The CRISPR-Cas9 System Is Used to Edit the Autoimmune Regulator Gene in Vitro and in Vivo

Although mutations in the AIRE gene in patients with autoimmune polyendocrine syndrome type 1 (APS-1) syndrome are associated with the onset of this autoimmune disease, much of what is known about its mechanisms has been obtained through studies with Aire mutant Mus musculus mouse model or with Aire mutant medullary thymic epithelial cells (mTEC) cultured in vitro. The in vivo murine model was soon established, and ten mutant strains are currently described. Most Aire mutant mice were obtained through homologous recombination, which generated Aire knockout (KO) animals. Nevertheless, long-term cultures of mTECs from APS-1 patients or Aire mutant mice are difficult to establish. The CRISPR-Cas9 system to edit Aire in a murine mTEC line in vitro and mouse embryo has been successfully used to overcome this. The ribonucleoprotein (RNP) complexes composed of the guide RNA (gRNA), the Cas9 enzyme, and single-stranded oligonucleotides (ssODN) were designed to target Aire exons 6 and 8 separately. The CRISPR-Cas9 makes it possible to produce NHEJ-derived indels or HDR-derived mutations. Efforts are being concentrated on using RNP complex rather than plasmid vectors, as RNP makes recurrent NHEJ-derived mutations among in vitro and in vivo editions. One recurrent mutation was described in the Aire exon 6 (del 3554G) and the other in the exon 8 (del 5676_5677TG), i.e., the exon 6 mutation was kept in an mTEC clone edited in vitro and in vivo in a mouse, and the exon 8 mutation was kept in several mTEC clones in vitro. In contrast, none of the mutations obtained with the nickase system (plasmid expression vector) were recurrent, indicating the participation of the RNP complex in recurring mutation, which offers advantages, as it does not involve recombinant plasmids and does not generate a genetically modified organism but rather a mutant animal or cell.