Molecular analysis of bcl-1/IgH junctional sequences in mantle cell lymphoma: potential mechanism of the t(11;14) chromosomal translocation

Epigenomic translocation of H3K4me3 broad domains over oncogenes following hijacking of super-enhancers

Chromosomal translocations are important drivers of haematological malignancies whereby proto-oncogenes are activated by juxtaposition with enhancers, often called enhancer hijacking. We analyzed the epigenomic consequences of rearrangements between the super-enhancers of the immunoglobulin heavy locus (IGH) and proto-oncogene CCND1 that are common in B cell malignancies. By integrating BLUEPRINT epigenomic data with DNA breakpoint detection, we characterized the normal chromatin landscape of the human IGH locus and its dynamics after pathological genomic rearrangement. We detected an H3K4me3 broad domain (BD) within the IGH locus of healthy B cells that was absent in samples with IGH-CCND1 translocations. The appearance of H3K4me3-BD over CCND1 in the latter was associated with overexpression and extensive chromatin accessibility of its gene body. We observed similar cancer-specific H3K4me3-BDs associated with hijacking of super-enhancers of other common oncogenes in B cell (MAF, MYC, and FGFR3/NSD2) and T cell malignancies (LMO2, TLX3, and TAL1). Our analysis suggests that H3K4me3-BDs can be created by super-enhancers and supports the new concept of epigenomic translocation, in which the relocation of H3K4me3-BDs from cell identity genes to oncogenes accompanies the translocation of super-enhancers.

KMT2D mutations and TP53 disruptions are poor prognostic biomarkers in mantle cell lymphoma receiving high-dose therapy: a FIL study

In recent years, the outcome of mantle cell lymphoma (MCL) has improved, especially in younger patients, receiving cytarabine-containing chemoimmunotherapy and autologous stem cell transplantation. Nevertheless, a proportion of MCL patients still experience early failure. To identify biomarkers anticipating failure of intensive chemotherapy in MCL, we performed target resequencing and DNA profiling of purified tumor samples collected from patients enrolled in the prospective FIL-MCL0208 phase 3 trial (high-dose chemoimmunotherapy followed by autologous transplantation and randomized lenalidomide maintenance). Mutations of KMT2D and disruption of TP53 by deletion or mutation associated with an increased risk of progression and death, both in univariate and multivariate analysis. By adding KMT2D mutations and TP53 disruption to the MIPI-c backbone, we derived a new prognostic index, the “MIPI-genetic” (“MIPI- g”). The “MIPI-g” improved the model discrimination ability compared to the MIPI-c alone, defining three risk groups: i) low-risk patients (4-year progression free survival and overall survival of 72.0% and 94.5%); ii) inter-mediate-risk patients (4-year progression free survival and overall survival of 42.2% and 65.8%) and iii) high-risk patients (4-year progression free survival and overall survival of 11.5% and 44.9%). Our results: i) confirm that TP53 disruption identifies a high-risk population characterized by poor sensitivity to conventional or intensified chemotherapy; ii) provide the pivotal evidence that patients harboring KMT2D mutations share the same poor outcome as patients harboring TP53 disruption; and iii) allow to develop a tool for the identification of high-risk MCL patients for whom novel therapeutic strategies need to be investigated. (Trial registered at clinicaltrials.gov identifier: NCT02354313).

The Minimal Residual Disease in Non-Hodgkin's Lymphomas: From the Laboratory to the Clinical Practice

Minimal residual disease (MRD) in non-Hodgkin's lymphomas (NHLs) still represents matter of interest and debate: indeed, the new available treatments offer higher rates of complete responses and MRD negativity than in the past, with a positive impact on the long-term survival. Furthermore, the introduction of more sensitive and accurate molecular techniques, such as digital PCR (ddPCR) and the next generation sequencing techniques (NGS), increased the possibility of identifying molecular targets to be followed after therapy (such as rearrangement of immunoglobulins, fusion genes, or mutations). This review focused on how molecular biology can help to detect MRD in different types of NHLs and how MRD can change the clinical practice in 2019. In follicular lymphoma (FL), contamination of the grafts and molecular disease persistence after transplantation represent a negative prognostic factors. The combination of Rituximab or Obinutuzumab with Bendamustine seems to be the most effective way to clear MRD in FL patients receiving chemo-immunotherapy (further studies are in progress), and also ⁹⁰Yttrium-Ibritumomab-Tiuxetan offers a deep clearance of molecular disease. Finally, molecular MRD can further stratify PET-negative cases, with subjects both PET- and MRD-negative presenting the best outcome. In aggressive lymphomas, MRD has a relevant prognostic power and can represent the platform for immunotherapy (such as CAR-T). In diffuse large B-cell lymphoma (DLBCL), the assessment of MRD in the plasma (where cell-free DNA and exosomes circulate) seems to be more predictive than the bone marrow analysis or peripheral blood mononuclear cells. Finally, NGS technologies could be more useful than the classical "patient allele-specific PCR" because they can identify any possible clone emerging during the treatment or follow-up, even if different from that identified at diagnosis, thus predicting relapse. After all, the present available molecular approaches can move MRD from the bench side to the clinical practice.

