Origin and pathogenesis of nodular lymphocyte-predominant Hodgkin lymphoma as revealed by global gene expression analysis

Arginine Methyltransferases Are Regulated by Epstein-Barr Virus in B Cells and Are Differentially Expressed in Hodgkin's Lymphoma

Although there is increasing evidence that aberrant expression of those enzymes which control protein arginine methylation contribute to carcinogenesis, their de-regulation by oncogenic viruses in primary cells has yet to be reported. We first show that the protein arginine methyltransferases, CARM1, PRMT1 and PRMT5 are strongly expressed in Hodgkin Reed-Sternberg (HRS) cells, and up-regulated in Hodgkin's lymphoma (HL) cell lines. Given that Epstein-Barr virus (EBV) can be detected in approximately 50% of primary HL, we next examined how EBV infection of germinal centre (GC) B cells, the presumptive precursors of HRS cells, modulated the expression of these proteins. EBV infection of GC B cells was followed by the up-regulation of CARM1, PRMT1 and PRMT5, and by the down-regulation of the arginine deiminase, PADI4. Latent membrane protein 1 (LMP1), the major EBV transforming gene was shown to induce PRMT1 in GC B cells and in a stably transfected B cell line. The recent development of compounds which inhibit PRMT-mediated reactions provides a compelling case for continuing to dissect the contribution of virus induced changes in these proteins to lymphomagenesis.

Gene expression profiling of microdissected Hodgkin Reed-Sternberg cells correlates with treatment outcome in classical Hodgkin lymphoma

In classical Hodgkin lymphoma (CHL), 20%-30% of patients experience relapse or progressive disease after initial treatment. The pathogenesis and biology of treatment failure are still poorly understood, in part because the molecular phenotype of the rare malignant Hodgkin Reed-Sternberg (HRS) cells is difficult to study. Here we examined microdissected HRS cells from 29 CHL patients and 5 CHL-derived cell lines by gene expression profiling. We found significant overlap of HL-specific gene expression in primary HRS cells and HL cell lines, but also differences, including surface receptor signaling pathways. Using integrative analysis tools, we identified target genes with expression levels that significantly correlated with genomic copy-number changes in primary HRS cells. Furthermore, we found a macrophage-like signature in HRS cells that significantly correlated with treatment failure. CSF1R is a representative of this signature, and its expression was significantly associated with progression-free and overall survival in an independent set of 132 patients assessed by mRNA in situ hybridization. A combined score of CSF1R in situ hybridization and CD68 immunohistochemistry was an independent predictor for progression-free survival in multivariate analysis. In summary, our data reveal novel insights into the pathobiology of treatment failure and suggest CSF1R as a drug target of at-risk CHL.

Pathogenetic importance and therapeutic implications of NF-κB in lymphoid malignancies

Derangement of the nuclear factor κB (NF-κB) pathway initiates and/or sustains many types of human cancer. B-cell malignancies are particularly affected by oncogenic mutations, translocations, and copy number alterations affecting key components the NF-κB pathway, most likely owing to the pervasive role of this pathway in normal B cells. These genetic aberrations cause tumors to be 'addicted' to NF-κB, which can be exploited therapeutically. Since each subtype of lymphoid cancer utilizes different mechanisms to activate NF-κB, several different therapeutic strategies are needed to address this pathogenetic heterogeneity. Fortunately, a number of drugs that block signaling cascades leading to NF-κB are in early phase clinical trials, several of which are already showing activity in lymphoid malignancies.

Vitamin D3 receptor is highly expressed in Hodgkin's lymphoma

Background

Hodgkin lymphoma (HL) is one of the most frequent lymphoma in the western world. Despite a good overall prognosis, some patients suffer relapsing tumors which are difficult to cure. Over a long period Vitamin D has been shown to be a potential treatment for cancer. Vitamin D acts via the vitamin D receptor, a nuclear receptor, acting as an inducible transcription factor. We aimed to investigate the expression of vitamin D receptor as a possible diagnostic marker and potential therapeutic target in HL as well as in B-cell derived non-Hodgkin lymphoma (B-NHL).

Methods

We used a panel of 193 formalin fixed tissues of lymphoma cases consisting of 55 cases of HL and 138 cases on several B-NHL entities.

Results

Vitamin D receptor is strongly expressed in tumor cells of HL, regardless of the sub entity with an overall positivity of 80% of all HL cases. In contrast, only about 17% of the analyzed origin-NHL showed positivity for vitamin D receptor. The detection of nuclear localization of vitamin D receptor in the tumor cells of HL suggests activated status of the vitamin D receptor.

Conclusions

Our study suggests VDR as a specific marker for tumor cells of HL, but not of B-NHL subtypes. Further, the observed nuclear localization suggests an activated receptor status in tumor cells of HL. Further investigations of mutational status and functional studies may shed some light in functional relevance of vitamin D receptor signaling in HL.

Genetic lesions of the TRAF3 and MAP3K14 genes in classical Hodgkin lymphoma

Hodgkin and Reed/Sternberg (HRS) cells in classical Hodgkin lymphoma (cHL) show constitutive activation of nuclear factor (NF)-κB. Several genetic lesions contribute to this deregulated NF-κB activity. Here, we analysed two further NF-κB regulators for genetic lesions, the inhibitory factor TRAF3 and the key signalling component of the alternative NF-κB pathway, MAP3K14 (NIK). Single nucleotide polymorphism (SNP) array analysis of cHL cell lines revealed a uniparental disomy of the long arm of chromosome 14 associated with a biallelic deletion of TRAF3 located on this chromosome in cell line U-HO1. Cloning of the deletion breakpoint showed a 123 371 bp deletion. No inactivating mutations of TRAF3 were found in six other cHL cell lines or in microdissected HRS cells from seven cHL. However, in primary cHL samples interphase cytogenetic analyses revealed signal patterns indicating monoallelic deletion of TRAF3 in 3/20 other cases. SNP array analysis revealed a gain of copy number for MAP3K14 in three cHL cell lines. Gains of MAP3K14 were detected in 5/16 cases of primary cHL. In conclusion, in rare instances, HRS cells harbour inactivating mutations of the TRAF3 gene and recurrently show gains of MAP3K14, indicating that more components of NF-κB signalling show genetic lesions in HRS cells than previously known.

