Diagnostic criteria for monoclonal B-cell lymphocytosis

Using gene co-expression network analysis to predict biomarkers for chronic lymphocytic leukemia

BACKGROUND

Chronic lymphocytic leukemia (CLL) is the most common adult leukemia. It is a highly heterogeneous disease, and can be divided roughly into indolent and progressive stages based on classic clinical markers. Immunoglobin heavy chain variable region (IgVH) mutational status was found to be associated with patient survival outcome, and biomarkers linked to the IgVH status has been a focus in the CLL prognosis research field. However, biomarkers highly correlated with IgVH mutational status which can accurately predict the survival outcome are yet to be discovered.

RESULTS

In this paper, we investigate the use of gene co-expression network analysis to identify potential biomarkers for CLL. Specifically we focused on the co-expression network involving ZAP70, a well characterized biomarker for CLL. We selected 23 microarray datasets corresponding to multiple types of cancer from the Gene Expression Omnibus (GEO) and used the frequent network mining algorithm CODENSE to identify highly connected gene co-expression networks spanning the entire genome, then evaluated the genes in the co-expression network in which ZAP70 is involved. We then applied a set of feature selection methods to further select genes which are capable of predicting IgVH mutation status from the ZAP70 co-expression network.

CONCLUSIONS

We have identified a set of genes that are potential CLL prognostic biomarkers IL2RB, CD8A, CD247, LAG3 and KLRK1, which can predict CLL patient IgVH mutational status with high accuracies. Their prognostic capabilities were cross-validated by applying these biomarker candidates to classify patients into different outcome groups using a CLL microarray datasets with clinical information.

Differentiating chronic lymphocytic leukemia from monoclonal B-lymphocytosis according to clinical outcome: on behalf of the GIMEMA chronic lymphoproliferative diseases working group

BACKGROUND

Optimal lymphocyte parameters and thresholds for the diagnosis of chronic lymphocytic leukemia have been proposed by The National Cancer Institute sponsored Working Group and recently updated by the International Workshop on chronic lymphocytic leukemia. However, it is not clear how these criteria apply to patient management in daily clinical practice and whether the lymphocyte thresholds recommended truly predict clinical outcome in early chronic lymphocytic leukemia.

DESIGN AND METHODS

For the purpose of this study, an observational database of the GIMEMA (Gruppo Italiano Malattie Ematologiche dell'Adulto) which included 1,158 patients with newly diagnosed Binet stage A chronic lymphocytic leukemia who were observed at different primary hematology centers during the period 1991-2000, was used.

RESULTS

Among 818 consecutive chronic lymphocytic leukemia patients with Rai stage 0 (i.e. no palpable lymphadenopathy or hepatosplenomegaly) who had flow cytometry evaluations at the time of diagnosis and were included in a GIMEMA database, both absolute lymphocyte count and B-cell count were of a similar value in predicting time to first treatment as continuous variables (P<0.0001). Receiver operating characteristic analysis identified an absolute lymphocyte count of 11.5×10(9)/L and an absolute B-cell count of 10.0×10(9)/L as the best thresholds capable of identifying patients who will require treatment from those with stable disease. However, in a Cox's multivariate analysis only the B-cell count retained its discriminating power (P<0.0001) and the estimated rate of progression to chronic lymphocytic leukemia requiring treatment among subjects with a B-cell count less than 10.0×10(9)/L was approximately 2.3% per year (95% CI 2.1-2.5%) while it was 2-fold higher for patients with a B-cell count of 10.0×10(9)/L or over (i.e. 5.2% per year; 95% CI 4.9-5.5%). Finally, in this community-based patient cohort, the B-cell threshold defined by investigators at the Mayo Clinic (i.e. 11.0×10(9)/L) allowed patients to be divided into two subsets with a higher and lower likelihood of treatment (P<0.0001).

CONCLUSIONS

Our results, based on a retrospective patients' cohort, provide a clear justification to retain the B-cell count as the reference gold standard of chronic lymphocytic leukemia diagnosis and imply that a count of 10×10(9)/L B cells is the best lymphocyte threshold to predict time to first treatment. The use of clinical outcome to distinguish chronic lymphocytic leukemia from other premalignant conditions, such as monoclonal B-cell lymphocytosis, is a pragmatic approach meeting the patients' need to minimize the psychological discomfort of receiving a diagnosis of leukemia when the risk of adverse clinical consequences is low.

Common occurrence of monoclonal B-cell lymphocytosis among members of high-risk CLL families

Monoclonal B-cell lymphocytosis (MBL) is an asymptomatic haematological condition characterized by low absolute levels of B-cell clones with a surface immunophenotype similar to that of chronic lymphocytic leukaemia (CLL). In the general population, MBL increases with age with a prevalence of 5-9% in individuals over age 60 years. It has been reported to be higher among first-degree relatives from CLL families. We report results of multi-parameter flow cytometry among 505 first-degree relatives with no personal history of lymphoproliferative disease from 140 families having at least two cases of CLL. Seventeen percent of relatives had MBL. Age was the most important determinant where the probability for developing MBL by age 90 years was 61%. MBL clustered in certain families but clustering was independent of the number of known CLL cases in a family. As is the case with CLL, males had a significantly higher risk for MBL than did females (P = 0·04). MBL patients had significantly higher mean absolute lymphocyte counts (2·4 × 10(9) /l) and B-cell counts (0·53 × 10(9) /l) than those with a normal B-cell immuno-phenotype. Our findings show that MBL occurs at a very high rate in high risk CLL families. Both the age and gender distribution of MBL are parallel to CLL, implying a shared inherited risk.

Familial chronic lymphocytic leukemia

PURPOSE OF REVIEW

Families with multiple individuals affected with chronic lymphocytic leukemia (CLL) and other related B-cell tumors have been described in the literature and strong familial aggregation has been seen in population studies. However, predisposing germline mutations have not been identified. We will discuss the spectrum of conditions associated with CLL in families and the advances in identifying the underlying susceptibility genes.

