Multiantigenic Modified Vaccinia Virus Ankara Vaccine Vectors To Elicit Potent Humoral and Cellular Immune Reponses against Human Cytomegalovirus in Mice

A Novel Monoclonal Antibody Against a Modified Vaccinia Ankara (MVA) Envelope Protein as a Tool for MVA Virus Titration by Flow Cytometry

Modified vaccinia Ankara (MVA) virus is a widely used vaccine platform, making accurate titration essential for vaccination studies. However, the current plaque forming unit (PFU) assay, the standard for MVA titration, is prone to observer bias and other limitations that affect accuracy and precision. To address these challenges, we developed a new flow cytometry-based quantification method using a highly specific monoclonal antibody (mAb) for the detection of MVA-infected cells, as a more accurate titration assay. Through previous work, we serendipitously identified three MVA-specific hybridoma antibody clones, which we characterized through ELISA, immunoblot, and flow cytometry, confirming their specificity for MVA. Sequencing confirmed that each antibody was monoclonal, and mass spectrometry results revealed that all mAbs target the MVA cell surface binding protein (CSBP, MVA105L). We next optimized the titration protocol using the most effective mAb, 33C7 by refining culture conditions and staining protocols to enhance sensitivity and minimize background. Our optimized method demonstrated superior sensitivity, reliability, and reduced processing time when compared with the traditional PFU assay, establishing it as a more accurate and efficient approach for MVA titration.

Multivalent MVA-vectored vaccine elicits EBV neutralizing antibodies in rhesus macaques that reduce EBV infection in humanized mice

Introduction

Epstein-Barr virus (EBV) is an oncogenic human herpesvirus associated with ~350,000 cases of lymphoid and epithelial malignancies every year, and is etiologically linked to infectious mononucleosis and multiple sclerosis. Despite four decades of research, no EBV vaccine candidate has yet reached licensure. Most previous vaccine attempts focused on a single viral entry glycoprotein, gp350, but recent data from clinical and pre-clinical studies, and the elucidation of viral entry mechanisms, support the inclusion of multiple entry glycoproteins in EBV vaccine design.

Methods

Here we generated a modified vaccinia Ankara (MVA)-vectored EBV vaccine, MVA-EBV5-2, that targets five EBV entry glycoproteins, gp350, gB, and the gp42gHgL complex. We characterized the genetic and translational stability of the vaccine, followed by immunogenicity assessment in BALB/c mice and rhesus lymphocryptovirus-negative rhesus macaques as compared to a gp350-based MVA vaccine. Finally, we assessed the efficacy of MVA-EBV5-2-immune rhesus serum at preventing EBV infection in human CD34+ hematopoietic stem cell-reconstituted NSG mice, under two EBV challenge doses.

Results

The MVA-EBV5-2 vaccine was genetically and translationally stable over 10 viral passages as shown by genetic and protein expression analysis, and when administered to female and male BALB/c mice, elicited serum EBV-specific IgG of both IgG1 and IgG2a subtypes with neutralizing activity in vitro. In Raji B cells, this neutralizing activity outperformed that of serum from mice immunized with a monovalent MVA-vectored gp350 vaccine. Similarly, MVA-EBV5-2 elicited EBV-specific IgG in rhesus macaques that were detected in both serum and saliva of immunized animals, with serum antibodies demonstrating neutralizing activity in vitro that outperformed serum from MVA-gp350-immunized macaques. Finally, pre-treatment with serum from MVA-EBV5-2-immunized macaques resulted in fewer EBV-infected mice in the two challenge experiments than pretreatment with serum from pre-immune macaques or macaques immunized with the monovalent gp350-based vaccine.

Discussion

These results support the inclusion of multiple entry glycoproteins in EBV vaccine design and position our vaccine as a strong candidate for clinical translation.

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.

Highly stable and immunogenic CMV T cell vaccine candidate developed using a synthetic MVA platform

Human cytomegalovirus (CMV) is the most common infectious cause of complications post-transplantation, while a CMV vaccine for transplant recipients has yet to be licensed. Triplex, a multiantigen Modified Vaccinia Ankara (MVA)-vectored CMV vaccine candidate based on the immunodominant antigens phosphoprotein 65 (pp65) and immediate-early 1 and 2 (IE1/2), is in an advanced stage of clinical development. However, its limited genetic and expression stability restricts its potential for large-scale production. Using a recently developed fully synthetic MVA (sMVA) platform, we developed a new generation Triplex vaccine candidate, T10-F10, with different sequence modifications for enhanced vaccine stability. T10-F10 demonstrated genetic and expression stability during extensive virus passaging. In addition, we show that T10-F10 confers comparable immunogenicity to the original Triplex vaccine to elicit antigen-specific T cell responses in HLA-transgenic mice. These results demonstrate improvements in translational vaccine properties of an sMVA-based CMV vaccine candidate designed as a therapeutic treatment for transplant recipients.

Ligands and receptors in human cytomegalovirus entry: Current therapies and new directions

The demand for human cytomegalovirus (HCMV) vaccines was first raised by a committee convened during the 1990s. A comprehensive investigation into the mechanism of viral infection supports the prioritization of developing drugs or vaccines that specifically target receptors and ligands involved in the infection process. As primary targets for neutralizing antibodies to combat HCMV, viral ligands (trimer, pentamer, and glycoprotein B) have crucial roles and exhibit substantial antiviral potential, which could be exploited for breakthroughs in antiviral research.

