ZAP-70 is expressed by a subset of normal human B-lymphocytes displaying an activated phenotype

Identification and Functional Investigation of Hub Genes Associated with Follicular Lymphoma

Follicular lymphoma (FL), the most common type of indolent lymphoma, originates from germinal center B cells within the lymphoid follicle. However, the underlying mechanisms of this disease remain unclear. This study aimed to identify the potential hub genes for FL and evaluate their functional roles in clinical applications. Microarray data and clinical characteristics of patients with FL were obtained from the Gene Expression Omnibus database. Differential expression analysis and weighted gene co-expression network analysis (WGCNA) were employed to explore hub genes for FL. Functional enrichment analysis was performed to investigate the potential roles of these hub genes in FL. Mendelian randomization (MR) analysis was performed to verify the causal effect of the top genes on FL risk. In addition, gene set enrichment analysis (GSEA) and immune cell analysis were performed to elucidate the involved mechanisms of the crucial genes in FL. A total of 1363 differentially expressed genes and 157 central genes were identified by differential expression analysis and WGCNA, respectively, resulting in 117 overlapping genes considered as hub genes for FL. Functional enrichment analysis revealed significant correlations between immune-related pathways and FL. MR analysis revealed a significant association only between zeta chain of T-cell receptor-associated protein kinase 70 (ZAP70) and FL risk, with no significance observed for the other top genes. GSEA and immune cell analysis suggested that ZAP70 may be involved in the development and progression of FL through immune-related pathways. By integrating bioinformatics and MR analyses, ZAP70 was successfully identified and validated as a promising FL biomarker. Functional investigations indicated a significant correlation between immune-related pathways and FL. These findings have important implications for the identification of targets for the diagnosis and treatment of FL and provide valuable insights into the molecular mechanisms underlying FL.

Normal B cells express ZAP70 in chronic lymphocytic leukemia: A link between autoimmunity and lymphoproliferation?

ZAP70 has a prognostic value in chronic lymphocytic leukemia (CLL), through altered B-cell receptor signaling, which is important in CLL pathogenesis. A good correlation between ZAP70 expression in CLL cells and the occurrence of autoimmune phenomena has been reported. Yet, the great majority of CLL-associated autoimmune cytopenia is due to polyclonal immunoglobulin (Ig) G synthesized by nonmalignant B cells, and this phenomenon is poorly understood. Here, we show, using flow cytometry, that a substantial percentage of CD5- nonmalignant B cells from CLL patients expresses ZAP70 compared with CD5- B cells from healthy subjects. This ZAP70 expression in normal B cells from CLL patients was also evidenced by the detection of ZAP70 mRNA at single-cell level with polyclonal Ig heavy- and light-chain gene transcripts. ZAP70+ normal B cells belong to various B-cell subsets and their presence in the naïve B-cell subset suggests that ZAP70 expression may occur during early B-cell development in CLL patients and potentially before malignant transformation. The presence of ZAP70+ normal B cells is associated with autoimmune cytopenia in CLL patients in our cohort of patients, and recombinant antibodies produced from these ZAP70+ nonmalignant B cells were frequently autoreactive including anti-platelet reactivity. These results provide a better understanding of the implication of ZAP70 in CLL leukemogenesis and the mechanisms of autoimmune complications of CLL.

ZAP-70 Shapes the Immune Microenvironment in B Cell Malignancies

Zeta-chain-associated protein kinase-70 (ZAP-70) is a tyrosine kinase mainly expressed in T cells, NK cells and a subset of B cells. Primarily it functions in T cell receptor (TCR) activation through its tyrosine kinase activity. Aberrant expression of ZAP-70 has been evidenced in different B cell malignancies, with high expression of ZAP-70 in a subset of patients with Chronic Lymphocytic Leukemia (CLL), associating with unfavorable disease outcomes. Previous studies to understand the mechanisms underlying this correlation have been focused on tumor intrinsic mechanisms, including the activation of B cell receptor (BCR) signaling. Recent evidence also suggests that ZAP-70, intrinsically expressed in tumor cells, can modulate the cross-talk between malignant B cells and the immune environment, implying a more complex role of ZAP-70 in the pathogenesis of B cell malignancies. Meanwhile, the indispensible roles of ZAP-70 in T cell and NK cell activation also demonstrate that the autologous expression of ZAP-70 in the immune environment can be a central target in modulation of tumor immunity. Here we review the evidences of the link between ZAP-70 and tumor immunology in the microenvironment in B cell malignancies. Considering an emerging role of immunotherapies in treating these conditions, understanding the distinct molecular functions of ZAP-70 in a broader cellular context could ultimately benefit patient care.

B cell signalling pathways-New targets for precision medicine in chronic lymphocytic leukaemia

The B cell receptor (BCR) is a master regulator of B cells, controlling cellular processes such as proliferation, migration and survival. Cell signalling downstream of the BCR is aberrantly activated in the B cell malignancy chronic lymphocytic leukaemia (CLL), supporting the pathophysiology of the disease. This insight has led to development and approval of small molecule inhibitors that target components of the BCR pathway. These advances have greatly improved the management of CLL, but the disease remains incurable. This may partly be explained by the inter-patient heterogeneity of the disease, also when it comes to treatment responses. Precision medicine is therefore required to optimize treatment and move towards a cure. Here, we discuss how the introduction of BCR signalling inhibitors has facilitated the development of functional in vitro assays to guide clinical treatment decisions on use of the same therapeutic agents in individual patients. The cellular responses to these agents can be analysed in high-throughput assays such as dynamic BH3 profiling, phospho flow experiments and drug sensitivity screens to identify predictive biomarkers. This progress exemplifies the positive synergy between basal and translational research needed to optimize patient care.

Profiling of human lymphocytes reveals a specific network of protein kinases modulated by endurance training status

To date, the effects of endurance exercise training on lymphocyte physiology at the kinome level are largely unknown. Therefore, the present study used a highly sensitive peptide-based kinase activity profiling approach to investigate if the basal activity of tyrosine (Tyr) and serine/threonine (Ser/Thr) kinases of human lymphocytes is affected by the aerobic endurance training status. Results revealed that the activity of various tyrosine kinases of the FGFR family and ZAP70 was increased, whereas the activity of multiple Ser/Thr kinases such as IKKα, CaMK4, PKAα, PKCα+δ (among others) was decreased in lymphocytes of endurance trained athletes (ET). Moreover, functional associations between several differentially regulated kinases in ET-derived lymphocytes were demonstrated by phylogenetic mapping and network analysis. Especially, Ser/Thr kinases of the AGC-kinase (protein kinase A, G, and C) family represent exercise-sensitive key components within the lymphocytes kinase network that may mediate the long-term effects of endurance training. Furthermore, KEGG (Kyoto Encyclopedia of Genes and Genomes) and Reactome pathway analysis indicate that Ras as well as intracellular signaling by second messengers were found to be enriched in the ET individuals. Overall, our data suggest that endurance exercise training improves the adaptive immune competence by modulating the activity of multiple protein kinases in human lymphocytes.