The role of cannabinoid receptors and the endocannabinoid system in mantle cell lymphoma and other non-Hodgkin lymphomas

The initiating oncogenic event in mantle cell lymphoma (MCL) is the translocation of cyclin D1, t(11;14)(q13;q32). However, other genetic aberrations are necessary for an overt lymphoma to arise. Like other B cell lymphomas, MCL at some points during the oncogenesis is dependent on interactions with other cells and factors in the microenvironment. The G protein coupled receptors cannabinoid receptors 1 and 2 (CB1 and CB2) are expressed at low levels on non-malignant lymphocytes and at higher levels in MCL and other lymphoma subtypes. In this review we give an overview of what is known on the role of the cannabinoid receptors and their ligands in lymphoma as compared to non-malignant T and B lymphocytes. In MCL cannabinoids mainly reduce cell proliferation and induce cell death. Importantly, our recent findings demonstrate that cannabinoids may induce either apoptosis or another type of programmed cell death, cytoplasmic vacuolation/paraptosis in MCL. The signalling to death has been partly characterized. Even though cannabinoid receptors seem to be expressed in many other types of B cell lymphoma, the functional role of cannabinoid receptor targeting is yet largely unknown. In non-malignant B and T lymphocytes, cannabinoid receptors are up-regulated in response to antigen receptor signalling or CD40. For T lymphocytes IL-4 has also a crucial role in transcriptional regulation of CB1. In lymphocytes, cannabinoid act in several ways - by affecting cell migration, cytokine response, at high doses inhibit cell proliferation and inducing cell death. The possible role for the endocannabinoid system in the immune microenvironment of lymphoma is discussed.

Early lymph node involvement by mantle cell lymphoma limited to the germinal center: report of a case with a novel "follicular in situ" growth pattern

Recently, several reports have described cases of "in situ" mantle cell lymphoma (MCL) in which scattered cyclin D1+ cells were present within the mantle zones of reactive-appearing lymphoid follicles. In this report, we describe an unusual histologic pattern of in situ MCL that was identified in a staging lymph node for colonic adenocarcinoma resected 4 years before a diagnosis of symptomatic MCL. Retrospective immunohistochemical studies showed scattered cyclin D1-expressing cells within otherwise reactive germinal centers but not in the surrounding mantle zones. The presence of early MCL cells limited to reactive germinal centers represents a novel "follicular in situ" growth pattern for MCL, which overlaps morphologically with reactive follicular hyperplasia and follicular lymphoma and which could have implications for MCL pathogenesis.

The t(14;18)(q32;q21)/IGH-MALT1 translocation in MALT lymphomas contains templated nucleotide insertions and a major breakpoint region similar to follicular and mantle cell lymphoma

The t(14;18)(q32;q21) involving the immunoglobulin heavy chain locus (IGH) and the MALT1 gene is a recurrent abnormality in mucosa-associated lymphoid tissue (MALT) lymphomas. However, the nucleotide sequence of only one t(14;18)-positive MALT lymphoma has been reported so far. We here report the molecular characterization of the IGH-MALT1 fusion products in 5 new cases of t(14;18)-positive MALT lymphomas. Similar to the IGH-associated translocations in follicular and mantle cell lymphomas, the IGH-MALT1 junctions in MALT lymphoma showed all features of a recombination signal sequence-guided V(D)J-mediated translocation at the IGH locus. Furthermore, analogous to follicular and mantle cell lymphoma, templated nucleotides (T-nucleotides) were identified at the t(14;18)/IGH-MALT1 breakpoint junctions. On chromosome 18, we identified a novel major breakpoint region in MALT1 upstream of its coding region. Moreover, the presence of duplications of MALT1 nucleotides in one case suggests an underlying staggered DNA-break process not consistent with V(D)J-mediated recombination. The molecular characteristics of the t(14;18)/IGH-MALT1 resemble those found in the t(14;18)/IGH-BCL2 in follicular lymphoma and t(11;14)/CCND1-IGH in mantle cell lymphoma, suggesting that these translocations could be generated by common pathomechanisms involving illegitimate V(D)J-mediated recombination on IGH as well as new synthesis of T-nucleotides and nonhomologous end joining (NHEJ) or alternative NHEJ repair pathways on the IGH-translocation partner.

