Hodgkin disease: pharmacologic intervention of the CD40-NFκB pathway by a protease inhibitor

Tackling the dysregulated immune-checkpoints in classical Hodgkin lymphoma: bidirectional regulations between the microenvironment and Hodgkin/Reed-Sternberg cells

Immune evasion is considered one of the modern hallmarks of cancer and is a key element in the pathogenesis of classical Hodgkin Lymphoma (cHL). This haematological cancer achieves effective avoidance of the host's immune system by overexpressing the PD-L1 and PD-L2 proteins on the surface of the neoplastic cells. Subversion of the PD-1/PD-L axis, however, is not the sole contributor to immune evasion in cHL, as the microenvironment nurtured by the Hodgkin/Reed-Sternberg cells is a major player in the creation of a biological niche that sustains their survival and hinders immune recognition. In this review, we will discuss the physiology of the PD-1/PD-L axis and how cHL is able to exploit a plethora of different molecular mechanisms to build an immunosuppressive microenvironment and achieve optimal immune evasion. We will then discuss the success obtained by checkpoint inhibitors (CPI) in treating cHL, both as single agents and as part of combination strategies, analysing the rationale for their combination with traditional chemotherapeutic compounds and the proposed mechanisms of resistance to CPI immunotherapy.

NFkB Pathway and Hodgkin Lymphoma

The tumor cells that drive classical Hodgkin lymphoma (cHL), namely, Hodgkin and Reed-Sternberg (HRS) cells, display hallmark features that include their rareness in contrast with an extensive and rich reactive microenvironment, their loss of B-cell phenotype markers, their immune escape capacity, and the activation of several key biological pathways, including the constitutive activation of the NFkB pathway. Both canonical and alternative pathways are deregulated by genetic alterations of their components or regulators, EBV infection and interaction with the microenvironment through multiple receptors, including CD30, CD40, BAFF, RANK and BCMA. Therefore, NFkB target genes are involved in apoptosis, cell proliferation, JAK/STAT pathway activation, B-cell marker expression loss, cellular interaction and a positive NFkB feedback loop. Targeting this complex pathway directly (NIK inhibitors) or indirectly (PIM, BTK or NOTCH) remains a challenge with potential therapeutic relevance. Nodular predominant HL (NLPHL), a distinct and rare HL subtype, shows a strong NFkB activity signature because of mechanisms that differ from those observed in cHL, which is discussed in this review.

The circuitry of the tumor microenvironment in adult and pediatric Hodgkin lymphoma: cellular composition, cytokine profile, EBV, and exosomes

BACKGROUND

Classical Hodgkin lymphoma (cHL) is a unique lymphoid malignancy with a tumor microenvironment (TME) consisting of a small number of neoplastic-Hodgkin and Reed-Sternberg (H-RS) cells (<1%), surrounded by a large number of nonneoplastic infiltrating immune cells (>90%). The TME of cHL critically depends on immune cells to support tumor growth as H-RS cells cannot survive and proliferate in isolation.

RECENT FINDINGS

Programmed cell death protein 1 (PD-1) ligand expressed on H-RS cells inhibits the clearance of tumor by causing T-cell exhaustion. Nivolumab and pembrolizumab, PD-1 inhibitors, have been proven to be effective in treating adult and pediatric patients with R/R cHL. Tumor-associated macrophages (TAMs) are a central component of TME and are known to cause poor prognosis in adult HL. However, the prognostic impact of CD68+ TAMs in pediatric HL remains ambiguous. EBV modulates the tumor milieu of HL and plays a strategic role in immune escape by enrichment of the TME with T_reg cells and associated immunosuppressive cytokines in adult HL. In contrast, EBV+ pediatric patients have increased infiltration of CD8⁺ T-cells and show a better therapeutic response suggesting viral-related TME is distinct in childhood HL. The role of CASP3 in apoptosis of H-RS cells and its correlation with response prediction in adult and pediatric HL suggest it may serve as a potential biomarker. In cHL, CD30, EBV, and NF-κB signaling employ exosomes for cell-cell communication that triggers the migration capacity of fibroblasts, stimulate to produce proinflammatory cytokines, and help to create a tumor-supportive microenvironment.

CONCLUSION

The cHL microenvironment is distinct in adult and pediatric HL. Future studies are required to understand the role of interplay between H-RS cells and EBV-associated microenvironment and their clinical outcome. They may present novel therapeutic targets for the development of antilymphoma therapy.

The Role of Immune Checkpoint Inhibitors in Classical Hodgkin Lymphoma

Hodgkin Lymphoma (HL) is a unique disease entity both in its pathology and the young patient population that it primarily affects. Although cure rates are high, survivorship can be linked with significant recent long-term morbidity associated with both chemotherapy and radiotherapy. The most significant advances have been with the use of the anti-CD30-drug conjugated antibody brentuximab vedotin (BV) and inhibitors of program death 1 (PD-1). HL is genetically wired to up-regulate program death ligand 1 (PD-L1) in >95% of cases, creating a state of so-called &ldquo;T cell exhaustion&rdquo;, which can be reversed with immune checkpoint-inhibitor blockade. The overall and complete response rates to PD-1 inhibitors in patients with relapsed or refractory HL are 70% and 20%, respectively, with a long median duration of response of ~16 months. In fact, PD-1 inhibitors can benefit a wide spectrum of relapsed HL patients, including some who have &ldquo;progressive disease&rdquo; by strict response criteria. We review the biology of HL, with a focus on the immune micro-environment and mechanisms of immune evasion. We also provide the rationale supporting the use of PD-1 inhibitors in HL and highlight some of the challenges of monitoring disease response in patients treated with this immunotherapy.

