MHC-I-restricted presentation of HIV-1 virion antigens without viral replication

Potentially exposed but uninfected individuals produce cytotoxic and polyfunctional human immunodeficiency virus type 1-specific CD8(+) T-cell responses which can be defined to the epitope level

We measured CD8(+) T-cell responses in 12 potentially exposed but uninfected men who have sex with men by using cytokine flow cytometry. Four of the individuals screened exhibited polyfunctional immune responses to human immunodeficiency virus type 1 Gag or Vif. The minimum cytotoxic T lymphocyte epitope was mapped in one Gag responder.

Differential antigen presentation kinetics of CD8+ T-cell epitopes derived from the same viral protein

The kinetics of peptide presentation by major histocompatibility complex class I (MHC-I) molecules may contribute to the efficacy of CD8+ T cells. Whether all CD8+ T-cell epitopes from a protein are presented by the same MHC-I molecule with similar kinetics is unknown. Here we show that CD8+ T-cell epitopes derived from SIVmac239 Gag are presented with markedly different kinetics. We demonstrate that this discrepancy in presentation is not related to immunodominance but instead is due to differential requirements for epitope generation. These results illustrate that significant differences in presentation kinetics can exist among CD8+ T-cell epitopes derived from the same viral protein.

Enhancement of immunostimulatory properties of exosomal vaccines by incorporation of fusion-competent G protein of vesicular stomatitis virus

Exosomes have been proposed as candidates for therapeutic immunization. The present study demonstrates that incorporation of the G protein of vesicular stomatitis virus (VSV-G) into exosome-like vesicles (ELVs) enhances their uptake and induces the maturation of dendritic cells. Targeting of VSV-G and ovalbumin as a model antigen to the same ELVs increased the cross-presentation of ovalbumin via an endosomal acidification mechanism. Immunization of mice with VSV-G and ovalbumin containing ELVs led to an increased IgG2a antibody response, expansion of antigen-specific CD8 T cells, strong in vivo CTL responses, and protection from challenge with ovalbumin expressing tumor cells. Thus, incorporation of VSV-G and targeting of antigens to ELVs are attractive strategies to improve exosomal vaccines.

A fusion inhibitor prevents spread of immunodeficiency viruses, but not activation of virus-specific T cells, by dendritic cells

Dendritic cells (DCs) play a key role in innate immune responses, and their interactions with T cells are critical for the induction of adaptive immunity. However, immunodeficiency viruses are efficiently captured by DCs and can be transmitted to and amplified in CD4(+) T cells, with potentially deleterious effects on the induction of immune responses. In DC-T-cell cocultures, contact with CD4(+), not CD8(+), T cells preferentially facilitated virus movement to and release at immature and mature DC-T-cell contact sites. This occurred within 5 min of DC-T-cell contact. While the fusion inhibitor T-1249 did not prevent virus capture by DCs or the release of viruses at the DC-T-cell contact points, it readily blocked virus transfer to and amplification in CD4(+) T cells. Higher doses of T-1249 were needed to block the more robust replication driven by mature DCs. Virus accumulated in DCs within T-1249-treated cocultures but these DCs were actually less infectious than DCs isolated from untreated cocultures. Importantly, T-1249 did not interfere with the stimulation of virus-specific CD4(+) and CD8(+) T-cell responses when present during virus-loading of DCs or for the time of the DC-T-cell coculture. These results provide clues to identifying strategies to prevent DC-driven virus amplification in CD4(+) T cells while maintaining virus-specific immunity, an objective critical in the development of microbicides and therapeutic vaccines.

Targeting HIV-1 Gag into the defective ribosomal product pathway enhances MHC class I antigen presentation and CD8+ T cell activation

The main source for endogenous peptides presented by the MHC class I (MHC-I) pathway are de novo-synthesized proteins which are degraded via the ubiquitin proteasome pathway. Different MHC-I Ag pools can be distinguished: first, short-lived defective ribosomal products, which are degraded in concert with or shortly after their synthesis, and, second, functional proteins that enter the standard protein life cycle. To compare the contribution of these two Ag sources to the generation of MHC-I-presented peptides, we established murine cell lines which express as a model Ag the HIV-1 Gag polyprotein fused to ubiquitin (Ub) carrying the epitope SIINFEKL (SL). Gag was expressed either in its wild-type form (UbMGagSL) or as a variant UbRGagSL harboring an N-end rule degron signal. Although UbRGagSL displayed wild-type protein stability, its inherent defective ribosomal products rate observed after proteasome shutdown was increased concomitant with enhanced presentation of the SL epitope. In addition, UbRGagSL induces enhanced T cell stimulation of SL-specific B3Z hybridoma cells as measured in vitro and of adoptively transferred TCR-transgenic OT-1 T cells in vivo. Furthermore, an elevated frequency of SL-specific T cells was detected by IFN-gamma ELISPOT after immunization of naive C57BL/6 mice with UbRGagSL/EL4 cells. These results further underline the role of the defective ribosomal product pathway in adaptive immunity.

