TAP1 down-regulation in primary melanoma lesions: an independent marker of poor prognosis

A diversity of novel type-2 innate lymphoid cell subpopulations revealed during tumour expansion

Type 2 innate lymphoid cells (ILC2s) perform vital functions in orchestrating humoral immune responses, facilitating tissue remodelling, and ensuring tissue homeostasis. Additionally, in a role that has garnered considerably less attention, ILC2s can also enhance Th1-related cytolytic T lymphocyte immune responses against tumours. Studies have thus far generally failed to address the mystery of how one ILC2 cell-type can participate in a multiplicity of functions. Here we utilized single cell RNA sequencing analysis to create the first comprehensive atlas of naïve and tumour-associated lung ILC2s and discover multiple unique subtypes of ILC2s equipped with developmental gene programs that become skewed during tumour expansion favouring inflammation, antigen processing, immunological memory and Th1-related anti-tumour CTL responses. The discovery of these new subtypes of ILC2s challenges current paradigms of ILC2 biology and provides an explanation for their diversity of function.

Expression of thimet oligopeptidase (THOP) modulated by oxidative stress in human multidrug resistant (MDR) leukemia cells

Thimet oligopeptidase (THOP) is a cytosolic metallopeptidase known to regulate the fate of post-proteasomal peptides, protein turnover and peptide selection in the antigen presentation machinery (APM) system. Oxidative stress influences THOP expression and regulates its proteolytic activity, generating variable cytosolic peptide levels, possibly affecting the immune evasion of tumor cells. In the present work, we examined the association between THOP expression/activity and stress oxidative resistance in human leukemia cells using the K562 cell line, a chronic myeloid leukemia (CML), and the multidrug-resistant (MDR) Lucena 1 (K562-derived MDR cell line) as model. The Lucena 1 phenotype was validated under vincristine treatment and the relative THOP1 mRNA levels and protein expression compared to K562 cell line. Our data demonstrated increased THOP1 gene and protein levels in K562 cells in contrast to the oxidative-resistant Lucena 1, even after H2O2 treatment, suggesting an oxidative stress dependence in THOP regulation. Further, it was observed higher basal levels of reactive oxygen species (ROS) in K562 compared to Lucena 1 cell line using DHE fluorescent probe. Since THOP activity is dependent on its oligomeric state, we also compared its proteolytic activity under reducing agent treatment, which demonstrated that its function modulation with respect to changes in redox state. Finally, the mRNA expression and FACS analyses demonstrated a reduced expression of MHC I only in K562 cell line. In conclusion, our results highlight THOP redox modulation, which could influence antigen presentation in multidrug resistant leukemia cells.

A novel cell-based screen identifies chemical entities that reverse the immune-escape phenotype of metastatic tumours

Genetic and epigenetic events have been implicated in the downregulation of the cellular antigen processing and presentation machinery (APM), which in turn, has been associated with cancer evasion of the immune system. When these essential components are lacking, cancers develop the ability to subvert host immune surveillance allowing cancer cells to become invisible to the immune system and, in turn, promote cancer metastasis. Here we describe and validate the first high-throughput cell-based screening assay to identify chemical extracts and unique chemical entities that reverse the downregulation of APM components in cell lines derived from metastatic tumours. Through the screening of a library of 480 marine invertebrate extracts followed by bioassay-guided fractionation, curcuphenol, a common sesquiterpene phenol derived from turmeric, was identified as the active compound of one of the extracts. We demonstrate that curcuphenol induces the expression of the APM components, TAP-1 and MHC-I molecules, in cell lines derived from both metastatic prostate and lung carcinomas. Turmeric and curcumins that contain curcuphenol have long been utilized not only as a spice in the preparation of food, but also in traditional medicines for treating cancers. The remarkable discovery that a common component of spices can increase the expression of APM components in metastatic tumour cells and, therefore reverse immune-escape mechanisms, provides a rationale for the development of foods and advanced nutraceuticals as therapeutic candidates for harnessing the power of the immune system to recognize and destroy metastatic cancers.

The Role of ABC Transporters in Skin Cells Exposed to UV Radiation

ABC transporters are expressed in skin cells to protect them against harmful xenobiotics. Moreover, these transmembrane proteins have a number of additional functions that ensure skin homeostasis. This review summarizes the current knowledge about the role of specific ABC proteins in the skin, including multi-drug resistance transporters (MDR1/3), the transporter associated with antigen processing 1/2 (TAP1/2), the cystic fibrosis transmembrane conductance regulator (CFTR), sulfonylurea receptors (SUR1/2), and the breast cancer resistance protein (BCRP). Additionally, the effect of UV radiation on ABC transporters is shown. The exposure of skin cells to UV radiation often leads to increased activity of ABC transporters-as has been observed in the case of MDRs, TAPs, CFTR, and BCRP. A different effect of oxidative stress has been observed in the case of mitochondrial SURs. However, the limited data in the literature-as indicated in this article-highlights the limited number of experimental studies dealing with the role of ABC transporters in the physiology and pathophysiology of skin cells and the skin as a whole. At the same time, the importance of such knowledge in relation to the possibility of daily exposure to UV radiation and xenobiotics, used for both skin care and the treatment of its diseases, is emphasized.

Post-transplant Malignancies Show Reduced T-cell Abundance and Tertiary Lymphoid Structures as Correlates of Impaired Cancer Immunosurveillance

PURPOSE

An increased risk to develop cancer is one of the most challenging negative side effects of long-term immunosuppression in organ transplant recipients and impaired cancer immunosurveillance is assumed as underlying mechanism. This study aims to elucidate transplant-related changes in the tumor immune microenvironment (TME) of cancer.

EXPERIMENTAL DESIGN

Data from 123 organ transplant recipients (kidney, heart, lung, and liver) were compared with historic data from non-immunosuppressed patients. Digital image analysis of whole-section slides was used to assess abundance and spatial distribution of T cells and tertiary lymphoid structures (TLS) in the TME of 117 tumor samples. Expression of programmed cell death 1 ligand 1 (PD-L1) and human-leucocyte-antigen class I (HLA-I) was assessed on tissue microarrays.

RESULTS

We found a remarkably reduced immune infiltrate in the center tumor (CT) regions as well as the invasive margins (IM) of post-transplant cancers. These differences were more pronounced in the IM than in the CT and larger for CD8+ T cells than for CD3+ T cells. The Immune-score integrating results from CT and IM was also lower in transplant recipients. Density of TLS was lower in cancer samples of transplant recipients. The fraction of samples with PD-L1 expression was higher in controls whereas decreased expression of HLA-I was more common in transplant recipients.

CONCLUSIONS

Our study demonstrates the impact of immunosuppression on the TME and supports impaired cancer immunosurveillance as important cause of post-transplant cancer. Modern immunosuppressive protocols and cancer therapies should consider the distinct immune microenvironment of post-transplant malignancies.

