Viruses within the Flaviviridae decrease CD4 expression and inhibit HIV replication in human CD4+ cells

Co-Infections and Superinfections between HIV-1 and Other Human Viruses at the Cellular Level

Co-infection or superinfection of the host by two or more virus species is a common event, potentially leading to viral interference, viral synergy, or neutral interaction. The simultaneous presence of two or more viruses, even distantly related, within the same cell depends upon viral tropism, i.e., the entry of viruses via receptors present on the same cell type. Subsequently, productive infection depends on the ability of these viruses to replicate efficiently in the same cellular environment. HIV-1 initially targets CCR5-expressing tissue memory CD4+ T cells, and in the absence of early cART initiation, a co-receptor switch may occur, leading to the infection of naïve and memory CXCR4-expressing CD4+ T cells. HIV-1 infection of macrophages at the G1 stage of their cell cycle also occurs in vivo, broadening the possible occurrence of co-infections between HIV-1 and other viruses at the cellular level. Moreover, HIV-1-infected DCs can transfer the virus to CD4+ T cells via trans-infection. This review focuses on the description of reported co-infections within the same cell between HIV-1 and other human pathogenic, non-pathogenic, or low-pathogenic viruses, including HIV-2, HTLV, HSV, HHV-6/-7, GBV-C, Dengue, and Ebola viruses, also discussing the possible reciprocal interactions in terms of virus replication and virus pseudotyping.

Characterization of "Off-Target" Immune Modulation Induced by Live Attenuated Yellow Fever Vaccine

BACKGROUND

Live attenuated vaccines alter immune functions and are associated with beneficial outcomes. We previously demonstrated that live attenuated yellow fever virus (YFV) vaccine (LA-YF-Vax) dampens T-cell receptor (TCR) signaling in vitro via an RNA-based mechanism. We examined study participants before and after LA-YF-Vax to assess TCR-mediated functions in vivo.

METHODS

Serum samples and peripheral blood mononuclear cells (PBMCs) were obtained before and after LA-YF-Vax (with or without additional vaccines) or quadrivalent influenza vaccine. TCR-mediated activation was determined by interleukin 2 release or phosphorylation of the lymphocyte-specific Src kinase. TCR-regulating phosphatase (protein tyrosine phosphatase receptor type E [PTPRE]) expression was also measured.

RESULTS

Compared with prevaccination findings, LA-YF-Vax recipient PBMCs demonstrated transient reduction in interleukin 2 release after TCR stimulation and PTPRE levels, unlike in control participants who received quadrivalent influenza vaccine. YFV was detected in 8 of 14 participants after LA-YF-Vax. After incubation of healthy donor PBMCs in serum-derived extracellular vesicles prepared from LA-YF-Vax recipients, TCR signaling and PTPRE levels were reduced after vaccination, even in participants without detectable YFV RNA.

CONCLUSIONS

LA-YF-Vax reduces TCR functions and PTPRE levels after vaccination. Extracellular vesicles from serum recapitulated this effect in healthy cells. This likely contributes to the reduced immunogenicity for heterologous vaccines after LA-YF-Vax administration. Identification of specific immune mechanisms related to vaccines should contribute to understanding of the "off-target," beneficial effects of live vaccines.

Clinical and molecular aspects of human pegiviruses in the interaction host and infectious agent

Background

Human pegivirus 1 (HPgV-1) is a Positive-sense single-stranded RNA (+ ssRNA) virus, discovered in 1995 as a Flaviviridae member, and the closest human virus linked to HCV. In comparison to HCV, HPgV-1 seems to be lymphotropic and connected to the viral group that infects T and B lymphocytes. HPgV-1 infection is not persuasively correlated to any known human disease; nevertheless, multiple studies have reported a connection between chronic HPgV-1 infection and improved survival in HPgV-1/HIV co-infected patients with a delayed and favorable impact on HIV infection development. While the process has not been thoroughly clarified, different mechanisms for these observations have been proposed. HPgV-1 is categorized into seven genotypes and various subtypes. Infection with HPgV-1 is relatively common globally. It can be transferred parenterally, sexually, and through vertical ways, and thereby its co-infection with HIV and HCV is common. In most cases, the clearance of HPgV-1 from the body can be achieved by developing E2 antibodies after infection.

Main body

In this review, we thoroughly discuss the current knowledge and recent advances in understanding distinct epidemiological, molecular, and clinical aspects of HPgV-1.

Conclusion

Due to the unique characteristics of the HPgV-1, so advanced research on HPgV-1, particularly in light of HIV co-infection and other diseases, should be conducted to explore the essential mechanisms of HIV clearance and other viruses and thereby suggest novel strategies for viral therapy in the future.