Resolution of de novo HIV production and trafficking in immature dendritic cells

The challenge in observing de novo virus production in human immunodeficiency virus (HIV)-infected dendritic cells (DCs) is the lack of resolution between cytosolic immature and endocytic mature HIV gag protein. To track HIV production, we developed an infectious HIV construct bearing a diothiol-resistant tetracysteine motif (dTCM) at the C terminus of HIV p17 matrix within the HIV gag protein. Using this construct in combination with biarsenical dyes, we observed restricted staining of the dTCM to de novo-synthesized uncleaved gag in the DC cytosol. Co-staining with HIV gag antibodies, reactive to either p17 matrix or p24 capsid, preferentially stained mature virions and thus allowed us to track the virus at distinct stages of its life cycle within DCs and upon transfer to neighboring DCs or T cells. Thus, in staining HIV gag with biarsenical dye system in situ, we characterized a replication-competent virus capable of being tracked preferentially within infected leukocytes and observed in detail the dynamic nature of the HIV production and transfer in primary DCs.

Inhibition of HIV-1 transmission in trans from dendritic cells to CD4+ T lymphocytes by natural antibodies to the CRD domain of DC-SIGN purified from breast milk and intravenous immunoglobulins

The present study demonstrates that human breast milk and normal human polyclonal immunoglobulins purified from plasma [intravenous immunoglobulins (IVIg)] contain functional natural immunoglobulin A (IgA) and IgG antibodies directed against the carbohydrate recognition domain (CRD) domain of the dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) molecule, which is involved in the binding of human immunodeficiency virus (HIV)-1 to dendritic cells (DCs). Antibodies to DC-SIGN CRD were affinity-purified on a matrix to which a synthetic peptide corresponding to the N-terminal CRD domain (amino-acid 342-amino-acid 371) had been coupled. The affinity-purified antibodies bound to the DC-SIGN peptide and to the native DC-SIGN molecule expressed by HeLa DC-SIGN+ cells and immature monocyte-derived dendritic cells (iMDDCs), in a specific and dose-dependent manner. At an optimal dose of 200 microg/ml, natural antibodies to DC-SIGN CRD peptide purified from breast milk and IVIg stained 25 and 20% of HeLa DC-SIGN+ cells and 32 and 12% of iMDDCs, respectively. Anti-DC-SIGN CRD peptide antibodies inhibited the attachment of virus to HeLa DC-SIGN by up to 78% and the attachment to iMDDCs by only 20%. Both breast milk- and IVIg-derived natural antibodies to the CRD peptide inhibited 60% of the transmission in trans of HIV-1(JRCSF), an R5-tropic strain, from iMDDCs to CD4+ T lymphocytes. Taken together, these observations suggest that the attachment of HIV to DCs and transmission in trans to autologous CD4+ T lymphocytes occur through two independent mechanisms. Our data support a role of natural antibodies to DC-SIGN in the modulation of postnatal HIV transmission through breast-feeding and in the natural host defence against HIV-1 in infected individuals.

Pathways utilized by dendritic cells for binding, uptake, processing and presentation of antigens derived from HIV-1

The outcome following HIV infection depends on the nature and durability of the HIV-specific T cell response induced initially. The activation of protective T cell responses depends upon dendritic cells (DC), antigen-presenting cells which have the capacity to process and present viral antigens. DC pulsed with aldrithiol-2-inactivated HIV and delivered in vivo were reported to induce immune responses and promote virologic control in chronically HIV-1-infected subjects. To gain an understanding of this phenomenon, we characterized the steps involved in the presentation of antigens derived from aldrithiol-2-treated vs. infectious HIV-1 by DC. Antigen presentation, on both MHC class I and II, was independent of DC-specific ICAM-3-grabbing integrin, DEC-205 and macrophage mannose receptor, C-type lectins expressed by the DC. Inhibitor studies showed that presentation on MHC class I was dependent on viral fusion in a CD4/coreceptor-dependent manner, both at the cell surface and within endosomes, and access to the classical endosomal processing pathway. MHC class II presentation of HIV-associated antigens was dependent on active endocytosis, probably receptor-mediated, and subsequent degradation of virions in acidified endosomes in the DC. Our study brings forth new facts regarding the binding, uptake, and processing of chemically inactivated virions leading to efficient antigen presentation and should aid in the design of more effective HIV vaccines.

Human immunodeficiency virus (HIV) gag antigen-specific T-helper and granule-dependent CD8 T-cell activities in exposed but uninfected heterosexual partners of HIV type 1-infected individuals in North India

Repeated exposure to human immunodeficiency virus (HIV) does not always result in HIV infection, and several cohorts of HIV-exposed but uninfected (EU) individuals have been described. We studied T-helper and granule-dependent cytotoxic T-lymphocyte (CTL) activities in a group of 30 EU partners of HIV type 1 (HIV-1)-infected individuals. HIV-1-specific helper-T-cell activity was studied by measuring the levels of interleukin 2 (IL-2) produced by peripheral blood mononuclear cells (PBMCs) and the granule-dependent CTL activity by measuring the intracellular levels of perforin and granzyme B expression in CD8+ T cells after stimulation with gag p24 antigen. Elevated IL-2 production by PBMCs after p24 stimulation occurred in EU individuals. The levels of perforin and granzyme B expression in CD8+ T cells were also higher among EU individuals than among healthy controls. HIV-specific helper-T-cell and granule-dependent CTL activities inversely correlated with the time since the last unprotected sexual exposure in these individuals. In our cohort, activation of T-helper and granule-dependent CTL activities against HIV might be due to unprotected sexual contact. These results indicate that HIV-1-specific T-cell responses could play a role in protection against acquiring infection in this cohort of EU individuals.

