Intratumoral T_reg cells suppressed autologous infiltrating CD4⁺CD25^- T-cell proliferation. Isolated CD4⁺CD25^- T cells (A) or CD25-depleted cell suspensions (B) from biopsy specimens of B-cell NHL were labeled with CFSE and cocultured with either CD4⁺CD25^- T cells or CD4⁺CD25⁺ T cells in the presence or absence of PHA for 5 days. CFSE^dim cells were measured as a percentage of the proliferated cells. The histogram shown is representative of 7 and 3 samples for panels B and C, respectively. Patient sample nos. 7 to 9 and nos. 20 to 23 were used in these experiments.