Molecular profiling of chronic lymphocytic ... - Wiley Online Library

review

Molecular profiling of chronic lymphocytic leukaemia: genetics meets epigenetics to identify predisposing genes Christoph Plass,1 John C. Byrd,2 Aparna Raval,3 Stephan M. Tanner1 and Albert de la Chapelle1 1

Department of Molecular Virology, Immunology, and Medical Genetics, Human Cancer Genetics Program, the Comprehensive Cancer Center at the Ohio State University, 2Division of Hematology and Oncology, Department of Internal Medicine, the Comprehensive Cancer Center at The Ohio State University, Columbus, OH, and 3Department of Oncology, CCSR 2250, Stanford University, Stanford, CA, USA

Summary Molecular profiling may lead to a better understanding of a disease. This knowledge is especially important in malignancies, where multiple alterations are required during the progression from premalignant to malignant stages. Such information can be useful for the development of novel biomarkers that allow the prediction of a clinical course, response to treatment or early detection. Molecular data is also utilized to develop targeted therapies. Moreover, gene defects identified in profiling studies will help to understand the molecular pathways disrupted in the disease. This review provides an overview of molecular profiling approaches in chronic lymphocytic leukaemia (CLL). We will describe our current understanding of genetic alterations in CLL, the use of familial CLL for the identification of predisposing mutations, and the search for epigenetic alterations in CLL. Keywords: chronic lymphocytic leukaemia, epigenetics, genetics, death associated protein kinase 1.

Chronic lymphocytic leukaemia Chronic lymphocytic leukaemia (CLL) is one of the most common types of leukaemia diagnosed in adults that is characterized by a typical immunophenotype expressing B-cell markers CD19, CD20, CD23, and surface immunoglobulin (sIg) (dim) with co-expression of the pan T-cell maker CD5. Patients presenting with CLL are a median 72 years old, are often symptomatic, and lack clinical or laboratory features that can predict their disease to be aggressive over time. Once recognized as a single disease, recent biological studies of CLL have demonstrated that CLL can be dichotomized based upon the presence of immunoglobulin heavy chain variable gene

Correspondence: Dr C. Plass, Division of Toxicology and Cancer Risk Factors, German Cancer Research Center (DKFZ), Im Neuenheimer

(IGHV) mutational status (Damle et al, 1999; Hamblin et al, 1999). Patients with IGHV un-mutated status (>98% germline) have a short time to developing symptoms, requiring therapy and inferior survival when compared to those patients with IGHV mutated status (Damle et al, 1999; Hamblin et al, 1999; Oscier et al, 2002). The adverse outcome associated with IGHV mutational status is partly due to a higher predisposition to develop either clonal evolution of a high risk genomic abnormality, such as del(11q22Æ3) and del(17p13Æ1) or Richter’s transformation (Krober et al, 2006; Shanafelt et al, 2006). Other surrogate markers of IGHV mutational status, including ZAP-70 (Crespo et al, 2003; Wiestner et al, 2003; Rassenti et al, 2004; Orchard et al, 2005) and CD38 (Hamblin et al, 2002; Ghia et al, 2003) expression have been put forward and subsequently have been directly linked to the biology of CLL. The contribution of epigenetic silencing of genes by both aberrant methylation (Rush et al, 2004; Raval et al, 2005, 2006; Liu et al, 2006) or overexpression of select microRNA (Calin et al, 2002, 2005; Calin & Croce, 2006) has recently been reported to also be important in the pathogenesis of CLL. Indeed, detailed biological studies of CLL have led to a better understanding of how to predict prognosis for patients at diagnosis and is now translating into new therapies for this disease. Due to an absence of studies demonstrating any benefit to early treatment of asymptomatic early stage CLL (Dighiero et al, 1998; Richards et al, 1999), therapy is generally withheld until symptoms referable to the disease develop. For many years, treatment of CLL had utilized alkylator-based therapy. Multiple randomized trials have demonstrated fludarabine to be superior to alkylator-based regimens with respect to response and progression-free survival (PFS) (Johnson et al, 1996; Rai et al, 2000; Leporrier, 2004). Several phase III studies have followed these trials comparing the use of alkylator therapy (cyclophosphamide) together with fludarabine versus fludarabine alone (Eichhorst et al, 2006; Flinn et al, 2007). These studies have shown the combination to be superior to fludarabine-based therapy with respect to response and PFS (Eichhorst et al, 2006; Flinn et al, 2007). Phase II studies of adding rituximab to fludarabine (Byrd et al, 2005) or

