Antibody binding to native cytomegalovirus glycoprotein B predicts efficacy of the gB/MF59 vaccine in humans

Human cytomegalovirus (CMV) is the most common infectious cause of infant brain damage and posttransplant complications worldwide. Despite the high global burden of disease, vaccine development to prevent infection remains hampered by challenges in generating protective immunity. The most efficacious CMV vaccine candidate tested to date is a soluble glycoprotein B (gB) subunit vaccine with MF59 adjuvant (gB/MF59), which achieved 50% protection in multiple historical phase 2 clinical trials. The vaccine-elicited immune responses that conferred this protection have remained unclear. We investigated the humoral immune correlates of protection from CMV acquisition in populations of CMV-seronegative adolescent and postpartum women who received the gB/MF59 vaccine. We found that gB/MF59 immunization elicited distinct CMV-specific immunoglobulin G (IgG)-binding profiles and IgG-mediated functional responses in adolescent and postpartum vaccinees, with heterologous CMV strain neutralization observed primarily in adolescent vaccinees. Using penalized multiple logistic regression analysis, we determined that protection against primary CMV infection in both cohorts was associated with serum IgG binding to gB present on a cell surface but not binding to the soluble vaccine antigen, suggesting that IgG binding to cell-associated gB is an immune correlate of vaccine efficacy. Supporting this, we identified gB-specific monoclonal antibodies that differentially recognized soluble or cell-associated gB, revealing that there are structural differences in cell-associated and soluble gB are relevant to the generation of protective immunity. Our results highlight the importance of the native, cell-associated gB conformation in future CMV vaccine design.

Multigenerational and Transgenerational Effects of Environmentally Relevant Concentrations of Endocrine Disruptors in an Estuarine Fish Model

Many pollutants cause endocrine disruption in aquatic organisms. While studies of the direct effects of toxicants on exposed organisms are commonplace, little is known about the potential for toxicant exposures in a parental (F0) generation to affect unexposed F1 or F2 generations (multigenerational and transgenerational effects, respectively), particularly in estuarine fishes. To investigate this possibility, we exposed inland silversides (Menidia beryllina) to environmentally relevant (low ng/L) concentrations of ethinylestradiol, bifenthrin, trenbolone, and levonorgestrel from 8 hpf to 21 dph. We then measured development, immune response, reproduction, gene expression, and DNA methylation for two subsequent generations following the exposure. Larval exposure (F0) to each compound resulted in negative effects in the F0 and F1 generations, and for ethinylestradiol and levonorgestrel, the F2 also. The specific endpoints that were responsive to exposure in each generation varied, but included increased incidence of larval deformities, reduced larval growth and survival, impaired immune function, skewed sex ratios, ovarian atresia, reduced egg production, and altered gene expression. Additionally, exposed fish exhibited differences in DNA methylation in selected genes, across all three generations, indicating epigenetic transfer of effects. These findings suggest that assessments across multiple generations are key to determining the full magnitude of adverse effects from contaminant exposure in early life.

Animal Models of Congenital Cytomegalovirus Transmission: Implications for Vaccine Development

Although cytomegaloviruses (CMVs) are species-specific, the study of nonhuman CMVs in animal models can help to inform and direct research aimed at developing a human CMV (HCMV) vaccine. Because the driving force behind the development of HCMV vaccines is to prevent congenital infection, the animal model in question must be one in which vertical transmission of virus occurs to the fetus. Fortunately, two such animal models-the rhesus macaque CMV and guinea pig CMV-are characterized by congenital infection. Hence, each model can be evaluated in "proof-of-concept" studies of preconception vaccination aimed at blocking transplacental transmission. This review focuses on similarities and differences in the respective model systems, and it discusses key insights from each model germane to the study of HCMV vaccines.

2772. HCMV gB Ectodomain Subunit and gB mRNA Vaccines Reduce AD-3 Immunodominance and Elicit More Durable Antibody Responses Than gB/MF59 Immunization

Background

A vaccine to prevent maternal acquisition of human cytomegalovirus (HCMV) during pregnancy is one potential strategy to reduce the incidence of congenital disease. The MF59-adjuvanted glycoprotein B (gB/MF59) protein subunit vaccine is the most efficacious tested to-date, though achieved only 50% efficacy in phase 2 trial. We previously identified that gB/MF59 vaccination elicited poor heterologous virus neutralization and an immunodominant response against non-neutralizing/cytosolic antigenic domain 3 (AD-3) (Figure 1). Thus, we sought novel gB vaccination strategies to improve functional antibody responses and reduce AD-3 immunodominance.

