Decreased frequency of cytomegalovirus (CMV)-specific CD4+ T lymphocytes in simian immunodeficiency virus-infected rhesus macaques: inverse relationship with CMV viremia

Relationship of maternal cytomegalovirus-specific antibody responses and viral load to vertical transmission risk following primary maternal infection in a rhesus macaque model

Cytomegalovirus (CMV) is the most common congenital infection and cause of birth defects worldwide. Primary CMV infection during pregnancy leads to a higher frequency of congenital CMV (cCMV) than maternal re-infection, suggesting that maternal immunity confers partial protection. However, poorly understood immune correlates of protection against placental transmission contributes to the current lack of an approved vaccine to prevent cCMV. In this study, we characterized the kinetics of maternal plasma rhesus CMV (RhCMV) viral load (VL) and RhCMV-specific antibody binding and functional responses in a group of 12 immunocompetent dams with acute, primary RhCMV infection. We defined cCMV transmission as RhCMV detection in amniotic fluid (AF) by qPCR. We then leveraged a large group of past and current primary RhCMV infection studies in late-first/early-second trimester RhCMV-seronegative rhesus macaque dams, including immunocompetent (n = 15), CD4+ T cell-depleted with (n = 6) and without (n = 6) RhCMV-specific polyclonal IgG infusion before infection to evaluate differences between RhCMV AF-positive and AF-negative dams. During the first 3 weeks after infection, the magnitude of RhCMV VL in maternal plasma was higher in AF-positive dams in the combined cohort, while RhCMV glycoprotein B (gB)- and pentamer-specific binding IgG responses were lower magnitude compared to AF-negative dams. However, these observed differences were driven by the CD4+ T cell-depleted dams, as there were no differences in plasma VL or antibody responses between immunocompetent AF-positive vs AF-negative dams. Overall, these results suggest that levels of neither maternal plasma viremia nor humoral responses are associated with cCMV following primary maternal infection in healthy individuals. We speculate that other factors related to innate immunity are more important in this context as antibody responses to acute infection likely develop too late to influence vertical transmission. Yet, pre-existing CMV glycoprotein-specific and neutralizing IgG may provide protection against cCMV following primary maternal CMV infection even in high-risk, immunocompromised settings.

The pentameric complex is not required for vertical transmission of cytomegalovirus in seronegative pregnant rhesus macaques

Congenital cytomegalovirus (cCMV) infection is the leading infectious cause of neonatal neurological impairment but essential virological determinants of transplacental CMV transmission remain unclear. The pentameric complex (PC), composed of five subunits, glycoproteins H (gH), gL, UL128, UL130, and UL131A, is essential for efficient entry into non-fibroblast cells in vitro . Based on this role in cell tropism, the PC is considered a possible target for CMV vaccines and immunotherapies to prevent cCMV. To determine the role of the PC in transplacental CMV transmission in a non-human primate model of cCMV, we constructed a PC-deficient rhesus CMV (RhCMV) by deleting the homologues of the HCMV PC subunits UL128 and UL130 and compared congenital transmission to PC-intact RhCMV in CD4+ T cell-depleted or immunocompetent RhCMV-seronegative, pregnant rhesus macaques (RM). Surprisingly, we found that the transplacental transmission rate was similar for PC-intact and PC-deleted RhCMV based on viral genomic DNA detection in amniotic fluid. Moreover, PC-deleted and PC-intact RhCMV acute infection led to similar peak maternal plasma viremia. However, there was less viral shedding in maternal urine and saliva and less viral dissemination in fetal tissues in the PC-deleted group. As expected, dams inoculated with PC-deleted RhCMV demonstrated lower plasma IgG binding to PC-intact RhCMV virions and soluble PC, as well as reduced neutralization of PC-dependent entry of the PC-intact RhCMV isolate UCD52 into epithelial cells. In contrast, binding to gH expressed on the cell surface and neutralization of entry into fibroblasts by the PC-intact RhCMV was higher for dams infected with PC-deleted RhCMV compared to those infected with PC-intact RhCMV. Our data demonstrates that the PC is dispensable for transplacental CMV infection in our non-human primate model.

One Sentence Summary

Congenital CMV transmission frequency in seronegative rhesus macaques is not affected by the deletion of the viral pentameric complex.

Relationship of maternal cytomegalovirus-specific antibody responses and viral load to vertical transmission risk following primary maternal infection in a rhesus macaque model

Cytomegalovirus (CMV) is the most common congenital infection and cause of birth defects worldwide. Primary CMV infection during pregnancy leads to a higher frequency of congenital CMV (cCMV) than maternal re-infection, suggesting that maternal immunity confers partial protection. However, poorly understood immune correlates of protection against placental transmission contributes to the current lack of an approved vaccine to prevent cCMV. In this study, we characterized the kinetics of maternal plasma rhesus CMV (RhCMV) viral load (VL) and RhCMV-specific antibody binding and functional responses in a group of 12 immunocompetent dams with acute, primary RhCMV infection. We defined cCMV transmission as RhCMV detection in amniotic fluid (AF) by qPCR. We then leveraged a large group of past and current primary RhCMV infection studies in late-first/early-second trimester RhCMV-seronegative rhesus macaque dams, including immunocompetent (n=15), CD4+ T cell-depleted with (n=6) and without (n=6) RhCMV-specific polyclonal IgG infusion before infection to evaluate differences between RhCMV AF-positive and AF-negative dams. During the first 3 weeks after infection, the magnitude of RhCMV VL in maternal plasma was higher in AF-positive dams in the combined cohort, while RhCMV glycoprotein B (gB)- and pentamer-specific binding IgG responses were lower magnitude compared to AF-negative dams. However, these observed differences were driven by the CD4+ T cell-depleted dams, as there were no differences in plasma VL or antibody responses between immunocompetent AF-positive vs AF-negative dams. Overall, these results suggest that levels of neither maternal plasma viremia nor humoral responses are associated with cCMV following primary maternal infection in healthy individuals. We speculate that other factors related to innate immunity are more important in this context as antibody responses to acute infection likely develop too late to influence vertical transmission. Yet, pre-existing CMV glycoprotein-specific and neutralizing IgG may provide protection against cCMV following primary maternal CMV infection even in high-risk, immunocompromised settings.

Pathologic characteristics of infectious diseases in macaque monkeys used in biomedical and toxicologic studies

Nonhuman primates (NHPs), which have many advantages in scientific research and are often the only relevant animals to use in assessing the safety profiles and biological or pharmacological effects of drug candidates, including biologics. In scientific or developmental experiments, the immune systems of animals can be spontaneously compromised possibly due to background infection, experimental procedure-associated stress, poor physical condition, or intended or unintended mechanisms of action of test articles. Under these circumstances, background, incidental, or opportunistic infections can seriously can significantly complicate the interpretation of research results and findings and consequently affect experimental conclusions. Pathologists and toxicologists must understand the clinical manifestations and pathologic features of infectious diseases and the effects of these diseases on animal physiology and experimental results in addition to the spectrum of infectious diseases in healthy NHP colonies. This review provides an overview of the clinical and pathologic characteristics of common viral, bacterial, fungal, and parasitic infectious diseases in NHPs, especially macaque monkeys, as well as methods for definitive diagnosis of these diseases. Opportunistic infections that can occur in the laboratory setting have also been addressed in this review with examples of cases of infection disease manifestation that was observed or influenced during safety assessment studies or under experimental conditions.

Modeling SARS-CoV-2: Comparative Pathology in Rhesus Macaque and Golden Syrian Hamster Models

Coronavirus disease 2019 (COVID-19) in humans has a wide range of presentations, ranging from asymptomatic or mild symptoms to severe illness. Suitable animal models mimicking varying degrees of clinical disease manifestations could expedite development of therapeutics and vaccines for COVID-19. Here we demonstrate that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection resulted in subclinical disease in rhesus macaques with mild pneumonia and clinical disease in Syrian hamsters with severe pneumonia. SARS-CoV-2 infection was confirmed by formalin-fixed, paraffin-embedded (FFPE) polymerase chain reaction (PCR), immunohistochemistry, or in situ hybridization. Replicating virus in the lungs was identified using in situ hybridization or virus plaque forming assays. Viral encephalitis, reported in some COVID-19 patients, was identified in one macaque and was confirmed with immunohistochemistry. There was no evidence of encephalitis in hamsters. Severity and distribution of lung inflammation were substantially more in hamsters compared with macaques and exhibited vascular changes and virus-induced cytopathic changes as seen in COVID-19 patients. Neither the hamster nor macaque models demonstrated evidence for multisystemic inflammatory syndrome (MIS). Data presented here demonstrate that macaques may be appropriate for mechanistic studies of mild asymptomatic COVID-19 pneumonia and COVID-19-associated encephalitis, whereas Syrian hamsters may be more suited to study severe COVID-19 pneumonia.