Feld 280, 69120 Heidelberg, Germany. E-mail: [email protected] First published online 24 October 2007 ª 2007 The Authors doi:10.1111/j.1365-2141.2007.06875.x Journal Compilation ª 2007 Blackwell Publishing Ltd, British Journal of Haematology, 139, 744–752

Review fludarabine and cyclophosphamide (Keating et al, 2005) have demonstrated very promising preliminary data and phase III studies are ongoing to definitively determine the value of this treatment. The monoclonal antibody alemtuzumab has also recently been tested in a phase III study that compared it to chlorambucil, which confirmed the superior PFS. Unfortunately, none of these therapies appear to produce durable remissions in high-risk genomic CLL, such as those patients bearing del(11q22Æ3) or del(17p13Æ1). Newer approaches for these patients including non-myeloablative stem cell transplant are now being applied earlier in the treatment of CLL for patients with these high-risk genomic features (Brown et al, 2006; Dreger et al, 2007). Similarly, other new therapies including flavopiridol (Byrd et al, 2007) and lenalidomide (Chanan-Khan et al, 2006) have also been shown to be effective in this patient population and for treating patients who relapse after initial combination therapy. In order to develop novel therapies, it will be necessary to both have a better understanding of molecular defects and to pursue selective targets that are present only in the CLL cells. This includes the understanding of genetic as well as epigenetic defects involved in leukaemogenesis. This review will summarize our current understanding of the known molecular defects and outline possible strategies for future directions.

Genomics of CLL In CLL, the current paradigm identifies the clonal B-cell as having a low proliferation rate and a disrupted apoptotic mechanism caused by primary tumour features and interactions with co-dependent stromal elements (Bannerji & Byrd, 2000; Burger et al, 2000; Granziero et al, 2001). A main focus in CLL research involved the evaluation of genetic features related to somatic gene mutation or deletions that disrupt apoptosis and enhance tumour cell proliferation. The best characterized genes are TP53 (also known as p53) (el Rouby et al, 1993; Wattel et al, 1994; Dohner et al, 1995; Cordone et al, 1998; Byrd et al, 2003) and ATM (Dohner et al, 1997, 2000; Schaffner et al, 1999; Stankovic et al, 1999, 2002; Pettitt et al, 2001), for which mutations and/or deletions have been described that predict rapid disease progression, resistance to conventional therapies and poor survival. Balanced translocations, such as those seen in acute myeloid leukaemia, are rare in CLL. Sporadic reports have described examples including chromosomal band 14q32, such as t(14;18) and t(14;19). However, CLL is a disease in which frequent chromosomal deletions as well as numerical changes in chromosome number (most frequent trisomy 12) have been detected (Table I). These alterations have been investigated using fluorescence in situ hybridization (FISH). A comprehensive study showed that over 80% of CLL samples are characterized by the occurrence of the major chromosomal lesions including deletions of 6q21 (in 6% of cases), 11q22-23 (18%), 13q14 (55%) and 17p13 (7%); copy number gains including chromosomal regions 3q26 (3%), 8q24 (5%) and

Table I. Common genetic and epigenetic alterations in chronic lymphocytic leukaemia. Genetic alterations*

Epigenetic alterations*

Deletion 13q14 Deletion 11q22-23 Deletion of 17p13 Deletion 6q21 Gain 12q13 Gain 8q24 Gain 3q26

Promoter methylation ID4 Promoter methylation DAPK1 Promoter methylation SFRP1 Promoter methylation ZAP70 Promoter methylation TWIST2 Hypomethylation BCL2 Hypomethylation TCL1A

*References can be found in the text.

12q13 (16%) (Dohner et al, 2000). Deletion studies using higher resolution single nucleotide polymorphism (SNP) arrays have recently confirmed the FISH studies and identified additional chromosomal regions affected by chromosomal alterations (Pfeifer et al, 2007). Most important for clinical practice is the observation that many of the genetic alterations are useful independent predictors for disease progression and/ or survival (Dohner et al, 2000).