Beyond TCR Signaling: Emerging Functions of Lck in Cancer and Immunotherapy

In recent years, the lymphocyte-specific protein tyrosine kinase (Lck) has emerged as one of the key molecules regulating T-cell functions. Studies using Lck knock-out mice or Lck-deficient T-cell lines have shown that Lck regulates the initiation of TCR signaling, T-cell development, and T-cell homeostasis. Because of the crucial role of Lck in T-cell responses, strategies have been employed to redirect Lck activity to improve the efficacy of chimeric antigen receptors (CARs) and to potentiate T-cell responses in cancer immunotherapy. In addition to the well-studied role of Lck in T cells, evidence has been accumulated suggesting that Lck is also expressed in the brain and in tumor cells, where it actively takes part in signaling processes regulating cellular functions like proliferation, survival and memory. Therefore, Lck has emerged as a novel druggable target molecule for the treatment of cancer and neuronal diseases. In this review, we will focus on these new functions of Lck.

Altered recruitment of Lyn, Syk and ZAP-70 into lipid rafts of activated B cells in Systemic Lupus Erythematosus

There is evidence that B cells from patients with Systemic Lupus Erythematosus (SLE) could be hyperactivated due to changes in their lipid rafts (LR) composition, leading to altered BCR-dependent signals. This study aimed to characterize possible alterations in the recruitment of protein tyrosine kinases (PTK) into B cells LR from SLE patients. Fifteen patients with SLE and ten healthy controls were included. Circulating B cells were isolated by negative selection and stimulated with goat Fab´2 anti-human IgM/IgG. LR were isolated with a non-ionic detergent and ultracentrifuged on 5-45% discontinuous sucrose gradients. Proteins from each fraction were analyzed by Western Blot. Total levels of Lyn, Syk, and ZAP-70 in resting B cells were similar in SLE patients and healthy controls. Upon BCR activation, Lyn, Syk and ZAP-70 recruitment into LR increased significantly in B cells of healthy controls and patients with inactive SLE. In contrast, in active SLE patients there was a great heterogeneity in the recruitment of signaling molecules and the recruitment of ZAP-70 was mainly observed in patients with decreased Syk recruitment into LR of activated B cells. The reduction in Flotilin-1 and Lyn recruitment in SLE patients seem to be associated with disease activity. These findings suggest that in SLE patients the PTK recruitment into B cell LR is dysregulated and that B cells are under constant activation through BCR signaling. The decrease of Lyn and Syk, the expression of ZAP-70 by B cells and the increase in Calcium fluxes in response to BCR stimulation in active SLE patients, further support that B cells from SLE patients are under constant activation through BCR signaling, as has been proposed.

Chronic Lymphocytic Leukemia B-Cell Normal Cellular Counterpart: Clues From a Functional Perspective

Chronic lymphocytic leukemia (CLL) is characterized by the clonal expansion of small mature-looking CD19+ CD23+ CD5+ B-cells that accumulate in the blood, bone marrow, and lymphoid organs. To date, no consensus has been reached concerning the normal cellular counterpart of CLL B-cells and several B-cell types have been proposed. CLL B-cells have remarkable phenotypic and gene expression profile homogeneity. In recent years, the molecular and cellular biology of CLL has been enriched by seminal insights that are leading to a better understanding of the natural history of the disease. Immunophenotypic and molecular approaches (including immunoglobulin heavy-chain variable gene mutational status, transcriptional and epigenetic profiling) comparing the normal B-cell subset and CLL B-cells provide some new insights into the normal cellular counterpart. Functional characteristics (including activation requirements and propensity for plasma cell differentiation) of CLL B-cells have now been investigated for 50 years. B-cell subsets differ substantially in terms of their functional features. Analysis of shared functional characteristics may reveal similarities between normal B-cell subsets and CLL B-cells, allowing speculative assignment of a normal cellular counterpart for CLL B-cells. In this review, we summarize current data regarding peripheral B-cell differentiation and human B-cell subsets and suggest possibilities for a normal cellular counterpart based on the functional characteristics of CLL B-cells. However, a definitive normal cellular counterpart cannot be attributed on the basis of the available data. We discuss the functional characteristics required for a cell to be logically considered to be the normal counterpart of CLL B-cells.

Targeting B cell receptor signalling in cancer: preclinical and clinical advances

B cell receptor (BCR) signalling is crucial for normal B cell development and adaptive immunity. BCR signalling also supports the survival and growth of malignant B cells in patients with B cell leukaemias or lymphomas. The mechanism of BCR pathway activation in these diseases includes continuous BCR stimulation by microbial antigens or autoantigens present in the tissue microenvironment, activating mutations within the BCR complex or downstream signalling components and ligand-independent tonic BCR signalling. The most established agents targeting BCR signalling are Bruton tyrosine kinase (BTK) inhibitors and PI3K isoform-specific inhibitors, and their introduction into the clinic is rapidly changing how B cell malignancies are treated. B cells and BCR-related kinases, such as BTK, also play a role in the microenvironment of solid tumours, such as squamous cell carcinoma and pancreatic cancer, and therefore targeting B cells or BCR-related kinases may have anticancer activity beyond B cell malignancies.

Selective Binders of the Tandem Src Homology 2 Domains in Syk and Zap70 Protein Kinases by DNA-Programmed Spatial Screening

Members of the Syk family of tyrosine kinases arrange Src homology 2 (SH2) domains in tandem to allow the firm binding of immunoreceptor tyrosine-based interaction motifs (ITAMs). While the advantages provided by the bivalency enhanced interactions are evident, the impact on binding specificity is less-clear. For example, the spleen tyrosine kinase (Syk) and the ζ-chain-associated protein kinase (ZAP-70) recognize the consensus sequence pYXXI/L(X)_6-8 pYXXI/L with near-identical nanomolar affinity. The nondiscriminatory recognition, on the one hand, poses a specificity challenge for the design of subtype selective protein binders and, on the other hand, raises the question as to how differential activation of Syk and ZAP-70 is ensured when both kinases are co-expressed. Herein, we identified the criteria for the design of binders that specifically address either the Syk or the Zap-70 tSH2 domain. Our approach is based on DNA-programmed spatial screening. Tyrosine-phosphorylated peptides containing the pYXXI/L motif were attached to oligonucleotides and aligned in tandem on a DNA template by means of nucleic acid hybridization. The distance between the pYXXI/L motifs and the orientation of strands were varied. The exploration exposed remarkably different recognition characteristics. While Syk tSH2 has a rather broad substrate scope, ZAP-70 tSH2 required a proximal arrangement of the phosphotyrosine ligands in defined strand orientation. The spatial screen led to the design of mutually selective, DNA-free binders, which discriminate Zap-70 and Syk tSH2 by 1 order of magnitude in affinity.

