N-myc suppresses major histocompatibility complex class I gene expression through down-regulation of the p50 subunit of NF-kappa B

Challenges and solutions for therapeutic TCR-based agents

Recent development of methods to discover and engineer therapeutic T-cell receptors (TCRs) or antibody mimics of TCRs, and to understand their immunology and pharmacology, lag two decades behind therapeutic antibodies. Yet we have every expectation that TCR-based agents will be similarly important contributors to the treatment of a variety of medical conditions, especially cancers. TCR engineered cells, soluble TCRs and their derivatives, TCR-mimic antibodies, and TCR-based CAR T cells promise the possibility of highly specific drugs that can expand the scope of immunologic agents to recognize intracellular targets, including mutated proteins and undruggable transcription factors, not accessible by traditional antibodies. Hurdles exist regarding discovery, specificity, pharmacokinetics, and best modality of use that will need to be overcome before the full potential of TCR-based agents is achieved. HLA restriction may limit each agent to patient subpopulations and off-target reactivities remain important barriers to widespread development and use of these new agents. In this review we discuss the unique opportunities for these new classes of drugs, describe their unique antigenic targets, compare them to traditional antibody therapeutics and CAR T cells, and review the various obstacles that must be overcome before full application of these drugs can be realized.

Igniting Hope for Tumor Immunotherapy: Promoting the "Hot and Cold" Tumor Transition

The discovery of immune checkpoint inhibitors (ICIs) has ushered a new era for immunotherapy against malignant tumors through the killing effects of cytotoxic T lymphocytes in the tumor microenvironment (TME), resulting in long-lasting tumor suppression and regression. Nevertheless, given that ICIs are highly dependent on T cells in the TME and that most tumors lack T-cell infiltration, promoting the conversion of such immunosuppressive "cold" tumors to "hot" tumors is currently a key challenge in tumor immunotherapy. Herein, we systematically outlined the mechanisms underlying the formation of the immunosuppressive TME in cold tumors, including the role of immunosuppressive cells, impaired antigen presentation, transforming growth factor-β, STAT3 signaling, adenosine, and interferon-γ signaling. Moreover, therapeutic strategies for promoting cold tumors to hot tumors with adequate T-cell infiltration were also discussed. Finally, the prospects of therapeutic tools such as oncolytic viruses, nanoparticles, and photothermal therapy in restoring immune activity in cold tumors were thoroughly reviewed.

Impaired Antitumor Immune Response in MYCN-amplified Neuroblastoma Is Associated with Lack of CCL2 Secretion and Poor Dendritic Cell Recruitment

In neuroblastoma, MYCN amplification is associated with sparse immune infiltrate and poor prognosis. Dendritic cells (DC) are crucial immune sentinels but their involvement in neuroblastoma pathogenesis is poorly understood. We observed that the migration of monocytes, myeloid and plasmacytoid DC induced by MYCN-nonamplified neuroblastoma supernatants was abrogated by the addition of anti-CCL2 antibodies, demonstrating the involvement of the CCR2/CCL2 axis in their recruitment by these tumors. Using public RNA sequencing and microarray datasets, we describe lower level of expression of CCL2 in MYCN-amplified neuroblastoma tumors, and we propose a working model for T-cell recruitment in neuroblastoma tumors in which CCL2 produced by neuroblastoma cells initiates the recruitment of monocytes, myeloid and plasmacytoid DCs. Among these cells, the CD1c⁺ subset may recruit T cells by means of CCL19/CCL22 secretion. In vitro, supernatants from DCs cocultured with neuroblastoma cell lines and activated contain CCL22 and CCL19, and are chemotactic for both CD4⁺ and CD8⁺ T cells. We also looked at immunomodulation induced by neuroblastoma cell lines, and found MYCN-nonamplified neuroblastoma cell lines were able to create a microenvironment where DC activation is enhanced. Overall, our findings highlight a major role for CCL2/CCR2 axis in monocytes, myeloid and plasmacytoid cells recruitment toward MYCN-nonamplified neuroblastoma, allowing further immune cell recruitment, and show that these tumors present a microenvironment that can favor DC responses.

Significance

In MYCN-nonamplified neuroblastoma, CCL2 produced by neuroblastoma cells induces the recruitment of antigen-presenting cells (DCs and monocytes/macrophages), allowing infiltration by T cells, in link with CCL19 and CCL22 production, hence favoring immune responses.

Playing hide and seek: Tumor cells in control of MHC class I antigen presentation

MHC class I (MHC-I) molecules present a blueprint of the intracellular proteome to T cells allowing them to control infection or malignant transformation. As a response, pathogens and tumor cells often downmodulate MHC-I mediated antigen presentation to escape from immune surveillance. Although the fundamental rules of antigen presentation are known in detail, the players in this system are not saturated and new modules of regulation have recently been uncovered. Here, we update the understanding of antigen presentation by MHC-I molecules and how this can be exploited by tumors to prevent exposure of the intracellular proteome. This knowledge can provide new ways to improve immune responses against tumors and pathogens.

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.

MHC Class I Downregulation in Cancer: Underlying Mechanisms and Potential Targets for Cancer Immunotherapy

In recent years, major advances have been made in cancer immunotherapy. This has led to significant improvement in prognosis of cancer patients, especially in the hematological setting. Nonetheless, translation of these successes to solid tumors was found difficult. One major mechanism through which solid tumors can avoid anti-tumor immunity is the downregulation of major histocompatibility complex class I (MHC-I), which causes reduced recognition by- and cytotoxicity of CD8⁺ T-cells. Downregulation of MHC-I has been described in 40-90% of human tumors, often correlating with worse prognosis. Epigenetic and (post-)transcriptional dysregulations relevant in the stabilization of NFkB, IRFs, and NLRC5 are often responsible for MHC-I downregulation in cancer. The intrinsic reversible nature of these dysregulations provides an opportunity to restore MHC-I expression and facilitate adaptive anti-tumor immunity. In this review, we provide an overview of the mechanisms underlying reversible MHC-I downregulation and describe potential strategies to counteract this reduction in MHC-I antigen presentation in cancer.

