Microenvironmental cell interactions are essential for sustaining functionality of myelofibrosis malignant stem cells

Cancer develops through the interactions between cancer stem cells and components of the tumor microenvironment (TME). To model in vivo cancer stem cell-TME interactions and elucidate their functional consequences, we focused on myelofibrosis (MF), a stem cell-driven myeloproliferative neoplasm. We cocultured MF hematopoietic stem and progenitor cells (HSPCs) with normal donor endothelial cells (ECs) and mesenchymal stromal cells (MSCs) to investigate the consequences of interactions between malignant MF HSPCs and nonmalignant microenvironmental cells. This tricultivation system proved to be a simple and reproducible platform, which promoted malignant clone dominance and the persistence of MF HSPCs that recapitulate the MF phenotype upon transplantation into immunodeficient mice, including splenomegaly and marrow fibrosis. Transcriptional profiling revealed extensive reprogramming of not only the cocultured MF HSPCs, but also MSCs and ECs. Although numerous disease-relevant pathways were upregulated, the proinflammatory response stood out as a key consequence of MF HSPC-TME interactions. We validated these findings through quantitation of proinflammatory transcript upregulation and cytokine production. This human multicellular model system has proven useful in demonstrating the multidirectional interactions of MF HSPCs with TME cells that are essential for sustaining fully functional MF stem cells.