LDA showing frequency of allo-reactive Treg (CD4+CD25+CD127−) and non-Treg (CD4+CD25−CD127+) populations in normal human blood. Serially diluted, purified Tregs or non-Tregs were stimulated with allogeneic DCs in the presence or absence of exogenous cytokines. Each LDA was performed with a minimum of 10-12 replicates per cell concentration. (A) Log-fraction plot of the LDA of allo-specific Tregs. The slope represents log-active cell fraction, bold lines represent frequency estimates, and non-bold lines show 95% CIs of Tregs calculated based on the likelihood ratio test of single-hit model. (B) LDA validation by testing CFSE− (replicated) or CFSE+ (resting) Tregs. Box plot represents the frequency estimate and the error bar shows 95% CIs calculated by extreme LDA. (C) Box plots show the frequencies of Tregs in the presence or absence of IL-2, IL-2 plus IL-15, and non-Tregs in the presence or absence of IL-2 with 95% CIs. *P < .05; **P < .01; ***P < .001.