An Evolutionarily Conserved Function of Polycomb Silences the MHC Class I Antigen Presentation Pathway and Enables Immune Evasion in Cancer

Loss of MHC class I (MHC-I) antigen presentation in cancer cells can elicit immunotherapy resistance. A genome-wide CRISPR/Cas9 screen identified an evolutionarily conserved function of polycomb repressive complex 2 (PRC2) that mediates coordinated transcriptional silencing of the MHC-I antigen processing pathway (MHC-I APP), promoting evasion of T cell-mediated immunity. MHC-I APP gene promoters in MHC-I low cancers harbor bivalent activating H3K4me3 and repressive H3K27me3 histone modifications, silencing basal MHC-I expression and restricting cytokine-induced upregulation. Bivalent chromatin at MHC-I APP genes is a normal developmental process active in embryonic stem cells and maintained during neural progenitor differentiation. This physiological MHC-I silencing highlights a conserved mechanism by which cancers arising from these primitive tissues exploit PRC2 activity to enable immune evasion.

Tumor mechanisms of resistance to immune attack

The immune system plays a key role in the interactions between host and tumor. Immune selection pressure is a driving force behind the sculpting and evolution of malignant cancer cells to escape this immune attack. Several common tumor cell-based mechanisms of resistance to immune attack have been identified and can be broadly categorized into three main classes: loss of antigenicity, loss of immunogenicity, and creation of an immunosuppressive microenvironment. In this review, we will discuss in detail the relevant literature associated with each class of resistance and will describe the relevance of these mechanisms to human cancer patients. To conclude, we will outline the implications these mechanisms have for the treatment of cancer using currently available therapeutic approaches. Immunotherapy has been a successful addition to current treatment approaches, but many patients either do not respond or quickly become resistant. This reflects the ability of tumors to continue to adapt to immune selection pressure at all stages of development. Additional study of immune escape mechanisms and immunotherapy resistance mechanisms will be needed to inform future treatment approaches.

MHC/HLA Class I Loss in Cancer Cells

In this chapter I describe Tumour Immune Escape mechanisms associated with MHC/HLA class I loss in human and experimental tumours. Different altered HLA class-I phenotypes can be observed that are produced by different molecular mechanisms. Experimental and histological evidences are summarized indicating that at the early stages of tumour development there is an enormous variety of tumour clones with different MHC class I expression patterns. This phase is followed by a strong T cell mediated immune-selection of MHC/HLA class-I negative tumour cells in the primary tumour lesion. This transition period results in a formation of a tumour composed only of HLA-class I negative cells. An updated description of this process observed in a large variety of human tumors is included. In the second section I focus on MHC/HLA class I alterations observed in mouse and human metastases, and describe the generation of different tumor cell clones with altered MHC class I phenotypes, which could be similar or different from the original tumor clone. The biological and immunological relevance of these observations is discussed. Finally, the interesting phenomenon of metastatic dormancy is analyzed in association with a particular MHC class I negative tumor phenotype.

The MYC oncogene is a global regulator of the immune response

The MYC proto-oncogene is a gene product that coordinates the transcriptional regulation of a multitude of genes that are essential to cellular programs required for normal as well as neoplastic cellular growth and proliferation, including cell cycle, self-renewal, survival, cell growth, metabolism, protein and ribosomal biogenesis, and differentiation. Here, we propose that MYC regulates these programs in a manner that is coordinated with a global influence on the host immune response. MYC had been presumed to contribute to tumorigenesis through tumor cell-intrinsic influences. More recently, MYC expression in tumor cells has been shown to regulate the tumor microenvironment through effects on both innate and adaptive immune effector cells and immune regulatory cytokines. Then, MYC was shown to regulate the expression of the immune checkpoint gene products CD47 and programmed death-ligand 1. Similarly, other oncogenes, which are known to modulate MYC, have been shown to regulate immune checkpoints. Hence, MYC may generally prevent highly proliferative cells from eliciting an immune response. MYC-driven neoplastic cells have coopted this mechanism to bypass immune detection. Thus, MYC inactivation can restore the immune response against a tumor. MYC-induced tumors may be particularly sensitive to immuno-oncology therapeutic interventions.

Cancer Immunotherapy: Whence and Whither

The current concepts and practice of cancer immunotherapy evolved from classical experiments that distinguished "self" from "non-self" and the finding that humoral immunity is complemented by cellular immunity. Elucidation of the biology underlying immune checkpoints and interactions between ligands and ligand receptors that govern the immune system's ability to recognize tumor cells as foreign has led to the emergence of new strategies that mobilize the immune system to reverse this apparent tolerance. Some of these approaches have led to new therapies such as the use of mAbs to interfere with the immune checkpoint. Others have exploited molecular technologies to reengineer a subset of T cells to directly engage and kill tumor cells, particularly those of B-cell malignancies. However, before immunotherapy can become a more effective method of cancer care, there are many challenges that remain to be addressed and hurdles to overcome. Included are manipulation of tumor microenvironment (TME) to enhance T effector cell infiltration and access to the tumor, augmentation of tumor MHC expression for adequate presentation of tumor associated antigens, regulation of cytokines and their potential adverse effects, and reduced risk of secondary malignancies as a consequence of mutations generated by the various forms of genetic engineering of immune cells. Despite these challenges, the future of immunotherapy as a standard anticancer therapy is encouraging. Mol Cancer Res; 15(6); 635-50. ©2017 AACR.

