Breast cancer remotely imposes a myeloid bias on hematopoietic stem cells by reprogramming the bone marrow niche.

Abstract Increased number of circulating myeloid cells is a hallmark of most cancers, however it remains unclear how primary tumors impact on myelopoiesis. Here we show that non-metastatic breast tumors remotely instruct the fate of long-term hematopoietic stem cell (HSCLT) in the bone marrow. We found that HSCLT from tumor bearing mice acquire a myeloid bias persisting upon primary and secondary HSCLT transfer in lethally-irradiated tumor-free animals. By imaging the bone marrow HSC niche, we found that the tumor-bearing status is associated with increased physical interactions between mesenchymal stem/stromal cells (MSC) and HSCLT. Moreover, ex vivo co-culture experiments demonstrate that MSC isolated from tumor-bearing mice increase myeloid differentiation of HSCLT isolated from tumor free mice. In summary, our data reveal that breast cancer remotely promotes myelopoiesis at the earliest stages of hematopoietic differentiation in the BM mesenchymal niche.