Comparison of Cas9 and Cas12a CRISPR editing methods to correct the W1282X-CFTR mutation.

• Cas9 and Cas12a can successfully correct W1282X-CFTR variant in 16HBE cells. • Cas9 shows higher levels W1282X-CFTR correction than Cas12a. • CRISPR/Cas9 gene editing of W1282X-CFTR increases levels of CFTR mRNA and protein. • CFTR function is fully restored in W1282X homozygous-corrected clones. W1282X-CFTR variant (c.3846G>A) is the second most common nonsense cystic fibrosis (CF)-causing mutation in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene. Even though remarkable breakthroughs have been done towards CF treatment with the approval of four CFTR protein modulators, none of these are approved for patients with nonsense mutations. CRISPR gene editing tools can be of great value to permanently correct the genetic defects caused by these mutations. We compared the capacity of homology-directed repair (HDR) mediated by Cas9 or Cas12a to correct W1282X CFTR mutation in the CFF-16HBEge W1282X CFTR cell line (obtained from CFF), using Cas9/gRNA and Cas12a/gRNA ribonucleoproteins (RNPs) and single strand DNA (ssODN) oligonucleotide donors. Cas9 shows higher levels of correction than Cas12a as, by electroporating cells with Cas9 RNPs and ssODN donor, nearly 18% of precise editing was achieved compared to just 8% for Cas12a. Such levels of correction increase the abundance of CFTR mRNA and protein, and partially restore CFTR function in the pool of edited cells to 18% of WT CFTR function. Moreover, homozygous corrected clones produced levels of mRNA, protein, and function comparable to those of cells expressing WT CFTR. Altogether, this work demonstrates the potential of gene editing as a therapeutic strategy for CF directly correcting the root cause of the disease. [ABSTRACT FROM AUTHOR]