Human cytomegalovirus tropism for mucosal myeloid dendritic cells

Cytomegalovirus infection during pregnancy

Cytomegalovirus (CMV) infection during pregnancy is a global silent problem. Additionally, it is the leading cause of congenital infections, non-genetic sensorineural hearing loss, and neurodevelopmental delays in infants. However, this has barely been recognized globally. This condition lacks adequate attention, which is further emphasized by the lack of awareness among healthcare workers and the general population. The impact of CMV infection is often overlooked because of the asymptomatic nature of its presentation in infected pregnant women and newborns, difficulty in diagnosis, and the perception that infants born to women with pre-existing antibodies against CMV have normal neonatal outcomes. This article highlights the latest information on the epidemiology, transmission, clinical manifestations, and development of CMV infection and its management. We reviewed the pathophysiology and clinical manifestations of CMV infection in pregnant women, diagnostic methods, including screening and prognostic markers, and updates in treatment modalities. Current advancements in research on vaccination and hyperimmunoglobulins with worldwide treatment protocols are highlighted.

How dendritic cells sense and respond to viral infections

The ability of dendritic cells (DCs) to sense viral pathogens and orchestrate a proper immune response makes them one of the key players in antiviral immunity. Different DC subsets have complementing functions during viral infections, some specialize in antigen presentation and cross-presentation and others in the production of cytokines with antiviral activity, such as type I interferons. In this review, we summarize the latest updates concerning the role of DCs in viral infections, with particular focus on the complex interplay between DC subsets and severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Despite being initiated by a vast array of immune receptors, DC-mediated antiviral responses often converge towards the same endpoint, that is the production of proinflammatory cytokines and the activation of an adaptive immune response. Nonetheless, the inherent migratory properties of DCs make them a double-edged sword and often viral recognition by DCs results in further viral dissemination. Here we illustrate these various aspects of the antiviral functions of DCs and also provide a brief overview of novel antiviral vaccination strategies based on DCs targeting.

Hematopoietic cell-mediated dissemination of murine cytomegalovirus is regulated by NK cells and immune evasion

Cytomegalovirus (CMV) causes clinically important diseases in immune compromised and immune immature individuals. Based largely on work in the mouse model of murine (M)CMV, there is a consensus that myeloid cells are important for disseminating CMV from the site of infection. In theory, such dissemination should expose CMV to cell-mediated immunity and thus necessitate evasion of T cells and NK cells. However, this hypothesis remains untested. We constructed a recombinant MCMV encoding target sites for the hematopoietic specific miRNA miR-142-3p in the essential viral gene IE3. This virus disseminated poorly to the salivary gland following intranasal or footpad infections but not following intraperitoneal infection in C57BL/6 mice, demonstrating that dissemination by hematopoietic cells is essential for specific routes of infection. Remarkably, depletion of NK cells or T cells restored dissemination of this virus in C57BL/6 mice after intranasal infection, while dissemination occurred normally in BALB/c mice, which lack strong NK cell control of MCMV. These data show that cell-mediated immunity is responsible for restricting MCMV to hematopoietic cell-mediated dissemination. Infected hematopoietic cells avoided cell-mediated immunity via three immune evasion genes that modulate class I MHC and NKG2D ligands (m04, m06 and m152). MCMV lacking these 3 genes spread poorly to the salivary gland unless NK cells were depleted, but also failed to replicate persistently in either the nasal mucosa or salivary gland unless CD8⁺ T cells were depleted. Surprisingly, CD8⁺ T cells primed after intranasal infection required CD4⁺ T cell help to expand and become functional. Together, our data suggest that MCMV can use both hematopoietic cell-dependent and -independent means of dissemination after intranasal infection and that cell mediated immune responses restrict dissemination to infected hematopoietic cells, which are protected from NK cells during dissemination by viral immune evasion. In contrast, viral replication within mucosal tissues depends on evasion of T cells.

Cytomegalovirus (CMV) is a common cause of disease in immune compromised individuals as well as a common cause of congenital infections leading to disease in newborns. The virus is thought to enter primarily via mucosal barrier tissues, such as the oral and nasal mucosa. However, it is not clear how the virus escapes these barrier tissues to reach distant sites. In this study, we used a mouse model of CMV infection. Our data illustrate a complex balance between the immune system and viral infection of “myeloid cells”, which are most commonly thought to carry the virus around the body after infection. In particular, our data suggest that robust immune responses at the site of infection force the virus to rely on myeloid cells to escape the site of infection. Moreover, viral genes designed to evade these immune responses were needed to protect the virus during and after its spread to distant sites. Together, this work sheds light on the mechanisms of immune control and viral survival during CMV infection of mucosal tissues and spread to distant sites of the body.