Rule-based induction method for haplotype comparison and identification of candidate disease loci

There is a need for methods that are able to identify rare variants that cause low or moderate penetrance disease susceptibility. To answer this need, we introduce a rule-based haplotype comparison method, Haplous, which identifies haplotypes within multiple samples from phased genotype data and compares them within and between sample groups. We demonstrate that Haplous is able to accurately identify haplotypes that are identical by descent, exclude common haplotypes in the studied population and select rare haplotypes from the data. Our analysis of three families with multiple individuals affected by lymphoma identified several interesting haplotypes shared by distantly related patients.

Constitutive AP-1 activity and EBV infection induce PD-L1 in Hodgkin lymphomas and posttransplant lymphoproliferative disorders: implications for targeted therapy

PURPOSE

Programmed cell death ligand 1 (PD-L1) is a molecule expressed on antigen-presenting cells that engages the PD-1 receptor on T cells and inhibits T-cell receptor signaling. The PD-1 axis can be exploited by tumor cells to dampen host antitumor immune responses and foster tumor cell survival. PD-1 blockade has shown promise in multiple malignancies but should be directed toward patients in whom it will be most effective. In recent studies, we found that the chromosome 9p24.1 amplification increased the gene dosage of PD-L1 and its induction by JAK2 in a subset of patients with classical Hodgkin lymphoma (cHL). However, cHLs with normal 9p24.1 copy numbers also expressed detectable PD-L1, prompting analyses of additional PD-L1 regulatory mechanisms.

EXPERIMENTAL DESIGN

Herein, we utilized immunohistochemical, genomic, and functional analyses to define alternative mechanisms of PD-L1 activation in cHL and additional EBV(+) lymphoproliferative disorders.

RESULTS

We identified an AP-1-responsive enhancer in the PD-L1 gene. In cHL Reed-Sternberg cells, which exhibit constitutive AP-1 activation, the PD-L1 enhancer binds AP-1 components and increases PD-L1 promoter activity. In addition, we defined Epstein-Barr virus (EBV) infection as an alternative mechanism for PD-L1 induction in cHLs with diploid 9p24.1. PD-L1 was also expressed by EBV-transformed lymphoblastoid cell lines as a result of latent membrane protein 1-mediated, JAK/STAT-dependent promoter and AP-1-associated enhancer activity. In addition, more than 70% of EBV(+) posttransplant lymphoproliferative disorders expressed detectable PD-L1.

CONCLUSIONS

AP-1 signaling and EBV infection represent alternative mechanisms of PD-L1 induction and extend the spectrum of tumors in which to consider PD-1 blockade.

"Intrafollicular neoplasia" of nodular lymphocyte predominant Hodgkin lymphoma: description of a hypothetic early step of the disease

The 2008 WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues has addressed the problem of intrafollicular neoplasia/"in situ" lesion for follicular lymphoma. The concept of intrafollicular neoplasia has also been proposed for other lymphomas in which the putative normal counterpart of the tumor cell is located in the germinal center or the mantle zone or the marginal zone of the follicle. However, unlike in situ follicular lymphoma, the precise histologic definition of this early lesion for other lymphomas is still lacking. When applied to nodular lymphocyte predominant Hodgkin lymphoma, another germinal center-derived lymphoma, "intrafollicular neoplasia" may be regarded as a neoplasia at an early stage of development, such as in situ follicular lymphoma. Interestingly, this early lesion can be observed in lymph nodes that otherwise show the most common nodular involvement by nodular lymphocyte predominant Hodgkin lymphoma. The recognition of intrafollicular neoplasia is based on the identification of typical, strongly stained BCL6+, lymphocyte predominant tumor cells located within altered follicles with a recognizable germinal center. Lymphocyte predominant tumor cells, surrounded by rosetting PD1+ T cells, reside in an environment reminiscent of a secondary follicle. Intrafollicular neoplasia in nodular lymphocyte predominant Hodgkin lymphoma is correctly identifiable based on immunohistochemical recognition of the CD23+ meshwork of follicular dendritic cells surrounded by an outer zone containing immunoglobulin D+ B cells. This immunoarchitectural pattern, highlighting the intrafollicular involvement by the neoplasia, is of great utility for diagnosis. An appropriate immunohistochemical characterization for diagnosis should include lymphocyte predominant (BCL6 and CD20) and microenvironmental (CD23, immunoglobulin D, and PD1) cell markers.

T cell/histiocyte-rich large B-cell lymphoma: an update on its biology and classification

T cell/histiocyte-rich large B-cell lymphoma (THRLBCL), originally considered an uncommon variant of Diffuse Large B-Cell Lymphoma (DLBCL), is recognized by the World Health Organisation as a separate clinicopathological entity since 2008. It predominantly affects middle aged men often presenting with advanced stage disease frequently involving spleen, liver and bone marrow at time of diagnosis. According to the WHO, this lymphoma is morphologically characterized by less than 10% of large neoplastic B cells in a background of abundant T cells and frequently histiocytes. Differentiating THRLBCL from other lymphoproliferative disorders such as Nodular Lymphocyte Predominant Hodgkin Lymphoma (NLPHL) and Lymphocyte-Rich classical Hodgkin lymphoma (LRcHL) is important from a clinical point of view and can be achieved in most cases, given adequate biopsy specimens, by careful morphological and immunohistochemical evaluation of both the neoplastic cells as well as the nonneoplastic stromal component. According to this WHO definition, THRLBCL is still considered a clinically heterogeneous entity, though it is noted that especially the cases containing numerous histiocytes behave aggressively and show resistance to current therapies for DLBCL. Gene expression profiling studies of THRLBCL provided evidence for a prominent role for this histiocytic component that is important for a tolerogenic host immune response in which they may assist neoplastic cells in escaping the T cell-mediated immune surveillance. Therefore, reserving the diagnosis of THRLBCL to cases containing a large proportion of histiocytes might be relevant, as modulating their activity could provide new therapeutic options.

