In vitro studies demonstrating that mycophenolic acid (MPA) held promi
se as a powerful immunosuppressant led to a series of in vivo studies
to further evaluate this interesting new agent. Experiments in mice sh
owed that MPA had powerful lymphocyte selective immunosuppressive effe
cts. A prodrug of MPA, mycophenolate mofetil (MMF), was developed to i
mprove bioavailability on oral administration. Numerous tests demonstr
ated that MMF, alone or in combination with other immunosuppressives,
prolonged allograft survival of various organs in several species and
may be useful for reversing ongoing rejection. MMF also was found to b
e useful in prolonging xenograft survival. These animal experiments in
dicated that MMF had the benefit of relatively low toxicity and a good
safety profile and drove early clinical trials of MMF. These trials s
howed that MMF is relatively safe and well tolerated in man and is of
potential use for the prevention and treatment of acute allograft reje
ction. This article describes the preclinical history of the developme
nt of MMF, concentrating on the animal experiments and phase I and II
trials that preceded the large-scale clinical testing of this new immu
dosuppressant.