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Disease progression in B-cell chronic lymphocytic leukaemia (B-CLL) is determined by the interplay between proliferation kinetics in the proliferating compartment and cell death in the accumulating compartment. Improving our knowledge of cell cycle regulation in B-CLL cells might therefore be important for identifying therapeutic targets. Cyclin E was detected by Western blotting in purified B-CLL cells from peripheral blood samples of all 12 patient tested but not in normal peripheral blood B cells. While cyclin-dependent kinase 2 (cdk2) expression was similar in different samples, p27 and cyclin E expression was highly variable. We further investigated the regulation of p27, cyclin E and cdk2 in an in vitro model of cycling B-CLL cells. Cyclin E and cdk2 expression was increased in B-CLL cells stimulated with a CpG-oligodeoxynucleotide and interleukin-2, while p27 expression rapidly declined. This was accompanied by the increased formation of cyclin E–cdk2 complexes, which were able to phosphorylate Histone H1 in vitro. Pharmacological inhibition of cdk2 activity with Roscovitine-inhibited thymidine incorporation and Histone H1 phosphorylation. We conclude that further evaluation of cyclin E and p27 in peripheral blood cells might help to identify prognostic subgroups. In addition, inhibition of Cyclin E–cdk2 activity by Roscovitine might be a new therapeutic strategy in B-CLL. [ABSTRACT FROM AUTHOR]

The treatment results of indolent lymphoid malignancies in Chinese are poorly reported. The efficacy of FND (fludarabine 25 mg/m2/d, ×3; mitoxantrone 10 mg/m2/d, ×1; dexamethasone 20 mg/d, ×5; monthly cycles, ×6) in 95 Chinese patients with indolent B-cell malignancies (at diagnosis: 55, relapse/refractory disease: 40) and nine Chinese patients with T-cell large granular lymphocyte leukaemia (T-LGL leukaemia) (at diagnosis: two, refractory disease: seven) was evaluated. For B-cell malignancies, the complete response (CR), partial response (PR) and overall response (OR) rates were 50·5%, 18% and 68·5% respectively. Better results were obtained for primary versus relapse/refractory disease (CR: 60% vs. 37·5%, P = 0·03; OR: 84% vs. 47·5%, P < 0·001; median progression-free survival (PFS): 44 months vs. 22 months; 2-year PFS: 66% vs. 47%, P = 0·039; overall survival (OS): not reached vs. 32%; 2-year OS: 92% vs. 58%, P < 0·001). Responsive patients (CR/PR) had a better median PFS (44 months vs. 5 months, P < 0·001) and OS (67 months vs. 13 months, P < 0·001) than unresponsive patients. For T-LGL leukaemia, the CR and molecular-remission rates were 56% and 67% (median follow-up: 23 months). FND is an active regimen for the treatment of indolent B- and T-cell malignancies in Chinese patients, with results comparable with Western patients with similar indolent lymphomas. [ABSTRACT FROM AUTHOR]

B-cell chronic lymphocytic leukaemia (B-CLL) is a neoplastic disorder characterized by defective apoptosis, cell accumulation in G0/G1, and high expression of BCL2 oncogene. Intracellular cyclic adenosine monophosphate (cAMP) accumulation increases the chemosensitivity of B-CLL cells in vitro and in vivo. In the present study, we investigated the effects of β2-adrenergic compounds, well known cAMP-inducing drugs, on the in vitro survival of leukaemia cells. In contrast to the short-acting β2-mimetic (β2Mim) salbutamol, a consistent pro-apoptotic effect was observed with the long-acting β2Mim salmeterol and formoterol. Normal B cells isolated from control donors were totally resistant to the above molecules. These compounds also increased chlorambucil- and fludarabine-induced death of B-CLL cells. Blockade of β-adrenergic receptor signalling or cAMP did not alter B-CLL apoptosis with β2 Mimagents. Leukaemia cell apoptosis by β2Mim correlated with an increase in calcium influx, decreased bcl-2 protein and mRNA levels, increase in BAX gene expression and a marked rise in BCL2/BAX mRNA ratios. Interleukin-4, a cytokine that increases bcl-2 expression in B-CLL cells, rescued leukaemia cell from apoptosis with β2Mim. These data show that long-acting β2-adrenergic agents promote apoptotic leukaemia cell death through an adrenoreceptor- and cAMP-independent, Ca2+-dependent mechanism. [ABSTRACT FROM AUTHOR]

