Protective immunity is dependent on CD8⁺ T cells. (A) Groups of mice were vaccinated on days −28 and −14 with DCs loaded with irradiated, mAb-coated tumor cells subcutaneously. On days −6, −5, −4, and 0 and weekly thereafter the animals were depleted of CD8⁺ T cells using mAb HB129 (n = 12), depleted of CD4⁺ T cells using mAb GK1.5 (n = 12), control depleted using control rat Ig (n = 11), or treated with HBSS (n = 9). On day 0, mice were challenged with 5000 38C13 cells subcutaneously. Animals were then followed for survival. Results are representative of 3 individual experiments. (B) In vivo cytotoxicity assay demonstrating the clearance of live tumor cells from vaccinated mice. Groups of 4 mice were vaccinated on days −28 and −14 with either DCs loaded with irradiated, mAb-coated tumor cells (ii,iii) or HBSS (i,iv). On days −6, −5, and −4 animals were depleted of CD8⁺ T cells using mAb HB129 (iii,iv) or control depleted using isotype-matched mAb UPC10 (i,ii). On day 0, mice were injected with 10⁷ CFSE-labeled 38C13 intravenously. After 4 hours, spleens were harvested, pooled, and analyzed via flow cytometry for loss of 38C13 target cells. Histograms depict CFSE-labeled cells from groups of 4 pooled mice; the percentage target cells recovered is indicated.