Cutting the umbilical cord doesn't necessarily sever the physical link between mother and child. Many cells pass back and forth between the mother and fetus during pregnancy and can be detected in the tissues and organs of both even decades later. This mixing of cells from two genetically distinct individuals is called microchimerism. The phenomenon is the focus of an increasing number of scientists who wonder what role these cells play in the body.
A potentially significant one, it turns out. Research implicates that maternal and fetal microchimerism plays both adverse and beneficial roles in some autoimmune diseases as well as the prevention of at least one cancer. This double-edged sword in turn has opened new avenues of study of the body's immune system and the possibility of developing new tests and therapies.
Two of the world's leading researchers in microchimerism are J. Lee Nelson, M.D., of Fred Hutchinson Cancer Research Center's Clinical Research Division; and V.K. Gadi, M.D., Ph.D., assistant professor of medicine at the University of Washington. Nelson also is a professor of medicine at the University of Washington. Gadi is also a research associate in the Hutchinson Center's Clinical Research Division.
In 2007, they were the first to report these potentially beneficial effects of microchimerism:
- In January, Nelson reported the first discovery that cells passed from mother to child during pregnancy can differentiate into functioning islet beta cells that produce insulin in the child. The same study also found maternal DNA in greater amounts in the blood of children and young adults with Type 1 diabetes than their healthy siblings and a control group, implying that the cells may be attempting to repair damaged tissue. There was no evidence that the mother's cells were attacking the child's insulin cells and no evidence that the maternal cells were targets of an immune response from the child's immune system. The findings could lead to new approaches to treating Type 1 diabetes. For example, if maternal microchimerism results in cells that make insulin, a mother's stem cells might be harvested and used to treat her diabetic child. Such cells would have a genetic edge over donated islet cells from a cadaver that are usually completely genetically mismatched.
- Last October, a research paper by Gadi and Nelson described findings that suggest fetal cells that persist in a woman's body long after pregnancy in some cases may reduce the woman's risk of breast cancer. The scientists examined the blood of 82 women post-pregnancy, 35 of whom had had breast cancer. They looked for male DNA in the blood, presuming it was present due to a prior pregnancy with a male. Fetal microchimerism (FMc) was found significantly more often in healthy women than women with a history of breast cancer, 43 percent versus 14 percent respectively. The scientists concluded that FMc may contribute to the reduction of breast cancer based on the hypothesis that residual fetal cells may provide immune surveillance of malignant cells in the mother. They caution that further studies are needed to confirm the theory.
Microchimerism reveals its Jekyll and Hyde personality in the case of autoimmune diseases. In the late 1990s, Nelson's group was the first to investigate microchimerism in an autoimmune disease: