Somatic hypermutation and V(H) gene usage in mantle cell lymphoma

Treatment of Mantle Cell Lymphoma in the Frontline Setting: Are We Ready for a Risk-Adapted Approach?

Mantle cell lymphoma (MCL), a type of B-cell non-Hodgkin lymphoma characterized by the t(11;14)(q13q32) translocation, is a clinically heterogenous disease which can range from indolent to highly aggressive. Numerous prognostic factors have been identified, including blastoid histology, the Mantle Cell Lymphoma International Prognostic Index (MIPI) score, high proliferation index, p53 deletions and/or mutations, complex karyotype, minimal residual disease, and several others. However, using these prognostic factors to guide treatment selection has largely remained elusive. Given the heterogeneous behavior of this disease and varying patient characteristics, we suggest that the time has come for a more risk-adapted approach to this disease. In this article, we review the numerous prognostic factors that have been described for MCL, both at the time of diagnosis and following first-line treatment. We then propose a risk-adapted approach to first-line therapy for MCL, which would reserve intensive therapy for the highest risk patients and spare others excessive toxicity.

Mantle cell lymphoma in 2022-A comprehensive update on molecular pathogenesis, risk stratification, clinical approach, and current and novel treatments

The field of mantle cell lymphoma (MCL) has witnessed remarkable progress due to relentless advances in molecular pathogenesis, prognostication, and newer treatments. MCL consists of a spectrum of clinical subtypes. Rarely, atypical cyclin D1-negative MCL and in situ MCL neoplasia are identified. Prognostication of MCL is further refined by identifying somatic mutations (such as TP53, NSD2, KMT2D), methylation status, chromatin organization pattern, SOX-11 expression, minimal residual disease (MRD), and genomic clusters. Lymphoid tissue microenvironment studies demonstrated the role of B-cell receptor signaling, nuclear factor kappa B (NF-kB), colony-stimulating factor (CSF)-1, the CD70-SOX-11 axis. Molecular mechanism of resistance, mutation dynamics, and pathogenic pathways (B-cell receptor (BCR), oxidative phosphorylation, and MYC) were identified in mediating resistance to various treatments (bruton tyrosine kinase (BTK) inhibitors [ibrutinib, acalabrutinib]. Treatment options range from conventional chemoimmunotherapy and stem cell transplantation (SCT) to targeted therapies against BTK (covalent and noncovalent), Bcl2, ROR1, cellular therapy such as anti-CD19 chimeric antigen receptor therapy (CAR-T), and most recently bispecific antibodies against CD19 and CD20. MCL patients frequently relapse. Complex pathogenesis and the management of patients with progression after treatment with BTK/Bcl2 inhibitors and CAR-T (triple-resistant MCL) remain a challenge. Next-generation clinical trials incorporating newer agents and concurrent translational and molecular investigations are ongoing.

Aberrant somatic hypermutation of CCND1 generates non-coding drivers of mantle cell lymphomagenesis

Aberrant somatic hypermutation (aSHM) can target proto-oncogenes and drive oncogenesis. In mantle cell lymphoma (MCL), CCND1 is targeted by aSHM in the non-nodal subtype (nnMCL), giving rise to exon1 encoded mutant proteins like E36K, Y44D, and C47S that contribute to lymphomagenesis by virtue of their increased protein stability and nuclear localization. However, the vast majority of somatic variants generated by aSHM are found in the first intron of CCND1 but their significance for mantle cell lymphomagenesis is unknown. We performed whole-genome and whole-transcriptome sequencing in 84 MCL patients to explore the contribution of non-coding somatic variants created by aSHM to lymphomagenesis. We show that non-coding variants are enriched in a MCL specific manner in transcription factor-binding sites, that non-coding variants are associated with increased CCND1 mRNA expression, and that coding variants in the first exon of CCND1 are more often synonymous or cause benign amino acid changes than in other types of lymphomas carrying a t(11;14) translocation. Therefore, the increased frequency of somatic variants due to aSHM might be a consequence of selection pressure manifested at the transcriptional level rather than being a mere mechanistic consequence of misguided activation-induced cytidine deaminase (AID) activity.

How to Diagnose and Treat CD5-Positive Lymphomas Involving the Spleen

Patients with CD5-expressing lymphomas presenting with splenomegaly are frequently diagnosed with chronic lymphocytic leukemia. The most important differential diagnosis is mantle cell lymphoma, both in its classical and leukemic, non-nodal forms, given its prognostic and therapeutic implications. Other small B-cell neoplasms that frequently involve the spleen and occasionally express CD5 include the splenic marginal zone lymphoma, hairy cell leukemia and, rarely, lymphoplasmacytic lymphoma. The frequency of CD5 positivity depends in part on the sensitivity of the detection methods employed. Usually, a combination of morphological, immunophenotypic and molecular findings allows for a precise sub-classification of CD5-positive, low-grade B-cell lymphomas of the spleen. Some of these tumors may display a mixture of small and larger B cells, raising the possibility of more aggressive lymphomas, such as diffuse large B-cell lymphomas (DLBCL). Approximately 5-10% of DLBCL are CD5-positive and some may manifest as primary splenic lesions. When available, the morphology of DLBCL in the splenic tissue is distinctive and a leukemic picture is very rare. In conclusion, the appropriate morphological and clinical context assisted by flow cytometry panels and/or immunohistochemistry allows the differential diagnosis of CD5-positive, non-Hodgkin, B-cell lymphomas involving the spleen.

Genetic mutations and features of mantle cell lymphoma: a systematic review and meta-analysis

Mantle cell lymphoma (MCL) is an incurable rare subtype of non-Hodgkin lymphoma and is subject to relapse and therapeutic resistance. Molecular aberrations in MCL affect pathogenesis, prognosis, and therapeutic response. In this systematic review, we searched 3 databases and selected 32 articles that described mutations in MCL patients. We then conducted a meta-analysis using a Bayesian multiregression model to analyze patient-level data in 2127 MCL patients, including prevalence of mutations. In tumor or bone marrow samples taken at diagnosis or baseline, ATM was the most frequently mutated gene (43.5%) followed by TP53 (26.8%), CDKN2A (23.9%), and CCND1 (20.2%). Aberrations were also detected in IGH (38.4%) and MYC (20.8%), primarily through cytogenetic methods. Other common baseline mutations were NSD2 (15.0%), KMT2A (8.9%), S1PR1 (8.6%), and CARD11 (8.5%). Our data also show a change in mutational status from baseline samples to samples at disease progression and present mutations of interest in MCL that should be considered for future analysis. The genes with the highest mutational frequency difference (>5%) are TP53, ATM, KMT2A, MAP3K14, BTK, TRAF2, CHD2, TLR2, ARID2, RIMS2, NOTCH2, TET2, SPEN, NSD2, CARD11, CCND1, SP140, CDKN2A, and S1PR1. These findings provide a summary of the mutational landscape of MCL. The genes with the highest change in mutation frequency should be included in targeted next-generation sequencing panels for future studies. These findings also highlight the need for analysis of serial samples in MCL. Patient-level data of prevalent mutations in MCL provide additional evidence emphasizing molecular variability in advancing precision medicine initiatives in MCL.

