CRISPR technology offers the promise to cure human genetic diseases with gene editing. This promise became a reality when the world’s first CRISPR therapy was approved by regulators to treat patients with sickle cell disease and beta-thalassemia last year.
American biopharma Vertex Pharmaceuticals’ CASGEVY works by turning on the BCL11A gene, which codes for fetal hemoglobin. While this form of hemoglobin is produced before a baby is born, the body begins to deactivate the gene after birth. As both sickle cell disease and beta-thalassemia are blood disorders that affect hemoglobin, by switching on the gene responsible for fetal hemoglobin production, CASGEVY presents a curative, one-time treatment for patients.
As CASGEVY’s clearance is a significant milestone, the technology has come a long way. CRISPR/Cas9 was first used as a gene-editing tool in 2012. Over the years, the technology exploded in popularity thanks to its potential for making gene editing faster, cheaper, and easier than ever before.
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How does CRISPR technology work?
CRISPR is short for clustered regularly interspaced short palindromic repeats. The term makes reference to a series of repetitive patterns found in the DNA of bacteria that form the basis of a primitive immune system, defending them from viral invaders by cutting their DNA.
Using this natural process as a basis, scientists developed a gene-editing tool called CRISPR/Cas that can cut a specific DNA sequence by simply providing it with an RNA template of the target sequence. This allows scientists to add, delete, or replace elements within the target DNA sequence. Slicing a specific part of a gene’s DNA sequence with the help of the Cas9 enzyme, aids in DNA repair.
This system represented a big leap from previous gene-editing technologies, which required designing and making a custom DNA-cutting enzyme for each target sequence rather than simply providing an RNA guide, which is much simpler to synthesize.
CRISPR gene editing has already changed the way scientists do research, allowing a wide range of applications across multiple fields. Here are some of the diseases that scientists aim to tackle using CRISPR/Cas technology, testing its possibilities and limits as a medical tool.
CRISPR for cancer
Cancer is a complex, multifactorial disease, and a cure remains elusive. There are hundreds of different types of cancer, each with a unique mutation signature. CRISPR technology is a game-changer for cancer research and treatment as it can be used for many things, including screening for cancer drivers, identifying genes and proteins that can be targeted by cancer drugs, cancer diagnostics, and as a treatment.
China spearheaded the first in-human clinical trials using CRISPR/Cas9 as a cancer treatment. The study tested the use of CRISPR to modify immune T cells extracted from a patient with late-stage lung cancer. The gene-editing technology was used to remove the gene that encodes for a protein called PD-1 that some tumor cells can bind to to block the immune response against cancer. This protein found on the surface of immune cells is the target of some cancer drugs termed checkpoint inhibitors.
CRISPR technology has also been applied to improve the efficacy and safety profiles of cancer immunotherapy, such as CAR-T cell and natural killer cell therapies. In the U.S., CRISPR Therapeutics is one of the leading companies in this space, developing off-the-shelf, gene-edited T cell therapies using CRISPR, with two candidates – targeting CD19 and CD70 proteins – in clinical trials.
In 2022, the FDA granted Orphan Drug designation to Intellia Therapeutics’ CRISPR/Cas9-gene-edited T cell therapy for acute myeloid leukemia (AML). Currently, Vor BioPharma’s VOR33 is undergoing phase 2 trials to treat AML, and the CRISPR trial is one to watch, according to a report published by Clinical Trials Arena earlier this year.
However, CRISPR technology still has limitations, including variable efficiency in the genome-editing process and off-target effects. Some experts have recommended that the long-term safety of the approach remain under review. Others have suggested using more precise gene-editing approaches such as base editing, an offshoot of CRISPR that hit the clinic in the U.S. last year.
CRISPR for AIDS
There are several ways CRISPR could help us in the fight against AIDS. One is using CRISPR to cut the viral DNA that the HIV virus inserts within the DNA of immune cells. This approach could be used to attack the virus in its hidden, inactive form, which is what makes it impossible for most therapies to completely get rid of the virus.
