Statistical modeling of the expansion/persistence kinetics of adoptively transferred CMV- and EBV-specific T cells and the presence of viral loads in the follow-up period after T-cell product infusion. Positive CMV or EBV viral loads were detected after infusion of T-cell products in 5 out of 13 patients and 8 out of 20 patients that received a T-cell product containing CMV- or EBV-specific T cells, respectively. Smoothed Loess curves were plotted to study the association between viremia and expansion/persistence kinetics of adoptively transferred CMV- and EBV-specific T cells. Kinetics of the numbers of product–derived CMV-specific T cells that were only detected after T-cell product infusion (A) or both before and after infusion (B) are shown for patients with a positive CMV viral load during follow-up (solid line) and without detectable viral loads in the follow-up period (dashed line). Product–derived EBV-specific T cells that were only detected after infusion (C) or both before and after infusion (D) are shown for patients with a positive EBV viral load during follow-up (solid line) and without detectable viral loads (dashed line).