NF-κB in Hematological Malignancies

NF-κB (Nuclear Factor Κ-light-chain-enhancer of activated B cells) transcription factors are critical regulators of immunity, stress response, apoptosis, and differentiation. Molecular defects promoting the constitutive activation of canonical and non-canonical NF-κB signaling pathways contribute to many diseases, including cancer, diabetes, chronic inflammation, and autoimmunity. In the present review, we focus our attention on the mechanisms of NF-κB deregulation in hematological malignancies. Key positive regulators of NF-κB signaling can act as oncogenes that are often prone to chromosomal translocation, amplifications, or activating mutations. Negative regulators of NF-κB have tumor suppressor functions, and are frequently inactivated either by genomic deletions or point mutations. NF-κB activation in tumoral cells is also driven by the microenvironment or chronic signaling that does not rely on genetic alterations.

Gene Expression Analysis of Single Neoplastic Cells and the Pathogenesis of Hodgkin's Lymphoma

The origin of the Reed–Sternberg cell of Hodgkin's disease remained clouded in mystery for almost a century after its discovery in 1898. The major obstacle to its understanding is that, unlike other cancers, the malignant cell of Hodgkin's disease is vastly outnumbered by surrounding non-neoplastic cells at approximately 1000:1. We have devised several strategies to isolate Reed–Sternberg T-cells to determine their origin, global gene expression and, ultimately, their pathogenesis. This has increased the number of genes known to be expressed in Reed–Sternberg cells by >100-fold to over 12,000. Approaches such as density gradients, microdissection, and cell sorting help to enrich Reed–Sternberg cells for genomic DNA analysis. However, single-cell micromanipulation of living Reed–Sternberg cells was required to determine the genome-wide gene expression profile of these cells. Combined analysis of single cells and cell lines revealed the expression of 2666 named genes. Further analysis with high-density gene expression microarrays has demonstrated the expression of approximately 12,000 genes by Reed–Sternberg cells. The gene expression profile is that of an aberrant germinal center B-lymphocyte that resists apoptosis through CD40 signaling and NFkB activation. Gene expression analysis of Hodgkin's disease is an extreme test case demonstrating the application of high-throughput gene expression studies even to individual cells from clinical samples.

NF-κB deregulation in Hodgkin lymphoma

Hodgkin and Reed/Sternberg (HRS) cells in classical Hodgkin lymphoma (HL) show constitutive activity of both the canonical and non-canonical NF-κB signaling pathways. The central pathogenetic role of this activity is indicated from studies with HL cell lines, which undergo apoptosis upon NF-κB inhibition. Multiple factors contribute to the strong NF-κB activity of HRS cells. This includes interaction with other cells in the lymphoma microenvironment through CD30, CD40, BCMA and other receptors, but also recurrent somatic genetic lesions in various factors of the NF-κB pathway, including destructive mutations in negative regulators of NF-κB signaling (e.g. TNFAIP3, NFKBIA), and copy number gains of genes encoding positive regulators (e.g. REL, MAP3K14). In Epstein-Barr virus-positive cases of classical HL, the virus-encoded latent membrane protein 1 causes NF-κB activation by mimicking an active CD40 receptor. NF-κB activity is also seen in the tumor cells of the rare nodular lymphocyte predominant form of HL, but the causes for this activity are largely unclear.

The role of T cells in the microenvironment of Hodgkin lymphoma

The cellular microenvironment in HL is dominated by a mixed infiltrate of inflammatory cells with typically only 1 or a few percent of HRS tumor cells. HRS cells orchestrate this infiltrate by the secretion of a multitude of chemokines. T cells are usually the largest population of cells in the HL tissue, encompassing Th cells, T(regs), and CTLs. Th cells and T(regs) presumably provide essential survival signals for the HRS cells, and the T(regs) also play an important role in rescuing HRS cells from an attack by CTLs and NK cells. The interference with this complex interplay of HRS cells with other immune cells in the microenvironment may provide novel strategies for targeted immunotherapies.

The microenvironment in classical Hodgkin lymphoma: an actively shaped and essential tumor component

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.

NF-κB in T-cell Acute Lymphoblastic Leukemia: Oncogenic Functions in Leukemic and in Microenvironmental Cells

Two main NF-κB signaling pathways, canonical and noncanonical, performing distinct functions in organisms have been characterized. Identification of mutations in genes encoding components of these NF-κB signaling pathways in lymphoid malignancies confirmed their key role in leukemogenesis. T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive malignancy of thymocytes that despite significant therapeutic advances can still be fatal. Although mutations in NF-κB genes have not been reported in T-ALL, NF-κB constitutive activation in human T-ALL and in acute T-cell leukemia mouse models has been observed. Although these studies revealed activation of members of both canonical and noncanonical NF-κB pathways in acute T-cell leukemia, only inhibition of canonical NF-κB signaling was shown to impair leukemic T cell growth. Besides playing an important pro-oncogenic role in leukemic T cells, NF-κB signaling also appears to modulate T-cell leukemogenesis through its action in microenvironmental stromal cells. This article reviews recent data on the role of these transcription factors in T-ALL and pinpoints further research crucial to determine the value of NF-κB inhibition as a means to treat T-ALL.

