Researchers at MIT have developed novel prime-editing tools with markedly improved precision, potentially reducing unwanted mutations and enhancing safety for therapeutic applications. Prime editing is viewed as an appealing alternative to traditional CRISPR-Cas9 because it can rewrite DNA without causing double-strand breaks, but a major limitation has been its tendency to introduce insertions and deletions (“indels”).
In a new paper published in Nature, the MIT team combined multiple engineering strategies to mitigate these errors without overly complicating the editing system. They began by mutating Cas9 nickase (Cas9n) variants to shift where nicks occur and to destabilize nicked DNA ends, promoting degradation of undesirable DNA fragments. This led to a “precision prime editor” (pPE) that showed a 118-fold reduction in indel formation compared to earlier systems, yielding a superior edit:indel ratio. To offset a slight drop in editing efficiency, the researchers then introduced additional mutations known to enhance Cas9n’s activity. Their optimized version, “extra-precise prime editor” (xPE), achieved an edit:indel ratio of 354:1. Finally, by protecting unstable 3′ ends of the pegRNA (prime editing guide RNA) using an RNA-binding protein (La poly-U), they built the “very-precise prime editor” (vPE), which improved efficiency further and reached an edit:indel ratio of 465:1.
The researchers emphasise that vPE integrates smoothly with existing prime editing methods and delivery approaches, which could make it a practical improvement for therapeutic applications. They note that the broader aim is to achieve efficient editing while limiting unintended effects.
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