When you choose to interfere with nature, you should be prepared for results that are far from natural. That’s the message of a new study out of the Columbia University Medical Center, where researchers are warning scientists that the CRISPR-Cas9 gene editing technology results in unintended mutations that could go undetected.
As a relatively new technology, there are a lot of unknowns when it comes to gene editing. Known for being precise, efficient, and quick, the CRISPR-Cas9 method has shown some promise. For example, scientists have used it to edit HIV out of some living organisms and modify mosquitoes to get rid of malaria.
However, this is far from a perfect science, and now a study published in the journal Nature Methods shows that it can cause unintended mutations in genomes. This is particularly concerning when you consider the fact that clinical trials of using CRISPR on humans are already underway in places like China.
Researchers urge scientists to use caution
Columbia University Medical Center’s Stephen Tsang, who co-authored the study, urged the scientific community to consider the possible hazards of off-target mutations. In the study, his team sequenced mice genomes that had previously been subjected to the CRISPR technology in order to cure blindness. They found 1,500 single-nucleotide mutations and more than 100 bigger deletions and insertions when they examined the genomes of two of the subjects in depth.
The scientists are pressing for a more accurate way to check for mutations, insertions and deletions in genomes, such as using whole-genome sequencing rather than depending on computer algorithms alone. Computer algorithms did not detect any of the mutations that were discovered in the study, which is startling.
Study co-author Alexander Bassuk of the University of Iowa concurred, saying that the predictive algorithms work well when CRISPR is used on tissues or cells in a dish, but it has serious shortcomings when used on living animals. With this method, a computer model is used to predict where mutations might occur, and then only those areas are checked in depth to see if any unintended changes took place in the genetic code.
Concerns about future applications of CRISPR
The technology has been particularly popular in China, where the government and some corporations are making huge investments in CRISPR. In fact, Chinese scientists say they were the first to make a type of wheat that is resistant to a fungal disease. They also claim to have created more muscular dogs and leaner pigs. What they often fail to mention, however, is the fact that 30 of the 32 pigs they subjected to the technique died prematurely, showing that even the simplest of genetic tweaks can have a big impact on the animal throughout its lifetime.
While few people would argue with the importance of finding a way to cure cancer, not all uses of CRISPR are ethical. For example, the Chinese scientists who found a way to make dogs more muscular, jump higher and run faster are considering using the technology to benefit the military and police by creating stronger dog breeds. If that happens, it’s only a matter of time before they start using it to alter human DNA to create “better” police officers and soldiers.
Other scientists are eyeing the use of the technology to bring back extinct species, with one team of researchers saying they could use it to bring the woolly mammoth back from extinction in the next two years. A Harvard University research team wants to create a hybrid elephant/mammoth embryo with a view to saving the endangered Asian elephant from extinction. Could the reemergence of dinosaurs be right around the corner?
When the Centers for Disease Control and Prevention announced last year that people who take HIV medication religiously for six months can theoretically get to point where they can’t transmit the virus, it was considered a huge advancement. There remains no cure for HIV and AIDS, although it is not the death sentence that it used to be. There have been triumphs and setbacks in the quest to find a cure, and now scientists are considering revisiting a past disaster in hopes of emerging victorious this time around.
A controversial gene editing procedure is at the heart of the new approach. Gene editing recently gained FDA approval for treating cancer and one type of blindness, and some researchers are hoping that HIV/AIDS can soon be added to the list.
Gene therapy has already helped some patients make their cells more resistant to HIV. In 2014, scientists removed some of Matt Chappell’s blood cells, disabled a gene in order to help the cells resist the HIV virus, and then returned the edited cells to his body. It has been the closest thing to a cure for Chappell, who has gone from taking the strongest AIDS drugs available for more than a decade to not needing the medications at all for more than three years. His body even managed to keep the virus in check in the midst of cancer treatments that wreaked havoc on his immune system last year.
Chappell’s story is far from ordinary. Of the 100 people who took part in those experiments, just a few of them were able to give up their HIV drugs in the long run. The rest of them still have to take medication to suppress their HIV.
Despite these discouraging numbers, the researchers want to give it another try. They believe that they can improve this treatment and are now testing some tweaked approaches in which they’ve doctored DNA in a different way.
Temple University researchers have developed a method of gene editing that can detect HIV DNA in a person’s T-cell genome, which is a set of DNA pertaining to a certain kind of white blood cells. When this DNA has been edited out, the loose genome ends that were previously attached to the HIV will be rejoined by the DNA repair system within the cell. This leaves the cell free from HIV and protected from new infections.
