Human dendritic cells transduced with herpes simplex virus amplicons encoding human immunodeficiency virus type 1 (HIV-1) gp120 elicit adaptive immune responses from human cells engrafted into NOD/SCID mice and confer partial protection against HIV-1 challenge

The Quest for Immunity: Exploring Human Herpesviruses as Vaccine Vectors

Herpesviruses are large DNA viruses that have long been used as powerful gene therapy tools. In recent years, the ability of herpesviruses to stimulate both innate and adaptive immune responses has led to their transition to various applications as vaccine vectors. This vaccinology branch is growing at an unprecedented and accelerated rate. To date, human herpesvirus-based vectors have been used in vaccines to combat a variety of infectious agents, including the Ebola virus, foot and mouth disease virus, and human immunodeficiency viruses. Additionally, these vectors are being tested as potential vaccines for cancer-associated antigens. Thanks to advances in recombinant DNA technology, immunology, and genomics, numerous steps in vaccine development have been greatly improved. A better understanding of herpesvirus biology and the interactions between these viruses and the host cells will undoubtedly foster the use of herpesvirus-based vaccine vectors in clinical settings. To overcome the existing drawbacks of these vectors, ongoing research is needed to further advance our knowledge of herpesvirus biology and to develop safer and more effective vaccine vectors. Advanced molecular virology and cell biology techniques must be used to better understand the mechanisms by which herpesviruses manipulate host cells and how viral gene expression is regulated during infection. In this review, we cover the underlying molecular structure of herpesviruses and the strategies used to engineer their genomes to optimize capacity and efficacy as vaccine vectors. Also, we assess the available data on the successful application of herpesvirus-based vaccines for combating diseases such as viral infections and the potential drawbacks and alternative approaches to surmount them.

Use of Hu-PBL Mice to Study Pathogenesis of Human-Restricted Viruses

Different humanized mouse models have been developed to study human diseases such as autoimmune illnesses, cancer and viral infections. These models are based on the use of immunodeficient mouse strains that are transplanted with human tissues or human immune cells. Among the latter, mice transplanted with hematopoietic stem cells have been widely used to study human infectious diseases. However, mouse models built upon the transplantation of donor-specific mature immune cells are still under development, especially in the field of viral infections. These models can retain the unique immune memory of the donor, making them suitable for the study of correlates of protection upon natural infection or vaccination. Here, we will review some of these models and how they have been applied to virology research. Moreover, the future applications and the potential of these models to design therapies against human viral infections are discussed.

Murine Bone Marrow-Derived Dendritic Cells Transduced by Light-Helper-Dependent Herpes Simplex Virus-1 Amplicon Vector Acquire a Mature Dendritic Cell Phenotype

Dendritic cells (DCs) turn into the most potent antigen-presenting cells following a complex transforming process, which leads to their maturation. Herpes simplex virus-1 (HSV-1) amplicon vectors represent highly versatile viral vector platforms with the ability to transduce immature DCs at exceedingly high efficiencies, while the efficiency of infection of mature DCs is significantly low. However, the bacterial artificial chromosome (BAC)-dependent (BD) amplicon vectors tested so far do not result in the maturation of mouse bone marrow-derived DCs (BMDCs) in vitro. In this study we investigated the effects of light-helper-dependent (LHD) amplicon vectors produced with the replication-defective HSV-1 LaLΔJ helper virus system. First, we observed that transgene expression in BMDC cultures was equally potent between the LHD and the BD amplicon vectors. We determined that the percentage of transduced cells and the duration of transgene expression were negatively influenced by the presence of increasing levels of helper virus. Second, infection by the LHD amplicon vector as well as the helper HSV-1 LaLΔJ virus alone resulted in the phenotypic maturation of BMDCs and the expression of both interferon-stimulated genes and proinflammatory cytokines. Further comparisons of the gene expression of infected DCs showed that while interferon-stimulated genes such as Ifit1, Ifit3, Mx2, Isg15, and Cxcl10 were induced by both BD and LHD amplicon vectors, early proinflammatory cytokine gene expression (Tnfa, Il1a, Il1b, Il6, Il10, Il12b, Cxcl1, and Cxcl16) and DC maturation were mediated only by the LHD amplicons.

Humanized mice: novel model for studying mechanisms of human immune-based therapies

The lack of relevant animal models is the major bottleneck for understanding human immunology and immunopathology. In the last few years, a novel model of humanized mouse has been successfully employed to investigate some of the most critical questions in human immunology. We have set up and tested in our laboratory the latest technology for generating mice with a human immune system by reconstituting newborn immunodeficient NOD/SCID-γ(c)(-/-) mice with human fetal liver-derived hematopoietic stem cells. These humanized mice have been deemed most competent as human models in a thorough comparative study with other humanized mouse technologies. Lymphocytes in these mice are of human origin while other hematopoietic cells are chimeric, partly of mouse and partly of human origin. We demonstrate that human CD8 T lymphocytes in humanized mice are fully responsive to our novel cell-based secreted heat shock protein gp96(HIV)-Ig vaccine. We also show that the gp96(HIV)-Ig vaccine induces powerful mucosal immune responses in the rectum and the vagina, which are thought to be required for protection from HIV infection. We posit the hypothesis that vaccine approaches tested in humanized mouse models can generate data rapidly, economically and with great flexibility (genetic manipulations are possible), to be subsequently tested in larger nonhuman primate models and humans.

