Investigating The Correction of IVS II-1 (G> A) Mutation in HBB Gene in TLS-12 Cell Line Using CRISPR/Cas9 System

Beta-thalassemia is a group of inherited hematologic. The most HBB gene variant among Iranianbeta-thalassemia patients is related to two mutations of IVSII-1 (G>A) and IVSI-5 (G>C). Therefore, our aim ofthis study is to use the knock in capability of CRISPR Cas9 system to investigate the correction of IVSII-1 (G>A)variant in Iran. In this experimental study, following bioinformatics studies, the vector containingPuromycin resistant gene (PX459) was cloned individually by designed RNA-guided nucleases (gRNAs), andcloning was confirmed by sequencing. Proliferation of TLS-12 was done. Then, the transfect was set up by thevector with GFP marker (PX458). The PX459 vectors carrying the designed gRNAs together with Single-strandedoligodeoxynucleotides (ssODNs) as healthy DNA pattern were transfected into TLS-12 cells. After taking the singlecell clones, molecular evaluations were performed on single clones. Sanger sequencing was then performed toinvestigate homology directed repair (HDR). The sequencing results confirmed that all three gRNAs were successfully cloned into PX459 vector. In thetransfection phase, The TLS-12 containing PX459-gRNA/ssODN was selected. Molecular evaluations showed thatthe HBB gene was cleaved by the CRISPR/Cas9 system, that indicates that the performance of non-homologous endjoining (NHEJ) repair system. Sequencing in some clones cleaved by the T7E1 enzyme showed that HDR was notconfirmed in these clones. IVS-II-1 (G> A) mutation, which is the most common thalassemia mutation especially in Iran, the CRISPR/Cas9 system was able to specifically target the HBB gene sequence. This could even lead to a correction in themutation and efficiency of the HDR repair system in future research.