GB virus C infection and B-cell, natural killer cell, and monocyte activation markers in HIV-infected individuals

Human Pegivirus Type 1: A Common Human Virus That Is Beneficial in Immune-Mediated Disease?

Two groups identified a novel human flavivirus in the mid-1990s. One group named the virus hepatitis G virus (HGV) and the other named it GB Virus type C (GBV-C). Sequence analyses found these two isolates to be the same virus, and subsequent studies found that the virus does not cause hepatitis despite sharing genome organization with hepatitis C virus. Although HGV/GBV-C infection is common and may cause persistent infection in humans, the virus does not appear to directly cause any other known disease state. Thus, the virus was renamed “human pegivirus 1” (HPgV-1) for “persistent G” virus. HPgV-1 is found primarily in lymphocytes and not hepatocytes, and several studies found HPgV-1 infection associated with prolonged survival in people living with HIV. Co-infection of human lymphocytes with HPgV-1 and HIV inhibits HIV replication. Although three viral proteins directly inhibit HIV replication in vitro, the major effects of HPgV-1 leading to reduced HIV-related mortality appear to result from a global reduction in immune activation. HPgV-1 specifically interferes with T cell receptor signaling (TCR) by reducing proximal activation of the lymphocyte specific Src kinase LCK. Although TCR signaling is reduced, T cell activation is not abolished and with sufficient stimulus, T cell functions are enabled. Consequently, HPgV-1 is not associated with immune suppression. The HPgV-1 immunomodulatory effects are associated with beneficial outcomes in other diseases including Ebola virus infection and possibly graft-versus-host-disease following stem cell transplantation. Better understanding of HPgV-1 immune escape and mechanisms of inflammation may identify novel therapies for immune-based diseases.

Tissue presentation of human pegivirus infection in liver transplanted recipients

Human pegivirus-1 (HPgV-1) is known for its protective role in HIV co-infected individuals. This immunomodulatory effect raised questions concerning the possible role of HPgV-1 infection and the risk of rejection in liver transplanted patients. We aimed to evaluate the possible protective effect of HPgV-1 on graft outcome of liver transplanted patients. A total of 283 patients were recruited. Formalin-fixed paraffin-embedded tissue samples were collected from the explanted liver. HBV-DNA, HCV-RNA, and HPgV-1-RNA were determined using PCR and multiplex RT-PCR assays. The clinical course of patients including the occurrence of acute cellular rejection was compared between HPgV-1-infected vs. uninfected patients. HBV-DNA, HCV-RNA and HPgV-1-RNA were detected in 42.6%, 4.9%, and 7.8% of samples, respectively. None of the HPgV-1-infected patients experienced graft rejection. Group LASSO logistic regression revealed that HPgV-1 infection was the only factor which significantly reduced the odds of graft rejection (OR = 0.5, 95% CI = 0.29-0.89). No significant association was found between the presence of HPgV-1 with HBV and HCV infections. The lack of graft rejection in HPgV-1-infected liver transplanted patients might indicate a possible role of this virus for graft surveillance. Since these are still preliminary findings, prospective studies should further elucidate the role of HPgV-1 in liver transplantation outcomes.

Human pegivirus-1 replication influences NK cell reconstitution after allogeneic haematopoietic stem cell transplantation

Introduction

Human pegivirus-1 (HPgV-1) is a so-called commensal virus for which no known associated organ disease has been found to date. Yet, it affects immune-reconstitution as previously studied in the HIV population, in whom active co-infection with HPgV-1 can modulate T and NK cell activation and differentiation leading to a protective effect against the evolution of the disease. Little is known on the effect of HPgV-1 on immune-reconstitution in allogeneic hematopoietic stem cell transplant (allo-HSCT) recipients, a patient population in which we and others have previously reported high prevalence of HPgV-1 replication. The aim of this study was to compare the immune reconstitution after allo-HSCT among HPgV-1-viremic and HPgV-1-non-viremic patients.

