All in vivo procedures were conducted in accordance with UK Home Office regulations [Animals (Scientific Procedures) Act of 1986, Home Office Project License number PPL 70/7349, Dr. Isabelle Leclerc]. Procedures were performed at the Central Biomedical Service at Imperial College, London. Isolation of islets from multiorgan donors was approved by the local ethics committee at the University of Pisa. Human pancreata were collected from brain-dead organ donors after informed consent was obtained in writing from family members. Use of human islets at Imperial College was approved by the local NRES Committee, Fulham; REC reference 07/H0711/114.