You are here
The microenvironment in classical Hodgkin lymphoma: An actively shaped and essential tumor component
Seminars in Cancer Biology, pages 15 - 22
Classical Hodgkin lymphoma (cHL) is characterized by a minority of tumor cells derived from germinal center B-cells and a vast majority of non-malignant reactive cells. The tumor cells show a loss of B-cell phenotype including lack of the B-cell receptor, which makes the tumor cells vulnerable to apoptosis. To overcome this threat, tumor cells and their precursors depend on anti-apoptotic and growth stimulating factors that are obtained via triggering of multiple membrane receptors. In addition, tumor cells shape the environment by producing a wide variety of chemokines and cytokines. These factors alter the composition of the microenvironment and modulate the nature and effectiveness of the infiltrating cells. The attracted cells enhance the pro-survival and growth stimulating signals for the tumor cells. To escape from an effective anti-tumor response tumor cells avoid recognition by T and NK cells, by downregulation of HLA molecules and modulating NK and T-cell receptors. In addition, the tumor cells produce immune suppressive cytokines that inhibit cytotoxic responses. In this review the relevance of the microenvironment in the pathogenesis of cHL will be discussed.
Keywords: Hodgkin lymphoma, Microenvironment, Tumor cell survival, Immune shaping, Immune escape, Immune suppression.
1. General background on classical Hodgkin lymphoma
Hodgkin lymphoma (HL) is a distinctive disease with a characteristic clinical presentation and it was the first lymphocyte malignancy to be described  . It has an incidence rate of 3 per 100,000 person years and is among the most common cancers in adolescents and younger adults. About 50% of the HL patients are diagnosed between ages 15 and 35 years and a second incidence peak can be observed in the elderly  . HL primarily involves lymph nodes and has a unique histomorphological presentation with a minority of neoplastic cells, which generally comprise less than 1% of the total cell population, and a large majority of non-malignant reactive immune cells ( Fig. 1 ). HL has been divided into classical HL (cHL), which accounts for 95% of all cases, and the less common nodular lymphocyte predominant HL form, which is considered to be a different disease entity.
The tumor cells in cHL are named Hodgkin and Reed–Sternberg (HRS) cells and they express diagnostic markers CD30 and usually CD15. The HRS cells are characterized by a very large (sometimes lobated) nucleus with little DNA condensation, one or more very large nucleoli, a large Golgi apparatus and much cytoplasm. This typical morphology indicates that the HRS cells are strongly activated and produce a large amount of proteins.
The origin of the HRS cells has been controversial for a long time because the immunophenotype of these cells is strikingly different from other hematopoietic cells. Detection of somatically mutated monoclonal immunoglobulin gene rearrangements indicated a germinal center B-cell origin in the majority of the cases  and . However, at the time of diagnosis, HRS cells have virtually lost their B-cell identity as they show no expression of the B-cell receptor (BcR), and no or strongly reduced expression of many common B-cell markers and B-cell transcription factors  and . Remarkably, they have often retained their professional antigen presenting cell phenotype including expression of the molecules necessary for antigen presentation, co-stimulation and cell adhesion  .
In 20–40% of cHL cases in the western world, monoclonal infection with Epstein Barr virus (EBV) is present in HRS cells and this is considered to be a tumor-initiating factor. EBV+ cHL patients show a latency type II infection pattern that is restricted to expression of latent membrane protein 1 (LMP1), LMP2 and EBV-related nuclear antigen 1 (EBNA1). LMP1 and LMP2 are oncogenes that mimic CD40 activation and BcR signaling respectively  and .
Based on growth pattern, morphology of the HRS cells and the composition of the background infiltrate, cHL is divided into four histological subtypes, of which nodular sclerosis (∼80%) and mixed cellularity (∼15%) are the most common subtypes. Lymphocyte depleted and lymphocyte rich subtypes are relatively uncommon. A nodular growth pattern, sclerotic bands and large HRS cells define the nodular sclerosis subtype. In mixed cellularity HL the growth pattern is diffuse, without sclerosis and somewhat smaller, often binucleated HRS cells. In virtually all cases the microenvironment contains numerous small T-cells with variable numbers of eosinophils, histiocytes/macrophages, B-cells, plasma cells and sometimes neutrophils ( Fig. 1 ). In mixed cellularity this microenvironment tends to be more mixed, usually with loose or granulomatous collections of histiocytes. Regardless of subtype, the tumor cells are usually in intimate contact with small CD4+ T-cells. This can be seen in tissue sections as a layer of lymphocytes directly surrounding single tumor cells (so-called rosettes)  .
cHL can be considered an extreme model of how the tumor microenvironment impacts cancer pathogenesis. Much research has been focused on the cross talk between HRS cells and the microenvironment and its (potential) functional relevance. However, there are no cHL animal models in which cross talk between HRS cells and the microenvironment can be studied. In addition, primary tissue derived HRS cells usually do not survive in culture. This hampers the possibilities to do functional studies that closely mimic the in vivo situation. Functional studies are usually done in cHL cell lines and/or specific subsets of the reactive infiltrate. Caution should be taken in interpreting putative autocrine effects especially for membrane bound factors, as tumor cell–tumor cell contact is very infrequent in cHL tissue. Relevant markers are tested for expression in cHL tissue samples to support these experimental findings. In general, this is the closest approximation possible.
This review focuses on the microenvironment of cHL to show that the reactive infiltrating cells are not innocent bystander cells but an essential component of the tumor. The most accepted mechanisms with respect to enabling tumor cell driving mechanisms, shaping of the microenvironment and disabling anti-tumor immune responses will be discussed.
2. Tumor cell driving mechanisms
Due to the lack of a functional BcR, HRS cells and their pre-cursors are dependent on anti-apoptotic and pro-survival signals from the microenvironment. This dependence most likely already exists at the initiation of the malignant transformation. Constitutive activation of the NF-κB pathway is one of the hallmarks of the HRS cells and provides the tumor cells with a strong pro-survival signal. Activation of NF-κB is achieved via multiple mechanisms, i.e. mutations of the NF-κB and JAK/STAT pathways  and signaling via the tumor necrosis factor receptor superfamily (TNFRSF), tyrosine kinases (TK) and cytokine receptors ( Fig. 2 ).
2.1. Tumor necrosis factor receptor superfamily
CD30, a member of the TNFRSF (TNFRSF5), is abundantly expressed on HRS in virtually all cHL patients and on cHL cell lines  . CD30L is expressed on eosinophils and mast cells  and  and these cells can enhance proliferation of cHL cell lines  . CD30 overexpression as observed in HRS cells can induce NF-κB activation by itself, independent of CD30L  and . CD40, another member of the TNFRSF (TNFRSF8), is also highly expressed on HRS cells and cHL cell lines  and . Triggering of CD40 results in activation of the NF-κB pathway in HL via proteolysis of TRAF3  . The CD40 ligand (CD40L) is mainly expressed on CD4+ T-cells that are present in the close vicinity of the HRS cells  . CD40 stimulation enhances colony formation of cHL cell lines and this effect is enhanced by IL-9 in some cHL cell lines  . In EBV+ cHL cases the EBV derived LMP1 acts as a constitutively activated CD40 receptor  .
