Induction of pluripotent protective immunity following immunisation with a chimeric vaccine against human cytomegalovirus

Identifying optimal vaccination scenarios to reduce varicella zoster virus transmission and reactivation

BACKGROUND

Varicella zoster virus (VZV) is one of the eight known human herpesviruses. Initial VZV infection results in chickenpox, while viral reactivation following a period of latency manifests as shingles. Separate vaccines exist to protect against both initial infection and subsequent reactivation. Controversy regarding chickenpox vaccination is contentious with most countries not including the vaccine in their childhood immunization schedule due to the hypothesized negative impact on immune-boosting, where VZV reactivation is suppressed through exogenous boosting of VZV antibodies from exposure to natural chickenpox infections.

METHODS

Population-level chickenpox and shingles notifications from Thailand, a country that does not vaccinate against either disease, were previously fitted with mathematical models to estimate rates of VZV transmission and reactivation. Here, multiple chickenpox and shingles vaccination scenarios were simulated and compared to a model lacking any vaccination to analyze the long-term impacts of VZV vaccination.

RESULTS

As expected, simulations suggested that an introduction of the chickenpox vaccine, at any coverage level, would reduce chickenpox incidence. However, chickenpox vaccine coverage levels above 35% would increase shingles incidence under realistic estimates of shingles coverage with the current length of protective immunity from the vaccine. A trade-off between chickenpox and shingles vaccination coverage was discovered, where mid-level chickenpox coverage levels were identified as the optimal target to minimize total zoster burden. Only in scenarios where shingles vaccine provided lifelong immunity or coverage exceeded current levels could large reductions in both chickenpox and shingles be achieved.

CONCLUSIONS

The complicated nature of VZV makes it impossible to select a single vaccination scenario as universal policy. Strategies focused on reducing both chickenpox and shingles incidence, but prioritizing the latter should maximize efforts towards shingles vaccination, while slowly incorporating chickenpox vaccination. Alternatively, countries may wish to minimize VZV complications of both chickenpox and shingles, which would lead to maximizing vaccine coverage levels across both diseases. Balancing the consequences of vaccination to overall health impacts, including understanding the impact of an altered mean age of infection for both chickenpox and shingles, would need to be considered prior to any vaccine introduction.

Common Childhood Viruses and Pubertal Timing: The LEGACY Girls Study

Earlier pubertal development is only partially explained by childhood body mass index; the role of other factors, such as childhood infections, is less understood. Using data from the LEGACY Girls Study (North America, 2011-2016), we prospectively examined the associations between childhood viral infections (cytomegalovirus (CMV), Epstein-Barr virus (EBV), herpes simplex virus (HSV) 1, HSV2) and pubertal timing. We measured exposures based on seropositivity in premenarcheal girls (n = 490). Breast and pubic hair development were classified based on mother-reported Tanner Stage (TS) (TS2+ compared with TS1), adjusting for age, body mass index, and sociodemographic factors. The average age at first blood draw was 9.8 years (standard deviation, 1.9 years). The prevalences were 31% CMV+, 37% EBV+, 14% HSV1+, 0.4% HSV2+, and 16% for both CMV+/EBV+ coinfection. CMV+ infection without coinfection was associated with developing breasts an average of 7 months earlier (hazard ratio (HR) = 2.12, 95% confidence interval (CI): 1.32, 3.40). CMV infection without coinfection and HSV1 and/or HSV2 infection were associated with developing pubic hair 9 months later (HR = 0.41, 95% CI: 0.24, 0.71, and HR = 0.42, 95% CI: 0.22, 0.81, respectively). Infection was not associated with menarche. If replicated in larger cohorts with blood collection prior to any breast development, this study supports the hypothesis that childhood infections might play a role in altering pubertal timing.

Discordance Between the Predicted Versus the Actually Recognized CD8+ T Cell Epitopes of HCMV pp65 Antigen and Aleatory Epitope Dominance

CD8+ T cell immune monitoring aims at measuring the size and functions of antigen-specific CD8+ T cell populations, thereby providing insights into cell-mediated immunity operational in a test subject. The selection of peptides for ex vivo CD8+ T cell detection is critical because within a complex antigen exists a multitude of potential epitopes that can be presented by HLA class I molecules. Further complicating this task, there is HLA class I polygenism and polymorphism which predisposes CD8+ T cell responses towards individualized epitope recognition profiles. In this study, we compare the actual CD8+ T cell recognition of a well-characterized model antigen, human cytomegalovirus (HCMV) pp65 protein, with its anticipated epitope coverage. Due to the abundance of experimentally defined HLA-A*02:01-restricted pp65 epitopes, and because in silico epitope predictions are most advanced for HLA-A*02:01, we elected to focus on subjects expressing this allele. In each test subject, every possible CD8+ T cell epitope was systematically covered testing 553 individual peptides that walk the sequence of pp65 in steps of single amino acids. Highly individualized CD8+ T cell response profiles with aleatory epitope recognition patterns were observed. No correlation was found between epitopes' ranking on the prediction scale and their actual immune dominance. Collectively, these data suggest that accurate CD8+ T cell immune monitoring may necessitate reliance on agnostic mega peptide pools, or brute force mapping, rather than electing individual peptides as representative epitopes for tetramer and other multimer labeling of surface antigen receptors.

