Characterization of humoral and cellular immunologic responses to an mRNA-based human cytomegalovirus vaccine from a phase 1 trial of healthy adults.

mRNA-1647 is an investigational mRNA-based vaccine against cytomegalovirus (CMV) that contains sequences encoding the CMV proteins glycoprotein B and pentamer. Humoral and cellular immune responses were evaluated in blood samples collected from healthy CMV-seropositive and CMV-seronegative adults who participated in a phase 1 trial of a three-dose series of mRNA-1647 (NCT03382405). Neutralizing antibody (nAb) titers against fibroblast and epithelial cell infection in sera from CMV-seronegative mRNA-1647 recipients were higher than those in sera from control CMV-seropositive samples and remained elevated up to 12 months after dose 3. nAb responses elicited by mRNA-1647 were comparable across 14 human CMV (HCMV) strains. Frequencies of antigen-specific memory B cells increased in CMV-seropositive and CMV-seronegative participants after each mRNA-1647 dose and remained elevated for up to 6 months after dose 3. mRNA-1647 elicited robust increases in frequencies and polyfunctionality of CD4+ T helper type 1 and effector CD8+ T cells in samples from CMV-seronegative and CMV-seropositive participants after stimulation with HCMV-specific peptides. The administration of three doses of mRNA-1647 to healthy adults elicited high nAb titers with wide-breadth, long-lasting memory B cells, and strong polyfunctional T-cell responses. These findings support further clinical development of the mRNA-1647 vaccine against CMV.IMPORTANCECytomegalovirus (CMV), a common virus that can infect people of all ages, may lead to serious health problems in unborn babies and those with a weakened immune system. Currently, there is no approved vaccine available to prevent CMV infection; however, the investigational messenger RNA (mRNA)-based CMV vaccine, mRNA-1647, is undergoing evaluation in clinical trials. The current analysis examined samples from a phase 1 trial of mRNA-1647 in healthy adults to better understand how the immune system reacts to vaccination. Three doses of mRNA-1647 produced a long-lasting immune response, thus supporting further investigation of the vaccine in the prevention of CMV infection.CLINICAL TRIALSRegistered at ClinicalTrials.gov (NCT03382405).

Cytokine responses to major human Cytomegalovirus antigens in mouse model.

Human cytomegalovirus (CMV) continues to be a source of severe complications in immunologically immature and immunocompromised hosts. Effective CMV vaccines that help diminish CMV disease in transplant patients and avoid congenital infection are essential. Though the exact roles of defense mechanisms are unidentified, virus-specific antibodies and cytokine responses are known to be involved in controlling CMV infections. Identifying the CMV antigens that trigger these protective immune responses will help us choose the most suitable CMV-related proteins for future vaccines. CMV envelope glycoprotein B (UL55/gB), matrix proteins (UL83/pp65, UL99/pp28, UL32/pp150), and assembly protein UL80a/pp38 are known to be targets for antiviral immune responses. We immunized mice intraperitoneally with these five CMV-related proteins for their ability to induce specific antibody responses and cytokine production in a mouse model. We observed a significant CMV-antigen-specific antibody response to UL80a/pp38 and UL83/pp65 (E/C>2.0). Mice immunized with UL80a/pp38 had significantly higher concentrations of GM-CSF, IFN-γ, IL-2, IL-4, IL-5, and IL-17A (p<0.05). Mice immunized with UL83/pp65 showed significantly higher concentrations of GM-CSF, IFN-γ, IL-2 IL-4, IL-10, IL-12, IL-17A, and TNF-α. Ratios of Th1 to Th2 cytokines revealed a Th1 cytokine bias in mice immunized with UL80a/pp38, UL83/pp65, UL32/pp150, and UL55/gB. We suggest that stimulation with multiple CMV-related proteins, which include UL80a/pp38, UL83/pp65, UL32/pp150, and UL55/gB antigens, will allow both humoral and cellular immune responses to be efficiently activated, thus serving as appropriate CMV antigens for future novel vaccines and immune-based therapeutic design.

