The fusion of CRISPR–Cas9 with cytidine deaminases leads to base editors (BEs) capable of programmable C-to-T editing, which has potential in clinical applications but suffers from off-target (OT) mutations. Here, we used a cleavable deoxycytidine deaminase inhibitor (dCDI) domain to construct a transformer BE (tBE) system that induces efficient editing with only background levels of genome-wide and transcriptome-wide OT mutations. After being produced, the tBE remains inactive at OT sites with the fusion of a cleavable dCDI, therefore eliminating unintended mutations. When binding at on-target sites, the tBE is transformed to cleave off the dCDI domain and catalyses targeted deamination for precise base editing. After delivery into mice through a dual-adeno-associated virus (AAV) system, the tBE system created a premature stop codon in Pcsk9 and significantly reduced serum PCSK9, resulting in a ~30–40% decrease in total cholesterol. The development of tBE establishes a highly specific base editing system and its in vivo efficacy has potential for therapeutic applications.

CRISPR-Cas9 与胞苷脱氨酶的融合导致碱基编辑器 (BEs) 能够进行可编程的 C-to-T 编辑，这在临床应用中具有潜力，但存在脱靶 (OT) 突变。在这里，我们使用可切割的脱氧胞苷脱氨酶抑制剂 (dCDI) 结构域构建了一个变压器 BE (tBE) 系统，该系统仅在全基因组和全转录组 OT 突变的背景水平下诱导有效编辑。产生后，tBE 在 OT 位点保持无活性，并融合了可切割的 dCDI，因此消除了意外突变。当在目标位点结合时，tBE 被转化以切割 dCDI 结构域并催化靶向脱氨基作用以进行精确的碱基编辑。通过双腺相关病毒 (AAV) 系统递送到小鼠体内后，tBE 系统在Pcsk9并显着降低血清 PCSK9，导致总胆固醇降低约 30-40%。tBE的发展建立了一个高度特异性的碱基编辑系统，其体内功效具有治疗应用的潜力。