Human Cytomegalovirus (HCMV)-Specific CD4+ T Cells Are Polyfunctional and Can Respond to HCMV-Infected Dendritic Cells In Vitro

Breadth and polyfunctionality of T cell responses to human cytomegalovirus in men who have sex with men: relationship with HIV infection and frailty

Cytomegalovirus (CMV)-seropositive adults have large T cell responses to a wide range of CMV proteins; these responses have been associated with chronic inflammation and frailty in people with or without HIV infection. We analyzed the relationships between chronic HIV infection, frailty, and the breadth and polyfunctionality of CD4 and CD8 T cell responses to CMV. Peripheral blood mononuclear cells from 42 men (20 without HIV and 22 with virologically suppressed HIV) in the Multicenter AIDS Cohort Study (MACS) were stimulated with peptide pools spanning 19 CMV open reading frames (ORFs). As measured by flow cytometry and intracellular cytokine staining for IFN-γ, TNF-α, and IL-2, CD8 T cells from men with HIV responded to significantly more CMV ORFs than those from men without HIV. This was primarily due to a broader response to ORFs that are expressed during the late phase of CMV replication. The number of ORFs to which a participant's T cells responded was positively correlated with the sum of all that individual's T cell responses; these correlations were weaker in men with than without HIV. Polyfunctional CMV-specific CD4 responses (production of more than one cytokine) were significantly lower in men with than without HIV. Frailty status did not substantially affect the breadth or magnitude of the CMV-specific T cell responses. These results suggest that immune control of CMV infection is affected more by chronic HIV infection than by frailty. The differences between men with and without HIV were similar to those reported between young and older adults without HIV.

IMPORTANCE

T cell responses to chronic cytomegalovirus (CMV) infection have significant biological and clinical implications in HIV infection and aging. Here, we systematically analyzed the breadth, magnitude, and polyfunctionality of T cell responses to multiple CMV antigens in men with and without HIV in the Multicenter AIDS Cohort Study (MACS), a longstanding study of the natural and treated history of HIV-1 infection in men who have sex with men. We found that the breadth and polyfunctionality of T cell responses to CMV were different between men with chronic, treated HIV and those without HIV. The reason for these differences is unknown, but these findings suggest that people with treated HIV may have more frequent CMV reactivation than people without HIV. Differences between people with and without HIV also resembled differences reported between young and older adults without HIV, supporting a role for the immune responses to CMV in the aging process.

Intra-host genomic diversity and integration landscape of human tissue-resident DNA virome

The viral intra-host genetic diversities and interactions with the human genome during decades of persistence remain poorly characterized. In this study, we analyzed the variability and integration sites of persisting viruses in nine organs from thirteen individuals who died suddenly from non-viral causes. The viruses studied included parvovirus B19, six herpesviruses, Merkel cell (MCPyV) and JC polyomaviruses, totaling 127 genomes. The viral sequences across organs were remarkably conserved within each individual, suggesting that persistence stems from single dominant strains. This indicates that intra-host viral evolution, thus far inferred primarily from immunocompromised patients, is likely overestimated in healthy subjects. Indeed, we detected increased viral subpopulations in two individuals with putative reactivations, suggesting that replication status influences diversity. Furthermore, we identified asymmetrical mutation patterns reflecting selective pressures exerted by the host. Strikingly, our analysis revealed non-clonal viral integrations even in individuals without cancer. These included MCPyV integrations and truncations resembling clonally expanded variants in Merkel cell carcinomas, as well as novel junctions between herpesvirus 6B and mitochondrial sequences, the significance of which remains to be evaluated. Our work systematically characterizes the genomic landscape of the tissue-resident virome, highlighting potential deviations occurring during disease.

Human cytomegalovirus UL23 exploits PD-L1 inhibitory signaling pathway to evade T cell-mediated cytotoxicity

Human cytomegalovirus (HCMV), a widely prevalent human beta-herpesvirus, establishes lifelong persistence in the host following primary infection. In healthy individuals, the virus is effectively controlled by HCMV-specific T cells and typically exhibits asymptomatic. The T cell immune response plays a pivotal role in combating HCMV infection, while HCMV employs various strategies to counteract it within the host. Previously, we reported that UL23, a tegument protein of HCMV, facilitates viral immune evasion from interferon-gamma (IFN-γ) responses, and it is well known that IFN-γ is mainly derived from T cells. However, the involvement of UL23 in viral immune evasion from T cell-mediated immunity remains unclear. Herein, we present compelling evidence that UL23 significantly enhances viral resistance against T cell-mediated cytotoxicity during HCMV infection from the co-culture assays of HCMV-infected cells with T cells. We found that IFN-γ plays a major role in regulating T cell cytotoxicity mediated by UL23. More interestingly, we demonstrated that UL23 not only regulates the IFN-γ downstream responses but also modulates the IFN-γ secretion by regulating T cell activities. Further experiments indicate that UL23 upregulates the expression and signaling of programmed death ligand 1 (PD-L1), which is responsible for inhibiting multiple aspects of T cell activities, including activation, apoptosis, and IFN-γ secretion, as determined through RNA-seq analysis and inhibitor-blocking experiments, ultimately facilitating viral replication and spread. Our findings highlight the potential role of UL23 as an alternative antagonist in suppressing T cell cytotoxicity and unveil a novel strategy for HCMV to evade T cell immunity.

IMPORTANCE

T cell immunity is pivotal in controlling primary human cytomegalovirus (HCMV) infection, restricting periodic reactivation, and preventing HCMV-associated diseases. Despite inducing a robust T cell immune response, HCMV has developed sophisticated immune evasion mechanisms that specifically target T cell responses. Although numerous studies have been conducted on HCMV-specific T cells, the primary focus has been on the impact of HCMV on T cell recognition via major histocompatibility complex molecules. Our studies show for the first time that HCMV exploits the programmed death ligand 1 (PD-L1) inhibitory signaling pathway to evade T cell immunity by modulating the activities of T cells and thereby blocking the secretion of IFN-γ, which is directly mediated by HCMV-encoded tegument protein UL23. While PD-L1 has been extensively studied in the context of tumors and viruses, its involvement in HCMV infection and viral immune evasion is rarely reported. We observed an upregulation of PD-L1 in normal cells during HCMV infection and provided strong evidence supporting its critical role in UL23-induced inhibition of T cell-mediated cytotoxicity. The novel strategy employed by HCMV to manipulate the inhibitory signaling pathway of T cell immune activation for viral evasion through its encoded protein offers valuable insights for the understanding of HCMV-mediated T cell immunomodulation and developing innovative antiviral treatment strategies.

Single-cell transcriptomic and T cell antigen receptor analysis of human cytomegalovirus (hCMV)-specific memory T cells reveals effectors and pre-effectors of CD8+- and CD4+-cytotoxic T cells

Latent human cytomegalovirus (hCMV) infection can pose a serious threat of reactivation and disease occurrence in immune-compromised individuals. Although T cells are at the core of the protective immune response to hCMV infection, a detailed characterization of different T cell subsets involved in hCMV immunity is lacking. Here, in an unbiased manner, we characterized over 8000 hCMV-reactive peripheral memory T cells isolated from seropositive human donors, at a single-cell resolution by analysing their single-cell transcriptomes paired with the T cell antigen receptor (TCR) repertoires. The hCMV-reactive T cells were highly heterogeneous and consisted of different developmental and functional memory T cell subsets such as, long-term memory precursors and effectors, T helper-17, T regulatory cells (TREGs) and cytotoxic T lymphocytes (CTLs) of both CD4 and CD8 origin. The hCMV-specific TREGs, in addition to being enriched for molecules known for their suppressive functions, showed enrichment for the interferon response signature gene sets. The hCMV-specific CTLs were of two types, the pre-effector- and effector-like. The co-clustering of hCMV-specific CD4-CTLs and CD8-CTLs in both pre-effector as well as effector clusters suggest shared transcriptomic signatures between them. The huge TCR clonal expansion of cytotoxic clusters suggests a dominant role in the protective immune response to CMV. The study uncovers the heterogeneity in the hCMV-specific memory T cells revealing many functional subsets with potential implications in better understanding of hCMV-specific T cell immunity. The data presented can serve as a knowledge base for designing vaccines and therapeutics.

