'Prime' genome editing inserts whole gene sequences

A type of genome editing capable of replacing entire genes in the human genome could potentially be used to treat a wide variety of genetic conditions.

Researchers at the Broad Institute of MIT and Harvard in Massachussetts have used so-called 'prime' genome editing to significantly improve the efficiency of integrating whole genes into mammalian cells in an approach termed eePASSIGE. Their findings were published in Nature.

'To our knowledge this is one of the first examples of programmable targeted gene integration in mammalian cells that satisfies the main criteria for potential therapeutic relevance,' said Professor David Liu, senior author of the study. 'At these efficiencies, we expect that many if not most loss-of-function genetic diseases could be ameliorated or rescued'.

Prime editing offers an alternative to the widely-used CRISPR/Cas9 genome editing approach. It avoids creating the double-strand DNA breaks which are central to CRISPR/Cas9's mechanism of action. These breaks can increase the risk of off-target effects and repair-based errors. Alone, it can make changes in DNA sequences of up to 200 base-pairs, many times shorter than the lenth of a whole gene.

In this recent study, Professor Liu, who was one of the inventors of prime editing (see BioNews 1021), combined prime editing with specific DNA recombinase enzymes that can insert larger pieces of DNA into the genome. It also builds on the development of PASTE (Programmable Addition via Site-specific Targeting Elements), a technique created by another research team based at Massachusetts General Hospital (see BioNews 1176).

By combining these elements, eePASSIGE may be capable of replacing a faulty gene with a complete, healthy version. The researchers believe that by replacing entire genes, prime editing can correct a range of variable mutations while preserving surrounding DNA sequences. They suggest that the approach could enhance the precision and safety of genome editing, and open new avenues for treating monogenic disorders like cystic fibrosis and sickle cell anaemia with greater accuracy and fewer unintended consequences.

'It's exciting to see the high efficiency and versatility of eePASSIGE, which could enable a new category of genomic medicines' said Dr David Gao, postdoctoral researcher and co-author of the paper.