Spark Therapeutics shares slide after a setback on its hemophilia gene therapy study

Shares of Spark Therapeutics $ONCE, the most advanced gene therapy company in a growing field, were badly dented this morning after the Pfizer $PFE partner noted that one of 7 patients treated with their hemophilia B treatment experienced an immune response to the viral delivery vehicle they use.

That’s exactly what you don’t want to see in a gene therapy study, especially one this small, and Spark’s shares dropped 17% in a nasty reaction.

Philadelphia-based Spark had been benefitting from strong results it posted for SPK-9001 in May on hemophilia, with three patients demonstrating significantly higher Factor IX levels. And their updated data still look good on that score:

Four of the seven participants had reached greater than 12 weeks post-vector administration at the time of abstract submission; those four participants experienced consistent and sustained Factor IX activity levels, with a mean greater than 30% of normal, with no sustained elevation in liver enzyme levels.

Despite the immune response and a drop in Factor IX levels, the biotech added, the patient who experienced the immune response did not experience any bleeds or require Factor replacement therapy. But that’s not likely to get investors to overlook the setback, which was posted in an abstract for the upcoming ASH conference.

Shares in this field have been heavily influenced by results from tiny numbers of patients as Spark and others try to prove that they have once-and-done treatments for some severe ailments like hemophilia. The comparison has hurt uniQure in the past, though its shares $QURE barely budged this morning.

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VP Oncology Biology
Skyhawk Therapeutics Waltham, MA
Research Scientist - Immunology
Recursion Pharmaceuticals Salt Lake City, UT

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