RECENT FINDINGS

Familial CLL does not appear to differ substantially from sporadic CLL in terms of prognostic markers and clinical outcome, although it may be associated with more indolent disease. The precursor condition, monoclonal B-cell lymphocytosis, also aggregates in CLL families. Linkage studies have been conducted in high-risk CLL families to screen the whole genome for susceptibility loci but no gene mutations have yet been identified by this method. Association studies of candidate genes have implicated several genes as being important in CLL but more studies are needed. Results from whole-genome association studies are promising.

SUMMARY

The ability to conduct large-scale genomic studies in unrelated CLL patients and in high-risk CLL families will play an important role in detecting susceptibility genes for CLL over the next few years and thereby help to delineate causal pathways.

CLL-like monoclonal B-cell lymphocytosis: are we all bound to have it?

CLL-like monoclonal B-cell lymphocytosis (MBL) shares a unique immunophenotype with chronic lymphocytic leukemia (CLL), and represents the vast majority of clonal B-cell expansions found in the peripheral blood of otherwise healthy subjects. Along with the improvement of laboratory techniques and the widespread availability of multiparameter flow cytometry, the finding of tiny aberrant B-cell populations became more frequent, prompting the need for clinical and biological definition of the nature of this condition and its relationship with leukemia development. MBL seems to be a melting-pot containing several entities, identical in terms of phenotype but with extremely different risks of leukemia development (from low to none) that seem to correlate with the number of B lymphocytes. CLL-like MBL observed in the clinical setting ("Clinical MBL"), usually being characterized by lymphocytosis, demonstrated a sizeable, even if low (1.1-1.4% per year), risk of leukemic progression, but represents a minority of all MBL cases. The vast majority of CLL-like MBL are detected in general population screenings and do not likely have a risk of CLL that is substantially higher than that of unaffected individuals. Interestingly, MBL frequency increases with age, being virtually undetectable under 40 years of age but being present in 50-75% of the people older than 90 years. It has been proposed that MBL could be interpreted as an epiphenomenon of a chronic and persistent antigenic stimulation. The (rare) possibility to evolve into a frank leukemia might then depend on biological and molecular factors insofar unknown that may modify the modality of cell reaction as well as the potential to acquire further genetic abnormalities. Therefore, the real challenge of the next years in the MBL research field is not to increase the sensitivity of detection, neither to implement screening protocols to be applied to the general population, rather to unravel the biologic features that, at individual level, will identify those (few) cases that are at risk of developing a progressive disease.

T/NK large granular lymphocyte leukemia and coexisting monoclonal B-cell lymphocytosis-like proliferations. An unrecognized and frequent association

T-cell large granular lymphocyte leukemia (T-LGLL) is a T-cell lymphoproliferative disorder that has recently been associated with B-cell dyscrasias on a spectrum ranging from dysgammaglobulinemia to lymphoma. To investigate the relationship between clonal B-cell and LGLL lymphoproliferations, we systematically studied lymphocytes in 57 patients with T-LGLL or NK lymphocytosis using flow cytometric methods sensitive to low-level B-cell populations. We identified 16 patients (28%) with abnormal B-cell populations; 9 (16%) of the patients had no known history of a B-cell lymphoproliferative disorder. We characterized these abnormal B-cell populations as monoclonal B-cell lymphocytosis and report a high frequency of monoclonal B-cell lymphocytosis in T/NK LGLL. Our findings suggest that certain pathologic factors may operate in patients with T/NK LGLL to drive low-level clonal B-cell proliferations.

Epigenetic alterations in a murine model for chronic lymphocytic leukemia

Early stages in the development of chronic lymphocytic leukemia (CLL) have not been explored mainly due to the inability to study normal B-cells en route to transformation. In order to determine such early events of leukemogenesis, we have used a well established mouse model for CLL. Over-expression of human TCL1, a known CLL oncogene in murine B-cells leads to the development of mature CD19+/CD5+/IgM+ clonal leukemia with a disease phenotype similar to that seen in human CLL. Herein, we review our recent study using this TCL1-driven mouse model for CLL and corresponding human CLL samples in a cross-species epigenomics approach to address the timing and relevance of epigenetic events occurring during leukemogenesis. We demonstrated that the mouse model recapitulates the epigenetic events that have been reported for human CLL, affirming the power and validity of this mouse model to study early epigenetic events in cancer progression. Epigenetic alterations are detected as early as three months after birth, far before disease manifests at about 11 months of age. These mice undergo NFkappaB repressor complex mediated inactivation of the transcription factor Foxd3, whose targets become aberrantly methylated and silenced in mouse and human CLL. Overall, our data suggest the accumulated epigenetic alterations during CLL pathogenesis as a consequence of gene silencing through TCL1 and NFkappaB repressor complex, suggesting the relevance for NFkappaB as a therapeutic target in CLL.

Low levels of monoclonal small B cells in the bone marrow of patients with diffuse large B-cell lymphoma of activated B-cell type but not of germinal center B-cell type

BACKGROUND

Multiparameter flow cytometry allows the detection of minor monoclonal B-cell populations. Using this technique combined with morphology, we were struck by the presence of minor populations of small monoclonal B cells in bone marrows of patients with diffuse large B-cell lymphoma in routine diagnostic samples and performed a systematic retrospective study.

DESIGN AND METHODS

Bone marrows of 165 patients with primary diffuse large B-cell lymphoma without histological evidence of concurrent non-Hodgkin's lymphoma were studied by routine microscopy of trephines and smears, immunohistochemistry and multiparameter flow cytometry.

RESULTS

Diffuse large B-cell lymphoma infiltration in marrows was documented in 11 of 165 patients. Morphological examination consistently revealed a higher tumor load than evidenced by flow cytometry. Of interest, only 3 of 119 patients with diffuse large B-cell lymphoma not otherwise specified, the largest subtype, showed marrow infiltration. By contrast, flow cytometry revealed a minor monoclonal B-cell population in 24 of 165 patients, none of whom showed diffuse large B-cell lymphoma infiltration by morphology. Of interest, morphological examination revealed the presence of small B cells in the marrows of those patients. Moreover, 11 of 39 (28.2%) of patients with diffuse large B-cell lymphoma not otherwise specified of ABC subtype and only 3 of 80 (3.7%) with the GCB subtype showed these monoclonal small B cells (P=0.0002). In addition 4 of 8 (50%), 4 of 15 (26.7%) and 2 of 3 (66.7%) patients with primary testicular, primary central nervous system and leg-type diffuse large B-cell lymphoma, respectively, showed monoclonal small B cells.