Epigenetic and transcriptional changes which follow Epstein-Barr virus infection of germinal center B cells and their relevance to the pathogenesis of Hodgkin's lymphoma

Although Epstein-Barr virus (EBV) usually establishes an asymptomatic lifelong infection, it is also implicated in the development of germinal center (GC) B-cell-derived malignancies, including Hodgkin's lymphoma (HL). Following primary infection, EBV remains latent in the memory B-cell population, where host-driven methylation of viral DNA contributes to the repression of viral gene expression. However, it is still unclear how EBV harnesses the cell's methylation machinery in B cells, how this contributes to viral persistence, and what impact this has on the methylation of cellular genes. We show that EBV infection of GC B cells is followed by upregulation of the DNA methyltransferase DNMT3A and downregulation of DNMT3B and DNMT1. We show that the EBV latent membrane protein 1 (LMP1) oncogene downregulates DNMT1 and that DNMT3A binds to the viral promoter Wp. Genome-wide promoter arrays performed with these cells showed that EBV-associated methylation changes in cellular genes were not randomly distributed across the genome but clustered at chromosomal locations, consistent with an instructive pattern of methylation, and were in part determined by promoter CpG content. Both DNMT3B and DNMT1 were downregulated and DNMT3A was upregulated in HL cell lines, recapitulating the pattern of expression observed following EBV infection of GC B cells. We also found, by using gene expression profiling, that genes differentially expressed following EBV infection of GC B cells were significantly enriched for those reported to be differentially expressed in HL. These observations suggest that EBV-infected GC B cells are a useful model for studying virus-associated changes contributing to the pathogenesis of HL.

Repression of the RHOH gene by JunD

RhoH is a member of the Rho family of small GTP-binding proteins that lacks GTPase activity. Since RhoH is constantly bound by GTP, it is thought to be constitutively active and controlled predominantly by changes in quantitative expression. RhoH is produced specifically in haematopoietic cells and aberrant expression has been linked to various forms of leukaemia. Transcription of the RHOH gene is the first level at which the quantitative levels of the RhoH protein are regulated. Previous studies have demonstrated that RHOH gene transcription is initiated by three distinct promoter regions designated P1, P2 and P3 that define the 5' end of exons 1, 2 and 4 respectively. In the present study we report that the P3 promoter is largely responsible for RHOH gene transcription in the B-lymphocytic cell line Raji. The P3 promoter contains a minimal promoter region and a repressor region extending from -236 to +67 and +68 to +245 respectively, relative to the 5' end of exon 4. Chromatin immunoprecipitation demonstrated that two AP1 (activator protein 1) sites in the minimal promoter region bind JunD. When JUND is overexpressed, the endogenous RHOH gene is repressed; however, when JUND is inhibited, expression of endogenous RHOH is induced both in the Raji cell line and AML (acute myeloid leukaemia) cells. In the HCL (hairy cell leukaemia) cell line JOK-1, induction of RHOH increases expression of the α isoform of protein kinase C. This downstream target of RHOH is also induced in AML cells by JUND inhibition. Collectively, these data indicate that JunD is an inhibitor of RHOH gene expression.

The role of CD40/CD40L and interferon regulatory factor 4 in Hodgkin lymphoma microenvironment

Inflammation and cancer are two independent biological events that can play an interdependent role. The model of such interaction is represented by Hodgkin lymphoma (HL), where the microenvironment is dominated by an extensive mixed, potentially cellular inflammatory infiltrate that plays a decisive role in the pathobiology of HL. In this review we summarize updated information on the complex interactions between Hodgkin Reed-Sternberg (HRS) cells and their tissue microenvironment, highlighting the functional role of CD40/CD40L and interferon regulatory factor 4 (IRF4).

Exome sequencing reveals germline NPAT mutation as a candidate risk factor for Hodgkin lymphoma

A strong clustering of Hodgkin lymphoma in certain families has been long acknowledged. However, the genetic factors in the background of familial Hodgkin lymphoma are largely unknown. We have studied a family of 4 cousins with a rare subtype of the disease, nodular lymphocyte predominant Hodgkin lymphoma. We applied exome sequencing together with genome-wide linkage analysis to this family and identified a truncating germline mutation in nuclear protein, ataxia-telangiectasia locus (NPAT) gene, which segregated in the family. We also studied a large number of samples from other patients with Hodgkin lymphoma, and a germline variation leading to the deletion of serine 724 was found in several cases suggesting an elevated risk for the disease (odds ratio = 4.11; P = .018). NPAT is thus far the first gene implicated in nodular lymphocyte predominant Hodgkin lymphoma predisposition.

Coexisting and clonally identical classic hodgkin lymphoma and nodular lymphocyte predominant hodgkin lymphoma

We report a case of concurrent nodular lymphocyte predominant Hodgkin lymphoma (NLPHL) and classic Hodgkin lymphoma (cHL), of nodular sclerosis subtype, in an otherwise healthy 24-year-old man with a strong family history of cHL. The patient was found to have a parotid mass, which was diagnosed as NLPHL, and a thymic mass diagnosed as cHL, of nodular sclerosis subtype concurrently. The lesion in the parotid showed features typical of NLPHL by morphology and immunophenotype. The LP cells were positive for PAX5, CD20, Oct2, weakly positive for CD30, and negative for CD15. The thymic lesion, diagnosed as cHL, of nodular sclerosis subtype, showed prominent bands of fibrosis and Hodgkin/Reed-Sternberg and lacunar cells positive for CD30 and CD15. These cells were variably positive for CD20 and negative for Oct2. PAX5 was weakly positive. Immunoglobulin gene rearrangement studies by polymerase chain reaction were carried out on microdissected Hodgkin/Reed-Sternberg and LP cells, which were shown to have identically sized peaks. NLPHL and cHL are 2 distinct diseases and are almost never seen concurrently. We present a case in which polymerase chain reaction analysis indicated that the tumor cells of these 2 distinct entities were clonally identical.

Nodular lymphocyte predominant Hodgkin lymphoma behaves as a distinct clinical entity with good outcome: evidence from 14-year follow-up in the West of Scotland Cancer Network

Clinically and biologically, nodular lymphocyte predominant Hodgkin lymphoma (NLPHL) has much more in common with germinal-center derived B-cell non-Hodgkin lymphoma (NHL) than with classical Hodgkin lymphoma (cHL). Management of NLPHL remains controversial. In a 14-year multicenter series, 69 cases were analyzed, and the median follow-up was 53 months (range 11-165.) B-symptoms were present in only 4.3% of patients, and 81.1% of patients had stage I/II disease. Treatment was with radiotherapy (53.6%), chemotherapy (21.7%), combined modality (17.4%), and observation (7.2%). In all, 10.1% of patients relapsed and 2.9% of patients developed high-grade transformation to DLBCL. All relapses and transformations were salvageable. No patient died of their disease. The 5-year relapse-free survival was 92%, transformation-free survival 98.4%, and overall survival 100%. We conclude that NLPHL behaves as a distinct clinical entity, often presenting at an early stage without risk factors. It has an excellent outcome. It may be possible, in early-stage disease, to reduce the intensity of therapy in NLPHL, to single-modality radiotherapy, without affecting OS.

