By now you’ve probably heard of CRISPR, the gene-editing tool that has made headlines for its unprecedented ability to edit DNA with relative ease. It’s the subject of a new documentary called “Human Nature” and was featured in the Netflix series “Unnatural Selection,” which was released this year. It also played a central role in the 2018 science fiction movie “Rampage” featuring Dwayne “The Rock” Johnson.

Hailed as one of the biggest scientific breakthroughs of the decade — and most likely, the century — CRISPR has the potential to change humans and our environment forever. It’s being used to fight cancer and genetic diseases, develop faster diagnostic tests, improve the animals we eat, and protect crops against disease and rising global temperatures. And all of it is happening at breakneck speed. It can be hard to keep up with all of these advances, so we’ve compiled a list of the most important gene-editing stories of 2019 to get you up to speed.

Astronauts used CRISPR in space for the first time

On May 4, a SpaceX Falcon 9 rocket launched a Dragon spacecraft to the International Space Station. Among its cargo was an experiment involving the CRISPR gene-editing system, which astronauts aboard the ISS used to successfully edit DNA in space. They made targeted cuts to the yeast genome that mimicked genetic damage caused by cosmic radiation, one of the biggest health risks that long-term spaceflight poses to humans. Cells have natural ways of correcting DNA damage, and the scientists behind the experiment wanted to investigate how those mechanisms are different in microgravity. They say the ISS experiment could yield clues about how cells repair their DNA in space.

Some imagine that gene-editing techniques like CRISPR could be used to make humans more fit for space travel.

Some imagine that gene-editing techniques like CRISPR could be used to make humans more fit for space travel. In one government-funded project, researchers are using CRISPR to see whether gene expression could be temporarily tweaked to protect astronauts from harmful space radiation.

Scientists edited chicken genes to resist bird flu

The 1918 flu killed 50 million people and infected an estimated 500 million more, making it one of the deadliest disease outbreaks in history. Ever since, public health experts have been on the lookout for the source of the next devastating flu pandemic. One potential source is birds. Avian flus can wipe out entire flocks of farmed chicken and, in rare cases, have infected people. Though bird flu does not spread easily from person to person, some experts are concerned that the virus that causes it could mutate to become more easily transmissible among humans.

U.K. scientists are trying to get ahead of a potential outbreak by engineering chicken cells that are resistant to flu. Using CRISPR, scientists at Imperial College London and the University of Edinburgh deleted a section of chicken DNA that prevented the flu virus from growing in lab-grown chicken cells. The researchers published their results in June. The next step, they say, will be to produce live chickens with the same genetic deletion. It’s one example of how CRISPR is being used to modify our food supply.

Meanwhile, in China, scientists are using CRISPR to protect pigs against a global outbreak of African swine fever. The disease doesn’t affect humans, but it has ravaged China’s pork supply over the past year.

Chinese doctors tried to eliminate a man’s HIV with CRISPR

The 27-year-old Chinese man had received a grim prognosis: He was both HIV-positive and had leukemia. However, the two diagnoses made him eligible for a clinical trial testing an experimental CRISPR treatment for both diseases. He was enrolled into a clinical trial, and in July 2017, Chinese doctors gave him a special stem cell treatment. As in other bone marrow transplants, the stem cells came from a healthy donor and were meant to replace the unhealthy ones in his body. But what made this transplant different was that the stem cells had been edited with CRISPR to knock out the CCR5 gene, in hopes of blocking the HIV virus from getting into cells.

Some people naturally carry non-working versions of the CCR5 gene and are virtually immune to HIV, an observation that has spurred hope for an HIV cure. The only two people believed to have been cured of HIV received bone marrow transplants from donors with this genetic mutation. Writing in the New England Journal of Medicine in September, the Chinese scientists who developed the treatment reported that the patient’s cancer is in remission but that the edited stem cells, though they didn’t cause any harmful side effects, weren’t enough to cure him of HIV. It was the first known attempt to treat a person infected with HIV using CRISPR. Though the treatment didn’t work, the study showed that it was not only possible but safe to treat patients with cells that had been edited outside the body with CRISPR.

A Russian scientist revealed plans to create more gene-edited babies

Amid calls to ban the creation of gene-edited babies, a Russian scientist revealed his plans to use CRISPR to modify human embryos and establish pregnancies with them. Denis Rebrikov says his aim is to allow some couples with an inherited form of deafness to have biological children who can hear. Rebrikov wants to edit the GJB2 gene, which causes a type of congenital deafness when mutated. He had intended to edit the CCR5 gene but switched his focus after his initial plans drew scrutiny. Rebrikov needs to gain approval from Russia’s Ministry of Health to conduct the experiment.

A Russian scientist revealed his plans to use CRISPR to modify human embryos and establish pregnancies with them.

Last year, the Chinese scientist He Jiankui was scorned after announcing that he had created the first gene-edited babies using CRISPR. He knocked out the CCR5 gene in embryos in an attempt to make the resulting babies resistant to HIV. Twin girls, known as Lulu and Nana, were born as a result. Scientists are now trying to prevent more gene-edited babies but can’t agree on how to do it.

A new, more precise version of CRISPR emerged

CRISPR isn’t the first gene-editing system that researchers have developed, but it’s revolutionary because it’s much easier and faster to use than previous tools. Still, a major concern with CRISPR is its potential to make so-called “off-target” effects — accidental edits to other parts of the genome. In October, researchers announced a new type of CRISPR called prime editing that could potentially avoid this pitfall. If CRISPR is like a pair of scissors, prime editing is like a search-and-replace tool for specific DNA sequences, according to inventor David Liu of Harvard and The Broad Institute.

Traditional CRISPR works by making a cut in DNA’s double helix, which can result in genetic errors when DNA tries to repair itself. By contrast, prime editing can simply change any of DNA’s four “letters” — A, T, C, and G — without breaking DNA. (These four letters stand for the chemical nucleotides that are the building blocks of the genetic code.) The approach has the potential to correct up to 89% of known disease-causing genetic variations. In human and mouse cells grown in petri dishes, Liu and his colleagues found that changes made using prime editing had a lower rate of off-target effects compared to traditional CRISPR. The team published their findings in October in the journal Nature and at the same time announced the formation of a company, Prime Medicine, to develop therapies based on the technology.

The first U.S. patients were treated with CRISPR

This year, a handful of patients became the first in the United States to receive CRISPR treatments. In November, a team at the University of Pennsylvania reported it had taken immune cells from three adult cancer patients, used CRISPR to modify those cells in a lab, then infused them back into the patients. The edits were meant to supercharge the cells against the patients’ cancers, which in all three cases proved resistant to conventional treatments like chemotherapy. So far, the approach seems safe but it’s too early to know whether it’s effective.

Even more promising news came a few weeks later, when the biotech company CRISPR Therapeutics announced that it eliminated disease symptoms in two adults with genetic disorders. The treatment involved editing blood-producing stem cells outside the body then returning those cells back to the bloodstream. One of the two people treated, a U.S. sickle cell patient named Victoria Gray, had suffered regular pain attacks all her life because of her disease. But since receiving CRISPR-edited cells at a Nashville hospital in July, she has yet to have a painful episode. The other patient, who has a related blood disorder called beta thalassemia, was treated in Europe. Doctors plan to follow the patients for much longer to know whether the treatment truly represents a cure.

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