High frequency of p53 dysfunction and low level of VH mutation in chronic lymphocytic leukemia patients using the VH3-21 gene segment

Association between immunoglobulin heavy-chain variable region mutational status and isolated favorable baseline genomic aberrations in chronic lymphocytic leukemia

Immunoglobulin heavy-chain variable region (IGHV) mutational status and karyotype abnormalities are important prognostic factors in chronic lymphocytic leukemia (CLL). The goal was to assess the impact of IGHV in CLL patients with isolated favorable genetic aberrations (del13q, trisomy 12, or negative fluorescence in situ hybridization [FISH]). We studied 273 CLL patients with both IGHV mutational status and cytogenetic information: 145 with isolated del13q 49 with sole trisomy 12 and 79 with negative FISH. After a median follow-up of 7.8 years, patients with del13q-unmutated IGHV had a shorter time to first treatment (TFT) (2.98 vs. 17.44 years; p < .001) and shorter overall survival (10.45 years vs. not reached; p = .0026). Patients with negative FISH-unmutated IGHV had shorter TFT (p = .02) (3.10 vs. 9.75 years, p = .053). IGHV status did not influence clinical outcomes in trisomy 12 CLL. In conclusion, IGHV mutational status shows prognostic impact in CLL patients with good prognosis genomic features.

Immunogenetic studies of chronic lymphocytic leukemia: revelations and speculations about ontogeny and clinical evolution

Over the last decade, immunogenetic analysis of B-cell receptor immunoglobulins (BcR IG) has proved instrumental in dissecting chronic lymphocytic leukemia (CLL) pathogenesis. Initially, it was the finding that the level of somatic hypermutations in rearranged IG heavy-chain genes could define two CLL subtypes associated with a different clinical course that drew attention. As the years ensued, this not only continued to hold strong, but also revealed an unprecedented BcR restriction (aptly coined as "stereotypy"), thus cementing the idea that antigenic elements select the leukemic clones. With all this in mind, in the present review, we focus on the CLL BcR IG, a molecule that clearly lies at the heart of disease pathogenesis, and attempt to distil from past and emerging biologic knowledge the most relevant aspects in the context of the immunogenetics of CLL, while at the same time provoking questions that remain unanswered. We juxtapose CLL with mutated BcR IGs against CLL with unmutated BcR IGs due to their striking clinicobiologic differences; however, when considering ontogeny, common derivation of the two mutational subtypes cannot be excluded. The issue of stereotypy is intertwined throughout and we also raise the subject of isotype-switched CLL, which, despite its rarity, contributes intriguing ontogenetic hints.

The emerging role of Twist proteins in hematopoietic cells and hematological malignancies

Twist1 and Twist2 (Twist1–2) are two transcription factors, members of the basic helix-loop-helix family, that have been well established as master transcriptional regulators of embryogenesis and developmental programs of mesenchymal cell lineages. Their role in oncogenesis in epithelium-derived cancer and in epithelial-to-mesenchymal transition has also been thoroughly characterized. Recently, emerging evidence also suggests a key role for Twist1–2 in the function and development of hematopoietic cells, as well as in survival and development of numerous hematological malignancies. In this review, we summarize the latest data that depict the role of Twist1–2 in monocytes, T cells and B lymphocyte activation, and in associated hematological malignancies.

Present status and perspectives in functional analysis of p53 in chronic lymphocytic leukemia

Aberrations of TP53 (mutations and/or deletions) are associated with a dismal prognosis in chronic lymphocytic leukemia (CLL). Complete loss of ATM is another mechanism of failed DNA damage response and also associated with poorer prognosis in CLL. However, p53 dysfunction may arise through alternative mechanisms unrelated to structural aberrations (deletion and/or mutation) of TP53 or ATM, and thus be undetectable by traditional DNA-directed approaches (fluorescence in situ hybridization [FISH], sequencing, karyotyping). In order to address the latter changes, and also to better understand the consequences of TP53/ATM aberrations, p53 functional assays have recently been developed. The purpose of dynamic assessment of p53 response in CLL is to carry out a comprehensive analysis of all mechanisms causing p53-deficient phenotype, including those unrelated to genomic aberrations of TP53 and ATM. The present review focuses on the current knowledge of p53 function assays in CLL, including important features such as technical issues, correlation with structural aberrations and clinical value.