Hematopoietic stem cell donor vaccination with cytomegalovirus triplex augments frequencies of functional and durable cytomegalovirus-specific T cells in the recipient: A novel strategy to limit antiviral prophylaxis

To enhance protective cytomegalovirus (CMV)-specific T cells in immunosuppressed recipients of an allogeneic hematopoietic cell transplant (HCT), we evaluated post-HCT impact of vaccinating healthy HCT donors with Triplex. Triplex is a viral vectored recombinant vaccine expressing three immunodominant CMV antigens. The vector is modified vaccinia Ankara (MVA), an attenuated, non-replicating poxvirus derived from the vaccinia virus strain Ankara. It demonstrated tolerability and immunogenicity in healthy adults and HCT recipients, in whom it also reduced CMV reactivation. Here, we report feasibility, safety, and immunological outcomes of a pilot phase 1 trial (NCT03560752 at ClinicalTrials.gov) including 17 CMV-seropositive recipients who received an HCT from a matched related donor (MRD) vaccinated with 5.1 × 108 pfu/ml of Triplex before cell harvest (median 15, range 11-28 days). Donor and recipient pairs who committed to participation in the trial resulted in exceptional adherence to the protocol. Triplex was well-tolerated with limited adverse events in donors and recipients, who all engrafted with full donor chimerism. On day 28 post-HCT, levels of functional vaccinia- and CMV-specific CD137+ CD8+ T cells were significantly higher (p < .0001 and p = .0174, respectively) in recipients of Triplex vaccinated MRD than unvaccinated MRD (control cohort). Predominantly, central and effector memory CMV-specific T-cell responses continued to steadily expand through 1-year follow-up. CMV viremia requiring antivirals developed in three recipients (18%). In summary, this novel approach represents a promising strategy applicable to different HCT settings for limiting the use of antiviral prophylaxis, which can impair and delay CMV-specific immunity, leading to CMV reactivation requiring treatment.

EEHV1A glycoprotein B subunit vaccine elicits humoral and cell-mediated immune responses in mice

Asian elephants are an endangered species facing many threats, including severe hemorrhagic disease (HD) caused by the elephant endotheliotropic herpesvirus (EEHV). EEHV-HD is the leading cause of death in captive juvenile Asian elephants in North America and Europe, and also affects elephants in their natural range countries. Significant challenges exist for successful treatment of EEHV-HD, which include timely recognition of disease onset and limited availability of highly effective treatment options. To address this problem, our goal is to prevent lethal disease in young elephants by developing a vaccine that elicits robust and durable humoral and cell-mediated immunity against EEHV. EEHV glycoprotein B (gB) is a major target for cellular and humoral immunity in elephants previously exposed to EEHV. Therefore, we generated a vaccine containing recombinant EEHV1A gB together with a liposome formulated TLR-4 and saponin combination adjuvant (SLA-LSQ). CD-1 mice that received one or two vaccinations with the vaccine elicited significant anti-gB antibody and polyfunctional CD4⁺ and CD8⁺ T cell responses, while no adverse effects of vaccination were observed. Overall, our findings demonstrate that an adjuvanted gB protein subunit vaccine stimulates robust humoral and cell-mediated immune responses and supports its potential use in elephants.

COH04S1 and beta sequence-modified vaccine protect hamsters from SARS-CoV-2 variants

COVID-19 vaccine efficacy is threatened by emerging SARS-CoV-2 variants of concern (VOC) with the capacity to evade protective neutralizing antibody responses. We recently developed clinical vaccine candidate COH04S1, a synthetic modified vaccinia Ankara vector (sMVA) co-expressing spike and nucleocapsid antigens based on the Wuhan-Hu-1 reference strain that showed potent efficacy to protect against ancestral SARS-CoV-2 in Syrian hamsters and non-human primates and was safe and immunogenic in healthy volunteers. Here, we demonstrate that intramuscular immunization of Syrian hamsters with COH04S1 and an analogous Beta variant-adapted vaccine candidate (COH04S351) elicits potent cross-reactive antibody responses and protects against weight loss, lower respiratory tract infection, and lung pathology following challenge with major SARS-CoV-2 VOC, including Beta and the highly contagious Delta variant. These results demonstrate efficacy of COH04S1 and a variant-adapted vaccine analog to confer cross-protective immunity against SARS-CoV-2 and its emerging VOC, supporting clinical investigation of these sMVA-based COVID-19 vaccine candidates.

Modified vaccinia Ankara expressing EEHV1A glycoprotein B elicits humoral and cell-mediated immune responses in mice

Elephant endotheliotropic herpesvirus (EEHV) can cause lethal hemorrhagic disease (EEHV-HD) in Asian elephants and is the largest cause of death in captive juvenile Asian elephants in North America and Europe. EEHV-HD also has been documented in captive and wild elephants in their natural range countries. A safe and effective vaccine to prevent lethal EEHV infection would significantly improve conservation efforts for this endangered species. Recent studies from our laboratory suggest that EEHV morbidity and mortality are often associated with primary infection. Therefore, we aim to generate a vaccine, particularly for EEHV1 naïve animals, with the goal of preventing lethal EEHV-HD. To address this goal, we generated a Modified Vaccinia Ankara (MVA) recombinant virus expressing a truncated form of glycoprotein B (gBΔfur731) from EEHV1A, the strain associated with the majority of lethal EEHV cases. Vaccination of CD-1 mice with this recombinant virus induced robust antibody and polyfunctional T cell responses significantly above mice inoculated with wild-type MVA. Although the vaccine-induced T cell response was mainly observed in CD8+ T cell populations, the CD4+ T cell response was also polyfunctional. No adverse responses to vaccination were observed. Overall, our data demonstrates that MVA-gBΔfur731 stimulates robust humoral and cell-mediated responses, supporting its potential translation for use in elephants.

