Tositumomab is a murine monoclonal antibody which targets the CD20 antigen produced in mammalian cell. It was combined with iodine-131 to produce a radiopharmaceutical for unsealed source radiotherapy, Iodine-131 Tositumomab (branded as Bexxar), for the treatment of non-Hodgkins lymphoma. It is classified as a IgG2a lambda antibody. The drug combination was developed by Corixa which was purchased by GlaxoSmithKline in 2005. It was sold for about $25,000 for one round of treatment. Bexxar competed with Zevalin, until the former's discontinuation in 2014.