An enveloped virus-like particle alum-adjuvanted cytomegalovirus vaccine is safe and immunogenic: A first-in-humans Canadian Immunization Research Network (CIRN) study.

INTRODUCTION: Cytomegalovirus (CMV) is the most common cause of congenital infection and affected children often have permanent neurodevelopmental sequelae, including hearing loss and intellectual disability. Vaccines to prevent transmission of CMV during pregnancy are a public health priority. This first-in-humans dose-ranging, randomized, placebo-controlled, observer-blinded study evaluated the safety and immunogenicity of an enveloped virus-like particle (eVLP) vaccine expressing a modified form of the CMV glycoprotein B (gB). METHODS: Healthy CMV-seronegative 18 to 40-year-olds at 3 Canadian study sites were randomized to one of 4 dose formulations (0.5 µg, 1 µg, or 2 µg gB content with alum) or 1 µg gB without alum, or placebo, given intramuscularly on days 0, 56 and 168. Outcome measures were solicited and unsolicited adverse events (AE), severe AE, gB and AD-2 epitope binding antibody titers and avidity, and neutralizing antibody (nAb) titers to CMV measured in fibroblast and epithelial cell infection assays. RESULTS: Among 125 participants, the most common solicited local and general AEs were pain and headache, respectively. A dose-dependent increase in gB binding, avidity and nAb titers was observed after doses 2 and 3, with the highest titers in the alum-adjuvanted 2.0 µg dose recipients after the third dose; in the latter 24 % had responses to the broadly neutralizing AD-2 epitope. Neutralizing activity to CMV infection of fibroblasts was seen in 100 % of 2.0 µg alum-adjuvanted dose recipients, and to epithelial cell infection in 31 %. Epithelial cell nAb titers were positively correlated with higher geometric mean CMV gB binding titers. CONCLUSIONS: An eVLP CMV vaccine was immunogenic in healthy CMV-seronegative adults and no safety signals were seen. Alum adjuvantation increased immunogenicity as did higher antigen content and a three dose schedule. This phase 1 trial supports further development of this eVLP CMV vaccine candidate.

Vaccine value profile for cytomegalovirus.

Cytomegalovirus (CMV) is the most common infectious cause of congenital malformation and a leading cause of developmental disabilities such as sensorineural hearing loss (SNHL), motor and cognitive deficits. The significant disease burden from congenital CMV infection (cCMV) led the US National Institute of Medicine to rank CMV vaccine development as the highest priority. An average of 6.7/1000 live births are affected by cCMV, but the prevalence varies across and within countries. In contrast to other congenital infections such as rubella and toxoplasmosis, the prevalence of cCMV increases with CMV seroprevalence rates in the population. The true global burden of cCMV disease is likely underestimated because most infected infants (85-90 %) have asymptomatic infection and are not identified. However, about 7-11 % of those with asymptomatic infection will develop SNHL throughout early childhood. Although no licensed CMV vaccine exists, several candidate vaccines are in development, including one currently in phase 3 trials. Licensure of one or more vaccine candidates is feasible within the next five years. Various models of CMV vaccine strategies employing different target populations have shown to provide substantial benefit in reducing cCMV. Although CMV can cause end-organ disease with significant morbidity and mortality in immunocompromised individuals, the focus of this vaccine value profile (VVP) is on preventing or reducing the cCMV disease burden. This CMV VVP provides a high-level, comprehensive assessment of the currently available data to inform the potential public health, economic, and societal value of CMV vaccines. The CMV VVP was developed by a working group of subject matter experts from academia, public health groups, policy organizations, and non-profit organizations. All contributors have extensive expertise on various elements of the CMV VVP and have described the state of knowledge and identified the current gaps. The VVP was developed using only existing and publicly available information.

Safety, efficacy, and immunogenicity of a replication-defective human cytomegalovirus vaccine, V160, in cytomegalovirus-seronegative women: a double-blind, randomised, placebo-controlled, phase 2b trial.