CONCLUSIONS

Bone marrow infiltration with diffuse large B-cell lymphoma in patients with diffuse large B-cell lymphoma not otherwise specified is rare at diagnosis. By contrast, a high number of diffuse large B-cell lymphoma not otherwise specified of the ABC subtype but not of GCB subtype is associated with monoclonal small B cells in the marrow. Whether these monoclonal small B cells are precursors of diffuse large B-cell lymphoma of the ABC type or arise in a common background that favors clonal B-cell expansion remains to be demonstrated.

Monoclonal B-cell lymphocytosis (MBL): biology, natural history and clinical management

Chronic lymphocytic leukemia (CLL) and the other low-grade non-Hodgkin lymphomas are among the most common lymphoid malignancies. Recent studies suggest that more than 4% of the general population over age 40 harbor a population of clonal B cells with the phenotype of either CLL or another B-cell malignancy, a condition now designated monoclonal B-cell lymphocytosis (MBL). Although all cases of CLL appear to be preceded by MBL, the majority of individuals with MBL will not develop a hematologic malignancy. The biologic characteristics and clinical implications of MBL appear to differ based on whether it is identified during the diagnostic evaluation of lymphocytosis or incidentally discovered through screening of individuals with normal lymphocyte counts as part of research studies using highly sensitive detection methods. In this paper, we provide a state of the art review on the prevalence, nomenclature, biology, natural history and clinical management of MBL.

Single-cell analysis reveals oligoclonality among 'low-count' monoclonal B-cell lymphocytosis

Monoclonal B cell lymphocytosis (MBL) is a pre-clinical hematologic syndrome characterized by small accumulations of CD5⁺ B lymphocytes. Most MBL share phenotypic characteristics with chronic lymphocytic leukemia (CLL). While some MBL progress to CLL, most MBL have apparently limited potential for progression to CLL, particularly those MBL with normal absolute B cell counts (“low count” MBL). Most CLL are monoclonal and it is not known whether MBL are monoclonal or oligoclonal; this is important because it is unclear whether MBL represent indolent CLL or represent a distinct pre-malignant precursor prior to the development of CLL. We used flow cytometry analysis and sorting to determine immunophenotypic characteristics, clonality, and molecular features of MBL from familial CLL kindreds. Single cell analysis indicated 4 of 6 low count MBL consisted of two or more unrelated clones; the other 2 MBL were monoclonal. 87% of low count MBL clones had mutated immunoglobulin genes, and no immunoglobulin heavy chain rearrangements of V_H family 1 were observed. Some MBL were diversified, clonally related populations with evidence of antigen-drive. We conclude that while low count MBL share many phenotypic characteristics with CLL, many MBL are oligoclonal. This supports a model for step-wise development of MBL into CLL.

Monoclonal B-cell lymphocytosis in first-degree relatives of patients with sporadic (non-familial) chronic lymphocytic leukaemia

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. Fluorescence 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.

Monoclonal B lymphocytosis in the general population

Monoclonal B lymphocytosis (MBL) is a frequent phenomenon in the general population. Despite a phenotype similar to chronic lymphocytic leukemia (CLL), the possibility exists that most cases are not necessarily a pre-leukemic condition. This is suggested by the fact that MBL is at least 100 times more frequent than CLL and the diagnosis of CLL is not an inevitable fate, even among MBL cases with lymphocytosis, where it occurs only in 1.1% of the cases per year. The high incidence of MBL, if coupled with the possibility of evolution into a frank leukemic state, poses evident clinical and health system concerns. MBL in the general population usually accounts for a very low number of all circulating B-cells, being <10% of all B lymphocytes. This creates the need for a better characterisation of MBL at molecular level, aiming to identify biological features that may define which cases are more likely to progress towards clinically overt CLL. This approach should also help to avoid unnecessary and prolonged follow-ups in all individuals carrying MBL, excluding those who are extremely unlikely to develop CLL.

Monoclonal B-cell lymphocytosis: definitions and natural history

The diagnostic term monoclonal B-cell lymphocytosis (MBL) is used to characterise individuals with a circulating population of clonal B-cells, a total B-cell count of <5 x 10(9)/L, and no other features of a B-cell lymphoproliferative disorder. The clinical implications of MBL may differ depending on whether an individual with a normal lymphocyte count is identified via a screening assay (screening MBL) or identified through clinical evaluation of lymphocytosis (clinical MBL). The B-cell count used to distinguish between clinical MBL (<5 x 10(9)/L) and CLL (> or = 5 x 10(9)/L) was selected largely based on tradition and technological advances and it is unknown whether the natural history of 'clinical MBL' differs from that of patients with Rai stage 0 CLL. Since, a diagnosis of 'leukemia' may lead to profound psychologic distress for patients, we believe the diagnosis of CLL should be based on an individual's risk of developing symptoms, requiring chemotherapeutic treatment and/or dying of disease. Additional studies are needed to determine whether the clinical outcome of patients with MBL differs from that of patients with Rai stage 0 CLL and to identify what B-cell threshold optimally distinguishes between these conditions.

Brief report: natural history of individuals with clinically recognized monoclonal B-cell lymphocytosis compared with patients with Rai 0 chronic lymphocytic leukemia

PURPOSE

The diagnosis of monoclonal B-cell lymphocytosis (MBL) is used to characterize patients with a circulating population of clonal B cells, a total B-cell count of less than 5 x 10(9)/L, and no other features of a B-cell lymphoproliferative disorder including lymphadenopathy/organomegaly. The natural history of clinically identified MBL is unclear. The goal of this study was to explore the outcome of patients with MBL relative to that of individuals with Rai stage 0 chronic lymphocytic leukemia (CLL).

