CRISPR << KRIHS puhr >> is part of a biological system in which a microbe modifies its own genetic material to protect itself against infection by viruses. CRISPR can also refer to a method, based on such a system, that scientists use to modify genes and genetic material. Genes are found in all living organisms. Genes carry chemical information that determines the organism’s characteristics. By changing an organism’s genes, scientists can give the organism different traits.
CRISPR systems work like an immune system in many microbes, including bacteria and archaea. When infected with a virus, the microbe captures a piece of the virus’s DNA. DNA stands for deoxyribonucleic acid, the molecule that makes up genetic material. The virus’s DNA is copied into the microbe’s own DNA in a special pattern. Biologists describe this pattern with the phrase Clustered Regularly Interspaced Short Palindromic Repeats, or CRISPR for short. The copied DNA helps the microbe “remember” the invading virus. If the virus infects the microbe again, the microbe copies the DNA pattern into pieces of RNA, a molecule similar to DNA. The RNA guides large molecules called enzymes to the matching DNA sections on the invading virus. The enzymes cut the virus’s DNA apart to destroy it.
Scientists use CRISPR enzymes like scissors to snip DNA at a precise spot. They provide a short piece of RNA to guide the enzymes to the correct location for the cut. They then manipulate a cell’s repair processes to delete, alter, or replace a gene. This method is extremely precise, accurate, and efficient compared with older gene-editing techniques. It requires few components: the “guide” RNA, an enzyme, and, if necessary, DNA to replace an edited gene. CRISPR systems are also easily customized. To modify a system to target a different gene, scientists can simply swap out one RNA sequence for another. If more than one RNA sequence is included, multiple genes can be targeted at once.
CRISPR gene-editing methods are referred to with the name of the enzyme they rely on. For example, the common CRISPR/Cas9 system uses the enzyme Cas9, which is an abbreviation of CRISPR-associated protein 9.
Uses.
Scientists have used CRISPR to introduce specific genetic mutations found in particular diseases into cells or animals that can then be used to study the diseases. Scientists can also use CRISPR to create changes in genes to find which genes or genetic mutations cause specific diseases. CRISPR has been used in genetic engineering to develop varieties of wheat that are resistant to mildew and other diseases, and to breed mosquitoes that do not transmit malaria.
In humans, CRISPR can be used to reprogram immune cells to attack cancer. Another medical application of CRISPR is in gene therapy, a treatment in which healthy genes are delivered into a patient’s cells to replace defective or missing genes. Using CRISPR, scientists can remove a damaged gene or correct a mutation in a gene. If the treatment is successful, abnormal cell functions caused by malfunctioning or missing genes will cease. Scientists think that such treatment could cure an inherited disease.
Medical researchers are also investigating the use of CRISPR to genetically alter pigs to make them more suitable for xenotransplants. In xenotransplants, nonhuman animal organs are used to replace diseased or damaged organs in human beings.
History.
CRISPR systems have been studied since the late 1980’s. Scientists first demonstrated proof of the role of CRISPR in microbe immunity in experiments in 2007. Techniques that use CRISPR to edit genes in human cells were developed several years later. CRISPR systems were quickly adopted by scientists and are now standard tools in laboratories. Scientists have created and shared tens of thousands of templates for guide RNA sequences that can be used with CRISPR. The 2020 Nobel Prize in chemistry was awarded to two researchers who discovered Cas9’s gene-editing abilities, Emanuelle Charpentier of France and Jennifer Doudna of the United States .
CRISPR-based medical treatments made rap id progress in the early 2020’s. Regulatory agencies first approved a CRISPR-based gene therapy in 2023. The treatment, called exa-cel, was approved in the United Kingdom and the United States. Exa-cel is a gene therapy for sickle cell anemia. Medical researchers think the treatment could permanently cure some patients.
Ethical concerns.
Current gene therapy using CRISPR focuses on somatic gene editing. In this process, the changes to DNA are made in somatic cells (body cells) and so cannot be passed on to the next generation. Body cells differ from germ line cells (eggs and sperm). Scientists avoid changing germ line cells in human beings because such changes could be passed down to an individual’s children. However, using gene therapy in germ line cells could potentially cure people of infertility.
Some experts are concerned that modifying the human genome could result in unintended consequences. The human genome is the set of chemical instructions that control heredity in human beings. However, scientists point out that CRISPR has the potential to eliminate many inherited diseases caused by a single malfunctioning gene. These diseases include cystic fibrosis, Huntington’s disease, sickle cell anemia, and Tay-Sachs disease.
In 2018, a Chinese scientist announced that he and his team had used CRISPR to alter the DNA of human embryos produced through in vitro fertilization. The embryos were successfully implanted and resulted in the birth of twin girls. The scientists had used CRISPR to remove a gene called CCR5 from the embryos. Removing this gene is thought to make individuals more resistant to infection by HIV, the virus that causes AIDS. However, the results of this experiment have not been confirmed by other scientists. Scientific authorities throughout the world considered the experiment to be a serious violation of scientific ethics and codes of conduct.