BACKGROUND: A vaccine that prevents cytomegalovirus (CMV) infection in women could reduce the incidence of congenital CMV infection, a major cause of neurodevelopmental disability. We aimed to assess the safety and efficacy of a replication-defective investigational CMV vaccine, V160, in CMV-seronegative women. METHODS: This phase 2b, randomised, double-blind, placebo-controlled study was conducted at 90 sites in seven countries (USA, Finland, Canada, Israel, Spain, Russia, and Australia). Eligible participants were generally healthy, CMV-seronegative, non-pregnant, 16-35-year-old women of childbearing potential with exposure to children aged 5 years or younger. Participants were randomly assigned using central randomisation via an interactive response technology system 1:1:1 to one of three groups: V160 three-dose regimen (V160 at day 1, month 2, and month 6), V160 two-dose regimen (V160 on day 1, placebo at month 2, and V160 at month 6), or placebo (saline solution at day 1, month 2, and month 6). The primary outcomes were the efficacy of three doses of V160 in reducing the incidence of primary CMV infection during the follow-up period starting 30 days after the last dose of vaccine using a fixed event rate design, and the safety and tolerability of the two-dose and three-dose V160 regimens. We planned to test the efficacy of a two-dose regimen of V160 in reducing the incidence of primary CMV infection only if the primary efficacy hypothesis was met. Analyses for the primary efficacy endpoint were performed on the per-protocol efficacy population; safety analyses included all randomly assigned participants who received study vaccine. The primary efficacy hypothesis was tested at prespecified interim and final analyses. The study was ongoing and efficacy data continued to accrue at the time of final testing of the primary efficacy hypothesis. Vaccine efficacy was re-estimated after final testing of the primary efficacy hypothesis based on all available efficacy data at end of study. This trial is registered at ClinicalTrials.gov (NCT03486834) and EudraCT (2017-004233-86) and is complete. FINDINGS: Between April 30, 2018, and Aug 30, 2019, 7458 participants were screened, of whom 2220 were randomly assigned to the V160 three-dose group (n=733), V160 two-dose group (n=733), or placebo group (n=734). A total of 523 participants in the V160 three-dose group and 519 in the placebo group were included in the final hypothesis testing. Of these, there were 11 cases of CMV infection in the V160 three-dose group and 20 cases in the placebo group. The vaccine efficacy for the V160 three-dose group was 44·6% (95% CI -15·2 to 74·8) at the final testing of the primary efficacy hypothesis, a result corresponding to failure to demonstrate the primary efficacy hypothesis. On the basis of this result, the study was terminated for futility. The re-estimate of vaccine efficacy for the V160 three-dose group based on all available efficacy data at end of study (556 participants in the V160 three-dose group and 543 in the placebo group) was 42·4% (95% CI -13·5 to 71·1). A total of 728 participants in the V160 three-dose group, 729 in the V160 two-dose group, and 732 in the placebo group were included in the safety analyses. The most common solicited injection-site adverse event was injection-site pain (680 [93%] in the V160 three-dose group, 659 [90%] in the V160 two-dose group, and 232 [32%] in the placebo group). The most common solicited systemic adverse event was fatigue (457 [63%] in the V160 three-dose group, 461 [63%] in the V160 two-dose group, and 357 [49%] in the placebo group). No vaccine-related serious adverse events or deaths were reported. INTERPRETATION: V160 was generally well tolerated and immunogenic; however, three doses of the vaccine did not reduce the incidence of primary CMV infection in CMV-seronegative women compared with placebo. This study provides insights into the design of future CMV vaccine efficacy trials, particularly for the identification of CMV infection using molecular assays. FUNDING: Merck Sharp & Dohme, a subsidiary of Merck & Co, Rahway, NJ, USA (MSD).

Characterization of epitopes of human monoclonal antibodies against cytomegalovirus glycoprotein B for neutralization and antibody-dependent phagocytosis.

