ASH19 Gene Therapy Sickle Cell
A colorized microscope of sickle cells (left) and normal red blood cells.Janice Haney Carr/CDC/Sickle Cell Foundation of Georgia via AP

Jason Mast is a general assignment reporter at STAT focused on the science behind new medicines and the systems and people that decide whether that science ever reaches patients. You can reach Jason on Signal at JasonMast.05.

Vertex executives warned that Casgevy, its curative treatment for sickle cell disease, would be slow to reach patients. But few expected it to be this slow.

More than two years after its approval, only about 60 patients across the U.S., Middle East, and Europe have been treated with the gene-editing therapy. Specialists at four sickle centers told STAT they’ve been surprised by one of the key stumbling blocks to faster rollout: They can’t collect enough cells to create the treatment.

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The problem comes at a crucial time for Vertex, which is trying to establish Casgevy even as it fights off rival therapies and braces for a major competitor next year.

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