Shares in Spark Therapeutics plunge on disappointing early data for haemophilia A gene therapy SPK-8011

Shares in Spark Therapeutics fell more than 40 percent Monday after the drugmaker announced early-stage data at the American Society of Hematology (ASH) annual meeting for the experimental gene therapy SPK-8011 for the treatment of haemophilia A. According to analysts, the therapy appears to be less effective than a similar one under development by BioMarin Pharmaceutical.

Spark said that it has dosed seven patients in the Phase I/II study, with results showing that among the first four patients, who have been followed up for at least 12 weeks after a single infusion of SPK-8011, the overall annualised bleeding rate (ABR) has been cut from 5.5 annualised bleeds to zero. Additionally, the overall annualised infusion rate (AIR) was reduced approximately 98 percent post-administration.

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Katherine High, head of R&D at Spark, remarked "while still early in the dose-escalation clinical trial of SPK-8011, we are encouraged these data show clinically significant reductions in ABR and AIR with no serious adverse events reported to date." The company added that two other patients were administrated a single dose of SPK-8011 and followed for more than 40 weeks and 30 weeks, respectively. Spark said that one patient achieved a mean factor VIII activity level of 10 percent after week 12, while the level in the second patient was 37 percent.

Spark CEO Jeff Marrazzo, who noted that no patients have experienced blood clots during treatment, cautioned that "further optimisation" is necessary, adding "obviously there's more work to be done in enrolling more patients and creating multiple data sets with more patients at more doses."

Commenting on the findings, Leerink analysts noted that although the enrolment size is small so far in the Spark trial, "early signs raise more caution than encouragement, on balance, and lead us to question whether there will be adequate dose-response for patients to reliably achieve normal factor VIII expression levels." Earlier this week, BioMarin disclosed Phase I/II data at ASH indicating that 11 of 13 patients with haemophilia A who received a single infusion of the experimental gene therapy valoctocogene roxaparvovec achieved normal or near-normal factor VIII levels.

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