As congenital cytomegalovirus (CMV) infections are the leading non-genetic cause of sensorineural hearing loss and significant neurological disabilities in children, the development of CMV vaccines should be given the highest public health priority. Although MF59-adjuvanted glycoprotein B (gB) vaccine (gB/MF59) is safe and immunogenic, its efficacy in terms of protection from natural infection was around 50 % in clinical trials. Although gB/MF59 induced high antibody titers, anti-gB antibodies contributed little to the neutralization of infection. Recent studies have found that non-neutralizing functions, including antibody-dependent phagocytosis of virions and virus-infected cells, are likely to play important roles in pathogenesis and vaccine design. Previously, we isolated human monoclonal antibodies (MAbs) that reacted with the trimeric form of gB ectodomain and found that preferential epitopes for neutralization were present on Domains (Doms) I and II of gB, while there were abundant non-neutralizing antibodies targeting Dom IV. In this study, we analyzed the phagocytosis activities of these MAbs and found the following: 1) MAbs effective for phagocytosis of the virions targeted Doms I and II, 2) the MAbs effective for phagocytosis of the virions and those of virus-infected cells were generally distinct, and 3) the antibody-dependent phagocytosis showed little correlation with neutralizing activities. Taking account of the frequency and levels of neutralization and phagocytosis, incorporation of the epitopes on Doms I and II into developing vaccines is considered desirable for the prevention of viremia.

Optimizing age specific strategies of vaccination for prevention of cytomegalovirus infection in the US using agent-based simulation.

BACKGROUND: There is an urgent need to develop a cytomegalovirus (CMV) vaccine as it remains the leading cause of birth defects in the United States. While several CMV vaccine candidates are currently in late-stage clinical trials, the most effective vaccination program remains an open research question. METHODS: To take into account the critical uncertainties when evaluating the vaccine impact on both vertical (congenital) and horizontal CMV transmissions, we developed a CMV agent-based model representative of the US population and contact network structures. RESULTS: We evaluated 648 vaccination scenarios under various assumptions of vaccination age, vaccine efficacy, protection duration, and vaccination coverage. The optimal age of vaccination under all scenarios is shown to be during early childhood. However, a relatively modest benefit was also seen with vaccination of females of reproduction age (around age of 25) assuming near universal coverage and long vaccine-mediated protection. CONCLUSIONS: This study highlights the important need for a pediatric vaccination program in mitigating CMV in the United States. Our model is poised to investigate further location-based vaccine effectiveness questions in future planning of both clinical trials as well as eventual program implementation.

Investigation into the use of gamma irradiated Cytodex-1 microcarriers to produce a human cytomegalovirus (HCMV) vaccine candidate in epithelial cells.

V160 is a viral vaccine candidate against human cytomegalovirus (HCMV) that is manufactured using Adult Retinal Pigment Epithelial cells (ARPE-19) grown on Cytodex-1 microcarriers. The microcarriers are generally hydrated, washed, and autoclaved prior to use, which can be limiting at large production scales. To minimize microcarrier preparation and sterilization, the use of gamma irradiated Cytodex-1 was investigated. Similar ARPE-19 cell growth was observed on heat-sterilized and gamma irradiated Cytodex-1; however, significantly reduced virus production was observed in cultures exposed to gamma irradiated Cytodex-1. Additional experiments suggest that infection inhibition is not exclusive to ARPE-19 but is most directly linked to HCMV V160, as evidenced by similar inhibition of V160 with Vero cells and no inhibition of Measles virus with either cell type. These observations suggest a putative impact on HCMV infection from the presence of extractable(s)/leachable(s) in the gamma irradiated microcarriers. Thorough aseptic rinsing of gamma irradiated Cytodex-1 prior to use can mitigate this impact and enable comparable process performance to heat-sterilized Cytodex-1. Though not fully a "ready-to-use" product for the HCMV V160 production process, utilization of Cytodex-1 microcarriers was possible without requiring heat sterilization, suggesting a potential path forward for large scale production of V160.

CRM197-conjugated peptides vaccine of HCMV pp65 and gH induce maturation of DC and effective viral-specific T cell responses.