Synthetic multiantigen MVA vaccine COH04S1 protects against SARS-CoV-2 in Syrian hamsters and non-human primates

Second-generation COVID-19 vaccines could contribute to establish protective immunity against SARS-CoV-2 and its emerging variants. We developed COH04S1, a synthetic multiantigen modified vaccinia Ankara-based SARS-CoV-2 vaccine that co-expresses spike and nucleocapsid antigens. Here, we report COH04S1 vaccine efficacy in animal models. We demonstrate that intramuscular or intranasal vaccination of Syrian hamsters with COH04S1 induces robust Th1-biased antigen-specific humoral immunity and cross-neutralizing antibodies (NAb) and protects against weight loss, lower respiratory tract infection, and lung injury following intranasal SARS-CoV-2 challenge. Moreover, we demonstrate that single-dose or two-dose vaccination of non-human primates with COH04S1 induces robust antigen-specific binding antibodies, NAb, and Th1-biased T cells, protects against both upper and lower respiratory tract infection following intranasal/intratracheal SARS-CoV-2 challenge, and triggers potent post-challenge anamnestic antiviral responses. These results demonstrate COH04S1-mediated vaccine protection in animal models through different vaccination routes and dose regimens, complementing ongoing investigation of this multiantigen SARS-CoV-2 vaccine in clinical trials.

Synthetic Multiantigen MVA Vaccine COH04S1 Protects Against SARS-CoV-2 in Syrian Hamsters and Non-Human Primates

Second-generation COVID-19 vaccines could contribute to establish protective immunity against SARS-CoV-2 and its emerging variants. We developed COH04S1, a synthetic multiantigen Modified Vaccinia Ankara-based SARS-CoV-2 vaccine that co-expresses spike and nucleocapsid antigens. Here, we report COH04S1 vaccine efficacy in animal models. We demonstrate that intramuscular or intranasal vaccination of Syrian hamsters with COH04S1 induces robust Th1-biased antigen-specific humoral immunity and cross-neutralizing antibodies (NAb) and protects against weight loss, lower respiratory tract infection, and lung injury following intranasal SARS-CoV-2 challenge. Moreover, we demonstrate that single-dose or two-dose vaccination of non-human primates with COH04S1 induces robust antigen-specific binding antibodies, NAb, and Th1-biased T cells, protects against both upper and lower respiratory tract infection following intranasal/intratracheal SARS-CoV-2 challenge, and triggers potent post-challenge anamnestic antiviral responses. These results demonstrate COH04S1-mediated vaccine protection in animal models through different vaccination routes and dose regimens, complementing ongoing investigation of this multiantigen SARS-CoV-2 vaccine in clinical trials.

Evasion of the Host Immune Response by Betaherpesviruses

The human immune system boasts a diverse array of strategies for recognizing and eradicating invading pathogens. Human betaherpesviruses, a highly prevalent subfamily of viruses, include human cytomegalovirus (HCMV), human herpesvirus (HHV) 6A, HHV-6B, and HHV-7. These viruses have evolved numerous mechanisms for evading the host response. In this review, we will highlight the complex interplay between betaherpesviruses and the human immune response, focusing on protein function. We will explore methods by which the immune system first responds to betaherpesvirus infection as well as mechanisms by which viruses subvert normal cellular functions to evade the immune system and facilitate viral latency, persistence, and reactivation. Lastly, we will briefly discuss recent advances in vaccine technology targeting betaherpesviruses. This review aims to further elucidate the dynamic interactions between betaherpesviruses and the human immune system.

Immunization with Epstein-Barr Virus Core Fusion Machinery Envelope Proteins Elicit High Titers of Neutralizing Activities and Protect Humanized Mice from Lethal Dose EBV Challenge

Epstein–Barr virus (EBV) is the primary cause of infectious mononucleosis and is strongly implicated in the etiology of multiple lymphoid and epithelial cancers. EBV core fusion machinery envelope proteins gH/gL and gB coordinately mediate EBV fusion and entry into its target cells, B lymphocytes and epithelial cells, suggesting these proteins could induce antibodies that prevent EBV infection. We previously reported that the immunization of rabbits with recombinant EBV gH/gL or trimeric gB each induced markedly higher serum EBV-neutralizing titers for B lymphocytes than that of the leading EBV vaccine candidate gp350. In this study, we demonstrated that immunization of rabbits with EBV core fusion machinery proteins induced high titer EBV neutralizing antibodies for both B lymphocytes and epithelial cells, and EBV gH/gL in combination with EBV trimeric gB elicited strong synergistic EBV neutralizing activities. Furthermore, the immune sera from rabbits immunized with EBV gH/gL or trimeric gB demonstrated strong passive immune protection of humanized mice from lethal dose EBV challenge, partially or completely prevented death respectively, and markedly decreased the EBV load in peripheral blood of humanized mice. These data strongly suggest the combination of EBV core fusion machinery envelope proteins gH/gL and trimeric gB is a promising EBV prophylactic vaccine.

A randomised, placebo-controlled phase 3 study to evaluate the efficacy and safety of ASP0113, a DNA-based CMV vaccine, in seropositive allogeneic haematopoietic cell transplant recipients

BACKGROUND

Cytomegalovirus (CMV) is a complication of allogeneic haematopoietic cell transplantation (allo-HCT). ASP0113, a DNA-based vaccine, contains two plasmids encoding human CMV glycoprotein B and phosphoprotein 65 (pp65). We assessed ASP0113 in CMV-seropositive allo-HCT recipients.