Prolyl-4-hydroxylase 2 enhances hypoxia-induced glioblastoma cell death by regulating the gene expression of hypoxia-inducible factor-α

Oxygen deprivation (hypoxia) is a common feature of solid tumors in advanced stages. The primary cellular transcriptional responses to hypoxia are mainly mediated by the transcription factor hypoxia-inducible factor (HIF). HIF consists of an oxygen-labile α-subunit (HIF-1α, -2α) and a stable β-subunit (ARNT). Prolyl-4-hydroxylase 2 (PHD2) is known as an important mediator of the oxygen-dependent degradation of HIF-α subunits. As HIF-α subunits are not confirmed to be the only substrates of PHD2, it is unknown whether PHD2 regulates HIF-1α and HIF-2α by interacting with other intracellular molecules. In this study, we found that in the glioblastoma cells, PHD2 maintains the gene expression of HIF-1α in dependence of nuclear factor κB and suppresses the gene expression of HIF-2α through HIF-1α. The PHD2-mediated degradation of HIF-1α and HIF-2α seems less important. Furthermore, PHD2 enhances hypoxia-induced glioblastoma cell death by modulating the expression of the HIF target genes glucose transporter 1, vascular endothelial growth factor-A and Bcl-2 binding protein 3. Our findings show that PHD2 inhibits the adaptation of glioblastoma cells to hypoxia by regulating the HIF-α subunits in a non-canonical way. Modulation of PHD2 activity might be considered as a new way to inhibit glioblastoma progression.

Identifying regulatory mechanisms underlying tumorigenesis using locus expression signature analysis

Retroviral insertional mutagenesis is a powerful tool for identifying putative cancer genes in mice. To uncover the regulatory mechanisms by which common insertion loci affect downstream processes, we supplemented genotyping data with genome-wide mRNA expression profiling data for 97 tumors induced by retroviral insertional mutagenesis. We developed locus expression signature analysis, an algorithm to construct and interpret the differential gene expression signature associated with each common insertion locus. Comparing locus expression signatures to promoter affinity profiles allowed us to build a detailed map of transcription factors whose protein-level regulatory activity is modulated by a particular locus. We also predicted a large set of drugs that might mitigate the effect of the insertion on tumorigenesis. Taken together, our results demonstrate the potential of a locus-specific signature approach for identifying mammalian regulatory mechanisms in a cancer context.

The MAPK pathway is a predominant regulator of HLA-A expression in esophageal and gastric cancer

Downregulation of HLA class I expression may contribute to a poor prognosis in cancer patients. There is limited information about epigenetic and oncogenic regulation of HLA class I, and multiple mechanisms may be involved. In the current study, we examined the relationship between the HER2-signaling pathway (MAPK and PI3K-Akt) and the expression of HLA class I and Ag-processing machinery (APM) components. A panel of gastric and esophageal cancer cell lines was treated with wortmannin as an Akt-signal inhibitor; the MAPK signal inhibitor PD98059; lapatinib, which inhibits both the epidermal growth factor receptor and HER2 tyrosine kinase; or siRNA for MAPK. The levels of HER2-signaling molecules, APM components, and HLA class I were evaluated by Western blot, quantitative PCR, and flow cytometry. Resected gastric tumor tissues (n = 102) were analyzed for p-Erk and HLA class I expression by immunohistochemistry. As a result, inhibition of the MAPK pathway induced upregulation of HLA-A02 and HLA-A24 expression in parallel with an increase in APM components and enhanced target sensitivity to tumor Ag-specific CTL lysis. HLA-A expression was predominantly regulated by the MAPK pathway, but it was also influenced, in part, by the Akt pathway. There was a strong inverse correlation between p-Erk expression and HLA class I expression in clinical tumor samples. In conclusion, HLA-A expression is predominantly regulated by the MAPK pathway in gastric and esophageal cancer.

Inverse correlation of HER2 with MHC class I expression on oesophageal squamous cell carcinoma

BACKGROUND

As HER2 is expressed in 30% of oesophageal squamous cell carcinomas (ESCCs), T-cell-based immunotherapy and monoclonal antibodies targeted against HER2 are attractive, novel approaches for ESCCs. However, it was shown that there is an inverse correlation between HER2 and MHC class I expression on tumours. Thus, the correlation between HER2 and MHC class I expressions on ESCC was evaluated.

METHODS

Expressions of MHC class I and HER2 in ESCC tissues (n=80) and cell lines were assessed by immunohistochemistry, fluorescence in situ hybridisation (FISH), and flow cytometry. We investigated whether HER2 downregulation with small interfering RNA (siRNA) in ESCC cell lines could upregulate the expression of MHC class I and the antigen presentation machinery components, and could increase their sensitivity for tumour antigen-specific CTLs.

RESULTS

There was an inverse correlation between HER2 and MHC class I expressions in both tumour tissues and cell lines. Downregulation of HER2 with siRNA resulted in the upregulation of MHC class I expression, leading to increased CTL recognition by tumour antigen-specific CTLs.

CONCLUSION

HER2-overexpressing ESCC tumour cells showed a reduced sensitivity for CTLs through the downregulation of MHC class I.

NF-kappaB, and not MYCN, regulates MHC class I and endoplasmic reticulum aminopeptidases in human neuroblastoma cells

Neuroblastoma (NB) is the most common solid extracranial cancer of childhood. Amplification and overexpression of the MYCN oncogene characterize the most aggressive forms and are believed to severely downregulate MHC class I molecules by transcriptional inhibition of the p50 NF-kappaB subunit. In this study, we found that in human NB cell lines, high MYCN expression is not responsible for low MHC class I expression because neither transfection-mediated overexpression nor small interfering RNA suppression of MYCN affects MHC class I and p50 levels. Furthermore, we identified NF-kappaB as the immediate upstream regulator of MHC class I because the p65 NF-kappaB subunit binds MHC class I promoter in chromatin immunoprecipitation experiments, and MHC class I expression is enhanced by p65 transfection and reduced by (a) the chemical NF-kappaB inhibitor sulfasalazine, (b) a dominant-negative IKBalpha gene, and (c) p65 silencing. Moreover, we showed that the endoplasmic reticulum aminopeptidases ERAP1 and ERAP2, which generate MHC class I binding peptides, are regulated by NF-kappaB, contain functional NF-kappaB-binding elements in their promoters, and mimic MHC class I molecules in the expression pattern. Consistent with these findings, nuclear p65 was detected in NB cells that express MHC class I molecules in human NB specimens. Thus, the coordinated downregulation of MHC class I, ERAP1, and ERAP2 in aggressive NB cells is attributable to a low transcriptional availability of NF-kappaB, possibly due to an unknown suppressor other than MYCN.