The Present and Future of Yellow Fever Vaccines

The disease yellow fever (YF) is prevented by a live-attenuated vaccine, termed 17D, which has been in use since the 1930s. One dose of the vaccine is thought to give lifelong (35+ years) protective immunity, and neutralizing antibodies are the correlate of protection. Despite being a vaccine-preventable disease, YF remains a major public health burden, causing an estimated 109,000 severe infections and 51,000 deaths annually. There are issues of supply and demand for the vaccine, and outbreaks in 2016 and 2018 resulted in fractional dosing of the vaccine to meet demand. The World Health Organization (WHO) has established the “Eliminate Yellow Fever Epidemics” (EYE) initiative to reduce the burden of YF over the next 10 years. As with most vaccines, the WHO has recommendations to assure the quality, safety, and efficacy of the YF vaccine. These require the use of live 17D vaccine only produced in embryonated chicken eggs, and safety evaluated in non-human primates only. Thus, any second-generation vaccines would require modification of WHO recommendations if they were to be used in endemic countries. There are multiple second-generation YF vaccine candidates in various stages of development that must be shown to be non-inferior to the current 17D vaccine in terms of safety and immunogenicity to progress through clinical trials to potential licensing. The historic 17D vaccine continues to shape the global vaccine landscape in its use in the generation of multiple licensed recombinant chimeric live vaccines and vaccine candidates, in which its structural protein genes are replaced with those of other viruses, such as dengue and Japanese encephalitis. There is no doubt that the YF 17D live-attenuated vaccine will continue to play a role in the development of new vaccines for YF, as well as potentially for many other pathogens.

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.

Tick-Borne Encephalitis Virus: A Quest for Better Vaccines against a Virus on the Rise

Tick-borne encephalitis virus (TBEV), a member of the family Flaviviridae, is one of the most important tick-transmitted viruses in Europe and Asia. Being a neurotropic virus, TBEV causes infection of the central nervous system, leading to various (permanent) neurological disorders summarized as tick-borne encephalitis (TBE). The incidence of TBE cases has increased due to the expansion of TBEV and its vectors. Since antiviral treatment is lacking, vaccination against TBEV is the most important protective measure. However, vaccination coverage is relatively low and immunogenicity of the currently available vaccines is limited, which may account for the vaccine failures that are observed. Understanding the TBEV-specific correlates of protection is of pivotal importance for developing novel and improved TBEV vaccines. For affording robust protection against infection and development of TBE, vaccines should induce both humoral and cellular immunity. In this review, the adaptive immunity induced upon TBEV infection and vaccination as well as novel approaches to produce improved TBEV vaccines are discussed.

Systems-Level Immunomonitoring from Acute to Recovery Phase of Severe COVID-19

Severe disease of SARS-CoV-2 is characterized by vigorous inflammatory responses in the lung, often with a sudden onset after 5–7 days of stable disease. Efforts to modulate this hyperinflammation and the associated acute respiratory distress syndrome rely on the unraveling of the immune cell interactions and cytokines that drive such responses. Given that every patient is captured at different stages of infection, longitudinal monitoring of the immune response is critical and systems-level analyses are required to capture cellular interactions. Here, we report on a systems-level blood immunomonitoring study of 37 adult patients diagnosed with COVID-19 and followed with up to 14 blood samples from acute to recovery phases of the disease. We describe an IFNγ-eosinophil axis activated before lung hyperinflammation and changes in cell-cell co-regulation during different stages of the disease. We also map an immune trajectory during recovery that is shared among patients with severe COVID-19.

Immunomonitoring from acute to recovery phase COVID-19

An IFNγ-eosinophil axis precedes lung hyperinflammation

Basophils modulate SARS-CoV-2 IgG responses

A shared trajectory of immunological recovery in COVID-19

Endemic infection can shape exposure to novel pathogens: Pathogen co-occurrence networks in the Serengeti lions

Pathogens are embedded in a complex network of microparasites that can collectively or individually alter disease dynamics and outcomes. Endemic pathogens that infect an individual in the first years of life, for example, can either facilitate or compete with subsequent pathogens thereby exacerbating or ameliorating morbidity and mortality. Pathogen associations are ubiquitous but poorly understood, particularly in wild populations. We report here on 10 years of serological and molecular data in African lions, leveraging comprehensive demographic and behavioural data to test if endemic pathogens shape subsequent infection by epidemic pathogens. We combine network and community ecology approaches to assess broad network structure and characterise associations between pathogens across spatial and temporal scales. We found significant non‐random structure in the lion‐pathogen co‐occurrence network and identified both positive and negative associations between endemic and epidemic pathogens. Our results provide novel insights on the complex associations underlying pathogen co‐occurrence networks.

Yellow Fever Virus, but Not Zika Virus or Dengue Virus, Inhibits T-Cell Receptor-Mediated T-Cell Function by an RNA-Based Mechanism

The Flavivirus genus within the Flaviviridae family is comprised of many important human pathogens including yellow fever virus (YFV), dengue virus (DENV), and Zika virus (ZKV), all of which are global public health concerns. Although the related flaviviruses hepatitis C virus and human pegivirus (formerly named GBV-C) interfere with T-cell receptor (TCR) signaling by novel RNA and protein-based mechanisms, the effect of other flaviviruses on TCR signaling is unknown. Here, we studied the effect of YFV, DENV, and ZKV on TCR signaling. Both YFV and ZKV replicated in human T cells in vitro; however, only YFV inhibited TCR signaling. This effect was mediated at least in part by the YFV envelope (env) protein coding RNA. Deletion mutagenesis studies demonstrated that expression of a short, YFV env RNA motif (vsRNA) was required and sufficient to inhibit TCR signaling. Expression of this vsRNA and YFV infection of T cells reduced the expression of a Src-kinase regulatory phosphatase (PTPRE), while ZKV infection did not. YFV infection in mice resulted in impaired TCR signaling and PTPRE expression, with associated reduction in murine response to experimental ovalbumin vaccination. Together, these data suggest that viruses within the flavivirus genus inhibit TCR signaling in a species-dependent manner.