METHODS

In this phase 3, randomised, placebo-controlled study, CMV-seropositive allo-HCT recipients were randomly assigned (1:1) via interactive response technology to receive five injections of 1 mL of 5 mg/mL ASP0113 or placebo. The pharmacist and designated staff were unblinded. Masked syringes maintained the blind for patients and study personnel. Efficacy and safety analyses included patients who received ≥1 dose of ASP0113/placebo. The primary efficacy endpoint was the proportion of allo-HCT recipients with composite all-cause mortality and adjudicated CMV end-organ disease (EOD) by 1 year post-transplant. ClinicalTrials.gov: NCT01877655 (not recruiting).

FINDINGS

Patients were recruited between Sept 11, 2013 and Sept 21, 2016. Overall, 501 patients received ≥1 dose of ASP0113 (n = 246) or placebo (n = 255). The proportion of patients with composite all-cause mortality and adjudicated CMV EOD by 1 year post-transplant was 35.4% (n = 87) with ASP0113 and 30•2% (n = 77) with placebo (odds ratio 1.27; 95% confidence interval: 0.87 to 1.85; p = 0.205). Incidence of injection site-related treatment-emergent adverse events (TEAEs) was higher with ASP0113 than placebo. Overall incidence and severity of other TEAEs was similar between groups. T-cell response to pp65 increased over time and was greater with placebo than ASP0113 (p = 0.027).

INTERPRETATION

ASP0113 did not reduce overall mortality or CMV EOD by 1 year post-transplant. Safety findings were similar between groups.

FUNDING

Astellas Pharma Global Development, Inc .

In utero human cytomegalovirus infection is associated with increased levels of putatively protective maternal antibodies in nonprimary infection: evidence for boosting but not protection

BACKGROUND

Although primary maternal cytomegalovirus infections are associated with higher risk of in utero transmission, most fetal infections worldwide result from nonprimary maternal infections. Antibodies directed at glycoprotein B and the gH/gL/pUL128-130-131 pentamer can neutralize virus, and higher levels of antibody directed at several particular pentamer epitopes defined by monoclonal antibodies (mAbs) are associated with reduced risk of fetal cytomegalovirus transmission during primary maternal infection. This had not been explored in maternal nonprimary infection.

METHODS

In a setting where most maternal cytomegalovirus infections are nonprimary, 42 mothers of infants with congenital CMV infections (transmitters) were compared to 75 cytomegalovirus-seropositive mothers whose infants were cytomegalovirus-uninfected (nontransmitters). Control infants were matched by sex, maternal HIV status and gestational age. We measured the ability of maternal antibodies to block three key pentameric epitopes: one in the gH subunit, another straddling UL130/UL131 and the third straddling gH/gL/UL128/UL130. We tested if levels of antibodies directed at these epitopes were higher in nontransmitters compared to transmitters.

RESULTS

Levels of all three putatively protective pentamer-directed antibodies were significantly higher in transmitters compared to nontransmitters. In contrast, antibodies targeting an epitope on glycoprotein B were not different. Total antibody specific for pentamer and for gB were also higher in transmitters.

CONCLUSIONS

We found no evidence that higher levels of any CMV-specific antibodies were associated with reduced risk of congenital CMV infection in nonprimary maternal infection. Instead, we found higher maternal antibody targeting epitopes on CMV pentamer in transmitters than nontransmitters, providing evidence for antibody boosting but not protection.

A vaccine to prevent initial loss of cognition and eventual Alzheimer's disease in elderly persons

Prevention is better than cure and prevention of Alzheimer's disease (AD) may be possible. In elderly persons who are cognitively normal, synaptic hypometabolism as shown by reduced cerebral uptake of fluorodeoxyglucose (18F-FDG), provides a premonitory signal of potential, future loss of cognition if those individuals also have present evidence of amyloid deposition seen in the Pittsburgh compound B positron emission tomography (PIB-PET) scan for amyloid. Those are the persons who should be targeted if one aims to prevent AD. The synaptic hypometabolism implies that the brain's availability of adenosine triphosphate (ATP) is inadequate for performance of all required synaptic functions. This review first describes the basis for asserting that reduced cerebral uptake of 18F-FDG accurately reflects synaptic hypometabolism; second, explains the basis for asserting that hypometabolism implies inadequate ATP; third, shows that amyloid beta (Aβ) itself, Aβ modified by pyroglutamate to become a molecule termed pE(3)Aβ, and cyclophilin-D, in concert are the main contributors to inadequate synaptic ATP and that, therefore, reducing all of their levels would neutralize their combined effect and correct the hypometabolism. pE(3)Aβ is more neurotoxic than unmodified Aβ; and cyclophilin D inhibits ATP synthase and reduces ATP formation. Finally, this review describes an mRNA self-replicating vaccine that will raise brain levels of ATP by reducing Aβ, pyroglutamate-modified Aβ, and cyclophilin-D, and thereby-in cognitively normal elderly persons who have synaptic hypometabolism-prevent initiation of the process that terminates in AD.

The Status of Vaccine Development Against the Human Cytomegalovirus

Numerous candidate vaccines against cytomegalovirus (CMV) infection and disease are in development. Whereas the previous article [1] provides background and opinions about the issues relating to vaccination, this article provides specifics about the vaccines in active development, as reported at a National Institutes of Health-sponsored meeting in Bethesda on September 4-6, 2018. Here, vaccine developers provide synopses of their candidate vaccines to immunize women to protect against congenital CMV disease and to prevent the consequences of CMV disease in recipients of transplanted organs or hematopoietic stem calls. The projects are presented here roughly in the descending order of their stage of development in the opinion of the first author.

