Myelodysplastic Syndrome-Derived Stromal Cells Support Leukemia-Initiating Cells and Contradirectly Eliminate Normal CD34+ Clonogenic Cells

The failure of normal hematopoiesis in myeloid neoplasm could be induced by a variety of mechanism. Regarding myelodysplastic syndrome (MDS)/acute leukemia (AML), aberrant hematopoietic stem/progenitor cells with exhibiting ineffective hematopoiesis and impaired differentiation ability gradually substitute it for normal hematopoietic stem/progenitor cells during a long term as a consequent of replacement of stem cell niche. However, it has not yet been clarified precise mechanism how MDS stem/progenitor cells could replace normal hematopoietic stem/progenitor cells.

In an attempt to analyze the supporting activity of bone marrow (BM) stromal cells, we first established the MDS/AML-derived stromal cells and healthy volunteer (HV)-derived-stromal cells. Next, MDS/AML-derived CD34+ cells or normal CD34+ cells were cocultured with established stromal cells using cytokines including stem cell factor, thrombopoietin, flt3-ligand in the presence of notch ligand (for normal CD34+ cells) or IL-3 (for AML/MDS derived cells). Subsequently, we analyzed clonogenic cells after 2 weeks coculture, 5 week cobblestone area-forming cells (CAFC) and repopulating cells in immunedeficient mice (NSG mice).

The support of clonogenic cells after 2 weeks coculture and 5 weeks CAFCs was observed after coculture with normal CD34+ cells and HV-derived stromal cells. Furthermore, these cocultured cells engrafted into immunedeficient mice. Interestingly, the number of colony-forming units (CFU) mixed cells (MIXs) and CAFC derived from CD34+ cells was drastically reduced after coculture with MDS/AML-derived stromal cells. Nevertheless, MDS/AML-derived stromal cells support the proliferation of leukemia-initiating cells (L-ICs) and L-ICs were detected after third replating. These results indicate that MDS/AML-derived stromal cells preferentially support leukemia stem/progenitor cells, but not normal CD34+ cells. We compared the mRNA expression between (HV)-derived-stromal cells, MDS/AML-derived stromal cells and 5-aza-dC-treated stromal cells. The expression of several factors including hedgehog-interacting protein (HHIP) was reduced in MDS/AML-derived stromal cells. 5-aza-dC treatment restored the expression in some of genes and the stromal supporting activity for normal CD34+ cells partially recovered.

These results suggest that reduction of several gene expressions was detected in MDS/AML stromal cells by changes of methylation status. The epigenetic alteration of stromal genome may be involved in the progression of myeloid disorders.

No relevant conflicts of interest to declare.