CRISPR/Cas9 and its applications
CRISPR technology is defined as genetic scissors because it allows one to cut the DNA at a specific location among all the million or billion nucleotides present in the genome of a cell. The use of CRISPR has revolutionised molecular biology because it allows us to manipulate the genome of a cell with high precision and in extremely short times.
CRISPR was first discovered in the bacterium Streptococcus pyogenes. In this and other species of bacteria, CRISPR acts as an immune system that allows them to degrade viral DNA and RNA that enter the bacterial cells, preventing viruses from infecting them.
Over the years, CRISPR technology has been applied and optimised for the genomic editing of organisms that play a fundamental role in basic and applied sciences, including microorganisms such as Escherichia coli, baker's yeast, plants and mammalian cells.
The use of CRISPR was implemented in 2012, and only eight years after its discovery it is now being used by scientists around the globe to introduce or correct mutations within genes of interest, to eliminate genes and study their function, and to introduce genes de novo into the genome of an organism.
For example, CRISPR is used for the genetic improvement of cultivated plants, and has made it possible to obtain soybean plants that are resistant to drought and high salinity; wheat with a low content of gliadin peptides, which are part of gluten and are toxic to people with celiac disease; as well as button mushrooms that resist browning when sliced.
We can anticipate that in the forthcoming years, CRISPR may also be used to treat human genetic diseases. Until now, CRISPR has been used in the medical field primarily as part of clinical trials to develop a treatment for genetic diseases through ex vivo experiments, in which the patient's cells are removed, treated and then re-introduced.
In 2018, it was announced by the Chinese scientist He Jiankui that CRISPR was used to allegedly confer immunity to HIV in twin embryos. The embryos were treated with CRISPR to deactivate a gene that allows the HIV virus to enter the cells. The announcement was criticised by the scientific community because it is thought to be too early to predict the repercussions of using CRISPR to knockout genes in human embryos.
The greatest risk associated with the use of CRISPR is that it may inadvertently cut the DNA outside of the intended target. CRISPR off-target effects have been widely described, and often result in gene loss or chromosomal truncation, with potentially deleterious consequences for the organism.
In March 2020, the first clinical trial for the in vivo treatment of a human genetic disease involving a CRISPR-based drug was announced. In this case, CRISPR was used experimentally to treat a patient suffering from retinal dystrophy, a condition that results in blindness. The pharmaceutical company that is testing this drug has announced that they are planning to expand the study to 18 more patients to evaluate its safety and efficacy.
The use of CRISPR to treat a retinal disease has the advantage that these cells do not divide, so the effect of the treatment is potentially more stable and long-lasting.
In conclusion, the discovery of CRISPR has revolutionised the way we do molecular biology and is shaping various scientific fields, including agriculture and medicine. The number of pharmaceutical companies that are undertaking clinical trials with CRISPR-based drugs is steadily increasing. Provided that ethical rules are followed, and that the risks associated with the use of CRISPR in humans can be evaluated, we will most likely see drugs based on this powerful technology reach the clinic in the years to come.