Gene therapy has experienced a complete renaissance — where will it go in 2024 and beyond?
Eleven years ago, gene therapy — where defective genes are snipped out of DNA and replaced with healthy ones — became a household name. A landmark paper proved that scientists could precisely manipulate DNA in ways previously thought unimaginable using CRISPR-Cas9, an editing tool adapted from the immune system found in some bacteria. Almost overnight, the idea of designer babies, kill-switch mosquitoes, and cancer-off buttons stormed into mainstream imagination.
Since then, gene therapy has experienced a complete renaissance, culminating this past November and early December when medical regulators in the U.K. and U.S. officially approved Casgevy, the first CRISPR-based gene therapy for treating two blood disorders: sickle cell anemia and beta-thalassemia (in the U.S., the new therapy has yet to be approved for the latter).
Casgevy is emblematic of gene therapy’s rapidly shifting expectations and direction. Numerous clinical trials are now underway across the globe, and we will undoubtedly see more and more gene-editing-based treatments making the approval list, changing the lives of countless individuals living with intractable health conditions and diseases.
“The future [of gene therapy] is very bright,” Kevin Davies, the executive editor of The CRISPR Journal and author of Editing Humanity: The CRISPR Revolution and the New Era of Genome Editing, tells Inverse. “But I don’t don’t think anybody in the field wants to get too complacent because it was less than 25 years ago that we were riding a similar initial wave of enthusiasm for the technology.”
It’s true. Long before the Human Genome Project would ever decode a DNA sequence, ambitious scientists were spurred by advances in biotechnology and the early success of initial human trials. In 1990, then-4-year-old Ashanti DeSilva became the first person to be successfully treated with gene therapy. The treatment, a precursor of sorts to CRISPR-based gene therapy, cured her of a rare immune-related genetic disorder.
But those high hopes of tweaking genes to prevent or treat disease were suddenly dashed when, in 1999, a teenager named Jesse Gelsinger, who had a rare metabolic disorder, died within four days of receiving an experimental gene therapy at the University of Pennsylvania. In response, the U.S. Food and Drug Administration (FDA) suspended the university’s entire gene therapy program — which had been the largest in the world at the time — and launched investigations into 69 other gene therapy trials that were underway across the United States. Years later, when CRISPR entered the world, enthusiasm rose again — and here we are.
So what will this new wave — Gene Therapy 2.0, if you will — look like? Certainly, a promising frontier for tackling not only rare but common diseases and exquisitely precise gene-editing tools. With it, though, will come side effects, including exorbitant prices, barriers to access, and a lingering, gigantic cause for concern because once you edit an embryo, there’s no turning back. Here’s what 2024 and beyond has in store for our gene-edited future.
Emmanuelle Charpentier and Jennifer A Doudna share the 2020 Nobel Prize in Chemistry for their research into CRISPR.JONATHAN NACKSTRAND/AFP/Getty Images
Better editing
In the early years of genetic therapy, scientists didn’t have many tools at their disposal to fix a gene (or genes) at the heart of a disease, Shoukhrat Mitalipov, director of Oregon Health and Science University’s Center for Embryonic Cell and Gene Therapy, tells Inverse.
If someone’s disease was due to a gene mutation or loss, Mitalipov says the fix was to introduce a synthetic, albeit normal copy of that gene with a virus stripped of its infectiousness but still retaining the ability to add new genetic information into DNA. With this new addition, a cell could then make a functional protein. While these essentially viral Ubers remain part of the gene therapy toolkit, the discovery and development of CRISPR-Cas9 gave scientists a more precise grip on the genetic engineering steering wheel.
CRISPR, or clustered regularly interspaced short palindromic repeats, originate from bacteria and archaea and is used by these microorganisms as an immune defense against viruses called phages. The CRISPR system also includes specialized enzymes called CRISPR-associated proteins (or Cas). Together, they look through and remove any genetic sequences that may have been inserted by a sneaky phage or other invader, keeping the microorganism safe from infection.
In 2012, researchers Jennifer Doudna and Emmanuelle Charpentier published a groundbreaking study detailing a novel CRISPR-Cas9 system they programmed to cut specific sites in isolated DNA. This was done using strands of RNA — a molecule that is like a working copy of DNA, containing the direct instructions for protein-making — guiding CRISPR-Cas9 to a specific genetic sequence.
Krishanu Saha, a bioengineer at the University of Wisconsin–Madison whose lab is working on gene therapies for treating blindness, says the precision allowed by CRISPR-Cas9’s programmability is its singular selling point.
