediated GM-CSF, B7-1 treatment resulted in a significant reduction in tumour growth and an increase in survival in both tumour models. Cured animals were resistant to re-challenge, and induction of T cell mediated anti-tumour responses were demonstrated. Adoptive transfer of splenocytes to naïve animals prevented tumour establishment. Systemic production of Nk4 induced by intra-muscular (IM) delivery of Nk4 significantly reduced subcutaneous tumour growth. However, combination of Nk4 treatment with GM-CSF, B7-1 therapy reduced the efficacy of the immune therapy.

Conclusions

Overall, this study demonstrates the potential for in vivo AAV2 mediated immune gene therapy, and provides data on the inter-relationship between tumour vasculature and immune cell recruitment.

Topoisomerase inhibitors modulate expression of melanocytic antigens and enhance T cell recognition of tumor cells

While there are many obstacles to immune destruction of autologous tumors, there is mounting evidence that tumor antigen recognition does occur. Unfortunately, immune recognition rarely controls clinically significant tumors. Even the most effective immune response will fail if tumors fail to express target antigens. Importantly, reduced tumor antigen expression often results from changes in gene regulation rather than irrevocable loss of genetic information. Such perturbations are often reversible by specific compounds or biological mediators, prompting a search for agents with improved antigen-enhancing properties. Some recent findings have suggested that certain conventional chemotherapeutic agents may have beneficial properties for cancer treatment beyond their direct cytotoxicities against tumor cells. Accordingly, we screened an important subset of these agents, topoisomerase inhibitors, for their effects on antigen levels in tumor cells. Our analyses demonstrate upregulation of antigen expression in a variety of melanoma cell lines and gliomas in response to nanomolar levels of certain specific topoisomerase inhibitors. To demonstrate the ability of CD8+ T cells to recognize tumors, we assayed cytokine secretion in T cells transfected with T cell receptors directed against Melan-A/MART-1 antigen. Three days of daunorubicin treatment resulted in enhanced antigen expression by tumor cells, in turn inducing co-cultured antigen-specific T cells to secrete Interleukin-2 and Interferon-γ. These results demonstrate that specific topoisomerase inhibitors can augment melanoma antigen production, suggesting that a combination of chemotherapy and immunotherapy may be of potential value in the treatment of otherwise insensitive cancers.

Interleukins 1alpha and 1beta secreted by some melanoma cell lines strongly reduce expression of MITF-M and melanocyte differentiation antigens

We report that melanoma cell lines expressing the interleukin-1 receptor exhibit 4- to 10-fold lower levels of mRNA of microphthalmia-associated transcription factor (MITF-M) when treated with interleukin-1beta. This effect is NF-kappaB and JNK-dependent. MITF-M regulates the expression of melanocyte differentiation genes such as MLANA, tyrosinase and gp100, which encode antigens recognized on melanoma cells by autologous cytolytic T lymphocytes. Accordingly, treating some melanoma cells with IL-1beta reduced by 40-100% their ability to activate such antimelanoma cytolytic T lymphocytes. Finally, we observed large amounts of biologically active IL-1alpha or IL-1beta secreted by two melanoma cell lines that did not express MITF-M, suggesting an autocrine MITF-M downregulation. We estimate that approximately 13% of melanoma cell lines are MITF-M-negative and secrete IL-1 cytokines. These results indicate that the repression of melanocyte-differentiation genes by IL-1 produced by stromal cells or by tumor cells themselves may represent an additional mechanism of melanoma immune escape.

Establishment of a screening system for chemicals that upregulate a melanoma antigen, Melan-A/MART-1