Pepstatin A, an aspartic proteinase inhibitor, suppresses RANKL-induced osteoclast differentiation

Pepstatin A is well known to be an inhibitor of aspartic proteinases such as pepsin, cathepsins D and E. Except for its role as a proteinase inhibitor, however, the pharmacological action of pepstatin A upon cells remain unclear. In this study, we found that pepstatin A suppressed receptor activator of NF-kappaB ligand (RANKL)-induced osteoclast differentiation. Pepstatin A suppressed the formation of multinuclear osteoclasts dose-dependently. This inhibition of the formation only affected osteoclast cells, i.e., not osteoblast-like cells. Furthermore, pepstatin A also suppressed differentiation from pre-osteoclast cells to mononuclear osteoclast cells dose-dependently. This inhibition seems to be independent of the activities of proteinases such as cathepsin D, because the formation of osteoclasts was not suppressed with the concentration that inhibited the activity of cathepsin D. Cell signaling analysis indicated that the phosphorylation of ERK was inhibited in pepstatin A-treated cells, while the phosphorylation of IkappaB and Akt showed almost no change. Furthermore, pepstatin A decreased the expression of nuclear factor of activated T cells c1 (NFATc1). These results suggest that pepstatin A suppresses the differentiation of osteoclasts through the blockade of ERK signaling and the inhibition of NFATc1 expression.

World Health Organization and beyond: new aspects in the pathology of an old disease

Hodgkin's lymphoma is a highly enigmatic lymphoma disease that still covers most of its secrets up to now. Much effort has been made to successfully wrest at least some of the pathogenetic particularities. The current diagnostic criteria are well established allowing hemato-pathologists to make a clear-cut distinction from other lymphomas in almost all cases. Although classic Hodgkin's lymphoma is curable in the vast majority of cases by treatment with highly aggressive drugs with or without radiotherapy, further molecular studies may lead to the identification of therapeutic targets that enable a more tailored treatment with fewer side effects.

The Pathogenesis of Classical Hodgkin's Lymphoma: A Model for B-Cell Plasticity

It has been shown that differentiated lymphoid cells can display a broad developmental potential and might even differentiate into other cell types. Recent data implicate such processes in the pathogenesis of classical Hodgkin's lymphoma (HL). In the malignant, B cell-derived Hodgkin's and Reed-Sternberg (HRS) cells of HL the expression of B cell-specific genes is lost, and B lineage-inappropriate genes are up-regulated. Experimental evidence has been presented in recent years that functional disruption of the B lineage-specific transcription factor program contributes to this process. HRS cells might be reprogrammed into cells resembling undifferentiated progenitor cells, which might offer an explanation for the unique HL phenotype and demonstrate a high degree of plasticity of human lymphoid cells.

Need for an improved molecular/genetic classification for CD30+ lymphomas involving the skin

BACKGROUND

The spectrum of diseases that constitute the CD30+ lymphomas, with lymphomatoid papulosis (LyP) at one end, and anaplastic large-cell lymphoma (ALCL) at the other end, shows variable morphology, immunophenotype, and clinical behavior. The border between these diseases is sometimes difficult to establish and there are many grey zones in their classification.

METHODS

We reviewed the clinical and research literature and guided by our experiences attempted to discern molecular and phenotypic criteria to improve the classification and identify molecular targets for therapy of CD30-positive cutaneous lymphomas.

RESULTS

Functional studies of ALCL cell lines clonally derived from LyP have revealed loss of growth inhibition by transforming growth factor beta (TGF-beta), due to TGF-beta receptor mutations. Studies of genetic variants of the CD30 promoter showed distinct microsatellite alleles associated with development of LyP and lymphoma progression. Studies of LyP and cutaneous ALCL tissues and cell lines suggest a dual role for CD30/CD30 ligand interactions in regression of LyP and progression to lymphoma. CD30 signaling activates NF-kappaB in cell lines derived from cutaneous ALCL but not anaplastic lymphoma kinase (ALK)-positive systemic ALCL in which growth arrest occurs through cell cycle inhibitor p21WAF1/Cip1. Other likely biomarkers of disease progression include differential expression of Bcl-2, fascin, cutaneous lymphocyte antigen, and T-cell receptor clonality. These may lead to improved classification, diagnoses, and therapeutic targets.

CONCLUSIONS

The current clinicopathologic classification of CD30+ cutaneous lymphoproliferative disorders is insufficient. Incorporating genetic and molecular criteria would better define the borders between benign/ malignant and aggressive/nonaggressive disorders.

