Telomerase activity and telomere length in acute and chronic leukemia, pre- and post-ex vivo culture

We studied telomerase regulation and telomere length in hematopoietic proge nitor cells from peripheral blood and bone marrow from patients with acute and chronic leukemia and myeloproliferative diseases. CD34(+) cells from a total of 93 patients with either acute myeloid leukemia (AML; n = 25), chro nic myeloid leukemia (CML; n = 21), chronic lymphocytic leukemia (CLL; n = 18), polycythemia vera (PV; n = 16), or myelodysplastic syndromes (MDS; n = 13) were analyzed before and in 19 patients after ex vivo expansion in the presence of multiple cytokines (kit ligand, interleukin-3, interleukin-6, and granulocyte colony-stimulating factor plus erythropoietin), Compared wi th hematopoietic progenitor cells from normal donors (n = 108), telomerase activity (TA) was increased 2- to 5-fold in chronic phase (CP)-CML, CLL, PV , and MDS. In AML, accelerated phase (AP) and blastic phase (BP)-CML, basal TA was 10- to 50-fold higher than normal. TA of CP-CML CD34+ cells was up- regulated within 72 h of ex vivo culture, peaked after 1 week, and decrease d below detection after 2 weeks. In contrast, TA in AP/BP-CML and AML CD34( +) cells was down-regulated after 1 week of culture and decreased further t hereafter. The expansion potential of CD34(+) cells from patients with leuk emia was considerably decreased compared with CD34(+) cells from normal don ors. The average expansion of cells from leukemic individuals was 6.5-, 2.3 -, 0.6-, and 0.2-fold in weeks 1, 2, 3, and 4, respectively, whereas expans ion of normal cells was 5- to 15-fold higher. In serial expansion culture, a median telomeric loss of 0.7 kbp was observed during 3-4 weeks of expansi on. Our results demonstrate that up-regulation of telomerase is similar in CD34(+) cells from CP-CML, CLL, PV, and MDS patients and in normal hematopo ietic cells during the first week of culture, whereas in AML and AP/BP-CML, telomerase is high at baseline and down-regulated during expansion culture . High levels of telomerase in leukemic progenitors at baseline may be a fe ature of both the malignant phenotype and rapid cycling. Telomerase down-re gulation during culture of leukemic cells may be due to the decreased expan sion potential or repression of normal hematopoiesis, or in ARIL it may be due to the partial differentiation of AML cells, shown previously to be ass ociated with loss of TA. Telomere shortening during ex vivo expansion corre lated dth low levels of TA, particularly in chronic leukemic and MDS progen itors n here telomerase was insufficient to protect against telomere bp los s during intense proliferation.