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.

Mantle cell lymphoma: 2019 update on the diagnosis, pathogenesis, prognostication, and management

Unprecedented advances in our understanding of the pathobiology, prognostication, and therapeutic options in mantle cell lymphoma (MCL) have taken place in the last few years. Heterogeneity in the clinical course of MCL-indolent vs aggressive-is further delineated by a correlation with the mutational status of the variable region of immunoglobulin heavy chain, methylation status, and SOX-11 expression. Cyclin-D1 negative MCL, in situ MCL neoplasia, and impact of the karyotype on prognosis are distinguished. Apart from Ki-67% and morphology pattern (classic vs blastoid/pleomorphic), the proliferation gene signature has helped to further refine prognostication. Studies focusing on mutational dynamics and clonal evolution on Bruton's tyrosine kinase (BTK) inhibitors (ibrutinib, acalabrutinib) and/or Bcl2 antagonists (venetoclax) have further clarified the prognostic impact of somatic mutations in TP53, BIRC3, CDKN2A, MAP3K14, NOTCH2, NSD2, and SMARCA4 genes. In therapy, long-term follow-up on chemo-immunotherapy studies has demonstrated durable remissions in some patients; however, long-term toxicities, especially from second cancers, are a serious concern with chemotherapy. The therapeutic options in MCL are constantly evolving, with dramatic responses from nonchemotherapeutic agents (ibrutinib, acalabrutinib, and venetoclax). Chimeric antigen receptor therapy and combinations of nonchemotherapeutic agents are actively being studied and our focus is shifting toward making the treatment of MCL chemotherapy-free. Still, MCL remains incurable. The following aspects of MCL continue to pose a challenge: disease transformation, role of the cytokine-microenvironmental milieu, incorporation of positron emission tomography-computerized tomography imaging, minimal residual disease in the prognosis, circulating tumor DNA testing for clonal evolution, predicting resistance to BTK inhibitors, and optimal management of patients who progress on BTK/Bcl2 inhibitors. Next-generation clinical trials should incorporate nonchemotherapeutic agents and personalize the treatment based upon the genomic profile of individual patient. Recent advances in the field of MCL are reviewed.

Stereotyped B Cell Receptor Immunoglobulins in B Cell Lymphomas

Comprehensive analysis of the clonotypic B cell receptor immunoglobulin (BcR IG) gene rearrangement sequences in patients with mature B cell neoplasms has led to the identification of significant repertoire restrictions, culminating in the discovery of subsets of patients expressing highly similar, stereotyped BcR IG. This finding strongly supports selection by common epitopes or classes of structurally similar epitopes in the ontogeny of these tumors. BcR IG stereotypy was initially described in chronic lymphocytic leukemia (CLL), where the stereotyped fraction of the disease accounts for a remarkable one-third of patients. However, subsequent studies showed that stereotyped BcR IG are also present in other neoplasms of mature B cells, including mantle cell lymphoma (MCL) and splenic marginal zone lymphoma (SMZL). Subsequent cross-entity comparisons led to the conclusion that stereotyped IG are mostly "disease-specific," implicating distinct immunopathogenetic processes. Interestingly, mounting evidence suggests that a molecular subclassification of lymphomas based on BcR IG stereotypy is biologically and clinically relevant. Indeed, particularly in CLL, patients assigned to the same subset due to expressing a particular stereotyped BcR IG display remarkably consistent biological background and clinical course, at least for major and well-studied subsets. Thus, the robust assignment to stereotyped subsets may assist in the identification of mechanisms underlying disease onset and progression, while also refining risk stratification. In this book chapter, we provide an overview of the recent BcR IG stereotypy studies in mature B cell malignancies and outline previous and current methodological approaches used for the identification of stereotyped IG.

Mantle cell lymphoma in the era of precision medicine-diagnosis, biomarkers and therapeutic agents

Despite advances in the development of clinical agents for treating Mantle Cell Lymphoma (MCL), treatment of MCL remains a challenge due to complexity and frequent relapse associated with MCL. The incorporation of conventional and novel diagnostic approaches such as genomic sequencing have helped improve understanding of the pathogenesis of MCL, and have led to development of specific agents targeting signaling pathways that have recently been shown to be involved in MCL. In this review, we first provide a general overview of MCL and then discuss about the role of biomarkers in the pathogenesis, diagnosis, prognosis, and treatment for MCL. We attempt to discuss major biomarkers for MCL and highlight published and ongoing clinical trials in an effort to evaluate the dominant signaling pathways as drugable targets for treating MCL so as to determine the potential combination of drugs for both untreated and relapse/refractory cases. Our analysis indicates that incorporation of biomarkers is crucial for patient stratification and improve diagnosis and predictability of disease outcome thus help us in designing future precision therapies. The evidence indicates that a combination of conventional chemotherapeutic agents and novel drugs designed to target specific dysregulated signaling pathways can provide the effective therapeutic options for both untreated and relapse/refractory MCL.

CD10-positive mantle cell lymphoma: clinicopathologic and prognostic study of 30 cases

Mantle cell lymphoma is usually negative for CD10 which is useful in distinguishing MCL from other CD10 + B cell lymphomas. Here we assessed the clinicopathologic features of 30 cases of CD10+ MCL, the largest series to date in the English literature, and compared them with a group of 212 typical MCL cases (CD5+, CD10-negative, CD23-negative, cyclin D1+). The 30 patients with CD10+ MCL included 17 men and 13 women with a median age of 68 years. Compared with CD10-negative MCL, patients with CD10+ MCL showed a lower male predominance (p = 0.01), more often had a diffuse growth pattern (p = 0.04) and blastoid/pleomorphic morphology (p < 0.0001), and more often showed BCL6 expression (p = 0.009). In all MCL patients, CD10 expression was not associated with overall survival (OS) (p = 0.16). However, in more aggressive subsets of MCL patients including those with high Ki67 (> 60%), blastoid/pleomorphic morphology, or high MCL International Prognostic Index (MIPI), CD10 expression was associated with a worse OS (p = 0.003, 0.04, and 0.001, respectively). High Ki67 (> 60%), blastoid/pleomorphic morphology, and high MIPI were also been identified as poor prognostic factors patients with in CD10+ MCL (p = 0.001, 0.0003, and 0.01, respectively). In summary, CD10+ MCL more often has a diffuse growth pattern, blastoid/pleomorphic morphology, and BCL6 expression. In MCL patients with a high Ki-67 (> 60%), blastoid/pleomorphic morphology, or high MIPI, CD10 expression contributes to an even worse prognosis. MCL should be included in the differential diagnosis of CD10 + B cell lymphomas.

