Improved Gene Editing System Makes Gene-Sized Edits

Rare Daily Staff

Scientists at the Broad Institute of MIT and Harvard have improved a gene-editing technology that they say is now capable of inserting or substituting entire genes in the genome in human cells, opening the way for therapeutic applications that can address diseases caused by varying genetic mutations with a single therapy.

The advance, from the lab of Broad core institute’s David Liu, could allow the insertion of a healthy copy of a gene at its native location in the genome, rather than having to create a different gene therapy to correct each mutation using other gene-editing approaches that make smaller edits.

The new approach uses a combination of prime editing, which can directly make a wide range of edits up to about 100 or 200 base pairs, and newly developed recombinase enzymes that efficiently insert large pieces of DNA thousands of base pairs in length at specific sites in the genome.

This system, called eePASSIGE, can make gene-sized edits several times more efficiently than other similar methods. The researchers published their work in the journal Nature Biomedical Engineering.

“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 Liu, who is senior author of the study and director of the Merkin Institute of Transformative Technologies in Healthcare at the Broad. “At these efficiencies, we expect that many if not most loss-of-function genetic diseases could be ameliorated or rescued, if the efficiency we observe in cultured human cells can be translated into a clinical setting.”

Many scientists have used prime editing to efficiently install changes to DNA that are up to dozens of base pairs in length, sufficient to correct the vast majority of known pathogenic mutations. But introducing entire healthy genes, often thousands of base pairs long, in their native location in the genome has been a long-standing goal of the gene-editing field.

Not only could this potentially treat many patients regardless of which mutation they have in a disease-causing gene, but it would also preserve the surrounding DNA sequences, which would increase the likelihood that the newly installed gene is properly regulated, rather than expressed too much, too little, or at the wrong time.

Liu’s team is now working on combining eePASSIGE with delivery systems such as engineered virus-like particles (eVLPs) that may overcome hurdles that have traditionally limited therapeutic delivery of gene editors in the body.

Photo: David Liu, senior author of the study and director of the Merkin Institute of Transformative Technologies in Healthcare at the Broad