Immunotherapy is well-practiced as one of the main adjuvant therapies for melanoma patients. Until now, many immunotherapeutic investigations have focused on improving the effector side of the antitumor response, but only a few studies have been concerned with preventing the loss of tumor-associated antigen (TAA) expression. Loss of TAA should be an important problem for the recognition of tumor cells by cytotoxic T lymphocytes. If any agents that augment the expression of melanoma antigens were found, they could improve the efficacy of immunotherapy by increasing the antigens. To detect effective chemicals, we made a fluorescent cellular reporter system for screening promising candidate chemicals. In this system, the fusion gene of the Melan-A/MART-1 promoter sequence followed by the green fluorescent protein (GFP) coding region was stably transfected into MUX human melanoma cells which are known to express little or no Melan-A/MART-1. Melan-A/MART-1 is a well-known melanoma antigen recognized by autologous cytotoxic T cells, and is a glycoprotein associated with the melanosome, the organelle in which melanin synthesis proceeds. By using this screening system, daunorubicin, doxorubicin and cytochalasin D, which enhanced the green fluorescent, were selected and then were confirmed to actually increase the expression of Melan-A/MART-1 mRNA and protein in human melanoma cells of MU89, MM96L(+) and SK-MEL-28, but also in low-antigen presenting cells such as MM96L(-), MUX, and A375. In conclusion, we have successfully established a well-functioning screening system, which will allow us to find candidate chemicals that up-regulate or maintain the melanoma antigen expression.

ICAM-1 has a critical role in the regulation of metastatic melanoma tumor susceptibility to CTL lysis by interfering with PI3K/AKT pathway

Human primary melanoma cells (T1) were found to be more susceptible to lysis by a Melan-A/MART-1-specific CTL clone (LT12) than their metastatic derivative (G1). We show that this differential susceptibility does not involve antigen presentation by target cells, synapse formation between the metastatic target and CTL clone, or subsequent granzyme B (GrB) polarization. Although PI-9, an inhibitor of GrB, was found to be overexpressed in metastatic G1 cells, knockdown of the PI-9 gene did not result in the attenuation of G1 resistance to CTL-induced killing. Interestingly, we show that whereas T1 cells express high levels of intercellular adhesion molecule-1 (ICAM-1), a dramatically reduced expression was noted on G1 cells. We also showed that sorted ICAM-1+ G1 cells were highly sensitive to CTL-induced lysis compared with ICAM-1- G1 cells. Furthermore, incubation of metastatic G1 cells with IFN-gamma resulted in the induction of ICAM-1 and the potentiation of their susceptibility to lysis by LT12. More importantly, we found that the level of ICAM-1 expression by melanoma cells correlated with decreased PTEN activity. ICAM-1 knockdown in T1 cells resulted in increased phosphorylation of PTEN and the subsequent activation of AKT. We have additionally shown that inhibition of the phosphatidylinositol (3,4,5)-triphosphate kinase (PI3K)/AKT pathway by the specific inhibitor wortmannin induced a significant potentiation of susceptibility of G1 and ICAM-1 small interfering RNA-treated T1 cells to CTL-induced lysis. The present study shows that a shift in ICAM-1 expression, which was associated with an activation of the PI3K/AKT pathway, can be used by metastatic melanoma cells to escape CTL-mediated killing.

Strategies to overcome obstacles to successful immunotherapy of melanoma

The immunogenicity of malignant melanomas has been recognized by the observed recruitment of tumor-specific cytotoxic T-cells (CTL), leading to the identification of several melanoma associated antigen (MAA). However, numerous strategies to treat melanoma with immunotherapy have resulted in only partial success. In this editorial, we discuss recent data related to the ability of tumors to elude immune responses. We therefore discuss different strategies to induce a clinically effective immune response. These approaches include 1) immunostimulation: including peptide/protein based vaccines, dendritic cell vaccines, and adoptive cell transfer; and 2) overcoming immunosuppression, including targeting of checkpoint molecules such as CTLA-4, circumventing the activity of Tregs, and assuring antigen expression by tumor cells (thwarting antigen silencing). Finally, we discuss recent advances in gene therapy, including adoptive therapy with engineered T cell receptors (TCRs). These issues lead to the conclusion that successful immunotherapy in malignant melanoma requires a combination of strategies aimed at both inducing immunostimulation and blocking immunosuppression.

