CD4⁺ T cells mainly mediate the remarkable rejection of second tumor challenge with WEHI3B cells where memory CD44^hiCD4⁺ T subset has an antitumor phenotype on adoptive cell transfer. All mice that had completely rejected the FTC with WGM cells were then subcutaneously inoculated with the STC on day 50 after the FTC, as described in Figure 1 (n = 4-6). For depletion of CD4⁺ and CD8⁺ T cells, mice received repeated intraperitoneal injections of anti–mouse-CD4 mAb or anti–mouse-CD8 mAb on days 3, 4, and 5 before the day of the STC and once every 3 days thereafter up to 13 times. For depletion of NK cells, mice received repeated intraperitoneal injections of rabbit anti-asialo GM1 antiserum 1 day before and 7 and 14 days after the STC. (A) Tumor volume was monitored and (B) a survival curve of the mice groups was examined. (C) For CD4⁺ T-cell ACT therapy, 5 × 10⁵ CD4⁺CD44^low or CD4⁺CD44^hi T cells harvested from spleen of WT/WGM or KO/WGM mice were flow cytometrically sorted on day 3 after the STC and intravenously injected into recipient syngeneic BLAB/c mice (n = 4-6). On the next day, they received subcutaneous challenge with 2 × 10⁵ parental WEHI3B cells in the right flank. Bar graphs represent mean ± SEM. Significant differences: *P < .05, **P < .01. Representative or combined data from 2 independent experiments with similar results are shown.