Methods

Within a cohort study of 40 allo-HSCT patients, 20 allo-HSCT recipients positive in plasma sample for HPgV-1 by rRT-PCR during the first year (1, 3, 6, 12 months) after transplantation were matched with 20 allo-HSCT recipients negative for HPgV-1. T and NK cell reconstitution was monitored by flow cytometry in peripheral blood samples from allo-HSCT recipients at the same time points.

Results

We observed no significant difference in the absolute number and subsets proportions of CD4 and CD8 T cells between patient groups at any analysed timepoint. We observed a significantly higher absolute number of NK cells at 3 months among HPgV-1-viremic patients. Immunophenotypic analysis showed a significantly higher proportion of CD56^bright NK cells mirrored by a reduced percentage of CD56^dim NK cells in HPgV-1-positive patients during the first 6 months after allo-HSCT. At 6 months post-allo-HSCT, NK cell phenotype significantly differed depending on HPgV-1, HPgV-1-viremic patients displaying NK cells with lower CD16 and CD57 expression compared with HPgV-1-negative patients. In accordance with their less differentiated phenotype, we detected a significantly reduced expression of granzyme B in NK cells in HPgV-1-viremic patients at 6 months.

Discussion

Our study shows that HPgV-1-viremic allo-HSCT recipients displayed an impaired NK cell, but not T cell, immune-reconstitution compared with HPgV-1-non-viremic patients, revealing for the first time a potential association between replication of the non-pathogenic HPgV-1 virus and immunomodulation after allo-HSCT.

Human pegivirus type 1 infection in kidney transplant recipients: Replication kinetics and clinical correlates

BACKGROUND

Increasing evidence suggests that infection with the nonpathogenic human pegivirus type 1 (HPgV-1) exerts a clinical benefit in human immunodeficiency virus (HIV) patients, which could be attributable to immunomodulatory effects. Whether this impact can be extrapolated to kidney transplantation (KT) remains largely unknown.

METHODS

We measured plasma HPgV-1 RNA by real-time polymerase chain reaction targeting the 5' untranslated region at various points (pretransplantation, day 7, months 1, 3, 6, and 12) in 199 KT recipients. Study outcomes included posttransplant serious infection, immunosuppression-related adverse event (opportunistic infection and/or de novo cancer), and acute graft rejection.

RESULTS

HPgV-1 infection was demonstrated in 52 (26.1%) patients, with rates increasing from 14.7% at baseline to 19.1% by month 12 (p-value = .071). De novo infection occurred in 13.8% of patients with no detectable HPgV-1 RNA before transplantation. Double-organ (liver-kidney or kidney-pancreas) transplantation (odds ratio [OR]: 5.62; 95% confidence interval [CI]: 1.52-20.82) and donation after brain death (OR: 2.21; 95% CI: 1.00-4.88) were associated with posttransplant HPgV-1 infection, whereas pretransplant hypertension was protective (OR: 0.23; 95% CI: 0.09-0.55). There were no significant differences in the incidence of study outcomes according to HPgV-1 status. Plasma HPgV-1 RNA levels at different points did not significantly differ between patients that subsequently developed outcomes and those remaining free from these events. No correlation between HPgV-1 RNA and immune parameters or torque teno virus DNA load was observed either.

CONCLUSION

Unlike patients living with HIV, HPgV-1 infection does not seem to influence patient or graft outcomes after KT.

Human pegivirus type 1 infection in Asia-A review of the literature

The human pegivirus type 1 (HPgV-1)-as known as hepatitis G virus and GB virus C-is a common single-stranded RNA flavivirus. Because few studies have demonstrated an association between HPgV-1 infection and disease, screening for HPgV-1 is not performed routinely. Nonetheless, a beneficial impact of HPgV-1 infection on HIV disease progression has been reported in multiple studies. Given the burden of HIV in Asia and the complex interactions between viral co-infections and the host, we provide a comprehensive overview of the existing data from Asia on HPgV-1 infection, including the prevalence and circulating genotypes in all Asian countries with data reported. This review highlights the research conducted thus far and emphasizes the need for additional studies on HPgV-1 across the Asian continent.

