CD70 is overexpressed on several tumor cell lines but not on normal lymphocytes. Less than 5% of B and T lymphocytes from the peripheral blood of healthy donors express CD70. K562 and K562.70 served as negative and positive controls, respectively. CD70 overexpression was observed on non-Hodgkin (Daudi, Raji, SNK6, and SNT16), Hodgkin (L1236), ALL (CCL-120), and multiple myeloma (U266) cells.