Familial cases of CLL It is well documented that the overall heritability of cancer is modest. Based on classical case–control studies in Utah (Goldgar et al, 1994) and Sweden (Goldin et al, 2004) the odds ratio (OR) or family risk ratio of first-degree relatives of probands with cancer was only 2Æ1, as calculated by Risch (2001). However, there are clear-cut differences among the different cancers: ORs range between values as high as 8 for thyroid and testis cancer to values as low as approximately 1Æ5 for bladder and pancreas cancer, for example, CLL had high to intermediate values (5Æ0 in Utah). In a more recent study of the entire Icelandic population, lymphoid leukaemia had the second highest OR of all cancers (Amundadottir et al, 2004). In a recent update from Sweden, a risk ratio of 7Æ52 was found in first-degree relatives of CLL patients (Goldin et al, 2004). In these case–control studies some of the most common cancers, such as colorectal and breast cancer had low to intermediate OR values (3 or less). Thus, even though subsets of these cancers are caused by highly penetrant dominant germline mutations (e.g. mismatch repair genes, BRCA genes), because they are rare, the overall effect on heritability is modest, and more common susceptibility genes, such as those recently identified by whole genome scans in breast and prostate cancer, may emerge to be more important. In searching for genes predisposing to multifactorially determined diseases, such as most cancers, the first breakthroughs have traditionally occurred after linkage analysis and positional cloning by taking advantage of relatively rare subsets of patients displaying regular Mendelian inheritance with high penetrance. For this purpose, well-characterized patients belonging to large multigeneration family pedigrees (with,

ª 2007 The Authors Journal Compilation ª 2007 Blackwell Publishing Ltd, British Journal of Haematology, 139, 744–752

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Review say, 8–10 affected individuals) are most informative. However, linkage analysis can successfully pinpoint a gene locus even when only small families (with say just two or three affected individuals) are available for study, because linkage results are additive. In CLL, large pedigrees are extremely rare (Jonsson et al, 2005). Pooling numerous families, two groups of researchers have used genome-wide linkage analysis in search of putative gene loci. In the study by Sellick et al (2005) comprising 115 pedigrees, a locus in chromosome 11p11 was pinpointed and considered to be statistically almost significant while peaks in four other chromosomal regions (5q22-23, 6p22, 10q25 and 14q32) showed lower significance. Goldin et al (2003) studied 18 families and found numerous regions suggestive of linkage (e.g. in chromosomes 1, 3, 6, 12, 13 and 17), but none achieved statistical significance. In a follow-up study, the same group (Ng et al, 2006) failed to find support for linkage to regions other than 13q21-33. In a joint effort by the European and American consortia, 206 families were studied using SNP array-based genotyping and chromosome 2q21Æ2 was identified with the highest statistical significance, followed by chromosomal positions 6p22Æ1 and 18q21Æ1 (Sellick et al, 2007). These linkage results suggest that one or even two or three loci directly responsible for a sizeable portion of the genetic predisposition to CLL are unlikely to exist. Likewise, in an earlier review, Houlston et al (2003) concluded that ‘at present there is no compelling evidence that any specific gene acts as a major susceptibility locus and part of the inherited susceptibility to the disease is mediated through low-risk alleles’. The same conclusions were reinforced more recently by the same authors (Sellick et al, 2006).

Loss of death associated protein kinase in a CLL family We undertook a genome-wide search for linkage using a panel of 400 microsatellite markers in a CLL family published by Lynch et al (2002). This is one of the largest families documented in the literature. At the time of the linkage study, samples were available from four affected brothers and one affected son of one of the brothers (IV1–IV4 and V4; for a pedigree see Fig 1). Of note, two of the brothers are identical twins, who were diagnosed with CLL at 56 and 54 years of age respectively. There was no sample available from the affected grandfather (III1), who had already died from the disease. A much enlarged pedigree comprising one additional affected individual (a female) and several presently unaffected members of the youngest adult generation has recently been published, together with a thorough clinical–haematological assessment of affected and unaffected members (Aoun et al, 2007). In our study, a maximum lod score of less than 1 had been predicted with the limited samples available. The result suggested linkage to 9q22 with a multipoint non-parametric lod (NPL) score of 0Æ96 (Raval et al, 2007). The second highest peak had a lod score less than half this value (0Æ42). Inspection of previously reported linkage results revealed no peak in 9q22 in the study by Sellick et al (2005), while Goldin et al (2003) reported an NPL score of just over 1 in the same 9q22 region. At this point we concluded that a high-penetrance predisposing allele might well reside in this locus, but is likely to be rare. Evidence for epigenetic silencing of death associated protein kinase 1 (DAPK1) in CLL was available; however, it was totally unclear what might underlie the inherited

