written by: Sarah Ning
The applications of CRISPR are endless with people genetically engineering spicy tomatoes, creating faster race horses, eradicating malaria, and even turning pigs into organ donors for humans! In this blog post, three applications of CRISPR will be covered: treating cancer, de-extinction, and editing human embryos.
1. Treating cancer with CRISPR
The first clinical trial of treating cancer with CRISPR in the United States was conducted in 2019. Using CRISPR, scientists were able to test a type of cancer immunotherapy, where the patient’s own immune system is genetically modified to fight against tumour cells. Using a process known as T cell infusion, a sample of blood is first taken from the patients to extract their T cells, which are molecules that can be found on certain cancer cells. Their T cells are then genetically engineered using CRISPR to fight the cancer cells in their bodies. First, a NY-ESO-1 receptor, a claw-shaped protein that binds to NY-ESO-1, is inserted into the T cells. This allows the edited T cell to bind to the cancer cells. Next, three gRNAs are inserted into the T cells to remove the TRAC, TRBC, and PDCD1 genes. The TRAC and TRBC genes could interfere with the NY-ESO-1 receptor, while the PDCD1 gene limited the cells’ antitumor immunity. After genetically modifying the T cells, they are amplified before getting infused back into the patient. These CRISPR-edited T cells are now able to attack and kill the tumour cells by binding onto them with their NY-ESO-1 receptor.
2. De-extinction
De-extinction is the process of generating an organism that has gone extinct, and can be thought of as bringing organisms “back from the dead”. Some conservation scientists argue that our focus should be on preserving the currently endangered organisms, rather than trying to bring back past organisms. Regardless, experiments have already begun, with scientists bringing back the extinct passenger pigeons.
Passenger pigeons were once the most abundant bird in North America; however, overhunting led them to extinction in 1914. The rise of CRISPR sparked interest in the possibility of bringing back these birds, and scientists have begun the early trials of editing the extinct passenger pigeons’ genes so they can be inserted into the existing band-tailed pigeons’ cells. A major reason for these de-extinction of the passenger pigeon is to support the eastern America’s woodland biodiversity.
Scientists are able to genetically engineer a library of digital and physical genetic codes, which will be used to edit the genomes of the band-tailed pigeons. After extracting germ cells from the band-tailed pigeon embryo, CRISPR-Cas9 will cut out DNA at designated target sites in the genome and replace it with those of passenger pigeons using homology directed repair. These edited cells are then put into the band-tailed pigeon embryos through a process called germ-line transfer, which is when DNA is transferred into the gonads, allowing the altered gene to be passed down through generations. These embryos will then develop into a germline chimera, meaning that its reproductive cells will contain a portion of the engineered cells containing passenger pigeon DNA, while the rest of the pigeon contains the band-tailed pigeon DNA. To form individuals containing purely the engineered pigeon DNA, two germline chimera must mate and have offspring. However, since their reproductive cells only contain a portion of the edited cells, they will produce either pure band-tailed pigeons, band-tailed-passenger pigeon hybrids, or the newly formed de-extinct passenger pigeon.
3. Editing human embryos
You’ve likely heard of the concept of creating “designer babies” in the future, and now with CRISPR, this possibility may not seem so far-fetched. In fact, Chinese researcher Dr. Jiankui He has already edited the genomes of human embryos. His experiment involved taking embryos created through in vitro fertilization, with the stated goal of providing them immunity from HIV. This process involved disabling the CCR5 gene using CRISPR, which would result in a nonfunctional cell receptor that prevents HIV from entering cells, thereby protecting the embryos against HIV infection. Twins Lulu and Nana were born from these genetically modified embryos, thus making them the world’s first gene-edited babies. There are plans to monitor the twins over the next 18 years to observe the long-term effects.
However, altering one gene can cause unintended effects on other genes. The CCR5 gene that was disabled is not only associated with HIV, but may also play a role in cognitive functions. In an experiment where scientists disabled the CCR5 gene in mice, results concluded that the mice had enhanced memory. It is hypothesized that the mutated CCR5 gene will also have an effect on the cognitive abilities of the twins, but it is uncertain whether that will be beneficial or detrimental in the long run. As well, the removal of the CCR5 gene has been reported to increase the risk of complications and death from other viral infections, including West Nile virus and influenza.
Though groundbreaking, Dr. He’s experiment was extremely controversial as he violated many academic ethical standards, causing scientists to call for a global moratorium on CRISPR. In fact, Dr. He has been recently sentenced to three years in jail, showing how polarizing this topic is.
Despite this though, the experiment has opened the possibility for a future where wealthy parents are able to select desired traits for their “designer babies”, enhancing characteristics such as height, eye colour, and even intelligence. As a result, there has been debate surrounding the capabilities and limitations of CRISPR gene editing: What should be allowed? Where do we draw the line? Tune in next week to read more on the ethical issues surrounding CRISPR!
Glossary
Immunotherapy: a treatment that boosts the body's natural immune system to fight cancer.
T cells: a type of white blood cell that helps protect the body from infection and may help fight cancer.
Receptor: chemical structures composed of protein that receive and send signals that cause biological responses.
Antitumor immunity: the innate and adaptive immune responses which lead to tumor control.
Amplify/amplification: replication of genetic material to produce millions of copies.
Germ cells: a reproductive cell of the body. Germ cells in females are egg cells and are sperm cells in males.
Embryo: an organism in an early stage of development. In humans, this lasts from conception to the eighth week of pregnancy.
Gonads: an organ that produces gametes; a testis or ovary.
Hybrids: the offspring of parents that are of different breeds, varieties, species or genera
HIV: stands for human immunodeficiency virus. HIV is a virus that attacks the body's immune system, and if left untreated, can lead to AIDS (acquired immunodeficiency syndrome). There is currently no effective cure.
In vitro fertilization: a method of assisted reproduction where egg and sperm are combined in the laboratory to form embryos.
Moratorium: the temporary period of suspension/delay of an activity.
References
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