With new strains of the Covid-19 virus emerging throughout the world, the human population is in need of an advanced and effective cure– one that would not only kill the virus but also inhibit its spread from person to person. CRISPR is considered a highly versatile gene-editing tool that has completely revolutionized multiple fields of science. It has a diverse range of clinical applications, the latest of which is its effect on the viral genome. This may prove to be a possible cure for the Covid-19 virus, among others viral infections and chronic diseases.
What is CRISPR?
CRISPR, which stands for Clustered Regularly Interspaced Palindromic Repeats, is essentially a gene-editing tool that has created big changes in biomedical research since its discovery. This technology consists of two main components, which include:
- Cas9: The CRISPR-associated protein 9 is an endonuclease that causes the breakdown of double-stranded DNA, hence promoting gene modification.
- Guide RNA: The Guide RNA allows the CRISPR to successfully match to the target gene and carry out its functions.
CRISPR has a number of clinical applications due to its ability to not only correct gene errors but also turn on or turn off the genes easily in the different cells and organisms. This allows it to be used in numerous cellular and animal models to cause rapid regeneration along with facilitating live imaging of numerous cellular genomes. Studies have also shown CRISPR to allow the repair of defective DNA that can lead to disease development and even cancerous growth, which was demonstrated in mice models. This technology can also be used for gene therapy which includes possible treatment of many infectious conditions, HIV virus, and other chronic diseases.
The Mechanisms of Action of CRISPR/Cas9
The type 2 CRISPR/Cas system consists of an effector DNA endonuclease, known as Cas9. The endonuclease Cas9 is first guided towards its target site by the help of small RNA molecules known as CRISPR RNA and trans-activating CRISPR RNA. Another RNA guide may also be used to enhance the ability of Cas9 to be guided towards its target site, known as Single Guide RNA (SgRNA), which is an artificially produced combination of the two RNA guides.
The target site of the CRISPR-Cas9 system usually consists of a seed sequence that is 20 base pairs long, which is followed by proto-spacer adjacent motifs, which are three base pairs long. After the binding of the Cas9 to its target site by the guidance of the sgRNA, the double-stranded DNA mediated by Cas9 starts to break down. This DNA may be fixed either by the host DNA repair mechanisms or by non-homologous ends joining reaction (NHEJ). This DNA repair caused by the NHEJ allows the possible insertion, deletion, or substitution of genes, which can lead to disruption of virus proteins and their ability to replicate. The inability of the virus to replicate inside the body ultimately causes an anti-viral status inside the body, and the person may then be considered treated. (1)
The Role of CRISPR in Treating Viral Infections
The multiple stages of the life cycle of the virus infecting the body significantly impacts how it may react to the anti-viral medications. Moreover, the ability of the virus to undergo latency causes the infected person to take the anti-viral medication throughout their life, which may greatly disrupt their quality of life. CRISPR technology has proved to be a promising replacement for lifelong anti-viral medications and is gaining more popularity as it continues to show its therapeutic effects against numerous viral infections.
CRISPR-CAS9 system may be used for the treatment of HIV infection, which was previously claimed to be untreatable due to the permanent integration of the virus in the host cells. Due to the ability of the CRISPR/Cas9 system ability to target the HIV-1 genome, it can successfully inactivate the gene expression and replication of this virus in the host cells without causing any toxic effects to the healthy cells. Moreover, this also leads to a possibility of immunization of the body cells against the HIV-1 infection, which may facilitate the eradication of the HIV virus. (2)
Hepatitis B Infection
CRISPR-Cas9 system can also be used for the treatment of Hepatitis B virus and has been a major target for the CRISPR-Cas9 system in previous studies. Even though the Hepatitis B virus is very stable due to its covalently closed circular DNA, the CRISPR-Cas9 system can successfully clear the majority of the virus from the body. By allowing co-transfection of the HBV expressing plasmid, and successful fragmentation of the HBV genome, the system ensures inhibition of Hepatitis B viral replication and the spread of infection in the affected individual. (3)
Hepatitis C Infection
CRISPR-Cas9 system may act as an excellent alternative for the prolonged anti-viral therapy for Hepatitis C infection due to its ability to cause disruption of the HCV genome. Furthermore, due to the ability of this system to cause RNA targeting, it can also lead to inhibition of the HCV RNA genomes activity inside the eukaryotic cells. Studies also showed that only an association between the CRISPR-FNCas9 systems was enough to cause inhibition of the viral translation and replication, and there was no need for direct digestion of the Viral RNAs. (4)
Herpes Simplex Virus
Since the Herpes Simplex Virus Type 1 requires the ICPO viral protein for the stimulation of its gene expression and spread of the virus inside the body, The CRISPR-Cas9 system’s ability to target this protein can promote an anti-viral state in the affected individual. Studies also show its ability to cause a complete reversal of the harmful effects exerted by the HSV-1 virus on the body, which includes the disintegration of promonocytic leukemia nuclear bodies. (5)
CRISPR as a Potential Cure for Covid-19 Virus
The previously investigated therapeutic effects of the CRISPR system for numerous viral infections have led to much discussion about its potential role in the treatment of the new Covid-19 virus and just how effective it can be against the various strains. Recently Abbott et al. proposed a Covid-19 therapy known as the Prophylactic Anti-viral CRISPR in human cells, which is also known as the PAC-MAN theory. Since the investigation showed significant degradation of SARS-COV-2 viral genomic sequences in the human epithelial cells found inside the lungs, it leads to the possibility of the CRISPR System as the new anti-viral therapy against the Covid-19 Virus strains and a possible end to the pandemic. (6)
- Lee C. CRISPR/Cas9-Based Anti-viral Strategy: Current Status and the Potential Challenge. Molecules. 2019;24(7):1349. Published 2019 Apr 5. doi:10.3390/molecules24071349
- Redman M, King A, Watson C, King D. What is CRISPR/Cas9?. Arch Dis Child Educ Pract Ed. 2016;101(4):213-215. doi:10.1136/archdischild-2016-310459
- Sakuma T, Masaki K, Abe-Chayama H, Mochida K, Yamamoto T, Chayama K. Highly multiplexed CRISPR-Cas9-nuclease and Cas9-nickase vectors for inactivation of hepatitis B virus. Genes Cells. 2016 Nov;21(11):1253-1262. doi: 10.1111/gtc.12437. Epub 2016 Sep 23. PMID: 27659023.
- Price AA, Sampson TR, Ratner HK, Grakoui A, Weiss DS. Cas9-mediated targeting of viral RNA in eukaryotic cells. Proc Natl Acad Sci U S A. 2015 May 12;112(19):6164-9. doi: 10.1073/pnas.1422340112. Epub 2015 Apr 27. PMID: 25918406; PMCID: PMC4434742.
- Roehm PC, Shekarabi M, Wollebo HS, Bellizzi A, He L, Salkind J, Khalili K. Inhibition of HSV-1 Replication by Gene Editing Strategy. Sci Rep. 2016 Apr 11;6:23146. doi: 10.1038/srep23146. PMID: 27064617; PMCID: PMC4827394.
- Kumar P, Malik YS, Ganesh B, et al. CRISPR-Cas System: An Approach With Potentials for COVID-19 Diagnosis and Therapeutics. Front Cell Infect Microbiol. 2020;10:576875. Published 2020 Nov 2. doi:10.3389/fcimb.2020.576875