Insight into Burkitt's lymphoma from immunoglobulin variable region gene analysis

Primary epidural sporadic Burkitt lymphoma in a 3-year-old: Case report and literature review

Background:

Burkitt lymphoma (BL) is a common tumor of childhood that usually arises in the abdomen or pelvis in its sporadic form. In a minority of cases, BL can present with CNS involvement, usually as a secondary site. Rarely, BL can arise primarily in the epidural space and present with back pain, or less commonly, acute myelopathy. This presentation is a surgical emergency and requires vigilant management.

Case Description:

We describe a case of pediatric BL arising primarily within the epidural space and presenting with progressive difficulty walking in a 3-year-old boy. Progression to complete inability to walk, absent lower extremity deep tendon reflexes, and new urinary incontinence prompted MRI of the spine, which showed a lesion extending from T5 to T10 and wrapping around the anterior and posterior portions of the spine with evidence of spinal cord compression. The patient underwent decompressive laminectomies from T5 to T10 and partial debulking of the posterior portions of the tumor. Microscopic examination showed a prominent “starry sky” pattern with abundant mitotic figures. Immunohistochemistry confirmed the diagnosis of BL. The patient is 10 months post-op and continues to undergo chemotherapy with partial neurologic improvement. He was free of recurrence 10 months post-operative.

Conclusion:

This appears to be the youngest described patient presenting with acute myelopathy in primary paraspinal BL. Management should include surgical decompression of the spinal cord followed by one of the various described chemotherapeutic regimens. Preoperative staging and neurologic function correlate with prognosis.

Dangerous Liaisons: Gammaherpesvirus Subversion of the Immunoglobulin Repertoire

A common biologic property of the gammaherpesviruses Epstein–Barr Virus and Kaposi sarcoma herpesvirus is their use of B lymphocytes as a reservoir of latency in healthy individuals that can undergo oncogenic transformation later in life. Gammaherpesviruses (GHVs) employ an impressive arsenal of proteins and non-coding RNAs to reprogram lymphocytes for proliferative expansion. Within lymphoid tissues, the germinal center (GC) reaction is a hub of B cell proliferation and death. The goal of a GC is to generate and then select for a pool of immunoglobulin (Ig) genes that will provide a protective humoral adaptive immune response. B cells infected with GHVs are detected in GCs and bear the hallmark signatures of the mutagenic processes of somatic hypermutation and isotype class switching of the Ig genes. However, data also supports extrafollicular B cells as a reservoir engaged by GHVs. Next-generation sequencing technologies provide unprecedented detail of the Ig sequence that informs the natural history of infection at the single cell level. Here, we review recent reports from human and murine GHV systems that identify striking differences in the immunoglobulin repertoire of infected B cells compared to their uninfected counterparts. Implications for virus biology, GHV-associated cancers, and host immune dysfunction will be discussed.

A Comparison of Immunoglobulin Variable Region N-Linked Glycosylation in Healthy Donors, Autoimmune Disease and Lymphoma

N-linked glycans play an important role in immunity. Although the role of N-linked glycans in the Fragment crystallizable (Fc) region of immunoglobulins has been thoroughly described, the function of N-linked glycans present in Ig-variable domains is only just being appreciated. Most of the N-linked glycans harbored by immunoglobulin variable domain are of the complex biantennary type and are found as a result of the presence of N-linked glycosylation that most often have been introduced by somatic hypermutation. Furthermore, these glycans are ubiquitously present on autoantibodies observed in some autoimmune diseases as well as certain B-cell lymphomas. For example, variable domain glycans are abundantly found by anti-citrullinated protein antibodies (ACPA) in rheumatoid arthritis (RA) as well as by the B-cell receptors of follicular lymphoma (FL). In FL, variable domain glycans are postulated to convey a selective advantage through interaction with lectins and/or microbiota, whereas the contribution of variable domain glycans on autoantibodies is not known. To aid the understanding how these seemingly comparable phenomena contribute to a variety of deranged B-responses in such different diseases this study summarizes the characteristics of ACPA and other auto-antibodies with FL and healthy donor immunoglobulins, to identify the commonalities and differences between variable domain glycans in autoimmune and malignant settings. Our finding indicate intriguing differences in variable domain glycan distribution, frequency and glycan composition in different conditions. These findings underline that variable domain glycosylation is a heterogeneous process that may lead to a number of pathogenic outcomes. Based on the current body of knowledge, we postulate three disease groups with distinct variable domain glycosylation patterns, which might correspond with distinct underlying pathogenic processes.

B Cell Receptor Immunogenetics in B Cell Lymphomas: Immunoglobulin Genes as Key to Ontogeny and Clinical Decision Making