The development of antibody-IL-2 based immunotherapy with hu14.18-IL2 (EMD-273063) in melanoma and neuroblastoma

Patients with high risk melanoma and neuroblastoma frequently experience recurrence despite surgical resection and appropriate adjuvant therapies. Immunotherapy with the immunocytokine hu14.18-IL2 (EMD-273063) was developed by means of fusion of two molecules of IL-2 to the monoclonal antibody, 14.18, that recognizes GD2, expressed on the earlier mentioned malignancies. This article will discuss the results of preclinical work using EMD-273063 therapy, including data suggesting that intratumoral therapy may have enhanced antitumor benefit compared with intravenous therapy. Initial clinical trials in adult melanoma and pediatric neuroblastoma have demonstrated acceptable toxicity profiles in dosing that induces immune activation. Preclinical and initial clinical data suggest greater efficacy in the setting of minimal residual disease; therefore, future clinical testing is planned to test the benefit of EMD-273063 in this setting.

Genetic alterations of HLA-class II in ovarian cancer

The immune system controls tumor formation through identification and elimination of cellular alterations. Consequently, cancer development in immune competent hosts depends on strategies to evade the immune system. Modulation of tumor antigen-specific immune responses by aberrant expression of HLA-class I and II molecules is well documented in a variety of carcinomas including ovarian cancer. To date, little data are available about molecular mechanisms responsible for altered HLA-class II phenotypes in tumors. In our sample of 10 Caucasian patients with ovarian carcinoma, a semiquantitative analysis was performed for HLA-class II loci DRB1 and DQB1 in malignant and normal ovarian tissue. Gene amplifications were identified in 62.5% of analyzed alleles and deletions in 17.5%, demonstrating that genomic aberrations of 6p21.3 are common and that copy number gain is more frequent than loss. Moreover, amplifications are most pronounced in advanced-stage tumors. To evaluate genotype-phenotype relation, immunohistochemical analyses were performed and revealed de novo expression of HLA-class II in 30% of tumors with an inverse association between antigen level and HLA copy number. It remains to be elucidated whether the profound changes of the latter quantities are the result of the host's immunological self-defense, indicate the presence of an oncogene located within the MHC-complex or merely reflect the increasing loss of differentiation of the tumor tissue.

Mechanisms of invasion and metastasis in human neuroblastoma

Neuroblastoma is the second most common solid tumor in children that is metastatic in 70% of patients at the time of diagnosis. The ability of neuroblastoma cells to colonize distant organs like the bone marrow and the bone is the result of close interactions between tumor cells and the microenvironment. Significant progress has been recently made in our understanding of the mechanisms that promote the colonization and invasion of the bone by neuroblastoma cells and these mechanisms are reviewed in this article. How this understanding is now allowing us to test new therapeutic agents specifically targeted at interfering with neuroblastoma metastasis is then discussed.

Expression of MHC class I, MHC class II, and cancer germline antigens in neuroblastoma

BACKGROUND

Neuroblastoma is the most common solid extracranial tumor in childhood, still with poor survival rates for metastatic disease. Neuroblastoma cells are of neuroectodermal origin and express a number of cancer germline (CG) antigens. These CG antigens may represent a potential target for immunotherapy such as peptide-based vaccination strategies.

OBJECTIVE

The purpose of this study was to analyze the presence of MAGE-A1, MAGE-A3/A6, and NY-ESO-1 on an mRNA and protein level and to determine the expression of MHC class I and MHC class II antigens within the same tumor specimens.

METHODS

A total of 68 tumors were available for RT-PCR, and 19/68 tumors were available for immunohistochemical (IHC) analysis of MAGE-A1, MAGE-A3/A6, and NY-ESO-1. In parallel, the same tumors were stained with a panel of antibodies for MHC class I and MHC class II molecules.

RESULTS

Screening of 68 tumor specimens by RT-PCR revealed expression of MAGE-A1 in 44%, MAGE-A3/A6 in 21%, and NY-ESO-1 in 28% of cases. Immunohistochemistry for CG antigens of selected tumors showed good agreement between protein and gene expression. However, staining revealed a heterogeneous expression of CG antigens. None of the selected tumors showed MHC class I or MHC class II expression.

CONCLUSIONS

mRNA expression of MAGE-A1, MAGE-A3/A6, and NY-ESO-1 is congruent with the protein expression as determined by immunohistochemistry. The heterogeneous CG-antigen expression and the lack of MHC class I and II molecules may have implications for T-cell-mediated immunotherapy in neuroblastoma.

Positive and negative regulation of EAAT2 by NF-kappaB: a role for N-myc in TNFalpha-controlled repression

The glutamate transporter gene, EAAT2/GLT-1, is induced by epidermal growth factor (EGF) and downregulated by tumor necrosis factor alpha (TNFalpha). While TNFalpha is generally recognized as a positive regulator of NF-kappaB-dependent gene expression, its ability to control transcriptional repression is not well characterized. Additionally, the regulation of NF-kappaB by EGF is poorly understood. Herein, we demonstrate that both TNFalpha-mediated repression and EGF-mediated activation of EAAT2 expression require NF-kappaB. We show that EGF activates NF-kappaB independently of signaling to IkappaB. Furthermore, TNFalpha can abrogate IKKbeta- and p65-mediated activation of EAAT2. Our results suggest that NF-kappaB can intrinsically activate EAAT2 and that TNFalpha mediates repression through a distinct pathway also requiring NF-kappaB. Consistently, we find that N-myc is recruited to the EAAT2 promoter with TNFalpha and that N-myc-binding sites are required for TNFalpha-mediated repression. Moreover, N-myc overexpression inhibits both basal and p65-induced activation of EAAT2. Our data highlight the remarkable specificity of NF-kappaB activity to regulate gene expression in response to diverse cellular signals and have implications for glutamate homeostasis and neurodegenerative disease.

