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A 37 year old mother of three comes into your clinic presenting abdominal pain, marked tiredness, and puffy ankles. The standard array of diagnostic tests suggests acute liver failure. Your patient rejects all treatment options, including radical liver transplantation surgery, and decides to wait and see how her disease state progresses. Remarkably, perhaps miraculously, six months later she shows signs of a complete recovery, despite a lack of medical intervention.
Just over a year ago, researchers at the New England Medical Center in Boston presented new data on an old cell type, pregnancy associated progenitor cells (PAPCs), which might help explain the deus ex machina mode of recovery in your patient. 1 As far back as 1979, 2 it was shown that women who give birth to sons retain some of their sons' fetal cells-for example, PAPCs, which can in turn give rise to multiple cell types along the haematopoietic stem cell (HSC) pathway of differentiation. i
i Presumably this effect occurs in women who give birth to daughters as well, but because Herzenberg et al were screening for a y chromosome, these daughters' fetal cells could not be detected at the time. 3, 4
After all, the reasoning goes, the placental/blood barrier is not a perfectly selective portal, and some fetal blood and cells will cross into maternal circulation. What is surprising, however, is the ubiquity and persistence of these fetal stem cells; they can be found in maternal circulation up to 27 years after the baby is born. 5 Additionally, these fetal stem cells were found to localise to diseased organs and repopulate them. For example, in one woman with a thyroid adenoma, biopsy revealed two populations of cells: her germline, cancerous thyroid cells were surrounded by healthy thyroid cells derived from her son's fetus. Even more strikingly, one woman with liver disease had significant repopulation of her liver with healthy fetal derived hepatocytes, the first indication of functional non-haematopoietic stem cell derived PAPCs. 1
Similarly, the liver recovery of our patient might involve some sort of natural defence mechanism whereby PAPCs patrol a mother's body and look for damaged tissues to repopulate. The principal researchers of the Boston study concluded that:
Whatever the mechanism involved, we believe that the idea of fetal...