BCL-6 protein is expressed in precursor T-cell lymphoblastic lymphoma and in prenatal and postnatal thymus

Evaluation of Novel Targets, Including CC-Chemokine Receptor 4, in Adult T-Cell Acute Lymphoblastic Leukemia/Lymphoma: A Mayo Clinic Clinical and Pathologic Study

CONTEXT.—

Unlike B-cell acute lymphoblastic leukemia/lymphoma (ALL/LBL), there have been few therapeutic advances in T-cell ALL (T-ALL)/LBL, an aggressive ALL/LBL subtype.

OBJECTIVE.—

To perform a focused tissue array study to elucidate tumor markers of therapeutic potential in T-ALL/LBL.

DESIGN.—

Using immunohistochemistry, we evaluated expression of leukemic antigens of interest, specifically CC-chemokine receptor 4 (CCR4), among others, on available remnant diagnostic material, including tumor tissue slides obtained from formalin-fixed, paraffin-embedded preserved tissues.

RESULTS.—

Our analysis identified, for the first time, expression of CCR4 in T-ALL/LBL in 11 of 27 cases (40.7%) and confirmed common expression of BCL2, CD38, and CD47, as reported previously. We also identified the expression of CD123 in 4 of 26 cases (15.4%), whereas BCL6 and PDL1 were expressed in a small number of T-ALL/LBL cases. The potential novel target CCR4 was significantly more common in the Pre/Pro-T immunophenotypic subtype, 6 of 9 (66.7%, P = .01). No additional differences in clinical and epidemiologic variables were noted among positive or negative CCR4 cases.

CONCLUSIONS.—

These findings support preclinical and clinical testing of therapies targeting CCR4, CD47, BCL2, CD38, and CD123 in T-ALL/LBL, and may help guide the development of targeted clinical trials in T-ALL/LBL, a rare disease in urgent need of novel therapies.

The 3D enhancer network of the developing T cell genome is shaped by SATB1

Mechanisms of tissue-specific gene expression regulation via 3D genome organization are poorly understood. Here we uncover the regulatory chromatin network of developing T cells and identify SATB1, a tissue-specific genome organizer, enriched at the anchors of promoter-enhancer loops. We have generated a T-cell specific Satb1 conditional knockout mouse which allows us to infer the molecular mechanisms responsible for the deregulation of its immune system. H3K27ac HiChIP and Hi-C experiments indicate that SATB1-dependent promoter-enhancer loops regulate expression of master regulator genes (such as Bcl6), the T cell receptor locus and adhesion molecule genes, collectively being critical for cell lineage specification and immune system homeostasis. SATB1-dependent regulatory chromatin loops represent a more refined layer of genome organization built upon a high-order scaffold provided by CTCF and other factors. Overall, our findings unravel the function of a tissue-specific factor that controls transcription programs, via spatial chromatin arrangements complementary to the chromatin structure imposed by ubiquitously expressed genome organizers.

B cell lymphoma 6A regulates immune development and function in zebrafish

BCL6A is a transcriptional repressor implicated in the development and survival of B and T lymphoctyes, which is also highly expressed in many non-Hodgkin’s lymphomas, such as diffuse large B cell lymphoma and follicular lymphoma. Roles in other cell types, including macrophages and non-hematopoietic cells, have also been suggested but require further investigation. This study sought to identify and characterize zebrafish BCL6A and investigate its role in immune cell development and function, with a focus on early macrophages. Bioinformatics analysis identified a homologue for BCL6A (bcl6aa), as well as an additional fish-specific duplicate (bcl6ab) and a homologue for the closely-related BCL6B (bcl6b). The human BCL6A and zebrafish Bcl6aa proteins were highly conserved across the constituent BTB/POZ, PEST and zinc finger domains. Expression of bcl6aa during early zebrafish embryogenesis was observed in the lateral plate mesoderm, a site of early myeloid cell development, with later expression seen in the brain, eye and thymus. Homozygous bcl6aa mutants developed normally until around 14 days post fertilization (dpf), after which their subsequent growth and maturation was severely impacted along with their relative survival, with heterozygous bcl6aa mutants showing an intermediate phenotype. Analysis of immune cell development revealed significantly decreased lymphoid and macrophage cells in both homozygous and heterozygous bcl6aa mutants, being exacerbated in homozygous mutants. In contrast, the number of neutrophils was unaffected. Only the homozygous bcl6aa mutants showed decreased macrophage mobility in response to wounding and reduced ability to contain bacterial infection. Collectively, this suggests strong conservation of BCL6A across evolution, including a role in macrophage biology.

BCL6 BTB-specific inhibition via FX1 treatment reduces Tfh cells and reverses lymphoid follicle hyperplasia in Indian rhesus macaque (Macaca mulatta)

BACKGROUND

The BTB domain of B-cell lymphoma 6 (BCL6) protein was identified as a therapeutic target for B-cell lymphoma. This study compared the pharmacokinetics (PK) of the BCL6 BTB inhibitor (FX1) between mice and macaques, as well as evaluating its lymphoid suppressive effect in uninfected macaques with lymphoid hyperplasia.

MATERIALS AND METHODS

Eight uninfected adult Indian rhesus macaques (Macaca mulatta) were used in the study, four animals carrying lymphoid tissue hyperplasia. Plasma FX1 levels were measured by HPLC-MS/MS. Lymph node biopsies were used for H&E and immunohistochemistry staining, as well as mononuclear cell isolation for flow cytometry analysis.

RESULTS

Inhibition of the BCL6 BTB domain with FX1 led to a reduction in the frequency of GC, Tfh CD4⁺ , and Tfh precursor cells, as well as resolving lymphoid hyperplasia, in rhesus macaques.

