Different levels of control prevent interferon-gamma-inducible HLA-class II expression in human neuroblastoma cells

Dysregulation in IFN-γ signaling and response: the barricade to tumor immunotherapy

Interferon-gamma (IFN-γ) has been identified as a crucial factor in determining the responsiveness to immunotherapy. Produced primarily by natural killer (NK) and T cells, IFN-γ promotes activation, maturation, proliferation, cytokine expression, and effector function in immune cells, while simultaneously inducing antigen presentation, growth arrest, and apoptosis in tumor cells. However, tumor cells can hijack the IFN-γ signaling pathway to mount IFN-γ resistance: rather than increasing antigenicity and succumbing to death, tumor cells acquire stemness characteristics and express immunosuppressive molecules to defend against antitumor immunity. In this review, we summarize the potential mechanisms of IFN-γ resistance occurring at two critical stages: disrupted signal transduction along the IFNG/IFNGR/JAK/STAT pathway, or preferential expression of specific interferon-stimulated genes (ISGs). Elucidating the molecular mechanisms through which tumor cells develop IFN-γ resistance help identify promising therapeutic targets to improve immunotherapy, with broad application value in conjugation with targeted, antibody or cellular therapies.

Human CD4 cytotoxic T lymphocytes mediate potent tumor control in humanized immune system mice

Efficacy of immune checkpoint inhibitors in cancers can be limited by CD8 T cell dysfunction or HLA-I down-regulation. Tumor control mechanisms independent of CD8/HLA-I axis would overcome these limitations. Here, we report potent CD4 T cell-mediated tumor regression and memory responses in humanized immune system (HIS) mice implanted with HT-29 colorectal tumors. The regressing tumors showed increased CD4 cytotoxic T lymphocyte (CTL) infiltration and enhanced tumor HLA-II expression compared to progressing tumors. The intratumoral CD4 T cell subset associated with tumor regression expressed multiple cytotoxic markers and exhibited clonal expansion. Notably, tumor control was abrogated by depletion of CD4 but not CD8 T cells. CD4 T cells derived from tumor-regressing mice exhibited HLA-II-dependent and tumor-specific killing ex vivo. Taken together, our study demonstrates a critical role of human CD4 CTLs in mediating tumor clearance independent of CD8 T cells and provides a platform to study human anti-tumor immunity in vivo.

Skewed fate and hematopoiesis of CD34+ HSPCs in umbilical cord blood amid the COVID-19 pandemic

Umbilical cord blood (UCB) is an irreplaceable source for hematopoietic stem progenitor cells (HSPCs). However, the effects of SARS-CoV-2 infection and COVID-19 vaccination on UCB phenotype, specifically the HSPCs therein, are currently unknown. We thus evaluated any effects of SARS-CoV-2 infection and/or COVID-19 vaccination from the mother on the fate and functionalities of HSPCs in the UCB. The numbers and frequencies of HSPCs in the UCB decreased significantly in donors with previous SARS-CoV-2 infection and more so with COVID-19 vaccination via the induction of apoptosis, likely mediated by IFN-γ-dependent pathways. Two independent hematopoiesis assays, a colony forming unit assay and a mouse humanization assay, revealed skewed hematopoiesis of HSPCs obtained from donors delivered from mothers with SARS-CoV-2 infection history. These results indicate that SARS-CoV-2 infection and COVID-19 vaccination impair the functionalities and survivability of HSPCs in the UCB, which would make unprecedented concerns on the future of HSPC-based therapies.

Bone Marrow Environment in Metastatic Neuroblastoma

The study of the interactions occurring in the BM environment has been facilitated by the peculiar nature of metastatic NB. In fact: (i) metastases are present at diagnosis; (ii) metastases are confined in a very specific tissue, the BM, suggestive of a strong attraction and possibility of survival; (iii) differently from adult cancers, NB metastases are available because the diagnostic procedures require morphological examination of BM; (iv) NB metastatic cells express surface antigens that allow enrichment of NB metastatic cells by immune-magnetic separation; and (v) patients with localized disease represent an internal control to discriminate specific alterations occurring in the metastatic niche from generic alterations determined by the neoplastic growth at the primary site. Here, we first review the information regarding the features of BM-infiltrating NB cells. Then, we focus on the alterations found in the BM of children with metastatic NB as compared to healthy children and children with localized NB. Specifically, information regarding all the BM cell populations and their sub-sets will be first examined in the context of BM microenvironment in metastatic NB. In the last part, the information regarding the soluble factors will be presented.

