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NPR has learned that scientists are trying to edit genes in human sperm. Now, this raises many of the same hopes and worries as editing the DNA of human embryos. NPR health correspondent Rob Stein recently got exclusive access to the lab where this controversial experiment is being conducted.
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ROB STEIN, BYLINE: At the Center for Reproductive Medicine at Weill Cornell Medicine in Manhattan, June Wang, a lab tech, punches a keypad to unlock a big door to a small windowless research lab.
What are we here to do today?
JUNE WANG: OK, so right now, this morning, we're going to do some CRISPR experiments.
STEIN: CRISPR lets scientists make very precise changes in DNA. They're using it these days to manipulate genes in everything from bacteria to babies. Last year, a Chinese scientist used CRISPR to make genetically modified twin girls, sparking outrage around the world. Wang and her colleagues aren't trying to do that yet.
WANG: We are trying to figure out if we can get CRISPR to work inside a sperm cell.
STEIN: To fix genetic mutations that make men infertile or cause terrible genetic diseases to maybe someday use gene-edited sperm to make healthy, genetically modified babies. Wang's starting with one of the genes that can cause breast cancer, which men can pass down to their children, too.
WANG: Yeah, I have high hopes that we can have a huge impact.
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STEIN: Wang and another lab tech snap open the latches on a frosty silver canister, pop off the lid and slide out a small vial.
WANG: We have the sperm samples frozen in liquid nitrogen right now.
STEIN: So that's a vial containing human sperm?
STEIN: Like, how much sperm is in there?
WANG: So it has about 58 million and has a volume of 0.5 milliliters.
STEIN: Fifty-eight million sperm - that's a lot of sperm.
WANG: (Laughter) Yeah, they're very small.
STEIN: After carefully thawing and preparing the sperm, Wang puts some on a slide under a microscope and lets me take a look.
Oh, wow. Yeah, there's a ton of - tons of sperm just squiggling around in all these little squares, but very lively. And so those are the guys you're going to try to edit with the CRISPR editing tool?
WANG: Yep. But nobody's tried to do CRISPR on sperm before, so we have to try to figure out the right parameters and the right way to do it.
STEIN: It may be that DNA is packed too tightly inside the heads of sperm to edit, but if it can be done, edited sperm could be safer than edited embryos to make babies, like the Chinese scientists did. So if it works, many scientists think it could be a big advance. Kyle Orwig is a reproductive scientist at the University of Pittsburgh.
KYLE ORWIG: Male infertility is a very common condition, and there's some diseases that are incredibly devastating to families. And for those diseases, for me, if you could get rid of it, why wouldn't you get rid of it?
STEIN: But others say editing DNA in sperm raises all the same troubling questions as editing DNA in embryos and modifying the human genetic blueprint in ways that could be passed down for generations. Would it really ever be safe to make babies that way? And would it open the door to someone someday trying to make designer babies? Francoise Baylis is a bioethicist at Dalhousie University advising the World Health Organization.
FRANCOISE BAYLIS: It doesn't matter whether you're manipulating the embryo or you're manipulating the sperm. The concern is what kind of world are you creating as you move down the path to start manipulating human genetics? We are on the cusp of prospective parents controlling the genetics of their offspring.
STEIN: Wang acknowledges the concerns but thinks the potential benefits make it worth at least trying.
WANG: I know that things can get dangerous and things can get kind of out of hand quickly. But on the other hand, I think that CRISPR can do so much, it has a lot of potential and that if we try to be cautious and stop it, that it won't get there.
STEIN: Her boss agrees. Gianpiero Palermo runs the lab.
GIANPIERO PALERMO: I think it's important from the scientific point of view to investigate in an ethical manner to be able to learn if it's possible to remove certain disease that afflict the family. If we can wipe out this particular gene would be incredible.
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STEIN: Now it's time to try to edit the breast cancer gene in the sperm. Wang drips a solution containing the microscopic CRISPR gene-editing tool into a vial with millions of sperm and places the mixture inside a special machine I've never seen before.
And what is that?
WANG: So that - it actually delivers a small shock to the sample.
STEIN: A shock?
WANG: Yeah, an electric shock through the sample. And that'll cause the sperm to kind of loosen up a little bit for just a moment. And then the CRISPR materials are kind of in the ambient fluid, and so when the cell loosens up, they hopefully will get inside.
STEIN: With the help of an 1,100-volt split-second zap.
WANG: I'm going to turn on the machine here, the machine that we are going to use to zap the sperm to hopefully get the CRISPR inside.
STEIN: I have to say that zapping is kind of - I don't know - kind of Frankenstein almost. It's like lightning or something.
WANG: Yeah, it's a little bit of a weird concept, but it works pretty well.
STEIN: Wang reaches over and flips a switch on the zapping machine.
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STEIN: That's it?
WANG: Yep, that is it.
STEIN: Is that the CRISPR in the sperm?
WANG: Yep. I just zapped all the sperm, and hopefully the CRISPR materials got in there.
STEIN: Wow, that was so fast.
STEIN: It was, like, a split second.
WANG: Yeah, very fast, very simple.
STEIN: Fast maybe, but the questions raised by the prospect of editing the genes in human sperm are far from simple. And it'll take a lot more work like this before anyone knows whether it can be done successfully - and a lot of debate about whether anyone should ever try to use genetically modified sperm to make a baby.
Rob Stein, NPR News, New York.
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