CRISPR/Cas systems: Delivery and application in gene therapy

The CRISPR/Cas systems in prokaryotes such as bacteria and archaea are the
adaptive immune system to prevent infection from viruses, phages, or other
foreign substances. When viruses or phages first invade the bacteria, Cas
proteins recognize and cut the DNA from viruses or phages into short
fragments that will be integrated into the CRISPR array. Once bacteria are
invaded again, the modified CRISPR and Cas proteins react quickly to cut DNA at
the specified target location, protecting the host. Due to its high efficiency,
versatility, and simplicity, the CRISPR/Cas system has become one of the most
popular gene editing technologies. In this review, we briefly introduce the
CRISPR/Cas systems, focus on several delivery methods including physical
delivery, viral vector delivery, and non-viral vector delivery, and the
applications of disease therapy. Finally, some problems in CRISPR/
Cas9 technology have been proposed, such as the off-target effects, the
efficiency of DNA repair mechanisms, and delivery of CRISPR/Cas system
safely and efficiently to the target location.