Computational assembly of a human Cytomegalovirus vaccine upon experimental epitope legacy

Background

Human Cytomegalovirus (HCMV) is a ubiquitous herpesvirus affecting approximately 90% of the world population. HCMV causes disease in immunologically naive and immunosuppressed patients. The prevention, diagnosis and therapy of HCMV infection are thus crucial to public health. The availability of effective prophylactic and therapeutic treatments remain a significant challenge and no vaccine is currently available. Here, we sought to define an epitope-based vaccine against HCMV, eliciting B and T cell responses, from experimentally defined HCMV-specific epitopes.

Results

We selected 398 and 790 experimentally validated HCMV-specific B and T cell epitopes, respectively, from available epitope resources and apply a knowledge-based approach in combination with immunoinformatic predictions to ensemble a universal vaccine against HCMV. The T cell component consists of 6 CD8 and 6 CD4 T cell epitopes that are conserved among HCMV strains. All CD8 T cell epitopes were reported to induce cytotoxic activity, are derived from early expressed genes and are predicted to provide population protection coverage over 97%. The CD4 T cell epitopes are derived from HCMV structural proteins and provide a population protection coverage over 92%. The B cell component consists of just 3 B cell epitopes from the ectodomain of glycoproteins L and H that are highly flexible and exposed to the solvent.

Conclusions

We have defined a multiantigenic epitope vaccine ensemble against the HCMV that should elicit T and B cell responses in the entire population. Importantly, although we arrived to this epitope ensemble with the help of computational predictions, the actual epitopes are not predicted but are known to be immunogenic.

The Third International Consensus Guidelines on the Management of Cytomegalovirus in Solid-organ Transplantation

Despite recent advances, cytomegalovirus (CMV) infections remain one of the most common complications affecting solid organ transplant recipients, conveying higher risks of complications, graft loss, morbidity, and mortality. Research in the field and development of prior consensus guidelines supported by The Transplantation Society has allowed a more standardized approach to CMV management. An international multidisciplinary panel of experts was convened to expand and revise evidence and expert opinion-based consensus guidelines on CMV management including prevention, treatment, diagnostics, immunology, drug resistance, and pediatric issues. Highlights include advances in molecular and immunologic diagnostics, improved understanding of diagnostic thresholds, optimized methods of prevention, advances in the use of novel antiviral therapies and certain immunosuppressive agents, and more savvy approaches to treatment resistant/refractory disease. The following report summarizes the updated recommendations.

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

As human cytomegalovirus (HCMV) is a common cause of disease in newborns and transplant recipients, developing an HCMV vaccine is considered a major public health priority. Yet an HCMV vaccine candidate remains elusive. Although the precise HCMV immune correlates of protection are unclear, both humoral and cellular immune responses have been implicated in protection against HCMV infection and disease. Here we describe a vaccine approach based on the well-characterized modified vaccinia virus Ankara (MVA) vector to stimulate robust HCMV humoral and cellular immune responses by an antigen combination composed of the envelope pentamer complex (PC), glycoprotein B (gB), and phosphoprotein 65 (pp65). We show that in mice, multiantigenic MVA vaccine vectors simultaneously expressing all five PC subunits, gB, and pp65 elicit potent complement-independent and complement-dependent HCMV neutralizing antibodies as well as mouse and human MHC-restricted, polyfunctional T cell responses by the individual antigens. In addition, we demonstrate that the PC/gB antigen combination of these multiantigenic MVA vectors can enhance the stimulation of humoral immune responses that mediate in vitro neutralization of different HCMV strains and antibody-dependent cellular cytotoxicity. These results support the use of MVA to develop a multiantigenic vaccine candidate for controlling HCMV infection and disease in different target populations, such as pregnant women and transplant recipients.IMPORTANCE The development of a human cytomegalovirus (HCMV) vaccine to prevent congenital disease and transplantation-related complications is an unmet medical need. While many HCMV vaccine candidates have been developed, partial success in preventing or controlling HCMV infection in women of childbearing age and transplant recipients has been observed with an approach based on envelope glycoprotein B (gB). We introduce a novel vaccine strategy based on the clinically deployable modified vaccinia virus Ankara (MVA) vaccine vector to elicit potent humoral and cellular immune responses by multiple immunodominant HCMV antigens, including gB, phosphoprotein 65, and all five subunits of the pentamer complex. These findings could contribute to development of a multiantigenic vaccine strategy that may afford more protection against HCMV infection and disease than a vaccine approach employing solely gB.

