Preparing for another set of CRISPR-modified babies.

Nature reports on another geneticist – a Russian, this time – who has announced that he, too, will be gene-modifying human babies for HIV-positive mothers:

Molecular biologist Denis Rebrikov has told Nature he is considering implanting gene-edited embryos into women, possibly before the end of the year if he can get approval by then. Chinese scientist He Jiankui prompted an international outcry when he announced last November that he had made the world’s first gene-edited babies — twin girls.

The experiment will target the same gene, called CCR5, that He did, but Rebrikov claims his technique will offer greater benefits, pose fewer risks and be more ethically justifiable and acceptable to the public. Rebrikov plans to disable the gene, which encodes a protein that allows HIV to enter cells, in embryos that will be implanted into HIV-positive mothers, reducing the risk of them passing on the virus to the baby in utero.

Rebrikov heads a genome-editing laboratory at Russia’s largest fertility clinic, the Kulakov National Medical Research Center for Obstetrics, Gynecology and Perinatology in Moscow and is a researcher at the Pirogov Russian National Research Medical University, also in Moscow.

According to Rebrikov he already has an agreement with an HIV centre in the city to recruit women infected with HIV who want to take part in the experiment.

Rebrikov expects the health ministry to clarify the rules on the clinical use of gene-editing of embryos in the next nine months. Rebrikov says he feels a sense of urgency to help women with HIV, and is tempted to proceed with his experiments even before Russia hashes out regulations.

To reduce the chance he would be punished for the experiments, Rebrikov plans to first seek approval from three government agencies, including the health ministry. That could take anywhere from one month to two years, he says.

Although He was widely criticized for conducting his experiments using sperm from HIV-positive fathers, his argument was that he just wanted to protect people against ever getting the infection. But scientists and ethicists countered that there are other ways to decrease the risk of infection, such as contraceptives. There are also reasonable alternatives, such as drugs, for preventing maternal transmission of HIV, says Charo.

Rebrikov agrees, and so plans to implant embryos only into a subset of HIV-positive mothers who do not respond to standard anti-HIV drugs. Their risk of transmitting the infection to the child is higher. If editing successfully disables the CCR5 gene, that risk would be greatly reduced, Rebrikov says. “This is a clinical situation which calls for this type of therapy,” he says.

One big concern with He’s experiment — and with gene-editing in embryos more generally — is that CRISPR-Cas9 can cause unintended ‘off-target’ mutations away from the target gene, and that these could be dangerous if they, for instance, switched off a tumour-suppressor gene.

What’s more, the unmutated CCR5 has many functions that are not yet well understood, but which offer some benefits, say scientists critical of Rebrikov’s plans. For instance, it seems to offer some protection against major complications following infection by the West Nile virus or influenza. “We know a lot about its [CCR5’s] role in HIV entry [to cells], but we don’t know much about its other effects,” says [Australian National University geneticist Gaetan] Burgio. A study published last week also suggested that people without a working copy of CCR5 might have a shortened lifespan.