Discovery and engineering of AiEvo2, a novel Cas12a nuclease for human gene editing applications.

The precision of gene editing technology is critical to creating safe and effective therapies for treating human disease. While the programmability of CRISPR-Cas systems has allowed for rapid innovation of new gene editing techniques, the off-target activity of these enzymes has hampered clinical development for novel therapeutics. Here, we report the identification and characterization of a novel CRISPR-Cas12a enzyme from Acinetobacter indicus (AiCas12a). We engineer the nuclease (termed AiEvo2) for increased specificity, protospacer adjacent motif recognition, and efficacy on a variety of human clinical targets. AiEvo2 is highly precise and able to efficiently discriminate between normal and disease-causing alleles in Huntington's patient-derived cells by taking advantage of a single nucleotide polymorphism on the disease-associated allele. AiEvo2 efficiently edits several liver-associated target genes including PCSK9 and TTR when delivered to primary hepatocytes as mRNA encapsulated in a lipid nanoparticle. The enzyme also engineers an effective CD19 chimeric antigen receptor-T-cell therapy from primary human T cells using multiplexed simultaneous editing and chimeric antigen receptor insertion. To further ensure precise editing, we engineered an anti-CRISPR protein to selectively inhibit off-target gene editing while retaining therapeutic on-target editing. The engineered AiEvo2 nuclease coupled with a novel engineered anti-CRISPR protein represents a new way to control the fidelity of editing and improve the safety and efficacy of gene editing therapies.