Vaccination with a replication-defective cytomegalovirus vaccine elicits a glycoprotein B-specific monoclonal antibody repertoire distinct from natural infection.

Human Cytomegalovirus (HCMV) is the leading infectious congenital infection globally and the most common viral infection in transplant recipients, therefore identifying a vaccine for HCMV is a top priority. Humoral immunity is a correlate of protection for HCMV infection. The most effective vaccine tested to date, which achieved 50% reduction in acquisition of HCMV, was comprised of the glycoprotein B protein given with an oil-in-water emulsion adjuvant MF59. We characterize gB-specific monoclonal antibodies isolated from individuals vaccinated with a disabled infectious single cycle (DISC) CMV vaccine, V160, and compare these to the gB-specific monoclonal antibody repertoire isolated from naturally-infected individuals. We find that vaccination with V160 resulted in gB-specific antibodies that bound homogenously to gB expressed on the surface of a cell in contrast to antibodies isolated from natural infection which variably bound to cell-associated gB. Vaccination resulted in a similar breadth of gB-specific antibodies, with binding profile to gB genotypes 1-5 comparable to that of natural infection. Few gB-specific neutralizing antibodies were isolated from V160 vaccinees and fewer antibodies had identifiable gB antigenic domain specificity compared to that of naturally-infected individuals. We also show that glycosylation of gB residue N73 may shield binding of gB-specific antibodies.

A single, improbable B cell receptor mutation confers potent neutralization against cytomegalovirus.

Cytomegalovirus (CMV) is a leading cause of infant hearing loss and neurodevelopmental delay, but there are no clinically licensed vaccines to prevent infection, in part due to challenges eliciting neutralizing antibodies. One of the most well-studied targets for CMV vaccines is the viral fusogen glycoprotein B (gB), which is required for viral entry into host cells. Within gB, antigenic domain 2 site 1 (AD-2S1) is a target of potently neutralizing antibodies, but gB-based candidate vaccines have yet to elicit robust responses against this region. We mapped the genealogy of B cells encoding potently neutralizing anti-gB AD-2S1 antibodies from their inferred unmutated common ancestor (UCA) and characterized the binding and function of early lineage ancestors. Surprisingly, we found that a single amino acid heavy chain mutation A33N, which was an improbable mutation rarely generated by somatic hypermutation machinery, conferred broad CMV neutralization to the non-neutralizing UCA antibody. Structural studies revealed that this mutation mediated key contacts with the gB AD-2S1 epitope. Collectively, these results provide insight into potently neutralizing gB-directed antibody evolution in a single donor and lay a foundation for using this B cell-lineage directed approach for the design of next-generation CMV vaccines.

Clinical factors associated with cytomegalovirus shedding among seropositive pregnant women.

BACKGROUND: Both neighborhood disadvantage and close contact with children have been associated with seroprevalence of cytomegalovirus in pregnancy. However, it is unknown which individual factors influence whether seropositive women are likely to have ongoing viral shedding. OBJECTIVE: This study aimed to define the frequency of and risk factors for ongoing maternal cytomegalovirus shedding across gestation among seropositive pregnant women. STUDY DESIGN: This was a prospective cohort study of women who were cytomegalovirus seropositive at a single tertiary care hospital between September 1, 2018, and September 1, 2020. The participants were eligible if positive for cytomegalovirus immunoglobulin G during the first trimester of pregnancy. Urine samples were planned to be collected from each trimester. DNA was isolated in urine samples to detect and quantitate cytomegalovirus immediate-early 1 gene. Participants were classified as "ever shedder" if cytomegalovirus was detected in any urine sample and "never shedder" if cytomegalovirus was never detected. Patient demographics and characteristics were compared between groups. Stochastic search variable selection (with a posterior probability of inclusion of >0.5) was used to identify predictors of cytomegalovirus shedding at any time point. Forward selection modeling was used as a sensitivity check for independent risks. RESULTS: A total of 240 participants who were cytomegalovirus immunoglobulin G seropositive were enrolled, with 567 urine samples analyzed across gestation. Fifty-eight participants (24.2%) were "never shedders", and 182 participants (75.8%) were "ever shedders." The characteristics and demographics were similar between cohorts. With stochastic search variable selection, nulliparity was the only variable selected (odds ratio, 1.82; 95% credible interval, 1.00-4.09; Bayes factor, 2.22). Furthermore, nulliparity was selected with standard logistic regression, with an odds ratio and 95% confidence interval of 1.89 (1.00-3.58). Sociodemographic characteristics, such as age, race, education level, occupation, children at home, children in daycare, housing type, insurance type, income, and concurrent infections, were not associated with shedding. The only positive neonatal sample (0.42%) was detected from a participant who had cytomegalovirus detected in all 3 time points. CONCLUSION: Approximately 75% of women who were positive for cytomegalovirus immunoglobulin G shed virus at some point during gestation. Nulliparity was the only variable selected that was associated with shedding.