Tumor-promoting effects of cells that are present in the reactive infiltrate can be enhanced by certain cytokines. CD30L expression by eosinophils increases in response to IL-5 and GM-CSF produced by the HRS cells  . Stimulation with CD30L and CD40L induces secretion of several cytokines, including IL-6, IL-8 (only with CD40L), TNF and LT-α and it also induces expression of ICAM-1 (CD54)  and . IL-10 derived from tumor cells and T-cells enhances membrane expression of CD40L on T-cells  . Thus IL-10 enhances the pro-survival CD40-CD40L signaling pathway in HL. In addition to CD30 and CD40, the HRS cells also express several other members of the TNFRSF family, i.e. receptor activator of NF-κB (RANK, TNFRSF11A), CD27 (TNRSF7), FAS (CD95, TNFRSF6), CD120a and CD120b (TNFR type I and II, TNFRSF1A and 1B), CD137 (4-1BB, TNFRSF9) , , , , and . However, the functional relevance of these receptors for survival of HRS cells has not been studied in detail.
2.2. Tyrosine kinase family members
TKs and receptor tyrosine kinases (RTKs) are important regulators of inter- and intracellular signaling and regulate cellular processes such as proliferation, differentiation and survival. CHL cell lines aberrantly express certain RTKs as compared to normal B-cells and B-cell non-Hodgkin lymphoma. HRS cells express PDGFRA in HRS cells in 75% of the patients, whereas DDR2, EPHB1, RON, TRKB and TRKA are expressed in HRS cells in at least 30% of the patients  . These RTKs are activated in HRS cells and can be detected as phosphorylated forms in cHL tissue. RTK activation is probably induced by binding of ligands, since there are no activating mutations in the RTKs in cHL cell lines. Collagen type 1 (ligand of DDR2) and Nerve growth factor (NGF; ligand of TRKA) are expressed by infiltrating reactive cells indicating a possible paracrine activation, whereas PDGFA (ligand of PDGFRA) is expressed by the tumor cells indicating a possible autocrine activation  . EphrinB1 (ligand of EPHB) is also expressed by the HRS cells, but autocrine signaling is unlikely since the receptor and its ligand are both membrane bound. The receptor for hepatocyte growth factor (HGF), c-Met, is a RTK that is expressed by HRS cells in the majority of the cHL patients  and . Expression of HGF by CD21+ dendritic-reticulum cells and in 20% of the patients also by the HRS cells indicates both paracrine and autocrine activation of c-Met+ HRS cells  and . Inhibition of c-Met suppresses cell growth by blocking the cells in the G2/M phase. Thus, c-Met acts as an oncogene, providing growth advantage for the HRS cells  and . Activation of RTKs results in activation of signal transduction pathways, such as the MAPK pathway resulting in pro-survival signals for the HRS cells.
In contrast to several other B-cell non-Hodgkin lymphomas, HRS cells show a strong expression of Notch1  . Inhibition of Notch1 activity reduces cell viability and enhances apoptosis in cHL cell lines via downregulation of the NF-κB transcriptional activity  . Stimulation of Notch1 via Jagged1, has a strong proliferative effect on cHL cells and reduces the number of apoptotic cells. Jagged1 expression is present on HRS cells and on smooth muscle cells and epithelial cells, two cell types that are not common in the cHL microenvironment  .
2.4. Cytokine receptors
Another signaling pathway frequently activated in cHL is the JAK/STAT pathway. This pathway can be activated via somatic mutations of SOCS1  and via stimulation of the cytokine receptors expressed on HRS cells. The IL-3R is highly expressed on HRS cells in the vast majority of cHL patients and cell lines  . Exogenous IL-3 promotes growth of cHL cells in a dose-dependent manner, and also rescues cells from apoptosis. Co-stimulation with IL-9 can further enhance the proliferative effect of IL-3  . Multiple cells present in the microenvironment of cHL produce IL-3 and as such presents a paracrine growth factor for the HRS cells. IL-9 is produced by HRS cells, which also express the receptor IL-9R  . Addition of IL-9 increases cell growth in the KM-H2 HL cell line that produces low amounts of endogenous IL-9. Inhibition of IL-9 function or production reduces growth in HDLM-2 cells that produce large amounts of endogenous IL-9. So, IL-9 can act as an autocrine growth factor in HL  . IL-13 and IL-13R are both expressed in HRS cells and in cHL cell lines  and . Treatment of cHL cells with a neutralizing antibody to IL-13 results in a dose-dependent inhibition of proliferation  and  indicating that IL-13 acts as an autocrine growth factor in cHL  . Co-expression of IL-7 and its receptor IL-7R is found on HRS cells in a high proportion of the cHL cases  and . Inhibition of IL-7 inhibits clonogenic growth while addition of IL-7 increases clonogenic growth in HL cell lines  . IL-7 is thus another potential autocrine growth factor in HL. HRS cells express the CC-chemokine receptor 5 (CCR5), which is one of the receptors of CC-chemokine ligand 5 (CCL5, Rantes)  . Treatment of cHL cells with neutralizing anti-CCL5 antibody inhibits proliferation, whereas treatment with recombinant CCL5 increases their clonogenic growth  . T-cells present in the microenvironment of HRS cells produce CCL5, indicating a paracrine activation mechanism  .
In conclusion, both autocrine and paracrine signaling are proposed in HRS cell activation, survival and proliferation. However, it has to be kept in mind that many of these tumor cell driving mechanisms rely on the use of cHL cell lines, which may introduce a bias toward autocrine stimulation mechanisms as opposed to the more likely paracrine and thus microenvironment dependent mechanisms.
3. Shaping the microenvironment
cHL arises in lymph nodes, but at the time of diagnosis the lymph node architecture and the microenvironment of the HRS cells has altered completely. The vast majority of reactive cells are CD4+ memory T-cells. These cells express a range of activation markers  , have a transcription factor profile that fits Th2 and Treg cells  and express cytokines that match to anergic Th2 and Treg cells  . To create this specific environment HRS cells apply multiple mechanisms that can be divided into those that alter the composition of the reactive infiltrate and those that modulate the nature or effectiveness of the cells that are present ( Fig. 3 ).
3.1. Chemokines produced by the HRS cells
HRS cells aberrantly express several chemokines  and these chemokines represent a mechanism to shape the environment. CCL17 (TARC) is expressed at extremely high levels by HRS cells in a high percentage of patients (85–91%) , , and . CCL17 attracts Th2 cells and Treg cells by binding to their CCR4 receptor and is the main driver in the formation of the intensive reactive infiltrate. CCL22 (MDC), the other chemokine that attracts CCR4 positive cells, is also expressed by HRS cells  , but at lower levels and with less specificity as it is also found in NLPHL and other B-cell non-Hodgkin lymphomas  . Consistent with the known function of CCL17 and CCL22, cHL cell lines and their culture supernatants are able to attract CCR4 positive T-cells including CD25+/FoxP3+ Treg cells. These cells have immunosuppressive potential as they can suppress the activation of effector CD4+ T-cells  . CCL20 (MIP-3α) expressed by HRS cells also recruits Tregs and its expression can be induced by EBNA-1 and IL-21  and . Gene expression profiling confirms higher CCL20 mRNA levels in EBV+ primary HRS cells in comparison to EBV− HRS cells  . Nevertheless, there is no difference in Treg cell numbers in EBV+ as compared to EBV− cHL cases, due to high CCL17 and CCL22 levels in all cHL cases irrespective of EBV status  and . CHL cell lines and HRS cells also produce chemokines, such as CXC chemokine ligand 9 (CXCL9, MIG) and CXCL10 (IP10) , , and , that can attract CXCR3+ activated T-cells and NK cells , , and . CXCL9 and CXCL10 are IFN-γ inducible chemokines, and production of IFN-γ by T-cells present in the cHL microenvironment can potentially enhance their production. CXCL9 and CXCL10 expression is associated with EBV+ cHL  and more CD8+ T-cells and NK cells are indeed detected in EBV+ cHL  . Although CXCL9 and CXCL10 supposedly support an anti-tumor immune response, this may be counteracted by the concomitant expression of multiple chemokines that attract high numbers of Th2 and Treg cells. CCL28 (MEC) is weakly expressed by HRS cells and leads to recruitment of eosinophils, T-cells and plasma cells into cHL affected lymph nodes  .