State of the art in immunotherapy of neuroblastoma

Neuroblastoma (NB) is a common and deadly malignancy mostly observed in children. Evolution of therapeutic options for NB led to the addition of immunotherapeutic modalities to the previously recruited chemotherapeutic options. Molecular studies of the NB cells resulted in the discovery of many tumor-associated genes and antigens such as MYCN gene and GD2. MYCN gene and GD2 surface antigen are two of the most practical discoveries regarding immunotherapy of neuroblastoma. The GD2 antigen has been targeted in many animal and human studies including Phase III clinical trials. Even though these antigens have changed the face of pediatric neuroblastoma, they do not take as much credit in immunotherapy of adult-onset neuroblastoma. Monoclonal antibodies have been designed to detect this antigen on the surface of NB tumor cells. Despite bettering the outcomes for NB patients, current therapies still fail in many cases. Studies are underway to discover more specific tumor-associated antigens and more effective treatment options. In the current narrative, immunotherapy of NB - from emerging of this therapeutic backbone in NB to the latest discoveries regarding this malignancy - has been reviewed.

Interferon-Gamma at the Crossroads of Tumor Immune Surveillance or Evasion

Interferon-gamma (IFN-γ) is a pleiotropic molecule with associated antiproliferative, pro-apoptotic and antitumor mechanisms. This effector cytokine, often considered as a major effector of immunity, has been used in the treatment of several diseases, despite its adverse effects. Although broad evidence implicating IFN-γ in tumor immune surveillance, IFN-γ-based therapies undergoing clinical trials have been of limited success. In fact, recent reports suggested that it may also play a protumorigenic role, namely, through IFN-γ signaling insensitivity, downregulation of major histocompatibility complexes, and upregulation of indoleamine 2,3-dioxygenase and of checkpoint inhibitors, as programmed cell-death ligand 1. However, the IFN-γ-mediated responses are still positively associated with patient's survival in several cancers. Consequently, major research efforts are required to understand the immune contexture in which IFN-γ induces its intricate and highly regulated effects in the tumor microenvironment. This review discusses the current knowledge on the pro- and antitumorigenic effects of IFN-γ as part of the complex immune response to cancer, highlighting the relevance to identify IFN-γ responsive patients for the improvement of therapies that exploit associated signaling pathways.

The HLA-DR mediated signalling increases the migration and invasion of melanoma cells, the expression and lipid raft recruitment of adhesion receptors, PD-L1 and signal transduction proteins

The constitutive expression of Major Histocompatibility Complex (MHC) class II molecules is restricted to professional Antigen-Presenting Cells (APCs), nevertheless almost 50% of melanomas express constitutively the MHC class II molecules. Therefore, in two MHC class II constitutive expressing melanoma cell lines we studied the signalling mediated by the HLA-DR molecules in the aim to understand the consequence of class II mediated signalling on metastatic dissemination of melanoma. In particular, we reported that the HLA-DR mediated signalling play a new role in melanoma progression, increasing the migration and invasion of melanoma cells. Furthermore, we showed that the HLA-DR mediated signalling increases the expression and the lipid raft localisation of class II molecules, PD-L1 receptor, Integrin and CAM adhesion receptors, FAK, AKT and STAT3 signalling proteins. We also showed that the HLA-DR mediated signalling increases the activation of FAK, AKT, ERK, PKC and STAT3 signalling proteins and the expression of ILK, PAX, BRAF, ERK and PKC. Indeed, the results showed suggest that the HLA-DR mediated signalling provides a platform useful to frustrate an effective anti-tumour response and to increase melanoma migration and metastatic dissemination of this cancer.

