The Determination of Acute Myeloid Leukemia Stem Cell (AML LSC) in Childhood Acute Leukemia and Its Clinical Significance

Introduction and objective: Leukemia stem cells (LSC) are the rare cell population in leukemia patients and are responsible for the occurrence and the relapse of the disease. Determination of this particular cell population and its clinical relevance has not been reported in the literature. The aim of this study was to determine the acute myeloid leukemia (AML) stem cell (AML LSC) concentrations in childhood acute leukemia and to analyze the clinical relevance between the AML LSC concentrations and the MRD levels at different time points after remission.

Methods: Using the multi-parameter flow cytometry (FCM) and AML-LSC specific immunophenotype defined by CD34+CD38− CD123+ combination, the concentrations of AML LSC in childhood AML patients (N = 11) or those of AML LSC immunophenotype-identical cells (AML LSC-IPIC) in acute lymphoblastic leukemia (ALL) (N =12) both at diagnosis and at remission were detected. Using the leukemia associated immunophenotypes (LAIP) and multi-parameter flow cytometry, the MRD levels were determined at the time of diagnosis and 1, 28, 60, 90 and 180 days after remission. The correlation between the AML-LSC or AML LSC IPIC and the MRD levels were analyzed.

Results: The median concentrations of the AML LSC or AML LSC-IPIC in newly diagnosed AML (N = 11), ALL (N = 12) and control (12 children with non-malignancy) were 147 (range 14~1357) cells/100,000 mononucleated cells (MNC), 8 (range 0~181) cells/100,000 MNC and 0 (range 0~6) cell/100,000 MNC, respectively, which were statistically significant between each other (P < 0.05). The AML LSC concentration in non-CR AML (N = 7) with a median of 43 (range 5~86) cells/100,000MNC was not significantly different from that at initial diagnosis (147/100,000, P > 0.05). After remission, the median concentrations of the AML LSC or AML LSC-IPIC in AML or ALL were 10 (range 0~187) cells/100,000MNC and 8 (range 0~94) cells/100,000MNC, respectively. The AML LSC concentration (10/100,000) after remission was significantly lower than that at diagnosis (147/100,000, P < 0.05). The median concentrations from AML (N = 42) and ALL (N = 42) after remission were not significantly different (10/100,000 vs 10/100,000, P > 0.05), while they remained significantly higher than those from non-malignancy control (0/100,000, N =12, P < 0.017). Real time detection of AML LSC at day 1, 28, 60, 90, 180 days in AML patients after remission revealed that the AML-LSC concentrations at all 5 time points were significantly lower than those at diagnosis (P < 0.05) while no significant differences were identified among different time points after remission (P > 0.05). When the AML LSC concentrations were compared with the levels of MRD for AML patients (N =39), the significant negative correlation between AML LSC concentrations and MRD levels was observed (r = −0.334, P = 0.038). Whereas, the correlation between the AML LSC-IPIC and the levels of MRD in ALL patients (N = 40) was not found (r = −0.014, P = 0.932).

Conclusions: The AML LSC concentrations in newly diagnosed AML are significantly higher than those in newly diagnosed ALL and control group. Those cell populations are significantly reduced after remission while they remain higher than that of non-malignancy control. The AML LSC-IPIC has also been found in ALL patients, but the concentrations are not significantly changed after remission. AML LSC-IPIC levels are not found elevated in non-malignancy group. Significant negative correlation between AML LSC concentrations and MRD levels in AML patients after remission has been found which indicates that AML LSC detection in AML patients may confer prognostic significance. Larger number of cases and long-term follow up for patients with AML are warranted in future studies.