Fig. 2.

Determining the linearity of the Dextramer assay. Titration series were generated from blood samples known to contain CMV-reactive T cells, in order to determine the lowest quantity of CASTs that could be accurately measured when employing Dextramer reagents. Seven different Dextramers were used to quantify the number of CASTs µl⁻¹ at 15 distinct quarter-log dilutions of blood from CAST-positive samples. Whole blood from a validated CAST-negative donor was used to dilute CAST-positive blood samples across three logs of titration. A titratable effect was observed in all cases. Dependent upon the specificity of the Dextramer, the titration point at which a dilution effect could no longer be observed was consistently measured to be ~0.2–0.5% of the undiluted sample. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]