Anti-G_D2 mAb inhibits growth of FcγRIIB1-positive tumor cells in vitro and in vivo, in an intracytoplasmic-dependent manner. (a) Expression of G_D2 on cells as assessed by flow cytometry using 7A4 or a control isotype (dotted histograms). (b) Inhibition of proliferation of melanoma cells in vitro. Cells (5 × 10³ cells per well) were incubated with the indicated concentrations of anti-G_D2 mAb 7A4 (filled symbols) or control mouse IgG3 (open symbols). ³H-thymidine incorporation rate and percentages of inhibition were measured as described in Figure 5. Each point represents results from three independent experiments performed in triplicate (mean ± SD). (c and d) Inhibition of growth of HT144IIB1 but not of HT144IIB(Cyto^–) tumors in SCID mice injected intravenously with anti-G_D2 mAb. SCID mice were inoculated subcutaneously with 2 × 10⁶ HT144IIB1 (c) and HT144IIB(Cyto^–) (d) cells, followed by biweekly intravenous injections of 50 μg of mAb 7A4 (filled symbols) or PBS (open symbols). Eight mice were used per experiment in each group, and mean tumor volume values, with SD, of mice bearing tumor are shown. *P < 0.05, **P < 0.0001.