Recent advances in gene therapy are bringing us closer to the day when CRISPR, a genetic editing technology, will be able to treat a wide range of diseases in a large number of patients.

In October 2020, French microbiologist Emanuel Charpentier and American biochemist Jennifer Dudna won Nobel Prize in chemistry for their pioneering work on CRISPR-based gene editing, which they have been doing since 2012.

The CRISPR system has revolutionized genetic engineering and can be used in the treatment of various diseases. Finding safe and effective ways to modify the human genome can lead to a cure for hereditary genetic diseases and even serve as a treatment for cancer.

Although today it is not a reality for the general public, technology offers enormous promise for medicine. Recent clinical trials have produced encouraging results. For example, last March, CRISPR was first used in the human body (in vivo) to test the curing of inherited eye disease.

The technology is interesting because it could turn the body itself into a «specialized drug manufacturing plant» instead of relying on synthetic drugs to reduce the effects of hereditary degenerative diseases or to kill mutant cancer cells.

Scientists began to understand the theory behind the technology as early as the 1980s when it was noticed that short segments of DNA were repeated in the immune system of certain bacteria. But then it was not yet clear why and for what purpose they serve.

Further research has shown that the repeating sections help bacteria fight viruses, and these sequences have been called Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR). Essentially, these are fragments of DNA from previous viruses that were used to detect and destroy the DNA of similar viruses during reinfection.

The next step was to find a way to reproduce this process in humans, by creating DNA segments that could detect certain damaged DNA sequences, and then change or remove them from the genome. The answer was found in the construction of an RNA (ribonucleic acid) molecule that reflects the genetic sequence of the defective DNA.

RNA looks for damaged target DNA in the genome and works together with enzymes that break down DNA (nucleases known as Cas9). The enzyme later acts as molecular scissors, cutting through the damaged portion of the DNA double helix.

It goes without saying that if the RNA driving the scissors or the DNA cutting process is not accurate enough, it can have serious and unexpected consequences, such as dangerous mutations and cancer. Ethics defining the potential applications of the technology are still emerging, and in the process, scientists have come to a consensus that its testing should be limited to patients with active diseases, and not try to genetically engineer future generations, as the controversial Chinese scientist did in 2018 (he got a three-year prison sentence for creating genetically modified babies).

Another problem with this method is that both the messenger RNA and the Cas9 protein are rather large molecules, which makes it difficult to place them in the right place.

However, a significant step was taken in 2019 when the American biotech company CRISPR Therapeutics conducted the first experimental in vitro (outside the body) treatment. The company, founded by Charpentier, is working to find a cure for blood diseases such as sickle cell anemia and beta-thalassemia, which are caused by defects in hemoglobin (a protein that carries oxygen in red blood cells).

At the start of the company’s Phase 1/2 clinical trial of CTX001, the CRISPR/Cas9 system was activated to edit the blood cells of five patients in a Petri dish. The cells were returned to the bodies of the patients, and last summer it was reported that the bodies of five patients received engineered cells.

According to later reports, the first two patients with beta-thalassemia did not require additional blood transfusions for 5 and 15 months, respectively, after CTX001 transfusion. The first patient who underwent an experiment with sickle cell anemia also did not have hemolytic vascular crises (the most common complication of this disease) within 9 months after treatment.

Then, in March, another gene-editing company, Editas Medicine, announced the first dose of AGN-151587 to a patient in a Phase 1/2 clinical trial to try to restore vision in people with Leber’s disease (LCA10). It is an inherited form of blindness caused by mutations in the CEP290 gene.

Additional CRISPR-based therapy for patients began in November when biotechnology company Intellia Therapeutics that was founded by Dudna began the first phase of clinical trial NTLA-2001 for the treatment of hereditary transthyretin amyloidosis (ATTR). This disease is caused by a mutation in the TTR gene and causes a malformed protein to be produced in the liver, which gradually builds up and can damage the nerves and heart.

The treatment is done through a vein. The RNA and Cas9 triggering mechanism has also been improved through the use of nanoparticles with significantly higher carrying capacity.

The good results in both studies could revolutionize treatment, not just the diseases they targeted. This is because this method also paves the way for the treatment of certain types of cancer.

Indeed, last November, researchers at Tel Aviv University reported success in using nanoparticle lipid-based CRISPR triggering systems to treat aggressive glioblastoma (brain cancer) cells in mice. Preliminary results showed that after treatment, tumor growth was halved, and the survival rate increased by 30%.

CRISPR Therapeutics also recently launched a phase 1 clinical trial of CTX110 for another malignant disease, non-Hodgkin’s lymphoma. The experiment was followed by negative headlines after the highest dose patient died when treatment reactivated a dormant herpes virus in his body that caused encephalitis.

The event again raised questions about the effects of gene therapy in people with weakened immune systems, and also somewhat overshadowed the positive results in eight patients with the relapsing disease who received a second dose at its level: four of them had complete remission after three months.

This experiment is based on the immunological discoveries made by companies such as Gilead and Novartis, which manufacture drugs for the treatment of CAR (chimeric antigen receptor) T cells. As part of the treatment, new DNA is injected into the T cells of the immune system to help them kill cancerous tumors. This is a time-consuming process that requires patients to visit the laboratory and does not allow for mass production.

On the other hand, CRISPR Therapeutics is at the forefront of developing allogeneic therapies that use cells from healthy donors. The risk of using foreign donor cells is that the recipient’s body will reject them and cause graft versus host disease (GvHD), which can be fatal. CRISPR Therapeutics and another biotech company called Allogenic Therapeutics hope to show that this won’t happen as a result of the treatments they are developing.

The creation of finished drugs at the cellular level will undoubtedly be significantly cheaper for the medical industry and will benefit patients as its availability increases worldwide.

In the long term, using CRISPR to replace defective DNA in combination with CAR-T (an immune system action capable of destroying existing tumors) may be the optimal combination when it comes to curing cancer.