CRISPR is undoubtedly one of the most remarkable discoveries of the era and has the potential to expand the domains of basic and clinical research. The presence of the CRISPR/Cas system was first observed in Escherichia coli K12 gram-negative bacteria in the late 1980s. Thereafter, CRISPR was also reported in the archaeal genome. However, the role of CRISPR in prokaryotes and archaea was unknown. Much later in the mid-2000s, the role of the CRISPR sequence in bacterial defence was comprehended.
Viruses or bacteriophages attack bacteria by binding to their surface proteins and inject their DNA through the bacterial cell wall to hijack the cellular machinery of the bacteria. Under such an attack, the CRISPR tool within the bacterial cell splits the viral DNA and integrates sequences of this DNA into the bacterial genome. Thus, in the future, when the bacteria are attacked by the same bacteriophage, the unique sequences of the integrated viral DNA helps the bacteria to quickly recognise and eliminate the threat. Thus, the CRISPR/Cas system provides adaptive immunity to bacteria and archaea.
Later, the identification of CRISPR-associated (Cas) proteins, and their functionality in bacteria and archaea, laid the foundation of the CRISPR/Cas system as a genome editing tool. Different types of CRISPR/Cas systems have been discovered to date and their mechanism of genome editing varies. However, the technology has not remained confined to prokaryotic systems and archaea but has expanded rapidly, finding potential applications as a genome editing toolkit in humans. In contrast to existing genome editing techniques such as ZFNs and TALENs, the CRISPR/Cas system offers a simple yet precise and site-specific genetic editing technology. Genetic editing by CRISPR/Cas technique relies on the coordinated functioning of Cas nuclease protein and chimeric sgRNA having a complementary sequence to target DNA.
In 2012, in vitro gene editing attempts were first documented. Thereafter, numerous attempts to edit the genome in plants, and animals including primates have been recorded. The works of Jennifer Doudna, a molecular biologist from the University of California, Berkeley, and Emmanuelle Charpentier, a researcher in microbiology, genetics, and biochemistry, and director at the Max Planck Institute for Infection Biology in Berlin have been particularly noteworthy. They were jointly awarded the 2020 Nobel Prize in Chemistry for their pioneering efforts to use CRISPR/Cas9 as a genome editing tool in human and animal models.
In the recent years, genome editing has rapidly advanced, and CRISPR/Cas technology has been a key driver. In addition to basic research, CRISPR/Cas technology has been successfully used as high-throughput genetic screens for diseases such as cancer and other genetic diseases. It also finds immense application in the development of gene therapy and immunotherapy such as chimeric antigen receptor (CAR) T therapy that are promising cancer therapies.