Clinical and Laboratory Prognostic Indicators in Chronic Lymphocytic Leukemia

Background

The clinical course of patients with chronic lymphocytic leukemia (CLL) is heterogeneous, with some patients experiencing rapid disease progression and others living for decades without requiring treatment. The Rai and Binet clinical staging systems are used to define disease extent and predict survival. The pathology laboratory also provides important prognostic information.

Methods

A review of the literature was performed on the subject of staging in CLL from clinical and pathologic standpoints. This article also reviews currently available diagnostic approaches related to disease prognosis and to timing of treatment and follow-up in patients with CLL.

Results

Novel biological and cytogenetic features such as immunoglobulin heavy-chain variable gene segment [IgVH], genomic aberrations including del(17p13), del(11q23), del(13q14), and trisomy 12, serum markers (thymidine kinase and beta-2 microglobulin), and cellular markers (CD38 and ZAP70) have become increasingly important in predicting prognosis at the time of diagnosis.

Conclusions

Current prognostic factors directly or indirectly influence the management of patients with CLL and help to predict treatment-free and overall survival.

B-cell receptor, clinical course and prognosis in chronic lymphocytic leukaemia: the growing saga of the IGHV3 subgroup gene usage

The immunoglobulin heavy chain variable gene (IGHV) mutational status has been recognized as an important predictor of prognosis in chronic lymphocytic leukaemia (CLL) since 1999. More recently, other features of the B-cell receptor, such as stereotypy, have been identified as capable of refining the prognostic potential of IGHV status in the clinical assessment of CLL patients. In this context, different genes belonging to the IGHV3 subgroup, the most frequently used subgroup in CLL, have been shown to denote disease subsets that either display a bad prognosis (i.e. IGHV3-21, IGHV3-23) or are associated with particularly good clinical outcomes, including a highly stable/indolent clinical course, even prone to spontaneous regression (i.e. IGHV3-72, IGHV3-30). The present review focuses on the molecular and biological features of CLL-expressing specific genes belonging to the IGHV3 subgroup that are known to mark disease subsets with completely different clinical courses, and may be possibly related to CLL pathogenesis via antigen and/or superantigen involvement.

Antigens in chronic lymphocytic leukemia--implications for cell origin and leukemogenesis

Several types of B cell tumors, particularly MALT lymphomas, are known to have an antigen-driven component in tumor development. Over the past two decades substantial data have accumulated regarding the restricted immunoglobulin (IG) gene repertoire in chronic lymphocytic leukemia (CLL) and its potential implications for antigenic drive in the disease development and progression. Herein we discuss how evidence first illustrated a link between certain B cell receptor (BCR) specificities and disease outcome and the subsequent large-scale IG analyses which revealed the extent of "stereotyped" BCRs in CLL. More recent studies on CLL antibody reactivity have gradually provided clues as to which antigens may be involved in the tumor development. Significantly, CLL monoclonal antibodies have been shown to resemble natural antibodies recognizing molecular motifs both on apoptotic cells (e.g. modified cytoskeletal proteins and oxidation-specific epitopes), as well as exogenous bacteria, indicating that CLL clones possibly arise from B cells which have dual function as scavengers of apoptotic debris, while also having the ability to bind conserved bacterial cell structures. Such revelations have led us to re-evaluate both the phenotypic and functional characteristics of the tumor B cells and the pathway by which CLL arises and develops.