The role of B cell antigen receptors in mantle cell lymphoma

Mantle cell lymphoma (MCL) is characterized by an aggressive clinical course and secondary resistance to currently available therapies in most cases. Therefore, despite recent advances in the treatment of this disease, it is still considered to be incurable in the majority of cases. MCL B cells retain their B cell antigen receptor (BCR) expression during and after neoplastic transformation. BCRs in MCL show distinct patterns of antigen selection and ongoing BCR signaling. However, little is known about the involved antigens and the mechanisms leading to lymphomagenesis and lymphoma progression in MCL. Recent preclinical and clinical studies have established a crucial role of the BCR and the potential of inhibiting its signaling in this disease. This has established the B cell antigen receptor signaling cascade as a very promising therapeutic target to improve outcome in MCL alone or in combination with chemo-immunotherapy in recent years.

Clinical utility of recently identified diagnostic, prognostic, and predictive molecular biomarkers in mature B-cell neoplasms

Genomic profiling studies have provided new insights into the pathogenesis of mature B-cell neoplasms and have identified markers with prognostic impact. Recurrent mutations in tumor-suppressor genes (TP53, BIRC3, ATM), and common signaling pathways, such as the B-cell receptor (CD79A, CD79B, CARD11, TCF3, ID3), Toll-like receptor (MYD88), NOTCH (NOTCH1/2), nuclear factor-κB, and mitogen activated kinase signaling, have been identified in B-cell neoplasms. Chronic lymphocytic leukemia/small lymphocytic lymphoma, diffuse large B-cell lymphoma, follicular lymphoma, mantle cell lymphoma, Burkitt lymphoma, Waldenström macroglobulinemia, hairy cell leukemia, and marginal zone lymphomas of splenic, nodal, and extranodal types represent examples of B-cell neoplasms in which novel molecular biomarkers have been discovered in recent years. In addition, ongoing retrospective correlative and prospective outcome studies have resulted in an enhanced understanding of the clinical utility of novel biomarkers. This progress is reflected in the 2016 update of the World Health Organization classification of lymphoid neoplasms, which lists as many as 41 mature B-cell neoplasms (including provisional categories). Consequently, molecular genetic studies are increasingly being applied for the clinical workup of many of these neoplasms. In this review, we focus on the diagnostic, prognostic, and/or therapeutic utility of molecular biomarkers in mature B-cell neoplasms.

Molecular evidence for antigen drive in the natural history of mantle cell lymphoma

To further our understanding about antigen involvement in mantle cell lymphoma (MCL), we analyzed the expression levels of activation-induced cytidine deaminase (AID), a key player in B-cell responses to antigen triggering, in 133 MCL cases; assessed the functionality of AID by evaluating in vivo class switch recombination in 52 MCL cases; and sought for indications of ongoing antigen interactions by exploring intraclonal diversification within 14 MCL cases. The AID full-length transcript and the most frequent splice variants (AID-ΔE4a, AID-ΔE) were detected in 128 (96.2%), 96 (72.2%), and 130 cases (97.7%), respectively. Higher AID full-length transcript levels were significantly associated (P < 0.001) with lack of somatic hypermutation within the clonotypic immunoglobulin heavy variable (IGHV) genes. Median AID transcript levels were higher in lymph node material compared to cases in which peripheral blood was analyzed, implying that clonal behavior is influenced by the microenvironment. Switched tumor-derived IGHV-IGHD-IGHJ transcripts were identified in 5 of 52 cases (9.6%), all of which displayed somatic hypermutation and AID-mRNA expression. Finally, although most cases exhibited low levels of intraclonal diversification, analysis of the mutational activity revealed a precise targeting of somatic hypermutation indicative of an active, ongoing interaction with antigen(s). Collectively, these findings strongly allude to antigen involvement in the natural history of MCL, further challenging the notion of antigen naivety.

Clinical observations on chemotherapy curable malignancies: unique genetic events, frozen development and enduring apoptotic potential

BACKGROUND

A select number of relatively rare metastatic malignancies comprising trophoblast tumours, the rare childhood cancers, germ cells tumours, leukemias and lymphomas have been routinely curable with chemotherapy for more than 30 years. However for the more common metastatic malignancies chemotherapy treatment frequently brings clinical benefits but cure is not expected. Clinically this clear divide in outcome between the tumour types can appear at odds with the classical theories of chemotherapy sensitivity and resistance that include rates of proliferation, genetic development of drug resistance and drug efflux pumps. We have looked at the clinical characteristics of the chemotherapy curable malignancies to see if they have any common factors that could explain this extreme differential sensitivity to chemotherapy.

DISCUSSION

It has previously been noted how the onset of malignancy can leave malignant cells fixed with some key cellular functions remaining frozen at the point in development at which malignant transformation occurred. In the chemotherapy curable malignancies the onset of malignancy is in each case closely linked to one of the unique genetic events of; nuclear fusion for molar pregnancies, choriocarcinoma and placental site trophoblast tumours, gastrulation for the childhood cancers, meiosis for testicular cancer and ovarian germ cell tumours and VDJ rearrangement and somatic hypermutation for acute leukemia and lymphoma. These processes are all linked to natural periods of supra-physiological apoptotic potential and it appears that the malignant cells arising from them usually retain this heightened sensitivity to DNA damage. To investigate this hypothesis we have examined the natural history of the healthy cells during these processes and the chemotherapy sensitivity of malignancies arising before, during and after the events. To add to the debate on chemotherapy resistance and sensitivity, we would argue that malignancies can be functionally divided into 2 groups. Firstly those that arise in cells with naturally heightened apoptotic potential as a result of their proximity to the unique genetic events, where the malignancies are generally chemotherapy curable and then the more common malignancies that arise in cells of standard apoptotic potential that are not curable with classical cytotoxic drugs.

Five important advances in hematopathology

CONTEXT

Hematopathology is a dynamic field that has always been on the frontier of clinical research within the scope of pathology. Several recent developments in hematopathology will likely affect its practice clinically.

OBJECTIVE

To review 5 important recent advances in hematopathology: (1) detection and prognostic implication of MYC in diffuse large B-cell lymphomas, (2) determining origin and prognosis through immunoglobulin gene usage in mature B-cell neoplasms, (3)detecting minimal residual disease in multiple myeloma, (4) using genome-wide analysis in myelodysplastic syndromes, and (5) employing whole-genome sequencing in acute myeloid leukemias.