RT in situ PCR detection of MART-1 and TRP-2 mRNA in formalin-fixed, paraffin-embedded tissues of melanoma and nevi

Melanoma antigen recognized by T cells 1 (MART-1) and tyrosinase-related protein-2 (TRP-2) are two useful markers for immunohistochemical detection of melanocytic tumors. However, these markers may be passively acquired (phagocytosed) rather than actively synthesized. Reverse transcriptase in situ polymerase chain reaction (RT in situ PCR) can amplify even small amounts of specific mRNA in cells and therefore confirm the cellular source of a marker. We developed a one-step RT in situ PCR procedure in which Thermus thermophilus DNA polymerase synthesizes and amplifies cDNA from mRNA in a single reaction mixture. To examine its practicability and feasibility with formalin-fixed, paraffin-embedded (FFPE) tissue, we compared the results of one-step RT in situ PCR with those of immunohistochemistry (IHC). MART-1 mRNA was identified in the cytoplasm of lesional cells from 23/26 primary melanomas (92%), 9/9 metastatic melanomas (100%) and 5/6 nevi (83%). MART-1 epitope was detected by IHC in 23/24 primary melanomas (96%), 9/9 metastatic melanomas (100%) and 5/6 nevi (83%). TRP-2 mRNA was identified in the cytoplasm of lesional cells from 17/26 primary melanomas (65%), 6/9 metastatic melanomas (67%) and 4/6 nevi (67%). TRP-2 epitope was detected by IHC in 20/24 primary melanomas (83%), 9/9 metastatic melanomas (100%) and 4/6 nevi (67%). Both techniques detected MART-1 and TRP-2 in FFPE melanoma cell lines. Neither marker was detected in squamous cell carcinomas or basal cell carcinomas by RT in situ PCR or IHC. We conclude that the RT in situ PCR technique can be successfully applied to FFPE tissue to determine the cellular sources of gene expression observed by conventional PCR approaches.

Dynamic cross-talk between tumor and immune cells in orchestrating the immunosuppressive network at the tumor microenvironment

Accumulating evidence indicates that a dynamic cross-talk between tumors and the immune system can regulate tumor growth and metastasis. Increased understanding of the biochemical nature of tumor antigens and the molecular mechanisms responsible for innate and adaptive immune cell activation has revolutionized the fields of tumor immunology and immunotherapy. Both the protective effects of the immune system against tumor cells (immunosurveillance) and the evasion of tumor cells from immune attack (tumor-immune escape) have led to the concept of cancer immunoediting, a proposal which infers that a bidirectional interaction between tumor and inflammatory/regulatory cells is ultimately responsible for orchestrating the immunosuppressive network at the tumor site. In this context, a major challenge is the potentiation or redirection of tumor antigen-specific immune responses. The success in reaching this goal is highly dependent on an improved understanding of the interactions and mechanisms operating during the different phases of the cancer immunoediting process. In this review, we discuss the multiple defense and counterattack strategies that tumors have devised in order to evade immune attack and to thwart the effectiveness of several immunotherapeutic approaches.

Generation of a prophylactic melanoma vaccine using whole recombinant yeast expressing MART-1

Malignant melanoma is a potentially deadly form of skin cancer and people at high-risk of developing melanoma will benefit from effective preventive intervention. Yeast can be used as an efficient vehicle of antigen loading and immunostimulation. Saccharomyces cerevisiae is not pathogenic to humans and can be easily engineered to express specific antigens. In this study, we have developed a melanoma vaccine using a yeast-based platform expressing a full-length melanocyte/melanoma protein to investigate its utility as a prophylactic melanoma vaccine in a transplantable mouse melanoma model. Yeast was engineered and expanded in vitro without technical difficulties, administered easily with subcutaneous injection, and did not show adverse effects, indicating its practical applicability and favourable safety profile. Despite the lack of knowledge of dominant epitopes of the protein recognized by mouse MHC-class I, the vaccine protected mice from tumor development and induced efficient immune responses, suggesting that the precise knowledge of epitopic sequences and the matched HLA type is not required when delivering a full-length protein using the yeast platform. In addition, the vaccine stimulated both CD4(+) T cells and CD8(+) T cells simultaneously. This study provides a 'proof of principle' that recombinant yeast can be utilized as an effective prophylactic vaccine to target patients at high-risk for melanoma.