Increased trisomy 12 frequency and a biased IgVH 3-21 gene usage characterize small lymphocytic lymphoma

Small lymphocytic lymphoma (SLL) and chronic lymphocytic leukemia (CLL) are considered as similar entity by the WHO classification. We assessed the distribution of the four prognostic cytogenetic markers (deletion 11q23, 13q14, 17p13 and trisomy 12) and VH mutational status in 32 SLL and 119 CLL. Trisomy 12 was most frequent (36% vs 13%, p=0.014) and 13q14 deletion was less frequent (9% vs 44%, p=0.001) in SLL in comparison with CLL. An over representation of VH3-21 gene usage was found in SLL (17% vs 1%, p=0.011). In conclusion, SLL show specific genetic markers that distinguish them from classical CLL.

A novel type of p53 pathway dysfunction in chronic lymphocytic leukemia resulting from two interacting single nucleotide polymorphisms within the p21 gene

The ATM-p53 pathway plays an important role in the biology of chronic lymphocytic leukemia (CLL). Its functional integrity can be probed by exposing CLL cells to ionizing radiation (IR) and measuring levels of p53 protein and one of its transcriptional targets, the cyclin-dependent kinase inhibitor p21. We have previously identified two abnormal p53/p21 response patterns associated with inactivating mutations of TP53 and ATM, respectively. Here, we describe a third abnormal response pattern characterized by failure of p21 protein accumulation despite a normal p53 protein response. This so-called "type C" response was detected in 10.6% of unselected patients and was associated with resistance of CLL cells to p53-dependent killing by IR, with the clinically more aggressive variant of CLL characterized by unmutated immunoglobulin heavy-chain genes and with a single nucleotide polymorphism at codon 31 of the p21 gene in which Ser is replaced by Arg. CLL samples with this allelic variant displayed impaired IR-induced up-regulation of total p21 mRNA and did not express the Arg-encoding transcript, except in those cases harboring an additional single nucleotide polymorphism (T instead of C) in the 3'-untranslated region of the same p21 allele. Our data provide new insight into the importance of p21 in CLL biology.

The role of prognostic factors in assessing ‘high-risk’ subgroups of patients with chronic lymphocytic leukemia

The management of chronic lymphocytic leukemia (CLL) has historically relied on 'watchful waiting' and palliative approaches to therapy. However, the course of disease is highly variable and a substantial proportion of patients with early-stage CLL develop rapidly progressive disease requiring therapy. In recent decades, numerous clinical and biological prognostic markers that are predictive of decreased survival outcomes, disease progression and/or resistance to therapy, and that may play a role in defining the subgroups of patients with 'high-risk' CLL have been identified. At the same time, highly effective treatment modalities have become available with the advent of chemoimmunotherapy combinations and allogeneic stem cell transplantation. Thus, we are approaching an era when patients with CLL may potentially benefit from individualized risk assessments based on prognostic markers and when specific therapies may be offered to the subgroup of patients with high-risk disease. This review provides a brief overview of newer biological prognostic markers, discusses the challenges associated with identifying the subgroup of patients with high-risk CLL and further aims to provide recommendations on how prognostic markers may be used to assess high-risk subgroups in different clinical situations in CLL.

Comprehensive characterization of IGHV3-21-expressing B-cell chronic lymphocytic leukemia: an Italian multicenter study