SLP76 integrates into the B-cell receptor signaling cascade in chronic lymphocytic leukemia cells and is associated with an aggressive disease course

I In the last decade, the B-cell receptor has emerged as a pivotal stimulus in the pathogenesis of chronic lymphocytic leukemia, and a very feasible therapeutic target in this disease. B-cell receptor responsiveness in chronic lymphocytic leukemia cells is heterogeneous among patients and correlates with aggressiveness of the disease. Here we show, for the first time, that SLP76, a key scaffold protein in T-cell receptor signaling, is ectopically expressed in chronic lymphocytic leukemia cells, with variable levels among patients, and correlates positively with unmutated immunoglobulin heavy chain variable gene status and ZAP-70 expression. We found that SLP76 was functionally active in chronic lymphocytic leukemia cells. A SYK-dependent basal level of phosphorylated SLP76 exists in the cells, and upon B-cell receptor engagement, SLP76 tyrosine phosphorylation is significantly enhanced concomitantly with increased physical association with BTK. B-cell receptor-induced SLP76 phosphorylation is mediated by upstream signaling events involving LCK and SYK. Knockdown of SLP76 in the cells resulted in decreased induction of BTK, PLCγ2 and IκB phosphorylation, as well as cell viability after B-cell receptor activation with anti-IgM. Consistent with our biochemical findings, high total SLP76 expression in chronic lymphocytic leukemia cells correlated with a more aggressive disease course.

IN CONCLUSION

SLP76 is ectopically expressed in chronic lymphocytic leukemia cells where it plays a role in B-cell receptor signaling.

Prognosis and therapy of chronic lymphocytic leukemia and small lymphocytic lymphoma

Chronic lymphocytic leukemia (CLL) is characterized by a highly variable clinical course that has guided treatment principles in as much as anti-leukemic therapy is reserved for patients with active disease. This heterogeneity is somewhat dissected by prognostic markers, many of which represent pathogenic mechanisms. Recently, the introduction of highly active targeted agents and maturing data on predictive markers may lead to more individualized therapeutic approaches. In this chapter, we review key prognostic markers, current and emerging therapy, and will attempt to outline a future "where the two may connect".

Gefitinib targets ZAP-70-expressing chronic lymphocytic leukemia cells and inhibits B-cell receptor signaling

Chronic lymphocytic leukemia (CLL) can be divided into groups based on biomarkers of poor prognosis. The expression of the tyrosine kinase ZAP-70 (member of the Syk tyrosine kinase family) in CLL cells is associated with shorter overall survival in CLL patients. Currently, there is a lack of targeted therapies for patients with ZAP-70 expression in CLL cells. The tyrosine kinase inhibitor gefitinib has been shown to be effective at induce apoptosis in acute myeloid leukemia through inhibition of Syk. In this study, we sought to test the efficacy of gefitinib in primary human ZAP-70+ CLL cells. We demonstrate that gefitinib preferentially induces cell death in ZAP-70-expressing CLL cells with a median IC₅₀ of 4.5 μM. In addition, gefitinib decreases the viability of ZAP-70+ Jurkat T leukemia cells but fails to affect T cells from CLL patients. Western blot analysis shows gefitinib reduces both basal and B-cell receptor (BCR)-stimulated phosphorylation of Syk/ZAP-70, ERK, and Akt in ZAP-70+ CLL cells. Moreover, gefitinib inhibits the pro-survival response from BCR stimulation and decreases pro-survival proteins such as Mcl-1. Finally, ZAP-70 expression sensitizes Raji cells to gefitinib treatment. These results demonstrate that gefitinib specifically targets ZAP-70+ CLL cells and inhibits the BCR cell survival pathway leading to apoptosis. This represents the likelihood of tyrosine kinase inhibitors being effective targeted treatments for ZAP-70+ CLL cells.

MIF promotes B cell chemotaxis through the receptors CXCR4 and CD74 and ZAP-70 signaling

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine with chemokine-like functions that plays a pivotal role in the pathogenesis of inflammatory diseases by promoting leukocyte recruitment. We showed that MIF promotes the atherogenic recruitment of monocytes and T cells through its receptors CXCR2 and CXCR4. Effects of MIF on B cell recruitment have not been addressed. In this study, we tested the involvement of MIF in B cell chemotaxis and studied the underlying mechanism. We show that MIF promotes primary murine B cell chemotaxis in a dose-dependent manner, comparable to the B cell chemokines CXCL13 and CXCL12. Splenic B cells express CXCR4 and the receptor CD74 but not CXCR2. Inhibition of CXCR4 or CD74 or a genetic deficiency of Cd74 in primary B cells fully abrogated MIF-mediated B cell migration, implying cooperative involvement of both receptors. MIF stimulation of B cells resulted in a rapid increase in intracellular Ca(2+) mobilization and F-actin polymerization. Intriguingly, the tyrosine kinase ZAP-70 was activated upon MIF and CXCL12 treatment in a CXCR4- and CD74-dependent manner. Pharmacological inhibition of ZAP-70 resulted in abrogation of primary B cell migration. Functional involvement of ZAP-70 was confirmed by small interfering RNA-mediated knockdown in Ramos B cell migration. Finally, primary B cells from ZAP-70 gene-deficient mice exhibited ablated transmigration in response to MIF or CXCL12. We conclude that MIF promotes the migration of B cells through a ZAP-70-dependent pathway mediated by cooperative engagement of CXCR4 and CD74. The data also suggest that MIF may contribute to B cell recruitment in vivo (e.g., in B cell-related immune disorders).

B cell receptor signaling in chronic lymphocytic leukemia

B cell receptor (BCR) signaling plays an important pathogenic role in chronic lymphocytic leukemia (CLL) and B cell lymphomas, based on structural restrictions of the BCR, and BCR-dependent survival and growth of the malignant B cells. In CLL and lymphoma subtypes, ligand-independent ('tonic') and ligand-dependent BCR signaling have been characterized, which can involve mutations of BCR pathway components or be triggered by (auto)antigens present in the tissue microenvironment. In CLL, based on high response rates and durable remissions in early-stage clinical trials, there is rapid clinical development of inhibitors targeting BCR-associated kinases [Bruton's tyrosine kinase (BTK), phosphoinositide 3-kinase (PI3K)δ], which will change treatment paradigms in CLL and other B cell malignancies. Here, we discuss the evolution of this field, from BCR-related prognostic markers, to mechanisms of BCR activation, and targeting of BCR-associated kinases, the emerging Achilles' heel in CLL pathogenesis.

