The researcher who created CRISPR twins defends his work but fails to quell controversy

A Chinese researcher who helped create the world’s first gene-edited babies publicly disclosed details of the work for the first time to an international audience of scientists and ethicists, and revealed that another gene-edited baby is due next year.

Lulu and Nana, twin girls whose DNA was edited with CRISPR/Cas9 to disable the CCR5 gene involved in HIV infections, may soon be joined by another child, Jiankui He said on November 28. Another woman participating in a gene-editing trial to make children resistant to HIV infection is in the early stages of pregnancy, He noted in a presentation at the second International Summit on Human Genome Editing, held in Hong Kong.

He performed the experiments largely in secret — not even the Southern University of Science and Technology in Shenzhen, China, where He worked until taking an unpaid leave in February was aware of the study. He apologized that information about his work “leaked unexpectedly,” a puzzling claim because He had granted interviews to the Associated Press and had recorded several online videos. A manuscript describing the work is under review at a scientific journal, He said.

Contentious experiments

In the presentation, He claimed that his experiments to disable the CCR5 gene might help susceptible children, especially in the developing world, avoid HIV infection. “I truly believe this is not only just for this case, but for millions of children that need this protection since an HIV vaccine is not available … I feel proud.”

But He’s first public explanation failed to quell the controversy over his actions (SN Online: 11/27/18).

Producing babies from gene-edited embryos is “irresponsible,” and runs counter to a consensus researchers reached in 2015 after the first international human gene-editing summit, said David Baltimore after He’s presentation. “I personally don’t think it was medically necessary,” said Baltimore, a Nobel laureate who has been influential in setting policy on DNA research and is chair of the summit’s organizing committee.

There are lots of ways to avoid to HIV infection that don’t require risky tinkering with DNA. And scientists aren’t convinced that editing human embryos with CRISPR/Cas9 is safe or ethical.

Scientists in the audience lined up to question He about how he recruited patients for the study, informed them of the risk and consequences of the research and why he did the work in the first place.

“I assume you’re well aware of this redline,” said Wensheng Wei of Peking University in Beijing, echoing more broadly the sentiment of many in the scientific community. “Why did you choose to cross it? And hypothetically if you didn’t know, why did you do all these clinical studies in secret?” He did not answer the question.

Drilling into the details

He said he and his colleagues began experimenting with mice, monkeys and nonviable human embryos to hone the editing technique. In that preliminary work, CRISPR editing of the CCR5 gene didn’t produce any unwanted changes to other genes, which scientists call “off-target” edits. Of 50 human embryos edited in one experiment, only one had a potential off-target edit. Researchers can’t tell if that off-target edit was caused by CRISPR/Cas9 or is a genetic tweak inherited from one of the embryo’s parents.

Lulu and Nana’s parents were one of seven couples recruited from an HIV patient group to take part in He’s study. A consent form posted to his website bills the research as an HIV vaccine development project. The baby’s father has HIV, but the virus is at undetectable levels in his blood. The mother is not infected.

He and colleagues performed in vitro fertilization after washing the sperm to remove any remaining traces of the virus. CRISPR/Cas9 protein and an RNA that guides the protein to the CCR5 gene were injected into the egg along with the sperm. When the resulting embryos had developed into a blastocyst, a stage just before implantation in the womb when the embryo is a ball of about 200 cells, researchers removed several cells. The team examined, or sequenced, three to five of those cells’ DNA for evidence of editing. In total, 31 embryos from the seven couples reached the blastocyst stage. Of those, about 70 percent had edits of the CCR5 gene, He said. 

The embryo that developed into Lulu contained an edit that mimics a naturally occurring mutation that helps protect some people from HIV. Initial testing also revealed evidence of an off-target edit far from any genes in that embryo, He said. The embryo that developed into Nana had a small deletion in the CCR5 gene that would remove five of 352 amino acids from the protein produced by the gene. Scientists don’t know whether that change would prevent HIV from getting into cells. Nana’s embryo had no discernible off-target edits, He said.

He left it up to the parents to decide whether to implant the edited embryos, knowing that one may have extra edits and the other may not be resistant to HIV. The couple decided to implant both embryos. 

After the girls were born, He and colleagues sequenced DNA from cells from the babies’ umbilical cord blood and determined that Lulu doesn’t have any off-target edits after all.

Unanswered questions

But researchers who saw He’s presentation aren’t convinced that he has presented enough evidence to verify that the editing was successful and didn’t damage other genes. Previous research has indicated that some cells in embryos may be incompletely edited or escape editing entirely, creating a “mosaic” embryo (SN: 9/2/17, p. 6).

There would be no way to determine if every cell in an embryo is edited equally without examining each cell’s DNA separately, says molecular geneticist Dennis Eastburn, who was not at the summit. Additionally, traditional sequencing methods can’t detect all the possible off-target changes CRISPR/Cas9 editing might produce in an embryo’s DNA, says Eastburn, cofounder and chief science officer of Mission Bio in South San Francisco. To find rearrangements of DNA, for example, researchers would need to do what’s called long-read sequencing that could span large portions of a chromosome.

Far more troubling is that He chose to implant the embryos to establish pregnancies, all without consulting scientific experts, ethicists and government regulators, says chemical biologist David Liu.

The moment He decided to implant an edited embryo to create a human pregnancy was “the critical juncture when his study went from being an eyebrow-raising, but not unprecedented human embryo study similar to other ones done in China and other countries, to a deplorable calamity,” says Liu, a Howard Hughes Medical Institute investigator at Harvard University and the Broad Institute of MIT and Harvard.

He claims he consulted with several other experts, including some in the United States, before moving ahead with his study. He’s university and Chinese authorities have launched investigations of his work. Rice University in Houston is investigating the role one of its researchers, Michael Deem, may have played in the research.