Translucent sperm wriggle slowly across a sepia-toned laptop screen. Normally they’re much faster, the embryologist tells me, but these little guys are slogging through a gooey liquid that slows them down. It makes them easier to catch.
A skinny, hollow needle enters the scene from screen right and approaches a swimmer. The device sucks it inside, tail first. Its tiny, round body remains visible inside the clear sperm vacuum.
The screen blinks to a new scene. The sperm disappear and are replaced by much larger, free-floating eggs. Human eggs.
Another instrument arrives on screen, nudging one of the eggs until it floats away like a gently bumped beach ball. After another try, the fingerlike device successfully grabs an egg, using gentle suction to hold it in place.
The producer of this show is researcher Nuria Marti-Gutierrez, who sits at the microscope near the screen, never taking her eyes off her quarry as her hands maneuver between a half-dozen knobs and dials. The process she’s running is invisible to the naked eye. Each of these acts plays out in a clear droplet on the microscopic stage.
Off screen, the sperm vacuum makes a quick pit stop to grab an additional solution before appearing again, poised and ready. In a moment, the egg will be injected not only with sperm but with a dose of CRISPR-Cas9, a DNA editing system that allows scientists to cut out a gene segment and replace it with another. If all goes well, the CRISPR system will cause this single-celled human embryo to repair a disease-causing mutation in its DNA.
This lab, at Oregon Health and Science University (OHSU) in Portland, is the only group in the U.S. to publish this kind of research in human embryos. The scientists are researching human gene editing in hopes of curing specific inherited diseases. Since their claims in 2017 to have successfully repaired embryos that had a disease-causing mutation, they’ve faced backlash from skeptical scientists and opponents of human gene editing. Now, after a Chinese researcher announced the birth of gene-editedtwin girls in late 2018, they will have even more hurdles to clear before they can bring their technology to clinics.
Perhaps no one was more surprised at the news that gene-edited babies had been born in China than the OHSU team at the Center for Embryonic Cell and Gene Therapy, led by Shoukhrat Mitalipov. “I thought I knew all the legitimate groups working [on this],” says Mitalipov.
Chinese researcher He Jiankui’s announcement last November came on the eve of the International Summit on Human Genome Editing in Hong Kong. He was scheduled to give a talk on his work shortly after Mitalipov’s colleague Paula Amato, an associate professor of obstetrics and gynecology and a doctor in the OHSU fertility clinic.
“I was quite shocked to hear that someone actually had the guts to transfer these embryos and establish a pregnancy, given the uncertainty regarding safety,” says Amato. Mitalipov estimates the gene editing technology won’t be ready for clinical trials — meaning tests in real pregnancies — for another five to 10 years.
Beyond the scientific challenges, the legal and ethical considerations normally keep this kind of research at a slower pace. In 2017, the National Academies of Science and Medicine brought together ethics experts and scientists to decide, in part, whether and how to allow changes to the human germline — changes to DNA that would be passed on to future generations. The report’s criteria were to serve as international guidelines for human gene editing research.
But He’s work fell well outside those parameters, triggering a huge backlash from scientific and ethics communities worldwide. For instance, the National Academies report specifies that any editing of DNA should prevent a serious heritable disease. However, He started with a healthy gene and created a mutation thought to increase resistance to HIV. Another criterion is that the edit should happen only “in the absence of reasonable alternatives.” But HIV is considered preventable and treatable. The list goes on, with many questions about the legality and transparency of his work.
Mitalipov’s group, on the other hand, is working to correct a mutation in a gene called MYBPC3, which causes hypertrophic cardiomyopathy (HCM). This thickening of heart muscle causes a wide variety of heart problems. HCM most often makes the news when it unexpectedly claims the life of a young athlete, and autopsies reveal a previously undiagnosed heart condition. There is no cure.
A Focus on Repair
Some of He’s most extreme critics have called for a moratorium on similar work, but Mitalipov hopes the backlash doesn’t interfere with his team’s research.
“Moratorium,” says Mitalipov. “I hate that word.”
A stall in the group’s work would mean turning away from an issue Mitalipov has felt strongly about for years. As a graduate student in clinical genetics, he recalls learning how to diagnose inherited diseases based on a patient’s genes. And he was unsatisfied with the endgame.
“You’d tell the patients, ‘Hey, we found it, this is a mutation causing this disease,’ ” he says. “And then the patient is going to say, ‘Now what?’ But that’s it, our work is done.”
It then became clear to him that one way to tackle these diseases — like cystic fibrosis, sickle cell anemia, and Huntington’s — would be to fix the genetic mutations early in life, before any damage to the gene is done. Really early: in the embryo.
But only recently has there been a clear way to do it.
The earliest work on what would become CRISPR (short for clustered regularly interspaced short palindromic repeats) happened some 30 years ago, but it took researchers nearly all that time to figure out the full CRISPR-Cas9 system and to begin harnessing it for gene editing. The system of DNA sequences occurs naturally in bacteria, helping them fight off attacking viruses. Bacteria incorporate a small chunk of DNA when they encounter a specific virus, a little souvenir to remember their viral attacker in the future. The bacteria’s defense system includes a seek-and-destroy function that uses the viral DNA as a search image. Part of the mechanism includes production of the protein Cas9, which snips the DNA that matches the template. For a virus trying to infiltrate a bacterial cell, this means game over.
