Haemophilia is a rare blood disorder affecting around 20,000 in the US. In those with the condition, blood fails to clot properly due to a deficiency of a protein known as Factor VIII. Spark’s therapy, known as SPK-8011, reduced bleeds and the need for infusions by 97% when tested in 12 patients in three different dosage levels. In the highest dose, five of seven patients saw Factor VIII levels rise to 30% of normal on average.

However, two of these seven patients responded negatively to the therapy, with their Factor VIII levels dropping to below 5%, and one of the patients experienced a serious adverse event, rendering them hospitalised. The news left shareholders dissatisfied in the drug’s performance, and shares in the company fell by almost a third.

"The clinical and safety profile of SPK-8011 has been highly encouraging, with no FVIII inhibitors observed. Transaminase elevations above the upper limit of normal have been seen in only three of 12 participants, with no evidence of persistent transaminase elevations," said Dr Katherine A High, President and Head of Research and Development at Spark. £We believe, based on the tempo and magnitude of the immune responses observed, that a prophylactic course of steroids will suppress these responses and should lead to long-term expression of FVIII above 12% in all participants at a dose of 2x1012 vg/kg of SPK-8011. We plan to implement this prophylactic approach to steroid administration moving forward.

"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 haemophilia A from the need for regular infusions," she continued.

Despite the issues identified in the trial, Spark confirmed plans to take the highest dose of the therapy through to Phase 3, with a run-in study scheduled for the fourth quarter of this year.

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