CRISPR (pronounced kris-pur) is a gene editing tool. It’s more something you’d expect to find in the plot of a sci-fi movie than in real life, but its recent application in cancer and COVID-19 shows that its reach into everyday life is growing in the healthcare sector.
Genes are made up of DNA, or deoxyribonucleic acid. DNA acts as a blueprint for living things and contains all the instructions needed for growth, development, survival and reproduction.
What is CRISPR and how does it work?
When scientists discovered that many bacteria had repetitive DNA sequences in their genes they called them CRISPRs, which stands for Clustered Regularly Interspaced Short Palindromic Repeats. Put more simply, the bacteria had repetitive DNA sequences that were interspaced with unique DNA sequences from viruses. Nearby these sequences, the scientists noticed CRISPR-associated genes (CAS genes) that encoded proteins and which taken together with the CRISPR sequences, formed a type of immune system that protected the bacteria from viruses.
Cells make copies of CRISPR sequences or arrays in the form of an RNA (ribonucleic acid) molecule, which gets broken up into smaller pieces called CRISPR RNA (crRNA). These smaller pieces each contain a unique sequence from a virus and the same repetitive sequence from the bacteria. These smaller pieces - crRNAs - combine with a second RNA called trans-activating crRNA (tracrRNA) to form a structure that binds to Cas9 (CRISPR-associated protein 9) protein. The CRISPR/Cas complex surveys the cell and recognizes invading viruses if they attack again. Cas9, or a similar enzyme, then acts like a pair of scissors and cuts the viral DNA, which deactivates the virus.
Scientists are now using the CRISPR/Cas system as a gene modification tool. Scientists can tailor the system using a complementary small guide RNA (sgRNA), which targets a selected DNA sequence of their choice. The DNA sequence is then cut with an enzyme such as Cas9. Unlike in the bacterial cells where the virus dies after its DNA is cut, in plant and animal cells (eukaryotic cells) the cell’s DNA repair mechanism kicks in, which can be used to add, delete or replace the target genetic material.
CRISPR is a tool used for gene modification including:
Gene editing - this is the most common use of this technology and may also be called genome editing. Gene editing usually involves the cut DNA being left to repair itself, which results in a mutation that disables the gene. Disabling a gene is not as precise as other gene editing options which can be more tricky, such as replacing or fixing a faulty gene with gene splicing. It is now possible to add or delete short sequences of DNA and even exchange one DNA base letter for another.
Gene silencing - CRISPR interference (CRISPRi) does not cut DNA, but turns a target gene off.
Gene activation - CRISPR activation (CRISPRa) does not cut DNA, but turns a target gene on allowing for the overexpression of a gene.
CRISPR gene editing technology shows potential in people with cancer
In one of the first phase I trials conducted in patients using CRISPR technology, T-cells edited using CRISPR proved to be safe in patients with advanced non-small cell lung cancer in China.
The patient’s own T-cells were edited using CRISPR technology to disable a gene called PD-1 (Programmed cell Death-1). The PD-1 protein is found on the surface of T-cells, which are part of the immune system and help to keep it in check. When this protein is blocked, it releases the brakes on the immune system increasing the ability of the T-cells to kill cancer cells.
A total of 12 patients were treated with T-cells in which PD-1 had been disabled using CRISPR. Edited T-cells were detected in the peripheral blood of patients following infusion and only mild side effects were observed. The level of off-target events, which are unintended mutations, appeared low enough to mean the treatment appears to be a safe and feasible option.
Similarly encouraging results have also been reported in another phase I trial that used CRISPR to edit three different genes in patients with advanced cancer. The edited T-cells in these patients remained at a stable level for at least nine months after they were administered. Much more research needs to be done, however, to investigate the true potential of these treatments in patients.
FDA issues Emergency Use Authorization for Sherlock’s CRISPR COVID-19 diagnostic kit
On May 6, 2020 the US Food and Drug Administration (FDA) issued an Emergency Use Authorization (EUA) for a Sherlock BioSciences SARS-CoV-2 diagnostic test, which utilizes CRISPR gene editing technology. SARS-CoV-2 is the virus responsible for causing COVID-19. This is the first time the FDA has allowed a CRISPR-based diagnostic tool to be used in people.
Sherlock’s test uses CRISPR technology to seek out a sequence of the SARS-CoV-2 virus in a patient’s sample. If the virus sequence is detected it creates a fluorescence glow. The test takes approximately one hour, which is quicker than regular PCR (polymerase chain reaction)-based tests for SARS-CoV-2. And while it is not as fast as the fastest SARS-CoV-2 testing option, it can be run using basic laboratory equipment without the need for a specialist machine.
CRISPR has the potential to change the world
Gene modification isn’t new, but this next-generation technology has made it cheaper, easier, faster and more accurate. While there is still much work to be done to perfect this technology, CRISPR has great potential not only in healthcare, but also in other areas such as agriculture and the environment. It has been used for some time in scientific research and is already an established part of the dairy industry, helping in the production of consistently good yogurt.
We’ve touched on its application here in cancer and COVID-19, but it has much wider applications in healthcare and is also set to be investigated in patients with sickle cell anaemia, HIV infection and many other conditions.
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