MicroRNA expression, chromosomal alterations, and immunoglobulin variable heavy chain hypermutations in Mantle cell lymphomas

The contribution of microRNAs (miR) to the pathogenesis of mantle cell lymphoma (MCL) is not well known. We investigated the expression of 86 mature miRs mapped to frequently altered genomic regions in MCL in CD5(+)/CD5(-) normal B cells, reactive lymph nodes, and purified tumor cells of 17 leukemic MCL, 12 nodal MCL, and 8 MCL cell lines. Genomic alterations of the tumors were studied by single nucleotide polymorphism arrays and comparative genomic hybridization. Leukemic and nodal tumors showed a high number of differentially expressed miRs compared with purified normal B cells, but only some of them were commonly deregulated in both tumor types. An unsupervised analysis of miR expression profile in purified leukemic MCL cells revealed two clusters of tumors characterized by different mutational status of the immunoglobulin genes, proliferation signature, and number of genomic alterations. The expression of most miRs was not related to copy number changes in their respective chromosomal loci. Only the levels of miRs included in the miR-17-92 cluster were significantly related to genetic alterations at 13q31. Moreover, overexpression of miR-17-5p/miR-20a from this cluster was associated with high MYC mRNA levels in tumors with a more aggressive behavior. In conclusion, the miR expression pattern of MCL is deregulated in comparison with normal lymphoid cells and distinguishes two subgroups of tumors with different biological features.

Analysis of mutagenic V(D)J recombinase mediated mutations at the HPRT locus as an in vivo model for studying rearrangements with leukemogenic potential in children

Pediatric acute lymphocytic leukemia (ALL) is a multifactorial malignancy with many distinctive developmentally specific features that include age specific acquisition of deletions, insertions and chromosomal translocations. The analysis of breakpoint regions involved in these leukemogenic genomic rearrangements has provided evidence that many are the consequence of V(D)J recombinase mediated events at both immune and non-immune loci. Hence, the direct investigation of in vivo genetic and epigenetic features in human peripheral lymphocytes is necessary to fully understand the mechanisms responsible for the specificity and frequency of these leukemogenic non-immune V(D)J recombinase events. In this review, I will present the utility of analyzing mutagenic V(D)J recombinase mediated genomic rearrangements at the HPRT locus in humans as an in vivo model system for understanding the mechanisms responsible for leukemogenic genetic alterations observed in children with leukemia.

Frequent joining of Bcl-2 to a JH6 gene in hepatitis C virus-associated t(14;18)

The t(14;18) chromosomal translocation, which joins the Bcl-2 proto-oncogene to an Ig J(H) gene, has increased prevalence in patients chronically infected with hepatitis C virus (HCV). We now establish a link between the molecular structure and clinical occurrence of HCV-associated t(14;18). A t(14;18) was detected by PCR in leukocytes from 22 of 46 HCV-infected patients (48%) and 11 of 54 healthy controls (20%) (p = 0.0053). Nucleotide sequence analysis of the Bcl-2/J(H) joins found a J(H)6 gene in 18 of 22 (82%) t(14;18) from HCV(+) patients, and 3 of 8 (38%) from controls (p = 0.031). The t(14;18) rarely contained J(H) gene mutations, or an intervening region sequence suggestive of D gene rearrangement or templated nucleotide insertion. Analysis of published t(14;18) nucleotide sequences established that the J(H)6 prevalence in t(14;18) from normal/nonneoplastic controls (48%) was significantly lower than in t(14;18) from our HCV(+) patients (p = 0.004) or from non-Hodgkin's lymphomas (66%, p = 0.003). We conclude that the increased prevalence of t(14;18) in HCV(+) patients occurs with a strong bias for Bcl-2/J(H)6 joins. In this regard, HCV-associated t(14;18) more closely resemble t(14;18) in lymphomas than t(14;18) from normal subjects.

