Stem cell field reacts somewhat cautiously to mammary pluripotent stem cell paper

An interesting paper just came out in PNAS reporting the apparent presence of pluripotent stem cells in the adult breast.

The paper is Roy, et al. and is from Thea Tlsty’s outstanding lab at UCSF.

I have read the paper and it seems very solid technically to me.

The finding has stimulated some powerful metaphors. For example, The San Francisco Business Journal called the paper an “Earthquake” for the field.

ePS cells

I have asked some leaders in the field behind the scenes for their impressions of the finding. Their reaction can be summed up as cautious interest.

One concern raised about the finding is that it is difficult to understand why the adult breast would need to have pluripotent stem cells. While the breast has inherent plasticity required for being able to gear up for milk production, why would the breast need stem cells that can make totally unrelated tissues?

Pancreas? Skin? Heart? Cartilage? Brain? (See image above of differentiation potential of ePS cells).


Mother nature usually makes good sense and there is an intrinsic logic in terms of how it works. Some people have said to me that the adult breast just does not need pluripotent stem cells so why would they be there? I don’t know, but just because it seems illogical for the breast to have pluripotent stem cells does not mean the paper is off-base, but it has made some experts cautious.

It is worth noting that just last year (2012), a paper (Hassiotou, et al) in the journal Stem Cells reported the presence of pluripotent stem cells in breast milk. Puzzlingly, the new 2013 Roy paper did not cite this 2012 paper at all. I find that concerning.

The reported stem cells in the new 2013 paper, what the authors called “endogenous pluripotent somatic” or ePS cells, are not identical to embryonic stem (ES) cells as the ePS cells are mortal, which means they will stop growing over time in the lab. ES cells are immortal and will grow forever. The lack of immortality of ePS cells is likely a good thing because it would make them safer. Also, ePS cells, if recapitulated, have another positive and that is no embryos are needed to make them.

The SF Biz Journal article says that the ePS cells are found in other adult tissues as well and in men:

Preliminary data suggest that ePS cells exist in parts of the body beyond adult breast tissue, Tlsty said, and in men as well as women.

“We have no idea if they’re different by gender,” she said.

EPS cells don’t appear to be left behind by embryonic stem cells, like pieces of bread dropped on a path to help someone find the way home, Tlsty said. The ePS cells, she said, have different expressions, surface markers and other characteristics than those found with embryonic stem cells.

CIRM itself has reacted publicly in a somewhat cautious manner to the paper as well:

“This really could be very exciting,” said Patricia Olson, executive director of scientific activities at the San Francisco-based California Institute for Regenerative Medicine, or CIRM. “If verified, I think it could be a big deal.”

Bottom line. Let’s see how this develops and whether the work can be verified without getting too overexuberant just yet. I hope that this finding on ePS cells holds up and is recapitulated by other labs. It would be exciting.