Spark Therapeutics Inc. said its experimental hemophilia A therapy, SPK-8011, reduced the annualized need for infusions across all 12 participants in its phase I/II study by 97 percent. But negative immune responses in two of 12, one of which sent a patient to the hospital, sent company shares (NASDAQ:ONCE) down about 28 percent on Tuesday. Plans for phase III trials of the treatment are set to begin in the fourth quarter. Meanwhile, shares of competitor Biomarin Pharmaceutical Inc. (NASDAQ:BMRN), which is developing its own gene therapy for the disorder, climbed, rising about nearly 8 percent.