FKBP5 and melanoma: Our group has recently identified a splice isoform of FK506-binding protein 51 (FKBP51, FKBP5) in PBMCs of melanoma patients, generated by an RNA-processing event induced by the co-inhibitory immune-checkpoint PD-L1/PD1 couple of ligand/receptor.7 FKBP51 is an immunophilin firstly cloned in lymphocytes8 and abundantly expressed by immune cells.9 This protein shares with other members of FKBP family proteins the domain of binding to the immunosuppressant agents FK506 and rapamycin.