Increasing line of evidence indicates that the NKG2D-activating receptor plays a relevant role in the effector functions of cytotoxic lymphocytes. In this study, we investigated the expression and function of NKG2D in CD8+ T cells from chronically HIV-1–infected patients with or without antiretroviral therapy (ART).Methods:
We measured by flow cytometry the expression of NKG2D on CD8+ T-cell subsets of ART-naive and ART patients as well as seronegative healthy subjects (HIV-neg). An intrapatient analysis before and after ART initiation was also performed. Results were correlated with viral load, CD4+ T-cell counts, markers of immune activation (CD38, sCD14), and soluble NKG2D ligands (sMICA and sULBP2). The function of NKG2D on CD8+ T cell cytotoxicity was tested by ex vivo degranulation assays.Results:
We showed that NKG2D was downregulated on all CD8+ T-cell subsets of ART-naive patients. The expression of NKG2D on CD8+ T cells inversely correlated with viral load and CD38 expression but not with plasma levels of sMICA and sULBP2. Importantly, we found that NKG2D-mediated costimulation of CD8+ T-cell lytic activity was strongly reduced in ART-naive patients if compared with HIV-neg and ART subjects. Finally, intrapatient analysis demonstrated that effective anti-HIV-1 therapy restores NKG2D expression and NKG2D-induced cytotoxicity by CD8+ T cells.Conclusions:
These data underscore that NKG2D downregulation contributes to impaired CD8+ T-cell responses in untreated HIV-1 infection and have implications for monitoring immune functions and response to treatments, and for the development of novel anti-HIV-1 strategies combining ART with drugs that stimulate NKG2D expression and function.