Association between viability and viable cell yield, revealing differences in quality of thawed PBMC between QAP rounds. Linear regression and 95% confidence interval curves are shown (for data taken from the single-donor PBMC only). In the fifth QAP round, there was a significant correlation between viability and yield for the HIV-negative single-donor specimens (dashed line) (r2 = 0.455; P = 0.046), but it was not significant for the HIV-positive donor specimens (solid line) (r2 = 0.175; P = 0.263); however, overall significance was reached when data from both donors were combined (r2 = 0.289; P = 0.022). Low yield was not associated with viability (uniformly high) in specimens from the seventh QAP round, consistent with improvements in PBMC quality from this round.