Dengue Virus Coinfection in Human Immunodeficiency Virus-1-Infected Patients on the West Coast of Mexico

Dengue virus infection in human immunodeficiency virus (HIV)-positive patients is not well studied. Previous reports suggest a transitory inhibition of the HIV-1 viral load, as well as a benign clinical progression of dengue. The follow-up of six HIV-1-infected patients, diagnosed and hospitalized with dengue virus infection in the State of Colima, Mexico, was carried out to analyze the progression of this viral coinfection. The presence of dengue virus serotype 1 was confirmed through molecular tests. No severe complications were observed in any of the patients during dengue virus infection. Significant alteration of the HIV-1 viral loads was not observed during dengue virus infection and 6 months after coinfection. Further studies are required to understand the pathology, as well as the clinical course, of these viral coinfections.

Survey of malaria and anti-dengue virus IgG among febrile HIV-infected patients attending a tertiary hospital in Abuja, Nigeria

BACKGROUND

Dengue and malaria are infections, of great public health concern, especially in sub-Saharan Africa where the burden of HIV infection is high. This study was conducted to determine the seroprevalence of dengue virus IgG antibodies and dengue/malaria coinfection among febrile HIV-infected patients attending the University of Abuja Teaching Hospital, Gwagwalada, Abuja.

METHODS

In this cross-sectional study, blood samples from 178 consenting HIV-infected patients receiving antiretroviral therapy were collected and tested for plasmodiasis and anti-Dengue virus IgG using malaria microscopy and ELISA, respectively. Interviewer-based questionnaires were used to assess subjects' sociodemographic variables and dengue risk factors.

RESULTS

Of the 178 screened participants, 44.4% were seropositive for dengue virus IgG antibody, whereas 29.2% were positive for Plasmodium falciparum. About 44.2% were positive for both dengue virus and P. falciparum. There was a statistical association between anti-dengue IgG and occupation (p=0.03) but not with age, residential area, educational level and patients' gender (p>0.05). Seroprevalence of anti-dengue specific IgG was relatively higher in participants who adopted protective measures. There was a statistical association between seroprevalence of anti-dengue IgG and adoption of preventive measures (p<0.05).

CONCLUSION

The high prevalence of malaria and dengue virus IgG indicates the need to strengthen vector control and dengue surveillance programs.

Zika virus infection reprograms global transcription of host cells to allow sustained infection

Zika virus (ZIKV) is an emerging virus causally linked to neurological disorders, including congenital microcephaly and Guillain-Barré syndrome. There are currently no targeted therapies for ZIKV infection. To identify novel antiviral targets and to elucidate the mechanisms by which ZIKV exploits the host cell machinery to support sustained replication, we analyzed the transcriptomic landscape of human microglia, fibroblast, embryonic kidney and monocyte-derived macrophage cell lines before and after ZIKV infection. The four cell types differed in their susceptibility to ZIKV infection, consistent with differences in their expression of viral response genes before infection. Clustering and network analyses of genes differentially expressed after ZIKV infection revealed changes related to the adaptive immune system, angiogenesis and host metabolic processes that are conducive to sustained viral production. Genes related to the adaptive immune response were downregulated in microglia cells, suggesting that ZIKV effectively evades the immune response after reaching the central nervous system. Like other viruses, ZIKV diverts host cell resources and reprograms the metabolic machinery to support RNA metabolism, ATP production and glycolysis. Consistent with these transcriptomic analyses, nucleoside metabolic inhibitors abrogated ZIKV replication in microglia cells.

Dengue Infection in a Human Immunodeficiency Virus-1 Positive Patient Chronically Infected with Hepatitis B Virus in Western Mexico

Human immunodeficiency virus (HIV) and dengue coinfection has not been extensively studied. We report herein a case of dengue serotype 1 infection in an HIV-1-positive patient coinfected with hepatitis B virus (HBV) in Colima State, Mexico. CD4⁺ cells and HIV-1 viremia remained at normal levels, and no severe complications were observed during this multiple viral infection. The alanine transaminase and aspartate transaminase values were elevated before and during dengue infection. Surprisingly, these parameters were significantly reduced 2 months later. Because of the lack of evidence regarding this multiple viral interaction, further research is required to understand the biologic and clinical course of dengue infection in HIV-1/HBV coinfected patients, especially in tropical regions where dengue virus transmission is highly active.

A sequential classification rule based on multiple quantitative tests in the absence of a gold standard

In many medical applications, combining information from multiple biomarkers could yield a better diagnosis than any single one on its own. When there is a lack of a gold standard, an algorithm of classifying subjects into the case and non-case status is necessary for combining multiple markers. The aim of this paper is to develop a method to construct a composite test from multiple applicable tests and derive an optimal classification rule under the absence of a gold standard. Rather than combining the tests, we treat the tests as a sequence. This sequential composite test is based on a mixture of two multivariate normal latent models for the distribution of the test results in case and non-case groups, and the optimal classification rule is derived returning the greatest sensitivity at a given specificity. This method is applied to a real-data example and simulation studies have been carried out to assess the statistical properties and predictive accuracy of the proposed composite test. This method is also attainable to implement nonparametrically.