Summary: Undetectable measurable residual disease (MRD) is associated with favourable clinical outcomes in chronic lymphocytic leukaemia (CLL). While assessment is commonly performed using multiparameter flow cytometry (MFC), this approach is associated with limitations including user bias and expertise that may not be widely available. Implementation of unsupervised clustering algorithms in the laboratory can address these limitations and have not been previously reported in a systematic quantitative manner. We developed a computational pipeline to assess CLL MRD using FlowSOM. In the training step, a self‐organising map was generated with nodes representing the full breadth of normal immature and mature B cells along with disease immunophenotypes. This map was used to detect MRD in multiple validation cohorts containing a total of 456 samples. This included an evaluation of atypical CLL cases and samples collected from two different laboratories. Computational MRD showed high correlation with expert analysis (Pearson's r > 0.99 for typical CLL). Binary classification of typical CLL samples as either MRD positive or negative demonstrated high concordance (>98%). Interestingly, computational MRD detected disease in a small number of atypical CLL cases in which MRD was not detected by expert analysis. These results demonstrate the feasibility and value of automated MFC analysis in a diagnostic laboratory. [ABSTRACT FROM AUTHOR]

Summary: Chronic lymphocytic leukaemia (CLL) is characterised by malignant mature‐like B cells. Supportive to CLL cell survival is chronic B‐cell receptor (BCR) signalling; however, emerging evidence demonstrates CLL cells proliferate in response to T‐helper (Th) cells in a CD40L‐dependent manner. We showed provision of Th stimulation via CD40L upregulated CD45 phosphatase activity and BCR signalling in non‐malignant B cells. Consequently, we hypothesised Th cell upregulation of CLL cell CD45 activity may be an important regulator of CLL BCR signalling and proliferation. Using patient‐derived CLL cells in a culture system with activated autologous Th cells, results revealed increases in both Th and CLL cell CD45 activity, which correlated with enhanced downstream antigen receptor signalling and proliferation. Concomitantly increased was the surface expression of Galectin‐1, a CD45 ligand, and CD43, a CLL immunophenotypic marker. Galectin‐1/CD43 double expression defined a proliferative CLL cell population with enhanced CD45 activity. Targeting either Galectin‐1 or CD43 using silencing, pharmacology, or monoclonal antibody strategies dampened CD45 activity and CLL cell proliferation. These results highlight a mechanism where activated Th cells drive CLL cell BCR signalling and proliferation via Galectin‐1 and CD43‐mediated regulation of CD45 activity, identifying modulation of CD45 phosphatase activity as a potential therapeutic target in CLL. [ABSTRACT FROM AUTHOR]

Summary: Non‐Hodgkin lymphoma (NHL) is the sixth most common cancer in Sub‐Saharan Africa (SSA). Comprehensive diagnostics of NHL are essential for effective treatment. Our objective was to assess the frequency of NHL subtypes, disease stage and further diagnostic aspects. Eleven population‐based cancer registries in 10 countries participated in our observational study. A random sample of 516 patients was included. Histological confirmation of NHL was available for 76.2% and cytological confirmation for another 17.3%. NHL subclassification was determined in 42.1%. Of these, diffuse large B cell lymphoma, chronic lymphocytic leukaemia and Burkitt lymphoma were the most common subtypes identified (48.8%, 18.4% and 6.0%, respectively). We traced 293 patients, for whom recorded data were amended using clinical records. For these, information on stage, human immunodeficiency virus (HIV) status and Eastern Cooperative Oncology Group Performance Status (ECOG PS) was available for 60.8%, 52.6% and 45.1%, respectively. Stage at diagnosis was advanced for 130 of 178 (73.0%) patients, HIV status was positive for 97 of 154 (63.0%) and ECOG PS was ≥2 for 81 of 132 (61.4%). Knowledge about NHL subclassification and baseline clinical characteristics is crucial for guideline‐recommended treatment. Hence, regionally adapted investments in pathological capacity, as well as standardised clinical diagnostics, will significantly improve the therapeutic precision for NHL in SSA. [ABSTRACT FROM AUTHOR]

The article discusses a study on the use of oral small molecule inhibitor of Bruton tyrosine kinase ibrutinib as an effective treatment for rare aggressive, mature lymphoid neoplasm B-cell prolymphocytic leukemia (B-PLL). Topics include characteristics of B-PLL, results of two patients with B-PLL who responded to therapy with single agent ibrutinib, the need to consider ibrutinib for upfront therapy of B-PLL.