The clonotypic B cell receptor immunoglobulin (BcR IG) plays a seminal role in B cell lymphoma development and evolution. From a clinical perspective, this view is supported by the remarkable therapeutic efficacy of BcR signaling inhibitors, even among heavily pre-treated, relapsed/refractory patients. This clinical development complements immunogenetic evidence for antigen drive in the natural history of these tumors. Indeed, BcR IG gene repertoire biases have been documented in different B cell lymphoma subtypes, alluding to selection of B cell progenitors that express particular BcR IG. Moreover, distinct entities display imprints of somatic hypermutation within the clonotypic BcR IG gene following patterns that strengthen the argument for antigen selection. Of note, at least in certain B cell lymphomas, the BcR IG genes are intraclonally diversified, likely in a context of ongoing interactions with antigen(s). Moreover, BcR IG gene repertoire profiling suggests that unique immune pathways lead to distinct B cell lymphomas through targeting cells at different stages in the B cell differentiation trajectory (e.g., germinal center B cells in follicular lymphoma, FL). Regarding the implicated antigens, although their precise nature remains to be fully elucidated, immunogenetic analysis has offered important hints by revealing similarities between the BcR IG of particular lymphomas and B cell clones with known antigenic specificity: this has paved the way to functional studies that identified relevant antigenic determinants of classes of structurally similar epitopes. Finally, in certain tumors, most notably chronic lymphocytic leukemia (CLL), immunogenetic analysis has also proven instrumental in accurate patient risk stratification since cases with differing BcR IG gene sequence features follow distinct disease courses and respond differently to particular treatment modalities. Overall, delving into the BcR IG gene sequences emerges as key to understanding B cell lymphoma pathophysiology, refining prognostication and assisting in making educated treatment choices.

High-throughput sequencing of the B-cell receptor in African Burkitt lymphoma reveals clues to pathogenesis

Burkitt lymphoma (BL), the most common pediatric cancer in sub-Saharan Africa, is a malignancy of antigen-experienced B lymphocytes. High-throughput sequencing (HTS) of the immunoglobulin heavy (IGH) and light chain (IGK/IGL) loci was performed on genomic DNA from 51 primary BL tumors: 19 from Uganda and 32 from Ghana. Reverse transcription polymerase chain reaction analysis and tumor RNA sequencing (RNAseq) was performed on the Ugandan tumors to confirm and extend the findings from the HTS of tumor DNA. Clonal IGH and IGK/IGL rearrangements were identified in 41 and 46 tumors, respectively. Evidence for rearrangement of the second IGH allele was observed in only 6 of 41 tumor samples with a clonal IGH rearrangement, suggesting that the normal process of biallelic IGHD to IGHJ diversity-joining (DJ) rearrangement is often disrupted in BL progenitor cells. Most tumors, including those with a sole dominant, nonexpressed DJ rearrangement, contained many IGH and IGK/IGL sequences that differed from the dominant rearrangement by < 10 nucleotides, suggesting that the target of ongoing mutagenesis of these loci in BL tumor cells is not limited to expressed alleles. IGHV usage in both BL tumor cohorts revealed enrichment for IGHV genes that are infrequently used in memory B cells from healthy subjects. Analysis of publicly available DNA sequencing and RNAseq data revealed that these same IGHV genes were overrepresented in dominant tumor-associated IGH rearrangements in several independent BL tumor cohorts. These data suggest that BL derives from an abnormal B-cell progenitor and that aberrant mutational processes are active on the immunoglobulin loci in BL cells.

Analysis of the IGHV region in Burkitt's lymphomas supports a germinal center origin and a role for superantigens in lymphomagenesis

The analysis of immunoglobulin heavy chain variable (IGHV) region may disclose the influence of antigens in Burkitt's lymphomas (BL). IGHV sequences from 38 patients and 35 cell lines were analyzed. IGHV3 subset genes were the most used and IGHV4-34 gene was overrepresented. IGHV genes were mutated in 98.6% of the cases, 36% acquired potential glycosylation sites, and in 52% somatic-hypermutation-process was ongoing. Binding motifs for superantigens like Staphylococcal protein A and carbohydrate I/i were preserved in 89% of the cases. IGHV analysis of BL cells supports a germinal center origin and points toward a role for superantigens in lymphomagenesis.

Deep sequencing of MYC DNA-binding sites in Burkitt lymphoma

Background

MYC is a key transcription factor involved in central cellular processes such as regulation of the cell cycle, histone acetylation and ribosomal biogenesis. It is overexpressed in the majority of human tumors including aggressive B-cell lymphoma. Especially Burkitt lymphoma (BL) is a highlight example for MYC overexpression due to a chromosomal translocation involving the c-MYC gene. However, no genome-wide analysis of MYC-binding sites by chromatin immunoprecipitation (ChIP) followed by next generation sequencing (ChIP-Seq) has been conducted in BL so far.

Methodology/Principal Findings

ChIP-Seq was performed on 5 BL cell lines with a MYC-specific antibody giving rise to 7,054 MYC-binding sites after bioinformatics analysis of a total of approx. 19 million sequence reads. In line with previous findings, binding sites accumulate in gene sets known to be involved in the cell cycle, ribosomal biogenesis, histone acetyltransferase and methyltransferase complexes demonstrating a regulatory role of MYC in these processes. Unexpectedly, MYC-binding sites also accumulate in many B-cell relevant genes. To assess the functional consequences of MYC binding, the ChIP-Seq data were supplemented with siRNA- mediated knock-downs of MYC in BL cell lines followed by gene expression profiling. Interestingly, amongst others, genes involved in the B-cell function were up-regulated in response to MYC silencing.

Conclusion/Significance

The 7,054 MYC-binding sites identified by our ChIP-Seq approach greatly extend the knowledge regarding MYC binding in BL and shed further light on the enormous complexity of the MYC regulatory network. Especially our observations that (i) many B-cell relevant genes are targeted by MYC and (ii) that MYC down-regulation leads to an up-regulation of B-cell genes highlight an interesting aspect of BL biology.