Cytomegalovirus Latency and Reactivation: An Intricate Interplay With the Host Immune Response

CMV is an ancient herpesvirus that has co-evolved with its host over millions of years. The 236 kbp genome encodes at least 165 genes, four non-coding RNAs and 14 miRNAs. Of the protein-coding genes, 43-44 are core replication genes common to all herpesviruses, while ~30 are unique to betaherpesviruses. Many CMV genes are involved in evading detection by the host immune response, and others have roles in cell tropism. CMV replicates systemically, and thus, has adapted to various biological niches within the host. Different biological niches may place competing demands on the virus, such that genes that are favorable in some contexts are unfavorable in others. The outcome of infection is dependent on the cell type. In fibroblasts, the virus replicates lytically to produce infectious virus. In other cell types, such as myeloid progenitor cells, there is an initial burst of lytic gene expression, which is subsequently silenced through epigenetic repression, leading to establishment of latency. Latently infected monocytes disseminate the virus to various organs. Latency is established through cell type specific mechanisms of transcriptional silencing. In contrast, reactivation is triggered through pathways activated by inflammation, infection, and injury that are common to many cell types, as well as differentiation of myeloid cells to dendritic cells. Thus, CMV has evolved a complex relationship with the host immune response, in which it exploits cell type specific mechanisms of gene regulation to establish latency and to disseminate infection systemically, and also uses the inflammatory response to infection as an early warning system which allows the virus to escape from situations in which its survival is threatened, either by cellular damage or infection of the host with another pathogen. Spontaneous reactivation induced by cellular aging/damage may explain why extensive expression of lytic genes has been observed in recent studies using highly sensitive transcriptome analyses of cells from latently infected individuals. Recent studies with animal models highlight the potential for harnessing the host immune response to blunt cellular injury induced by organ transplantation, and thus, prevent reactivation of CMV and its sequelae.

Phase 1 Clinical Trial of a Conditionally Replication-Defective Human Cytomegalovirus (CMV) Vaccine in CMV-Seronegative Subjects

Background

A conditionally replication-defective human cytomegalovirus (CMV) vaccine (V160) derived from AD169 and genetically engineered to express CMV pentameric complex (gH/gL/pUL128/pUL130/pUL131) was developed and evaluated for phase 1 vaccine safety and immunogenicity in CMV-seronegative and CMV-seropositive adults.

Methods

Subjects received 3 doses of V160 or placebo on day 1, month 1, and month 6. Four vaccine dose levels, formulated with or without aluminum phosphate adjuvant, were evaluated. Injection-site and systemic adverse events (AEs) and vaccine viral shedding were monitored. CMV-specific cellular and humoral responses were measured by interferon-gamma ELISPOT and virus neutralization assay up to 12 months after last dose.

Results

V160 was generally well-tolerated, with no serious AEs observed. Transient, mild-to-moderate injection-site and systemic AEs were reported more frequently in vaccinated subjects than placebo. Vaccine viral shedding was not detected in any subject, confirming the nonreplicating feature of V160. Robust neutralizing antibody titers were elicited and maintained through 12 months postvaccination. Cellular responses to structural and nonstructural viral proteins were observed, indicating de novo expression of viral genes postvaccination.

Conclusions

V160 displayed an acceptable safety profile. Levels of neutralizing antibodies and T-cell responses in CMV-seronegative subjects were within ranges observed following natural CMV infection.

Clinical Trial Registration

. NCT01986010.

Neutralization of rhesus cytomegalovirus IL-10 reduces horizontal transmission and alters long-term immunity

