This Project focuses on improving antibody based immunotherapy for the treatment of CD20-positive Non-Hodgkin's Lymphoma utilizing two different mechanisms. The first two specific aims will focus on the development of anti-CD20 antibodies as carriers of radioactivity for the purpose of achieving better imaging and more effective treatment of NHL. Although there are soon to be two FDA approved radioimmunotherapeutics for CD20+ NHL, they offer the opportunity to build on their success with reagents specifically designed as carriers of radioisotopes. In the first specific aim, we will develop molecularly engineered antibody fragments for imaging lymphoma, building on our successful experience with engineering CEA antibodies, focusing on diabodies and minibodies which should provide both faster targeting and more rapid clearance from the blood stream thereby providing better images of sites of lymphomatous disease. With the advent of PET scanners, faster targeting reagents are required to take advantage of the general shorter half lives of positron emitting isotopes. Although these agents are being evaluated in solid tumors, this will be the first time they will be investigated in lymphomas, where we hypothesize that they will show improved performance given the different relationship of lymphomas to the vascular supply. Refinements in reagents used for tumor imaging are not only worthwhile as imaging agents in B cell lymphoma but also will verify in the given patient whether the target antigen is present for a range of novel immune directed therapeutics. The second aim focuses on the therapeutic aspect of radioimmunoconjugates, defining by molecular engineering the optimal characteristics for improved radioimmunotherapy. The desired features of the antibody are likely to be different than that for imaging since a longer residence time at the tumor site is needed for better therapeutic applications. The third specific aim deals with the utilizing antibodies to carry immunologic agents to sites of tumor. The success of Rituxan in the treatment of lymphoma confirms the important role of the immune system as an anti-cancer therapeutic. In this project we will conduct laboratory and clinical studies of a RituxanlL-2 fusion protein which has significant pre-clinical therapeutic activity, by harnessing the tumor localization capabilities of the antibody to the cellular potency of IL2 in activating lymphocytes. In the last specific aim, we will conduct clinical trials of a humanized (delmmunized) antiCD20-1L2 immunocytokine to determine the activity of this novel reagent in the treatment of relapsed B cell lymphoma. This aim will provide an important opportunity for additional translational research as the patient studies will allow an in depth exploration of the mechanisms by which the endogenous immune system can be harnessed to destroy lymphoma. These studies will be important for understanding the immune mechanisms necessary for optimal development of effective immune system based therapeutics for lymphoma as well as for other malignancies in humans.