HIV-associated immune dysfunction and viral infection: role in the pathogenesis of AIDS-related lymphoma

HIV infection is associated with a much higher risk for the development of non-Hodgkin lymphoma (AIDS-NHL). The principal causes of lymphomagenesis in HIV-infected individuals are thought to be the loss of immune function seen in HIV infection, which results in the loss of immunoregulation of Epstein-Barr virus-infected B cells, as well as HIV infection-associated immune dysregulation, including chronic B-cell activation. In this review, we discuss recent reports that further support the importance of these factors, and we highlight emerging evidence of different mechanisms that potentially drive lymphomagenesis in HIV-infected individuals.

c-Myc overexpression promotes a germinal center-like program in Burkitt's lymphoma

The germinal center (GC) reaction has a pivotal function in human B-cell lymphomagenesis. Genetic aberrations occurring during somatic hypermutation and class switch recombination deregulate key factors controlling B-cell physiology and proliferation. Several human lymphoma entities are characterized by a constitutive GC phenotype and ongoing somatic hypermutation, but the molecular basis for this phenomenon is only partly understood. We have investigated the reasons for a constitutive GC-like program in Burkitt's lymphoma cells. Here, overexpression of c-Myc leads to a centroblast phenotype, promotes high constitutive expression of the key GC factors Bcl-6, E2A and activation-induced cytidine deaminase and contributes to proliferation and somatic hypermutation. Our findings elucidate how the activity of a pivotal transcription factor may freeze B-cell lymphoma cells in a constitutive GC-like state that is even maintained at an extrafollicular location.

Epstein-Barr virus and its role in the pathogenesis of Burkitt's lymphoma: an unresolved issue

For several reasons Burkitt's lymphoma (BL) has become a paradigm in cancer research: for its particular geographical distribution, the presence of Epstein-Barr virus (EBV) in the cases in high incidence areas, and for the activation of the proto-oncogene c-myc by chromosomal translocation in one of the immunoglobulin gene loci. As c-MYC activates both, proliferation and apoptosis, at least two events have to cooperate in lymphomagenesis: activation of c-MYC and a shift in the balance from apoptosis towards survival. Antigenic and/or polyclonal stimulation of the B cell receptor, genetic instability imposed by activation induced deaminase (AID), as well as the viral gene products EBNA1 and several small non-coding non-polyadenylated RNAs are the main factors suspected to play an important role in the pathogenesis of BL. Despite intensive research, the role of the virus has remained largely elusive in the past decades, but the discovery of two viral microRNA clusters that are expressed in EBV associated tumors including BL has raised new hopes and expectations that EBV is going to reveal its mystery. This review focuses on the interplay between cellular and viral factors and puts special emphasis on mouse models and experimental cell culture systems that address these points.

Screening for residual disease in pediatric burkitt lymphoma using consensus primer pools

Assessing molecular persistent or minimal residual disease (PD/MRD) in childhood Burkitt lymphoma (BL) is challenging because access to original tumor is usually needed to design patient-specific primers (PSPs). Because BL is characterized by rearranged immunoglobulin heavy chain (IgV_H) genes, IgV_H primer pools from IgV_H1–IgV_H7 regions were tested to detect PD/MRD, thus eliminating the need for original tumor. The focus of the current study was to assess the feasibility of using IgV_H primer pools to detect disease in clinical specimens. Fourteen children diagnosed with B-NHL had follow-up repository specimens available to assess PD/MRD. Of the 14 patients, 12 were PD/MRD negative after 2 months of therapy and remained in remission at the end of therapy; 2/14 patients were PD/MRD positive at 2-3 months and later relapsed. PSP-based assays from these 14 patients showed 100% concordance with the current assay. This feasibility study warrants further investigation to assess PD/MRD using IgV_H primer pools, which could have clinical significance as a real-time assessment tool to monitor pediatric BL and possibly other B-cell non-Hodgkin lymphoma therapy.

The B cell antigen receptor and overexpression of MYC can cooperate in the genesis of B cell lymphomas

A variety of circumstantial evidence from humans has implicated the B cell antigen receptor (BCR) in the genesis of B cell lymphomas. We generated mouse models designed to test this possibility directly, and we found that both the constitutive and antigen-stimulated state of a clonal BCR affected the rate and outcome of lymphomagenesis initiated by the proto-oncogene MYC. The tumors that arose in the presence of constitutive BCR differed from those initiated by MYC alone and resembled chronic B cell lymphocytic leukemia/lymphoma (B-CLL), whereas those that arose in response to antigen stimulation resembled large B-cell lymphomas, particularly Burkitt lymphoma (BL). We linked the genesis of the BL-like tumors to antigen stimulus in three ways. First, in reconstruction experiments, stimulation of B cells by an autoantigen in the presence of overexpressed MYC gave rise to BL-like tumors that were, in turn, dependent on both MYC and the antigen for survival and proliferation. Second, genetic disruption of the pathway that mediates signaling from the BCR promptly killed cells of the BL-like tumors as well as the tumors resembling B-CLL. And third, growth of the murine BL could be inhibited by any of three distinctive immunosuppressants, in accord with the dependence of the tumors on antigen-induced signaling. Together, our results provide direct evidence that antigenic stimulation can participate in lymphomagenesis, point to a potential role for the constitutive BCR as well, and sustain the view that the constitutive BCR gives rise to signals different from those elicited by antigen. The mouse models described here should be useful in exploring further the pathogenesis of lymphomas, and in preclinical testing of new therapeutics.

