PBMCs were incubated with overlapping peptide pools representing all 5 BK virus expressed proteins and analyzed by intracellular cytokine analysis. Panel A shows frequency of BK virus-specific CD8+ T cells expressing single cytokines IFN-γ, TNF-α, and IL-2. Panel B shows frequency of BK virus-specific CD4+ T cells expressing single cytokines IFN-γ, TNF-α, and IL-2. Double asterisk indicates p<0.01, single asterisk indicates p<0.05. Controllers are indicated by triangles, noncontrollers by circles, and patients with low level viremia by grey squares.