Virus Replicon Particles Research Articles

Alphavirus replicon-based enhancement of mucosal and systemic immunity is linked to the innate response generated by primary immunization

Venezuelan equine encephalitis virus replicon particles (VRP) function as an effective systemic, cellular and mucosal adjuvant when codelivered with antigen, and show promise for use as a component in new and existing human vaccine formulations. We show here that VRP are effective at low dose and by intramuscular delivery, two useful features for implementation of VRP as a vaccine adjuvant. In mice receiving a prime and boost with antigen, we found that VRP are required in prime only to produce a full adjuvant effect. This outcome indicates that the events triggered during prime with VRP are sufficient to establish the nature and magnitude of the immune response to a second exposure to antigen. Events induced by VRP in the draining lymph node after prime include robust secretion of many inflammatory cytokines, upregulation of CD69 on leukocytes, and increased cellularity, with a disproportionate increase of a cell population expressing CD11c, CD11b, and F4/80. We show that antigen delivered 24h after administration of VRP does not benefit from an adjuvant effect, indicating that the events which are critical to VRP-mediated adjuvant activity occur within the first 24h. Further studies of the events induced by VRP will help elucidate the mechanism of VRP adjuvant activity and will advance the safe implementation of this adjuvant in human vaccines.

A chimeric alphavirus replicon particle vaccine expressing the hemagglutinin and fusion proteins protects juvenile and infant rhesus macaques from measles.

Measles remains a major cause of child mortality, in part due to an inability to vaccinate young infants with the current live attenuated virus vaccine (LAV). To explore new approaches to infant vaccination, chimeric Venezuelan equine encephalitis/Sindbis virus (VEE/SIN) replicon particles were used to express the hemagglutinin (H) and fusion (F) proteins of measles virus (MV). Juvenile rhesus macaques vaccinated intradermally with a single dose of VEE/SIN expressing H or H and F proteins (VEE/SIN-H or VEE/SIN-H+F, respectively) developed high titers of MV-specific neutralizing antibody and gamma-interferon (IFN-gamma)-producing T cells. Infant macaques vaccinated with two doses of VEE/SIN-H+F also developed neutralizing antibody and IFN-gamma-producing T cells. Control animals were vaccinated with LAV or with a formalin-inactivated measles vaccine (FIMV). Neutralizing antibody remained above the protective level for more than 1 year after vaccination with VEE/SIN-H, VEE/SIN-H+F, or LAV. When challenged with wild-type MV 12 to 17 months after vaccination, all vaccinated juvenile and infant monkeys vaccinated with VEE/SIN-H, VEE/SIN-H+F, and LAV were protected from rash and viremia, while FIMV-vaccinated monkeys were not. Antibody was boosted by challenge in all groups. T-cell responses to challenge were biphasic, with peaks at 7 to 25 days and at 90 to 110 days in all groups, except for the LAV group. Recrudescent T-cell activity coincided with the presence of MV RNA in peripheral blood mononuclear cells. We conclude that VEE/SIN expressing H or H and F induces durable immune responses that protect from measles and offers a promising new approach for measles vaccination. The viral and immunological factors associated with long-term control of MV replication require further investigation.

Acute Infection with Venezuelan Equine Encephalitis Virus Replicon Particles Catalyzes a Systemic Antiviral State and Protects from Lethal Virus Challenge

The host innate immune response provides a critical first line of defense against invading pathogens, inducing an antiviral state to impede the spread of infection. While numerous studies have documented antiviral responses within actively infected tissues, few have described the earliest innate response induced systemically by infection. Here, utilizing Venezuelan equine encephalitis virus (VEE) replicon particles (VRP) to limit infection to the initially infected cells in vivo, a rapid activation of the antiviral response was demonstrated not only within the murine draining lymph node, where replication was confined, but also within distal tissues. In the liver and brain, expression of interferon-stimulated genes was detected by 1 to 3 h following VRP footpad inoculation, reaching peak expression of >100-fold over that in mock-infected animals. Moreover, mice receiving a VRP footpad inoculation 6, 12, or 24 h prior to an otherwise lethal VEE footpad challenge were completely protected from death, including a drastic reduction in challenge virus titers. VRP pretreatment also provided protection from intranasal VEE challenge and extended the average survival time following intracranial challenge. Signaling through the interferon receptor was necessary for antiviral gene induction and protection from VEE challenge. However, VRP pretreatment failed to protect mice from a heterologous, lethal challenge with vesicular stomatitis virus, yet conferred protection following challenge with influenza virus. Collectively, these results document a rapid modulation of the host innate response within hours of infection, capable of rapidly alerting the entire animal to pathogen invasion and leading to protection from viral disease.

