This kind of interference with human embryos is banned in the US because the implications of altered genetic traits passed on to future generations have not yet been studied.
The China government in retaliation to worldwide scientific furore has ordered a "thorough investigation" into the project and has stopped further work.
There is no independent confirmation of what He says he did.
The scientists gathered in Hong Kong this week for an worldwide conference on gene editing, the ability to rewrite the code of life to try to correct or prevent diseases.
Some scientists were astounded to hear of the claim and strongly condemned it.
The revelation shone a light on a new technology called CRISPR-Cas9, a tool that allows researchers to replace faulty genes with new ones, but research is not fully clear on its effect on humans. Some feel it is too premature to try, others feel it is justifiable.
The ethical implications of modifying the genes of humans have been hotly debated for many years already, but the emergence of CRISPR gene editing technology has made it relatively easy for researchers to conduct such work if they so choose.
Gene editing could potentially help avoid heritable diseases by deleting or changing troublesome coding in embryos.
When the embryos were 3 to 5 days old, a few cells were removed and checked for editing.
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His comments made clear that his communications with Trump about the project were much more frequent than he had suggested. Warner's committee was one of the two to which Cohen gave statements that his guilty plea now admits were lies.
Organisers of the Second International Summit on Human Genome Editing denounced He Jiankui's "unexpected and deeply disturbing" claim that human embryos had been edited and implanted. Lovell-Badge says he does not think He was aiming for genetic enhancement when editing the girls' genes, however. Those with one copy of the gene can still get infected with HIV, however some research suggests their health might decline more slowly if they do.
They also noted evidence that the editing was incomplete and that at least one twin appears to be a patchwork of cells with various changes.
Professor He said there had been "another potential pregnancy" involving a second couple, but it is unclear whether that pregnancy is still ongoing. This is roughly in line with a recent Pew poll in the United States that found 60 percent of Americans support using gene editing on babies to reduce lifetime risk of contracting certain diseases.
It's unclear whether participants fully understood the goal and potential risks and benefits.
Several prominent scientists said the case showed a failure of the field to police itself and the need for stricter regulations.
Some staff at some of the other hospitals were kept in the dark about the nature of the research, which He and Deem said was done to keep some participants' HIV infection from being disclosed.
But details of the experiment, which has not been independently verified, triggered an immediate backlash and He said the trial had been halted. China's National Health Commission and Health and Family Planning commission in Shenzhen both opened investigations.
Criticism didn't come only from China. The scientist also faces probes by the Shenzhen City Medical Ethics Expert Board and the Chinese Academy of Science's academic division.
In this October 10, 2018 photo, He Jiankui speaks during an interview at a laboratory in Shenzhen in southern China's Guangdong province. He Jiankui has been on leave but remains on the faculty and has a lab at the school.