Summary Human cluster of differentiation (CD) antigen 19 is a B cell-specific surface antigen and an attractive target for therapeutic monoclonal antibody (mAb) approaches to treat malignancies of B cell origin. MEDI-551 is an affinity-optimized and afucosylated CD19 mAb with enhanced antibody-dependent cellular cytotoxicity (ADCC). The results from in vitro ADCC assays with Natural Killer cells as effector cells, demonstrate that MEDI-551 is effective at lower mAb doses than rituximab with multiple cell lines as well as primary chronic lymphocytic leukaemia and acute lymphoblastic leukaemia samples. Targeting CD19 with MEDI-551 was also effective in several severe combined immunodeficiency lymphoma models. Furthermore, the combination of MEDI-551 with rituximab resulted in prolonged suppression of tumour growth, demonstrating that therapeutic mAbs with overlapping effector function can be combined for greater tumour growth inhibition. Together, the data demonstrate that MEDI-551 has potent antitumour activity in preclinical models of B cell malignancies. The results also suggest that the combination of the ADCC-enhanced CD19 mAb with an anti-CD20 mAb could be a novel approach for the treatment of B cell lymphomas. [ABSTRACT FROM AUTHOR]

The article reports on the use of CpG oligodeoxynucleotides (CpG) in clinical laboratories as a mitogenic tool to reveal chromosomal abnormalities in malignant B-cells from chronic lymphocytic leukemia (CLL) patients . It reports on a study conducted to validate the role of CpG in revealing cytogenetic abnormalities in CLL B-cells. It also reports on a study conducted to validate whether CpG stimulated B-cells.

We report the cloning and characterization of a novel 54-kDa high-mobility group (HMG)-box protein as the ligand for the human pan-B cell co-receptor CD19 (CD19-L), which interacts with the extracellular domain of CD19 in trans. CD19-L is the first CD19-specific recombinant human protein with potent anti-leukaemic activity against B-lineage acute lymphoblastic leukaemia (ALL), the most common form of childhood cancer and the second most common form of acute leukaemia in adults. Soluble recombinant CD19-L protein exhibited exquisite specificity for the extracellular domain of CD19 and strong binding to the surface of B-lineage leukaemia/lymphoma cells. Engagement of CD19 co-receptor on B-lineage ALL cells with CD19-L perturbed the CD19-associated signalling network, altering the expression levels of multiple genes directly involved in regulation of apoptosis, and triggered rapid apoptotic cell death in a CD19-specific manner. The identification of human CD19-L may lead to therapeutic innovation for B-lineage ALL and other B-lineage lymphoid malignancies as well as B-cell lymphoproliferative states and systemic autoimmunity. [ABSTRACT FROM AUTHOR]

Interphase fluorescent in situ hybridization (FISH) was applied on diagnostic BM smears from 519 children with acute lymphoblastic leukaemia (ALL) in order to establish the frequency and prognostic importance of 9p21 deletion in children enrolled in the Nordic Society of Paediatric Haematology and Oncology (NOPHO) - 2000 treatment protocol. Among the patients, 452 were diagnosed with B-cell precursor (BCP)-ALL and 66 with T-ALL. A higher incidence of 9p21 deletions was found in T-ALL (38%) compared to BCP-ALL (15·7%). Homozygous deletions were found in 19·7% of T-ALL and 4·0% of BCP-ALL; hemizygous deletions were found in 18·2% and 11·7% respectively. In our series, 9p21 deletions were detected in all age groups with a steady rise in the frequency with age. There was no significant difference in outcome between cases with or without 9p21 deletion or between cases with hemi- or homozygous deletions of 9p21. In conclusion, in this large series of childhood ALL deletion of 9p21 was not associated with worse prognosis. However, interphase FISH deletion analysis of 9p21 could be used as a first step to detect unfavourable subtle cytogenetic aberrations such as the dic(9;20) rearrangement. [ABSTRACT FROM AUTHOR]

