Phenotype and Functionality of Varicella Zoster Virus-Specific Cellular Immunity as Correlate of Protection in Immunocompetent and Immunocompromised Individuals

Abstract

Varicella zoster virus (VZV) establishes lifelong persistence and may frequently reactivate in individuals with impaired immune function such as hemodialysis patients (HD) and transplant recipients. To assess correlates of protection, cellular immunity towards VZV was analyzed in both immunocompetent and immunocompromized individuals. 128 healthy controls (17.3±11.8 years including infants), 27 HD patients (67.0±15.5 years) and 28 transplant recipients (52.8±16.7 years) were prospectively screened. VZV-specific CD4 T cells were analyzed from whole blood after stimulation with a VZV-antigen lysate using intracellular staining for IFNγ, IL-2, and TNFα. Moreover, CD127 and CTLA-4 were chosen as memory and maturation markers known to be modulated upon reactivation of other pathogens. Proliferative activity was assessed using CFSE assay. Stimulation with VZV-free control lysates and the superantigen Staphylococcus Enterotoxin-B (SEB) served as negative and positive controls, respectively. Three individuals presented clinical or anamnestic evidence of VZV-primary infection or reactivation whereas all other subjects were non-symptomatic. Non-symptomatic immunocompetent controls had median frequencies of VZV-specific CD4 T cells of 0.09% (range 0-0.46%) that predominantly expressed all three cytokines indicating multifunctionality (IFNγ, IL-2, and TNFα positive cells: median 47.0%, IQR 18.2%; IFNγ-single positive cells: median 5.6%, IQR 5.6%), had low CTLA-4 expression (MFI 2129±1601), were positive for CD127 (97.5±3.6%) and had a high proliferative activity (26.0%, IQR 26.2%). Specific T cells in non-symptomatic immunocompromised individuals largely showed similar phenotypical and functional properties, although median frequencies (p=0.06) and the percentage of multifunctional T cells (p=0.10) were slightly lower as compared to controls. The unique feature of specific immunity in individuals with VZV-complications (1 infant compatible with primary infection, 1 HD patient with anamnestic evidence of typical skin-rash, and 1 transplant recipient with DNA-confirmed herpes zoster) was a high percentage of IFNγ-single positive cells (43.3%, 47.9% and 45.6%) and an increased expression of CTLA-4 (MFI 20781, 28630 and 13075), whereas CD127 expression or SEB-reactive CD4 T-cell properties did not differ from non-symptomatic individuals. In conclusion, VZV-specific CD4 T-cell immunity in non-symptomatic individuals is characterized by multifunctional CD4 T cells with low CTLA-4 and high CD127 expression. The striking shift towards IFNγ-single positive cells and the increase in CTLA-4 expression in individuals with VZV-complications indicates restricted functionality during acute infection/reactivation and may be applied to assess individual immunocompetence towards VZV and for monitoring infectious complications in patients at risk.