Telomere shortening correlates with leukemic stem cell burden at diagnosis of chronic myeloid leukemia

Abstract

Telomere length (TL) in peripheral blood (PB) cells of patients with chronic myeloid leukemia (CML) has been shown to correlate with disease stage, prognostic scores, response to therapy, and disease progression. However, due to considerable genetic interindividual variability, TL varies substantially between individuals, limiting its use as a robust prognostic marker in individual patients. Here, we compared TL of BCR-ABL-, nonleukemic CD34+CD38- hematopoietic stem cells (HSC) in the bone marrow of CML patients at diagnosis to their individual BCR-ABL+ leukemic stem cell (LSC) counterparts. We observed significantly accelerated telomere shortening in LSC compared with nonleukemic HSC. Interestingly, the degree of LSC telomere shortening was found to correlate significantly with the leukemic clone size. To validate the diagnostic value of nonleukemic cells as internal controls and to rule out effects of tyrosine kinase inhibitor (TKI) treatment on these nontarget cells, we prospectively assessed TL in 134 PB samples collected in deep molecular remission after TKI treatment within the EURO-SKI study (NCT01596114). Here, no significant telomere shortening was observed in granulocytes compared with an age-adjusted control cohort. In conclusion, this study provides proof of principle for accelerated telomere shortening in LSC as opposed to HSC in CML patients at diagnosis. The fact that the degree of telomere shortening correlates with leukemic clone's size supports the use of TL in leukemic cells as a prognostic parameter pending prospective validation. TL in nonleukemic myeloid cells seems unaffected even by long-term TKI treatment arguing against a reduction of telomere-mediated replicative reserve in normal hematopoiesis under TKI treatment.

Conflict of interest statement

Conflict-of-interest disclosure: T.H.B. received research funding from Novartis and Pfizer, gave presentations, and participated in advisory boards for Novartis, Pfizer, Ariad, and Janssen (no personal honoraria). H.H.-H. leads the NCMLSG, which conducted the NordCML006 trial with support from BMS. J.J. receives research support from Novartis and BMS, received speaker’s fees from Incyte, Pfizer, Celgene, Roche, and BMS, and participated in advisory boards of BMS, Pfizer, and Novartis. S.K. received research funding from Novartis, BMS, and Janssen (none related to this study), gave presentations, and participated in advisory boards for Novartis, Pfizer, BMS, Incyte/Ariad, and Janssen. S.M. has received honoraria and research funding from Novartis, Pfizer, and BMS (not related to this study). G.O. received honoraria and/or research funding form Novartis, ARIAD, BMS, ROCHE, J&J, and Celgene. J.R. has received honoraria and research funding from Novartis, Pfizer, and BMS (not related to this study). S.S. received honoraria from Novartis, BMS, Incyte, Pfizer, and research funding from Novartis and BMS. The remaining authors declare no competing financial interests.

© 2018 by The American Society of Hematology.

Figures

Graphical abstract

Figure 1.

Representative laser scanning confocal microscopy images obtained after applying a 2-phase combined FISH technique based on coordinate assembly protocol for assessment of TL within the same CP CML patient’s CD34+38−compartment. (A) In phase 1, BCR-ABL+ and BCR-ABL− cells were identified by BCR-ABL FISH staining. (B) In phase 2, PNA-Tel Q-FISH is used to restain the samples allowing telomere quantification in the BCR-ABL+ and BCR-ABL− cells within the same individual’s CD34+38− compartment. Image magnification ×630. Digital zoom ×2.5. DAPI, 4′,6-diamidino-2-phenylindole.

Figure 2.

TL in BCR-ABL−vs BCR-ABL+cells of CP CML patients at first diagnosis. (A) TL (in a.u.) in CD34+CD38− BCR-ABL+ LSC is significantly shortened compared with BCR-ABL− HSC (P = .040). (B) Difference in TL between BCR-ABL+ LSC and BCR-ABL− HSC (ΔTLLSC-HSC, in a.u.) as a function of clone size (ie, the percentage of Ph+ cells) in the BM CD34+CD38− population of CP CML patients at diagnosis (r2 = 0.367, P = .016).

Figure 3.

TL of 134 CML patients within the EURO-SKI study. (A) TL (in kb) vs age (in years) in PB lymphocytes of CML patients with loss of (orange squares; n = 58) or maintained (blue circles; n = 75) molecular residual disease. (B) TL (in kb) vs age (in years) in PB granulocytes of CML patients with loss of (green squares; n = 58) or maintained (yellow circles; n = 75) molecular residual disease. (C) Age-adjusted TL (aaTL) of PB lymphocytes (shown in blue; P = .020) and granulocytes (shown in yellow; P = .100) from the EURO-SKI study patients. n.s., not significant.