From which fungus is the immunosuppressant drug cyclosporine derived?

The immunosuppressant drug cyclosporine was derived from the fungus Tolypocladium inflatum. The fungus produces cyclosporin A, a cyclic peptide whose powerful immune-suppressing activity transformed organ transplantation.

The producing strain came from a Norwegian soil sample collected in 1969. It was initially misidentified as Trichoderma polysporum, but mycologist Walter Gams reclassified it in 1971 and named the new species Tolypocladium inflatum. The compound was first isolated in the early 1970s during research that originally focused on finding antifungal agents.

Cyclosporine works mainly by binding to cyclophilin, a protein inside immune cells. This complex inhibits calcineurin, reducing activation of T lymphocytes and production of interleukin-2. The result is suppression of immune attacks against transplanted organs and, in some settings, treatment of autoimmune or inflammatory disease.

The drug entered medical use in the 1970s and was approved for transplantation in 1983. Tolypocladium inflatum is also an insect-pathogenic soil fungus. Its name has remained in pharmaceutical use despite historical proposals involving related or earlier names.