The effects of two CD20 antibodies, namely rituximab, the current standard for treatment of chronic lymphocytic leukaemia (CLL) in combination with chemotherapy, and GA101, a glyco-engineered type II antibody were compared on CLL cells ex vivo. Antibody-induced phosphatidylserine exposure was examined in isolated CLL cells. For a more comprehensive assessment of antibody-mediated cell killing including Fc-mediated mechanisms, B cell depletion from whole blood samples was monitored. Treatment with rituximab or GA101 reduced the average viability of isolated CLL cells by 6% or 11%, and the ratio of B to T cells in whole blood samples by 12% or 33%, respectively. Combination with GA101 enhanced the cytotoxicity of the chemotherapeutic agent chlorambucil on isolated CLL cells. CD20 surface expression on CLL cells correlated with GA101-induced B cell depletion, but not with direct cell death induction. Treatment of whole blood samples from CLL patients with a CpG-containing oligonucleotide increased CD20 expression on CLL cells and GA101-dependent B cell depletion. Despite the variable responses of individual CLL samples, the CLL cell depletion from whole blood by GA101 was consistently much stronger than by rituximab, which argues for clinical investigation of GA101 in CLL patients. [ABSTRACT FROM AUTHOR]

Richter syndrome (RS) represents the transformation of chronic lymphocytic leukaemia (CLL) to aggressive lymphoma. Risk factors of CLL transformation to RS are only partly known. We explored the role of the host genetic background as a risk factor for RS occurrence. Forty-five single nucleotide polimorphisms (SNPs) known to be relevant for CLL prognosis were genotyped in a consecutive cohort of 331 CLL, of which 21 had transformed to RS. After correcting for multiple testing and adjusting for previously reported RS risk factors, the LRP4 rs2306029 TT variant genotype was the sole SNP independently associated with a higher risk of RS transformation (Hazard Ratio: 4·17; P = 0·001; q = 0·047). The enrichment of LRP4 TT genotype in RS was confirmed in an independent series ( n = 44) used for validation purposes. The LRP4 protein was expressed in CLL ( n = 66). Bioinformatic analysis scored LRP4 rs2306029 as a variant with possible deleterious and damaging variant of LRP4. LRP4 genotyping may help the recognition of patients with increased risk of RS at the time of CLL diagnosis. [ABSTRACT FROM AUTHOR]

The clinical heterogeneity of B-cell chronic lymphocytic leukaemia (B-CLL) makes it necessary to identify potent prognostic indicators to predict individual clinical course and select risk-adapted therapy. In recent years, numerous gene expression models have been suggested as prognostic factors of B-CLL. Today, quantitative polymerase chain reaction (qPCR) is a preferred method for rapid quantification of gene expression and validation of microarray data. The reliability of qPCR data is highly dependent on the use of appropriate reference genes for normalization. To date, no validated reference genes have been reported for the normalization of gene expression in B-CLL. Therefore, the present study was conducted to identify suitable reference genes for gene expression studies in CD19+ B cells isolated from B-CLL patients' peripheral blood . The stability of ACTB, B2M, GAPDH, GUSB, HMBS, HPRT1, MRPL19, TBP and UBC genes was determined by three different descriptive statistics, geNorm, NormFinder and BestKeeper-1, which produced highly comparable results. Based on our results, B2M, HPRT1, and GUSB were found to be the most suitable reference genes for qPCR studies in B-CLL patients' peripheral blood B cells. [ABSTRACT FROM AUTHOR]

The presence of a dicentric chromosome dic(9;20) has been reported to have an unfavourable prognosis in children with B-cell precursor acute lymphoblastic leukaemia (BCP-ALL). As outcome may be influenced by type and composition of treatment, we analyzed 19 BCP-ALL patients with dic(9;20) who have been treated with ALL-BFM (Berlin-Frankfurt-Münster) protocols that included a 4-drug induction and subsequent consolidation therapy. All patients were good responders to prednisone and in complete remission after induction therapy. Eight patients had no molecular disease after induction and another eight patients had levels ≤10−4 after consolidation therapy. After a median follow-up of 3·4 years, probabilities of 5-year event-free and overall survival were 75 ± 11% and 94 ± 6%, respectively. Of note, there was a tendency for extramedullary disease in case of relapse (two of three relapses with central nervous system involvement). In conclusion, in the context of ALL-BFM protocols dic(9;20)-positivity appeared to have a favourable prognosis, which could be due to a dose- and time-intensified induction and induction consolidation therapy. Given that in vitro studies have shown high cellular sensitivity of dic(9;20)-positive leukemic blasts tol-asparaginase and cytarabine, it is reasonable to speculate that both drugs, as given early during BFM-like induction and consolidation therapy, may have contributed to this good outcome. [ABSTRACT FROM AUTHOR]

