Cytomegalovirus reactivation following allogeneic stem cell transplantation is associated with the presence of dysfunctional antigen-specific CD8⁺ T cells

Cytomegalovirus (CMV) infection causes significant morbidity and mortality in the setting of immunodeficiency, including the immune reconstitution phase following allogeneic stem cell transplantation (SCT). We assessed CMV-specific CD4⁺ and CD8⁺ T-cell responses in 87 HLA-A*0201-positive (A2+) and/or B*0702-positive (B7+) allogeneic stem cell transplant recipients using HLA-peptide tetramer staining and cytokine flow cytometry (CFC) to examine the association of CMV-specific immune reconstitution and CMV antigenemia following SCT. Strong CMV-specific T-cell responses recovered in most subjects (77 of 87, 88%) after SCT. Frequencies of CMV-specific CD8⁺ T cells were significantly higher in those subjects who experienced early antigenemia relative to those who did not (2.2% vs 0.33%, P = .0002), as were frequencies of CMV-specific CD4⁺ T cells (1.71% vs 0.75%, P = .002). Frequencies of CMV-specific CD8⁺ T cells were also higher in subjects experiencing late antigenemia (2.4% vs 0.57%). When we combined tetramer staining and an assessment of cytokine production in a single assay, we found that individuals who experienced CMV antigenemia had lower tumor necrosis factor-α (TNF-α)-producing fractions of tetramer-staining CMV-specific CD8⁺ T cells than subjects who did not (25% vs 65%, P = .015). Furthermore, individuals at high risk for CMV reactivation, including patients with acute graft-versus-host disease and those receiving steroids, had low fractions of cytokine-producing CMV-specific CD8⁺ T cells (25% and 27%, respectively). These data suggest that the inability to control CMV reactivation following allogeneic SCT is due to the impaired function of antigen-specific CD8⁺ T cells rather than an inability to recover sufficient numbers of CMV-specific T cells.