David Liu, a chemical biologist at the MIT and Harvard University, his post-doc Andrew Abzalone and their coworkers, published an article in Nature on the 21st of October, where they present a new gene-editing method: prime-editing promises to ‘correct about 89% of the known pathogenic human genetic variants’.
The method is one of the latest developed ones using the Cas9 enzyme, similar to the popular CRISP-Cas9 technique; however, compared to this one, it is more precise and less prone to possible errors – a problem which has so far limited the use of CRISP-Cas9 in medicine and agriculture.
Both methods work by using Cas9 to recognise a specific sequence on the DNA molecule, and then cut the genome at specific points. CRISP-Cas9 cuts both strands of DNA and then relies on the cell’s repair system to make the necessary edits. This last process cannot be controlled by researchers and thus can lead to errors, inserting or deleting extra code. David Liu and colleagues had the idea to modify Cas9 so that only one strand of DNA is cut off. Then an RNA strand sample can be used with a reverse transcriptase enzyme to make the edits required. This way, researchers do not need to rely on the cell’s repair system and errors can be avoided. Because prime-editing relies on a RNA strand, it cannot be used for long genome corrections, as the RNA could be attacked by enzymes inside the cell. For this reason, prime-editing will not simply replace the CRISP-Cas9 method, but it will help treat specific genetic diseases.
David Liu is also responsible for the development of another technique, called base editing, which is even more precise as it can be used to change single nucleotides of the genetic code. In this case, the method will be developed to address pathologies related to modifications of a few letters of DNA.
These new studies demonstrate the great interest and success in gene-editing research since the discovery of CRISP-Cas9 in 2013, and give hope that it will become sufficiently reliable to be used to cure human diseases in the future. To this aim, David Liu has already founded a company, Prime Medicine, to help deliver the technology.