Researchers from London’s Imperial College have employed a Trojan Horse-like form of genetic engineering in a lab setting to wipe out a population of malaria-transmitting mosquitoes in less than 11 generations.
Armed with a CRISPR gene-edited sterilization mutation, biologists infiltrated a group of Anopheles gambiae and introduced the deadly gene modification to just a few of the unsuspecting insects. As Megan Molteni reports for Wired, the mutation completed its insidious task within seven to 11 generations, rapidly spreading sterility across the population and signaling the rise of a powerful—albeit controversial—tool in the worldwide fight against malaria.
The Imperial team’s findings, newly published in Nature Biotechnology, represent one of the first successful deployments of the “gene drive” technique. Gene drives defy the laws of genetics by greatly increasing the odds of a trait being passed down to offspring.
According to Science News’ Tina Hesman Saey, the researchers’ gene drive worked to alter the mosquitoes’ doublesex gene. Females that inherited two copies of this mutated gene developed antenna and claspers similar to males, rendering them unable to lay eggs or bite their prey. Males and females that inherited just one copy were largely unaffected.
To test the success of their gene drive, the biologists filled two cages with a mixture of 300 female mosquitoes, 150 unaffected males and 150 genetically modified males. In one caged population, the altered gene spread to all of the mosquitoes by the seventh generation, leaving the eighth and final generation unable to produce any offspring. The second population took 11 generations to similarly die out.
Under normal circumstances, offspring have a 50 percent chance of inheriting a parent’s given gene. If, for example, a male mosquito carries an altered gene, he might pass it down to one of his two children. Then, the new altered gene carrier could, in turn, pass down the gene to one of his two children, and so on. When gene drives enter the picture, however, altered genes have a much higher chance of spreading to offspring. The aforementioned male mosquito might pass his modified gene down to both children, increasing the likelihood of his distant descendants inheriting the gene, too.
The Imperial team was able to bypass “resistance”—one of the major issues associated with gene drives—by targeting the doublesex gene, which does not tolerate mutations. According to an Imperial College press release, previous gene drive experiments have been thwarted by genes that adapt to researcher-induced alterations, enabling them to function normally and resist the drive.
“We are not saying this is 100 percent resistance-proof,” lead author Andrea Crisanti tells The New York Times’ Nicholas Wade. “But it looks very promising.”
Replicating the study’s results in the wild could help scientists fight malaria, a disease that runs rampant across the African continent. The World Health Organization states that a staggering 216 million cases (with a death toll of 445,000) were recorded across the globe in 2016.
Still, the technology poses significant risks: Once a gene drive is released into the wild, it can’t simply be recalled. And, Wade notes, the effects likely can’t be contained to a single country, meaning that global insect populations could face unwanted side effects.
Biologist Ricarda Steinbrecher tells NPR’s Rob Stein that the eradication of an entire species could lead to ecosystem crashes or the emergence of other potentially harmful insect groups. Jim Thomas, co-executive director of the technology-centered ETC Group, adds that the defense industry could even transform gene drives into weapons of war that spread “toxic” substances across populations.
Before these concerns can be addressed, researchers will need to spend several years fine-tuning the technology. As BBC News reports, the scientists’ next step will be testing their technique on larger populations housed in less artificial settings.
The worldwide eradication of malaria-transmitting mosquitoes may remain a relatively distant objective, but Kevin Esvelt, a biologist at Massachusetts Institute of Technology who was not involved in the study, tells The New York Times’ Wade that advancing gene drive techniques may be the key—despite the potential risks associated with the technology.
Esvelt concludes, “The known harm of malaria greatly outweighs every possible ecological side-effect that has been posited to date, even if all of them occurred at once."