Sensitivity of T cells isolated from HIV-infected individuals to Fas-mediated costimulation in the presence or absence of IL-7. T cells isolated from a group of HIV-infected individuals (n = 5) were activated using 1 μg/mL anti-CD3 Abs combined with anti-Fas or control IgM used at (A) 1-μg/mL or (B) 0.25-μg/mL concentrations. Alternatively, T cells were cultured for 5 days in the presence or absence of 25 ng/mL IL-7 before activation. Proliferation was measured after 4 days of activation using CFSE staining. Different symbols represent individual donors.