Back in 2018, CCR5 was mostly known for its ability to let the HIV virus into cells. Today, there’s an emerging consensus that it has a variety of functions – including in brain development, recovery from strokes, Alzheimer’s disease, the spread of certain cancers, and the outcome of infection with other pathogens.
“We don’t know how the babies’ lives are going to be affected,” says Saha, “how susceptible they would be to various types of infectious diseases, and what this means in terms of current and future pandemics.” Indeed, typical CCR5 proteins are thought to protect against a range of pathogens, such as malaria, West Nile Virus, the tick-borne encephalitis virus, yellow fever, and respiratory viruses such as the flu – suggesting that Jiankui may have robbed his subjects of a useful adaptation.
A potential fix
It’s not all bad news, however.
First up, it’s not certain that somatic cell editing would necessarily alter reproductive cells – it’s just a theoretical possibility. To find out if this is really happening, Saha and his team have been developing reporter systems in lab mice, which tag any altered cells with a fluorescent red protein and allow them to be found under the microscope. This means that it’s possible to see visually whether injecting a mouse with an editor that’s meant for, say, the brain, will end up affecting its sperm or eggs. “We’ve seen plenty of red cells in the brain,” says Saha. “Thus far, we haven’t seen anything in the reproductive organs, which is a good reassuring outcome.”
Secondly, not all somatic editing needs to happen inside the body. For some disorders, such as sickle cell disease, the affected tissue – in this case, red blood cells – can be extracted and treated outside the body, in a petri dish. This means that the editor only ever encounters the cells being targeted, and there is almost no risk of mutations being passed down the generations.
Finally, any potential risks might end up dictating who somatic cell editing is provided to, in order to limit them. For example, if it turns out there is a possibility of altering a person’s heritable DNA, they might only be offered to patients who are either past childbearing age or are nearing the end of their lives.
“In some cases, zero is probably not the threshold that’s needed to get into the clinic,” says Saha, explaining that there are likely to be plenty of people who would be willing to sacrifice ever having children in order to improve their quality of life. He believes the way forward is making sure that patients are well-informed of the risks before agreeing to such procedures.
An inter-generational experiment
But let’s say that we do end up with artificial mistakes in the human gene pool. Exactly how permanent could they become? Could new mutations created today still be washing around in 10,000 years, as future humans watch the red supergiant Antares’ scheduled explosion into a supernova as bright as the full Moon?