A Crack in Creation by Jennifer Doudna

Author:Jennifer Doudna [Doudna, Jennifer and Sternberg, Samuel]
Language: eng
Format: epub
Publisher: Random House
Published: 2017-06-15T00:00:00+00:00

Using CRISPR to build gene-drive mosquitoes

It’s not the first time that scientists have turned to genetic engineering to reduce insect populations. A common practice used for decades involves the release of sterilized males into the environment; the technique has all but eliminated certain agricultural pests through North and Central America.84 Another approach being developed by a British company called Oxitec involves inserting a lethal gene into the mosquito genome, and field trials have already commenced in Malaysia, Brazil, and Panama.85 However, these strategies are inherently self-limiting; the genetic alterations are rapidly eliminated by natural selection, and the only way to make a dent in mosquito populations is to repeatedly release large batches of the modified insects.

CRISPR gene drives, by contrast, are self-sustaining; since the mode of inheritance appears to outsmart natural selection, the modified insects propagate and pass on their defective traits indefinitely. This thoroughness is what makes gene drives so powerful—and so alarming. It’s been estimated that, had a fruit fly escaped the San Diego lab during the first gene drive experiments, it would have spread genes encoding CRISPR, along with the yellow-body trait,86 to between 20 and 50 percent of all fruit flies worldwide.

Scientists pursuing CRISPR gene drives have been outspoken about the need to carefully weigh the risks before conducting further experiments and about the importance of developing guidelines that ensure future research proceeds safely.87 Perhaps the most obvious safeguard to prevent accidentally unleashing a gene drive into the world is stringent containment, such as physical barriers separating organisms from the environment and ecological barriers between the animal’s habitable range and the geographical location of the laboratory. At a recent conference at which Ethan Bier presented his research, he showed the audience pictures of the extensive containment procedures in place to prevent the accidental release of test insects. But if all else fails, scientists have proposed a variety of strategies that could theoretically inactivate gene drives that run amok. One of these is the so-called reversal drive,88 a gene drive that essentially functions as an antidote by overwriting any changes in the genome created by the original gene drive.

Even with the most cautious experimental design and planning, we can’t predict all of the environmental effects that a gene drive might have, and we can’t completely eliminate the possibility of a gene drive getting out of control and disrupting an ecosystem’s delicate balance. These risks were reflected in a recent report authored by the National Academies of Sciences,89 Engineering, and Medicine, which endorsed ongoing research and limited field trials but stopped short of recommending that gene drives be released into the environment.

There’s also no way to guarantee that this incredibly powerful tool won’t wind up in the hands of people who have no compunction about using gene drives to cause harm—and who may, indeed, be attracted to them for exactly that purpose. The ETC Group, a biotech watchdog organization, worries that gene drives—what they call “gene bombs”—could be militarized and weaponized to target the human microbiome or major food sources.

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