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A researcher in China used the gene editing technique known as CRISPR to change the DNA of human embryos. Hank unpacks why this is being universally condemned by scientists.

Hosted by: Hank Green

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Hank: Once in a while, there's a development in science that gets an unusual amount of press.  Often, that's a good thing.  We discover a new subatomic particle or detect gravitational waves for the first time or land something on Mars.  This time is different.  Last week, a researcher in China announced that he had used the gene editing technique known as CRISPR to change the DNA of human embryos created via in vitro fertilization, and that these two embryos had been successfully implanted in their mom and developed into twin baby girls that were born last month.

The experiment has been universally condemned by scientists and according to practically every expert on medical ethics, should never have been done in the first place.  Here's why: CRISPR is a revolutionary gene editing technique that's been used for a ton of research in the last few years.  It allows scientists to delete genes, turn off genes, or insert genes, all more easily, cheaply, and accurately than ever before.  In this latest experiment, He Jiankui, a scientist at the Southern University of Science and Technology in Shenzhen, China used CRISPR to disable a gene called CCR5 in human embryos.  CCR5 is involved in the immune system and the HIV virus exploits it in order to infect human cells.  So by disabling this gene, he aimed to make the babies resistant to HIV.  

We don't know many of the details of this experiment because He Jiankui hasn't published the research in a peer-reviewed scientific journal, but according to reports, the parents of the babies went through IVF and shortly after the eggs were fertilized, He used the CRISPR technique to cause a genetic mutation that would disable the CCR5 gene.  The embryos were then implanted into their mother's uterus and were carried to term.  The twin girls were born around the beginning of November and so far, they seem healthy. 

There's been speculation that the parents may have decided to participate in this experiment because the father is HIV+, but there are other, less risky ways to ensure that a baby with an HIV+ parent doesn't contract the virus. 

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In an episode we did on CRISPR back in 2016, we mentioned that scientists are aware of the 'just because you can, doesn't mean you should' principle, but it seems like He (?~2:08) was not.  CRISPR had been used to edit genes in human embryos before now, but only for research purposes and never with the intention of implanting the embryos or allowing them to develop, and the consensus among both scientists and policy-makers was that we were nowhere near ready to implant genetically-edited embryos.  We needed more research first.

Ethically, there are still some open questions about the implications of editing someone's entire genome before they're born, whether it will lead to so-called designer babies, for example, or if it's okay to alter the course of human evolution in this way.  No matter how you feel about those questions, we're not ready for CRISPR-edited babies because of some pretty basic safety concerns.  CRISPR isn't perfect yet, and sometimes it will change a gene in unexpected ways, causing an unintended mutation, and the last thing you want is an accidental potentially dangerous change in every single cell in someone's body.  

The few approved gene therapies that involve directly editing someone's DNA inside of their body use older, better studied techniques, not CRISPR.  There are a few CRISPR-based treatments in trials right now, but they work by taking certain types of cells out of the patient, modifying them, and then putting them back in, and no matter what technique they use, all these treatments have something in common: they don't touch the germ line.  

Germline cells are the ones that divide to produce eggs or sperm, and by making sure they stay unmodified, you can't pass on the edited DNA to a child.  So even if something goes wrong, you avoid the risk of introducing that problem to future generations.  He (?~3:39) basically took all those precautions and threw them out the window.  

For the experiment, he used CRISPR to edit DNA in very early embryos consisting of only a few cells at most.  At that stage, CRISPR can alter genes in every cell of the embryo, which eventually generate every cell in the fetus' body, including their germline cells.  Even if everything had gone exactly as planned, this research would have been controversial because it skipped so many steps in the usual careful process that goes into developing new treatments, especially new gene-editing treatments, but it didn't all go exactly as planned.

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The babies are healthy right now, but the mutations in their CCR5 genes are slightly different from the naturally occuring ones He was trying to reproduce.  We have no idea if those new mutations will have other effects and now the girls are stuck with them for the rest of their lives.  It also seems like in at least one of  the babies, only half of the CCR5 genes were edited.  Depending on how the edited genes are distributed, that could mean that she didn't even get the HIV resistance after all that.

So yeah, it turns out there are reasons we are cautious about research like this, but it's not just about the fact that He tried a treatment and it didn't work out exactly as expected.  That happens all the time.  It's that he went against scientific consensus so strong that there are laws to enforce it.  The Chinese government now seems to be investigating him, although the details of that are not yet clear.  Either way, this was not a good strategy for pushing scientific progress.

Scientists had pretty much agreed that if they ever used CRISPR on a human embryo that would be carried to term, they would use it to correct a genetic disease for which there was no other reasonable treatment.  In a YouTube video he posted, because of course this all came out via a YouTube video, He explained that he chose the gene because it's extremely well-studied thanks to years of HIV research, but there was no medical need for this.  

The goal was just to make the babies more resistant to HIV infection, which they didn't have and again, could have prevente in a number of less expensive and much less controversial ways.  Scientists are all for progress, that's kind of their job, and gene editing has the potential to completely transform the face of medicine, but if there's anything scientists have learned from past mistakes, it's that we need to be careful about how we wield that type of power, because it can be dangerous, too, and with CRISPR being such an amazing potential treatment, the last thing we want to do is sour the whole world on its use because of some mistakes made early in the process.

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