IGHV-unmutated and IGHV-mutated chronic lymphocytic leukemia cells produce activation-induced deaminase protein with a full range of biologic functions

Clonal evolution occurs during the course of chronic lymphocytic leukemia (CLL) and activation-induced deaminase (AID) could influence this process. However, this possibility has been questioned in CLL because the number of circulating AID mRNA(+) cells is exceedingly low; synthesis of AID protein by blood CLL cells has not been demonstrated; the full range of AID functions is lacking in unmutated CLL (U-CLL), and no prospective analysis linking AID expression and disease severity has been reported. The results of the present study show that circulating CLL cells and those within secondary lymphoid tissues can make AID mRNA and protein. This production is related to cell division because more AID mRNA was detected in recently divided cells and AID protein was limited to the dividing fraction and was up-regulated on induction of cell division. AID protein was functional because AID(+) dividing cells exhibited more double-stranded DNA breaks, IGH class switching, and new IGHV-D-J mutations. Each of these actions was documented in U-CLL and mutated CLL (M-CLL). Furthermore, AID protein was associated with worse patient outcome and adverse cytogenetics. We conclude that the production of fully functional AID protein by U-CLL and M-CLL cells could be involved in clonal evolution of the disease.

Pitfalls and limitations of ZAP-70 detection in chronic lymphocytic leukemia

Zeta-associated protein of 70 kDa (ZAP-70) is a tyrosine kinase that plays a role in signal transduction from the T-cell receptor. ZAP-70 is expressed in normal T-cells and NK-cells. Increased expression of ZAP-70 has been identified in chronic lymphocytic leukemia (CLL). CLL patients with increased ZAP-70 expression have significantly worse prognosis in terms of both progression-free survival and overall survival. There are several methods to quantify ZAP-70: polymerase chain reaction (PCR), immunoblotting, immunohistochemistry, and flow cytometry. Use of flow cytometry for ZAP-70 detection seems to be advantageous as this technique enables us to assess the presence of ZAP-70 separately on CLL clone, T-cells, and NK-cells. On the other hand, detection of ZAP-70 by flow cytometry is substantially influenced by many variables. The principal drawback of flow cytometry is the absence of consensus regarding selection of optimal anti-ZAP-70 antibody, fluorochrome conjugate, the most reliable staining technique, and optimal positivity threshold. This article summarizes pitfalls of flow cytometric analysis of ZAP-70 in CLL.

Shaping the niche: lessons from the Drosophila testis and other model systems

Stem cells are fascinating, as they supply the cells that construct our adult bodies and replenish, as we age, worn out, damaged, and diseased tissues. Stem cell regulation relies on intrinsic signals but also on inputs emanating from the neighbouring niche. The Drosophila testis provides an excellent system for studying such processes. Although recent advances have uncovered several signalling, cytoskeletal and other factors affecting niche homeostasis and testis differentiation, many aspects of niche regulation and maintenance remain unsolved. In this review, we discuss aspects of niche establishment and integrity not yet fully understood and we compare it to the current knowledge in other model systems such as vertebrates and plants. We also address specific questions on stem cell maintenance and niche regulation in the Drosophila testis under the control of Hox genes. Finally, we provide insights on the striking functional conservation of homologous genes in plants and animals and their respective stem cell niches. Elucidating conserved mechanisms of stem cell control in both lineages could reveal the importance underlying this conservation and justify the evolutionary pressure to adapt homologous molecules for performing the same task.

ZAP-70 enhances migration of malignant B lymphocytes toward CCL21 by inducing CCR7 expression via IgM-ERK1/2 activation

ZAP-70 in chronic lymphocytic leukemia (CLL) has been associated with enhanced B-cell receptor (BCR) signaling, survival, and migration. We investigated whether ZAP-70 can directly govern migration and the underlying mechanisms. In the ZAP-70 stably transfected Ramos cell line, IgM stimulation, but no IgD, enhanced phosphorylation of ERK1/2, Akt and Syk, and delayed IgM and CD79b internalization. In contrast, in the Raji cell line, where ZAP-70 was constitutively phosphorylated, ERK1/2, but not Akt, was phosphorylated, suggesting that MAPK pathway mediates ZAP-70 effects. BCR stimulation modulated the expression of CCR7, CXCR4, CXCR5, CD44, CD49d, and CD62L, which were up-regulated in ZAP-70-positive CLL primary subclones. The most dramatic change after BCR engagement in ZAP-70-transfected cells was CCR7 up-regulation, this being impaired by ERK1/2 inhibition and translating into both increased signaling and migration toward CCL21. Primary CLL subclones with high ZAP-70 expression showed increased migration toward CCL21. In conclusion, ZAP-70 ectopic expression led to enhanced BCR signaling after IgM stimulation and increased the expression of CCR7 predominantly via ERK1/2, increasing the response and migration toward CCL21. In primary CLL samples, cellular subsets with high ZAP-70 expression had increased expression of adhesion molecules and chemokine receptors in addition to an enhanced ability to migrate toward CCL21.

Management of patients with chronic lymphocytic leukemia with a high risk of adverse outcome: the Mayo Clinic approach

Chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL) is usually an incidental diagnosis in patients with early-intermediate stage disease. However, most patients with a diagnosis of CLL will subsequently have significant morbidity and die from their disease and its complications. For these patients, CLL is not the 'good leukemia' with a predictably 'benign' outcome. Indeed, we can now identify a cohort of patients with high-risk CLL at diagnosis who will have rapid disease progression, poor response to treatment, and poor survival based on prognostic methods developed from an improved understanding of the biology of CLL. The concomitant development of improved treatments has led to risk-adjusted management approaches that could improve outcomes. We discuss the clinical and laboratory components of comprehensive risk evaluation of patients with CLL and our approach to the management of patients with a high to very high risk of disease progression and poor outcome. In addition, we review the challenges and prospects for improving prognostic precision and the development of new drugs to improve the treatment of patients with CLL with a high risk of adverse outcome.

Differential and tumor-specific expression of CD160 in B-cell malignancies

CD160 is a human natural killer (NK)-cell-activating receptor that is also expressed on T-cell subsets. In the present study, we examined 811 consecutive cases of B-cell lymphoproliferative disorders (B-LPDs), and demonstrated CD160 expression in 98% (590 of 600) of chronic lymphocytic leukemia (CLL) cases, 100% (32 of 32) of hairy cell leukemia (HCL) cases, 15% (5 of 34) of mantle cell lymphoma (MCL) in the leukemic phase, and 16% (23 of 145) of other B-LPD cases. CD160 transcript and protein were absent in the normal B-cell hierarchy, from stem cells, B-cell precursors, maturing B cells in the germinal center, and circulating B cells, including CD5(+)CD19(+) B1 cells in umbilical cord. CD160 positivity was significantly higher in CLL and HCL in terms of percentage (65.9% and 67.8%, respectively, P < .0001) and median fluorescence intensity (552 and 857, respectively, P < .0001) compared with all other B-LPD cases. Lymph node CLL samples were also CD160(+). Using the disease-specific expression of CD5, CD23, and CD160, a score of 3 characterized CLL (diagnostic odds ratio, 1430); a score of 0 excluded CLL, MCL, and HCL; and the CD23/CD5 ratio differentiated CLL from leukemic CD23(+) MCL. In the B-cell lineage, CD160 is a tumor-specific antigen known to mediate cellular activation signals in CLL, and is a novel target for therapeutic manipulation and monitoring of minimal residual disease.