In situ follicular lymphoma: pathologic characteristics and diagnostic features

The diagnosis of in situ follicular lymphoma (FL) is feasible when immunohistochemical characterization is carried out and genetic abnormalities are assessed. We usually use a selected diagnostic panel of antibodies (CD10, CD20, CD23, BCL2, BCL6, and Ki67) in lymph nodes with follicular hyperplasia only when we analyze an unexplained lymphadenopathy. Molecular studies, for example, fluorescence in situ hybridization analysis for t(14;18), are restricted to doubtful cases in which immunohistochemistry data are ambiguous. Immunohistochemically, the involved follicles show strongly positive staining for BCL2 and CD10. The BCL2+ cells are confined only to germinal centers and are not seen in the interfollicular region or elsewhere in the lymph node. The BCL2 staining in the abnormal follicles is notable for its high-level and uniform intensity. In situ FL may be associated with overt FL or with lymphomas other than FL or with other malignancies. The crucial point relies on distinguishing in situ FL arising in asymptomatic patients from cases with presence of lymphoma at the same or other sites. Other open questions remain on the frequency with which in situ FLs occur and the frequency of concomitant systemic disease.

Molecular Pathogenesis of Hodgkin's Lymphoma: Increasing Evidence of the Importance of the Microenvironment

Hodgkin's lymphoma (HL) represents the most common subtype of malignant lymphoma in young people in the Western world. Most patients can be cured with modern treatment strategies, although approximately 20% will die after relapse or progressive disease. The histologic hallmark of the disease is the presence of the characteristic Hodgkin Reed-Sternberg (HRS) cells in classical HL and so-called lymphocyte-predominant (LP) cells in nodular lymphocyte-predominant HL. HL is unique among all cancers because malignant cells are greatly outnumbered by reactive cells in the tumor microenvironment and make up only approximately 1% of the tumor. Expression of a variety of cytokines and chemokines by the HRS and LP cells is believed to be the driving force for an abnormal immune response, perpetuated by additional factors secreted by reactive cells in the microenvironment that help maintain the inflammatory milieu. The malignant HRS and LP cells manipulate the microenvironment, permitting them to develop their malignant phenotype fully and evade host immune attack. Gene expression signatures derived from non-neoplastic cells correlate well with response to initial and subsequent therapies, reflecting their functional relevance. Recent biomarker studies have added texture to clinical outcome predictors, and their incorporation into prognostic models may improve our understanding of the biologic correlates of treatment failure. Moreover, recent preclinical and clinical studies have demonstrated that the tumor microenvironment represents a promising therapeutic target, raising hope that novel treatment strategies focused on the interface between malignant and reactive cells will soon emerge.

Predicting treatment outcome in classical Hodgkin lymphoma: genomic advances

Classical Hodgkin lymphoma is considered a highly curable disease; however, 20% of patients cannot be cured with standard first-line chemotherapy and have a dismal outcome. Current clinical parameters do not allow accurate risk stratification, and personalized therapies are lacking. In fact, Hodgkin lymphoma (HL) is often over- or undertreated because of this lack of accurate risk stratification. In recent years, the early detection of chemoresistance by fluorodeoxyglucose positron emission tomography has become the most important prognostic tool in the management of HL. However, to date, no prognostic scores or molecular markers are available for the early identification of patients at very high risk of failure of induction therapy. In the last decade, many important advances have been made in understanding the biology of HL. In particular, the development of new molecular profiling technologies, such as SNP arrays, comparative genomic hybridization, and gene-expression profiling, have allowed the identification of new prognostic factors that may be useful for risk stratification and predicting response to chemotherapy. In this review, we focus on the prognostic tools and biomarkers that are available for newly diagnosed HL, and we highlight recent advances in the genomic characterization of classical HL and potential targets for therapy.

Down-regulation of BLIMP1α by the EBV oncogene, LMP-1, disrupts the plasma cell differentiation program and prevents viral replication in B cells: implications for the pathogenesis of EBV-associated B-cell lymphomas

An important pathogenic event in Epstein-Barr virus (EBV)-associated lymphomas is the suppression of virus replication, which would otherwise lead to cell death. Because virus replication in B cells is intimately linked to their differentiation toward plasma cells, we asked whether the physiologic signals that drive normal B-cell differentiation are absent in EBV-transformed cells. We focused on BLIMP1α, a transcription factor that is required for plasma cell differentiation and that is inactivated in diffuse large B-cell lymphomas. We show that BLIMP1α expression is down-regulated after EBV infection of primary germinal center B cells and that the EBV oncogene, latent membrane protein-1 (LMP-1), is alone capable of inducing this down-regulation in these cells. Furthermore, the down-regulation of BLIMP1α by LMP-1 was accompanied by a partial disruption of the BLIMP1α transcriptional program, including the aberrant induction of MYC, the repression of which is required for terminal differentiation. Finally, we show that the ectopic expression of BLIMP1α in EBV-transformed cells can induce the viral lytic cycle. Our results suggest that LMP-1 expression in progenitor germinal center B cells could contribute to the pathogenesis of EBV-associated lymphomas by down-regulating BLIMP1α, in turn preventing plasma cell differentiation and induction of the viral lytic cycle.

Classical Hodgkin's lymphoma shows epigenetic features of abortive plasma cell differentiation

BACKGROUND

Epigenetic changes are involved in the extinction of the B-cell gene expression program of classical Hodgkin's lymphoma. However, little is known regarding epigenetic similarities between cells of classical Hodgkin's lymphoma and plasma cell myeloma, both of which share extinction of the gene expression program of mature B cells.