Human Pegivirus Infection and Lymphoma Risk: A Systematic Review and Meta-analysis

BACKGROUND

Human pegivirus (HPgV) is a single-strand RNA virus belonging to the Flaviviridae. Although no definitive association between HPgV infection and disease has been identified, previous studies have suggested an association of HPgV viremia with risk of lymphomas.

METHODS

We conducted a systematic review and meta-analysis, including 1 cohort study and 14 case-control studies, assessing the association of HPgV viremia with adult lymphomas. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated using a random-effects model, overall and by geographic region and lymphoma subtype.

RESULTS

The overall OR for lymphoma was 2.85 (95% CI, 1.98-4.11), with statistically significantly elevated ORs observed in 8 of 15 studies. There was a small amount of heterogeneity among studies (I2 = 28.9%; Q = 18.27, P = .16), and the funnel plot provided no evidence for publication bias. The strongest association with lymphoma risk was observed for studies from Southern Europe (OR, 5.68 [95% CI, 1.98-16.3]), whereas weaker ORs (with 95% CIs) were observed for studies from North America (2.24 [1.76-2.85]), Northern Europe (2.90 [.45-18.7), and the Middle East (2.51 [.87-7.27]), but all of similar magnitude. Participants with HPgV viremia had statistically significantly increased risks (OR [95% CI]) for developing diffuse large B-cell (3.29 [1.63-6.62]), follicular (3.01 [1.95-4.63]), marginal zone (1.90 [1.13-3.18]), and T-cell (2.11 [1.17-3.89]) lymphomas, while the risk for Hodgkin lymphoma (3.53 [.48-25.9]) and chronic lymphocytic leukemia (1.45 [.45-4.66]) were increased but did not achieve statistical significance.

CONCLUSIONS

This meta-analysis supports a positive association of HPgV viremia with lymphoma risk, overall and for the major lymphoma subtypes.

Human pegivirus-1 infection in kidney transplant recipients: A single-center experience

Kidney transplantation is the treatment of choice for patients with end-stage renal disease. In the posttransplant period, the induced immunosuppression leads to an increased risk of developing infectious diseases, a leading cause of death after kidney transplantation. Human pegivirus-1 (HPgV-1) is considered a nonpathogenic human virus and is highly frequent in individuals parenterally exposed, however, its impact on kidney transplantation outcome is poorly understood. Given the scarcity of epidemiological data for this infection on organ recipients in Brazil, we conducted a study in a single center for kidney transplantation in Rio de Janeiro, aiming to determine HPgV-1 prevalence and genotypic distribution. Serum samples from 61 renal recipients, followed up for the first year after transplantation, were evaluated for viral RNA and genotypes were determined by sequencing of the 5'-untranslated region. HPgV-1 RNA was detected in 36.1% (22/61) of patients. Genotype 2 was the most commonly found (80.9%), followed by genotypes 3 (9.5%), 1, and 5, in 4.8% each. Statistical comparisons did not reveal any significant impact of HPgV-1 in patient outcome. Further epidemiologic studies are needed to understand if immunosuppression may interfere in HPgV-1 persistence rates and if viremia might impact graft dysfunction rates in kidney recipients.

Discovery of a Novel Simian Pegivirus in Common Marmosets (Callithrix jacchus) with Lymphocytic Enterocolitis

