David L. Hallal has been appointed chief executive officer of Alexion Pharmaceuticals, effective April 1, 2015. Mr. Hallal currently serves as chief operating officer and is director of the board. He will succeed Leonard Bell, M.D., who will retire and continue to serve as chairman. Dr. Bell was the principal founder of Alexion in 1992 and has served as chief executive officer for the past 23 years.   Mr. Hallal has more than 25 years of experience in the biopharma industry. He joined the compan...