Human cytomegalovirus (HCMV) causes severe disease in infants and immunocompromised people. There is no approved HCMV vaccine, and vaccine development strategies are complicated by evidence of both persistent infection and reinfection of people with prior immunity. The greatest emphasis has been placed on reducing transmission to seronegative pregnant women to prevent vertical transmission and its potentially severe sequelae. Increasing evidence suggests that the earliest host-HCMV interactions establish conditions for viral persistence, including evasion of host immune responses to the virus. Using a nonhuman primate model of HCMV infection, we show that rhesus macaques immunized against viral interleukin-10 (IL-10) manifest delayed rhesus cytomegalovirus (RhCMV) acquisition and altered immune responses to the infection when it does occur. Among animals with the greatest antiviral IL-10-neutralizing activity, the timing of RhCMV seroconversion was delayed by an average of 12 weeks. After acquisition, such animals displayed an antibody response to the new infection, which peaked as expected after 2 weeks but then declined rapidly. In contrast, surprisingly, vaccination with glycoprotein B (gB) protein had no discernible impact on these outcomes. Our results demonstrate that viral IL-10 is a key regulator of successful host immune responses to RhCMV. Viral IL-10 is, therefore, an important target for vaccine strategies against cytomegalovirus (CMV). Furthermore, given the immunoregulatory function of viral IL-10, targeting this protein may prove synergistic with other vaccine therapies and targets. Our study also provides additional evidence that the earliest host-CMV interactions can have a significant impact on the nature of persistent infection.

Single-Cell Transcriptome Analysis of CD34+ Stem Cell-Derived Myeloid Cells Infected With Human Cytomegalovirus

Myeloid cells are important sites of lytic and latent infection by human cytomegalovirus (CMV). We previously showed that only a small subset of myeloid cells differentiated from CD34⁺ hematopoietic stem cells is permissive to CMV replication, underscoring the heterogeneous nature of these populations. The exact identity of resistant and permissive cell types, and the cellular features characterizing the latter, however, could not be dissected using averaging transcriptional analysis tools such as microarrays and, hence, remained enigmatic. Here, we profile the transcriptomes of ∼7000 individual cells at day 1 post-infection using the 10× genomics platform. We show that viral transcripts are detectable in the majority of the cells, suggesting that virion entry is unlikely to be the main target of cellular restriction mechanisms. We further show that viral replication occurs in a small but specific sub-group of cells transcriptionally related to, and likely derived from, a cluster of cells expressing markers of Colony Forming Unit – Granulocyte, Erythrocyte, Monocyte, Megakaryocyte (CFU-GEMM) oligopotent progenitors. Compared to the remainder of the population, CFU-GEMM cells are enriched in transcripts with functions in mitochondrial energy production, cell proliferation, RNA processing and protein synthesis, and express similar or higher levels of interferon-related genes. While expression levels of the former are maintained in infected cells, the latter are strongly down-regulated. We thus propose that the preferential infection of CFU-GEMM cells may be due to the presence of a pre-established pro-viral environment, requiring minimal optimization efforts from viral effectors, rather than to the absence of specific restriction factors. Together, these findings identify a potentially new population of myeloid cells permissive to CMV replication, and provide a possible rationale for their preferential infection.

A replication-defective human cytomegalovirus vaccine for prevention of congenital infection

Congenital human cytomegalovirus (HCMV) infection occurs in ~0.64% of infants born each year in the United States and is the leading nongenetic cause of childhood neurodevelopmental disabilities. No licensed HCMV vaccine is currently available. Natural immunity to HCMV in women before pregnancy is associated with a reduced risk of fetal infection, suggesting that a vaccine is feasible if it can reproduce immune responses elicited by natural infection. On the basis of this premise, we developed a whole-virus vaccine candidate from the live attenuated AD169 strain, with genetic modifications to improve its immunogenicity and attenuation. We first restored the expression of the pentameric gH/gL/pUL128-131 protein complex, a major target for neutralizing antibodies in natural immunity. We then incorporated a chemically controlled protein stabilization switch in the virus, enabling us to regulate viral replication with a synthetic compound named Shield-1. The virus replicated as efficiently as its parental virus in the presence of Shield-1 but failed to produce progeny upon removal of the compound. The vaccine was immunogenic in multiple animal species and induced durable neutralizing antibodies, as well as CD4⁺ and CD8⁺ T cells, to multiple viral antigens in nonhuman primates.