PATIENTS AND METHODS

We used hematopathology records to identify a cohort of 631 patients with newly diagnosed MBL or Rai stage 0 CLL. Within this cohort, 302 patients had MBL (B-cell counts of 0.02 to 4.99 x 10(9)/L); 94 patients had Rai stage 0 CLL with an absolute lymphocyte count (ALC) < or = 10 x 10(9)/L; and 219 patients had Rai stage 0 CLL with an ALC more than 10 x 10(9)/L. Data on clinical outcome were abstracted from medical records.

RESULTS

The percentage of MBL patients free of treatment at 1, 2, and 5 years was 99%, 98%, and 93%, respectively. B-cell count as a continuous variable (hazard ratio [HR] = 2.9, P = .04) and CD38 status (HR = 10.8, P = .006) predicted time to treatment (TTT) among MBL patients. The likelihood of treatment for MBL patients was lower (HR = 0.32, P = .04) than that of both Rai stage 0 CLL patients with an ALC less than 10 x 10(9)/L (n = 94) and Rai stage 0 CLL patients with an ALC more than 10 x 10(9)/L (n = 219; P = .0003).

CONCLUSION

Individuals with MBL identified in clinical practice have a low risk for progression at 5 years. Because B-cell count seems to relate to TTT as a continuous variable, additional studies are needed to determine what B-cell count should be used to distinguish between MBL and CLL.

[Large granular lymphocytic leukaemia]

BACKGROUND

Large granular lymphocytic leukaemia (LGL-leukaemia) is considered a rare disease. LGL-leukaemia is usually of the T-cell type, but a minority displays an NK-cell phenotype. Incidence and prevalence are unknown.

MATERIAL AND METHODS

We identified patients with LGL-leukaemia (with well-defined diagnostic criteria) diagnosed at Rikshospitalet University Hospital between 01.10.2001 and 31.12.2007. Their medical records were assessed retrospectively.

RESULTS

LGL-leukaemia was diagnosed in 52 patients, 26 women and 26 men, median age of 59 (26 - 86) years, during the study period. The leukaemia displayed NK-cell phenotype in one patient and T-cell phenotype in the remaining 51 patients. Slightly more than one third of the patients were asymptomatic. Cytopenia, mostly neutropenia, was usually the cause of the clinical phenotype in symptomatic patients. Co-morbidity with autoimmune disease was common, and we also found a high prevalence of clonal B-cell disease (17 %).

INTERPRETATION

Our data support the notion that LGL-leukaemia is under-diagnosed. Unexplained cytopenias should suggest the possibility of LGL-leukaemia, and appropriate diagnostic measures should be undertaken. An early diagnosis may save patients an extensive and unnecessary diagnostic work-up and ensure that a simple and effective treatment is offered.

Increased frequency (12%) of circulating chronic lymphocytic leukemia-like B-cell clones in healthy subjects using a highly sensitive multicolor flow cytometry approach

Monoclonal B-cell lymphocytosis (MBL) indicates the presence of less than 5 x 10(9)/L circulating monoclonal B cells in otherwise healthy subjects. Recently, it has been reported that circulating chronic lymphocytic leukemia (CLL)-like B cells can be detected using 4- or 5-multicolor flow cytometry in 5% to 7% of adults with normal lymphocyte counts. We investigated the frequency of circulating monoclonal B cells in 608 healthy subjects older than 40 years with normal blood counts, using a highly sensitive 8-color flow cytometry approach and systematic screening for total PB leukocyte count higher than 5 x 10(6). We show that the frequency of PB monoclonal B cells is markedly higher than previously reported (12% for CLL-like B cells, found at frequencies of 0.17 +/- 0.13 x 10(9) cells/L), the incidence progressively increasing with age. Most cases (62%) showed clonal B-cell levels below the maximum sensitivity of the techniques described by others (< 0.01%), supporting the notion that detection of MBL may largely depend on the sensitivity of the flow cytometry approach used.

The prognosis of clinical monoclonal B cell lymphocytosis differs from prognosis of Rai 0 chronic lymphocytic leukaemia and is recapitulated by biological risk factors

Monoclonal B-cell lymphocytosis (MBL) is an asymptomatic monoclonal expansion of <5.0 x 10(9)/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 x 10(9)/l and >3.7 x 10(9)/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.

Expression of CD27 and CD23 on peripheral blood B lymphocytes in humans of different ages

BACKGROUND

Due to the fact that the coexpression of CD23 and CD27 has been reported to occur in B lymphocytic leukaemic clones and that there is debate about CD23 expression on memory B cells, we evaluated the behaviour of naive B cells (CD23-/CD27-) and memory B cells (CD27+) in the peripheral blood of a large number of humans of all ages. B cells were also distinguished into B2 (CD5-) and B1-a cells (CD5+).

METHODS

The cell surface expression of CD19, CD5, CD23 and CD27 was assessed on peripheral blood lymphocytes from 1,427 subjects of all ages undergoing peripheral blood immunophenotyping for a variety of reasons.

RESULTS

The absolute number of B lymphocytes and the percentage of naive cells (CD23-/CD27-) decreased with age whereas there was an increase in memory cells (CD27+). A small subset of B cells co-expressing CD23 and CD27 was present in humans of all ages, although the majority of CD27+ cells were CD23-. The percentages and rate of increase with age of B1-a CD23+/CD27+ were slightly higher than those of B2 cell counterparts.

CONCLUSIONS

On the basis of our data, age-associated changes in surface markers of B cells seem to be finely balanced and probably related to functional changes after antigen encounters, while the whole peripheral blood B-cell compartment undergoes a quantitative regression.

