By Alice Park
Updated: November 27, 2018 11:21 AM ET | Originally published: November 26, 2018

It’s not the usual way that reputable scientists announce their breakthroughs to the world, but on Monday, Jiankui He released a video proclaiming that he had produced the world’s first human babies whose genomes were edited using the powerful technique called CRISPR. He had also previously spoken with the Associated Press about his study, which he says resulted in twin girls born with the first genomes edited by man.

The report was met with instant concern and skepticism by the scientific community. He’s experiment altered the genomes of embryos produced through IVF; their genetic changes will therefore be passed on to any future generations. What’s more, most experts in CRISPR are not convinced that the technology is ready — or safe — for treating humans.

“Given the current early state of genome editing technology, I’m in favor of a moratorium on implantation of edited embryos … until we have come up with a thoughtful set of safety requirements first,” Feng Zhang, one of the co-discoverers of CRISPR and from the Broad Institute of MIT and Harvard, said in a statement responding to the report. “Not only do I see this as risky, but I am also deeply concerned about the lack of transparency surrounding this trial.”

Scientists also expressed concern that the report would negatively impact future research on using CRISPR to find new treatments for disease. “The premature use of gene-editing technology described today in China could set back legitimate efforts to prevent inherited disease,” says Shoukhrat Mitalipov, director of the Oregon Health & Science University center for embryonic cell and gene therapy.

In 2015, prominent members of the scientific community familiar with the technology, including Zhang and another co-discoverer, Jennifer Doudna from University of California, Berkeley, agreed to voluntarily stop research on using CRISPR in human embryos because the safety and long term consequences of the technology were too uncertain. The researchers support studies in which CRISPR is used to develop treatments that would affect cells that aren’t passed on to the next generation — i.e. anything except egg and sperm — but say that more research is needed before CRISPR is used to make changes in genomes that can be carried by generation after generation.

“It is imperative that the scientists responsible for this work fully explain their break from the global consensus that application of CRISPR-cas9 for human germline editing should not proceed at the present time,” Doudna said in a statement.

While editing the DNA of a human embryo is not currently allowed in the U.S., in 2017, an international committee of the National Academy of Sciences called for loosening the moratorium and allowing trials of CRISPR in human embryos, under strict oversight, to treat rare genetic diseases that can’t be addressed in any other way. In the U.K., officials approved studies of CRISPR in human embryos in 2016, but those embryos will not be transplanted to create a pregnancy. Those trials call for destroying the embryos after a week, since the technology’s safety remains unclear. In 2017, Mitalipov also published his work on using CRISPR to correct an inherited heart defect in human embryos. But unlike He, he did not transfer those embryos for pregnancy.

Alta Charo, professor law and bioethics at University of Wisconsin, says to TIME, “First-in-human experiments always require a particularly high degree of caution, as the need to generalize from data solely accrued from laboratory and animal studies adds a new dimension to the uncertainties around not only risk and possible benefit, but around how to predict the range of risks and how to evaluate their possible impact.”

He, on the other hand, has apparently jumped ahead and produced the first human babies born with CRISPR editing. He is on the faculty of Southern University of Science and Technology in Shenzhen China, but in a statement released in response to He’s videos, the university said he is on unpaid leave from February 2018 to January 2021; officials did not provide a reason for the leave.

“The University was deeply shocked by this event and has taken immediate action to reach Dr. Jiankui He for clarification,” the officials said in the statement. “The research was conducted outside of the campus and was not reported to the University nor the Department [to which He belongs].” The statement went on to note that the university “believes that Dr. Jiankui He’s conduct in utilizing CRISPR/Cas9 to edit human embryos has seriously violated academic ethics and codes of conduct … The University will call for international experts to form an independent committee to investigate this incident, and to release the results to the public.”

Rice University is also launching a “full investigation” of the involvement of one of its researchers, Michael Deem, a professor of bioengineering, who said he worked with He on the experiment. “Rice had no knowledge of this work. Regardless of where it was conducted, this was as described in press reports, violates scientific conduct guidelines and is inconsistent with ethical norms of the scientific community and Rice University,” officials said in a statement.

CRISPR, first described in 2012, gives scientists the most precise and effective way to edit the human genome by snipping out offending mutations or genes and either allowing the genome to repair itself or providing researchers with the ability to insert new genetic material to correct disease genes. But studies suggest that controlling CRISPR in human cells remains a challenge; in some cases CRISPR may cut unintended parts of the genome.

In his promotional video, He describes targeting the CCR5 gene, which helps the HIV virus enter healthy human cells. He worked with seven heterosexual couples in which the male partner was HIV positive and the women were HIV negative. After the couples produced embryos through IVF, he used CRISPR to cut the CCR5 gene, disabling it in the hopes of making the embryos less vulnerable to HIV infection. He claims that of 22 embryos, 16 showed signs of successful CRISPR editing, and 11 were implanted, resulting in a single pregnancy with twin girls who were born in November. One twin, according to He’s tests, showed signs that both copies of the CCR5 gene it inherited (one from its mother and one from its father) were successfully altered, while the other twin showed that one version of the gene it inherited was altered.

That so-called mosaicism, in which some but not all of the embryo’s cells are altered, is troubling since in this case, it would mean that girl may not be entirely protected from HIV infection like her sister. That’s one of the reasons why researchers are concerned about the report. Normally such scientific milestones are reported in scientific journals complete with detailed descriptions of how the researcher accomplished the feat along with data supporting their claims. Without such documentation, it’s impossible to verify whether the girls indeed showed successful CRISPR editing or not. “Because the data have not been peer reviewed, the fidelity of the gene editing process cannot be evaluated,” said Doudna.

He, who created two companies based on his studies, is scheduled to present his findings at the Second International Summit on Human Genome Editing, and will certainly be the target of numerous questions from the leading gene-editing scientists in attendance.

Contact us at editors@time.com.

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