Regulatory function of CD4⁺CD25⁻ T cells in biopsy specimens of B-cell NHL. CFSE-labeled CD8⁺ T cells were cocultured either alone or with intratumoral CD4⁺CD25⁻ T cells or intratumoral T_reg cells (CD4⁺CD25⁺) in the presence (Stim) or absence (Unstim) of PHA for 3 days. Proliferation of CD8⁺ T cells is measured based on CFSE^dim cells. The figure shown is representative of 3 independent experiments (3 samples) with similar results. Percentages indicate number of proliferated CD8⁺ T cells (CFSE^dim) of just the CD8⁺ cell population.