Detection methods of ZAP-70 in chronic lymphocytic leukemia

The clinical course of patients with chronic lymphocytic leukemia (CLL) is highly heterogeneous, with some patients experiencing rapid disease progression and others living for decades without requiring treatment. Immunoglobulin heavy chain variable region (IGHV) mutation status is a powerful prognostic factor in patients with CLL. The presence or absence of IGHV mutation status is currently the gold-standard prognostic factor, but this technique is labor-intensive and costly. The expression of ζ-chain-associated protein kinase 70 kDa (ZAP-70), detected by flow cytometry, has been served as a potential surrogate for the absence of IGHV mutation status since 2003. Given the current problems with the standardization of ZAP-70 assessment by flow cytometry, this chapter reviews the analysis of ZAP-70 expression by flow cytometry and the relative experimental conditions using the associated publications for "ZAP-70" and "detection method" on Medline since 2003. Thus, mean fluorescence intensity (MFI) ratio method yielded a more reproducible and easily adaptable method to routine use in the clinical diagnostic laboratory. In conclusion, though ZAP-70 is a valuable prognostic factor in CLL, detection methods of ZAP-70 remain to be fully standardized.

Cellular origin(s) of chronic lymphocytic leukemia: cautionary notes and additional considerations and possibilities

Several cell types have been suggested as giving rise to chronic lymphocytic leukemia (CLL), and these suggestions have reflected the sophistication of technology available at the time. Although there is no consensus as to the normal cellular counterpart(s) in the disease, an antigen-experienced B lymphocyte appears required based on surface membrane phenotypes and gene expression profiles. However, what is still unclear is whether a single or multiple normal precursors were stimulated to evolve into CLL and at what stage(s) this occurred. A unifying, parsimonious theory is that CLL clones with either mutated or unmutated IGHVs derive from marginal zone B cells. However, evidence for remarkably similar B-cell receptor amino acid sequence and striking differences in polyantigen and autoantigen-binding activity, found in some but not all CLL clones, challenge a single-cell derivation for CLL. In this Perspective, we summarize data regarding normal counterparts of CLL cells and suggest that a multistep process of leukemogenesis is important to consider when assigning a cellular origin for this disease. Finally, although available data do not definitively identify the cell(s) of origin, we offer possibilities for single- and multiple-cell origin models as straw men that can be improved on and hopefully lead to final answers to this puzzle.

High expression of the immature laminin receptor protein correlates with mutated IGVH status and predicts a favorable prognosis in chronic lymphocytic leukemia

The immature laminin receptor (iLR) is a tumor-associated antigen. We analyzed the expression of iLR on malignant B cells of 134 unselected patient samples with CLL and hypothesized that iLR expression would have prognostic significance due to a differential expression pattern. High ILR expression (cut-off value 30%) was correlated with mutated IGVH status (p<0.0001). Patients with high iLR-expression had a significantly longer time to progression (p=0.039). Combination of CD38, ZAP-70, and iLR by flow cytometry can be used to construct a diagnostic score identifying patients with a median progression free survival of 80 months, if no adverse marker is present.

A single tube, four-color flow cytometry assay for evaluation of ZAP-70 and CD38 expression in chronic lymphocytic leukemia

We describe a simple and robust flow cytometry assay for ZAP-70 and CD38 expression. The steps required to validate this assay in a clinical flow cytometry laboratory are described. Two criteria were used to characterize ZAP-70 expression into positive, negative, and indeterminate categories and applied to 111 cases of chronic lymphocytic leukemia (CLL) resulting in 29.7% positive, 56.8% negative, and 13.5% indeterminate cases. A sensitivity-specificity crossover plot between ZAP-70 and CD38 suggested a cutoff of 12.5% for defining CD38 positivity. ZAP-70+ cases were significantly more likely to be at a higher clinical stage and, together with CD38+ cases, were more likely to have unmutated IgV(H). However, for individual patients, the concordance between these markers was not perfect. It may be necessary to evaluate several prognostic markers simultaneously in CLL, and availability of convenient assays for ZAP-70 and CD38 is desirable for optimal clinical decision making.

The Src, Syk, and Tec family kinases: distinct types of molecular switches

The Src, Syk, and Tec family kinases are three of the most well characterized tyrosine kinase families found in the human genome. Members of these kinase families function downstream of antigen and F(c) receptors in hematopoietic cells and transduce signals leading to calcium mobilization, altered gene expression, cytokine production, and cell proliferation. Over the last several years, structural and biochemical studies have begun to uncover the molecular mechanisms regulating activation of these kinases. It appears that each kinase family functions as a distinct type of molecular switch. This review discusses the activation of the Src, Syk, and Tec kinases from the perspective of structure, phosphorylation, allosteric regulation, and kinetics. The multiple factors that regulate the Src, Syk, and Tec families illustrate the important role played by each of these kinases in immune cell signaling.

Chronic lymphocytic leukaemia: a disease of activated monoclonal B cells

B cell-type chronic lymphocytic leukaemia (CLL) has long been considered a disease of resting lymphocytes. However, cell surface and intracellular phenotypes suggest that most CLL cells are activated cells, although only a small subset progresses beyond the G1 stage of the cell cycle. In addition, traditional teaching says that CLL cells divide rarely, and therefore the build-up of leukaemic cells is due to an inherent defect in cell death. However, in vivo labelling of CLL cells indicates a much more active rate of cell birth than originally estimated, suggesting that CLL is a dynamic disease. Here we review the observations that have led to these altered views of the activation state and proliferative capacities of CLL cells and also provide our interpretation of these observations in light of their potential impact on patients.

ZAP-70 intron1 DNA methylation status: determination by pyrosequencing in B chronic lymphocytic leukemia

ZAP-70 expression is a strong prognostic indicator in chronic lymphocytic leukemia. However, ZAP-70 quantification by flow cytometry lacks sufficient standardization. Based upon the correlation between ZAP-70 expression and its gene methylation status, we have developed a quantitative pyrosequencing assay for the determination of ZAP-70 methylation adapted for routine use. Methylation in four CpG pairs (C-223, C-243, C-254, and C-267) in the first intron of ZAP-70 is associated with repression of ZAP-70. Moreover, it correlates with CD38 expression (n=111, p<.0001), IgHv mutation status (n=106, p<.0001), time to treatment (p<.0001), and overall survival (p=.0014). Pyrosequencing of ZAP-70 provides a good alternative to flow cytometry.

