Just eleven days after a study appeared describing the use of gene-editing in human embryos, the NIH issued a firm response: Work of this sort will not receive NIH funds.

The prohibition was announced April 29 in a crisply worded release. “The concept of altering the human germline in embryos for clinical purposes has been debated over many years from many different perspectives,” the release read, “and has been viewed almost universally as a line that should not be crossed.”

Although the NIH indicated that it recognizes the potential for genomic editing, and that it already supports many investigations and applications of genomic editing technologies, the agency will not countenance genomic revisions to germline cells. Such revisions, unlike revisions to somatic cells, could be passed to future generations.

In its announcement, the NIH specifically cited the CRISPR/Cas9 technique, without which the recent manipulation of human embryo genomes would have been much less practical. CRISPR/Cas9, a relatively new genome-editing technology, has greatly simplified various interventions—the production of knockout mouse models of disease, the development of next-generation microbials, and even clinical applications, such as the creation of HIV-1 resistance in human immune cells.

Going further, researchers in China used a CRISPR/Cas9 system in experiments with human embryos. Although the ostensible goal of this work was to modify the gene responsible for β-thalassemia, a potentially fatal blood disorder, the researchers may have intended to demonstrate the limitations of their CRISPR/Cas9 technique. As it turned out, the researchers created more genetic problems than they resolved, and they concluded that “clinical applications of the CRISPR/Cas9 system may be premature at this stage.”

The embryos the researchers used were collected from in vitro fertilization clinics and selected for study on the basis of one key criterion: they were nonviable. Because the embryos could not have survived, no matter the outcome of the experiments, the Chinese researchers may have hoped they would be able to prevent, or at least blunt, any bioethical objections.

Some of these objections featured prominently in the NIH statement: “Advances in technology have given us an elegant new way of carrying out genome editing, but the strong arguments against engaging in this activity remain. These include the serious and unquantifiable safety issues, ethical issues presented by altering the germline in a way that affects the next generation without their consent, and a current lack of compelling medical applications justifying the use of CRISPR/Cas9 in embryos.”

The NIH’s criticisms were preceded by calls for a voluntary moratorium on the use of gene-editing technologies in human embryos. Statements to this effect were issued by International Society for Stem Cell Research, which reiterated a stand it had taken previously, and the Society for Developmental Biology.

“[We support] a voluntary moratorium by members of the scientific community on all manipulation of preimplantation human embryos by genome editing,” declared the Society for Developmental Biology. “Such studies raise deep ethical concerns on their own, and in addition could lead to unanticipated consequences if manipulated embryos were implanted into a womb and allowed to develop to term.”

Smarting from such criticism, perhaps, is Protein & Cell, the publisher of the Chinese study. In an editorial that was posted on April 28, the journal maintained that its decision to publish the study “should not be viewed as an endorsement of this practice or an encouragement of similar attempts.” Instead, the journal continued, the appearance of the article should “[sound] an alarm to draw immediate attention to the urgent need to rein in applications of gene-editing technologies, especially in the human germ cells or embryos.”

The article emphasized that the Chinese researchers used nonviable embryos, tripronuclear zygotes (fertilized zygotes with one oocyte nucleus and two sperm nuclei). Tripronuclear zygotes, the article noted, occur in common in vitro fertilization procedures and are clinically discarded because they are unable to develop at later stages.

This point was also made in a news article that appeared April 29 in Nature, one of two journals that reportedly refused, on ethical grounds, to publish the Chinese study. This article even allowed that many scientists “see no problem with the type of research that [the Chinese researchers] did, in part because the embryos could not have led to a live birth.” The article also noted, however, that “researchers agree that a moratorium on clinical applications is needed while the ethical and safety concerns of human-embryo editing are worked out.”

A news piece in Science, the other journal that reportedly declined to publish the Chinese study, made a similar point: “The paper has split scientists, with consensus on the need for a moratorium on clinical applications but disagreement about whether to support basic research on editing genes in human sperm, eggs, or embryos.”

For its part, the NIH concluded its statement by saying it will “continue to support a wide range of innovations in biomedical research, but will do so in a fashion that reflects well-established scientific and ethical principles.”

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