Characterization of acute myeloid leukemia stem cells by niche like coculture system

AML heterogeneity show evidence of hierarchical cellular organization and at the top of this hierarchical structure there is a rare group of LSCs. It was mentioned that there is an association between LSCs and disease prognosis. For better understanding of the leukemogenesis and therapy resistant mechanism, LSC in vitro culture is important and still challenging area. In this study, LSCs were maintained using niche like co-culture system in AML patient samples for long-term culture. Proliferation rate, blastic colony formation capacity, leukemia cobblestone formation capacity and ALDH activity was evaluated for determining the LSC frequency, and their self-renewal and leukemia formation capacity in leukemia population. For short-term culture, proliferation index was determined using CFSE analysis. Unlike healthy donor samples, blastic colony formation and cobblestone area formation were observed in AML samples. Majority of cell populations in the control samples show low ALDH activity whereas, AML samples show intermediate ALDH activity. Besides, in ALDH intermediate population LSC percentage was stable during long-term culture for AML samples. For remission samples the LSC percentage decreased. There was a dispersion among sample proliferation capacity because of the heterogeneity. Selected LSC surface markers (VEGFR-2, CD25, TIM3 ve CLL-1) can be used to determine LSC in leukemia samples for distinguishing HSCs and their expressions levels higher in AML diagnose and relapse samples than remission samples. In conclusion, using this niche like coculture system especially at the time of diagnose and ALDH assay, we can determine the LSC frequency and get information for early prognose. This in vitro assay can be used to assess investigating pathways of chemoresistance and screening of new LSC-targeted therapies.