Recent Approaches and Strategies in the Generation of Anti-human Cytomegalovirus Vaccines

Human cytomegalovirus is the largest human herpesvirus and shares many core features of other herpesviruses such as tightly regulated gene expression during genome replication and latency as well as the establishment of lifelong persistence following infection. In contrast to stereotypic clinical syndromes associated with alpha-herpesvirus infections, almost all primary HCMV infections are asymptomatic and acquired early in life in most populations in the world. Although asymptomatic in most individuals, HCMV is a major cause of disease in hosts with deficits in adaptive and innate immunity such as infants who are infected in utero and allograft recipients following transplantation. Congenital HCMV is a commonly acquired infection in the developing fetus that can result in a number of neurodevelopmental abnormalities. Similarly, HCMV is a major cause of disease in allograft recipients in the immediate and late posttransplant period and is thought to be a major contributor to chronic allograft rejection. Even though HCMV induces robust innate and adaptive immune responses, it also encodes a vast array of immune evasion functions that are thought aid in its persistence. Immune correlates of protective immunity that prevent or modify intrauterine HCMV infection remain incompletely defined but are thought to consist primarily of adaptive responses in the pregnant mother, thus making congenital HCMV a potentially vaccine modifiable disease. Similarly, HCMV infection in allograft recipients is often more severe in recipients without preexisting adaptive immunity to HCMV. Thus, there has been a considerable effort to modify HCMV specific immunity in transplant recipient either through active immunization or passive transfer of adaptive effector functions. Although efforts to develop an efficacious vaccine and/or passive immunotherapy to limit HCMV disease have been underway for nearly six decades, most have met with limited success at best. In contrast to previous efforts, current HCMV vaccine development has relied on observations of unique properties of HCMV in hopes of reproducing immune responses that at a minimum will be similar to that following natural infection. However, more recent findings have suggested that immunity following naturally acquired HCMV infection may have limited protective activity and almost certainly, is not sterilizing. Such observations suggest that either the induction of natural immunity must be specifically tailored to generate protective activity or alternatively, that providing targeted passive immunity to susceptible populations could be prove to be more efficacious.

In vitro and in vivo characterization of a recombinant rhesus cytomegalovirus containing a complete genome

Cytomegaloviruses (CMVs) are highly adapted to their host species resulting in strict species specificity. Hence, in vivo examination of all aspects of CMV biology employs animal models using host-specific CMVs. Infection of rhesus macaques (RM) with rhesus CMV (RhCMV) has been established as a representative model for infection of humans with HCMV due to the close evolutionary relationships of both host and virus. However, the only available RhCMV clone that permits genetic modifications is based on the 68-1 strain which has been passaged in fibroblasts for decades resulting in multiple genomic changes due to tissue culture adaptations. As a result, 68-1 displays reduced viremia in RhCMV-naïve animals and limited shedding compared to non-clonal, low passage isolates. To overcome this limitation, we used sequence information from primary RhCMV isolates to construct a full-length (FL) RhCMV by repairing all mutations affecting open reading frames (ORFs) in the 68-1 bacterial artificial chromosome (BAC). Inoculation of adult, immunocompetent, RhCMV-naïve RM with the reconstituted virus resulted in significant viremia in the blood similar to primary isolates of RhCMV and furthermore led to high viral genome copy numbers in many tissues at day 14 post infection. In contrast, viral dissemination was greatly reduced upon deletion of genes also lacking in 68-1. Transcriptome analysis of infected tissues further revealed that chemokine-like genes deleted in 68-1 are among the most highly expressed viral transcripts both in vitro and in vivo consistent with an important immunomodulatory function of the respective proteins. We conclude that FL-RhCMV displays in vitro and in vivo characteristics of a wildtype virus while being amenable to genetic modifications through BAC recombineering techniques.

Development and evaluation of a whole blood-based approach for flow cytometric quantification of CD154+ mould-reactive T cells

CD154+ mould-reactive T cells were proposed as a novel biomarker in the diagnosis of invasive mycoses. As PBMC-based protocols for flow cytometric quantification of these cells are logistically challenging and susceptible to preanalytic delays, this study evaluated and optimized a whole blood-based method for the detection of mould-reactive T cells. Blood collection tubes containing costimulatory antibodies and Aspergillus fumigatus mycelial lysates were inoculated with heparinized whole blood from healthy adults, and detection rates of CD154+/CD4+A. fumigatus reactive T cells were compared with PBMC-based detection using samples from the same donors. In contrast to the PBMC-based method, double costimulation with αCD28 and αCD49d was crucial for reliable whole blood stimulation. Optimizing stimulation schemes for both matrixes, significantly higher specific T-cell detection rates were achieved by the whole blood-based method, whereas the unspecific background stimulation remained low. MHC II-dependent CD154+ upregulation was demonstrated for both matrixes. Excellent correlation and reproducible conversion factors between whole blood and PBMC-based results were observed. Using frozen ready-to-use test tubes containing costimulatory antibodies and lysates, detection rates of specific T cells were comparable to freshly prepared blood collection tubes. The optimized whole blood-based protocol was also used to detect Rhizopus arrhizus and Rhizomucor pusillus reactive T cells, resulting in 1.5- to 2.7-fold higher detection rates compared with PBMC-based measurement. In summary, the whole blood protocol is a robust, highly sensitive, and cost-effective method for mould-reactive T-cell quantification, allowing for point-of-care sample stimulation and contributing to better assay standardization in multi-centre evaluation of mould reactive T-cell quantification.

Viral opportunistic infections in Mauritian cynomolgus macaques undergoing allogeneic stem cell transplantation mirror human transplant infectious disease complications

Allogeneic hematopoietic stem cell transplantation (HSCT) and xenotransplantation are accompanied by viral reactivations and virus-associated complications resulting from immune deficiency. Here, in a Mauritian cynomolgus macaque model of fully MHC-matched allogeneic HSCT, we report reactivations of cynomolgus polyomavirus, lymphocryptovirus, and cytomegalovirus, macaque viruses analogous to HSCT-associated human counterparts BK virus, Epstein-Barr virus, and human cytomegalovirus. Viral replication in recipient macaques resulted in characteristic disease manifestations observed in HSCT patients, such as polyomavirus-associated hemorrhagic cystitis and tubulointerstitial nephritis or lymphocryptovirus-associated post-transplant lymphoproliferative disorder. However, in most cases, the reconstituted immune system, alone or in combination with short-term pharmacological intervention, exerted control over viral replication, suggesting engraftment of functional donor-derived immunity. Indeed, the donor-derived reconstituted immune systems of two long-term engrafted HSCT recipient macaques responded to live attenuated yellow fever 17D vaccine (YFV 17D) indistinguishably from untransplanted controls, mounting 17D-targeted neutralizing antibody responses and clearing YFV 17D within 14 days. Together, these data demonstrate that this macaque model of allogeneic HSCT recapitulates clinical situations of opportunistic viral infections in transplant patients and provides a pre-clinical model to test novel prophylactic and therapeutic modalities.

High-fat diet exacerbates SIV pathogenesis and accelerates disease progression

Consuming a high-fat diet (HFD) is a risk factor for obesity and diabetes; both of these diseases are also associated with systemic inflammation, similar to HIV infection. A HFD induces intestinal dysbiosis and impairs liver function and coagulation, with a potential negative impact on HIV/SIV pathogenesis. We administered a HFD rich in saturated fats and cholesterol to nonpathogenic (African green monkeys) and pathogenic (pigtailed macaques) SIV hosts. The HFD had a negative impact on SIV disease progression in both species. Thus, increased cell-associated SIV DNA and RNA occurred in the HFD-receiving nonhuman primates, indicating a potential reservoir expansion. The HFD induced prominent immune cell infiltration in the adipose tissue, an important SIV reservoir, and heightened systemic immune activation and inflammation, altering the intestinal immune environment and triggering gut damage and microbial translocation. Furthermore, HFD altered lipid metabolism and HDL oxidation and also induced liver steatosis and fibrosis. These metabolic disturbances triggered incipient atherosclerosis and heightened cardiovascular risk in the SIV-infected HFD-receiving nonhuman primates. Our study demonstrates that dietary intake has a discernable impact on the natural history of HIV/SIV infections and suggests that dietary changes can be used as adjuvant approaches for HIV-infected subjects, to reduce inflammation and the risk of non-AIDS comorbidities and possibly other infectious diseases.