Translocation and gross deletion breakpoints in human inherited disease and cancer II: Potential involvement of repetitive sequence elements in secondary structure formation between DNA ends

Translocations and gross deletions are responsible for a significant proportion of both cancer and inherited disease. Although such gene rearrangements are nonuniformly distributed in the human genome, the underlying mutational mechanisms remain unclear. We have studied the potential involvement of various types of repetitive sequence elements in the formation of secondary structure intermediates between the single-stranded DNA ends that recombine during rearrangements. Complexity analysis was used to assess the potential of these ends to form secondary structures, the maximum decrease in complexity consequent to a gross rearrangement being used as an indicator of the type of repeat and the specific DNA ends involved. A total of 175 pairs of deletion/translocation breakpoint junction sequences available from the Gross Rearrangement Breakpoint Database [GRaBD; www.uwcm.ac.uk/uwcm/mg/grabd/grabd.html] were analyzed. Potential secondary structure was noted between the 5' flanking sequence of the first breakpoint and the 3' flanking sequence of the second breakpoint in 49% of rearrangements and between the 5' flanking sequence of the second breakpoint and the 3' flanking sequence of the first breakpoint in 36% of rearrangements. Inverted repeats, inversions of inverted repeats, and symmetric elements were found in association with gross rearrangements at approximately the same frequency. However, inverted repeats and inversions of inverted repeats accounted for the vast majority (83%) of deletions plus small insertions, symmetric elements for one-half of all antigen receptor-mediated translocations, while direct repeats appear only to be involved in mediating simple deletions. These findings extend our understanding of illegitimate recombination by highlighting the importance of secondary structure formation between single-stranded DNA ends at breakpoint junctions.

Translocation and gross deletion breakpoints in human inherited disease and cancer I: Nucleotide composition and recombination-associated motifs

Translocations and gross deletions are important causes of both cancer and inherited disease. Such gene rearrangements are nonrandomly distributed in the human genome as a consequence of selection for growth advantage and/or the inherent potential of some DNA sequences to be frequently involved in breakage and recombination. Using the Gross Rearrangement Breakpoint Database [GRaBD; www.uwcm.ac.uk/uwcm/mg/grabd/grabd.html] (containing 397 germ-line and somatic DNA breakpoint junction sequences derived from 219 different rearrangements underlying human inherited disease and cancer), we have analyzed the sequence context of translocation and deletion breakpoints in a search for general characteristics that might have rendered these sequences prone to rearrangement. The oligonucleotide composition of breakpoint junctions and a set of reference sequences, matched for length and genomic location, were compared with respect to their nucleotide composition. Deletion breakpoints were found to be AT-rich whereas by comparison, translocation breakpoints were GC-rich. Alternating purine-pyrimidine sequences were found to be significantly over-represented in the vicinity of deletion breakpoints while polypyrimidine tracts were over-represented at translocation breakpoints. A number of recombination-associated motifs were found to be over-represented at translocation breakpoints (including DNA polymerase pause sites/frameshift hotspots, immunoglobulin heavy chain class switch sites, heptamer/nonamer V(D)J recombination signal sequences, translin binding sites, and the chi element) but, with the exception of the translin-binding site and immunoglobulin heavy chain class switch sites, none of these motifs were over-represented at deletion breakpoints. Alu sequences were found to span both breakpoints in seven cases of gross deletion that may thus be inferred to have arisen by homologous recombination. Our results are therefore consistent with a role for homologous unequal recombination in deletion mutagenesis and a role for nonhomologous recombination in the generation of translocations.

Real-time polymerase chain reaction estimation of bone marrow tumor burden using clonal immunoglobulin heavy chain gene and bcl-1/JH rearrangements in mantle cell lymphoma

OBJECTIVE

In mantle cell lymphoma (MCL), detection of minimal residual disease in bone marrow (BM) samples by qualitative polymerase chain reaction (PCR) is insufficient to predict relapse. The aim of this study was to evaluate whether a quantitative estimation of tumor burden in consecutive BM samples from MCL patients was feasible and of clinical value.

MATERIALS AND METHODS

In combination with standard qualitative PCR, we developed a sensitive and accurate real-time PCR for detection of bcl-1/JH (joining region) rearrangement and used a recently described real-time PCR analysis of clonal immunoglobulin rearrangement. To assess clinical utility, we quantified tumor cells in 27 BM samples from three MCL patients undergoing combined CHOP (cyclophosphamide, doxorubicin [hydroxydaunomycin], vincristine [Oncovin], prednisone) and anti-CD20 antibody treatment and three MCL patients undergoing up-front autologous stem cell transplantation.