Advancing Our Understanding of Protective Maternal Immunity as a Guide for Development of Vaccines To Reduce Congenital Cytomegalovirus Infections

Human cytomegalovirus (HCMV) is the most common congenitally transmitted pathogen worldwide, impacting an estimated 1 million newborns annually. Congenital HCMV (cCMV) infection is a major global contributor to long-term neurologic deficits, including deafness, microcephaly, and neurodevelopmental delay, as well as to fetal loss and occasional infant mortality. Accordingly, design of a maternal vaccine to prevent cCMV continues to be a top public health priority. Nevertheless, we remain without a licensed vaccine. Maternal immunity provides partial protection, as the risk of vertical HCMV transmission from chronically infected mothers is reduced compared to settings in which the mother is newly infected during pregnancy. Therefore, an understanding of the maternal immune correlates of protection against cCMV is critical to informing design of an efficacious maternal vaccine. Although vaccine development is being assiduously pursued by a large number of pharmaceutical manufacturers, biotechnology organizations, and academic researchers, some pessimism has been expressed regarding the issue of whether a vaccine to protect against cCMV is possible. This pessimism is based on observations that natural immunity is not completely protective against maternal reinfection and congenital transmission. However, we assert that optimism regarding vaccine development is indeed justified, on the basis of accruing evidence of immune correlates of protection-readily achievable by vaccination-that are associated with reduced transmission of HCMV to the fetus in seronegative women. In light of the substantial burden on society conferred by cCMV infection, even a modest reduction in the occurrence of this fetal disease is an important public health goal and justifies aggressive clinical evaluation of vaccines currently in the pipeline.

Asian Elephant T Cell Responses to Elephant Endotheliotropic Herpesvirus

Elephant endotheliotropic herpesvirus (EEHV) can cause lethal hemorrhagic disease in juvenile Asian elephants, an endangered species. One hypothesis to explain this vulnerability of some juvenile elephants is that they fail to mount an effective T cell response to the virus. To our knowledge, there have been no studies of Asian elephant T cell responses to EEHV. To address this deficiency, we validated the gamma interferon (IFN-γ) enzyme-linked immunospot assay for tracking antigen-directed T cell activity by monitoring rabies-specific responses in vaccinated elephants. In addition, we generated monoclonal antibodies to Asian elephant CD4 and CD8 to facilitate phenotypic T cell profiling. Using these tools, we screened healthy elephants with a history of EEHV infection for reactivity against nine EEHV proteins whose counterparts in other herpesviruses are known to induce T cell responses in their natural hosts. We identified glycoprotein B (gB) and the putative regulatory protein E40 as the most immunogenic T cell targets (IFN-γ responses in five of seven elephants), followed by the major capsid protein (IFN-γ responses in three of seven elephants). We also observed that IFN-γ responses were largely from CD4⁺ T cells. We detected no activity against the predicted major immediate early (E44) and large tegument (E34) proteins, both immunodominant T cell targets in humans latently infected with cytomegalovirus. These studies identified EEHV-specific T cells in Asian elephants for the first time, lending insight into the T cell priming that might be required to protect against EEHV disease, and will guide the design of effective vaccine strategies.

IMPORTANCE Endangered Asian elephants are facing many threats, including lethal hemorrhagic disease from elephant endotheliotropic herpesvirus (EEHV). EEHV usually establishes chronic, benign infections in mature Asian elephants but can be lethal to juvenile elephants in captivity and the wild. It is the leading cause of death in captive Asian elephants in North America and Europe. Despite the availability of sensitive tests and protocols for treating EEHV-associated illness, these measures are not always effective. The best line of defense would be a preventative vaccine. We interrogated normal healthy elephants previously infected with EEHV for T cell responses to nine EEHV proteins predicted to induce cellular immune responses. Three proteins elicited IFN-γ responses, suggesting their potential usefulness as vaccine candidates. Our work is the first to describe T cell responses to a member of the proposed fourth subfamily of mammalian herpesviruses, the Deltaherpesvirinae, within a host species in the clade Afrotheria. An EEHV vaccine would greatly contribute to the health care of Asian and African elephants that are also susceptible to this disease.

