Tumor-specific T_effs outcompete T_regs during early immune reconstitution. Mice with a 10D established tumor burden were lethally irradiated and received transplants with BM along with T_regs only, T_effs only, or T_regs plus T_effs. Mice were killed 2 weeks after HSCT, and spleens were harvested. CD4⁺ T cell frequency was measured by flow cytometry (A) and absolute CD4⁺ cell numbers were calculated (B). CD4⁺ T-cell frequency as measured by flow cytometry is shown in panel A. Data in panel B represent mean (± SE) of 2–4 mice per group. (P = .1). A total of 50 000 tumor-purged splenocytes were cultured with 200 000 WT splenocytes to serve as APCs. HA peptide was added at the indicated concentrations. Proliferation (C) and IFNγ production (D) were measured as described in “Methods.” P values were calculated using the Student t test. Data in panels C and D represent mean (± SE) of triplicate cultures.