3.2. Chemokines produced by the microenvironment
In addition to the chemokines produced by HRS cells, chemokines produced by the microenvironment may also contribute to the composition of the infiltrate. CCL5 expressed in T-cells surrounding the tumor cells  is a chemo-attractant for monocytes, T lymphocytes, eosinophils, basophils and mast cells. CCL5 producing cHL cell lines indeed attract mast cells, CD4+ T-cells and eosinophils , , and . Fibroblasts co-cultured with cHL cell lines are stimulated by tumor cell derived TNF-α to produce CCL11 (Eotaxin), which results in the attraction of CCR3+ Th2 cells  and eosinophils  . CXCL8 (IL-8) is mainly produced by macrophages, neutrophils, and mesenchymal cells in the cHL microenvironment, especially in the nodular sclerosis subtype and attracts neutrophils  . An important feature of the infiltrating Th2 cells that directly surround the HRS cells, is their lack of CD26 expression  , an enzyme that can proteolytically process and inactivate several chemokines like CCL5, CCL11 and CCL22  .
A second group of molecules that contribute to shaping of the environment is the cytokine family. M2 macrophages dominate the macrophage population in the cHL microenvironment  and these cells are induced by macrophage migration inhibitory factor (MIF) produced by the HRS cells  and . In mice MIF can increase the generation of Treg cells from unstimulated T-cells by downmodulation of IL-2 production  . IL-10 secreting Treg cells (Tr-1 cells) are induced by both LMP1 and Galectin-1 produced by the HRS cells  and . Consistent with these findings, co-culture of an irradiated cHL cell line with naïve CD4+ T-cells results in differentiation toward IL-10 producing CD25+FoxP3+ Treg cells and to a lesser extent CD4+ cytotoxic T-cells  . Moreover, IL-7 production by HRS cells induces proliferation of Treg cells  . Thus, HRS cells apply multiple mechanisms to induce and enhance the number of Tr-1 and Treg cells in the microenvironment. A Th2 cell differentiation can be induced via IL-13, which is secreted by HRS cells  and by T-cells. Eosinophils are attracted to the HL microenvironment by IL-5 and IL-9 produced by the HRS cells  and . IL-9 also contributes to the proliferation and survival of eosinophils and is involved in mast cell differentiation  . Mast cells promote growth of HRS cells by the production of pro-angiogenic factors and they also induce fibrosis  .
In conclusion, HRS cells modulate their microenvironment by actively attracting certain cell types and influencing the differentiation of other cells in such a way that it is favorable for HRS cell survival.
4. Immune escape mechanisms
Despite actively shaping the environment, HRS cells intuitively also need to apply mechanisms to escape from both antigen-dependent and innate immune responses ( Fig. 4 ). Escape from effective anti-tumor responses seems important especially in EBV+ cHL cases. The latency type II infection pattern observed in EBV+ cases, includes expression of LMP1, LMP2 and EBNA-1. LMP1 and LMP2 derived antigenic peptides can induce CTL responses in healthy individuals, albeit at much lower frequencies than the more immune-dominant peptides derived from EBNA-3A, EBNA-3B, EBNA-3C and the lytic proteins that are not expressed in HRS cells  . In cHL, EBV-specific CTL can be detected in blood and biopsy samples of both EBV− and EBV+ cHL patients  . In EBV− cHL, expression of the tumor-specific protein MAGE-A4 is expressed in a proportion of the cases  . Moreover, cytotoxic T-cell responses recognizing MAGE-A4 expressed by HRS cells can be induced  .
4.1. HLA molecules
Loss of HLA class I and II expression is frequently observed in cHL and presents a way to avoid recognition by the immune system. This loss of HLA is most prominent in EBV− cHL patients  . The tumor cells in EBV+ cHL generally have normal or even elevated HLA class I expression levels. Besides being positive for HLA, EBV+ cases also have increased numbers of cytotoxic CD8+ and Granzyme B positive T-cells. These cells are usually not observed in close vicinity of the HRS cells, limiting their potential effectiveness  . It remains enigmatic why HLA loss is most prominent in EBV− cHL patients and less pronounced in EBV+ cHL. This suggests that EBV derived antigenic peptides are not effectively presented, whereas other antigenic peptides present in EBV− cHL are effectively presented and require HLA downregulation. Around 15% of the cHL patients have translocations involving the MHC class II transactivator (CIITA) gene locus and as a consequence of these translocations HLA class II expression is downregulated  , but probably not absent. The mechanism of complete HLA loss has not been studied in cHL, but most likely includes both genetic and epigenetic mechanisms.
The risk of getting EBV+ cHL is associated with genetic variants in the HLA class I region  . More specifically, HLA-A*01 is a risk and HLA-A*02 a protective HLA-A type for the development of EBV+ cHL  and . It has been shown that HLA-A*01 has a low affinity and HLA-A*02 has a high affinity for LMP1 and LMP2 derived antigenic peptides  . Together, these data indicate that lack of HLA-A*02 contributes to the immune escape of EBV+ HRS cells despite normal or even elevated HLA class I expression levels.
A potential threat for HLA class I negative HRS cells is recognition and killing by NK or CTL mediated responses. Expression of both HLA-G and HLA-E can protect HLA class I negative cells from NK and CTL cell mediated cytotoxicity via binding to inhibitory receptors expressed by NK and CTL cells  and . HLA-G is expressed on HRS cells in more than 50% of the patients, and is associated with lack of HLA class I expression and EBV− tumor cell status  . HLA-E is expressed on the vast majority of HRS cells in more than 50% of the cHL patients, but it is unclear if HLA-E expression is related to presence of EBV or downregulation of the expression of the classical HLA class I genes  . Expression of both HLA-E and HLA-G might thus contribute to the escape of an anti-tumor response that is a potential threat for HLA class I negative HRS cells.
4.2. NKG2D ligands
Low levels of the membranous NKG2D-ligands, i.e. MHC class I related chain-A (MIC-A) and UL16 binding protein 3 (ULBP3), on the HRS cells presents another way to escape from cytotoxic T-cell responses  . These low levels are the result of proteolytic cleavage of the NKG2D-ligands by ERp5 and ADAM10 produced by HRS cells and mesenchymal stromal cells. In addition, T-cells in cHL tissue have lower NKG2D receptor expression levels as compared to T-cells in normal lymph nodes. This is caused by TGF-β produced by the mesenchymal stromal and HRS cells, which blocks the IL-15-induced expression of NKG2D receptor on cytotoxic T-cells  . Thus, the anti-tumor activity of CD8+ T-cells is blocked by lack of membrane NKG2D-ligands, release of soluble NKG2D-ligands and by reduced NKG2D receptor levels on effector T-cells  .
