FDA panel weighs CRISPR-based sickle cell therapy

• But there still are safety concerns around "off-target" edits that zero in on the wrong genetic sequence and could increase the risk of developing cancer.

How it works: Exa-cel, from Vertex Pharmaceuticals and CRISPR Therapeutics, is a one-time treatment for patients 12 years and older.

• A patient's stem cells are edited to produce high levels of fetal hemoglobin, which can offset the effects of defective hemoglobin produced in patients with sickle cell.
• Black patients account for a disproportionate amount of hospitalizations for sickle cell disease, many younger than 35, federal data show.

Go deeper: FDA staff in briefing documents didn't take issue with the efficacy of exa-cel but questioned if the companies did sufficient analysis to adequately assess the off-target risk.

• Members of the FDA advisory panel on Tuesday said more research would be helpful but expressed confidence that the technology is ready for prime time.

• The panel did not take a formal vote on whether clinical trial results warrant FDA approval.
• "Overall, it's not clear to us that panelists were able to either demonstrate the inadequacy of the approach employed by Vertex-CRISPR or demonstrate the necessity of additional analyses," Leerink analyst Mani Foroohar wrote in a note.

What's next: The FDA must decide whether to approve exa-cel by a Dec. 8 deadline.

• The agency is also set to decide on Bluebird Bio's gene therapy for sickle cell disease by Dec. 20.