CONCLUSIONS

B-cell lymphoma 6 inhibition may represent a novel strategy to reduce hyperplastic lymphoid B-cell follicles and decrease Tfh cells.

Immunohistochemical expression of Mum-1, Oct-2 and Bcl-6 in systemic anaplastic large cell lymphomas

Aims and backround

Several transcription factors predominantly used for B-cell lineage identification are also expressed in a small percentage of T cells within germinal centers and interfollicular areas. The aim of the study was to evaluate the expression of Mum-1, Oct-2 and Bcl-6 in systemic anaplastic large cell lymphoma.

Methods

Thirty cases of anaplastic large cell lymphoma were retrieved from our archives and tissue microarray constructed. Immunohistochemistry was carried out using an avidin-biotin peroxidase complex method.

Results

A predominance of nuclear staining was observed for all transcription factors. Mum-1 was positive in all but one case (96.7%). Half of the cases displayed Oct-2 expression (15/30 cases). A considerable number of cases also had Bcl-6 expression (9/30). Bcl-6 staining was noted to be more common in ALK positive cases.

Conclusion

Our findings emphasize that these markers are not restricted to B-cell lineage and that extensive expression can be observed in anaplastic large cell lymphoma of T/null cell phenotype.

Inhibition of RORγT Skews TCRα Gene Rearrangement and Limits T Cell Repertoire Diversity

Recent studies have elucidated the molecular mechanism of RORγT transcriptional regulation of Th17 differentiation and function. RORγT was initially identified as a transcription factor required for thymopoiesis by maintaining survival of CD4⁺CD8⁺ (DP) thymocytes. While RORγ antagonists are currently being developed to treat autoimmunity, it remains unclear how RORγT inhibition may impact thymocyte development. In this study, we show that in addition to regulating DP thymocytes survival, RORγT also controls genes that regulate thymocyte migration, proliferation, and T cell receptor (TCR)α selection. Strikingly, pharmacological inhibition of RORγ skews TCRα gene rearrangement, limits T cell repertoire diversity, and inhibits development of autoimmune encephalomyelitis. Thus, targeting RORγT not only inhibits Th17 cell development and function but also fundamentally alters thymic-emigrant recognition of self and foreign antigens. The analysis of RORγ inhibitors has allowed us to gain a broader perspective of the diverse function of RORγT and its impact on T cell biology.

A negative feedback loop mediated by the Bcl6-cullin 3 complex limits Tfh cell differentiation

Bcl6 and E3 ligase cullin 3 complexes mediate negative feedback regulation during thymocyte development and T cell activation to restrain exaggerated Tfh responses.

Induction of Bcl6 (B cell lymphoma 6) is essential for T follicular helper (Tfh) cell differentiation of antigen-stimulated CD4⁺ T cells. Intriguingly, we found that Bcl6 was also highly and transiently expressed during the CD4⁺CD8⁺ (double positive [DP]) stage of T cell development, in association with the E3 ligase cullin 3 (Cul3), a novel binding partner of Bcl6 which ubiquitinates histone proteins. DP stage–specific deletion of the E3 ligase Cul3, or of Bcl6, induced the derepression of the Bcl6 target genes Batf (basic leucine zipper transcription factor, ATF-like) and Bcl6, in part through epigenetic modifications of CD4⁺ single-positive thymocytes. Although they maintained an apparently normal phenotype after emigration, they expressed increased amounts of Batf and Bcl6 at basal state and produced explosive and prolonged Tfh responses upon subsequent antigen encounter. Ablation of Cul3 in mature CD4⁺ splenocytes also resulted in dramatically exaggerated Tfh responses. Thus, although previous studies have emphasized the essential role of Bcl6 in inducing Tfh responses, our findings reveal that Bcl6–Cul3 complexes also provide essential negative feedback regulation during both thymocyte development and T cell activation to restrain excessive Tfh responses.

GFI1B, EVI5, MYB--additional genes that cooperate with the human BCL6 gene to promote the development of lymphomas

The BCL6 gene, which is expressed in certain B- and T-cell human lymphomas, is involved with chromosomal rearrangements and mutations in a number of these neoplasms. Lymphomagenesis is believed to evolve through a multi-step accumulation of genetic alterations in these tumors. We used retroviral insertional mutagenesis in transgenic mice expressing the human BCL6 transgene in order to identify genes that cooperate with BCL6 during lymphomatous transformation. We previously reported PIM1 as the most frequently recurring cooperating gene in this model. We now report three newly identified cooperating genes-GFI1B, EVI5, and MYB-that we identified in the lymphomas of retroviral-injected BCL6 transgenic mice (but not in retroviral-injected non-transgenic controls); mRNA and protein expression of GFI1B and EVI5 were decreased in the murine tumors, whereas MYB mRNA and protein expression were increased or decreased. These findings correlated with protein expression in human lymphomas, both B- and T-cell. Improved therapy of lymphomas may necessitate the development of combinations of drugs that target the alterations specific to each neoplasm.