DESIGN AND METHODS

Global histone H3 acetylation patterns were determined in cell lines derived from classical Hodgkin's lymphoma, plasma cell myeloma and B-cell lymphoma by chromatin immunoprecipitation and subsequent hybridization onto promoter tiling arrays. H3K27 trimethylation was analyzed by chromatin immunoprecipitation and real-time DNA polymerase chain reaction for selected genes. Epigenetic modifications were compared to gene expression data.

RESULTS

Characteristic B-cell genes were hypoacetylated in classical Hodgkin's lymphoma and plasma cell myeloma cell lines as demonstrated by comparison of their histone H3 acetylation patterns to those of B-cell lines. However, the number of genes jointly hyperacetylated and expressed in classical Hodgkin' lymphoma and plasma cell myeloma cell lines, such as IRF4/MUM1 and RYBP, is limited. Moreover, H3K27 trimethylation for selected characteristic B-cell genes revealed that this additional epigenetic silencing is much more prevalent in classical Hodgkin's lymphoma than in plasma cell myeloma.

CONCLUSIONS

Our epigenetic data support the view that classical Hodgkin's lymphoma is characterized by abortive plasma cell differentiation with a down-regulation of characteristic B-cell genes but without activation of most genes typical of plasma cells.

Recent Advances in the Pathobiology of Hodgkin's Lymphoma: Potential Impact on Diagnostic, Predictive, and Therapeutic Strategies

From its first description by Thomas Hodgkin in 1832, Hodgkin's disease, now called Hodgkin's lymphoma, has continued to be a fascinating neoplasm even to this day. In this review, historical aspects, epidemiology, diagnosis, tumor biology, new observations related to host-microenvironment interactions, gene copy number variation, and gene expression profiling in this complex neoplasm are described, with an exploration of chemoresistance mechanisms and potential novel therapies for refractory disease.

The H3K27me3 demethylase, KDM6B, is induced by Epstein-Barr virus and over-expressed in Hodgkin's Lymphoma

There is now evidence for both increased and decreased activity of the enzymes controlling the methylation of lysine 27 on histone 3 (H3K27) in cancer. One of these enzymes, KDM6B formally known as JMJD3, a histone demethylase, which removes the trimethyl mark from H3K27, is required for the lineage commitment and terminal differentiation of neural stem cells and of keratinocytes. Our results suggest that KDM6B may also have a role in antigen-driven B-cell differentiation. KDM6B expression increases in B-cell subsets with increasing stage of differentiation, and gene expression profiling shows that KDM6B transcriptional targets in germinal centre B (GC B) cells are significantly enriched for those differentially expressed during memory and plasma cell differentiation. Our results also suggest that aberrant expression of KDM6B may contribute to the pathogenesis of Hodgkin's Lymphoma (HL), an Epstein-Barr virus (EBV) associated malignancy. KDM6B is over-expressed in primary HL and induced by the EBV oncogene, latent membrane protein (LMP1) in GC B cells, the presumptive progenitors of HL. Consistent with these observations, we found that KDM6B transcriptional targets in GC B cells are enriched for genes differentially expressed in HL, and that KDM6B depletion can restore the tri-methylation of H3K27 on these genes.

Pathobiology of hodgkin lymphoma

Despite its well-known histological and clinical features, Hodgkin's lymphoma (HL) has recently been the object of intense research activity, leading to a better understanding of its phenotype, molecular characteristics, histogenesis, and possible mechanisms of lymphomagenesis. There is complete consensus on the B-cell derivation of the tumor in most cases, and on the relevance of Epstein-Barr virus infection and defective cytokinesis in at least a proportion of patients. The REAL/WHO classification recognizes a basic distinction between lymphocyte predominance HL (LP-HL) and classic HL (cHL), reflecting the differences in clinical presentation and behavior, morphology, phenotype, and molecular features. cHL has been classified into four subtypes: lymphocyte rich, nodular sclerosing, with mixed cellularity, and lymphocyte depleted. The borders between cHL and anaplastic large-cell lymphoma have become sharper, whereas those between LP-HL and T-cell-rich B-cell lymphoma remain ill defined. Treatments adjusted to the pathobiological characteristics of the tumor in at-risk patients have been proposed and are on the way to being applied.

Hodgkin's Lymphomas: A Tumor Recognized by Its Microenvironment

Thomas Hodgkin's and Samuel Wilks first recognized Hodgkin disease in the first half of the 19th century. Initially described as lymphogranulomatosis, it was later recognized to be a lymphoid neoplasm derived from B cells and was classified on the basis of its histopathological features. Hodgkin lymphomas are now regarded as encompassing two clearly defined entities according to the WHO classification: nodular lymphocyte-predominant Hodgkin Lymphoma (NLPHL) and classical Hodgkin Lymphoma (CHL). This paper focuses on the current knowledge about the biological features that characterize both NLPHL and CHL, highlighting those relevant to correct pathological diagnosis and those that might be associated with patient outcome.

Programmed death 1 expression in variant immunoarchitectural patterns of nodular lymphocyte predominant Hodgkin lymphoma: comparison with CD57 and lymphomas in the differential diagnosis

Recent studies have exploited an antibody directed against programmed death 1 expressed by follicular helper T-cells in the diagnosis of nodular lymphocyte predominant Hodgkin lymphoma. We had previously described clinically relevant, variant immunoarchitectural patterns of nodular lymphocyte predominant Hodgkin lymphoma and, in this study, sought to address the diagnostic utility of programmed death 1 in comparison with CD57 in variant nodular lymphocyte predominant Hodgkin lymphoma. Immunohistologic staining for programmed death 1 was carried out on biopsies of 67 patients with variant nodular lymphocyte predominant Hodgkin lymphoma. Thirty-four additional cases of nodular lymphocyte predominant Hodgkin lymphoma with associated diffuse areas, de novo T-cell and histiocyte-rich large B-cell lymphoma, and lymphocyte-rich classic Hodgkin lymphoma were also studied. Our results show that programmed death 1 positivity was found in the majority of nodular lymphocyte predominant Hodgkin lymphoma cases with a classic nodular architecture (87%) as compared with 50% for CD57 and was particularly helpful in identifying extranodular large atypical cells. Nodular lymphocyte predominant Hodgkin lymphoma with diffuse areas showed a gradual decrease in programmed death 1 reactivity from nodular to diffuse areas, although a significant proportion (40%-50%) of cases retained programmed death 1 positivity also in diffuse areas. In addition, T-cell and histiocyte-rich large B-cell lymphoma and lymphocyte-rich classic Hodgkin lymphoma displayed programmed death 1 positivity in a significant subset of cases (33%-40%). In conclusion, our study supports the utility of programmed death 1 in the diagnosis of nodular lymphocyte predominant Hodgkin lymphoma and shows greater sensitivity of staining of programmed death 1 as compared with CD57 across all variants of nodular lymphocyte predominant Hodgkin lymphoma. Loss of programmed death 1 reactivity did not correlate with diffuse areas, progression, or the ability to differentiate nodular lymphocyte predominant Hodgkin lymphoma from T-cell and histiocyte-rich large B-cell lymphoma. These findings suggest the need for continued vigilance in the diagnosis of nodular lymphocyte predominant Hodgkin lymphoma and its immunoarchitectural variants as well as related lymphomas in their differential diagnosis.

