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RENEE MONTAGNE, host:

What would you say if we told you that when a woman has a baby, she gets not just a son or daughter, she gets an army of protective cells--gifts from her children that will stay inside her and defend her for the rest of her life? It's such an enticingly beautiful idea, the scientists who proposed it worry that maybe it's too beautiful. NPR's Robert Krulwich has the story.

ROBERT KRULWICH reporting:

For years it was thought as soon as a baby is conceived, once it starts to grow inside a mom, it gets its own very private space.

Dr. KIRBY JOHNSON, PH.D. (Research Assistant Professor, Pediatrics, Tufts University School of Medicine): There is, there's a placenta.

KRULWICH: Yeah.

Dr. JOHNSON: Placenta was thought to be a fairly impenetrable barrier.

KRULWICH: So says Dr. Kirby Johnson, of Tufts University. The baby and its cells stay on the baby side. The mommy cells stay on the mommy side and nature keeps them separate until ...

(Soundbite of baby crying)

KRULWICH: It's, yeah, time to go. And here's the surprise. When scientists at Tufts took blood from ordinary pregnant moms ...

Dr. JOHNSON: We would find, for example, in a teaspoon of blood, dozens, perhaps even hundreds of cells.

KRULWICH: From the baby.

Dr. JOHNSON: From the baby.

KRULWICH: So, baby cells were slipping out of the placenta into the moms. But, because babies do have different genes ...

Dr. JOHNSON: One would expect them to be attacked fairly rapidly. You would expect them to be cleared within hours if not days. What we found is that that is not the case, not anywhere near the case.

KRULWICH: It turns out that babies' cells stay in their moms, not for days or weeks, but for decades.

Dr. JOHNSON: Four to five decades following the last pregnancy.

KRULWICH: So, 40 years after conception, that son or daughter who could now be a middle-aged pharmacist or somethin', yet their fetal cells, their baby cells, are still floating around inside the mother?

Dr. JOHNSON: Yes.

KRULWICH: Even his 60-year-old mother? 70?

Dr. JOHNSON: 70, 80, perhaps 90-year-old women.

KRULWICH: You're sure of this?

Dr. JOHNSON: Absolutely.

Dr. CAROL ARTLETT, PH.D. (Postdoctoral Fellow, Department of Medicine, Division of Rheumatology, Thomas Jefferson University): Yeah, these cells last essentially forever.

KRULWICH: In the mom!

Dr. ARTLETT: In the mom.

KRULWICH: And, says Carol Artlett, who studies fetal cells at Thomas Jefferson University in Philadelphia, even if a woman has a miscarriage or an abortion, even if there is no baby, the cells of an unborn child will stay in the mother for decades. But, why? What exactly are they doin' in there for years and years and years?

Dr. ARTLETT: (Laughs) That's a good question.

KRULWICH: (Laughs) Well, one early hypothesis--and it's not the nicest idea, says Kirby Johnson--is that certain autoimmune diseases...

Dr. JOHNSON: Such as lupus, rheumatoid arthritis, scleroderma are much more common in women than men and that's one component of the hypothesis is that this prevalence in women is due to fetal cells.

KRULWICH: So, later in life, when the mother's joints inflame, maybe it's her fetal cells--her own baby's--taking a poke at her. In fact, Kirby's mom did have an autoimmune disease. It was a bad one and for awhile Kirby thought, well, his cells were responsible.

Dr. JOHNSON: So, I apologized immediately and said, well, there's nothing much I can do about it.

KRULWICH: (Laughing) Yeah, yeah, but it's like, stop it, Kirby.

Dr. JOHNSON: But, you know what? I was always doing that to my mother. Always causing problems and it was just another in a long line of those kinds of things.

KRULWICH: But happily the folks at Tufts proposed an alternative, a second theory, to explain what fetal cells are doing in the moms.

Dr. JOHNSON: Well, theory number two is the polar opposite of theory number one.

KRULWICH: The good fetal cell hypothesis proposes that the son or daughter cells stay in mom, not to hurt her, but to protect, defend and repair her for the rest of her life whenever she gets seriously ill and that's a more attractive idea.

