Gerald E. Marti

Chronic lymphocytic leukemia (CLL), an incurable malignancy of mature B lymphocytes, involves blood, bone marrow, and secondary lymphoid organs such as the lymph nodes (LN). A role of the tissue microenvironment in the pathogenesis of CLL is hypothesized based on in vitro observations, but its contribution in vivo remains ill-defined. To elucidate the effects of tumor-host interactions in vivo, we purified tumor cells from 24 treatment-naive patients. Samples were obtained concurrently from blood, bone marrow, and/or LN and analyzed by gene expression profiling. We identified the LN as a key site in CLL pathogenesis. CLL cells in the LN showed up-regulation of gene signatures, indicating B-cell receptor (BCR) and nuclear factor-κB activation. Consistent with antigen-dependent BCR signaling and canonical nuclear factor-κB activation, we detected phosphorylation of SYK and IκBα, respectively. Expression of BCR target genes was stronger in clinically more aggressive CLL, indicating more effective BCR signaling in this subtype in vivo. Tumor proliferation, quantified by the expression of the E2F and c-MYC target genes and verified with Ki67 staining by flow cytometry, was highest in the LN and was correlated with clinical disease progression. These data identify the disruption of tumor microenvironment interactions and the inhibition of BCR signaling as promising therapeutic strategies in CLL. This study is registered at http://clinicaltrials.gov as NCT00019370.

Very low levels of circulating monoclonal B-cell subpopulations can now be detected in apparently healthy individuals using flow cytometry. We propose the term 'monoclonal B-cell lymphocytosis' (MBL) to describe this finding. The aim of this document is to provide a working definition of MBL for future clinical, epidemiological and laboratory studies. We propose that the detection of a monoclonal B-cell population by light chain restriction is sufficient to define this condition in individuals not meeting the diagnostic criteria for other B-lymphoproliferative disorders. The majority of individuals with MBL will have cells that are indistinguishable from chronic lymphocytic leukaemia (CLL). However, this blood cell clonal expansion of CD5+ or CD5- B-lymphocytes is age-dependent and immunophenotypic heterogeneity is common. Longitudinal studies are required to determine whether MBL is a precursor state to CLL or other B-lymphoproliferative disease in a situation analogous to a monoclonal gammopathy of undetermined significance and myeloma. Future studies of MBL should be directed towards determining its relationship to clinical disease, particularly in individuals from families with a genetic predisposition to developing CLL.

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.