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

Objective: 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.Materials and Methods: 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).Results: 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.Conclusion: 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.