The immunosuppressant action of cyclosporine appears to be due to :

Cyclosporine and tacrolimus acts by inhibiting calcineurin, which is involved in the activation of NFAT. Final result of this process is increased transcription of IL-2 gene. Sirolimus does not inhibit the transcription of IL-2 but interferes with its action. It inhibits the enzyme tyrosine kinase, known as mTOR (which is activated by IL-2).