Oncogenic activation of NF-kappaB

Recent genetic evidence has established a pathogenetic role for NF-kappaB signaling in cancer. NF-kappaB signaling is engaged transiently when normal B lymphocytes respond to antigens, but lymphomas derived from these cells accumulate genetic lesions that constitutively activate NF-kappaB signaling. Many genetic aberrations in lymphomas alter CARD11, MALT1, or BCL10, which constitute a signaling complex that is intermediate between the B-cell receptor and IkappaB kinase. The activated B-cell-like subtype of diffuse large B-cell lymphoma activates NF-kappaB by a variety of mechanisms including oncogenic mutations in CARD11 and a chronic active form of B-cell receptor signaling. Normal plasma cells activate NF-kappaB in response to ligands in the bone marrow microenvironment, but their malignant counterpart, multiple myeloma, sustains a variety of genetic hits that stabilize the kinase NIK, leading to constitutive activation of the classical and alternative NF-kappaB pathways. Various oncogenic abnormalities in epithelial cancers, including mutant K-ras, engage unconventional IkappaB kinases to activate NF-kappaB. Inhibition of constitutive NF-kappaB signaling in each of these cancer types induces apoptosis, providing a rationale for the development of NF-kappaB pathway inhibitors for the treatment of cancer.

Genome-wide copy number analysis of Hodgkin Reed-Sternberg cells identifies recurrent imbalances with correlations to treatment outcome

In classical Hodgkin lymphoma (cHL) the mechanisms underlying primary refractory disease and relapse remain unknown. To gain further insight into cHL pathogenesis and genomic changes linked to treatment response, we studied 53 cHL patients by array comparative genomic hybridization, including 23 patients whose primary treatment failed, using DNA from microdissected HRS cells. Copy number alterations found in more than 20% of cases included gains of 2p, 9p, 16p, 17q, 19q, 20q, and losses of 6q, 11q, and 13q. We identified at high resolution recurrent changes defining minimally gained and lost regions harboring genes involved in nuclear factor kappaB signaling, such as REL, IKBKB, CD40, and MAP3K14. Gains of chromosome 16p11.2-13.3 were significantly more frequent in pretreatment and relapse biopsies of unresponsive patients and were associated with shortened disease-specific survival (P = .028). In the therapy-resistant HL cell line KMH2, we found genomic gains and overexpression of the multidrug resistance gene ABCC1 mapping to cytoband 16p13.11. We show that doxorubicin exposure to KMH2 induces ABCC1 expression and that siRNA silencing of ABCC1 sensitizes KMH2 cells to doxorubicin toxicity in vitro, suggesting that overexpression of ABCC1 contributes to the drug resistance phenotype found in KMH2.

SRC induces podoplanin expression to promote cell migration

Nontransformed cells can force tumor cells to assume a normal morphology and phenotype by the process of contact normalization. Transformed cells must escape this process to become invasive and malignant. However, mechanisms underlying contact normalization have not been elucidated. Here, we have identified genes that are affected by contact normalization of Src-transformed cells. Tumor cells must migrate to become invasive and malignant. Src must phosphorylate the adaptor protein Cas (Crk-associated substrate) to promote tumor cell motility. We report here that Src utilizes Cas to induce podoplanin (Pdpn) expression to promote tumor cell migration. Pdpn is a membrane-bound extracellular glycoprotein that associates with endogenous ligands to promote tumor cell migration leading to cancer invasion and metastasis. In fact, Pdpn expression accounted for a major part of the increased migration seen in Src-transformed cells. Moreover, nontransformed cells suppressed Pdpn expression in adjacent Src-transformed cells. Of >39,000 genes, Pdpn was one of only 23 genes found to be induced by transforming Src activity and suppressed by contact normalization of Src-transformed cells. In addition, we found 16 genes suppressed by Src and induced by contact normalization. These genes encode growth factor receptors, adaptor proteins, and products that have not yet been annotated and may play important roles in tumor cell growth and migration.

The emerging role for rituximab in the treatment of nodular lymphocyte predominant Hodgkin lymphoma

PURPOSE OF REVIEW

Nodular lymphocyte predominant Hodgkin lymphoma (NLPHL) is a rare subset of Hodgkin lymphoma that is distinct from classical Hodgkin lymphoma (cHL). The unique malignant 'popcorn' cells express the B-cell antigen CD20 and lack expression of the cHL markers CD15 and CD30. Traditionally, NLPHL has been included with cHL in clinical trials with excellent prognosis reported in several series. The reliable expression of CD20 has led to the evaluation of the chimeric monoclonal anti-CD20 antibody rituximab in several recent trials.

RECENT FINDINGS

Three series have reported the efficacy of 4 weekly doses of rituximab in all stages of NLPHL, both in the treatment-naive and relapsed settings. Emerging data also suggest that longer courses of antibody therapy may improve the duration of response.

SUMMARY

Rituximab appears to offer a nonchemotherapy-based effective treatment option, which is well tolerated. Ongoing studies are required to further define the optimal patient population who may benefit from rituximab and evaluate its role in maintenance as well as in combination with radiotherapy and chemotherapy.

[Grayzone lymphoma. Clinical relevance]

Malignant lymphomas are classified into different entities according to their morphology, immunohistochemical parameters and clinical behavior. Several important pathogenetic events can be assigned to certain lymphoma entity types. Nevertheless, some cases present overlapping morphologic and immunohistochemical characteristics and a clear-cut diagnosis cannot be made. This is particularly the case with aggressive lymphomas for which a clear distinction cannot be made between the entities of diffuse large cell lymphoma/Burkitt lymphoma or primary mediastinal B cell lymphoma/classic Hodgkin's lymphoma. In order to redress this situation, two new gray zone entities were introduced in the WHO 2008 classification. Until further knowledge regarding the therapy, behavior and prognosis of these gray zone lymphomas has been gained, they should continue to be considered as distinct entities.