New molecular markers in resistant B-CLL

B-chronic lymphocytic leukemia (B-CLL) is characterized by a highly variable clinical course which has long remained a stumbling block for clinicians. This variability appears to arise from complex molecular alterations identified in malignant cells from patient subsets. Recent studies have focused in particular on identifying new molecular markers to help predict the most effective and adapted treatments. In addition to the mutation status of immunoglobulin variable heavy-chain region (IgVH) genes, which is a well-established predictive factor in B-CLL, these new markers include defects of cell factors involved in the maintenance of genome stability, such as telomere function, DNA repair, ATM and p53. Other predictive factors, such as tyrosine kinase Zap-70 and soluble factors found in patient sera, may be associated with B-cell receptor signal transduction. Interestingly, an alteration of these factors fits closely, though not strikingly, with the absence of somatic mutations in IgVH genes, suggesting that the latter may be due either to epigenetic events leading to an unstable genome or to an inherited defect in the immune response of malignant B-cells. Recent lessons from Zap-70 expression/phosphorylation suggest that some of these markers may reflect the defective pathways in B-CLL cells rather than being markers of cell malignancy per se. Furthermore, specific subsets of markers are found in patient cells resistant to treatment. Current studies on gene expression profiling and proteomic analyses should soon lead to a better understanding of how these pathways are affected, especially in multi-drug resistant B-CLL.

Multi-drug resistance mediated by P-glycoprotein overexpression is not correlated with ZAP-70/CD38 expression in B-cell chronic lymphocytic leukemia

ZAP-70 and CD38 expression can identify B-cell chronic lymphocytic leukemia with an inferior clinical outcome. Many groups have investigated the meaning of the expression of these two proteins and the correlation with the bad prognosis in B-CLL. But nobody has investigated the relation between the multidrug resistance mediated by Pgp overexpression (MDR1) and ZAP-70/CD38 coexpression. Forty-one untreated and stage A patients, either ZAP-70(+)CD38(+) or ZAP-70(-)CD38(-), were tested to determine the MDR1 status. MDR1 was observed in 41% of CLL ZAP-70(+)CD38(+) and in 37% of CLL ZAP-70(-)CD38(-). The difference was not significant (p = 0.745). Patients with ZAP-70 and CD38 positive CLL can not be candidates for MDR1 antagonists.

Steroid effects on ZAP-70 and SYK in relation to apoptosis in poor prognosis chronic lymphocytic leukemia

There is resurgent interest in glucocorticoids (GCs) in the treatment of poor prognosis chronic lymphocytic leukemia (CLL). Little is known however on how GCs induce apoptosis in CLL. Methylprednisolone (MP) induces apoptosis in ZAP-70 positive CLL more readily than in ZAP-70 negative CLL, which is in contrast to the effects of radiation and chemotherapy. The increased GC sensitivity of ZAP-70+ CLL was studied in relation to the expression status of ZAP-70 and the related signal transducing tyrosine kinase SYK. Both ZAP-70 and SYK were downregulated by GC treatment. Moreover, SYK was dephosphorylated by the phosphatase PTP1B of which the expression and translation levels were induced by GCs. Inhibition of PTP1B successfully restored ZAP-70 expression and SYK phosphorylation but did not interfere with GC-induced apoptosis. Therefore, the downregulation of ZAP-70 and P-SYK per se during treatment with GCs is not sufficient to induce apoptosis, and different mechanisms must therefore be responsible for the increased steroid sensitivity of ZAP-70+ CLL.

TLR9-activating DNA up-regulates ZAP70 via sustained PKB induction in IgM+ B cells

In the past, ZAP70 was considered a T cell-specific kinase, and its aberrant expression in B-CLL cells was interpreted as a sign of malignant transformation and dedifferentiation. It was only recently that ZAP70 was detected in normal human B cells. In this study, we show that TLR9-activated B cells resemble B-cell chronic lymphocytic leukemia cells with regard to CD5, CD23, CD25, and heat shock protein 90 expression. Furthermore, stimulatory CpG and GpC DNA oligonucleotides target CD27(+)IgM(+) and CD27(-)IgM(+) B cells (but not IgM(-) B cells) and enhance ZAP70 expression predominantly in the IgM(+)CD27(+) B cell subset. ZAP70 is induced via activation of TLR-7 or -9 in a MyD88-dependent manner, depends on protein kinase B (PKB)/mammalian target of rapamycin signaling and is rapamycin sensitive. Furthermore, ZAP70 expression levels correlate with induction of cyclin A2, prolonged B cell proliferation, and sustained induction of PKB. These events are not observed upon CD40 ligation. However, this deficit can be overcome by the expression of constitutively active PKB, given that CD40 ligation of PKB-transgenic B cells induces B cell proliferation and ZAP70 expression. These results highlight a major difference between CD40- and TLR-7/9-mediated B cell activation and suggest that ZAP70 expression levels in B cells give an estimate of the proliferative potential and the associated PKB availability.

Synovial B cells of rheumatoid arthritis express ZAP-70 which increases the survival and correlates with the inflammatory and autoimmune phenotype

B cells have acquired an important role in the pathogenesis of rheumatoid arthritis (RA) since B cell depletion allowed to rescue patients poorly responders to TNFalpha blockers. This study focused on the involvement of ZAP-70 as a bio-marker of B cells immune activation in RA. ZAP-70 expression in synovial fluid (SF) B cells obtained from RA patients was increased compared to SF B cells of osteoarthritis (OA) patients. Moreover we found that ZAP-70 positive/CD38 positive and ZAP-70 positive/CD5 positive B cells were enriched in SF. The analysis of B cell apoptosis in vitro showed that the percentage of ZAP-70 negative B cells spontaneously undergoing apoptosis was significantly higher than ZAP-70 positive B cells. The ZAP-70 positive B cell ratio (SF/peripheral blood (PB)) showed a positive correlation with SF autoantibody levels and with local levels of BAFF and IL6. ZAP-70 positive B cells seem to define a subset characterized by increased survival and high relationship with local inflammation and autoimmunity.

Chronic lymphocytic leukaemia

Chronic lymphocytic leukaemia is the commonest form of leukaemia in Europe and North America, and mainly, though not exclusively, affects older individuals. It has a very variable course, with survival ranging from months to decades. Major progress has been made in identification of molecular and cellular markers that could predict disease progression in patients with chronic lymphocytic leukaemia. In particular, the mutational profile of immunoglobulin genes and some cytogenetic abnormalities are important predictors of prognosis. However, these advances have raised new questions about the biology, prognosis, and management of chronic lymphocytic leukaemia, some of which are addressed here. In particular, we discuss how better understanding of the function of the B-cell receptor, the nature of genetic lesions, and the balance between proliferation and apoptosis have affected our ability to assess prognosis and to manage chronic lymphocytic leukaemia. Available treatments generally induce remission, although nearly all patients relapse, and chronic lymphocytic leukaemia remains an incurable disease. Advances in molecular biology have enhanced our understanding of the pathophysiology of the disease and, together with development of new therapeutic agents, have made management of chronic lymphocytic leukaemia more rational and more effective than previously. Unfortunately, we know of no way that chronic lymphocytic leukaemia can be prevented. Early detection is practised widely, but seemingly makes no difference to the patient's eventual outcome.

An improved flow cytometric method using FACS Lysing Solution for measurement of ZAP-70 expression in B-cell chronic lymphocytic leukemia

BACKGROUND

B-cell expression of ZAP-70, normally expressed in T and NK cells, correlates with poor prognosis in B-CLL. Poor discrimination between ZAP-70 positive and negative cells hampers routine application of flow cytometry. We examined the usefulness of FACS Lysing Solution.

