NSG mice older than 3-4 weeks could be thymectomized with this method. First, mice are weighed and anesthetized using ketamine (100mg/kg, intraperitoneal) and xylazine (10mg/kg, intraperitoneal). Surgeons wear a mask, head cover, clean lab coat and sterile gloves and the surgery is performed under aseptic conditions in a laminar hood to avoid contamination. As the NSG mice are immunodeficient, these measures are very important to prevent any infection.