“Traditional gene therapy, which we call gene augmentation, is essentially flooding the cell with extra copies of a normal gene; in some cases, this doesn’t work,” Saha tells Inverse. “We found in a few cases, it’s really important to destroy the mutant copy of the [gene] or fix the underlying mutation and that’s where you have to have the precision of CRISPR to go in and specifically do that.”
CRISPR has a unique drawback, however. When it goes in to patch up the bit of DNA as instructed, it does so by fracturing both strands of the DNA double helix. A cell is left to repair the breaks on its own, ideally using the synthetic DNA offered by the CRISPR-Cas9 system. But because it’s a klutzy repairperson, the cell may also introduce errors such as inserting or deleting DNA.
This is why the focus of the next generation of gene editing tools is to try to minimize, as much as possible, the risk of new mutations, says Mitalipov.
These tools include base editing, where specific base pairs — the building blocks of DNA — are swapped out without requiring a double-stranded break. Base editing was used in a recent gene therapy clinical trial treating individuals with a genetic form of high cholesterol called familial hypercholesterolemia. The gene-editing technique, which is based on CRISPR, was developed in 2016 by Harvard University’s David Liu, considered a founding pioneer of CRISPR.
Another CRISPR-based tool is a leveled-up version of base editing. Called prime editing (also co-invented by Liu), it can swap base pairs in addition to inserting and deleting without double-breaking the DNA helix.
More recently, a gene-editing tool called NICER developed by researchers in Japan is said to create little single-strand nicks that didn’t seem to cause mutations, according to a September 2023 Nature Communications study.
Despite the appeal of finer precision and avoiding inadvertent mutations, Mitalipov and Saha say it’s unlikely the original CRISPR-Cas9 system will be ousted or replaced entirely by these newer gene editors.
“Basically, you would have to look at the specific gene mutation and then decide what would be the best — it could be base or prime editing,” says Mitalipov. “So far, prime editing hasn’t been widely used. There’s only one or two labs [doing research] and nothing commercially available. So, it remains to be seen if [prime editing] is really going to be applicable.”
A laboratory staff works at Genethon, a non-profit gene therapy R&D organization in Evry, France. ERIC PIERMONT/AFP/Getty Images
More targets
CRISPR-based gene therapies are being devised to treat all sorts of conditions and disorders, from neurological to autoimmune and cancers. Currently, the only FDA-approved therapy using CRISPR is Casgevy; others on the market, such as Luxturna for people with a rare genetic defect that often leads to blindness and Zolgensma for treating spinal muscular atrophy, use a disabled virus bearing a normal version of the target gene to cells.
Currently, the focus is treating disorders or diseases caused by mutations in single genes in somatic cells (the body’s non-reproductive cells). This route makes it easier to identify and target relatively straightforward biological mechanisms than cracking at multiple genes acting in complex and sometimes unpredictable ways with which tinkering may lead to unintended, potentially life-threatening consequences. Understandably, since the late 1990s, there’s been a reasonably high regulatory bar for the research a gene therapy requires to meet FDA approval.
However, that doesn’t mean more genetically complex diseases are off the table. Editing multiple genes is quite possible and regularly done with transgenic animals (as well as plants), says Saha. Attempting this engineering feat for human health will take extensive research to uncover the genetic pathways and interactions involved and figuring out how to safely target all these genes with minimal off-target effects.
In the future, we may see gene therapies used increasingly for common health problems, not only rare genetic diseases, says Mitalipov and Saha. For example, a recent clinical trial in people with familial hypercholesterolemia found that one gene therapy targeting a mutated gene behind the build-up of bad cholesterol slashed cholesterol levels on par with similar-acting pharmaceutical drugs. These findings offer a tantalizing glimpse of an exciting beginning for gene therapy within preventative medicine, promising that someday, a simple edit in your genome may protect you against high cholesterol and blood pressure or any other commonplace ailments.
Therapies for all
There’s another barrier that could ultimately prevent even the safest, most promising gene therapy from seeing the light of clinical day: cost. Luxturna, for example, was reported at a whopping $425,000 per eye back in 2018. It’s a bit of a bargain compared to the average million-dollar price tag for emerging gene therapies such as Casgevy, the gene therapy for sickle-cell anemia/beta-thalassemia. The gene therapy market itself was valued at $1.46 billion in 2020 and is estimated to reach over $5 billion by 2028, according to a report by Polaris Market Research.