Fig 1. Pedigree of a large family affected with chronic lymphocytic leukaemia (CLL) first described by (Lynch et al, 2002) and later expanded by (Aoun et al, 2007). For the linkage study by (Raval et al, 2007), samples were available from the four affected brothers (IV1–IV4), one affected son (V10), and two unaffected sons (V8 & V9) of one of the brothers (IV4). Heterozygous affected carriers of the DAPK1 promoter mutation c.1-6531A>G are indicated by an arrow. The mutational status of unaffected individuals cannot be shown here for reasons of patient confidentiality. Of note, two of the brothers are identical twins (IV3 & IV4), who were diagnosed with CLL at 56 and 54 years of age respectively. There was no sample available from the affected grandfather (III1), who had already died from the disease. Female V9 has CLL but does not share the mutation or the mutation-carrying haplotype with the other CLL patients. This fact and the paucity of CLL in her branch of the family suggest that she represents a rare phenocopy. Her grandfather (II3) died of unknown cancer cause at the age of 67 years, while her father (III7) died of prostate cancer and one uncle (III6) died of colon cancer. The generation numbering is the same as in (Aoun et al, 2007); however, note that the order in the generations has changed to reflect the birth order and that all family members are numbered. The age at diagnosis (CLL), age at death (d.x), diagnosis of cancer, and year of birth (if known) are indicated below each individual.

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Review predisposition. As is described in detail elsewhere (Raval et al, 2007) an early observation occurred while cDNA from DAPK1 was resequenced in search of germline mutations in family members. It was noted that, in the affected family members, RNA from one allele appeared less abundant than the other, and this was the same allele that co-segregated with the disease based on haplotypes extending over the entire gene. This observation emanated from peak heights of SNPs in sequencing chromatograms; it was confirmed and quantified using quantitative primer extension assays and the enumeration of clones identified by SNPs (Raval et al, 2007). In conclusion, affected family members consistently showed reduced expression of the allele that by linkage co-segregated with the disease. As this observation was based on studies conducted in fibroblasts, it was clear that the reduced expression of one DAPK1 allele was a constitutional, heritable (‘germline’) phenomenon. As no obvious germline mutations had been found, massive genomic sequencing was undertaken. Monoallelic germline DNA (one clone from each allele) from an affected member of the family was cloned in bacterial artificial chromosomes, shotgun sequenced, and the sequence assembled. In all, approximately 400 kb of DNA comprising the large DAPK1 gene and regions flanking it was re-sequenced in this way. No obvious mutations were found, but 281 SNPs were seen that differed between the wild type and CLL alleles. Obviously one or some of these SNPs could represent the germline mutation. In an effort to narrow down the most likely candidates, two categories of SNPs were excluded from further consideration: (i) those that were found more than once in existing databases, or that we found by genotyping in up to 383 healthy controls, and (ii) those that occurred in repetitive sequences. This arbitrary triaging left four candidate SNPs, one of which appeared to be a possible candidate for a mutation based on its location and the fact that it was not seen in 383 control samples from healthy individuals from the US and Europe. It was an A to G polymorphism in nucleotide 6531 upstream of the A of the translation initiation codon, abbreviated c.1-6531A>G (Raval et al, 2007). The rare G allele for this SNP greatly increases the binding of HOXB7 to this region, resulting in repression of DAPK1 transcription. Hence, the region can be labeled as a repressor binding region. A crucial question is whether the c.1-6531A>G SNP is a mutation among others contributing to CLL or the only mutation predisposing to CLL in the family. The pedigree displays dominant inheritance and apparently high penetrance, arguing in favour of a single gene. The functional significance of the SNP is clearly established. However, for it to be the only mutation it should be present in all affected individuals. In this case the ‘CLL’ haplotype and the SNP occur in all affected individuals with one exception; they do not occur in the more distantly related female individual (IV-9) (Fig 1). This individual was diagnosed with typical CLL at 58 years of age; had a somatic deletion of 13q14, trisomy 12, IGHV mutated,