IGHV3-21-using chronic lymphocytic leukemia (CLL) is a distinct entity with restricted immunoglobulin gene features and poor prognosis and is more frequently encountered in Northern than Southern Europe. To further investigate this subset and its geographic distribution in the context of a country (Italy) with both continental and Mediterranean areas, 37 IGHV3-21 CLLs were collected out of 1076 cases enrolled by different institutions from Northern or Central Southern Italy. Of the 37 cases, 18 were identified as homologous (hom)HCDR3-IGHV3-21 CLLs and were found almost exclusively (16 of 18) in Northern Italy; in contrast, 19 nonhomHCDR3-IGHV3-21 cases were evenly distributed throughout Italy. Clinically, poor survivals were documented for IGHV3-21 CLLs as well as for subgroups of mutated and homHCDR3-IGHV3-21 CLLs. Negative prognosticators CD38, ZAP-70, CD49d, and CD79b were expressed at higher levels in homHCDR3 than nonhomHCDR3-IGHV3-21 cases. Differential gene expression profiling (GEP) of 13 IGHV3-21 versus 52 non-IGHV3-21 CLLs identified, among 122 best-correlated genes, TGFB2 and VIPR1 as down- and up-regulated in IGHV3-21 CLL cases, respectively. Moreover, GEP of 7 homHCDR3 versus 6 nonhomHCDR3-IGHV3-21 CLLs yielded 20 differentially expressed genes, with WNT-16 being that expressed at the highest levels in homHCDR3-IGHV3-21 CLLs. Altogether, IGHV3-21 CLLs, including those with homHCDR3, had a peculiar global phenotype in part explaining their worse clinical outcome.

Over 20% of patients with chronic lymphocytic leukemia carry stereotyped receptors: Pathogenetic implications and clinical correlations

The chronic lymphocytic leukemia (CLL) immunoglobulin repertoire is biased and characterized by the existence of subsets of cases with closely homologous ("stereotyped") complementarity-determining region 3 (CDR3) sequences. In the present series, 201 (21.9%) of 916 patients with CLL expressed IGHV genes that belonged to 1 of 48 different subsets of sequences with stereotyped heavy chain (H) CDR3. Twenty-six subsets comprised 3 or more sequences and were considered "confirmed." The remaining subsets comprised pairs of sequences and were considered "potential"; public database CLL sequences were found to be members of 9 of 22 "potential" subsets, thereby allowing us to consider them also "confirmed." The chance of belonging to a subset exceeded 35% for unmutated or selected IGHV genes (eg, IGHV1-69/3-21/4-39). Comparison to non-CLL public database sequences showed that HCDR3 restriction is "CLL-related." CLL cases with selected stereotyped immunoglobulins (IGs) were also found to share unique biologic and clinical features. In particular, cases expressing stereotyped IGHV4-39/IGKV1-39-1D-39 and IGHV4-34/IGKV2-30 were always IgG-switched. In addition, IGHV4-34/IGKV2-30 patients were younger and followed a strikingly indolent disease, contrasting other patients (eg, those expressing IGHV3-21/IGLV3-21) who experienced an aggressive disease, regardless of IGHV mutations. These findings suggest that a particular antigen-binding site can be critical in determining the clinical features and outcome for at least some CLL patients.

IGHV gene insertions and deletions in chronic lymphocytic leukemia: "CLL-biased" deletions in a subset of cases with stereotyped receptors

Nucleotide insertions/duplications or deletions in immunoglobulin heavy chain genes have been found in 24/760 patients (3.15%) with chronic lymphocytic leukemia (CLL). In 21/24 cases, the inserted/duplicated or lost nucleotides occurred in multiples of 3; therefore, the original reading frame was maintained and a potentially intact receptor was coded. The pattern and location of insertions/duplications or deletions in CLL and their restriction to mutated IGHV rearranged genes strongly suggests that they resulted from somatic hypermutation. Their incidence in CLL is consistent with previous reports in normal, auto-reactive and neoplastic human B cells, thus seemingly indicating that these modifications generally arise without any particular disease-specific associations. A striking exception to this rule was identified in CLL IGHV3-21-expressing cases: one amino acid was deleted from the CDR2 region in 16/63 (25.4%) mutated CLL IGHV3-21 sequences (including public database-derived IGHV3-21 CLL cases + the present series) vs. only 2/257 (0.78%) public database-derived mutated non-CLL IGHV3-21 sequences; 15/16 CLL IGHV3-21 sequences carrying this deletion belonged to a subset with unique, shared HCDR3 and light chain CDR3 motifs. This finding further supports the idea of selective antigenic pressures playing a pathogenetic role in some CLL cases.

