We are a group of researchers interested in the biology of key cell types: hematopoietic stem cells, which give rise to all blood cells, endothelial cells lining all blood vessels, and perivascular cells, the priceless supporters. We used to study them as separate entities. Recently, we started to investigate their mutual cross-talks within the vascular niches. We are interested in their physiology, but we also want to understand why this balanced system sometimes stops working properly. And we remember about the heme, the ring that rules them all...