Development of a multi-antigenic SARS-CoV-2 vaccine candidate using a synthetic poxvirus platform

Modified Vaccinia Ankara (MVA) is a highly attenuated poxvirus vector that is widely used to develop vaccines for infectious diseases and cancer. We demonstrate the construction of a vaccine platform based on a unique three-plasmid system to efficiently generate recombinant MVA vectors from chemically synthesized DNA. In response to the ongoing global pandemic caused by SARS coronavirus-2 (SARS-CoV-2), we use this vaccine platform to rapidly produce fully synthetic MVA (sMVA) vectors co-expressing SARS-CoV-2 spike and nucleocapsid antigens, two immunodominant antigens implicated in protective immunity. We show that mice immunized with these sMVA vectors develop robust SARS-CoV-2 antigen-specific humoral and cellular immune responses, including potent neutralizing antibodies. These results demonstrate the potential of a vaccine platform based on synthetic DNA to efficiently generate recombinant MVA vectors and to rapidly develop a multi-antigenic poxvirus-based SARS-CoV-2 vaccine candidate.

Development of a Multi-Antigenic SARS-CoV-2 Vaccine Using a Synthetic Poxvirus Platform

Modified Vaccinia Ankara (MVA) is a highly attenuated poxvirus vector that is widely used to develop vaccines for infectious diseases and cancer. We developed a novel vaccine platform based on a unique three-plasmid system to efficiently generate recombinant MVA vectors from chemically synthesized DNA. In response to the ongoing global pandemic caused by SARS coronavirus-2 (SARS-CoV-2), we used this novel vaccine platform to rapidly produce fully synthetic MVA (sMVA) vectors co-expressing SARS-CoV-2 spike and nucleocapsid antigens, two immunodominant antigens implicated in protective immunity. Mice immunized with these sMVA vectors developed robust SARS-CoV-2 antigen-specific humoral and cellular immune responses, including potent neutralizing antibodies. These results demonstrate the potential of a novel vaccine platform based on synthetic DNA to efficiently generate recombinant MVA vectors and to rapidly develop a multi-antigenic poxvirus-based SARS-CoV-2 vaccine candidate.

Repertoire characterization and validation of gB-specific human IgGs directly cloned from humanized mice vaccinated with dendritic cells and protected against HCMV

Human cytomegalovirus (HCMV) causes serious complications to immune compromised hosts. Dendritic cells (iDCgB) expressing granulocyte-macrophage colony-stimulating factor, interferon-alpha and HCMV-gB were developed to promote de novo antiviral adaptive responses. Mice reconstituted with a human immune system (HIS) were immunized with iDCgB and challenged with HCMV, resulting into 93% protection. Immunization stimulated the expansion of functional effector memory CD8⁺ and CD4⁺ T cells recognizing gB. Machine learning analyses confirmed bone marrow T/CD4⁺, liver B/IgA⁺ and spleen B/IgG⁺ cells as predictive biomarkers of immunization (≈87% accuracy). CD8⁺ and CD4⁺ T cell responses against gB were validated. Splenic gB-binding IgM^-/IgG⁺ B cells were sorted and analyzed at a single cell level. iDCgB immunizations elicited human-like IgG responses with a broad usage of various IgG heavy chain V gene segments harboring variable levels of somatic hypermutation. From this search, two gB-binding human monoclonal IgGs were generated that neutralized HCMV infection in vitro. Passive immunization with these antibodies provided proof-of-concept evidence of protection against HCMV infection. This HIS/HCMV in vivo model system supported the validation of novel active and passive immune therapies for future clinical translation.

Human cytomegalovirus (HCMV) is a ubiquitous pathogen. As long as the immune system is functional, T and B cells can control HCMV. Yet, for patients who have debilitated immune functions, HCMV infections and reactivations cause major complications. Vaccines or antibodies to prevent or treat HCMV are not yet approved. Novel animal models for testing new immunization approaches are emerging and are important tools to identify biomedical products with a reasonable chance to work in patients. Here, we used a model based on mice transplanted with human immune cells and infected with a traceable HCMV. We tested a cell vaccine (iDCgB) carrying gB, a potent HCMV antigen. The model showed that iDCgB halted the HCMV infection in more than 90% of the mice. We found that antibodies were key players mediating protection. Using state-of-the-art methods, we were able to use the sequences of the human antibodies generated in the mice to construct and produce monoclonal antibodies in the laboratory. Proof-of-concept experiments indicated that administration of these monoclonal antibodies into mice protected them against HCMV infection. In summary, this humanized mouse model was useful to test a vaccine and to generate and test novel antibodies that can be further developed for human use.

Development of a Synthetic Poxvirus-Based SARS-CoV-2 Vaccine

Modified Vaccinia Ankara (MVA) is a highly attenuated poxvirus vector that is widely used to develop vaccines for infectious diseases and cancer. We developed a novel vaccine platform based on a unique three-plasmid system to efficiently generate recombinant MVA vectors from chemically synthesized DNA. In response to the ongoing global pandemic caused by SARS coronavirus-2 (SARS-CoV-2), we used this novel vaccine platform to rapidly produce fully synthetic MVA (sMVA) vectors co-expressing SARS-CoV-2 spike and nucleocapsid antigens, two immunodominant antigens implicated in protective immunity. Mice immunized with these sMVA vectors developed robust SARS-CoV-2 antigen-specific humoral and cellular immune responses, including potent neutralizing antibodies. These results demonstrate the potential of a novel vaccine platform based on synthetic DNA to efficiently generate recombinant MVA vectors and to rapidly develop a multi-antigenic poxvirus-based SARS-CoV-2 vaccine candidate.