4.3. Tumor necrosis factor receptor superfamily
Two of the TNFRSF members expressed on HRS cells, have a potential function in immune suppression by targeting T-cells. FAS and its ligand FASL are expressed in a high percentage of cHL cases  . Expression of FAS could make the HRS cells sensitive to apoptosis, but HRS cells escape from this apoptosis pathway via expression of FLICE inhibitory protein (cFLIP) , , and . On the other hand, FASL expressed on the HRS cells can drive activated Th1 and CD8+ T-cells in apoptosis. CD137 (4-1BB, TNFRSF9) and CD137L expression are observed on the tumor cells in the majority of the cHL cases  . Co-culture of HRS cells with pre-activated T-cells reduces production of IFNγ. This effect is most pronounced in CD137low and CD137Lhigh HRS cells. Inhibition of CD137 resulted in a significant upregulation of CD137L indicating a direct regulatory effect by CD137. Moreover, co-culture of wild type HRS cells treated with neutralizing anti-CD137 antibodies with pre-activated T-cells, enhances the CD137L levels on HRS cells and induces higher IFNγ production by the T-cells. Thus low CD137L levels promote escape from immune surveillance by reducing T-cell co-stimulation.
4.4. PD-1 and PD-1-ligand
Another mechanism to escape effective anti-tumor responses is achieved by T-cell exhaustion via continuous stimulation of the programmed death-1 (PD-1) receptor expressed on T-cells by PD-1 ligand (PD-1L) expressed on HRS cells  . Functionality of this pathway has been demonstrated by increased IFN-γ production upon inhibition of the PD-1L signaling pathway  . Amplification of the 9p24 locus, containing the PD-1L 1 and 2 gene loci, is common in nodular sclerosis cHL and HRS cells in this cHL subtype show a higher PD-1L expression level  . The translocation partner of the CIITA chromosomal translocations is the PD-1L gene locus in some cases and these translocations also result in enhanced PD-L1 and PD-L2 expression  . The number of PD-1 positive T-cells in cHL tissue samples is low in nodular sclerosis subtype and 9p24 amplification positive cases  . Together these studies indicate that enhanced expression of PD-1L is a potential immune escape mechanism in cHL. The low numbers of PD-1 positive cells observed in nodular sclerosis cHL characterized by high PD-1L levels, might indicate an effective apoptosis induction.
Galectin-1 is highly expressed in HRS cells in more than 50% of the cHL patients  and also in cHL derived cell lines. High expression of Galectin-1 in HRS cells is correlated with a low number of CD8+ T-cells in cHL tissues and with impaired LMP1 and LMP2 specific T-cell responses  . T-cells co-cultured with Galectin-1 positive cHL cell lines are skewed toward a Th2 phenotype. Upon downmodulation of Galectin-1, co-culture experiments show a restoration of the Th1/Th2 balance  .
The Th1-polarizing cytokine IL-12 is produced by T-cells surrounding the neoplastic cells in EBV+ cHL  . However, its functionality is hampered due to expression of an EBV-induced cytokine called EBI3 by the HRS cells that can antagonize IL-12 effects and thereby block the development of an effective Th1 immune response  .
By producing large amounts of immune suppressive cytokines, such as IL-10 and TGF-β, HRS cells protect themselves from being attacked by cytotoxic T-cells. TGF-β1 mRNA was found predominantly in HRS cells of the nodular sclerosis subtype of cHL  and . The L428 cell line produces a high molecular weight active form of TGF-β  and this same active form is also found in the urine of patients with active nodular sclerosis cHL  . CD4+ T-cells in cHL indeed show a genomic TGF-β fingerprint, comparable to a fingerprint established in vitro in which T-cells treated with TGF-β show inhibition of proliferation and IFN-γ production  . Both the percentage of IL-10 positive cases and the percentage of IL-10 positive HRS cells are higher in EBV+ cHL patients as compared to EBV− cHL patients  . Moreover, also the percentage of IL-10 producing lymphocytes is higher in EBV+ cases  . Immunosuppressive regulatory T-cells, both Treg and IL-10 producing Tr-1 cells, are abundant in the reactive infiltrate and contribute to the immune suppressive environment  . Together these studies support a role of both IL-10 and TGF-β in suppressing cytotoxic anti-tumor cell responses. In addition to the production of immunosuppressive cytokines, HRS cells also actively attract Th2 and Treg cells. These cells form a physical layer between the HRS cells and cytotoxic cells in the microenvironment and thereby prevent targeting of the HRS cells.
In conclusion, the immune escape and immune suppressive mechanisms that the HRS cells employ are complex and multifaceted and seem to be redundant in providing immune escape strategies for the HRS cells.
5. Concluding remarks
cHL is a malignancy at the crossroads of oncology and immunology. The characteristic tumor cells have gone a long way from small B-cell to the very large atypical and deregulated HRS cells. Because HL arises in a lymph node, the tumor cells and their precursors have to orchestrate the nature and effectivity of the immune cells constantly. This is not only by escaping from anti-tumor immune responses, but also via their critical dependence on the microenvironment for survival. In the development of cHL the tumor cells and the environment have to develop simultaneously and probably the tumor cells acquire tumor-promoting mechanisms in a step-wise manner. It is therefore not surprising that the cross talk between the tumor cells and the reactive infiltrate is very complex and that multiple mechanisms exist. Many of these mechanisms are redundant and therefore specific mechanisms can usually only be found in a subset of cases, making cHL a very heterogeneous disease.
Based on current knowledge it is evident that the microenvironment in cHL is actively shaped and an essential component of the tumor. There is still much to learn about the importance of the microenvironment in malignancies in general and cHL stresses the possible extent of this importance by its highly characteristic phenotype with less than 1% of tumor cells.
Conflict of interest statement
The authors declare that there are no conflicts of interest.
This work was supported by grants from the Abel Tasman Talent Program (ATTP), University Medical Center Groningen and by two grants from the Dutch Cancer Society (KWF: RUG 2009-4313 and RUG 2010-4646).