We have previously shown an expansion of cytotoxic antigen-experienced CD4+T cells (CTLs) that express perforin (PF) in the peripheral blood of patients with B cell chronic lymphocytic leukaemia (B-CLL). Increased frequencies of CD4+CTLs have since been attributed to chronic viral infections, particularly, human cytomegalovirus (HCMV). The present study examined the involvement of CD4+CTLs in responses to HCMV in B-CLL, and characterized their differentiation. We studied 36 HCMV seropositive (SP) and seronegative B-CLL patients and 20 healthy age-matched individuals. The HCMV reactivity of CD4+PF+ and CD4+PF− cells was determined by interferon-gamma expression, and expression of CD45RA and CCR7 was assessed by flow cytometry. Fluorescence in-situ hybridization was used to measure relative telomere lengths. CD4+PF+T cell expansion in B-CLL patients and controls was strongly associated with HCMV seropositivity. CD4+PF+ compared to CD4+PF− cells from SP B-CLL patients elicited major histocompatibility complex (MHC) class II-restricted responses to HCMV. CD4+PF+T cells from patients and controls were enriched with highly differentiated T-effector/memory (CCR7−) and revertant (CCR7−CD45RA+) phenotype. CD4+PF+T cells from B-CLL patients had shorter telomeres than CD4+PF−T cells, indicating an extensive replicative history. We conclude that persistent exposure to HCMV antigens in SP B-CLL patients leads to an expansion of the circulating MHC class II-restricted CD4+PF+T cell population with effector/memory phenotype. [ABSTRACT FROM AUTHOR]

It was hypothesized that contact between chronic lymphocytic leukaemia (CLL) B-cells and marrow stromal cells impact both cell types. To test this hypothesis, we utilized a long-term primary culture system from bone biopsies that reliably generates a mesenchymal stem cell (MSC). Co-culture of MSC with CLL B-cells protected the latter from both spontaneous apoptosis and drug-induced apoptosis. The CD38 expression in previously CD38 positive CLL B-cells was up-regulated with MSC co-culture. Upregulation of CD71, CD25, CD69 and CD70 in CLL B-cells was found in the co-culture. CD71 upregulation was more significantly associated with high-risk CLL, implicating CD71 regulation in the microenvironment predicting disease progression. In MSC, rapid ERK and AKT phosphorylation (within 30 min) were detected when CLL B-cells and MSC were separated by transwell; indicating that activation of MSC was mediated by soluble factors. These findings support a bi-directional activation between bone marrow stromal cells and CLL B-cells. [ABSTRACT FROM AUTHOR]

The transcription factor Pax5 plays a critical role in B cell development. It has been shown that alternative splicing of its gene ( PAX5) produces several distinct transcripts that modify the amino acid sequence of the putative Pax5 proteins. Subsequent studies have attempted to correlate the expression of PAX5 isoforms with certain B-cell lymphomas, the conclusions of which suggest that altered isoform expression is involved in lymphomagenesis. However, in the absence of definitive data for PAX5 isoform expression patterns in normal B cells it is difficult to confirm whether aberrant isoform expression can indeed be correlated with disease. Using a high-resolution method of analysis of reverse transcription polymerase chain reaction products, we sought to analyse the expression of the different PAX5 isoforms in normal B-cells as well as a number of B-cell lymphoma and chronic lymphocytic leukaemia cases. It was found that multiple PAX5 isoforms were expressed in both normal and malignant B cells. Immunodetection and polysomal RNA analyses also confirmed that the different PAX5 mRNAs were translated into their corresponding proteins. No consistent deregulation of PAX5 isoform expression was observed in B-cell lymphomas, but rather, complex isoform expression patterns were found in normal B cell as well as B-cell lymphoma and CLL cases. [ABSTRACT FROM AUTHOR]

Although biological similarities have been described among monoclonal B-cell lymphocytosis (MBL) and chronic lymphocytic leukaemia (CLL), the relationships between these two conditions are not fully understood, and new epidemiological studies in different populations and different countries continue to be reported. Here, we investigated 167 first-degree relatives from 42 families of patients with non-familial (sporadic) CLL, using four-colour flow cytometry. MBL was found in seven of 167 subjects (4·1%). Monoclonality was detected in all cases either by light-chain restriction or by polymerase chain reaction. Fluourescence in situ hybridization did not show any chromosomal abnormality. The prevalence of MBL according to age was 0 (0/54) in individuals aged less than 40 years, 2·5% (2/81) between 40 and 60 years, and 15·6% (5/32) in individuals over 60 years. The prevalence of MBL cases in individuals over 60 years was similar to that found in familial CLL relatives at the same age group. This suggests that in older first-degree relatives of patients with sporadic CLL, the risk of MBL detection is as high as in older first-degree relatives from CLL families, which could render these individuals belonging to ‘sporadic CLL families’ as susceptible as individuals from ‘familial CLL’ to the development of clinical CLL. [ABSTRACT FROM AUTHOR]

