CRISPR: On its way to change the world

Introduction

Did you know we can edit the DNA of any living organism? CRISPR-Cas9 (abbreviation for ‘clustered regularly interspaced short palindromic repeats’) is a revolutionary technology able to edit and engineer the DNA of any living organism, being used to treat complex diseases such as AIDS and even cancer. CRISPR makes it possible for scientists to correct errors in a genome and to quickly create cell and animal models, making it easier for researchers to treat genetic and infectious diseases. This gene editing can be done in vivo for cheap but still very precisely and efficiently with the potential of being used in various fields. The technology was developed by biochemist Jennifer Doudna and microbiologist Emmanuelle Charpentier, who received a Nobel Prize in chemistry for their extraordinary invention.

How does CRISPR work?

Researchers are able to edit parts of a genome by removing, adding, or alerting parts of their DNA sequence; this ability could go on to treat and even prevent diseases deemed incurable before, such as infertility. The ground-breaking system works by using two essential molecules, gRNA (guide RNAs) and Cas-9 (CRISPR-associated protein 9). A short pre-designed RNA sequence (approximately 20 bases long) is put inside a longer RNA scaffold, this scaffold binds to the DNA and the pre-designed sequence guides Cas-9 to the targeted area. Cas-9 then causes the DNA to break, acting as a pair of scissors and allowing modifications to be made to the genome.

The system was developed after researchers spotted bacteria using a similar gene-modifying method that acted as an immune system against pathogens. The bacteria broke apart parts of the viruses’ DNA which would be kept behind in case the virus attacked again. If the pathogen did attack the bacteria again, the natural CRISPR system the bacteria developed would be able to recognize the virus which would help the bacteria defend itself. CRISPRs were first recognized in E.coli by Japanese scientist Yoshizumi Ishino and his team in 1987.

Applications and Uses

Antiviral Applications

CRISPR can be used as an antiviral agent against infections such as covid-19 and influenza according to a study conducted by Abbott et al. This is done by using a specific enzyme called Cas13d, and specially engineered guide RNAs (crRNAs) which were made to match parts of the virus's RNA (viruses genetic information). This is the PAC-MAN (Prophylactic Antiviral CRISPR in human cells) strategy. For example, in the case of COVID-19, when the crRNA and Cas13d are introduced into the human lung epithelial cells, the crRNA directs the enzyme to the viral RNAs, where the Cas13d then cuts the SARS-cov-2s RNA and destroys its genetic code which in return effectively stops the virus from reproducing further. No antiviral treatment against SARS-cov-2 directly targets the RNA sequence, could CRISPR-cas13d be the first?

CRISPR can also inhibit dangerous infections such as human immunodeficiency virus type 1 (HIV-1) using the same mechanism used against Covid-19. In a study by Yin et al, Cas13a was found to inhibit HIV-1 by stopping its replication during multiple stages of infection. When HIV-1 infects a cell, it enters inside with a viral capsid which contains a viral RNA. Once inside, the viral capsid breaks open and releases the viral RNA into the cell’s cytoplasm. Guided by a crRNA that binds to the viral RNA, the Cas13a cleaves the RNA and destroys it. This prevents an enzyme called ‘reverse transcriptase’ from conducting a synthesis of DNA from the viral RNA and causing infection. Not only that, but Cas13a can reduce the production of new virions (infective forms of a virus without a host cell) in the late stages of infection. This further proves that CRISPR has a future role in fighting against dangerous infectious diseases such as HIV-1 and Covid-19.

Agricultural Application

Besides its impact on the world of medicine, CRISPR has made headlines in the world of agriculture. Although DNA changes occur in vegetation through the process of selective breeding, CRISPR speeds up that process with precision. The technology allows researchers to give plants valued and desired traits such as a stronger resistance to pests, diseases, and harsh weather conditions through DNA modification. CRISPR has also been shown to improve crop quality and increase crop yield. However, public concern about biodiversity being lost as a result of using gene-modifying technology and strict government policy that requires substantial evidence of efficiency blocks the path for a world of gene-edited vegetables, fruits, and rice.

Real-time use

Enough of what it CAN do, what has it DONE already? In late 2023, the FDA and the UK Medicines and Healthcare Products Regulatory Agency approved the world's first CRISPR-based cure against Sickle Cell disease, named Casgevy. A biopsy needle is inserted into the patient, and stem cells are extracted. These cells have a regulator that blocks the production of Fetal Hemoglobin (A molecule that delivers oxygen to the cells around the body). The stem cells are edited with CRISPR-Cas9 technology, now being able to produce the ex-inhibited molecule. The cells are then infused back into the patient, and the treatment is complete. However, common side effects of the disease are reduced levels of white blood cells and platelet cells which makes the patient susceptible to bleeding and infection, the treatment may also make the patient unable to have children for both men and women. Nonetheless, this shows CRISPR can be approved as a treatment against complex diseases.

Challenges

Although CRISPR has a lot of pros in its usage in medicine and agriculture, it also has its cons. ‘Off-target’ is when a modification is unwanted and unexpected which causes serious adverse effects on the genome. Another cause for concern is unwanted immunogenicity, which is when a therapeutic protein causes an immune response in the body, leading to the treatment possibly becoming ineffective and possibly even causing adverse effects. These two concerns must be taken seriously especially when used in clinical trials. Thankfully, there are strategies that could reduce the potential of off-target effects - making guide RNAs even more specific with different chemical modifications and GC content (percentage of nitrogenous bases that are either guanine or cytosine in an RNA) and by using improved Cas variants. For immunogenicity, CRISPR-Cas9 can be applied in immune-privileged organs, which are the brain, eyes, and testes. These organs have lowered immune surveillance meaning a chance of an immune response is unlikely. This helps mitigate the risk of an attack and helps the stability and longevity of the treatment administered.

Conclusion

CRISPR has proven its potential in the realm of medicine and agriculture. By its simple, inexpensive usage and applications against infectious diseases that affect millions of people around the world such as Sickle cell disease. And its ability to improve crop quality and life. The gene-modifying technology has changed the world and will continue to do so as clinical trials of its use against COVID-19 and HIV-1 launch. However, off-target and immunogenicity effects of the technology must be addressed and solved in the industry as they can pose safety concerns in clinical trials involving humans. The FDA and other health and medicine regulatory organizations need to embrace the new era of gene-editing technology, as CRISPR is on its way to pose as a treatment against some of the most complex diseases humanity faces. It's time we stop being scared, and time we start helping and improving all lives around the world.

Writer: Kiana Danesh Manesh

Editor: Sanjana