Human cytomegalovirus (HCMV) infection is prevalent worldwide, and there is currently no licenced HCMV vaccine to control it. Therefore, developing an effective HCMV vaccine is a significant priority. Because of their excellent immunogenicity, the crucial components of HCMV, phosphoprotein 65 (pp65) and glycoproteins H (gH) are potential target proteins for HCMV vaccine design. In this study, we predicted and screened the dominant antigenic epitopes of B and T cells from pp65 and gH conjugated with the carrier protein cross-reacting material 197 (CRM197) to form three peptide-CRM197 vaccines (pp65-CRM197, gH-CRM197, and pp65-CRM197+gH-CRM197). Furthermore, the immunogenicity of the peptide-CRM197 vaccines and their effects on dendritic cells (DCs) were explored. The results showed that three peptide-CRM197 vaccines could induce maturation of DCs through the p38 MAPK signalling pathway and promote the release of proinflammatory factors, such as TNF-α and interleukin (IL) -6. Meanwhile, the peptide-CRM197 vaccines could effectively activate T cell and humoral immunity, which were far better than the inactivated HCMV vaccine. In conclusion, we constructed three peptide-CRM197 vaccines, which could induce multiple immune effects, providing a novel approach for HCMV vaccine design.

The cytomegalovirus gB/MF59 vaccine candidate induces antibodies against an antigenic domain controlling cell-to-cell spread.

Vaccination against human cytomegalovirus (CMV) infection remains high priority. A recombinant form of a protein essential for CMV entry, glycoprotein B (gB), demonstrated partial protection in a clinical trial (NCT00299260) when delivered with the MF59 adjuvant. Although the antibody titre against gB correlated with protection poor neutralising responses against the 5 known antigenic domains (AD) of gB were evident. Here, we show that vaccination of CMV seronegative patients induces an antibody response against a region of gB we term AD-6. Responses to the polypeptide AD-6 are detected in >70% of vaccine recipients yet in <5% of naturally infected people. An AD-6 antibody binds to gB and to infected cells but not the virion directly. Consistent with this, the AD-6 antibody is non-neutralising but, instead, prevents cell-cell spread of CMV in vitro. The discovery of AD-6 responses has the potential to explain part of the protection mediated by gB vaccines against CMV following transplantation.

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.

Horizontal transmission of endemic viruses among rhesus macaques (Macaca mulatta): Implications for human cytomegalovirus vaccine/challenge design.

INTRODUCTION: Rhesus macaques are natural hosts to multiple viruses including rhesus cytomegalovirus (RhCMV), rhesus rhadinovirus (RRV), and Simian Foamy Virus (SFV). While viral infections are ubiquitous, viral transmissions to uninfected animals are incompletely defined. Management procedures of macaque colonies include cohorts that are Specific Pathogen Free (SPF). Greater understanding of viral transmission would augment SPF protocols. Moreover, vaccine/challenge studies of human viruses would be enhanced by leveraging transmission of macaque viruses to recapitulate expected challenges of human vaccine trials. MATERIALS AND METHODS: This study characterizes viral transmissions to uninfected animals following inadvertent introduction of RhCMV/RRV/SFV-infected adults to a cohort of uninfected juveniles. Following co-housing with virus-positive adults, juveniles were serially evaluated for viral infection. RESULTS: Horizontal viral transmission was rapid and absolute, reaching 100% penetrance between 19 and 78 weeks. CONCLUSIONS: This study provides insights into viral natural histories with implications for colony management and modeling vaccine-mediated immune protection studies.

Indirect effects of cytomegalovirus infection: Implications for vaccine development.

Development of a cytomegalovirus (CMV) vaccine is a high priority due to its significant global impact-contributing to mortality in immunosuppressed individuals, neurodevelopmental delay in infected neonates and non-genetic sensorineural hearing loss. The impact of CMV on the general population has been less well studied; however, a wide range of evidence indicates that CMV may increase the risk of atherosclerosis, cancer, immunosenescence, and progression of tuberculosis (TB) and human immunodeficiency virus. Due to the high seroprevalence of CMV worldwide, any modulation of risk by CMV is likely to have a significant impact on the epidemiology of these diseases. This review will evaluate how CMV may cause morbidity and mortality outside of the neonatal and immunosuppressed populations and consider the potential impact of a CMV vaccine on these outcomes.