Enhancement of Human Melanoma Antigen Expression by IFN-β

Although many immunotherapeutic investigations have focused on improving the effector limb of the antitumor response, few studies have addressed preventing the loss of tumor-associated Ag (TAA) expression, associated with immune escape by tumors. We found that TAA loss from human melanomas usually results from reversible gene down-regulation, rather than gene deletion or mutation. Previously, we showed that inhibitors of MAPK-signaling pathways up-regulate TAA expression in melanoma cell lines. We have now identified IFN-beta as an additional stimulus to TAA expression, including Melan-A/MART-1, gp100, and MAGE-A1. IFN-beta (but neither IFN-alpha nor IFN-gamma) augmented both protein and mRNA expression of melanocytic TAA in 15 melanoma lines (irrespective of initial Ag-expression levels). Treatment of low Ag melanoma lines with IFN-beta increased expression of melanocyte-lineage Ags, inducing susceptibility to lysis by specific CTLs. Treatment with IFN-beta also enhances expression of class I HLA molecules, thereby inducing both nominal TAA and the presenting HLA molecule. Data from fluorescent cellular reporter systems demonstrated that IFN-beta triggers promoter activation, resulting in augmentation of Ag expression. In addition to enhancing TAA expression in melanomas, IFN-beta also stimulated expression of the melanocytic Ag gp100 in cells of other neural crest-derived tumor lines (gliomas) and certain unrelated tumors. Because IFN-beta is already approved for human clinical use in other contexts, it may prove useful as a cotreatment for augmenting tumor Ag expression during immunotherapy.

Constitutive and IFNgamma-induced activation of MHC2TA promoter type III in human melanoma cell lines is governed by separate regulatory elements within the PIII upstream regulatory region

Cell lines established from tumor tissue of cutaneous melanoma biopsies often display constitutive and IFNgamma-inducible expression of MHC class II molecules. The expression of MHC class II molecules in melanoma is associated with an overall poor prognosis and unfavorable clinical outcome. We have analyzed the DNA elements and interacting transcription factors that control the constitutive and IFNgamma-inducible expression of the class II transactivator (CIITA), a co-activator essential for transcription of all MHC class II genes. Our studies reveal the activation of multiple CIITA promoter regions (CIITA-PII, -PIII and -PIV) in melanoma cell lines for both the constitutive and IFNgamma-inducible expression of MHC class II molecules. Furthermore, we show that constitutive and IFNgamma-inducible expression of the CIITA-PIII isoform is governed by separate regulatory elements within the PIII upstream regulatory region (PURR). Similarly constitutive activation in melanoma of CIITA-PII, CIITA-PIII, and CIITA-PIV does not require components of the IFNgamma signaling pathway. However, these components are readily recruited to the PURR and CIITA-PIV after exposure of cells to IFNgamma and account for the IFNgamma-induced expression of CIITA. Together, our data reveal the contribution of distinct elements and factors in the constitutive and IFNgamma-inducible expression of CIITA in melanoma cell lines of the skin.

Role of the Mitogen-Activated Protein Kinase Signaling Pathway in the Regulation of Human Melanocytic Antigen Expression

Heterogeneous expression of melanocytic antigens occurs frequently in melanomas and represents a potent barrier to immunotherapy. We previously showed that coordinated losses of several melanocytic antigens are generally attributable to down-regulation of antigen gene expression rather than irreversible mutation. Treatment of melanoma cells with mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase (MEK) inhibitors blocks ERK activation and increases steady-state levels of mRNAs and corresponding protein expression for the melanocytic antigens Melan-A/MART-1, gp100, and tyrosinase. Although the degree of MEK inhibitor enhancement of antigen expression varied among different cell lines irrespective of their antigen expression status, all showed detectable responses. Notably, the antigen-enhancing effects of the MEK inhibitors could not be attributed to the master melanocytic regulator MITF-M. Because MAPK pathway activation via constitutively active mutant forms of BRAF is common in melanomas, correlation between BRAF function and antigen expression was investigated. No simple correlation of endogenous BRAF mutational status and antigen levels was observed, but transient overexpression of V600E BRAF increased ERK activation and reduced Melan-A/MART-1 levels in antigen-positive cell lines. These data indicate that whereas multiple factors may regulate antigen expression in melanomas, enhancement of MAPK signaling can act as a negative influence. Blocking such signaling with MEK inhibitors accordingly augments antigen levels, thereby enhancing Melan-A/MART-1-specific cytotoxic T-cell responses to antigen-negative cells following MEK inhibition treatment. Consequently, MAPK inhibition may assist targeting of melanomas for immunotherapy.

