FOXP3 and neoplasm: Next, in order to study the effect of IDO expression on tumor-infiltrating T cell numbers, we quantified cytotoxic CD8+ T cells, FoxP3+(CD8−) Tregs, proliferating CD8+Ki67+ T cells, proliferating FoxP3+Ki67+(CD8−) T cells (proliferative Tregs), and FoxP3+CD8+ T cells per square millimeters in a representative subset of patients (n = 35) (Figure 5A).