Characterization of immunoglobulin heavy and light chain gene expression in chronic lymphocytic leukemia and related disorders

The incidence of chronic lymphocytic leukemia is low in the Japanese population compared with populations in western countries, suggesting a role for genetic factors in the occurrence of this disease. We have previously shown that chronic lymphocytic leukemia in Japan rarely expresses the immunoglobulin heavy chain variable region (IGHV) 1-69 gene (1 out of 43 patients, 2.3%), which is a gene most commonly expressed in chronic lymphocytic leukemia cases from western countries. In the current study, we extended the previous study by examining immunoglobulin heavy chain and light chain gene expression in 80 Japanese patients with chronic lymphocytic leukemia and in 52 Japanese patients with other leukemic chronic lymphoproliferative disorders. IGHV1-69 gene expression was again quite low in our cohort, found in only two patients: one with chronic lymphocytic leukemia and the other with splenic marginal zone lymphoma. The IGHV4-34 gene was most frequently expressed in chronic lymphocytic leukemia (27.5%), whereas it was rarely found in leukemic chronic lymphoproliferative disorders (7.7%, P = 0.005). There was also a significant difference in the expression of IGLV3-21 between chronic lymphocytic leukemia and leukemic chronic lymphoproliferative disorders (29.4 vs 4.8%, P = 0.018). The IGLV3-21 gene in the majority of chronic lymphocytic leukemia cases was associated with homologous complementarity determining region 3 sequences. Recent studies identified subsets of cases expressing almost identical B-cell receptors. We found that two patients with chronic lymphocytic leukemia and the patient with splenic marginal zone lymphoma expressed IGHV4-39/IGKV1-39 and IGHV1-69/IGKV3-20, respectively, which belong to these subsets.

Clinical features and outcome of Chinese patients with monoclonal B-cell lymphocytosis

B-cell chronic lymphocytic leukemia (CLL) is the most common type of adult leukemias in the Western countries, however, infrequent in the Eastern. A diagnosis of CLL requires a count of B-lymphocytes >/=5.0x10(9)/L. Asymptomatic person with <5.0x10(9)/L B-lymphocytes is defined as monoclonal B-cell lymphocytosis (MBL). To compare the clinical characteristics, prognostic factors, and outcome of Chinese patients with MBL and CLL, we present a study from our single centre of 20 patients with MBL and 136 patients with CLL. The factors included: age at diagnosis, gender, direct antiglobulin test (DAT), immunoglobulin heavy chain variable gene (IgHV) mutational status, ZAP-70 protein, CD38 expression level, and molecular cytogenetic aberrations were analyzed in MBL and CLL subgroups. The Kaplan-Meier method was used to construct survival curves, and results were compared using the log-rank test. Patients in the MBL category were slightly older than in the CLL category. There was no significant difference of these clinical and biological characteristics between patients in MBL subgroup and early stage CLL (Binet A). The incidence of positive DAT was significantly increased in CLL patients at Binet B and C, compared with MBL (P=0.036). IgHV gene mutation in MBL is skewed, with more than 92.3% of subjects harbored mutated IgVH genes (P=0.025). The proportion of MBL patients with a 13q14 deletion or trisomy 12 was similar to that of CLL patients. Moreover, markers associated with poor prognosis (deletion of 11q22 or 17p13) in these MBL populations were less than those in Binet B and C CLL patients (P=0.025). No statistically significant differences in ZAP-70 and CD38 status were observed between the MBL and CLL subgroups. During a median follow-up period of 45.5 months, MBL patients had a low probability of progression, with no patients transformed to aggressive non-Hodgkin's lymphoma or dying of CLL-related causes. The overall survival of MBL was very similar to Binet A CLL, but longer than that of CLL patients at advanced stages (Binet B and C) (P=0.024). Our study demonstrated that a more indolent clinical course and superior clinical outcome for patients with MBL compared to CLL.

B-cell clones as early markers for chronic lymphocytic leukemia

BACKGROUND

Otherwise healthy persons with a small number of B-cell clones circulating in the peripheral blood have been designated as having monoclonal B-cell lymphocytosis (MBL). Hospital-based series indicate an excess risk of progression from MBL to chronic lymphocytic leukemia (CLL). In this prospective cohort study, we tested the hypothesis that CLL is always preceded by MBL.

METHODS

Among 77,469 healthy adults who were enrolled in the nationwide, population-based Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial, we identified 45 subjects in whom CLL was subsequently diagnosed (up to 6.4 years later) through the collection of a peripheral-blood sample. Using six-color flow cytometry (with antibodies CD45, CD19, CD5, CD10, kappa, and lambda) and immunoglobulin heavy-chain gene rearrangement by reverse-transcriptase-polymerase-chain-reaction assay, we determined the association between MBL and subsequent CLL and characterized the immunoglobulin gene repertoire of the prediagnostic B-cell clones.

RESULTS

On the basis of either flow-cytometric or molecular analysis, 44 of 45 patients with CLL (98%; 95% confidence interval [CI], 88 to 100) had a prediagnostic B-cell clone; in 41 patients (91%; 95% CI, 79 to 98), the presence of the B-cell clone was confirmed by both methods. The presence of immunoglobulin heavy-chain variable (IGHV) genes was determined in 35 of 45 prediagnostic clones (78%). Of these clones, 16 (46%) were IGHV3 subgroup genes (including 6 [17%] IGHV3-23 genes) and 9 (26%) were IGHV4 subgroup genes (including 4 [11%] IGHV4-34 genes). Furthermore, 27 of 35 of the IGHV sequences (77%) had mutations, with similar distributions after stratification either below or above the median time between the collection of the prediagnostic blood sample and the subsequent CLL diagnosis.

CONCLUSIONS

In peripheral blood obtained up to 77 months before a CLL diagnosis, prediagnostic B-cell clones were present in 44 of 45 patients with 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.