CRM197-conjugated multi antigen dominant epitope for effective human cytomegalovirus vaccine development.

Human cytomegalovirus (HCMV) infection is a major cause of neonatal neurodevelopmental disorders and serious complications in organ transplantation. Previous HCMV vaccines focused on humoral immunity but had limited effect on viral infection. T-cell responses are essential to prevent HCMV infection, indicating that effective vaccines require T cells activation. In this study, we designed a novel polypeptides vaccine conjugated to a CRM197 carrier protein, encoding 15 CD8+ T-cell epitopes, five CD4+ T-cell epitopes, and four B-cell epitopes from gB287-320 and pp150311-325 of HCMV to induce T-cell immune responses. To evaluate the effectiveness of vaccines, we subsequently measured the expression of surface molecule markers and proinflammatory cytokines from antigen presenting cells in vivo and in vitro as well as the activation of T cells and antibodies. The results demonstrated that this polypeptide vaccine could activate innate immunity including up-regulating MHCI, II, CD80, CD86, and cytokine expression through the TLR4/NF-κB pathway. Meanwhile, vaccinations elicited potent neutralizing antibody and cellular immune responses producing TNF-α, INF-γ and IL-2, indicating Th1-biased polarization. This finding underlines that CRM197-conjugated polypeptide vaccines facilitate a synergism of humoral and cellular immunity, providing enhanced protection against HCMV, which could be a potential strategy to prevent CMV-associated diseases.

Alternative splicing and genetic variation of mhc-e: implications for rhesus cytomegalovirus-based vaccines.

Rhesus cytomegalovirus (RhCMV)-based vaccination against Simian Immunodeficiency virus (SIV) elicits MHC-E-restricted CD8+ T cells that stringently control SIV infection in ~55% of vaccinated rhesus macaques (RM). However, it is unclear how accurately the RM model reflects HLA-E immunobiology in humans. Using long-read sequencing, we identified 16 Mamu-E isoforms and all Mamu-E splicing junctions were detected among HLA-E isoforms in humans. We also obtained the complete Mamu-E genomic sequences covering the full coding regions of 59 RM from a RhCMV/SIV vaccine study. The Mamu-E gene was duplicated in 32 (54%) of 59 RM. Among four groups of Mamu-E alleles: three ~5% divergent full-length allele groups (G1, G2, G2_LTR) and a fourth monomorphic group (G3) with a deletion encompassing the canonical Mamu-E exon 6, the presence of G2_LTR alleles was significantly (p = 0.02) associated with the lack of RhCMV/SIV vaccine protection. These genomic resources will facilitate additional MHC-E targeted translational research.

Cytomegalovirus-vaccine-induced unconventional T cell priming and control of SIV replication is conserved between primate species.

Strain 68-1 rhesus cytomegalovirus expressing simian immunodeficiency virus (SIV) antigens (RhCMV/SIV) primes MHC-E-restricted CD8+ T cells that control SIV replication in 50%-60% of the vaccinated rhesus macaques. Whether this unconventional SIV-specific immunity and protection is unique to rhesus macaques or RhCMV or is intrinsic to CMV remains unknown. Here, using cynomolgus CMV vectors expressing SIV antigens (CyCMV/SIV) and Mauritian cynomolgus macaques, we demonstrate that the induction of MHC-E-restricted CD8+ T cells requires matching CMV to its host species. RhCMV does not elicit MHC-E-restricted CD8+ T cells in cynomolgus macaques. However, cynomolgus macaques vaccinated with species-matched 68-1-like CyCMV/SIV mounted MHC-E-restricted CD8+ T cells, and half of the vaccinees stringently controlled SIV post-challenge. Protected animals manifested a vaccine-induced IL-15 transcriptomic signature that is associated with efficacy in rhesus macaques. These findings demonstrate that the ability of species-matched CMV vectors to elicit MHC-E-restricted CD8+ T cells that are required for anti-SIV efficacy is conserved in nonhuman primates, and these data support the development of HCMV/HIV for a prophylactic HIV vaccine.

