He Jiankui, the Chinese researcher who claimed this week to have helped produce the world’s first genetically altered babies, said Wednesday there was another “potential pregnancy” involved in his study as he defended a procedure that has shaken the scientific world.

Appearing in public for the first time since revealing he had successfully altered the DNA of twin girls while they were embryos to make them resistant to HIV infection, the Stanford-trained bioengineering professor said he felt “proud” of his work and its implications for public health in the face of nearly universal condemnation.

“We should, for millions of families with inherited disease, show compassion,” he told a packed audience at the Second International Summit on Human Genome Editing in Hong Kong. “If we have this technology, we can make it available earlier. We can help earlier those people in need.”

He’s scientific talk chronicled the development of this line of research, from early mouse experiments to primates and eventually a human clinical trial. He said eight couples were enrolled in the trial, but one dropped out. All had fathers with well-controlled HIV and mothers who were not infected.

There were 31 embryos created through in vitro fertilization, and 70 percent were successfully edited. He showed data indicating he had not detected unintended genetic changes caused by CRISPR/Cas-9, the gene-editing tool he used — although it remains to be seen whether outside scientists will find the evidence convincing.

The disclosure this week of He’s research — carried out in southern China mostly under a shroud of secrecy — has sparked urgent debate about the ethics of gene editing and raised the prospect of a future in which parents produce “designer babies” with selectively improved traits such as intelligence or strength.

Midway during He’s talk, Nobel laureate David Baltimore said the study resulting in the birth of two girls showed “there has been a failure of self-regulation in the scientific community.”

The ethics of the procedure are also complicated by the fact that targeting specific segments of DNA may not be fully precise or could carry side effects that are difficult to predict. 

He said Wednesday he was “against genome editing for enhancement” and that he would conduct the experiment on his own unborn daughter if she were at risk with HIV infection. He said he worked with seven couples and 31 embryos, more than 20 of which were edited. Aside from “Lulu” and “Nana,” two apparently healthy girls who have been born, there is another mother in the study in the “early stages” of pregnancy, he said.

He’s work came to light this week on the eve of the Hong Kong conference after the Associated Press and MIT Technology Review published extensive on-camera interviews with the researcher, whose lab also posted videos about the breakthrough on YouTube. The revelation was stunning, not only because the genomics field had declared a voluntary international moratorium on editing embryos three years ago, but also because it came before He’s work was peer-reviewed or published in a journal.

He opened his appearance on Wednesday by apologizing for news about his work “leaking” before it passed peer review. He said the work has been submitted to a journal, but he did not specify which publication.

Asked why he had kept his work secret, He said he had talked openly about his research at conferences, including at Berkeley, and had consulted with “several experts” in the United States at Stanford and in China as he moved into clinical trials. He did not name those people.

Amid repeated questions about the ethics and methodology of his experiment, He said he found volunteers through a social network of HIV carriers and explained, line by line and over 70 minutes, the implications of the study to seek their informed consent. When asked if he had considered the implications of carrying out the procedure on behalf of two unborn girls with potentially unknown physical or emotional consequences, He said he could not answer the question.

But He, seated and speaking calmly throughout, said he saw profound value in what he had accomplished, having visited villages in China where a third of the population was ravaged by AIDS and having helped an HIV-infected father produce a daughter. 

“I feel proud,” He said. “I feel proudest because the father thought he lost hope for life. When the baby was born, he sent a message at the first saying I will work hard for and take care of my two daughters for the second half of his life.”

He said his job was to be “transparent, open and share the knowledge I accumulated to society, to the world, and then, let society decide what it should do in the next step.”

Born in China’s Hunan province, He graduated from the University of Science and Technology of China in 2006 and pursued a PhD at Rice and postdoctoral research at Stanford.

In 2012, he was recruited by a Chinese government-backed Thousand Talents Plan, which aims to bring leading international experts in science and technology to the country.

This week, hundreds of Chinese scientists signed two letters condemning He’s research as “crazy” and calling on the government to explicitly ban the practice of implanting edited embryos from reproduction.

National and local health authorities in China announced investigations on Monday into He’s research.

Several institutions affiliated with the researcher also grappled with the fallout as they distanced themselves from He or denied knowledge of his work.

He’s Southern University of Science and Technology said this week the work was carried out “outside of the school” and seriously violated academic ethics and norms. A copy of the informed consent form used for the study and posted online, however, listed the university as a funder of the experiments.  

The Shenzhen Harmonicare Women’s and Children’s Hospital where He carried out procedures also denied knowledge of the experiments — even though a hospital executive, Lin Zhitong, appeared on camera in an AP interview hailing the research. The hospital said it would lodge a police complaint against He.

In an interview before He’s talk, Timothy Henrich, a translational HIV researcher at the University of California at San Francisco, said unless there was full editing of both copies of the gene, which does not appear to be the case for one of the twins, she would not have immunity. There are also other ways to prevent HIV infection.

“I cannot find a scientific rationale to do this, other than the proof of concept that you could modify the embryo and bring it to term,” Henrich said.

But while many scientists have been quick to condemn He’s experiment, some leaders began to give cautionary warnings about foreclosing a promising field of biomedical research.

Harvard Medical School dean and stem cell scientist George Q. Daley gave a presentation at the summit arguing that while He’s experiment was a “misstep,” gene-editing technology has advanced in the past three years. He warned of dangers if the scientific community were to “stick our heads in the sand” and ignore the potential benefit of the technology to eliminate diseases.

“After yesterday, with the revelations of the births of gene-edited twins, I think the tide was largely negative and the prospect of anticipating ethical uses in the future was almost set aside,” Daley said. “I think we do that with some risk. Just because the first steps into a new technology are missteps, it doesn’t mean we shouldn’t step back, restart and think about a plausible and responsible pathway for clinical translation.”

Johnson reported from Washington.