RESULTS

The approach is capable of detecting tumor cells over a wide range of BM contamination compared to qualitative PCR analysis alone. Tumor burden in consecutive BM samples decreases during therapy and either increases or stabilizes at low levels in patients who relapse or remain in continuous clinical remission, respectively.

CONCLUSIONS

Dynamic range estimation of BM tumor burden is feasible in MCL patients undergoing therapy using clonal immunoglobulin heavy chain gene and bcl-1/JH rearrangement-based real-time PCR.

A novel bcl-1/JH breakpoint from a patient affected by mantle cell lymphoma extends the major translocation cluster

Mantle cell lymphoma (MCL) is a B-lymphocytic malignancy frequently associated with the presence of the t(11;14) chromosomal translocation. By using a polymerase chain reaction (PCR) strategy to detect breakpoints within the major translocation cluster (MTC), an unexpectedly large product (about 1.1 kb by using first-round bcl-1/JH primers) has been identified in one out of 16 patients harbouring the t(11;14) translocation. Sequence analysis of the atypical PCR product, re-amplified and cloned with second-round primers, revealed a 459 bp portion corresponding exactly to the 3'-end segment of the MTC, followed by a sequence of 433 bp that lacked homology with any previously known sequence. PCR experiments using DNA from healthy donors identified that fragment as an extension of MTC fused, through a N-region of seven nucleotides, to the JH4 region of IgH gene. A computer-based search of the novel MTC portion aimed at detecting potential recombination motifs revealed the presence of several 4-bp sequences (5'-CCAG-3' or its complement 5'-CTGG-3'), one of them within seven nucleotides from the putative breakpoint, known to play a role in non-homologous recombination events at the Ig loci. The recognition of this novel breakpoint may have important implications for the diagnosis and detection of minimal residual disease in t(11;14)-positive lymphomas.

Diversity of genomic breakpoints in TFG-ALK translocations in anaplastic large cell lymphomas: identification of a new TFG-ALK(XL) chimeric gene with transforming activity

Anaplastic large cell lymphomas are associated with chromosomal aberrations involving the anaplastic lymphoma kinase (ALK) gene at 2p23 that result in the expression of novel chimeric ALK proteins with transforming properties. In most of these tumors, the t(2;5)(p23;q35) generates the NPM-ALK fusion gene. However, several studies have now demonstrated that genes other than NPM may be fused to the ALK gene. We have recently described two different ALK rearrangements involving the TRK-fused gene (TFG) in which the same portion of ALK was fused to different length fragments of the 5' TFG region. These two rearrangements encoded chimeric proteins of 85 kd (TFG-ALK(S)) and 97 kd (TFG-ALK(L)), respectively. In this study, we have identified a new ALK rearrangement in which the catalytic domain of ALK was fused to a larger fragment of the TFG gene (TFG-ALK(XL)), encoding for a fusion protein of 113 kd. Genomic analysis of these three TFG-ALK rearrangements revealed that the TFG breakpoints occur at introns 3, 4, and 5, respectively, whereas the ALK breakpoints always occur in the same intron. No homologous regions or known recombination sequences were found in these regions. Transfection experiments using NIH-3T3 fibroblasts showed a similar transforming efficiency of TFG-ALK variants compared with NPM-ALK. In addition, in common with NPM-ALK, the TFG-ALK proteins formed stable complexes with the signaling proteins Grb2, Shc, and PLC-gamma. In conclusion, these findings indicate that the TFG may use a variety of intronic breakpoints in ALK rearrangements generating fusion proteins of different molecular weights, but with similar transforming potential than NPM-ALK.

