Refined Assessment of the CMV Infection Status by Determination of CMV Specific T-Cell Immunity in Children with Passive Maternal Antibody Titers

The correct identification of CMV donor and recipient serostatus in children less than 18 months of age is complicated by the variable persistence of maternal CMV antibodies which hampers correct assignment of the actual CMV risk in the setting of transplantation. As adaptive cellular immunity is not passively transferred, this study was carried out to assess whether the presence of CMV specific T cells may represent a more correct parameter to assign the individual CMV status. 166 children below the age of 18 years were analysed. Among those, 59 were < 18 months of age including 29 cord blood samples. In addition, 53 mothers were recruited. Humoral immunity was determined using standard ELISA, CMV specific CD4 T cells were assessed by flow-cytometry after specific stimulation with CMV lysate. Specific T cells were identified based on intracellular accumulation of IFNγ, IL2, and TNFα. CMV-negative control lysates and polyclonal stimulation with staphylococcal superantigen SEB served as negative and positive controls, respectively. In general, CMV-specific T cells mainly produced IFNγ across all age groups, whereas polyclonally stimulated T-cell immunity in cord blood and newborns was dominated by IL2 and TNFα. Among mother, 50.9% (27/53) were seropositive, 54.7% (29/53) had detectable CMV specific T-cell frequencies (median 0.97%, IQR 1.55%), and agreement between both tests was perfect (K=0.92). Likewise, in children above 18 months of age (10.6±4.9 years), 20.6% (22/107) were CMV seropositive, all had detectable CMV specific T-cell frequencies (median 0.33%, IQR 1.82%), and agreement between both tests was perfect (K=1.0). Cord-blood samples had the same serostatus as the mothers (18 negative, 11 positive, K=1.0), while expectedly no CMV specific T cells were detectable. Among the 30 children < 18 months of age, 17 were negative in both tests. Interestingly, among 13 children with a positive serostatus, 8 had detectable CMV specific T-cell immunity indicating true positive infection status, whereas only 5 children were seropositive and T-cell negative indicating passive immunity due to maternal antibodies. In conclusion, the majority of infants (8/13) with CMV specific antibodies already had evidence of true infection, which may indicate that passive CMV immunity in infants below the age of 18 months is overestimated. Thus, the additional determination of CMV specific T cells may allow a refined definition of the true CMV infection status in children where serological testing is limited by the presence of maternal antibodies. Our data may have important implications for refined risk stratification and improved CMV management in infants in the setting of transplantation. In newborns, combined analysis with IL2 and TNFα may help to increase diagnostic accuracy of T-cell analysis.