Tumor antigen expression in melanoma varies according to antigen and stage

PURPOSE

Melanoma cells express antigens that can induce T-cell and antibody responses. Obtaining a detailed understanding of antigen expression in primary and metastatic melanoma is essential if these molecules are to be useful targets for immunotherapy of melanoma.

EXPERIMENTAL DESIGN

Malignant melanomas (n = 586) from 426 patients were typed for antigen expression. Multiple samples were available from 86 individuals, enabling analysis of antigen expression patterns over time. Paraffin-embedded samples were tested by immunohistochemistry for the presence of the differentiation antigens: gp100, Melan-A, tyrosinase, and the "cancer/testis" antigens MAGE-A1, MAGE-A4, and NY-ESO-1.

RESULTS

Samples were primary tumors (n = 251), lymph node metastases (n = 174), s.c. metastases (n = 71), and distant metastases (n = 90). The differentiation antigens were strongly expressed in 93% to 95% of tumors regardless of stage. In contrast, the frequency of cancer/testis antigen expression in primary tumors for MAGE-A1, MAGE-A4, and NY-ESO-1 was lower (20%, 9%, and 45%, respectively). MAGE-A1 and MAGE-A4 were acquired with advancing disease (to 51% and 44% in distant metastases, respectively) but not NY-ESO-1, which remained positive in 45%. MAGE-A1 expression was twice as prevalent in ulcerated primaries as in nonulcerated primaries (30% versus 15%; P = 0.006) and in thicker as opposed to thin melanomas (26% versus 10%; P = 0.1).

CONCLUSIONS

This large series describes patterns of antigen expression in melanoma and their evolution over time. This will help inform decisions about selection of patients and target antigens for melanoma immunotherapy clinical trials.

Frequency of telomerase-specific CD8+ T lymphocytes in patients with cancer

Telomerase is considered a universal tumor-associated antigen (TAA) due to its high rate of expression by cancers (≈90%), and clinical trials are in progress to test the immunotherapeutical efficacy of antitelomerase immunization in patients with cancer. However, the data concerning frequency and functional activity of telomerase-specific cytotoxic T lymphocytes (CTLs) in patients with cancer are few and conflicting, although their knowledge would be mandatory to predict the efficacy of telomerase-specific immunotherapy in selected patients. We performed this study to analyze frequency and cytolytic function of circulating CD8+ T lymphocytes specific for the p540 telomerase peptide in a series of human leukocyte antigen (HLA)–A2+ cancer patients. The results show that most patients with cancer have circulating telomerase-specific CD8+ T lymphocytes, but a high frequency of telomerase-specific CTLs are present only in a fraction of them. Furthermore, CTL lines able to kill telomerase-positive tumor cells, including autologous cancer cells, can be expanded ex vivo from some, but not all, patients with cancer. In conclusion, the results of the study support the development of clinical protocols using telomerase peptides as an immunizing agent. However, they underline the necessity to study single patients immunologically before undergoing vaccination, to select the patients adequately, and to eventually adapt the immunization schedule to the patient's immunologic status.

Culture of melanoma cells in 3-dimensional architectures results in impaired immunorecognition by cytotoxic T lymphocytes specific for Melan-A/MART-1 tumor-associated antigen

OBJECTIVE

To assess the effects of the culture of melanoma cells in 3-dimensional (3D) architectures on their immunorecognition by cytotoxic T lymphocytes (CTLs) specific for tumor-associated antigens.

SUMMARY BACKGROUND DATA

Growth in 3D architectures has been shown to promote the resistance of cancers to treatment with drugs, cytokines, or irradiation, thereby potentially playing an important role in tumor expansion. We investigated the effects of 3D culture on the recognition of melanoma cells by antigen-specific HLA class I-restricted CTLs.

