Assessment of leukemic stem cell CD26+ in Chronic Myeloid Leukemia patients with deep molecular response

BENGIO, R.; PEÑA, M.; PALACIOS, F.; MOIRAGHI, B.; NEGRI ARANGUREN, P.; ENRICO MATTOS, A.; MARIANO, R.; TOLOZA, M. J.; LARRIPA, I.

Congreso; EHA2021 Virtual Congress; 2021

European Hematology Association

Background: Chronic Myeloid leukemia (CML) is a myeloproliferative neoplasm characterized by the reciprocal translocation t(9;22) (q34;q21) resulting in the BCR-ABL1 fusion gene and the oncogenicprotein P210 with constitutive tyrosine kinase activity. The study of this protein led to the development of tyrosine kinase inhibitors (TKI). It has been shown that patients with a deep and sustained molecular response could stop treatment. It is likely that relapse after TKI discontinuationis due to the persistence of Leukemic Stem Cell (LSC), which are transcriptionally quiescent. The expression of the enzyme dipeptidylpeptidase IV (CD26) is restricted to CD45+/CD34+/CD38- LSC in CML BCR/ABL1+, but is not found in other myeloid or lymphoid LSC. For this reason it is considered a novel specific biomarker of neoplastic cell in CML.Aims: To detect the LSC (CD26+) in CML patients with different molecular responses (MR) and to assess if these cells remain in deep molecular response (DMR).Methods: Peripheral blood samples from 174 CML patients (94 males and 80 females) were evaluated for detection of LSC by flow cytometry and quantitative PCR (qRT-PCR) for BCR-ABL1 rearrangement. All individuals provided an informed consent, in accordance with our Institutional Ethics Committee. The analysis of both studies was carried out simultaneously on the same sample, during the follow up at different time points after diagnosis and under TKI treatment (Imatinib, Nilotinib, Dasatinib). Median age was 48 years old (range 18-82). The molecular responses in International Scale (IS) were: 6% (10/174) Null MR, 9% (15/174) Minimal MR, 16% (28/174) Minor MR, 27% (47/174) Major MR and 42% (74/174) DMR (BCR-ABL1 transcripts reduction ≥ 4 log, including MR4.0, RM4.5 and RM5.0).Flow cytometry studies were performed with 200 μl of whole blood stained with a panel of 8 antibodies: HLA-DR/CD45/CD38/CD26/CD34/CD117/CD123/CD3 using BD FACS Canto? II flow cytometer. BCR-ABL1 qRT-PCR was performed by Taqman method with the Molecular MD One-Step kit using a Rotor-Gene 6000 Q real-time thermal-cycler (QIAGEN).Results: The immunophenotype and molecular response were analyzed in all 174 cases. It was observed that patients with good molecular response (≥3log BCR-ABL1 reduction) had a significantly lower percentage of cases with LSC compared to those who had