Polycomb Repressive Complex 2 Confers BRG1 Dependency on the CIITA Locus

CIITA (or MHC2TA) coordinates constitutive and IFN-γ-induced expression of MHC class II genes. IFN-γ responsiveness of CIITA requires BRG1 (SMARCA4), the ATPase engine of the chromatin remodeling SWI/SNF complex (also called BAF). SWI/SNF is defective in many human cancers, providing a mechanism to explain IFN-γ resistance. BRG1 dependency is mediated through remote elements. Short CIITA reporters lacking these elements respond to IFN-γ, even in BRG1-deficient cells, suggesting that BRG1 counters a remote repressive influence. The nature of this distal repressor is unknown, but it would represent a valuable therapeutic target to reactivate IFN-γ responsiveness in cancer. In this article, we show that the polycomb repressive complex 2 (PRC2) components EZH2 and SUZ12, as well as the associated histone mark H3K27me3, are codetected at interenhancer regions across the CIITA locus. IFN-γ caused a BRG1-dependent reduction in H3K27me3, associated with nucleosome displacement. SUZ12 knockdown restored IFN-γ responsiveness in BRG1-null cells, and it mimicked the ability of BRG1 to induce active histone modifications (H3K27ac, H3K4me) at the -50-kb enhancer. Thus, PRC2 confers BRG1 dependency on the CIITA locus. Our data suggest that, in addition to its known roles in promoting stemness and proliferation, PRC2 may inhibit immune surveillance, and it could be targeted to reactivate CIITA expression in SWI/SNF deficient cancers.

Epigenetic drugs as immunomodulators for combination therapies in solid tumors

Continuously improving knowledge of the fine mechanisms regulating cross-talk between immune cells, and of their multi-faceted interactions with cancer cells, has prompted the development of several novel immunotherapeutic strategies for cancer treatment. Among these, modulation of the host's immune system by targeting immunological synapses has shown notable clinical efficacy in different tumor types. Despite this, objective clinical responses and, more importantly, long-term survival are achieved only by a fraction of patients; therefore, identification of the mechanism(s) responsible for the differential effectiveness of immune checkpoint blockade in specific patient populations is an area of intense investigation. Neoplastic cells can activate multiple mechanisms to escape from immune control; among these, epigenetic reprogramming is emerging as a key player. Selected tumor-associated antigens, Human Leukocyte Antigens, and accessory/co-stimulatory molecules required for efficient recognition of neoplastic cells by the immune system have been shown to be epigenetically silenced or down-regulated in cancer. Consistent with the inherent reversibility of epigenetic silencing, "epigenetic" drugs, such as inhibitors of DNA methyltransferases and of histone deacetylases, can restore the functional expression of these down-regulated molecules, thus improving the recognition of cancer cells by both the innate and adaptive immune responses. This review focuses on the immunomodulatory activity of epigenetic drugs and on their proposed clinical use in novel combined chemo-immunotherapeutic regimens for the treatment of solid tumors.

Dysregulated recruitment of the histone methyltransferase EZH2 to the class II transactivator (CIITA) promoter IV in breast cancer cells

One mechanism frequently utilized by tumor cells to escape immune system recognition and elimination is suppression of cell surface expression of Major Histocompatibility Class II (MHC II) molecules. Expression of MHC II is regulated primarily at the level of transcription by the Class II Transactivator, CIITA, and decreased CIITA expression is observed in multiple tumor types. We investigate here contributions of epigenetic modifications to transcriptional silencing of CIITA in variants of the human breast cancer cell line MDA MB 435. Significant increases in histone H3 lysine 27 trimethylation upon IFN-γ stimulation correlate with reductions in transcription factor recruitment to the interferon-γ inducible CIITA promoter, CIITApIV, and with significantly increased CIITApIV occupancy by the histone methyltransferase enhancer of zeste homolog 2 (EZH2). Most compelling is evidence that decreased expression of EZH2 in MDA MB 435 variants results in significant increases in CIITA and HLA-DRA mRNA expression, even in the absence of interferon-γ stimulation, as well as increased cell surface expression of MHC II. Together, these data add mechanistic insight to prior observations of increased EZH2 expression and decreased CIITA expression in multiple tumor types.

Cytokines in neuroblastoma: from pathogenesis to treatment

Cytokines released by cancer cells or by cells of the tumor microenvironment stimulate angiogenesis, act as autocrine or paracrine growth factors for malignant cells, promote tumor cell migration and metastasis or create an immunosuppressive microenvironment. These tumor-promoting effects of cytokines also apply to neuroblastoma (NB), a pediatric neuroectodermal malignancy with frequent metastatic presentation at diagnosis and poor prognosis. IL-6 and VEGF are the best characterized cytokines that stimulated tumor growth and metastasis, while others such as IFN-γ can exert anti-NB activity by inducing tumor cell apoptosis and inhibiting angiogenesis. On the other hand, cytokines are part of the anti-NB therapeutic armamentarium, as exemplified by IL-2 and granulocyte-macrophage colony stimulating factor that potentiate the activity of anti-NB antibodies. These recent results raise hope for more efficacious treatment of this ominous pediatric malignancy.