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.

Spontaneous, persistent, T cell-dependent IFN-γ release in patients who progress to Long Covid

After acute infection with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), a proportion of patients experience persistent symptoms beyond 12 weeks, termed Long Covid. Understanding the mechanisms that cause this debilitating disease and identifying biomarkers for diagnostic, therapeutic, and monitoring purposes are urgently required. We detected persistently high levels of interferon-γ (IFN-γ) from peripheral blood mononuclear cells of patients with Long Covid using highly sensitive FluoroSpot assays. This IFN-γ release was seen in the absence of ex vivo peptide stimulation and remains persistently elevated in patients with Long Covid, unlike the resolution seen in patients recovering from acute SARS-CoV-2 infection. The IFN-γ release was CD8+ T cell-mediated and dependent on antigen presentation by CD14+ cells. Longitudinal follow-up of our study cohort showed that symptom improvement and resolution correlated with a decrease in IFN-γ production to baseline levels. Our study highlights a potential mechanism underlying Long Covid, enabling the search for biomarkers and therapeutics in patients with Long Covid.

Late-rising CD4 T cells resolve mouse cytomegalovirus persistent replication in the salivary gland

Conventional antiviral memory CD4 T cells typically arise during the first two weeks of acute infection. Unlike most viruses, cytomegalovirus (CMV) exhibits an extended persistent replication phase followed by lifelong latency accompanied with some gene expression. We show that during mouse CMV (MCMV) infection, CD4 T cells recognizing an epitope derived from the viral M09 protein only develop after conventional memory T cells have already peaked and contracted. Ablating these CD4 T cells by mutating the M09 genomic epitope in the MCMV Smith strain, or inducing them by introducing the epitope into the K181 strain, resulted in delayed or enhanced control of viral persistence, respectively. These cells were shown to be unique compared to their conventional memory counterparts; producing higher IFNγ and IL-2 and lower IL-10 levels. RNAseq analyses revealed them to express distinct subsets of effector genes as compared to classical CD4 T cells. Additionally, when M09 cells were induced by epitope vaccination they significantly enhanced protection when compared to conventional CD4 T cells alone. These data show that late-rising CD4 T cells are a unique memory subset with excellent protective capacities that display a development program strongly differing from the majority of memory T cells.

Indirect CD4+ T cell protection against persistent MCMV infection by NK cells requires IFNγ

Host control of mouse cytomegalovirus (MCMV) infection of MHCII- salivary gland acinar cells is mediated by CD4+ T cells, but how they protect is unclear. Here, we show CD4+ T cells control MCMV indirectly in the salivary gland, via IFNγ engagement with uninfected, but antigen+ MHCII+ APC and recruitment of NK cells to infected cell foci. This immune mechanism renders direct contact of CD4+ T cells with infected cells unnecessary and may represent a host strategy to overcome viral immune evasion.

Immune modulation via dendritic cells by the effect of Thymosin-alpha-1 on immune synapse in HCMV infection

Tα1 (Thymosin-alpha-1) is a thymus-derived hormone that has been demonstrated to be effective on diverse immune cell subsets. The objective of this study was to determine the in vitro immunomodulatory effect of Tα1 in human cytomegalovirus (HCMV) infection. Dendritic cells (DCs) were isolated from peripheral blood mononuclear cells (PBMCs) by negative selection and cultured in the presence or absence of Tα1. The immunophenotyping of DCs was characterised by multiparametric flow cytometry assessing CD40, CD80, TIM-3 and PDL-1 markers, as well as intracellular TNFα production. Then, autologous CD4+ or CD8+ T-Lymphocytes (TLs) isolated by negative selection from PBMCs were co-cultured with DCs previously treated with Tα1 in the presence or absence of HCMV. Intracellular TNFα, IFNγ, IL-2 production, CD40-L and PD-1 expression were assessed through immunophenotyping, and polyfunctionality in total TLs and memory subsets were evaluated. The results showed that Tα1 increased CD40, CD80, TIM-3 and TNFα intracellular production while decreasing PDL-1 expression, particularly on plasmacytoid dendritic cells (pDCs). Therefore, Tα1 modulated the production of TNFα, IFNγ and IL-2 in both total and memory subsets of CD4+ and CD8+ TLs by upregulating CD40/CD40-L and downregulating PDL-1/PD-1 expression. Our study concludes that Tα1 enhances antigen-presenting capacity of DCs, improves TLs responses to HCMV infection, and enhances the polyfunctionality of CD8+ TLs. Consequently, Tα1 could be an alternative adjuvant for use in therapeutic cell therapy for immunocompromised patients.

Cytotoxic CD4 T cells in the mucosa and in cancer

CD4 T cells were initially described as helper cells that promote either the cellular immune response (Th1 cells) or the humoral immune response (Th2 cells). Since then, a plethora of functionally distinct helper and regulatory CD4 T cell subsets have been described. CD4 T cells with cytotoxic function were first described in the setting of viral infections and autoimmunity, and more recently in cancer and gut dysbiosis. Regulatory CD4 T cell subsets such as Tregs and T-regulatory type 1 (Tr1) cells have also been shown to have cytotoxic potential. Indeed, Tr1 cells have been shown to be important for maintenance of stem cell niches in the bone marrow and the gut. This review will provide an overview of cytotoxic CD4 T cell development, and discuss the role of inflammatory and Tr1-like cytotoxic CD4 T cells in maintenance of intestinal stem cells and in anti-cancer immune responses.

A temperature-dependent virus-binding assay reveals the presence of neutralizing antibodies in human cytomegalovirus gB vaccine recipients' sera

Human cytomegalovirus (HCMV) remains an important cause of mortality in immune-compromised transplant patients and following congenital infection. Such is the burden, an effective vaccine strategy is considered to be of the highest priority. The most successful vaccines to date have focused on generating immune responses against glycoprotein B (gB) - a protein essential for HCMV fusion and entry. We have previously reported that an important component of the humoral immune response elicited by gB/MF59 vaccination of patients awaiting transplant is the induction of non-neutralizing antibodies that target cell-associated virus with little evidence of concomitant classical neutralizing antibodies. Here we report that a modified neutralization assay that promotes prolonged binding of HCMV to the cell surface reveals the presence of neutralizing antibodies in sera taken from gB-vaccinated patients that cannot be detected using standard assays. We go on to show that this is not a general feature of gB-neutralizing antibodies, suggesting that specific antibody responses induced by vaccination could be important. Although we can find no evidence that these neutralizing antibody responses are a correlate of protection in vivo in transplant recipients their identification demonstrates the utility of the approach in identifying these responses. We hypothesize that further characterization has the potential to aid the identification of functions within gB that are important during the entry process and could potentially improve future vaccine strategies directed against gB if they prove to be effective against HCMV at higher concentrations.

Human Cytomegalovirus pUL11, a CD45 Ligand, Disrupts CD4 T Cell Control of Viral Spread in Epithelial Cells

Human cytomegalovirus (HCMV) encodes numerous immunomodulatory genes that facilitate its persistence. Previously described mechanisms by which HCMV avoids T cell control typically involve evasion of detection by infected cells. Here, we show that the virus also inhibits T cells directly via an interaction between the pUL11 glycoprotein on infected cells and the CD45 phosphatase on T cells. The antiviral functions of CD4 T cells are impaired as a result of this interaction, largely via induced interleukin 10 (IL-10) secretion in the CD4 T cell central memory compartment, resulting in enhanced viral spread. This establishes CD45 as an inhibitory receptor that regulates antiviral T cell functions and has parallels with the manipulation of natural killer (NK) cells by HCMV. By coculturing donor T cells with HCMV-infected epithelial cells, we observed that CD4 T cells can respond to epithelial cell antigen presentation and can control HCMV spread via cytolytic and cytokine-dependent mechanisms. pUL11 impairs both mechanisms. We showed that pUL11-induced IL-10 secretion requires IL-2, mTOR, and T cell receptor signaling. This characterization of the effects of the pUL11-CD45 interaction may allow for the development of new antiviral therapies and treatments for inflammatory disorders. IMPORTANCE Human cytomegalovirus (HCMV) is adept at avoiding its host's immune defenses, both by evading detection and by directly inhibiting immune cells. This can lead to a loss of control of the infection, and dangerous disease can result, particularly in cases in which an individual's immune system is immature, weak, or suppressed. T cells form a crucial part of the response to HCMV and are used in cellular HCMV therapies. We show that an interaction between a viral glycoprotein (pUL11) and a T cell surface receptor (CD45) impairs T cell memory functions and allows for increased viral spread. This defines a new immunomodulatory strategy for the virus as well as a new T cell regulatory mechanism. These results are important, as they increase our understanding of how T cells function and how HCMV disrupts them. This will allow for the development of new antiviral therapies that restore T cell functions and indicates a new target for controlling pathological T cell disorders.