Assessment of Ebola Specific Antibody Responses in Vaccinated Macaques (128.20)

Abstract Ebola virus (EBOV) infection causes severe disease accompanied by high mortality rates. Several vaccine platforms have shown promise in protecting against Ebola exposure; however, there are no licensed vaccines or therapies approved and available for human use. A vaccine approach utilizing Venezuelan equine encephalitis virus (VEE) replicon particles (VRP) expressing filovirus protein(s) was the first vaccine approach that provided complete protection against Marburg infection in non-human primates (NHP). We evaluated the ability of VEE replicons expressing the glycoprotein (GP), nucleoprotein (NP), VP24, VP30, VP35, and VP40 to protect against Ebola Zaire (ZEBOV) exposure in NHP by various routes of administration, intramuscular (IM) versus subcutaneous (SC). To further evaluate protective efficacy, NHP were vaccinated IM or SC with VEE replicon expressing the viral glycoprotein or expressing all six proteins. Protective efficacy was demonstrated in the both cynomolgus macaques and rhesus macaques. Enzyme-Linked ImmunoSorbent Assays (ELISA) were developed using the whole antigen or recombinant Ebola GP to assess vaccine induced immunity against EBOV. The ELISA based assay assessing humoral responses did not accurately predict protection. The protection generated by the VEE replicon expression of Ebola proteins demonstrates the efficacy of the vaccines platform and warrants further evaluation as a human use vaccine. Further studies are needed to develop accurate correlate of immunity assays.

Replicon Particles of Venezuelan Equine Encephalitis Virus as a Reductionist Murine Model for Encephalitis

Venezuelan equine encephalitis virus (VEE) replicon particles (VRP) were used to model the initial phase of VEE-induced encephalitis in the mouse brain. VRP can target and infect cells as VEE, but VRP do not propagate beyond the first infected cell due to the absence of the structural genes. Direct intracranial inoculation of VRP into mice induced acute encephalitis with signs similar to the neuronal phase of wild-type VEE infection and other models of virus-induced encephalitis. Using the previously established VRP-mRNP tagging system, a new method to distinguish the host responses in infected cells from those in uninfected bystander cell populations, we detected a robust and rapid innate immune response in the central nervous system (CNS) by infected neurons and uninfected bystander cells. Moreover, this innate immune response in the CNS compromised blood-brain barrier integrity, created an inflammatory response, and directed an adaptive immune response characterized by proliferation and activation of microglia cells and infiltration of inflammatory monocytes, in addition to CD4(+) and CD8(+) T lymphocytes. Taken together, these data suggest that a naïve CNS has an intrinsic potential to induce an innate immune response that could be crucial to the outcome of the infection by determining the composition and dynamics of the adaptive immune response. Furthermore, these results establish a model for neurotropic virus infection to identify host and viral factors that contribute to invasion of the brain, the mechanism(s) whereby the adaptive immune response can clear the infection, and the role of the host innate response in these processes.

Acute Infection with Venezuelan Equine Encephalitis Virus Replicon Particles Catalyzes a Systemic Antiviral State and Protects from Lethal Virus Challenge

Acute Infection with Venezuelan Equine Encephalitis Virus Replicon Particles Catalyzes a Systemic Antiviral State and Protects from Lethal Virus Challenge

Construction and packaging of Semliki forest virus replicon particles efficiently expressing Influenza A virus (H5N1) hemagglutinin

Construction and packaging of Semliki forest virus replicon particles efficiently expressing Influenza A virus (H5N1) hemagglutinin

An alphavirus replicon-based human metapneumovirus vaccine is immunogenic and protective in mice and cotton rats.