Interferon-triggered transcriptional cascades in the oligodendroglial lineage: a comparison of induction of MHC class II antigen between oligodendroglial progenitor cells and mature oligodendrocytes

Interferon-gamma induces major histocompatibility complex class II (MHC-II) in proliferating oligodendroglial progenitor cells (OPC), but to a much lesser extent in mature oligodendrocytes. Interferon-beta has virtually no effects on MHC-II induction even in OPC. Interferon-gamma-mediated transcriptional induction of CIITA, a critical regulator of MHC-II induction, was 6-fold lower in mature oligodendrocytes than in OPC, and entirely dependent on promoter IV, suggesting that the transcriptional activity of promoter IV is down-regulated after differentiation. The distinct difference in MHC-II induction between interferon-gamma and interferon-beta is attributed to transient interferon-beta-mediated activation of STAT1-IRF1 signaling compared to the sustained interferon-gamma-mediated activation.

Methylation of CIITA promoter IV causes loss of HLA-II inducibility by IFN-gamma in promyelocytic cells

The human promyelocytic cell line THP-1 expresses high level of HLA class II (HLA-II) molecules after IFN-gamma treatment. Here, we report a variant of THP-1 that does not express HLA-II after IFN-gamma. The variant's HLA-II phenotype is constant over time in culture and it is not related to a defective IFN-gamma-signalling pathway. Transfection of CIITA, the HLA-II transcriptional activator, under the control of a cytomegalovirus promoter rescues high level of HLA-DR surface expression in the variant indicating that the biosynthetic block resides in the expression of CIITA and not in the CIITA-dependent transactivation of the HLA-II promoters. Treatment of the variant with 5-azacytidine (5-aza), which inhibits CpG methylation, restores inducibility of HLA-II by IFN-gamma both at transcriptional and phenotypic level and antigen presenting and processing function of the variant. DNA studies demonstrate that the molecular defect of the THP-1 variant originates from the methylation of the CIITA promoter IV. Furthermore, treatment with 5-aza produces a substantial demethylation of CIITA promoter IV and a significant increase of IFN-gamma-dependent HLA-II expression in another myelomonocytic cell line, U937. Therefore hyper-methylation of CIITA promoter IV may be a relevant mechanism of epigenetic control preventing HLA-II IFN-gamma inducibility in the myelomonocytic cell lineage.

Ups and downs: the STAT1:STAT3 seesaw of Interferon and gp130 receptor signalling

Downstream of cytokine or growth factor receptors, STAT3 counteracts inflammation and promotes cell survival/proliferation and immune tolerance while STAT1 inhibits proliferation and favours innate and adaptive immune responses. STAT1 and STAT3 activation are reciprocally regulated and perturbation in their balanced expression or phosphorylation levels may re-direct cytokine/growth factor signals from proliferative to apoptotic, or from inflammatory to anti-inflammatory. Here we review the functional canonical and non-canonical effects of STAT1/3 activation and discuss the hypothesis that perturbation of their expression and/or activation levels may provide novel therapeutic strategies in different clinical settings and particularly in cancer.

A novel c-Jun-dependent signal transduction pathway necessary for the transcriptional activation of interferon gamma response genes

The biological effects of interferon gamma (IFNgamma) are mediated by interferon-stimulated genes (ISGs), many of which are activated downstream of Janus kinase (JAK)/signal transducer and activator of transcription 1 (STAT1) signaling. Herein we have shown that IFNgamma rapidly activated AP-1 DNA binding that required c-Jun but was independent of JAK1 and STAT1. IFNgamma-induced c-Jun phosphorylation and AP-1 DNA binding required the MEK1/2 and ERK1/2 signaling pathways, whereas the JNK1/2 and p38 mitogen-activated protein kinase pathways were dispensable. The induction of several ISGs, including ifi-205 and iNOS, was impaired in IFNgamma-treated c-Jun-/- cells, but others, such as IP-10 and SOCS3, were unaffected, and chromatin immunoprecipitation demonstrated that c-Jun binds to the iNOS promoter following treatment with IFNgamma. Thus, IFNgamma induced JAK1- and STAT1-independent activation of the ERK mitogen-activated protein kinase pathway, phosphorylation of c-Jun, and activation of AP-1 DNA binding, which are important for the induction of a subset of ISGs. This represents a novel signal transduction pathway induced by IFNgamma that proceeds in parallel with conventional JAK/STAT signaling to activate ISGs.

