He took the extraordinary step of performing genetic modification on human embryos with the intention of having them carried to term.
Our genomes contain two copies of the CCR5 gene. This mutation makes the cell able to thwart the HIV binding and infection. One of the twin babies was reported to have one copy of CCR5 modified by CRISPR-Cas9 gene editing, while the other baby had both copies edited. He Jiankui might never have expected the two genetically-edited babies to suffer from the risk of dying younger, but it is his experiment and "research" that have created that possibility.
Once edited, the embryos were implanted into the mother's uterus.
When Chinese scientist He Jiankui's CRISPR experiment resulted in the live birth of twins carrying this double mutation previous year, it sparked global outrage. Nana was born with two edited copies of CCR5, which theoretically means she can not contract the most common strain of H.I.V., while her sister Lulu has one functional and one edited copy of the gene. The researchers compared death records and genomic profiles in the UK Biobank database. Overall, the team found that those with the CCR5 mutation were over 20% more likely to die before the age of 76 than those without it. The study's authors suggest this could be because CCR5 modifications are also linked to higher susceptibility to viruses such as West Nile and influenza. "In this case, it is probably not a mutation that most people would want to have".
The new study "doesn't show anything about the effects of the mutation per se, but what it does show is an overall effect on mortality", said Nielsen. Prominent stem cell scientist Robin Lovell-Badge, who was also not involved in the recent research, says that He had been "foolish" because the Chinese researcher "may have compromised lifespan in the two girls", reports Karen Weintraub of Scientific American. He's work, which has been presented at a gene-editing summit but not published in a peer-reviewed journal, has been widely criticized as rash, lacking in transparency, medically unnecessary and even ineffective.
"It's shocking and unacceptable", Xu Nanping, vice-minister of science and technology said in November last, adding that his act is a blatant violation of China's laws and regulations and violated the bottom line of academic morality and ethics.
The analysis of the researchers poses a caution for gene editing done in somatic as well as germline cells, that would have to be considered in future by the scientific community.
The Nature Medicine study highlights another of the many reasons why He's use of CRISPR on viable human embryos was so ill-advised.
"What we discovered is that they had significantly increased mortality", lead researcher Rasmus Nielsen advised NPR.