The first ever patient with HIV was dosed with a CRISPR-based gene-editing therapy in a phase 1/2 trial led by Excision Biotherapeutics and researchers at the Lewis Katz School of Medicine at Temple University in Philadelphia back in 2022.
The decision to move the therapy to the clinic was bolstered by the success of an analog of the drug EBT-101 – called EBT-001 – in rhesus macaques infected with simian immunodeficiency virus (SIV). In a phase 1/2 study, EBT-101 was found to be safe.
Another approach could make us resistant to HIV infections. A small percentage of the world’s population is born with a natural resistance to HIV, thanks to a mutation in a gene known as CCR5, which encodes for a protein on the surface of immune cells that HIV uses as an entry point to infect the cells. The mutation changes the structure of the protein so that the virus is no longer able to bind to it.
This approach was used in a highly controversial case in China in 2018, where human embryos were genetically edited to make them resistant to HIV infections. The experiment caused outrage among the scientific community, with some studies pointing out that the ‘CRISPR babies’ might be at a higher risk of dying younger.
The general consensus seems to be that more research is needed before this approach can be used in humans, especially as recent studies have pointed out this practice can have a high risk of unintended genetic edits in embryos.
CRISPR for cystic fibrosis
Cystic fibrosis is a genetic disease that causes severe respiratory problems. Cystic fibrosis can be caused by multiple different mutations in the target gene CFTR – more than 700 of which have been identified – making it difficult to develop a drug for each mutation. With CRISPR technology, mutations that cause cystic fibrosis can be individually edited.
In 2020, researchers in the Netherlands used base editing to repair CFTR mutations in vitro in the cells of people with cystic fibrosis without creating damage elsewhere in their genetic code. Moreover, aiming to strike again with yet another win is the duo Vertex Pharmaceuticals and CRISPR Therapeutics, which have collaborated to develop a CRISPR-based medicine for cystic fibrosis. However, it might be a while until it enters the clinic as it is currently in the research phase.
CRISPR for muscular dystrophy
Duchenne muscular dystrophy is caused by mutations in the DMD gene, which encodes for a protein necessary for the contraction of muscles. Children born with this disease experience progressive muscle degeneration, and existing treatments are limited to a fraction of patients with the condition.
Research in mice has shown CRISPR technology could be used to fix the multiple genetic mutations behind the disease. In 2018, a group of researchers in the U.S. used CRISPR to cut at 12 strategic mutation hotspots covering the majority of the estimated 3,000 different mutations that cause this muscular disease. Following this study, Exonics Therapeutics was spun out to further develop this approach, which was then acquired by Vertex Pharmaceuticals for approximately $1 billion to accelerate drug development for the disorder. Currently, Vertex is in the research stage, and is on a mission to restore dystrophin protein expression by targeting mutations in the dystrophin gene.
However, a CRISPR trial run by the Boston non-profit Cure Rare Disease targeting a rare DMD mutation resulted in the death of a patient owing to toxicity back in November 2022. Further research is needed to ensure the safety of the drug to treat the disease.
CRISPR for Huntington’s disease
Huntington’s disease is a neurodegenerative condition with a strong genetic component. The disease is caused by an abnormal repetition of a certain DNA sequence within the huntingtin gene. The higher the number of copies, the earlier the disease will manifest itself.
Treating Huntington’s can be tricky, as any off-target effects of CRISPR in the brain could have very dangerous consequences. To reduce the risk, scientists are looking at ways to tweak the genome-editing tool to make it safer.
In 2018, researchers at the Children’s Hospital of Philadelphia revealed a version of CRISPR/Cas9 that includes a self-destruct button. A group of Polish researchers opted instead for pairing CRISPR/Cas9 with an enzyme called nickase to make the gene editing more precise.
More recently, researchers at the University of Illinois Urbana-Champaign used CRISPR/Cas13, instead of Cas9, to target and cut mRNA that codes for the mutant proteins responsible for Huntington’s disease. This technique silences mutant genes while avoiding changes to the cell’s DNA, thereby minimizing permanent off-target mutations because RNA molecules are transient and degrade after a few hours.
