Blood cells are critically important to human health and a significant perturbation of blood production is life-threatening. In addition, the transformation of blood cell precursors leads to fatal leukemias, lymphomas and myeloma that remain difficult to treat and are often fatal within a few years of diagnosis. All blood cells must be produced from a common pool of self-maintaining cells called blood stem cells. Understanding the regulation of these cells and their immediate derivatives is critical because they are thought to be the origin of most blood cancers and it is the transplantation of these cells that is required to rescue the blood-forming system in patients who can benefit from treatment with an otherwise lethal dose of chemotherapy or require replacement of a defective blood-forming system. Although the use of blood stem cell transplants can be life-saving, its application is still limited. A major barrier to more widespread use is the extremely limited number of blood stem cells in the tissues where they are produced, and our inability to grow or expand these cells in tissue culture. Previous research has demonstrated that as they develop from fetal to adult cells, blood stem cells undergo an abrupt change that reduces their capacity to expand. Michael Copley’s research at the Terry Fox Lab focuses on improving our understanding in molecular terms of the mechanism that switches the ability of blood stem cells to expand that occurs shortly after birth. This could lead to the development of ways to block or reverse the switch, so that adult stem cells can be made more effective. It could also lead to an increased understanding of why different types of leukemias and other early onset blood disorders develop in children and adults.