High levels of bcl-2 protein expression do not correlate with genetic abnormalities but predict worse prognosis in patients with lymphoblastic lymphoma

We aimed to investigate bcl-2, bcl-6, and c-myc rearrangements in patients with lymphoblastic lymphoma (LBL), especially focus on the correlation of protein expression with genetic abnormalities. Moreover, their prognostic significance was further analyzed in LBL. Protein expression and genetic abnormalities of bcl-2, bcl-6, and c-myc were investigated in microarrayed tumors from 33 cases of T cell LBL and eight cases of B cell lineage. Immunohistochemical (IHC) staining was performed to evaluate protein expression, including bcl-2, bcl-6, c-myc, TdT, CD1α, CD34, Ki-67, PAX-5, CD2, CD3, CD4, CD8, and CD20. Genetic abnormalities of bcl-2, bcl-6, and c-myc were detected by dual color fluorescence in situ hybridization (FISH). Bcl-2 protein was positive in 51.2 % (21/41) of the patients, bcl-6 protein in 7.3 % (three out of 41), and c-myc protein in 78.0 % (32/41). Bcl-2 breakpoint was found in two cases by FISH analysis. There was no evidence of bcl-6 or c-myc rearrangement in patients with LBL. However, both gene gain and loss events occurred in bcl-2, bcl-6, and c-myc. A univariate analysis showed that stage III or IV, elevated lactate dehydrogenase (LDH), and positivity for bcl-2 protein were associated with shorter survival (p<0.05). Enhanced protein expression and detectable genetic abnormalities of bcl-2, bcl-6, and c-myc were observed in patients with LBL. No statistical correlation was found between IHC results and cytogenetic findings. Stage III or IV, elevated LDH, and positivity for bcl-2 protein were identified as adverse prognostic factors. The patients with more adverse factors would have increasingly worse prognosis.

BTB-ZF factors recruit the E3 ligase cullin 3 to regulate lymphoid effector programs

The differentiation of several T and B cell effector programs in the immune system is directed by signature transcription factors that induce rapid epigenetic remodeling. We report that PLZF, the BTB-ZF transcription factor directing the innate-like effector program of NKT thymocytes ^1,2 was prominently associated with cullin 3 (Cul3), an E3 ubiquitin ligase previously shown to use BTB domain-containing proteins as adaptors for substrate binding ^3–7. PLZF transported Cul3 to the nucleus where the two proteins were associated within a chromatin modifying complex. Furthermore, PLZF expression resulted in selective changes of ubiquitination of multiple components of this complex. Cul3 was also found associated with another BTB-ZF transcription factor, Bcl6, which directs the B cell germinal center and the T follicular helper programs. Conditional deletion in mice demonstrated an essential role of Cul3 for the development of PLZF- and Bcl6-dependent lineages. We conclude that distinct lineage-specific BTB-ZF transcription factors recruit Cul3 to alter the ubiquitination pattern of their associated chromatin modifying complex. We propose that this novel function is essential to direct the differentiation of several T and B lymphocyte effector programs, and may also be involved in the oncogenic role of PLZF and Bcl6 in leukemias and lymphomas ^8,9.

PIM1 gene cooperates with human BCL6 gene to promote the development of lymphomas

Diffuse large B-cell lymphomas in humans are associated with chromosomal rearrangements (∼40%) and/or mutations disrupting autoregulation (∼16%) involving the BCL6 gene. Studies of lymphoma development in humans and mouse models have indicated that lymphomagenesis evolves through the accumulation of multiple genetic alterations. Based on our prior studies, which indicated that carcinogen-induced DNA mutations enhance the incidence of lymphomas in our mouse model expressing a human BCL6 transgene, we hypothesized that mutated genes are likely to play an important cooperative role in BCL6-associated lymphoma development. We used retroviral insertional mutagenesis in an effort to identify which genes cooperate with BCL6 in lymphomagenesis in our BCL6 transgenic mice. We identified PIM1 as the most frequently recurring cooperating gene in our murine BCL6-associated lymphomas (T- and B-cell types), and we observed elevated levels of PIM1 mRNA and protein expression in these neoplasms. Further, immunohistochemical staining, which was performed in 20 randomly selected BCL6-positive human B- and T-cell lymphomas, revealed concurrent expression of BCL6 and PIM1 in these neoplasms. As PIM1 encodes a serine/threonine kinase, PIM1 kinase inhibition may be a promising therapy for BCL6/PIM1-positive human lymphomas.

Functional interaction of HTLV-1 tax protein with the POZ domain of the transcriptional repressor BCL6

The Tax protein encoded by human T-cell leukaemia virus type 1 (HTLV-1) has a pivotal role in T-cell transformation by deregulating cellular signalling pathways. Using the yeast two-hybrid system to screen a human leukocyte cDNA library, we identified BCL6 (B-cell lymphoma 6) as a cellular protein, which interacts with Tax 1. The BCL6 gene encodes a sequence-specific transcriptional repressor that contains a conserved N-terminal poxvirus and zinc finger (POZ) repressor domain and a C-terminal Kruppel-like zinc finger DNA binding domain. Using both in vivo and in vitro methods, we demonstrate that the POZ domain of BCL6 is sufficient for its interaction with Tax 1. Using functional assays, we demonstrate that Tax 1 enhanced the repressive activity of BCL6 and increased the levels of apoptosis induced by BCL6 in osteosarcoma cells indicating that both proteins cooperate in vivo to cause a physiological affect. Furthermore, BCL6 recruited Tax 1 into punctate nuclear structures, which suggests that Tax 1 colocalizes with BCL6 in repressor complexes in vivo. BCL6 expression significantly downregulated both basal and Tax-induced nuclear factor-kappaB and long terminal repeat activation. This suggests that the expression of BCL6 in HTLV infected cells may contribute to the silencing of viral gene expression and to the long clinical latency associated with HTLV infection.

Best practices in contemporary diagnostic immunohistochemistry: panel approach to hematolymphoid proliferations

CONTEXT

The complexities of diagnostic hematopathology in the modern era are well known, and even in this molecular era, immunophenotypic studies, together with routine histopathology, remain a critical component in the evaluation of many lymphoid proliferations. With numerous antibodies that can be used on routinely fixed, paraffin-embedded tissue sections, immunohistochemistry has become increasingly valuable. It then becomes a challenge knowing the best approach to the selection of antibodies to use and how to interpret them.

