Applications and challenges for CRISPR/Cas9-mediated gene editing

Recently, many types of CRISPR/Cas9 have been utilized for clinical purpose. As a new and promising method, CRISPR/Cas9 manages to correct mutant and deficit DNA sequence to cure certain diseases fundamentally. Until now, CRISPR-based therapeutic gene editors have mainly been used to cure diseases related to single gene mutations like sickle cell anemia, and much advance has been achieved. Other applications involve editing chimeric antigen receptor T cells, creating human disease phenotype on animals, knocking out genes whose transcription products may give rise to life-threatening diseases. Some gene therapies have already been carried out on patients, showing certain curative effects. However, many challenges emerged during the progress of gene editing, such as off-target editing, low editing and delivery efficiency, and chromosomal translocation due to error repair after double strand breaks. These uncertain factors severely hamper the forward pace of gene editing. Accordingly, many solutions are raised to tackle these problems, including the optimization of the tools, usage of different cell repair pathways and invention of engineered editors. In this review, we will discuss the traditional approaches and other newly-invented ways of gene editing, how they can be used in therapeutic treatment, the challenges that come up in applications and the related moral issues.