By Nujhat Tabassum
Queen Biology has always reigned supreme in meticulously designing everything that lives and breathes, and no one has ever come close to threatening her talent and authority…until now. It looks like CRISPR-Cas9, nature’s spunky new genome-editing makeup artist, is coming dangerously close to throwing Biology off her artistic throne. Biology may be ancient and all-powerful, but she’s made a lot of mistakes – creating diseases that CRISPR can now fix with just a few snips. The DNA ‘touch-ups’ that take Biology millions of years to do can now be done by CRISPR in just a few hours.
CRISPR-Cas9 technology has been creating a buzz in the scientific community recently, working towards fixing nature’s deadliest flaws left and right. But how long before she begins abusing her skills? How long before her helpful makeovers turn into superficial, irreversibly botched surgeries?
What is CRISPR-Cas9?
CRISPRs, aka clustered regularly interspaced short palindromic repeats, are naturally-occurring DNA sequences found in yogurt-making bacteria and other prokaryotes1. Whenever a virus infects a bacterium, the bacterium grabs unique portions of viral DNA, called ‘spacers’, and stores them in its CRISPR sequence for protection against future invasions. When the same type of nasty virus tries to attack again, the bacterium produces RNA sequences to match the viral sequences based on the stored sequences in the CRISPR library. This ‘guide RNA’ then forms a complex with its partner in crime, the DNA-snipping Cas9 enzyme, to chop up the matching gene sequence in the virus, stopping viral replication in its tracks.
But what exactly does this have to do with genetic engineering? Well, in 2012, Drs. Jennifer Doudna and Emmanuelle Charpentier figured out how to use this bacterial defense system to cleave DNA in other organisms at specific sites of interest. By combining this system with the organism’s own DNA-repair mechanism, specific DNA sequences can be deleted, and new gene sequences of interest can be added and integrated into the genome.
What’s so great about CRISPR-Cas9?
CRISPR-Cas9 is, according to researchers everywhere, by far the most precise, versatile and cheapest gene editing tool in current existence. In fact, it’s so simple and accessible that it was recently added to the curriculum of a University of Toronto undergraduate lab course3.
Furthermore, CRISPR has sparked somewhat of a scientific movement in the research community, revolutionizing genome editing in the fields of biology, agriculture, and medicine. CRISPR has been used to produce pest-resistant, harsh-climate-tolerant, better-tasting, high-yield crops with greater accuracy at a fraction of the cost and production-time, even leading to the creation of novelties like gluten-free wheat and decaffeinated coffee beans.
Scientists are actively investigating CRISPR’s therapeutic applications in treating diseases like HIV-AIDs, Duchenne muscular dystrophy, cystic fibrosis, and cancer therapy with promising results, even starting to be introduced into human clinical trials. For allowing so much progress to be made in so little time, CRISPR has been hailed to be nothing short of a scientific miracle. However, the novelty of this technology and its easy accessibility has raised a lot of concern about its ethical implications and long-term consequences.
On November 25, 2018, Dr. He Jianku shocked researchers and the public alike when he revealed that he had created the world’s first gene-edited baby twins by using CRISPR-Cas9 to genetically disable the CCR5 gene in the embryos and purportedly implanting them into the mother. This was done to confer HIV resistance into the children1. This initially sounds like a good thing, so why are scientists so angry about it?
Changing genes in the embryos means that these changes are permanent, and will be passed onto future generations without their explicit knowledge or consent. Therefore, ethically speaking, these changes should’ve only been made as a last resort when no other options are available. Dr. He did not do this, as he disabled a completely normal gene, and the disabling of it may have even increased the twins’ susceptibility to the West Nile virus and Japanese encephalitis. It appears even the parents may not have completely understood or consented to the procedure, as the technical details and full risks associated with the procedure may not have been properly explained to them. His actual procedure may have also been flawed, as there appeared to be signs of mosaicism in one of the twin’s placenta, a phenomenon common in CRISPR applications where only a portion of the dividing cells contain the edited gene while the rest do not. Furthermore, it is thought that in order to be born with HIV-resistance, both copies of the CCR5 gene must be disabled, yet in one of the twins, only one copy of the gene was shown to be disabled. At this point, it is impossible to know what long-term consequences his added mutations will have on the children.
Besides CRISPR’s mosaicism problems, recent studies seem to show that CRISPR may cause large unintended deletions and rearrangements near the target site in cells, causing possible unwanted damage. In fact, some CRISPR-edited cells have shown to be missing crucial anti-cancer mechanisms, possibly promoting tumour growth. This may be because it’s hard to fully regulate the activity of CRISPR-Cas9 once it’s inside the cell. Luckily, University of Toronto’s Drs. Alan Davidson and Karen Maxwell have come up with a possible solution. They have discovered a Cas9 enzyme inhibitor that could be used as an ‘off-switch’ to control the CRISPR-Cas9 complex activity more precisely. Ironically, these inhibitor proteins come from the same viral bacteriophages that target bacteria hosting CRISPR. Hopefully, with advances like these, CRISPR will become safer for human trials.
Whether it’s due to the physical shortcomings of the technology or the general confusion surrounding the ethics and regulations behind it, we are still a long way away from employing the widespread use of CRISPR-Cas9 in agriculture and medicine. Hopefully, when we do arrive at that point in the not-so-distant future, CRISPR-Cas9 will learn to work together with Biology to safely fix some of her worst mistakes, while preserving all of her greatest creations.