Dysfunctional CMV-specific CD8⁺ T cells are present in individuals experiencing CMV reactivation following SCT.

A combination of HLA-pp65 tetramer staining and cytokine flow cytometry was used to assess the functional fraction of CMV-specific CD8⁺ T cells stratified by the occurrence of CMV antigenemia. (A) Individuals experiencing early CMV antigenemia (ie, prior to post-SCT day +100) had a significantly lower fraction of tetramer-staining CMV-specific CD8⁺ T cells capable of cytokine production following cognate peptide stimulation (○, median 25%) relative to those who did not experience early CMV antigenemia (●, median 65%) (P = .015). (B) Individuals experiencing late CMV antigenemia (ie, after post-SCT day +100) had a significantly lower fraction of tetramer-staining CMV-specific CD8⁺ T cells capable of cytokine production following cognate peptide stimulation (○, median 28%) relative to those who did not experience early CMV antigenemia (●, median 53%) (P = .035). (C) CMV reactivation is associated with a decreased functional fraction of CMV-specific CD8⁺ T cells. Functional fractions of CMV-specific CD8⁺ T cells were stratified by the number of episodes of CMV reactivation occurring prior to day 100 after SCT. A strong trend toward a decreased functional fraction of CMV-specific CD8⁺ T cells was noted between groups of subjects stratified by the number of episodes of CMV antigenemia (● = none, median 64%; ○ = 1 episode, median 38%; ♦ = 2 or more episodes, median 23%). P values are noted for intergroup comparisons, and were attained by the Mann-Whitney test.