Impact of CMV Infection on Natural Killer Cell Clonal Repertoire in CMV-Naïve Rhesus Macaques

Recent functional, gene expression, and epigenetic studies have suggested the presence of a subset of mature natural killer (NK) cells responsible for maintaining NK cell memory. The lack of endogenous clonal markers in NK cells impedes understanding the genesis of these cell populations. In humans, primates, and mice, this phenotype and memory or adaptive functions have been strongly linked to cytomegalovirus or related herpes virus infections. We have used transplantation of lentivirally-barcoded autologous hematopoietic stem and progenitor cells (HSPC) to track clonal hematopoiesis in rhesus macaques and previously reported striking oligoclonal expansions of NK-biased barcoded clones within the CD56⁻CD16⁺ NK cell subpopulation, clonally distinct from ongoing output of myeloid, B cell, T cell, and CD56⁺16⁻ NK cells from HSPC. These CD56⁻CD16⁺ NK cell clones segregate by expression of specific KIR surface receptors, suggesting clonal expansion in reaction to specific environmental stimuli. We have now used this model to investigate the impact of rhesus CMV(RhCMV) infection on NK clonal dynamics. Following transplantation, RhCMV^neg rhesus macaques display less dominant and oligoclonal CD16⁺ NK cells biased clones compared to RhCMV^pos animals, however these populations of cells are still clearly present. Upon RhCMV infection, CD16⁺ NK cells proliferate, followed by appearance of new groups of expanded NK clones and disappearance of clones present prior to RhCMV infection. A second superinfection with RhCMV resulted in rapid viral clearance without major change in the mature NK cell clonal landscape. Our findings suggest that RhCMV is not the sole driver of clonal expansion and peripheral maintenance of mature NK cells; however, infection of macaques with this herpesvirus does result in selective expansion and persistence of specific NK cell clones, providing further information relevant to adaptive NK cells and the development of NK cell therapies.

Natural history of postnatal rhesus cytomegalovirus shedding by dams and acquisition by infant rhesus monkeys

BACKGROUND

Human infants frequently acquire human cytomegalovirus (HCMV) through breastfeeding, resulting in persistent high-level viral shedding in saliva and urine and infectivity to others, including pregnant women. Thus, vaccination to interrupt postnatal HCMV transmission is an attractive strategy to prevent HCMV spread and congenital infection. Rhesus CMV (RhCMV) in nonhuman primates is a valuable model for the study of immune strategies to prevent CMV transmission. Although rhesus monkeys typically acquire RhCMV before 1 year of age, the timing and mode of natural infant RhCMV transmission remain unknown.

METHODS

We followed 5 RhCMV-seropositive dams and their infants from birth until weaning, approximately 6 months later. RhCMV DNA levels in plasma, breast milk, saliva, and urine were measured every 2 weeks by quantitative PCR. RhCMV-specific T cell responses in peripheral blood and breast milk were measured by interferon gamma ELISpot assays. Serum IgG antibody levels were measured by ELISA.

RESULTS

Four of five postpartum RhCMV-seropositive mothers had intermittent, low-level RhCMV shedding in breast milk, whereas all had high-magnitude RhCMV shedding in saliva and urine. The kinetics of maternal blood RhCMV-specific T cell responses and viral shedding in urine and saliva did not strongly associate, though dams with consistently high systemic RhCMV-specific T cell responses tended to have undetectable RhCMV shedding in breast milk. All RhCMV-exposed infants had intermittent, low-level RhCMV shedding in saliva during the lactation period, with minimal systemic RhCMV-specific T cell responses.

CONCLUSIONS

Despite exposure to RhCMV shedding in breast milk and other maternal fluids, postnatal mother-to-child RhCMV transmission appears to be less efficient than that of HCMV. A greater understanding of the determinants of RhCMV transmission and its usefulness as a model of HCMV mucosal acquisition may provide insight into strategies to prevent HCMV infections in humans.

Absence of interaction between porcine endogenous retrovirus and porcine cytomegalovirus in pig-to-baboon renal xenotransplantation in vivo

BACKGROUND

Studies of xenotransplantation from swine have identified porcine viruses as potential barriers to clinical trials. The biology of these viruses has not been extensively investigated in the in vivo xeno-environment. Enhancement of viral gene expression by viral and cellular factors acting in trans has been demonstrated for certain viruses, including bidirectional interactions between human herpesviruses and endogenous (HERV) and exogenous (HIV) retroviruses. Both porcine cytomegalovirus (PCMV) and porcine endogenous retrovirus (PERV) infections have been identified in xenografts from swine. PERV receptors exist on human cells with productive infection in vitro in permissive human target cell lines. PCMV is largely species-specific with infection restricted to the xenograft in pig-to-baboon transplants. It is unknown whether coinfection by PCMV affects the replication of PERV within xenograft tissues which might have implications for the risk of retroviral infection in the human host.

METHODS

A series of 11 functioning, life-supporting pig-to-baboon kidney xenografts from PERV-positive miniature swine were studied with and without PCMV co-infection. Frozen biopsy samples were analyzed using quantitative, real-time PCR with internal controls.

RESULTS

PERV replication was not altered in the presence of PCMV coinfection (P = .70). The absence of variation with coinfection was confirmed when PERV quantitation was expressed relative to simultaneous cellular GAPDH levels with or without PCMV coinfection (P = .59).

CONCLUSIONS

PCMV coinfection does not alter the replication of PERV in life-supporting renal xenotransplantation in vivo in baboons.

Rhesus monkeys for a nonhuman primate model of cytomegalovirus infections

Human cytomegalovirus (HCMV) is the leading opportunistic viral infection in solid organ transplant patients and is the most common congenitally transmitted pathogen worldwide. Despite the significant burden of disease HCMV causes in immunosuppressed patients and infected newborns, there are no licensed preventative vaccines or effective immunotherapeutic treatments for HCMV, largely due to our incomplete understanding of the immune correlates of protection against HCMV infection and disease. Though CMV species-specificity imposes an additional challenge in defining a suitable animal model for HCMV, nonhuman primate (NHP) CMVs are the most genetically related to HCMV. In this review, we discuss the advantages and applicability of rhesus monkey models for studying HCMV infections and pathogenesis and ultimately informing vaccine development.

Preexisting antibodies can protect against congenital cytomegalovirus infection in monkeys

Human cytomegalovirus (HCMV) is the most common congenital infection and a known cause of microcephaly, sensorineural hearing loss, and cognitive impairment among newborns worldwide. Natural maternal HCMV immunity reduces the incidence of congenital infection, but does not prevent the disease altogether. We employed a nonhuman primate model of congenital CMV infection to investigate the ability of preexisting antibodies to protect against placental CMV transmission in the setting of primary maternal infection and subsequent viremia, which is required for placental virus exposure. Pregnant, CD4+ T cell-depleted, rhesus CMV-seronegative (RhCMV-seronegative) rhesus monkeys were treated with either standardly produced hyperimmune globulin (HIG) from RhCMV-seropositive macaques or dose-optimized, potently RhCMV-neutralizing HIG prior to intravenous challenge with an RhCMV mixture. HIG passive infusion provided complete protection against fetal loss in both groups. The dose-optimized, RhCMV-neutralizing HIG additionally inhibited placental transmission of RhCMV and reduced viral replication and diversity. Our findings suggest that the presence of durable and potently neutralizing antibodies at the time of primary infection can prevent transmission of systemically replicating maternal RhCMV to the developing fetus, and therefore should be a primary target of vaccines to eliminate this neonatal infection.