Serum TK levels in CLL identify Binet stage A patients within biologically defined prognostic subgroups most likely to undergo disease progression

OBJECTIVE

Serum thymidine kinase (TK) levels have been shown to be correlated with survival in many malignancies, including chronic lymphocytic leukaemia (CLL). This study was designed to investigate associations between TK levels and other prognostic markers, in newly and previously diagnosed Binet stage A patients. Furthermore, the use of serum TK measurement to identify subcategories of disease within those defined by IgV(H) mutational status, gene usage and chromosomal aberrations was investigated.

METHODS

Ninety-one CLL patients were enrolled. Serum TK levels were measured using a radioenzyme assay. IgV(H) mutational status and V(H) gene usage were determined using BIOMED-2 primers and protocol. Recurring chromosomal abnormalities were detected by interphase fluorescent in situ hybridisation (FISH). Flow cytometry and reverse transcriptase polymerase chain reaction (RT-PCR) determined CD38 and Zap-70 expression, respectively.

RESULTS

Significantly higher serum TK levels were found in IgV(H) unmutated, compared with IgV(H) mutated, patients (P < 0.001). Elevated TK levels were also found in patients with CD38 and Zap-70 positivity (P = 0.004, P < 0.001, respectively), short lymphocyte doubling time (LDT) (P = 0.044) and poor or intermediate prognosis chromosomal aberrations (P < 0.001).

CONCLUSION

A TK level of >8.5 U/L best identified patients with progressive disease. Elevated TK levels could identify patients categorised, at diagnosis, into good prognosis subgroups by the various biological markers (mutated IgV(H), good prognosis chromosomal aberrations, Zap-70(-) and CD38(-)) who subsequently showed disease progression. Additionally, patients with V(H)3-21 gene usage showed high TK levels, irrespective of mutational status, and serum TK measurement retained predictive power as disease progressed in all subcategories studied.

What is the current evidence for antigen involvement in the development of chronic lymphocytic leukemia?

For many years it has been evident that B-cell chronic lymphocytic leukemia (CLL) displays preferential usage of individual immunoglobulin (Ig) variable heavy chain (V(H)) genes. The V(H)1-69 gene was the first to be reported overrepresented in a large number of CLL patients, where the V(H)1-69(+) CLL rearrangements showed characteristic molecular features, such as unmutated V(H) genes, usage of specific diversity/joining gene segments, and a longer than average complementarity determining region (CDR) 3 with certain common amino acid motifs. Also, biased usage of the V(H)3-07 and V(H)4-34 genes with specific rearrangement characteristics was reported in CLL. These findings led to the speculation that antigens could be involved during CLL development by triggering proliferation of B-cells with specific B-cell receptors (BCRs) leading to an increased risk of transforming events. Recently, we characterized a subset of CLL utilizing the V(H)3-21 gene that also displayed peculiar Ig features, e.g. very short and homologous CDR3s, predominant lambda expression and preferential V(lambda)2-14 gene usage. This V(H)3-21(+) subgroup also had poor prognosis despite the fact that two-thirds of cases carried mutated V(H) genes. Moreover, we and others have thereafter described further CLL subsets with very similar heavy and light chain gene rearrangement features. These latter findings of subsets expressing restricted BCRs have emphasized the hypothesis that antigens could play a role during the pathogenesis of CLL. Interestingly, recombinant antibodies produced from these restricted subsets showed similar cytoplasmatic reactivity within each group, thus suggesting recognition of a limited number of autoantigens. Further characterization of antigens is now necessary in order to understand their nature and exact role in CLL development.

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.

Clinical and laboratory parameters that define clinically relevant B-CLL subgroups

B cell-type chronic lymphocytic leukemia (B-CLL) is a heterogeneous disease. This is reflected by the very wide-ranging clinical courses that B-CLL patients experience and by the marked variation in laboratory findings between patients. In this chapter, we will review the various clinical and laboratory parameters that divide B-CLL patients into "subgroups," and correlate the parameters that define them. When feasible, we will also link clinical features to the cellular and genetic characteristics recently defined for these leukemic cells. The discussion is limited to parameters that define phenotypes or subgroups that may relate to disease activity and clinical outcome.