METHODS

Culture of HBL melanoma cells expressing Melan-A/Mart-1 tumor-associated antigen and HLA-A0201 on poly-2-hydroxyethyl methacrylate (polyHEMA)-coated plates resulted in the generation of aggregates of 400- to 500-microm diameters containing on average 30,000 cells and characterized by slower proliferation, as compared with monolayer (2-dimensional) cultures. HLA-A0201 restricted Melan-A/Mart-127-35-specific CTL clones were used to evaluate tumor cell immunorecognition measured as specific IFN-gamma production. Comparative gene and protein expression in 2D and 3D cultures was studied by real-time PCR and flow cytometry, respectively. Overall differences in gene expression profiles between 2D and 3D cultures were evaluated by high-density oligonucleotide array hybridization.

RESULTS

HLA-A0201 restricted Melan-A/Mart-127-35 specific CTL clones produced high amounts of IFN-gamma upon short-term (4-24 hours) coincubation with HBL cells cultured in 2D but not in 3D, thus suggesting altered antigen recognition. Indeed, Melan-A/Mart-1 expression, at both gene and protein levels, was significantly decreased in 3D as compared with 2D cultures. Concomitantly, a parallel decrease of HLA class I molecule expression was also observed. Differential gene profiling studies on HBL cells showed an increased expression of genes encoding molecules involved in intercellular adhesion, such as junctional adhesion molecule 2 and cadherin-like 1 (>20- and 8-fold up-regulated, respectively) in 3D as compared with 2D cultures.

CONCLUSIONS

Taken together, our data suggest that mere growth of melanoma cells in 3D architectures, in the absence of immunoselective pressure, may result in defective recognition by tumor-associated antigen-specific CTL.

A soluble divalent class I MHC/IgG1 fusion protein activates CD8+ T cells in vivo

CD8+ T lymphocytes recognize tumor and viral antigens bound to class I major histocompatibility complexes (MHC). Tumors and viruses may evade detection by preventing antigen presentation. The present study was designed to determine whether a soluble divalent fusion protein, containing the extracellular domains of a class I MHC molecule fused to beta2-microglobulin and the constant domains of IgG1, could induce an immune response in vivo. Administration to mice of the fusion protein loaded with a tumor peptide induced peptide-specific T cell activation and retarded tumor growth. Administration of the fusion protein loaded with a glycoprotein B (gB) peptide derived from herpes simplex virus type 1 (HSV-1) induced gB-specific cytotoxic T lymphocytes and protected mice from a lethal HSV-1 challenge. These data suggest that antigen-loaded MHC/IgG fusion proteins may enhance T cell immunity in conditions where antigen presentation is altered.

Current strategies in cancer gene therapy

Cancer gene therapy is the most studied application of gene therapy. Many genetic alterations are involved in the transformation of a normal cell into a neoplastic one. The two main gene groups involved in cancer development are oncogenes and tumor suppressor genes. While the latter eliminates cancerous cells via apoptosis, the former enhances cell proliferation. Therefore, apoptotic genes and anti-oncogenes are widely used in cancer gene therapy. In addition to oncogenes and tumor suppressor genes, chemotherapy and gene therapy can be combined through suicide gene strategy. A suicide gene encodes for a non-mammalian enzyme; this enzyme is used to convert a non-toxic prodrug into its active cytotoxic metabolite within the cancerous cells. Tumor suppressor genes, anti-oncogenes and suicide genes target cancer cells on the molecular level. On the other hand, cancer is immunogenic in nature; therefore, it can also be targeted on the immunological level. Boosting the immune response against cancerous cells is usually achieved via genes encoding for cytokines. Interleukin-12 gene, for example, is one of the most studied cytokine genes for cancer gene therapy applications. DNA vaccines are also used after conventional treatments to eliminate remnant malignant cells. All these therapeutic strategies and other strategies namely anti-angiogenesis and drug resistant genes are briefly reviewed and highlighted in this article.

A different pattern of cytotoxic T lymphocyte recognition against primary and metastatic tumor cells in a patient with nonsmall cell lung carcinoma

BACKGROUND

Lung carcinoma represents the most frequent cause of cancer death worldwide because of tumor metastases. The objective of the current study was to analyze the immunologic response during the progress of lung carcinoma metastasis.

METHODS

The authors established two tumor cell lines that were derived from primary and metastatic lesions in a patient with lung carcinoma (Patient G603). One cell line (G603L) was established from the primary lesion, and the other cell line (G603AD) was established from a metastatic lesion in the right adrenal gland 7 months after the patient underwent surgery for the primary lesion. Autologous regional lymph node lymphocytes were stimulated with CD80-transfected G603L cells, then cytotoxic T lymphocytes (CTLs) were induced against both lung carcinoma cell lines.

