CD4 and neoplasm: CD20xCD3-induced T cell activation was blunted in co-culture with RL tumor cells, as evidenced by weak CD4+ and CD8+ T cell proliferation and relatively modest induction of IFNγ and Granzyme B. These data suggest that tumor-intrinsic factors in addition to target expression level determine the magnitude of CD3 bsAb-induced T cell activation and ultimate cytotoxicity.