Advance genome editing technologies in the treatment of human diseases: CRISPR therapy (Review)

Abstract

Genome editing techniques are considered to be one of the most challenging yet efficient tools for assisting therapeutic approaches. Several studies have focused on the development of novel methods to improve the efficiency of gene editing, as well as minimise their off‑target effects. Clustered regularly interspaced short palindromic repeats (CRISPR)‑associated protein (Cas9) is a tool that has revolutionised genome editing technologies. New applications of CRISPR/Cas9 in a broad range of diseases have demonstrated its efficiency and have been used in ex vivo models of somatic and pluripotent stem cells, as well as in in vivo animal models, and may eventually be used to correct defective genes. The focus of the present review was the recent applications of CRISPR/Cas9 and its contribution to the treatment of challenging human diseases, such as various types of cancer, neurodegenerative diseases and a broad spectrum of other disorders. CRISPR technology is a novel method for disease treatment, enhancing the effectiveness of drugs and improving the development of personalised medicine.

Figure 1

Schematic representation of the CRISPR immune system in the acquisition of foreign genetic material. The CRISPR system consists of a Cas operon containing Cas genes, and a CRISPR array that contains identical repeat sequences and spacers. In the case of viral or plasmid-based invasion, CRISPR acquires the protospacer sequence (red) of the viral DNA, which is achieved via a Cas1-Cas2 complex and integrated into the CRISPR array, which is further transcribed to pre-crRNA. CRISPR, clustered regularly interspaced short palindromic repeats.

Figure 2

DNA repair mechanisms used for gene editing. Formation of double-stranded breaks to initiate endogenous DNA repair by NHEJ, resulting in acci-dental insertions/deletions, or by HDR, which uses a template DNA strand for repair. NHEJ, non-homologous end joining; HDR, homology directed repair.

Figure 3

Comparison of ZFNs and TALENs, non-specific nucleases designed to cleave the genome at a specific site. ZFNs, zinc finger nucleases; TALENs, transcription activator-like effector nucleases.

Figure 4

Comparison of type I, II and III CRISPR systems in crRNA maturation and interference. Upon transcription of CRISPR following the acquisition stage, pre-crRNA undergoes a maturation stage, which is processed by Cas6 in type I and III. In type II, the maturation step is performed by Cas9 accompanied by tracer RNA and RNase III. The interference step varies notably between the different types. CRISPR, clustered regularly interspaced short palindromic repeats; crRNA, CRISPR-associated RNA; Cas, CRISPR-associated protein; pre-crRNA, precursor crRNA; PAM, protospacer adjacent motif.