Global correlation of genome and transcriptome changes in classical Hodgkin lymphoma

To identify genes involved in the pathogenesis of classical Hodgkin lymphoma (cHL), we performed serial analysis of gene expression (SAGE) and array-based comparative genomic hybridization (aCGH). Comparison of SAGE libraries of cHL cell lines L428 and L1236 with that of germinal centre B cells revealed consistent overexpression of only 14 genes. In contrast, 141 genes were downregulated in both cHL cell lines, including many B cell and HLA genes. aCGH revealed gain of 2p, 7p, 9p, 11q and Xq and loss of 4q and 11q. Eighteen percent of the differentially expressed genes mapped to regions with loss or gain and a good correlation was observed between underexpression and loss or overexpression and gain of DNA. Remarkably, gain of 2p and 9p did not correlate with increased expression of the proposed target genes c-REL and JAK2. Downregulation of many genes within the HLA region also did not correlate with loss of DNA. FSCN1 and IRAK1 mapping at genomic loci (7p and Xq) that frequently showed gain were overexpressed in cHL cell lines and might be involved in the pathogenesis of cHL.

From Hodgkin disease to Hodgkin lymphoma: biologic insights and therapeutic potential

Reclassification of Hodgkin disease as Hodgkin lymphoma (HL) represents a milestone in the lymphoma field, awarding recent insights in the molecular biology of Hodgkin and Reed-Sternberg (H-RS) cells and their environment. This review summarizes antiapoptotic and proproliferative pathways involved in the pathogenesis of this disease with the ultimate goal of translating laboratory knowledge into clinical decision making. The focus is on potential targets and novel drugs, which are discussed in the context of the complex biology of HL. Considering that HL patients are more likely to die from acute and late treatment-related toxicities than from HL itself, the introduction of targeted, biologically based therapies for HL patients with palliative and eventually curative intention might be justified. (Blood. 2005;105:4553-4560)

HLXB9 activates IL6 in Hodgkin lymphoma cell lines and is regulated by PI3K signalling involving E2F3

Multiple cytokines are secreted by Hodgkin lymphoma (HL) cells, notably interleukin-6 (IL6), which is believed to play a significant pathobiological role in this and certain other tumors. Previous work on prostate carcinoma cells has shown that IL6 expression is activated therein by the homeodomain protein GBX2, which we found to be absent in HL cells. Instead, we observed expression of a closely related gene, HLXB9, albeit restricted to HL cells coexpressing IL6. Treatment of HL cell lines with antisense-oligonucleotides directed against HLXB9, forced expression of recombinant HLXB9, and analysis of reporter gene constructs containing IL6 promoter sequences all confirmed the potential of HLXB9 to drive expression of IL6. Chromosomal rearrangements of the HLXB9 locus at 7q36 were not detected in HL cells unlike AML subsets expressing HLXB9. However, inhibition of certain signal transduction pathways revealed that the phosphatidylinositol 3 kinase (PI3K) pathway contributes to HLXB9 expression. AKT/phospho-AKT analysis revealed constitutively active PI3K signalling in HL cell lines. Downstream analysis of PI3K revealed that E2F3 may mediate activation of HLXB9. Taken together, our data show that the PI3K signalling pathway in HL cells is constitutively activated and promotes HLXB9 expression, probably via E2F3, thereby enhancing malignant expression of IL6.

[Classical Hodgkin's lymphoma: biology and grey zones]

Advances in the biology of Hodgkin's lymphoma have lead to the distinction between two entities, "classical" Hodgkin's lymphoma and nodular lymphocyte predominance Hodgkin's lymphoma, previously called nodular paragranuloma, which share distinct clinical aspects. The definition of diagnostic criteria has also been helpful to separate Hodgkin's lymphoma from other lymphomas which can mimick Hodgkin's disease such as anaplastic large cell lymphomas, T-cell/histiocyte rich diffuse large B-cell lymphoma, and some peripheral T-cell lymphomas, mainly angioimmunoblastic-type. Reed-Sternberg cell, the neoplastic cell of "classical" Hodgkin's lymphoma, still retains some secrets. Despite some controversies, there is more and more evidence for a lymphoid B cell origin. The involvement of Epstein-Barr virus, cytokines and/or oncogenes expression in the pathogeny can be suggested, although the precise mechanisms leading to transformation and/or accounting for tumour progression are still elusive. Recently, the roles of the pathway implicating the activation of NFkappaB as well as the autocrine secretion of interleukin-13 have been demonstrated.

TRAF3 forms heterotrimers with TRAF2 and modulates its ability to mediate NF-{kappa}B activation

FRET experiments utilizing confocal microscopy or flow cytometry assessed homo- and heterotrimeric association of human tumor necrosis factor receptor-associated factors (TRAF) in living cells. Following transfection of HeLa cells with plasmids expressing CFP- or YFP-TRAF fusion proteins, constitutive homotypic association of TRAF2, -3, and -5 was observed, as well as heterotypic association of TRAF1-TRAF2 and TRAF3-TRAF5. A novel heterotypic association between TRAF2 and -3 was detected and confirmed by immunoprecipitation in Ramos B cells that constitutively express both TRAF2 and -3. Experiments employing deletion mutants of TRAF2 and TRAF3 revealed that this heterotypic interaction minimally involved the TRAF-C domain of TRAF3 as well as the TRAF-N domain and zinc fingers 4 and 5 of TRAF2. A novel flow cytometric FRET analysis utilizing a two-step approach to achieve linked FRET from CFP to YFP to HcRed established that TRAF2 and -3 constitutively form homo- and heterotrimers. The functional importance of TRAF2-TRAF3 heterotrimerization was demonstrated by the finding that TRAF3 inhibited spontaneous NF-kappaB, but not AP-1, activation induced by TRAF2. Ligation of CD40 on Ramos B cells by recombinant CD154 caused TRAF2 and TRAF3 to dissociate, whereas overexpression of TRAF3 in Ramos B cells inhibited CD154-induced TRAF2-mediated activation of NF-kappaB. Together, these results reveal a novel association between TRAF2 and TRAF3 that is mediated by unique portions of each protein and that specifically regulates activation of NF-kappaB, but not AP-1.