and was ZAP-70 positive; thus, the diagnosis was hardly in doubt. However, inspection of the pedigree (Fig 1) showed no other instances of CLL in her branch of the family. Thus, it is likely that she represents a very rare phenocopy. While it is clear that epigenetic silencing of DAPK1 is an extraordinarily common event in both sporadic and familial CLL, how commonly is there an inherited germline change affecting DAPK1? The available data do not provide an immediate response, but we have searched for the c.1-6531A>G SNP in 263 CLL patients from the US and Sweden and found only one Swedish patient with the rare G allele. Further studies regarding family history and allelic expression of DAPK1 of this patient are pending. Assuming that other mutations might be responsible, we have sequenced the entire coding region, splice sites, and promoter regions of 75 US patients, including both familial and sporadic subjects, and have not observed any changes that are plausible mutations. This evidence suggests, in full agreement with the various linkage results referred to above, that heritable changes in DAPK1 are indeed rare. One might hypothesize that overexpression of HOXB7 could constitute an inherited mechanism. Again, linkage of CLL to the genomic region of HOXB7 (17q21-22) has not been suggested, so any heritable upregulation of HOXB7 probably requires participation of other, regulatory genes located elsewhere, a plausible but unexplored possibility. In summary, the genetic analyses we have performed so far favour the occurrence of a mechanism that downregulates the transcription of DAPK1 in an allele-specific heritable, cisacting way. This event is probably quite rare and probably involves a repressor region 6Æ5 kb upstream of the gene interacting with trans-acting factors, such as HOX proteins. The c. 75% downregulation of one allele either is capable of inducing CLL (acting over many years to produce this lateonset disease) or induces epigenetic downregulation or silencing of both alleles. In sporadic CLL, an unknown mechanism triggers widespread methylation of DAPK1 leading to its downregulation. The loss or reduction in DAPK1 protein strongly inhibits apoptosis, a cardinal feature of CLL.

Epigenetic defects in CLL Epigenetic alterations in cancer genomes have been recognized as major contributors to the malignant phenotype. Epigenetic alterations do not change the DNA sequences and are transmitted to daughter cells during mitosis. Two main epigenetic alterations, DNA methylation and modifications of chromatin proteins, have been described. These epigenetic alterations are interrelated and it is thought that these alterations co-operate in the silencing of genes through the change in chromatin conformation [for a review see (Esteller, 2007)]. DNA methylation or the addition of a methyl group to position 5 of the cytosine ring in a CG dinucleotide is mediated by DNA methyltransferases, which utilize S-adenosylmethionine as the methyl-donor. DNA methylation is


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Review recognized by DNA methylbinding domain proteins that are found in large repressor complexes. The concept that evolved over the past years highlights the association of a closed chromatin conformation with promoter DNA methylation as well as with histone tail modifications characteristic for condensed chromatin (Jones & Baylin, 2002). The first indications for the involvement of DNA methylation changes in CLL came from the finding of global loss of methylation (hypomethylation) measured by the use of HpaII and MspI digestions of genomic DNA followed by validation using high-performance liquid chromatography (HPLC) measuring the 5-methylcytosine content (Wahlfors et al, 1992). Hypomethylation was found in almost all patient samples analysed and was most predominant in freshly diagnosed/ untreated CLL cells. Recent work confirmed the finding of global loss of DNA methylation in the CLL genome (Lyko et al, 2004) and in one study demonstrated a gradual loss of global methylation, as measured by the methylation index (ration of 5-methylcytosine/cytosine), with age (Yu et al, 2007). While the majority of global 5-methylcytosine loss can be accounted for by the loss of methylation in large repetitive sequences (satellite DNA, centromeric repeats, rDNA) some reports have described hypomethylation events associated with the MYC oncogene (Deguchi et al, 1987), anti-apoptotic gene BCL2 (Hanada et al, 1993), pro-survival gene TCL1A (Yuille et al, 2001) and the human immunoglobulin light kappa constant genes (Bianchi et al, 1988). The observation that gain of methylation (hypermethylation) in GC-rich promoter regions, so-called CpG islands, results in the silencing of tumour suppressor genes, led to a change in research directions (Baylin et al, 1986, 1991). Many groups have now reported epigenetic silencing of selected tumour suppressor genes in CLL (Table I). The list of genes is growing rapidly and includes DAPK1, WIF1, ID4, SFRPs, genes involved in apoptosis (Chim et al, 2006a,b; Liu et al, 2006), CDKN2A (p16INK4) and CDKN2B (p15INK4) cell cycle regulators (Pinyol et al, 1998; Chim et al, 2006c; Tsirigotis et al, 2006), and MLH1, a mismatch repair gene whose silencing correlated with Richter’s transformation of CLL (Fulop et al, 2003). In two of these instances, promoter methylation was associated with clinical outcome of CLL, highlighting the relevance of epigenetic alterations in the disease. TWIST2, a basic helix–loop–helix transcription factor and a regulator of the p53 pathway, is selectively silenced in IGHV mutated CLL characterized by favourable prognosis, when compared to IGHV unmutated CLLs with a poor prognosis (Raval et al, 2005). Similarly, methylation of a single CG dinucleotide located 344bp downstream of ZAP70 (a tyrosine kinase regulating T-cell receptor signalling) transcription start site was associated with ZAP-70 expression, which is a recognized prognostic biomarker for CLL (Rassenti et al, 2004; Corcoran et al, 2005). A candidate gene approach for the studies of promoter methylation does not provide information about the extent of promoter methylation and does not identify those genes 748