Cytomegaloviral hypophysitis in a simian immunodeficiency virus-infected rhesus macaque (Macacca mulatta)

Rhesus macaques experimentally infected with Simian Immunodeficiency Virus (SIV) experience immunosuppression and often opportunistic infection. Among the most common opportunistic infections are rhesus cytomegalovirus (RhCMV), a ubiquitous betaherpesvirus that undergoes continuous low-level replication in immunocompetent monkeys. Upon SIV-mediated immunodeficiency, RhCMV reactivates and results in lesions in numerous organ systems including the nervous and reproductive systems. We report the first case of cytomegaloviral hypophysitis in a SIV-immunocompromised rhesus macaque.

The Knife's Edge of Tolerance: Inducing Stable Multilineage Mixed Chimerism but With a Significant Risk of CMV Reactivation and Disease in Rhesus Macaques

Although stable mixed-hematopoietic chimerism induces robust immune tolerance to solid organ allografts in mice, the translation of this strategy to large animal models and to patients has been challenging. We have previously shown that in MHC-matched nonhuman primates (NHPs), a busulfan plus combined belatacept and anti-CD154-based regimen could induce long-lived myeloid chimerism, but without T cell chimerism. In that setting, donor chimerism was eventually rejected, and tolerance to skin allografts was not achieved. Here, we describe an adaptation of this strategy, with the addition of low-dose total body irradiation to our conditioning regimen. This strategy has successfully induced multilineage hematopoietic chimerism in MHC-matched transplants that was stable for as long as 24 months posttransplant, the entire length of analysis. High-level T cell chimerism was achieved and associated with significant donor-specific prolongation of skin graft acceptance. However, we also observed significant infectious toxicities, prominently including cytomegalovirus (CMV) reactivation and end-organ disease in the setting of functional defects in anti-CMV T cell immunity. These results underscore the significant benefits that multilineage chimerism-induction approaches may represent to transplant patients as well as the inherent risks, and they emphasize the precision with which a clinically successful regimen will need to be formulated and then validated in NHP models.

Maternal CD4+ T cells protect against severe congenital cytomegalovirus disease in a novel nonhuman primate model of placental cytomegalovirus transmission

Elucidation of maternal immune correlates of protection against congenital cytomegalovirus (CMV) is necessary to inform future vaccine design. Here, we present a novel rhesus macaque model of placental rhesus CMV (rhCMV) transmission and use it to dissect determinants of protection against congenital transmission following primary maternal rhCMV infection. In this model, asymptomatic intrauterine infection was observed following i.v. rhCMV inoculation during the early second trimester in two of three rhCMV-seronegative pregnant females. In contrast, fetal loss or infant CMV-associated sequelae occurred in four rhCMV-seronegative pregnant macaques that were CD4(+) T-cell depleted at the time of inoculation. Animals that received the CD4(+) T-cell-depleting antibody also exhibited higher plasma and amniotic fluid viral loads, dampened virus-specific CD8(+) T-cell responses, and delayed production of autologous neutralizing antibodies compared with immunocompetent monkeys. Thus, maternal CD4(+) T-cell immunity during primary rhCMV infection is important for controlling maternal viremia and inducing protective immune responses that prevent severe CMV-associated fetal disease.

The Cellular Localization of Human Cytomegalovirus Glycoprotein Expression Greatly Influences the Frequency and Functional Phenotype of Specific CD4+ T Cell Responses

CMV infection is a significant cause of morbidity and mortality in immunocompromised individuals, and the development of a vaccine is of high priority. Glycoprotein B (gB) is a leading vaccine candidate but the glycoprotein H (gH) pentameric complex is now recognized as the major target for neutralizing Abs. However, little is known about the T cell immune response against gH and glycoprotein L (gL) and this is likely to be an important attribute for vaccine immunogenicity. In this study, we examine and contrast the magnitude and phenotype of the T cell immune response against gB, gH, and gL within healthy donors. gB-specific CD4(+) T cells were found in 95% of donors, and 29 epitopes were defined with gB-specific response sizes ranging from 0.02 to 2.88% of the CD4(+) T cell pool. In contrast, only 20% of donors exhibited a T cell response against gH or gL. Additionally, gB-specific CD4(+) T cells exhibited a more cytotoxic phenotype, with high levels of granzyme B expression. Glycoproteins were effectively presented following delivery to APCs but only gB-derived epitopes were presented following endogenous synthesis. gB expression was observed exclusively within vesicular structures colocalizing with HLA-DM whereas gH was distributed evenly throughout the cytoplasm. Grafting of the C-terminal domain from gB onto gH could not transfer this pattern of presentation. These results reveal that gB is a uniquely immunogenic CMV glycoprotein and this is likely to reflect its unique pattern of endogenous Ag presentation. Consideration may be required toward mechanisms that boost cellular immunity to gH and gL within future subunit vaccines.

Limited dissemination and shedding of the UL128 complex-intact, UL/b'-defective rhesus cytomegalovirus strain 180.92

The UL128 complex of human cytomegalovirus (CMV) is a major determinant of viral entry into epithelial and endothelial cells and a target for vaccine development. The UL/b' region of rhesus CMV contains several open reading frames, including orthologs of the UL128 complex. We recently showed that the coding content of the rhesus CMV (RhCMV) UL/b' region predicts acute endothelial tropism and long-term shedding in vivo in the rhesus macaque model of CMV infection. The laboratory-passaged RhCMV 180.92 strain has a truncated UL/b' region but an intact UL128 complex. To investigate whether the presence of the UL128 complex alone was sufficient to confer endothelial and epithelial tropism in vivo, we investigated tissue dissemination and viral excretion following experimental RhCMV 180.92 inoculation of RhCMV-seronegative rhesus macaques. We show the presence of at least two virus variants in the RhCMV 180.92 infectious virus stock. A rare variant noted for a nontruncated wild-type-virus-like UL/b' region, rapidly emerged during in vivo replication and showed high-level replication in blood and tissues and excretion in urine and saliva, features similar to those previously reported in naturally occurring wild-type RhCMV infection. In contrast, the predominant truncated version of RhCMV 180.92 showed significantly lower plasma DNAemia and limited tissue dissemination and viral shedding. These data demonstrate that the truncated RhCMV 180.92 variant is attenuated in vivo and suggest that additional UL/b' genes, besides the UL128 complex, are required for optimal in vivo CMV replication and dissemination.

IMPORTANCE

An effective vaccine against human CMV infection will need to target genes that are essential for virus propagation and transmission. The human CMV UL128 complex represents one such candidate antigen since it is essential for endothelial and epithelial cell tropism, and is a target for neutralizing antibodies in CMV-infected individuals. In this study, we used the rhesus macaque animal model of CMV infection to investigate the in vivo function of the UL128 complex. Using experimental infection of rhesus macaques with a rhesus CMV virus variant that contained an intact UL128 complex but was missing several other genes, we show that the presence of the UL128 complex alone is not sufficient for widespread tissue dissemination and virus excretion. These data highlight the importance of in vivo studies in evaluating human CMV gene function and suggest that additional UL/b' genes are required for optimal CMV dissemination and transmission.

Postnatal acquisition of primary rhesus cytomegalovirus infection is associated with prolonged virus shedding and impaired CD4+ T lymphocyte function

BACKGROUND

Although virus-specific CD4(+) T lymphocytes emerge rapidly during primary cytomegalovirus (CMV) infection in humans, they exhibit a state of prolonged functional exhaustion of unknown etiology. To investigate the suitability of rhesus macaques as a model of primary human CMV infection, we examined the virologic and immunologic features of naturally acquired primary CMV infection in rhesus macaques.

METHODS

CMV-specific CD4(+) T lymphocytes and CMV load in blood, saliva, and urine were evaluated in a cohort of simian immunodeficiency virus (SIV)-negative rhesus macaques stratified by age into infant, juvenile, and adult groups.

RESULTS

CMV infection was detected in juvenile and adult monkeys but not in infant monkeys. CMV loads and shedding frequency in urine and saliva were significantly higher in the 2-3-year old juvenile monkeys, compared with the adult monkeys. The increased CMV load in juvenile monkeys was associated with lower polyfunctionality, impaired proliferation, and increased expression of the inhibitory receptor PD-1 in CMV-specific CD4(+) T lymphocytes. The proliferative defect was partially reversible by exogenous PD-1 blockade or addition of interleukin 2.

CONCLUSIONS

Postnatal acquisition of primary CMV infection in rhesus macaques results in prolonged virus excretion and impaired CMV-specific CD4(+) T-lymphocyte function, findings that recapitulate key features of primary CMV infection in humans.