Human Cytomegalovirus Congenital (cCMV) Infection Following Primary and Nonprimary Maternal Infection: Perspectives of Prevention through Vaccine Development

Congenital cytomegalovirus (cCMV) might occur as a result of the human cytomegalovirus (HCMV) primary (PI) or nonprimary infection (NPI) in pregnant women. Immune correlates of protection against cCMV have been partly identified only for PI. Following either PI or NPI, HCMV strains undergo latency. From a diagnostic standpoint, while the serological criteria for the diagnosis of PI are well-established, those for the diagnosis of NPI are still incomplete. Thus far, a recombinant gB subunit vaccine has provided the best results in terms of partial protection. This partial efficacy was hypothetically attributed to the post-fusion instead of the pre-fusion conformation of the gB present in the vaccine. Future efforts should be addressed to verify whether a new recombinant gB pre-fusion vaccine would provide better results in terms of prevention of both PI and NPI. It is still a matter of debate whether human hyperimmune globulin are able to protect from HCMV vertical transmission. In conclusion, the development of an HCMV vaccine that would prevent a significant portion of PI would be a major step forward in the development of a vaccine for both PI and NPI.

Immunization with Human Cytomegalovirus Core Fusion Machinery and Accessory Envelope Proteins Elicit Strong Synergistic Neutralizing Activities

Human cytomegalovirus (HCMV) core fusion machinery proteins gB and gH/gL, and accessory proteins UL128/UL130/UL131A, are the key envelope proteins that mediate HCMV entry into and infection of host cells. To determine whether these HCMV envelope proteins could elicit neutralizing activities synergistically, we immunized rabbits with individual or various combinations of these proteins adsorbed to aluminum hydroxide mixed with CpG-ODN. We then analyzed serum neutralizing activities with multiple HCMV laboratory strains and clinical isolates. HCMV trimeric gB and gH/gL elicited high and moderate titers of HCMV neutralizing activity, respectively. HCMV gB in combination with gH/gL elicited up to 17-fold higher HCMV neutralizing activities compared to the sum of neutralizing activity elicited by the individual proteins analyzed with both fibroblasts and epithelial cells. HCMV gB+gH/gL+UL128/UL130/UL131A in combination increased the neutralizing activity up to 32-fold compared to the sum of neutralizing activities elicited by the individual proteins analyzed with epithelial cells. Adding UL128/UL130/UL131A to gB and gH/gL combination did not increase further the HCMV neutralizing activity analyzed with fibroblasts. These data suggest that the combination of HCMV core fusion machinery envelope proteins gB+gH/gL or the combination of gB and pentameric complex could be ideal vaccine candidates that would induce optimal immune responses against HCMV infection.

A Pentavalent Epstein-Barr Virus-Like Particle Vaccine Elicits High Titers of Neutralizing Antibodies against Epstein-Barr Virus Infection in Immunized Rabbits

Primary infection with Epstein-Barr virus (EBV) is associated with acute infectious mononucleosis, whereas persistent infection is associated with chronic diseases such as autoimmune diseases and various types of cancer. Indeed, approximately 2% of all new cancer cases occurring annually worldwide are EBV-associated. Currently, there is no licensed EBV prophylactic vaccine. Selection of appropriate viral protein subunits is critical for development of an effective vaccine. Although the major EBV surface glycoprotein gp350/220 (gp350) has been proposed as an important prophylactic vaccine target, attempts to develop a potent vaccine based on gp350 alone have shown limited success in the clinic. We provide data showing that five EBV glycoproteins (gp350, gB, gp42, gH, and gL) involved in viral entry and infection can successfully be incorporated on the surface of EBV-like particles (EBV-LPs). These EBV-LPs, when administered together with aluminum hydroxide and monophosphoryl lipid A as adjuvants to New Zealand white rabbits, elicited EBV glycoprotein-specific antibodies capable of neutralizing viral infection in vitro in both B cells and epithelial cells, better than soluble gp350 ectodomain. Our findings suggest that a pentavalent EBV-LP formulation might be an ideal candidate for development as a safe and immunogenic EBV vaccine.

Modeling Human Cytomegalovirus in Humanized Mice for Vaccine Testing

Human cytomegalovirus (HCMV or HHV-5) is a globally spread pathogen with strictly human tropism that establishes a life-long persistence. After primary infection, high levels of long-term T and B cell responses are elicited, but the virus is not cleared. HCMV persists mainly in hematopoietic reservoirs, whereby occasional viral reactivation and spread are well controlled in immunocompetent hosts. However, when the immune system cannot control viral infections or reactivations, such as with newborns, patients with immune deficiencies, or immune-compromised patients after transplantations, the lytic outbursts can be severely debilitating or lethal. The development of vaccines for immunization of immune-compromised hosts has been challenging. Several vaccine candidates did not reach the potency expected in clinical trials and were not approved. Before anti-HCMV vaccines can be tested pre-clinically in immune-compromised hosts, reliable in vivo models recapitulating HCMV infection might accelerate their clinical translation. Therefore, immune-deficient mouse strains implanted with human cells and tissues and developing a human immune system (HIS) are being explored to test anti-HCMV vaccines. HIS-mice resemble immune-compromised hosts as they are equipped with antiviral human T and B cells, but the immune reactivity is overall low. Several groups have independently shown that HCMV infections and reactivations can be mirrored in HIS mice. However, these models and the analyses employed varied widely. The path forward is to improve human immune reconstitution and standardize the analyses of adaptive responses so that HIS models can be forthrightly used for testing novel generations of anti-HCMV vaccines in the preclinical pipeline.