Today, biologists have learned to reprogram CRISPR-Cas9 to cut any type of DNA in a cell — not just viral — in a location of their choosing by giving it a new target to seek out. They’ve also discovered that after the DNA is cut by Cas9, cells will try to repair the break in the DNA. That repair system can then be manipulated into using a template provided by scientists, effectively cutting out one gene and replacing it with another.
Mitalipov and like-minded colleagues believe the promise of CRISPR is that they will be able to use it to replace a defective gene with a functioning one. To test this, the OHSU team’s experiments, published in the journal Nature, were straightforward. Using sperm from a man carrying the defective MYBPC3 gene and eggs from a healthy woman, they would see if they could use CRISPR-Cas9 to repair the disease-causing gene.
They injected each egg with a sperm carrying the mutation and a CRISPR-Cas9 package. In this case, the package included the DNA search image that would help Cas9 find the defective gene. They also included a sequence of DNA that matched the normal version of the gene, which the cell uses as a repair template to mend the cut in its DNA. They added a little calling card to this repair template — swapping out two nucleotide bases that would change the sequence, but not the function, of the normal gene. With this, they could know whether the cell used their template.
Their experiments worked, but not in the way they expected. Cas9 did locate and cut the disease-causing gene the embryo had inherited from its father. But instead of using the template the researchers provided, the embryo used the normal gene from the mother as a template, resulting in two normal genes.
However, some scientists remain skeptical the experiments worked as well as Mitalipov’s group claimed because of the difficulties of confirming that the gene editing went as planned. Their biggest holdup? It’s possible that instead of two normal genes, the embryos actually have one normal gene and one missing gene, caused by what’s called a large deletion. This phenomenon has been documented in a handful of other CRISPR studies and could explain why the researchers didn’t detect any disease-causing genes when they examined the edited embryos. If critics are right, these embryos would be far from healthy.
Paul Thomas, leader of the Genome Editing Laboratory and director of the South Australia Genome Editing Facility at the University of Adelaide and South Australian Health and Medical Research Institute, sought to directly answer the large-deletion question. His team tested Mitalipov’s methods in mouse embryos, and found these suspected large deletions were common.
In response, Mitalipov’s group did a follow-up experiment to show that their embryos didn’t have the deletions. But the critics, including Dieter Egli, a cell biologist at Columbia University, weren’t terribly satisfied. “Conclusive evidence for the proposed repair mechanism is still missing,” he says.
Thomas had a similar reaction. “The reason for this difference [between the two studies] remains unclear,” he says. “It will be interesting to see if the results from [Mitalipov’s group] are replicated in studies using human embryos from independent laboratories.”
Science aside, human embryo research is a logistically tricky business. The work is not eligible for financial support by the National Institutes of Health, the main source of biomedical research funding in the U.S.
The OHSU team has worked around this with private funding, but it will face a big obstacle when it’s ready to take the gene repair treatment — that’s how they refer to their disease-removing embryo edits — to clinical trial. To do that, the team needs FDA approval. In 2015, however, Congress removed the FDA’s funding to review “research in which a human embryo is intentionally created or modified to include a heritable genetic modification.”
This doesn’t stop Mitalipov from moving his work forward; it just doesn’t allow him to seek official approval in the U.S. So Mitalipov says that when embryonic gene repair is ready for clinical trials, he’ll take it to a country that allows it but also has strong legal and ethical oversight, such as the U.K.
He believes it’s actually irresponsible not to continue to study and test the embryo repair techniques coming out of the lab. That’s because once research is published, the ideas are out there, with instructions in each study’s methods section. He worries researchers or clinicians in other countries with different regulations would run with them before they’ve been properly vetted.
“Of course, we will do [clinical trials overseas] in a responsible way, with proper oversight,” says Mitalipov. “We have no choice — we have to do it. We already started, and we cannot leave it to [in vitro fertilization] clinics to do this job.”
When parents want to avoid passing their genetic condition to their children, Amato says, a viable option is to undergo in vitro fertilization (IVF) using what’s called pre-implantation genetic diagnosis (PGD). During PGD, doctors examine each embryo created in vitro and discard the ones that carry the disease.
If gene repair can replace PGD, that process wouldn’t have to happen, which could shorten stressful IVF treatments. Although human embryos are created and subsequently discarded in this research process, the team hopes that in the long run, fewer embryos will be destroyed.
What’s in Store
Mitalipov thinks we won’t see a legitimate gene-repaired human baby for up to a decade, though He Jiankui already demonstrated that someone might move forward with the technique, with or without scientific vetting and adequate oversight.
Is this a slippery slope into “designer babies?” Not really, says Amato. Right now, she says, scientists don’t even know the complex genetic underpinnings behind desirable traits, such as intelligence or athletic ability. “It’s not technically feasible,” she says, “but some would say that’s a cop-out. Maybe one day we’ll know those genes.”
“I think [designer babies are] way far off,” says Amato — but not so distant that researchers shouldn’t be thinking about taking steps now to regulate the technology that could create them. “I definitely think [it’s] something we should be thinking about and aware of.”
Anna Funk is an assistant editor at Discover. Follow her on Twitter @DrAnnaFunk. This story originally appeared in print as "Repairing the Future."
This story is part of "The Future of Fertility" a new series on Discover exploring the frontiers of reproduction.