Cytomegalovirus Vaccines: Current Status and Future Prospects

Congenital human cytomegalovirus (HCMV) infection can result in severe and permanent neurological injury in newborns, and vaccine development is accordingly a major public health priority. HCMV can also cause disease in solid organ transplant (SOT) and hematopoietic stem-cell transplant (HSCT) recipients, and a vaccine would be valuable in prevention of viremia and end-organ disease in these populations. Currently there is no licensed HCMV vaccine, but progress toward this goal has been made in recent clinical trials. A recombinant HCMV glycoprotein B (gB) vaccine has been shown to have some efficacy in prevention of infection in young women and adolescents, and has provided benefit to HCMV-seronegative SOT recipients. Similarly, DNA vaccines based on gB and the immunodominant T-cell target, pp65 (ppUL83), have been shown to reduce viremia in HSCT patients. This review provides an overview of HCMV vaccine candidates in various stages of development, as well as an update on the current status of ongoing clinical trials. Protective correlates of vaccine-induced immunity may be different for pregnant woman and transplant patients. As more knowledge emerges about correlates of protection, the ultimate licensure of HCMV vaccines may reflect the uniqueness of the target populations being immunized.

Animal models of human cytomegalovirus congenital infection

Human cytomegalovirus (HCMV) infection is highly species-specific, which means that it is unable to productively infect laboratory animals. Despite this caveat, studies of animal CMV counterparts in their natural hosts have revealed significant correlations with observed neuropathological effects of congenital HCMV infection and have improved our understanding of host responses to vaccination. The biological relatedness between human and animal CMVs has been confirmed by phylogenetic analyses; the conservation of ‘core' genes that are essential for virus replication as well as genes that contribute similar mechanisms for virus persistence in their respective host species. The common animal models of HCMV congenital infection include Rhesus CMV (RhCMV), guinea-pig CMV (GPCMV) and mouse CMV (MCMV). Whilst animal models of CMV do not fully recapitulate HCMV infection, they each offer specific advantages in understanding HCMV congenital/perinatal infection (summarised in Table 1).

mRNA Structural constraints on EBNA1 synthesis impact on in vivo antigen presentation and early priming of CD8+ T cells

Recent studies have shown that virally encoded mRNA sequences of genome maintenance proteins from herpesviruses contain clusters of unusual structural elements, G-quadruplexes, which modulate viral protein synthesis. Destabilization of these G-quadruplexes can override the inhibitory effect on self-synthesis of these proteins. Here we show that the purine-rich repetitive mRNA sequence of Epstein-Barr virus encoded nuclear antigen 1 (EBNA1) comprising G-quadruplex structures, limits both the presentation of MHC class I-restricted CD8⁺ T cell epitopes by CD11c⁺ dendritic cells in draining lymph nodes and early priming of antigen-specific CD8⁺ T-cells. Destabilization of the G-quadruplex structures through codon-modification significantly enhanced in vivo antigen presentation and activation of virus-specific T cells. Ex vivo imaging of draining lymph nodes by confocal microscopy revealed enhanced antigen-specific T-cell trafficking and APC-CD8⁺ T-cell interactions in mice primed with viral vectors encoding a codon-modified EBNA1 protein. More importantly, these antigen-specific T cells displayed enhanced expression of the T-box transcription factor and superior polyfunctionality consistent with the qualitative impact of translation efficiency. These results provide an important insight into how viruses exploit mRNA structure to down regulate synthesis of their viral maintenance proteins and delay priming of antigen-specific T cells, thereby establishing a successful latent infection in vivo. Furthermore, targeting EBNA1 mRNA rather than protein by small molecules or antisense oligonucleotides will enhance EBNA1 synthesis and the early priming of effector T cells, to establish a more rapid immune response and prevent persistent infection.

Maintenance proteins of viruses establishing latent infections regulate their synthesis to levels sufficient for maintaining persistent infection but below threshold levels for host immune detection. The Epstein-Barr virus maintenance protein, EBNA1, has recently been shown to contain unusual G-quadruplex structures within its repeat mRNA that reduces its translational efficiency. In this study we assess how modification of the EBNA1 mRNA repeat sequence to destabilize the native G-quadruplex structures and thereby increase translation, impacts on the activation of EBNA1-specific T cells in vivo. Mice primed with viral vectors encoding a more efficiently translated EBNA1 mRNA revealed increased trafficking of EBNA1-specific T cells, an enhanced functional profile and increased expression of transcription factors providing evidence for a potential link between mRNA translational efficiency and antigen presentation in vivo and the resultant impact on the functional programming of effector T cells. These findings suggest a novel approach to therapeutic development through the use of antisense strategies or small molecules targeting EBNA1 mRNA structure.

