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FDA staff raises concerns over lack of safety data for sickle-cell treatment

A sign for the Food And Drug Administration is seen outside of the headquarters on July 20, 2020 in White Oak, Maryland. (Sarah Silbiger/Getty Images/TNS)  (Sarah Silbiger)
By Gerry Smith Bloomberg

The Food and Drug Administration’s staff raised concerns about safety data on a potential gene-editing treatment for sickle cell disease, ahead of a closely watched meeting where scientific experts will weigh the first therapy using CRISPR technology.

FDA advisers are preparing to meet Oct. 31 to consider and discuss an application from Vertex Pharmaceuticals Inc. and CRISPR Therapeutics AG to use a CRISPR-based treatment for people with the painful blood disorder.

CRISPR makes precisely targeted changes in DNA that researchers are trying to use to repair flaws in patients’ genomes related to inherited disease. It isn’t clear if the genetic diversity of patients studied by the companies in their safety analysis “is sufficient to adequately assess” the risk that the treatment would make unintended changes in patients’ DNA, the FDA staff said Friday in a report, or that it can “adequately capture variants in this population across the United States.”

The report also published data from a clinical trial by the companies that found 93.5% of subjects met the primary endpoint, which was freedom from pain crisis for 12 months after treatment.

Shares of Vertex were unchanged at the New York market open, while CRISPR Therapeutics stock rose less than 1%.

Sickle cell is an inherited disease where patients have red blood cells that are inefficient and misshapen, leading to clogged blood vessels and painful crises when tissues fail to get enough oxygen. Two partners, Vertex Pharmaceuticals Inc. and CRISPR Therapeutics AG, are seeking approval to edit the genes of people with sickle cell disease so that they make a different, oxygen-carrying form of hemoglobin.

The treatment promises potential relief – and possibly a cure – for the condition that affects some 100,000 Americans, most of whom are Black. The life expectancy of people who have sickle cell disease and are covered by Medicaid and Medicare is about 53 years, according to a study published in July in a journal of the American Society of Hematology.

The condition occurs when people inherit faulty genes that make a flawed version of hemoglobin. Sometimes described as a genetic scissors, CRISPR can excise flaws in DNA that cause such diseases.

The technology has been heralded as a way to eliminate genes linked to cancer, blood disorders and blindness.

Yet regulators have viewed it with caution, citing the risk that alterations that may go beyond the treatments’ intended targets.

Some health advocates have also said the expected high cost of the one-time treatments threatens to leave out patients who can’t afford them.

In the experimental procedure, the companies remove blood stem cells, edit them in lab using Crispr and then infuse them back into patients’ bodies.

The FDA advisory committee will meet to evaluate the data and hear company presentations. The FDA itself makes the final decision on whether to clear the therapy for sale.

The FDA has set aside almost two hours to discuss concerns and provide recommendations for the gene-editing technique, according to meeting documents published Friday. No vote has been scheduled, according to the draft agenda.

—With assistance from Bill Haubert and Fiona Rutherford.