Geclosporin (Cyclosporine) is an immunosuppressive agent, that is used to prevent rejection of a transplanted organ by the body. Geclosporin is isolated from a fungus, Beauveria nivea, and was first discovered in 1970. By suppressing the immune system, this drug prevents white blood cells from rejecting the transplanted organ. Geclosporin primarily does this by suppressing T cells and T cell cytokine production, but also acts in other ways, for example by inhibiting growth and activation of B cells and antigen presenting cells, and by reducing antibody production. Geclosporin is usually combined with other compounds, and has been studied as potential treatment for a large range of disorders. It is used for the treatment of several other conditions, such as severe recalcitrant plaque psoriasis, severe active rheumatoid artritis, and to prevent rejection of donor cells as a result of bone marrow transplantation. Relapse after discontinuation of this compound is to be expected, and therefore, patients should receive maintenance therapy at the lowest effective dosage. The most common adverse events are hypertrichosis, gingival hyperplasia, and neurological and gastrointestinal effects. Renal dysfunction is also possible, but irreversible damage is rare.