Antiviral peptide nanocomplexes as a potential therapeutic modality for HIV/HCV co-infection

It is estimated that 4 to 5 million people are currently co-infected with Human Immunodeficiency Virus (HIV) and Hepatitis C Virus (HCV). HIV/HCV co-infection is associated with unique health risks including increased hepatotoxicity of antiretrovirals, accelerated progression of HCV and liver diseases. The standard interferon-based therapy is effective only in about 50% of patients and often is associated with autoimmune and neuro-psychiatric complications. The treatment of co-infection (HIV/HCV) requires new strategic approaches. To this end, the formulations of an amphiphatic α-helical peptide, a positively charged analog of C5A peptide derived from the HCV NS5A protein, with a reported virocidal activity were prepared by electrostatic coupling with anionic poly(amino acid)-based block copolymers. The self-assembled antiviral peptide nanocomplexes (APN) were ca. 35 nm in size, stable at physiological pH and ionic strength, and retained in vitro antiviral activity against HCV and HIV. Moreover, incorporation of the peptide into APN attenuated its cytotoxicity associated with the positive charge. In vivo APN were able to decrease the viral load in mice transplanted with human lymphocytes and HIV-1-infected. Overall, these findings indicate the potential of these formulations for stabilization and delivery of antiviral peptides while maintaining their functional activity.

Platelet-derived growth factor (PDGF)-BB-mediated induction of monocyte chemoattractant protein 1 in human astrocytes: implications for HIV-associated neuroinflammation

Chemokine (C-C motif) ligand 2, also known as monocyte chemoattractant protein 1 (MCP-1) is an important factor for the pathogenesis of HIV-associated neurocognitive disorders (HAND). The mechanisms of MCP-1-mediated neuropathogenesis, in part, revolve around its neuroinflammatory role and the recruitment of monocytes into the central nervous system (CNS) via the disrupted blood-brain barrier (BBB). We have previously demonstrated that HIV-1/HIV-1 Tat upregulate platelet-derived growth factor (PDGF)-BB, a known cerebrovascular permeant; subsequently, the present study was aimed at exploring the regulation of MCP-1 by PDGF-BB in astrocytes with implications in HAND. Specifically, the data herein demonstrate that exposure of human astrocytes to HIV-1 LAI elevated PDGF-B and MCP-1 levels. Furthermore, treating astrocytes with the human recombinant PDGF-BB protein significantly increased the production and release of MCP-1 at both the RNA and protein levels. MCP-1 induction was regulated by activation of extracellular-signal-regulated kinase (ERK)1/2, c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein (MAP) kinases and phosphatidylinositol 3-kinase (PI3K)/Akt pathways and the downstream transcription factor, nuclear factor κB (NFκB). Chromatin immunoprecipitation (ChIP) assays demonstrated increased binding of NFκB to the human MCP-1 promoter following PDGF-BB exposure. Conditioned media from PDGF-BB-treated astrocytes increased monocyte transmigration through human brain microvascular endothelial cells (HBMECs), an effect that was blocked by STI-571, a tyrosine kinase inhibitor (PDGF receptor (PDGF-R) blocker). PDGF-BB-mediated release of MCP-1 was critical for increased permeability in an in vitro BBB model as evidenced by blocking antibody assays. Since MCP-1 is linked to disease severity, understanding its modulation by PDGF-BB could aid in understanding the proinflammatory responses in HAND. These results suggest that astrocyte activation by PDGF-BB exaggerates monocyte recruitment into the brain via MCP-1 and underscores the critical role astrocytes play in HAND.

Pharmacodynamic and antiretroviral activities of combination nanoformulated antiretrovirals in HIV-1-infected human peripheral blood lymphocyte-reconstituted mice

Lack of adherence, inaccessibility to viral reservoirs, long-term drug toxicities, and treatment failures are limitations of current antiretroviral therapy (ART). These limitations lead to increased viral loads, medicine resistance, immunocompromise, and comorbid conditions. To this end, we developed long-acting nanoformulated ART (nanoART) through modifications of existing atazanavir, ritonavir, and efavirenz suspensions in order to establish cell and tissue drug depots to achieve sustained antiretroviral responses. NanoART's abilities to affect immune and antiviral responses, before or following human immunodeficiency virus type 1 infection were tested in nonobese severe combined immune-deficient mice reconstituted with human peripheral blood lymphocytes. Weekly subcutaneous injections of drug nanoformulations at doses from 80 mg/kg to 250 mg/kg, 1 day before and/or 1 and 7 days after viral exposure, elicited drug levels that paralleled the human median effective concentration, and with limited toxicities. NanoART treatment attenuated viral replication and preserved CD4(+) Tcell numbers beyond that seen with orally administered native drugs. These investigations bring us one step closer toward using long-acting antiretrovirals in humans.