DATA SOURCES

Literature review and the authors' experiences in an academic center.

CONCLUSIONS

These advances will bring hematopathology into a new molecular era and help us to better understand the molecular, pathologic mechanisms of lymphomas, leukemias, myelomas, and myelodysplastic syndromes. They will help us to identify diagnostic and prognostic markers and eventually provide new therapeutic targets and treatments for these diseases.

Mantle cell lymphoma in cyclin D1 transgenic mice with Bim-deficient B cells

Mantle cell lymphoma (MCL) is a highly aggressive B-cell lymphoma resistant to conventional chemotherapy. Although defined by the characteristic t(11;14) translocation, MCL has not been recapitulated in transgenic mouse models of cyclin D1 overexpression alone. Indeed, several genetic aberrations have been identified in MCL that may contribute to its pathogenesis and chemoresistance. Of particular interest is the frequent biallelic deletion of the proapoptotic BCL-2 family protein BIM. BIM exerts its pro-death function via its α-helical BH3 death domain that has the dual capacity to inhibit antiapoptotic proteins such as BCL-2 and MCL-1 and directly trigger proapoptotic proteins such as the mitochondrial executioner protein BAX. To evaluate a functional role for Bim deletion in the pathogenesis of MCL, we generated cyclin D1-transgenic mice harboring Bim-deficient B cells. In response to immunization, Eμ(CycD1)CD19(CRE)Bim(fl/fl) mice manifested selective expansion of their splenic mantle zone compartment. Three distinct immune stimulation regimens induced lymphomas with histopathologic and molecular features of human MCL in a subset of mice. Thus, deletion of Bim in B cells, in the context of cyclin D1 overexpression, disrupts a critical control point in lymphoid maturation and predisposes to the development of MCL. This genetic proof of concept for MCL pathogenesis suggests an opportunity to reactivate the death pathway by pharmacologic mimicry of proapoptotic BIM.

Mantle cell lymphoma cell lines show no evident immunoglobulin heavy chain stereotypy but frequent light chain stereotypy

Mantle cell lymphoma shows a peculiar immunogenetic profile, but the functional consequences of this fact are unknown. We have determined the precise sequences of rearranged heavy and light chain genes in several mantle cell lymphoma cell lines and investigated the presence of heavy and light chain stereotypy. These cell lines use IGHV and IGLV genes that are known to be preferentially rearranged in mantle cell lymphoma, but we found no evidence of heavy chain stereotypy. In contrast, one cell line (Mino) showed a nearly identical light chain complementarity-determining region 3 when compared to the only published light chain cluster. Two cell line couples (Jeko-1/UPN-2 and JVM-2/JVM-13) showed a highly similar light chain that satisfied the criteria for stereotypy. Our data show that mantle cell lymphoma cell lines resemble the IGHV and IGLV usage of mantle cell lymphoma, and foster the hypothesis that light chain stereotypy might be under-recognized.

B cell receptor and antigens in CLL

Nowadays, chronic lymphocytic leukemia (CLL) is considered as a prototypic antigen-driven lymphoma, with antigenic stimuli from the microenvironment promoting tumor outgrowth. Antigen recognition is a function of both the clonotypic B cell receptor immunoglobulin (BcR IG) and various other immune sensors, e.g., the Toll-like receptors. The critical role of BcR IG-mediated signaling in CLL development and evolution is underscored by the following: the disease-biased IG gene repertoire; the subdivision of CLL based on the somatic hypermutation load of the BcR IG into two broad categories with vastly different prognosis and eventual outcome; the existence of subsets of cases with distinct, quasi-identical (stereotyped) BcR IGs; and the clinical efficacy of novel therapeutics inhibiting BcR signaling. Here, we trace the immunogenetic evidence for antigen selection in CLL and also consider the types of implicated antigens as well as the immune signaling pathways relevant for CLL ontogeny and clonal progression.

Composite mantle cell lymphoma and chronic lymphocytic leukemia/small lymphocytic lymphoma: a clinicopathologic and molecular study

Mantle cell lymphoma (MCL) and chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) share many features and both arise from CD5+ B-cells; their distinction is critical as MCL is a more aggressive neoplasm. Rarely, cases of composite MCL and CLL/SLL have been reported. Little is known about the nature of these cases and, in particular, the clonal relationship of the 2 lymphomas. Eleven composite MCL and CLL/SLL cases were identified. The clinical, morphologic and immunophenotypic features of the MCL and CLL/SLL were characterized. IGH (immunoglobulin heavy chain) gene analysis was performed on microdissected MCL and CLL/SLL components to assess their clonal relationship. Ten patients had lymphadenopathy, and 7 patients had bone marrow involvement. The MCL component had the following growth patterns: in situ (n = 1), mantle zone (n = 3), nodular and diffuse (n = 3), diffuse (n = 3), and interstitial in the bone marrow (the only patient without lymphadenopathy) (n = 1); 6 MCLs had blastoid or pleomorphic and 5 small lymphocytic features. The CLL/SLL component was nodular (n = 9) or diffuse (n = 2). All MCL were CD5(+) and cyclin D1(+) with t(11;14) translocation. All CLL/SLL were CD5(+), CD23(+) and negative for cyclin D1 or t(11;14). IGH gene analysis showed that the MCL and CLL/SLL components displayed different sized fragments, indicating that the MCL and CLL/SLL are likely derived from different neoplastic B-cell clones. The lack of a clonal relationship between the MCL and CLL/SLL components suggests that MCL and CLL/SLL components represent distinct disease processes and do not share a common progenitor B-cell.

Molecular subsets of mantle cell lymphoma defined by the IGHV mutational status and SOX11 expression have distinct biologic and clinical features

Mantle cell lymphoma (MCL) is a heterogeneous disease with most patients following an aggressive clinical course, whereas others having an indolent behavior. We conducted an integrative and multidisciplinary analysis of 177 MCL to determine whether the immunogenetic features of the clonotypic B-cell receptors (BcR) may identify different subsets of tumors. Truly unmutated (100% identity) IGHV genes were found in 24% cases, 40% were minimally/borderline mutated (99.9%-97%), 19% significantly mutated (96.9%-95%), and 17% hypermutated (<95%). Tumors with high or low mutational load used different IGHV genes, and their gene expression profiles were also different for several gene pathways. A gene set enrichment analysis showed that MCL with high and low IGHV mutations were enriched in memory and naive B-cell signatures, respectively. Furthermore, the highly mutated tumors had less genomic complexity, were preferentially SOX11-negative, and showed more frequent nonnodal disease. The best cut-off of germline identity of IGHV genes to predict survival was 97%. Patients with high and low mutational load had significant different outcome with 5-year overall survival (OS) of 59% and 40%, respectively (P = 0.004). Nodal presentation and SOX11 expression also predicted for poor OS. In a multivariate analysis, IGHV gene status and SOX11 expression were independent risk factors. In conclusion, these observations suggest the idea that MCL with mutated IGHV, SOX11-negativity, and nonnodal presentation correspond to a subtype of the disease with more indolent behavior.

