Establishment and validation of an enzyme-linked immunosorbent assay for IgG antibody against cytomegalovirus based on pp150 antigen.

The development of HCMV vaccines for the prevention of congenital HCMV has been identified as a top priority by the Institute of Medicine (USA), and virus infection is an important endpoint for the efficacy evaluation of the candidate vaccines. However, it is technically difficult to capture the HCMV viremia or uremia in infected individuals because the viremia or uremia can be detected only transiently during acute infection, and most people who are infected are asymptomatic. Thus, it is much desired to develop a serological assay for effectively distinguishing anti-HCMV antibodies as a result of natural infection from those elicited by subunit antigen vaccination. In this study, five HCMV proteins other than antigens commonly used as subunit vaccine candidates were expressed in Escherichia coli and purified, and out of them, the HCMV tegument protein pp150 exhibited the most robust reactivity to seropositive sera and the faintest cross reaction to seronegative sera. With a coefficient of variability less than 15%, an ELISA based on pp150 antigen (pp150-ELISA) showed 100% (366/366) sensitivity and 100% (77/77) specificity (using neutralizing activity as a gold standard) and good quantitative correlation with an in-house ELISA based on virus lysate antigens. Taken together, these results indicate that pp150-ELISA, which has comparable performance to generally used assays based on virus lysate antigens, might provide a simple method to detect HCMV infection or reactivation and could be useful in future HCMV subunit vaccine efficacy trials.