“How do we get the pricing down is an outrageously important and unsolvable question,” says Davies of The CRISPR Journal. “Some will point to ‘Well, it’s early days, and as more of these therapies get approved, we start to see competition and prices drop’… but we see when companies get a monopoly on something, they seem more than willing to take advantage of the situation.”
Saha says there’s an active discussion within the scientific community about how to make gene therapy equitable within the low- and middle-income countries that make up the Global South. But how gene therapy accessibility will play out in the coming years is yet to be seen.
“One of the key questions in our analysis is, who’s at the table making these decisions? It’s a fairly easy critique to say that the people in the room are not representative in various ways, perhaps Global North versus Global South, socioeconomic, scientific expertise versus the lay public,” says Saha. “There are important questions about power and democracy and whose knowledge should drive policymaking that needs to be settled. I think the deliberation and the process are as important as the end set of guidelines or policies.”
Then there’s the dreaded ethical prophecy augured by science fiction in films like Gattaca, set in a world where genetic engineering and socioeconomic status go hand in hand. Both before and after the infamous incident involving Chinese scientist He Jiankui creating the world’s first CRISPR-edited human babies with a gene for HIV immunity, there have been strict worldwide regulations on any gene editing research involving embryos.
But scientists like Mitalipov are looking into using CRISPR to potentially adjust an embryo’s risk for disease. His own research at OHSU involves gene-editing germline cells — or reproductive cells that pass on genetic information to the offspring — in what Mitalipov calls “IVF gene therapy.”
He says such a technique could help improve the success of embryo implantation during IVF by creating stronger, more viable embryos. Mitalipov acknowledges, however, that there needs to be a robust regulatory framework in place before we can ever truly consider genetically engineered babies.
“In terms of regulation, we have to focus only on those 10,000 gene defects we know today that cause human disease,” says Mitalipov. “It could be easily mandated that gene therapies in embryos have to be towards severe disease in children.”
But that, and the rest of gene therapy’s optimistically bright future, remains hedged with abundant yet much-warranted caution.
Researchers say a new CRISPR-Cas9 gene editing therapy may help treat heart disease and repair damaged tissue following a heart attack. The Laundry Room/Stocksy
Every year cardiovascular disease accounts for about 32% of all deaths worldwide.
Researchers from the University of Texas Southwestern Medical Center say a new gene editing therapy may help treat heart disease.
The research team also found evidence the therapy can help repair damaged tissue immediately after a heart attack.
The most common type of heart disease is coronary artery disease, where blood is not able to flow properly to the heart. If blood flow is completely blocked to the heart, this can cause a heart attack.
Researchers from the University of Texas Southwestern Medical Center believe a new CRISPR-Cas9 gene editing therapy can both help treat heart disease and repair damaged tissue immediately after a heart attack via a mouse model.
The study was recently published in the journal Science.
According to Eric N. Olson, Ph.D., professor and chairman for the Department of Molecular Biology at the University of Texas Southwestern Medical Center, and senior author of the new study, cardiovascular disease is the most frequent cause of death worldwide.
“Gene editing enables (scientists) to target disease mediators with high specificity and only in the injured organ (i.e., the heart), which means potentially high therapeutic benefit with less adverse side effects,” he explained to Medical News Today.
Using a mouse model, Dr. Olson and his team studied their new CRISPR-Cas9 gene editing therapy. In order for the components of the gene editing system to reach the heart, they were packaged into a viral delivery system that targets the heart of mice and large mammals.
“CRISPR-Cas9 gene editing system consists of a guide RNA and a base editor,” he detailed when asked how the new gene therapy worked.
“The guide RNA corresponds to a specific region in the genome and acts to bring the base editor in close contact to a specific gene. The base editor precisely modifies the gene. In our approach, we used a specific guide RNA to target the base editor to the CaMKIIδ gene. The base editor modified this gene to prevent chronic overactivation of the CaMKIIδ protein that is aninducer of cardiac diseaseTrusted Source.”
– Eric N. Olson, Ph.D., senior study author
Researchers also discovered that using CRISPR-Cas9 therapy to subdue the CaMKIIδ gene in mice helped protect them from ischemia/reperfusion injury (IRI)Trusted Source to the heart due to heart disease.
In addition, the team found injecting mice with gene editing reagents soon after an IRI helped them recover cardiac function after severe damage, such as from a heart attack.
When asked how this type of gene therapy might impact how heart disease is treated in the future, Dr. Olson said revascularization of the infarct arteryTrusted Source with a catheter intervention will remain the first therapeutic step for patients with an acute heart attack.