Specific cannabinoids revive adaptive immunity by reversing immune evasion mechanisms in metastatic tumours

Emerging cancers are sculpted by neo-Darwinian selection for superior growth and survival but minimal immunogenicity; consequently, metastatic cancers often evolve common genetic and epigenetic signatures to elude immune surveillance. Immune subversion by metastatic tumours can be achieved through several mechanisms; one of the most frequently observed involves the loss of expression or mutation of genes composing the MHC-I antigen presentation machinery (APM) that yields tumours invisible to Cytotoxic T lymphocytes, the key component of the adaptive cellular immune response. Fascinating ethnographic and experimental findings indicate that cannabinoids inhibit the growth and progression of several categories of cancer; however, the mechanisms underlying these observations remain clouded in uncertainty. Here, we screened a library of cannabinoid compounds and found molecular selectivity amongst specific cannabinoids, where related molecules such as Δ9-tetrahydrocannabinol, cannabidiol, and cannabigerol can reverse the metastatic immune escape phenotype in vitro by inducing MHC-I cell surface expression in a wide variety of metastatic tumours that subsequently sensitizing tumours to T lymphocyte recognition. Remarkably, H3K27Ac ChIPseq analysis established that cannabigerol and gamma interferon induce overlapping epigenetic signatures and key gene pathways in metastatic tumours related to cellular senescence, as well as APM genes involved in revealing metastatic tumours to the adaptive immune response. Overall, the data suggest that specific cannabinoids may have utility in cancer immunotherapy regimens by overcoming immune escape and augmenting cancer immune surveillance in metastatic disease. Finally, the fundamental discovery of the ability of cannabinoids to alter epigenetic programs may help elucidate many of the pleiotropic medicinal effects of cannabinoids on human physiology.

Cancer-specific immune evasion and substantial heterogeneity within cancer types provide evidence for personalized immunotherapy

The immune response against cancer is orchestrated by various parameters and site-dependent specificities have been poorly investigated. In our analyses of ten different cancer types, we describe elevated infiltration by regulatory T cells as the most common feature, while other lymphocyte subsets and also expression of immune-regulatory molecules on tumor-infiltrating lymphocytes showed site-specific variation. Multiparametric analyses of these data identified similarities of renal and liver or lung with head and neck cancer. Co-expression of immune-inhibitory ligands on tumor cells was most frequent in colorectal, lung and ovarian cancer. Genes related to antigen presentation were frequently dysregulated in liver and lung cancer. Expression of co-inhibitory molecules on tumor-infiltrating T cells accumulated in advanced stages while T-cell abundance was related to enhanced expression of genes related to antigen presentation. Our results promote evaluation of cancer-specific or even personalized immunotherapeutic combinations to overcome primary or secondary resistance as major limitation of immune-checkpoint inhibition.

Cancer Immune Evasion Through Loss of MHC Class I Antigen Presentation

Major histocompatibility class I (MHC I) molecules bind peptides derived from a cell's expressed genes and then transport and display this antigenic information on the cell surface. This allows CD8 T cells to identify pathological cells that are synthesizing abnormal proteins, such as cancers that are expressing mutated proteins. In order for many cancers to arise and progress, they need to evolve mechanisms to avoid elimination by CD8 T cells. MHC I molecules are not essential for cell survival and therefore one mechanism by which cancers can evade immune control is by losing MHC I antigen presentation machinery (APM). Not only will this impair the ability of natural immune responses to control cancers, but also frustrate immunotherapies that work by re-invigorating anti-tumor CD8 T cells, such as checkpoint blockade. Here we review the evidence that loss of MHC I antigen presentation is a frequent occurrence in many cancers. We discuss new insights into some common underlying mechanisms through which some cancers inactivate the MHC I pathway and consider some possible strategies to overcome this limitation in ways that could restore immune control of tumors and improve immunotherapy.

Metastatic Colonization: Escaping Immune Surveillance

Cancer immunotherapy has shifted the paradigm in cancer therapy by revitalizing immune responses against tumor cells. Specifically, in primary tumors cancer cells evolve in an immunosuppressive microenvironment, which protects them from immune attack. However, during tumor progression, some cancer cells leave the protective tumor mass, disseminating and seeding secondary organs. These initial disseminated tumor cells (DTCs) should potentially be susceptible to recognition by the immune system in the new host tissues. Although Natural Killer or T cells eliminate some of these DTCs, a fraction escape anti-tumor immunity and survive, thus giving rise to metastatic colonization. How DTCs interact with immune cells and the underpinnings that regulate imperfect immune responses during tumor dissemination remain poorly understood. Uncovering such mechanisms of immune evasion may contribute to the development of immunotherapy specifically targeting DTCs. Here we review current knowledge about systemic and site-specific immune-cancer crosstalk in the early steps of metastasis formation. Moreover, we highlight how conventional cancer therapies can shape the pre-metastatic niche enabling immune escape of newly arrived DTCs.

Genomics-based immuno-oncology: bridging the gap between immunology and tumor biology

The first hypotheses about how the immune system affects cancers were proposed in the early 20th century. These early concepts about cancer immunosurveillance were further developed in the decades that followed, but a detailed understanding of cancer immunity remained elusive. It was only recently, through the advent of high-throughput technologies, that scientists gained the ability to profile tumors with a resolution that allowed for granular assessment of both tumor cells and the tumor microenvironment. The advent of immune checkpoint inhibitors (ICIs), which have proven to be effective cancer therapies in many malignancies, has spawned great interest in developing biomarkers for efficacy, an endeavor that highlighted the value of dissecting tumor immunity using large-scale methods. Response to ICI therapy has been shown to be a highly complex process, where the dynamics of tumor and immune cells is key to success. The need to understand the biologic mechanisms at the tumor-immune interface has given rise to the field of cancer immunogenomics, a discipline that aims to bridge the gap between cancer genomics and classical immunology. We provide a broad overview of this emerging branch of translational science, summarizing common platforms used and recent discoveries in the field, which are having direct clinical implications. Our discussion will be centered around the genetic foundations governing tumor immunity and molecular determinants associated with clinical benefit from ICI therapy. We emphasize the importance of molecular diversity as a driver of anti-tumor immunity and discuss how these factors can be probed using genomic approaches.

Role of Human Leukocyte Antigen System as A Predictive Biomarker for Checkpoint-Based Immunotherapy in Cancer Patients

Recent advances in cancer immunotherapy have clearly shown that checkpoint-based immunotherapy is effective in a small subgroup of cancer patients. However, no effective predictive biomarker has been identified so far. The major histocompatibility complex, better known in humans as human leukocyte antigen (HLA), is a very polymorphic gene complex consisting of more than 200 genes. It has a crucial role in activating an appropriate host immune response against pathogens and tumor cells by discriminating self and non-self peptides. Several lines of evidence have shown that down-regulation of expression of HLA class I antigen derived peptide complexes by cancer cells is a mechanism of tumor immune escape and is often associated to poor prognosis in cancer patients. In addition, it has also been shown that HLA class I and II antigen expression, as well as defects in the antigen processing machinery complex, may predict tumor responses in cancer immunotherapy. Nevertheless, the role of HLA in predicting tumor responses to checkpoint-based immunotherapy is still debated. In this review, firstly, we will describe the structure and function of the HLA system. Secondly, we will summarize the HLA defects and their clinical significance in cancer patients. Thirdly, we will review the potential role of the HLA as a predictive biomarker for checkpoint-based immunotherapy in cancer patients. Lastly, we will discuss the potential strategies that may restore HLA function to implement novel therapeutic strategies in cancer patients.

