The cells we share

13:20Lee Nelson:And that's maybe one of the biggest criticisms of they're just there. There's a few of them. You're just trying to find a purpose to this randomness of cells there.

13:29Amy Boddy:But if you just sort of step away from humans for a second, there is some more definitive research that has been done in mice. So in mice, they'll breed female mice with these special males so that some of their fetuses can create cells that fluoresce. It's like a glow-in-the-dark feature. And then the researchers can sort of dissect the mice or use machines to sort of track these glow-in-the-dark mouse fetus cells as they move through the mouse parent body.

14:03Lee Nelson:If a mouse gets an ear injury, the fetal cells will migrate up to the tissue. It seems like they're primed to be able to go in and kind of help recover and heal the maternal body. Huh.

14:19Amy Boddy:Which is cool. That's cool. And again, like, something like that could also be happening in other mammals, including humans. So it's not just sort of like C-section scars, healing injuries. There's also been some research on how these cells that the parent gets from their fetus could potentially help with heart health.

14:42Lee Nelson:There was a mouse model where the heart was injured and they saw these cells, these fetal cells migrating to the injury, specializing in helping repair.

14:57Amy Boddy:So this is in mice, but it would actually help explain a phenomenon that doctors have seen in humans, which is basically like a lot of pregnant people develop heart issues. So your heart is actually doing like a huge workout during pregnancy. This will be no surprise to you. But, you know, it's pumping a lot of blood. There's just like more of you and your body is working a lot harder. And so researchers have actually compared it to athletes who do long distance sports.

15:27Lee Nelson:So you could just be pregnant and be like, I'm basically an endurance athlete. No wonder I hated it.

15:36Amy Boddy:But because the heart is doing this, this sort of nine-month-long workout, it makes sense that a lot of pregnant people develop problems with their heart during this time. What's interesting is that sometimes these problems just kind of fix themselves. Like, they go away, and researchers aren't totally sure why. And some are wondering if the cells from the fetus actually help fix things. Like if the cells from the fetus are traveling to the heart and giving it some kind of boost that could explain the sort of heart healing that is happening here.

16:15Lee Nelson:So it's quite fantastic, I think, in thinking about the coolest, weirdest biology.

16:22Amy Boddy:And again, like, this is just one example of the ways that researchers think that these cells could be helping a parent's body sort of heal or fix issues, right? So maybe, you know, my cells at some point helped heal something in you as well.

16:42Lee Nelson:I think your cells need to get the right together. Let's get going here. Okay, we'll work on it.

16:51Amy Boddy:Nothing wrong with your heart, but I'll work on curing your various other ailments and diseases. Sorry. Sorry, I've been such a disappointment to you. You have not been a disappointment.

17:02Lee Nelson:Your cells are just, you know, let's get open. This feels like a perfect transition to the next thing here, which is that sometimes the parent-fetus-cell relationship becomes strained in certain ways.

17:24Amy Boddy:Like any communication between parent and child, it's not all sort of heart healing and scar knitting. Sometimes the cells from the kid can be somewhat obnoxious.

17:36Lee Nelson:This is the playing less well with others. Yes.

17:40Amy Boddy:So up next, how these cells might actually play a role in a whole range of pretty serious diseases.

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19:31So, Mama, when I was in your womb, I gave you a bunch of my cells.

19:38Amy Boddy:This happens whenever there's a fetus inside a pregnant person for a while. And in this exchange, Amy Boddy says that there are trade-offs.

19:48Lee Nelson:It might be helpful during pregnancy. It might be helpful in the postpartum period. But long term, there could be some tradeoffs where actually at some point it can lead to health complications.

20:02Amy Boddy:And one of the main complications that researchers have been exploring is related to autoimmune disease. Wow. So, like, to be really clear from the get-go, right, like, this is all very much theoretical, right? It's something researchers are still trying to figure out. So I would not want anyone with sort of an autoimmune disease to immediately assume that it comes from Mycocrimera or this like exchange of cells. Right. But basically, the way that Amy explained it to me is that we have this immune system and its whole job is to sort of cruise around, check up on various cells and say, like, is this me?

20:49Lee Nelson:typically your body recognizes self by specific markers on your cell that says you know like hey

20:57Amy Boddy:i am me and it leaves those cells alone but then if it comes across cells that don't look like

21:03Lee Nelson:itself then my immune system might say nope let's get rid of this but in an autoimmune disorder the

21:09Amy Boddy:immune system kind of goes haywire right like it starts attacking cells that are part of the body that are part of itself in some way. And that leads to sort of the swelling, the pain, tiredness, like a whole bunch of different issues that are associated with autoimmune disorders. And so the way that this is potentially linked to microchimera is it turns out that people who have carried fetuses at some point in their lives do seem to be at higher risk for autoimmune diseases. The data that we have now focuses on women, but it shows that these diseases are significantly more likely to affect women as compared to men.

