CD4⁺Foxp3⁺ Tregs from post septic mice suppress antitumor responses in vivo. The immune response in tumor-draining LNs from sham and post septic mice (at day 15 after surgery) was analyzed at day 23 after LLC injection. (A) Comparative assessment of proportion of Foxp3⁺ Treg cells in total viable CD4⁺ T-cell population. (B) Dot plots gated in viable CD8⁺ T cells were analyzed for the intracellular expression of perforin × side scatter (SSC) in tumor-draining LNs from post septic and sham mice bearing tumor or in LNs without tumor. (A-B) Numbers in quadrants indicate percentage of cell types. (C) CD8⁺ gated T cells were analyzed for the expression of perforin in peripheral LNs from post septic and sham mice without tumor implantation. (D) The ratio between tumor-draining LNs, Tregs, and CD8⁺T lymphocytes producing IFN-γ (analyzed after TCR stimulation with anti-CD3/28) was compared between the groups. (C-D) Data represent the mean ± SEM from 5 individual mice per group. (E) Naive CD8⁺ T cells (5 × 10⁵) from C57BL/6 mice were transferred intravenously into C57BL/6 Rag^−/− mice that 20 hours before were transferred with or without 0.9 × 10⁵ CD4⁺ FoxP3⁺ from FoxP3^−eGFP knock-in mice T cells isolated from post septic (A) or sham mice (B). After 16 hours, 0.5 × 10⁶ LLC cells were subcutaneously injected, and the tumor measurements were performed at the indicated time points. Data are representative of 2 experiments with similar results. *P ≤ .05; **P ≤ .01 compared with sham Treg cells transferred in the presence of naive CD8⁺ T cells or only naive CD8⁺ T cells. No differences between the sham Tregs and CD8⁺ T cells or the CD8⁺ T-cell group alone were observed. Horizontal lines indicate comparison between panels A and B, and the comparison between panels A and C.