Mutations and regulatory anomalies effecting tumor cell immune functions

The immune system is capable of interacting with tumor cells in such a way as to lead to tumor cell death, and this knowledge has inspired therapies to manipulate patient immune systems to eradicate cancer. However, tumor cells are able to mitigate the antitumor immune response, a fact that has rarely been addressed in the design of immunotherapies. There are many different tumor cell immune functions that play a role in mitigating the antitumor immune response. In some cases, these functions appear to be intimately associated with the tumor cell abnormalities that lead to loss of growth control, such as the cases where classical tumor suppressor proteins regulate tumor cell immune function genes. In other cases, tumor cell mutations appear to affect only the antitumor response, such as tumor cell mutations that eliminate MHC class I expression. Here I review the bases for tumor cell immune functions, noting in particular where tumor cell mutations, the gold standard for identifying a tumor-specific function, are known to be responsible for the tumor cell immune function. This review also discusses other known regulatory anomalies, in the absence of a known mutation, that are apparently important for tumor development and that regulate tumor cell immune functions. Surprisingly, in many cases where the tumor cell immune function is well understood in terms of its effect on the antitumor immune response, the tumor abnormality underlying the tumor cell immune function is completely uncharacterized.

Complicated mechanisms of class II transactivator transcription deficiency in small cell lung cancer and neuroblastoma

Small cell lung cancer (SCLC) and neuroblastoma (NB), the most aggressive adult and infant neuroendocrine cancers, respectively, are immunologically characterized by a severe reduction in major histocompatibility complex (MHC) that is indispensable for anti-tumor immunity. We had reported that the severe reduction of MHC in SCLC was caused by a deficient interferon (IFN)-gamma-inducible expression of class II transactivator (CIITA) that is known as a very important transcription factor for IFN-gamma-inducible class II and class I MHC expression (Yazawa T, Kamma H, Fujiwara M, Matsui M, Horiguchi H, Satoh H, Fujimoto M, Yokohama K, Ogata T: Lack of class II transactivator causes severe deficiency of HLA-DR expression in small cell lung cancer. J Pathol 1999, 187:191-199). Here, we demonstrate that the reduction of MHC in NB was also caused by a deficient IFN-gamma-inducible expression of CIITA and that the deficiency in SCLC and NB was caused by similar mechanisms. Human achaete-scute complex homologue (HASH)-1, L-myc, and N-myc, which are specifically overexpressed in SCLC and NB, bound to the E-box in CIITA promoter IV and reduced the transcriptional activity. Anti-sense oligonucleotide experiments revealed that overexpressed L-myc and N-myc lie upstream in the regulatory pathway of HASH-1 expression. The expression of HASH-1 was also up-regulated by IFN-gamma. Our results suggest that SCLC and NB have complicated mechanisms of IFN-gamma-inducible CIITA transcription deficiency through the overexpressed HASH-1, L-myc, and N-myc. These complicated mechanisms may play an important role in the escape from anti-tumor immunity.

Impaired surface antigen presentation in tumors: implications for T cell-based immunotherapy

The identification of tumor-associated antigens has suggested new possibilities for cancer therapy. However, multiple mechanisms may contribute to the ability of tumor to escape antitumor immune responses. Tumor antigen heterogeneity, modulation of HLA expression and immune suppressive mechanisms may occur at any time during tumor cell progression, and can affect the outcome of therapeutic immune intervention. In particular, the appearance of altered HLA class I phenotypes during tumor development may have important biological and medical implications due to the role of these molecules in T and NK cell functions. Exhaustive tumor tissue studies are necessary before deciding whether a particular patient is suitable for inclusion in T cell-based immunotherapy protocols.

Identifying genes involved in regulating differentiation of neuroblastoma cells

The genes regulating the induction of differentiation in neurons are not definitively known. Some neuronal tumors retain the ability to differentiate into mature, functional neurons in response to pharmacological agents, despite the presence of genetic anomalies. We hypothesized that some of the genes whose expression is altered between undifferentiated and differentiated states may be those responsible for inducing differentiation. To investigate this, we used a mouse neuroblastoma (NB) cell line, NBP(2), in which > or =90% of the cells in the culture terminally differentiate upon elevation of intracellular adenosine 3',5'-cyclic monophosphate (cAMP) levels. Gene expression was analyzed using cDNA array blots containing 588 known genes. mRNA from cultures of undifferentiated and differentiated NB cells was used to make cDNA probes for blot hybridization. We identified several genes that are predominantly expressed in either undifferentiated or differentiated NB cells. In addition, numerous genes are moderately up- or down-regulated during differentiation of NB cells. We identified the N-myc protooncogene, cyclin B1, and protease nexin 1 as genes that are expressed in undifferentiated NB cells and whose levels are significantly down-regulated upon differentiation. In contrast, the c-fes and c-fos protooncogenes and the RAG-1 gene activator are genes whose expression is significantly up-regulated during differentiation of NB cells. These findings were confirmed by RT-PCR analysis. The transcript size and expression level of N-myc, cyclin B1, protease nexin 1, c-fes, and c-fos were verified by Northern blotting. These genes may represent key mediators involved in the regulation of NB cell differentiation.

Identification of CCAAT displacement protein (CDP/cut) as a locus-specific repressor of major histocompatibility complex gene expression in human tumor cells

Human major histocompatibility (MHC) class I antigen expression is important in controlling the metastatic growth of malignant tumors. Locus-specific down-regulation of MHC class I gene expression is frequently observed in human tumors, leading to decreased susceptibility to cytotoxic T-cell-mediated lysis. The mechanism of this down-regulation is incompletely understood. Here, we describe the identification of human CCAAT displacement protein (CDP/cut) as a locus-specific repressor of HLA-B and C gene expression. Transient and stable transfections in HeLa and K562 cells demonstrated the presence of a repressor element 650 base pairs upstream of the first exon of HLA-B7. A specific binding complex with the HLA-B7 and Cw2 repressor elements was demonstrated by EMSA. Formation of the EMSA complex was inhibited specifically with polyclonal antiserum to human CDP/cut, demonstrating that CDP/cut binds the HLA-B7 repressor element. The corresponding region of the HLA-A2 promoter neither repressed HLA-A2 gene expression nor bound CDP/cut. Overexpression of CDP/cut in cell lines deficient in CDP/cut resulted in a nearly 4-fold repression of reporter constructs containing the HLA-B7 repressor element but not the corresponding region of the HLA-A2 promoter. Repression of HLA-B and C gene expression by CDP/cut does not involve displacement of NF-Y, nor is CDP/cut associated with the histone deacetylase HDAC1 when bound to the HLA-B7 repressor element. To our knowledge, these results identify CDP/cut as the first example of a locus-specific repressor of MHC class I gene transcription in human tumor cells.

