It’s the technology, which won two scientists the Nobel Prize for Chemistry this October. French microbiologist, Emmanuelle Charpentier and American biochemist, Jennifer Doudna, were hailed for their pioneering work developing the CRISPR gene-editing technique since 2012.
CRISPR heralds a potential revolution in the way that diseases are treated. Finding safe and effective ways to alter the human genome could not only lead to a cure for inherited genetic diseases but also cancers too.
At the moment, the technology is still more of a promise rather than a reality for the general population. But recent clinical trials are already beginning to deliver encouraging results. Notably this March, CRISPR was used in vivo (in body) for the first time on humans to try and find a cure for an inherited eye disease.
What makes CRISPR so exciting is the way that it could turn the body into its own precisely targeted drug-making factory rather than relying on artificial pharmaceuticals to mitigate the effects of inherited degenerative diseases, or kill off mutant cancer cells.
Scientists began to understand the theory back in the 1980’s when they noticed how certain bacteria had repeated short stretches of DNA in their immune systems. At the time, no one understood why this happened, or what purpose it served.
Ongoing research revealed that these sequences enabled bacteria to fight off viruses and were given a name: clustered regularly interspaced short palindromic repeats (CRISPR). In essence, they were DNA fragments from past viruses that were used to detect and destroy DNA from similar viruses during subsequent infections.
The next step was to find a way of replicating this process in humans by creating DNA fragments that could target and then alter or remove specific defective DNA sequences. The answer lay in formulating an RNA (ribonucleic acid) molecule mirroring the genomic sequence of defective DNA.
The RNA seeks out the target defective DNA on the genome in tandem with an engineered nuclease (the Cas9 enzyme is the most famous). The nuclease then acts like a pair of molecular scissors cutting double strand breaks on the specific defective part of the DNA helix.
Clearly if either the RNA guide or the DNA cutting process are not accurate enough then there could be severe and unforeseen consequences such as mutations and potentially cancer. The ethics of how far the technology should be deployed are still a work in progress, although scientists agree that the experiments should be limited to patients with active diseases rather than trying to genetically engineer future generations, as a Chinese scientist controversially did in 2018 (he was jailed for three years for producing genetically altered babies).
Secondly, both the messenger RNA and Cas9 protein are both quite large in molecular terms. This makes it more difficult to get them to the right spot in the first place.
Nevertheless in 2019, the science took a major step forwards when US biotech CRISPR Therapeutics conducted the first-ever experimental treatment in vitro (outside the body). The company, founded by Charpentier, wants to find a cure for blood disorders such as sickle cell anemia and beta-thalassemia, which are caused by defects in hemoglobin (the protein that carries oxygen in red blood cells).
In the first stage of their Phase 1/2 CTX001 clinical trial, blood cells from five patients were modified in a petri dish using the CRISPR-Cas9 gene-editing tool then returned back to each patient’s body. This summer it was reported that the bodies of all five patients had accepted the modified cells.
More promisingly, the first two beta thalassemia patients no longer needed blood transfusions five and 15 months after receiving their CTX001 infusions. The first sickle cell patient was also free of vaso-occlusive crises (the most common complication) nine months after theirs.
Then in March, another gene editing company called Editas Medicine conducted the first in vivo patient dosing for a Phase 1/2 AGN-151587 clinical trial to try and restore the sight of people suffering Leber congenital amaurosis 10 (LCA10). This is an inherited form of blindness caused by mutations in the CEP290 gene.
A second in vivo dosing began in November when another biotech firm called Intellia Therapeutics, founded by Doudna, launched a Phase I NTLA-2001 clinical trial for hereditary transthyretin amyloidosis (ATTR). This disease is caused by a mutation in the TTR gene, which produces a misshapen protein in the liver that progressively builds up, causing nerve and heart damage.
The therapy was administered through a vein. The delivery mechanism for the RNA and Cas9 was also improved by using lipid nanoparticles, which have a much larger carrying capacity.
If both trials report good results, they should revolutionise treatments and not just for the diseases they are targeting. For the technique also opens the door to hunting down cancers and treating solid tumours.
Indeed, this November researchers from Tel Aviv University said that they had successfully deployed lipid nanoparticles as the CRISPR delivery system to deal with aggressive glioblastoma (brain cancer) cells in mice. Initial results showed that tumour growth was halved and survival rates improved by 30%.
CRISPR Therapeutics also recently launched a Phase I CTX110 clinical trial for another type of cancer, non-Hodgkin lymphoma. The trial garnered negative newspaper headlines after the patient who received the highest dosage died when the therapy re-activated latent herpes virus triggering encephalitis.
The adverse event raised questions about the impact gene editing technology might have on immunocompromised individuals. It also threatened to overshadow positive findings concerning the eight previously relapsed patients who received the second highest dosage: after three months, four had experienced complete remissions.
This trial builds on immunology-related breakthroughs pioneered by companies like Gilead Sciences and Novartis, which produce chimeric antigen receptor (CAR)-T cell therapies – injecting new DNA into the immune system’s T-cells to help them kill cancer. However, it differs in one key respect.
Previous treatments are autologous. This means that the T-cells come from the patient’s own body. It is a time consuming process, requiring patients to visit the lab and precludes the possibility of mass-producing treatments based on the technique.
CRISPR Therapeutics is at the frontline of trying to develop allogeneic treatments whereby any healthy donor’s cells can be used. The risk with using another donor’s cells is that the recipient’s body will reject them causing graft versus host disease (GvHD), which can be fatal. CRISPR Therapeutics and another biotech called Allogenic Therapeutics are hoping to show that this will not be the case.
The creation of mass off-the-shelf cell-based medicines would clearly be a lot cheaper for the medical industry and would also benefit patients as they would become more widely available across the world.
Over the longer term, using CRISPR (replacing defective DNA) in combination with CAR-T (equipping the immune system to destroy existing tumours) could also be a marriage made in heaven when it comes to eradicating cancer for good.