A specific subset of Mesenchymal Stromal Cells identified in poor prognosis pediatric AML favor leukemic stem cells persistence in the bone marrow [scRNA-seq]

Pediatric Acute Myeloid Leukemia (AML) emerge likely from highly complex, dynamic and multiparametric mechanism. The importance of stromal cells from the hematopoietic bone marrow (BM) microenvironment in early steps of pediatric AML (pAML) was explored in this study, based on samples of patients collected at diagnosis from a multicenter cohort (CONECT-AML). BM-Mesenchymal stem cells (BM-MSC) were isolated and characterized. Flow cytometry analysis revealed in more than a third of patients, the presence of a CD117(c-kit)-expressing sub-population of BM-MSC, rarely observed in healthy donors, associated with a higher LSC-17 score and a poor risk patient's group. Lastly, single cell RNAseq data from pAML leukemic cells cocultured in a robust 3D-BM physio-pathological system built with CD117+ BM-MSC cells, indicate a high level of cell-cell interaction specific of this MSC. Very importantly, the presence of CD117+ BM-MSC significantly protect leukemic cells from chemotherapy killing trough cell-cell contacts. To summarize, we revealed the existence of a BM-MSC population associated with high risk pAML and that protect leukemic cells from treatments. Overall design: Mesenchymal stroma cells isolated from bone marrow of either pediatric donors or leukemic patients were categorized according to their phenotypic status for the CD117 / c-Kit / Kit marker. One condition was sent to single cell RNA-seq : a mix of endothelial cells, CD117 positive stromal cells, and hematopoietic cells untreated