Human Herpesvirus 8 Infects and Replicates in Langerhans Cells and Interstitial Dermal Dendritic Cells and Impairs Their Function

The predominant types of dendritic cells (DC) in the skin and mucosa are Langerhans cells (LC) and interstitial dermal DC (iDDC). LC and iDDC process cutaneous antigens and migrate out of the skin and mucosa to the draining lymph nodes to present antigens to T and B cells. Because of the strategic location of LC and iDDC and the ability of these cells to capture and process pathogens, we hypothesized that they could be infected with human herpesvirus 8 (HHV-8) (Kaposi's sarcoma [KS]-associated herpesvirus) and have an important role in the development of KS. We have previously shown that HHV-8 enters monocyte-derived dendritic cells (MDDC) through DC-SIGN, resulting in nonproductive infection. Here we show that LC and iDDC generated from pluripotent cord blood CD34⁺ cell precursors support productive infection with HHV-8. Anti-DC-SIGN monoclonal antibody (MAb) inhibited HHV-8 infection of iDDC, as shown by low expression levels of viral proteins and DNA. In contrast, blocking of both langerin and the receptor protein tyrosine kinase ephrin A2 was required to inhibit HHV-8 infection of LC. Infection with HHV-8 did not alter the cell surface expression of langerin on LC but downregulated the expression of DC-SIGN on iDDC, as we previously reported for MDDC. HHV-8-infected LC and iDDC had a reduced ability to stimulate allogeneic CD4⁺ T cells in the mixed-lymphocyte reaction. These results indicate that HHV-8 can target both LC and iDDC for productive infection via different receptors and alter their function, supporting their potential role in HHV-8 pathogenesis and KS.

IMPORTANCE Here we show that HHV-8, a DNA tumor virus that causes Kaposi's sarcoma, infects three types of dendritic cells: monocyte-derived dendritic cells, Langerhans cells, and interstitial dermal dendritic cells. We show that different receptors are used by this virus to infect these cells. DC-SIGN is a major receptor for infection of both monocyte-derived dendritic cells and interstitial dermal dendritic cells, yet the virus fully replicates only in the latter. HHV-8 uses langerin and the ephrin A2 receptor to infect Langerhans cells, which support full HHV-8 lytic replication. This infection of Langerhans cells and interstitial dermal dendritic cells results in an impaired ability to stimulate CD4⁺ helper T cell responses. Taken together, our data show that HHV-8 utilizes alternate receptors to differentially infect and replicate in these tissue-resident DC and support the hypothesis that these cells play an important role in HHV-8 infection and pathogenesis.

The pentameric complex drives immunologically covert cell-cell transmission of wild-type human cytomegalovirus

Human cytomegalovirus (HCMV) strains that have been passaged in vitro rapidly acquire mutations that impact viral growth. These laboratory-adapted strains of HCMV generally exhibit restricted tropism, produce high levels of cell-free virus, and develop susceptibility to natural killer cells. To permit experimentation with a virus that retained a clinically relevant phenotype, we reconstructed a wild-type (WT) HCMV genome using bacterial artificial chromosome technology. Like clinical virus, this genome proved to be unstable in cell culture; however, propagation of intact virus was achieved by placing the RL13 and UL128 genes under conditional expression. In this study, we show that WT-HCMV produces extremely low titers of cell-free virus but can efficiently infect fibroblasts, epithelial, monocyte-derived dendritic, and Langerhans cells via direct cell-cell transmission. This process of cell-cell transfer required the UL128 locus, but not the RL13 gene, and was significantly less vulnerable to the disruptive effects of IFN, cellular restriction factors, and neutralizing antibodies compared with cell-free entry. Resistance to neutralizing antibodies was dependent on high-level expression of the pentameric gH/gL/gpUL128-131A complex, a feature of WT but not passaged strains of HCMV.

Luciferase-tagged wild-type and tropism-deficient mouse cytomegaloviruses reveal early dynamics of host colonization following peripheral challenge

Cytomegaloviruses (CMVs) establish persistent, systemic infections and cause disease by maternal-foetal transfer, suggesting that their dissemination is a key target for antiviral intervention. Late clinical presentation has meant that human CMV (HCMV) dissemination is not well understood. Murine CMV (MCMV) provides a tractable model. Whole mouse imaging of virus-expressed luciferase has proved a useful way to track systemic infections. MCMV, in which the abundant lytic gene M78 was luciferase-tagged via a self-cleaving peptide (M78-LUC), allowed serial, unbiased imaging of systemic and peripheral infection without significant virus attenuation. Ex vivo luciferase imaging showed greater sensitivity than plaque assay, and revealed both well-known infection sites (the lungs, lymph nodes, salivary glands, liver, spleen and pancreas) and less explored sites (the bone marrow and upper respiratory tract). We applied luciferase imaging to tracking MCMV lacking M33, a chemokine receptor conserved in HCMV and a proposed anti-viral drug target. M33-deficient M78-LUC colonized normally in peripheral sites and local draining lymph nodes but spread poorly to the salivary gland, suggesting a defect in vascular transport consistent with properties of a chemokine receptor.