Epidemiology, pathology and treatment of non-follicular indolent lymphomas

Non-follicular indolent subtypes of non-Hodgkin lymphoma (NHL), which include chronic lymphocytic leukemia, small lymphocytic lymphoma (SLL) and marginal zone lymphomas (MZL), are a diverse group of disorders with different presenting features, behaviour patterns and treatment outcomes. Current knowledge of these subtypes is largely based on retrospective analyses. A precise diagnosis can be difficult to achieve, and specific diagnostic criteria are needed to more precisely define some of the rarer indolent tumors, such as nodal and splenic MZLs. Although some subtypes of NHL have a prolonged indolent course, with a good prognosis (e.g. SLL), others (e.g. nodal and splenic MZLs) can rapidly evolve into more aggressive subtypes. In asymptomatic patients, treatment may be deferred until the disease progresses and the patient becomes symptomatic. Universally accepted therapeutic guidelines do not exist, however, and carefully designed, prospective clinical studies are needed to further assess optimal therapeutic approaches for these indolent NHLs.

Classification of lymphoid neoplasms: the microscope as a tool for disease discovery

In the past 50 years, we have witnessed explosive growth in the understanding of normal and neoplastic lymphoid cells. B-cell, T-cell, and natural killer (NK)-cell neoplasms in many respects recapitulate normal stages of lymphoid cell differentiation and function, so that they can be to some extent classified according to the corresponding normal stage. Likewise, the molecular mechanisms involved the pathogenesis of lymphomas and lymphoid leukemias are often based on the physiology of the lymphoid cells, capitalizing on deregulated normal physiology by harnessing the promoters of genes essential for lymphocyte function. The clinical manifestations of lymphomas likewise reflect the normal function of lymphoid cells in vivo. The multiparameter approach to classification adopted by the World Health Organization (WHO) classification has been validated in international studies as being highly reproducible, and enhancing the interpretation of clinical and translational studies. In addition, accurate and precise classification of disease entities facilitates the discovery of the molecular basis of lymphoid neoplasms in the basic science laboratory.

Predicting clinical outcome in CLL: how and why

The clinical course of patients with chronic lymphocytic leukemia (CLL) is heterogeneous, with some patients experiencing rapid disease progression and others living for decades without requiring treatment. Clinical features and molecular/biologic factors such as ZAP-70, immunoglobulin heavy chain (IGHV) gene mutation status, and cytogenetic abnormalities on fluorescent in situ hybridization (FISH) have been found to be robust predictors of treatment-free survival and overall survival among newly diagnosed patients. Beyond their widely recognized value for providing insight into disease biology and utility for stratifying patient risk in clinical trials, these prognostic tools play an important role in the current counseling and management of patients with CLL. Recent studies have focused on how to combine the results of multiple prognostic assays into an integrated risk stratification system and explored how these characteristics influence response to treatment. This chapter reviews the available tools to stratify patient risk and discusses how these tools can be used in routine clinical practice to individualize patient counseling, guide the frequency of follow-up, and inform treatment selection.

Monoclonal B-cell lymphocytosis

The incidence and presenting features of chronic lymphocytic leukemia (CLL) have changed significantly over the last century. Routine diagnostic techniques can now detect very low levels of CLL phenotype cells. Monoclonal B-cell lymphocytosis (MBL) is a relatively recent diagnostic category encapsulating individuals with an abnormal B-cell population but not meeting the diagnostic criteria for a B-cell malignancy. This review focuses on CLL-type MBL, which represents the majority of MBL cases identified in diagnostic laboratories. CLL-type MBL has a phenotype identical to CLL and shares the same chromosomal abnormalities even at the lowest levels detectable. Recent evidence suggests that the immunoglobulin gene usage plays a key role in whether the abnormal cells will develop in significant numbers. In most cases, CLL-type MBL is a stable condition with only 1% per year among those presenting for clinical attention developing progressive disease requiring treatment, although suppressed immune function may have a more significant impact on outcome.

The immunoglobulin gene repertoire of low-count chronic lymphocytic leukemia (CLL)-like monoclonal B lymphocytosis is different from CLL: diagnostic implications for clinical monitoring

In the revised National Cancer Institute Working Group (NCI-WG)/International Workshop on Chronic Lymphocytic Leukemia (IWCLL) guidelines for CLL, CLL-like monoclonal B lymphocytosis (MBL) is defined as the presence of less than 5 x 10(9)/L B lymphocytes in the peripheral blood. However, the concentration of MBL in the blood is extremely variable. MBL in subjects with lymphocytosis require treatment at a rate of 1.1% per year and present immunoglobulin (IG) gene features and similar to good prognosis CLL. Little is known about low-count MBL cases, accidentally found in the general population. We analyzed IGHV-D-J rearrangements in 51 CLL-like MBL cases from healthy individuals, characterized by few clonal B cells. Seventy percent of the IGHV genes were mutated. The most frequent IGHV gene was IGHV4-59/61, rarely used in CLL, whereas the IGHV1-69 gene was lacking and the IGHV4-34 gene was infrequent. Only 2 of 51 (3.9%) MBL cases expressed a CLL-specific stereotyped HCDR3. Therefore, the IG gene repertoire in low-count MBL differs from both mutated and unmutated CLL, suggesting that the detection of MBL in an otherwise healthy subject is not always equivalent to a preleukemic state. Detailed IG analysis of individual MBL may help to identify cases that necessitate continuous clinical monitoring to anticipate disease progression.

B-cell count and survival: differentiating chronic lymphocytic leukemia from monoclonal B-cell lymphocytosis based on clinical outcome

The diagnosis of chronic lymphocytic leukemia (CLL) in asymptomatic patients has historically been based on documenting a characteristic lymphocyte clone and the presence of lymphocytosis. There are minimal data regarding which lymphocyte parameter (absolute lymphocyte count [ALC] or B-cell count) and what threshold should be used for diagnosis. We analyzed the relationship of ALC and B-cell count with clinical outcome in 459 patients with a clonal population of CLL phenotype to determine (1) whether the CLL diagnosis should be based on ALC or B-cell count, (2) what lymphocyte threshold should be used for diagnosis, and (3) whether any lymphocyte count has independent prognostic value after accounting for biologic/molecular prognostic markers. B-cell count and ALC had similar value for predicting treatment-free survival (TFS) and overall survival as continuous variables, but as binary factors, a B-cell threshold of 11 x 10(9)/L best predicted survival. B-cell count remained an independent predictor of TFS after controlling for ZAP-70, IGHV, CD38, or fluorescence in situ hybridization (FISH) results (all P < .001). These analyses support basing the diagnosis of CLL on B-cell count and retaining the size of the B-cell count in the diagnostic criteria. Using clinically relevant criteria to distinguish between monoclonal B-cell lymphocytosis (MBL) and CLL could minimize patient distress caused by labeling asymptomatic people at low risk for adverse clinical consequences as having CLL.

