Mitochondrial dsRNA from B-ALL cells stimulates mesenchymal stromal cells to become cancer associated fibroblasts
Cancer associated fibroblasts (CAF) arising from bone marrow-derived mesenchymal stromal cells (MSC) are prominent in B-precursor acute lymphoblastic leukaemia (B-ALL). We have previously shown that CAF formation is triggered by exposure to reactive oxygen species-inducing chemotherapy and that CAF support chemoresistance by donating mitochondria to the cancer cells, through tunnelling nanotubes. In the present study, we show that exposure of MSC to ALL cell lines, PDX and primary cells or their conditioned media can also trigger CAF formation, in an oncogene-dependent manner. Using bulk RNA sequencing in cell lines, we show that the MSC to CAF transition is accompanied by a robust interferon pathway response and we have validated this finding in primary cells. Using confocal microscopy and flow cytometry, we identify the take up of leukaemia cell-derived mitochondrial dsRNA by MSC as a proximate trigger for the MSC to CAF transition. We show that degradation of dsRNA in ALL cell conditioned media by DMSO ablates the ability of the conditioned media to stimulate MSC to CAF transition. Since we find that only specific primary driver genetic subtypes of B-ALL possess the property to directly generate CAFs, we propose this phenomenon as the first mechanistic insight into the strong relationship between acute lymphoblastic leukaemia genetic subtype and survival outcomes. Key pointsX Exposure of MSC to B-precursor ALL cell lines triggers cancer-associated fibroblast formation in an oncogene-dependent manner The proximate trigger for CAF formation is ALL-derived mitochondrial double stranded RNA