What we have learned from animal models of HCMV

Although human cytomegalovirus (HCMV) primary infection is generally asymptomatic, in immune-compromised patients HCMV increases morbidity and mortality. As a member of the betaherpesvirus family, in vivo studies of HCMV are limited due to its species specificity. CMVs from other species are often used as surrogates to express HCMV genes/proteins or used as models for inferring HCMV protein function in humans. Using innovative experiments, these animal models have answered important questions about CMV's life cycle, dissemination, pathogenesis, immune evasion, and host immune response. This chapter provides CMV biologists with an overview of the insights gained using these animal models. Subsequent chapters will provide details of the specifics of the experimental methods developed for each of the animal models discussed here.

Recent approaches and strategies in the generation of antihuman cytomegalovirus vaccines

The development of prophylactic and to lesser extent therapeutic vaccines for the prevention of disease associated with human cytomegalovirus (HCMV) infections has received considerable attention from biomedical researchers and pharmaceutical companies over the previous 15 years, even though attempts to produce such vaccines have been described in the literature for over 40 years. Studies of the natural history of congenital HCMV infection and infection in allograft recipients have suggested that prophylaxis of disease associated with HCMV infection could be possible, particularly in hosts at risk for more severe disease secondary to the lack of preexisting immunity. Provided a substantial understanding of immune response to HCMV together with several animal models that faithfully recapitulate aspects of human infection and immunity, investigators seem well positioned to design and test candidate vaccines. Yet more recent studies of the role of a maternal immunity in the natural history of congenital HCMV infection, including the recognition that reinfection of previously immune women by genetically distinct strains of HCMV occur in populations with a high seroprevalence, have raised several questions about the nature of protective immunity in maternal populations. This finding coupled with observations that have documented a significant incidence of damaging congenital infections in offspring of women with immunity to HCMV prior to conception has suggested that vaccine development based on conventional paradigms of adaptive immunity to viral infections may be of limited value in the prevention of damaging congenital HCMV infections. Perhaps a more achievable goal will be prophylactic vaccines to modify HCMV associated disease in allograft transplant recipients. Although recent descriptions of the results from vaccine trials have been heralded as evidence of an emerging success in the quest for a HCMV vaccine, careful analyses of these studies have also revealed that major hurdles remain to be addressed by current strategies.

Measuring T-cell responses against LCV and CMV in cynomolgus macaques using ELISPOT: potential application to non-clinical testing of immunomodulatory therapeutics

A number of immunomodulatory therapeutics increase the risk of disease associated with latent herpesviruses such as cytomegalovirus (CMV) and Epstein-Barr virus (EBV), a member of the lymphocryptovirus (LCV) family that infects humans. The diseases associated with loss of immunity to these viruses can have major impacts on patients as well as on the commercial viability of the immunomodulatory therapeutics. In an effort to develop non-clinical methods for measuring effects on anti-viral immunity, we have developed an interferon (IFN)-γ enzyme-linked immunosorbent spot (ELISPOT) assay to quantify the number of CMV or LCV-reactive T-cells in peripheral blood of cynomolgus macaques. After optimization of various parameters, the IFN-γ ELISPOT assay was characterized for specificity, intra-assay, monkey-to-monkey, and longitudinal variability and sensitivity to immunosuppression. The results show that nearly all animals have detectable responses against both CMV and LCV and responses were derived from T-cells specific to the virus of interest. Analyses of variability show assay reproducibility (≤23% CV), and that variability over time in anti-viral responses in individual animals (larger for LCV than for CMV) was ∼2-fold in most animals over a 3-month time period, which is predicted to allow for detection of drug-induced changes when using group sizes typical of non-clinical studies. In addition, the IFN-γ ELISPOT assay was capable of detecting decreases in the numbers of CMV and LCV reactive T-cells induced by immunosuppressive drugs in vitro. This assay may allow for non-clinical assessment of the effects of immunomodulatory therapeutics on anti-viral T-cell immunity in monkeys, and may help determine if therapeutics increase the risk of reactivating latent viral infections.

Evaluation of high-throughput sequencing for identifying known and unknown viruses in biological samples

High-throughput sequencing furnishes a large number of short sequence reads from uncloned DNA and has rapidly become a major tool for identifying viruses in biological samples, and in particular when the target sequence is undefined. In this study, we assessed the analytical sensitivity of a pipeline for detection of viruses in biological samples based on either the Roche-454 genome sequencer or Illumina genome analyzer platforms. We sequenced biological samples artificially spiked with a wide range of viruses with genomes composed of single or double-stranded DNA or RNA, including linear or circular single-stranded DNA. Viruses were added at a very low concentration most often corresponding to 3 or 0.8 times the validated level of detection of quantitative reverse transcriptase PCRs (RT-PCRs). For the viruses represented, or resembling those represented, in public nucleotide sequence databases, we show that the higher output of Illumina is associated with a much greater sensitivity, approaching that of optimized quantitative (RT-)PCRs. In this blind study, identification of viruses was achieved without incorrect identification. Nevertheless, at these low concentrations, the number of reads generated by the Illumina platform was too small to facilitate assembly of contigs without the use of a reference sequence, thus precluding detection of unknown viruses. When the virus load was sufficiently high, de novo assembly permitted the generation of long contigs corresponding to nearly full-length genomes and thus should facilitate the identification of novel viruses.

Early induction of polyfunctional simian immunodeficiency virus (SIV)-specific T lymphocytes and rapid disappearance of SIV from lymph nodes of sooty mangabeys during primary infection

Although the cellular immune response is essential for controlling SIV replication in Asian macaques, its role in maintaining nonpathogenic SIV infection in natural hosts such as sooty mangabeys (SM) remains to be defined. We have previously shown that similar to rhesus macaques (RM), SM are able to mount a T lymphocyte response against SIV infection. To investigate early control of SIV replication in natural hosts, we performed a detailed characterization of SIV-specific cellular immunity and viral control in the first 6 mo following SIV infection in SM. Detection of the initial SIV-specific IFN-γ ELISPOT response in SIVsmE041-infected SM coincided temporally with a decline in peak plasma viremia and was similar in magnitude, specificity, and breadth to SIVsmE041-infected and SIVmac239-infected RM. Despite these similarities, SM showed a greater reduction in postpeak plasma viremia and a more rapid disappearance of productively SIV-infected cells from the lymph node compared with SIVmac239-infected RM. The early Gag-specific CD8(+) T lymphocyte response was significantly more polyfunctional in SM compared with RM, and granzyme B-positive CD8(+) T lymphocytes were present at significantly higher frequencies in SM even prior to SIV infection. These findings suggest that the early SIV-specific T cell response may be an important determinant of lymphoid tissue viral clearance and absence of lymph node immunopathology in natural hosts of SIV infection.

Choice of Immunosuppression Influences Cytomegalovirus DNAemia in Cynomolgus Monkey (Macaca fascicularis) Islet Allograft Recipients

This retrospective study reviews the results of our experience with the occurrence of CMV DNAemia in islet cell transplanted cynomolgus monkeys subjected to different immunosuppressive protocols, including induction treatment with thymoglobulin (TMG), with a combination of thymoglobulin and fludarabine (FLUD), with cyclophosphamide, or with daclizumab. CMV DNA in the peripheral blood (CMV DNAemia) of 47 monkeys was quantified by real-time PCR on a weekly to biweekly basis. As compared to other immunosuppressive regimens, and in association with greater decreases in WBC, lymphocyte, CD3+CD4+, and CD3+CD8+ lymphocyte counts, frequent CMV DNAemia occurred earlier (within the first month posttransplant), and was of greater severity and duration in recipients of TMG ± FLUD. Treatment of recipients with alternative induction agents that resulted in less dramatic reductions in WBC and lymphocyte counts, however, resulted in occurrence of CMV DNAemia after postoperative day 60. The frequency, average intensity, duration, and area under the curve (AUC) for CMV DNAemia in animals receiving TMG ± FLUD were 75–100%, 4.02 ± 1.75 copies/ng DNA, 23.0 ± 5.3 days, and 367.0 ± 121.1 days x copies/ng DNA, respectively; corresponding values in animals receiving other treatments (0–44%, 0.19 ± 0.10 copies/ng DNA, 0.5 ± 0.3 days, and 75.4 ± 40.2 days x copies/ng DNA, respectively) were significantly different. The value of WBC, T and B cells at the nadir of cell depletion greatly affects the occurrence of CMV DNAemia. No animals developed CMV DNAemia within the next 3 weeks when the lowest value of WBC, lymphocyte, CD3+, CD3+CD4+, CD3+CD8+, or CD20+ cells was above 4500, 1800, 300, 200, 150, or 300 cells/μl, respectively. Oral valganciclovir prophylaxis did not completely prevent the appearance of CMV DNAemia.

