CRISPR is one of the most groundbreaking inventions of the century, with the potential to revolutionize gene therapy for a range of diseases, as well as increase crop yield or nutrition, create beneficial microbes, and a variety of other uses. It works like a pair of “molecular scissors,” snipping out problematic genes and inserting more helpful ones.
The problem is that sometimes it can target the wrong part of DNA and make changes there — known as off-target mutations — that have the potential to cause health problems. Even if it does find the right target, the DNA repair process can go awry, leading to so-called target mutations.
Preventing these two problems is the focus of new research by researchers at the Max Delbrück Center for Molecular Medicine (MDC) and Humboldt University of Berlin. The team modified these “molecular scissors” to be gentler, making a fundamentally different way of cutting.
Instead of making one nick that cuts directly through the entire DNA double-strand, the new tool makes two smaller cuts, each cutting a DNA strand. A built-in spacer keeps these cuts a safe distance — between 200 and 350 base pairs.
“Our experiments with hematopoietic stem cells and T cells showed that this is the optimal distance to minimize target and non-target mutations,” said study author Dr. Van Trung Chu. “Anything short, we could potentially cut through the entire DNA molecule — albeit using two separate scissors.”
In tests on cells in a lab dish, the team found that the new spacer-nick tool was as effective as traditional CRISPR at making edits — 20 to 50 percent of the treated cells were repaired. But importantly, the new tool did a better job of reducing errors, with less than 2% of the targeted mutations occurring in edits using spacer-nicks, compared to more than 40% with CRISPR-Cas9. Meanwhile, off-target mutations appear to be “rare, or even nonexistent,” in our approach, Chu said.
The team hopes that future work will test the spacer-nick editing tool in animals before proceeding to human trials. One of the first potential targets is to treat inherited blood disorders.
The study was published inscientific progress” magazine.