Physicians may one day be able to treat genetic blood diseases before a child is even born. In a study of mice that was published this week in the Journal of Clinical Investigation, researchers at the University of California, San Francisco, have found that transplanting a mother's own stem cells into her fetus populates its bone marrow with healthy cells while avoiding immune rejection. If the findings hold true in humans, stem-cell transplants from mother to fetus could prime the fetus.