HLA Class I Antigen Processing Machinery Defects in Cancer Cells-Frequency, Functional Significance, and Clinical Relevance with Special Emphasis on Their Role in T Cell-Based Immunotherapy of Malignant Disease

MHC class I antigen abnormalities have been shown to be one of the major immune escape mechanisms murine and human cancer cells utilize to avoid recognition and destruction by host immune system. This mechanism has clinical relevance, since it is associated with poor prognosis and/or reduced patients' survival in many types of malignant diseases. The recent impressive clinical responses to T cell-based immunotherapies triggered by checkpoint inhibitors have rekindled tumor immunologists and clinical oncologists' interest in the analysis of the human leukocyte antigen (HLA) class I antigen processing machinery (APM) expression and function in malignant cells. Abnormalities in the expression, regulation and/or function of components of this machinery have been associated with the development of resistances to T cell-based immunotherapies. In this review, following the description of the human leukocyte antigen (HLA) class I APM organization and function, the information related to the frequency of defects in HLA class I APM component expression in various types of cancer and the underlying molecular mechanisms is summarized. Then the impact of these defects on clinical response to T cell-based immunotherapies and strategies to revert this immune escape process are discussed.

HLA Expression in Uveal Melanoma: An Indicator of Malignancy and a Modifiable Immunological Target

Uveal melanoma (UM) is the most common primary intraocular malignancy in adults, and gives rise to metastases in 50% of cases. The presence of an inflammatory phenotype is a well-known risk factor for the development of metastases. This inflammatory phenotype is characterized by the presence of high numbers of lymphocytes and macrophages, and a high expression of the HLA Class I and II antigens. An abnormal expression of HLA Class I may influence cytotoxic T lymphocyte (CTL) as well as Natural Killer (NK) cell responses. We provide a comprehensive review regarding the inflammatory phenotype in UM and the expression of locus- and allele-specific HLA Class I and of Class II antigens in primary UM and its metastases. Furthermore, we describe the known regulators and the role of genetics (especially chromosome 3 and BRCA-Associated Protein 1 (BAP1 status)), and, last but not least, the effect of putative therapeutic treatments on HLA expression.

Identification of candidate neoantigens produced by fusion transcripts in human osteosarcomas

Osteosarcomas are characterized by highly disrupted genomes. Although osteosarcomas lack common fusions, we find evidence of many tumour specific gene-gene fusion transcripts, likely due to chromosomal rearrangements and expression of transcription-induced chimeras. Most of the fusions result in out-of-frame transcripts, potentially capable of producing long novel protein sequences and a plethora of neoantigens. To identify fusions, we explored RNA-sequencing data to obtain detailed knowledge of transcribed fusions, by creating a novel program to compare fusions identified by deFuse to de novo transcripts generated by Trinity. This allowed us to confirm the deFuse results and identify unusual splicing patterns associated with fusion events. Using various existing tools combined with this custom program, we developed a pipeline for the identification of fusion transcripts applicable as targets for immunotherapy. In addition to identifying candidate neoantigens associated with fusions, we were able to use the pipeline to establish a method for measuring the frequency of fusion events, which correlated to patient outcome, as well as highlight some similarities between canine and human osteosarcomas. The results of this study of osteosarcomas underscores the numerous benefits associated with conducting a thorough analysis of fusion events within cancer samples.

Cytosolic Processing Governs TAP-Independent Presentation of a Critical Melanoma Antigen

Cancer immunotherapy has been flourishing in recent years with remarkable clinical success. But as more patients are treated, a shadow is emerging that has haunted other cancer therapies: tumors develop resistance. Resistance is often caused by defects in the MHC class I Ag presentation pathway critical for CD8 T cell-mediated tumor clearance. TAP and tapasin, both key players in the pathway, are frequently downregulated in human cancers, correlating with poor patient survival. Reduced dependence on these factors may promote vaccine efficiency by limiting immune evasion. In this study, we demonstrate that PMEL209-217, a promising phase 3 trial-tested antimelanoma vaccine candidate, is robustly presented by various TAP- and/or tapasin-deficient cell lines. This striking characteristic may underlie its potency as a vaccine. Surprisingly, cytosolic proteasomes generate the peptide even for TAP-independent presentation, whereas tripeptidyl peptidase 2 (TPP2) efficiently degrades the epitope. Consequently, inhibiting TPP2 substantially boosts PMEL209-217 presentation, suggesting a possible strategy to improve the therapeutic efficacy of the vaccine.

Defective HLA class I antigen processing machinery in cancer

Malignant transformation of cells is frequently associated with defective HLA class I antigen processing machinery (APM) component expression. This abnormality may have functional relevance, since it may have a negative impact on tumor cell recognition by cognate T cells. Furthermore, HLA class I APM abnormalities appear to have clinical significance, since they are associated with poor prognosis in several malignant diseases and may play a role in the resistance to immune checkpoint inhibitor-based immunotherapy. In this paper, we have reviewed the literature describing abnormalities in HLA class I APM component expression in many types of cancer. These abnormalities have been reported in all types of cancer analyzed with a frequency ranging between a minimum of 35.8% in renal cancer and a maximum of 87.9% in thyroid cancer for HLA class I heavy chains. In addition, we have described the molecular mechanisms underlying defects in HLA class I APM component expression and function by malignant cells. Lastly, we have discussed the clinical significance of HLA class I APM component abnormalities in malignant tumors.

Dysfunction of antigen processing and presentation by dendritic cells in cancer

The ability to mount an effective anti-tumor immune response requires coordinate control of CD4 T cell and CD8 T cell function by antigen presenting cells (APCs). Unfortunately, tumors create an immunosuppressive microenvironment that helps protect tumor cells from immune recognition. In many cases this defect can be traced back to a failure of APCs (most importantly dendritic cells (DCs)) to recognize, process, and present tumor antigens to T cells. In this review, we will summarize work addressing the role of different DC subsets in anti-tumor immunity and the various mechanisms used by tumor cells to suppress the ability of APCs to stimulate potent anti-tumor T cell responses.

