Telomere Dynamics in Monoclonal B-Cell Lymphocytosis and Binet a Chronic Lymphocytic Leukemia

Monoclonal B-Cell lymphocytosis (MBL) is an asymptomatic clinical entity characterized by monoclonal B-cell proliferation not meeting criteria for chronic lymphocytic leukemia. It is hypothesized that MBL may precede all CLL cases, but the molecular mechanisms responsible for disease progression and evolution are not known. Telomeres are the ends of linear chromosomes composed of tandem hexameric nucleotide repeats (5'-TTAGGG-3') coated by specific protective proteins (shelterin complex). Telomeres are usually short in CLL and telomere length is an independent prognostic factor for disease progression. Additionally, telomere attrition has been shown to increase chromosomal instability and acquisition of karyotypic abnormalities in CLL (Brugat, Blood 116:239-249, 2010). However, the telomere length of MBL clonal cells is not known. The purpose of this study was to evaluate the telomere length of clonal B-cells in Binet A CLL patients and subjects with clinic or population-screening MBL (Rawstron, Curr Hematol Malig Rep 8:52-59,2013).Twenty Binet A CLL patients, four with population-screening MBL detected in a previous study (Matos, Br J Haematol 147:339-46, 2009), and nine subjects with clinic MBL were studied. Mononuclear cells from the peripheral blood were separated by density gradient centrifugation and CD19+CD5+ cells were sorted in a FACSAria (Becton Dickinson) or a JSAN (Bay Bioscience) flow cytometers. Telomere length (TL) was determined in sorted CD19+CD5+ cells by quantitative polymerase chain reaction (qPCR) and expressed as telomere/single gene (T/S) ratio in comparison to a standard; TL also was adjusted for age. TL was measured in peripheral blood leukocytes from 52 healthy volunteers aged 50 to 86 years and used as controls. The CLL group had a medium age of 70 years (range, 58 to 81), the clinic MBL, 79 years (range, 57 to 97), and the population-screening MBL, 67 years (range, 53 to 82). In the CLL group, half of the patients was female; and all individuals were male in the clinic MBL group; in the population-screening MBL, 3/4 were males. The medium total lymphocytes count for the CLL patients was 36650/μL (range, 7500 to 147000), 3833 (range 2900 to 5900) in the clinic MBL, and 1625 (range 900 to 2100) in the population-screening MBL. The median percentage of CD19+CD5+ cells in total B-lymphocytes was 78% (range 59 to 91), 38% (range, 6 to 61), and 1.89% (range, 0.97 to 3.4) in CLL, clinic MBL, and population-screening MBL, respectively. Median TL was 0.32 (range, 0.13 to 0.78), 0.21 (range, 0.13 to 0.48) and 0.42 (range, 0.36 to 0.45) for CLL, clinic MBL and population-screening MBL, respectively. Age-adjusted TL was shorter in CLL and clinic MBL as compared to healthy controls (P<0.05; Figure). TL also tended to be shorter in population-screening MBL in comparison to healthy subjects, although not reaching statistic significance probably due to the low number of individuals in this group (Figure). In healthy individuals, TL of peripheral blood leukocytes shortened with aging, but in the three patient groups anlayzed, clonal B-cells TLs were equally short regardless of patient's age. These findings indicate that telomere erosion is an early phenomenon of leukemogenesis in B-clonal disorders and that MBL and CLL represent different stages of the same disease with different tumor burden.