NK and CD8 T cell phenotypes predict onset and control of CMV viremia post-kidney transplant.

Cytomegalovirus (CMV) causes mostly asymptomatic but lifelong infection. Primary infection or reactivation in immunocompromised individuals can be life-threatening. CMV viremia often occurs in solid organ transplant (SOT) recipients and associates with decreased graft survival and higher mortality. Furthering understanding of impaired immunity allowing CMV reactivation is critical to guiding anti-viral therapy and examining CMV's impact on outcomes of SOT. This study characterized longitudinal immune responses to CMV in 31 kidney transplant recipients with CMV viremia and matched, non-viremic recipients. Subjects were sampled three- and twelve-months post-transplant, with additional samples one-week and one-month post-viremia. Peripheral blood mononuclear cells (PBMC) were stained for NK and T cell markers. PBMC transcriptomes were characterized by RNA-Seq. Plasma proteins were quantified by Luminex. CD8 T cell transcriptomes were characterized by single-cell RNA-Seq. Pre-viremia, patients had high levels of IL-15 with concurrent expansion of immature CD56bright NK cells. Post-viremia, mature CD56dim NK cells and CD28- CD8 T cells upregulating inhibitory and NK-associated receptors were expanded. Phenotype of NK cells and CD28- CD8 T cells were associated with control of viremia. These findings suggest signatures of innate activation may be prognostic for CMV reactivation post-transplant, while CD8 T cell functionality is critical for effective control of CMV.