Is there a role for "watch and wait" in patients with mantle cell lymphoma?

Up to one third of patients with mantle cell lymphoma (MCL) may be observed for a period of months to years before developing indications for therapy. Importantly, observational studies suggest that this approach has no apparent negative impact on their overall survival. Although there is broad agreement on which patients require early therapy, identification of patients with less aggressive disease can be challenging. Clinical tools such as the Mantle Cell International Prognostic Index (MIPI) and Ki67 are effective at predicting survival but may not always correspond with indications for treatment. Research tools such as the proliferative signature are attractive but have yet to be evaluated in this context. Physicians, therefore, must make decisions regarding therapy based on the best available evidence. In the absence of evidence that treatment necessarily influences long-term survival, it may be reasonable to observe selected patients for a period of time prior to making definitive treatment-related decisions. Collaborative efforts are required to better understand the pathophysiology of the disease and potentially identify patients amenable to "watch and wait." Similarly, patients with less aggressive MCL may be an ideal group in which to evaluate novel treatment approaches.

Anti-tumor activity of a B-cell receptor-targeted peptide in a novel disseminated lymphoma xenograft model

Receptor-targeted therapies have become standard in the treatment of various lymphomas. In view of its unparalleled specificity for the malignant B-cell clone, the B-cell receptor (BCR) on B cell lymphoma cells is a potential therapeutic target. We have used two BCR epitope mimicking peptides binding to the Burkitt's lymphoma cell lines CA46 and SUP-B8. We proved their functionality by demonstrating calcium flux and BCR-mediated endocytosis upon peptide receptor binding. Toxicity experiments in vitro via cross-linking of the BCR with tetramerized epitope mimics lead to apoptosis in both cell lines but was far more effective in SUP-B8 cells. We established a SUP-B8-based disseminated Burkitt's lymphoma model in NOD/SCID mice. Treatment of tumor-bearing mice with tetramerized epitope mimics had significant anti-tumor effects in vivo. We conclude that peptide-mediated, BCR-targeted therapy is a promising approach which may be explored and further developed for application in highly aggressive lymphoma.

Is there a role for antigen selection in mantle cell lymphoma? Immunogenetic support from a series of 807 cases

We examined 807 productive IGHV-IGHD-IGHJ gene rearrangements from mantle cell lymphoma (MCL) cases, by far the largest series to date. The IGHV gene repertoire was remarkably biased, with IGHV3-21, IGHV4-34, IGHV1-8, and IGHV3-23 accounting for 46.3% of the cohort. Eighty-four of 807 (10.4%) cases, mainly using the IGHV3-21 and IGHV4-34 genes, were found to bear stereotyped heavy complementarity-determining region 3 (VH CDR3) sequences and were placed in 38 clusters. Notably, the MCL stereotypes were distinct from those reported for chronic lymphocytic leukemia. Based on somatic hypermutation (SHM) status, 238/807 sequences (29.5%) carried IGHV genes with 100% germ line identity; the remainder (569/807; 70.5%) exhibited different SHM impact, ranging from minimal (in most cases) to pronounced. Shared replacement mutations across the IGHV gene were identified for certain subgroups, especially those using IGHV3-21, IGHV1-8, and IGHV3-23. Comparison with other entities, in particular CLL, revealed that several of these mutations were "MCL-biased." In conclusion, MCL is characterized by a highly restricted immunoglobulin gene repertoire with stereotyped VH CDR3s and very precise SHM targeting, strongly implying a role for antigen-driven selection of the clonogenic progenitors. Hence, an antigen-driven origin of MCL could be envisaged, at least for subsets of cases.

Parallel gene expression profiling of mantle cell lymphoma - how do we transform 'omics data into clinical practice

DNA microarray technology has been a valuable tool to provide a global view of the changes in gene expression that characterize different types of B cell lymphomas, both in relation to clinical parameters but also in comparison with the non-malignant counterparts. The number of transcripts that can be analyzed on an array has dramatically increased, and now most commercially available arrays cover the whole genome, enabling overall analysis of the transcriptome.The backside of collecting this massive amount of information is that even after strict data filtering, it is impossible to do follow-up studies on all findings. Down-stream analysis is time-consuming and when performing confirmatory experiments on the protein level, the experiments are in most cases restricted to proteins recognized by commercially available reagents. Furthermore, since gene expression data is a comparative method not only are the experimental set-up but also the characteristics of both the sample and reference crucial for our ability to answer the questions posed. Thus, initial care must be taken in the design of the experiment and the preparation of the samples.The aim of this review is to discuss the progress in mantle cell lymphoma research enabled by gene expression analysis and to pinpoint the difficulties in making efficient use of the generated data to provide a fast and accurate clinical diagnosis, efficient stratification of patients into disease sub-groups and improved therapy.

Mantle cell lymphoma with features of marginal-zone lymphoma

We present seven cases of mantle cell lymphoma with morphological features of marginal-zone lymphoma. Of particular interest, four of the patients had predominant involvement of the gastrointestinal tract. All cases displayed the translocation t(11;14)(q13;q32) and expressed cyclin D1. Cytogenetic analysis revealed trisomy 3 in one case and somatic hypermutation of immunoglobulin heavy genes could be demonstrated in two out of four cases. The latter features are reminiscent of marginal-zone lymphoma. The localization of these lymphomas mainly in the gastrointestinal tract and the higher exposure to antigens in this area may explain why this variant of mantle cell lymphoma harbours features of marginal-zone lymphoma.

Chronic lymphocytic leukemia in a Japanese population: varied immunophenotypic profile, distinctive usage of frequently mutated IGH gene, and indolent clinical behavior

Chronic lymphocytic leukemia (CLL) is relatively rare in Japan. Among 46 cases of mature B-cell leukemia, we identified 28 Japanese patients with CLL, including prolymphocytoid and lymphoplasmacytoid morphological variants. Compared with Western patients with CLL, only 52.0% of cases showed the typical immunophenotypic profile. IgG-bearing (15.4%) and clearly CD20-expressing (71.4%) cases were frequently observed. Most cases harbored a mutated immunoglobulin heavy-chain (VH) gene (88.5%) and commonly used a VH3 family member (61.5%) other than VH3-21. During the median follow-up period of 64 months, 20 cases (71.4%) showed an indolent clinical course without any treatment, and six cases (21.4%) were accompanied by other malignancies. Binet A stage (p = 0.003), low-risk category according to the modified Rai classification (p = 0.016), and ≤ 15 U/mL level of serum thymidine kinase activity (p = 0.016) were associated with prolongation of treatment-free status. Although Japanese cases of CLL showed heterogeneity in morphology and immunophenotype, most cases arose from post-antigen-selected B cells and presented with indolent clinical behavior.

