The drugs used to stop rejection of organs that are transplanted in patients have evolved over the decades.
Steroids (GC) were developed very early on in the history of transplantation and are still used today.
Azathioprine was discovered in the 1960's with the experiments of Sir Roy Calne and this really moved transplantation along.
Cyclosprorine, discovered in the 1980's, was instrumental in allowing heart transplantation to be successful, as well as heart-lung transplantation.
Tacrolimus, also known as FK5060, was discovered in the 1990s. Tacrolimus is very similar to cyclosporine in its mode of action, but it has fewer side effects and is better tolerated in liver transplantation.
Mycophenolate Mofetil, introduced in 1995, is similar to azathioprine but does not affect the immune system as severely and is currently used instead of azathioprine in almost all transplant patients.
Sirolimus is the latest drug to have been discovered, in 1999, and its mechanism of action is not really well understood. It is often used late in the clinical course of a transplant patient to prevent or halt chronic rejection.