From 2010 to 2015, 73 common marmosets (Callithrix jacchus) housed at the Wisconsin National Primate Research Center (WNPRC) were diagnosed postmortem with lymphocytic enterocolitis. We used unbiased deep-sequencing to screen the blood of deceased enterocolitis-positive marmosets for viruses. In five out of eight common marmosets with lymphocytic enterocolitis, we discovered a novel pegivirus not present in ten matched, clinically normal controls. The novel virus, which we named Southwest bike trail virus (SOBV), is most closely related (68% nucleotide identity) to a strain of simian pegivirus A isolated from a three-striped night monkey (Aotus trivirgatus). We screened 146 living WNPRC common marmosets for SOBV, finding an overall prevalence of 34% (50/146). Over four years, 85 of these 146 animals died or were euthanized. Histological examination revealed 27 SOBV-positive marmosets from this cohort had lymphocytic enterocolitis, compared to 42 SOBV-negative marmosets, indicating no association between SOBV and disease in this cohort (p = 0.0798). We also detected SOBV in two of 33 (6%) clinically normal marmosets screened during transfer from the New England Primate Research Center, suggesting SOBV could be exerting confounding influences on comparisons of common marmoset studies from multiple colonies.

Human Pegivirus infection and lymphoma risk and prognosis: a North American study

We evaluated the association of Human Pegivirus (HPgV) viraemia with risk of developing lymphoma, overall and by major subtypes. Because this virus has also been associated with better prognosis in the setting of co-infection with human immunodeficiency virus, we further assessed the association of HPgV with prognosis. We used risk factor data and banked plasma samples from 2094 lymphoma cases newly diagnosed between 2002 and 2009 and 1572 frequency-matched controls. Plasma samples were tested for HPgV RNA by reverse transcription polymerase chain reaction (RT-PCR), and those with RNA concentrations <5000 genome equivalents/ml were confirmed using nested RT-PCR methods. To assess the role of HPgV in lymphoma prognosis, we used 2948 cases from a cohort study of newly diagnosed lymphoma patients (included all cases from the case-control study). There was a positive association of HPgV viraemia with risk of lymphoma overall (Odds ratio = 2·14; 95% confidence interval [CI] 1·63-2·80; P < 0·0001), and for all major subtypes except Hodgkin lymphoma and chronic lymphocytic leukaemia/small lymphocytic lymphoma, and this was not confounded by other lymphoma risk factors. In contrast, there was no association of HPgV viraemia with event-free survival (Hazard ratio [HR] = 1·00; 95% CI 0·85-1·18) or overall survival (HR = 0·97; 95% CI 0·79-1·20) for lymphoma overall, or any of the subtypes. These data support the hypothesis for a role of HPgV in the aetiology of multiple lymphoma subtypes.

Pegivirus avoids immune recognition but does not attenuate acute-phase disease in a macaque model of HIV infection

Human pegivirus (HPgV) protects HIV+ people from HIV-associated disease, but the mechanism of this protective effect remains poorly understood. We sequentially infected cynomolgus macaques with simian pegivirus (SPgV) and simian immunodeficiency virus (SIV) to model HIV+HPgV co-infection. SPgV had no effect on acute-phase SIV pathogenesis-as measured by SIV viral load, CD4+ T cell destruction, immune activation, or adaptive immune responses-suggesting that HPgV's protective effect is exerted primarily during the chronic phase of HIV infection. We also examined the immune response to SPgV in unprecedented detail, and found that this virus elicits virtually no activation of the immune system despite persistently high titers in the blood over long periods of time. Overall, this study expands our understanding of the pegiviruses-an understudied group of viruses with a high prevalence in the global human population-and suggests that the protective effect observed in HIV+HPgV co-infected people occurs primarily during the chronic phase of HIV infection.

CD4/CD8 Ratio and KT Ratio Predict Yellow Fever Vaccine Immunogenicity in HIV-Infected Patients

Background

HIV-infected individuals have deficient responses to Yellow Fever vaccine (YFV) and may be at higher risk for adverse events (AE). Chronic immune activation–characterized by low CD4/CD8 ratio or high indoleamine 2,3-dioxygenase-1 (IDO) activity—may influence vaccine response in this population.

Methods

We prospectively assessed AE, viremia by the YFV virus and YF-specific neutralizing antibodies (NAb) in HIV-infected (CD4>350) and -uninfected adults through 1 year after vaccination. The effect of HIV status on initial antibody response to YFV was measured during the first 3 months following vaccination, while the effect on persistence of antibody response was measured one year following vaccination. We explored CD4/CD8 ratio, IDO activity (plasma kynurenine/tryptophan [KT] ratio) and viremia by Human Pegivirus as potential predictors of NAb response to YFV among HIV-infected participants with linear mixed models.

