Since NHLs typically express one or more B cell markers, these markers can be used to target antibody-based cytotoxic agents. Although normal B cells will be destroyed, they are repopulated from stem cells lacking the targeted antigens. Alternatively, since B cell tumors are clonal, the immunoglobulin idiotype can be considered a tumor-specific marker. In mice with human lymphoma xenografts, antibodies conjugated to radionuclides, drugs, or toxins can be curative, particularly when combined with other therapies. These immunoconjugates are highly potent in vitro and in mice. However, because they carry a toxic moiety, their safety profile in humans must be carefully established. In the case ofantibody toxin conjugates (immunotoxins, or ITs), these agents have displayed better antilymphoma activity at lower concentrations than did unconjugated antibodies both in vitro