A macrolide isolated from the fungus Streptomyces tsukubaensis. Tacrolimus binds to the FKBP-12 protein and forms a complex with calcium-dependent proteins, thereby inhibiting calcineurin phosphatase activity and resulting in decreased cytokine production. This agent exhibits potent immunosuppressive activity in vivo and prevents the activation of T-lymphocytes in response to antigenic or mitogenic stimulation. Tacrolimus possesses similar immunosuppressive properties to cyclosporine, but is more potent. Check for "https://www.cancer.gov/about-cancer/treatment/clinical-trials/intervention/C1311" active clinical trials using this agent. ("http://ncit.nci.nih.gov/ncitbrowser/ConceptReport.jsp?dictionary=NCI%20Thesaurus&code=C1311" NCI Thesaurus)