HCMV carriage in the elderly diminishes anti-viral functionality of the adaptive immune response resulting in virus replication at peripheral sites

Human cytomegalovirus (HCMV) infection and periodic reactivation is, generally, well controlled by adaptative immune responses in the healthy. In older people, overt HCMV disease is rarely seen despite the association of HCMV with increased risk of mortality; evidence from studies of unwell aged populations suggest that HCMV seropositivity is an important co-morbidity factor. HCMV genomes have been detected in urine from older donors, suggesting that the immune response prevents systemic disease but possibly immunomodulation due to lifelong viral carriage may alter its efficacy at peripheral tissue sites. Previously we have demonstrated that there were no age-related expansions of T cell responses to HCMV or increase in latent viral carriage with age and these T cells produced anti-viral cytokines and viremia was very rarely detected. To investigate the efficacy of anti-HCMV responses with increasing age, we used an in vitro Viral Dissemination Assay (VDA) using autologous dermal fibroblasts to determine the anti-viral effector capacity of total PBMC, as well as important subsets (T cells, NK cells). In parallel we assessed components of the humoral response (antibody neutralization) and combined this with qPCR detection of HCMV in blood, saliva and urine in a cohort of young and old donors. Consistent with previous studies, we again show HCMV specific cIL-10, IFNγ and TNFα T cell responses to peptides did not show an age-related defect. However, assessment of direct anti-viral cellular and antibody-mediated adaptive immune responses using the VDA shows that older donors are significantly less able to control viral dissemination in an in vitro assay compared to young donors. Corroborating this observation, we detected viral genomes in saliva samples only from older donors, these donors had a defect in cellular control of viral spread in our in vitro assay. Phenotyping of fibroblasts used in this study shows expression of a number of checkpoint inhibitor ligands which may contribute to the defects observed. The potential to therapeutically intervene in checkpoint inhibitor pathways to prevent HCMV reactivation in the unwell aged is an exciting avenue to explore.

IL-10-Secreting CD8+ T Cells Specific for Human Cytomegalovirus (HCMV): Generation, Maintenance and Phenotype

HCMV-specific CD8⁺ T-cells are potent anti-viral effector cells in HCMV infected individuals, but evidence from other viral infections suggests that CD8⁺ T-cells can also produce the immunomodulatory cytokine IL-10. In this work we show that there are HCMV-specific IL-10 CD8⁺ T-cell responses in a cohort of individuals aged 23-76 years of age, predominantly directed against the HCMV proteins known to be expressed during latent infections as well as towards the proteins US3 and pp71. The analysis of HCMV-specific responses established during primary infection has shown that the IL-10 responses to US3 and pp71 HCMV proteins are detectable in the first weeks post infection, but not the responses to latency-associated proteins, and this IL-10 response is produced by both CD8⁺ and CD4⁺ T-cells. Phenotyping studies of HCMV-specific IL-10⁺ CD8⁺ T-cells show that these are CD45RA⁺ effector memory cells and co-express CD28 and CD57, however, the expression of the inhibitory receptor PD-1 varied from 90% to 30% between donors. In this study we have described for the first time the HCMV-specific IL-10 CD8⁺ T-cell responses and have demonstrated their broad specificity and the potential immune modulatory role of the immune response to HCMV latent carriage and periodic reactivation.

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.

Laboratory diagnostic testing for cytomegalovirus infection in solid organ transplant patients

Human cytomegalovirus (CMV) infection, which is one of the most common complications in transplant recipients, increases the risk of graft loss and rejection. Laboratory strategies for diagnosing CMV infection rely on the measurement of viral DNAemia and CMV-specific cell-mediated immunity (CMV-CMI). The CMV quantitative nucleic acid amplification test (QNAT) enabled the spread of preemptive therapy and prompted recommendations for surveillance, diagnosis, and monitoring. Despite the implementation of the World Health Organization international standard for calibration, variability of QNAT persists due to technical issues. CMV immunoglobulin G serology is the standard method for CMV immune screening of transplant candidates and donors. Assays for CMV-CMI play an important role in helping to predict the risk and to develop an individualized CMV management plan. Genotypic testing for resistance is needed when drug-resistant CMV infection is suspected. Here, we review the state of the art of laboratory tests for CMV infection in solid organ transplantation.

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.

Longitudinal association of cytokine-producing CMV-specific T cells with frailty in HIV-infected and -uninfected men who have sex with men

BACKGROUND

Chronic cytomegalovirus (CMV) infection has been postulated as a driver of chronic inflammation that has been associated with frailty and other age-related conditions in both HIV-infected (HIV+) and -uninfected (HIV-) people.

METHODS

To study the T cell response to CMV as a predictor of onset and maintenance of frailty, baseline CMV-specific T cell responses of 42 men (20 HIV-, 22 HIV+; 21 frail, 21 nonfrail) in the Multicenter AIDS Cohort Study (MACS) were assessed by flow cytometric analysis of cytokine production (IFN-γ, TNF-⍺, and IL-2) in response to overlapping peptide pools spanning 19 CMV open reading frames. The Fried frailty phenotype was assessed at baseline and semiannually thereafter. Times to transition into or out of frailty were compared by tertiles of percentages of cytokine-producing T cells using Kaplan-Meier estimators and the exact log-rank test.

RESULTS

Over a median follow-up of 6.5 (interquartile range: 2) years, faster onset of frailty was significantly predicted by higher (HIV- men) or lower (HIV+ men) percentages of CD4 T cells producing only IFN-γ (IFN-γ-single-producing (SP)), and by lower percentages of IFN-γ-, TNF-⍺-, and IL-2-triple-producing CD8 T cells (HIV- men). Greater maintenance of frailty was significantly predicted by lower percentages of both these T cell subsets in HIV- men, and by lower percentages of IFN-γ-SP CD4 T cells in HIV+ men. The antigenic specificity of IFN-γ-SP CD4 T cells was different between HIV- and HIV+ nonfrail men, as were the correlations between these cells and serum inflammatory markers.

CONCLUSIONS

In this pilot study, percentages of CMV-specific T cells predicted the onset and maintenance of frailty in HIV- and HIV+ men. Predictive responses differed by HIV status, which may relate to differential control of CMV reactivation and inflammation by anti-CMV T cell responses.

Detection and Enumeration of Cytokine-Secreting Cells by FluoroSpot

The FluoroSpot assay is a development of the highly sensitive enzyme-linked immunospot (ELISpot) assay which enables functional measurement of immunity at the single-cell level. Both assays are performed in a 96-well format and measures the frequency of analyte-secreting cells, in ELISpot usually limited to one analyte per well due to the use of enzymes and precipitating substrates for detection. FluoroSpot, performed in a similar way as ELISpot, overcomes this limitation by detecting each analyte with an assigned fluorophore instead of an enzyme. By using readers equipped with fluorophore-specific filters, cells producing single or multiple cytokines can be identified simultaneously in the same well. This greatly facilitates the analysis of functionally distinct subpopulations in heterogenous cell samples, for example, the frequency of polyfunctional T cells, suggested to be of importance in various disease states. FluoroSpot maintains the simplicity and sensitivity of the ELISpot while taking the assay a step further towards a multiplex analysis and an in-depth understanding of the quality of an immune response. We describe here a 96-well plate method to analyze cells that have secreted up to four different cytokines simultaneously (Four-color Fluorospot).