Inhibition of adaptive immune responses leads to a fatal clinical outcome in SIV-infected pigtailed macaques but not vervet African green monkeys

African green monkeys (AGM) and other natural hosts for simian immunodeficiency virus (SIV) do not develop an AIDS-like disease following SIV infection. To evaluate differences in the role of SIV-specific adaptive immune responses between natural and nonnatural hosts, we used SIV_agmVer90 to infect vervet AGM and pigtailed macaques (PTM). This infection results in robust viral replication in both vervet AGM and pigtailed macaques (PTM) but only induces AIDS in the latter species. We delayed the development of adaptive immune responses through combined administration of anti-CD8 and anti-CD20 lymphocyte-depleting antibodies during primary infection of PTM (n = 4) and AGM (n = 4), and compared these animals to historical controls infected with the same virus. Lymphocyte depletion resulted in a 1-log increase in primary viremia and a 4-log increase in post-acute viremia in PTM. Three of the four PTM had to be euthanized within 6 weeks of inoculation due to massive CMV reactivation and disease. In contrast, all four lymphocyte-depleted AGM remained healthy. The lymphocyte-depleted AGM showed only a trend toward a prolongation in peak viremia but the groups were indistinguishable during chronic infection. These data show that adaptive immune responses are critical for controlling disease progression in pathogenic SIV infection in PTM. However, the maintenance of a disease-free course of SIV infection in AGM likely depends on a number of mechanisms including non-adaptive immune mechanisms.

Simian immunodeficiency virus (SIV) is a naturally occurring infection in a wide range of African nonhuman primates, including African green monkeys (AGM), which generally results in a clinically inapparent infection. In contrast, SIV infection of Asian nonhuman primates such as macaques can result in an AIDS-like disease similar to that observed in humans infected with human immunodeficiency virus (HIV). This different pathogenic outcome occurs despite similar levels of viremia. In order to evaluate the contribution of adaptive immune responses to these different outcomes, we transiently inhibited the generation of CD8+ and CD20+ lymphocyte-mediated immune responses in vervet AGM and pigtailed macaques (PTM) during primary SIV infection. PTM experienced higher viremia and accelerated progression to disease, whereas AGM showed only a short prolongation of peak viremia but exhibited no signs of illness. These results demonstrate that protection against development of disease in AGM does not solely rely on adaptive immune responses. Future efforts should aim to determine the underlying mechanisms that enable natural hosts to cope with SIV infection and to apply these findings to develop new treatment modalities for humans infected with HIV.

Rhesus cytomegalovirus a nonhuman primate model for the study of human cytomegalovirus

Human cytomegalovirus (HCMV), a member of an ancient family of viruses (Herpesviridae), has acquired the capacity to maintain a lifelong persistent infection within an immunocompetent host. Since both primary and recurrent infections are generally subclinical, host antiviral immune responses are effective at limiting the pathogenic potential of HCMV. However, the fact that HCMV can persist in the presence of those protective immune responses indicates that host immunity is unable to prevent or eliminate long-term reservoirs of virus. The ability of HCMV to persist has important clinical implications, a fact reflected by the spectrum of pathogenic outcomes observed in those without a fully functional immune system. Recurrence of viral replication or transmission of HCMV from an infected individual to those most susceptible to primary infection during immune suppression, deficiency, or immaturity can lead to multiorgan disease and, sometimes, death. The clinical need for a protective HCMV vaccine has been recognized for decades, but due to a conspiracy of factors, there is no approved vaccine despite intensive investigations to develop one. Animal models of HCMV have been used as systems of discovery and translation to understand viral mechanisms of persistence and pathogenesis, and to test concepts and modalities for the generation of immune responses that protect from primary infection and sequelae. This review summarizes studies in a nonhuman primate model of HCMV involving infection of rhesus macaques (Macaca mulatta) with rhesus cytomegalovirus (RhCMV). The RhCMV model serves as an important complement to those in other animals, particularly small animals, and the lessons learned from RhCMV should have direct clinical relevance to HCMV and the design of protective vaccines.

Manifestations of human cytomegalovirus infection: proposed mechanisms of acute and chronic disease

Infections with human cytomegalovirus (HCMV) are a major cause of morbidity and mortality in humans with acquired or developmental deficits in innate and adaptive immunity. In the normal immunocompetent host, symptoms rarely accompany acute infections, although prolonged virus shedding is frequent. Virus persistence is established in all infected individuals and appears to be maintained by both a chronic productive infections as well as latency with restricted viral gene expression. The contributions of the each of these mechanisms to the persistence of this virus in the individual is unknown but frequent virus shedding into the saliva and genitourinary tract likely accounts for the near universal incidence of infection in most populations in the world. The pathogenesis of disease associated with acute HCMV infection is most readily attributable to lytic virus replication and end organ damage either secondary to virus replication and cell death or from host immunological responses that target virus-infected cells. Antiviral agents limit the severity of disease associated with acute HCMV infections, suggesting a requirement for virus replication in clinical syndromes associated with acute infection. End organ disease secondary to unchecked virus replication can be observed in infants infected in utero, allograft recipients receiving potent immunosuppressive agents, and patients with HIV infections that exhibit a loss of adaptive immune function. In contrast, diseases associated with chronic or persistent infections appear in normal individuals and in the allografts of the transplant recipient. The manifestations of these infections appear related to chronic inflammation, but it is unclear if poorly controlled virus replication is necessary for the different phenotypic expressions of disease that are reported in these patients. Although the relationship between HCMV infection and chronic allograft rejection is well known, the mechanisms that account for the role of this virus in graft loss are not well understood. However, the capacity of this virus to persist in the midst of intense inflammation suggests that its persistence could serve as a trigger for the induction of host-vs-graft responses or alternatively host responses to HCMV could contribute to the inflammatory milieu characteristic of chronic allograft rejection.

Rhesus CMV: an emerging animal model for human CMV

Human CMV is the predominant infectious cause of congenital birth defects and an opportunistic pathogen in immunosuppressed individuals, including AIDS patients. Most individuals are infected early during their life followed by life-long latent infection. During this latent phase, frequent reactivation and antigen production continue to stimulate the immune system. While the immune response is able to control the virus, it is unable to eradicate it. Moreover, super-infection by different CMV strains has been observed despite a strong immune response. Long-term immune stimulation by CMV has also been implicated in immune senescence and chronic conditions such as atherosclerosis. CMVs are highly species-specific and the relatedness of CMV genomes exactly mirrors the relatedness of their hosts. Thus, each CMV species is highly adapted to its respective host species, but is unable to infect other, even closely related hosts. While fascinating from an evolutionary perspective, this host restriction prevents studying HCMV in experimental animals. Exceptions are severely immunocompromised mice, e.g. SCID mice, or SCID/NOD mice, which might allow partial reconstitution of CMV infection in rodents. More practical however, is to study CMVs in their natural host, e.g. murine, rat or guinea pig CMVs. However, while these small animal models have many advantages, such as the availability of inbred animals as well as lower cost, the limited homology of the viral genomes with HCMV limits the functional analysis of homologous gene products. The closest relative to HCMV is chimpanzee CMV (CCMV), but this is not a practical animal model since chimps are a protected species, extremely expensive and of very limited availability. In contrast, rhesus macaques are a more widely used experimental animal species and, while more distant than CCMV, rhesus CMV (RhCMV) contains most of the HCMV gene families thus allowing the study of their role in acute and latent CMV infection. In this review we will discuss the current state of developing RhCMV as a model for HCMV.