Bortezomib resistance in mantle cell lymphoma is associated with plasmacytic differentiation

Bortezomib induces remissions in 30%-50% of patients with relapsed mantle cell lymphoma (MCL). Conversely, more than half of patients' tumors are intrinsically resistant to bortezomib. The molecular mechanism of resistance has not been defined. We generated a model of bortezomib-adapted subclones of the MCL cell lines JEKO and HBL2 that were 40- to 80-fold less sensitive to bortezomib than the parental cells. Acquisition of bortezomib resistance was gradual and reversible. Bortezomib-adapted subclones showed increased proteasome activity and tolerated lower proteasome capacity than the parental lines. Using gene expression profiling, we discovered that bortezomib resistance was associated with plasmacytic differentiation, including up-regulation of IRF4 and CD38 and expression of CD138. In contrast to plasma cells, plasmacytic MCL cells did not increase immunoglobulin secretion. Intrinsically bortezomib-resistant MCL cell lines and primary tumor cells from MCL patients with inferior clinical response to bortezomib also expressed plasmacytic features. Knockdown of IRF4 was toxic for the subset of MCL cells with plasmacytic differentiation, but only slightly sensitized cells to bortezomib. We conclude that plasmacytic differentiation in the absence of an increased secretory load can enable cells to withstand the stress of proteasome inhibition. Expression of CD38 and IRF4 could serve as markers of bortezomib resistance in MCL. This study has been registered at http://clinicaltrials.gov as NCT00131976.

Constitutive and B-cell receptor-induced activation of STAT3 are important signaling pathways targeted by bortezomib in leukemic mantle cell lymphoma

BACKGROUND

The deregulation of several transcription factors contribute to the aggressive course of mantle cell lymphoma. This study focuses on survival signals emanating from the tumor environment and involving the signal transducer and activator of transcription (STAT) 3 through cytokines or antigen recognition.

DESIGN AND METHODS

Primary mantle cell lymphoma cells were isolated from 20 leukemic patients. The phosphorylation status of STAT3 was evaluated by immunoblottting and immunofluorescence, the levels of cytokine secretion by enzyme-linked immunosorbent assay and the cell survival signals by apoptosis and cell viability assays.

RESULTS

STAT3 was constitutively phosphorylated in the Jeko-1 mantle cell lymphoma cell line and in 14 out of 20 (70%) cases of leukemic mantle cell lymphoma as the result of an autocrine secretion of interleukin-6 and/or interleukin-10. In addition, B-cell receptor engagement resulted in an increase of both in vitro cell survival and STAT3 phosphorylation in primary mantle cell lymphoma cells. Inhibition of the Janus-activated kinase/STAT3 pathway increased spontaneous apoptosis and suppressed B-cell receptor-induced cell survival in all cases analyzed. The impact of in vitro exposure to the proteasome inhibitor bortezomib was next evaluated in primary mantle cell lymphoma cells. Bortezomib induced apoptosis and a decrease of both interleukin-6/interleukin-10 secretion and STAT3 phosphorylation. In addition, bortezomib inhibited B-cell receptor-triggered STAT3 phosphorylation and cell survival.

CONCLUSIONS

We demonstrated that STAT3 was activated in primary mantle cell lymphoma cells either constitutively through a cytokine autocrine loop or in response to B-cell receptor engagement, both processes leading to a survival signal inhibited by bortezomib. STAT3 appears, therefore, to play a pivotal role in mantle cell lymphoma and represents a promising therapeutic target.

Mantle cell lymphoma: biological insights and treatment advances

Mantle cell lymphoma (MCL) exhibits considerable molecular heterogeneity and complexity, and is regarded as one of the most challenging lymphomas to treat. With increased understanding of the pathobiology of MCL, it is proposed that MCL is the result of 3 major converging factors, namely, deregulated cell cycle pathways, defects in DNA damage responses, and dysregulation of cell survival pathways. In the present era of targeted therapies, these biologic insights have resulted in the identification of several novel rational targets for therapeutic intervention in MCL that are undergoing active clinical testing. To date, there is no standard of care in MCL. Several approaches including conventional anthracycline-based therapies and intensive high-dose strategies with and without stem cell transplantation have failed to produce durable remissions for most patients. Moreover, considering the heterogeneity of MCL, it is increasingly being recognized that risk-adapted therapy might be a relevant therapeutic approach in this disease. At the first and second Global Workshops on Mantle Cell Lymphoma, questions addressing advances in the pathobiology of MCL, optimization of existing therapies, assessment of current data with novel therapeutic strategies, and the identification of molecular or phenotypic risk factors for utilization in risk-adapted therapies were discussed and will be summarized herein.

A comparison between protein profiles of B cell subpopulations and mantle cell lymphoma cells

Background

B-cell lymphomas are thought to reflect different stages of B-cell maturation. Based on cytogenetics and molecular markers, mantle cell lymphoma (MCL) is presumed to derive predominantly from naïve, pre-germinal centre (pre-GC) B lymphocytes. The aim of this study was to develop a method to investigate the similarity between MCL cells and different B-cell compartments on a protein expression level.

Methods

Subpopulations of B cells representing the germinal centre (GC), the pre-GC mantle zone and the post-GC marginal zone were isolated from tonsils using automated magnetic cell sorting (AutoMACS) of cells based on their expression of CD27 and IgD. Protein profiling of the B cell subsets, of cell lines representing different lymphomas and of primary MCL samples was performed using top-down proteomics profiling by surface-enhanced laser detection/ionization time-of-flight mass spectrometry (SELDI-TOF-MS).

Results

Quantitative MS data of significant protein peaks (p-value < 0.05) separating the three B-cell subpopulations were generated. Together, hierarchical clustering and principal component analysis (PCA) showed that the primary MCL samples clustered together with the pre- and post-GC subpopulations. Both primary MCL cells and MCL cell lines were clearly separated from the B cells representing the GC compartment.

Conclusion

AutoMACS sorting generates sufficient purity to enable a comparison between protein profiles of B cell subpopulations and malignant B lymphocytes applying SELDI-TOF-MS. Further validation with an increased number of patient samples and identification of differentially expressed proteins would enable a search for possible treatment targets that are expressed during the early development of MCL.

Autoimmunity and lymphoma: is mantle cell lymphoma a mistake of the receptor editing mechanism?

