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.

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).

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.

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.

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.

Myeloid cell tropism enables MHC-E-restricted CD8+ T cell priming and vaccine efficacy by the RhCMV/SIV vaccine

The strain 68-1 rhesus cytomegalovirus (RhCMV)-based vaccine for simian immunodeficiency virus (SIV) can stringently protect rhesus macaques (RMs) from SIV challenge by arresting viral replication early in primary infection. This vaccine elicits unconventional SIV-specific CD8+ T cells that recognize epitopes presented by major histocompatibility complex (MHC)-II and MHC-E instead of MHC-Ia. Although RhCMV/SIV vaccines based on strains that only elicit MHC-II- and/or MHC-Ia-restricted CD8+ T cells do not protect against SIV, it remains unclear whether MHC-E-restricted T cells are directly responsible for protection and whether these responses can be separated from the MHC-II-restricted component. Using host microRNA (miR)-mediated vector tropism restriction, we show that the priming of MHC-II and MHC-E epitope-targeted responses depended on vector infection of different nonoverlapping cell types in RMs. Selective inhibition of RhCMV infection in myeloid cells with miR-142-mediated tropism restriction eliminated MHC-E epitope-targeted CD8+ T cell priming, yielding an exclusively MHC-II epitope-targeted response. Inhibition with the endothelial cell-selective miR-126 eliminated MHC-II epitope-targeted CD8+ T cell priming, yielding an exclusively MHC-E epitope-targeted response. Dual miR-142 + miR-126-mediated tropism restriction reverted CD8+ T cell responses back to conventional MHC-Ia epitope targeting. Although the magnitude and differentiation state of these CD8+ T cell responses were generally similar, only the vectors programmed to elicit MHC-E-restricted CD8+ T cell responses provided protection against SIV challenge, directly demonstrating the essential role of these responses in RhCMV/SIV vaccine efficacy.

Novel adjuvants enhance immune responses elicited by a replication-defective human cytomegalovirus vaccine in nonhuman primates

Adjuvants have long been explored to enhance vaccine efficacy. Current adjuvants approved for human vaccines are mostly studied for their ability to improve antibody responses. There remains a need for development of novel adjuvants, especially those able to enhance cell-mediated immunity (CMI). In this preclinical study we assessed the effect of two novel adjuvants, a delta inulin microparticle Advax formulated with or without a toll-like receptor 9 (TLR9) agonist CpG oligonucleotide, and a Merck & Co., Inc., Kenilworth, NJ, USA proprietary lipid nanoparticle (LNP), on immune responses elicited by V160, an experimental replication-defective human cytomegalovirus vaccine. Adult rhesus macaques were immunized with a low dose of V160 (10 units) either alone or in combination with the adjuvants as compared to those immunized with a high dose of V160 alone (100 units). While neither adjuvant conferred a significant benefit to vaccine-elicited humoral immune responses at the dose tested, both enhanced cellular immune responses to V160, where Advax promoted both CD4⁺ and CD8⁺ T cells and LNP predominantly impacted the CD4⁺ T cell response. Transcriptome analyses of peripheral blood samples demonstrated different modes of action for these adjuvants. One day post vaccination, LNP induced upregulation of a large number of genes involved in the innate immune response similar to those triggered by viral infection. In contrast, Advax did not activate any known inflammatory pathways and did not significantly impact gene expression pattern until day 7 post administration, suggesting a unique, non-inflammatory mechanism. These data warrant further exploration of Advax and LNP as adjuvants in clinical trials for vaccines desiring to elicit both humoral and T cell responses.