MVA-Vectored Pentameric Complex (PC) and gB Vaccines Improve Pregnancy Outcome after Guinea Pig CMV Challenge, but Only gB Vaccine Reduces Vertical Transmission

(1) Background: A congenital cytomegalovirus (cCMV) vaccine is a major research priority, but the essential glycoprotein target(s) remain unclear. We compared CMV gB (gpgB), gH/gL (gp75/gL), and pentameric complex (gpPC, composed of gH/gL/GP129/GP131/GP133) vaccines in a guinea pig CMV (GPCMV) congenital infection model. (2) Methods: Modified vaccinia virus Ankara (MVA) vaccines expressing GPCMV glycoproteins were used to immunize GPCMV-seronegative, female Hartley guinea pigs (three-dose series, 3 × 10⁷ pfu/dose). After pregnancy was established, the dams underwent an early third-trimester challenge with salivary gland (SG)-adapted GPCMV. (3) Results: All vaccines elicited GPCMV-specific binding and neutralizing antibodies. Preconception immunization resulted in 19.5-, 4.9-, and 698-fold reductions in maternal DNAemia in MVA-gp75/gL, MVA-gpPC and MVA-gpgB groups, respectively, at day 14, post-SG challenge. Vaccination improved pups’ birth weight and reduced mortality and congenital CMV transmission. In controls, cCMV infection was observed in 100% of pups (mean viral load in all visceral organs, 2.4 × 10⁴ genomes/mg), versus 50% in the gB group (visceral viral load, 9.4 × 10² genomes/mg; p < 0.05). No significant reductions in congenital transmission were noted in the MVA-gp75/gL and MVA-gpPC groups. (4) Conclusions: MVA-vectored gB, gH/gL, and PC vaccines were immunogenic, and protected against maternal DNAemia and pup mortality. These results support the inclusion of multiple glycoprotein complexes in a cCMV vaccine.

Dense Bodies of a gH/gL/UL128/UL130/UL131 Pentamer-Repaired Towne Strain of Human Cytomegalovirus Induce an Enhanced Neutralizing Antibody Response

The development of a vaccine against human cytomegalovirus infection (HCMV) is a high-priority medical goal. The viral pentameric protein complex consisting of glycoprotein H (gH)/gL/UL128-131A (PC) is considered to be an important vaccine component. Its relevance to the induction of a protective antibody response is, however, still a matter of debate. We addressed this issue by using subviral dense bodies (DBs) of HCMV. DBs are exceptionally immunogenic. Laboratory HCMV strain DBs harbor important neutralizing antibody targets, like the glycoproteins B, H, L, M, and N, but they are devoid of the PC. To be able to directly compare the impact of the PC on the levels of neutralizing antibody (NT-abs) responses, a PC-positive variant of the HCMV laboratory strain Towne was established by bacterial artificial chromosome (BAC) mutagenesis (Towne-UL130rep). This strain synthesized PC-positive DBs upon infection of fibroblasts. These DBs were used in side-by-side immunizations with PC-negative Towne DBs. Mouse and rabbit sera were tested to address the impact of the PC on DB immunogenicity. The neutralizing antibody response to PC-positive DBs was superior to that of PC-negative DBs, as tested on fibroblasts, epithelial cells, and endothelial cells and for both animal species used. The experiments revealed the potential of the PC to enhance the antibody response against HCMV. Of particular interest was the finding that PC-positive DBs induced an antibody response that blocked the infection of fibroblasts by a PC-positive viral strain more efficiently than sera following immunizations with PC-negative particles.IMPORTANCE Infections with the human cytomegalovirus (HCMV) may cause severe and even life-threatening disease manifestations in newborns and immunosuppressed individuals. Several strategies for the development of a vaccine against this virus are currently pursued. A critical question in this respect refers to the antigenic composition of a successful vaccine. Using a subviral particle vaccine candidate, we show here that one protein complex of HCMV, termed the pentameric complex (PC), enhances the neutralizing antibody response against viral infection of different cell types. We further show for the first time that this not only relates to the infection of epithelial or endothelial cells; the presence of the PC in the particles also enhanced the neutralizing antibody response against the infection of fibroblasts by HCMV. Together, these findings argue in favor of including the PC in strategies for HCMV vaccine development.

Immunization of Rabbits with Recombinant Human Cytomegalovirus Trimeric versus Monomeric gH/gL Protein Elicits Markedly Higher Titers of Antibody and Neutralization Activity

Congenital human cytomegalovirus (HCMV) infection and HCMV infection of immunosuppressed patients cause significant morbidity and mortality, and vaccine development against HCMV is a major public health priority. HCMV envelope glycoproteins gB, gH, and gL, which constitute the core fusion machinery, play critical roles in HCMV fusion and entry into host cells. HCMV gB and gH/gL have been reported to elicit potent neutralizing antibodies. Recently, the gB/gH/gL complex was identified in the envelope of HCMV virions, and 16–50% of the total gH/gL bound to gB, forming the gB/gH/gL complex. These findings make the gB/gH/gL a unique HCMV vaccine candidate. We previously reported the production of HCMV trimeric gB and gH/gL heterodimers, and immunization with a combination of trimeric gB and gH/gL heterodimers elicited strong synergistic HCMV-neutralizing activity. To further improve the immunogenicity of gH/gL, we produced trimeric gH/gL. Rabbits immunized with HCMV trimeric gH/gL induced up to 38-fold higher serum titers of gH/gL-specific IgG relative to HCMV monomeric gH/gL, and elicited ~10-fold higher titers of complement-dependent and complement-independent HCMV-neutralizing activity for both epithelial cells and fibroblasts. HCMV trimeric gH/gL in combination with HCMV trimeric gB would be a novel promising HCMV vaccine candidate that could induce highly potent neutralizing activities.

