T_regs isolated from transplant recipients maintain their suppressive activity in vitro. Donor mice were prepared as in Figure 4. Tumor-bearing transplant recipients were killed 2 weeks after HSCT, and their spleens were harvested. T_regs were then sorted out of recipients and cultured in vitro with or without CD4⁺-enriched T cells from 6.5/Rag2^−/− mice as responder cells, as described in Figure 4. Proliferation (A) and IL-2 production (B) were measured. Data represent mean (± SE) of triplicate cultures.