Denileukin diftitox, known as Ontak received its FDA approval in 1999 for treatment of T-cell lymphoma. It consists of recombinant diphtheria toxin protein conjugated to IL-2 and was designed to bind to the IL-2 receptor. Ontak was used in leukemia and lymphoma treatment, because it could deliver diphtheria toxin selectively to target cells which expressed interleukin-2 receptors. There have been some studies which showed Ontak could be used for treatment of mycosis fungoides, which is the most common form of cutaneous T-cell lymphoma. Hypersensitivity reactions during the infusion with symptoms such as low blood pressure, back pain, fever, breath shortness, nausea and vomiting, blood test abnormalities and liver problems, weakness, rash and poor appetite are some of the side effects of using Ontak. In 2006 serious problems with loss of vision emerged, and the FDA added a black box warning to the drug labeling include a description of ophthalmologic adverse events. In 2014 marketing of Ontak was discontinued in the USA.