It is produced by the strain of Polypocladiurn inflatum. It has a strong immunosuppressive action, but also has anti-inflammatory and weak antifungal effects. The mechanism of immunosuppression is the combination of cyclosporin A and cyclosporin-binding protein in T cells, which inhibits the activity of Calcineurin, and then impedes the transposition of intracellular transcription factors into the nucleus, and inhibits the interleukin-2 transcription, resulting in immunosuppression. It is mainly used for kidney transplantation, bone marrow and heart transplantation, and is one of the most important immunosuppressive agents in clinical application.