Total CMV-specific CD4⁺ and CD8⁺ T-cell responses in donors, recipients before HSCT, and recipients after HSCT. CD4⁺ (top panel) and CD8⁺ (bottom panel) T-cell responses are shown in donors (green), recipients before HSCT (red), and recipients after HSCT (yellow). After stimulation for 6 hours, the frequency of CMV-specific memory T cells was calculated using all possible Boolean combinations (where at least a single response was present) of cytokines (MIP-1β, IL-2, TNF-α, and IFN-γ) and CD107a expression for each ORF, and the total frequency was determined by the summation of responses to the 19 ORFs for both CD4⁺ and CD8⁺ subsets (after background subtraction). *Patients who received a DLI.