Molecular diagnostic of cytomegalovirus, Epstein Barr virus and Herpes virus 6 infections among blood donors by multiplex real-time PCR in Ouagadougou, Burkina Faso

Introduction

In most developing countries, Cytomegalovirus (CMV), Epstein Barr virus (EBV) and Herpes virus 6 (HHV-6) are not diagnosed in blood donors. The aim of this study is to determine the prevalence of these viruses in blood donors from the city of Ouagadougou, Burkina Faso.

Methods

The study included 198 blood donors of the Regional Blood Transfusion Centre of Ouagadougou. Multiplex real time PCR was used to diagnose the three viruses. Statistical analysis was performed with the software EpiInfo version 6 and SPSS version 17. P values ≤ 0.05 were considered significant.

Results

Of 198 samples tested, 18 (9.1%) were positive to at least one of the three viruses. In fact, 10 (5.1%) were positive for EBV, 10 (5.1%) positive for CMV and 12 (6.1%) positive for HHV-6. Viral infections were higher in women than in men, EBV (8,6% versus 4.3%), CMV (8.6% versus 3.7%) and HHV-6 (11.4% versus 4.9%). EBV / CMV / HHV-6 co-infection was found in 3.5% (7/198) of blood donors.

Conclusion

The prevalence recorded in this study is low compared to those found in previous studies from the sub-region among blood donors. The molecular diagnostic test used in our study could explain the differences with previous studies.

Role of cytomegalovirus on the maturation and function of monocyte derived dendritic cells of liver transplant patients

AIM: To study the impact of association between cytomegalovirus (CMV) pathogenesis with dendritic cell (DC) maturation and function was evaluated in CMV reactivated liver transplanted patients in comparing with non-reactivated ones, and healthy controls.

METHODS: Monocyte derived dendritic cells (MoDCs) was generated from collected ethylenediaminetetraacetic acid-treated blood samples from patient groups and controls. In these groups, expression rates and mean fluorescent intensity of DC markers were evaluated using flowcytometry technique. Secretion of cytokines including: interleukin (IL)-6, IL-12 and IL-23 were determined using enzyme-linked immunosorbent assay methods. The gene expression of toll-like receptor 2 (TLR2), TLR4 and IL-23 were analyzed using in-house real-time polymerase chain reaction protocols.

RESULTS: Results have been shown significant decreases in: Expression rates of MoDC markers including CD83, CD1a and human leukocyte antigen DR (HLA-DR), the mean fluorescence intensitys for CD1a and HLA-DR, and secretion of IL-12 in CMV reactivated compared with non-reactivated liver transplanted patients. On the other hand, significant increases have been shown in the secretions of IL-6 and IL-23 and gene expression levels of TLR2, TLR4 and IL-23 from MoDCs in CMV reactivated compared with non-reactivated liver transplanted recipients.

CONCLUSION: DC functional defects in CMV reactivated recipients, such as decrease in expression of DC maturation markers, increase in secretion of proinflammatory cytokines, and TLRs can emphasize on the importance of CMV infectivity in development of liver rejection in transplanted patients.

The intimate relationship between human cytomegalovirus and the dendritic cell lineage

Primary infection of healthy individuals with human cytomegalovirus (HCMV) is normally asymptomatic but results in the establishment of a lifelong infection of the host. One important cellular reservoir of HCMV latency is the CD34+ haematopoietic progenitor cells resident in the bone marrow. Viral gene expression is highly restricted in these cells with an absence of viral progeny production. However, cellular differentiation into mature myeloid cells is concomitant with the induction of a full lytic transcription program, DNA replication and, ultimately, the production of infectious viral progeny. Such reactivation of HCMV is a major cause of morbidity and mortality in a number of immune-suppressed patient populations. Our current understanding of HCMV carriage and reactivation is that cellular differentiation of the CD34+ progenitor cells through the myeloid lineage, resulting in terminal differentiation to either a macrophage or dendritic cell (DC) phenotype, is crucial for the reactivation event. In this mini-review, we focus on the interaction of HCMV with DCs, with a particular emphasis on their role in reactivation, and discuss how the critical regulation of viral major immediate-early gene expression appears to be delicately entwined with the activation of cellular pathways in differentiating DCs. Furthermore, we also explore the possible immune consequences associated with reactivation in a professional antigen presenting cell and potential countermeasures HCMV employs to abrogate these.