Results

12 HIV-infected and 45-uninfected participants were included in the final analysis. HIV was not significantly associated with AE, YFV viremia or NAb titers through the first 3 months following vaccination. However, HIV–infected participants had 0.32 times the NAb titers observed for HIV-uninfected participants at 1 year following YFV (95% CI 0.13 to 0.83, p = 0.021), independent of sex, age and prior vaccination. In HIV-infected participants, each 10% increase in CD4/CD8 ratio predicted a mean 21% higher post-baseline YFV Nab titer (p = 0.024). Similarly, each 10% increase in KT ratio predicted a mean 21% lower post-baseline YFV Nab titer (p = 0.009). Viremia by Human Pegivirus was not significantly associated with NAb titers.

Conclusions

HIV infection appears to decrease the durability of NAb responses to YFV, an effect that may be predicted by lower CD4/CD8 ratio or higher KT ratio.

Yellow Fever (YF) vaccine is considered one of the most effective vaccines ever produced. However, previous studies suggest that HIV impairs YF vaccine response. In this study, we assessed if HIV infection impacts the risk of adverse events and could reduce antibody response to YF vaccine. We explored if laboratory markers of persistent inflammation, frequently present among HIV-infected patients, could predict antibody response to YF vaccine in this population. We found that HIV had no significant effect on adverse events or levels of antibodies through 3 months after vaccination, but this may be limited by the small sample size of 12 HIV-infected and 45-uninfected participants in the study. However, we were able to show that, compared to HIV-uninfected participants, HIV–infected patients had lower antibody titers 1 year following YF vaccine even after statistical adjustment for the potential effects of sex, age and prior vaccination. Persistent inflammation seems to reduce YF vaccine antibody response in HIV-infected participants. In conclusion, HIV-infected individuals have impaired antibody response to YFV due to a poorer persistence of antibodies, despite a seemingly normal initial response. HIV-infected patients at permanent or recurring risk of YF infection may benefit from a booster dose of YF vaccine.

CD4/CD8 Ratio Predicts Yellow Fever Vaccine-Induced Antibody Titers in Virologically Suppressed HIV-Infected Patients

BACKGROUND

Yellow fever vaccine (YFV) induces weaker immune responses in HIV-infected individuals. However, little is known about YFV responses among antiretroviral-treated patients and potential immunological predictors of YFV response in this population.

METHODS

We enrolled 34 antiretroviral therapy (ART)-treated HIV-infected and 58 HIV-uninfected adults who received a single YFV dose to evaluate antibody levels and predictors of immunity, focusing on CD4(+) T-cell count, CD4(+)/CD8(+) ratio, and Human Pegivirus (GBV-C) viremia. Participants with other immunosuppressive conditions were excluded.

RESULTS

Median time since YFV was nonsignificantly shorter in HIV-infected participants than in HIV-uninfected participants (42 and 69 months, respectively, P = 0.16). Mean neutralizing antibody (NAb) titers was lower in HIV-infected participants than HIV-uninfected participants (3.3 vs. 3.6 log10mIU/mL, P = 0.044), a difference that remained significant after adjustment for age, sex, and time since vaccination (P = 0.024). In HIV-infected participants, lower NAb titers were associated with longer time since YFV (rho: -0.38, P = 0.027) and lower CD4(+)/CD8(+) ratio (rho: 0.42, P = 0.014), but not CD4(+) T-cell count (P = 0.52). None of these factors were associated with NAb titers in HIV-uninfected participant. GBV-C viremia was not associated with difference in NAb titers overall or among HIV-infected participants.

CONCLUSIONS

ART-treated HIV-infected individuals seem to have impaired and/or less durable responses to YFV than HIV-uninfected individuals, which were associated with lower CD4(+)/CD8(+) ratio, but not with CD4(+) T-cell count. These results supports the notion that low CD4(+)/CD8(+) ratio, a marker linked to persistent immune activation, is a better indicator of functional immune disturbance than CD4(+) T-cell count in patients with successful ART.