Prognosis of stage III colorectal carcinomas with FOLFOX adjuvant chemotherapy can be predicted by molecular subtype

Individualizing adjuvant chemotherapy is important in patients with advanced colorectal cancers (CRCs), and the ability to identify molecular subtypes predictive of good prognosis for stage III CRCs after adjuvant chemotherapy could be highly beneficial. We performed microarray-based gene expression analysis on 101 fresh-frozen primary samples from patients with stage III CRCs treated with FOLFOX adjuvant chemotherapy and 35 matched non-neoplastic mucosal tissues. CRC samples were classified into four molecular subtypes using nonnegative matrix factorization, and for comparison, we also grouped CRC samples using the proposed consensus molecular subtypes (CMSs). Of the 101 cases, 80 were classified into a CMS group, which shows a 79% correlation between the CMS classification and our four molecular subtypes. We found that two of our subtypes showed significantly higher disease-free survival and overall survival than the others. Group 2, in particular, which showed no disease recurrence or death, was characterized by high microsatellite instability (MSI-H, 6/21), abundant mucin production (12/21), and right-sided location (12/21); this group strongly correlated with CMS1 (microsatellite instability immune type). We further identified the molecular characteristics of each group and selected 10 potential biomarker genes from each. When these were compared to the previously reported molecular classifier genes, we found that 31 out of 40 selected genes were matched with those previously reported. Our findings indicate that molecular classification can reveal specific molecular subtypes correlating with clinicopathologic features of CRCs and can have predictive value for the prognosis for stage III CRCs with FOLFOX adjuvant chemotherapy.

Immunological and clinical significance of HLA class I antigen processing machinery component defects in malignant cells

Experimental as well as clinical studies demonstrate that the immune system plays a major role in controlling generation and progression of tumors. The cancer immunoediting theory supports the notion that tumor cell immunogenicity is dynamically shaped by the immune system, as it eliminates immunogenic tumor cells in the early stage of the disease and then edits their antigenicity. The end result is the generation of a tumor cell population able to escape from immune recognition and elimination by tumor infiltrating lymphocytes. Two major mechanisms, which affect the target cells and the effector phase of the immune response, play a crucial role in the editing process. One is represented by the downregulation of tumor antigen (TA) processing and presentation because of abnormalities in the HLA class I antigen processing machinery (APM). The other one is represented by the anergy of effector immune infiltrates in the tumor microenvironment caused by aberrant inhibitory signals triggered by immune checkpoint receptor (ICR) ligands, such as programmed death ligand-1 (PD-L1). In this review, we will focus on tumor immune escape mechanisms caused by defects in HLA class I APM component expression and/or function in different types of cancer, with emphasis on head and neck cancer (HNC). We will also discuss the immunological implications and clinical relevance of these HLA class I APM abnormalities. Finally, we will describe strategies to counteract defective TA presentation with the expectation that they will enhance tumor recognition and elimination by tumor infiltrating effector T cells.

Interferon Alpha Signalling and Its Relevance for the Upregulatory Effect of Transporter Proteins Associated with Antigen Processing (TAP) in Patients with Malignant Melanoma

INTRODUCTION

Interferon alpha (IFNα) is routinely used in the clinical practice for adjuvant systemic melanoma therapy. Understanding the molecular mechanism of IFNα effects and prediction of response in the IFNα therapy regime allows initiation and continuation of IFNα treatment for responder and exclusion of non-responder to avoid therapy inefficacy and side-effects. The transporter protein associated with antigen processing-1 (TAP1) is part of the MHC class I peptide-loading complex, and important for antigen presentation in tumor and antigen presenting cells. In the context of personalized medicine, we address this potential biomarker TAP1 as a target of IFNα signalling.

RESULTS

We could show that IFNα upregulates TAP1 expression in peripheral blood mononuclear cells (PBMCs) of patients with malignant melanoma receiving adjuvant high-dose immunotherapy. IFNα also induced expression of TAP1 in mouse blood and tumor tissue and suppressed the formation of melanoma metastasis in an in vivo B16 tumor model. Besides its expression, TAP binding affinity and transport activity is induced by IFNα in human monocytic THP1 cells. Furthermore, our data revealed that IFNα clearly activates phosphorylation of STAT1 and STAT3 in THP1 and A375 melanoma cells. Inhibition of Janus kinases abrogates the IFNα-induced TAP1 expression. These results suggest that the JAK/STAT pathway is a crucial mediator for TAP1 expression elicited by IFNα treatment.

CONCLUSION

We suppose that silencing of TAP1 expression provides tumor cells with a mechanism to escape cytotoxic T-lymphocyte recognition. The observed benefit of IFNα treatment could be mediated by the shown dual effect of TAP1 upregulation in antigen presenting cells on the one hand, and of TAP1 upregulation in 'silent' metastatic melanoma cells on the other hand. In conclusion, this work contributes to a better understanding of the mode of action of IFNα which is essential to identify markers to predict, assess and monitor therapeutic response of IFNα treatment in the future.

Overcoming tumor-mediated immunosuppression

Mechanisms of tumor-mediated immunosuppression have been described for several solid and hematological tumors. Tumors inhibit immune responses by attraction of immunosuppressive lymphocytic populations, secretion of immunosuppressive cytokines or expression of surface molecules, which inhibit immune responses by induction of anergy or apoptosis in tumor-infiltrating lymphocytes. This tumor-mediated immunosuppression represents a major obstacle to many immunotherapeutic or conventional therapeutic approaches. In this review we discuss how tumor-mediated immunosuppression interferes with different immunotherapeutic approaches and then give an overview of strategies to overcome it. Particular emphasis is placed on agents or approaches already transferred into clinical settings. Finally the success of immune checkpoint inhibitors targeting CTLA-4 or the PD-1 pathway highlights the enormous therapeutic potential of an effective overcoming of tumor-mediated immunosuppression.

Human Tumor Antigens and Cancer Immunotherapy

With the recent developments of adoptive T cell therapies and the use of new monoclonal antibodies against the immune checkpoints, immunotherapy is at a turning point. Key players for the success of these therapies are the cytolytic T lymphocytes, which are a subset of T cells able to recognize and kill tumor cells. Here, I review the nature of the antigenic peptides recognized by these T cells and the processes involved in their presentation. I discuss the importance of understanding how each antigenic peptide is processed in the context of immunotherapy and vaccine delivery.

Genetic variations of TAP1 gene exon 3 affects gene expression and Escherichia coli F18 resistance in piglets

Firstly, our research group identified Sutai pigs’ phenotypes that exhibited extreme resistance and susceptibility to the Escherichia coli F18 respectively, and then eight ETEC (Enterotoxigenic Escherichia coli) F18-resistant piglets and eight ETEC F18-sensitive piglets were selected. Then, the TAP1 (Transporter associated with antigen processing) mRNA relative expression levels were analyzed in 11 tissues of the resistant and susceptible phenotypes. Simultaneously, we detected the genetic variations in exon 3 of the TAP1 gene and evaluated the TAP1 mRNA expression levels among the different genotype pigs to study the effects of the genetic variation on gene expression, and the E. coli F18 resistance. The results revealed higher expression levels in the resistant genotypes than that in the susceptible genotypes in 11 tissues, with significant differences in the spleen, lymph node, lung, thymus, duodenum and jejunum. Furthermore, a G729A mutation was identified in the TAP1 gene exon 3, and this mutation deviates from Hardy-Weinberg equilibrium (p < 0.01). The TAP1 mRNA levels in GG genotype were significantly higher than that in the other two genotypes, with significant differences in the liver, lung, kidney, thymus, lymph node, duodenum and jejunum tissues. We speculated that high expression of the TAP1 gene might confer resistance against the E. coli F18, the G729A mutation had a significant effect on the mRNA expression, and individuals with the GG genotype possessed a stronger ability to resist the E. coli F18 infection.

