The Loh lab is exploring new strategies to replace an animal’s immune system and organs using embryonic stem cells (ESCs). Nationally, there is a major organ shortage and alternate means of organ regeneration are needed. One potential method is to use human embryonic stem cells as source material to develop new organs or cells for transplantation. To this end, our lab previously generated nearly-pure batches of human bone, heart, and liver precursors in a Petri dish from embryonic stem cells. However, even with the advent of new technologies to produce replacement organs, transplant recipients must take immune-suppressing drugs to keep their immune cells from attacking the foreign tissue, a regimen that can leave them vulnerable to infection. One way to circumvent the issue of immune rejection would be to replace an individual’s immune system with an ESC-derived immune system, a treatment that would then allow them to tolerate tissues that are also derived from ESCs. Our work could lead to the establishment of a system for organ transplantation that would eliminate the need for long-term immune suppression. Broadly speaking, the ability to safely replace an individual’s blood and immune system with a healthy, ESC-derived one opens the possibility to prevent or treat many diseases of the blood and immune systems, including autoimmune disorders.