It has long been suspected that the malignant proliferation of B lymphocytes known as lymphomas might represent a perversion of how the cells normally respond to antigen. In particular, the molecular receptor on the surface of the cells that signals the presence of antigen might be abnormally active in lymphomas. We have tested this hypothesis by engineering the genome of mice so that virtually all of the B cells are commandeered by a single version of the surface receptor, then stimulated that receptor with the molecule it is designed to recognize. Our results indicate that both the unstimulated and stimulated states of the receptor can cooperate with an oncogene known as MYC in the genesis of lymphomas. But the two states of the receptor give rise to different forms of lymphoma. In particular, the stimulated form cooperates with MYC to produce a disease that closely resembles Burkitt lymphoma. These results illuminate the mechanisms that are responsible for lymphomas and could inform the development of new strategies to treat the disease.

A series of genetically engineered mice were used to substantiate a long-standing speculation that chronic immune-stimulus may be involved in the genesis of certain lymphomas, illuminating the pathogenesis of B cell lymphomas and suggesting new strategies to treat several forms of this malignancy, including Burkitt lymphoma.

Epstein-Barr virus and Burkitt lymphoma

Burkitt lymphoma (BL) is an aggressive B-cell malignancy with endemic, sporadic and immunodeficiency-associated variants. It has been known for many years that the fundamental transforming event in BL is the translocation of the MYC gene, and the events that bring about this translocation and those that allow cells to survive with the constitutive expression of MYC have been the subject of intense investigation. Epstein-Barr virus (EBV) infection, malaria, immunodeficiency and spontaneous, somatic mutation can all contribute to the origin and maintenance of this cancer and their mechanisms are the subject of this review.

Episomal vectors to monitor and induce somatic hypermutation in human Burkitt-Lymphoma cell lines

Somatic hypermutation (SHM) occurs at a specific B-cell differentiation stage, during the germinal centre reaction, and provides a means to diversify and shape the antibody repertoire of the adaptive immune system. Burkitt-Lymphoma (BL) is a germinal centre derived B-cell malignancy. Presumably deregulation of the somatic hypermutation- and/or class switch recombination process causes a translocation between the myc-locus and one of the Ig-loci, which is characteristic for BL. We show here that we developed an episomal-based vector system to monitor and induce AID-dependent somatic hypermutation in human cell lines. Exemplarily, we utilized this system to investigate the hypermutation status of various BL cell lines. Analysis of the influence of Ig-specific cis-regulatory elements for the mutability of a green fluorescent protein (GFP) reporter transgene revealed, that the presence of Ig-enhancers is required for an efficient targeting of a constitutively transcribed GFP transgene. In contrast, a transcriptional inducible GFP transgene was hypermutated by overexpression of activation-induced cytidine deaminase (AID), even in the absence of Ig-specific sequences. This observation verifies that overexpression of AID in non hypermutating BL cell lines as well as the expression of endogenous AID in the hypermutating BL cell line Raji can overcome the target restriction of AID.

Immunoglobulin gene analysis in polyneuropathy associated with IgM monoclonal gammopathy

Antineural antibody activity is the implicated pathogenic mechanism in polyneuropathy associated with monoclonal gammopathy. Recognition of antigen depends on immunoglobulin variable regions, encoded by V genes. We studied V(H)DJ(H) and V(L)J(L) gene use in monoclonal B cells by clonal analysis in 20 patients with polyneuropathy and IgM monoclonal gammopathy. V genes associated with bacterial responses appear over-represented and V(H)3-23 was preferentially used, without association with specific D, J(H) or V(L)J(L). V genes revealed somatic mutation and intraclonal variation was found in 9 of 20 patients. Polyneuropathy associated with monoclonal gammopathy may be caused by an immune response to bacterial antigens, which recruit somatically mutated autoreactive B cells.

Immunoglobulin gene analysis reveals 2 distinct cells of origin for EBV-positive and EBV-negative Burkitt lymphomas

The normal counterpart of the neoplastic B cells in Burkitt lymphoma (BL) is still unclear. Based on immunoglobulin gene rearrangement studies, some authors suggest an origin from germinal center cells and others from memory B cells. However, most of these studies rely on cell lines or on a small series of cases. To help clarify the cell of origin of BL, semi-nested polymerase chain reaction (PCR) was performed to amplify the VDJ rearrangements of the immunoglobulin heavy chain (VH) genes, and the resultant amplificates were sequenced for comparison with known germline VH segments. The results of this approach revealed that all cases (15 endemic BL [eBL], 10 sporadic BL [sBL], and 6 AIDS-related BL) harbor mutated VH genes, with different mutation ranges among the 3 types of BL. The eBL and AIDS-related forms showed considerably higher mutation rates than the sBL form (5.1%, 5.4%, and 1.5%, respectively). The mutations in eBL and AIDS-related BL also showed signs of antigen selection, whereas no signs of antigen selection were found in sBL. Finally, after subcloning the amplificates, sequence analysis revealed no signs of ongoing mutations in any of the cases analyzed. Given that one of the main differences between eBL and AIDS-related BL on the one hand and sBL on the other hand is the association with Epstein-Barr virus (EBV), we compared EBV-positive and EBV-negative BLs independently of their geographic origin and HIV status. The differences in the number of somatic mutations and antigen selection were even more evident when this approach was used. According to our molecular results, it appears that EBV-positive and EBV-negative BL may originate from 2 distinct subsets of B cells, pointing to a particular role for the germinal-center reaction in the pathogenesis of these tumors. The different types of C-MYC translocation reported in BL may also be related to the different stages of B-cell maturation.