MHC class I gene expression and regulation

Major histocompatibility complex (MHC) is a conglomerate of genes that play an important role in recognition of self and nonself. These genes are under tight control. In this review we have discussed the transcription processes regulating MHC gene expression. Various biological or chemical modulators can modulate MHC gene expression. The promoter region of class I genes can be activated through several pathways. Hence, these genes are not typical "domestic" genes. Extensive studies on regulation of MHC class I expression, using transfection techniques and transgenic animal models, have resulted in identification of various cis-acting sequences involved in positive and negative regulation of class I genes. Work is in progress to identify the transacting proteins that bind to these sites and to delineate the mechanisms that regulate constitutive and inducible expression of class I genes in normal and diseased cells. It has been seen that various biological molecules (IFN, GM-CSF, IL-2) and other chemicals up-regulate the MHC expression. If the exact mechanisms are known by which the expression of class I genes is up regulated, the efforts can be made to balance the beneficial and toxic effects of biological molecules with one another, which may facilitate the use of combination of these molecules in subpharmacological doses (to eliminate toxicity) for early and better management of neoplastic diseases, as it is well-known that during malignancy MHC gene expression is down-regulated. In the future, the use of transgenic and knockout mice will be useful in acquiring a better understanding, which may further help in cancer therapy.

Characterization of antigen-presenting properties of tumour cells using virus-specific cytotoxic T lymphocytes

Immunotherapy of tumours by induction of tumour-specific cytotoxic T-lymphocytes (CTLs) will only be effective for tumours with a functional antigen processing and presentation machinery. However, many tumours are known to down-regulate expression of major histocompatibility complex (MHC) class I molecules and/or to impair antigen processing. It is therefore desirable to evaluate the ability of a given tumour to present antigenic epitopes before developing an immunotherapy protocol. In this study we have used influenza virus as a tool to determine the antigen-presenting capacities of the murine neuroblastoma C1300 cell line NB41A3, a frequently used model for human neuroblastoma. Immunofluorescence analyses revealed low and moderate expression of MHC class I molecules Dd and Kk respectively. Nevertheless, infected NB41 A3 cells were lysed efficiently by influenza-specific CTLs. These results demonstrate that all steps of the antigen-processing pathway function properly in the NB tumour cells, and that the limited MHC class I expression suffices for efficient recognition by CTLs. In addition, lysis of the NB tumour cells shows that the cells are susceptible to CTL-induced apoptosis, a pathway that is often impaired in tumour cells. These characteristics make neuroblastoma a suitable target for immunotherapy. The presented assay allows evaluation of various immunological properties of tumour cells and, thus, represents a valuable tool to assess whether a given tumour will be susceptible to immunotherapy or not.

Characterization of antigen-presenting properties of tumour cells using virus-specific cytotoxic T lymphocytes

Immunotherapy of tumours by induction of tumour-specific cytotoxic T-lymphocytes (CTLs) will only be effective for tumours with a functional antigen processing and presentation machinery. However, many tumours are known to down-regulate expression of major histocompatibility complex (MHC) class I molecules and/or to impair antigen processing. It is therefore desirable to evaluate the ability of a given tumour to present antigenic epitopes before developing an immunotherapy protocol. In this study we have used influenza virus as a tool to determine the antigen-presenting capacities of the murine neuroblastoma C1300 cell line NB41A3, a frequently used model for human neuroblastoma. Immunofluorescence analyses revealed low and moderate expression of MHC class I molecules Dd and Kk respectively. Nevertheless, infected NB41 A3 cells were lysed efficiently by influenza-specific CTLs. These results demonstrate that all steps of the antigen-processing pathway function properly in the NB tumour cells, and that the limited MHC class I expression suffices for efficient recognition by CTLs. In addition, lysis of the NB tumour cells shows that the cells are susceptible to CTL-induced apoptosis, a pathway that is often impaired in tumour cells. These characteristics make neuroblastoma a suitable target for immunotherapy. The presented assay allows evaluation of various immunological properties of tumour cells and, thus, represents a valuable tool to assess whether a given tumour will be susceptible to immunotherapy or not.

Heterogeneity in expression of human leukocyte antigens and melanoma-associated antigens in advanced melanoma

The study of tumor immunology has led to many innovative therapeutic strategies for the treatment of melanoma. The strategies are primarily dependent on melanoma-associated antigen peptide vaccination or T-cell-based therapy. These immunotherapies are totally reliant on proper copresentation of human leukocyte antigen class I molecules in sufficient quantity and the presence and availability of melanoma-associated antigenic peptides. Altered expression of either HLA class I molecules or melanoma antigens is known to occur. These defects lead to altered manufacture and copresentation of HLA class I molecules with melanoma-associated antigens to T-cells. Defects in any one combination can lead to loss of recognition of melanoma cells and their subsequent destruction by cytotoxic T-lymphocytes. Thus, these immunotherapy strategies can be thwarted by defects or heterogeneity of expression of human leukocyte antigen class I or of melanoma-associated antigens.

Dominant negative suppression of major histocompatibility complex genes occurs in trophoblasts

BACKGROUND

Polymorphic class I and II major histo-: compatibility complex (MHC) genes are not transcribed in trophoblasts although many immune system cells express these genes constitutively. To study the molecular biology of MHC suppression for the purposes of potential transgenic animal development, we examined the effect on MHC expression in B cells by fusing them with trophoblasts.

