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Biological Chemistry

Summit Urges Caution But Doesn’t Rule Out Future Gene Editing Of Human Embryos

Researchers and bioethicists call for stringent safety testing, regulatory approval, and broader public buy-in before gene editing is applied to human embryos

by Sarah Everts
December 4, 2015

Credit: Adapted from OriGene Technologies
Clustered regularly interspaced short palindromic repeats (CRISPR) technology is widely used for gene editing. A guide RNA directs the Cas9 enzyme to the target DNA sequence. Cas9 cuts both strands of the DNA, priming the gene for editing.
Shown is a scheme describing how the CRISPR/Cas9 system edits DNA.
Credit: Adapted from OriGene Technologies
Clustered regularly interspaced short palindromic repeats (CRISPR) technology is widely used for gene editing. A guide RNA directs the Cas9 enzyme to the target DNA sequence. Cas9 cuts both strands of the DNA, priming the gene for editing.

International scientists and bioethicists who debated gene editing at a summit earlier this week in Washington, D.C., have issued a statement that does not rule out the controversial use of the technology on human eggs, sperm, and early-stage embryos.

The statement, released Thursday by the organizers of the International Summit on Human Gene Editing, strongly advocates, however, that any clinical use of edited human embryo or germline DNA should move forward only after certain criteria are met. Scientists should not proceed in using gene-editing techniques to remove disease-associated DNA or to enhance human capabilities in clinical settings, until safety and efficacy concerns have been thoroughly allayed, until there is broad social consensus to do this sort of editing, and until the research has followed appropriate regulatory oversight, the statement says.

“At present, these criteria have not been met for any proposed clinical use,” summit organizers note.

They also emphasize that edited human embryos or germline cells produced during basic research “should not be used to establish a pregnancy.”

Although the statement is not legally binding, organizers hope it will guide the development of gene-editing regulations worldwide.

Scientists have been editing genes since the 1970s, but four years ago researchers discovered a way to dramatically improve the speed, ease, specificity and accuracy of gene editing compared with previous techniques. The new technology, called CRISPR/Cas9, was developed from cellular machinery that bacteria use to excise foreign viral DNA.

CRISPR/Cas9 is now being tested experimentally in a multitude of ways in academic and biotech labs: to modify pig DNA to produce organs for human transplants, to alter mosquito DNA so that the insect destroys malaria, and to remove a rare blood disorder gene from nonviable human embryos. This last application, reported by Chinese scientists in the spring, is what motivated pioneers of the technology to hold the summit. Many in the research community saw the work as an alarming step toward designer babies.

“The overriding question is when, if ever, we will want to use gene editing to change human inheritance,” said summit chair David Baltimore of Caltech during the meeting. The summit was organized by the National Academy of Sciences, the National Academy of Medicine, the U.K.’s Royal Society and the Chinese Academy of Sciences.

While the summit’s concluding statement is extremely cautionary about the editing of human embryos and germline DNA, because these genetic modifications could be passed down from generation to generation, the statement is more enthusiastic about using gene-editing technology to modify somatic cells—things like skin cells that cannot be passed down to future generations.

“Many promising and valuable clinical applications of gene editing are directed at altering genetic sequences only in somatic cells,” summit leaders note. “Examples that have been proposed include editing genes for sickle-cell anemia in blood cells or for improving the ability of immune cells to target cancer.”

At press time, the National Institutes of Health had not issued a reaction to the summit’s statement, which challenges the funding body’s position on editing human embryos and germline DNA. In April, NIH director Francis S. Collins stated: “NIH will not fund any use of gene-editing technologies in human embryos. The concept of altering the human germline in embryos for clinical purposes has been debated over many years from many different perspectives, and has been viewed almost universally as a line that should not be crossed.”

Harvard Medical School’s George Church, an advocate of human embryo research and organizer of the summit, recently argued in a Nature commentary that “banning human-germline editing could put a damper on the best medical research and instead drive the practice underground to black markets and uncontrolled medical tourism, which are fraught with much greater risk and misapplication.”


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