CTLA4 and chronic granulomatous disease: Several studies have demonstrated that gene expression can be enhanced in mammalian cells by the inclusion of an intron, such as when correcting CYBB gene mutations in chronic granulomatous disease (CGD) and when editing the CD40 ligand gene.39–44 However, our intronic editing approach targets the 3’ end of the first intron of CTLA4 thus preserving the majority of the first intronic sequence.