HSV-1 amplicon vectors launch the production of heterologous rotavirus-like particles and induce rotavirus-specific immune responses in mice

Virus-like particles (VLPs) are promising vaccine candidates because they represent viral antigens in the authentic conformation of the virion and are therefore readily recognized by the immune system. As VLPs do not contain genetic material they are safer than attenuated virus vaccines. In this study, herpes simplex virus type 1 (HSV-1) amplicon vectors were constructed to coexpress the rotavirus (RV) structural genes VP2, VP6, and VP7 and were used as platforms to launch the production of RV-like particles (RVLPs) in vector-infected mammalian cells. Despite the observed splicing of VP6 RNA, full-length VP6 protein and RVLPs were efficiently produced. Intramuscular injection of mice with the amplicon vectors as a two-dose regimen without adjuvants resulted in RV-specific humoral immune responses and, most importantly, immunized mice were partially protected at the mucosal level from challenge with live wild-type (wt) RV. This work provides proof of principle for the application of HSV-1 amplicon vectors that mediate the efficient production of heterologous VLPs as genetic vaccines.

Current trends in negative immuno-synergy between two sexually transmitted infectious viruses: HIV-1 and HSV-1/2

In the current era of effective anti-retroviral therapy, immuno-compromised patients with HIV-1 infection do live long enough to suffer diseases caused by many opportunistic infections, such as herpes simplex virus type 1 and/or type 2 (HSV-1/2). An estimated two-third of the 40 million individuals that have contracted HIV-1 worldwide are co-infected with HSV-1/2 viruses, the causative agents of ocular oro-facial and genital herpes. The highest prevalence of HIV and HSV-1/2 infections are confined to the same regions of Sub-Saharan Africa. HSV-1/2 infections affect HIV-1 immunity, and vice versa. While important research gains have been made in understanding herpes and HIV immunity, the cellular and molecular mechanisms underlying the crosstalk between HSV-1/2 and HIV co-infection remain to be fully elucidated. Understanding the mechanisms behind the apparent HSV/HIV negative immuno-synergy maybe the key to successful HSV and HIV vaccines; both are currently unavailable. An effective herpes immunotherapeutic vaccine would in turn - indirectly - contribute in reducing HIV epidemic. The purpose of this review is: (i) to summarize the current trends in understanding the negative immuno-crosstalk between HIV and HSV-1/2 infections; and (ii) to discuss the possibility of developing a novel mucosal herpes immunotherapeutic strategy or even a combined or chimeric immunotherapeutic vaccine that simultaneously targets HIV and HSV-1/2 infections. These new trends in immunology of HSV-1/2 and HIV co-infections should become part of current efforts in preventing sexually transmitted infections. The alternative is needed to balance the ethical and financial concerns associated with the rising number of unsuccessful mono-valent clinical vaccine trials.

Preconditioning therapy with lentiviral vector-programmed dendritic cells accelerates the homeostatic expansion of antigen-reactive human T cells in NOD.Rag1-/-.IL-2rγc-/- mice

Dendritic cell (DC)-based immunization is a potent strategy to direct prompt and durable immune responses against viral reactivations after transplantations. Here, we show that overnight lentiviral vector (LV) gene transfer into human monocytes co-expressing granulocyte-macrophage colony stimulating factor and interleukin (IL)-4 induced self-differentiated DCs (SMART-DCs) with stable DC immunophenotype over weeks in culture and secreted several inflammatory cytokines. SMART-DCs injected subcutaneously in immunodeficient NOD.Rag1(-/-).IL2rγ(-/-) (NRG) mice 1 day after LV transduction were stable for a month in vivo. "Conventional" DCs (cDCs) and SMART-DCs were compared with regard to their potency to accelerate the expansion, biodistribution, and antigenic stimulation of autologous human T cells. Peripheral blood cells obtained from human cytomegalovirus (hCMV)-reactive donors and full-length hCMV pp65 antigenic protein or peptides were used. DCs loaded with pp65 were administered subcutaneously into NRG mice as a preconditioning treatment a week prior to intravenous infusion with T cells. Optical imaging analyses demonstrated that in mice preconditioned with SMART-DC-pp65, T cells were directly recruited to the immunization site and subsequently spread to the spleen and other organs. A dramatic expansion of both human CD8(+) and CD4(+) T cells could be observed within a few days after infusion, and this was associated with consistent measurable CD8(+) effector memory T-cell responses against different pp65 epitopes. Thus, this mouse model demonstrates the proof-of-principle for SMART-DCs to accelerate expansion of human lymphocytes, resulting in poly-functional and antigen-specific immune responses against hCMV-pp65.

