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We’ve Edited the First Human Embryos, and Taken a Step Towards Captain America

In a world first, Chinese scientists have published the results of the first genetic editing of a human embryo. The paper, appearing in the journal Protein & Cell (after being rejected by both top-tier journals Nature and Science for ethical concerns), describes a relatively new technique called CRISPR/Cas9 that the researchers used to alter the genes inside 86 non-viable embryos. Their goal was to replace a faulty gene that would go on to cause a debilitating blood disorder if the embryo were to divide into personhood. What they did was open up the largest can of worms in recent medical history, and bring us much closer to the genetics in science-fiction.

Genetic disorders are hard to treat. A disease hidden in our genes comes from a faulty DNA code, not an invading virus or bacteria or other pathogen (though some pathogens can distort our DNA) that we can bathe in drugs. Just a mutation to a single letter of a single gene can cause horrible illnesses, as science writer Carl Zimmer outlines in a fantastic piece called “The Girl Who Turned to Bone”.

Some genetic disorders can be kept in check by drugs, while others can be mitigated by watching your diet. However, as long as the code is faulty, the body will keep building bad blocks, and keep making someone sick. For the last few decades, doctors and scientists have been looking for new ways to fight genetic disease, and the thinking has now turned to fixing the genes themselves. This is what so-called “gene therapy” wanted to address. The success and clinical use of gene therapy has waxed and waned since the 90s, hinging on the ability of certain viruses injected into a patient’s body to deliver working copies of a malfunctioning gene.

“That’s why we stopped.

We still think it’s too immature.”

Though gene therapy has seen some clinical success, it’s a blunt tool for a sometimes very precise problem. So when scientists developed the CRISPR/Cas9 technique, a gene-editing tool that could cut theoretically any stretch of DNA in any organism, gene therapy looked like it might finally live up to the hype.

CRISPR, or Clustered Regularly Interspaced Short Palindromic Repeats, is a relatively new way to edit DNA based on how bacteria protect themselves from viruses. When a bacterium senses invading viral DNA, it can send out short sequences of single-stranded RNA, which have the same coding as a certain stretch of the viral DNA. Then, using a unzipping and cutting protein called Cas9, the RNA strands lock on to their DNA doppelganger and engage a nano-scale snip. This deactivates critical genes, destroying the viral danger.

CRISPR does the same thing, but under a scientist’s control. She finds the gene she wants to deactivate, copies its code, then “programs” the CRISPR/Cas9 process accordingly. Deactivating certain genes can show researchers exactly which gene has which function, but a snipped sequence of code can also be supplemented with a mutated or properly functioning gene. This technique has seen some success in trials or animal and human cells, and the thinking is that, using CRISPR, we can fix almost any gene and therefore greatly increase our chances of curing certain genetic disorders. But there haven’t been trials on anything beyond simple human cells…until this Chinese paper.

EmbryoEdit_FEATAn 8-cell human embryo, day three.

Junjiu Huang and colleagues are the first to test CRISPR on human embryos. The 86 single-celled embryos used were never going to become people, and therefore were considered suitable for experimentation. The team then used CRISPR to target a single gene called HBB, mutations of which cause a blood disorder later in life. If a properly functioning HBB gene could be inserted, the team would show that CRISPR could fight disease before a patient is even born.

Only 71 of the 86 embryos survived the 48 hours after CRISPR/Cas9 was injected into them, and 54 of those were genetically tested afterwards. Only 28 embryos had successful gene splicing, and “only a fraction of those contained the replacement genetic material,” Nature reports. In other words, not all of the cells in the embryos that were spliced contained the desired changes. Another problem was that CRIPSR inserted DNA in the wrong spots in some embryos. That could cause multiple diseases, rather than cure one.

“That’s why we stopped,” said Huang. “We still think it’s too immature.”

Huang‘s doubts about the currently viability of CRISPR to edit human embryos — rather than treating genetic diseases after they manifest, editing genes in embryos could provide a “corrected” genome in a few cells from which trillions of healthy cells sprout — are echoed by scientists and ethicists alike. In March, researchers wrote an editorial in Nature titled “Don’t edit the human germ line,” out of fear that the editing techniques are in their infancy, the benefits are not clear, and the potential harms are serious (and maybe inheritable, as changes would feasibly be infused into future generations too). This new paper seems to bolster those fears; rather than igniting a new frontier, germ line editing is for now only igniting debate.

This first embryo study shows us

just how far science is from

making superheroes.

But if editing our genes with something like CRISPR was ethically and scientifically sound, where could it take us? The worst always comes to mind first: Eugenics programs, GATTACA, etc. For all that could go wrong however, a few things could go right, including turning everyone into Captain America.

Captain America: The First Avenger

In my latest Because Science, I explored what it would take to take an average person and turn him or her into the epitome of human performance. That’s what happened with Steve Rogers after being given a super-soldier serum and bombarded with “vita-rays.” If Rodgers was injected with light-activated nano-materials carrying CRISPR/Cas9 coded to target genes responsible for muscle growth and how much oxygen his blood carries, for example, a perfected human might just emerge.

Of course, results like those in this first embryo study show us just how far science is from making superheroes. CRISPR’s genetic scalpel is still too dull to really make a cut in the thick skin of genetic disease. And the ethics of editing our genes needs to be considered, and fast, before the ability to do so outpaces our doubts. We may have the technology to alter our blueprints, but we still need to have the discussion about how we should, or if we should.

Kyle Hill is the Science Editor at Nerdist Industries. Follow on Twitter @Sci_Phile.

IMAGES: Marvel; 8-cell human embryo, day 3 by RWJMS IVF Program

STUDY: CRISPR/Cas9-mediated gene editing in human tripronuclear zygotes

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