Pharmacokinetics, toxicity, and functional studies of the selective Kv1.3 channel blocker 5-(4-phenoxybutoxy)psoralen in rhesus macaques

The small molecule 5-(4-phenoxybutoxy)psoralen (PAP-1) is a selective blocker of the voltage-gated potassium channel Kv1.3 that is highly expressed in cell membranes of activated effector memory T cells (TEMs). The blockade of Kv1.3 results in membrane depolarization and inhibition of TEM proliferation and function. In this study, the in vitro effects of PAP-1 on T cells and the in vivo toxicity and pharmacokinetics (PK) were examined in rhesus macaques (RM) with the ultimate aim of utilizing PAP-1 to define the role of TEMs in RM infected with simian immunodeficiency virus (SIV). Electrophysiologic studies on T cells in RM revealed a Kv1.3 expression pattern similar to that in human T cells. Thus, PAP-1 effectively suppressed TEM proliferation in RM. When administered intravenously, PAP-1 showed a half-life of 6.4 hrs; the volume of distribution suggested extensive distribution into extravascular compartments. When orally administered, PAP-1 was efficiently absorbed. Plasma concentrations in RM undergoing a 30-day, chronic dosing study indicated that PAP-1 levels suppressive to TEMs in vitro can be achieved and maintained in vivo at a non-toxic dose. PAP-1 selectively inhibited the TEM function in vivo, as indicated by a modest reactivation of cytomegalovirus (CMV) replication. Immunization of these chronically treated RM with the live influenza A/PR8 (flu) virus suggested that the development of an in vivo, flu-specific, central memory response was unaffected by PAP-1. These RM remained disease-free during the entire course of the PAP-1 study. Collectively, these data provide a rational basis for future studies with PAP-1 in SIV-infected RM.

Flow cytometric detection of degranulation reveals phenotypic heterogeneity of degranulating CMV-specific CD8+ T lymphocytes in rhesus macaques

Flow-cytometric conditions for detection of lysosomal-associated membrane proteins (LAMPs) on the surface of recently degranulated cells were optimized for rhesus macaques and used to investigate the functional properties of rhesus cytomegalovirus (rhCMV)-specific CD8+ T lymphocytes with regards to cytotoxicity and interferon (IFN)-gamma secretion in six asymptomatic CMV-seropositive rhesus macaques. Unlike humans, the rhesus macaque LAMP-1 protein CD107a underwent little or no endocytosis over a six to 18 h stimulation period. Following in vitro stimulation, rhCMV-specific CD8+ T lymphocytes were heterogeneous with regards to the composition of cells positive for CD107a and/or IFN-gamma, time to reach peak degranulation, and kinetics of IFN-gamma secretion relative to degranulation. Responder CD8+ T lymphocytes that underwent degranulation without IFN-gamma production (CD107a+IFN-gamma-) were predominantly composed of terminally differentiated effectors (CD28-CD45RA+). Moreover, they had significantly lower frequencies of effector memory (CD28-CD45RA-) cells compared to the IFN-gamma-secreting cells that did or did not undergo degranulation (CD107a+IFN-gamma+ or CD107a-IFN-gamma+). The perforin content of effector CD8+ T lymphocytes was significantly greater than that of effector memory CD8+ T lymphocytes in rhesus macaques, suggesting that they were more cytolytic. Our findings suggest that the composition of rhCMV-specific CD8+ T lymphocytes with regards to CD107a+IFN-gamma- responders may be an important determinant of their ability to control CMV replication.

Induction of a virus-specific effector-memory CD4+ T cell response by attenuated SIV infection

We investigated simian immunodeficiency virus (SIV)-specific CD4⁺ T cell responses in rhesus macaques chronically infected with attenuated or pathogenic SIV strains. Analysis of SIVΔnef-infected animals revealed a relatively high frequency of SIV-specific CD4⁺ T cells representing 4–10% of all CD4⁺ T lymphocytes directed against multiple SIV proteins. Gag-specific CD4⁺ T cells in wild-type SIV-infected animals were 5–10-fold lower in frequency and inversely correlated with the level of plasma viremia. SIV-specific CD4⁺ cells from SIVΔnef animals were predominantly CD27⁻CD28⁻CD45RA^lowCCR7⁻CCR5⁻, consistent with an effector–memory subset, and included a fully differentiated CD45RA⁺CCR7⁻ subpopulation. In contrast, SIV-specific CD4⁺ T cells from SIV-infected animals were mostly CD27⁺CD28⁺CD45RA⁻CCR7⁺CCR5⁺, consistent with an early central memory phenotype. The CD45RA⁺CCR7⁻CD4⁺ subset from SIVΔnef animals was highly enriched for effector CD4⁺ T cells, as indicated by the perforin expression and up-regulation of the lysosomal membrane protein CD107a after SIV Gag stimulation. SIV-specific CD4⁺ T cells in attenuated SIV-infected animals were increased in frequency in bronchioalveolar lavage and decreased in lymph nodes, consistent with an effector–memory T cell population. The ability of SIVΔnef to induce a high frequency virus-specific CD4⁺ T cell response with direct effector function may play a key role in protective immunity produced by vaccination with attenuated SIV strains.

Immunogenicity and protective efficacy of DNA vaccines expressing rhesus cytomegalovirus glycoprotein B, phosphoprotein 65-2, and viral interleukin-10 in rhesus macaques

Rhesus cytomegalovirus (RhCMV) infection of macaques exhibits strong similarities to human CMV (HCMV) persistence and pathogenesis. The immunogenicity of DNA vaccines encoding three RhCMV proteins (a truncated version of glycoprotein B lacking the transmembrane region and endodomain [gBDeltaTM], phosphoprotein 65-2 [pp65-2], and viral interleukin-10 [vIL-10]) was evaluated in rhesus macaques. Two groups of monkeys (four per group) were genetically immunized four times with a mixture of either pp65-2 and gBDeltaTM or pp65-2, vIL-10, and gBDeltaTM. The vaccinees developed anti-gB and anti-pp65-2 antibodies in addition to pp65-2 cellular responses after the second booster immunization, with rapid responses observed with subsequent DNA injections. Weak vIL-10 immune responses were detected in two of the four immunized animals. Neutralizing antibodies were detected in seven monkeys, although titers were weak compared to those observed in naturally infected animals. The immunized monkeys and naïve controls were challenged intravenously with 10(5) PFU of RhCMV. Anamnestic binding and neutralizing antibody responses were observed 1 week postchallenge in the vaccinees. DNA vaccination-induced immune responses significantly decreased peak viral loads in the immunized animals compared to those in the controls. No difference in peak viral loads was observed between the pp65-2/gBDeltaTM DNA- and pp65-2/vIL-10/gBDeltaTM-vaccinated groups. Antibody responses to nonvaccine antigens were lower postchallenge in both vaccine groups than in the controls, suggesting long-term control of RhCMV protein expression. These data demonstrated that DNA vaccines targeting the RhCMV homologues of HCMV gB and pp65 altered the course of acute and persistent RhCMV infection in a primate host.

Identification of a cytotoxic T-lymphocyte (CTL) epitope recognized by Gag-specific CTLs in cynomolgus monkeys infected with simian/human immunodeficiency virus

Infection of Macaca fascicularis (cynomolgus monkey) with chimeric simian/human immunodeficiency virus (SHIV) provides a valuable experimental animal model of AIDS and is widely used for the development of human immunodeficiency virus vaccine strategies. In these settings, analysis of CD8(+) T-cell responses during infection represents one of the key parameters for monitoring the evaluation of containment of virus replication. The generation of Gag-specific CD8(+) T cells was reported previously from a cynomolgus monkey infected with SHIV89.6P by taking advantage of a B-lymphoblastoid cell line transduced with a retroviral vector expressing simian immunodeficiency virus (SIV) Gag. Here, it was shown that these cytotoxic T lymphocytes (CTLs) demonstrated specificity for a single 9 aa peptide (NCVGDHQAA) spanning aa 192-200 of the SIVmac239 p55(gag) protein. Furthermore, a positive response was found against the same epitope in one of six other SHIV-infected monkeys. This newly identified SIV Gag CTL epitope in SHIV-infected cynomolgus monkeys will be a useful tool for monitoring and evaluating Gag-specific immune responses during vaccination and infection in the cynomolgus monkey model of AIDS.