HIV-1 Tat-mediated induction of platelet-derived growth factor in astrocytes: role of early growth response gene 1

HIV-associated neurologic disorders (HAND) are estimated to affect almost 60% of HIV-infected individuals. HIV encephalitis, the pathologic correlate of the most severe form of HAND, is often characterized by glial activation, cytokine-chemokine dysregulation, and neuronal damage and loss. However, the severity of HIV encephalitis correlates better with glial activation rather than viral load. Using the macaque model, it has been demonstrated that SIV encephalitis correlates with increased expression of the mitogen platelet-derived growth factor (PDGF) B chain in the brain. The goal of this study was to explore the role of PDGF-B chain in HIV-associated activation and proliferation of astrocytes. Specifically, the data demonstrate that exposure of rat and human astrocytes to the HIV-1 protein Tat resulted in the induction of PDGF at both the mRNA and protein levels. Furthermore, PDGF-BB induction was regulated by activation of ERK1/2 and JNK signaling pathways and the downstream transcription factor early growth response 1. Chromatin immunoprecipitation assays demonstrated binding of Egr-1 to the PDGF-B promoter. Exposure of astrocytes to PDGF-BB in turn led to increased proliferation and the release of proinflammatory cytokines MCP-1 and IL-1β. Because astrogliosis is linked to disease severity, understanding its regulation by PDGF-BB could aid in the development of therapeutic intervention strategies for HAND.

Engineered herpes simplex virus vectors for antitumor therapy and vaccine delivery

Genetically modified herpes simplex viruses (HSVs) have been exploited for both antitumor therapy and vaccine delivery. These mutant viruses retain their ability to replicate and lyse permissive cells, including many tumor types, and are referred to as oncolytic HSVs. In addition, deletion of nonessential genes permits the introduction of foreign genes to augment the antitumor effect by either immune stimulation, targeting for select tumors, or expression of tumor or vaccine antigens. This article reviews the development of oncolytic HSVs as an anticancer therapy, as well as the application of HSV-1 vectors for delivery of targeted antigens or as vaccine adjuvants. The impact of these novel vectors with respect to enhanced antitumor activity and development of antitumor vaccination strategies is discussed.

Reconstitution of huPBL-NSG mice with donor-matched dendritic cells enables antigen-specific T-cell activation

Humanized mouse models provide a unique opportunity to study human immune cells in vivo, but traditional models have been limited to the evaluation of non-specific T-cell interactions due to the absence of antigen-presenting cells. In this study, immunodeficient NOD/SCID/IL2r-γ^null (NSG) mice were engrafted with human peripheral blood lymphocytes alone or in combination with donor-matched monocyte-derived dendritic cells (DC) to determine whether antigen-specific T-cell activation could be reconstituted. Over a period of 3 weeks, transferred peripheral blood lymphocytes reconstituted the spleen and peripheral blood of recipient mice with predominantly human CD45-positive lymphocytes. Animals exhibited a relatively normal CD4/CD8 ratio (average 1.63:1) as well as reconstitution of CD3/CD56 (averaging 17.8%) and CD20 subsets (averaging 4.0%). Animals reconstituted with donor-matched CD11c+ DC also demonstrated a CD11c+ population within their spleen, representing 0.27% to 0.43% of the recovered human cells with concurrent expression of HLA-DR, CD40, and CD86. When immunized with adenovirus, either as free replication-incompetent vector (AdV) or as vector-transduced DC (DC/AdV), there was activation and expansion of AdV-specific T-cells, an increase in Th1 cytokines in serum, and skewing of T-cells toward an effector/memory phenotype. T-cells recovered from animals challenged with AdV in vivo proliferated and secreted a Th1-profile of cytokines in response to DC/AdV challenge in vitro. Our results suggest that engrafting NSG mice with a combination of lymphocytes and donor-matched DC can reconstitute antigen responsiveness and allow the in vivo assessment of human immune response to viruses, vaccines, and other immune challenges.

CD8+ cell depletion accelerates HIV-1 immunopathology in humanized mice

Stable engraftment of human lymphoid tissue in NOD/scid-IL-2Rgammacnull mice after CD34+ hematopoietic stem cell reconstitution permits the evaluation of ongoing HIV-1 infection for weeks to months. We demonstrate that HIV-1-infected rodents develop virus-specific cellular immune responses. CD8+ cell depletion, 2 or 5-7 wk after viral infection, resulted in a significant increase of HIV-1 load, robust immune cell activation, and cytopathology in lymphoid tissues but preserved CD4/CD8 double-positive thymic T cell pools. Human CD8+ cells reappeared in circulation as early as 2-3 wk. These data support a role of CD8+ cells in viral surveillance and the relevance of this humanized mouse model for the studies of HIV-1 pathobiology and virus-specific immunity.