OBJECTIVE

To present a pragmatic immunohistochemical approach to the evaluation of lymphoid proliferations that stresses the utility of 2 limited panels to deal with the most commonly encountered lymphomas.

DATA SOURCES

English-language literature published between 1990 and 2008.

CONCLUSIONS

A relatively limited panel of immunohistochemical stains may be used to diagnose and subclassify many of the more common lymphomas, although some cases will require additional stains and others fewer, depending on the case complexity. Immunohistochemical stains must always be interpreted in the context of the histopathologic and other ancillary studies.

Characterization of childhood precursor T-lymphoblastic lymphoma by immunophenotyping and fluorescent in situ hybridization: a report from the Children's Oncology Group

BACKGROUND

T-lymphoblastic lymphoma (T-LBL) accounts for 25-30% of childhood non-Hodgkin's lymphoma and is closely related to T-lymphoblastic leukemia (T-ALL). Recently, we demonstrated distinct differences in gene expression between childhood T-LBL and T-ALL, but molecular pathogenesis and relevant protein expression patterns in T-LBL remain poorly understood.

PROCEDURE

Children with T-LBL with disseminated disease were registered and treated on COG protocol 5971. Paraffin-embedded tumor tissue was obtained at diagnosis for immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) studies. We determined the pattern and intensity of staining for c-Myc, Skp2, Mib-1, p53, TCL-1, bcl-2, and bcl-6 proteins by IHC and c-Myc, p53, bcl-2, bcl-6, and TCR alpha/delta molecular alterations by FISH in 22 pediatric T-LBL cases.

RESULTS

The majority of T-LBL samples expressed Mib-1 (59%) and c-Myc (77%) proteins in greater than 50% of the cells, but Skp2 (14%), p53 (14%), and bcl-2 (23%) expression was less common. FISH studies demonstrated 18% gains and 10% losses in c-Myc, 16% gains in p53, 12% gains and 6% losses in bcl-2, and 6% gains and 19% losses in bcl-6 with little direct correlation between the IHC and FISH studies.

CONCLUSIONS

Childhood T-LBL is a highly proliferative tumor associated with enhanced expression of c-Myc protein, but without detectable c-Myc molecular alterations. FISH studies did not identify consistent etiologies of molecular dysregulation, and future studies with other molecular approaches may be required to elucidate the molecular pathogenesis of childhood T-LBL.

Acute leukemia immunohistochemistry: a systematic diagnostic approach

CONTEXT

The diagnosis and classification of leukemia is becoming increasingly complex. Current classification schemes incorporate morphologic features, immunophenotype, molecular genetics, and clinical data to specifically categorize leukemias into various subtypes. Although sophisticated methodologies are frequently used to detect characteristic features conferring diagnostic, prognostic, or therapeutic implications, a thorough microscopic examination remains essential to the pathologic evaluation. Detailed blast immunophenotyping can be performed with lineage- and maturation-specific markers. Although no one marker is pathognomonic for one malignancy, a well-chosen panel of antibodies can efficiently aid the diagnosis and classification of acute leukemias.

OBJECTIVE

To review important developments from recent and historical literature. General immunohistochemical staining patterns of the most commonly encountered lymphoid and myeloid leukemias are emphasized. The goal is to discuss the immunostaining of acute leukemias when flow cytometry and genetic studies are not available.

DATA SOURCES

A comprehensive review was performed of the relevant literature indexed in PubMed (National Library of Medicine) and referenced medical texts. Additional references were identified in the reviewed manuscripts.

CONCLUSIONS

Immunophenotyping of blasts using an immunohistochemical approach to lymphoid and myeloid malignancies is presented. Initial and subsequent additional antibody panels are suggested to confirm or exclude each possibility in the differential diagnosis and a general strategy for diagnostic evaluation is discussed. Although the use of immunohistochemistry alone is limited and evaluation by flow cytometry and genetic studies is highly recommended, unavoidable situations requiring analysis of formalin-fixed tissue specimens arise. When performed in an optimized laboratory and combined with a careful morphologic examination, the immunohistochemical approach represents a useful laboratory tool for classifying various leukemias.

The critical role of histology in an era of genomics and proteomics: a commentary and reflection

The role of histologic examination in lymphoma diagnosis has been called into question by proponents of new technologies, such as genomics and proteomics. We review the history and salient features of morphologic evaluation in lymphoid diseases, and discuss the general and specific limitations of mature ancillary techniques, such as immunohistochemistry, flow cytometry, and molecular studies. We then speculate on the future relationship between morphology and the new genomic and proteomic technologies as they become integrated into clinical practice.

BCL6 gene mutations in transitional cell carcinomas

The B-cell lymphoma-6 (BCL6) gene was initially identified at a translocation site observed frequently in diffuse large B-cell lymphomas. In the present study, BCL6 mutations at the 5' non-coding region in 47 cases of transitional call carcinoma (TCC) were analysed using polymerase chain reaction-single-strand conformation polymorphism. The results were compared with data obtained previously by immunohistochemical staining for the BCL6 protein. Overall, BCL6 mutations were observed in 44.7% of cases. Mutation of the 5' non-coding region was not correlated with histological grade of the tumour; however, the better the histological grade, the greater the mutation rate of the E1.12 fragment. The BCL6 mutation occurred independently of over-expression of the protein. The BCL6 gene mutation and the protein expression were detectable in a large proportion of TCCs. BCL6 protein over-expression as well as BCL6 gene mutation of the E1.12 fragment may play an important role in the morphological differentiation of TCC.

