Cyclosporin A: Cyclosporin A (CsA) is a non-polar cyclic oligopeptide metabolite from the fungus Tolypocladium inflatum. It has too narrow a spectrum of antifungal activity to be very useful as an antibiotic, but it possesses potent immunosuppressive properties, affecting primarily Tlymphocytes. It has been shown to inhibit the functioning of several nuclear proteins involved in T-cell activation at the level of mRNA transcription. Cyclosporin is the primary tool used to prevent rejection following solid organ and bone marrow transplantation. It forms a complex with its intracellular receptor cyclophilin, which can then bind to calcineurin, inhibiting its enzymatic activity. CsA was found to suppress the replication of hepatitis C virus genome in cultured hepatocytes.