Prevalence of human pegivirus (HPgV) infection in patients carrying HIV-1C or non-C in southern Brazil

Previous studies have demonstrated that coinfection with HPgV is a protective factor for human immunodeficiency virus (HIV)-infected patients, leading to slower disease progression, and longer survival after established disease. The present study sought to estimate the prevalence of HPgV infection and associated risk factors in patients harboring C or non-C HIV-1 subtypes followed-up at HU-FURG, southern Brazil. Samples from 347 HIV-1-infected subjects were subjected to plasma RNA extraction, cDNA synthesis, HPgV RNA detection, and HIV-1 genotyping. The overall prevalence of HPgV RNA was 34%. Individuals aged 18-30 years had higher chances of infection compared with those 50 years or older (95%CI 1.18-52.36, P = 0.03). The number of sexual partner between one and three was a risk factor for HPgV infection (95%CI 1.54-10.23; P < 0.01), as well as the time since diagnosis of HIV-1 ≥ 11 years (95%CI 1.01-2.89; P = 0.04). Patients infected with HIV non-C subtypes had six times more chance of being HPgV-infected when compared to subtype C-infected subjects (95%CI 2.28-14.78; P < 0.01). This was the first study conducted in southern Brazil to find the circulation of HPgV. HIV/HPgV coinfection was associated with a longer survival among HIV⁺ patients. Of novelty, individuals infected by HIV non-C subtypes were more susceptible to HPgV infection. However, additional studies are needed to correlate the HIV-1 subtypes with HPgV infection and to clarify cellular and molecular pathways through which such associations are ruled. J. Med. Virol 88:2106-2114, 2016. © 2016 Wiley Periodicals, Inc.

Human Pegivirus (HPgV; formerly known as GBV-C) inhibits IL-12 dependent natural killer cell function

Human Pegivirus (HPgV, formally GB virus C) infects lymphocytes and NK cells in vivo, and infection is associated with reduced T cell and NK cell activation in HIV-infected individuals. The mechanism by which HPgV inhibits NK cell activation has not been assessed. Following IL-12 stimulation, IFNγ expression was lower in HIV-HPgV co-infected subjects compared to HIV mono-infected subjects (p=0.02). In addition, HPgV positive human sera, extracellular vesicles containing E2 protein, recombinant E2 protein and synthetic E2 peptides containing a predicted Tyk2 interacting motif inhibited NK cell IL-12-mediated IFNγ release. E2 protein also inhibited Tyk2 activation following IL-12 stimulation. In contrast, cytolytic NK cell function was not altered by HPgV. Inhibition of NK cell-induced proinflammatory/antiviral cytokines may contribute to both HPgV persistence and reduced immune activation during HIV-coinfection. Understanding mechanisms by which HPgV alters immune activation may contribute towards novel immunomodulatory therapies to treat HIV and inflammatory diseases.

Tropism of human pegivirus (formerly known as GB virus C/hepatitis G virus) and host immunomodulation: insights into a highly successful viral infection

Human pegivirus (HPgV; originally called GB virus C/hepatitis G virus) is an RNA virus within the genus Pegivirus of the family Flaviviridae that commonly causes persistent infection. Worldwide, ~750 million people are actively infected (viraemic) and an estimated 0.75-1.5 billion people have evidence of prior HPgV infection. No causal association between HPgV and disease has been identified; however, several studies described a beneficial relationship between persistent HPgV infection and survival in individuals infected with human immunodeficiency virus. The beneficial effect appeared to be related to a reduction in host immune activation. HPgV replicates well in vivo (mean plasma viral loads typically >1×107 genome copies ml-1); however, the virus grows poorly in vitro and systems to study this virus are limited. Consequently, mechanisms of viral persistence and host immune modulation remain poorly characterized, and the primary permissive cell type(s) has not yet been identified. HPgV RNA is found in liver, spleen, bone marrow and PBMCs, including T- and B-lymphocytes, NK-cells, and monocytes, although the mechanism of cell-to-cell transmission is unclear. HPgV RNA is also present in serum microvesicles with properties of exosomes. These microvesicles are able to transmit viral RNA to PBMCs in vitro, resulting in productive infection. This review summarizes existing data on HPgV cellular tropism and the effect of HPgV on immune activation in various PBMCs, and discusses how this may influence viral persistence. We conclude that an increased understanding of HPgV replication and immune modulation may provide insights into persistent RNA viral infection of humans.