Select high-risk genetic features predict earlier progression following chemoimmunotherapy with fludarabine and rituximab in chronic lymphocytic leukemia: justification for risk-adapted therapy

PURPOSE

Several new prognostic factors predicting rapid disease progression in chronic lymphocytic leukemia (CLL) have been identified, including unmutated Ig V(H) mutational status, del(11)(q23), del(17)(p13.1), and p53 mutations. To date, the impact of these same prognostic factors have not been examined relative to treatment outcome with chemoimmunotherapy.

METHODS

We examined the impact of these new prognostic factors on predicting treatment outcome in symptomatic, untreated CLL patients who received chemoimmunotherapy with fludarabine and rituximab as part of a completed, randomized phase II study, Cancer and Leukemia Group B (CALGB) 9712.

RESULTS

Eighty-eight patients treated as part of CALGB 9712 had detailed prognostic factor assessment performed. Using Ig V(H) mutational status to classify risk, there was no association between complete response rate with either unmutated Ig V(H) mutational status or high-risk interphase cytogenetics. However, the median progression-free survival (PFS; P = .048) and overall survival (OS; P = .01) were shorter among the Ig V(H) unmutated patients as compared with the Ig V(H) mutated patients. Using the hierarchical classification of Döhner, PFS (P = .005) and OS (P = .004) were significantly longer as the classification moved from high risk [del (11)(q22.3) or del (17)(p13.1)] to low risk.

CONCLUSION

These data demonstrate that high-risk CLL patients characterized by Ig V(H) unmutated (> or = 98%) or high-risk interphase cytogenetics, including either del(17p) or del(11q), appear to have a shorter PFS and OS with chemoimmunotherapy. Larger prospective studies will be required to determine the independent influence of Ig V(H) mutational status and interphase cytogenetics on treatment outcome.

Decitabine in chronic leukemias

5-Aza-2'-deoxycitidine (decitabine, Dacogen, Bloomington, MN) is a cytosine analogue that promotes hypomethylation of DNA and has documented efficacy in myeloid malignancies. Indeed, promising clinical results have been observed in acute myeloid leukemia (AML) and the myelodysplastic syndromes (MDS). Aberrant methylation has also been found in chronic leukemias, providing a rationale for investigating the use of decitabine in these diseases. There is clear evidence of molecular (hypomethylation) as well as hematologic and cytogenetic responses to decitabine in chronic myelogenous leukemia of all phases, including in patients resistant to imatinib mesylate. Clinical trials of decitabine in chronic lymphocytic leukemia are ongoing. There are many unanswered questions regarding optimizing this treatment for chronic leukemias, but successful proof-of-concept studies for hypomethylating agents move us closer to approaches that may have a significant impact on patient outcomes.

Distinctive gene expression pattern in VH3-21 utilizing B-cell chronic lymphocytic leukemia

The usage of the immunoglobulin (Ig) V(H)3-21 gene is associated with poor prognosis in B-cell chronic lymphocytic leukemia (B-CLL) despite V(H) gene mutation status. Many V(H)3-21+ patients also display restricted heavy- and light-chain Ig gene rearrangements, implying a role of antigen selection in disease development. To explore the specific phenotypic/genotypic features among V(H)3-21+ B-CLLs, we compared gene expression patterns in 15 V(H)3-21+ and 24 non-V(H)3-21 patients (11 with unmutated and 13 with mutated V(H) genes) using Affymetrix microarray analysis (approximately 12,500 genes). A distinct expression profile was identified for V(H)3-21+ patients in contrast to the Ig-unmutated and -mutated groups. By applying different algorithms, the data enabled an efficient class discrimination of the V(H)3-21+ subset based on 27 or 57 genes. A set of genes was sorted out which, using different analytical methods, consistently gave a distinction between V(H)3-21+ and non-V(H)3-21 samples. Several of these genes are involved in regulation of DNA replication/cell-cycle control, transcription and protein kinase activity, which may render the V(H)3-21+ cells with a higher proliferative drive. However, no clear evidence of increased B-cell receptor signaling was found in the V(H)3-21+ group. Altogether, our identification of a specific V(H)3-21 profile may provide insights into the pathogenesis of the V(H)3-21+ subgroup.

