Abstract 4865: Differential survival and self-renewal of LSC and HSC in aged and leukemic niches
Authors: Balaian Larisa , Crews Leslie , Kulidjian Anna , Ball Edward , Jamieson Catriona 
Published: May 2015

Abstract
Background:
Acute myelogenous leukemia (AML) is a highly lethal disease with only 20% of 5 years survival. Progression to therapy resistant AML is driven by leukemia stem cells (LSC) harboring enhanced survival, dormancy and self-renewal capacity in supportive niches. Evidence indicates that in the development of AML deregulation of stem cells activity is as important as deregulation of the microenvironment. We have recently reported that inflammatory changes in the aging bone marrow (BM) niche via aberrant RNA editing and splicing may predispose patients to leukemic transformation. However, little is known about the functional effects of niche driven aberrant RNA processing in the AML pathogenesis, as well as of role of aberrant RNA editing and splicing in human aged stem cell fate, dormancy and regeneration in the context of microenvironment. Here we investigate: 1/ the LSC impacts to the BM niche and 2/ changes in the activity of BM niche cells contribute to AML pathogenesis.
Methods:
BM CD34- cell from normal donors and AML patients were used for the development of the primary human stromal monolayers : young (y-BM, n=3); old (a-BM, n=3) and AML (n=3). Human CD34+ cells were selected from AML primary samples (n=6). As a control, CD34+ cells from cord blood (CB, n=5), y-BM (n=3) or a-BM (n=3) were used for the co-culture experiments and then plated in survival and self-renewal assays.
Results:
AML- and normal BM-derived stroma differ in their ability to support HSC and LSC: LSC (n=6) were capable to self-renew after 9 weeks of co-culture with both normal and AML stroma, while cord blood HSC (n=5) lost their self-renewal potential after only 2 weeks of co-culture with the AML stroma. Aged BM also impaired survival and self-renewal of cord blood HSC (n=3) in stromal co-culture models. In similar experiments HSC from a-BM (n=3) demonstrated significantly higher survival and self-renewal capacity then co-cultured with y-BM stroma (n=3) compared to a-BM stroma (n=3). Conditioned media (CM) both from-, or co-culture with-, old or AML stroma impaired HSC survival and self-renewal. Notably, co-culture conditions resulted in a greater reduction in survival and self- renewal capacity, suggesting that cell-cell contact or unstable secreted factors exacerbate the effects. Cord blood HSC were also co-cultured with AML-derived stroma or CM , and this severely impaired their survival and self-renewal. Moreover, pre-treatment of the HS-5 cells with CM from a-BM or AML stroma for 4 weeks prior to co-culture experiments led to significant inhibition of the cord blood HSC (n=3) survival and self-renewal.
Conclusions:
Together these data indicate that microenvironmental cues play a key role in regulating normal HSC versus LSC survival and maintenance, and leukemic and aged stroma exibit severely compromised ability to maintain normal HSCs, but effectively support LSCs. Targeting this pathological interplay could represent a novel avenue for treatment of AML.
Citation Format: Larisa Balaian, Leslie Crews, Anna Kulidjian, Edward Ball, Catriona Jamieson. Differential survival and self-renewal of LSC and HSC in aged and leukemic niches. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4865. doi:10.1158/1538-7445.AM2014-4865