CD4⁺CD25⁺ cells isolated from HIV-infected patients are hyporesponsive/anergic to polyclonal and antigen-specific stimulation. (A) Purified CD4⁺CD25^– (□) or CD4⁺CD25⁺ (▪) T cells (1 × 10⁵ each) were stimulated for 3 days with 5 μg/mL plate-bound anti-CD3 mAb in the presence or absence of soluble anti-CD28 mAb (5 μg/mL). (B) Freshly purified CD4⁺CD25^– (□) or CD4⁺CD25⁺ (▪) T cells (1 × 10⁵ each) were cultured for 5 days with 5 μg/mL purified tuberculin (PPD), 5 μg/mL p24, or 1:50 dilution of the CMV antigen. [³H] thymidine (0.5 μCi/well [0.0185 MBq]) was added during the last 16 hours of culture. Results are expressed as median [³H] thymidine incorporation from 8 HIV-infected patients (P < .05 for all of the antigens studied).