GB virus C coinfections in west African Ebola patients

In 49 patients with known Ebola virus disease outcomes during the ongoing outbreak in Sierra Leone, 13 were coinfected with the immunomodulatory pegivirus GB virus C (GBV-C). Fifty-three percent of these GBV-C(+) patients survived; in contrast, only 22% of GBV-C(-) patients survived. Both survival and GBV-C status were associated with age, with older patients having lower survival rates and intermediate-age patients (21 to 45 years) having the highest rate of GBV-C infection. Understanding the separate and combined effects of GBV-C and age on Ebola virus survival may lead to new treatment and prevention strategies, perhaps through age-related pathways of immune activation.

Downregulation of Cytokines and Chemokines by GB Virus C After Transmission Via Blood Transfusion in HIV-Positive Blood Recipients

BACKGROUND

An association between GB virus C (GBV-C) and improved outcomes of human immunodeficiency virus (HIV) infection has been reported in HIV-positive individuals with active GBV-C coinfection. This study provides insights into the immune mechanisms underlying the protective role of GBV-C in HIV-infected patients.

METHODS

The concentrations of 64 cytokines and chemokines were measured in plasma samples obtained from the Viral Activation Transfusion Study cohort before transfusion and longitudinally from 30 patients positive for both HIV and GBV-C (hereafter, "cases") and 30 patients positive for HIV and negative for GBV-C (hereafter, "controls").

RESULTS

Cases had lower HIV viral loads and higher CD4 T-cell counts than controls after acquisition of GBV-C infection. Most of the modulated cytokines and chemokines were reduced after GBV-C detection, including many proinflammatory cytokines, suggesting an overall antiinflammatory effect of GBV-C in HIV-positive subjects. Most pathways and functions of the measured cytokines were downregulated in cases, except cell death pathways, which were upregulated in various cell subsets in the 3 months after GBV-C detection.

CONCLUSIONS

GBV-C has a protective effect, in part through a competition mechanism leading to decreased inflammation and improved HIV disease outcome in cases. Further studies are necessary to establish whether GBV-C may have deleterious effects on the host at the cellular level, including depleting the cells that are the targets of HIV.

GBV-C infection and risk of NHL among U.S. adults

Some retrospective studies suggest an association between infection with GB virus-C (GBV-C) and non-Hodgkin lymphoma (NHL). We evaluated this association prospectively in a nested case-control study within the U.S. Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial. Cases (N = 658) and controls (N = 1,316) were individually matched by age, sex, race/ethnicity, timing of study entry, and sample selection. Prediagnostic PLCO serum samples were tested for GBV-C RNA (as a measure of active infection) and E2 antibody (active or resolved infection). Logistic regression was used to estimate odds ratios (OR) for the association between GBV-C and NHL overall and NHL subtypes. Twelve cases (1.8%) and seven controls (0.5%) were GBV-C RNA-positive. GBV-C RNA positivity was associated with NHL overall [OR, 3.43; 95% confidence interval (CI), 1.35-8.71] and, based on small numbers, diffuse large B-cell lymphoma (OR, 5.31; 95% CI, 1.54-18.36). The association with NHL persisted when the interval between testing and selection was greater than 4 years (OR, 6.00; 95% CI, 1.21-29.73). In contrast, E2 antibody positivity was not associated with NHL risk (OR, 1.08; 95% CI, 0.74-1.58). Our study demonstrates that GBV-C infection precedes development of NHL. GBV-C infection may play an etiologic role in a small proportion of NHL cases, perhaps by causing chronic immune stimulation or impaired immunosurveillance.