Methods

Groups of juvenile New Zealand White rabbits (n = 6) were administered 3 sequential doses of gB protein with an MF59-like squalene adjuvant IM, gB ectodomain protein (lacking AD-3) + squalene adjuvant IM, or lipid nanoparticle (LNP)-packaged nucleoside-modified mRNA encoding gB ID.

Results

The AD-3 immunodominant IgG response seen in human vaccinees was closely mimicked in rabbits, with 78% of binding antibodies directed against this region in the gB protein group compared with 1% and 46% in the ectodomain and mRNA-LNP-vaccinated groups respectively (Figure 2). All vaccines were highly immunogenic with similar kinetics and comparable peak gB-binding/functional antibody responses. However, both ectodomain and mRNA-LNP-immunized rabbits exhibited enhanced durability of IgG binding to gB protein (P = 0.04 and 0.02, respectively), and the mRNA-LNP group had more durable binding of cell membrane-associated gB (P < 0.001) (Figure 3). Additionally, ectodomain and mRNA-LNP-vaccinated rabbits had increased durability of antibodies targeting neutralizing epitopes AD-4 and AD-5 (P < 0.01). Finally, low-magnitude gB-specific T-cell activity was observed in the gB protein and mRNA-LNP groups, though not in ectodomain-vaccinated rabbits.

Conclusion

Altogether these data suggest that gB ectodomain subunit and gB mRNA-LNP vaccine formulations reduced targeting of non-neutralizing epitope AD-3 and elicited more durable IgG responses than gB protein vaccination. These next-generation HCMV vaccine candidates aiming to improve upon the partial efficacy of gB/MF59 vaccination should be further evaluated in preclinical models.

Disclosures

All authors: No reported disclosures.

2651. Protection Against Human Cytomegalovirus Acquisition Is Associated with IgG Binding to Cell-Associated CMV glycoprotein B in Two Historical gB/MF59 Vaccine Cohorts

Background

Human cytomegalovirus (CMV) is the most common congenital infection worldwide. A CMV glycoprotein B (gB) subunit vaccine with MF59 adjuvant achieved ~50% protection in phase II clinical trials in postpartum and adolescent women. Interestingly, postpartum vaccinees showed poor virus neutralization but robust antibody-dependent cellular phagocytosis (ADCP). In this study, we performed a combined humoral immune correlate of risk analysis in vaccinees to define vaccine-elicited immune responses associated with protection and targets for vaccine candidate immunogenicity.

Methods

gB/MF59 vaccinees who became infected and those who remained uninfected were 2:1 matched on race and number of vaccine doses. This study included 42 women from the adolescent (14 infected, 28 uninfected) and 33 from the postpartum cohorts (11 infected, 22 uninfected). IgG binding to whole gB, gB-neutralizing epitopes, FCRs, and whole virions were assessed by standard or multiplex ELISA. IgG binding to gB mRNA-transfected HEK293Ts was measured by flow cytometry. Neutralization of Towne, TB40/E, and AD169-repaired-GFP strains were measured in MRC-5, BJ5Ta, and/or ARPE-19 cells. Phagocytosis was assessed by THP-1 uptake of fluorescently conjugated TB40/E and AD169-repaired-GFP virions. Multiple linear regression controlling for cohort was performed for the combined log-transformed group data (apriori significance cut-off of P < 0.05, Benjamin–Hochberg FDR < 0.2).

Results

Vaccine-elicited antibodies in adolescent and postpartum cohorts exhibited similar magnitude IgG binding to soluble HCMV gB protein, gB-neutralizing domains, and gB-transfected cells. Autologous Towne strain neutralization was observed in both cohorts, but heterologous strain neutralization was observed only in adolescent vaccinees (P = 0.001). Both cohorts exhibited robust phagocytosis of HCMV virions. Regression analyses revealed that risk of HCMV acquisition in vaccinees was associated with magnitude IgG binding to gB-transfected cells (P = 0.006, FDR = 0.15), not neutralization or phagocytosis responses.

Conclusion

Protection against primary HCMV infection was significantly associated with vaccine-elicited IgG binding to gB-transfected cells, suggesting the importance of a native, cell-associated gB conformation in future vaccine candidates.

Disclosures

All authors: No reported disclosures.