21:53Amy Boddy:And some studies have found that the chances of getting some of these diseases actually increases after women's reproductive years. So researchers were kind of looking at microchimera and they were thinking like, okay, people who are getting pregnant are bringing kind of foreign cells into themselves that look a lot like them. Because usually half our DNA comes from each of our parents. So these cells come in, they become part of the body, sort of part of the tissue. And then down the line, one scenario is that they do something that the body cells wouldn't usually do, right? Something more unique to the kid's cells.

22:37Lee Nelson:So maybe, for example, they're expressing a protein you've never seen before. Then your immune system might say, hey, that's not self. We need to go ahead and get rid of this. And that can, you know, elicit an autoimmune response. I don't know if we can call it autoimmune because that means self, right?

22:59Amy Boddy:Like, is it autoimmune? Because it's not attacking the self. It's attacking these foreign cells. And that's kind of the whole problem here, right? Like, these cells are both part of the parent self and also genetically foreign. So maybe, and again, emphasis on maybe, this could be contributing to autoimmune diseases. Like maybe these foreign but not so foreign cells are why the body starts attacking itself. And there have been a few studies to sort of look at people with autoimmune diseases to look for proof that this might be happening.

23:40Lee Nelson:There's a few different studies looking at individuals with autoimmune disease, and they find these fetal cells in the tissue. But once again, like, these are mostly sort of correlations.

23:53Amy Boddy:Like, we saw these cells and we saw this problem. Maybe they're related.

23:59Lee Nelson:We don't know the root cause. We don't know if these individuals would have gone on to get autoimmune diseases anyways, and the cells, again, just happen to be there.

24:09Amy Boddy:So, like, there's still work to be done here to sort of tease this relationship out and figure out what's going on. But it is sort of one way, at least, that people think that some of these sort of cells from, like, fetuses could be causing issues.

24:27Lee Nelson:Okay. I am fascinated by this. I wish there were more information. But what an interesting possibility.

24:37Amy Boddy:I think so, too. Right. So there's this possibility, this possibility that they're involved in autoimmune diseases. And then the other possibility, which you are not going to like, is that these microchimera might also play a role in cancer. Okay. Play it on. Just play it on. So basically, cancer is almost one of the best examples of maybe this is helpful, maybe this is harmful. Like right now, it's just kind of deeply confusing. Amy was saying she actually got interested in microchimera when she was studying breast cancer. So she was sort of like reading through these papers.

25:20Lee Nelson:And some women had higher amounts of fetal cells in their body and were diagnosed with cancer.

25:28Amy Boddy:Which would suggest that there could be some kind of a connection again or like a correlation, right? Like more cells from the fetus, more cancer potentially.

25:40Lee Nelson:But then there's other papers. This is where it gets really confusing. There's other studies showing that, no, actually, those cells might be in there trying to help fight the cancer. And actually, these cells are protective. And so it's a big, like, we don't know what they're doing. Are they fighting the tumor? Are they making, you know, the immune system more aggressive and making this cancer worse? And we don't know the answer to that.

26:09Amy Boddy:So, again, there are a lot of questions here, right? But if we can figure this stuff out, like, if we can figure out exactly the effects that microchimera have on our body in terms of cancer or also autoimmune diseases, like, that could potentially be huge, right? Amy was saying that maybe we could figure out if people are high risk for certain issues and help them early, for example.

26:35Lee Nelson:The other exciting thing is some people are, again, seeing these potential fetal cells helping with wound healing. And the thought is that it could be a therapy as well, providing a boost of stem cells to actually help fight a disease or help heal.

26:55Amy Boddy:Right now, because this is all such a mystery, like we're still a very long way away from these kinds of applications, right? Which I guess kind of just left me wondering why, right? Like why do we still have so many questions instead of answers here and know so little? That is a good question. Lee Nelson agrees with you. That's a good question. Lee Nelson is actually one of the researchers that I mentioned before who first started diving into microchimera in the 1990s. And she's been doing a lot of work for many decades on the autoimmune stuff specifically. So I asked her essentially, like, why we are still so far from answers.

27:41Lee Nelson:The most direct two answers to that are technical. So it's the techniques. And the other one is funding.

27:51Amy Boddy:Reproductive health in general is very underfunded, but this work is also just very hard from a technical perspective. The big challenge is very simple. There are all these little chimerical cells that are very hard to track. And, you know, you can put tracers in mice, like we mentioned before, but mice are not humans. Like, mouse pregnancy just looks different than human pregnancy, which could lead to different effects.

28:21Lee Nelson:I mean, routinely, mice are multiple gestations.

28:25Amy Boddy:They're routinely having, like, eight pups all at the same time, for example.

