Scientists edit viable human embryo DNA with CRISPR for the first time


9 week human embryo from ectopic pregnancy
Ed
Uthman / Wikimedia Commons


In a step that some of the nation’s leading scientists have long
warned against and that has never before been accomplished,
biologists in Oregon have edited the DNA of viable human embryos
efficiently and apparently with few mistakes, according to
a report in
Technology Review.

The experiment, using the revolutionary genome-editing
technique CRISPR-Cas9, was led
by Shoukhrat Mitalipov of
Oregon Health & Science University. It went beyond previous
experiments using CRISPR to alter the DNA of human embryos, all
of which were conducted in China, in that it edited the genomes
of many more embryos and targeted a gene associated with a
significant human disease.

“This is the kind of research that is essential if we are to know
if it’s possible to safely and precisely make corrections” in
embryos’ DNA to repair disease-causing genes,” legal scholar and
bioethicist R. Alta Charo of the University of Wisconsin,
Madison, told STAT. “While there will be time for the public to
decide if they want to get rid of regulatory obstacles to these
studies, I do not find them inherently unethical.” Those
regulatory barriers include a ban on
using National Institutes of Health funding for experiments that
use genome-editing technologies in human embryos.

The first experiment
using CRISPR to alter the DNA of human embryos, in 2015, used
embryos obtained from fertility clinics that had such serious
genetic defects they could never have developed. In the new work,
Technology Review reported, Mitalipov and his colleagues created
human embryos using sperm donated by men with the genetic
mutation that they planned to try to repair with CRISPR. The
embryos are described as “clinical quality.” A
2017 experiment,
also in China, used CRISPR to edit DNA in normal, presumably
viable fertilized eggs, or one-cell human embryos.

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Also in contrast to the experiments in China, those led by
Mitalipov reportedly produced very few “

off-target
” effects, or editing of genes
that CRISPR was supposed to leave alone. And the experiment
avoided what is called “mosaicism,” in which only some cells of
an embryo have the intended DNA changes. The embryos were not
allowed to develop beyond a very early stage.

Because changing the DNA of an early embryo results in changes to
cells that will eventually produce sperm and eggs, if the embryo
is born and grows to adulthood, any children he or she has will
inherit the genetic alteration, which is called germline editing.
That has led to fears that such manipulations could alter the
course of human evolution.

It has also triggered warnings about “designer babies,” in which
parents customize their IVF embryos by adding, removing, or
changing genes for certain traits.

A recent report on genome editing
from the National Academies did not call for a moratorium on
research into germline editing, arguing that it might one day be
a way for some parents to have healthy, biological children, such
as when both mother and father carry genetic mutations that cause
severe diseases.

“But we anticipated that there would need to be a lot of research
to see if you could make these changes without any unintentional
effects,”said Charo, who co-chaired the Academies committee.
Mitalipov, who did not respond to requests for comment, has now
shown that the answer to that might be yes.

Some scholars questioned how important the new study is, however.
Stanford University law professor and bioethicist Hank
Greely tweeted that
“the key point” is that no one has tried to implant any edited
embryos. “Research embryos” that are “not to be transferred for
possible implantation” are “not a big deal,”
he argued.

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This story has been updated with additional comments by
experts and details of similar experiments.

Read the original article on STAT. Copyright 2017. Follow STAT on Twitter.

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