FK-506, a novel immunosuppressant isolated from a Streptomyces. II. Immunosuppressive effect of FK-506 in vitro.

The immuno-pharmacological profile of a novel immunosuppressive agent, FK-506 produced by a streptomycete, is presented here. We proceeded to test the effect of the agent on various in vitro immune systems. It showed that mixed lymphocyte reaction, cytotoxic T cell generation, the production of T cell-derived soluble mediators such as interleukin 2 (IL-2), interleukin 3 and gamma-interferon and the expression of the IL-2 receptor were suppressed by this agent. The IC50 values of FK-506 and ciclosporin (CS) in all tests were approximately 0.1 nM and 10 nM, respectively. Therefore, the novel agent, FK-506 suppressed in vitro immune systems at about hundred times lower concentration than CS.