-  T. Hodgkin. On some morbid appearances of the absorbent glands and spleen. Med Chir Trans. 1832;17:68-114
-  H. Hjalgrim, E.A. Engels. Infectious aetiology of Hodgkin and non-Hodgkin lymphomas: a review of the epidemiological evidence. J Intern Med. 2008;264:537-548 Crossref
-  R. Kuppers, K. Rajewsky, M. Zhao, G. Simons, R. Laumann, R. Fischer, et al. Hodgkin disease: Hodgkin and Reed–Sternberg cells picked from histological sections show clonal immunoglobulin gene rearrangements and appear to be derived from B cells at various stages of development. Proc Natl Acad Sci USA. 1994;91:10962-10966 Crossref
-  H. Kanzler, R. Kuppers, M.L. Hansmann, K. Rajewsky. Hodgkin and Reed–Sternberg cells in Hodgkin's disease represent the outgrowth of a dominant tumor clone derived from (crippled) germinal center B cells. J Exp Med. 1996;184:1495-1505 Crossref
-  C.B. Hertel, X.G. Zhou, S.J. Hamilton-Dutoit, S. Junker. Loss of B cell identity correlates with loss of B cell-specific transcription factors in Hodgkin/Reed–Sternberg cells of classical Hodgkin lymphoma. Oncogene. 2002;21:4908-4920 Crossref
-  I. Schwering, A. Brauninger, U. Klein, B. Jungnickel, M. Tinguely, V. Diehl, et al. Loss of the B-lineage-specific gene expression program in Hodgkin and Reed–Sternberg cells of Hodgkin lymphoma. Blood. 2003;101:1505-1512 Crossref
-  J. Delabie, W.C. Chan, D.D. Weisenburger, C. De Wolf-Peeters. The antigen-presenting cell function of Reed–Sternberg cells. Leuk Lymphoma. 1995;18:35-40 Crossref
-  E. Kilger, A. Kieser, M. Baumann, W. Hammerschmidt. Epstein–Barr virus-mediated B-cell proliferation is dependent upon latent membrane protein 1, which simulates an activated CD40 receptor. EMBO J. 1998;17:1700-1709 Crossref
-  C. Mancao, W. Hammerschmidt. Epstein–Barr virus latent membrane protein 2A is a B-cell receptor mimic and essential for B-cell survival. Blood. 2007;110:3715-3721 Crossref
-  C.S. Morris, A.E. Stuart. Reed–Sternberg/lymphocyte rosette: lymphocyte subpopulations as defined by monoclonal antibodies. J Clin Pathol. 1984;37:767-771 Crossref
-  R. Kuppers, A. Engert, M.L. Hansmann. Hodgkin lymphoma. J Clin Invest. 2012;122:3439-3447 Crossref
-  B. Falini, H. Stein, S. Pileri, S. Canino, R. Farabbi, M.F. Martelli, et al. Expression of lymphoid-associated antigens on Hodgkin's and Reed–Sternberg cells of Hodgkin's disease. An immunocytochemical study on lymph node cytospins using monoclonal antibodies. Histopathology. 1987;11:1229-1242 Crossref
-  A. Pinto, D. Aldinucci, A. Gloghini, V. Zagonel, M. Degan, S. Improta, et al. Human eosinophils express functional CD30 ligand and stimulate proliferation of a Hodgkin's disease cell line. Blood. 1996;88:3299-3305
-  D. Molin, M. Fischer, Z. Xiang, U. Larsson, I. Harvima, P. Venge, et al. Mast cells express functional CD30 ligand and are the predominant CD30L-positive cells in Hodgkin's disease. Br J Haematol. 2001;114:616-623 Crossref
-  R. Horie, T. Watanabe, Y. Morishita, K. Ito, T. Ishida, Y. Kanegae, et al. Ligand-independent signaling by overexpressed CD30 drives NF-kappaB activation in Hodgkin–Reed–Sternberg cells. Oncogene. 2002;21:2493-2503 Crossref
-  M. Watanabe, K. Nakano, T. Togano, M. Nakashima, M. Higashihara, M.E. Kadin, et al. Targeted repression of overexpressed CD30 downregulates NF-kappaB and ERK1/2 pathway in Hodgkin lymphoma cell lines. Oncol Res. 2011;19:463-469 Crossref
-  H.J. Gruss, D. Hirschstein, B. Wright, D. Ulrich, M.A. Caligiuri, M. Barcos, et al. Expression and function of CD40 on Hodgkin and Reed–Sternberg cells and the possible relevance for Hodgkin's disease. Blood. 1994;84:2305-2314
-  A. Carbone, A. Gloghini, H.J. Gruss, A. Pinto. CD40 ligand is constitutively expressed in a subset of T cell lymphomas and on the microenvironmental reactive T cells of follicular lymphomas and Hodgkin's disease. Am J Pathol. 1995;147:912-922
-  C.M. Annunziata, Y.J. Safiran, S.G. Irving, U.N. Kasid, J. Cossman. Hodgkin disease: pharmacologic intervention of the CD40-NF kappa B pathway by a protease inhibitor. Blood. 2000;96:2841-2848
-  A. Carbone, A. Gloghini, V. Gattei, D. Aldinucci, M. Degan, P. De Paoli, et al. Expression of functional CD40 antigen on Reed–Sternberg cells and Hodgkin's disease cell lines. Blood. 1995;85:780-789
-  R.F. Jarrett. Viruses and Hodgkin's lymphoma. Ann Oncol. 2002;13(Suppl. 1):23-29 Crossref
-  H.J. Gruss, D. Ulrich, S. Braddy, R.J. Armitage, S.K. Dower. Recombinant CD30 ligand and CD40 ligand share common biological activities on Hodgkin and Reed–Sternberg cells. Eur J Immunol. 1995;25:2083-2089 Crossref
-  P. Fiumara, V. Snell, Y. Li, A. Mukhopadhyay, M. Younes, A.M. Gillenwater, et al. Functional expression of receptor activator of nuclear factor kappaB in Hodgkin disease cell lines. Blood. 2001;98:2784-2790 Crossref
-  B. Ryffel, M. Brockhaus, U. Durmuller, F. Gudat. Tumor necrosis factor receptors in lymphoid tissues and lymphomas. Source and site of action of tumor necrosis factor alpha. Am J Pathol. 1991;139:7-15
-  H.J. Gruss, S.K. Dower. Tumor necrosis factor ligand superfamily: involvement in the pathology of malignant lymphomas. Blood. 1995;85:3378-3404
-  S.S. Metkar, K.N. Naresh, A.A. Redkar, C.S. Soman, S.H. Advani, J.J. Nadkarni. Expression of Fas and Fas ligand in Hodgkin's disease. Leuk Lymphoma. 1999;33:521-530
-  W.T. Ho, W.L. Pang, S.M. Chong, A. Castella, S. Al-Salam, T.E. Tan, et al. Expression of CD137 on Hodgkin and Reed–Sternberg cells inhibits T-cell activation by eliminating CD137 ligand expression. Cancer Res. 2013;73:652-661 Crossref
-  C. Renne, K. Willenbrock, R. Kuppers, M.L. Hansmann, A. Brauninger. Autocrine- and paracrine-activated receptor tyrosine kinases in classic Hodgkin lymphoma. Blood. 2005;105:4051-4059 Crossref
-  L. Teofili, A.L. Di Febo, F. Pierconti, N. Maggiano, M. Bendandi, S. Rutella, et al. Expression of the c-met proto-oncogene and its ligand, hepatocyte growth factor, in Hodgkin disease. Blood. 2001;97:1063-1069 Crossref
