Cyclosporin. Computer graphic showing a molecule of the drug cyclosporin. The cyclic (circular) structure of this hydrophobic peptide molecule is seen here. Atoms are colour-coded: carbon (green); nitrogen (blue); oxygen (red). The atomic skeleton with atomic bonds are depicted as lines. Cyclosporins are a group of biologically active metabolites produced by certain hyphomycetes fungi (Tolypocladium inflatum, Cylindrocarpon lucidum). Cyclosporin A is typically administered as an immunosuppressant drug to reduce the risk of tissue rejection that occurs in organ transplants. Cyclosporin A appears to act mainly on T- lymphocyte cells, and thus has limited toxicity.