Deregulated expression of the Myc cellular oncogene drives development of mouse “Burkitt-like” lymphomas from naive B cells

Chromosomal translocations juxtaposing immunoglobulin (Ig) and MYC genes are the hallmarks of human Burkitt lymphoma (BL), with deregulated MYC expression being a critical factor in pathogenesis. By inserting an intact mouse Myc gene into the mouse genome, proximal to the Ig enhancer Eμ, the effect of a precise mimic of the major t(8;14) translocation of human endemic BL (eBL) could be investigated. Knock-in mice developed IgM-positive B-cell tumors, with most being typical of eBL by histology and immunophenotype, including expression of the germinal center (GC)–associated protein, BCL6. Unlike eBL, however, analysis of Ig VH sequences revealed no significant level of somatic mutation. Thus, constitutive expression of Myc in the knock-in mice is apparently able to induce “Burkitt-like” lymphomas before antigen stimulation and formation of a GC. In contrast, human eBL development occurs in a GC or post-GC site with a likely contribution to pathogenesis from Epstein-Barr virus (EBV) and other epigenetic factors.

Insertion of c-Myc into Igh Induces B-Cell and Plasma-Cell Neoplasms in Mice

We used gene targeting in mice to insert a His(6)-tagged mouse c-Myc cDNA, Myc(His), head to head into the mouse immunoglobulin heavy-chain locus, Igh, just 5' of the intronic enhancer, Emu. The insertion of Myc(His) mimicked both the human t(8;14)(q24;q32) translocation that results in the activation of MYC in human endemic Burkitt lymphomas and the homologous mouse T(12;15) translocation that deregulates Myc in certain mouse plasmacytomas. Beginning at the age of 6 months, Myc(His) transgenic mice developed B-cell and plasma neoplasms, such as IgM(+) lymphoblastic B-cell lymphomas, Bcl-6(+) diffuse large B-cell lymphomas, and CD138(+) plasmacytomas, with an overall incidence of 68% by 21 months. Molecular studies of lymphoblastic B-cell lymphoma, the most prevalent neoplasm (50% of all tumors), showed that the lymphomas were clonal, overexpressed Myc(His), and exhibited the P2 to P1 promoter shift in Myc expression, a hallmark of MYC/Myc deregulation in human endemic Burkitt lymphoma and mouse plasmacytoma. Only 1 (6.3%) of 16 lymphoblastic B-cell lymphomas contained a BL-typical point mutation in the amino-terminal transactivation domain of Myc(His), suggesting that most of these tumors are derived from naive, pregerminal center B cells. Twelve (46%) of 26 lymphoblastic B-cell lymphomas exhibited changes in the p19(Arf)-Mdm2-p53 tumor suppressor axis, an important pathway for Myc-dependent apoptosis. We conclude that Myc(His) insertion into Igh predictably induces B-cell and plasma-cell tumors in mice, providing a valuable mouse model for understanding the transformation-inducing consequences of the MYC/Myc-activating endemic Burkitt lymphoma t(8;14)/plasmacytoma T(12;15) translocation.

Adult Burkitt leukemia and lymphoma

The World Health Organization Classification of Lymphoid Neoplasms identifies Burkitt lymphoma/leukemia as a highly aggressive mature B-cell neoplasm consisting of endemic, sporadic, and immunodeficiency-associated variants. These subtypes share many morphologic and immunophenotypic features, but differences exist in their clinical and geographic presentations. All of these subtypes possess chromosomal rearrangements of the c-myc oncogene, the genetic hallmark of Burkitt lymphoma that contributes to lymphomagenesis through alterations in cell cycle regulation, cellular differentiation, apoptosis, cellular adhesion, and metabolism. Brief-duration, high-intensity chemotherapy regimens containing aggressive central nervous system prophylaxis have had remarkable success in the treatment of this disease, with complete remission rates of 75% to 90% and overall survivals reaching 50% to 70% in adults. Although Burkitt lymphoma cells are extremely chemosensitive, biologically targeted therapies should be developed because current treatment options are suboptimal for patients with poor prognostic features or in the setting of relapsed disease.

The role of DNA breaks in genomic instability and tumorigenesis

DNA double-strand breaks (DSBs) represent dangerous chromosomal lesions that can lead to mutation, neoplastic transformation, or cell death. DSBs can occur by extrinsic insult from environmental sources or may occur intrinsically as a result of cellular metabolism or a genetic program. Mammalian cells possess potent and efficient mechanisms to repair DSBs, and thus complete normal development as well as mitigate oncogenic potential and prevent cell death. When DSB repair (DSBR) fails, chromosomal instability results and can be associated with tumor formation or progression. Studies of mice deficient in various components of the non-homologous end joining pathway of DSBR have revealed key roles in both the developmental program of B and T lymphocytes as well as in the maintenance of general genome stability. Here, we review the current thinking about DSBs and DSBR in chromosomal instability and tumorigenesis, and we highlight the implications for understanding the karyotypic features associated with human tumors.

