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Spark’s gene therapy for childhood blindness set for FDA review

The $1 million medicine is coming.

On Thursday, a committee of experts invited by the Food and Drug Administration will meet outside Washington, D.C., to review an experimental gene therapy from Spark Therapeutics. Barring unexpected surprises, the panel will advise the FDA to approve the one-time shot, which will be used to treat a rare, inherited form of childhood blindness.

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It would be the first true gene therapy — meant to replace or repair a defective gene — approved in the United States.

Spark, based in Philadelphia, has not talked publicly about what it will charge for Luxturna, but Wall Street analysts expect the gene therapy to command a $1 million price tag — another first, but not necessarily a welcome one. At a time when drug prices are coming under intense scrutiny, Spark will need to convince insurers, politicians, and pharma critics that Luxturna’s benefit justifies its high cost.

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Like other gene therapies, Luxturna inserts a functional piece of DNA into cells to replace or override a disease-causing gene. For Spark, the injection site is the eyes of people, mostly children and young adults, who have a type of inherited retinal disease caused by a mutation in a gene. People born with the mutation suffer from severe vision problems, including night blindness.

As the disease progresses, people lose all functional vision and can eventually become totally blind. There is no current treatment.

Luxturna is not technically a cure. The surgical injection — one in each eye — aims to halt disease progression and restore some functional vision. Evercore analyst Steven Breazzano calls Luxturna a “genetic flashlight” that helps patients see better at night.

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But the FDA wanted clinical evidence showing that the therapy improves quality of life for patients, beyond just allowing them to see additional letters on an eye chart. So, for the phase 3 clinical trial, Spark devised a mobility test — basically a walk-through maze — that required the 31 patients enrolled to execute the activities of daily life at different light levels.

During the test, patients were required to follow arrows on the floor, make turns, step over objects, go up and down steps, avoid household items, and find and exit through a designated door. Spark reconfigured the maze for each test so patients couldn’t learn to navigate by memory. The goal each time was to determine the lowest light level at which patients could get through the maze successfully.

The results: Patients treated with Luxturna, on average, showed improved light sensitivity equal to nearly 2 lux, or light, levels after one year compared to an average improvement of 0.2 lux levels for control patients. The difference was statistically significant. Seventy-two percent were able to navigate the maze successfully at a lux level of one, which is equivalent to a room illuminated by an indoor night light. None of the control patients was able to do the same.

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The debate at Thursday’s FDA advisory panel is likely to focus on the clinical relevance of Spark’s mobility test to measure functional vision, the durability of effect, and patient selection using genetic testing.

“The expectation is that Spark will get a positive panel vote given the overall totality of the safety and efficacy data,” said Jefferies analyst Michael Yee, adding, “This is an important de-risking event for gene therapy.”

Investors will get their first indication of how FDA feels about Luxturna on Tuesday when the reviewers’ clinical assessment and questions for the panel experts are posted to the agency’s website.

Spark shares are up 75 percent this year to $88, an all-time high. Spark is also developing promising gene therapies for hemophilia A and B, both inherited bleeding disorders.

Other companies working on gene therapy include Cambridge-based Bluebird Bio Inc., BioMarin Inc., and uniQure Inc. Just last week, data about Bluebird’s experimental treatment for a fatal brain disease were published in the New England Journal of Medicine. The study of 17 boys with adrenoleukodystrophy, or ALD, found that the gene therapy can stave off deterioration if it’s given early enough.

The FDA does not consider drug costs as part of its review, so the price tag for Luxturna — whatever that turns out to be — will not be formally discussed at the advisory panel meeting. Still, do not be surprised if the concerns cost cast a shadow over the proceedings.

On average, analysts expect Spark to charge approximately $1 million per patient for Luxturna. There is no precedent in the United States for insurance reimbursement of a one-time “curative” treatment, so the pricing and payment scheme that Spark establishes could have far-reaching impact on other companies like Bluebird Bio, BioMarin, and UniQure.

Adam Feuerstein can be reached at adam.feuerstein@statnews.com. Follow him on Twitter @adamfeuerstein.
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