Differential clinical outcome of dengue infection among patients with and without HIV infection: a matched case-control study

Clinical characteristics and outcome among dengue patients with and without human immunodeficiency virus (HIV) infection remain elusive. A total of 10 dengue virus (DENV)-HIV Chinese patients were compared with 40 Chinese dengue patients without HIV, who were matched for age, gender, type of care received, methods, and year of dengue diagnosis from 2005 to 2008. Univariate and multivariate conditional logistics regression were applied. DENV-HIV patients were significantly associated with the World Health Organization (WHO) 2009 severe dengue (conditional odds ratio [COR] = 5.72; 95% confidence interval [CI] = 1.01-32.64) but not with the WHO 1997 dengue hemorrhagic fever/dengue shock syndrome (COR = 0.40; 95% CI = 0.09-1.71). This is mainly due to severe plasma leakage and the lack of hemorrhagic manifestations. Hospitalization duration was longer for DENV-HIV patients (10.5 days; interquartile range [IQR] = 5.5-26.3 days) compared with dengue patients (5 days; IQR = 4-6 days). There were no significant differences in presentation of clinical warning signs and symptoms at admission and during hospitalization, except for rash (adjusted COR [ACOR] = 0.06; 95% CI = 0.03-0.92). DENV-HIV patients were associated with higher pulse rate (ACOR = 1.13; 95% CI = 1.02-1.25), eosinophils proportion (ACOR = 3.07; 95% CI = 1.12-8.41) and lower hematocrit level (ACOR = 0.79; 95% CI = 0.64-0.98) compared with dengue patients. Even though DENV-HIV patients may present similarly to dengue patients, they may be more likely to have severe dengue outcome. Hence, close monitoring of DENV-HIV patients is highly recommended as part of dengue clinical care and management.

Signal peptide-binding drug as a selective inhibitor of co-translational protein translocation

In eukaryotic cells, surface expression of most type I transmembrane proteins requires translation and simultaneous insertion of the precursor protein into the endoplasmic reticulum (ER) membrane for subsequent routing to the cell surface. This co-translational translocation pathway is initiated when a hydrophobic N-terminal signal peptide (SP) on the nascent protein emerges from the ribosome, binds the cytosolic signal recognition particle (SRP), and targets the ribosome-nascent chain complex to the Sec61 translocon, a universally conserved protein-conducting channel in the ER-membrane. Despite their common function in Sec61 targeting and ER translocation, SPs have diverse but unique primary sequences. Thus, drugs that recognise SPs could be exploited to inhibit translocation of specific proteins into the ER. Here, through flow cytometric analysis the small-molecule macrocycle cyclotriazadisulfonamide (CADA) is identified as a highly selective human CD4 (hCD4) down-modulator. We show that CADA inhibits CD4 biogenesis and that this is due to its ability to inhibit co-translational translocation of CD4 into the lumen of the ER, both in cells as in a cell-free in vitro translation/translocation system. The activity of CADA maps to the cleavable N-terminal SP of hCD4. Moreover, through surface plasmon resonance analysis we were able to show direct binding of CADA to the SP of hCD4 and identify this SP as the target of our drug. Furthermore, CADA locks the SP in the translocon during a post-targeting step, possibly in a folded state, and prevents the translocation of the associated protein into the ER lumen. Instead, the precursor protein is routed to the cytosol for degradation. These findings demonstrate that a synthetic, cell-permeable small-molecule can be developed as a SP-binding drug to selectively inhibit protein translocation and to reversibly regulate the expression of specific target proteins.

West Nile virus seroprevalence and behavioral risks in HIV-1 infected individuals, Northern Greece, 2011

OBJECTIVES

This study sought to assess the West Nile Virus (WNV) seroprevalence and behavioral risk factors for WNV infection in HIV-1 infected individuals in Northern Greece in 2011.

METHODS

We prospectively enrolled 91 HIV-1 consecutive patients followed up in the HIV clinic of the AHEPA University Hospital in the period from November to December 2011. Serum samples were tested for the presence of WNV IgG antibodies. All subjects were administered a standardized questionnaire to evaluate for risk factors for WNV infection.

RESULTS

WNV IgG antibodies were detected in three subjects (3.3%, 95% CI 0.7-9.3%), two of whom were of African origin. The prevalence of WNV antibodies in HIV patients of Greek origin was 1.2% (95% CI: 0.03% - 6.3%). In the sample surveyed, 53.6% (95% CI: 42.4% to 64.5%) were aware of WNV prevention measures; 2.2% reported no implementation of prevention measures, whereas 46.1% implemented at least three measures. Approximately one half of the patients reported outdoor activities for more than two hours from dusk to dawn. None of the IgG-positive patients reported any symptoms compatible with WNV disease during the season at risk.

CONCLUSIONS

Among native Greek HIV patients, the WNV seroprevalence is 1.2%. A considerable proportion of patients was aware of WNV prevention measures and implemented some of these. HIV patients and other categories of immunocompromised patients are at increased risk of neuroinvasive disease, and widespread implementation of prevention measures should be strongly encouraged in this patient population.

