Dr. J. Lee Nelson studies microchimerism, a state in which cells exchanged by mother and child during pregnancy persist in both individuals for many years. Her interdisciplinary research team investigates the health consequences of this phenomenon. In 1998, Dr. Nelson reported the first study linking an autoimmune disease with the lasting presence of fetal cells in mothers. Because women generally develop autoimmune diseases more often than men, these findings have led to a new avenue of investigation into a range of diseases in which the immune system begins attacking the body’s own tissues. By learning more about microchimerism, Dr. Nelson hopes to help improve the success of blood stem cell and organ transplantation. Her team also investigates the role of microchimerism in cancer development, infectious diseases such as AIDS and complications of pregnancy.