Using peripheral smear review, age and absolute lymphocyte count as predictors of abnormal peripheral blood lymphocytoses diagnosed by flow cytometry

Absolute lymphocytosis in the elderly raises the possibility of malignancy and generally warrants further investigation. To better correlate clinical variables with the frequency of neoplastic lymphoid processes in this population, we retrospectively reviewed archived flow cytometric analyses from peripheral blood specimens on patients of 50 years of age and older that had been deemed suspicious for a lymphoproliferative process after peripheral smear review. Age, absolute lymphocyte count (ALC), white blood cell count and relative lymphocyte count were correlated with the results of flow cytometry. Of 71 total cases, 42 (59%) had an abnormal immunophenotype. Independent variables that showed significant differences between normal and abnormal immunophenotype were mean age (p = 0.001) and ALC (p = 0.0032). We combined age and absolute lymphocyte count variables to look for the best possible cutoff values to predict the likelihood of an abnormal immunophenotype. ALC cutoff values of >or=4 x 10(9) cells/L for patients over 67 years of age, and >6.7 x 10(9) cells/L for patients between 50 and 67 years of age, had a high sensitivity for detecting an abnormal immunophenotype.

Immunophenotypic features distinguishing familial chronic lymphocytic leukemia from sporadic chronic lymphocytic leukemia

BACKGROUND

Familial chronic lymphocytic leukemia (CLL) has the most frequent familial aggregation among hematological malignancies. Familial CLL families have been studied to identify susceptibility genes and other factors that contribute in the etiology of CLL. To date no study has been conducted to evaluate and compare patterns of cell surface antigen expression in familial CLL and sporadic CLL.

METHODS

The pattern of cell surface antigen expression was studied in familial and sporadic CLL to determine if unique identifiers of familial CLL could be detected. Survival in familial CLL verses sporadic CLL was compared and the association between prognosis and CD38 expression studied.

RESULTS

Familial and sporadic CLL demonstrated the same characteristic immunophenotype (positive for surface immunoglobulin, CD5, CD19, and CD23 with dim CD20, and CD22). CD2 and CD13 expression, however, were more frequent (30% of cases) in familial CLL (P = 0.0003 for CD2, P = 0.006 for CD13) than in sporadic CLL (2-6%). There was no significant difference in survival in the two groups studied. Although the incidence of CD38 expression was similar in familial and sporadic CLL (47% and 44% respectively) the association with prognosis differed. There was a trend to decreased survival in CD38 positive sporadic (P = 0.06) but not familial CLL patients.

CONCLUSIONS

We conclude that detection of CD2 or CD13 expression in CLL suggests familial CLL and examination of family history for additional affected members is warranted. Furthermore, CD38 expression does not carry the negative prognosis observed in sporadic CLL.

Monoclonal B-cell lymphocytosis and chronic lymphocytic leukemia

BACKGROUND

A diagnosis of chronic lymphocytic leukemia (CLL) requires a count of over 5000 circulating CLL-phenotype cells per cubic millimeter. Asymptomatic persons with fewer CLL-phenotype cells have monoclonal B-cell lymphocytosis (MBL). The goal of this study was to investigate the relation between MBL and CLL.

METHODS

We investigated 1520 subjects who were 62 to 80 years of age with a normal blood count and 2228 subjects with lymphocytosis (>4000 lymphocytes per cubic millimeter) for the presence of MBL, using flow cytometry. Monoclonal B cells were further characterized by means of cytogenetic and molecular analyses. A representative cohort of 185 subjects with CLL-phenotype MBL and lymphocytosis were monitored for a median of 6.7 years (range, 0.2 to 11.8).

RESULTS

Monoclonal CLL-phenotype B cells were detected in 5.1% of subjects (78 of 1520) with a normal blood count and 13.9% (309 of 2228) with lymphocytosis. CLL-phenotype MBL had a frequency of 13q14 deletion and trisomy 12 similar to that of CLL and showed a skewed repertoire of the immunoglobulin heavy variable group (IGHV) genes. Among 185 subjects presenting with lymphocytosis, progressive lymphocytosis occurred in 51 (28%), progressive CLL developed in 28 (15%), and chemotherapy was required in 13 (7%). The absolute B-cell count was the only independent prognostic factor associated with progressive lymphocytosis. During follow-up over a median of 6.7 years, 34% of subjects (62 of 185) died, but only 4 of these deaths were due to CLL. Age above 68 years and hemoglobin level below 12.5 g per deciliter were the only independent prognostic factors for death.

CONCLUSIONS

The CLL-phenotype cells found in the general population and in subjects with lymphocytosis have features in common with CLL cells. CLL requiring treatment develops in subjects with CLL-phenotype MBL and with lymphocytosis at the rate of 1.1% per year.

Novel insights in chronic lymphocytic leukemia: are we getting closer to understanding the pathogenesis of the disease?

Chronic lymphocytic leukemia (CLL) has unique epidemiologic, biologic, and clinical features. The progressively emerging picture leads us to consider that the critical genes for malignant CLL cells are those regulated by a number of microRNAs revealed by refined cytogenetic and molecular studies, and that the key molecule is the B-cell receptor (BCR). The hypothesis that CLL cells might be selected by some sort of antigenic pressure is strengthened by numerous findings indicating that a BCR-mediated stimulation plays a relevant role in the natural history of the disease and that autoantigens, as well as molecular structures instrumental in eliminating and scavenging apoptotic cells and pathogenic bacteria, may be relevant in triggering and/or facilitating the evolution of CLL. An important question is whether the tiny monoclonal B-cell populations phenotypically similar to CLL (that occur in the peripheral blood of about 3.5% of healthy individuals and are termed monoclonal B lymphocytosis) might be a critical step in the development of CLL. All relevant events of CLL occur in tissues in which a number of cellular and molecular interactions shape a microenvironment conducive to the accumulation of malignant cells and favor the organization of proliferating cells in focal aggregates of variable size that form the pseudofollicular proliferation centers. Given the impact that understanding the pathogenesis of CLL might have on the development of new treatments, the purposes of this review are to discuss whether the novel insights in CLL are leading us closer to understanding the tenet of the disease; to define the emerging new, stimulating questions; and to unfold the major challenges that still need to be addressed.

