PROTEINS, carbohydrates and vitamins are all on the menu for a breastfed baby. Now it seems you can add stem cells to that list. Evidence is piling up that both breast milk and breast tissue contain embryonic-like stem cells.
That might mean we will soon have access to a source of stem cells without destroying embryos. This would be a boon as stem cells can turn into any type of human tissue, making them useful for treating degenerative diseases like Alzheimer's or for regrowing damaged heart muscle.
In 2011 Foteini Hassiotou at the University of Western Australia in Crawley and colleagues found stem cells in lactating breast tissue and breast milk. When they grew the breast milk cells they turned into the three types of cells from which all tissues and organs develop ? just like human embryonic stem cells (hESCs) do.
Hassiotou has since found this "pluripotency" in many more breast milk samples and thinks that breast milk stem cells could one day replace those from embryos. In one study, her team looked at fresh breast milk from more than 70 healthy breastfeeding women. They found that BMSCs expressed several genes that are also found in hESCs and help them replicate. Cultured samples also grew into different tissues including bone, neuron, heart and pancreatic cells (Human Lactation, DOI: 10.1177/0890334413477242).
In some cases, the team found that 30 per cent of all cells in breast milk were stem cells. In studies with monkeys and mice the cells were shown to pass into the bloodstream.
"One can speculate wildly about what they do in the baby," says Hassiotou. But she thinks that breastfed infants could be getting a developmental head start, with stem cells from the mother contributing to organ development in the newborn.
However, BMSCs fail one widely accepted test for embryonic cells: when injected into mice, they don't form a type of tumour called a teratoma. For many this failure is a deal-breaker.
But BMSCs are not alone. Mari Dezawa at Tohuku University in Sendai, Japan, and colleagues have found pluripotent cells called MUSE cells in bone marrow and connective tissue that do not form teratomas.
"The best stem cells might not make tumours," says Hassiotou. Dezawa agrees, and says that MUSE and BMSCs could be superior if they turn into a wide variety of cells without the risk of forming tumours.
Thea Tlsty at the University of California in San Francisco says she can imagine that there are pluripotent cells that do not make tumours. Her team recently identified pluripotent stem cells in breast tissue from non-lactating women and men (PNAS, doi.org/krn). Although her cells do form tumours, she agrees that the standard test needs revisiting.
Tlsty is not convinced that BMSCs are truly pluripotent, since they have yet to be shown to differentiate fully into living tissue. Nevertheless, she is open-minded. It used to be thought that these cells were restricted to the testes or ovaries, "now we're finding them all over the body".
This article appeared in print under the headline "Are breast milk stem cells the real deal"
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