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Materials and methods
Results
Discussion
Conclusions The following are the supplementary data related to this article.
Acknowledgments This work was supported by grants from the Ministry of Education, Culture, Sports, Science and Technology [22500340 to M.H., 24300197 to M.H., T.O.] and a grant from the Strategic Research Foundation Grant-aided Project for Private Schools at Heisei 23rd from the Ministry of Education, Culture, Sports, Science and Technology of Japan, 2011–2015 [to M.H.].
Introduction Acute myeloid leukemia (AML) is the best studied human tumor for cancer stem cell research and has contributed to our understanding of the cancer stem cell model (Dick, 2008; Lapidot et al., 1994; Bhatia et al., 1998). Since leukemic stem na inhibitor (LSCs) are considered to be associated with relapse, chemotherapy resistance and overall poor prognosis (Eppert et al., 2011; Gentles et al., 2010), targeting LSCs has been proposed as a promising strategy for cure of AML (Saito et al., 2010, 2013; Misaghian et al., 2009). Immuno-deficient mouse xenotransplantation models are the gold standard assay for LSCs, and SCID leukemia-initiating cells (SL-ICs) are thought to possess the functional and molecular characteristics of LSCs (Lapidot et al., 1994; Bhatia et al., 1998). However SL-ICs in primary human AML are rare and heterogeneous (Eppert et al., 2011; Gentles et al., 2010; Sarry et al., 2011), therefore patient-derived human primary AML samples are not always sufficient to allow hematopoietic reconstitution in xenotransplantation model. Development of an in vitro LSC culture system would facilitate further advances in cancer stem cell research and assist in the development of novel therapeutic targets of LSCs (Kennedy and Barabe, 2008). Mesenchymal stromal cells (MSCs) are known to support the growth and differentiation of normal hematopoietic stem cells (HSCs) (de Lima et al., 2012; Keating, 2012; Robinson et al., 2006) through various molecular signals such as CXCL12-mediated CXCR4 signaling and Wnt-induced β-catenin signaling. Murine stromal cell lines and growth factors have been used to expand primary human AML blasts in vitro, however the leukemic blasts eventually lost their original CD34+CD38− phenotype in long-term in vitro culture systems (Klco et al., 2013; van Gosliga et al., 2007). We hypothesized that human MSCs may also provide a survival benefit for LSCs since they share similar molecular signatures with normal HSCs (Eppert et al., 2011; Gentles et al., 2010), and MSC co-culture systems can be utilized for long-term maintenance of LSCs in vitro even without growth factors. Furthermore, understanding relationships between AML and its stromal niche is of importance for defining mechanisms of leukemic persistence and preventing leukemic relapse. Here we co-cultured human primary leukemic blasts with unrelated bone marrow (BM) derived human MSCs and characterized the phenotype and function of leukemic blasts and their ability to engraft in a xenotransplantation mouse model.
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Discussion BM-derived MSCs represent part of the multicellular stromal support that creates a milieu to maintain HSC function and allow growth and differentiation of hematopoietic progenitors. The ease with which MSCs can be expanded in vitro facilitates the study of the interaction of MSCs with hematopoietic progenitors. MSCs have been successfully employed to increase the hematopoietic stem and progenitor cell numbers in cord blood for transplantation (de Lima et al., 2012). A current interest is whether the marrow milieu is also supportive to AML stem cells and represents a sanctuary for persistence of LSCs after remission. Understanding the nature of the stroma-LSC interactions would inform more effective therapy to eliminate residual leukemia persisting after induction chemotherapy. Furthermore an in vitro stromal/LSC co-culture system that replicates favorable conditions for LSC persistence would serve as a more relevant model for testing agents active against LSCs.