Human metapneumovirus (hMPV) is a recently discovered paramyxovirus that causes upper and lower respiratory tract infections in infants, the elderly, and immunocompromised individuals worldwide. Here, we developed Venezuelan equine encephalitis virus replicon particles (VRPs) encoding hMPV fusion (F) or attachment (G) glycoproteins and evaluated the immunogenicity and protective efficacy of these vaccine candidates in mice and cotton rats. VRPs encoding hMPV F protein, when administered intranasally, induced F-specific virus-neutralizing antibodies in serum and immunoglobulin A (IgA) antibodies in secretions at the respiratory mucosa. Challenge virus replication was reduced significantly in both the upper and lower respiratory tracts following intranasal hMPV challenge in these animals. However, vaccination with hMPV G protein VRPs did not induce neutralizing antibodies or protect animals from hMPV challenge. Close examination of the histopathology of the lungs of VRP-MPV F-vaccinated animals following hMPV challenge revealed no enhancement of inflammation or mucus production. Aberrant cytokine gene expression was not detected in these animals. Together, these results represent an important first step toward the use of VRPs encoding hMPV F proteins as a prophylactic vaccine for hMPV.

The contribution of type I interferon signaling to immunity induced by alphavirus replicon vaccines

The type I interferon (IFN) system is critical for protecting the mammalian host from numerous virus infections and plays a key role in shaping the antiviral adaptive immune response. In this report, the importance of type I IFN signaling was assessed in a mouse model of alphavirus-induced humoral immune induction. Venezuelan equine encephalitis virus replicon particles (VRP) expressing the hemagglutinin (HA) gene from influenza virus (HA-VRP) were used to vaccinate both wildtype (wt) and IFN α/β receptor knockout (RKO) mice. HA-VRP vaccination induced equivalent levels of flu-specific systemic IgG, mucosal IgG, and systemic IgA antibodies in both wt and IFN RKO mice. In contrast, HA-VRP vaccination of IFN RKO mice failed to induce significant levels of flu-specific mucosal IgA antibodies at multiple mucosal surfaces. In the VRP adjuvant system, co-delivery of null VRP with ovalbumin (OVA) protein significantly increased the levels of OVA-specific serum IgG, fecal IgG, and fecal IgA antibodies in both wt and RKO mice, suggesting that type I IFN signaling plays a less significant role in the VRP adjuvant effect. Taken together, these results suggest that (1) at least in regard to IFN signaling, the mechanisms which regulate alphavirus-induced immunity differ when VRP are utilized as expression vectors as opposed to adjuvants, and (2) type I IFN signaling is required for the induction of mucosal IgA antibodies directed against VRP-expressed antigen. These results shed new light on the regulatory networks which promote immune induction, and specifically mucosal immune induction, with alphavirus vaccine vectors.

Nonmucosal Alphavirus Vaccination Stimulates a Mucosal Inductive Environment in the Peripheral Draining Lymph Node

The strongest mucosal immune responses are induced following mucosal Ag delivery and processing in the mucosal lymphoid tissues, and much is known regarding the immunological parameters which regulate immune induction via this pathway. Recently, experimental systems have been identified in which mucosal immune responses are induced following nonmucosal Ag delivery. One such system, footpad delivery of Venezuelan equine encephalitis virus replicon particles (VRP), led to the local production of IgA Abs directed against both expressed and codelivered Ags at multiple mucosal surfaces in mice. In contrast to the mucosal delivery pathway, little is known regarding the lymphoid structures and immunological components that are responsible for mucosal immune induction following nonmucosal delivery. In this study, we have used footpad delivery of VRP to probe the constituents of this alternative pathway for mucosal immune induction. Following nonmucosal VRP delivery, J chain-containing, polymeric IgA Abs were detected in the peripheral draining lymph node (DLN), at a time before IgA detection at mucosal surfaces. Further analysis of the VRP DLN revealed up-regulated alpha4beta7 integrin expression on DLN B cells, expression of mucosal addressin cell adhesion molecule 1 on the DLN high endothelia venules, and production of IL-6 and CC chemokines, all characteristics of mucosal lymphoid tissues. Taken together, these results implicate the peripheral DLN as an integral component of an alternative pathway for mucosal immune induction. A further understanding of the critical immunological and viral components of this pathway may significantly improve both our knowledge of viral-induced immunity and the efficacy of viral-based vaccines.

