Prime Editing, a Novel Genome-Editing Tool That May Surpass Conventional CRISPR-Cas9

Background: Genome editing mediated by clustered regularly interspaced short palindromic repeat -CRISPR-Cas- was first reported using cell lines in 2012, and since then, its applications in other systems have steadily increased. However, this approach still needs improvement and optimization. Prime Editing (PE) was originally proposed by Anzalone and colleagues in 2019, who showed significant lower rates of "off target" effects compared to conventional CRISPR-Cas9. Objectives: In this review, we describe and compare the "conventional" CRISPR-Cas9 system with a novel homology-directed repair-independent editing approach called Prime Editing (PE). Methods: Numerous recent publications involving the PE molecular mechanism for targeted-mutagenesis, advantages, limitations, and applications of the approach in different biomedicine fields were reviewed. Results: From the literature, it appears that PE neither relies on DSB nor needs HDR with exogenous donor DNA templates, which shows the clinical potential of PEs in correcting a broad range of mutations for genetic diseases. Four generations of PE mechanisms have been developed, reaching higher efficiency from one generation to the next one. However, reviewed studies support that PE also introduces new challenges such as unwanted mutations mediated by the double nicking strategy required for the PE3's efficiency, the selection of the optimal combination of PBS and RT templates, and the limitation of large DNA insertions that conventional CRISPR-Cas9 is capable of. Conclusion: The reviewed literature demonstrate that genome editing-based PE is a promising technology aiming at decreasing the common undesirable effects associated with conventional genome editing approaches such as CRISPR-Cas9 or BE. Even though progress has been made to improve the efficiency of the genome editing by the PE ribonucleo-protein complex, further research is required to optimize PE tools and maximize its efficiency.