CRISPR will straighten red blood cells

Americans used CRISPR for the first time to treat a genetic disease

Svetlana Yastrebova, N+1

For the first time, a US citizen participates in clinical trials of CRISPR therapy for a hereditary disease. A resident of Missouri, Victoria Gray, was injected with her own blood stem cells for the treatment of a severe form of sickle cell anemia, the genes of which are edited so that the descendants of these cells can produce a special form of hemoglobin. In total, up to 45 people can participate in these tests.

Sickle cell anemia is a disease in which mutant hemoglobin S is formed in erythrocytes. Compared to ordinary hemoglobin A, it tolerates oxygen worse. The red blood cells that are filled with it are deformed: they resemble a sickle, not a biconcave disk. In addition, they live less than normal red blood cells. Sickle cell anemia provides some protection against malaria, this disease weakens a person, manifesting itself in frequent pain, hypoxia and increased fatigue. The disease is especially common among residents of Africa, as well as India and the Mediterranean, since their red blood cells are more resistant to infection with malaria plasmodium, and in these areas malaria is common.

The life expectancy of patients with severe sickle cell anemia is reduced compared to the norm. In theory, this anemia can be cured if the precursors of red blood cells are provided with a normal version of the hemoglobin gene. However, the effectiveness and safety of this method have not yet been tested.

The company Vertex and CRISPR Therapeutics, which specialize in creating therapies based on genome editing, have begun clinical trials of editing the genome of blood stem cells ex vivo to combat severe sickle cell anemia. As part of the new method, a part of the patient's own blood stem cells is taken from the patient, a mutant version of the hemoglobin gene is corrected using CRISPR/Cas9 (it differs from the normal one by only a few pairs of nucleotides) and then these cells are returned to the patient's body.

So far, this procedure has been performed on one person – 34-year-old Victoria Gray from Forrest, Missouri. If the therapy does not give severe side effects and helps her, the editing will be repeated to another person. If successful, ten more volunteers are planned to join the trials, and the total number of participants can be increased to 45. It is planned to complete the current stage by May 2022.

Victoria is being treated at the Sarah Cannon Research Institute in Nashville, Tennessee. Tests can also be carried out in other hospitals in the United States, as well as in several hospitals in Canada, Belgium, Germany and Italy.

In February 2019, the same companies launched a similar genome editing study using CRISPR/Cas9 to combat another hereditary blood disease, beta-thalassemia. It is also due to be completed in May 2022, and the number of possible participants there is the same as in the CRISPR trials against sickle cell anemia. But in this case, the patients are citizens of Canada, Germany and the UK.

CRISPR Therapeutics and Vertex are not the first to conduct clinical trials of CRISPR technology. Earlier, at the Hangzhou Cancer Hospital in China, where the legislation in many biomedical matters is not as strict as in the West, 16 patients with esophageal cancer were injected with their immune cells with the PD1 gene switched off using CRISPR at late stages. The tests ended on February 28, 2018, but their results have not yet been published. In addition, in early 2019, the University of Pennsylvania received permission to test the effectiveness and safety of genome editing in myeloma.

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