Alphavirus replicon particles acting as adjuvants promote CD8 + T cell responses to co-delivered antigen

Alphavirus replicon particles induce strong antibody and CD8 + T cell responses to expressed antigens in numerous experimental systems. We have recently demonstrated that Venezuelan equine encephalitis virus replicon particles (VRP) possess adjuvant activity for systemic and mucosal antibody responses. In this report, we demonstrate that VRP induced an increased and balanced serum IgG subtype response to co-delivered antigen, with simultaneous induction of antigen-specific IgG1 and IgG2a antibodies, and increased both systemic and mucosal antigen-specific CD8 + T cell responses, as measured by an IFN-γ ELISPOT assay. Additionally, VRP further increased antigen-specific T cell immunity in an additive fashion following co-delivery with the TLR ligand, CpG DNA. VRP infection led to recruitment of CD8 + T cells into the mucosal compartment, possibly utilizing the mucosal homing receptor, as this integrin was upregulated on CD8 + T cells in the draining lymph node of VRP-infected animals, where VRP-infected dendritic cells reside. This newly recognized ability of VRP to mediate increased T cell response towards co-delivered antigen provides the potential to both define the molecular basis of alphavirus-induced immunity, and improve alphavirus-based vaccines.

Venezuelan equine encephalitis virus replicon particles encoding respiratory syncytial virus surface glycoproteins induce protective mucosal responses in mice and cotton rats.

Respiratory syncytial virus (RSV) is an important viral pathogen that causes severe lower respiratory tract infection in infants, the elderly, and immunocompromised individuals. There are no licensed RSV vaccines to date. To prevent RSV infection, immune responses in both the upper and lower respiratory tracts are required. Previously, immunization with Venezuelan equine encephalitis virus replicon particles (VRPs) demonstrated effectiveness in inducing mucosal protection against various pathogens. In this study, we developed VRPs encoding RSV fusion (F) or attachment (G) glycoproteins and evaluated the immunogenicity and efficacy of these vaccine candidates in mice and cotton rats. VRPs, when administered intranasally, induced surface glycoprotein-specific virus neutralizing antibodies in serum and immunoglobulin A (IgA) antibodies in secretions at the respiratory mucosa. In addition, fusion protein-encoding VRPs induced gamma interferon (IFN-gamma)-secreting T cells in the lungs and spleen, as measured by reaction with an H-2K(d)-restricted CD8(+) T-cell epitope. In animals vaccinated with F protein VRPs, challenge virus replication was reduced below the level of detection in both the upper and lower respiratory tracts following intranasal RSV challenge, while in those vaccinated with G protein VRPs, challenge virus was detected in the upper but not the lower respiratory tract. Close examination of histopathology of the lungs of vaccinated animals following RSV challenge revealed no enhanced inflammation. Immunization with VRPs induced balanced Th1/Th2 immune responses, as measured by the cytokine profile in the lungs and antibody isotype of the humoral immune response. These results represent an important first step toward the use of VRPs encoding RSV proteins as a prophylactic vaccine for RSV.

A Heterologous DNA Prime-Venezuelan Equine Encephalitis Virus Replicon Particle Boost Dengue Vaccine Regimen Affords Complete Protection from Virus Challenge in Cynomolgus Macaques

A candidate vaccine (D1ME-VRP) expressing dengue virus type 1 premembrane and envelope proteins in a Venezuelan equine encephalitis (VEE) virus replicon particle (VRP) system was constructed and tested in conjunction with a plasmid DNA vaccine (D1ME-DNA) expressing identical dengue virus sequences. Cynomolgus macaques were vaccinated with three doses of DNA (DDD), three doses of VRP (VVV group), or a heterologous DNA prime-VRP boost regimen (DDV) using two doses of DNA vaccine and a third dose of VRP vaccine. Four weeks after the final immunization, the DDV group produced the highest dengue virus type 1-specific immunoglobulin G antibody responses and virus-neutralizing antibody titers. Moderate T-cell responses were demonstrated only in DDD- and DDV-vaccinated animals. When vaccinated animals were challenged with live virus, all vaccination regimens showed significant protection from viremia. DDV-immunized animals were completely protected from viremia (mean time of viremia = 0 days), whereas DDD- and VVV-vaccinated animals had mean times of viremia of 0.66 and 0.75 day, respectively, compared to 6.33 days for the control group of animals.