Repression of the PDCD2 gene by BCL6 and the implications for the pathogenesis of human B and T cell lymphomas

The human BCL6 gene on chromosome 3 band q27, which encodes a transcriptional repressor, is implicated in the pathogenesis of human lymphomas, especially the diffuse large B-cell type. We previously identified the human PDCD2 (programmed cell death-2) gene as a target of BCL6 repression. PDCD2 encodes a protein that is expressed in many human tissues, including lymphocytes, and is known to interact with corepressor complexes. We now show that BCL6 can bind directly to the PDCD2 promoter, repressing its transcription. Knockdown of endogenous BCL6 in a human B cell lymphoma line by introduction of small interfering RNA duplexes increases PDCD2 protein expression. Furthermore, there is an inverse relationship between the expression levels of the BCL6 and PDCD2 proteins in the lymphoid tissues of mice overexpressing human BCL6 (high BCL6 levels, minimal PDCD2) and controls (minimal BCL6, high PDCD2) as well as in tissues examined from some human B and T cell lymphomas. These data confirm PDCD2 as a target of BCL6 and support the concept that repression of PDCD2 by BCL6 is likely important in the pathogenesis of certain human lymphomas.

Kaposi sarcoma-associated herpesvirus in non-Hodgkin lymphoma and reactive lymphadenopathy in Uganda

Kaposi sarcoma-associated herpesvirus (KSHV) causes Kaposi sarcoma and is also associated with primary effusion lymphoma, a subset of diffuse large B-cell lymphomas, and multicentric Castleman disease. Because KSHV infection is endemic in sub-Saharan Africa, we sought to identify cases of KSHV-positive non-Hodgkin lymphomas (NHLs) and reactive lymphadenopathy in this region. One hundred forty-four cases (80 NHLs, 64 reactive lymph nodes) from the major pathology laboratory in Uganda were reviewed. One NHL was KSHV-positive, as indicated by staining for the viral latent nuclear antigen. This NHL was a diffuse large B-cell lymphoma in a 5-year-old boy. The tumor was also Epstein-Barr virus-positive. In addition, 2 reactive lymph nodes, both classified histologically as follicular involution, stained KSHV latent nuclear antigen-positive and thus most likely represent multicentric Castleman disease. In all 3 KSHV-positive cases, a minority of cells expressed KSHV viral interleukin 6, a biologically active cytokine homolog. In conclusion, we show that KSHV is rarely associated with lymphoproliferative disorders in sub-Saharan Africa. We describe the first case of a KSHV-positive NHL from this region; this case is also the first reported pediatric lymphoma associated with KSHV infection.

The rationale for the IL‐2‐independent generation of the self‐renewing central memory CD8 + T cells

Clones of CD8+ T cells that have been selected in the primary response must have a mechanism by which they can continuously or intermittently generate new effector cells. Several years ago, this mechanism was proposed to involve a self-renewing, stem cell-like subset that could avoid the differentiating effects of interleukin-2 (IL-2). The model considered the stem cell subset to be contained within the central memory population of CD8+ T cells (T(CM)). This proposal was inconsistent with subsequent findings suggesting that all antigen-activated CD8+ T cells differentiated to effector cells (T(EFF)) during the primary response and that T(CM) developed during the memory phase by de-differentiating from effector memory cells (T(EM)). However, findings have since been reported that support the stem cell model. First, studies indicate that T(EM) do not serve as the precursors of T(CM). Second, transcriptional repressors of IL-2 signaling do enhance the memory response. Third, memory cells lacking effector functions and with a capacity to replicate in a secondary response develop in the absence of signaling through the IL-2/IL-15 receptor. Taken together, these findings suggest that antigen-activated CD8+ T cells with a stem cell-like capability for maintaining proliferative potential develop by an unknown IL-2-independent process. The challenge is now to identify this unknown pathway of clonal expansion.

Peripheral T-cell lymphoma with involvement of the expanded mantle zone

Peripheral T-cell lymphoma (PTCL) with a nodular architecture is rare. Recently, two variants have been described with infiltration of the B-cell follicle, one variant that localizes to the marginal zone with a so-called perifollicular growth pattern, and a variant that localizes to the germinal center. These lymphomas have a CD4+ phenotype and may express Bcl-6. We have studied five similar cases of PTCL with involvement of the B-cell follicle. However, our cases differ from the cases previously described by their predominant and frequently patchy involvement of the expanded mantle zone of the B-cell follicle at onset. Later biopsies in three of the cases show diffuse infiltration of the lymph node, without features of angioimmunoblastic TCL (AILT). All cases expressed Bcl-6 in addition to CD4. Cytogenetics was available in four of the cases but revealed no recurrent chromosomal aberrations or changes associated with other types of PTCL. No mutations of the BCL-6 gene were observed. Together, the cases seem to have an intermediately aggressive clinical behavior. Whether our cases are part of a spectrum of PTCLs that encompasses previously described variants with predominant marginal zone or germinal center infiltration or they represent a separate T-cell lymphoma type remains to be demonstrated by a study of more of such cases.

Immunophenotyping of lymphoproliferative disorders: state of the art

Immunophenotyping was introduced into diagnostic pathology over 30 years ago to assist in the diagnosis and classification of lymphoproliferative disorders. Today the role of immunophenotyping has been expanded beyond this to include the detection of markers of prognosis, determination of disease phenotypes associated with specific chromosomal abnormalities, detection of targets for immunotherapy and to monitor residual disease. Immunoperoxidase detection methods remain the most popular in histopathology, whilst flow cytometry is most commonly applied for haematological samples. The range of monoclonal antibodies available, including those which work in routinely performed tissue specimens, continues to increase. This is in part a result of gene expression studies identifying precise genetic signatures for certain lymphoproliferative disorders and the generation of new protein markers to gene products of upregulated genes. This review summarises the current status and applications of immunophenotyping in the assessment of many of the lymphoid malignancies.