Stabilization of p53 is a novel mechanism for proapoptotic function of NF-kappaB

Both pro- and antiapoptotic activities of NF-kappaB transcription factor have been observed; however, less is known about the mechanism by which NF-kappaB induces apoptosis. To elucidate how NF-kappaB regulates proapoptotic signaling, we performed functional analyses using wild-type, ikk1(-/-), ikk2(-/-), rela(-/-) murine fibroblasts, MDAPanc-28/Puro, MDAPanc-28/IkappaBalphaM, and HCT116/p53(+/+) and HCT116/p53(-/-) cells with investigational anticancer agent doxycycline as a superoxide inducer for generating apoptotic stimulus. In this report, we show that doxycycline increased superoxide generation and subsequently activated NF-kappaB, which in turn up-regulated p53 expression and increased the stability and DNA binding activity of p53. Consequently, NF-kappaB-dependent p53 activity induced the expression of p53-regulated genes PUMA and p21(waf1) as well as apoptosis. Importantly, lack of RelA, IKK, and p53 as well as expression of a dominant negative IkappaBalpha (IkappaBalphaM) inhibited NF-kappaB-dependent p53 activation and apoptosis. The doxycycline-induced NF-kappaB activation was not inhibited in HCT116/p53(-/-) cells. Our results demonstrate that NF-kappaB plays an essential role in activation of wild-type p53 tumor suppressor to initiate proapoptotic signaling in response to overgeneration of superoxide. Thus, these findings reveal a mechanism of NF-kappaB-regulated proapoptotic signaling.

Interleukin 4 production by peripheral blood lymphocytes in patients with classical Hodgkin lymphoma

Although the production of interleukin (IL) 2 and interferon (IFN) gamma by peripheral blood lymphocytes in patients with Hodgkin lymphoma (HL) is well documented, the synthesis of IL4 has not been investigated before. The present study examines the production of IL4 by 2-day phytohaemaglutinin (PHA)-stimulated peripheral blood (PB) cells in HL and correlates the cytokine levels with the proportion of the different T-cell sub-populations. We observed a significant increase in the mean level of production of IL4 in patients with HL when compared with normal controls. The increased amount of IL4 in patients with HL correlated significantly with the proportion of the CD3(+)CD8(+) cells but not with CD3(+)CD4(+). The intensity of cytoplasmic IL4 (expressed as relative median fluorescence (RMF)) was significantly higher in the CD3(+)CD8(+) cells of the patients with HL compared with the CD3(+)CD4(+) sub-population, or with the normal CD3(+)CD8(+) cells and correlated with the levels of IL4 release in culture supernatants. In conclusion, there is increased production of IL4 by PHA-activated PB lymphocytes in HL. The CD3(+)CD8(+) T-cell population appears to be responsible for this increased synthesis.

Part I: Hodgkin's lymphoma—molecular biology of Hodgkin and Reed-Sternberg cells

Classic Hodgkin's lymphoma is characterised by Hodgkin and Reed-Sternberg cells and in most cases are derived from germinal-centre B cells. Despite progress in basic research showing the natural precursor cells of Hodgkin's lymphoma, most key questions still remain unanswered. Among these are the basic transforming events, the involvement of oncogenic viruses, the mechanisms enabling Hodgkin and Reed Sternberg cells to resist apoptosis in the germinal centre, and the molecular causes of their characteristic phenotype. Beyond the disclosure of these issues, the detection of changes in gene expression, gene mutations, and chromosomal imbalances specific of Hodgkin's lymphoma are central to recent research that may allow one a better understanding of the natural history of this type of lymphoma.

Bystander cells and prognosis in Hodgkin lymphoma. Review based on a doctoral thesis

Hodgkin lymphoma (HL) is characterised histologically by a minority of malignant Hodgkin and Reed-Sternberg (HRS) cells surrounded by benign cells, and clinically by a relatively good prognosis. The treatment, however, leads to a risk of serious side effects. Knowledge about the biology of the disease, particularly the interaction between the HRS cells and the surrounding cells, is essential in order to improve diagnosis and treatment. HL patients with abundant eosinophils in the tumours have a poor prognosis, therefore the eosinophil derived protein eosinophil cationic protein (ECP) was studied. Serum-ECP (S-ECP) was elevated in most HL patients. It correlated to number of tumour eosinophils, nodular sclerosis (NS) histology, and the negative prognostic factors high erythrocyte sedimentation rate (ESR) and blood leukocyte count (WBC). A polymorphism in the ECP gene (434(G>C)) was identified and the 434GG genotype correlated to NS histology and high ESR. The poor prognosis in patients with abundant eosinophils in the tumours has been proposed to depend on HRS cell stimulation by the eosinophils via a CD30 ligand (CD30L)-CD30 interaction. However, CD30L mRNA and protein were detected in mast cells and the predominant CD30L expressing cell in HL is the mast cell. Mast cells were shown to stimulate HRS cell lines via CD30L-CD30 interaction. The number of mast cells in HL tumours correlated to worse relapse-free survival, NS histology, high WBC, and low blood haemoglobin. Survival in patients with early and intermediate stage HL, diagnosed between 1985 and 1992, was generally favourable and comparatively limited treatment was sufficient to produce acceptable results for most stages. The majority of relapses could be salvaged. Patients treated with a short course of chemotherapy and radiotherapy had an excellent outcome. In conclusion prognosis is favourable in early and intermediate stages and there are possibilities for further improvements based on the fact that mast cells and eosinophils affect the biology and prognosis of HL.

