Using Cut-and-Paste to Edit Out Human Disease
Jan 02, 2020 10:07AM
By Susan Meyers
What if we could remove or correct the genes in humans that are responsible for chronic genetic diseases such as sickle cell anemia or cystic fibrosis? Or snip out genes of infectious disease agents like HIV? What if we could introduce cancer-fighting genes into the body’s immune cells to eradicate cancer? The possibilities are enormous.
Those possibilities now appear to be within reach with the introduction of some of the latest ground-breaking advancements in gene editing happening in Omaha.
Gene editing technology called CRISPR was first demonstrated in 2012-2013 by UC-Berkley and MIT/Harvard. The next year a comprehensive protocol paper on editing a mouse using the CRISPR tool was published by the UNMC Mouse Genome Engineering Core Facility. Mice are the primary model with genome research as its genome is similar to humans.
CRISPR was groundbreaking, allowing scientists to “cut” individual genes from a genome. But it was inefficient and expensive to use. In 2014, Channabasavaiah B. Gurumurthy, MVSC, Ph.D., Exec. MBA, began looking into ways to advance CRISPER technology. In 2017, he succeeded when he and Masato Ohtsuka, Ph.D., of Japan’s Tokai University co-invented the efficient additions with ssDNA inserts (Easi)-CRISPR. Easi-CRISPR is now used by researchers worldwide and is speeding up genetic research by leaps and bounds, as it allows researchers to create animal models faster and less expensively than before.
“Genome editing represents a new era in medicine,” said Howard Gendelman, M.D., chairman and professor of the Department of Pharmacology and Experimental Neurosciences at UNMC. Gurumurthy works under Gendelman. “We are in the earliest stages of this new technology, but it is gaining momentum and beginning to explode. There is no question that Dr. Gurumurthy is a trailblazer in this area.”
The technology shook the scientific world, especially that of genetics research.
“Dr. Gurumurthy’s expertise has been attracting collaboration from scientists around the world,” said Dr. Jeffrey P. Gold, chancellor of UNMC and UNO. “Some of the top universities in the world are currently collaborating with UNMC’s team for their gene-editing needs. These universities include Harvard…as well as Oxford in England and the Karolinska Institute in Sweden.”
Gurumurthy’s studies have been so significant that in late August 2019, he was awarded a $2.5 million grant ($500,000 per year for 5 years) from the National Institutes for Health to continue to improve technologies for biomedical research that will accelerate advances in genetic engineering.
The technology has medical implications worthy of the movies. A person has approximately 20,000 genes that are part of human DNA located within cells that control everything from hair and eye color to athletic prowess and susceptibility to disease. Some people, however, are born with genetic mutations that are responsible for inherited disorders like cystic fibrosis, sickle cell anemia, color-blindness, or certain genetic cancers.
Scientists have been using traditional genetic engineering technologies to develop custom animal models that mimic diseases and understand the function of each gene. Such models have enabled scientists to learn gene functions, to understand mutations in human diseases, and to explore the use of developing new drugs to control or cure genetic diseases.
The CRISPR tool consists of two components: a GPS system that finds the specific spot or mutation in the genome and scissors to make the cut. The tool allows scientists to engineer genes more elegantly; to repair a gene mutation by adding, removing, or altering the mutated gene. The problem, however, was delivery of the new gene to replace the mutant copy.
“Efficiency was so poor that it took a year or more to make one mouse model, which could be used to identify a gene,” Gurumurthy said.
The Easi-CRISPR system can complete the mouse model process in less than two months; it’s like cutting and pasting in a word-processing document, Gurumurthy explained.
Easi-CRISPR system uses a single-stranded DNA that is inserted into the sliced genome; previous CRISPR-based methods relied on double-stranded DNA. “The new Easi-CRISPR method is 100% successful at some genes, compared to the old method which was only successful 1 to 10% of the time,” Gurumurthy said.
Study of the human genome has been around for more than 40 years, and scientists are determining, one by one, the function of the approximately 20,000 genes in the human body. The introduction of CRISPR has expedited the process, and with Easi-CRISPR, Gurumurthy estimates scientists should be able to identify the function of the remaining genes (at least 1/3 have been identified) within the next few years.
The advanced technology is improving medicine. There are a growing number of clinical trials being approved for use in terminally ill patients who have no other treatments available, said Gurumurthy.
Several of these trials involve immunotherapy modalities in which Easi-CRISPR could become a valuable tool that allows researchers to add new genes back in the human genome.
In a recent trial for people with sickle cell anemia, a patient in the trial who was born with the disease appears to be successfully treated. The disease is caused by a genetic defect that turns red blood cells into hard, sticky, sickle-shaped cells that don’t carry oxygen well, clog the bloodstream, damage organs, and cause extreme pain. The experimental treatment involves removing the stem cells from the patients’ bone marrow, modifying a gene in the defective cells and then returning them to the patient in hopes that the corrected cells will produce red blood cells that will prevent the production of sickle cells.
Scientists also appear to be on the brink of curing chronic diseases like HIV. In a highly touted study using CRISPR technology, Gendelman, a lead investigator working together with Kamel Khalili, M.D., at Temple University in Philadelphia, Pennsylvania, demonstrated that HIV can be eliminated from nine of 23 infected humanized mice. In this study, the immune system of the animals were replaced with their human counterpart and then infected with HIV. The infected mice were next treated with an anti-retroviral drug cocktail to suppress viral growth. Using a CRISPR excision tool, the researchers were able to eliminate the virus from the human genome.
“This is the first time that anyone has been able to eliminate virus from a live animal,” Gendelman said. “It provides proof of concept that it can be achieved and may eventually be applied to other infectious agents such as hepatitis C or herpes.”
“We couldn’t be more proud of Dr. Gurumurthy and his team,” said Gold. “They are a perfect example of how UNMC is leading the world. Nebraskans should be thrilled that this kind of life-changing expertise is right here in Omaha.”
While scince has made great strides, there are still many obstacles to overcome, Gurumurthy said. Curing genetic diseases involving mutations in multiple genes or diseases where a large number of cells need to be treated pose more challenges. Some conditions, like liver disease, affects billions and trillions of cells. The engineered genes have to be injected into a large number of cells. The problem, Gurumurthy said, is that the gene copy is not stable.
There are also ethical considerations with gene editing. Could someone genetically modify an embryo to eliminate undesirable genes, perhaps those for a specific eye color, and add preferred genes? The United States government has rigid regulations in this field that restrict gene editing technology for human enhancement as well as for use on eggs, sperms, embryos, and even adults. “We just don’t know the side effects of genetic editing and how it will affect future generations,” Gurumurthy said.
Although Hollywood makes gene editing for human enhancement appear feasible, Gurumurthy said, “There is no magic bullet for any single biologic function.” Editing genes for certain traits or human functions is more complex. Oftentimes, there are several genes or multiple genes responsible.
The impact on medicine, however, looms large.
“Learning the functions of all of our genes and using this knowledge to cure diseases are two areas where genetic engineering has the ability to make the most impact in the future,” Gurumurthy said. “While there are still obstacles to overcome, gene editing has the ability to change how we treat diseases in the future,” he said. “In the next five to 10 years, I anticipate we will have 50 to 100 diseases in clinical trials.”
Visit UNMC.edu for more information about Gurumurthy’s work.This article was printed in the January/February 2020 edition of Omaha Magazine. To receive the magazine, click here to subscribe.