Breast milk stem cells

There’s more than just “milk” present in breast milk - it turns out that a hungry baby is actually gulping down millions of its mother's stem cells too. This week, University of Western Australia scientist Foteini Hassiotou has published work in the journal PloS One showing how the levels of these cells vary in breast milk. But do they survive in the baby, and what are they doing in milk in the first place? She spoke to Chris Smith...

Foteini - So we’ve been examining stem cells in human milk. We find them in all the milk samples that we’ve analysed so far, which is hundreds and hundreds of them. What we think is happening is that some of these stem cells come from the mother’s breast tissue and some come from the mother’s blood. So the question is, how they get into the milk, and what they do as soon as they are ingested by the baby.

Chris - Are they viable? In other words, are they living cells, they’re not just dead cells that have fallen out of the breast in the course of making the milk?

Foteini - They are very alive, and they are able to survive for quite a while in the milk. When we get freshly expressed breast milk from the mother and we isolate the cells and look at them under the microscope, in most of the cases you find a cell viability of more than 90%, so more than 90% of these cells are alive.

Chris - Do you think they have a physiological role, in other words do they do something for the developing baby?

Foteini - I do think so. And for something to be doing something it needs to have been there for quite a while, so these cells have been there in evolutionary terms for many, many, many millions of years.

Chris - How do you know that?

Foteini - The very early mammals, they also have cells in their milk. Every mammal has cells in their milk, so I think that is proof that they’ve been there for quite a while.

Chris - But when the baby eats the milk, it goes into the baby’s stomach, where there is acid and protein digesting enzymes – pretty harsh environment. Do they survive that?

Foteini - Apparently some of them do. And we’re doing a pretty cool experiment at the moment where we are trying to track these milk cells in mice. What we see happening is that some of these cells stick to the walls of the stomach and then they infiltrate through the walls, so they pass through the walls of the stomach into the blood vessels. That’s probably something that happens very quickly so that these cells can survive.

Chris - So they go beyond the gastrointestinal system, to other organs in the, in this case, mouse, but one presumes therefore also human.

Foteini - Certainly, yeah. If you think about this, every day a baby ingests millions of these cells from the mother’s milk, so there is a great chance that at least some of them make it to the blood circulation and from there to different organs.

Chris - Where do they go in the young animal when they’re ingested?

Foteini - So far it looks like they go to organs such as the thymus, liver, spleen, pancreas, and there’s also evidence from previous studies that cells from milk go to the bone marrow – those studies didn’t really examine whether these were stem cells or not but potentially some could have been stem cells.

Chris - Do you know how long they survive for? Obviously you can show they’re getting in, but that’s not the same thing as showing that they persist.

Foteini - We don’t know that yet. But we are looking into it. I think that would be the ultimate proof that they have a role, especially if they persist. But you can see this exchange of cells between the mother and the offspring starting very early on, even from the uterine environment where we know that there is exchange of stem cells between the mother and the embryo. These stem cells have been shown to persist both in the mother and in the embryo for many, many years after birth. So if this happens for these cells, why not for those cells that are exchanged or transferred to the offspring or transferred during breast feeding?

Chris - So what do you think they are doing, what could their role be?

Foteini - Of course I am speculating now. They could secrete factors that facilitate the local development of those tissues early on. We know that these cells secrete very important growth factors because we get these cells from milk and we grow them in culture, and they do secrete a number of important growth factors. They also make neurotrophins, which are very important for the brain development of the baby. And other very important factors that facilitate the development of the different tissues that we have, so that’s indirect evidence that they may actually have a role in the development of the offspring.

Chris - Do epidemiological studies looking at individuals that have or haven’t been breast fed with subsequent outcomes, do they give you any clues as to what these cells might be doing?

Foteini - We’ve only just found these cells, so there are no epidemiological studies!

Chris - But people have looked in the past at individuals who have been breast fed and then compared their outcome, in terms of health and allergy and all that kind of thing, with individuals who are not breast fed. So, are there any trends there that might fit with what you think these cells might be doing?

Foteini - From an immunological perspective, you do see a lot of things happening in the breast-fed babies, beneficial things that would not see them in formula-fed babies - for example, breast-fed babies don’t really get allergies, whereas formula-fed babies do. Breast-fed babies are protected from infections, so there are benefits, and these that can be facilitated through biochemical factors, molecules in the milk, but also by the cells – immune cells, but also, maybe, the stem cells, so that’s what we’re trying to find out.

Chris - What happens, then, if I drink unpasteurised cow’s milk?

Foteini - You take live cow’s milk stem cells and immune cells and other cells. What do the cells do in your body? I don’t know! Maybe there is a way for these cow stem cells to get into your blood and go into your tissues and stay there. So you develop to be a cow, I guess, rather than a man!

Chris - One wonders, yes, whether there might be some kind of, what they call microchimaerism, with a cow. You end up with cow cells, unless obviously the baby’s immue system kicks in and deals with them, but then if the baby has an immature immune system and it’s fed cow milk from birth, one wonders whether cow cells do maybe persist?