CRISPR基因编辑技术 z-bo 2020-10-21 361

   　Change thinking: Edit any gene with precision

　　Doprey will sometimes imagine that if this tiny mistake doesn't exist, his life would be better! Last December, he learned that a gene editing technology called CRISPR could make this dream come true.

　　A few months ago, the biologist Eric Olsen of the University of Texas Southwestern Medical Center took a blood sample of Doprey. Soon, Olson’s laboratory told him: As scientists predicted, CRISPR is the most likely way to cure him.

　　Olsen’s team performed gene editing on Doprey’s cells in the laboratory and cut off the disease-causing pseudo-exons. The editing process was completed in one step and only took three days. Doprey and the research team saw his cells perfectly surrounded by dystrophin through a microscope. Doprey said: "I didn't have much hope, but when I saw it, I couldn't help but yelled out loudly."

　　"CRISPR can edit any genome accurately and easily"-this recognition is changing the way people think. Scientists scramble to carry out relevant experiments in the laboratory, and publish an average of 8 relevant scientific papers describing the new uses of this technology every day. Some people even use the technology to design babies with certain appearance characteristics, and others develop mosquito genes to make The test of their extinction.

　　But if CRISPR is to be truly convincing, it needs to realize its potential to cure patients like Doprene. Some preliminary studies have shown that this gene editing technology can provide cancer treatment, prevent HIV and hepatitis virus transmission, and even reverse the symptoms of blindness and deafness. Olsen said that CRISPR technology is far beyond our imagination and will definitely lead us further.

　　Beyond tradition: gene therapy version upgrade

　　Scientists now know that there are more than 5,000 genetic variants related to genetic coding errors. Sequencing technology can help discover more than 300 similar causes every year, and some of these diseases have a chance of only one in a billion. Duchenne muscular dystrophy is a relatively common genetic disease, about one in 4,000 boys is affected, and girls are usually only recessive carriers.

　　Gene editing may be the only way to eliminate this type of disease. Only one treatment can change the patient's DNA for a long time. CRISPR surpasses the traditional gene therapy that uses viruses to insert genetic instructions into living cells for 30 years. For dystrophin, because it contains too many exons, it is impossible to put it into a viral vector. Gene therapy is no longer feasible, but CRISPR can accurately perform DNA cutting. Many diseases only need to cut the wrong gene without adding new genes. Therefore, by deleting the gene code, CRISPR will treat more diseases on a large scale. Many doctors call it It is "Gene Therapy 2.0".

　　After 30 years of research, only two gene replacement therapies have been approved in Europe to treat genetic diseases. But Olsen firmly believes that CRISPR is the best choice to cure Duchenne muscular dystrophy. Earlier this year, he proved through mouse experiments that intravenous injection of viral vectors containing CRISPR components successfully repaired the mutations in muscle atrophy. "Once the human test is effective, this disease may be completely cured."

　　Human test: it may start within two years

　　Olsen said that he will carry out the first human clinical trials of Duchenne’s disease within two years, possibly a small-scale trial involving only a few boys. He will also cooperate with Jerry Mendel of the Gene Therapy Research Center of the American Children's Hospital to carry out trials on monkeys within a year to prepare humans for clinical trials. Researchers are all looking forward to their experiments can bring exciting results.

　　Doprey, who has been following up the progress of the experiment, does not have much hope of curing himself. He knows that the research will take several years, and because his mutation is unique, researchers need to design therapies specifically for him. "Rather than treating my disease, I pay more attention to the scientific significance of this research." But his mother joined a social group formed by parents who have the same disease as Doprey. Parents always ask, when To join the clinical trial.

　　Not only these patients and their parents are anxiously paying attention, but countless cancer, AIDS, and sickle cell anemia patients are also paying attention to the Olson laboratory, and whether CRISPR technology can create a new medical era?

　　Treatment limitation: Can only delete but not join

　　CRISPR greatly simplifies the process of gene editing, but its use to treat human diseases is another matter. Scientists can only use it to precisely delete a certain key part of a gene, and cannot add a normal gene to complete the repair, that is, it cannot simply complete the exchange of two gene codes. Therefore, this technology can only be used to study those conditions that can eliminate symptoms by deleting the wrong gene. Duchenne’s disease is one of them, and the other is sickle cell anemia, which is relatively common among African Americans. disease.

　　In the past, medical researchers paid relatively little attention to the latter. As they realized that only deleting the mutation part can achieve a cure, more and more people are concerned. Mitchell Weiss, who has focused on sickle cell disease for many years, now receives calls from gene editing companies every day, asking him to collaborate with him on gene therapy trials.

　　In the research process, in addition to testing whether deleting genetic variants can cure the disease, it is also necessary to find a way to load CRISPR commands into the body. At present, most laboratories still choose viruses as carriers.

　　CRISPR is easier to delete genes in certain parts of the body. For example, deleting genes in blood cells is the easiest. You only need to extract these cells from the body, delete the genes, and then import them back. As long as you dare to think, maybe one day you can use CRISPR to rewrite the genes in the human brain to treat various neurological diseases.

　　Olsen said that using CRISPR to delete only a key mutation can cure about 80% of cases of muscle atrophy. What they are currently conducting is a trial targeting exon-51. Deleting this exon can cure 13% of Duchenne muscular atrophy patients.

　　The biggest unknown now is whether CRISPR can edit a sufficient number of muscle cells in the human body and synthesize a sufficient amount of anti-atropin. 40% of the human body is composed of muscles, including myocardium, gluteus maximus and biceps, which contain billions of cells. So far, Olsen has successfully produced anti-atropin in 5% to 25% of muscle fibers. Even if it cannot be cured, editing 15% of muscle cells is enough to alleviate the symptoms of muscle atrophy in sick boys.

　　The tortoise and the hare race: "The tortoise" will eventually win

　　The human clinical trial of Duchenne’s disease designed by Olsen has received commercial support. Editas will entrust him to cooperate with Duke University, but the exact date of the trial is not yet public. The most well-known CRISPR company has always been low-key. Although gene editing technology has great potential, it often takes more than a decade to prove its effectiveness. Companies often receive emails from desperate parents asking: "Can CRISPR cure my child?" In theory, the answer is yes, but in reality it can only give a disappointing answer: "I heard that your son is suffering. I am very sad about the illness. Unfortunately, we are still in the early clinical stage and human trials are not yet available."

　　In addition, a certain CRISPR therapy often cuts a specific type of gene mutation, so it may only cure a few people or even a certain person. For example, Doprey, his genetic mutation is unique, because he is not near exon-51, he cannot participate in the first batch of CRISPR clinical trials to be carried out by Olsen, and can only wait for the CRISPR therapy for his wrong exon gene. . Through contact with Olsen, Dopree still sees the hope of healing. "Although it is only a treatment for me alone, because it can be cured once, the cost may not be too expensive."

　　But will anyone design a drug trial for someone? Who pays for the trial? This blank area, which has not been encountered before, requires careful consideration and extensive discussion. Perhaps compared with lifelong medication, wheelchair life, inability to be independent, etc., a one-time CRISPR therapy is not expensive even if it costs millions of dollars.

　　Just like Gene Therapy 1.0 has not been widely used after 30 years of development, if CRISPR therapy is regarded as the tortoise in the tortoise and the hare race, rather than the rabbit, although the process will be slow, it will eventually reach the end. The doctor had expected Doprey to not live past 19 years old, but he was already 24 years old, and maybe he will be alive in 10 years. "By then, he will be able to receive treatment." Doprey's mother's eyes were full of expectation.