Gadd45 beta mediates the protective effects of CD40 costimulation against Fas-induced apoptosis

In B lymphocytes, induction of apoptosis or programmed cell death (PCD) by Fas (CD95/APO-1) is suppressed by the triggering of CD40. This suppression controls various aspects of the humoral immune response, including antibody affinity maturation. The opposing effects of these receptors are also crucial to B-cell homeostasis, autoimmune disease, and cancer. Cytoprotection by CD40 involves activation of protective genes mediated by NF-kappa B transcription factors; however, its basis remains poorly understood. Here, we report that, in B cells, Gadd45 beta is induced by CD40 through a mechanism that requires NF-kappa B and that this induction suppresses Fas-mediated killing. Importantly, up-regulation of Gadd45 beta by CD40 precedes Fas-induced caspase activation, as well as up-regulation of other NF-kappa B-controlled inhibitors of apoptosis such as Bcl-xL and c-FLIPL. In the presence of Gadd45 beta, the Fas-induced apoptotic cascade is halted at mitochondria. However, in contrast to Bcl-xL, Gadd45 beta is unable to hamper the "intrinsic" pathway for apoptosis and in fact appears to block Fas cytotoxicity herein by suppressing a mitochondria-targeting mechanism activated by this receptor. These findings identify Gadd45 beta as a critical mediator of the prosurvival response to CD40 stimulation and provide important new insights into the apoptotic mechanism that is triggered by Fas in B cells.

Emerging applications of the tumor necrosis factor family of ligands and receptors in cancer therapy

Abnormalities of the tumor necrosis factor (TNF) family members have been linked to several human diseases, including cancer. Novel treatment strategies for cancer are emerging based on an understanding of the function of TNF family members. The advantage of these strategies is their potential to selectively target cancer cells, while sparing normal cells. Combining these new strategies with currently available treatments such as chemotherapy and radiation therapy is under investigation, with promising results. However, because some TNF family members are toxic to normal mammalian cells when administered systemically, only a few TNF family members have potential therapeutic value. This concise review focuses on the clinical implications of four TNF family members for cancer treatment: CD30/CD30 ligand, CD40/CD40 ligand, receptor activator of nuclear factor-kappaB (RANK)/RANK ligand, and TNF-related apoptosis-inducing ligand (TRAIL) Apo-2L/TRAIL receptors.

MEK/ERK pathway is aberrantly active in Hodgkin disease: a signaling pathway shared by CD30, CD40, and RANK that regulates cell proliferation and survival

The mitogen-activated protein kinase (MAPK) (also called extracellular signal-regulated kinase [ERK]) pathway has been implicated in malignant transformation and in the regulation of cellular growth and proliferation of several tumor types, but its expression and function in Hodgkin disease (HD) are unknown. We report here that the active phosphorylated form of MAPK/ERK is aberrantly expressed in cultured and primary HD cells. Inhibition of the upstream MAPK kinase (also called MEK) by the small molecule UO126 inhibited the phosphorylation of ERK and demonstrated a dose- and time-dependent antiproliferative activity in HD cell lines. UO126 modulated the levels of several intracellular proteins including B-cell lymphoma protein 2 (Bcl-2), myeloid cell leukemia-1 (Mcl-1) and caspase 8 homolog FLICE-inhibitory protein (cFLIP), and induced G2M cell-cycle arrest or apoptosis. Furthermore, UO126 potentiated the activity of apoliprotein 2/tumor necrosis factor-related apoptosis-inducing ligand (APO2L/TRAIL) and chemotherapy-induced cell death. Activation of CD30, CD40, and receptor activator of nuclear kappabeta (RANK) receptors in HD cells by their respective ligands increased ERK phosphorylation above the basal level and promoted HD cell survival. UO126 inhibited basal and ligand-induced ERK phosphorylation, and inhibited ligand-induced cell survival of HD cell lines. These findings provide a proof-of-principle that inhibition of the MEK/ERK pathway may have therapeutic value in HD.

