FK-779

Chemical immunosuppression developed at the beginning of clinical transplantation remains the basis of immunosuppressive protocols used today. Clinical trials of new agents focus on the incremental improvement in one of four areas of immunotherapy: induction, basic maintenance, adjuvant and steroid therapy. Induction immunotherapy developments include the use of humanized antibodies, specific targets (basiliximab, daclizumab) and lymphocyte depletion (anti-thymocyte globulin, campath-1H). Promising results from pilot trials allow for subsequent low dose maintenance monotherapy. New inhibitors of calcineurin isoforms (ISATx247) may disassociate the anti-rejection effect from the toxicity of conventional calcineurin inhibitors. Revived investigation of older anti-proliferative or anti-metabolite drugs (rapamycin, mycophenolic acid, leflunomide) show promise in preventing B-cell responses and reducing chronic rejection but development of derivatives (everolimus, mycophenolate mofetil, ERL 080, MNA 279, MNA 715) may have a stronger commercial than experimental basis. Trials of steroid immunotherapy have focused on steroid elimination but trial of newer locally active steroids may be beneficial.

Immunosuppression is currently the major approach used for the prevention and management of transplant rejection. In this overview, preclinical and clinical studies of the small molecule immunosuppressive agents are reviewed from the discovery of cyclosporine. More recently it was demonstrated that certain agents, namely tacrolimus (FK506), sirolimus (rapamycin), and mycophenolate mofetil (CellCept, MMF), act selectively on adaptive host responses at different stages of T- and B-cell cycles and spare nonspecific host resistance. Because each agent has its specific and significant toxic effects, it has been difficult to optimize the use of individual agents in monotherapy. Therefore, drug combination therapy has been of great interest in addition to the introduction of new small molecule agents, such as malononitrilamides [MNAs (leflunomide, FK778, FK779)], 15-deoxyspergualin (DSG) and its analogues, FTY720 and inhibitors of signal transduction, which offer promising modes of immunosuppression.