Prognostic significance of HLA EMR8-5 immunohistochemically analyzed expression in osteosarcoma

Background

Defects in Human Leukocyte Antigen (HLA) class I antigen expression and/or function in tumor cells have been extensively investigated, because of their potential role in the escape of tumor cells from T cell recognition and destruction. The researchers evaluated HLA class I expression in tumor tissue as a prognostic factor in osteosarcoma patients and as a predictor of their survival. This retrospective cohort study was conducted at the pathology laboratory of Ain Shams University Hospital, and Ain Shams University Specialized Hospital during the period between January 2009 and January 2012.

Methods

The researchers investigated HLA class I expression in primary osteosarcoma by immunohistochemistry using EMR8-5 mAbs. Furthermore, researchers evaluated the correlation between HLA class I expression and the clinicopathological status and outcome in formalin fixed paraffin embedded tissues from thirty six (36) patients with osteosarcoma.

Results

A high expression of HLA class I was detected in 18 (50) % of tumor samples examined; while tumors with low or negative expression represented 9 (25%) cases each. Data indicate that the overall survival rate of patients with tumors highly expressing HLA class I was significantly higher than those with low or negative expression.

Conclusion

Down-regulation of class I antigen expression is associated with features of aggressive disease and a poorer prognosis. Therefore, it is imperative to identify HLA as a prognostic factor at the time of diagnosis to detect chemotherapy-resistant tumors and to generate a modified treatment regimen.

Virtual slides

The virtual slides for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1159334857109547.

MHC class I antigen processing and presenting machinery: organization, function, and defects in tumor cells

The surface presentation of peptides by major histocompatibility complex (MHC) class I molecules is critical to all CD8(+) T-cell adaptive immune responses, including those against tumors. The generation of peptides and their loading on MHC class I molecules is a multistep process involving multiple molecular species that constitute the so-called antigen processing and presenting machinery (APM). The majority of class I peptides begin as proteasome degradation products of cytosolic proteins. Once transported into the endoplasmic reticulum by TAP (transporter associated with antigen processing), peptides are not bound randomly by class I molecules but are chosen by length and sequence, with peptidases editing the raw peptide pool. Aberrations in APM genes and proteins have frequently been observed in human tumors and found to correlate with relevant clinical variables, including tumor grade, tumor stage, disease recurrence, and survival. These findings support the idea that APM defects are immune escape mechanisms that disrupt the tumor cells' ability to be recognized and killed by tumor antigen-specific cytotoxic CD8(+) T cells. Detailed knowledge of APM is crucial for the optimization of T cell-based immunotherapy protocols.

Rescue of MHC-1 antigen processing machinery by down-regulation in expression of IGF-1 in human glioblastoma cells

Escape from immune recognition has been hypothesized to be a factor in carcinogenesis. It may be mediated for many cancers through down-regulation in the MHC class 1 antigen processing and presentation pathway. TAP-1, TAP-2, tightly linked to LMP-2 and LMP-7 are multiple components of the endogenous, antigen presentation pathway machinery. We addressed the question of alterations in this pathway in human Glioblastoma (HGB) and of its relationship to modulation in expression of IGF-1 that is highly expressed in this cancer. Deficiencies in expression of TAP-1 were demonstrated by RT-PCR and/or by immuno-flow cytometry in the HGB cell line T98G obtained from ATCC, and in 3 of 4 human cell lines established from patients with Glioblastoma Multiforme. Deficiencies in expression of TAP-2 were observed in 3 of 4, deficiencies in expression of LMP-2 in 4 of 4 and deficiencies in LMP-7 in 3 of 4 HGB cell lines examined by RT-PCR and Western blot. Following down-regulation of IGF-1 by transfection with the pAnti IGF-1 vector that expresses IGF-1 RNA in antisense orientation, or by the exogenous addition of IGF-1 receptor monoclonal antibody to cell culture media, the deficiencies in components of the MHC-1 antigen presentation pathway were up-regulated and/or rescued in all HGB cell lines tested. Moreover, this up-regulation in expression was aborted by addition of 100 ng/ml of IGF-1 to the culture media. Unlike in the case of IFN-γ, the restoration of TAP-1 and LMP-2 by down-regulation of IGF-1 in Glioblastoma cells was not correlated to the tyrosine phosphorylation of STAT 1. In summary, the simultaneous reversion in expression of the multiple constituents of MHC-1 antigen processing path and up-regulation in expression of MHC-1 occurring with down-regulation in IGF-1 may have a role in reinforcement of immunity against tumor antigen(s) in some animal cancers and in humans with Glioblastoma Multiforme.

Establishment of a monoclonal anti-pan HLA class I antibody suitable for immunostaining of formalin-fixed tissue: unusually high frequency of down-regulation in breast cancer tissues

A novel monoclonal anti-pan human leukocyte antigen (HLA) class I heavy chain antibody, EMR8-5, was established. It could detect HLA-A, -B, and -C antigens in formalin-fixed paraffin embedded tissues. By immunohistochemical staining using the EMR8-5 antibody, various cancer tissues from 246 cases were examined for HLA class I expression. It was found that HLA class I expression was decreased in 20% to 42% of the cases of lung cancer, hepatocellular carcinoma, colon cancer, renal cell carcinoma, and urothelial carcinoma. In contrast, 85% of breast cancer cases had loss of or decreased HLA class I expression. Of the 35 breast cancer cases that had decreased HLA class I heavy chain expression, 33 (94%) also had decreased beta2-microglobulin expression detected by immunohistochemical staining. It was suggested that HLA class I down-regulation might be a common characteristic of breast cancer mostly caused by the down-regulation of beta2-microglobulin expression.

CD8+ T cell responses against TAP-inhibited cells are readily detected in the human population

Target cell recognition by CTLs depends on the presentation of peptides by HLA class I molecules. Tumors and herpes viruses have adopted strategies to greatly hamper this peptide presentation at the important bottleneck, the peptide transporter TAP. Previously, we described the existence of a CD8(+) CTL subpopulation that selectively recognizes such TAP-deficient cells in mouse models. In this study, we show that the human counterpart of this CTL subset is readily detectable in healthy subjects. Autologous PBMC cultures were initiated with dendritic cells rendered TAP-impaired by gene transfer of the viral evasion molecule UL49.5. Strikingly, specific reactivity to B-LCLs expressing one of the other viral TAP-inhibitors (US6, ICP47, or BNLF2a) was already observed after three rounds of stimulation. These short-term T cell cultures and isolated CD8(+) CTL clones derived thereof did not recognize the normal B-LCL, indicating that the cognate peptide-epitopes emerge at the cell surface upon an inhibition in the MHC class I processing pathway. A diverse set of TCRs was used by the clones, and the cellular reactivity was TCR-dependent and HLA class I-restricted, implying the involvement of a broad antigenic peptide repertoire. Our data indicate that the human CD8(+) T cell pool comprises a diverse reactivity to target cells with impairments in the intracellular processing pathway, and these might be exploited for cancers that are associated with such defects and for infections with immune-evading herpes viruses.