Increased Sensitivity of Radiated Murine Cervical Cancer Tumors to E7 Subunit Vaccine–driven CTL-mediated Killing Induces Synergistic Anti-tumor Activity

The development of therapeutic vaccines has important implications for the treatment of cancer patients. Here we investigate whether human papillomavirus (HPV) E7 subunit vaccines can enhance tumor radioresponse using an established cervical cancer animal model. Radiation plus E7 subunit vaccines improved complete response, cure, and recurrence rates of tumors dramatically compared with single therapy alone. In particular, both components of the E7 subunit vaccines (E7 protein and CpG-oligodeoxynucleotide) were required for the induction of antigen (Ag)-specific cytotoxic T-lymphocyte (CTL) responses and for therapeutic synergy with radiotherapy. Moreover, with combined therapy the radiation dose could be reduced by 16 Gy to achieve an equivalent anti-tumor efficacy to radiation treatment alone. This therapeutic synergy was found to be mediated by CD8(+) CTLs and was concomitant with histological changes (presence of apoptotic bodies and multinucleated giant cells; heavy infiltration of lymphocytes), as determined by in vivo T-cell depletion and histological analysis. Finally, phenotypic changes of radiated tumors and their increased sensitivity to CTL-mediated killing appeared to be responsible for therapeutic synergy. These results show that E7 subunit vaccines act as a potent enhancer of tumor radioresponse and that this is mediated by increased sensitivity of radiated tumors to CTL-mediated killing. This study further suggests that E7-targeted therapeutic vaccines have the potential to improve radiotherapy in patients with cervical cancer.

An Immunogenic and Protective Alphavirus Replicon Particle-Based Dengue Vaccine Overcomes Maternal Antibody Interference in Weanling Mice

A candidate pediatric dengue virus (DENV) vaccine based on nonpropagating Venezuelan equine encephalitis virus replicon particles (VRP) was tested for immunogenicity and protective efficacy in weanling mice in the presence and absence of potentially interfering maternal antibodies. A gene cassette encoding envelope proteins prM and E from mouse-adapted DENV type 2 (DENV2) strain NGC was cloned into a VEE replicon vector and packaged into VRP, which programmed proper in vitro expression and processing of DENV2 envelope proteins upon infection of Vero cells. Primary immunization of 3-week-old weanling BALB/c mice in the footpad with DENV2 VRP resulted in high levels of DENV-specific serum immunoglobulin G antibodies and significant titers of neutralizing antibodies in all vaccinates. A booster immunization 12 weeks after the prime immunization resulted in increased neutralizing antibodies that were sustained for at least 30 weeks. Immunization at a range of doses of DENV2 VRP protected mice from an otherwise-lethal intracranial DENV2 challenge. To model vaccination in the presence of maternal antibodies, weanling pups born to DENV2-immune or DENV2-naïve dams were immunized with either DENV2 VRP or live DENV2 given peripherally. The DENV2 VRP vaccine induced neutralizing-antibody responses in young mice regardless of the maternal immune status. In contrast, live-DENV2 vaccination performed poorly in the presence of preexisting anti-DENV2 antibodies. This study demonstrates the feasibility of a VRP vaccine approach as an early-life DENV vaccine in populations with high levels of circulating DENV antibodies and suggests the utility of VRP-based vaccines in other instances where maternal antibodies make early vaccination problematic.

Alphaviral vector-transduced dendritic cells are successful therapeutic vaccines against neu-overexpressing tumors in wild-type mice.

