Antitumor effect of bispecific CD3x19 in xenotransplanted SCID mice. (a) 10⁷ Raji Burkitt lymphoma were injected subcutaneously together with 10⁷ activated T cells. CD3x19 and anti-CD28 (clone 15E8) were injected intraperitoneally at the same time (b) 10⁷ Nalm-6 cells were injected intraperitoneally. Activated T cells (10⁷), CD3x19, and anti-CD28 were injected intraperitoneally 24-hours later. ▵, tumor cells alone; □, tumor cells plus monospecific control antibodies (anti-CD19 [HD37] plus anti-CD3 [OKT3], 100 μg each as single dose); ○, tumor cells plus CD3x19 (200 μg single dose); •, tumor cells plus CD3x19 (200 μg single dose) plus anti-CD28 (clone 15E8, 50 μg single dose).