Spark slides on hemophilia A data, aims for phase 3

red blood cells
Spark plans to start phase 3 trials of the highest dose of its hemophilia A gene therapy later this year. (Arek Socha)

Spark Therapeutics’ hemophilia A gene therapy reduced bleeding by 97% in a phase 1/2 trial, building on data reported in December that suggested it may not be as potent as a rival in development at BioMarin.

The study tested three different doses of the treatment, SPK-8011, which is designed to remedy hemophilia A patients’ deficiency of clotting factor VIII. Two patients received a dose of 5 x 1011 vector genomes (vg)/kg body weight, three received 1 x 1012 vg/kg and seven received 2 x 1012 vg/kg. Four weeks after treatment, all three groups had twin 97% decreases in annualized bleeding rate and in annualized infusion rate.

Five of the seven patients on the highest dose had 100% reductions in bleeding rate and infusion rate. The treatment also boosted their factor VIII levels, on average, to 30% of normal. The Philadelphia-based biotech will move this dose into phase 3, starting with a run-in study slated to begin in the fourth quarter, Spark said in a statement.


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But the data aren’t perfect; the treatment triggered an immune response in the remaining two patients that dropped their factor VIII levels to less than 5% of normal. One of the patients didn’t respond to oral steroids and had to be hospitalized. Spark was down about 30% before the market opened Tuesday.

RELATED: Spark’s hemophilia A data causes investor jitters

To avoid this kind of immune response in the future, Spark will add prophylactic oral steroids to its treatment, said Spark President and R&D chief Katherine High, M.D.

“These early data further support the dramatic impact on patient outcomes that can result from factor activity levels above 12% and bring us closer to our goal of one day eliminating spontaneous bleeding altogether, while potentially freeing patients with hemophilia A from the need for regular infusions,” High said.

RELATED: A transplant of CRISPR-edited liver cells could replace lifelong injections for hemophilia B patients

People with hemophilia A need lifelong treatment, which includes regular infusions of factor VIII or a clotting promoter that raises their factor VIII levels. Treatments can be expensive and time-consuming, and because they require an injection, patient adherence can become an issue. A gene therapy would be a game changer in the space.

Spark is playing catch-up to BioMarin, whose own hemophilia A gene therapy is in phase 3. At two years after infusion with BioMarin’s Valoctocogene Roxaparvovec, patients’ average factor VIII levels were at 59%, outperforming Spark’s SPK-8011. However, the average factor VIII levels at one year postinfusion were close to double that, at 104% of normal, suggesting that the treatment’s efficacy wanes over time.

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