METHODS

ZAP-70 expression in 65 healthy volunteers was measured by four-color flow cytometry, comparing FACS Lysing Solution for fixation and permeabilization with the Fix & Perm kit. Separation between ZAP-70 positive T cells and negative B cells was based on a ratio of median ZAP-70 staining of T cells to B cells. In 25 B-CLL patients, ZAP-70 expression was estimated using the lower limit of the fluorescence range corresponding with 98% of ZAP-70 positive T cells as threshold marker as well as a ratio of B-CLL cell to internal T-cell median ZAP-70 staining.

RESULTS

Use of FACS Lysing Solution resulted in approximately fourfold increased separation between ZAP-70 positive T cells and negative B cells, when compared with the Fix & Perm kit. In B-CLL samples, ZAP-70 negative and positive B-cell expression could be clearly discerned.

CONCLUSIONS

FACS Lysing Solution is a simple procedure that markedly improves discrimination between ZAP-70 positive and negative cells.

ZAP70 expression assessed by immunohistochemistry on peripheral blood: a simple prognostic assay for patients with chronic lymphocytic leukemia

The somatic hypermutational (SHM) status of the immunoglobulin heavy-chain variable (IgVH) gene is a powerful prognostic factor in patients with chronic lymphocytic leukemia (CLL). However, IgVH SHM analysis is not well-suited to routine use in the clinical diagnostic laboratory. ZAP70 expression is a potential surrogate for the absence of SHM. Given the current problems with the standardization of ZAP70 assessment by flow cytometry, we sought an alternative approach, using immunohistochemistry (IHC). The utility of IHC is largely restricted to tissues, precluding its routine application to most patients with CLL who are typically diagnosed based upon peripheral blood (PB) findings. Accordingly, we developed an IHC assay that can be performed on PB. Enriched PB mononuclear cells from 29 patients with CLL were analyzed for ZAP70 expression by IHC on paraffin-embedded cell blocks, using standard techniques. IgVH SHM analysis was performed on all cases, and clinical features recorded. Seventeen specimens (59%) were negative for ZAP70 expression and 12 (41%) were positive for ZAP70 expression. SHM was evident in 20 specimens (69%), and absent in 9 (31%). Seventy-six percent of the specimens (22/29) displayed "concordant" ZAP70 and SHM results, in that 15 (52%) were SHM-positive/ZAP70 negative, whereas 7 (24%) were SHM-negative/ZAP70 positive. ZAP70 expression in this small cohort correlated with poor clinical outcome. Importantly, IHC analysis of ZAP70 in PB is a simple, reliable, robust assay that may have a valuable role in the routine clinical laboratory assessment of patients with CLL.

Flow cytometry for ZAP-70: New colors for chronic lymphocytic leukemia

ZAP-70 has become one of the most studied prognostic markers in Chronic Lymphocytic Leukemia (CLL). ZAP-70 is remarkable in many ways: ZAP-70 has been identified as the best discriminating gene between prognostically distinct CLL subtypes using large scale gene expression profiling; ZAP-70 has been shown to enhance signal transduction in CLL B-cells and therefore could contribute to disease progression; and ZAP-70 is one of the rare examples of an intracellular target considered for clinical flow cytometry. This issue attests to the enormous effort and the steady progress made in overcoming technical challenges of testing for ZAP-70 expression and sets the foundation for a successful translation of this important marker into clinical practice. Despite the best effort, one will likely have to accept that not all cases can be clearly assigned to one or the other group, given that ZAP-70 expression between CLL patients falls along a continuum from absent to high. Nevertheless, ZAP-70 expression could become a key parameter to guide patients towards risk adapted treatment strategies in prospective clinical trials.

ZAP-70 expression in B-cell chronic lymphocytic leukemia: evaluation by external (isotypic) or internal (T/NK cells) controls and correlation with IgV(H) mutations

BACKGROUND

Expression of T cell specific zeta-associated protein 70 (ZAP-70) by B-cell chronic lymphocytic leukemia (B-CLL) cells, as investigated by flow cytometry, has both prognostic relevance and predictive power as surrogate for immunoglobulin heavy chain variable region (IgV(H)) mutations, although a standardization of the cytometric protocol is still lacking.

METHODS

Flow cytometric analyses for ZAP-70 were performed in peripheral blood samples from 145 B-CLL (124 with IgV(H) mutations) by a standard three-color protocol. Identification of ZAP-70(+) cell population was based on an external negative control, i.e., the isotypic control (ISO method) or an internal positive control, i.e., the population of residual normal T/NK cells (TNK method). A comparison between these two approaches was performed.

RESULTS

While 86/145 cases were concordant as for ZAP-70 expression according to the two methods (ISO(+)TNK(+) or ISO(-)TNK(-)), 59/145 cases had discordant ZAP-70 expression, mainly (56/59) showing a ISO(+)TNK(-) profile. These latter cases express higher levels of ZAP-70 in their normal T cell component. Moreover, discordant ISO(+)TNK(-) cases had a IgV(H) gene mutation profile similar to that of concordantly positive cases and different from ZAP-70 concordantly negative B-CLL.

CONCLUSION

Analysis of ZAP-70 expression by B-CLL cells by using the ISO method allows to overcome the variability in the expression of ZAP-70 by residual T cells and yields a better correlation with IgV(H) gene mutations. A receiver operating characteristic analysis suggests to employ a higher cut-off than the commonly used 20%. A parallel evaluation of the prognostic value of ZAP-70 expression, as determined according to the ISO and TNK methods, is still needed.

Discordant results of flow cytometric ZAP-70 expression status in B-CLL samples if different gating strategies are applied

BACKGROUND

Recent studies have identified ZAP-70 expression status as an excellent prognostic parameter in chronic lymphocytic leukemia (CLL). ZAP-70 expression can be determined by direct antibody staining followed by flow cytometric analysis. However, there are currently several different gating strategies for analysis. We compared those strategies for ZAP-70 expression analysis.

METHODS

One hundred and one patients with B-CLL were analyzed employing a directly labeled alexa-fluor-488-ZAP-70-antibody. In 27 cases, we additionally measured and analyzed ZAP-70 expression, together with healthy controls as described previously.

RESULTS

Applying either T-/NK-cell isotype or healthy control analysis strategies on patient samples that were processed in parallel revealed discrepant results in 48% (12/25) of all cases. Taken together with the 74 B-CLL patients, who were analyzed with regard to average reference values, disconcordant results were obtained in 58% of the samples. We demonstrate that high variances in ZAP-70 T-/NK-cell staining within B-CLL patients, paired with a close proximity of ZAP-70 B-cell values to the suggested cut-off levels, may lead to interpretation difficulties of ZAP-70 status.

CONCLUSIONS

We conclude that different gating strategies for determining flow cytometric ZAP-70 expression status produce highly discordant results. Further standardization is required before ZAP-70 can be used as a reliable prognostic parameter in immunophenotyping of B-CLL.

