The news that Chinese scientist He Jiankui had edited the genomes of twin baby girls who were born last fall was greeted with outrage and widespread condemnation by the scientific community. Now scientists are trying to put the cat back in the bag. The International Commission on the Clinical Use of Human Germline Genome Editing met in Washington, D.C., Tuesday in an effort to develop a framework for assessing the scientific, medical and ethical considerations for any experiments to edit the genomes of human cells that can be passed on to future generations—in other words, editing embryos and germ-line cells. The commission, convened by the U.S.’s National Academy of Medicine and National Academy of Sciences and the U.K.’s Royal Society, will hold a second meeting in London this November and plans to release a final report in the spring of 2020.

An international summit on genome editing in 2015 resulted in a report laying out some of the conditions under which editing the human germ line for clinical purposes might one day be allowable. But the language was intentionally vague. The controversial Chinese experiment (which was reported shortly before a second summit in Hong Kong in 2018) and a Russian scientist’s recently announced plan to create more gene-edited babies have prompted the scientific community to call for concrete criteria that must be met before further clinical uses of the technology, if any, are pursued.

“The commission has made no conclusions yet, and it would be a mistake for anyone to leave here today thinking otherwise,” said Kay Davies, one of the commission’s two co-chairs and a professor of anatomy at the University of Oxford, at the recent meeting’s outset. Whether such a framework could discourage additional experiments like the one in China remains to be seen, however.

Many of those at the meeting supported a full moratorium on germ-line gene editing for clinical use. Carrie Wolinetz, acting chief of staff and associate director for science policy at the National Institutes of Health, was among the first to call for one: “We currently do not, cannot and will not support gene editing in human embryos,” Wolinetz said. (The Dickey-Wicker Amendment already bans the NIH from funding any research on human embryos, including editing their genes.) Wolinetz herself had a child who died from the rare genetic disease Smith-Lemli-Opitz syndrome, for which she is a carrier. Despite this fact, “I personally would have trouble articulating that I have felt a truly compelling case for this technology moving forward,” she said.

Bruce Levine, a professor of cancer gene therapy at the University of Pennsylvania who attended the meeting, agrees. “I definitely think there should be a moratorium,” he told Scientific American. “There has not been a conversation with society at large—the lay public, government, religious groups, NGOs [nongovernmental organizations], stakeholders—because the science has been moving faster than [our own] conversations have been.”

Whether or not the commission will adopt a full ban remains to be seen. “It’s hard to prejudge the merits of a moratorium until all the evidence is evaluated,” Leslie Biesecker, president of the American Society of Human Genetics, said to Scientific American. “I think that’s exactly what the [National Academies of Science and Medicine] and the [World Health Organization] are going to try and do.”

Another option would be to allow clinical germ-line editing to go forward but only under strict conditions. Matthew Porteus, a professor of pediatrics at Stanford University, proposed some potential criteria for the technology’s use: it should only be done in the absence of alternatives, such as in vitro fertilization with preimplantation genetic diagnosis (a method for identifying embryos with genetic defects); it should be applied to serious diseases with proved genetic causality; and it should be restricted to altering DNA to yield genetic sequences that are common and known to be healthy in the population at large. This last criterion would help ensure the changes do not introduce unintended effects and could avoid the thorny ethical issues around genetic enhancement.

Representatives from the WHO serve on an expert advisory committee to the commission, and the organization is developing its own report on germ-line editing in parallel. According to Margaret Hamburg, co-chair of the advisory committee and foreign secretary of the National Academy of Medicine, the committee has called for the establishment of a registry of relevant research in this area. It has also released a statement saying “it would be irresponsible at this time for anyone to proceed with clinical applications of human germline genome editing.” Finally, the advisory group called on the WHO to proactively ensure input from a broad range of stakeholders. The WHO plans to release its report in the summer of 2020, after the commission releases its own.

The commission’s first meeting also included representatives from funding and regulatory agencies, as well as patient advocacy groups. Sharon Terry, president and CEO of the nonprofit Genetic Alliance, has two children with a genetic disease. She praised the commission’s efforts but added, “I would have liked to have seen at least one patient on the committee.”

The meeting contained only a brief public comment period, during which the commission took questions from the audience and online. These ranged from the need to reach out to additional groups—including religious ones—to how the commission might prevent the commercialization of germ-line gene editing. (Additional comments can be sent to the commission at geneediting@nas.edu.)

Perhaps one of the strongest takeaways from the meeting was how much we still do not know about how genes influence human traits and diseases. Despite significant progress, noted Aravinda Chakravarti, director of the Center for Human Genetics and Genomics at the New York University School of Medicine, “not a single complex disease or trait is completely understood.”