Induction of innate immune signatures following polyepitope protein-glycoprotein B-TLR4&9 agonist immunization generates multifunctional CMV-specific cellular and humoral immunity

Recent studies have suggested that a successful subunit human cytomegalovirus (CMV) vaccine requires improved formulation to generate broad-based anti-viral immunity following immunization. Here we report the development of a non-live protein-based vaccine strategy for CMV based on a polyepitope protein and CMV glycoprotein B (gB) adjuvanted with TLR4 and/or TLR9 agonists. The polyepitope protein includes contiguous multiple MHC class I-restricted epitopes with an aim to induce CD8⁺ T cell immunity, while gB is an important target for CD4⁺ T cell immunity and neutralizing antibodies. Optimal immunogenicity of this bivalent non-live protein vaccine formulation was dependent upon the co-administration of both the TLR4 and TLR9 agonist, which was associated with the activation of innate immune signatures and the influx of different DC subsets including plasmacytoid DCs and migratory CD8-DEC205+CD103-CD326- langerin-negative dermal DCs into the draining lymph nodes. Furthermore these professional antigen presenting cells also expressed IL-6, IL-12p70, TNFα, and IFNα which play a crucial role in the activation of adaptive immunity. In summary, this study provides a novel platform technology in which broad-based anti-CMV immune responses upon vaccination can be maximized by co-delivery of viral antigens and TLR4 and 9 agonists which induce activation of innate immune signatures and promote potent antigen acquisition and cross-presentation by multiple DC subsets.

Developing a Vaccine against Congenital Cytomegalovirus (CMV) Infection: What Have We Learned from Animal Models? Where Should We Go Next?

Congenital human cytomegalovirus (HCMV) infection can lead to long-term neurodevelopmental sequelae, including mental retardation and sensorineural hearing loss. Unfortunately, CMVs are highly adapted to their specific species, precluding the evaluation of HCMV vaccines in animal models prior to clinical trials. Several species-specific CMVs have been characterized and developed in models of pathogenesis and vaccine-mediated protection against disease. These include the murine CMV (MCMV), the porcine CMV (PCMV), the rhesus macaque CMV (RhCMV), the rat CMV (RCMV), and the guinea pig CMV (GPCMV). Because of the propensity of the GPCMV to cross the placenta, infecting the fetus in utero, it has emerged as a model of particular interest in studying vaccine-mediated protection of the fetus. In this paper, a review of these various models, with particular emphasis on the value of the model in the testing and evaluation of vaccines against congenital CMV, is provided. Recent exciting developments and advances in these various models are summarized, and recommendations offered for high-priority areas for future study.

Cellular immune therapy for viral infections in transplant patients

Stem cell and organ transplantation are considered as the major advances of modern medicine. Unfortunately the success of transplantation is limited by its toxicity and infectious complications as a result of profound immunosuppression. Viral infections are an extremely common and predictable problem in these patients. Antiviral drugs given either prophylactically or as early therapy for patients with detectable viral loads appear to be an effective strategy for reducing viral infections. However, long-term treatment with these drugs is associated with significant toxicity, expense and the appearance of drug resistant virus isolates ultimately resulting in treatment failure. Over the last few years, there is increasing evidence that cellular immune therapies can reverse the outgrowth of haematological malignancies and can also provide therapeutic benefit against lethal viral infections. While the expansion and adoptive transfer of virus-specific T-cells from the healthy donor can be an effective strategy to control viral replication, this is not possible when donors are seronegative or are subsequently inaccessible. Recent studies have demonstrated successful expansion of virus-specific T-cells from seropositive stem cell transplant recipients of a seronegative graft with active virus disease and the long term reconstitution of protective anti-viral immunity following their adoptive transfer back into the patients. Furthermore, this immunotherapeutic strategy has also been extended for multiple pathogens including cytomegalovirus, Epstein-Barr virus, adenovirus and BK polyoma-virus. This approach can be employed to rapidly expand multiple pathogens-specific T cells that can be used for adoptive immunotherapy. Finally, new assays to monitor T cell immunity have been developed which will allow to identify the high risk transplant patients who may develop virus-associated complications post-transplantation and can be given adoptive T cell therapy prophylactically.