The role of dendritic cells in alphaherpesvirus infections: archetypes and paradigms

Dendritic cells (DCs) play a critical role in orchestrating both innate and adaptive components of the immune system and are therefore of pivotal importance in the initiation of immune responses to control and eliminate viral infections. A major focus of this review is to give an overview on the recent findings that point out the importance of DCs in controlling alphaherpesvirus infections, but also indicate that these viruses have evolved several strategies to inhibit and/or exploit DC functions to delay or escape elimination by the immune system. In addition, we point out the common features and interspecies differences between DCs from man and animal, and discuss the potential use of animal alphaherpesvirus homologues to gain further insights into the interaction between alphaherpesviruses and DCs in their natural virus-host environment. Finally, recent knowledge on the potential of alphaherpesviruses as vectors for DC stimulation and their use for immunotherapy is presented.

Herpes Virus Amplicon Vectors

Since its emergence onto the gene therapy scene nearly 25 years ago, the replication-defective Herpes Simplex Virus Type-1 (HSV-1) amplicon has gained significance as a versatile gene transfer platform due to its extensive transgene capacity, widespread cellular tropism, minimal immunogenicity, and its amenability to genetic manipulation. Herein, we detail the recent advances made with respect to the design of the HSV amplicon, its numerous in vitro and in vivo applications, and the current impediments this virus-based gene transfer platform faces as it navigates a challenging path towards future clinical testing.

Induction of robust cellular and humoral virus-specific adaptive immune responses in human immunodeficiency virus-infected humanized BLT mice

The generation of humanized BLT mice by the cotransplantation of human fetal thymus and liver tissues and CD34(+) fetal liver cells into nonobese diabetic/severe combined immunodeficiency mice allows for the long-term reconstitution of a functional human immune system, with human T cells, B cells, dendritic cells, and monocytes/macrophages repopulating mouse tissues. Here, we show that humanized BLT mice sustained high-level disseminated human immunodeficiency virus (HIV) infection, resulting in CD4(+) T-cell depletion and generalized immune activation. Following infection, HIV-specific humoral responses were present in all mice by 3 months, and HIV-specific CD4(+) and CD8(+) T-cell responses were detected in the majority of mice tested after 9 weeks of infection. Despite robust HIV-specific responses, however, viral loads remained elevated in infected BLT mice, raising the possibility that these responses are dysfunctional. The increased T-cell expression of the negative costimulator PD-1 recently has been postulated to contribute to T-cell dysfunction in chronic HIV infection. As seen in human infection, both CD4(+) and CD8(+) T cells demonstrated increased PD-1 expression in HIV-infected BLT mice, and PD-1 levels in these cells correlated positively with viral load and inversely with CD4(+) cell levels. The ability of humanized BLT mice to generate both cellular and humoral immune responses to HIV will allow the further investigation of human HIV-specific immune responses in vivo and suggests that these mice are able to provide a platform to assess candidate HIV vaccines and other immunotherapeutic strategies.

Genetic engineering of a modified herpes simplex virus 1 vaccine vector

The herpes simplex virus 1 (HSV-1) d106 mutant virus is a multiple immediate-early gene deletion mutant virus that has been effective as an AIDS vaccine vector in rhesus macaques (Kaur A, Sanford HB, Garry D, Lang S, Klumpp SA, Watanabe D, et al. Ability of herpes simplex virus vectors to boost immune responses to DNA vectors and to protect against challenge by simian immunodeficiency virus. Virology 2007;357:199-214). Further analysis of this vector is needed to advance development into clinical trials. In this study we have defined the precise nature of the multiple IE gene mutations in the d106 viral genome and have used this information to construct a new transfer plasmid for gene transfer into d106. We tested the effect of an additional mutation in the U(L)41 gene on d106 immunogenicity and found that it did not improve the efficacy of the d106 vector, in contrast with results from other studies with U(L)41 gene mutants. The safety profile of d106 was improved by generating a new vector strain, d106S, with increased sensitivity to acyclovir. Finally, we have constructed a d106S recombinant vector that expresses the HIV clade C envelope protein. The d106S HIVenvC recombinant has retained the sensitivity to acyclovir, indicating that this phenotype is a stable property of the d106S vector.

