BA (Philosophy): Stanford University, Stanford, CA; 1971
MD (Medicine): University of California, Davis, CA; 1977
Dr. Nelson is a scientist physician with a background in rheumatology, who has a primary interest in the interface of pregnancy with autoimmune disease, infectious disease, and cancer.
Dr. Nelson’s research group investigates immunologic consequences of maternal-fetal exchange during pregnancy and the legacy that maternal-fetal exchange creates for both individuals years later. A mother’s cells persist in her children into adult life and cells of fetal origin remain in the mother decades later. “Microchimerism” refers to harboring a small number of cells (or DNA) that originated in a genetically different individual. Dr. Nelson’s multidisciplinary research group investigates microchimerism in autoimmune disease, infectious disease, cancer, and transplantation.
Early research by her group evaluated immunologic consequences of pregnancy in the setting of autoimmune disease. Women with rheumatoid arthritis often experience arthritis amelioration during pregnancy. The group found that fetal-maternal differences for particular molecules, called HLA class II, correlated with arthritis improvement during pregnancy. In a subsequent study the team directly identified fetal-specific DNA in maternal blood and showed that higher levels correlated with pregnancy-induced arthritis amelioration. These HLA molecules are also important in transplantation and must be well-matched for organ and bone marrow transplantation to be successful.
Some HLA “types” are associated with risk of specific diseases, while other HLA molecules are protective. The Nelson team found that women who themselves lacked HLA “risk” molecules could acquire disease risk through cells from pregnancy (microchimerism), a kind of “mini-gene transfer of pregnancy”. On the other hand they also found that if microchimerism was acquired that had “protective” HLA molecules, pregnancy could result in a vaccine-like protection against disease that persisted for many years.
The autoimmune disease systemic sclerosis (also called scleroderma) has striking similarities to a syndrome that can develop after hematopoietic cell transplantation called “graft-versus-host disease”. Reasoning that cells exchanged during pregnancy create a legacy that lasts for decades Dr. Nelson proposed that microchimerism plays a role in some autoimmune diseases and first reported the novel finding of greater fetal origin microchimerism in women with systemic sclerosis compared to healthy women. Moreover, in studies of neonatal lupus, a passively acquired autoimmune disease associated with serious congenital heart block, the team identified maternal microchimerism in the heart and found that most maternal cells were not simply blood cells but rather were cardiac muscle cells. They also found maternal cells in the pancreas that produced insulin. Her team and others have found that maternal cells are normally present in a variety of organs and increased in some diseases.
While work on microchimerism in autoimmune disease continues, the group has since become interested in much broader ways in which consequences of maternal-fetal exchange are likely to impact human health. Women who have given birth generally have reduced breast cancer risk, suggesting fetal origin microchimerism may be protective. Consistent with this idea, they found less fetal microchimerism in women with breast cancer, compared to those without.
The Nelson group also found that microchimerism from a woman’s own mother becomes less detected after the woman has had her own children, suggesting child-derived microchimerism can displace microchimerism from the ‘grandmother. They are interested in whether this type of “graft-versus-graft” effect is analogous to the observation in double cord blood transplantation that only one unit appears to “win out” over time. The group is currently investigating maternal microchimerism in recipients of cord blood transplantation as potentially giving a protective boost against recurrent leukemia in the recipient. They previously showed that microchimerism is present in products that are administered to patients during hematopoietic stem cell transplantation.
These findings are giving us important clues as to precisely how maternal-fetal microchimerism can impact human health, and may lead to strategies to predict and perhaps prevent a variety of different diseases.