“Unfortunately, cardiac function is often impaired after that event,” he explained. “That is where our approach might be applied in the future to improve cardiac function after a heart attack. However, there is still a lot of work to be done.”
Dr. Olson said for the next steps in this research, his team will next try to improve the efficiency and specificity of their CRISPR-Cas9 gene editing construct and also try to find other, non-viral-based delivery methods.
“There are several safety studies to be performed, and we will also need to test whether our approach works in large mammals,” he added.
MNT also spoke with Dr. Richard Wright, a cardiologist at Providence Saint John’s Health Center in Santa Monica, CA, about this research. He said if this new gene therapy works, it would be a “game changer.”
“What this shows is that if you can manipulate the body’s response to injury, you could potentially avoid what we used to think was unavoidable (damage),” he explained. “In this case, cardiac dysfunction following ischemic injury to the heart. So it’s huge if it pans out.”
Dr. Wright did caution, however, that since this study was conducted in mice, not all therapies that work for mice will work for humans.
“Some things in this field that work in rats or mice may not work in pigs or people, so it has to be translated into larger animals to see whether it still holds. And of course, the whole issue of changing — and with CRISPR technology, you change forever — those particular cells, so whether that will be safe in people remains to be determined.”
Sensitized pet lovers may see respiratory relief as scientists have targeted an allergenic protein to delete from cat DNA, according to a study presented at the American Academy of Allergy, Asthma & Immunology Annual Meeting.
“We’re trying to use CRISPR gene editing to edit out the major allergen from cats, so that means you could have an allergen-free cat,” Nicole F. Brackett, PhD, senior scientist at INDOOR Biotechnologies told Healio.
By examining 136 publicly available exotic cat genomes across 38 species in the National Center for Biotechnology Information’s sequence read archive database, the researchers performed a bioinformatics analysis to determine the evolution and functional significance of the major cat allergen Fel d 1.
“The exotic cats I looked at ranged from cats in the same genus as domestic cats all the way to lions, tigers and the Panthera species that diverge from domestic cats up to 11 million years ago,” Brackett said.
Two chains, chain 1 and chain 2, code for Fel d 1. Chain 2 is more variable than chain 1.
“But interestingly, the protein sequences were more variable than the DNA sequences, which was surprising. Normally, you would expect the protein to be more conserved than the DNA. We saw the exact opposite,” Brackett said.
The researchers also found up to 90 different unique amino acid substitutions across all the different cats they examined and mapped them on to the recombinant structure of Fel d 1.
“Oftentimes we’re asked the question, ‘Is the allergen conserved?’ And if it’s conserved, that could mean it’s essential to cats. If we’re trying to eventually use CRISPR to map out the major allergen in cats, if it were something that’s essential, that could be detrimental to the cat,” Brackett said.
“The nice thing about this study is it’s showing us it doesn’t look like the allergen is conserved. There’s a lot of variability and a lot more than what we would expect per a traditionally conserved protein,” she continued.
Because Fel d 1 does not appear to be essential, the researchers concluded, it is a viable and appropriate target that could be deleted with gene editing.
“It could mean an allergen-free cat, which would be amazing for a cat-allergic patient who wants a cat,” Brackett said.
Ideally, the researchers said the treatment would be applied to adult cats.
“From an ethics standpoint, and even from a marketing standpoint, I think that’s what most people would prefer,” she said.
Scientifically, however, Brackett said it would be easier to perform this editing at the germline level during the embryo stage. Once these cats are born and grown, they could be bred, passing on their nonallergenic properties to the next generation.
“Ideally, that’s not what we would like to do. But I think the limiting factors right now, which are the limiting factors in CRISPR in general, are delivery mechanisms for delivering CRISPR reagents to adult animals outside of things like the blood, liver or eye, which are relatively easier to target,” Brackett said.
The researchers now are compiling their data and expect to publish it soon.
“The next step for the science is then going to be trying to do the knockout potentially at the embryo stage,” Brackett said. “We’ve shown proof of principle of the knockout in vitro at the cellular stage, and that paper is going to be published in April.”
Draft guidelines permit gene-editing tools for research into early human development, but would discourage manipulation of embryos for reproduction.
Japan has issued draft guidelines that allow the use of gene-editing tools in human embryos. The proposal was released by an expert panel representing the country’s health and science ministries on 28 September.
Although the country regulates the use of human embryos for research, there have been no specific guidelines on using tools such as CRISPR–Cas9 to make precise modifications in their DNA until now.