TWIST2 demonstrates differential methylation in immunoglobulin variable heavy chain mutated and unmutated chronic lymphocytic leukemia

PURPOSE

Chronic lymphocytic leukemia (CLL) is a clinically heterogeneous disease for which natural history can be predicted based on the presence or absence of immunoglobulin (Ig) variable heavy chain (V(H)) gene mutations. Herein we report selective epigenetic silencing of the transcription factor TWIST2 (DERMO1) in Ig V(H) mutated CLL and describe a semiquantitative assay to study promoter methylation of this gene in primary tumor cells.

MATERIALS AND METHODS

TWIST2 promoter methylation was identified by restriction landmark genome scanning. Southern blot (SB), bisulfite sequencing, and combined bisulfite restriction analysis (COBRA), and quantitative SB-COBRA was performed to study methylation of the TWIST2 promoter. Reverse transcription polymerase chain reaction assays were used to study TWIST2 expression in CLL cells.

RESULTS

Following identification and confirmation of TWIST2 methylation in CLL patients, we demonstrated that expression of this transcription factor is related to the degree of promoter methylation. Expression of TWIST2 in a CLL cell line in which the promoter is methylated was increased following decitabine treatment. We next studied 53 patients by COBRA and demonstrated that 72% of patient samples with mutated Ig V(H) show TWIST2 methylation, while only 16% of patient samples with unmutated Ig V(H) were methylated (P < .001). In a subset of patients, methylation of TWIST2 correlated with mRNA expression.

CONCLUSION

TWIST2 is differentially methylated in CLL cells relative to Ig V(H) mutational status and can be quantitatively monitored by SB-COBRA. Based on the known role of TWIST2 in silencing p53 function in other malignancies, future studies should focus on the role of TWIST2 in CLL and related lymphoproliferative diseases.

Analysis of VH gene sequences using two web-based immunogenetics resources gives different results, but the affinity maturation status of chronic lymphocytic leukaemia clones as assessed from either of the resulting data sets has no prognostic significance

Some cellular and molecular features of chronic lymphocytic leukaemia (CLL) cells that are associated with prognosis may reflect the context within which their progenitors encountered antigen. It follows that the nature of antigen drive in CLL could influence the clinical course and we were prompted to assess the impact, if any, of affinity maturation (an antigen-driven process) on prognosis. Statistical models for assessing affinity maturation status are typically applied to V(H) gene sequence data analysed using a web-based resource like IMGT or VBASE. Since these resources differ with respect to some key relevant features, we evaluated a cohort of CLL cases by applying statistical models to V(H) data derived from both IMGT and VBASE. Important differences between the resulting data sets became apparent. These resulted from database variance and because IMGT and VBASE define complementarity-determining and framework regions (CDRs, FRs) in different ways. Thus, the numbers of mutations identified and their distribution between CDRs/FRs varied between the data sets for the majority of clones. Consequently, two different but overlapping sets of cases with evidence of affinity maturation were defined. Notwithstanding their differences, no significant associations of affinity maturation status with CD38 expression, p53 functional status or survival were identifiable in either data set.

Histopathology of B-cell chronic lymphocytic leukemia

Histologic and immunohistologic findings of B-cell chronic lymphocytic leukemia/small lymphocytic leukemia are revised in the light of the more recent knowledge on the pathobiology of the disease. The guidelines for the optimal handling of the bioptic samples are provided. The relevance of the examination of trephines and surgical specimens is outlined with special reference to the identification of risk factors in individual patients.