Dr. JOHNSON: It's such a personal thing and it does touch the heartstrings of even the most hardnosed research scientist.

KRULWICH: But they all have mothers.

Dr. JOHNSON: But they all have mothers.

KRULWICH: And happily they now have evidence--more and more evidence says Kirby Johnson--that looks like the good hypothesis may be correct. For example, here's a case.

Dr. JOHNSON: Well, this was a woman who came into a neighboring hospital in Boston with symptoms of hepatitis. She was an intravenous drug user ...

KRULWICH: And she had had five conceptions. She'd had one child, two miscarriages, two abortions, that's five in all; she could be carrying, therefore, a lot of fetal cells and they examined her ...

Dr. JOHNSON: And in the process, she had a liver biopsy ...

KRULWICH: And the doc said well, why don't we send her liver to the lab to see if there are any fetal cells gathering where she's got trouble, and when they looked ...

Dr. JOHNSON: We found hundreds...

KRULWICH: Wow!

Dr. JOHNSON: ...and hundreds of fetal cells.

KRULWICH: Normally they'd expect five or ten cells.

Dr. JOHNSON: But this was a very large--we saw, literally, sheets of cells, whole areas that seemed to be normal ...

KRULWICH: Meaning that those fetal cells had gathered at the liver and like stem cells, they just turned themselves, in this case, into healthy liver cells.

Dr. JOHNSON: And most interestingly, this woman did not desire to have any further treatment done. In fact, she wanted to get back to her normal life and be left alone.

KRULWICH: And so she left the hospital with hepatitis but when they checked months later, they learned ...

Dr. JOHNSON: That she is completely healthy, no signs of further liver damage ...

KRULWICH: So, no medical intervention, but just a huge number of her babies' fetal cells? Could that lead you to think the poetic thought, that she was saved by her kids?

Dr. JOHNSON: (Hesitates) We want to think that.

KRULWICH: (Laughs) I know you do.

Dr. JOHNSON: There, it's the most likely obser-, explanation.

KRULWICH: But, in science there is such a thing as a too dangerously beautiful idea.

Dr. JOHNSON: That's right, right! And we say the same thing to ourselves because it shows such a basic wonderful thing, but it has to be right and we can't be led astray by our own desire for it to be true.

KRULWICH: So they are systematically testing the good hypothesis and the bad hypothesis, all these ideas, on laboratory mice--and when they see mother mice with all kinds of diseases--infectious disease, cancer...

Dr. JOHNSON: Ovarian cancer, endometrial cancer, cervical cancers, we find fetal cells there. We know that fetal cells...

KRULWICH: Over and over and over and over?

Dr. JOHNSON: Over and over and over and over.

KRULWICH: Suggesting that fetal cells regularly rush to the places where they're needed in the mom, and, says Carol Artlett...

Dr. ARTLETT: There's a lot of evidence now starting to come out that these cells may actually be repairing tissue.

KRULWICH: That is, protecting the mom. While the other hypothesis, the fetal cells hurt the moms, there, the more they look, the less they find.

Dr. JOHNSON: I can't recall a single study that's been truly reproduced to verify the bad fetal cell hypothesis.

KRULWICH: So, while no one knows in the end which way it'll go...

Dr. JOHNSON: I think that that's something that we're going to see within the next five years or less.

KRULWICH: So far, a sense is building that fetal cells probably stay in mothers for decades to defend and to protect them, which increasingly, is a quiet consolation to Kirby Johnson, because it's now more likely that his cells and his brother's cells were helping their mom, not hurting, and even though his mother did die, Kirby's beginning to feel differently.

Dr. JOHNSON: Well, maybe if it wasn't for my brother and I, she may have passed a few years earlier. Maybe we bought her a couple of extra years of time so she could have a few more birthdays and a few more mother's days and then, if I can just say that, that there is some way where I can even have the remotest thought that I contributed to the extension of my mother's life, even if it was a few days, that would make all of the years that I've spent doing this research worthwhile.

KRULWICH: Robert Krulwich, NPR News, New York.

RENEE MONTAGNE, host:

And Robert shares his thoughts on fetal cell research, Hunches and Questions, at NPR.org.

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