2006 Bethesda International Consensus recommendations on the flow cytometric immunophenotypic analysis of hematolymphoid neoplasia: medical indications

The clinical indications for diagnostic flow cytometry studies are an evolving consensus, as the knowledge of antigenic definition of hematolymphoid malignancies and the prognostic significance of antigen expression evolves. Additionally the standard of care is not routinely communicated to practicing clinicians and diagnostic services, especially as may relate to new technologies. Accordingly there is often uncertainty on the part of clinicians, payers of medical services, diagnostic physicians and scientists as to the appropriate use of diagnostic flow cytometry. In an attempt to communicate contemporary diagnostic utility of immunophenotypic flow cytometry in the diagnosis and follow-up of patients with hematolymphoid malignancies, the Clinical Cytometry Society organized a two day meeting of international experts in this area to reach a consensus as to this diagnostic tool. This report summarizes the appropriate use of diagnostic flow cytometry as determined by unanimous approval of these experienced practitioners.

Guidelines for the diagnosis and treatment of chronic lymphocytic leukemia: a report from the International Workshop on Chronic Lymphocytic Leukemia updating the National Cancer Institute-Working Group 1996 guidelines

Standardized criteria for diagnosis and response assessment are needed to interpret and compare clinical trials and for approval of new therapeutic agents by regulatory agencies. Therefore, a National Cancer Institute-sponsored Working Group (NCI-WG) on chronic lymphocytic leukemia (CLL) published guidelines for the design and conduct of clinical trials for patients with CLL in 1988, which were updated in 1996. During the past decade, considerable progress has been achieved in defining new prognostic markers, diagnostic parameters, and treatment options. This prompted the International Workshop on Chronic Lymphocytic Leukemia (IWCLL) to provide updated recommendations for the management of CLL in clinical trials and general practice.

Analysis of a large multi-generational family provides insight into the genetics of chronic lymphocytic leukemia

We report the genetic analysis of a large multi-generational family composed of 144 individuals in which 11 members have been diagnosed with chronic lymphocytic leukaemia (CLL). The observation of a significant over-representation of monoclonal B-cell lymphocytosis (MBL) in unaffected family members strongly supports MBL being a surrogate marker of carrier status. A genome-wide linkage scan of the family using high-density 10K single nucleotide polymorphisms provided no significant evidence for a single gene model of disease susceptibility, inviting speculation that susceptibility to CLL has a more complex basis. The absence of a correlation in IGHV usage between affected family members does however argue strongly against exposure to a single super-antigen in disease development.

Multiple myeloma, chronic lymphocytic leukaemia and associated precursor diseases

Multiple myeloma and chronic lymphocytic leukaemia share common biological and clinical features including the presence of defined precursor conditions (monoclonal gammopathy of undetermined significance and monoclonal B-cell lymphocytosis respectively). Here, we discuss evidence from the literature on the potential aetiological roles for genetic and chronic immune stimulatory factors on the pathway from precursor to malignancy. Also, we speculate on the relationship between precursor and malignancy and talk about future directions and gaps in the literature.

Chronic lymphocytic leukaemia genetics overview

Although the familial aspect of chronic lymphocytic leukaemia (CLL) has been appreciated for decades, it is only with the recent confluence of improved molecular and gene technologies and world-wide collaborative networks that accelerated progress has become apparent. In this summary we highlight selected themes in the genetics of CLL emphasizing the opportunities and challenges of this malignancy.

Waldenström macroglobulinaemia and IgM monoclonal gammopathy of undetermined significance: emerging understanding of a potential precursor condition

Previously thought to be best described as a plasma cell disorder, Waldenström macroglobulinaemia (WM) is now understood to be a distinct clinicobiological entity. WM shares B-cell origin and certain other features with both chronic lymphocytic leukaemia (CLL) and multiple myeloma (MM). WM and CLL arise from B-cells at discrete stages in their maturation process, and MM arises from B-cells that have fully differentiated into plasma cells. While MM has a well-known precursor condition, monoclonal gammopathy of undetermined significance (MGUS), CLL and WM may also have associated precursor states, monoclonal B-cell lymphocytosis (MBL) and IgM MGUS, respectively. This review explores the features that link or distinguish these haematolymphoid malignancies, with special attention to emerging data regarding IgM MGUS and its unique relationship to WM, and identifies important gaps in our understanding of the putative precursor conditions, MBL and IgM MGUS.

The biological and clinical relationship between CD5+23+ monoclonal B-cell lymphocytosis and chronic lymphocytic leukaemia

A CD5(+)23(+) monoclonal B-cell population is detectable in approximately 3% of the general adult population. The phenotype of the monoclonal CD5(+)23(+) B cells is identical to chronic lymphocytic leukaemia (CLL) with respect to a large number of proteins in addition to the standard diagnostic markers used to identify CLL. Studies in CLL families and direct assessment of genetic features indicate a close biological association between indolent CLL and the CLL-phenotype cells detected in individuals with a normal blood count. Patients with a CLL-phenotype monoclonal B-cell lymphocytosis (MBL) often have increasing CLL cell counts with time and some progress to a stage requiring treatment. Analysis of intraclonal variation in the immunoglobulin heavy chain gene suggests a process of clonal diversification rather than clonal selection in the early stages of disease progression. CLL-phenotype MBL is detectable in approximately 10% of cases referred for investigation of a lymphocytosis and future studies should be directed towards the detection of factors which identify MBL patients at risk of disease progression.