Immune Landscape of CMV Infection in Cancer Patients: From "Canonical" Diseases Toward Virus-Elicited Oncomodulation

Human Cytomegalovirus (HCMV) is an immensely pervasive herpesvirus, persistently infecting high percentages of the world population. Despite the apparent robust host immune responses, HCMV is capable of replicating, evading host defenses, and establishing latency throughout life by developing multiple immune-modulatory strategies. HCMV has coexisted with humans mounting various mechanisms to evade immune cells and effectively win the HCMV-immune system battle mainly through maintaining its viral genome, impairing HLA Class I and II molecule expression, evading from natural killer (NK) cell-mediated cytotoxicity, interfering with cellular signaling, inhibiting apoptosis, escaping complement attack, and stimulating immunosuppressive cytokines (immune tolerance). HCMV expresses several gene products that modulate the host immune response and promote modifications in non-coding RNA and regulatory proteins. These changes are linked to several complications, such as immunosenescence and malignant phenotypes leading to immunosuppressive tumor microenvironment (TME) and oncomodulation. Hence, tumor survival is promoted by affecting cellular proliferation and survival, invasion, immune evasion, immunosuppression, and giving rise to angiogenic factors. Viewing HCMV-induced evasion mechanisms will play a principal role in developing novel adapted therapeutic approaches against HCMV, especially since immunotherapy has revolutionized cancer therapeutic strategies. Since tumors acquire immune evasion strategies, anti-tumor immunity could be prominently triggered by multimodal strategies to induce, on one side, immunogenic tumor apoptosis and to actively oppose the immune suppressive microenvironment, on the other side.

Profiling Human CMV-specific T cell responses reveals novel immunogenic ORFs

Despite the prevalence and medical significance of human cytomegalovirus (HCMV) infections, a systematic analysis of the targets of T cell recognition in humans that spans the entire genome and includes recently described potential novel ORFs is not available. Here, we screened a library of epitopes predicted to bind HLA class II that spans over 350 different HCMV ORFs and includes ∼150 previously described and ∼200 recently described potential novel ORFs using an ex vivo IFNγ fluorospot assay. We identified 235 unique HCMV specific epitopes derived from 100 ORFs, some previously described as immunodominant and others that were not previously described to be immunogenic. Of those, 41 belong to the set of recently reported novel ORFs, thus providing evidence that at least some of these are actually expressed in vivo in humans. These data reveal that the breadth of the human T cell response to HCMV is much greater than previously thought. The ORFs and epitopes identified will help elucidate how T cell immunity relates to HCMV pathogenesis and instruct ongoing HCMV vaccine research. Importance To understand the crucial role of adaptive immunity in controlling cytomegalovirus infection and disease, we systematically analyzed the CMV 'ORFeome' to identify new CMV epitopes targeted primarily by CD4 T cells in humans. Our study identified >200 new T cell epitopes derived from both canonical and novel ORFs, highlighting the substantial breadth of anti-CMV T cell response and providing new targets for vaccine design.

Optimal CD8+ T-cell memory formation following subcutaneous cytomegalovirus infection requires virus replication but not early dendritic cell responses

Cytomegalovirus (CMV) induction of large frequencies of highly functional memory T cells has attracted much interest in the utility of CMV‐based vaccine vectors, with exciting preclinical data obtained in models of infectious diseases and cancer. However, pathogenesis of human CMV (HCMV) remains a concern. Attenuated CMV‐based vectors, such as replication‐ or spread‐deficient viruses, potentially offer an alternative to fully replicating vectors. However, it is not well understood how CMV attenuation impacts vector immunogenicity, particularly when administered via relevant routes of immunization such as the skin. Herein, we used the murine cytomegalovirus (MCMV) model to investigate the impact of vector attenuation on T‐cell memory formation following subcutaneous administration. We found that the spread‐deficient virus (ΔgL‐MCMV) was impaired in its ability to induce memory CD8⁺ T cells reactive to some (M38, IE1) but not all (IE3) viral antigens. Impaired‐memory T‐cell development was associated with a preferential and pronounced loss of polyfunctional (IFN‐γ⁺ TNF‐α⁺) T cells and also reduced accumulation of TCF1⁺ T cells, and was not rescued by increasing the dose of replication‐defective MCMV. Finally, whilst vector attenuation reduced dendritic cell (DC) recruitment to skin‐draining lymph nodes, systematic depletion of multiple DC subsets during acute subcutaneous MCMV infection had a negligible impact on T‐cell memory formation, implying that attenuated responses induced by replication‐deficient vectors were likely not a consequence of impaired initial DC activation. Thus, overall, these data imply that the choice of antigen and/or cloning strategy of exogenous antigen in combination with the route of immunization may influence the ability of attenuated CMV vectors to induce robust functional T‐cell memory.

Is It Feasible to Use CMV-Specific T-Cell Adoptive Transfer as Treatment Against Infection in SOT Recipients?

During the last decade, many studies have demonstrated the role of CMV specific T-cell immune response on controlling CMV replication and dissemination. In fact, it is well established that transplanted patients lacking CMV-specific T-cell immunity have an increased occurrence of CMV replication episodes and CMV-related complications. In this context, the use of adoptive transfer of CMV-specific T-cells has been widely investigated and applied to Hematopoietic Stem Cell Transplant patients and may be useful as a therapeutic alternative, to reconstitute the CMV specific T-cell response and to control CMV viremia in patients receiving a transplantation. However, only few authors have explored the use of T-cell adoptive transfer in SOT recipients. We propose a novel review in which we provide an overview of the impact of using CMV-specific T-cell adoptive transfer on the control of CMV infection in SOT recipients, the different approaches to stimulate, isolate and expand CMV-specific T-cells developed over the years and a discussion of the possible use of CMV adoptive cellular therapy in this SOT population. Given the timeliness and importance of this topic, we believe that such an analysis will provide important insights into CMV infection and its treatment/prevention.

Latent Cytomegalovirus-Driven Recruitment of Activated CD4+ T Cells Promotes Virus Reactivation

Human cytomegalovirus (HCMV) infection is not cleared by the initial immune response but persists for the lifetime of the host, in part due to its ability to establish a latent infection in cells of the myeloid lineage. HCMV has been shown to manipulate the secretion of cellular proteins during both lytic and latent infection; with changes caused by latent infection mainly investigated in CD34+ progenitor cells. Whilst CD34+ cells are generally bone marrow resident, their derivative CD14+ monocytes migrate to the periphery where they briefly circulate until extravasation into tissue sites. We have analyzed the effect of HCMV latent infection on the secretome of CD14+ monocytes, identifying an upregulation of both CCL8 and CXCL10 chemokines in the CD14+ latency-associated secretome. Unlike CD34+ cells, the CD14+ latency-associated secretome did not induce migration of resting immune cell subsets but did induce migration of activated NK and T cells expressing CXCR3 in a CXCL10 dependent manner. As reported in CD34+ latent infection, the CD14+ latency-associated secretome also suppressed the anti-viral activity of stimulated CD4+ T cells. Surprisingly, however, co-culture of activated autologous CD4+ T cells with latently infected monocytes resulted in reactivation of HCMV at levels comparable to those observed using M-CSF and IL-1β cytokines. We propose that these events represent a potential strategy to enable HCMV reactivation and local dissemination of the virus at peripheral tissue sites.

