Prognostic implications of differences in telomere length between normal and malignant cells from patients with chronic myeloid leukemia measured by flow cytometry

Chronic myeloid leukemia (CML) is a clonal, multilineage myeloproliferative disorder characterized by the Philadelphia chromosome (Ph) and a marked expansion of myeloid cells. Previous studies have indicated that the telomere length in blood cells may indicate their replicative history. However, the large variation in telomere length between individuals complicates the use of this parameter in CML and other hematologic disorders. To circumvent this problem, we compared the telomere length in peripheral blood or bone marrow cells with purified normal (Ph-) T lymphocytes from the same CML patient using fluorescence in situ hybridization and flow cytometry. Overall telomere fluorescence was significantly reduced in Ph+ cells from patients with CML compared to blood leukocytes from normal individuals (P < 0.001) or normal (Ph-) T lymphocytes from the same individuals (n = 51, P < 0.001), Cells from patients in accelerated phase or blast phase (AP/BP) showed significantly shorter average telomere length than cells from patients in chronic phase (CP, P = 0.02) or cytogenetic remission (CR, P = 0.03), Patients in CP who subsequently developed BP within 2 years had significantly shorter telomeres than those who did not develop BP for at least 2 years(P < 0.05). Accelerated replication-dependent telomere shortening in Ph+ versus Ph- leukocytes supports previous evidence that Ph+ stem cells cycle more actively than their counterparts in normal individuals. Our data further suggest that telomere shortening may serve as a surrogate marker of disease progression in patients with CP CML, supporting a mechanistic link between CML stem cell turnover, genetic instability, and malignant evolution in this disease. (C) 2000 by The American Society of Hematology.