Surface behavior of peptides from E1 GBV-C protein: Interaction with anionic model membranes and importance in HIV-1 FP inhibition

The interaction between a peptide sequence from GB virus C E1 protein (E1P8) and its structural analogs (E1P8-12), (E1P8-13), and (E1P8-21) with anionic lipid membranes (POPG vesicles and POPG, DPPG or DPPC/DPPG (2:1) monolayers) and their association with HIV-1 fusion peptide (HIV-1 FP) inhibition at the membrane level were studied using biophysical methods. All peptides showed surface activity but leakage experiments in vesicles as well as insertion kinetics in monolayers and lipid/peptide miscibility indicated a low level of interaction: neither E1P8 nor its analogs induced the release of vesicular content and the exclusion pressure values (πe) were clearly lower than the biological membrane pressure (24-30 mN m(-1)) and the HIV-1 FP (35 mN m(-1)). Miscibility was elucidated in terms of the additivity rule and excess free energy of mixing (GE). E1P8, E1P8-12 and E1P8-21 (but not E1P8-13) induced expansion of the POPG monolayer. The mixing process is not thermodynamically favored as the positive GE values indicate. To determine how E1 peptides interfere in the action of HIV-1 FP at the membrane level, mixed monolayers of HIV-1 FP/E1 peptides (2:1) and POPG were obtained. E1P8 and its derivative E1P8-21 showed the greatest HIV-1 FP inhibition. The LC-LE phase lipid behavior was morphologically examined via fluorescence microscopy (FM) and atomic force microscopy (AFM). Images revealed that the E1 peptides modify HIV-1 FP-lipid interaction. This fact may be attributed to a peptide/peptide interaction as indicated by AFM results. Finally, hemolysis assay demonstrated that E1 peptides inhibit HIV-1 FP activity.

Virus against virus (VIVI): a potential solution against HIV/AIDS

Most therapeutic regimens are aimed at the use of pharmacologic agents or the induction of immunological response against the pathological agent. However, these methods tend to be insufficient for the management of some of the most debilitating infectious diseases. Here we present a novel therapeutic approach. It involves voluntary super-infection of a subject having HIV/AIDS with a virus (GBV-C), which to date has not been shown to be responsible for any pathology. It has been shown to counter, suppress or eradicate the agent responsible for the severe disease. Several studies demonstrate the role of different micro-organisms in influencing the growth of other pathogens in the human body. This hypothesis requires meticulous testing before its implementation on humans. If the trials are successful, the implications for this hypothesis are promising considering the compliance issues and adverse effects associated with current standard of HIV care.

Specificities of human CD4+ T cell responses to an inactivated flavivirus vaccine and infection: correlation with structure and epitope prediction

Tick-borne encephalitis (TBE) virus is endemic in large parts of Europe and Central and Eastern Asia and causes more than 10,000 annual cases of neurological disease in humans. It is closely related to the mosquito-borne yellow fever, dengue, Japanese encephalitis, and West Nile viruses, and vaccination with an inactivated whole-virus vaccine can effectively prevent clinical disease. Neutralizing antibodies are directed to the viral envelope protein (E) and an accepted correlate of immunity. However, data on the specificities of CD4(+) T cells that recognize epitopes in the viral structural proteins and thus can provide direct help to the B cells producing E-specific antibodies are lacking. We therefore conducted a study on the CD4(+) T cell response against the virion proteins in vaccinated people in comparison to TBE patients. The data obtained with overlapping peptides in interleukin-2 (IL-2) enzyme-linked immunosorbent spot (ELISpot) assays were analyzed in relation to the three-dimensional structures of the capsid (C) and E proteins as well as to epitope predictions based on major histocompatibility complex (MHC) class II peptide affinities. In the C protein, peptides corresponding to two out of four alpha helices dominated the response in both vaccinees and patients, whereas in the E protein concordance of immunodominance was restricted to peptides of a single domain (domain III). Epitope predictions were much better for C than for E and were especially erroneous for the transmembrane regions. Our data provide evidence for a strong impact of protein structural features that influence peptide processing, contributing to the discrepancies observed between experimentally determined and computer-predicted CD4(+) T cell epitopes. Importance: Tick-borne encephalitis virus is endemic in large parts of Europe and Asia and causes more than 10,000 annual cases of neurological disease in humans. It is closely related to yellow fever, dengue, Japanese encephalitis, and West Nile viruses, and vaccination with an inactivated vaccine can effectively prevent disease. Both vaccination and natural infection induce the formation of antibodies to a viral surface protein that neutralize the infectivity of the virus and mediate protection. B lymphocytes synthesizing these antibodies require help from other lymphocytes (helper T cells) which recognize small peptides derived from proteins contained in the viral particle. Which of these peptides dominate immune responses to vaccination and infection, however, was unknown. In our study we demonstrate which parts of the proteins contribute most strongly to the helper T cell response, highlight specific weaknesses of currently available approaches for their prediction, and demonstrate similarities and differences between vaccination and infection.