Comprehensive Analysis of CD4+ T Cell Responses to CMV pp65 Antigen Restricted by Single HLA-DR, -DQ, and -DP Allotype Within an Individual

Within an individual, six different HLA class II heterodimers are expressed co-dominantly by two alleles of HLA-DR, -DQ, and -DP loci. However, it remained unclear which HLA allotypes were used in T cell responses to a given antigen. For the measurement of the CD4⁺ T cell responses restricted by a single HLA allotype, we established a panel of artificial antigen-presenting cells (aAPCs) expressing each single HLA allele of 20 HLA-DRB1, 16 HLA-DQ, and 13 HLA-DP alleles. CD4⁺ T cell responses to cytomegalovirus (CMV) pp65 restricted by single HLA class II allotype defined in 45 healthy donors. The average magnitude of CD4⁺ T cell responses by HLA-DR allotypes was higher than HLA-DQ and HLA-DP allotypes. CD4⁺ T cell responses by DRA*01:01/DRB1*04:06, DQA1*01:02/DQB1*06:02, DPA1*02:02/DPB1*05:01 were higher among the other alleles in each HLA-DR, -DQ, and -DP locus. Interestingly, the frequencies of HLA-DR alleles and the positivity of specific allotypes showed an inverse correlation. One allotype within individuals is dominantly used in CD4⁺ T cell response in 49% of donors, and two allotypes showed that in 7% of donors, and any positive response was detected in 44% of donors. Even if one individual had several dominant alleles, CD4⁺ T cell responses tended to be restricted by only one of them. Furthermore, CD8⁺ and CD4⁺ T cell responses by HLA class I and class II were correlated. Our results demonstrate that the CD4⁺ T cell preferentially use a few dominant HLA class II allotypes within individuals, similar to CD8⁺ T cell response to CMV pp65.

Comparison of Three Cellular Assays to Predict the Course of CMV Infection in Liver Transplant Recipients

To estimate protection from cytomegalovirus (CMV) replication after solid organ transplantation, CMV serology has been considered insufficient and thus CMV immunity is increasingly assessed by cellular in vitro methods. We compared two commercially available IFN-γ ELISpot assays (T-Track CMV and T-SPOT.CMV) and an IFN-γ ELISA (QuantiFERON-CMV). Currently, there is no study comparing these three assays. The assays were performed in 56 liver transplant recipients at the end of antiviral prophylaxis and one month thereafter. In CMV high- or intermediate-risk patients the two ELISpot assays showed significant correlation (p < 0.0001, r > 0.6) but the correlation of the ELISpot assays with QuantiFERON-CMV was weaker. Results of both ELISpot assays were similarly predictive of protection from CMV-DNAemia ≥500 copies/mL [CMV pp65 T-SPOT.CMV at the end of prophylaxis: area under curve (AUC) = 0.744, cut-off 142 spot forming units (SFU), sensitivity set to 100%, specificity 46%; CMV IE-1 T-Track CMV at month 1: AUC = 0.762, cut-off 3.5 SFU, sensitivity set to 100%, specificity 59%]. The QuantiFERON-CMV assay was inferior, reaching a specificity of 23% when setting the sensitivity to 100%. In conclusion, both CMV-specific ELISpot assays appear suitable to assess protection from CMV infection/reactivation in liver transplant recipients.

The Many Faces of CD4+ T Cells: Immunological and Structural Characteristics

As a major arm of the cellular immune response, CD4+ T cells are important in the control and clearance of infections. Primarily described as helpers, CD4+ T cells play an integral role in the development and activation of B cells and CD8+ T cells. CD4+ T cells are incredibly heterogeneous, and can be divided into six main lineages based on distinct profiles, namely T helper 1, 2, 17 and 22 (Th1, Th2, Th17, Th22), regulatory T cells (Treg) and T follicular helper cells (Tfh). Recent advances in structural biology have allowed for a detailed characterisation of the molecular mechanisms that drive CD4+ T cell recognition. In this review, we discuss the defining features of the main human CD4+ T cell lineages and their role in immunity, as well as their structural characteristics underlying their detection of pathogens.

New viral vectors for infectious diseases and cancer

Since the discovery in 1796 by Edward Jenner of vaccinia virus as a way to prevent and finally eradicate smallpox, the concept of using a virus to fight another virus has evolved into the current approaches of viral vectored genetic vaccines. In recent years, key improvements to the vaccinia virus leading to a safer version (Modified Vaccinia Ankara, MVA) and the discovery that some viruses can be used as carriers of heterologous genes encoding for pathological antigens of other infectious agents (the concept of 'viral vectors') has spurred a new wave of clinical research potentially providing for a solution for the long sought after vaccines against major diseases such as HIV, TB, RSV and Malaria, or emerging infectious diseases including those caused by filoviruses and coronaviruses. The unique ability of some of these viral vectors to stimulate the cellular arm of the immune response and, most importantly, T lymphocytes with cell killing activity, has also reawakened the interest toward developing therapeutic vaccines against chronic infectious diseases and cancer. To this end, existing vectors such as those based on Adenoviruses have been improved in immunogenicity and efficacy. Along the same line, new vectors that exploit viruses such as Vesicular Stomatitis Virus (VSV), Measles Virus (MV), Lymphocytic choriomeningitis virus (LCMV), cytomegalovirus (CMV), and Herpes Simplex Virus (HSV), have emerged. Furthermore, technological progress toward modifying their genome to render some of these vectors incompetent for replication has increased confidence toward their use in infant and elderly populations. Lastly, their production process being the same for every product has made viral vectored vaccines the technology of choice for rapid development of vaccines against emerging diseases and for 'personalised' cancer vaccines where there is an absolute need to reduce time to the patient from months to weeks or days. Here we review the recent developments in viral vector technologies, focusing on novel vectors based on primate derived Adenoviruses and Poxviruses, Rhabdoviruses, Paramixoviruses, Arenaviruses and Herpesviruses. We describe the rationale for, immunologic mechanisms involved in, and design of viral vectored gene vaccines under development and discuss the potential utility of these novel genetic vaccine approaches in eliciting protection against infectious diseases and cancer.

Understanding human γδ T cell biology toward a better management of cytomegalovirus infection

Cytomegalovirus (CMV) infection is responsible for significant morbidity and mortality in immunocompromised patients, namely solid organ and hematopoietic cell transplant recipients, and can induce congenital infection in neonates. There is currently an unmet need for new management and treatment strategies. Establishment of an anti-CMV immune response is critical in order to control CMV infection. The two main human T cells involved in HCMV-specific response are αβ and non-Vγ9Vδ2 T cells that belong to γδ T cell compartment. CMV-induced non-Vγ9Vδ2 T cells harbor a specific clonal expansion and a phenotypic signature, and display effector functions against CMV. So far, only two main molecular mechanisms underlying CMV sensing have been identified. Non-Vγ9Vδ2 T cells can be activated either by stress-induced surface expression of the γδT cell receptor (TCR) ligand annexin A2, or by a multimolecular stress signature composed of the γδTCR ligand endothelial protein C receptor and co-stimulatory signals such as the ICAM-1-LFA-1 axis. All this basic knowledge can be harnessed to improve the clinical management of CMV infection in at-risk patients. In particular, non-Vγ9Vδ2 T cell monitoring could help better stratify the risk of infection and move forward a personalized medicine. Moreover, recent advances in cell therapy protocols open the way for a non-Vγ9Vδ2 T cell therapy in immunocompromised patients.

Assessing Anti-HCMV Cell Mediated Immune Responses in Transplant Recipients and Healthy Controls Using a Novel Functional Assay

HCMV infection, reinfection or reactivation occurs in 60% of untreated solid organ transplant (SOT) recipients. Current clinical approaches to HCMV management include pre-emptive and prophylactic antiviral treatment strategies. The introduction of immune monitoring to better stratify patients at risk of viraemia and HCMV mediated disease could improve clinical management. Current approaches quantify T cell IFNγ responses specific for predominantly IE and pp65 proteins ex vivo, as a proxy for functional control of HCMV in vivo. However, these approaches have only a limited predictive ability. We measured the IFNγ T cell responses to an expanded panel of overlapping peptide pools specific for immunodominant HCMV proteins IE1/2, pp65, pp71, gB, UL144, and US3 in a cohort of D+R- kidney transplant recipients in a longitudinal analysis. Even with this increased antigen diversity, the results show that while all patients had detectable T cell responses, this did not correlate with control of HCMV replication in some. We wished to develop an assay that could directly measure anti-HCMV cell-mediated immunity. We evaluated three approaches, stimulation of PBMC with (i) whole HCMV lysate or (ii) a defined panel of immunodominant HCMV peptides, or (iii) fully autologous infected cells co-cultured with PBMC or isolated CD8+ T cells or NK cells. Stimulation with HCMV lysate often generated non-specific antiviral responses while stimulation with immunodominant HCMV peptide pools produced responses which were not necessarily antiviral despite strong IFNγ production. We demonstrated that IFNγ was only a minor component of secreted antiviral activity. Finally, we used an antiviral assay system to measure the effect of whole PBMC, and isolated CD8+ T cells and NK cells to control HCMV in infected autologous dermal fibroblasts. The results show that both PBMC and especially CD8+ T cells from HCMV seropositive donors have highly specific antiviral activity against HCMV. In addition, we were able to show that NK cells were also antiviral, but the level of this control was highly variable between donors and not dependant on HCMV seropositivity. Using this approach, we show that non-viraemic D+R+ SOT recipients had significant and specific antiviral activity against HCMV.

