Figure 4. CD4⁺ T cells are necessary for optimal tumor protection. (A and B) Tumor-bearing mice were injected with anti-CD4 depleting antibodies (GK1.5) on day 33, 39 and 45 and treated with CD45.1⁺ wtNKG2D-expressing or chNKG2D-expressing T cells on day 35. (A) Eight weeks after tumor-cell injection, the number of solid tumors on the peritoneal wall and number of tumor cells in the peritoneal wash was assessed. (B) Spleen and peritoneal cells were isolated from mice 8 weeks after tumor cell injection and cultured for 24 h. Cell-free supernatants were then assessed for the presence of interferon γ (IFNγ). (C) Tumor bearing mice were injected with anti-CD4 depleting antibodies on day 33 and then treated with T cells on day 35. Peritoneal cells were harvested 7 d after T-cell transfer and CD45.2⁺CD8b⁺ cells were assayed for IFNγ expression by flow cytometry. Cumulative data of two independent experiments are shown. The average of each group and SD (n = 8) are shown (*p < 0.01; ***p < 0.001 as compared with mice receiving wtNKG2D-expressing T cells; ^†p < 0.05 as compared with non-depleted mice receiving chNKG2D-expressing T cells).