Characterization of signaling function and expression of HLA class I molecules in medulloblastoma

Although known for the important function in the immune system, MHC class I molecules are increasingly ascribed an alternative role in modifying signal transduction. In medulloblastoma, HLA class I molecules are associated with poor prognosis, and can induce ERK1/2 activation upon engagement with ligands that bind to incompletely assembled complexes (so called open conformers). We here demonstrate that ERK1/2 activation in medulloblastoma can occur in the absence of endogenously synthesized β2m, formally excluding involvement of closed HLA class conformation. In addition, several experimental observations suggest that heterogeneity of HLA class I expression may be a reflection of the status of original cells before transformation, rather than a consequence of immune-based selection of HLA-loss mutants. These results contribute to our understanding of an immune system-independent role of HLA class I in the pathology of medulloblastoma, and cancer in general.

Down-regulation of HLA class I antigen-processing machinery components in esophageal squamous cell carcinomas: association with disease progression

OBJECTIVE

Lack of human leukocyte antigen (HLA) presentation has been proposed to contribute to the immune evasion of cancer cells in some cancers including esophageal cancer. The aim of this study was to examine the expression of HLA class I antigen and the antigen-processing machinery (APM) components in esophageal squamous cell carcinoma (ESCC) lesions and to assess their association with histopathological characteristics.

MATERIAL AND METHODS

A total of 143 formalin-fixed, paraffin-embedded ESCC lesions collected in two hospitals in Shandong Province of China were studied. The expression levels were determined by immunohistochemistry.

RESULTS

TAP1, TAP2, LMP2, LMP7, beta2m, and HLA class I antigen were lost or down-regulated in 30.8%, 35.0%, 45.0%, 48.0%, 56.0%, and 60.8% of the ESCC lesions tested, respectively. The loss of or down-regulated expressions of HLA class I, beta2m, TAP1, LMP2, and LMP7 in tumor lesions were all significantly correlated to tumor grade and lymph node status. Expression of HLA class I antigens was strongly correlated to the expression levels of beta2m, TAP1, TAP2, LMP2, and LMP7, suggesting APM component defects as a mechanism underlying HLA class I antigen down-regulation in ESCC lesions. Expression of APM components and HLA class I antigens was significantly associated with the extent of intratumoral T-cell infiltration.

CONCLUSIONS

Our results indicate that lack or reduction of HLA class I antigens and expression of APM components in ESCC may render some tumor cells to escape the immunosurveillance mediated by CD8(+) T cells and contribute to the clinical course of ESCC.

Human leukocyte antigen class I down-regulation in muscle-invasive bladder cancer: its association with clinical characteristics and survival after cystectomy

Using a novel monoclonal anti-pan human leukocyte antigen (HLA) class I heavy chain antibody (EMR 8-5) reacting with paraffin-embedded sections, we examined the prognostic significance of HLA class I molecules in muscle-invasive bladder cancer patients who underwent radical cystectomy. Immunohistochemical staining for HLA class I molecules with monoclonal antibody EMR 8-5 was performed on specimens from 65 clinically muscle-invasive bladder cancer patients who underwent radical cystectomy and pelvic lymph node dissection without neoadjuvant chemotherapy. We analyzed the clinicopathological and prognostic significance of HLA class I expression. Immunohistochemical analysis revealed HLA class I down-regulation in 22 (33.8%) invasive bladder cancers. This down-regulation had no correlation with clinicopathological parameters such as pathologic stage, nodal status, and grade. The recurrence-free survival of patients with HLA class I-positive tumors was significantly better than that of those with down-regulation (log rank, P = 0.0337). Multivariate analysis revealed that HLA class I expression was a significant factor influencing the recurrence-free survival of bladder cancer patients after cystectomy (P = 0.0155). Our data demonstrate that HLA class I down-regulation in tumor cells was clearly observed in about one-third of the patients. HLA class I expression could be a prognostic marker for muscle-invasive bladder cancer patients after cystectomy.

A novel role of HLA class I in the pathology of medulloblastoma

BACKGROUND

MHC class I expression by cancer cells enables specific antigen recognition by the immune system and protection of the host. However, in some cancer types MHC class I expression is associated with an unfavorable outcome. We explored the basis of MHC class I association with unfavorable prognostic marker expression in the case of medulloblastoma.

METHODS

We investigated expression of four essential components of MHC class I (heavy chain, beta2m, TAP1 and TAP2) in 10 medulloblastoma mRNA samples, a tissue microarray containing 139 medulloblastoma tissues and 3 medulloblastoma cell lines. Further, in medulloblastoma cell lines we evaluated the effects of HLA class I engagement on activation of ERK1/2 and migration in vitro.

RESULTS

The majority of specimens displayed undetectable or low levels of the heavy chains. Medulloblastomas expressing high levels of HLA class I displayed significantly higher levels of anaplasia and c-myc expression, markers of poor prognosis. Binding of beta2m or a specific antibody to open forms of HLA class I promoted phosphorylation of ERK1/2 in medulloblastoma cell line with high levels, but not in the cell line with low levels of HLA heavy chain. This treatment also promoted ERK1/2 activation dependent migration of medulloblastoma cells.

CONCLUSION

MHC class I expression in medulloblastoma is associated with anaplasia and c-myc expression, markers of poor prognosis. Peptide- and/or beta2m-free forms of MHC class I may contribute to a more malignant phenotype of medulloblastoma by modulating activation of signaling molecules such as ERK1/2 that stimulates cell mobility.

Mapping ATP-binding cassette transporter gene expression profiles in melanocytes and melanoma cells

ATP-binding cassette (ABC) transporters regulate the transport of a variety of physiologic substrates. Moreover, several human ABC proteins are responsible for drug exclusion in compound-treated tumor cells, providing cellular mechanisms for the development of multidrug resistance and, therefore, playing an important role in malignant transformation. As only limited information exists on the role of ABC transporters in melanoma, the aim of the study was to generate a complete expression profile of ABC transporters in this tumor entity. Using a TaqMan low-density array for 47 human ABC transporters, mRNA expression analysis was performed from normal human epidermal melanocytes (NHEM P2 and NHEM P3), nine different cell lines originating from primary melanoma (Mel Ei, Mel Juso, Mel Ho and Mel Wei), and metastases of malignant melanoma (Mel Im, Mel Ju, SK Mel 28, HTZ 19 and HMB2). Cell line-specific expression levels were compared with gene expression in pooled RNA from a variety of other human tissues. High expression levels were detected in pooled tissue RNA as well as in cells of melanocytic origin for ABCA5, ABCB2, ABCB6, ABCD3, ABCD4, ABCF1, ABCF2 and ABCF3, whereas ABCB5 revealed a melanocyte-specific high transcript level. In relation to normal melanocytes, ABCB3, ABCB6, ABCC2, ABCC4, ABCE1 and ABCF2 were significantly increased in melanoma cell lines, whereas ABCA7, ABCA12, ABCB2, ABCB4, ABCB5 and ABCD1 showed lower expression levels. In summary, we present here for the first time an ABC-transporter mRNA expression profile in melanoma in comparison to normal melanocytes. The differentially regulated ABC transporters detected by our approach may be candidate genes involved in melanoma tumorigenesis, progression and therapy resistance and could therefore be of great importance to identify novel options for melanoma therapy.

