Amplified NKG2C+ NK Cells in Cytomegalovirus (CMV) Infection Preferentially Express Killer Cell Ig-like Receptor 2DL: Functional Impact in Controlling CMV-Infected Dendritic Cells

CMV infection represents a major complication in hematopoietic stem cell transplantation, which compromises graft outcome. Downregulation of HLA class I expression is one mechanism by which CMV evades T cell–mediated immune detection, rendering infected cells vulnerable to killer cell Ig-like receptor (KIR)+ NK cells. In this study, we observed that the amplified NKG2C+ NK cell population observed specifically in CMV seropositive individuals mainly expressed KIR2DL receptors. We have shown that HLA class I expression was downregulated on CMV-infected immature dendritic cells (iDCs), which escape to HLA-A2-pp65–specific T lymphocytes but strongly trigger the degranulation of KIR2D+ NK cells. CMV infection conferred a vulnerability of C2C2+ iDCs to educated KIR2DL1+ and KIR2DL3+ NK cell subsets. Alloreactivity of KIR2DL1+ NK cell subsets against C1C1+ iDCs was maintained independently of CMV infection. Unexpectedly, CMV-infected C1C1+ iDCs did not activate KIR2DL3+ NK cell reactivity, suggesting a potential CMV evasion to KIR2DL3 NK cell recognition. Altogether, the coexpression of KIR and NKG2C on expanded NK cell subsets could be related to a functional contribution of KIR in CMV infection and should be investigated in hematopoietic stem cell transplantation, in which the beneficial impact of CMV infection has been reported on the graft-versus-leukemia effect.