Frequency and dynamics of ex-vivo AML-culture initiating cells reflect patients ’ outcome

(188 out of 250) Acute Myeloid Leukemia (AML) is sustained by a sub-population of rare Leukemia initiating cells (LICs) detected in the xenograft assay by their capacity to self-renew and to generate non-LICs in vivo. The xenotransplantation model captures functional properties of LICs that have clinical prognostic value. However, the long duration of this in vivo assay has hampered its use as a prognostic tool. Here, we show using an ex vivo co-culture system, that intermediate and poor risk AML patient samples at diagnosis have a 5 to 7 times higher frequency of Leukemic-Long Term Culture-Initiating cells (L-LTC-ICs) compared to the good risk group. We defined a Fluorescence Dilution Factor (FDF) parameter that monitors sample proliferation over 1 week and established a strong correlation of this parameter with the L-LTC-IC frequency. A higher FDF was found for poor prognostic AMLs or for samples capable of engrafting NSG mice compared to good risk AMLs or non-engrafters. Importantly, FDF could classify normal karyotype-intermediate risk patients into 2 groups with a significant difference in their overall survival, thus making this non-genetic and nonin vivo approach a new clinically relevant tool for a better diagnosis of AML patients. Word count: 1981 /2500 words. INTRODUCTION Leukemia initiating cells (LICs) are functionally defined as SCID Leukemia-initiating cells (SL-ICs) (1) in the xenograft assay by their capacity to initiate, propagate and maintain bulk leukemia in vivo (2). SL-ICs functional studies showed a correlation between the xenograft capacity of a sample as well as “stem cell gene signature” with poorer overall survival of the respective patient (3, 4). Additionally, an AML mathematical modelling of LICs proliferation was also separately shown to correlate with the clinical outcome of the patients (5). Thus, LICs quantification and their monitoring could have strong clinical applications especially for intermediate risk-normal karyotype AMLs that account for approximately 60% of all AML patients. However, the recently described heterogeneous on March 14, 2016. © 2016 American Association for Cancer Research. cancerres.aacrjournals.org Downloaded from Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. Author Manuscript Published OnlineFirst on March 9, 2016; DOI: 10.1158/0008-5472.CAN-15-2063