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 Iranian beta-thalassemia patients is related to two mutations of IVSII-1 (G>A) and IVSI-5 (G>C). Therefore, our aim of this 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 containing Puromycin resistant gene (PX459) was cloned individually by designed RNA-guided nucleases (gRNAs), and cloning was confirmed by sequencing. Proliferation of TLS-12 was done. Then, the transfect was set up by the vector with GFP marker (PX458). The PX459 vectors carrying the designed gRNAs together with Single-stranded oligodeoxynucleotides (ssODNs) as healthy DNA pattern were transfected into TLS-12 cells. After taking the single cell clones, molecular evaluations were performed on single clones. Sanger sequencing was then performed to investigate homology directed repair (HDR).

The sequencing results confirmed that all three gRNAs were successfully cloned into PX459 vector. In the transfection phase, The TLS-12 containing PX459-gRNA/ssODN was selected. Molecular evaluations showed that the HBB gene was cleaved by the CRISPR/Cas9 system, that indicates that the performance of non-homologous end joining (NHEJ) repair system. Sequencing in some clones cleaved by the T7E1 enzyme showed that HDR was not confirmed 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 the mutation and efficiency of the HDR repair system in future research.