T-Cell lymphoblastic lymphoma presenting as bilateral multinodular breast masses: a case report and review of the literature

Non-Hodgkin lymphoma of T-cell lineage involving the breast is rare. We report on a 41-year-old woman with T-cell lymphoblastic lymphoma who presented with multiple bilateral breast masses. The patient was treated with intensive chemotherapy and mediastinal and whole-brain irradiation. She remains in complete remission 24 months after diagnosis. The clinical, histologic, phenotypic, and cytogenetic features are described, with a review of the literature.

Targeted somatic mutation of the BCL6 proto-oncogene and its impact on lymphomagenesis

Cloning translocation breakpoints which cluster suspiciously to specific chromosomal loci has proved fruitful, leading to the identification of genes implicated in the onset of hematological malignancy. One of the most notable is BCL6, located on chromosome 3q27. The BCL6 is now known to encode a nuclear transcriptional repressor, with pivotal roles in germinal center (GC) formation and regulation of lymphocyte function, differentiation and survival. Unusually, the BCL6 gene locus is also actively targeted by the somatic mutation (SM) mechanism, at a rate indicative of specific, regulated events in both normal and malignant B-cells. These mutations occur in approximately 30% of normal centrocytes and centroblasts, but not in naive or pre-GC B-cells. They are also observed in approximately 70% of diffuse large B-cells lymphomas, approximately 30% of follicular lymphomas (FL) and at various frequencies in many lymphoma subtypes. Mutations are generated in the 5' proximity of the BCL6 promoter, including the first intron and are mainly single nucleotide substitutions, but with insertions and deletions also observed. Mutations in BCL6 occur independently of translocations, although mutational levels can be dramatically influenced by aberrantly translocated chromosomal elements, which map in the vicinity of the gene. Indeed, SMs are directly implicated in the generation of chromosomal translocations, as suggested by the overlap of the breakpoint cluster region and the mutational cluster domain. The prognostic value of the overall level of BCL6 mutations in specific lymphoma populations is, in the main, not as yet fully resolved. The accumulation of mutations in BCL6 during high grade transformation of FL, a mutational clustering and specific recurrent mutations suggest that some mutations may be selected for by their effect on the survival of the tumoral clone. In fact, it is now clear that SM can target and disrupt regulatory motifs in BCL6 to result in upregulated gene expression. Exogenous factors can also perturbate SM in BCL6. Viral infection elevates BCL6 mutational activity, suggesting a potential link with onset of virus-associated lymphoma. These findings to date reveal several mechanisms which can influence specific mutations targeting BCL6, and which may contribute to lymphomagenesis by dysregulating control of BCL6 expression.

Molecular cloning of the BCL-6 gene, a transcriptional repressor for B-cell differentiation, in torafugu (Takifugu rubripes)

B-cell lymphoma-6 (BCL-6) is a transcriptional repressor that prevents the terminal differentiation of mature B-cells to plasma cells, and is essential for germinal center formation in the primary lymphoid organs of mammals. In this study, we identified the BCL-6 gene in torafugu (Takifugu rubripes) using the torafugu genome database, and analyzed the expression of BCL-6 mRNA in various tissues of torafugu, using RT-PCR. The BCL-6 gene consisted of eight exons and seven introns spanning a genome of ca. 3.3 kb. BCL-6 mRNA contained a 2112 bp open reading frame encoding 703 amino acids, with a predicted protein size of 78.8 kDa. The predicted torafugu BCL-6 primary structure contains two conserved specific motifs, the BTB/POZ domain at the N-terminus and the sixC2H2-type zinc finger motifs at the C-terminal region. The homology of torafugu BCL-6 to those of zebrafish (Danio rerio), Xenopus laevis, mouse (Mus musculus) and human (Homo sapiens) is 76, 59, 60 and 60%, respectively. RT-PCR analysis revealed that BCL-6 mRNA is highly expressed in pronephros, thymus, intestine, ovary, brain, nasal cavity and muscle. These results imply that torafugu BCL-6 is involved in regulation of B-cell differentiation in torafugu.

CD10 and BCL6 expression in the diagnosis of angioimmunoblastic T-cell lymphoma: utility of detecting CD10+ T cells by flow cytometry

Angioimmunoblastic T-cell lymphoma (AITCL) is a histologically distinct and relatively common subtype of T-cell lymphoma. Although the putative normal cell counterpart is a mature CD4+ T cell, the precise cell of origin remains elusive. We evaluated cases with a diagnosis of AITCL to determine the specificity and utility of CD10 coexpression, particularly by flow cytometry (FCM), in facilitating this diagnosis. Coexpression of BCL6 was also assessed. Eight AITCL cases were evaluated histologically, immunohistochemically, and by 4-color FCM. Four cases of peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS), were also analyzed. The lymphoma cells in all 8 AITCL cases were CD4+, CD45RO+ T cells, with classic extrafollicular meshworks of CD21/CD23/CD35+ follicular dendritic cells. Furthermore, all cases of AITCL cases contained interfollicular CD10+ cells by immunohistochemistry, and increased coexpression of CD10 on T cells was also detected in 6 of 8 cases by FCM. CD10 coexpression was not observed in all 4 PTCL-NOS cases. Although not specific for AITCL, increased numbers of BCL6+ cells were seen in AITCL as compared with PTCL-NOS. Double immunohistochemistry performed on an AITCL case with high numbers of BCL6+ cells highlighted coexpression of BCL6 and CD4 on the same cells. The finding suggests that AITCL may be a neoplasm of (possibly intrafollicular) CD10+, BCL6+, and CD4+ memory T cells. Although our series is small, our results suggest that CD10 coexpression may be a useful discriminant, particularly if the differential diagnosis is PTCL-NOS, and demonstrate that this can be determined by FCM.

