Cyclosporine (Immunosuppressive Fungal Metabolite)

Cyclosporine, produced by the soil fungus Tolypocladium inflatum as a natural antifungal/antibiotic compound, found instead to have potent, selective immunosuppressive activity. Borel, Feurer, Gubler & Stahelin (Sandoz), "Biological effects of cyclosporin A: a new antilymphocytic agent" (Agents and Actions 6, 468-475, 1976-07-01, OpenAlex W2080064179, 1,517 citations). Made modern solid-organ transplantation clinically viable by preventing graft rejection -- created the modern transplant-immunosuppression drug market, still generating billions of dollars annually across the drug class it founded. Classified under Chemistry/Biochemistry, not Biology, matching the statins node above.