T-cell/histiocyte-rich large B-cell lymphoma shows transcriptional features suggestive of a tolerogenic host immune response

BACKGROUND

Gene expression profiling has successfully identified the prognostic significance of the host response in lymphomas. The aggressive T-cell/histiocyte-rich large B-cell lymphoma and the indolent nodular lymphocyte-predominant Hodgkin's lymphoma are both characterized by a paucity of tumor cells embedded in an overwhelming background. The tumor cells of both lymphomas share several characteristics, while the cellular composition of their microenvironment is clearly different.

DESIGN AND METHODS

We collected 33 cases of T-cell/histiocyte-rich large B-cell lymphoma and 56 cases of nodular lymphocyte-predominant Hodgkin's lymphoma and performed microarray gene expression profiling on ten cases of each lymphoma, to obtain a better understanding of the lymphoma host response. By quantitative reverse transcriptase polymerase chain reaction we verified that these 20 selected cases were representative of the entire population of T-cell/histiocyte-rich large B-cell and nodular lymphocyte-predominant Hodgkin's lymphomas.

RESULTS

We observed that the microenvironment in nodular lymphocyte-predominant Hodgkin's lymphoma is molecularly very similar to a lymph node characterized by follicular hyperplasia, while the microenvironment in T-cell/histiocyte-rich large B-cell lymphoma is clearly different. The T-cell/histiocyte-rich large B-cell lymphoma signature is hallmarked by up-regulation of CCL8, interferon-gamma, indoleamine 2,3 dioxygenase, VSIG4 and Toll-like receptors. These features may be responsible for the recruitment and activation of T cells, macrophages and dendritic cells, characterizing the stromal component of this lymphoma, and may point towards innate immunity and a tumor tolerogenic immune response in T-cell/histiocyte-rich large B-cell lymphoma.

CONCLUSIONS

The gene expression profile of T-cell/histiocyte-rich large B-cell lymphoma, in comparison with that of nodular lymphocyte-predominant Hodgkin's lymphoma, shows features suggestive of a distinct tolerogenic host immune response that may play a key role in the aggressive behavior of this lymphoma, and that may serve as a potential target for future therapy.

Gene expression profiling of isolated tumour cells from anaplastic large cell lymphomas: insights into its cellular origin, pathogenesis and relation to Hodgkin lymphoma

Anaplastic large cell lymphoma (ALCL) is a main type of T-cell lymphomas and comprises three distinct entities: systemic anaplastic lymphoma kinase (ALK) positive, systemic ALK(-) and cutaneous ALK(-) ALCL (cALCL). Little is known about their pathogenesis and their cellular origin, and morphological and immunophenotypical overlap exists between ALK(-) ALCL and classical Hodgkin lymphoma (cHL). We conducted gene expression profiling of microdissected lymphoma cells of five ALK(+) and four ALK(-) systemic ALCL, seven cALCL and sixteen cHL, and of eight subsets of normal T and NK cells. The analysis supports a derivation of ALCL from activated T cells, but the lymphoma cells acquired a gene expression pattern hampering an assignment to a CD4(+), CD8(+) or CD30(+) T-cell origin. Indeed, ALCL display a down-modulation of many T-cell characteristic molecules. All ALCL types show significant expression of NFkappaB target genes and upregulation of genes involved in oncogenesis (e.g. EZH2). Surprisingly, few genes are differentially expressed between systemic and cALCL despite their different clinical behaviour, and between ALK(-) ALCL and cHL despite their different cellular origin. ALK(+) ALCL are characterized by expression of genes regulated by pathways constitutively activated by ALK. This study provides multiple novel insights into the molecular biology and pathogenesis of ALCL.

Mutations in the genes coding for the NF-κB regulating factors IκBα and A20 are uncommon in nodular lymphocyte-predominant Hodgkin's lymphoma

Nodular lymphocyte-predominant Hodgkin's lymphoma (NLPHL) shows constitutive NF-kappaB activity in the malignant lymphocyte-predominant (LP) cells. Constitutive NF-kappaB activity also plays a central pathogenetic role in classical Hodgkin's lymphoma (cHL), where inactivating mutations in the NFKBIA and TNFAIP3 genes, coding for the negative NF-kappaB regulators IkappaBalpha and A20, respectively, contribute to NF-kappaB activation. To determine whether mutations in NFKBIA and TNFAIP3 are also involved in the pathogenesis of NLPHL these genes were sequenced from microdissected LP cells of 10 primary NLPHL. We also studied DEV, the only cell line proposedly derived from LP cells, after we had confirmed its derivation from NLPHL by gene expression analysis. A heterozygous somatic missense mutation in the NFKBIA gene was found in one NLPHL, and a heterozygous, possibly subclonal, two base pair insertion in TNFAIP3 in another case. The low mutation frequency and the absence of biallelic destructive mutations propose a minor contribution of NFKBIA and TNFAIP3 mutations to the NF-kappaB activity of NLPHL, suggesting different mechanisms of NF-kappaB activation in NLPHL and cHL.

Differentiating germinal center-derived lymphomas through their cellular microenvironment

Recent studies on normal and malignant B-cells have provided evidence that the germinal center (GC) of lymphoid follicles exerts a role in B-cell physiology and malignancy. GC-derived lymphomas include both B-cell and T-cell lymphomas. Remarkably, tumor cells of GC-derived lymphomas proliferate in close association with cellular environment that retains key features of normal GC cellular microenvironment. Neoplastic follicles in follicular lymphoma contain, in addition to follicular dendritic cells (FDC) other non-neoplastic cells including macrophages and GC T-cells. In addition to aggregates of FDCs, the background infiltrate of nodular lymphocyte predominant Hodgkin lymphoma includes small B-cells, T-cells, and histiocytes. Typically, most of the lymphocyte predominant (LP) cells are ringed by CD3+/CD4+ T-cells expressing CD57, PD1, BCL6, and MUM1/IRF4. By contrast, Reed-Sternberg cells of classic Hodgkin lymphoma (cHL) are surrounded by CD3+/CD4+ T-cells expressing CD40L. Unlike cHL and other peripheral T-cell lymphomas, the AITL microenvironment characteristically contain a prominent proliferation of high endothelial venules and FDC. Thus, these findings shed new light on the characterization of GC-derived lymphomas and may help in the differential diagnosis and acknowledge several novel pathogenetic mechanisms on these lymphomas. Am. J. Hematol., 2009. (c) 2009 Wiley-Liss, Inc.