Nonhuman primate models of intrauterine cytomegalovirus infection

Congenital human cytomegalovirus (HCMV) infection has long been recognized as a threat to the developing fetus, even though studies have shown that only a subset of congenital infections results in clinical signs of disease. Among the estimated 8000 children who develop sequelae from congenital CMV infection each year in the United States alone, most suffer permanent developmental defects within the central nervous system. Because there is currently no approved vaccine for HCMV, and anti-HCMV drugs are not administered to gravid women with congenital infection because of potential toxicity to the fetus, there is a clear clinical need for effective strategies that minimize infection in the mother, transplacental transmission of the virus, and/or fetal disease. Animal models provide a method to understand the mechanisms of HCMV persistence and pathogenesis, and allow for testing of novel strategies that limit prenatal infection and disease. The rhesus macaque model is especially well suited for these tasks because monkeys and humans share strong developmental, immunological, anatomical, and biochemical similarities due to their close phylogenetic relationship. This nonhuman primate model provides an invaluable system to accelerate the clinical development of promising new therapies for the treatment of human disease. This review addresses salient findings with the macaque model as they relate to HCMV infection and potential avenues of discovery, including studies of intrauterine CMV infection. The complexity of the natural history of HCMV is discussed, along with the ethical and logistical issues associated with studies during pregnancy, the recent contributions of animal research in this field of study, and future prospects for increasing our understanding of immunity against HCMV disease.

Ability of herpes simplex virus vectors to boost immune responses to DNA vectors and to protect against challenge by simian immunodeficiency virus

The immunogenicity and protective capacity of replication-defective herpes simplex virus (HSV) vector-based vaccines were examined in rhesus macaques. Three macaques were inoculated with recombinant HSV vectors expressing Gag, Env, and a Tat-Rev-Nef fusion protein of simian immunodeficiency virus (SIV). Three other macaques were primed with recombinant DNA vectors expressing Gag, Env, and a Pol-Tat-Nef-Vif fusion protein prior to boosting with the HSV vectors. Robust anti-Gag and anti-Env cellular responses were detected in all six macaques. Following intravenous challenge with wild-type, cloned SIV239, peak and 12-week plasma viremia levels were significantly lower in vaccinated compared to control macaques. Plasma SIV RNA in vaccinated macaques was inversely correlated with anti-Rev ELISPOT responses on the day of challenge (P value<0.05), anti-Tat ELISPOT responses at 2 weeks post challenge (P value <0.05) and peak neutralizing antibody titers pre-challenge (P value 0.06). These findings support continued study of recombinant herpesviruses as a vaccine approach for AIDS.

Foamy virus infection in primates

Foamy viruses (FV), the oldest known genus of Retroviridae, are unique among the retroviruses in having no disease association. It is not known why FV are non-pathogenic while infection by their closest relatives can be deadly. This may be related to the estimated 60 million years of coevolution of FV and their primate hosts. We review the current state of knowledge of FV infection, including information about the sites of viral replication and host immune responses, and discuss the role these may play in establishing persistent yet non-pathogenic infections. Whether FV has pathologic consequences in immunosuppressed hosts has not been thoroughly investigated. As most primates in HIV/SIV research are coinfected with FV, investigation into possible interactions between these viruses is of interest. The use of FV as a vector for gene therapy is also discussed.

Expression of CD8alpha identifies a distinct subset of effector memory CD4+ T lymphocytes

Circulating CD4+ CD8+ T lymphocytes have been described in the peripheral blood of humans and several animal species. However, the origin and functional properties of these cells remain poorly understood. In the present study, we evaluated the frequency, phenotype and function of peripheral CD4+ CD8+ T cells in rhesus macaques. Two distinct populations of CD4+ CD8+ T cells were identified: the dominant one was CD4hi CD8lo and expressed the CD8alphaalpha homodimer, while the minor population was CD4lo CD8hi and expressed the CD8alphabeta heterodimer. The majority of CD4hi CD8alphalo T cells exhibited an activated effector/memory phenotype (CCR5lo CD7- CD28- HLA-DR+) and expressed relatively high levels of granzyme B. Intracellular cytokine staining assays demonstrated that the frequency of cytomegalovirus-specific T cells was enriched five-fold in CD4hi CD8alphalo T cells compared to single-positive CD4+ T cells, whereas no consistent enrichment was observed for simian immunodeficiency virus (SIV)-specific T cells. Cross-sectional studies of SIV-infected animals demonstrated that the frequency of CD4hi CD8alphalo T cells was lower in wild-type SIV-infected animals compared to uninfected controls, although prospective studies of SIV-infected animals demonstrated depletion of CD4hi CD8alphalo lymphocytes only in a subset of animals. Taken together, these data suggest that CD4+ T cells expressing CD8alpha represent an effector/memory subset of CD4+ T cells and that this cell population can be depleted during the course of SIV infection.

Characterization and immunological analysis of the rhesus cytomegalovirus homologue (Rh112) of the human cytomegalovirus UL83 lower matrix phosphoprotein (pp65)

Rhesus cytomegalovirus (RhCMV) contains two open reading frames (Rh111 and Rh112) that encode proteins homologous to the phosphoprotein 65 (pp65) of the human cytomegalovirus (HCMV) UL83 gene. As HCMV pp65 elicits protective immune responses in infected humans and represents an important vaccination target, one RhCMV homologue of HCMV pp65, pp65-2 (Rh112), was characterized and analysed for its ability to induce host immune responses. Similar to its HCMV counterpart, RhCMV pp65-2 was expressed as a late gene, localized to the nucleus within pp65-2-expressing cells and was present within infectious virions. Longitudinal and cross-sectional studies of pp65-2 immunity in naturally infected rhesus macaques showed that humoral responses to pp65-2 were elicited early during infection, but were not always sustained over time. In contrast, pp65-2-specific T-cell responses, examined by gamma interferon ELISPOT, were broadly detectable in all of the animals studied during primary infection and persisted in the vast majority of RhCMV-seropositive monkeys. Moreover, there was considerable inter-animal variability in the pattern of the immune responses to pp65-2. Together, these results demonstrated that RhCMV pp65-2 exhibited biological and immunological homology to HCMV pp65. Thus, the rhesus macaque model of HCMV persistence and pathogenesis should be relevant for addressing pp65-based vaccine modalities.

The BZLF1 homolog of an Epstein-Barr-related gamma-herpesvirus is a frequent target of the CTL response in persistently infected rhesus macaques

Although CD8(+) T lymphocytes targeting lytic infection proteins dominate the immune response to acute and persistent EBV infection, their role in immune control of EBV replication is not known. Rhesus lymphocryptovirus (rhLCV) is a gamma-herpesvirus closely related to EBV, which establishes persistent infection in rhesus macaques. In this study, we investigated cellular immune responses to the rhLCV BZLF1 (rhBZLF1) homolog in a cohort of rhLCV-seropositive rhesus macaques. rhBZLF1-specific IFN-gamma ELISPOT responses ranging between 56 and 3070 spot-forming cells/10(6) PBMC were detected in 36 of 57 (63%) rhesus macaques and were largely mediated by CD8(+) T lymphocytes. The prevalence and magnitude of ELISPOT responses were greater in adult (5-15 years of age) rather than juvenile macaques (<5 years of age), suggesting that rhBZLF1-specific CTL increase over time following early primary infection. A highly immunogenic region in the carboxyl terminus of the rhBZLF1 protein containing overlapping CTL epitopes restricted by Mamu-A*01 and other as yet unidentified MHC class I alleles was identified. The presence of a robust CD8(+) T lymphocyte response targeting this lytic infection protein in both rhesus macaques and humans suggests that these CTL may be important for immune control of EBV-related gamma-herpesvirus infection. These data underscore the utility of the rhLCV-macaque model for studies of EBV pathogenesis.

Genomic sequence of rhesus cytomegalovirus 180.92: insights into the coding potential of rhesus cytomegalovirus

A pathogenic isolate of rhesus cytomegalovirus (rhCMV 180.92) was cloned, sequenced, and annotated. Comparisons with the published rhCMV 68.1 genome revealed 8 open reading frames (ORFs) in isolate 180.92 that are absent in 68.1, 10 ORFs in 68.1 that are absent in 180.92, and 34 additional ORFs that were not previously annotated. Most of the differences appear to be due to genetic rearrangements in both isolates from a region that is frequently altered in human CMV (hCMV) during in vitro passage. These results indicate that the rhCMV ORF repertoire is larger than previously recognized. Like hCMV, understanding of the complete coding capacity of rhCMV is complicated by genomic instability and may require comparisons with additional isolates in vitro and in vivo.