Panel A shows the frequency of BK virus-specific CD8+ T cells expressing at least two cytokines simultaneously. Panel B shows the frequency of BK virus-specific CD4+ T cells expressing at least two cytokines simultaneously. Panel C shows frequency of BK virus-specific total polyfunctional CD8+ T cells (sum of double and triple cytokine secreting cells) and total polyfunctional CD4+ T cells. 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. Panel D shows the frequency of the total population of CD8+ or CD4+ T cells secreting IFN-γ, regardless of single, double, or triple-cytokine secretion status.