Pathogenesis of classical and lymphocyte-predominant Hodgkin lymphoma

Hodgkin and Reed-Sternberg (HRS) cells in classical Hodgkin lymphoma (HL) and lymphocytic and histiocytic (L&H) cells in nodular lymphocyte-predominant HL (NLPHL) are derived from germinal-center B cells. HRS cells have, however, largely lost their B cell phenotype and aberrantly express markers and transcriptional regulators of other hematolymphoid cell types. Deregulation of multiple signaling pathways and downstream transcription factors, including receptor tyrosine kinases, nuclear factor-kappa B (NF-kappaB), and Janus kinase/signal transducer and activator of transcription (JAK/STAT), is a further hallmark of HRS cells. These cells harbor genetic lesions that contribute to or cause increases in the activity of transcription factors of the NF-kappaB and STAT families. HRS cells are found within a mixed reactive cellular infiltrate and interact with these nonmalignant cells in a complex fashion that appears to be essential for HRS cell survival and proliferation. Less is known about the pathogenesis of L&H cells in NLPHL, but increases in the activity of receptor tyrosine kinases, NF-kappaB, and JAK/STAT have also been detected.

APRIL is overexpressed in cancer: link with tumor progression

Background

BAFF and APRIL share two receptors – TACI and BCMA – and BAFF binds to a third receptor, BAFF-R. Increased expression of BAFF and APRIL is noted in hematological malignancies. BAFF and APRIL are essential for the survival of normal and malignant B lymphocytes, and altered expression of BAFF or APRIL or of their receptors (BCMA, TACI, or BAFF-R) have been reported in various B-cell malignancies including B-cell non-Hodgkin's lymphoma, chronic lymphocytic leukemia, Hodgkin's lymphoma, multiple myeloma, and Waldenstrom's macroglobulinemia.

Methods

We compared the expression of BAFF, APRIL, TACI and BAFF-R gene expression in 40 human tumor types – brain, epithelial, lymphoid, germ cells – to that of their normal tissue counterparts using publicly available gene expression data, including the Oncomine Cancer Microarray database.

Results

We found significant overexpression of TACI in multiple myeloma and thyroid carcinoma and an association between TACI expression and prognosis in lymphoma. Furthermore, BAFF and APRIL are overexpressed in many cancers and we show that APRIL expression is associated with tumor progression. We also found overexpression of at least one proteoglycan with heparan sulfate chains (HS), which are coreceptors for APRIL and TACI, in tumors where APRIL is either overexpressed or is a prognostic factor. APRIL could induce survival or proliferation directly through HS proteoglycans.

Conclusion

Taken together, these data suggest that APRIL is a potential prognostic factor for a large array of malignancies.

Molecular biology of Hodgkin lymphoma

Hodgkin lymphoma (HL) is derived from mature B cells and subdivided into classical HL and nodular lymphocyte predominant HL (NLPHL). HL is unique among human B cell lymphomas because of the rarity of the lymphoma cells, the Hodgkin and Reed-Sternberg (HRS) cells in classical HL and the lymphocyte-predominant (LP) cells in NLPHL, which usually account for 0.1% to 10% of the cells in the affected tissues. Moreover, HRS cells are unique in the extent to which they have lost their B cell-typical gene expression pattern. Deregulation of transcription factor networks plays a key role in this reprogramming process. HRS cells show strong constitutive activity of the transcription factor NF-kappaB. Multiple mechanisms likely contribute to this deregulated activation, including signaling through particular receptors and genetic lesions. Inactivating mutations in the TNFAIP3 tumor suppressor gene, encoding a negative regulator of NF-kappaB activity, were recently identified in about 40% of patients with classical HL. HRS cells are latently infected by Epstein-Barr virus in about 40% of patients, and an important role of this virus in HL pathogenesis-in particular for cases in which HRS cells had lost the capacity to express a B-cell receptor due to destructive somatic mutation-was recently substantiated.

The biology of Hodgkin's lymphoma

Hodgkin's lymphoma was first described in 1832. The aetiology of this lymphoma, however, remained enigmatic for a long time. Only within the past 10 years has the B-cell nature of the pathognomonic Hodgkin and Reed-Sternberg (HRS) cells been revealed, along with several recurrent genetic lesions. The pathogenetic role for Epstein-Barr virus infection has also been substantiated. HRS cells in classical Hodgkin's lymphoma have several characteristics that are unusual for lymphoid tumour cells, and the Hodgkin's lymphoma microenvironment is dominated by an extensive mixed, potentially inflammatory cellular infiltrate. Understanding the contribution of all of these changes to the pathogenesis of this disease is essential for the development of novel therapies.

The Germinal centre-derived lymphomas seen through their cellular microenvironment

The human lymph node is a complex tissue resulting from the microenvironmental organisation of different cell populations linked by topographical and/or functional relationships. Germinal centres (GCs) of lymphoid follicles contain a meshwork of follicular dendritic cells in addition to B-cells and some CD4(+) T cells. Moreover, there is a sharp demarcation around the whole follicle centre, which is highlighted by fibroblastic reticulum cells. On the whole, GC exerts a role in B cell physiology and malignancy. In GC-derived lymphomas, gene expression profiling studies have raised the possibility that survival of the affected patients may be associated with signatures preferentially expressed in non-malignant T cells and macrophages and/or dendritic cells. Immunohistological analyses in lymphoma biopsy samples have confirmed that the biological behaviour and tumour progression may be influenced by the tumour microenvironment. This review will examine GC-derived lymphomas, including follicular lymphomas, Hodgkin lymphomas and angioimmunoblastic T-cell lymphoma, through their integrated cellular microenvironment, highlighting those findings which may serve as a useful surrogate marker for tumour diagnosis or tumour progression, together with key molecules involved in tumour development.