Human cytomegalovirus (HCMV) infection/re-infection: development of a protective HCMV vaccine

In recent years, one of the main objectives in the field of medical virology has been the development of a human cytomegalovirus (HCMV) vaccine that can prevent congenital HCMV infection in the offspring of pregnant women as well as systemic and end-organ disease in immunocompromised (AIDS and transplanted) patients. Major obstacles to the development of an efficacious HCMV vaccine are lack of protection provided by immune memory cells against HCMV re-activation (replication relapse of a latent strain following primary infection) and HCMV re-infection (infection of a seropositive individual by a new virus strain). Thus, while initial efforts were directed at the development of a vaccine for the prevention of primary infection, in the last decade the primary vaccine development endpoint was the prevention of primary HCMV infection, as well as HCMV re-activation and re-infection. Along this line of research, both HCMV live (including Towne, AD169 and its derivatives, Towne/Toledo chimeras, Viral-Vectored vaccines, and Virus Replicon Particles) and non-living vaccines (including the recombinant gB subunit, DNA- and RNA-based vaccines, Virus-like particles, Dense bodies, Peptide vaccines, and the Pentamer Complex) have been developed. To date, Phase I, II, and III clinical trials have been variably conducted in humans, and experimental inoculation in different animal models has been performed with different vaccine formulations. Notwithstanding the variable research conditions, clinical and experimental results achieved thus far predict that the ideal HCMV vaccine should be able to elicit both robust humoral (both neutralizing and binding) and HCMV-specific CD4+ and CD8+ T-cell responses. This vaccine should hypothetically contain: 1) gB, inducing both humoral and T-cell responses; 2) the pentameric complex (PC), inducing the most potent neutralizing antibody response; 3) pp65, inducing the most potent HCMV-specific T-cell response. Although the protective role of cell-mediated immunity has been repeatedly documented, while the protective effect of (mostly neutralizing) antibodies remains partly to be documented, a vaccine stimulating both arms of the immune response would likely confer the highest level of protection against HCMV infection/disease in both HCMV-seronegative and -seropositive individuals.

[Congenital cytomegalovirus infection: current status and future perspectives]

In recent years, infection with cytomegalovirus (CMV) was the subject of numerous studies, one side being the most frequent congenital infection in newborns and one that determines the increased incidence of sequelae distance (about one third of childhood deafness is due to CMV), and the other one of the most frequent and serious opportunistic infections in immunocompromised individuals. Of newborns with congenital infection, approximately 10% are symptomatic at birth. Of the remaining 90%, asymptomatic at birth, 10-15% will develop sequelae from a distance. Regarding the possibility of vertical transmission of the disease from mother to fetus, the debate is still open on the usefulness or not to set a screening during pregnancy in order to prevent or limit the damage caused fetal infection. Despite detailed knowledge about the epidemiology and pathogenesis of CMV disease in pregnant women, this infection remains largely unknown to most women. The opportunity of a serological screening is important, however, since more than 90% of primary CMV infection in pregnancy are asymptomatic and may remain asymptomatic in the fetus. The education on methods to prevent transmission of CMV, particularly among young women of childbearing age, must continue until an effective vaccine becomes available. In this article we summarize the current concepts regarding the epidemiology, pathogenesis, symptoms and prevention of CMV disease, with particular focus on strategies to improve awareness of the risk of CMV infection in women of childbearing age.

Cytomegalovirus: recent progress in understanding pathogenesis and control

Cytomegalovirus continues to be an important pathogen in a variety of patient groups especially the neonate and the transplant recipient, and has implicated in a range of pathologies including inflammatory disease and in contributing to early death in ageing populations. This review will focus on advances in understanding the virus-host interaction and options for the new therapeutic control measures.

Translational mini-review series on infectious disease: congenital cytomegalovirus infection: 50 years on

Cytomegalovirus (CMV) is the leading cause of congenital viral infection, with an incidence of 0.5-3% of live births worldwide. Clinical evidence has shown hearing and vision loss, mental retardation and sometimes death in affected newborns. Primary maternal CMV infection during gestation poses a 40% risk of intrauterine transmission in contrast to recurrent infection. European laboratories have made significant progress in the last decade in solving diagnostic problems linked to infection in pregnancy. With the advances in CMV serology, such as detection of anti-CMV IgM by enzyme immunoassays (EIA), confirmed by Western blot, together with seroconversion and anti-CMV IgG avidity evaluation in pregnant mothers, can help to identify recent infection. Preventative measures such as screening for CMV in the routine serological work-up of pregnant women have been introduced in countries such as Spain and Italy. The development of specific T cell-mediated immune responses in mothers, fetus and neonates is now emerging with regard to antigen-specific CD4 and CD8 T cells, differentiation status, proliferative and cytokine responses. A protective vaccine against CMV is a major public health priority and the study of vaccines in animal model systems has identified potential strategies for interrupting transmission and preventing disease in newborns. Congenital CMV infection has a variable outcome and therefore novel diagnostic methods are required to identify those at risk and therapeutic interventions are needed to improve the long-term prognosis of those infected. CMV was first isolated in 1957. We are now 50 years on, so procrastination is not an option.