Human Cytomegalovirus Interleukin 10 Homologs: Facing the Immune System

Human Cytomegalovirus (HCMV) can cause a variety of health disorders that can lead to death in immunocompromised individuals and neonates. The HCMV lifecycle comprises both a lytic (productive) and a latent (non-productive) phase. HCMV lytic infection occurs in a wide range of terminally differentiated cell types. HCMV latency has been less well-studied, but one characterized site of latency is in precursor cells of the myeloid lineage. All known viral genes are expressed during a lytic infection and a subset of these are also transcribed during latency. The UL111A gene which encodes the viral IL-10, a homolog of the human IL-10, is one of these genes. During infection, different transcript isoforms of UL111A are generated by alternative splicing. The most studied of the UL111A isoforms are cmvIL-10 (also termed the "A" transcript) and LAcmvIL-10 (also termed the "B" transcript), the latter being a well-characterized latency associated transcript. Both isoforms can downregulate MHC class II, however they differ in a number of other immunomodulatory properties, such as the ability to bind the IL10 receptor and induce signaling through STAT3. There are also a number of other isoforms which have been identified which are expressed by differential splicing during lytic infection termed C, D, E, F, and G, although these have been less extensively studied. HCMV uses the viral IL-10 proteins to manipulate the immune system during lytic and latent phases of infection. In this review, we will discuss the literature on the viral IL-10 transcripts identified to date, their encoded proteins and the structures of these proteins as well as the functional properties of all the different isoforms of viral IL-10.

The CD4+ T Cell Response to Human Cytomegalovirus in Healthy and Immunocompromised People

While CD8+ T cells specific for human cytomegalovirus (HCMV) have been extensively studied in both healthy HCMV seropositive carriers and patients undergoing immunosuppression, studies on the CD4+ T cell response to HCMV had lagged behind. However, over the last few years there has been a significant advance in our understanding of the importance and contribution that CMV-specific CD4+ T cells make, not only to anti-viral immunity but also in the potential maintenance of latently infected cells. During primary infection with HCMV in adults, CD4+ T cells are important for the resolution of symptomatic disease, while persistent shedding of HCMV into urine and saliva is associated with a lack of HCMV specific CD4+ T cell response in young children. In immunosuppressed solid organ transplant recipients, a delayed appearance of HCMV-specific CD4+ T cells is associated with prolonged viremia and more severe clinical disease, while in haematopoietic stem cell transplant recipients, it has been suggested that HCMV-specific CD4+ T cells are required for HCMV-specific CD8+ T cells to exert their anti-viral effects. In addition, adoptive T-cell immunotherapy in transplant patients has shown that the presence of HCMV-specific CD4+ T cells is required for the maintenance of HCMV-specific CD8+ T cells. HCMV is a paradigm for immune evasion. The presence of viral genes that down-regulate MHC class II molecules and the expression of viral IL-10 both limit antigen presentation to CD4+ T cells, underlining the important role that this T cell subset has in antiviral immunity. This review will discuss the antigen specificity, effector function, phenotype and direct anti-viral properties of HCMV specific CD4+ T cells, as well as reviewing our understanding of the importance of this T cell subset in primary infection and long-term carriage in healthy individuals. In addition, their role and importance in congenital HCMV infection and during immunosuppression in both solid organ and haemopoietic stem cell transplantation is considered.

The direct and indirect consequences of cytomegalovirus infection and potential benefits of vaccination

Active infection with cytomegalovirus (CMV) occurs in patients who are immunocompromised and may produce the high viral loads required to cause end-organ disease. Such patients have complex medical histories and many experienced physicians have speculated that CMV may, additionally, contribute to adverse clinical outcomes. In 1989, Dr Bob Rubin coined the term "indirect effects" to describe this potential relationship between virus and patient. Examples include accelerated atherosclerosis in patients after heart transplant or with underlying HIV infection, the number of days patients require ventilation after admission to intensive care units, the development of immunosenescence in the elderly and mortality in many groups of patients, including the general population. It is difficult to distinguish between CMV acting as causal contributor to such diverse pathology or simply having a benign bystander effect. However, recruitment of patients into placebo-controlled randomised trials of antiviral drugs with activity against CMV offers such a potential. This article describes the studies that have been conducted to date and emphasises that mortality after stem cell transplant (not attributed to CMV end-organ disease) has recently become the first proven indirect effect of CMV now that letermovir has significantly reduced non-relapse deaths. The implications for CMV vaccines are then discussed. Vaccines are already predicted to be highly cost-effective if they can reduce CMV end-organ disease. Health planners should now consider that cost effectiveness is likely to be enhanced further through reduction of the indirect effects of CMV. A prototype scheme for assessing this possibility is provided in order to stimulate discussion within the field. This article forms part of an online symposium on the prevention and therapy of DNA virus infections, dedicated to the memory of Mark Prichard.

Clinical experience with a novel assay measuring cytomegalovirus (CMV)-specific CD4+ and CD8+ T-cell immunity by flow cytometry and intracellular cytokine staining to predict clinically significant CMV events

BACKGROUND

Cytomegalovirus (CMV) infection is one of the most common opportunistic infections following organ transplantation, despite administration of CMV prophylaxis. CMV-specific T-cell immunity (TCI) has been associated with reduced rates of CMV infection. We describe for the first time clinical experience using the CMV T-Cell Immunity Panel (CMV-TCIP), a commercially available assay which measures CMV-specific CD4+ and CD8+ T-cell responses, to predict clinically significant CMV events.

METHODS

Adult (> 18-year-old) patients with CMV-TCIP results and ≥ 1 subsequent assessment for CMV DNAemia were included at Brown University and the University of Maryland Medical Center-affiliated hospitals between 4/2017 and 5/2019. A clinically significant CMV event was defined as CMV DNAemia prompting initiation of treatment. We excluded indeterminate results, mostly due to background positivity, allogeneic hematopoetic cell transplant (HCT) recipients, or patients who were continued on antiviral therapy against CMV irrespective of the CMV-TCIP result, because ongoing antiviral therapy could prevent a CMV event.

RESULTS

We analyzed 44 samples from 37 patients: 31 were solid organ transplant recipients, 4 had hematologic malignancies, 2 had autoimmune disorders. The CMV-protection receiver operating characteristic (ROC) area under the curve (AUC) was significant for %CMV-specific CD4+ (AUC: 0.78, P < 0.001) and borderline for CD8+ (AUC: 0.66, P = 0.064) T-cells. At a cut-off value of 0.22% CMV-specific CD4+ T-cells, positive predictive value (PPV) for protection against CMV was 85% (95%CI 65-96%), and negative predictive value (NPV) was 67% (95%CI 41-87%).

CONCLUSIONS

The CMV-TCIP, in particular %CMV-specific CD4+ T-cells, showed good diagnostic performance to predict CMV events. The CMV-TCIP may be a useful test in clinical practice, and merits further validation in larger prospective studies.