Tetsuya Ishii, a bioethicist at Hokkaido University in Sapporo, says that before the draft guidelines were issued, Japan’s position on gene editing in human embryos was neutral. The proposal now encourages this kind of research, he says.
But if adopted, the guidelines would restrict the manipulation of human embryos for reproduction, although this would not be legally binding.
Manipulating DNA in embryos could reveal insights into early human development. Researchers also hope that in the long term, these tools could be used to fix genetic mutations that cause diseases, before they are passed on.
But the editing of genes in human embryos, even for research, has been controversial. Ethicists and many researchers worry that the technique could be used to alter DNA in embryos for non-medical reasons. Many countries ban the practice, allowing gene-editing tools to be used only in non-reproductive adult cells.
Researchers around the world have published at least eight studies on gene editing in human embryos. Some of the work was done in Chinaand the United States, where using the technique does not break any laws if done with private funding; some was done in the United Kingdom, where permission must be granted by a national regulatory body.
Japan’s draft guidelines will be open for public comment from next month and are likely to be implemented in the first half of next year.
We now have a precise way to correct, replace or even delete faulty DNA. Ian Sample explains the science, the risks and what the future may hold
So what is gene editing? Scientists liken it to the find and replace feature used to correct misspellings in documents written on a computer. Instead of fixing words, gene editing rewrites DNA, the biological code that makes up the instruction manuals of living organisms. With gene editing, researchers can disable target genes, correct harmful mutations, and change the activity of specific genes in plants and animals, including humans.
What’s the point? Much of the excitement around gene editing is fuelled by its potential to treat or prevent human diseases. There are thousands of genetic disorders that can be passed on from one generation to the next; many are serious and debilitating. They are not rare: one in 25 children is born with a genetic disease. Among the most common are cystic fibrosis, sickle cell anaemia and muscular dystrophy. Gene editing holds the promise of treating these disorders by rewriting the corrupt DNA in patients’ cells. But it can do far more than mend faulty genes. Gene editing has already been used to modify people’s immune cells to fight cancer or be resistant to HIV infection. It could also be used to fix defective genes in human embryos and so prevent babies from inheriting serious diseases. This is controversial because the genetic changes would affect their sperm or egg cells, meaning the genetic edits and any bad side effects could be passed on to future generations.
What else is it good for? The agricultural industry has leapt on gene editing for a host of reasons. The procedure is faster, cheaper and more precise than conventional genetic modification, but it also has the benefit of allowing producers to improve crops without adding genes from other organisms – something that has fuelled the backlash against GM crops in some regions. With gene editing, researchers have made seedless tomatoes, gluten-free wheat and mushrooms that don’t turn brown when old. Other branches of medicine have also seized on its potential. Companies working on next-generation antibiotics have developed otherwise harmless viruses that find and attack specific strains of bacteria that cause dangerous infections. Meanwhile, researchers are using gene editing to make pig organs safe to transplant into humans. Gene editing has transformed fundamental research too, allowing scientists to understand precisely how specific genes operate.
So how does it work? There are many ways to edit genes, but the breakthrough behind the greatest achievements in recent years is a molecular tool called Crispr-Cas9. It uses a guide molecule (the Crispr bit) to find a specific region in an organism’s genetic code – a mutated gene, for example – which is then cut by an enzyme (Cas9). When the cell tries to fix the damage, it often makes a hash of it, and effectively disables the gene. This in itself is useful for turning off harmful genes. But other kinds of repairs are possible. For example, to mend a faulty gene, scientists can cut the mutated DNA and replace it with a healthy strand that is injected alongside the Crispr-Cas9 molecules. Different enzymes can be used instead of Cas9, such as Cpf1, which may help edit DNA more effectively.
Remind me what genes are again? Genes are the biological templates the body uses to make the structural proteins and enzymes needed to build and maintain tissues and organs. They are made up of strands of genetic code, denoted by the letters G, C, T and A. Humans have about 20,000 genes bundled into 23 pairs of chromosomes all coiled up in the nucleus of nearly every cell in the body. Only about 1.5% of our genetic code, or genome, is made up of genes. Another 10% regulates them, ensuring that genes turn on and off in the right cells at the right time, for example. The rest of our DNA is apparently useless. “The majority of our genome does nothing,” says Gerton Lunter, a geneticist at the University of Oxford. “It’s simply evolutionary detritus.”