Rituximab does not improve clinical outcome in a randomized phase 3 trial of CHOP with or without rituximab in patients with HIV-associated non-Hodgkin lymphoma: AIDS-Malignancies Consortium Trial 010

The addition of rituximab to cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) chemotherapy results in significant improvement in clinical outcome for individuals with non-HIV-associated aggressive B-cell lymphoma. To assess the potential risks and benefits of the addition of rituximab to CHOP for HIV-associated non-Hodgkin lymphoma (HIV-NHL) 150 patients receiving CHOP for HIV-NHL were randomized (2:1) to receive 375 mg/m(2) rituximab with each chemotherapy cycle (n = 99) or no immunotherapy (n = 50) in a multicenter phase 3 trial. The complete response rate (CR + CRu) was 57.6% for R-CHOP and 47% for CHOP (P = .147). With a median follow-up of 137 weeks, time to progression, progression-free survival, and overall survival times were 125, 45, and 139 weeks, respectively, for R-CHOP and 85, 38, and 110 weeks, respectively, for CHOP (P = not significant, all comparisons). Treatment-related infectious deaths occurred in 14% of patients receiving R-CHOP compared with 2% in the chemotherapy-alone group (P = .035). Of these deaths, 60% occurred in patients with CD4 counts less than 50/mm(3). Progression-free survival was significantly influenced by CD4(+) count (P < .001) and International Prognostic Index score (P = .022), but not bcl-2 status. The addition of rituximab to CHOP in patients with HIV-NHL may be associated with improved tumor responses. However, these benefits may be offset by an increase in infectious deaths, particularly in those individuals with CD4(+) lymphocyte counts less than 50/mm(3).

PU.1 protein expression has a positive linear association with protein expression of germinal centre B cell genes includingBCL-6, CD10, CD20 andCD22: identification of PU.1 putative binding sites in theBCL-6 promotor

The transcription factor PU.1 has been shown to be crucial for the early stages of B cell development but its function at later stages of B cell development is less well known. We observed previously that PU.1 is expressed uniformly throughout the mature pre-plasma cell B cell population, the only exception being a subpopulation of germinal centre (GC) cells which showed exceptionally high expression of PU.1. This suggested that PU.1 may also have a role in GC B cell biology. To test this hypothesis and to screen for possible genes regulated by PU.1, we first evaluated semi-quantitatively the possible co-expression of PU.1 with proteins known to be upregulated or downregulated during GC B cell development. Normal lymphoid tissues and 255 B cell non-Hodgkin lymphomas of putative GC B cell origin were evaluated. PU.1 expression was positively associated with CD10 (p < 0.0001), CD20 (p = 0.043), CD22 (p = 0.005), CD79a (p = 0.024) and Bcl-6 (p < 0.0001) and negatively associated with cytoplasmic immunoglobulin light-chain expression (p = 0.036) in diffuse large B cell lymphoma. Identical or nearly identical associations were found in follicular lymphoma. Since CD20 is known to be partly regulated by PU.1 and putative PU.1-binding sites have been described in the regulatory regions of the CD22, CD79a and CD10 genes, we looked for putative PU.1 binding sites in the BCL6 promotor. Four such putative PU.1 binding sites were identified. Further analysis by gel-shift electromobility essay showed that PU.1 protein binds to three of the four putative binding sites in the BCL6 promotor. PU.1 and Bcl-6 were also found to be upregulated in centroblasts in the normal GC, but jointly downregulated in a subpopulation of centrocytes. Our findings support the contention that PU.1 may also have an important role in GC B cell development.

KSHV-Positive Solid Lymphomas Represent an Extra-Cavitary Variant of Primary Effusion Lymphoma

Primary effusion lymphoma (PEL) is a unique form of non-Hodgkin lymphoma (NHL) associated with Kaposi sarcoma-associated herpesvirus (KSHV; HHV-8) that displays a distinct constellation of clinical, morphologic, immunologic, and molecular characteristics. Rare KSHV-containing immunoblastic lymphomas occurring in solid tissues have been described. Whether they represent part of the spectrum of PEL has not been determined. The morphologic, immunophenotypic, and molecular features of KSHV-positive solid lymphomas occurring in 8 HIV+/AIDS patients were systematically investigated and compared with those of 29 similarly analyzed PELs. The 8 KSHV-positive solid lymphomas were virtually indistinguishable from the 29 PELs based on morphology (immunoblastic/anaplastic), immunophenotype (CD45 positive; T cell antigen negative; CD30, EMA, CD138 positive; CD10, CD15, BCL6 negative) and genotype (100% immunoglobulin genes rearranged; no identifiable abnormalities in C-MYC, BCL6, BCL1, BCL2; and uniformly EBV positive). The only identifiable phenotypic difference was that the KSHV-positive solid lymphomas appeared to express B cell-associated antigens (25%) and immunoglobulin (25%) slightly more often than the PELs (<5% and 15%, respectively; P = 0.11 and P = 0.08, respectively). The clinical presentation and course of the patients who develop KSHV-positive solid lymphomas were also similar, except for the lack of an effusion and somewhat better survival (median 11 months vs. 3 months). However, the 3 KSHV-positive solid lymphoma patients alive without disease 11, 25, and 44 months following initial presentation were recently diagnosed patients and, unlike the other patients with KSHV-positive solid lymphomas, received anti-retroviral therapy. These findings strongly suggest that these decidedly rare KSHV-positive solid lymphomas belong to the spectrum of PEL. Therefore, we propose that the KSHV-positive solid lymphomas be designated extra-cavitary PELs.

