Acute Myeloid Leukemia Induced Remodelling of the Human Bone Marrow Niche Predicts Clinical Outcome

The hematopoietic stem cell (HSC) niche consists of different cellular and non-cellular constituents which regulate HSC maintenance and retention in the bone marrow. It has been shown in a number of murine models of myeloid neoplasia how leukemia infiltration alters the HSC niche to reinforce malignancy. Acute myeloid leukemia (AML) is characterized in human by a high relapse rate indicating that leukemia initiating cells are protected by its niche. However, despite our knowledge in murine models little is known about the bone marrow architecture in human and the impact of the leukemic niche on clinical outcome. In this study, we combined immunohistochemical stainings (IHC) with protein and global gene expression analyses together with clinical data to dissect the human bone marrow architecture in AML and assess its clinical impact. Human bone marrow was collected from AML patients at first diagnosis and matching non-leukemic donors. To evaluate the bone marrow architecture CD271+ mesenchymal stem and progenitor cells (MSPCs) were automatically quantified on bone marrow sections. In fact, AML patients showed 1.5-fold increase in bone marrow MSPCs compared to non-leukemic donors (Median (IQR), AML: 5.5% (2.8-9.5), n=36; control: 3.7% (2.1-5.7), n=58; p Next, to globally assess the gene expression profile of MSPCs in AML bone marrow we performed microarray analyses (ClariomTM S Human Assay) of freshly isolated uncultured lineage- CD146+ CD271+ MSPCs. Strikingly, HSC-regulating genes in particular CXCL12, ANGPT1 and VCAM1 showed lower expression in AML MSPCs which correlated with the degree of hematopoietic failure in AML patients. Along with the increased number of MSPCs, geneset enrichment analysis (GSEA) revealed higher proliferation of MSPCs in AML. In murine models loss of quiescence of MSPCs was previously found to be due to bone marrow sympathetic neuropathy. We therefore measured catecholamines and neurotrophic factor in the bone marrow extracellular fluid of AML patients and non-leukemic donors at first diagnosis. In fact, noradrenalin and brain-derived neurotrophic factor (BDNF) showed a 2-fold (p=0.26) resp. 4-fold (p In order to get an overview of alterations of canonical pathways in bone marrow MSPCs upon AML infiltration, we applied QIAGEN9s Ingenuity® Pathway Analysis software. Several of the major differently regulated pathways proved to involve differentiation and mineralization of MSPCs. We therefore assessed bone metabolism in AML patients at first diagnosis and quantified serum osteocalcin levels. Notably, AML patients showed 30% lower osteocalcin levels than non-leukemic donors (Median (IQR), AML, 12.15ng/ml (7.53-16.28) n=58; control, 17.2ng/ml (12.5-23.45) n=31; p In summary, we globally characterized the bone marrow architecture in AML patients in comparison to non-leukemic donors and assessed its clinical significance. This increasing understanding of the human AML bone marrow microenvironment might open the window for new niche-targeted therapies to eradicate leukemic stem cells and eventually decrease the high relapse rate in AML. Disclosures Duehrsen:Amgen: Research Funding; Roche: Honoraria, Research Funding; Gilead: Consultancy, Honoraria; Celgene: Honoraria, Research Funding; AbbVie: Consultancy, Honoraria; Janssen: Honoraria.