What are all those Gs, Cs, Ts and As? The letters of the genetic code refer to the molecules guanine (G), cytosine (C), thymine (T) and adenine (A). In DNA, these molecules pair up: G with C and T with A. These “base pairs” become the rungs of the familiar DNA double helix. It takes a lot of them to make a gene. The gene damaged in cystic fibrosis contains about 300,000 base pairs, while the one that is mutated in muscular dystrophy has about 2.5m base pairs, making it the largest gene in the human body. Each of us inherits about 60 new mutations from our parents, the majority coming from our father.
But how do you get to the right cells? This is the big challenge. Most drugs are small molecules that can be ferried around the body in the bloodstream and delivered to organs and tissues on the way. The gene editing molecules are huge by comparison and have trouble getting into cells. But it can be done. One way is to pack the gene editing molecules into harmless viruses that infect particular types of cell. Millions of these are then injected into the bloodstream or directly into affected tissues. Once in the body, the viruses invade the target cells and release the gene editing molecules to do their work. In 2017, scientists in Texas used this approach to treat Duchenne muscular dystrophy in mice. The next step is a clinical trial in humans. Viruses are not the only way to do this, though. Researchers have used fatty nanoparticles to carry Crispr-Cas9 molecules to the liver, and tiny zaps of electricity to open pores in embryos through which gene editing molecules can enter.
Does it have to be done in the body? No. In some of the first gene editing trials, scientists collected cells from patients’ blood, made the necessary genetic edits, and then infused the modified cells back into the patients. It’s an approach that looks promising as a treatment for people with HIV. When the virus enters the body, it infects and kills immune cells. But to infect the cells in the first place, HIV must first latch on to specific proteins on the surface of the immune cells. Scientists have collected immune cells from patients’ blood and used gene editing to cut out the DNA that the cells need in order to make these surface proteins. Without the proteins, the HIV virus can no longer gain entry to the cells. A similar approach can be used to fight certain types of cancer: immune cells are collected from patients’ blood and edited so they produce surface proteins that bind to cancer cells and kill them. Having edited the cells to make them cancer-killers, scientists grow masses of them in the lab and infuse them back into the patient. The beauty of modifying cells outside the body is that they can be checked before they are put back to ensure the editing process has not gone awry.
What can go wrong? Modern gene editing is quite precise but it is not perfect. The procedure can be a bit hit and miss, reaching some cells but not others. Even when Crispr gets where it is needed, the edits can differ from cell to cell, for example mending two copies of a mutated gene in one cell, but only one copy in another. For some genetic diseases this may not matter, but it may if a single mutated gene causes the disorder. Another common problem happens when edits are made at the wrong place in the genome. There can be hundreds of these “off-target” edits that can be dangerous if they disrupt healthy genes or crucial regulatory DNA.
Will it lead to designer babies? The overwhelming effort in medicine is aimed at mending faulty genes in children and adults. But a handful of studies have shown it should be possible to fix dangerous mutations in embryos too. In 2017, scientists convened by the US National Academy of Sciences and the National Academy of Medicine cautiously endorsed gene editing in human embryos to prevent the most serious diseases, but only once shown to be safe. Any edits made in embryos will affect all of the cells in the person and will be passed on to their children, so it is crucial to avoid harmful mistakes and side effects. Engineering human embryos also raises the uneasy prospect of designer babies, where embryos are altered for social rather than medical reasons; to make a person taller or more intelligent, for example. Traits like these can involve thousands of genes, most of them unknown. So for the time being, designer babies are a distant prospect.
How long before it’s ready for patients? The race is on to get gene editing therapies into the clinic. A dozen or so Crispr-Cas9 trials are underway or planned, most led by Chinese researchers to combat various forms of cancer. One of the first launched in 2016, when doctors in Sichuan province gave edited immune cells to a patient with advanced lung cancer. More US and European trials are expected in the next few years.
What next?
Base editing A gentler form a gene editing that doesn’t cut DNA into pieces, but instead uses chemical reactions to change the letters of the genetic code. It looks good so far. In 2017, researchers in China used base editing to mend mutations that cause a serious blood disorder called beta thalassemia in human embryos.
Gene drives Engineered gene drives have the power to push particular genes through an entire population of organisms. For example, they could be used to make mosquitoes infertile and so reduce the burden of disease they spread. But the technology is highly controversial because it could have massive unintended ecological consequences.
Epigenome editing Sometimes you don’t want to completely remove or replace a gene, but simply dampen down or ramp up its activity. Scientists are now working on Crispr tools to do this, giving them more control than ever before.
National Academies panel outlines ‘stringent’ criteria for human germline editing
Every year at this time, MedPage Today‘s writers select a few of the most important stories published earlier in the year and examine what happened afterward. One of those original stories, which first appeared Feb. 14, is republished below; click here to read the follow-up.