The human BCL6 transgene promotes the development of lymphomas in the mouse

BCL6, a gene on chromosome 3, band q27, encodes a zinc finger transcriptional repressor that is needed for germinal center formation and has been implicated in the pathogenesis of some human lymphomas when it is mutated or involved in chromosomal rearrangements. To explore further the mechanisms of action of BCL6 in lymphomagenesis, we developed a transgenic mouse model mimicking a common translocation, the t(3, 14)(q27;q32), in human lymphomas. The transgenic mice develop normally and express the transgenic BCL6 protein constitutively in lymphocytes. A small fraction of the animals develop B and T cell lymphomas after a long latency period, but the incidence is dramatically enhanced following administration of N-ethyl-N-nitrosourea, a carcinogen that induces DNA mutations. The N-ethyl-N-nitrosourea-induced lymphomas spread widely, were exclusively T cell, expressed the BCL6 protein, and occurred only in the transgenic mice. Because BCL6 expression has been reported in a number of T cell tumors as well as in the more commonly occurring B cell lymphomas in humans, our transgenic mice provide a model for the study of human lymphomas.

Proteins encoded by genes involved in chromosomal alterations in lymphoma and leukemia: clinical value of their detection by immunocytochemistry

Acquired chromosomal anomalies (most commonly translocations) in lymphoma and leukemia usually result in either activation of a quiescent gene (by means of immunoglobulin or T-cell-receptor promotors) and expression of an intact protein product, or creation of a fusion gene encoding a chimeric protein. This review summarizes current immunocytochemical studies of these 2 categories of oncogenic protein, with emphasis on the clinical relevance of their detection in diagnostic samples. Among the quiescent genes activated by rearrangement, expression of cyclin D1 (due to rearrangement of the CCND1 [BCL-1] gene) is a near-specific marker of t(11;14) in mantle cell lymphoma; BCL-2 expression distinguishes follicular lymphoma cells from their nonneoplastic counterparts in reactive germinal centers and appears to be an independent prognostic marker in diffuse large cell lymphoma; and TAL-1 (SCL) expression identifies T-cell acute lymphoblastic neoplasms in which this gene is activated. The protein products of other genes activated by chromosomal rearrangement have a role as markers of either lineage (eg, PAX-5 [B-cell-specific activator protein] for B cells, including B-lymphoblastic neoplasms), or maturation stage (eg, BCL-6 for germinal-center and activated B cells and MUM-1/IRF4 for plasma cells). Currently, no hybrid protein encoded by fusion genes is reliably detectable by antibodies recognizing unique junctional epitopes (ie, epitopes absent from the wild-type constituent proteins). Nevertheless, staining for promyelocytic leukemia (PML) protein will detect acute PML with t(15;17) because the microspeckled nuclear labeling pattern for PML-RARalpha is highly distinctive. Similarly, antibodies to the anaplastic lymphoma kinase (ALK) tyrosine kinase are valuable (because wild-type ALK is not found in normal lymphoid tissue) in detecting neoplasms (CD30-positive large T-cell lymphomas) with t(2;5) or its variants. Thus, immunocytochemical detection of the products of many rearranged genes in lymphoma and leukemia can be clinically informative and provide information on cellular and subcellular protein expression that cannot be inferred from studies based on messenger RNA.

Alterations on the 5' noncoding region of the BCL-6 gene are not correlated with BCL-6 protein expression in T cell non-Hodgkin lymphomas

The BCL-6 proto-oncogene is expressed in germinal center B lymphocytes, in their neoplastic counterparts, and in a subpopulation of germinal center and perifollicular T lymphocytes. Rearrangements and/or mutations of the 5' noncoding region of the bcl-6 gene have been demonstrated in a large majority of diffuse large B cell lymphomas. Some, but not all, of these genetic alterations lead to dysregulation of the protein. Recently, anaplastic large cell lymphomas with T and null cell phenotypes, as well as T lymphoblastic lymphomas, have also been reported to exhibit immunoreactivity to the anti-BCL-6 antibody. We collected 33 T cell non-Hodgkin lymphomas (T-NHLs) and analyzed their expression of the BCL-6 protein by immunohistochemistry and investigated the organization of the bcl-6 gene by Southern blot and single strand conformation polymorphism (SSCP). The expression of BCL-6 was demonstrated in 37.5% of lymphoblastic (LBL), 40% of anaplastic large cell (ALCL), and 33% of peripheral T cell lymphomas (PTCL). BCL-6-positive malignant cells exhibited the CD4+ or CD4+/CD8+ phenotype. The bcl-6 gene was in a germline configuration in all T-NHLs examined, and a mutation at the first exon-intron boundary region structure of the wild-type bcl-6 gene was detected in 3 of 12 PTCL. One case of PTCL with mutations of the 5' noncoding region expressed BCL-6. In conclusion, expression of the BCL-6 protein is demonstrable independently of bcl-6 alterations in T-NHLs. This further suggests that molecular mechanisms other than rearrangements and/or mutations of the 5' noncoding region of the bcl-6 gene can result in expression of the protein. Whether these lymphomas arose from T cells expressing BCL-6 or expressed BCL-6 as part of the malignant transformation process needs to be determined. Finally, structural alterations of bcl-6 are rare in T-NHLs, but mutations do occur in the 5' noncoding region. We suggest that expression of BCL-6 in T cells may facilitate lymphomagenesis by repressing critical cytokines and cell cycle regulators.