Mantle cell lymphoma (MCL) is an aggressive B cell malignancy, which is believed to originate from naïve B cells in the mantle zone of lymph nodes. We speculate that a possible mechanistic hypothesis for the generation of MCL is one in which receptor editing and germinal centre exclusion could be involved in the molecular development and in the display of clinical characteristics of this rare, aggressive and scarcely understood lymphoma. The hypothesis is supported by a preferential autoimmune related IGVH gene utilization in MCL, where VH3-21, VH4-34 and VH5-51 genes are predominant, and by the fact that MCL expresses immunoglobulin light chain (IgL) lambda more frequently than other non-Hodgkin's lymphomas and that IgL lambda-producing B cells usually delete one or both their IgL kappa genes.

Hypermutation in mantle cell lymphoma does not indicate a clinical or biological subentity

Mantle cell lymphoma is a prime example of a well-defined entity based on morphology, phenotype, genetics and also clinical features. Although most patients have an adverse clinical course, some have a better survival than others. The most consistently reported adverse prognostic parameter is a high mitotic rate. Recently, it has been shown that hypermutation in the immunoglobulin heavy-chain gene occurs in a subset of mantle cell lymphomas. It is, however, unclear whether the mutational status is stable over time within a given case, whether hypermutation might be influenced by therapy and how it is related to other relevant biological features of mantle cell lymphoma. In this study, we analyzed 23 typical mantle cell lymphoma cases with respect to mutational status and compared the results with clinicopathological and genetic data to determine whether the presence of mutation indicates a subentity with clinical or pathological relevance. We found somatic hypermutation in 26% of our cases and, interestingly, one case showed ongoing somatic hypermutation. In tumor cells of both mutated and unmutated cases, we found a preferential usage of V(H)3-21 (23%) and V(H)4-34 (19%). No significant correlations were found between mutation status and the other morphological and genetic features analyzed. In conclusion, our results provide additional evidence that mutation status in mantle cell lymphoma is better interpreted as a feature within the spectrum of disease that seems to have little clinical or pathological relevance.

A unique case of mantle cell lymphoma with an aberrant CD5-/CD10+ immunophenotype and typical morphology

Mantle cell lymphoma (MCL) is a non-Hodgkin lymphoma with a poor prognosis that may be confused with less aggressive diseases, such as small lymphocytic lymphoma and follicular lymphoma. In many cases immunophenotyping, particularly analysis of reactivity for CD5 and CD10, is an important adjunct to morphology that usually distinguishes MCL from follicular lymphoma; the former is CD5(+)/CD10(-), whereas follicular lymphoma is the reverse. We report a case of MCL, initially diagnosed as follicular lymphoma, that at presentation expressed neither CD5 nor CD10. At relapse, it was still CD5(-), but CD10 was now detected. Studies for a t(11;14) translocation and CYCLIN D1 protein expression, however, permitted a revised diagnosis of MCL. An MCL with this immunophenotype and classical morphology has not been previously reported.

Advances in the understanding of mantle cell lymphoma

Mantle cell lymphoma (MCL) is a well-defined lymphoid neoplasm characterized by a proliferation of mature B lymphocytes expressing CD5 that may show a spectrum of morphological and phenotypic features broader than initially described. Although some patients may follow an indolent clinical evolution, in most of them the tumour has an aggressive behaviour with poor response to conventional chemotherapy. The genetic hallmark is the t(11;14)(q13;q32) translocation leading to the overexpression of cyclin D1, which is considered the initial oncogenic event. In addition to this translocation, MCL may carry a high number of secondary chromosomal and molecular alterations that target regulatory elements of the cell cycle machinery and senescence (BMI1/INK4/ARF/CDK4/RB1), DNA damage response pathways (ATM/CHK2/p53), and cell survival signals. The knowledge of these mechanisms and their influence on the behaviour of the tumour are facilitating the development of prognostic models with a more precise prediction of the clinical evolution of the patients. This information coupled with the availability of a new generation of innovative drugs targeting basic molecular process of the tumour cells, should facilitate the design of new therapeutic protocols able to overcome the resistance of this aggressive lymphoma to conventional treatments and improve the life expectancy of the patients.

Detailed assessment of copy number alterations revealing homozygous deletions in 1p and 13q in mantle cell lymphoma

Mantle cell lymphoma (MCL) is characterized by over-expression of cyclin Dl as a result of the characteristic t(11;14)(q13;q32). However, this translocation alone has proven not to be sufficient for lymphomagenesis, suggesting the involvement of additional alterations. We have characterized 35 cases of MCL by array comparative genomic hybridization with an average resolution of 0.97 Mb distributed over the complete human genome. The most common alterations were losses in 1p13.2-p31.1, 6q16.2-q27, 8p21.3, 9p13.2-p24.3, 9q13-q31.3, 11q14.3-q23.3, 13q14.13-q21.31, 13q33.1-q34, and 22q11.23-q13.33 and gains involving 3q21.2-q29, 7p12.1-p22.3, 8q24.13-q24.23, and 18q21.33-q22.3. Four homozygous deletions were identified in totally three patients; two overlapping at 1p32.3, and two adjacent at 13q32.3. The homozygous deletions at 1p32.3 cover the CDKN2C locus (coding for p18), while the region at 13q32.3 does not encompass any known tumor suppressor genes. A gain in 3q was significantly associated with shorter survival (P=0.047).

Molecular genetic analysis of haematological malignancies II: mature lymphoid neoplasms

Molecular genetic techniques have become an integral part of the diagnostic assessment for many lymphomas and other chronic lymphoid neoplasms. The demonstration of a clonal immunoglobulin or T cell receptor gene rearrangement offers a useful diagnostic tool in cases where the diagnosis is equivocal. Molecular genetic detection of other genomic rearrangements may not only assist with the diagnosis but can also provide important prognostic information. Many of these rearrangements can act as molecular markers for the detection of low levels of residual disease. In this review, we discuss the applications of molecular genetic analysis to the chronic lymphoid malignancies. The review concentrates on those disorders for which molecular genetic analysis can offer diagnostic and/or prognostic information.

Telomere length and correlation with histopathogenesis in B-cell leukemias/lymphomas

Telomere length was recently reported to correlate with cellular origin of B-cell malignancies in relation to the germinal center (GC). In this report, we measured telomere length by quantitative-PCR in 223 B-cell lymphomas/leukemias and correlated results with immunoglobulin (Ig) mutation status and immunostainings for GC/non-GC subtypes of diffuse large B-cell lymphoma (DLBCL). Shortest telomeres were found in Ig-unmutated chronic lymphocytic leukemia (CLL) [median telomere to single copy gene value (T/S) 0.33], differing significantly to Ig-mutated CLL (0.63). Contrary to this, mantle cell lymphomas (MCLs) exhibited similar telomere lengths regardless of Ig mutation status (0.47). Telomere length differed significantly between GC-like (0.73) and non-GC-like DLBCLs (0.43), and follicular lymphomas (FLs) had shorter telomeres (0.53) than GC-DLBCL. Hairy cell leukemias, which display Ig gene intraclonal heterogeneity, had longer telomeres (0.62) than FLs and non-GC-DLBCL, but shorter than GC-DLBCL. We conclude that although DLBCL and CLL subsets can be clearly distinguished, telomere length reflects many parameters and may not simply correlate with GC-related origin.