Herpesviruses: latency and reactivation - viral strategies and host response

Eight members of the Herpesviridae family commonly infect humans, and close to 100% of the adult population is infected with at least one of these. The five that cause the most health concerns are: herpes simplex virus (HSV) type 1 and 2, Epstein-Barr virus (EBV), cytomegalovirus (CMV), and varicella zoster virus (VZV). In addition, there are human herpes virus (HHV) types 6-8. The review starts by introducing possible viral strategies in general. The particular biology and host relationship of the various human herpesviruses, including their pathology, are examined subsequently. Factors that contribute to the maintenance of latency and reactivation of viral replication are discussed. There will be special reference to how these viruses exploit and contribute to pathology in the oral cavity. Reactivation does not necessarily imply clinical symptoms, as reflected in the asymptomatic shedding of EBV and CMV from oral mucosa. The immune response and the level of viral output are both important to the consequences experienced.

Updated international consensus guidelines on the management of cytomegalovirus in solid-organ transplantation

Cytomegalovirus (CMV) continues to be one of the most common infections after solid-organ transplantation, resulting in significant morbidity, graft loss, and adverse outcomes. Management of CMV varies considerably among transplant centers but has been become more standardized by publication of consensus guidelines by the Infectious Diseases Section of The Transplantation Society. An international panel of experts was reconvened in October 2012 to revise and expand evidence and expert opinion-based consensus guidelines on CMV management, including diagnostics, immunology, prevention, treatment, drug resistance, and pediatric issues. The following report summarizes the recommendations.

Recent advances in designing an effective vaccine to prevent cytomegalovirus-associated clinical diseases

It is now well over a decade since the US Institute of Medicine of the National Academy of Sciences assigned the highest priority for a vaccine to prevent congenital human CMV infection, which was subsequently endorsed by the US National Vaccine Program Office. In spite of extensive efforts over many years, successful licensure of a CMV vaccine formulation remains elusive. While the understanding of immune regulation of CMV infection in healthy virus carriers and diseased patients has dramatically improved, traditional vaccine development programs have failed to exploit this knowledge. Until recently, most efforts have concentrated on designing vaccine formulations that block CMV infection through neutralizing antibodies. However, studies carried out in various disease settings, especially in transplant patients, have clearly emphasized the importance of cellular immunity and it is indeed encouraging to see that recent CMV vaccine development programs have started to incorporate this arm of the immune system. A number of new vaccine candidates have been found to be effective in preclinical studies, and are able to induce CMV-specific immune responses in clinical studies, although firm evidence for long-term efficacy is not yet available. For successful implementation of these vaccines in clinical settings, it will be important to demonstrate that the vaccine can induce effective levels of immunity for prevention of transmission of viral infection from mother to unborn baby and thus reduce CMV-related pathogenesis. For transplant recipients, vaccine strategies should be aimed at the induction of immunity that restricts viral reactivation and limits development of disease.

Endogenous antigen presentation impacts on T-box transcription factor expression and functional maturation of CD8+ T cells

T-box transcription factors T-bet (Tbx21) and Eomesodermin (Eomes) are critical players in CD8(+) cytotoxic T lymphocyte effector function and differentiation, but how the expression of these transcription factors is regulated remains poorly defined. Here we show that dominant T cells directed toward human CMV, expressing significantly higher levels of T-bet with graded loss of Eomes expression (T-bet(hi)Eomes(hi/lo)), are more efficient in recognizing endogenously processed peptide-major histocompatibility complexes (pMHC) compared with subdominant virus-specific T cells expressing lower levels of T-bet and high levels of Eomes (T-bet(int)Eomes(hi)). Paradoxically, the T-bet(hi)Eomes(hi/lo) dominant populations that efficiently recognized endogenous antigen demonstrated lower intrinsic avidity for pMHC, whereas T-bet(int)Eomes(hi) subdominant populations were characterized by higher pMHC avidity and less efficient recognition of virus-infected cells. Importantly, differential endogenous viral antigen recognition by CMV-specific CD8(+) T cells also correlated with the differentiation status and expression of perforin, granzyme B and K. Furthermore, we demonstrate that the expression of T-bet correlates with clonal expansion, differentiation status, and expression of perforin, granzyme B and K in antigen-specific T cells. These findings illustrate how endogenous viral antigen presentation during persistent viral infection may influence the transcriptional program of virus-specific T cells and their functional profile in the peripheral blood of humans.

[Immunological monitoring strategies for cytomegalovirus infection. Immune-based therapies]

T-cell response to cytomegalovirus (CMV) is essential in the control of viral replication. Quantification of functional CD4(+) and CD8(+) T lymphocytes against certain CMV-antigen specificities through flow cytometry, ELISPOT or the QuantiFERON-CMV kit allows fairly accurate estimation of the risk of active infection and CMV disease in solid organ transplantation (SOT). Combined virological and immunological monitoring of CMV infection could allow antiviral treatments to be individually tailored and optimized in SOT, although clinical experience is currently lacking. The adoptive transfer of CMV-specific T cells before selection with multimer HLA peptides or after activation and expansion ex vivo could be an effective therapeutic alternative in the management of active infection or organic CMV disease refractory to antiviral therapy. Several CMV vaccines have been developed, which have been shown to be safe and immunogenic in preclinical and Phase I clinical trials. However, to date, none of these vaccines has been evaluated in Phase III clinical trials and consequently none has been approved for clinical use.

