National Geographic : 2016 Aug
44 national geographic • August 2016 The potential for CRISPR research to improve human medicine would be hard to over- state. The technology has already transformed cancer research by making it easier to engineer tumor cells in the laboratory, then test various drugs to see which can stop them from grow- ing. Soon doctors may be able to use CRISPR to treat some diseases directly. Stem cells taken from people with hemo- philia, for example, could be edited outside of the body to correct the genetic flaw that causes the disease, and then the normal cells could be inserted to repopulate a patient’s bloodstream. In the next two years we may see an even more dramatic medical advance. There are 120,000 Americans on waiting lists to receive organ transplants, and there will never be enough for all of them. Thousands of people die every year before reaching the top of the list. Hundreds of thousands never even meet the criteria to be placed on the list. For years, scientists have searched for a way to use animal organs to ease the donor shortage. Pigs have long been considered the mammal of choice, in part because their organs are similar in size to ours. But a pig ’s genome is riddled with viruses called PERVs (porcine endogenous ret- roviruses), which are similar to the virus that causes AIDS and have been shown to be capable of infecting human cells. No regulatory agency would permit transplants with infected organs. And until recently, nobody has been able to rid the pig of its retroviruses. Now, by using CRISPR to edit the genome in pig organs, researchers seem well on their way to solving that problem. A group led by George Church, a professor at Harvard Medical School and MIT, used the tool to remove all 62 occur- rences of PERV genes from a pig’s kidney cell. It was the first time that so many cellular changes had been orchestrated into a genome at once. When the scientists mixed those edited cells with human cells in a laboratory, none of the human cells became infected. The team also modified, in another set of pig cells, 20 genes that are known to cause reactions in the human immune system. That too would be a critical mate in nature. But scientists hope that using CRISPR to alter DNA could appease the oppo- sition. It gives researchers the ability to rede- sign specific genes without having to introduce DNA from another species. Golden rice, for example, is a GMO engi- neered to contain genes necessary to produce vitamin A in the edible part of the grain— something that doesn’t happen naturally in rice plants. Each year up to half a million children in the developing world go blind for lack of vita- min A—but anti- GMO activists have interfered with research and prevented any commercial production of the rice. With CRISPR, scientists could almost certainly achieve the same result simply by altering genes that are already active in rice plants. Scientists in Japan have used CRISPR to ex- tend the life of tomatoes by turning off genes that control ripening. By deleting all three cop- ies of one wheat gene, Caixia Gao and her team at the Chinese Academy of Sciences in Beijing have created a strain that is resistant to pow- dery mildew. Farmers have been adjusting genes in single species—by crossbreeding them—for thousands of years. CRISPR simply offers a more precise way to do the same thing. In some countries, including Germany, Sweden, and Argentina, regulators have made a distinction between GMOs and editing with tools such as CRISPR. There have been signs that the U.S. Food and Drug Administration might follow suit, which could make CRISPR-created products more readily available and easily regulated than any other form of genetically modified food or drug. Whether the public will take advantage of them remains to be seen. Without regulation, the tremendous potential of this revolution could be overshadowed by fear.