-  C. Xu, W. Plattel, A. van den Berg, N. Ruther, X. Huang, M. Wang, et al. Expression of the c-Met oncogene by tumor cells predicts a favorable outcome in classical Hodgkin's lymphoma. Haematologica. 2012;97:572-578 Crossref
-  F. Jundt, I. Anagnostopoulos, R. Forster, S. Mathas, H. Stein, B. Dorken. Activated Notch1 signaling promotes tumor cell proliferation and survival in Hodgkin and anaplastic large cell lymphoma. Blood. 2002;99:3398-3403 Crossref
-  R. Schwarzer, B. Dorken, F. Jundt. Notch is an essential upstream regulator of NF-kappaB and is relevant for survival of Hodgkin and Reed–Sternberg cells. Leukemia. 2011;26:806-813
-  D. Aldinucci, V. Gattei. The role of interleukin-3 and stem cell factor in classical Hodgkin disease. Blood. 2003;101:376-377
-  H.J. Gruss, M.A. Brach, H.G. Drexler, K.J. Bross, F. Herrmann. Interleukin 9 is expressed by primary and cultured Hodgkin and Reed–Sternberg cells. Cancer Res. 1992;52:1026-1031
-  U. Kapp, W.C. Yeh, B. Patterson, A.J. Elia, D. Kagi, A. Ho, et al. Interleukin 13 is secreted by and stimulates the growth of Hodgkin and Reed–Sternberg cells. J Exp Med. 1999;189:1939-1946 Crossref
-  B.F. Skinnider, U. Kapp, T.W. Mak. The role of interleukin 13 in classical Hodgkin lymphoma. Leuk Lymphoma. 2002;43:1203-1210 Crossref
-  H.D. Foss, M. Hummel, S. Gottstein, K. Ziemann, B. Falini, H. Herbst, et al. Frequent expression of IL-7 gene transcripts in tumor cells of classical Hodgkin's disease. Am J Pathol. 1995;146:33-39
-  L. Cattaruzza, A. Gloghini, K. Olivo, R. Di Francia, D. Lorenzon, R. De Filippi, et al. Functional coexpression of interleukin (IL)-7 and its receptor (IL-7R) on Hodgkin and Reed–Sternberg cells: involvement of IL-7 in tumor cell growth and microenvironmental interactions of Hodgkin's lymphoma. Int J Cancer. 2009;125:1092-1101 Crossref
-  D. Aldinucci, D. Lorenzon, L. Cattaruzza, A. Pinto, A. Gloghini, A. Carbone, et al. Expression of CCR5 receptors on Reed–Sternberg cells and Hodgkin lymphoma cell lines: involvement of CCL5/Rantes in tumor cell growth and microenvironmental interactions. Int J Cancer. 2008;122:769-776 Crossref
-  C. Buri, M. Korner, P. Scharli, D. Cefai, M. Uguccioni, C. Mueller, et al. CC chemokines and the receptors CCR3 and CCR5 are differentially expressed in the nonneoplastic leukocytic infiltrates of Hodgkin disease. Blood. 2001;97:1543-1548 Crossref
-  S. Poppema. Immunology of Hodgkin's disease. Baillieres Clin Haematol. 1996;9:447-457 Crossref
-  S. Schreck, D. Friebel, M. Buettner, L. Distel, G. Grabenbauer, L.S. Young, et al. Prognostic impact of tumour-infiltrating Th2 and regulatory T cells in classical Hodgkin lymphoma. Hematol Oncol. 2009;27:31-39 Crossref
-  Y. Ma, L. Visser, T. Blokzijl, G. Harms, C. Atayar, S. Poppema, et al. The CD4+CD26− T-cell population in classical Hodgkin's lymphoma displays a distinctive regulatory T-cell profile. Lab Invest. 2008;88:482-490
-  E. Maggio, A. van den Berg, A. Diepstra, J. Kluiver, L. Visser, S. Poppema. Chemokines, cytokines and their receptors in Hodgkin's lymphoma cell lines and tissues. Ann Oncol. 2002;13(Suppl 1):52-56 Crossref
-  A. van den Berg, L. Visser, S. Poppema. High expression of the CC chemokine TARC in Reed–Sternberg cells. A possible explanation for the characteristic T-cell infiltratein Hodgkin's lymphoma. Am J Pathol. 1999;154:1685-1691 Crossref
-  W.J. Plattel, A. van den Berg, L. Visser, A.M. van der Graaf, J. Pruim, H. Vos, et al. Plasma thymus and activation-regulated chemokine as an early response marker in classical Hodgkin's lymphoma. Haematologica. 2011;97:410-415
-  S.C. Peh, L.H. Kim, S. Poppema. TARC, a CC chemokine, is frequently expressed in classic Hodgkin's lymphoma but not in NLP Hodgkin's lymphoma, T-cell-rich B-cell lymphoma, and most cases of anaplastic large cell lymphoma. Am J Surg Pathol. 2001;25:925-929 Crossref
-  C.V. Hedvat, E.S. Jaffe, J. Qin, D.A. Filippa, C. Cordon-Cardo, G. Tosato, et al. Macrophage-derived chemokine expression in classical Hodgkin's lymphoma: application of tissue microarrays. Mod Pathol. 2001;14:1270-1276 Crossref
-  E.M. Maggio, A. Van Den Berg, L. Visser, A. Diepstra, J. Kluiver, R. Emmens, et al. Common and differential chemokine expression patterns in rs cells of NLP, EBV positive and negative classical Hodgkin lymphomas. Int J Cancer. 2002;99:665-672 Crossref
-  T. Ishida, T. Ishii, A. Inagaki, H. Yano, H. Komatsu, S. Iida, et al. Specific recruitment of CC chemokine receptor 4-positive regulatory T cells in Hodgkin lymphoma fosters immune privilege. Cancer Res. 2006;66:5716-5722 Crossref
-  K.R. Baumforth, A. Birgersdotter, G.M. Reynolds, W. Wei, G. Kapatai, J.R. Flavell, et al. Expression of the Epstein–Barr virus-encoded Epstein–Barr virus nuclear antigen 1 in Hodgkin's lymphoma cells mediates up-regulation of CCL20 and the migration of regulatory T cells. Am J Pathol. 2008;173:195-204 Crossref
-  B. Lamprecht, S. Kreher, I. Anagnostopoulos, K. Johrens, G. Monteleone, F. Jundt, et al. Aberrant expression of the Th2 cytokine IL-21 in Hodgkin lymphoma cells regulates STAT3 signaling and attracts Treg cells via regulation of MIP-3alpha. Blood. 2008;112:3339-3347 Crossref
-  S.D. Hudnall, E. Betancourt, E. Barnhart, J. Patel. Comparative flow immunophenotypic features of the inflammatory infiltrates of Hodgkin lymphoma and lymphoid hyperplasia. Cytometry B Clin Cytom. 2008;74:1-8
-  N.A. Marshall, D.J. Culligan, J. Tighe, P.W. Johnston, R.N. Barker, M.A. Vickers. The relationships between Epstein–Barr virus latent membrane protein 1 and regulatory T cells in Hodgkin's lymphoma. Exp Hematol. 2007;35:596-604 Crossref
-  J. Teruya-Feldstein, G. Tosato, E.S. Jaffe. The role of chemokines in Hodgkin's disease. Leuk Lymphoma. 2000;38:363-371 Crossref
-  K. Ohshima, K. Karube, M. Hamasaki, T. Tutiya, T. Yamaguchi, H. Suefuji, et al. Differential chemokine, chemokine receptor and cytokine expression in Epstein–Barr virus-associated lymphoproliferative diseases. Leuk Lymphoma. 2003;44:1367-1378 Crossref
