AML FAB Subtypes Shows Different Proportion of Leukemia Initiating Cell Which Has Lower Single Cell Dividing Property.

Acute myeloid leukemias (AML) are maintained by a subpopulation of leukemia initiating cell that can regenerate themselves as well as give rise to more differentiated and less proliferative cells that constitute the bulk of the disease. Recent studies discovered both the nature of leukemia stem cells and their origin. Immunophenotype of AML stem cell (ASC) is known as CD34⁺CD38^– leukemic cells. Yet, despite their critical importance, much remains to be learned about the frequency, proportion and dividing activity of ASC in a single cell levels. To address these issues, the current study investigated the frequency, proportion according to AML FAB subtypes and single cell plating efficiency of ASC from bone marrow (BM) at the initial diagnosis.

The proportion and frequency of ASC were examined on BM samples of twenty AML patients using single cell sorter (BD FACS Aria cell sorter, BD Biosciences, USA). Growth and proliferation capacities of single normal hematopoietic stem cells and LSC were determined using plating efficiency (number of the wells in which more than two cells grew / total number of cells in 96-well plate culture x 100). Individual single cells were cultured in 96-well plates with each well containing 100 uL of serum media with each 100 ng/mL of stem cell factor, Flt-3, thrombopoietin and G-CSF for five days.

The frequency and proportion of ASC varied according to FAB subtypes. The mean proportion of ASC from AML M2, M4 and M3 showed 25.1±22.5% (mean±SD), 15.1±16.6% and 6.5±3.3%, respectively. The mean proportion of remaining other subtypes was 13.6±16.2%. CD34 percentage in BM at the initial diagnosis closely correlated with the proportion of ASC. ASC proportion was statistically significant different between patient's group with more than 20% of CD34 and those with less than 20% (P=0.003). Single cell plating efficiency of ASC was markedly reduced compared with non-ASC (CD34+CD38+ leukemic cell population) (7.2 ± 4.7% in ASC vs. 12.6 ± 7.6% in non-ASC).

ASC proportion and frequency in BM samples were very diverse according to FAB subtypes. This study directly proved lower dividing activity of single ASC, and also implicated strategies for single ASC cloning to develop new therapeutics targeting ASC.

No relevant conflicts of interest to declare.