The interaction between PD-1 and B7-H1 is involved in intratumoral T_reg cell-mediated inhibition of CD4⁺CD25⁺ T cells in B-cell NHL. (A) Dot plots showing the expression of B7-H1 and PD-1 on tumor-infiltrating CD4⁺CD25^+/- T cells freshly isolated from B-cell NHL (n = 6). (B) Dot plots showing the expression of B7-H1 on resting (middle) or PHA-activated (right) CD4⁺CD25⁺ T cells (n = 3). (C) Histograms showing the effect of the interaction between B7-H1 and PD-1 on intratumoral T_reg cell-mediated suppression of infiltrating CD4⁺CD25^- T cells in B-cell NHL. CFSE-labeled CD4⁺CD25^- T cells were cocultured either with CD4⁺CD25^- or CD4⁺CD25⁺ T cells in the presence or absence of PHA stimulation for 5 days. Cells in the coculture system were treated with an anti-B7-H1 antibody or PD-1 fusion protein as well as their corresponding controls. The histogram is a representative of 7 samples using the B7-H1 antibody, and of 5 samples using PD-1 Fc. Patient sample no. 11, nos. 15 to 18, and nos. 20 to 23 were used in these experiments.