Modestly protective cytomegalovirus vaccination of young children effectively prevents congenital infection at the population level.

A vaccine to prevent congenital cytomegalovirus infection (cCMV) is a public health priority. cCMV results from maternal primary or non-primary CMV infection (reinfection, or reactivation of chronic infection) during pregnancy. Young children are a major source of transmission to pregnant women because they shed CMV at high viral loads for prolonged periods. CMV vaccines evaluated in clinical trials so far have demonstrated only approximately 50% efficacy against maternal primary infection. None of these have been approved, as higher levels of vaccine efficacy are assumed to be required to substantially reduce cCMV prevalence. Here, we designed a mathematical model to capture the relationship between viral shedding by young children and maternal CMV infections during pregnancy. Using this model, we were able to quantify the impact of CMV post-infection immunity on protecting against reinfection and viral shedding. There was a 36% reduction in the risk of infection to a seropositive person with post-infection immunity (reinfection) versus a seronegative person without this immunity (primary infection), given the same exposure. Viral shedding following reinfection was only 34% the quantity of that following primary infection. Our model also predicted that a vaccine that confers the equivalent of post-infection immunity, when given to young children, would markedly reduce both CMV transmission to pregnant women and the prevalence of cCMV. Thus, we predict that existing vaccine candidates that have been shown to be only modestly protective may in fact be highly effective at preventing cCMV by interrupting child-to-mother transmission.

Lessons from Acquired Natural Immunity and Clinical Trials to Inform Next-Generation Human Cytomegalovirus Vaccine Development.

Human cytomegalovirus (HCMV) infection, the most common cause of congenital disease globally, affecting an estimated 1 million newborns annually, can result in lifelong sequelae in infants, such as sensorineural hearing loss and brain damage. HCMV infection also leads to a significant disease burden in immunocompromised individuals. Hence, an effective HCMV vaccine is urgently needed to prevent infection and HCMV-associated diseases. Unfortunately, despite more than five decades of vaccine development, no successful HCMV vaccine is available. This review summarizes what we have learned from acquired natural immunity, including innate and adaptive immunity; the successes and failures of HCMV vaccine human clinical trials; the progress in related animal models; and the analysis of protective immune responses during natural infection and vaccination settings. Finally, we propose novel vaccine strategies that will harness the knowledge of protective immunity and employ new technology and vaccine concepts to inform next-generation HCMV vaccine development.

Maternal Fc-mediated non-neutralizing antibody responses correlate with protection against congenital human cytomegalovirus infection.

Human cytomegalovirus (HCMV) is the most common congenital infection and a leading cause of stillbirth, neurodevelopmental impairment, and pediatric hearing loss worldwide. Development of a maternal vaccine or therapeutic to prevent congenital HCMV has been hindered by limited knowledge of the immune responses that protect against HCMV transmission in utero. To identify protective antibody responses, we measured HCMV-specific IgG binding and antiviral functions in paired maternal and cord blood sera from HCMV-seropositive transmitting (n = 41) and non-transmitting (n = 40) mother-infant dyads identified via a large, US-based, public cord blood bank. We found that high-avidity IgG binding to HCMV and antibody-dependent cellular phagocytosis (ADCP) were associated with reduced risk of congenital HCMV infection. We also determined that HCMV-specific IgG activation of FcγRI and FcγRII was enhanced in non-transmitting dyads and that increased ADCP responses were mediated through both FcγRI and FcγRIIA expressed on human monocytes. These findings suggest that engagement of FcγRI/FcγRIIA and Fc effector functions including ADCP may protect against congenital HCMV infection. Taken together, these data can guide future prospective studies on immune correlates against congenital HCMV transmission and inform HCMV vaccine and immunotherapeutic development.