preferentially targeted by epigenetic mechanisms. A recent study from our group addressed this concern by applying a genome scanning approach (Restriction Landmark Genomic Scanning or RLGS) to search for novel methylated genes and to determine the degree of CpG island methylation in the disease (Rush et al, 2004). RLGS is a two-dimensional gel-electrophoresis in which DNA restriction fragments are separated following a restriction digest using a rear cutting methylation sensitive restriction enzyme (e.g. NotI or AscI) (Smiraglia & Plass, 2002). These restriction enzyme sites are localized preferentially in CpG islands and are used as a tag to identify methylated CpG islands. In a screen for aberrant DNA methylation in over 3000 CpG islands in 10 primary CLL samples, an average of 4Æ8% (range: 2Æ5–8Æ1%) of all CpG islands were found to be methylated (Rush et al, 2004). The patterns of methylation were non-random, as indicated by the finding of several sequences methylated in the majority of CLL samples analysed. This study identified a total of 193 novel sequences that are targets for aberrant DNA methylation in CLL. One outstanding question is whether genetic and epigenetic alterations target the same genes or if certain genes have a propensity to become solely silenced by one of the mechanisms or in a combination of genetic and epigenetic events. A report indicating that the gene cluster located in the most frequently deleted region in CLL on chromosome 13q14 is already downregulated by epigenetic mechanisms in non-malignant cells (Mertens et al, 2006). Other genes are under study and the answer to this question will require further investigation. The high frequency of epigenetically silenced genes in CLL suggests that DNA methylation changes are a required step in the development of CLL. It would be intriguing to speculate that epigenetic alterations do not only play a role in sporadic cases but also in familial CLL. Would it be possible that preexisting ‘epimutations’, similar to those described in cases of familial colon cancer (Chan et al, 2006; Hitchins et al, 2007; Valle et al, 2007), predispose to the silencing of a tumour suppressor gene and subsequently to the development of CLL?

Future directions We have learned a lot about genetic alterations in CLL and we are starting to unravel the contributions of epigenetic alterations to the development of CLL. With emerging new technology for the simultaneous evaluation of genetic and epigenetic alterations, we will be in a better position to obtain a more comprehensive picture of the molecular profile of the CLL genome. Novel genomics tools, such as oligo-based arrays, will provide new data on copy-number changes and even on minute sequence changes (insertions and deletions) in a CLL genome. Similarly, one can envision that methylation arrays will increase the number of genes identified that are aberrantly regulated by epigenetic processes. Future studies will need to integrate genetic and epigenetic data to better understand the mechanisms leading to a particular alteration and to evaluate their consequences on gene functions.


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Acknowledgements This publication was supported by National Cancer Institute grants CA101956 (JCB, CP), CA81534 to the CLL Research Consortium (JCB), P30 CA16058 (AdlC, CP, JCB), Leukemia and Lymphoma Society Translational Grant and Specialized Center of Research in CLL (JCB, CP), and the D. Warren Brown Foundation (JCB, CP). CP is a Leukemia and Lymphoma Society Scholar and JCB is a Leukemia and Lymphoma Society Clinical Scholar.

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