Opexa Therapeutics, Inc. (NASDAQ: OPXA ) today announced the execution of an agreement with Merck Serono, a division of Merck, Darmstadt, Germany, for the development and commercialization of Tcelna^™ (imilecleucel-T), a potential first-in-class personalized T-cell therapy for patients suffering from multiple sclerosis (MS). Tcelna (imilecleucel-T) is being developed by Opexa and currently is in