CD8 T cells were required for antitumor efficacy, while the role of CD4 T cells depended upon the source of adoptively transferred T cells. (A) Experimental design for these studies: A/J mice were treated as depicted in Figure 1A, some mice were treated with in vivo–depleting anti-CD8 or anti-CD4 mAb (250 μg intraperitoneal) on days −1, 2, 5, and 8 before and after HSCT. (B) Depletion of CD8 cells in hosts given adoptive T-cell transfer with tumor-sensitized T cells resulted in significantly decreased tumor-free survival rates (P < .0001) compared with historical treatment groups from Figure 1D (Sen T and Sen T + Vac). (C) Depletion of CD4 cells in hosts given naive T-cell transfer resulted in significantly worse tumor-free survival compared with a historical group from Figure 1D (Naive T + Vac; P = .035). Depletion of CD4 cells in hosts given tumor-sensitized T cells resulted in better tumor-free survival compared with historical treatment groups from Figure 1D (Sen T and Sen T + Vac). The survival differences between the nonvaccinated and vaccinated groups did not reach statistical significance. The data for the antibody-treated groups represents the combined results of 2 to 3 independent experiments, except for the Naive T + anti-CD4 + Vac group, which is from 1 experiment. Each group consisted of 5 to 15 total mice.