Ideas for a brighter future for all

Why CRISPR gene editing is a promising but imperfect solution to genetic disease

You may have heard about gene therapy over the years the promise that we could replace genes in those people born with as little as one unwanted variance in the 3 billion ‘bits’ that make up our genome. These variations cause diseases, such as haemophilia or cystic fibrosis, that were seen as incurable—many people who suffer from them have reduced quality of life and die prematurely.  

Recent advances in technology have brought the promise of gene therapy closer than ever to being realised. One true breakthrough is clustered regularly interspaced short palindromic repeats (CRISPR), and this year its pioneers, Emmanuelle Charpentier and Jennifer A. Doudna were awarded the Nobel Prize for Chemistry. CRISPR offers a radical new method for gene therapy that builds on decades of science. What’s clear is that there is much more to learn, all while navigating some deep ethical questions. 

Three decades of progress

Gene therapy had its first approved clinical trial in 1990, when doctors from the United States National Institute of Health treated four-year-old Ashanti DeSilva, who was suffering from a rare genetic disease known as severe combined immunodeficiency. She was unable to make a key enzymeImportant for immunity so  was at constant risk of contracting a deadly infections. Doctors injected her with a virus that replaced a malfunctioning copy of a gene needed to get her immune system working. This treatment markedly improved her immune system function, allowing her to live a normal life for the first time.  

Since then, there have been close to 3,000 clinical trials worldwide. It was only in 2017, though, that the FDA approved the first gene therapy treatment for inherited disease. Progress has been slow due to trouble perfecting the drug delivery, intellectual property complexity and clinical trial issues. The approved product, Luxturna, by   Spark Therapies, treated retinal dystrophya degenerative condition of the eye that can cause total blindness. 

This form of total gene replacement therapy is promising, but it has a critical limitation: only a small amount of DNA can be fitted into the virus vectors used to deliver the gene to cells. These vectors simply do not have the capability to facilitate truly transformative gene therapy—they are unruly and imprecise. This meant we needed another solution. Enter CRISPR. 

Green Eyes
A bacterial discovery

The story of the development of CRISPR starts in 1987, when scientists in Japan noticed something unusual in the DNA of E.coli bacteria. Subsequent study by other groups confirmed that this strange pattern, named the clustered regularly interspaced short palindromic repeat (CRISPR), was the mechanism by which bacteria defended themselves from viruses. This capacity was repurposed by Charpentier and Doudna to edit human genes in 2012. Their effort was hailed as the scientific breakthrough of the year by Science magazine in 2015, and in 2020 it won Nobel prize in Chemistry. 

CRISPR technology was able to repair genes in living cells and living organisms using a tiny payload, meaning we no longer had to replace whole genes. It’s like fixing a fence where only one pale is broken: you don’t replace the whole fence, just the broken pale. Indeed, many genetic diseases only have one or two deviations in the entire gene, so the advantages were obvious. CRISPR, it turns out, is also fairly safe and specific.   

With great promise for CRISPR comes great responsibilities 

The potential for CRISPR is that those suffering from a genetic condition may in the future have an avenue for treatment that did not exist in the past. But CRISPR can do more than that. It is also able to destroy bad genes, such as those that cause cancer, by editing them to be turned off. Indeed, here at Griffith, we were the first in the world to take this approach to destroy a cancer gene from the virus that causes cervical cancers and cure animals of cancer using CRISPR. This ability to destroy genes means—like the bacteria CRISPR originally came from—we can use CRISPR to attack viral or bacterial infections, handy in the face of increasing antibiotic resistance.   

But there is a dark side. In 2018, a Chinese researcher announced the world’s first CRISPR babies. He had edited their DNA to delete a gene that allowed HIV to infect cells. This gene is naturally mutated in 1 per cent of northern European people, making them resistant to HIV disease—the researcher’s intention was to make these babies also resistant to infection. But this gene is known to also affect cognitive function, and so the unethical experiment may have harmed these children. The scientist, He Jiankui, at the time a researcher at the Southern University of Science and Technology of China, Shenzhen, was sentenced to three years’ jail by a China court in 2019 after being found guilty of illegal medical practices. It reminds us that with any new technology there is always the potential to harm.  

There are numerous ethical questions that arise from the use of CRISPR, especially surrounding safety, consent, justice and equity, and use on human embryos. In the end, it’s up to society as a whole to decide on the best way to use this new technology.   

"This may be the tool we need to end cancer"​

Watch this space, because the technology is improving every month and the first treatments are already being tested in the clinic. We can navigate the ethics of this technology, and in the futurefuture, I believe it will be seen as the greatest medical breakthrough in human history. CRISPR will allow us to consign genetic diseases and most cancers to the archives of history.  

DNA Sequence
Author

Professor Nigel McMillanProfessor Nigel McMillan is a cancer researcher interested in the infectious causes of cancer. Nearly ⅓ of all cancers are caused by viruses, bacteria and other microorganisms. He is an internationally recognised expert in the area of human papillomavirus, gene editing and gene silencing. He has over 90 publications and has had continuous NHRMC funding for 22 years. He has graduated over 40 Masters or Honours students and 22 PhD students.

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