Diversity and somatic hypermutation of the Ig VHDJH, V kappa J kappa, and V lambda J lambda gene segments in lymphoma B cells: relevance to the origin of the neoplastic B cell clone

Burkitt's lymphoma (BL) is a malignancy of B cells characterized by chromosomal translocations involving the immunoglobulin (Ig) and c-MYC gene loci. To address the putative role of antigen in the clonal expansion of these neoplastic B cells, we analyzed the VHDJH and VLJL gene segments expressed by the established cell lines derived from six endemic BL and six sporadic BL. Eight BL cell lines used genes of the VH3 family, two of the VH4, and two of the VH1. Eight VL chains were kappa (four members of the V kappa3, two of the V kappa1, and two of the V kappa2 subgroups) and four lambda (three members of the V lambda1 and one of the Vl ambda3 subgroup). The VH gene utilization was stochastic (i.e., it reflected the relative representation of the different VH gene family members in the human haploid genome). In contrast, the VL gene utilization was skewed toward the overutilization of the V kappa3 and V lambda1 gene subgroups. When compared with those of the respective germline genes, the sequences of the expressed Ig VDJ genes displayed nucleotide differences that resulted from somatic hypermutation. In three endemic and three sporadic BL cells, nucleotide changes yielding amino acid substitutions segregated within the complementarity determining region, indicating the application of a positive pressure for replacement mutations and suggesting that these neoplastic lymphocytes underwent a process of clonal selection driven by antigen, perhaps emerging from or transitioning through germinal centers.

Incidence of potential glycosylation sites in immunoglobulin variable regions distinguishes between subsets of Burkitt's lymphoma and mucosa-associated lymphoid tissue lymphoma

Recently, a high incidence of novel N-glycosylation sites introduced by somatic mutation was observed in the immunoglobulin variable region genes of follicular lymphoma. As these are positively selected and are uncommon in normal B cells, they may have a role in tumour growth and behaviour. Sites are not characteristic of chronic lymphocytic leukaemia or myeloma, but are detectable in approximately 50% of diffuse large cell lymphomas. Another feature of the variable region genes of certain lymphomas is ongoing somatic mutation. To determine whether glycosylation is associated with this phenomenon, we analysed variable region gene sequences of Burkitt's lymphoma (BL) and mucosa-associated lymphoid tissue (MALT) lymphoma. Novel sites were common in endemic BL (82%) and in 4/5 patients with Iranian BL. However, sporadic BL had a lower incidence (43%). Patients with MALT lymphoma had a low frequency (9%) of novel sites, comparable to normal B cells. These findings distinguish glycosylation sites from ongoing mutation and may reflect different environmental influences on these tumours.

VH gene analysis in sporadic Burkitt's lymphoma: somatic mutation and intraclonal diversity with special reference to the tumor cells involving germinal center

We analyzed the immunoglobulin heavy chain variable region (V(H)) gene in seven cases of sporadic Burkitt's lymphoma (sBL) to elucidate their cell of origin. In particular, we focused on the V(H) gene status of tumor cells involving adjacent germinal center (GC) by microdissecting histological sections. Among the seven V(H) genes V(H)1 family was found in two, V(H)3 in four, and V(H)4 in one. All rearranged V(H) genes demonstrated somatic mutations at percentages ranging from 1.4 to 7.5% (mean, 4.2%), which is a similar level to that seen in IgM-only B cells. Three out of four V(H) genes with more than 2% sequence difference from their corresponding germline counterpart showed evidence of antigen selection in their framework region 3. Three cases demonstrated signs of intraclonal diversity with a mutational frequency of 0.47-0.98%, which was 13.5-28.8 times as great as the Taq infidelity in our experimental conditions. However the level of somatic mutation and the effect of antigen selection on V(H) gene were diverse in these three cases, and the relationship between V(H) gene somatic mutation status and intraclonal diversity was unclear in sBL. In the analysis of microdissected tissues, all 20 tumor clones in the adjacent GCs showed additional replacement mutations in complementarity determining region 3, suggesting a role of antigen in tumor progression. This finding resembles the phenomenon that memory B-cells reenter into GC to undergo further affinity maturation. In contrast, 7/11 V(H) gene sequences irrelevant to GC were identical to those of the major tumor clone. Thus our findings suggested that sBL is derived from memory B-cells rather than GC B-cells, and that antigen stimulation is involved in the clonal expansion of a proportion of sBL.

Immunoglobulin variable region structure and B-cell malignancies

The enormous diversity of immunoglobulin (Ig) variable (V) gene sequences encoding the antibody repertoire are formed by the somatic recombination of relatively few genetic elements. In B-lineage malignancies, Ig gene rearrangements have been widely used for determining clonality and cell origin. The recent development of rapid cloning and sequencing techniques has resulted in a substantial accumulation of IgV region sequences at various stages of B-cell development and has revealed stage-specific trends in the use of V, diversity, joining genes, the degree of noncoding nucleotide addition, and the rate of somatic mutations. Furthermore, sequences from B-lineage malignant cells nearly reflect the characteristics of the normal counterpart at each respective stage of development. Alternatively, from the IgV region structure of the malignant cells, it is possible to speculate at which stage of B-cell development the cells were transformed. As the complete nucleotide sequences of the human Ig heavy and Ig light V region loci have now been determined, the study of Ig genetics has entered into the super-information era.