Human pegivirus (GB virus C) NS3 protease activity inhibits induction of the type I interferon response and is not inhibited by HCV NS3 protease inhibitors

We previously found that human pegivirus (HPgV; formerly GBV-C) NS3 protease activity inhibits Human Immunodeficiency Virus (HIV) replication in a CD4+ T cell line. Given the protease׳s similarity to the Hepatitis C virus (HCV) NS3 protease, we characterized HPgV protease activity and asked whether it affects the type I interferon response or is inhibited by HCV protease antagonists. We characterized the activity of proteases with mutations in the catalytic triad and demonstrated that the HCV protease inhibitors Telaprevir, Boceprevir, and Danoprevir do not affect HPgV protease activity. HPgV NS3 protease cleaved MAVS but not TRIF, and it inhibited interferon responses sufficiently to enhance growth of an interferon-sensitive virus. Therefore, HPgV׳s inhibition of the interferon response could help promote HPgV persistence, which is associated with clinical benefits in HIV-infected patients. Our results also imply that HCV protease inhibitors should not interfere with the beneficial effects of HPgV in HPgV/HCV/HIV infected patients.

Chimpanzee GB virus C and GB virus A E2 envelope glycoproteins contain a peptide motif that inhibits human immunodeficiency virus type 1 replication in human CD4⁺ T-cells

GB virus type C (GBV-C) is a lymphotropic virus that can cause persistent infection in humans. GBV-C is not associated with any disease, but is associated with reduced mortality in human immunodeficiency virus type 1 (HIV-1)-infected individuals. Related viruses have been isolated from chimpanzees (GBV-Ccpz) and from New World primates (GB virus type A, GBV-A). These viruses are also capable of establishing persistent infection. We determined the nucleotide sequence encoding the envelope glycoprotein (E2) of two GBV-Ccpz isolates obtained from the sera of captive chimpanzees. The deduced GBV-Ccpz E2 protein differed from human GBV-C by 31 % at the amino acid level. Similar to human GBV-C E2, expression of GBV-Ccpz E2 in a tet-off human CD4(+) Jurkat T-cell line significantly inhibited the replication of diverse HIV-1 isolates. This anti-HIV-replication effect of GBV-Ccpz E2 protein was reversed by maintaining cells in doxycycline to reduce E2 expression. Previously, we found a 17 aa region within human GBV-C E2 that was sufficient to inhibit HIV-1. Although GBV-Ccpz E2 differed by 3 aa differences in this region, the chimpanzee GBV-C 17mer E2 peptide inhibited HIV-1 replication. Similarly, the GBV-A peptide that aligns with this GBV-C E2 region inhibited HIV-1 replication despite sharing only 5 aa with the human GBV-C E2 sequence. Thus, despite amino acid differences, the peptide region on both the GBV-Ccpz and the GBV-A E2 protein inhibit HIV-1 replication similar to human GBV-C. Consequently, GBV-Ccpz or GBV-A infection of non-human primates may provide an animal model to study GB virus-HIV interactions.

Role of GB virus C in modulating HIV disease

GB virus C (GBV-C) is a member of the Flaviviridae family and the most closely related human virus to HCV. However, GBV-C does not replicate in hepatocytes, but rather in lymphocytes. GBV-C has a worldwide distribution and is transmitted sexually, parenterally and through mother-to-child transmission. Thus, co-infection with HCV and HIV is common. Until now, no human disease has been associated with GBV-C infection. However, there are several reports of a beneficial effect of GBV-C on HIV disease progression in vivo. Different mechanisms to explain these observations have been proposed, including modification of antiviral cytokine production, HIV co-receptor expression, direct inhibition of HIV-1 entry, T-cell activation and Fas-mediated apoptosis. Further understanding of these mechanisms may open new strategies for the treatment of HIV/AIDS.

Characterization of a peptide domain within the GB virus C envelope glycoprotein (E2) that inhibits HIV replication

GB virus C (GBV-C) infection is associated with prolonged survival in HIV-infected cohorts, and GBV-C E2 protein inhibits HIV entry when added to CD4+ T cells. To further characterize E2 effects on HIV replication, stably transfected Jurkat cell lines expressing GBV-C E2 or control sequences were infected with HIV and replication was measured. HIV replication (all 6 isolates studied) was inhibited in all cell lines expressing a region of 17 amino acids of GBV-C E2, but not in cell lines expressing E2 without this region. In contrast, mumps and yellow fever virus replication was not inhibited by E2 protein expression. Synthetic GBV-C E2 17mer peptides did not inhibit HIV replication unless they were fused to a tat-protein-transduction-domain (TAT) for cellular uptake. These data identify the region of GBV-C E2 protein involved in HIV inhibition, and suggest that this GBV-C E2 peptide must gain entry into the cell to inhibit HIV.

GB virus type C infection polarizes T-cell cytokine gene expression toward a Th1 cytokine profile via NS5A protein expression

Human immunodeficiency virus (HIV) disease progression is associated with a helper T cell 1 (Th1) to helper T cell 2 (Th2) cytokine profile switch. Persistent GB virus type C (GBV-C) infection is associated with survival and a serum Th1 cytokine profile in HIV-infected individuals. We found that GBV-C infection increased gene expression of Th1 cytokines and decreased Th2 cytokine expression in peripheral blood mononuclear cells. Furthermore, expression of GBV-C NS5A protein in a CD4(+) cell line resulted in upregulation of Th1 cytokines (tumor necrosis factor α) and downregulation of Th2 cytokines (interleukin 4, interleukin 5, interleukin 10, interleukin 13). GBV-C-induced modulation in T-cell cytokines may contribute to the beneficial effect of GBV-C in HIV-infected individuals.

