Blood stem cells — key to transplants that are used as life-saving treatments for blood cancers and blood and immune disorders — have the capacity to self-renew, but quickly lose their ability to do so in a lab dish. Scientists have identified a protein that not only enables blood stem cells to self-renew in a lab dish, but also allows these expanded cells to function effectively after being transplanted into mouse models. The findings could help make blood stem cell transplants available to more people and improve the accessibility and safety of gene therapies that use these cells.