METHODS

Trophoblasts and B cells with separate selection markers were fused with polyethylene glycol. After growth in double selection media, the hybrids were analyzed for HLA-A, -B, -C, -DR, -DP, and -DQ expression by fluorescence-activated cell scanning and class I and II mRNA by Northern blotting. Class II promoter activity in trophoblasts was then analyzed by transfection of a lethal reporter construct and subsequently, the class II transactivator.

RESULTS

Class I and II surface antigens and their corresponding mRNA were completely suppressed in the hybrids. The lethal reporter construct demonstrated that class II suppression resulted from lack of activation of the class II promoter. This in turn was caused by lack of functional class II transactivator.

CONCLUSIONS

These data indicate that dominant negative trophoblast factors, either directly or indirectly, suppress expression of the MHC genes. If these factors can be cloned, the potential exists for developing transgenic animals that cannot express MHC or peptide antigen to T cell receptors through the MHC system.

HLA-B down-regulation in human melanoma is mediated by sequences located downstream of the transcription-initiation site

Major histocompatibility complex (MHC, HLA in humans) class I molecules play an important role in cellular immunology by presenting viral, tumor-associated or minor histocompatibility antigen-derived peptides to T cells. Tumor cells frequently fail to express one or more of the different MHC class I loci (HLA-A, -B and -C), thereby avoiding elimination by T cells. In primary human melanomas as well as melanoma cell lines, HLA class I expression is frequently down-regulated in a B locus-specific manner. The HLA class I promoter contains a number of cis-regulatory elements located upstream of the transcription-initiation site, among them enhancer A and an interferon-stimulated response element. In the present study, we show that novel sequences located 13 to 33 bp downstream of the transcription-initiation site mediate HLA-B locus-specific down-regulation in human melanoma cell lines. Furthermore, involvement of the +13 to +33-bp region in HLA-B locus-specific down-regulation in vivo is supported by in vitro experiments showing locus-specific binding of protein complexes to the +13 to +33-bp region.

Iodide suppression of major histocompatibility class I gene expression in thyroid cells involves enhancer A and the transcription factor NF-kappa B

High concentrations of iodide can induce transient, clinical improvement in patients with autoimmune Graves' disease. Previous work has related this iodide action to the autoregulatory effect of iodide on the growth and function of the thyroid; more recently, we additionally related this to the ability of iodide to suppress major histocompatibility (MHC) class I RNA levels and antigen expression on thyrocytes. In this report, we describe a transcriptional mechanism involved in iodide suppression of class I gene expression, which is potentially relevant to the autoregulatory action of iodide. Transfection experiments in FRTL-5 cells show that iodide decreases class I promoter activity and that this effect can be ascribed to the ability of iodide to modulate the formation of two specific protein/DNA complexes with enhancer A, -180 to -170 bp, of the class 1 5'-flanking region. Thus, iodide decreases the formation of Mod-1, an enhancer A complex involving the p50 subunit of NF-kappa B and a c-fos family member, fra-2, which was previously shown to be important in the suppression of class I levels by hydrocortisone. Unlike hydrocortisone, iodide also increases the formation of a complex with enhancer A, which we show, in antibody shift experiments, is a heterodimer of the p50 and p65 subunits of NF-kappa B. The changes in these complexes are not duplicated by chloride and are related to the action of iodide on class I RNA levels by the following observations. First, FRTL-5 thyroid cells with an aged phenotype coincidentally lose the ability of iodide to decrease MHC class I RNA levels and to induce changes in either complex. Second, the effect of iodide on class I RNA levels and on enhancer A complex formation with Mod-1 and the p50/p65 heterodimer is inhibited by agents that block the inositol phosphate, Ca++, phospholipase A2, arachidonate signal transduction pathway: acetylsalicylate, indomethacin, and 5,8,11,14-eicosatetraynoic acid. Interestingly, iodide can also decrease formation of the Mod-1 complex and increase formation of the complex with the p50/p65 subunits of NF-kappa B when the NF-kappa B enhancer sequence from the Ig kappa light chain, rather than enhancer A, is used as probe; and both actions mimic the action of a phorbol ester. This suggests that iodide may regulate complex formation with NF-kappa B regulatory elements on multiple genes associated with growth and function, providing a potential mechanism relating the autoregulatory action of iodide on thyroid cells and its action on class I gene expression.

The transcriptional silencer protein NRF: a repressor of NF-kappa B enhancers

NF-kappa B/rel proteins are present in most cell types. In concert with other transcriptional factors they regulate a variety of genes which contribute to a wide spectrum of physiological activities like inflammation and apoptosis. An excellent example of this combinatorial regulation takes place in the IFN-beta promoter. In this promoter the fundamental regulatory elements are assembled within less than 100 base pairs including a NF-kappa B/rel enhancer and a negative regulatory element, called NRE. NRE is a member of a new class of transcriptional repressor sequences with a silencing capacity targeted to the NF-kappa B/rel enhancer. NRF is a novel transcriptional factor that binds to NRE. NRF belongs to a major class of transcriptional repressors that interact with specific promoter elements and repress transcription by separable repression domains. Such molecules have been termed active repressors, because they act by inhibitory protein-protein interaction and not simply by steric hindrance.

Interferon regulatory factor 1 is induced by interferon-gamma equally in neurons and glial cells

Class I MHC protein is induced in glia but not mature neurons by IFN-gamma. We have compared IFN-gamma signal transduction in these populations. There were identical levels of STAT1 homodimers and IRF-1 by gel-shift and IRF-1 mRNA was induced equally. However class I MHC, beta2-microglobulin and interleukin 1-beta converting enzyme mRNA levels were greatly reduced in neurons. These experiments show that there is no defect in expression of IRF-1 in response to IFN-gamma in mature mouse neurons but that insufficient class I MHC gene expression is induced for detectable cell surface protein expression.