V(D)J-mediated translocations in lymphoid neoplasms: a functional assessment of genomic instability by cryptic sites

Most lymphoid malignancies are initiated by specific chromosomal translocations between immunoglobulin (Ig)/T cell receptor (TCR) gene segments and cellular proto-oncogenes. In many cases, illegitimate V(D)J recombination has been proposed to be involved in the translocation process, but this has never been functionally established. Using extra-chromosomal recombination assays, we determined the ability of several proto-oncogenes to target V(D)J recombination, and assessed the impact of their recombinogenic potential on translocation rates in vivo. Our data support the involvement of 2 distinct mechanisms: translocations involving LMO2, TAL2, and TAL1 in T cell acute lymphoblastic leukemia (T-ALL), are compatible with illegitimate V(D)J recombination between a TCR locus and a proto-oncogene locus bearing a fortuitous but functional recombination site (type 1); in contrast, translocations involving BCL1 and BCL2 in B cell non-Hodgkin's lymphomas (B-NHL), are compatible with a process in which only the IgH locus breaks are mediated by V(D)J recombination (type 2). Most importantly, we show that the t(11;14)(p13;q32) translocation involving LMO2 is present at strikingly high frequency in normal human thymus, and that the recombinogenic potential conferred by the LMO2 cryptic site is directly predictive of the in vivo level of translocation at that locus. These findings provide new insights into the regulation forces acting upon genomic instability in B and T cell tumorigenesis.

From centrocytic to mantle cell lymphoma: a clinicopathologic and molecular review of 3 decades

Mantle cell lymphoma (MCL), described almost 3 decades ago as centrocytic lymphoma and by a variety of other names, was initially recognized morphologically. MCL is a classic illustration of how the field of hematopathology and our basic understanding of neoplasia have evolved. The advent of immunophenotypic and increasingly sophisticated genotypic and cytogenetic studies, together with clinical investigations, have led to a better practical and biologic understanding of MCL and have broader implications as well. MCL is now recognized as an aggressive, difficult to treat, B-cell lymphoma with a broader morphologic spectrum than was initially appreciated and a characteristic phenotype (CD5+, CD10-, CD23-, FMC7+). Virtually all MCLs carry the translocation t(11;14)(q13;q32) with overexpression of the involved CCND1 (cyclin D1) gene. Additional cytogenetic and molecular abnormalities have been identified, including some that are early events (such as ATM gene deletion and mutation) and others that appear to be late events (such as deletions and mutations in the negative cell cycle regulatory elements p53, p16, and p18). The latter are often associated with a blastoid morphology and more aggressive clinical course. Ongoing clinical and basic investigations including microarray analysis will undoubtedly provide additional insights into MCL and perhaps more effective and specific therapeutic modalities.

Origin and diversification of the clonogenic cell in multiple myeloma: lessons from the immunoglobulin repertoire

The study of immunoglobulin genes in multiple myeloma over the last decade has provided important information regarding biology, ontogenetic assignment, disease evolution, pathogenic consequences and tumor-specific therapeutic intervention. Detailed analysis of VH genes has revealed the clonal relationship between switch variants expressed by the bone marrow plasma cell and myeloma progenitors in the marrow and peripheral blood. Regarding VH usage, a bias was found against the V4-34 gene encoding antibodies with cold agglutinin specificity (anti-I/i), thus explaining in part the absence of autoimmune phenomena in myeloma compared to other B cell lymphoproliferative disorders. However, in some studies a substantial number of cases analyzed were carrying the rearranged Humkappav325 Vkapppa gene, known to be over utilized by B cell chronic lymphocytic leukemia clones and possessing autoantibody binding activity. VH genes accumulate somatic hypermutations following a distribution compatible with antigen selection, but with no intraclonal heterogeneity. The analysis of Vkappa genes indicates a bias in usage of Vkappa family members; somatic hypermutation, in line with antigen selection, of the expressed Vkappa genes is higher than any other B cell lymphoid disorder. Similar conclusions were reached for Vlambda genes; in this case, the analysis raises the controversial issue of N nucleotide insertion at Vlambda-Jlambda junctions, apparently as a result of TdT activity. A complementary imprint of antigen selection as evidenced by somatic hypermutation of either the VH or VL clonogenic genes has been observed. The absence of ongoing somatic mutations in either VH or VL genes gives rise to the notion that the cell of origin in myeloma is a post-germinal center memory B cell.

Molecular insights into the immunopathogenesis of follicular lymphoma

Follicular lymphoma is caused by the transformation of a germinal-center-derived B cell with a t(14;18) chromosomal translocation. The distribution of somatic mutations within immunoglobulin genes indicates that follicular-lymphoma cells can interact with antigen. In addition, nonimmunoglobulin genes such as BCL6 seem to undergo somatic hypermutation. Here, Kostas Stamatopoulos and colleagues relate the molecular data about immunoglobulin genes and the protooncogenes BCL2 and BCL6 to the pathogenesis and evolution of follicular lymphoma.