Immunoglobulin heavy chain variable region (VH) genes of B cell chronic lymphocytic leukemia cells from lymph nodes show somatic mutations and intraclonal diversity irrespective of follicular dendritic cell network

We analyzed the immunoglobulin heavy chain variable region (VH) gene in 4 Japanese cases of B cell chronic lymphocytic leukemia (B-CLL) with enlarged lymph nodes to clarify the presence of somatic mutations and intraclonal diversity. We also attempted to determine the role of the follicular dendritic cell (FDC) network in some proliferation centers, where tumor cells are mitotically active. Immunohistochemical studies revealed that all 4 cases showed the typical immunophenotype: CD5+, CD23+, IgM+ and IgD+. DNA was extracted from paraffin sections (lymph node) and rearranged VH gene was amplified by PCR. All but one exhibited a moderate number of somatic mutations, with percentages ranging from 4.1 to 9.5, and one of which indicated the effect of antigen selection on its VH gene. Multiple clone analysis of whole tissues showed intraclonal diversity in one case, whose VH gene carried a somatic mutation but the effect of antigen selection was not apparent. We further examined microdissected tissues to elucidate the relationship between FDC network and VH gene status in 2 cases. In one case, intraclonal diversity was not apparent irrespective of FDC network, however, both tumor cells around the FDC network and those apart from the FDC showed signs of intraclonal diversity in another case, suggesting that intraclonal diversity was not related to the FDC network in B-CLL. Here we demonstrate that some cases of B-CLL involved in lymph node carried mutated VH genes and showed intraclonal diversity like the tumor cells in the peripheral blood. However, the significance of the FDC network in the proliferation center still remains to be resolved.

Immunoglobulin heavy-chain gene rearrangement in adult acute lymphoblastic leukemia reveals preferential usage of J(H)-proximal variable gene segments

The aim of this study was to characterize individual-segment and overall patterns of V(H) gene usage in adult B-lineage acute lymphoblastic leukemia (ALL). Theoretical values of V(H) segment usage were calculated with the assumption that all V(H) segments capable of undergoing rearrangement have an equal probability of selection for recombination. Leukemic clones from 127 patients with adult B-lineage acute leukemias were studied by fingerprinting by means of primers for the framework 1 and joining segments. Clones from early preimmune B cells (245 alleles identified) show a predominance of V(H)6 family rearrangements and, consequently, do not conform to this hypothesis. However, profiles of V(H) gene family usage in mature B cells, as investigated in peripheral blood (6 samples), B-cell lymphomas (36 clones) and chronic lymphocytic leukemia (56 clones), are in agreement with this theoretical profile. Sequence analyses of 64 V(H) clones in adult ALL revealed that the rate of V(H) usage is proportional to the proximity of the V(H) gene to the J(H) locus and that the relationship can be mathematically defined. Except for V(H)6, no other V(H) gene is excessively used in adult ALL. V(H) pseudogenes are rarely used (n = 2), which implies the existence of early mechanisms in the pathway to B-cell maturation to reduce wasteful V(H)-(D(H))-J(H) recombination. Finally, similar to early immunoglobulin-H rearrangement patterns in the mouse, B cells of ALL derive from a pool of cells more immature than the cells in chronic lymphoid B-cell malignancies.

Autoimmune hemolytic anemia in patients with non-Hodgkin's lymphoma: characteristics and significance

BACKGROUND

The occurrence of autoimmune hemolytic anemia (AIHA) in patients with non-Hodgkin's lymphoma (NHL) is well known. However, there is lack of information in the literature in terms of the significance and impact of such phenomenon on the clinical course of these patients.

PATIENTS AND METHODS

We analyzed the clinical and laboratory features, course and response of 16 patients with non-Hodgkin's lymphoma (NHL) and autoimmune hemolytic anemia (AIHA). Patients with small lymphocytic lymphoma and angioimmunoblastic lymphadenopathy with dysproteinemia were excluded from the analysis. The significance of certain parameters, such as cell type (B- vs. T-cell), stage of NHL and presence of serum monoclonal immunoglobulin were examined. The cohort consisted of 501 patients with NHL evaluated during the study period.

RESULTS

The response rate for the group of patients with NHL/AIHA and for the cohort was 44% and 62%, respectively; P = 0.0138. T-cell histology was overrepresented in the patients with AIHA/NHL (33% vs. 14%; P = 0.048). The occurrence of AIHA was not statistically significant among the four stages of NHL (P = 0.722), while a significantly higher proportion of patients with AIHA had serum monoclonol gammopathy when compared to the cohort (25% vs. 8%; P = 0.03). The patients with NHL who did not develop AIHA had better overall survival and median survival compared to the NHL/AIHA group (P = 0.006 and P = 0.0001, respectively).

CONCLUSIONS

The study provides for the first time a descriptive clinicopathologic analysis of patients with AIHA and NHL. Certain pathologic and laboratory features were more likely to be associated with the occurrence of AIHA in patients with NHL. Most importantly, was the adverse impact of AIHA on the survival of patients with NHL. Therefore, this finding should be taken in consideration when risk-stratifying patients with NHL.

