Genetic Subtype Driven Changes in Bone Marrow Stromal Cells of Children with B-Cell Precursor Acute Lymphoblastic Leukemia

Abstract

Introduction We previously showed that B-cell precursor acute lymphoblastic leukemia (BCP-ALL) cells hijack the normal bone marrow microenvironment to create a leukemic niche which facilitates blast cell survival and promotes drug resistance [1-3]. Bone marrow-derived mesenchymal stromal cells (MSCs) are a major component of the bone marrow microenvironment . Ex vivo,these cells provide a survival benefit to co-cultured leukemic cells and induce resistance to chemotherapeutic drugs [1, 2]. We previously showed that leukemic cells re-sensitize to chemotherapeutics ex vivo when the interaction with MSCs is disrupted [2]. Results We here report that patients' BCP-ALL cells induce an Interferon (IFN)-related gene signature in patients'-derived MSCs; a.o. IFI6, MX1, and OAS3 were 4.3 to 7.7-fold upregulated in MSCs flow-sorted after co-culture with BCP-ALL cells compared to the same MSCs flow-sorted after mono-culture . BCP-ALL samples (n=15) with an ETV6-RUNX1 translocation (5 out of 8 samples) were the most potent inducers of the IFN-related gene expression signature in MSCs compared to B-other BCP-ALL (1 out of 6 samples), with IFI6 3.0-fold (p=0.03), MX1 2.6-fold(p=0.05) and OAS3 2.1-fold (p=0.04) higher in MSCs after co-culture with ETV6-RUNX1 BCP-ALL cells. Similarly, an ETV6-RUNX1cell line (REH) also induced this IFN-response more strongly in MSCs compared to cell lines representing other BCP-ALL subtypes (SUPB15, MUTZ5, RCH-ACV and NALM6). Addition of specific inhibitors to these ex vivo BCP-ALL and MSCs cultures, revealed that the ETV6-RUNX1 induced IFN signature was dependent on IFNα/β signaling, whereas no such effect was seen for inhibitors of IFNγ signaling. Additionally, inhibition of direct contact between BCP-ALL cells and MSCs also negatively affected the expression of some IFN responsive genes in MSCs ( CXCL10 3.3-fold, p=0.02, IFI44L 1.57-fold, p=0.01 and IFITM1 1.5-fold, p=0.005) while other genes remained unaltered, suggesting that the transcriptional changes in MSCs are driven by close contact with BCP-ALL cells and not by soluble factors released by these cells or those being part of the culture medium. Normal immune cells including various populations of T-cells, monocytes, NK cells and dendritic cells did not alter the expression levels of the IFN-related genes in MSCs. We also observed that, while MSCs provide a survival benefit to (ETV6-RUNX1) BCP-ALL cells and induce resistance to chemotherapeutic drugs (prednisolone, daunorubicin, L-asparaginase) in these leukemic cells, this was not counteracted by inhibition of IFNα/β signaling. Conclusion Our data show that leukemic cells, more specifically ETV6-RUNX1 positive BCP-ALL cells, induce an IFNα/β signature in MSCs. Activation of this IFNα/β pathway in MSCs does not cause resistance of BCP-ALL cells to chemotherapeutic drugs and hence the IFNα/β activation may serve a different role, e.g., affecting the migration (recruitment and/or repelling) of specific immune cells to the leukemic bone marrow niche. Our findings warrant further studies into the role of the BCP-ALL-induced IFNα/β response in chemotaxis of healthy immune cells to create a beneficial microenvironment for BCP-ALL cells. This knowledge might point to alternative, maybe less intensive ways to eradicate leukemic cells.