Harvesting of cell sheets When the endoscopists approximate that there is 40 minutes left of the ESD the investigators will put the dishes in a 20°C incubator for 30 minutes. The cell sheets will be transferred to a support membrane and transplanted to the esophageal ulcer by endoscopic forceps. A light pressure will be applied to improve attachment. Depending on the size of the ulcer, several cell sheets will be transplanted in the described manner.