Transmission of GB virus type C via transfusion in a cohort of HIV-infected patients

BACKGROUND

GB virus C (GBV-C) infection is transmitted by blood exposure and associated with lower human immunodeficiency virus (HIV) load and slower HIV disease progression. Few studies describe predictors of acute GBV-C infection following transfusion in HIV-infected patients.

METHODS

We used a limited-access database from the National Heart Lung and Blood Institute's Viral Activation Transfusion Study, a randomized controlled trial of leukoreduced versus nonleukoreduced transfusions received by HIV-infected, transfusion-naive patients. Blood samples from 489 subjects were tested for GBV-C markers in pretransfusion and posttransfusion samples. We estimated the risk of acquiring GBV-C RNA and predictors of GBV-C acquisition, using pooled logistic regression.

RESULTS

GBV-C RNA was detected ≤120 days following the first transfusion in 22 (7.5%) of 294 subjects who were GBV-C negative before transfusion. The risk of GBV-C RNA acquisition increased with each unit transfused (odds ratio, 1.09; 95% confidence interval, 1.06-1.11). Lower baseline HIV load and use of antiretroviral therapy were associated with subsequent GBV-C RNA acquisition, after control for units of blood transfused. Leukoreduced status of transfused units was not associated with GBV-C transmission.

CONCLUSIONS

Blood transfusion is associated with a significant risk of GBV-C acquisition among HIV-infected patients. Transmission of GBV-C by blood transfusion was inversely related to HIV load.

GB virus C: the good boy virus?

GB virus C (GBV-C) is a lymphotropic human virus discovered in 1995 that is related to hepatitis C virus (HCV). GBV-C infection has not been convincingly associated with any disease; however, several studies found an association between persistent GBV-C infection and improved survival in HIV-positive individuals. GBV-C infection modestly alters T cell homeostasis in vivo through various mechanisms, including modulation of chemokine and cytokine release and receptor expression, and by diminution of T cell activation, proliferation and apoptosis, all of which may contribute to improved HIV clinical outcomes. In vitro studies confirm these clinical observations and demonstrate an anti-HIV replication effect of GBV-C. This review summarizes existing data on potential mechanisms by which GBV-C interferes with HIV, and the research needed to capitalize on this epidemiological observation.

The GB virus C (GBV-C) NS3 serine protease inhibits HIV-1 replication in a CD4+ T lymphocyte cell line without decreasing HIV receptor expression

INTRODUCTION

Persistent infection with GBV-C (GB Virus C), a non-pathogenic virus related to hepatitis C virus (HCV), prolongs survival in HIV infection. Two GBV-C proteins, NS5A and E2, have been shown previously to inhibit HIV replication in vitro. We investigated whether the GBV-C NS3 serine protease affects HIV replication.

RESULTS

GBV-C NS3 protease expressed in a human CD4+ T lymphocyte cell line significantly inhibited HIV replication. Addition of NS4A or NS4A/4B coding sequence to GBV-C NS3 increased the effect on HIV replication. Inhibition of HIV replication was dose-dependent and was not mediated by increased cell toxicity. Mutation of the NS3 catalytic serine to alanine resulted in loss of both HIV inhibition and protease activity. GBV-C NS3 expression did not measurably decrease CD4 or CXCR4 expression.

CONCLUSION

GBV-C NS3 serine protease significantly inhibited HIV replication without decreasing HIV receptor expression. The requirement for an intact catalytic serine at the active site indicates that inhibition was mediated by proteolytic cleavage of an unidentified target(s).

Improving potencies and properties of CD4 down-modulating CADA analogs

INTRODUCTION

CADA is a synthetic small molecule that inhibits HIV replication in cell cultures through down-modulating cell surface CD4 by inhibiting cotranslational translocation of nascent CD4 across the ER membrane in a signal sequence-specific manner. Analogs have been prepared mainly to increase potency and investigate the mechanism of action.

AREAS COVERED

This article reviews progress on discovery of more potent CADA analogs, including symmetrical and unsymmetrical compounds, as well as fluorescent derivatives. The article also discusses some properties of CADA and a more potent analog (KKD023) that are relevant to drug development, including aqueous solubility, permeability, metabolism and oral bioavailability.

EXPERT OPINION

Further studies on CADA analogs should focus on improving both potency and drug-like properties, and on elucidating the detailed mechanism of action. Solubility and permeability may be improved by reducing molecular weight, decreasing molecular flexibility and symmetry, or by a prodrug approach inducing active transport. Identifying the molecular mechanism of CD4 down-modulation may aid in assessing potential side effects of such immunomodulatory/anti-HIV drugs, and it could potentially lead to a general approach to designing drugs for specifically down-modulating other cell-surface proteins.