Altered MHC class I antigens in tumors

MHC class I antigens are lost or downregulated in invasive tumors compared with autologous normal tissues. This is observed in most of the newly induced experimental tumors analyzed if they are cloned before passaging in vivo. Similarly, this is observed in 40%-90% of human tumors using the available panel of anti-HLA class I monoclonal antibodies. In both systems the tumor populations are heterogeneous for H-2/HLA expression and composed of clones that express different amounts of MHC class I antigens. This heterogeneity may have a profound influence on tumor behavior, considering the role that MHC antigens play in T and natural killer cell-mediated responses. It is possible that the tumor escape mechanisms from T and natural killer cells select variants that express a particular MHC class I altered phenotype. We review the MHC changes detected in different experimental as well as human tumors and demonstrate the relevance of these altered H-2/HLA tumor phenotypes for implementing immunotherapeutic strategies based on T or natural killer cell-mediated responses.

Active repression of major histocompatibility complex class I genes in a human neuroblastoma cell line

Human neuronal cells express neither major histocompatibility complex (MHC) class I RNA nor cell surface molecules but can be induced to do so by various cytokines. In the present studies, we report that expression of MHC class I in a neuroblastoma cell line, CHP-126, is actively repressed. This repression is mediated by the combined effects of a series of upstream silencer elements. Removal of the silencers reveals not only an active promoter element but also the presence of an active enhancer. Four silencers have been identified and shown to have distinct sequences, binding factors, and patterns of function. One element is located between -724 and -697 base pairs (bp) and corresponds to a silencer involved in tissue-specific regulation of class I gene expression. Three additional elements occur between -503 and -402 bp. One of these corresponds to a c-jun responsive element. Neither of the remaining elements corresponds to DNA sequences known to regulate expression of other genes. These data demonstrate that MHC class I expression normally is actively repressed in neuronal cells and suggest a model of rapid and specific triggering of class I in neuronal cells in response to infection.

Loss of an HLA haplotype in pancreas cancer tissue and its corresponding tumor derived cell line

A combination of immunohistochemical, biochemical, and recombinant DNA techniques were used to investigate class I expression in 26 pancreatic adenocarcinomas and 6 autologous tumor-derived cells. The prevalence of HLA losses was found to be comparable to that observed in other tumor types (> 35%), using monomorphic and locus-specific antibodies. In one patient, the original tumor tissue, a tumor derived cell line (IMIM-PC-2), and EBV-transformed lymphocytes were available for study. The patient's phenotype was A25, A30, B18, B18. However, A30 allele product could not be detected in the original tumor not in the cultured tumor cells. In addition, A30 allele could not be isolated from cDNA or genomic clones from the cultured tumor cells whereas it was isolated from the autologous lymphoblastoid cell line. Using isoelectric focusing analysis a significant reduction in the B18 heavy chain product was also observed in the tumor cell line, IMIM-PC-2, suggesting the absence of expression of one allele. Further studies revealed loss of heterozygosity at DR and other loci of chromosome 6 and cytogenetic data strongly suggested deletion of a full chromosome 6. This work indicates for the first time that loss of a full HLA haplotype occurs in tumor tissue and suggests that this mechanism may contribute to the progression of human cancer.

C-myc represses transiently transfected HLA class I promoter sequences not locus-specifically

Overexpression of the c-myc oncogene is frequently accompanied by downregulation of Major Histocompatibility Complex (MHC, HLA in humans) class I antigens. In human melanoma c-myc overexpression downmodulates HLA-B expression, whereas HLA-A is hardly affected. Repression of HLA-B is mediated through the core promoter, containing a CAAT-box and a non-conventional TATA-box. We show evidence that in transient transfection assays the HLA-A2 and HLA-B7 promoters are repressed by c-myc to the same extent. Therefore, other sequences of the HLA-A and HLA-B genes, possibly intron/exon sequences, should contribute to the locus B-specificity of the downregulation. Furthermore, c-myc does not seem to alter binding of protein complexes to the CAAT- or TATA-box of HLA-B7 or HLA-A2 in gel retardation assays. Comparison of promoters repressed by c-myc reveals a weak consensus sequence of the initiator (Inr) element: TCA(+1)YYYNY. The presence of a TCA sequence in the initiator region of the MHC class I promoter makes downregulation by c-myc through the Inr likely. We speculate that the Inr contributes to MHC class I promoter activity by stimulating recruitment of TFIID to the weak, non-conventional TATA-box, thereby making it susceptible to repression by c-myc through the Inr.

Inverse expressions of the N-myc oncogene and beta 1 integrin in human neuroblastoma: relationships to disease progression in a nude mouse model system

A nude mouse model for human neuroblastoma has been developed to examine possible relationships between amplification/over-expression of the N-myc oncogene and altered regulation of expression of specific integrin subunits during tumor progression. Subcutaneous (ectopic) or intra-adrenal (orthotopic) injection of the neuroblastoma cell lines SK-N-SH or IMR-32 has generated a number of derivative tumor cell lines. Tumor cell lines derived from SK-N-SH cells (which do not express N-myc) or IMR-32 cells (which over-express N-myc) produce tumors at higher rates when re-injected into the subcutaneous space of nude mice. Moreover, cell lines derived from tumors initiated by IMR-32 cells exhibit shorter latent periods than do IMR-32 cells direct from tissue culture. With regard to integrin subunit expression, SK-N-SH and related cell lines express high levels of beta 1 integrin, which is associated with the alpha 2 and alpha 3 integrin subunits (predominantly alpha 3). IMR-32 cells display reduced beta 1 expression, and that which is produced is not associated with common alpha subunits. LaN1 cells, which express N-myc at even higher levels than do IMR-32 cells, express even less beta 1. Interestingly, the tumor-derived cell lines (especially those from tumors initiated in adrenal glands) also exhibit reduced integrin expression compared with the parental cell lines; this reduction is associated with the enhanced tumor take rate observed when the cells are re-injected into nude mice. Our results raise the possibility of a relationship between over-expression of N-myc and down-regulation of beta 1 integrin expression (possibly some alpha subunits also). In addition, the data suggest that human neuroblastoma-derived cell lines which exhibit reduced integrin expression display more aggressive tumor growth in nude mice.