SCGE Disease Models Studies Supplement: Repair of a CFTR Nonsense Mutation Using Adenine Base Editing

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Abstract: CFTR nonsense mutations cause a severe cystic fibrosis (CF) phenotype, unresponsive to current small molecule therapies. Correcting CFTR nonsense mutations in 5–15% of airway epithelia by installing a single nucleotide A>G change using an adenine base editor (ABE) should restore CFTR mediated Cl− secretion to healthy levels. We have optimized amphiphilic shuttle peptides for delivery of CRISPR associated nuclease ribonucleoproteins (RNP) to mouse airways and ABE RNP to rhesus monkeys, achieving therapeutic editing levels ≥5%. We propose to deliver ABE RNP to the airways of mice bearing the human CFTR R553X nonsense mutation. In this model, mouse CFTR exon 12 was entirely replaced with human exon 12 sequence. While substitution for wildtype human sequence has no negative consequences on mice, introduction of human R553X mutation in the substituted exon 12 causes a CF phenotype (intestinal obstruction at weaning, loss of CFTR function in airway epithelia and intestinal organoids). This is one of the only animal models of a CFTR nonsense mutation with a disease phenotype. We previously demonstrated ex vivo that ABE RNP delivered using shuttle peptides can efficiently revert the R553X mutation in human airway cells. Our overarching goals are 1) to optimize ABE8e RNP editing, 2) to repair the R553X mutation in the airway epithelia of mice with sufficient efficiency to restore CFTR function, and 3) to investigate the safety, toxicity, and off-target effects of the editing approach while advancing towards clinical trials with this method.