-  K. Ohshima, T. Tutiya, T. Yamaguchi, K. Suzuki, J. Suzumiya, C. Kawasaki, et al. Infiltration of Th1 and Th2 lymphocytes around Hodgkin and Reed–Sternberg (H&RS) cells in Hodgkin disease: relation with expression of CXC and CC chemokines on H&RS cells. Int J Cancer. 2002;98:567-572 Crossref
-  M. Teichmann, B. Meyer, A. Beck, G. Niedobitek. Expression of the interferon-inducible chemokine IP-10 (CXCL10), a chemokine with proposed anti-neoplastic functions, in Hodgkin lymphoma and nasopharyngeal carcinoma. J Pathol. 2005;206:68-75 Crossref
-  J.J. Oudejans, N.M. Jiwa, J.A. Kummer, A. Horstman, W. Vos, J.P. Baak, et al. Analysis of major histocompatibility complex class I expression on Reed–Sternberg cells in relation to the cytotoxic T-cell response in Epstein–Barr virus-positive and -negative Hodgkin's disease. Blood. 1996;87:3844-3851
-  H. Hanamoto, T. Nakayama, H. Miyazato, S. Takegawa, K. Hieshima, Y. Tatsumi, et al. Expression of CCL28 by Reed–Sternberg cells defines a major subtype of classical Hodgkin's disease with frequent infiltration of eosinophils and/or plasma cells. Am J Pathol. 2004;164:997-1006 Crossref
-  M. Fischer, M. Juremalm, N. Olsson, C. Backlin, C. Sundstrom, K. Nilsson, et al. Expression of CCL5/RANTES by Hodgkin and Reed–Sternberg cells and its possible role in the recruitment of mast cells into lymphomatous tissue. Int J Cancer. 2003;107:197-201 Crossref
-  F. Liu, Y. Zhang, Z.Q. Wu, T. Zhao. Analysis of CCL5 expression in classical Hodgkin's lymphoma L428 cell line. Mol Med Rep. 2011;4:837-841
-  F. Jundt, I. Anagnostopoulos, K. Bommert, F. Emmerich, G. Muller, H.D. Foss, et al. Hodgkin/Reed–Sternberg cells induce fibroblasts to secrete eotaxin, a potent chemoattractant for T cells and eosinophils. Blood. 1999;94:2065-2071
-  H. Heath, S. Qin, P. Rao, L. Wu, G. LaRosa, N. Kassam, et al. Chemokine receptor usage by human eosinophils. The importance of CCR3 demonstrated using an antagonistic monoclonal antibody. J Clin Invest. 1997;99:178-184 Crossref
-  H.D. Foss, H. Herbst, S. Gottstein, G. Demel, I. Araujo, H. Stein. Interleukin-8 in Hodgkin's disease. Preferential expression by reactive cells and association with neutrophil density. Am J Pathol. 1996;148:1229-1236
-  M. Wolf, S. Albrecht, C. Marki. Proteolytic processing of chemokines: implications in physiological and pathological conditions. Int J Biochem Cell Biol. 2008;40:1185-1198 Crossref
-  M.A. Zaki, N. Wada, J. Ikeda, H. Shibayama, K. Hashimoto, T. Yamagami, et al. Prognostic implication of types of tumor-associated macrophages in Hodgkin lymphoma. Virchows Arch. 2011;459:361-366 Crossref
-  Y. Ma, L. Visser, H. Roelofsen, M. de Vries, A. Diepstra, G. van Imhoff, et al. Proteomics analysis of Hodgkin lymphoma: identification of new players involved in the cross-talk between HRS cells and infiltrating lymphocytes. Blood. 2008;111:2339-2346 Crossref
-  K. Yaddanapudi, K. Putty, B.E. Rendon, G.J. Lamont, J.D. Faughn, A. Satoskar, et al. Control of tumor-associated macrophage alternative activation by macrophage migration inhibitory factor. J Immunol. 2013;190:2984-2993 Crossref
-  S. Choi, H.R. Kim, L. Leng, I. Kang, W.L. Jorgensen, C.S. Cho, et al. Role of macrophage migration inhibitory factor in the regulatory T cell response of tumor-bearing mice. J Immunol. 2012;189:3905-3913 Crossref
-  P. Juszczynski, J. Ouyang, S. Monti, S.J. Rodig, K. Takeyama, J. Abramson, et al. The AP1-dependent secretion of galectin-1 by Reed Sternberg cells fosters immune privilege in classical Hodgkin lymphoma. Proc Natl Acad Sci USA. 2007;104:13134-13139 Crossref
-  T. Tanijiri, T. Shimizu, K. Uehira, T. Yokoi, H. Amuro, H. Sugimoto, et al. Hodgkin's Reed–Sternberg cell line (KM-H2) promotes a bidirectional differentiation of CD4+CD25+Foxp3+ T cells and CD4+ cytotoxic T lymphocytes from CD4+ naive T cells. J Leukoc Biol. 2007;82:576-584 Crossref
-  M. Samoszuk, L. Nansen. Detection of interleukin-5 messenger RNA in Reed–Sternberg cells of Hodgkin's disease with eosinophilia. Blood. 1990;75:13-16
-  I. Glimelius, A. Edstrom, R.M. Amini, M. Fischer, G. Nilsson, C. Sundstrom, et al. IL-9 expression contributes to the cellular composition in Hodgkin lymphoma. Eur J Haematol. 2006;76:278-283 Crossref
-  H. Mizuno, T. Nakayama, Y. Miyata, S. Saito, S. Nishiwaki, N. Nakao, et al. Mast cells promote the growth of Hodgkin's lymphoma cell tumor by modifying the tumor microenvironment that can be perturbed by bortezomib. Leukemia. 2012;26:2269-2276 Crossref
-  P. Meij, A. Leen, A.B. Rickinson, S. Verkoeijen, M.B. Vervoort, E. Bloemena, et al. Identification and prevalence of CD8(+) T-cell responses directed against Epstein–Barr virus-encoded latent membrane protein 1 and latent membrane protein 2. Int J Cancer. 2002;99:93-99 Crossref
-  A.L. Chapman, A.B. Rickinson, W.A. Thomas, R.F. Jarrett, J. Crocker, S.P. Lee. Epstein–Barr virus-specific cytotoxic T lymphocyte responses in the blood and tumor site of Hodgkin's disease patients: implications for a T-cell-based therapy. Cancer Res. 2001;61:6219-6226
-  H. Chambost, N. Van Baren, F. Brasseur, D. Godelaine, L. Xerri, S.J. Landi, et al. Expression of gene MAGE-A4 in Reed–Sternberg cells. Blood. 2000;95:3530-3533
-  C.R. Cruz, U. Gerdemann, A.M. Leen, J.A. Shafer, S. Ku, B. Tzou, et al. Improving T-cell therapy for relapsed EBV-negative Hodgkin lymphoma by targeting upregulated MAGE-A4. Clin Cancer Res. 2011;17:7058-7066 Crossref
-  A. Diepstra, G.W. van Imhoff, H.E. Karim-Kos, A. van den Berg, G.J. te Meerman, M. Niens, et al. HLA class II expression by Hodgkin Reed–Sternberg cells is an independent prognostic factor in classical Hodgkin's lymphoma. J Clin Oncol. 2007;25:3101-3108 Crossref
-  C. Steidl, S.P. Shah, B.W. Woolcock, L. Rui, M. Kawahara, P. Farinha, et al. MHC class II transactivator CIITA is a recurrent gene fusion partner in lymphoid cancers. Nature. 2011;471:377-381 Crossref
-  A. Diepstra, M. Niens, E. Vellenga, G.W. van Imhoff, I.M. Nolte, M. Schaapveld, et al. Association with HLA class I in Epstein–Barr-virus-positive and with HLA class III in Epstein–Barr-virus-negative Hodgkin's lymphoma. Lancet. 2005;365:2216-2224 Crossref