The molecular basis for the generation of Hodgkin and Reed-Sternberg cells in Hodgkin's lymphoma

Hodgkin's lymphoma (HL) is a lymphoid neoplasm with a low frequency of malignant tumor cells, known as Hodgkin and Reed-Sternberg (H-RS) cells, in a background of mixed cellular infiltrates. Despite extensive studies on H-RS cells, the molecular mechanisms of their growth and regulation have remained uncertain for a long period. Recently, constitutively activated nuclear factor-kappaB (NF-kappaB) was reported to be a unique and common characteristic of H-RS cells that prevents the cells from undergoing apoptosis. NF-kappaB triggers proliferation and provides a molecular basis for these cells' aberrant growth and cytokine gene expression. In HL pathogenesis associated with Epstein-Barr virus infection, the activation of NF-kappaB is induced by viral latent membrane protein 1 (LMP1). Coupled with recent insights into the molecular mechanisms of activation of NF-kappaB signaling in H-RS cells, this review discusses a linkage between LMP1 and HL via CD99, which has recently been reported to be down-regulated by LMP1 through the NF-kappaB signaling pathway. This down-regulation leads to the generation of cells with H-RS phenotypes related to the clinical and histologic characteristics of HL.

Hodgkin's lymphoma

Hodgkin's lymphoma was first described in 1832, but the nature of the pathognomic Reed-Sternberg cell, on which diagnosis of the disease is based, has only been elucidated in the past few years. Radiotherapy has been used to treat localised disease since the 1940s, and in the 1960s, effective combination chemotherapy regimens were introduced for anatomically advanced disease. The past three decades have witnessed continued improvement in outcome to such an extent that Hodgkin's lymphoma is now one of the most curable of all non-cutaneous malignancies. With improved survival and extended follow-up, relevance of treatment-induced late effects has become apparent, and modern therapeutic strategies must fully account for these effects. We review the pathology of Hodgkin's lymphoma, and its clinical presentation, investigation, present management, and natural history, including late effects of treatment.

Molecular biology of Hodgkin's lymphoma

Hodgkin's lymphoma (HL) is characterized by typical mononucleated Hodgkin and multinucleated Reed-Sternberg cells, which occur at low frequency in a mixed cellular infiltrate in the tumor tissue. Because of the rarity of these cells and their unusual immunophenotype, which is strikingly different from those of all normal hematopoietic cell types, the origin of these cells and their clonality have long been unclear. Single-cell studies of rearranged immunoglobulin genes showed that Hodgkin and Reed-Sternberg (HRS) cells represent clonal tumor-cell populations derived from germinal center B cells. In classical HL, the detection of obviously crippling immunoglobulin gene mutations in a fraction of the cases suggests that HRS cells may derive from germinal center B cells that have lost the capacity to be positively selected by antigen and that normally would have undergone apoptosis. In rare cases, HRS cells represent transformed T lymphocytes. The transforming events involved in malignant transformation of HRS cells are still largely unknown. Constitutive activation of the transcription factor NFkappaB, which can, for example, be induced through Epstein-Barr virus transformation of HRS cells or destructive somatic mutations of the inhibitor of NFkappaB, is likely to be a key event in HL pathogenesis. Significant progress has been made in our understanding of the cellular interactions in HL tissues, which are mainly mediated by a large variety of cytokines and chemokines.

The role of cytokines in classical Hodgkin lymphoma

The clinical and pathologic features of classical Hodgkin lymphoma (cHL) reflect an abnormal immune response that is thought to be due to the elaboration of a variety of cytokines by the malignant Reed-Sternberg (RS) cells or surrounding tissues. The majority of cHL cases are characterized by expression of tumor necrosis factor receptor (TNFR) family members and their ligands, as well as an unbalanced production of Th2 cytokines and chemokines. Activation of TNFR members results in constitutive activation of nuclear factor-kappa B (NF-kappa B), a transcription factor important for the in vitro and in vivo growth of RS cell lines. The expression of Th2 cytokines and chemokines leads to the reactive infiltrate of eosinophils, Th2 cells, and fibroblasts characteristic of cHL, and can also contribute to a local suppression of Th1 cell-mediated cellular immune response. Another particularly important growth and survival factor for RS cell lines is the Th2 cytokine interleukin 13, which is also commonly expressed by primary RS cells. In approximately 40% of cHL cases, the presence of Epstein-Barr virus influences the Th1/Th2 balance toward the production of Th1 cytokines and chemokines, but this shift is apparently insufficient for the stimulation of an effective antitumor cell-mediated immune response. This review summarizes the current literature on cytokine expression by and activity on RS cell lines and primary cHL tissues, examines cytokine signaling pathways in RS cells, and discusses the role that cytokines play in the specific clinical and pathologic features of cHL.

Cytoplasmic aggregation of TRAF2 and TRAF5 proteins in the Hodgkin-Reed-Sternberg cells

We previously reported that ligand-independent signaling by highly expressed CD30 in Hodgkin-Reed-Sternberg (H-RS) cells is responsible for constitutive activation of NF-kappa B. In the present study, we characterize the intracellular localization of tumor necrosis factor (TNF) receptor associated factor (TRAF) proteins in H-RS cells. Confocal immunofluorescence microscopy of cell lines derived from H-RS cells and HEK293 transformants highly expressing CD30 revealed aggregation of TRAF2 and TRAF5 in the cytoplasm as well as clustering near the cell membrane. In contrast, TRAF proteins were diffusely distributed in the cytoplasm in cell lines unrelated to Hodgkin's disease (HD) and control HEK293 cells. Furthermore, the same intracellular distribution of TRAF proteins was demonstrated in H-RS cells of lymph nodes of HD, but not in lymphoma cells in lymph nodes of non-Hodgkin's lymphoma. Dominant-negative TRAF2 and TRAF5 suppressed cytoplasmic aggregation along with constitutive NF-kappa B activation in H-RS cell lines. Confocal immunofluorescence microscopy also revealed co-localization of IKK alpha, NIK, and I kappa B alpha with aggregated TRAF proteins in H-RS cell lines. These results suggest involvement of TRAF protein aggregation in the signaling process of highly expressed CD30 and suggest they function as scaffolding proteins. Thus, cytoplasmic aggregation of TRAF proteins appears to reflect constitutive CD30 signaling which is characteristic of H-RS cells.