Reactivation of Cytomegalovirus Increases Nitric Oxide and IL-10 Levels in Sepsis and is Associated with Changes in Renal Parameters and Worse Clinical Outcome

CMV reactivation has been widely associated with bacterial sepsis and occurs in approximately 30% of these individuals, is associated with a longer ICU stay, prolongation of the need for mechanical ventilation, and over 80% increase in the mortality rate, being directly associated with severe organ dysfunction and hemodynamic imbalance. Thus, the aim of this study was to evaluate the role of CMV reactivation in sepsis progression. The overall occurrence of cytomegalovirus reactivation in the cohort was 17.58%. Was observed an increase in plasma levels of NO, reduction of percentage of free days of mechanical ventilation and arterial pH, as well as changes in coagulation parameters in the reactivated group. There was also a significant increase in IL-10, creatinine, urea levels and reduction of 24-hour urine output. These variables still correlated with viral load, demonstrating an association between the reactivation process and kidney failure present in sepsis. The reactivated group still had 2.1 times the risk of developing septic shock and an increase in the mortality rates. CMV is reactivated in sepsis and these patients presented a higher risk of developing septic shock and higher mortality rates and our data suggest that IL-10 and NO may be involved in this process.

Cytomegalovirus: Shape-Shifting the Immune System

Systems-based based approaches have begun to shed light on extrinsic factors that contribute to immune system variation. Among these, CMV (HHV-5, a β-herpesvirus) imposes a surprisingly profound impact. Most of the world's population is CMV⁺, and the virus goes through three distinct infection phases en route to establishing lifelong détente with its host. Immune control of CMV in each phase recruits unique arms of host defense, and in turn the virus employs multiple immune-modulatory strategies that help facilitate the establishment of lifelong persistence. In this review, we explain how CMV shapes immunity and discuss the impact it may have on overall health.

Human Cytomegalovirus Antigen Presentation by HLA-DR+ NKG2C+ Adaptive NK Cells Specifically Activates Polyfunctional Effector Memory CD4+ T Lymphocytes

Natural killer (NK) cells play a dual role in the defense against viral pathogens by directly lysing infected cells as well as by regulating anti-viral T cell immunity. Infection by human cytomegalovirus (HCMV) promotes a persistent expansion of NKG2C+ adaptive NK cells which have been shown to display enhanced antibody-dependent responses against infected targets and associated to viral control in transplanted patients. Based on gene expression data showing increased transcription of CIITA and several genes related to the MHC class II pathway in adaptive NK cells, we explored their putative capacity for antigen presentation to CD4+ T cells. Phenotypic analysis confirmed a preferential steady-state expression of HLA-DR by circulating NKG2C+ adaptive NK cells in healthy individuals. Expression of HLA-DR in NKG2C+ adaptive NK cells was variable and unrelated to the expression of activation (i.e., CD69 and CD25) or differentiation (i.e., FcRγ chain, CD57) markers, remaining stable over time at the individual level. Incubation of purified NK cells with HCMV complexed with serum specific antibodies induced an up-regulation of surface HLA-DR concomitant to CD16 loss whereas no changes in CD80/CD86 co-stimulatory ligands were detected. In addition, surface CX3CR1 decreased upon antigen-loading while HLA-DR+ NK cells maintained a CCR7-, CXCR3^low homing profile. Remarkably, HCMV-loaded purified NK cells activated autologous CD4+ T cells in an HLA-DR dependent manner. The fraction of T lymphocytes activated by antigen-loaded NK cells was smaller than that stimulated by monocyte-derived dendritic cells, corresponding to CD28-negative effector-memory CD4+ T cells with cytotoxic potential. Antigen presentation by NK cells activated a polyfunctional CD4+ T cell response characterized by degranulation (CD107a) and the secretion of Th1 cytokines (IFNγ and TNFα). Overall, our data discloses the capacity of NKG2C+ adaptive NK cells to process and present HCMV antigens to memory CD4+ cytotoxic T cells, directly regulating their response to the viral infection.

Generation, maintenance and tissue distribution of T cell responses to human cytomegalovirus in lytic and latent infection

Understanding how the T cell memory response directed towards human cytomegalovirus (HCMV) develops and changes over time while the virus persists is important. Whilst HCMV primary infection and periodic reactivation is well controlled by T cell responses in healthy people, when the immune system is compromised such as post-transplantation, during pregnancy, or underdeveloped such as in new-born infants and children, CMV disease can be a significant problem. In older people, HCMV infection is associated with increased risk of mortality and despite overt disease rarely being seen there are increases in HCMV-DNA in urine of older people suggesting that there is a change in the efficacy of the T cell response following lifelong infection. Therefore, understanding whether phenomenon such as “memory inflation” of the immune response is occurring in humans and if this is detrimental to the overall health of individuals would enable the development of appropriate treatment strategies for the future. In this review, we present the evidence available from human studies regarding the development and maintenance of memory CD8 + and CD4 + T cell responses to HCMV. We conclude that there is only limited evidence supportive of “memory inflation” occurring in humans and that future studies need to investigate immune cells from a broad range of human tissue sites to fully understand the nature of HCMV T cell memory responses to lytic and latent infection.

US28: HCMV's Swiss Army Knife

US28 is one of four G protein coupled receptors (GPCRs) encoded by human cytomegalovirus (HCMV). The US28 protein (pUS28) is a potent signaling molecule that alters a variety of cellular pathways that ultimately alter the host cell environment. This viral GPCR is expressed not only in the context of lytic replication but also during viral latency, highlighting its multifunctional properties. pUS28 is a functional GPCR, and its manipulation of multiple signaling pathways likely impacts HCMV pathogenesis. Herein, we will discuss the impact of pUS28 on both lytic and latent infection, pUS28-mediated signaling and its downstream consequences, and the influence this viral GPCR may have on disease states, including cardiovascular disease and cancer. We will also discuss the potential for and progress towards exploiting pUS28 as a novel therapeutic to combat HCMV.

Impact of Aging on the Frequency, Phenotype, and Function of CD161-Expressing T Cells

Immune-aging is associated with perturbed immune responses in the elderly. CD161-expressing T cells, i.e., the previously described subsets of CD161⁺ CD4⁺ T cells, CD161^high CD8⁺ T cells, and CD161^int CD8⁺ T cells, are highly functional, pro-inflammatory T cells. These CD161-expressing T cells are critical in immunity against microbes, while possibly contributing to autoimmune diseases. So far, little is known about the impact of aging on the frequency, phenotype, and function of these CD161-expressing T cells. In the current study, we investigated the impact of aging on CD161⁺ CD4⁺ T cells, CD161^high CD8⁺ T cells, and CD161^int CD8⁺ T cells in peripheral blood samples of 96 healthy subjects (age 20–84). Frequencies of CD161⁺ CD4⁺ T cells and CD161^int CD8⁺ T cells were stable with aging, whereas frequencies of CD161^high CD8⁺ T cells declined. Although CD161^high CD8⁺ T cells were mostly T cell receptor-Vα7.2⁺ mucosal-associated invariant T cells, CD161 expressing CD4⁺ and CD8⁺ T cells showed a limited expression of markers for gamma–delta T cells or invariant natural killer (NK) T cells, in both young and old subjects. In essence, CD161-expressing T cells showed a similar memory phenotype in young and old subjects. The expression of the inhibitory NK receptor KLRG1 was decreased on CD161⁺ CD4⁺ T cells of old subjects, whereas the expression of other NK receptors by CD161-expressing T cells was unaltered with age. The expression of cytotoxic effector molecules was similar in CD161^high and CD161^int CD8⁺ T cells of young and old subjects. The ability to produce pro-inflammatory cytokines was preserved in CD161^high and CD161^int CD8⁺ T cells of old subjects. However, the percentages of IFN-γ⁺ and interleukin-17⁺ cells were significantly lower in CD161⁺ CD4⁺ T cells of old individuals than those of young individuals. In addition, aging was associated with a decrease of nonclassic T helper 1 cells, as indicated by decreased percentages of CD161-expressing cells within the IFN-γ⁺ CD4⁺ T cell compartment of old subjects. Taken together, aging is associated with a numerical decline of circulating CD161^high CD8⁺ T cells, as well as a decreased production of pro-inflammatory cytokines by CD161⁺ CD4⁺ T cells. These aging-associated changes could contribute to perturbed immunity in the elderly.

