Characterization of a Unique γδ T-Cell Subset as a Specific Marker of Cytomegalovirus Infection Severity

Cytomegalovirus (CMV) is a major infectious cause of death and disease after transplantation. We have previously demonstrated that the tissue-associated adaptive Vδ2neg γδ T cells are key effectors responding to CMV and associated with recovery, contrasting with their innatelike circulating counterparts, the Vγ9posVδ2pos T cells that respond to phosphoantigens but not to CMV. A third Vγ9negVδ2pos subgroup with adaptive functions has been described in adults. In the current study, we demonstrate that these Vγ9negVδ2pos T cells are also components of the CMV immune response while presenting with distinct characteristics from Vδ2neg γδ T cells. In a cohort of kidney transplant recipients, CMV seropositivity was the unique clinical parameter associated with Vγ9negVδ2pos T-cell expansion and differentiation. Extensive phenotyping demonstrated their substantial cytotoxic potential and activation during acute CMV primary infection or reinfection. In vitro, Vγ9negVδ2pos T cells responded specifically to CMV-infected cells in a T-cell receptor-dependent manner and through strong interferon γ production. Finally, Vγ9negVδ2pos T cells were the only γδ T-cell subset in which expansion was tightly correlated with the severity of CMV disease. To conclude, our results identify a new player in the immune response against CMV and open interesting clinical perspectives for using Vγ9negVδ2pos T cells as an immune marker for CMV disease severity in immunocompromised patients.