Unsymmetrical cyclotriazadisulfonamide (CADA) compounds as human CD4 receptor down-modulating agents

Cyclotriazadisulfonamide (CADA) inhibits HIV at submicromolar levels by specifically down-modulating cell-surface and intracellular CD4. The specific biomolecular target of CADA compounds is unknown, but previous studies led to an unsymmetrical binding model. To test this model, methods were developed for effective synthesis of diverse, unsymmetrical CADA compounds. A total of 13 new, unsymmetrical target compounds were synthesized, as well as one symmetrical analogue. The new compounds display a wide range of potency for CD4 down-modulation in CHO·CD4-YFP cells. VGD020 (IC(50) = 46 nM) is the most potent CADA compound discovered to date, and VGD029 (IC(50) = 730 nM) is the most potent fluorescent analogue. Structure-activity relationships are analyzed from the standpoint of additive or nonadditive energy effects of different substituents. They appear to be consistent with the zipper-type mechanism in which entropy costs are reduced for additional stabilizing interactions between the small molecule and its protein target.

Yellow fever 17D-vectored vaccines expressing Lassa virus GP1 and GP2 glycoproteins provide protection against fatal disease in guinea pigs

Yellow Fever (YF) and Lassa Fever (LF) are two prevalent hemorrhagic fevers co-circulating in West Africa and responsible for thousands of deaths annually. The YF vaccine 17D has been used as a vector for the Lassa virus glycoprotein precursor (LASV-GPC) or their subunits, GP1 (attachment glycoprotein) and GP2 (fusion glycoprotein). Cloning shorter inserts, LASV-GP1 and -GP2, between YF17D E and NS1 genes enhanced genetic stability of recombinant viruses, YF17D/LASV-GP1 and -GP2, in comparison with YF17D/LASV-GPC recombinant. The recombinant viruses were replication competent and properly processed YF proteins and LASV GP antigens in infected cells. YF17D/LASV-GP1 and -GP2 induced specific CD8+ T cell responses in mice and protected strain 13 guinea pigs against fatal LF. Unlike immunization with live attenuated reassortant vaccine ML29, immunization with YF17D/LASV-GP1 and -GP2 did not provide sterilizing immunity. This study demonstrates the feasibility of YF17D-based vaccine to control LF in West Africa.

GB virus C coinfection in advanced HIV type-1 disease is associated with low CCR5 and CXCR4 surface expression on CD4(+) T-cells

BACKGROUND

Coinfection with the flavivirus GB virus C (GBV-C) is frequent in patients suffering from HIV type-1 (HIV-1) infection because of shared routes of transmission. GBV-C coinfection has been proposed to exert a beneficial influence on HIV-1 infection. In vitro studies demonstrated down-regulation of C-C chemokine receptor type 5 (CCR5) as a potential mechanism by which GBV-C modulates HIV-1 disease progression. We therefore studied surface expression of the two major HIV-1 coreceptors, CCR5 and CXC chemokine receptor type 4 (CXCR4), on CD4(+) and CD8(+) T-cells in 128 HIV-1-positive patients stratified with respect to their GBV-C status, immune function and highly active antiretroviral therapy (HAART) status in vivo.

METHODS

GBV-C infection was studied in 128 HIV-1-infected patients by nested reverse transcriptase PCR. Fluorescence-activated cell sorting analysis was used to measure CCR5 and CXCR4 surface expression on CD4(+) and CD8(+) T-cells.

RESULTS

GBV-C RNA replication was detected in 30% (38/128) of patients. In HIV-1-positive patients with advanced immunodeficiency, we found up-regulation of CCR5 surface expression on CD4(+) T-cells; however, in patients with GBV-C coinfection, no up-regulation of CCR5 CD4(+) T-cells was detected. Furthermore, CXCR4 surface expression was reduced in GBV-C-coinfected patients. These findings were independent of HAART status and HIV-1 viral load. HIV-1 coreceptor expression on CD8(+) T-cells was not altered in patients with GBV-C coinfection.

CONCLUSIONS

GBV-C coinfection in HIV-1 disease leads to reduced expression of the two major HIV-1 coreceptors, CCR5 and CXCR4, on CD4(+) T-cells in patients at an advanced stage of immunodeficiency, providing a possible molecular explanation for the clinical benefit of GBV-C coinfection in late-stage HIV-1 disease.

Semen protects CD4+ target cells from HIV infection but promotes the preferential transmission of R5 tropic HIV

Sexual intercourse is the major means of HIV transmission, yet the impact of semen on HIV infection of CD4(+) T cells remains unclear. To resolve this conundrum, we measured CD4(+) target cell infection with X4 tropic HIV IIIB and HC4 and R5 tropic HIV BaL and SF162 after incubation with centrifuged seminal plasma (SP) from HIV-negative donors and assessed the impact of SP on critical determinants of target cell susceptibility to HIV infection. We found that SP potently protects CD4(+) T cells from infection with X4 and R5 tropic HIV in a dose- and time-dependent manner. SP caused a diminution in CD4(+) T cell surface expression of the HIVR CD4 and enhanced surface expression of the HIV coreceptor CCR5. Consequently, SP protected CD4(+) T cells from infection with R5 tropic HIV less potently than it protected CD4(+) T cells from infection with X4 tropic HIV. SP also reduced CD4(+) T cell activation and proliferation, and the magnitude of SP-mediated suppression of target cell CD4 expression, activation, and proliferation correlated closely with the magnitude of the protection of CD4(+) T cells from infection with HIV. Taken together, these data show that semen protects CD4(+) T cells from HIV infection by restricting critical determinants of CD4(+) target cell susceptibility to HIV infection. Further, semen contributes to the selective transmission of R5 tropic HIV to CD4(+) target cells.