Chronic lymphocytic leukemia: biology and current treatment

There has been considerable recent progress in understanding of the biology of chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL). These accomplishments have been accompanied by progressive improvement in the management of CLL and its complications. This review summarizes these changes and provides guidelines for a comprehensive approach to patient care.

What is ZAP-70?

Zap-70, a crucial molecule for the selective activation of T cells, through its interaction with the zeta chain of the TCR/CD3 complex, is a tyrosine kinase. This well studied molecule has gained a renewed interest upon the demonstration of its transduction and expression in B cells from patients with chronic lymphocytic leukemia. Here the major characteristics of this cytosolic protein are reviewed, as well as its expression in various cell types and some indications about its detection.

Evaluation of ZAP-70 expression by flow cytometry in chronic lymphocytic leukemia: A multicentric international harmonization process

The clinical course of patients with chronic lymphocytic leukemia (CLL) is heterogeneous with some patients requiring early therapy whereas others will not be treated for years. The evaluation of an individual CLL patient's prognosis remains a problematic issue. The presence or absence of somatic mutations in the IgVH genes is currently the gold-standard prognostic factor, but this technique is labor intensive and costly. Genomic studies uncovered that 70 kDa zeta-associated protein (ZAP-70) expression was associated with unmutated IgVH genes and ZAP-70 protein expression was proposed as a surrogate for somatic mutational status. Among the available techniques for ZAP-70 detection, flow cytometry is most preferable as it allows the simultaneous quantification of ZAP-70 protein expression levels in CLL cells and residual normal lymphocyte subsets. However, several factors introduce variability in the results reported from different laboratories; these factors include the anti-ZAP-70 antibody clone and conjugate, the staining procedure, the gating strategy, and the method of reporting the results. The need for standardization of the approach led to the organization of an international working group focused on harmonizing all aspects of the technique. During this workshop, a technical consensus was reached on the methods for cell permeabilization and immunophenotyping procedures. An assay was then designed that allowed comparison of two clones of anti-ZAP-70 antibody and the identification of the expression of this molecule in B, T, and NK cells identified in a four multicolor analysis. This procedure was applied to three stabilized blood samples, provided by the UK NEQAS group to all participating members of this study, in order to minimize variability caused by sample storage and shipment. Analysis was performed in 20 laboratories providing interpretable data from 14 centers. Various gating strategies were used and the ZAP-70 levels were expressed as percentage positive (POS) relative to isotype control or normal B-cells or normal T-cells; in addition the levels were reported as a ratio of expression in CLL cells relative to T-cells. The reported level of ZAP-70 expression varied greatly depending on the antibody and the method used to express the results. The CLL/T-cell ZAP-70 expression ratio showed a much lower interlaboratory variation than other reporting strategies and is recommended for multicenter studies. Stabilization results in decreased expression of CD19 making gating more difficult and therefore stabilized samples are not optimal for multicentric analysis of ZAP-70 expression. We assessed the variation of ZAP-70 expression levels in fresh cells according to storage time, which demonstrated that ZAP-70 is labile but sufficiently stable to allow comparison using fresh samples distributed between labs in Europe. These studies have demonstrated progress toward a consensus reporting procedure, and further work is underway to harmonize the preparation and analysis procedures.

CD38 expression labels an activated subset within chronic lymphocytic leukemia clones enriched in proliferating B cells

Chronic lymphocytic leukemia (CLL) cells are thought to have diminished cell-cycling capacity, a view challenged by their phenotypic resemblance to activated human B lymphocytes. The present study addresses the cell-cycling status of CLL cells, focusing on those leukemic cells expressing CD38, a molecule involved in signaling and activation that also serves as a prognostic marker in this disease. CD38(+) and CD38(-) members of individual CLL clones were analyzed for coexpression of molecules associated with cellular activation (CD27, CD62L, and CD69), cell-cycle entry (Ki-67), signaling (ZAP-70), and protection from apoptosis (telomerase and Bcl-2). Regardless of the size of the CD38(+) fraction within a CLL clone, CD38(+) subclones are markedly enriched for expression of Ki-67, ZAP-70, human telomerase reverse transcriptase, and telomerase activity. Although the percentage of cells (approximately 2%) entering the cell cycle as defined by Ki-67 expression is small, the absolute number within a clone can be sizeable and is contained primarily within the CD38(+) fraction. Despite these activation/proliferation differences, both CD38(+) and CD38(-) fractions have similar telomere lengths, suggesting that CD38 expression is dynamic and transient. These findings may help explain why high percentages of CD38(+) cells within clones are associated with poor clinical outcome.

The normal counterpart to the chronic lymphocytic leukemia B cell

Chronic lymphocytic leukemia (CLL) is characterized by the monoclonal expansion of small mature-looking B cells that accumulate in the blood, marrow, and lymphoid organs, and have a remarkable phenotypic homogeneity. By definition, CLL cells co-express CD5 and CD23 with faint to undetectable amounts of monoclonal surface immunoglobulins (sIg). The concept of phenotypic homogeneity has been reinforced by gene expression profiling data, which suggest that the pathogenesis of CLL has to be associated with a fairly common mechanism of transformation. In recent years the biology of CLL has been enriched by an unprecedented flurry of new observations that are leading to a better understanding of the natural history of the disease. Still CLL cells have so far defied any attempt to satisfactorily answer the simple time-honored question of what their cell of origin is. It is the purpose of this review to discuss the features a cell must possess to be considered with reasonable approximation the normal counterpart of a CLL B cell.

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.

ZAP70 in chronic lymphocytic leukaemia

The protein tyrosine kinase zeta-chain associated protein kinase (ZAP70), normally expressed in T cells and a subset of B cells, is solely expressed in poor prognosis chronic lymphocytic leukaemia and implicated in enhanced B cell receptor signalling. As a result, the expression of this protein provides an ideal prognostic marker for the disease. A previous study has shown differential CpG methylation of a 5' region of ZAP70 in leukaemic lymphoid cells, although no further epigenetic studies have been reported. Further investigation into the expression of ZAP70 may therefore provide targets for therapies.

Update on risk-stratified management for chronic lymphocytic leukemia

Major recent advances in understanding the biology of chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL) have improved clinical evaluation and influenced treatment decisions. CLL can be diagnosed early and accurately, and biological measurements can be used to predict a prognosis at diagnosis. Individual patient care can be risk stratified to optimize benefit and minimize complications of therapy. Purine analogs and monoclonal antibodies have markedly improved the efficacy of initial therapy but are not curative. The treatment of relapsed and refractory CLL is less successful. However, recent developments suggest that allogeneic stem cell transplant could have a larger role in a selected group of these patients. Potential new treatment modalities include targeted molecules that interrupt key components of CLL cell survival pathways, and active and passive immunotherapy. The management of CLL is in a dynamic phase of rapid evolution. Risk stratification using biological prognostic markers can improve current patient care and direct future clinical research.