Intravenous gene therapy

Editing with CRISPR/Cas was first tested intravenously

Polina Loseva, N+1

Six patients easily underwent genetic editing of the liver using CRISPR/Cas. All of them suffer from transtiretin amyloidosis, a disease in which the protein transtiretin accumulates in vital organs. Just a month after the start of therapy, the concentrations of transthyretin in their blood decreased by 50-90 percent, and there were no serious side effects. So the researchers demonstrated that CRISPR therapy can be administered intravenously – and it finds its target. The trial report is published in The New England Journal of Medicine (Gillmore et al., CRISPR-Cas9 In Vivo Gene Editing for Transthyretin Amyloidosis).

Despite the fact that the CRISPR/Cas genetic editing system is very popular among molecular biologists, it is still used with caution in medicine. Basically, CRISPR editing is used to correct something in the blood cells isolated from the patient's body - for example, to make them resistant to HIV or make them produce the "correct" version of hemoglobin - and then return it back to the bloodstream.

It is theoretically much more risky to run "molecular scissors" inside the body – at the same time, it is important to check that CRISPR/Cas has made the necessary edits to the DNA and has not made unnecessary ones. Therefore, until now, in vivo genetic editing has been used only in a relatively isolated organ from the bloodstream – inside the eye. The patient was injected under the retina, but it was assumed that CRISPR/Cas would not go beyond the organ.

Now Julian Gilmore (Julian Gillmore) from University College London and his colleagues from the companies Intellia Therapeutics and Regeneron Pharmaceuticals for the first time tested CRISPR/Cas on the whole body – that is, they injected "molecular scissors" directly into the blood, intravenously.

Hereditary transthyretin amyloidosis became the target for repair. This is a disease during which the protein transtiretin (normally it is needed to transport the hormone thyroxine and vitamin And by blood) is improperly coagulated and forms aggregates in the heart, kidneys and peripheral nerves. It is possible to cure this disease once and for all only by transplanting the liver – since it produces almost all the transthyretin. You can also try to ban transthyretin from aggregating or stopping its synthesis in cells (for this, the first drug based on RNA interference was approved in the USA) – but then you will have to drink medicines all the time. Genetic editing could solve the problem once and for all by cutting the transtiretin gene from DNA in liver cells.

Gilmore and colleagues selected six patients with hereditary amyloidosis for the first phase of the trial, who were not treated with RNA interference and already showed symptoms of polyneuropathy in the form of loss of sensitivity. There were four men and two women among them, and they had amyloidosis caused by three different mutations. All of them were given a single dose of the drug – lipid nanoparticles with guide RNA and mRNA for the Cas9 protein, aimed at penetrating liver cells. Three received a small dose, three received a larger dose. The doctors then monitored the concentration of transthyretin in the patients' blood for 28 days.

In three of the six trial participants, doctors noticed adverse reactions to therapy – but all of them turned out to be mild and were not associated with the dose of the drug. In five patients, the concentration of D-dimer in the blood increased (one of the signs of thrombosis), but by the end of the first week after the injection, the indicators returned to normal. Therefore, the researchers considered their therapy safe.

Two weeks and a month after the injection, the authors noticed that the concentration of transthyretin in the blood of the subjects decreased. By day 28, in the group with a lower dose – by an average of 52 percent, and in the group with a higher dose – by 87 percent. One of the patients from the second group had 96 percent less transthyretin.

The concentration of transthyretin in the blood of patients after injection of low (A) and high (B) doses of the drug. A drawing from an article by Gillmore et al.

The authors plan to continue monitoring their patients for at least a year. Despite the fact that they did not have serious side effects, and preclinical tests on cells and monkeys showed that accidental edits in the genome should not occur, the safety of therapy in humans has yet to be confirmed. In addition, it will be necessary to check that the decrease in transthyretin levels is constant – only then it will be possible to talk about the treatment of amyloidosis. So far, researchers have demonstrated only the fact that intravenous injection of CRISPR/Cas can be effective and, at least at first, safe.

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