Zenapax, known generically as daclizumab, is a humanized monoclonal antibody synthesized from a combination of human and mouse antibody structures. It attained FDA approval in 1997.
It is an IL-2 receptor antagonist which suppresses certain IL-2 mediated lymphocyte stimulation, which makes it ideal for mitigating allograft rejection. This (prevention of tissue rejection in transplant patients) is the purpose for which Zenapax was originally developed. Since then, however, it has found uses in treating autoimmune disease, specifically birdshot retinochoroidopathy and multiple sclerosis.
Zenapax has a much more tolerable side effects profile than many other immunomodulators, however in some patients, a serious hypersensitivity reaction can occur.