RESULTS

Both G603L cells and G603AD cells expressed Class I human leukocyte antigen, intracellular cell adhesion molecule 1, and lymphocyte-associated antigen type 3 (LFA-3), but not Fas or Fas ligand on their surfaces. By stimulation with CD80-transfected G603L cells, 2 CTL clones (H2/17 and H2/36) were established from the bulk CTLs. CTL clone H2/17 lysed G603L cells but not G603AD cells, suggesting that the antigen recognized by CTL clone H2/17 was abrogated during the process of metastasis. In contrast, CTL clone H2/36 lysed both G603L cells and G603AD cells, indicating that the antigen recognized by CTL clone H2/36 was maintained in the tumor cells throughout tumor progression.

CONCLUSIONS

The results demonstrated the possibility that some tumor-associated antigens may be abrogated during the process of metastasis, although others are maintained. The identification of these antigens will lead to a better understanding of their immunologic role during disease progression in patients with lung carcinoma.

Immunity to melanoma: unraveling the relation of tumor immunity and autoimmunity

Cancer cells express self-antigens that are weakly recognized by the immune system. Even though responses against autologous cells are difficult to induce, the immune system is still able to mount a response against cancer. The discovery of the molecular identity of antigens that are recognized by the immune system of melanoma patients has led to the elucidation of tumor immunity at a cellular and molecular level. Multiple pathways in both the priming and effector phases of melanoma rejection have been described. Animal models' active immunotherapies for melanoma show a requirement for the cellular compartment of the immune system in the priming phase, primarily CD4+T cells. More diverse elements are required for the effector phase, including components from the innate immune system (macrophages, complement and/or natural killer cells) and from the adaptive immune system (CD8+T cells and B cells). Minor differences in amino-acid sequences of antigens must determine the particular mechanisms involved in tumor rejection. Since the immune system contains T and B cells that recognize and reject autologous cells, a consequence of tumor immunity is potential autoimmunity. There are distinct pathways for tumor immunity and autoimmunity. The requirements for autoimmunity at the priming phase seem to be CD4+/IFN-gamma dependent while the effector mechanisms are alternative and redundant. Vitiligo (autoimmune hypopigmentation) can be mediated by T cells, FcgammaR+macrophages and/or complement.

Cancer/testis-associated genes: identification, expression profile, and putative function

Cancer/testis-associated genes (CTAs) are a subgroup of tumor antigens with a restricted expression in testis and malignancies. During the last decade, many of these immunotherapy candidate genes have been discovered using various approaches. Most of these genes are localized on the X-chromosome, often as multigene families. Methylation status seems to be the main, but not the only regulator of their specific expression pattern. In testis, CTAs are exclusively present in cells of the germ cell lineage, though there is a lot of variation in the moment of expression during different stages of sperm development. Likewise, there is also a lot of heterogeneity in the expression of CTAs in melanoma samples. Clues regarding functionality of CTAs for many of these proteins point to a role in cell cycle regulation or transcriptional control. Better insights in the function of these genes may shed light on the link between spermatogenesis and tumor growth and could be of use in anti-tumor therapies. This review outlines the CTA family and focuses on their expression and putative function during male germ cell development and melanocytic tumor progression.

Complete loss of HLA class I antigen expression on melanoma cells: a result of successive mutational events

Alterations in the surface expression of HLA class I molecules have been described as a strategy of tumors to evade recognition by cytotoxic T cells. We detected complete loss of HLA class I antigen presentation for 2 tumor cell lines from 1 melanoma patient, the first originated from a regional lymph node lesion diagnosed simultaneously with the primary tumor and the second established 8 months later from a metastatic pleural effusion sample. Antigen presentation was not inducible with IFN-gamma but could be restored after transfection of tumor cells with b2m cDNA, indicating a defect in b2m expression. Analysis of the nature of this defect revealed that it originated from at least 2 mutational events affecting both copies of the b2m gene: a microdeletion of 498 bp in one b2m gene, including its entire exon 1, and a macrodeletion involving the entire copy of the second b2m gene. Microsatellite analysis pointed to the macrodeletion by demonstrating LOH for several specific markers on the long arm (q) of chromosome 15. Structural imbalance of 15q was verified by FISH. FISH studies also indicated the coexistence of a structurally abnormal variant of chromosome 15q with 2 apparently entire chromosomes 15q harboring the homozygous b2m microdeletion. Block of b2m expression in tumor cells builds a barrier to immunotherapy of cancer patients, and its early incidence should be of major consideration in the development and design of immunotherapeutic strategies.

