A Shot of CRISPR Could Restore Sight to the Blind

It’s the first time the gene-editing tool has been used inside the human body

Photo: Rolando Caponi/EyeEm/Getty Images

Scientists have used the gene-editing technique CRISPR in an attempt to restore vision in a patient with a type of inherited blindness, researchers announced last week.

The experimental treatment is meant to snip out a genetic mutation that causes severe visual impairment, often starting at birth. It also marks the first time doctors have used CRISPR directly inside a person’s body. In a few weeks, they hope to know whether the treatment is working. If it works and is safe, it opens up the possibility of using CRISPR against many more conditions.

CRISPR is a powerful technique often likened to molecular scissors for its ability to cut DNA with relative ease. Scientists think it could be applied to a variety of diseases to delete or correct faulty segments of DNA. Repairing DNA at its source could stop or reverse diseases in their tracks rather than just treating symptoms like the vast majority of drugs are designed to do. The hope is that CRISPR could be a one-time, permanent treatment.

It has already been used to treat a handful of people with genetic blood disorders and advanced cancers. In those cases, doctors removed cells from patients’ bodies, used CRISPR to edit the cells in a lab, and infused the edited cells back into patients. So far, that approach looks safe in these studies, but it’s too soon to know how effective it is.

The blindness trial uses CRISPR in a different way. Doctors plan to treat up to 18 adults and children with a particular genetic mutation that causes Leber congenital amaurosis, a rare genetic eye disorder. Many people who have the disorder are legally blind, though some can recognize light or movement. It can be caused by mutations in several genes, but this trial will only target one gene, known as CEP290. Mutations in this gene prevent cells in the retina from making a protein that’s crucial to vision.

The hope is that CRISPR could be a one-time, permanent treatment.

CRISPR is made up of two parts: a cutting protein and a guide molecule programmed to tell the cutting protein what sequence of DNA to cut. The scientists behind this treatment programmed CRISPR to find and slice out the problematic mutation in CEP290. The hope is that cutting out the mutation will kickstart the production of the necessary protein and restore some degree of vision.

Doctors at Oregon Health and Science University injected a few drops of the treatment behind the patient’s retina, and now they must wait. To test vision improvement, the patients will eventually walk through obstacle courses in rooms with different levels of light.

The therapy, developed by Irish pharmaceutical company Allergan and the Cambridge, Massachusetts-based CRISPR startup Editas Medicine, is still in its early stages. For one thing, the investigators don’t know what dose will be enough to restore eyesight. They plan to test three different doses, starting with the lowest dose in older patients with the most profound vision loss. If the first few attempts go smoothly, they will treat more patients. As another precaution, doctors will only treat one eye at first. If the treatment works, people in the trial could get the CRISPR injection in the other eye, too.

Promising as it could be, the treatment comes with risks. One of the biggest is that CRISPR could cause unintended edits elsewhere in the body known as off-target effects. The eye is a good first target for using CRISPR in the body because it’s easily accessible and only requires a short procedure. By directly injecting a small amount of CRISPR in the eye, scientists can ensure that gene editing won’t occur in other body parts.

In the other ongoing CRISPR trials, scientists can confirm they’ve made the right edits to cells in the lab before putting the cells back into the body.

CRISPR could have the power to create a permanent fix for certain diseases, but that also means it could also create permanent DNA damage — something scientists want to avoid at all costs. Despite its promise, scientists are moving cautiously to make sure these treatments are safe and don’t cause any unwanted edits. They may be starting small by focusing on the eye, but what they learn from this research could have big impacts in the years to come.

Former staff writer at Medium, where I covered biotech, genetics, and Covid-19 for OneZero, Future Human, Elemental, and the Coronavirus Blog.

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