CRISPR gene editing

**CRISPR** (clustered regularly interspaced short palindromic repeats) is a family of DNA sequences (called CRISPR-Cas9) found in the genomes of approximately 50% of sequenced bacterial genomes and nearly 90% of sequenced archaea (prokaryotes or single-celled organisms). These sequences are derived from DNA fragments of bacteriophages (viruses that infect and replicate within bacteria and archaea) that had previously infected the prokaryote. They are used to detect and destroy DNA from similar bacteriophages during subsequent infections. Hence these sequences play a key role in antiviral defense systems and provide a form of acquired immunity.

**CRISPR gene editing** is the genetic engineering technique by which the genomes of living organisms may be modified. It is based on a simplified version of the bacterial CRISPR-Cas9 antiviral defense system. By delivering the Cas9 DNA and guide RNA (gRNA) into a cell, the cell's genome can be cut at a desired location, allowing existing genes to be removed and/or new ones added *in vivo* (in living organisms) with extremely high precision, cheaply, and with ease.

The development of the technique earned Jennifer Doudna and Emmanuelle Charpentier the Nobel Prize in Chemistry in 2020.

Base editing, or “CRISPR 2.0”, is a more targeted approach. Instead of simply making cuts to shut off specific genes, scientists can now swap a single DNA base for another. You’re less likely to cut an important gene by mistake, and you can avoid potential errors that may occur when DNA repairs itself after being cut. This has been used in cholesterol-lowering treatment.

Prime editing, or “CRISPR 3.0”, allows scientists to insert chunks of DNA into a genome. If it works in people, it could let scientists replace disease-causing genes.

### Applications

* the creation of new medicines, agricultural products, and genetically modified organisms, and a means of controlling pathogens and pests
* the treatment of inherited genetic diseases as well as diseases arising from somatic mutations such as cancer
* can also be a diagnostic fool; for example SHERLOCK-based Profiling of IN vitro Transcription (SPRINT) which is used to detect a variety of substances, such as metabolites (e.g. antibiotics) in patients, or environmental contaminants.
* the detection  and inactivation of SARS-CoV-2, the virus that causes COVID-19.

However, its use in human germline genetic modification is highly controversial. Many bioethical concerns have been raised about the prospect of using CRISPR for germline editing, especially in human embryos.

### News

* In 2018 a Chinese scientist He Jiankui genetically engineered a human baby using CRISPR editing that was immune to HIV. This was a scientific and bioethical controversy concerning the use of genome editing following its first use in humans, and resulted in He Jiankui being jailed.
* In July 2019, CRISPR was used to experimentally treat a 34-year-old woman with sickle cell disease, a genetic disorder.
* In February 2020, progress was made on HIV treatments with 60-80% of the integrated viral DNA removed in mice and some being completely free from the virus after edits involving both LASER ART, a new anti-retroviral therapy, and CRISPR.
* In March 2020, a CRISPR-modified virus was injected into a patient's eye in an attempt to treat a congenital condition.
* July 2033: CRISPR’d mosquitoes with all-male offspring could help eradicate malaria
* Nov 2023: First trial of VERVE-101 ‘base editing’ in humans lowers cholesterol