Murine models for HIV vaccination and challenge

HIV-1 only infects humans and chimpanzees. SIV or SHIV are, therefore, used as models for HIV in rhesus, cynomologus and pigtail macaques. Since conducting experiments in primate models does not fully mimic infection or vaccination against HIV-1 and is expensive, there is a great need for small-animal models in which it is possible to study HIV-1 infection, immunity and vaccine efficacy. This review summarizes the available murine models for studying HIV-1 infection with an emphasis on our experience of the HIV-1-infected-cell challenge as a model for evaluating candidate HIV-1 vaccines. In the cell-based challenge model, several important factors that, hopefully, can be related to vaccine efficacy in humans were discovered: the efficiency of combining plasmid DNA representing several of the viral genes originating from multiple clades of HIV-1, the importance of adjuvants activating innate and induced immunity and the enhanced HIV eradication by drug-conjugated antibody.

Humanized mice for human retrovirus infection

Inbred mice with specific genetic defects have greatly facilitated the analysis of complex biological events. Several humanized mouse models using the C.B.-17 scid/scid mouse (referred to as the SCID mouse) have been created from two transplantation protocols, and these mice have been utilized for the investigation of human immunodeficiency virus type 1 (HIV-1) and human T-lymphotropic virus type I (HTLV-I) pathogenesis and the evaluation of antiviral compounds. To generate a more prominent small animal model for human retrovirus infection, especially for examination of the pathological process and the immune reaction, a novel immunodeficient mouse strain derived from the NOD SCID mouse was created by backcrossing with a common gamma chain (gamma(c))-knockout mouse. The NOD-SCID gamma(c)null (NOG) mouse has neither functional T and B cells nor NK cells and has been used as a recipient in humanized mouse models for transplantation of human immune cells particularly including hematopoietic stem cells (HSC). From recent advances in development of humanized mice, we are now able to provide a new version of the animal model for human retrovirus infection and human immunity.

HSV-1 amplicon vectors: a promising and versatile tool for gene delivery

Amplicons are defective and non-integrative vectors derived from herpes simplex virus type 1. They carry no virus genes in the vector genome and are, therefore, not toxic to the infected cells or pathogenic for the transduced organisms, making these vectors safe. In addition, the large transgenic capacity of amplicons, which allow delivery of < or = 150 Kbp of foreign DNA, make these vectors one of the most powerful, interesting and versatile gene delivery platforms. Here, the authors present recent technological developments that have significantly improved and extended the use of amplicons, both in cultured cells and in living organisms. In addition, this review illustrates the many possible applications that are presently being developed with amplicons and discuss the many difficulties still pending to be solved in order to achieve stable and physiologically regulated transgenic expression.

HIV-1(89.6) Gag expressed from a replication competent HSV-1 vector elicits persistent cellular immune responses in mice

We have constructed a replication competent, gamma(1)34.5-deleted herpes simplex virus type-1 (HSV-1) vector (J200) that expresses the gag gene from human immunodeficiency virus type-1, primary isolate 89.6 (HIV-1(89.6)), as a candidate vaccine for HIV-1. J200 replicates in vitro, resulting in abundant Gag protein production and accumulation in the extracellular media. Immunization of Balb/c mice with a single intraperitoneal injection of J200 elicited strong Gag-specific CD8 responses, as measured by intracellular IFN-gamma staining and flow cytometry analysis. Responses were highest between 6 weeks and 4 months, but persisted at 9 months post-immunization, the last time-point evaluated. These data highlight the potential utility of neuroattenuated, replication competent HSV-1 vectors for delivery of HIV-1 immunogens.

Spatial and temporal expression of herpes simplex virus type 1 amplicon-encoded genes: implications for their use as immunization vectors

There is great interest in developing new immunization vectors. Helper virus-free herpes amplicons, plasmid-based vectors that encode no viral gene products and have an extremely large coding capacity, are attractive viral vaccine candidates for expressing recombinant proteins in vivo for immunization. Earlier studies in mice, using amplicons encoding the gp120 protein of human immunodeficiency virus (HIV), resulted in strikingly robust cellular immune responses as measured by cytotoxicity and interferon gamma enzyme-linked immunospot assays. To begin to understand how such vectors function in vivo to generate an immune response, we used amplicons encoding reporter constructs including green fluorescent protein (GFP) and luciferase to examine the duration of expression after administration to mice. Luciferase expression, measured with the IVIS system from Xenogen/Caliper Life Sciences (Hopkinton, MA) and by enzymatic assays of tissue extracts, revealed that expression after injection of the HSVluc amplicons peaked earlier than 24 hr after injection into mice. HSVegfp injection resulted in peak accumulation of GFP 24 hr after administration in vivo. Thus, both reporter genes revealed a rather rapid and robust expression pattern of short duration. The short period of expression appears in part to be due to gene silencing. Examination of the cells transduced by amplicons encoding GFP and human B7.1 suggested that the amplicons transduce a variety of cells, including professional antigen-presenting cells. From this and previous work, we conclude that amplicons may engender a potent immune response by directly transducing dendritic cells as well as by cross-priming of antigen produced by other transduced host cells.