[Treatment of cytomegalovirus disease]

For years, intravenous ganciclovir has been the recommended treatment for cytomegalovirus (CMV) in transplant recipients. Recently, oral valganciclovir has been shown to induce a response to CMV similar to that produced by intravenous ganciclovir and could consequently be an alternative to ganciclovir in patients with non-severe disease. Sequential therapy with ganciclovir followed by valganciclovir, after the onset of clinical improvement, reduces costs and avoids prolonged hospital stays, thus benefitting patients. Optimal treatment duration is guided by clinical response and virological monitoring (polymerase chain reaction or antigenemia) and is maintained until the results are negative. Some groups use secondary prophylaxis in patients with risk factors for recurrence of CMV disease. Reducing the intensity of immunosuppression or complementing antiviral therapy with immunoglobulins can be considered in patients with severe disease or immunodepression. There are no conclusive data on the most effective treatment in ganciclovir-resistant CMV. Therapeutic decisions should be based on genotypic resistance studies, the patient's immune status and disease severity. Treatment consists of foscarnet alone or in combination with ganciclovir in the most severe forms and in high-resistance mutations, or in increasing the dose of ganciclovir in clinical forms or in mild resistance. There are no conclusive data on alternative antiviral drugs or complementary therapy with mTOR inhibitors. Several CMV vaccines are under development and the preclinical results are encouraging.

Recombinant glycoprotein B vaccine formulation with Toll-like receptor 9 agonist and immune-stimulating complex induces specific immunity against multiple strains of cytomegalovirus

Natural human cytomegalovirus (CMV) infection is characterized by a strain-specific neutralizing antibody response. This is particularly relevant in clinical settings such as transplantation and pregnancy where reinfection with heterologous strains occurs and the immune system does not mount an effective response against the infecting strain due to underlying immunosuppression. There is an emerging argument that a CMV vaccine that induces high titres of cross-neutralizing antibodies will be more effective in protecting individuals from infection with antigenically different CMV strains. In addition, induction of cell-mediated immunity offers the additional advantage of targeting virus-infected cells. This study presents a novel formulation of a CMV vaccine that, by combining recombinant soluble gB protein with a Toll-like receptor 9 agonist (CpG ODN1826) and immune-stimulating complexes (AbISCO 100), was able to elicit strong polyfunctional CMV-specific cellular and cross-neutralizing humoral immune responses. These data demonstrated that prime-boost immunization of human leukocyte antigen (HLA)-A2 mice with gB protein in combination with CpG ODN1826 and AbISCO 100 induced long-lasting CMV-specific CD4(+) and CD8(+) T-cell and humoral responses. Furthermore, these responses neutralized infection with multiple strains of CMV expressing different gB genotypes and afforded protection against challenge with recombinant vaccinia virus encoding the gB protein. These observations argue that this novel vaccine strategy, if applied to humans, should facilitate the generation of a robust, pluripotent immune response, which may be more effective in preventing infection with multiple strains of CMV.

Update on the current status of cytomegalovirus vaccines

Human cytomegalovirus (HCMV) is ubiquitous in all populations, and is the most commonly recognized cause of congenital viral infection in developed countries. On the basis of the economic costs saved and the improvement in quality of life that could potentially be conferred by a successful vaccine for prevention of congenital HCMV infection, the Institute of Medicine has identified HCMV vaccine development as a major public health priority. An effective vaccine could potentially also be beneficial in preventing or ameliorating HCMV disease in immunocompromised individuals. Although there are no licensed HCMV vaccines currently available, enormous progress has been made in the last decade, as evidenced by the recently reported results of a Phase II trial of a glycoprotein B vaccine for the prevention of HCMV infection in seronegative women of childbearing age. HCMV vaccines currently in clinical trials include: glycoprotein B subunit vaccines; alphavirus replicon particle vaccines; DNA vaccines; and live-attenuated vaccines. A variety of vaccine strategies are also being examined in preclinical systems and animal models of infection. These include: recombinant vesicular stomatitis virus vaccines; recombinant modified vaccinia virus Ankara; replication-deficient adenovirus-vectored vaccines; and recombinant live-attenuated virus vaccines generated by mutagenesis of cloned rodent CMV genomes maintained as bacterial artificial chromosomes in Escherichia coli. In this article, we provide an overview of the current state of clinical trials and preclinical development of vaccines against HCMV, with an emphasis on studies that have been conducted in the past 5 years. We also summarize a number of recent advances in the study of the biology of HCMV, particularly with respect to epithelial and endothelial cell entry of the virus, which have implications for future vaccine design.