Genomic imbalances during transformation from follicular lymphoma to diffuse large B-cell lymphoma

Follicular lymphoma is commonly transformed to a more aggressive diffuse large B-cell lymphoma (DLBCL). In order to provide molecular characterization of this histological and clinical transformation, comparative genomic hybridization was applied to 23 follicular lymphoma and 35 transformed DLBCL tumors from a total of 30 patients. The results were also compared with our published findings in de novo DLBCL. Copy number changes were detected in 70% of follicular lymphoma and in 97% of transformed DLBCL. In follicular lymphoma, the most common alterations were +18q21 (33%), +Xq25-26 (28%), +1q31-32 (23%), and -17p (23%), whereas transformed DLBCL most frequently exhibited +Xq25-26 (36%), +12q15 (29%), +7pter-q22 (25%), +8q21 (21%), and -6q16-21(25%). Transformed DLBCL showed significantly more alterations as compared to follicular lymphoma (P=0.0001), and the alterations -6q16-21 and +7pter-q22 were only found in transformed DLBCL but not in follicular lymphoma (P=0.02). Alterations involving +13q22 were significantly less frequent, whereas -4q13-21 was more common in transformed as compared to de novo DLBCL (P=0.01 and P=0.02, respectively). Clinical progression from follicular lymphoma to transformed DLBCL is on the genetic level associated with acquisition of increasing number of genomic copy number changes, with non-random involvement of specific target regions. The findings support diverse genetic background between transformed and de novo DLBCL.

Sequence analysis proves clonal identity in five patients with typical and blastoid mantle cell lymphoma

Mantle cell lymphoma (MCL) is typically composed of small irregular lymphoid cells. Blastoid variants, composed of lymphoblast-like (classic type) or large (pleomorphic type) cells, arise de novo or in patients with typical MCL. Although it has been assumed that blastoid variant represents histologic transformation of typical MCL, the clonal relationship between the two tumors has rarely been assessed at the molecular level. We identified five patients with typical MCL who subsequently developed the blastoid variant. There were two men and three women with a median age of 65 years (range, 34-70) at diagnosis of typical MCL involving lymph nodes. The median interval between typical and blastoid MCL was 36 months (range, 11-103). Subsequent blastoid variant MCL involved soft tissue (two), lymph node (one), ileum (one), or rectum (one). All typical and blastoid neoplasms were positive for CD20, cyclin D1, and monotypic surface immunoglobulin light chain, and all typical cases were positive for CD5. Two blastoid neoplasms lost CD5 expression, one of which aberrantly expressed CD10. Immunostaining for Ki-67 showed a median proliferative fraction of 20% in typical and 70% in blastoid neoplasms. Sequence analysis of the VDJ regions of the rearranged IgH allele proved clonal identity in each set of paired samples in all five patients. These results support the concept that blastoid MCL arising in patients with typical MCL represents histologic transformation of the original neoplastic clone.

A novel human B cell subpopulation representing the initial germinal center population to express AID

We have identified a novel mature human B-cell subpopulation in the human tonsil that has characteristics of both naive B cells and germinal center B cells including the expression of activation-induced cytidine deaminase (AID), which is essential for the process of immunoglobulin somatic hypermutation and class-switch recombination. These cells are clearly somatically hypermutated, albeit modestly. Their phenotype (IgD(+)CD38(-)CD23(-)FSC(hi)CD71(+)) is unique and suggests they may be intermediate between both naive and germinal center cells. Morphologically they are also distinct from other B-cell subpopulations. The evidence presented suggests these cells may be the founder cells of the germinal center reaction (a pro-GC cell) and may be the normal counterpart of the mantle cell lymphoma cell.

Mantle cell lymphomas acquire increased expression of CCL4, CCL5 and 4-1BB-L implicated in cell survival

We have analyzed mantle cell lymphomas (MCLs), using high-density DNA microarrays, and confirmed the expression of differentially regulated antigens, using flow cytometry and immunohistochemistry. The results show that MCLs acquire expression of molecules that normally are involved in interaction with other immune cells and, thus, might affect the ability of the tumor to survive. The MCL signature is represented by the overexpression of the chemokine CCL4 (MIP-1beta), implicated in the recruitment of regulatory T cells, as well as CCL5 and 4-1BB-L. The latter molecules are normally involved in chemotaxis of T cells and B cell activation, respectively. Signaling through 4-1BB-L allows B cells to proliferate and the expression of its ligand, by the intra-tumoral mesh of follicular dendritic cells (FDC), could thus serve as a paracrine loop facilitating growth and survival of MCL cells.

Prognostic usage of V(H) gene mutation status and its surrogate markers and the role of antigen selection in chronic lymphocytic leukemia

B-cell chronic lymphocytic leukemia (CLL) is a clinically heterogeneous disease with many patients surviving for decades with minimal or no treatment, whereas others succumb rapidly to their disease despite therapy. In recent years, new molecular prognostic factors have emerged in CLL that have significantly improved the subgrouping of the disease. One of the most important molecular predictors, the immunoglobulin V(H) gene mutation status, divides CLL into two prognostic groups, depending on the presence or absence of somatic hypermutation, where unmutated V(H) genes are associated with considerably worse prognosis than mutated V(H) genes. An exception to this appears to be CLL patients utilizing the V(H)3-21 gene as they have poor outcome irrespective of mutation status. Surrogate markers for the VH gene mutation status have been suggested, such as CD38 and ZAP-70 expression. However, the CD38 level was later shown to display poor correlation to the mutation status, although it may still serve as an independent prognostic factor. More promising is the expression levels of ZAP-70, which appears to be both a strong surrogate marker for V(H) gene mutation status, although discrepancies have been reported, as well as an independent prognostic marker. Immunoglobulin gene analysis has also indicated the possibility of antigen selection in CLL considering the significant bias in V(H) gene usage. Intriguingly, the V(H)3-21+ group and several other CLL subsets using certain V(H) genes was recently reported to display strikingly restricted immunoglobulin gene features, in both their heavy and light chain gene rearrangements, thus further high-lighting the possible role of antigen involvement in CLL development.