Immunological protection against HPV16 E7-expressing human esophageal cancer cell challenge by a novel HPV16-E6/E7 fusion protein based-vaccine in a Hu-PBL-SCID mouse model

Increasing evidence has suggested that infection with high-risk human papillomavirus (HPVs) is closely associated with esophageal squamous cell carcinoma (ESCC) in China. The E6 and E7 oncoproteins expressed in ESCC are considered as attractive tumor-specific antigen targets for immunotherapy. We have reported that the HPV16 mE6delta/mE7/TBhsp70delta fusion protein vaccination induced powerful anti-tumor immunity against TC-1 tumor cells in a C57BL/6 mouse model. In the present study, we further evaluate the protective efficacy of this fusion protein vaccine using an HPV E7-expressing human ESCC cell line (EC9706) and a Hu-PBL-SCID mouse model. We demonstrated that immunization with the fusion protein vaccine caused significant inhibition of tumor growth with the delay time to tumor detection (tests vs. controls, 16 d vs. 9 d, p<0.01) and much smaller tumor size (p<0.01) in vivo. The inhibitory rate was ca. 69.6%, and 25% of the fusion protein vaccinated-mice remained tumor free by the end of the experiment (42 d). Furthermore, the activated lymphocytes (CD8+) were capable of infiltrating into the tumor site, and much more apoptotic cells along with activation of caspase-3 were observed in the tumors from vaccinated-mice. Also, high expression levels of human IFN-gamma, TNF-alpha, granzyme B and perforin were detected in the tumors from vaccinated-mice. Therefore, we concluded that the HPV16 mE6delta/mE7/TBhsp70delta fusion protein vaccine is able to stimulate cellular-mediated immune response against E7-containing ESCC cells through CD8+-dependent CTL-induced apoptosis in Hu-PBL-SCID mice. These findings provide a scientific basis for HPV E7-expressing ESCC active immunotherapy.

Effect of promoter strength on protein expression and immunogenicity of an HSV-1 amplicon vector encoding HIV-1 Gag

Helper-free herpes simplex virus type-1 (HSV-1) amplicon vectors elicit robust immune responses to encoded proteins, including human immunodeficiency virus type-1 (HIV-1) antigens. To improve this vaccine delivery system, seven amplicon vectors were constructed, each encoding HIV-1 Gag under the control of a different promoter. Gag expression levels were analyzed in murine and human cell lines, as well as in biopsied tissue samples from injected mice; these data were then compared with Gag-specific T cell responses in BALB/c mice. The magnitude of the amplicon-induced immune response was found to correlate strongly with the level of Gag production both in vitro and in vivo. Interestingly, the best correlation of the strength of the amplicon-induced immune response was with antigen expression in cultured DC rather than expression at the tissue site of injection or in cultured cell lines. These findings may have implications for the generation of improved HSV-1 amplicon vectors for HIV-1 vaccine delivery.

Properties of a herpes simplex virus multiple immediate-early gene-deleted recombinant as a vaccine vector

Herpes simplex virus (HSV) recombinants induce durable immune responses in rhesus macaques and mice and have induced partial protection in rhesus macaques against mucosal challenge with virulent simian immunodeficiency virus (SIV). In this study, we evaluated the properties of a new generation HSV vaccine vector, an HSV-1 multiple immediate-early (IE) gene deletion mutant virus, d106, which contains deletions in the ICP4, ICP27, ICP22, and ICP47 genes. Because several of the HSV IE genes have been implicated in immune evasion, inactivation of the genes encoding these proteins was expected to result in enhanced immunogenicity. The d106 virus expresses few HSV gene products and shows minimal cytopathic effect in cultured cells. When d106 was inoculated into mice, viral DNA accumulated at high levels in draining lymph nodes, consistent with an ability to transduce dendritic cells and activate their maturation and movement to lymph nodes. A d106 recombinant expressing Escherichia coli beta-galactosidase induced durable beta-gal-specific IgG and CD8(+) T cell responses in naive and HSV-immune mice. Finally, d106-based recombinants have been constructed that express simian immunodeficiency virus (SIV) gag, env, or a rev-tat-nef fusion protein for several days in cultured cells. Thus, d106 shows many of the properties desirable in a vaccine vector: limited expression of HSV gene products and cytopathogenicity, high level expression of transgenes, ability to induce durable immune responses, and an ability to transduce dendritic cells and induce their maturation and migration to lymph nodes.