28:30Lee Nelson:I don't know anybody that's had eight or nine kids.

28:32Amy Boddy:And meanwhile, you can't, like, inject human fetuses with glow-in-the-dark tracers or cut up human parents in the same way as mice to see what's going on.

28:44Lee Nelson:And so as a result, when you're looking at some of these cells in human tissue, you can't really know both where it came from and where it went to and kind of everything about it.

28:55Amy Boddy:And then even if you do have sort of some tissue that you're looking at from a human, finding these cells isn't easy, right? It's a couple of cells in a million. And so it's kind of like looking for a needle in the haystack if the needle looked like a lot like hay, right? Because it's actually got half the hay's DNA. And then one extra wrinkle that I talked about with both Lee and Amy, but which I've sort of been saving for the end, is that microchimerism isn't just about fetuses passing cells to their parents. It's actually a lot more complicated because it goes both ways. so not only am I kind of giving you my cells but when I was in your womb you gave me some of your cells as well of course which means that you're not just sort of a chimera of of me and and my sister Chloe and any miscarriages that you might have had you also have my grandmother muddy cells swimming around inside of you as well.

30:06Lee Nelson:That makes perfect sense. How far back does it go?

30:11Amy Boddy:So it is also possible that your mom, so my grandmother, gave you some of your grandmother's cells. So any researcher sort of looking, Mama, at your tissue would be saying, is this cell from Anber Platt or is it from her daughter Chloe or her daughter Bird or her mother or her grandmother or a miscarriage she had or like what? And so Amy says it's just hard to parse.

30:43Lee Nelson:So we've been talking very simply about this because it is so complex that we, our minds can't even wrap around the fact that there's actually multiple generations happening all at once.

30:55Amy Boddy:And so studying microchimera is so hard because you have to find just like a few cells in a million, untangle this whole intergenerational jumble, and then figure out like what those cells are doing, what they're up to. And that's part of why this research is going so slowly. You're getting these like two of, you know, a thousand piece puzzle, right?

31:24Lee Nelson:And you're like, I think it's a horse, but then you haven't seen, you know, the rest of the body or something like that.

31:36And I find it, I mean, I find it, like, I guess there's something about it that, like, there might be things that we'd never fully understand here, right?

31:48Amy Boddy:Like, we are potentially never going to be able to completely untangle the way that, like, my cells and my sister's cells and the cells from your miscarriages have affected your body. Like, it's possible it's always going to remain kind of like a parent-child relationship, right? Like, on a tiny scale, there'll be sort of pushing and pulling and hurting and healing and, you know, it's a relationship we can explore forever. and never fully untangle?

32:20Lee Nelson:To be sure. But to me, the whole benefit of this kind of research is that what you know now, let's say you really, not you, one was really able to go into this into a lot more depth. They're always surprised. That's the reason everybody does research. They're always like, oh, we were looking for X and we found a whole different section of the alphabet. It strikes me as a good enough reason to pursue it.

32:58Amy Boddy:I'm beginning to realize where I came from. It's beginning to make sense that I have maybe some of your cells in my body and our brain. question would you say I'm overall more of like a scar healing helper or an autoimmune disease trigger of a child

33:19Lee Nelson:oh sweetheart you are a scar healing helper it's on the record

33:30Lee Nelson:and I'm so happy you're here I'm happy you're here mama I love you

33:40Amy Boddy:I assume that's it. We're done. Yeah, I think that's it. I think we're done. Okay. Thank you for doing this.

33:47Lee Nelson:You're very welcome. In a separate space, I will bring you up to date on certain postal events coming your way soon. And you can bring me up to date on other events in your life.

34:13Amy Boddy:This episode was reported and produced by me, Bird Pinkerton. It was edited by Brian Resnick and Catherine Wells, as well as Meredith Hodnott, who runs the show. We had sound design and mixing from Christian Ayala, music from Noam Hasenfeld, Serena Solon checked our facts, and Mandy Nguyen is just really lovely to have nearby. I want to say a special thank you this episode to Lee Nelson, who sent so many articles that just really helped orient me and deepen my knowledge here. So if you want to read more about microchimera and autoimmune disorders, look up her body of research. I would also recommend the article that Amy Boddy co-authored in Bioessays in 2015.

34:59Amy Boddy:If you would like to support the show and the journalism that Vox does, we would love it if you would become a member. It is very easy to do. Just go to Vox.com slash members and you will get access to all of Vox's journalism. But you will also know that you are supporting all of Vox's journalism. And for those of you who have emailed to let us know that you signed up because of Unexplainable, thank you. And thank you to those of you who have left us a nice review on your podcast platform or told someone in your life about the show. You are all excellent. unexplainable is part of the vox media podcast network and we will be back very soon with another episode about everything that we do not yet know

36:13Lee Nelson:We'll see you next time.

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