While dendritic cell (DC) vaccines can protect hosts from tumor challenge, their ability to effectively inhibit the growth of established tumors remains indeterminate. Previously, we have shown that human DCs transduced with Venezuelan equine encephalitis virus replicon particles (VRPs) were potent stimulators of antigen-specific T cells in vitro. Therefore, we investigated the ability of VRP-transduced DCs (VRP-DCs) to induce therapeutic immunity in vivo against tumors overexpressing the neu oncoprotein. Transduction of murine DCs with VRPs resulted in high-level transgene expression, DC maturation and secretion of proinflammatory cytokines. Vaccination with VRP-DCs expressing a truncated neu oncoprotein induced robust neu-specific CD8(+) T cell and anti-neu IgG responses. Furthermore, a single vaccination with VRP-DCs induced the regression of large established tumors in wild-type mice. Interestingly, depletion of CD4(+), but not CD8(+), T cells completely abrogated inhibition of tumor growth following vaccination. Taken together, our results demonstrate that VRP-DC vaccines induce potent immunity against established tumors, and emphasize the importance of the generation of both CD4(+) T cell and B cell responses for efficient tumor inhibition. These findings provide the rationale for future evaluation of VRP-DC vaccines in the clinical setting.

Structure and immunogenicity of alternative forms of the simian immunodeficiency virus gag protein expressed using Venezuelan equine encephalitis virus replicon particles

Venezuelan equine encephalitis virus replicon particles (VRP) were engineered to express different forms of SIV Gag to compare expression in vitro, formation of intra- and extracellular structures and induction of humoral and cellular immunity in mice. The three forms examined were full-length myristylated SIV Gag (Gag myr+), full-length Gag lacking the myristylation signal (Gag myr−) or a truncated form of Gag myr− comprising only the matrix and capsid domains (MA/CA). Comparison of VRP-infected primary mouse embryo fibroblasts, mouse L929 cells and primate Vero cells showed comparable expression levels for each protein, as well as extracellular virus-like particles (VRP-Gag myr+) and distinctive cytoplasmic aggregates (VRP-Gag myr−) with each cell type. VRP were used to immunize BALB/c mice, and immune responses were compared using an interferon (IFN)-γ ELISPOT assay and a serum antibody ELISA. Although all three VRP generated similar levels of IFN-γ-producing cells at 1 week post-boost, at 10 weeks post-boost the MA/CA-VRP-induced response was maintained at a significantly higher level relative to that induced by Gag myr+-VRP. Antibody responses to MA/CA-VRP and Gag myr+-VRP were not significantly different.

Structure and immunogenicity of alternative forms of the simian immunodeficiency virus gag protein expressed using Venezuelan equine encephalitis virus replicon particles

Structure and immunogenicity of alternative forms of the simian immunodeficiency virus gag protein expressed using Venezuelan equine encephalitis virus replicon particles

Structure and immunogenicity of alternative forms of the simian immunodeficiency virus gag protein expressed using Venezuelan equine encephalitis virus replicon particles

Structure and immunogenicity of alternative forms of the simian immunodeficiency virus gag protein expressed using Venezuelan equine encephalitis virus replicon particles

Engineering the Japanese encephalitis virus RNA genome for the expression of foreign genes of various sizes: Implications for packaging capacity and RNA replication efficiency

Using the RNA replication machinery of Japanese encephalitis virus (JEV), the authors have established and characterized three strategies for the expression of foreign genes. Initially, approximately 11 kb genomic RNA was engineered to express heterologous genes of various sizes by preferentially inserting a new cistron at the beginning of the 3' nontranslated variable region. RNA transfection yielded recombinant viruses that initiated foreign gene expression after infecting permissive cells. JEV was capable of packaging recombinant genomes as large as approximately 15 kb. However, larger genome size was inversely correlated with RNA replication efficiency and cytopathogenicity, with no significant change in infectivity. Second, a variety of self-replicating propagation-deficient viral replicons were constructed by introducing one to three in-frame deletions into the ectodomains of all the structural proteins of JEV. These replicons displayed a spectrum of RNA replication efficiency upon transfection, suggesting that remnant transmembrane domains play a suppressive role in this process. Third, the authors generated a panel of stable packaging cell lines (PCLs) providing all three JEV structural proteins in trans. These PCLs efficiently packaged viral replicon RNAs into single-round infectious viral replicon particles. These JEV-based virus/vector systems may provide useful tools for a variety of biological applications, including foreign gene expression, antiviral compound screening, and genetic immunization.