HIV-1 vaginal transmission: cell-free or cell-associated virus?

The vast majority of new HIV infections in male-to-female transmission occurs through semen, where HIV-1 is present in two different forms: as free and as cell-associated virus. In the female lower genital tract, semen mixes with female genital secretions that contain various factors, some of which facilitate or inhibit HIV-1 transmission. Next, HIV-1 crosses the genital epithelia, reaches the regional lymph nodes, and disseminates through the female host. Cervico-vaginal mucosa contains multiple barriers, resulting in a low probability of vaginal transmission. However, in some cases, HIV-1 is able to break these barriers. Although the exact mechanisms of how these barriers function remain unclear, their levels of efficiency against cell-free and cell-associated HIV-1 are different, and both cell-free and cell-associated virions seem to use different strategies to overcome these barriers. Understanding the basic mechanisms of HIV-1 vaginal transmission is required for the development of new antiviral strategies to contain HIV-1 epidemics.

Human pegivirus RNA is found in multiple blood mononuclear cells in vivo and serum-derived viral RNA-containing particles are infectious in vitro

Human pegivirus (HPgV; previously called GB virus C/hepatitis G virus) has limited pathogenicity, despite causing persistent infection, and is associated with prolonged survival in human immunodeficiency virus-infected individuals. Although HPgV RNA is found in and produced by T- and B-lymphocytes, the primary permissive cell type(s) are unknown. We quantified HPgV RNA in highly purified CD4(+) and CD8(+) T-cells, including naïve, central memory and effector memory populations, and in B-cells (CD19(+)), NK cells (CD56(+)) and monocytes (CD14(+)) using real-time reverse transcription-PCR. Single-genome sequencing was performed on viruses within individual cell types to estimate genetic diversity among cell populations. HPgV RNA was present in CD4(+) and CD8(+) T-lymphocytes (nine of nine subjects), B-lymphocytes (seven of ten subjects), NK cells and monocytes (both four of five). HPgV RNA levels were higher in naïve (CD45RA(+)) CD4(+) cells than in central memory and effector memory cells (P<0.01). HPgV sequences were highly conserved among subjects (0.117±0.02 substitutions per site; range 0.58-0.14) and within subjects (0.006±0.003 substitutions per site; range 0.006-0.010). The non-synonymous/synonymous substitution ratio was 0.07, suggesting a low selective pressure. Carboxyfluorescein succinimidyl ester (CFSE)-labelled HPgV RNA-containing particles precipitated by a commercial exosome isolation reagent delivered CSFE to uninfected monocytes, NK cells and T- and B-lymphocytes, and HPgV RNA was transferred to PBMCs with evidence of subsequent virus replication. Thus, HPgV RNA-containing serum particles including microvesicles may contribute to delivery of HPgV to PBMCs in vivo, explaining the apparent broad tropism of this persistent human RNA virus.

A novel T cell evasion mechanism in persistent RNA virus infection

Hepatitis C virus (HCV) and GB virus type C (GBV-C) are associated with impaired T cell function despite the fact that HCV replicates in hepatocytes and GBV-C in a small proportion of lymphocytes. Recently, we showed that HCV and GBV-C E2-envelope proteins reduce T cell activation via the T cell receptor (TCR) by competing for phosphorylation with a critical kinase in the TCR signaling cascade (Lck). E2 interfered with TCR signaling in E2 expressing cells and in bystander cells. The bystander effect was mediated by virus particles and extracellular microvesicular particles (exosomes). Multiple kinase substrate sites are predicted to reside on viral structural proteins and based on bioinformatic predictions, many RNA virus pathogens may interfere with TCR signaling via a similar mechanism. Identification of T cell inhibitory effects of virus structural proteins may provide novel approaches to enhance the immunogenicity and memory of viral vaccines.