-  M. Niens, R.F. Jarrett, B. Hepkema, I.M. Nolte, A. Diepstra, M. Platteel, et al. HLA-A*02 is associated with a reduced risk and HLA-A*01 with an increased risk of developing EBV+ Hodgkin lymphoma. Blood. 2007;110:3310-3315 Crossref
-  H. Hjalgrim, K. Rostgaard, P.C. Johnson, A. Lake, L. Shield, A.M. Little, et al. HLA-A alleles and infectious mononucleosis suggest a critical role for cytotoxic T-cell response in EBV-related Hodgkin lymphoma. Proc Natl Acad Sci USA. 2010;107:6400-6405 Crossref
-  S.P. Lee, R.J. Tierney, W.A. Thomas, J.M. Brooks, A.B. Rickinson. Conserved CTL epitopes within EBV latent membrane protein 2: a potential target for CTL-based tumor therapy. J Immunol. 1997;158:3325-3334
-  J. Bukur, S. Jasinski, B. Seliger. The role of classical and non-classical HLA class I antigens in human tumors. Semin Cancer Biol. 2012;22:350-358 Crossref
-  J. Wischhusen, A. Waschbisch, H. Wiendl. Immune-refractory cancers and their little helpers—an extended role for immunetolerogenic MHC molecules HLA-G and HLA-E. Semin Cancer Biol. 2007;17:459-468 Crossref
-  A. Diepstra, S. Poppema, M. Boot, L. Visser, I.M. Nolte, M. Niens, et al. HLA-G protein expression as a potential immune escape mechanism in classical Hodgkin's lymphoma. Tissue Antigens. 2008;71:219-226 Crossref
-  L. Kren, P. Fabian, O. Slaby, A. Janikova, O. Soucek, J. Sterba, et al. Multifunctional immune-modulatory protein HLA-E identified in classical Hodgkin lymphoma: possible implications. Pathol Res Pract. 2011;208:45-49
-  M.R. Zocchi, S. Catellani, P. Canevali, S. Tavella, A. Garuti, B. Villaggio, et al. High ERp5/ADAM10 expression in lymph node microenvironment and impaired NKG2D ligands recognition in Hodgkin lymphomas. Blood. 2012;119:1479-1489 Crossref
-  D. Re, A. Hofmann, J. Wolf, V. Diehl, A. Staratschek-Jox. Cultivated H-RS cells are resistant to CD95L-mediated apoptosis despite expression of wild-type CD95. Exp Hematol. 2000;28:31-35 Crossref
-  S. Mathas, A. Lietz, I. Anagnostopoulos, F. Hummel, B. Wiesner, M. Janz, et al. c-FLIP mediates resistance of Hodgkin/Reed–Sternberg cells to death receptor-induced apoptosis. J Exp Med. 2004;199:1041-1052 Crossref
-  E.M. Maggio, A. Van Den Berg, D. de Jong, A. Diepstra, S. Poppema. Low frequency of FAS mutations in Reed–Sternberg cells of Hodgkin's lymphoma. Am J Pathol. 2003;162:29-35 Crossref
-  S. Muenst, S. Hoeller, S. Dirnhofer, A. Tzankov. Increased programmed death-1+ tumor-infiltrating lymphocytes in classical Hodgkin lymphoma substantiate reduced overall survival. Hum Pathol. 2009;40:1715-1722 Crossref
-  R. Yamamoto, M. Nishikori, T. Kitawaki, T. Sakai, M. Hishizawa, M. Tashima, et al. PD-1–PD-1 ligand interaction contributes to immunosuppressive microenvironment of Hodgkin lymphoma. Blood. 2008;111:3220-3224 Crossref
-  M.R. Green, S. Monti, S.J. Rodig, P. Juszczynski, T. Currie, E. O’Donnell, et al. Integrative analysis reveals selective 9p24.1 amplification, increased PD-1 ligand expression, and further induction via JAK2 in nodular sclerosing Hodgkin lymphoma and primary mediastinal large B-cell lymphoma. Blood. 2010;116:3268-3277 Crossref
-  M.K. Gandhi, G. Moll, C. Smith, U. Dua, E. Lambley, O. Ramuz, et al. Galectin-1 mediated suppression of Epstein–Barr virus specific T-cell immunity in classic Hodgkin lymphoma. Blood. 2007;110:1326-1329 Crossref
-  J. Schwaller, A. Tobler, G. Niklaus, N. Hurwitz, I. Hennig, M.F. Fey, et al. Interleukin-12 expression in human lymphomas and nonneoplastic lymphoid disorders. Blood. 1995;85:2182-2188
-  G. Niedobitek, D. Pazolt, M. Teichmann, O. Devergne. Frequent expression of the Epstein–Barr virus (EBV)-induced gene, EBI3, an IL-12 p40-related cytokine, in Hodgkin and Reed–Sternberg cells. J Pathol. 2002;198:310-316 Crossref
-  M.E. Kadin, B.A. Agnarsson, L.R. Ellingsworth, S.R. Newcom. Immunohistochemical evidence of a role for transforming growth factor beta in the pathogenesis of nodular sclerosing Hodgkin's disease. Am J Pathol. 1990;136:1209-1214
-  S.R. Newcom, L. Gu. Transforming growth factor beta 1 messenger RNA in Reed–Sternberg cells in nodular sclerosing Hodgkin's disease. J Clin Pathol. 1995;48:160-163 Crossref
-  S.R. Newcom, M.E. Kadin, A.A. Ansari, V. Diehl. L-428 nodular sclerosing Hodgkin's cell secretes a unique transforming growth factor-beta active at physiologic pH. J Clin Invest. 1988;82:1915-1921 Crossref
-  S.R. Newcom, K.K. Tagra. High molecular weight transforming growth factor beta is excreted in the urine in active nodular sclerosing Hodgkin's disease. Cancer Res. 1992;52:6768-6773
-  J.M. Chemnitz, D. Eggle, J. Driesen, S. Classen, J.L. Riley, S. Debey-Pascher, et al. RNA fingerprints provide direct evidence for the inhibitory role of TGFbeta and PD-1 on CD4+ T cells in Hodgkin lymphoma. Blood. 2007;110:3226-3233 Crossref
-  H. Herbst, H.D. Foss, J. Samol, I. Araujo, H. Klotzbach, H. Krause, et al. Frequent expression of interleukin-10 by Epstein–Barr virus-harboring tumor cells of Hodgkin's disease. Blood. 1996;87:2918-2929
-  D.F. Dukers, L.H. Jaspars, W. Vos, J.J. Oudejans, D. Hayes, S. Cillessen, et al. Quantitative immunohistochemical analysis of cytokine profiles in Epstein–Barr virus-positive and -negative cases of Hodgkin's disease. J Pathol. 2000;190:143-149 Crossref
-  N.A. Marshall, L.E. Christie, L.R. Munro, D.J. Culligan, P.W. Johnston, R.N. Barker, et al. Immunosuppressive regulatory T cells are abundant in the reactive lymphocytes of Hodgkin lymphoma. Blood. 2004;103:1755-1762 Crossref
Department of Pathology & Medical Biology, University of Groningen, University Medical Center Groningen, Netherlands
Corresponding author at: Department of Pathology & Medical Biology, University Medical Center Groningen, Hanzeplein 1, P.O. Box 30.001, 9700 RB Groningen, Netherlands. Tel.: +31 50 3611476; fax: +31 50 3619107.
1 These authors contributed equally.
© 2013 Elsevier Ltd, All rights reserved.