Sirolimus (SRL; rapamycin, Rapamune, Wyeth-Ayerst, Princeton, NJ, USA), a macrolide antibiotic produced by the actinomycete Streptomyces hygroscopicus,was isolated from a soil sample in the Vai Atare region of Rapa Nui (Easter Island) [1]. SRL is a 31-membered macrocyclic lactone (molecular weight 914.2; CSIH79N013), which contains an unusual hemiketal masked a/p-diketo amide moiety [2].The first demonstration of SRL's anticandidal and tumoricidal activities was subsequently superseded by the discovery of the drug's potent immunosuppressive effects on allograft rejection [3-6]. However, the mosacteristic of Socumentation of its potent synergism with cyclosporine (CsA; Sandoz, Basel, Switzerland). Studies of the mechanism of action of SRL and CsA in T cells helped to increase the understanding of these drugs' synergism [7].

Keywords: Immunosuppression, Sirolimus