Monoclonal B-cell lymphocytosis (MBL) is an asymptomatic monoclonal expansion of <5·0 × 109/l circulating CLL-phenotype B-cells. The relationship between MBL and Rai 0 CLL, as well as the impact of biological risk factors on MBL prognosis, are unknown. Out of 460 B-cell expansions with CLL-phenotype, 123 clinical MBL (cMBL) were compared to 154 Rai 0 CLL according to clinical and biological profile and outcome. cMBL had better humoral immune capacity and lower infection risk, lower prevalence of del11q22-q23/del17p13 and TP53 mutations, slower lymphocyte doubling time, and longer treatment-free survival. Also, cMBL diagnosis was a protective factor for treatment risk. Despite these favourable features, all cMBL were projected to progress, and lymphocytes <1·2 × 109/l and >3·7 × 109/l were the best thresholds predicting the lowest and highest risk of progression to CLL. Although IGHV status, CD38 and CD49d expression, and fluorescence in situ hybridization (FISH) karyotype individually predicted treatment-free survival, multivariate analysis identified the presence of +12 or del17p13 as the sole independent predictor of treatment requirement in cMBL (Hazard ratio: 5·39, 95% confidence interval 1·98–14·44, P = 0·001). Overall, these data showed that cMBL has a more favourable clinical course than Rai 0 CLL. Given that the biological profile can predict treatment requirement, stratification based on biological prognosticators may be helpful for cMBL management. [ABSTRACT FROM AUTHOR]

The effect of CMC-544, a calicheamicin-conjugated anti-CD22 monoclonal antibody, was analysed in relation to CD22 and P-glycoprotein (P-gp) in B-cell chronic lymphocytic leukaemia (CLL) and non-Hodgkin lymphoma (NHL) in vitro. The cell lines used were CD22-positive parental Daudi and Raji, and their P-gp positive sublines, Daudi/MDR and Raji/MDR. Cells obtained from 19 patients with B-cell CLL or NHL were also used. The effect of CMC-544 was analysed by viable cell count, morphology, annexin-V staining, and cell cycle distribution. A dose-dependent, selective cytotoxic effect of CMC-544 was observed in cell lines that expressed CD22. CMC-544 was not effective on Daudi/MDR and Raji/MDR cells compared with their parental cells. The MDR modifiers, PSC833 and MS209, restored the cytotoxic effect of CMC-544 in P-gp-expressing sublines. In clinical samples, the cytotoxic effect of CMC-544 was inversely related to the amount of P-gp ( P = 0·003), and to intracellular rhodamine-123 accumulation ( P < 0·001). On the other hand, the effect positively correlated with the amount of CD22 ( P = 0·010). The effect of CMC-544 depends on the levels of CD22 and P-gp. Our findings will help to predict the clinical effectiveness of this drug on these B-cell malignancies, suggesting a beneficial effect with combined use of CMC-544 and MDR modifiers. [ABSTRACT FROM AUTHOR]

B-cell chronic lymphocytic leukaemia (B-CLL) cells display low amounts of surface immunoglobulins (sIg). To investigate the mechanisms underlying this phenomenon, we performed a thorough study of surface and intracellular expression of the B-cell receptor (BCR) components in B-CLL cells using flow cytometry. There was an heterogeneous pattern of expression. Overall, 20 of 22 samples showed reduced sIgM levels, compared with normal B cells. Among them, three (15%) had very low to undetectable intracellular IgM levels and variable amounts of CD79a and CD79b; nine (45%) had low intracellular CD79b levels but appreciable levels of IgM and CD79a; and eight (40%) had relatively normal intracellular levels of all BCR components. To investigate whether surface BCR levels could be controlled by the rate of CD79b synthesis, adenoviral vectors encoding CD79b were generated and used for gene transfer experiments. Delivery of CD79b to non-B cells transfected with IgM and CD79a lead to high-level expression of a functional BCR. Moreover, CD79b gene transfer in a B cell line derived from a B-CLL patient and characterised by low intracellular levels of endogenous CD79b consistently increased sIgM levels. These findings indicate that the phenotype of B-CLL cells in a subset of patients may depend primarily on poor CD79b expression, and suggest that upregulation of CD79b expression may correct the phenotype of these cells. [ABSTRACT FROM AUTHOR]