Loss of expression of antigen-presenting molecules in human pancreatic cancer and pancreatic cancer cell lines

Tumours evade immune recognition and destruction through loss or down-regulation of expression of antigen processing and antigen-presenting molecules such as the human leucocyte antigen (HLA class I) and transporter for antigen presentation (TAP). This study examined the expression of HLA class I, class II and TAP in human pancreatic carcinoma tissue and 19 immortalized pancreatic cancer lines using a panel of antibodies directed against allele-specific as well as monomorphic determinants of these molecules. In tissue samples, reduction or loss of HLA class I and TAP was observed in 76% of cases, loss or down-regulation of TAP expression in 53%. In pancreatic cell lines down-regulation or loss of class I and TAP expression was also observed frequently. However, reductions in class I and TAP expression were reversible upon exposure to interferon-gamma in vitro, suggesting a regulatory rather than structural defect in these genes. De novo class II expression was observed in 26% of tumours and 42% of cell lines and may reflect the differentiation status of the cells. The high rate of class I and TAP loss has implications for immunotherapy strategies for pancreatic cancer, as such changes could facilitate a selective growth advantage for malignant cells. However, the reinduction of expression of these molecules with cytokines such as interferon-gamma may ultimately allow their cytotoxic T cell-mediated destruction.

TAP expression reduces IL-10 expressing tumor infiltrating lymphocytes and restores immunosurveillance against melanoma

Many immune therapeutic strategies are under development for melanoma to treat metastatic disease and prevent disease reoccurrence. However, human melanoma cells are often deficient in antigen processing and this appears to play a role in their expansion and escape from immunosurveillance. For example, expression of the transporters associated with antigen processing (TAP1 and TAP2) is down‐regulated in the mouse melanoma cell line B16F10. This results in a lack of tumor‐associated antigen processing, low surface expression of MHC Class I molecules and low immunogenicity. We observe that restoration of TAP1 expression by transfection resurrects the processing and presentation of viral antigens, and the melanoma‐associated antigen, TRP‐2. Immunization with irradiated B16F10/rTAP1 transfected cells generates CTLs that are capable of killing B16F10/rTAP1 transfected targets and B16F10 targets deficient in TAP1. Furthermore, B16F10/rTAP1 transfectants grow at a significantly slower rate in mice than B16F10 cells. In an experimental model that closely recapitulates the clinical situation, treatment of B16F10 tumors in mice with a vaccinia virus vector expressing TAP1 also significantly decreases tumor growth in vivo. Furthermore, tumors treated with vaccinia TAP1 had significantly reduced numbers of immunosuppressive, CD3⁺/IL‐10 positive, tumor infiltrating lymphocytes. Therefore, TAP1 expression restores both antigen presentation and immunogenicity in B16F10 melanoma cells and concomitantly reduces immunosuppressive IL‐10 production at the local tumor site, thereby increasing immunosurveillance mechanisms against tumors. © 2007 Wiley‐Liss, Inc.

HLA-A, -B, -C expression in colon carcinoma mimics that of the normal colonic mucosa and is prognostically relevant

Whether human leukocyte antigen (HLA)-A, -B, -C expression has any predictive value on the prognosis of human malignancies remains controversial. Herein, monoclonal antibodies with preferential reactivity for HLA-A, HLA-B, and HLA-C (HCA2, HC10, and L31) were used to stain an archival collection of 291 formalin-fixed/paraffin-embedded tissues, comprising neoplastic lesions from stages II and III colon carcinoma patients (n=165), and the uninvolved, morphologically normal mucosae from a subset (n=126) of these patients. Marked staining variability was detected not only in the tumors as in previous studies, but also in the normal paired mucosae. HLA-A, -B, -C expression was similar in approximately two thirds of the available 126 normal/neoplastic pairs, confirming in vivo our previous observation that most tumor cells mimic the HLA phenotypes of their normal counterparts. Both up and down-regulation occurred in the remaining third of the pairs, but did not coincide with high and low expression, respectively, conventionally evaluated on the tumor lesion only. Remarkably, a "paired" evaluation, but not high or low expression in the tumor, was predictive of the clinical outcome. Deviations from the expression in the normal paired mucosa (both increases and decreases) of HCA2-reactive class I molecules (possibly HLA-A), and down-regulation of L31-reactive class I molecules (possibly HLA-C), particularly in tumors from stage II patients, correlated with poor 5-year overall and disease-free survival, hazard risk ranging from 2 to 6, approximately. Thus, a paired immunohistochemical comparison reveals a novel immune evasion strategy that may impact on the prognosis of colon carcinoma.

Association of Antigen-Processing Machinery and HLA Antigen Phenotype of Melanoma Cells with Survival in American Joint Committee on Cancer Stage III and IV Melanoma Patients

Because changes in the expression level of antigen-processing machinery (APM) components and HLA class I and II antigens in melanoma cells are expected to affect their interactions with the immune system of the host, we assessed the clinical relevance of quantitative variations in the expression of these molecules in melanoma lesions. Short-term (<10 in vitro passages) melanoma cell lines isolated from 85 American Joint Committee on Cancer (AJCC) stage III and IV patients were stained with APM component and HLA class I antigen-specific and HLA class II antigen-specific monoclonal antibodies and analyzed by flow cytometry. The phenotype of all tumors was characterized by intertumor and intratumor heterogeneity in the expression of all the markers and by significant correlations in the level of expression of markers belonging to the HLA class I antigen-processing and presentation pathway. Hierarchical clustering of the mean fluorescence intensity data defined two main clusters of tumors. The corresponding groups of patients differed significantly in the overall survival but not in other relevant clinical variables, including AJCC stage and therapy received after surgery. Cox regression analysis showed that beta2-microglobulin and HLA class II antigen expression were significantly associated with patients' survival. This evidence was corroborated by the immunohistochemical analysis for HLA class II antigen expression of melanoma lesions from an unrelated group of 52 AJCC stage III and IV patients. These results suggest that quantitative variations in APM component and HLA expression in melanoma lesions from AJCC stage III and IV patients may have an effect on the clinical course of the disease.

Reduced expression of the transporter associated with antigen processing 1 molecule in malignant glioma cells, and its restoration by interferon-gamma and -beta

OBJECT

It remains unclear whether malignant glioma cells can deliver tumor antigens efficiently to major histocompatibility complex (MHC) Class I molecules. To elucidate the mechanism of antigen presentation in malignant gliomas, the authors examined the expression of the transporter associated with antigen processing 1 (TAP1), which transports antigens to MHC Class I molecules, and low-molecular-mass polypeptide 2 (LMP2), which is a subunit of a proteasome. They also analyzed the effects of interferon (IFN)-gamma and IFN-beta on the expression of these molecules.

