Cyclosporin A is an immunosuppressive agent, binds to the cyclophilin and then inhibits calcineurin with IC50 of 7 nM, widely used in organ transplantation to prevent rejection.

Cyclosporin A is an immunosuppressant drug that binds cyclophilin D, inhibiting the phosphatase activity of calcineurin in T cells (IC50 = 5 nM).It blocks the transcription of genes involved in T cell activation by interfering with the calcineurin-driven nuclear import of the transcription factor NFAT.Because of its powerful immunosuppressant activity, cyclosporin A has long been used for the prevention of transplant rejection.