Epigenetic silencing of MHC2TA transcription in cancer

Lack of expression of major histocompatibility complex (MHC) molecules of both classes is frequently noted on tumour cells . It is thought that in this way tumour cells escape immunosurveillance. The genes encoding both classes of MHC molecules are localized on the distal part of chromosome 6 (6p21.3). The class II transactivator (CIITA), encoded by the MHC2TA gene, is essential for transcriptional activation of all MHC-II genes, while it has a helper function in the transcriptional regulation of MHC-I genes (with the exception of human leukocyte antigen (HLA)-G) and of the gene encoding beta2-microglobulin (beta2m) . Here we discuss our current knowledge on the expression characteristics of MHC2TA and argue for an important role of epigenetic factors and mechanisms in the transcriptional silencing of MHC2TA in cancer cells.

Epigenetic regulation of MHC-II and CIITA genes

This review describes recent advances in understanding how epigenetic events control MHC-class-II-family (MHC-II) gene expression. To address this issue, two phases of gene transcription have to be considered. First, the control of MHC-II by chromatin-modifying events such as histone acetylation, methylation, deacetylation, ubiquitination and the interplay between these different epigenetic events will be examined. The interactions of chromatin-modifying enzymes with class II transactivator (CIITA) and relevant DNA-binding proteins for activating and silencing MHC-II gene transcription will be reviewed. Second, the transcriptional control of the promoter of CIITA, the master regulator of MHC-II, by DNA methylation and chromatin modification will be discussed, and the novel role of noncoding RNA will be explored. Finally, the relevance of these findings to infection, transplantation and cancer will be reviewed.

Chaperoning antigen presentation by MHC class II molecules and their role in oncogenesis

Tumor vaccine development aimed at stimulating the cellular immune response focuses mainly on MHC class I molecules. This is not surprising since most tumors do not express MHC class II or CD1 molecules. Nevertheless, the most successful targets for cancer immunotherapy, leukemia and melanoma, often do express MHC class II molecules, which leaves no obvious reason to ignore MHC class II molecules as a mediator in anticancer immune therapy. We review the current state of knowledge on the process of MHC class II-restricted antigen presentation and subsequently discuss the consequences of MHC class II expression on tumor surveillance and the induction of an efficient MHC class II mediated antitumor response in vivo and after vaccination.

Epigenetic inactivation of class II transactivator (CIITA) is associated with the absence of interferon-gamma-induced HLA-DR expression in colorectal and gastric cancer cells

Tightly regulated at the level of transcription, expression of MHC class II molecules varies significantly among gastrointestinal cancers. High levels of MHC class II expression are often associated with a better prognosis, which is indicative of the involvement of CD4+ lymphocytes in tumor suppression, but the molecular mechanism by which MHC class II expression is regulated remains unclear. In the present study, we investigated the expression of one inducible MHC class II molecule, HLA-DR, and its coactivators in a panel of colorectal and gastric cancer cell lines. Interferon-gamma induced expression of HLA-DR in 14 of 20 cell lines tested; the remaining six cell lines did not express HLA-DR. Analysis of the expression of transcription factors and coactivators associated with HLA-DR revealed that the loss of CIITA expression was closely associated with the absence of HLA-DR induction. Moreover, DNA methylation of the 5' CpG island of CIITA-PIV was detected in all cancer cells that lacked CIITA. The methylation and resultant silencing of CIITA-PIV depended on the activities of two DNA methyltransferases, DNMT1 and DNMT3B, and their genetic inactivation restored CIITA-PIV expression. It thus appears that CIITA methylation is a key mechanism that enables some gastrointestinal cancer cells to escape immune surveillance.