However, heritable germline editing — genetic manipulations that can be passed down to offspring — could potentially be allowed in the future for “serious disease or conditions” and with strict oversight, provided certain criteria are met, according to a committee of science, healthcare, and legal experts that made up the Committee on Human Gene Editing.
The report is the result of a year-long examination of the science and policy of human gene editing and its ethical ramifications.
In weighing the benefits and risks of these techniques, the committee decided that “caution is absolutely needed, but being cautious does not mean prohibition,” said R. Alta Charo, JD, committee co-chair and bioethics scholar at the University of Wisconsin Law School in Madison.
According to Charo, the committee agreed to six “strict” and “stringent” criteria under which germline editing could begin to be considered:
Lack of reasonable alternatives
Limiting to genes “convincingly demonstrated to cause or predispose” one to serious illness
“Credible pre-clinical and/or clinical data” regarding the potential risks and benefits
Strong and continuous oversight during clinical trials
A broad plan for long-term, multi-generational follow-up
Extensive and continued review of “health and societal benefits and risks” that involves public engagement
“If those conditions are met, it was the committee’s conclusion that germline heritable editing clinical trials would be permissible — not obligatory, but permissible,” she said, adding that “we are not even close to the amount of research we need before you could actually move forward at a technical level, in terms of the precision and safety, in this particular technique.”
The committee also weighed in on non-heritable clinical trials or the editing of somatic cells.
Basic scientific trials in this category of genome editing are underway, and are in the nascent stages of clinical trials and applications. Treatments that enable “corrected” genes to implant themselves in cells, often using a virus, have shown promise in research studies of cystic fibrosis, HIV, and Duchenne muscular dystrophy.
Since these changes cannot be inherited by future generations, they should be allowed to continue only when the research or therapy aims to treat or prevent disease or disability, and not for the purpose of genetic enhancement, according to the committee.
New technologies such as the CRISPR-Cas9 — an enzyme that can slice DNA at targeted points — offer the possibility of altering an individual’s genome, or even a generation’s genome. CRISP-CAS9 is easy, efficient, and relatively cheap, as committee members noted, and with its introduction, the risk of off-target events or “mistaken edits” is shrinking.
Instead of worrying “it’s too risky,” stakeholders are now beginning to shift their focus to the ethical ramifications of germline editing, said committee Jeffrey Kahn, PhD, MPH, director of the Johns Hopkins Berman Institute of Bioethics in Baltimore.
Rather than fully opening a door that was previously closed for germline editing, Kahn told MedPage Today that the report is more “like a knock on the door. The door’s not open yet.”
He pointed out that the committee’s criteria are “pretty rigid,” and not necessarily easy to meet. In addition, in the U.S., the NIH Recombinant DNA Advisory Committee and the FDA also have regulations regarding germline editing.
The NIH committee previously stated that it will “not entertain proposals for germline alterations,” so those restrictions still need to be relaxed, Kahn noted, describing the NIH stance as “more than a door — that’s a locked door.”
Rules about germline editing are not necessarily as strict in other countries. For instance, in 2015, scientists at Sun Yat-sen University in Guangzhou, China, were the first to use CRISPR-CAS9 on human embryos, according to Nature.
While the embryos were defective and could not have led to a live birth, the experiment was likely tied to a call for a moratorium by an international group of scientists on gene editing that could cause “inheritable changes to the genome,” according to The New York Times.
Former Director of National Intelligence James Clapper expressed concern that CRISPR could be used as a weapon of mass destruction, according toScience.
In the current report, the committee issued guiding principles “that should be used by any nation in governing human genome editing research or applications.” These are:
Promote well-being
Transparency
Due care
Responsible science
Respect for persons
Fairness
Transnational cooperation
“These overarching principles, and the responsibilities that flow from them, should be reflected in each nation’s scientific community and regulatory processes,” said committee co-chair Richard Hynes, PhD, of Massachusetts Institute of Technology in Boston, in a press release.
Charo noted that the guidelines set forth in the report, including its criteria, might be weighted differently in different jurisdictions.
“In some countries, [germline editing] is entirely illegal,” she noted, adding that some states have made embryo research unlawful.
“The bottom line is that there is no planetary government with enforcement power, but the goal of the human genome initiative [and] the goal of this study committee is to help develop international norms that will be influential, with the policymakers, with physicians, with researchers, with patient groups … so that to the greatest extent possible, there is some global agreement” on a set of guiding principles that aim toward beneficial purposes, Charo stated.
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