Location, location, timing: analysis of cytomegalovirus epitopes for neutralizing antibodies

Attempts to produce a vaccine to human cytomegalovirus (HCMV) have failed. The principal target of the humoral immune response to HCMV is the viral envelope glycoprotein gB, which contains several immunodominant epitopes. Here we discuss human antibodies reacting with gB and offer an explanation as to why most humans make antibodies to an epitope that does not always elicit neutralizing antibodies. We suggest modifications to gB for an improved HCMV vaccine design.

Detection of cytomegalovirus infection during a vaccine clinical trial in healthy young women: seroconversion and viral shedding

BACKGROUND

An antibody method based on absorption of serum with cytomegalovirus (CMV) glycoprotein B (gB) was developed for detection of infection during clinical trials of CMV gB vaccine. Previous study showed that this method detected the antibody response to infection and was negative with vaccine induced immunity.

OBJECTIVES

In an ongoing efficacy trial of CMV gB vaccine the ability of the gB-absorbed CMV IgG assay to detect CMV infection was assessed and compared with viral culture results.

STUDY DESIGN

Two hundred and ninety two healthy, seronegative young women in a phase II, double-blind, placebo-controlled, clinical trial of recombinant CMV gB vaccine (sanofi pasteur) with MF59 adjuvant (Chiron) were randomized to receive CMV gB vaccine or placebo (1:1) on a 0, 1 and 6 month schedule. Participants were screened every 3 months for CMV infection using the gB-absorbed CMV IgG assay, and a subgroup was also screened for infection with viral cultures. Viral culture (urine, vaginal swab and saliva) was used to confirm CMV infection in all subjects with a positive gB-absorbed CMV IgG result.

RESULTS

Evidence of CMV infection (gB-absorbed CMV IgG levels>or=5.0 AU/ml) was found in 23/292 (7.88%) study participants. The gB-absorbed CMV IgG levels of their first positive serum ranged from 15.7 to 251.0 AU/ml with a mean of 77.0 AU/ml and a median of 44.9 AU/ml. Cytomegalovirus was isolated from all 23 of them from culture specimens collected after their first positive gB-absorbed CMV IgG. The time to first CMV positive culture from first positive gB-absorbed CMV IgG ranged from 0 to 12 weeks with a median of 2 weeks.

CONCLUSIONS

The gB-absorbed CMV IgG assay detects CMV infection in CMV gB vaccine clinical trials earlier and more rapidly than virus culture and does not reveal whether subjects received CMV gB vaccine or placebo.

Progress in cytomegalovirus vaccine development

Cytomegalovirus (CMV) causes considerable morbidity and disability in infants who acquire the infection in utero. Despite potent antiviral therapies, CMV also continues to be a major cause of disease in immunocompromised patients. Vaccines for CMV, therefore, could provide protection against CMV disease in an array of high-risk patient populations. Although the correlates of vaccine-engendered immunity that limit CMV disease are not fully understood, there has been significant progress in elucidating some of the key immunological correlates of protection. The optimal CMV vaccine strategy may depend on the patient population being targeted for protection. This review provides an update on CMV vaccines that are currently in preclinical and clinical development, and outlines important, as yet unanswered, questions about the nature of protective immune responses that will be required of potential CMV immunization strategies. Such questions must be answered before an optimal vaccine, and vaccine use strategy, can be implemented in clinical practice.