CD25⁺ Treg cells induced by NHL tumor cells are suppressive. CFSE-labeled CD25⁻ fraction of PBMCs was incubated with tumor cells in the ratio of 1:4. On day 5, induced CD25⁺ and CD25⁻CD4⁺ fractions (n = 3 patients) were sorted by flow cytometry (A) and stimulated with either anti-CD3/28 or the recall antigen PPD. Histogram illustrates inhibition of proliferation of effector cells (CD25⁻ fraction) on addition of CD25⁺ cells in a ratio of 4:1. (B) Patient 12. (C) Patients 4 and 16. Error bars represent SD.