A multivalent Kaposi sarcoma-associated herpesvirus-like particle vaccine capable of eliciting high titers of neutralizing antibodies in immunized rabbits

Kaposi sarcoma-associated herpesvirus (KSHV) is an emerging pathogen and the causative agent of multiple cancers in immunocompromised patients. To date, there is no licensed prophylactic KSHV vaccine. In this study, we generated a novel subunit vaccine that incorporates four key KSHV envelope glycoproteins required for viral entry in diverse cell types (gpK8.1, gB, and gH/gL) into a single multivalent KSHV-like particle (KSHV-LP). Purified KSHV-LPs were similar in size, shape, and morphology to KSHV virions. Vaccination of rabbits with adjuvanted KSHV-LPs generated strong glycoprotein-specific antibody responses, and purified immunoglobulins from KSHV-LP-immunized rabbits neutralized KSHV infection in epithelial, endothelial, fibroblast, and B cell lines (60-90% at the highest concentration tested). These findings suggest that KSHV-LPs may be an ideal platform for developing a safe and effective prophylactic KSHV vaccine. We envision performing future studies in animal models that are susceptible to KSHV infection, to determine correlates of immune protection in vivo.

Development of novel vaccines against human cytomegalovirus

Congenital human cytomegalovirus (HCMV) infection and HCMV infection of the immunosuppressed patients cause significant morbidity and mortality, and vaccine development against HCMV is a major public health priority. Efforts to develop HCMV vaccines have been ongoing for 50 y, though no HCMV vaccine has been licensed; encouraging and promising results have obtained from both preclinical and clinical trials. HCMV infection induces a wide range of humoral and T cell-mediated immune responses, and both branches of immunity are correlated with protection. In recent years, there have been novel approaches toward the development of HCMV vaccines and demonstrated that vaccine candidates could potentially provide superior protection over natural immunity acquired following HCMV infection. Further, rationally designed HCMV protein antigens that express native conformational epitopes could elicit optimal immune response. HCMV vaccine candidates, using a multi-antigen approach, to maximize the elicited protective immunity will most likely be successful in development of HCMV vaccine.

Vaccinia virus-mediated cancer immunotherapy: cancer vaccines and oncolytics

Cancer vaccines and oncolytic immunotherapy are promising treatment strategies with potential to provide greater clinical benefit to patients with advanced-stage cancer. In particular, recombinant vaccinia viruses (VV) hold great promise as interventional agents. In this article, we first summarize the current understanding of virus biology and viral genes involved in host-virus interactions to further improve the utility of these agents in therapeutic applications. We then discuss recent findings from basic and clinical studies using VV as cancer vaccines and oncolytic immunotherapies. Despite encouraging results gleaned from translational studies in animal models, clinical trials implementing VV vectors alone as cancer vaccines have yielded largely disappointing results. However, the combination of VV vaccines with alternate forms of standard therapies has resulted in superior clinical efficacy. For instance, combination regimens using TG4010 (MVA-MUC1-IL2) with first-line chemotherapy in advanced-stage non-small cell lung cancer or combining PANVAC with docetaxel in the setting of metastatic breast cancer have clearly provided enhanced clinical benefits to patients. Another novel cancer vaccine approach is to stimulate anti-tumor immunity via STING activation in Batf3-dependent dendritic cells (DC) through the use of replication-attenuated VV vectors. Oncolytic VVs have now been engineered for improved safety and superior therapeutic efficacy by arming them with immune-stimulatory genes or pro-apoptotic molecules to facilitate tumor immunogenic cell death, leading to enhanced DC-mediated cross-priming of T cells recognizing tumor antigens, including neoantigens. Encouraging translational and early phase clinical results with Pexa-Vec have matured into an ongoing global phase III trial for patients with hepatocellular carcinoma. Combinatorial approaches, most notably those using immune checkpoint blockade, have produced exciting pre-clinical results and warrant the development of innovative clinical studies. Finally, we discuss major hurdles that remain in the field and offer some perspectives regarding the development of next generation VV vectors for use as cancer therapeutics.

A fifty-year odyssey: prospects for a cytomegalovirus vaccine in transplant and congenital infection

INTRODUCTION

It has been almost fifty years since the Towne strain was used by Plotkin and collaborators as the first vaccine candidate for cytomegalovirus (CMV). While that approach showed partial efficacy, there have been a multitude of challenges to improve on the promise of a CMV vaccine. Efforts have been dichotomized into a therapeutic vaccine for patients with CMV-infected allografts, either stem cells or solid organ, and a prophylactic vaccine for congenital infection.

AREAS COVERED

This review will evaluate research prospects for a therapeutic vaccine for transplant recipients that recognizes CMV utilizing primarily T cell responses. Similarly, we will provide an extensive discussion on attempts to develop a vaccine to prevent the manifestations of congenital infection, based on eliciting a humoral anti-CMV protective response. The review will also describe newer developments that have upended the efforts toward such a vaccine through the discovery of a second pathway of CMV infection that utilizes an alternative receptor for entry using a series of antigens that have been determined to be important for prevention of infection.

EXPERT COMMENTARY

There is a concerted effort to unify separate therapeutic and prophylactic vaccine strategies into a single delivery agent that would be effective for both transplant-related and congenital infection.