Immunity to cancer: attack and escape in T lymphocyte-tumor cell interaction

Tumor cells may express antigens which are recognized in a form of HLA/peptide complexes by T cells. The frequency at which different antigens are seen by T cells of melanoma patients and healthy donors was evaluated by human leukocyte antigen (HLA)/peptide tetramer technology which stains T cells bearing the specific receptor for a given epitope. By this technique, it was found that the majority of metastatic melanoma patients can recognize differentiation antigens (particularly Melan-A/MART-1), whereas such a recognition is scanty in the early phase of the disease and in healthy subjects. Despite the presence of melanoma-specific T cells infiltrating tumor lesions, tumor rejection rarely occurs. Among the different mechanisms of such inefficient antitumor response, this review discusses the possible anti-T-cell counterattack mediated by FasL-positive tumor cells, and shows that FasL is located in the cytoplasm of melanoma cells and is transported in the tumor microenvironment through the release of melanosomes. Additionally, mechanisms of suboptimal T cell activation through tumor cell expression of peptide analogs with antagonist activity are described, together with the possibility of overcoming such anergy induction by the usage of optimized tumor epitopes. Down-modulation of HLA expression by target tumor cells and its multiple mechanisms is also considered. Finally, we discuss the role of inducible nitric oxide synthases in determining the inhibition of apoptosis in melanoma cells, which can make such tumor cells resistant to the T-cell attack.

Specific immunotherapy of cancer in elderly patients

The concept of immunotherapy of cancer is more than a century old, but only recently have molecularly defined therapeutic approaches been developed. In this review, we focus on the most promising approach, active therapeutic vaccination. The identification of tumour antigens can now be accelerated by methods allowing the amplification of gene products selectively or preferentially transcribed in the tumour. However, determining the potential immunogenicity of such gene products remains a demanding task, since major histocompatibility complex (MHC) restriction of T cells implies that for any newly defined antigen, immunogenicity will have to be defined for any individual MHC haplotype. Tumour-derived peptides eluted from MHC molecules of tumour tissue are also a promising source of antigen. Tumour antigens are mostly of weak immunogenicity, because the vast majority are tumour-associated differentiation antigens already 'seen' by the patient's immune system. Effective therapeutic vaccination will thus require adjuvant support, possibly by new approaches to immunomodulation such as bispecific antibodies or antibody-cytokine fusion proteins. Tumour-specific antigens, which could be a more potent target for immunotherapy, mostly arise by point mutations and have the disadvantage of being not only tumour-specific, but also individual-specific. Therapeutic vaccination will probably focus on defined antigens offered as protein, peptide or nucleic acid. Irrespective of the form in which the antigen is applied, emphasis will be given to the activation of dendritic cells as professional antigen presenters. Dendritic cells may be loaded in vitro with antigen, or, alternatively, initiation of an immune response may be approached in vivo by vaccination with RNA or DNA, given as such or packed into attenuated bacteria. The importance of activation of T helper cells has only recently been taken into account in cancer vaccination. Activation of cytotoxic T cells is facilitated by the provision of T helper cell-derived cytokines. T helper cell-dependent recruitment of elements of non-adaptive defence, such as leucocytes, natural killer cells and monocytes, is of particular importance when the tumour has lost MHC class I expression. Barriers to successful therapeutic vaccination include: (i) the escape mechanisms developed by tumour cells in response to immune attack; (ii) tolerance or anergy of the evoked immune response; (iii) the theoretical possibility of provoking an autoimmune reaction by vaccination against tumour-associated antigens; and (iv) the advanced age of many patients, implying reduced responsiveness of the senescent immune system.