International consensus guidelines on the management of cytomegalovirus in solid organ transplantation

Cytomegalovirus (CMV) remains one of the most common infections after solid organ transplantation, resulting in significant morbidity, graft loss, and occasional mortality. Management of CMV varies considerably among transplant centers. A panel of experts on CMV and solid organ transplant was convened by The Infectious Diseases Section of The Transplantation Society to develop evidence and expert opinion-based consensus guidelines on CMV management including diagnostics, immunology, prevention, treatment, drug resistance, and pediatric issues.

Novel approach to the formulation of an Epstein-Barr virus antigen-based nasopharyngeal carcinoma vaccine

Epstein-Barr virus (EBV) is associated with several malignant diseases including nasopharyngeal carcinoma (NPC), a common neoplasm throughout southeast Asia. Radiotherapy and chemotherapy can achieve remission, but a reemergence of disease is not uncommon. Therefore, there is a need for specific therapies that target the tumor through the recognition of EBV antigens. In NPC, latent membrane protein 1 (LMP1) and LMP2 offer the best opportunity for specific targeting since they are typically expressed and T-cell determinants in each of these proteins have been defined. We have attempted to maximize the opportunity of incorporating every possible CD4 and CD8 determinant in a single formulation. We have achieved this by generating a scrambled protein incorporating random overlapping peptide sets from EBNA1, LMP1, and LMP2, which was then inserted into a replication-deficient strain of adenovirus (adenovirus scrambled antigen vaccine [Ad-SAVINE]). This report describes the construction of this Ad-SAVINE construct, its utility in generating LMP1 and LMP2 responses in healthy individuals as well as NPC patients, and its capacity to define new epitopes. This formulation could have a role in NPC immunotherapy for all ethnic groups since it has the potential to activate all possible CD4 and CD8 responses within EBNA1 and LMPs.

Discerning regulation of cis- and trans-presentation of CD8+ T-cell epitopes by EBV-encoded oncogene LMP-1 through self-aggregation

Activation of the nuclear factor–κB pathway by Epstein-Barr virus–encoded latent membrane protein-1 (LMP-1) leads to an up-regulation of the major histocompatibility complex class I antigen–processing pathway. Paradoxically, LMP-1 itself induces a subdominant CD8+ T-cell response and appears to have evolved to avoid immune recognition. Here we show that, although expression of LMP-1 in human cells dramatically enhanced the trans-presentation of CD8+ T-cell epitopes, cis-presentation of LMP-1–derived epitopes was severely impaired. Testing of a series of LMP-1 mutants revealed that deletion of the first transmembrane domain of LMP-1, which prevented self-aggregation, significantly enhanced cis-presentation of T-cell epitopes from this protein, whereas it lost its ability to up-regulate trans-presentation. Interestingly, we also found that cis-presentation of LMP-1 epitopes was rescued by blocking the proteasome function. Taken together, these results delineate a novel mechanism of immune evasion, which renders a virally encoded oncogene inaccessible to the conventional major histocompatibility complex class I pathway limiting its cis-presentation to effector cells.

Immunobiology of human cytomegalovirus: from bench to bedside

SUMMARY

Following primary infection, human cytomegalovirus (HCMV) establishes lifelong latency and periodically reactivates without causing symptoms in healthy individuals. In the absence of an adequate host-derived immune response, this fine balance of permitting viral reactivation without causing pathogenesis is disrupted, and HCMV can subsequently cause invasive disease and an array of damaging indirect immunological effects. Over the last decade, our knowledge of the immune response to HCMV infection in healthy virus carriers and diseased individuals has allowed us to translate these findings to develop better diagnostic tools and therapeutic strategies. The application of these emerging technologies in the clinical setting is likely to provide opportunities for better management of patients with HCMV-associated diseases.

Cytomegalovirus vaccines: at last, a major step forward

Yow and Demmler published an editorial in 1992 entitled Congenital cytomegalovirus disease--20 years is long enough. This editorial pointed out that, despite the long-standing recognition of the major public health importance of congenital human cytomegalovirus (CMV) infection, few solutions had been forthcoming. In no area has the lack of progress been more frustrating than in the realm of CMV vaccine development. Although a number of vaccine strategies have been considered, few have advanced to the stage of efficacy testing.