Whether the scientific community was ready or not, the first genetically edited babies were reportedly born in China earlier this month.
The biologist responsible, He Jiankui, said he used the gene-editing technique CRISPR to confer HIV resistance to twin girls named “Lulu” and “Nana”.
While the claims are yet to be verified, the news was met with a widespread chorus of condemnation from doctors, scientists and ethicists.
“I think that it was irresponsible for [Dr He] to create them in the first place,” Ben Hurlbut, a bioscience ethicist at Arizona State University, told Science Friction.
Merlin Crossley, a molecular biologist at the University of New South Wales, said researchers felt “shock and indignation” when they first heard of the work.
“This was a big undertaking. It’s not something you do in your backyard.”
When presenting his work at the Second International Human Gene Editing Summit in Hong Kong, Dr He acknowledged the risks associated with CRISPR, but said the procedure was safe.
So what are the implications of Dr He’s research — and what will happen to the girls?
The girls’ father is HIV positive and their mother is negative.
When the twins were just days-old bundles of cells, Dr He disabled a gene called CCR5, which builds a protein that allows HIV to infect white blood cells.
He did this using CRISPR (also called CRISPR-Cas9), a tailored molecule that gives scientists the ability to cut out, insert and replace very specific chunks of DNA in cells.
The CRISPR segment guides a pair of molecular scissors — Cas9 — to a snip a target piece of the genome.
Gene editing comes with risks, said Gaeten Burgio, a genetics researcher at the Australian National University.
“The first is what we call ‘off-target effects’, which means the CRISPR goes outside of what it was meant to cut,” he told Natasha Mitchell on this week’s episode of Science Friction.
These effects can be life-threatening. What if CRISPR disabled a gene that, for instance, suppressed tumour growth?
Dr He said he screened the genomes while they were still tiny bundles of cells and found one off-target mutation in one twin that could be attributed to CRISPR.
After speaking with him, the parents decided to go ahead with the embryonic implantation.
“I think he did his best to detect the off-target effects, but to me, it appears to be insufficient,” Dr Burgio said.
“It doesn’t rule out the possibility of further off-target effects.”
Also insufficient, he added, were the methods Dr He used to rule out “on-target effects”, which arise when CRISPR keeps cutting a target gene.
“[It] leads to unintended consequences, such as massive deletion of a chunk of DNA, or insertion of a chunk of DNA.”
Indeed, Dr He said that CRISPR worked better in one twin than the other.
Each had two copies of the CCR5 gene — one inherited from each parent.
But while both copies were switched off in one twin, Lulu, only one copy was successfully disabled in her sister Nana.
This effect, known as mosaicism, means that while Nana is more HIV-resistant, she’s not immune. Other strains of the virus use other avenues to worm their way into cells.
Source: ABC News