美国国家公共电台 NPR To Fight Malaria, Scientists Try Genetic Engineering To Wipe Out Mosquitoes（在线收听）

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What if scientists could genetically modify mosquitoes to wipe out a disease that kills hundreds of thousands of people each year? They're trying to do that with a new genetic engineering technique. They hope it will help them fight some of the world's other big problems, too.

Now, there are fears about releasing insects made this way into the wild. NPR's health correspondent Rob Stein visited one of the first labs to engineer a living creature with this technology.

ROB STEIN, BYLINE: What you're about to hear may just sound like static at first, but if you listen closely, you can hear them.

(SOUNDBITE OF MOSQUITOES BUZZING)

STEIN: Mosquitoes - hundreds of genetically modified mosquitoes.

(SOUNDBITE OF MOSQUITOES BUZZING)

STEIN: And not just any genetically modified mosquitos. These are some of the first living things engineered to do something that has long been considered taboo - spread their mutant genes fast, really fast and as far as they can. For my close encounter with these mosquitoes, I traveled to London and found Andrew Hammond. He's a genetic engineer at Imperial College London.

ANDREW HAMMOND: You want me to show you the insectary and where we do some of the work.

STEIN: That'd be fabulous. Thanks.

The insectary is where Hammond keeps these new mosquitoes. He leads me to a highly secure elevator and takes me down five floors to the basement.

COMPUTER-GENERATED VOICE: Going down.

HAMMOND: There's a few layers of security to get down here.

STEIN: We pass through a series of heavy doors equipped with special blowers to push back any genetically modified mosquitoes that try to escape before finally arriving at the insectary. Even though outside London is cold and gray, in here, it's hot and humid like the tropics to keep the mosquitoes happy. Hammond picks up a small cage made out of white mosquito netting.

HAMMOND: Inside this cage, you've got the adult mosquitoes.

STEIN: What kind of mosquitoes are these?

HAMMOND: Everything in this cubicle is genetically modified.

STEIN: They look like regular mosquitoes, but they're not. They've had something new spliced into their genes, something known as a gene drive, which is a sequence of DNA created in the lab that drives its way through the gene pool much faster than most genes. The research is funded by the Gates Foundation, which also supports NPR.

HAMMOND: These gene drives - they're able to copy themselves. So instead of half of the offspring inheriting the gene drive, almost all of them do.

STEIN: That's huge. Scientists have always tried to keep genetically engineered creatures from spreading their new DNA to keep them from messing up the natural world. A gene drive genetic modification - it's designed to spread.

HAMMOND: So what happens is it spreads, and it spreads, and it spreads. And this is the fantastic thing because in a very short amount of time, you can actually transform an entire wild population into a modified population.

STEIN: Wow.

HAMMOND: Yeah, it's powerful.

STEIN: So powerful that Hammond and his colleagues think they can use their gene drive mosquitoes to do something humanity's been trying to do for decades - wipe out malaria because these mosquitoes spread mutations designed to sterilize the mosquitoes that spread the malaria parasite.

HAMMOND: And if we sterilize the females, you can actually eliminate a whole mosquito population without affecting those mosquitoes that don't have the capability to transmit malaria. It's fantastic.

STEIN: And that's just the beginning. Scientists think gene drives could let them do all sorts of things - eradicate other diseases spread by insects like Lyme disease and Zika, feed the world more safely by creating crops that don't need polluting pesticides, save endangered species and entire ecosystems. But critics worry gene drives are just too powerful.

RICARDA STEINBRECHER: It has huge implications. It's a tool that's never been in our hands before, and it's just a high-risk technology.

STEIN: Ricarda Steinbrecher is a scientist at the genetic watchdog group EcoNexus in Oxford, England.

STEINBRECHER: You can have a collapse of ecosystems. You can have more diseases arising. You can make the whole system fragile towards climatic conditions. It basically is an unknown we are dealing with here.

STEIN: Back in the lab, Andrew Hammond takes me to another area to show me how he creates gene drive mosquitoes.

HAMMOND: This is our microinjection facility. So this is what we use to actually make the transgenic mosquitoes.

STEIN: It's a big, dark room. Hammond sits down in front of a microscope and picks up a slide. It's got dozens of tiny black specks on it. Each speck is a mosquito embryo. Hammond lets me take a quick peek under the microscope. Each embryo looks like a big black blob. A thin glass needle is pointing at one of the blobs.

HAMMOND: Inside this needle is a solution that contains the DNA. And we're going to use this to modify the genome and integrate into it our gene drive.

STEIN: To integrate the gene drive, Hammond's using a new DNA editing technique called CRISPR that's revolutionizing genetic engineering by making it way easier and faster. It's letting scientists like Hammond harness the power of gene drives.

(SOUNDBITE OF ELECTRIC MOTOR)

STEIN: That sound...

HAMMOND: That sound is manipulating this needle into the right place.

STEIN: Hammond has less than an hour to edit as many embryos as he can before they dry out.

HAMMOND: Need to be very quick when you put the needle inside, and you need to inject just the right amount of DNA. Too much will kill it, and too little won't modify it. But if you place it in and inject - there, that's done.

STEIN: And that's how you edit the DNA in a mosquito embryo.

HAMMOND: That's right.

STEIN: After they're edited, Hammond lets the embryos mature and mate with normal mosquitoes then examines their larva under another microscope that lights them up with a laser. The modified mosquitoes also get a marker that makes their eyes and other parts of their bodies glow if the gene drive is working.

HAMMOND: When I look at them, if I see that half of them are red, then our gene drive is not working. But if we see that almost all of them are red, then it's definitely working.

STEIN: And what are you seeing?

HAMMOND: That it's definitely working (laughter).

STEIN: He shows me one of the gene drive mosquito larva magnified on a screen. It looks like something out of a horror film, like a huge radioactive worm.

HAMMOND: We can see it glowing up in the eyes and glowing down the body. It's beautiful.

STEIN: Why do you call it beautiful?

HAMMOND: Just these incredible patterns that are formed by the neurons and the bright red fluorescence. I mean it's a stunning image - beautiful scientifically and beautiful visually.

STEIN: But not everyone thinks this is so beautiful. Critics find it frightening. They say there's no way to know what gene drive creatures might do if they're ever let loose. They could mutate, unleash new epidemics, cause famines. And Jim Thomas of the genetic watchdog the ETC Group says that's not all.

JIM THOMAS: This potentially could be a way of creating some quite nasty bio weapons. You could engineer an insect - stinging insect, for example, to deliver a toxin. Mosquitoes would be an obvious possible target. That would be a way that you could weaponize this technology. That certainly is of concern.

STEIN: Andrew Hammond and his colleagues doubt gene drives would ever be used that way, and they argue the potential benefits are so huge that they have to try to find a way to use them safely. Molecular biologist Tony Nolan is Hammond's boss.

TONY NOLAN: We don't work in an ivory tower. We are fully aware of people's concerns on this. I think that we've got to weigh up the benefits whenever you consider risk. And I think that given that there are still half a million people dying, most of them children, from malaria, I think it's a worthwhile goal to investigate this technology.

STEIN: But Nolan acknowledges that gene drives could be dangerous and be misused, so he and his colleagues are planning years of careful testing to make sure their mosquitoes are safe before they try to convince any countries to let them release them into the wild.

Meanwhile, other scientists, along with the U.S. military, are trying to develop antidotes to gene drive modifications just in case one does run amok someday. Rob Stein, NPR News, London.