Embryonic-like stem cells have been isolated from breast milk in large numbers. The discovery raises the possibility of sourcing stem cells for regenerative medicine, without the need to destroy embryos.
Peter Hartmann at the University of Western Australia in Crawley and his colleagues first announced the discovery of stem cells in breast milk in 2008. Now they have grown them in the lab and shown that they can turn into cells representative of all three embryonic germ layers, called the endoderm, mesoderm and ectoderm – a defining property of embryonic stem cells (ESC).
"They can become bone cells, joint cells, fat cells, pancreatic cells that produce their own insulin, liver cells that produce albumin and also neuronal cells," says Foteini Hassiotou, a member of Hartmann's lab team, who led the recent work.
The breast cells also express the majority of protein markers that you would expect to find in ESCs. "What is really amazing is that these cells can be obtained in quite large amounts in breast milk," Hassiotou adds.
She says the stem cells constitute around 2 per cent of cells in breast milk although the number varies according to how long the woman has been producing milk and how full her breasts are. Hassiotou will present the team's work at the 7th International Breastfeeding and Lactation Symposium in Vienna, Austria early next year.
Many remain sceptical, however. "Perhaps there are some mammary gland stem cells that can be coaxed to have a slightly broader potential than normal, but I very much doubt that embryonic-like cells normally exist in the breast," says Robin Lovell-Badge of the National Institute for Medical Research in London. For one thing, you would expect tumours to be more common than they are.
The real test will be to inject these cells into mice and see if they form teratomas – tumours containing tissue or structures derived from all three germ layers. "That's the gold standard for whether you have a true pluripotent cell," says Chris Mason of University College London. Hassitou says they plan to start these tests in the coming weeks.
Embryonic-like stem cells have previously been discovered in amniotic fluid and in the umbilical cord, but this is the first time they have been discovered in an adult. Other adult stems cells exist – such as hematopoietic stem cells, which can generate all types of blood cell and mesenchymal stem cells, which can turn into bone, fat and cartilage cells. But these stem cells cannot generate as many cell types as the breast milk cells apparently can. "If they are truly embryonic, this would be another way of getting stem cells that would not raise ethical concerns," says Mason.
However, even if they do not turn out to be ESCs, these breast milk cells could still have great potential for regenerative medicine. "It might be possible to grow these cells in culture then bank them so that if or when the mother develops some disease later in life, such as diabetes, her cells may be defrosted and differentiated into pancreatic beta cells," says Lyle Armstrong of Newcastle University, UK, although he too, cautions that more tests are needed to determine exactly what these cells are.
The discovery also raises intriguing questions about the role of these cells in breastfed babies. "It has been shown in mice that live immune cells in breast milk pass through the intestinal mucosa into the blood circulation of the pups and engraft in various tissues," says Hassiotou. "If these cells are in human milk and in such high amounts they probably have a role. They might contribute to tissue regeneration and development of the baby or play certain roles if there is a disease."
The team is planning experiments to track what happens to these cells once they get into infants.
New Scientist: November 2011 by Linda Geddes