METHODS

Five glioma cells expressed undetectable or very low levels of TAP1 protein and did not express TAP1 messenger (m)RNA. Normal brain tissue and glioma tissue specimens also showed undetectable levels of TAP1 protein and the same levels of LMP2 protein as lymphoblastoid B cells. Treatments of the tumor cells with IFN-gamma, or -beta enhanced the expression of both TAP1 protein and mRNA as well as the expression of MHC Class I molecules. The expression of LMP2 protein was not altered by the IFN treatments. The authors analyzed structural alterations in the TAP1 promoter region in eight malignant glioma cell lines. Single nucleotide polymorphism was found in 446 bp up-stream of the translation start site of the TAP1 gene, and a point mutation was found in 34 bp upstream of the TAP1 gene.

CONCLUSIONS

Malignant glioma cells may be less immunogenic due to low levels of TAP1 expression. Upregulated expression of TAP1 and MHC Class I molecules by IFN-gamma and -beta may enhance antigen presentation in malignant glioma cells.

Sequential Immune Escape and Shifting of T Cell Responses in a Long-Term Survivor of Melanoma

Immune-mediated control of tumors may occur, in part, through lysis of malignant cells by CD8(+) T cells that recognize specific Ag-HLA class I complexes. However, tumor cell populations may escape T cell responses by immune editing, by preventing formation of those Ag-HLA complexes. It remains unclear whether the human immune system can respond to immune editing and recognize newly arising escape variants. We report an example of shifting immune responses to escape variants in a patient with sequential metastases of melanoma and long-term survival after surgery alone. Tumor cells in the first metastasis escaped immune recognition via selective loss of an HLA haplotype (HLA-A11, -B44, and -Cw17), but maintained expression of HLA-A2. In the second metastasis, immune escape from an immunodominant MART-1-specific T cell response was mediated by HLA class I down-regulation, resulting in a failure to present this epitope, but persistent presentation of a tyrosinase-derived epitope. Consequent to this modification in tumor Ag presentation, the dominant CTL response shifted principally toward a tyrosinase-targeted response, even though tyrosinase-specific CTL had been undetectable during the initial metastatic event. Thus, in response to immune editing of tumor cells, a patient's spontaneous T cell response adapted, gaining the ability to recognize and to lyse "edited" tumor targets. The observation of both immune editing and immune adaptation in a patient with long-term survival after surgery alone demonstrates an example of immune system reactivity to counteract the escape mechanism(s) developed by tumor cells, which may contribute to the clinical outcome of malignant disease.

Immunohistochemistry in melanocytic proliferative lesions

Melanoma incidence is rising worldwide. Early diagnosis is very important, as the most effective treatment for melanoma still consists of excision of the tumour before onset of the metastatic growth phase. Immunohistochemistry is a valuable tool for (dermato)pathologists to aid establishing diagnosis. Melanoma markers can be classified into two main categories: melanocytic differentiation markers and melanoma progression markers. Melanocytic differentiation markers are mostly used to distinguish poorly differentiated melanomas from non-melanocytic tumours and for staging of melanocytic proliferative lesions. Melanoma progression markers are most suitable to determine the level of malignancy and/or aggressiveness of tumour cells. This review describes the classification of melanoma markers, including commonly used and recently identified antigens with potential marker function. We characterize their expression profile in melanocytic proliferative lesions and their potential usefulness for diagnosis, prognosis, microstaging, immunotherapeutic purposes and evaluation of therapies.

Results of clinical trials with an allogeneic melanoma tumor cell lysate vaccine: Melacine®

The identification of proteins and carbohydrates associated with melanoma led to development of defined antigen vaccines. However, vaccines derived from whole allogeneic cells have a number of advantages. Melacine is an allogeneic melanoma tumor cell lysate combined with an immunologic adjuvant, DETOX. Phase I and II trials in stage IV melanoma showed low-level antitumor activity, but this vaccine has its greatest promise in the adjuvant setting. A phase III trial indicated a survival benefit for Melacine in the subset of melanoma patients who express the HLA class I antigens A2 and/or HLA-C3. This finding must now be prospectively confirmed.

Association of TAP1 downregulation in human primary melanoma lesions with lack of spontaneous regression

Spontaneous regression of primary melanoma lesions is regarded as the result of the recognition of melanoma-associated antigen (MAA)-derived peptides by cytotoxic T-lymphocytes and destruction of melanoma cells. The transporter associated with antigen processing (TAP1/2) is likely to play a crucial role in this process since it loads antigen peptides onto MHC class I molecules. To determine the impact of TAP defects on the spontaneous regression of melanoma lesions, we have compared the expression of TAP1 and TAP2 in 39 primary melanoma lesions exhibiting clinical and histological signs of tumour regression and in 35 primary melanoma lesions without regression phenomena. TAP1 expression was significantly associated with regression of melanoma lesions, since the staining pattern with anti-TAP1 antibody was positive in 38 of the 39 lesions exhibiting regression phenomena and in only 24 of the 35 lesions without histopathological signs of tumour regression. In the latter group, six lesions were stained with a heterogeneous pattern and five with a negative pattern. Furthermore, in lesions with a heterogeneous staining pattern, a clear association was found between TAP1 expression in melanoma cells and the presence of tumour-infiltrating lymphocytes. These results suggest that TAP1 plays an important role in the MAA-specific cytotoxic T-lymphocyte response, which has been suggested to underlie the spontaneous regression of primary melanoma.

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.

Exogenous peptides delivered by ricin require processing by signal peptidase for transporter associated with antigen processing-independent MHC class I-restricted presentation

In this study we demonstrate that a disarmed version of the cytotoxin ricin can deliver exogenous CD8(+) T cell epitopes into the MHC class I-restricted pathway by a TAP-independent, signal peptidase-dependent pathway. Defined viral peptide epitopes genetically fused to the N terminus of an attenuated ricin A subunit (RTA) that was reassociated with its partner B subunit were able to reach the early secretory pathway of sensitive cells, including TAP-deficient cells. Successful processing and presentation by MHC class I proteins was not dependent on proteasome activity or on recycling of MHC class I proteins, but rather on a functional secretory pathway. Our results demonstrated a role for signal peptidase in the generation of peptide epitopes associated at the amino terminus of RTA. We showed, first, that potential signal peptide cleavage sites located toward the N terminus of RTA can be posttranslationally cleaved by signal peptidase and, second, that mutation of one of these sites led to a loss of peptide presentation. These results identify a novel MHC class I presentation pathway that exploits the ability of toxins to reach the lumen of the endoplasmic reticulum by retrograde transport, and suggest a role for endoplasmic reticulum signal peptidase in the processing and presentation of MHC class I peptides. Because TAP-negative cells can be sensitized for CTL killing following retrograde transport of toxin-linked peptides, application of these results has direct implications for the development of novel vaccination strategies.