Molecular biology of Burkitt's lymphoma

The diagnostic category of Burkitt's lymphoma encompasses a closely related group of aggressive B-cell tumors that includes sporadic, endemic, and human immunodeficiency virus-associated subtypes. All subtypes are characterized by chromosomal rearrangements involving the c-myc proto-oncogene that lead to its inappropriate expression. This review focuses on the roles of c-myc dysregulation and Epstein-Barr virus infection in Burkitt's lymphoma. Although the normal function of c-Myc remains enigmatic, recent data indicate that it has a central role in several fundamental aspects of cellular biology, including proliferation, differentiation, metabolism, apoptosis, and telomere maintenance. We discuss new insights into the molecular mechanisms of these c-Myc activities and their potential relevance to the pathogenesis of Burkitt's lymphoma and speculate on the role of Epstein-Barr virus.

Burkitt lymphoma in the mouse

Chromosomal translocations juxtaposing the MYC protooncogene with regulatory sequences of immunoglobulin (Ig) H chain or kappa (Ig kappa) or lambda (Ig lambda) L chain genes and effecting deregulated expression of MYC are the hallmarks of human Burkitt lymphoma (BL). Here we report that lymphomas with striking similarities to BL develop in mice bearing a mutated human MYC gene controlled by a reconstructed Ig lambda locus encompassing all the elements required for establishment of locus control in vitro. Diffusely infiltrating lymphomas with a typical starry sky appearance occurred in multiple founders and an established line, indicating independence from positional effects. Monoclonal IgM(+)CD5(-)CD23(-) tumors developed from an initially polyclonal population of B cells. These results demonstrate that the phenotype of B lineage lymphomas induced by MYC dysregulation is highly dependent on cooperativity among the regulatory elements that govern expression of the protooncogene and provide a new system for studying the pathogenesis of BL.

Clinical relevance of immunoglobulin mutation analysis

The precise diagnosis of malignant B-cell lymphoproliferations is essential for their appropriate clinical management. Histologic and immunophenotypical features alone are often insufficient in discriminating between various lymphoma entities and subtypes. The analysis of clonally rearranged immunoglobulin chain genes of the tumor cells was therefore suggested as an additional parameter. This article reviews current knowledge and describes which conclusions can be drawn for lymphoma diagnosis based on the type of immunoglobulin chain gene rearrangement, as well as on the number and distribution of somatic immunoglobulin mutations. Although there are striking correlations between the clinical outcome and the immunoglobulin mutations in some entities, many additional studies are required in order to draw final conclusions for most types of lymphoma.

Primary central nervous system lymphomas are derived from germinal-center B cells and show a preferential usage of the V4-34 gene segment

Primary central nervous system lymphomas (PCNSLs) have recently received considerable clinical attention due to their increasing incidence. To clarify the histogenetic origin of these intriguing neoplasms, PCNSLs from 10 HIV-negative patients were analyzed for immunoglobulin (Ig) gene rearrangements. All tumors exhibited clonal IgH gene rearrangements. Of the 10 cases, 5 used the V4-34 gene segment, and all of these lymphomas shared an amino acid exchange from glycine to aspartate due to a mutation in the first codon of the complementarity-determining region 1. No preferential usage of D(H), J(H), V(kappa), J(kappa), V(lambda), or J(lambda) gene segments was observed. All potentially functional rearrangements exhibited somatic mutations. The pattern of somatic mutations indicated selection of the tumor cells (or their precursors) for expression of a functional antibody. Mean mutation frequencies of 13. 2% and 8.3% were detected for the heavy and light chains, respectively, thereby exceeding other lymphoma entities. Cloning experiments of three tumors showed ongoing mutation in at least one case. These data suggest that PCNSLs are derived from highly mutated germinal-center B cells. The frequent usage of the V4-34 gene and the presence of a shared replacement mutation may indicate that the tumor precursors recognized a shared (super) antigen.

V(H) gene analysis of Burkitt's lymphoma in children from north-western Iran

Cases of Burkitt's lymphoma (BL) from north-western Iran were investigated for the usage and somatic mutational pattern of their immunoglobulin variable region genes. Potentially functional V(H) genes were amplified from 6/12 of the tumour masses and all of these were derived from the V(H)3 family, with 4/6 being derived from the most commonly used V(H)3 family member, V3-23. All of the tumour sequences were mutated from their germline counterparts, to varying degrees, with a mean level of 5.8%, indicating that the cell of origin had encountered the germinal centre. Intraclonal sequence heterogeneity was also evident in 4/6 of the lymphomas, showing that the tumour cells had undergone further somatic mutation following neoplastic transformation. Analysis of the five potentially functional mutated V(H) sequences showed a significant clustering of replacement mutations in the complementarity-determining region 2, consistent with a role for antigen in selection of tumour cell sequences. The pattern of extensive somatic mutation, and intraclonal variation, in these mainly EBV+ve tumours, was similar to that previously reported in V(H) sequences of EBV+ve endemic BL (eBL) and EBV-ve sporadic BL (sBL), with the mean level of somatic mutation lying between those reported for eBL (7.7%) and sBL (4.0%). However, VH gene bias and the distribution of mutations in the Iranian cases showed features which differed from those reported for endemic or sporadic BL.