In addition, a 2023 study published in Nature went on to prove that treatment of Huntington’s disease in mice delayed disease progression and that it protected certain neurons from cell death in the mice.
CRISPR for blood disorders
With CASGEVY’s go-ahead to treat transfusion-dependent beta-thalassemia and sickle cell disease in patients aged 12 and older, this hints that CRISPR-based medicines could even be a curative therapy to treat other blood disorders like hemophilia.
Hemophilia is caused by mutations that impair the activity of proteins that are required for blood clotting. Although Intellia severed its partnership with multinational biopharma Regeneron to advance its CRISPR candidate for hemophilia B – a drug that was recently cleared by the FDA to enter the clinic – the latter will take the drug ahead on its own.
As hemophilia B is caused by mutations in the F9 gene, which encodes a clotting protein called factor IX (FIX), Regeneron’s drug candidate uses CRISPR/Cas9 gene editing to place a copy of the F9 gene in cells in order to get the taps running for FIX production.
The two biopharmas will continue their collaboration in developing their CRISPR candidate to treat hemophilia A, which manifests as excessive bleeding because of a deficit of factor VIII. The therapy is currently in the research phase.
CRISPR for COVID-19
While healthcare companies were creating polymerase chain reaction (PCR) tests to screen for COVID-19 in the wake of the pandemic, CRISPR was also being put to use for speedy screening. A study conducted by researchers in China in 2023, found that the CRISPR-SARS-CoV-2 test had a comparable performance with RT-PCR, but it did have several advantages like short assay time, low cost, and no requirement for expensive equipment, over RT-PCRs.
To add to that, the gene editing tool could fight COVID-19 and other viral infections.
For instance, scientists at Stanford University developed a method to program a version of the gene editing technology known as CRISPR/Cas13a to cut and destroy the genetic material of the virus behind COVID-19 to stop it from infecting lung cells. This approach, termed PAC-MAN, helped reduce the amount of virus in solution by more than 90 percent.
Another research group at the Georgia Institute of Technology used a similar approach to destroy the virus before it enters the cell. The method was tested in live animals, improving the symptoms of hamsters infected with COVID-19. The treatment also worked on mice infected with influenza, and the researchers believe it could be effective against 99 percent of all existing influenza strains.
The future of CRISPR technology
As European, U.S., and U.K. regulators have given their stamp of approval for the first-ever CRISPR-based drug to treat patients, who is to say we won’t see another CRISPR-drug hitting this milestone in the near future.
And apart from the diseases mentioned, CRISPR is also being studied to treat other conditions like vision and hearing loss. In blindness caused by mutations, CRISPR gene editing could eliminate mutated genes in the DNA and replace them with normal versions of the genes. Researchers have also demonstrated how getting rid of the mutations in the Atp2b2 and Tmc1 genes helped partially restore hearing.
However, one of the biggest challenges to turn CRISPR research into real cures is the many unknowns regarding the potential risks of CRISPR therapy. Some scientists are concerned about possible off-target effects as well as immune reactions to the gene-editing tool. But as research progresses, scientists are proposing and testing a wide range of approaches to tweak and improve CRISPR in order to increase its efficacy and safety.
Hopes are high that CRISPR technology will soon provide a way to address complex diseases such as cancer and AIDS, and even target genes associated with mental health disorders.
New technologies related to CRISPR research:
- CRISPR System for Genome Editing – Tuscan Academic Community
- Methods for Modulating MHC-I Expression in Merkel Cell Carcinoma – Dana-Farber Cancer Institute
- CDC7 Kinase Inhibitor Combination Therapy to Treat Cancer – University of Galway
- Development of an Oral Vaccine using Recombinant Probiotics to Combat the Spreading of COVID-19 Infection – The Chinese University of Hong Kong
This article was originally published in June 2018, and has since been updated by Roohi Mariam Peter.