Wouldn't it be great if scientists could genetically engineer
mosquitoes to be immune to the malaria parasite, thus protecting
people from that disease? How about restoring the effectiveness of
a pesticide by eliminating resistance genes in weeds and insect
pests? Or altering genomes to eradicate a pesky invasive
species?
These are exactly the sorts of things that a new
biotechnological tool could do-and that's got some people
worried.
In a July article for eLIFE, a team of
researchers led by the Harvard biotechnologist Kevin Esvelt
outlines a system that uses the new CRISPR gene editing technique
to alter the genomes of wild populations of plants and animals.
CRISPR is based on bacterial genes and proteins that can identify
and cut any desired segment of DNA in an organism's genome.
Appropriately configured and guided, it can replace any gene with a
newly engineered version. Esvelt and company want to use CRISPR to
construct "gene drives" that can quickly spread beneficial
engineered genes through sexually reproducing populations. A gene
drive works by making sure that both copies of a targeted natural
gene are replaced with the engineered version.
For example, researchers could take a gene drive specifying an
anti-malarial protein and insert it into mosquitoes in the
laboratory. They would then release the insects to breed with wild
mosquitoes. Ordinarily, the progeny would get one copy of a gene
from each parent, but in this case, the gene drive would excise and
replace the natural copy from the wild parent with the
anti-malarial version, thus guaranteeing that it would get passed
along when the next generation of mosquitoes breeds. Eventually,
essentially all of the mosquitoes in the targeted species would
carry the engineered version.
Another proposal would get rid of invasive species by creating a
suppression gene drive that biases the production of sperm
containing Y chromosomes, so that only males are born. The spread
of the Y-drive would result in a population crash of the targeted
species.
And then there's a potential solution to a big agricultural
problem: weeds and pests that develop resistance to herbicides and
pesticides over time. Researchers could create sensitizing gene
drives that would replace resistant alleles with their vulnerable
ancestral equivalents and thus restore the effectiveness of the
pest-exterminating treatments.
Naturally, the development of a technology this powerful freaks
some people out. The Hastings Center bioethicist Gregory E.
Kaebnick told The Boston Globe that he "would be
opposed to playing around with this technology unless there are
very significant benefits."
Gene drives could go wrong, as Esvelt and his colleagues
acknowledge. Engineered drives might spread to non-targeted species
through interbreeding. Suppression drives that aim to crash a
population of an invasive species might spread back to that
species' natural habitat. Bad guys might try to use gene drives to
damage crops and livestock. And then there's the possibility that
gene drives might be used to alter the genetics of human
beings.
To be useful, gene drives would have to be released into the
wild, which is the equivalent of an open access commons. The
Harvard biologist George Church, a co-author of the
eLIFE article, writes in Scientific
American, "Because we are all affected by the state of our
ecosystems, public oversight of technologies capable of ecological
management will be essential." Owing to these concerns, Esvelt and
his colleagues make some suggestions about how to regulate gene
drives in a companion article for the journal Science.
First, they describe some technical fixes. Before any gene drive
is released into the wild, researchers should create a reversal
drive that can restore the original phenotype of a targeted
species. Suppression drives should be released only after
researchers have developed a corresponding immunizing drive that
would prevent a specific unwanted drive from being able to spread.
Such precautionary measures would enable researchers to swiftly
counteract the effects of an accidental release.
One technically sweet proposal for how suppression and
immunizing drives could be used together is to let loose a
suppression drive among invasive rat populations on islands while
simultaneously releasing an immunizing drive in Europe and Asia to
keep the suppression drive from spreading among native rat
populations. Of course, rats with immunizing drive might eventually
re-invade habitats where they are not wanted, so over time
researchers would have to develop different suppression and
immunizing drives to keep up.
The researchers discount the possibility that villains could
successfully use gene drives to attack a country's crops and
livestock. In developed countries, they argue, gene drives would be
quickly detected by seed and livestock companies, and carrier
organisms would be purged before they could breed extensively. In a
poor country where farmers still save and replant seed and breed
their own livestock, agriculture might be more vulnerable. But even
there, if something appeared wonky, modern genome testing could
quickly identify such an attack and countermeasures could be
taken.
Esvelt and his colleagues downplay the possibility that gene
drives could be used to change human genetics. "Gene drives will be
ineffective in altering human populations because of our long
generation times," they claim. "Furthermore, whole-genome
sequencing in medical diagnostics could be used to detect the
presence of drives."
The technology isn't ready to be deployed yet, but we're getting
close. As Church told The New York Times, "In a
year or two, we could be doing field trials if there was a general
consensus this was a good idea."
The usual Luddites will strive mightily to scare policy makers
into banning gene drives. But with the proper safeguards, the
benefits clearly outweigh the possible downsides. To prove that,
let's go after malaria first.
Rep. Luis Gutierrez
House Democrat Average