Expression of CD40 ligand (CD154) in B and T lymphocytes of Hodgkin disease: potential therapeutic significance

BACKGROUND

The malignant Hodgkin and Reed-Sternberg (H/RS) cells of Hodgkin disease (HD) express CD30 and CD40 receptors that can activate nuclear factor kappa B and transduce survival signals. The authors have reported previously that the B lymphocytes of HD express CD30 ligand (CD30L, CD153). Furthermore, they and others have reported previously that the CD40L survival pathway is augmented in patients with B-cell malignancies, as CD40L was constitutively expressed by the malignant B cells and infiltrating T cells, and sera from those patients contained elevated levels of soluble CD40L. In this study, the authors investigated the hypothesis that the survival of H/RS cells was similarly promoted by an augmented CD40L signals in HD patients.

METHODS

The expression of CD40L on lymphocyte subsets of patients with classic HD was determined by two-color fluorescent-activated cell sorter analysis. Serum soluble CD40L levels were determined by enzyme linked immunosorbent assay.

RESULTS

CD40L was constitutively expressed on both the T and B cells of HD patients but was more prominently expressed on the B lymphocytes. Soluble CD40L was detected in the serum of 17 of 37 patients (45%) and was higher than 1 ng/mL in 4 patients (10%). Both interleukin (IL)-4 and IL-10, which are known to be secreted by H/RS cells and surrounding T cells, up-regulated CD40L expression on normal B cells.

CONCLUSIONS

Thus, the expression of CD40L and CD30L on the B cells of HD patients suggests that B lymphocytes may play a role in the regulation of H/RS cell growth in vivo. Depriving H/RS cells from CD30L and CD40L survival signals by eliminating B cells from HD lesions may be of therapeutic value.

Differential effects of HIV-1 protease inhibitors on dendritic cell immunophenotype and function

Recent findings show that human immunodeficiency virus (HIV)-1 protease inhibitors designed to specifically inhibit the aspartic protease of HIV-1 nonetheless exert various effects on immune cell function in vitro and in vivo. Dendritic cells (DC), central players of the immune system, express several aspartic proteases that are important for DC function. In the present study, we demonstrate that all of the HIV-1 protease inhibitors tested affect DC maturation. In addition, saquinavir had a strong inhibitory effect on the T-cell stimulatory capacity of mature DC. In contrast, indinavir had only a slight effect on DC induced T-cell proliferation and allowed efficient transduction of DC with a replication-incompetent HIV-1 vector designed for DC-based immunotherapy. HIV-1 protease inhibitors that have little or no effect on DC function may be preferable for combination with immunotherapy for HIV/AIDS.

CD40 signaling and plaque instability

Today, multiple lines of evidence support the view of atherosclerosis as a chronic inflammatory disease and implicate components of the immune system in atherogenesis. Recent work has documented overexpression of the potent immune mediator CD40 and its counterpart CD40 ligand (CD40L) in experimental and human atherosclerotic lesions. Notably, interruption of CD40/CD40L interactions not only diminished the formation and progression of mouse atheroma, but also fostered changes in lesion biology and structure, which are associated in humans with "plaque stabilization." In accordance with the hypothesis that CD40 signaling promotes plaque instability, in vitro studies demonstrated that ligation of CD40 on atheroma-associated cell types, namely endothelial cells, smooth muscle cells, and macrophages, mediates functions considered crucial to the process of atherogenesis, such as the expression of cytokines, chemokines, growth factors, matrix metalloproteinases, and procoagulants. The combination of the broad gamut of proatherogenic biological responses triggered by ligation of CD40 on endothelial cells, smooth muscle cells, and macrophages in vitro and the results of in vivo studies of interruption of CD40 signaling suggests a central role for this receptor/ligand dyad during atherogenesis, proposing CD40/CD40L interactions as a novel potential therapeutic target for this prevalent human disease.

Recent publications in hematological oncology

In order to keep subscribers up-to-date with the latest developments in their field, John Wiley & Sons are providing a current awareness service in each issue of the journal. The bibliography contains newly published material in the field of hematological oncology. Each bibliography is divided into 14 sections: 1 Books, Reviews & Symposia; 2 General; Leukemias: 3 Lymphoblastic; 4 Myeloid & Myelodysplastic Syndromes; 5 Chronic; 6 Others; Lymphomas: 7 Hodgkin's; 8 Non-Hodgkin's; 9 Plasmacytomas/Multiple Myelomas; 10 Others; 11 Bone Marrow Transplantation; 12 Cytokines; 13 Diagnosis; 14 Cytogenetics. Within each section, articles are listed in alphabetical order with respect to author. If, in the preceding period, no publications are located relevant to any one of these headings, that section will be omitted.