Foxp3+ T cells suppress immunotherapy of established tumors. A, Treatment schematic and illustration of cell isolation for adoptive cell transfer into tumor-bearing recipients. B, Flow cytometry showing the percentage of Foxp3+ T cells in sorted CD45.1 Treg and CD45.2 Th cell populations at the single-cell level. C, Treg cells suppress and Th cells help immunotherapy of established tumors. Tumor-bearing RAG-1−/− hosts were treated with pmel-1 CD8+ T cells (1 × 106), rFP vaccine (2.0 × 107 PFU), and either 1 × 106 Th cells or 1 × 105 Treg cells and Th cells (1:10 ratio). Tumor graphs represent the average tumor measurement ± SEM with at least three mice per group. Experiments were repeated independently six times.