Retuxin is an. Antibody directed against cd-20, which marks b-lymphocytes. So, the "biotherapy" destroys b cells with this marker, and many lymphomas have this characteristic. Iodine 125 and yttrium 90 have been bonded to form the products Bexxar (tositumomab) and zevlin to deliver targeted bioradiotherpy to b cell tumors. Rituximab has also been used in rheumatoid arthritis. It works; it's expensive.