One of the scientists who discovered powerful tools for altering genes is not convinced the case has been made for using the technology on human sperm, eggs and embryos.

"The tools are not ready," biologist Emmanuelle Charpentier said in an interview on Wednesday during a global meeting on the technology.

Changes made in the genes of human reproductive cells, known as germline cells, would be passed along to future generations. Several groups have called for restrictions on use of the technology known as CRISPR-Cas9, which has opened new frontiers in genetic medicine because of its ability to modify genes quickly and efficiently.

At the meeting, several researchers presented potential near-term uses of the technology that would require the editing of germline cells. They include editing immature sperm cells to allow infertile men to father children.

As long as they are not perfect and ready, I think it's good to have this ban against editing the germline. - Emmanuelle Charpentier, biologist

But Charpentier, one of the scientists credited with discovering the technology, said: "As of today, I'm in favor of not having the manipulation of the human germlines."

"As long as they are not perfect and ready, I think it's good to have this ban against editing the germline," said Charpentier of the Max Planck Institute for Infection Biology in Berlin and Umea University, Sweden.

Charpentier and colleague Jennifer Doudna of the University of California at Berkeley did pioneering work on developing the CRISPR-Cas9 system, a technology that can strategically delete specific stretches of DNA and add in genes.

She said she would need very strong convincing about the immediate benefits of editing human germline cells. "For the moment, I don't see any."

Regulations vary

Charpentier is a member of the German National Academy of Sciences, a country where research involving germline editing is banned.

But regulations vary. In Britain, scientists can apply for a license to edit the germline. In the United States, researchers are banned from using federal funding for the research, but the work is permitted in private labs.

Gene editing

University at California Berkeley biochemist Jennifer Doudna speaks at the National Academy of Sciences international summit on the safety and ethics of human gene editing on Tuesday. (Susan Walsh/Associated Press)

Such work has already taken place in China, where a team of scientists reported carrying out the first experiment to alter the DNA of non-viable human embryos.

That ignited an outcry and a call for a voluntary ban on such work by a group of leading biologists, including Doudna​.

But the work is still going on. "The moratorium didn't have much effect," Charpentier said.

Her hope is that the meeting produces a framework that will provide guidance to other scientists as this work proceeds. The three-day Washington meeting was convened by the National Academies of Medicine and Sciences, the Chinese Academy of Sciences and the Royal Society of the United Kingdom.

Several scientists expressed concern on Tuesday the germline controversy might hamper research on non-reproductive cells, known as somatic cells, that could potentially help people with inherited or infectious diseases.

Fyodor Urnov, senior scientist at Sangamo Biosciences , a company using a different gene editing tool to create treatments in somatic cells, said the company wrote an article in Nature calling for a moratorium on germline research. "We don't want there to be a conflation in the mind of the public or in the mind of the regulators or policymakers or the ethical community between the two," Urnov said in an interview.