Development of a macrophage-based nanoparticle platform for antiretroviral drug delivery

Complex dosing regimens, costs, side effects, biodistribution limitations, and variable drug pharmacokinetic patterns have affected the long-term efficacy of antiretroviral medicines. To address these problems, a nanoparticle indinavir (NP-IDV) formulation packaged into carrier bone marrow-derived macrophages (BMMs) was developed. Drug distribution and disease outcomes were assessed in immune-competent and human immunodeficiency virus type 1 (HIV-1)-infected humanized immune-deficient mice, respectively. In the former, NP-IDV formulation contained within BMMs was adoptively transferred. After a single administration, single-photon emission computed tomography, histology, and reverse-phase-high-performance liquid chromatography (RP-HPLC) demonstrated robust lung, liver, and spleen BMMs and drug distribution. Tissue and sera IDV levels were greater than or equal to 50 microM for 2 weeks. NP-IDV-BMMs administered to HIV-1-challenged humanized mice revealed reduced numbers of virus-infected cells in plasma, lymph nodes, spleen, liver, and lung, as well as, CD4(+) T-cell protection. We conclude that a single dose of NP-IDV, using BMMs as a carrier, is effective and warrants consideration for human testing.

DENDRITIC CELL-DERIVED EXOSOMES CONTAINING MILK FAT GLOBULE EPIDERMAL GROWTH FACTOR-FACTOR VIII ATTENUATE PROINFLAMMATORY RESPONSES IN SEPSIS

In sepsis, several cell types (e.g., lymphocytes) undergo apoptosis and have the potential to harm the host if not cleared by professional phagocytes. Apoptotic cells display "eat me" signals such as phosphatidylserine that can be readily recognized by phagocytes. For full engulfment of these cells, binding to integrin alpha(v)beta(3), mediated by the bridging protein, milk fat globule epidermal growth factor-factor VIII (MFG-E8), is necessary. We hypothesized that, in sepsis, phagocytosis of apoptotic cells is impaired due to decreased MFG-E8 expression and that adoptive transfer of exosomes containing MFG-E8 is beneficial. Sepsis was induced in rats by cecal ligation and puncture (CLP) and MFG-E8 expression assessed by Western blot 20 h later. Dendritic cells were generated from bone marrow cells, and secreted exosomes were collected and injected into CLP animals. Plasma cytokines (enzyme-linked immunosorbent assay) and thymocyte apoptosis (TC-Ao, annexin V) were assessed. The ability of peritoneal macrophages from septic animals to engulf apoptotic cells was determined in an ex vivo phagocytosis assay. A 10-day survival study was conducted. Cecal ligation and puncture reduced MFG-E8 protein levels in the spleen and liver by 48% and 70%, respectively, and increased TC-Ao by 1.6-fold. Injection of MFG-E8-containing exosomes, however, led to a 33% reduced detection of TC-Ao, without directly inhibiting apoptosis. In fact, peritoneal macrophages from exosome-treated rats displayed a 2.8-fold increased ability to phagocytose apoptotic thymocytes. Inhibition of MFG-E8 before injection of exosomes completely abrogated the enhanced phagocytosis. Treatment with bone marrow dendritic cell-derived exosomes also reduced plasma tumor necrosis factor alpha and interleukin (IL)-6 levels and improved survival from 44% to 81%. We conclude that, by providing the indispensable factor MFG-E8 for complete engulfment of apoptotic cells, these exosomes lead to an attenuation of the systemic inflammatory response and overall beneficial effect in sepsis.

Replication-defective viruses as vaccines and vaccine vectors

The classical viral vaccine approaches using inactivated virus or live-attenuated virus have not been successful for some viruses, such as human immunodeficiency virus or herpes simplex virus. Therefore, new types of vaccines are needed to combat these infections. Replication-defective mutant viruses are defective for one or more functions that are essential for viral genome replication or synthesis and assembly of viral particles. These viruses are propagated in complementing cell lines expressing the missing gene product; however, in normal cells, they express viral gene products but do not replicate to form progeny virions. As vaccines, these mutant viruses have advantages of both classical types of viral vaccines in being as safe as inactivated virus but expressing viral antigens inside infected cells so that MHC class I and class II presentation can occur efficiently. Replication-defective viruses have served both as vaccines for the virus itself and as a vector for the expression of heterologous antigens. The potential advantages and disadvantages of these vaccines are discussed as well as contrasting them with single-cycle mutant virus vaccines and replicon/amplicon versions of vaccines. Replication-defective viruses have also served as important probes of the host immune response in helping to define the importance of the first round of infected cells in the host immune response, the mechanisms of activation of innate immune response, and the role of the complement pathway in humoral immune responses to viruses.

Mouse models for HIV-1 infection

The generation of small animal models, which preserve the ability for the generation of primary and memory immune responses of the engrafted human immune cells and in which a robust HIV-1 infection may occur, may enable the rapid screening, development and evaluation of HIV-1 protective vaccines and adjuvants. This manuscript reviews the existing mouse HIV-1 models used to study virologic, immunologic and pathogenic aspects of HIV-1 infection and disease and discusses their limitations and advantages, especially in the context of vaccine development, with special focus on the recently developed Trimera-HIV-1 animal model.