Programming large target genomic deletion and concurrent insertion via a prime editing-based method: PEDAR

Genomic insertions, duplications, and insertion/deletions (indels) account for ~14% of human pathogenic mutations. Current gene editing methods cannot accurately or efficiently correct these abnormal genomic rearrangements, especially larger alterations (>100 bp). Thus, developing a method to accurately delete insertions/duplications and repair the deletion junction could improve the scope of gene therapies. Here, we engineer a novel gene editor, PE-Cas9, by conjugating Cas9 nuclease to reverse transcriptase. Combined with two prime editing guide RNAs (pegRNAs) targeting complementary DNA strands, PE-Cas9 can direct the replacement of a genomic fragment, ranging from to ~1-kb to >10-kb, with a desired sequence at the target site without requiring an exogenous DNA template. In a reporter cell line, this PE-Cas9-based deletion and repair (PEDAR) method restored mCherry expression through in-frame deletion of a disrupted GFP sequence. We further show that PEDAR efficiency could be enhanced by using pegRNAs with high cleavage activity or increasing transfection efficiency. In tyrosinemia mice, PEDAR removed a 1.38-kb pathogenic insertion within the Fah gene and precisely repaired the deletion junction to restore FAH expression in liver. This study highlights PEDAR as a tool for correcting pathogenic mutations.