During their lifetime, all organisms encounter various pathogens, including parasites, bacteria, and viruses; therefore, organisms have developed an array of immune defenses to protect from pathogenic insults. Over ten years ago, scientists discovered that prokaryotic organisms, including archaea and bacteria, possess adaptive and sophisticated immune defense mechanisms, despite being regarded as primitive organisms. Notably, they identified the presence of Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and CRISPR-associated proteins (Cas) in prokaryotic organisms. Since then, the CRISPR-Cas system has been employed to develop methods to protect bacterial species against viral parasites. More recently, the CRISPR-Cas system has emerged a powerful and versatile genome editing tool that holds great potential for the treatment of genetic diseases in humans (Edze Westra, 2016; Michael Criscitiello and Paul de Figueiredo, 2013).

In 1987, Japanese scientists were the first to report the presence of CRISPR repeat arrays in the genome of Escherichia coli. Specifically, they observed the presence of repeated fragments consisting of 29 nucleotides (nt). They also noted that these repeated fragments were interspersed with 32-nt-long non-repetitive variable sequences.