Cytomegalovirus-specific T-cells are associated with immune senescence, but not with systemic inflammation, in people living with HIV

In people living with HIV (PLWHIV), coinfection with cytomegalovirus (CMV) has been associated with inflammation, immunological ageing, and increased risk of severe non-AIDS related comorbidity. The effect of CMV-specific immune responses on systemic inflammation, immune activation and T-cell senescence was evaluated in 53 PLWHIV treated with combination antiretroviral therapy (cART). Activated-, terminally differentiated-, naïve-, and senescent T-cells were assessed by flow cytometry, and plasma levels of CMV IgG, interleukin-6, tumor necrosis factor-α, high-sensitivity C-reactive protein and soluble-CD14 were measured. In PLWHIV, expression of interleukin-2, tumor necrosis factor-α and interferon-γ was measured by intracellular-cytokine-staining after stimulation of T-cells with CMV-pp65, CMV-IE1, and CMV-gB. Increased CMV-specific T-cell responses were associated with a higher ratio of terminally differentiated/naïve CD8+ T-cells and with increased proportions of senescent CD8+ T-cells, but not with systemic inflammation or sCD14. Increased CMV-specific CD4+ T-cell responses were associated with increased proportions of activated CD8+ T-cells. In PLWHIV with expansion of CMV-specific T-cells or increased T-cell senescence, CMV-specific polyfunctionality was maintained. That the magnitude of the CMV-specific T-cell response was associated with a senescent immune phenotype, suggests that a dysregulated immune response against CMV may contribute to the immunological ageing often described in PLWHIV despite stable cART.

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.

Extracellular Lactate: A Novel Measure of T Cell Proliferation

Following activation, T cells rapidly divide and acquire effector functions. This energetically demanding process depends upon the ability of T cells to undergo metabolic remodeling from oxidative phosphorylation to aerobic glycolysis, during which glucose is converted into lactate and released extracellularly. In this article, we demonstrate that extracellular lactate can be used to dynamically assess human T cell responses in vitro. Extracellular lactate levels strongly correlated with T cell proliferation, and measuring lactate compared favorably with traditional methods for determining T cell responses (i.e., [3H]thymidine incorporation and the use of cell proliferation dyes). Furthermore, we demonstrate the usefulness of measuring lactate as a read-out in conventional suppression assays and high-throughput peptide-screening assays. Extracellular lactate was stably produced over 7 d, and results were reproducibly performed over several freeze-thaw cycles. We conclude that the use of extracellular lactate measurements can be a sensitive, safe, stable, and easy-to-implement research tool for measuring T cell responses and cellular metabolic changes in vitro.

Novel viral vectors in infectious diseases

Since the development of vaccinia virus as a vaccine vector in 1984, the utility of numerous viruses in vaccination strategies has been explored. In recent years, key improvements to existing vectors such as those based on adenovirus have led to significant improvements in immunogenicity and efficacy. Furthermore, exciting new vectors that exploit viruses such as cytomegalovirus (CMV) and vesicular stomatitis virus (VSV) have emerged. Herein, we summarize these recent developments in viral vector technologies, focusing on novel vectors based on CMV, VSV, measles and modified adenovirus. We discuss the potential utility of these exciting approaches in eliciting protection against infectious diseases.

Myeloid Dendritic Cells Repress Human Cytomegalovirus Gene Expression and Spread by Releasing Interferon-Unrelated Soluble Antiviral Factors

Cytomegalovirus (CMV) is a betaherpesvirus that latently infects most adult humans worldwide and is a major cause of morbidity and mortality in immunocompromised hosts. Latent human CMV (HCMV) is believed to reside in precursors of myeloid-lineage leukocytes and monocytes, which give rise to macrophages and dendritic cells (DC). We report here that human monocyte-derived DC (mo-DC) suppress HCMV infection in coculture with infected fibroblast target cells in a manner dependent on the effector-to-target ratio. Intriguingly, optimal activation of mo-DC was achieved under coculture conditions and not by direct infection with HCMV, implying that mo-DC may recognize unique molecular patterns on, or within, infected fibroblasts. We show that HCMV is controlled by secreted factors that act by priming defenses in target cells rather than by direct viral neutralization, but we excluded a role for interferons (IFNs) in this control. The expression of lytic viral genes in infected cells and the progression of infection were significantly slowed, but this effect was reversible, indicating that the control of infection depended on the transient induction of antiviral effector molecules in target cells. Using immediate early or late-phase reporter HCMVs, we show that soluble factors secreted in the cocultures suppress HCMV replication at both stages of the infection and that their antiviral effects are robust and comparable in numerous batches of mo-DC as well as in primary fibroblasts and stromal cells.IMPORTANCE Human cytomegalovirus is a widespread opportunistic pathogen that can cause severe disease and complications in vulnerable individuals. This includes newborn children, HIV AIDS patients, and transplant recipients. Although the majority of healthy humans carry this virus throughout their lives without symptoms, it is not exactly clear which tissues in the body are the main reservoirs of latent virus infection or how the delicate balance between the virus and the immune system is maintained over an individual's lifetime. Here, for the first time, we provide evidence for a novel mechanism of direct virus control by a subset of human innate immune cells called dendritic cells, which are regarded as a major site of virus latency and reactivation. Our findings may have important implications in HCMV disease prevention as well as in development of novel therapeutic approaches.

The self-curing phenomenon of schistosome infection in rhesus macaques: insight from in vitro studies

A reduction in the burden of schistosomiasis is potentially achievable by integrating a schistosomiasis vaccine with current control measures. Here, we determine parasite-specific in vitro responses of B, T, and NK cells from naive uninfected rhesus macaques to Schistosoma mansoni (Sm) egg (SmEA) and worm antigen (SmWA) preparations isolated from infected baboons. Pronounced B cell responses to SmEA and NK cell responses to both SmEA and SmWA were observed. High levels of IL-2 and IL-21 responses against Sm antigens were observed in T and non-T cells of lymph nodes (LNs) and gut lamina propria-derived lymphocytes (LPLs). Data analysis showed multifunctionality of LN-derived CD4⁺ , CD8⁺ , and CD4⁺ CD8⁺ double positive T cells against either SmWA or SmWA+SmEA antigen preparations. Distinct SmEA-specific multifunctional responses were observed in gut LPLs, suggesting simultaneous responses against egg antigens. These data provide insight into the immune effectors involved in schistosome responses by rhesus macaques.

Naïve T cells are activated by autologous HCMV-infected endothelial cells through NKG2D and can control HCMV transmission in vitro

Apart from classical antigen-presenting cells (APCs) like dendritic cells and macrophages, there are semiprofessional APCs such as endothelial cells (ECs) and Langerhans' cells. Human cytomegalovirus (HCMV) infects a wide range of cell types including the ECs which are involved in the trafficking and homing of T cells. By investigating the interaction of naïve T cells obtained from HCMV-seronegative umbilical cord blood with autologous HCMV-infected human umbilical vein ECs (HUVECs), we could show that the activation of naïve T cells occurred after 1 day of peripheral blood mononuclear cell (PBMC) exposure to HCMV-infected HUVECs. The percentage of activated T cells increased over time and the activation of naïve T cells was not induced by either autologous uninfected HUVECs or by autologous HCMV-infected fibroblasts. The activation of T cells occurred also when purified T cells were co-cultured with HCMV-infected HUVECs. In addition, in most of the donors only CD8⁺ T cells were activated, when the purified T cells were exposed to HCMV-infected HUVECs. The activation of naïve T cells was inhibited when the NKG2D receptor was blocked on the surface of T cells and among the different NKG2D ligands, we identified two ligands (ULBP4 and MICA) on HCMV-infected HUVECs which might be the interaction partners of the NKG2D receptor. Using a functional cell culture assay, we could show that these activated naïve T cells specifically inhibited HCMV transmission. Altogether, we identified a novel specific activation mechanism of naïve T cells from the umbilical cord by HCMV-infected autologous HUVECs through interaction with NKG2D.