Macrophages transmit human immunodeficiency virus type 1 products to CD4-negative cells: involvement of matrix metalloproteinase 9

It was previously reported that human immunodeficiency virus type 1 (HIV-1) spreads in CD4 lymphocytes through cell-to-cell transmission. Here we report that HIV-1-infected macrophages, but not lymphocytes, transmit HIV-1 products to CD4-negative cells of either epithelial, neuronal, or endothelial origin in the absence of overt HIV-1 infection. This phenomenon was detectable as early as 1 h after the start of cocultivation and depended on cell-to-cell contact but not on the release of viral particles from donor cells. Transfer of HIV-1 products occurred upon their polarization and colocalization within zones of cell-to-cell contact similar to virological synapses. Neither HIV-1 Env nor Nef expression was required but, interestingly, we found that an HIV-1-dependent increase in matrix metalloproteinase 9 production from donor cells significantly contributed to the cell-to-cell transmission of the viral products. The macrophage-driven transfer of HIV-1 products to diverse CD4-negative cell types may have a significant role in AIDS pathogenesis.

Lentiviral Vectors Encoding HIV-1 Polyepitopes Induce Broad CTL Responses In Vivo

Lentiviral vectors have been tested as vaccination vectors in anti-tumoral and anti-viral models. They efficiently transduce dendritic cells and stimulate strong T-cell responses against the encoded antigen. However, their capacity to stimulate a cytotoxic T-lymphocyte (CTL) response against several antigens has not been evaluated. Broad anti-human immunodeficiency virus 1 (HIV-1) T-cell immune responses are important for the control of HIV replication. We evaluated the potential of polyepitope-encoding lentiviral vectors to induce broad anti-HIV CTL responses. We constructed two lentiviral vectors coding for an HLA-A2- or HLA-B7-restricted polyepitope and evaluated their immunogenicity by direct injection of vector particles in HLA-A2 or HLA-B7 transgenic mice. In vitro cytotoxicity assays showed that a single immunization induces a strong, diversified, and long-lasting CTL response in both mouse models. CTL responses were directed against all 13 epitopes in the HLA-A2 system and 8 out of 12 in the HLA-B7 system. A second immunization augmented the number of responding mice in the HLA-A2 system but not in the HLA-B7 system. HLA-B7-immunized mice mounted strong interferon-gamma (IFN-gamma)-secreting T-cell responses against a majority of the epitopes and lysed peptide-loaded target cells in vivo. CTL responses in HLA-B7 mice were only partially dependent on CD4 T-cell help. This work underlines the potential of lentiviral vectors as candidates for therapeutic vaccination against acquired immunodeficiency syndrome.

Evaluation of aldrithiol-2-inactivated preparations of HIV type 1 subtypes A, B, and D as reagents to monitor T cell responses

The development of HIV vaccines is an urgent priority and there is need to generate reagents representing multiple subtypes that can be used to screen HIV-1-specific responses. We used Aldrithiol-2 (AT-2), a mild oxidizing reagent, to eliminate the infectivity of HIV while maintaining its structure and ability to be processed for presentation to T cells. Inactivated subtype A, B, and D viruses were evaluated for their ability to stimulate T cell responses in PBMC samples from 18 U.S. subjects infected with HIV-1 subtype B and 32 Ugandan subjects infected with subtypes A and D or recombinants AC and AD. Five HIV-1-negative samples were also analyzed. T cell responses to AT-2-inactivated viral isolates were monitored by interferon-gamma (IFN-gamma) intracellular cytokine secretion (ICS) analysis; matched microvesicle preparations served as negative controls. Among the 18 subtype B infected subjects, 39% had CD3(+) CD4 (+) IFN-gamma responses and 67% had CD3(+) CD8(+) IFN-gamma responses. Of the 32 Ugandan subjects, 34% demonstrated CD3(+) CD4(+) IFN-gamma responses and 78% demonstrated CD3(+) CD8(+) IFN-gamma responses. Both subtype-specific and cross-reactive responses were observed. Responses to the AT-2 viruses tended to be lower in magnitude than those detected by a set of overlapping gag peptides. Robust lymphoproliferative responses to AT-2 viruses were seen in a subset of subjects. In conclusion, AT-2-inactivated HIV-1 virions stimulated both CD4 and CD8 HIV-1-specific responses and may provide an additional reagent for screening HIV-1-specific responses in HIV seropositives and vaccinees.

Noninfectious entry of HIV-1 into peripheral and brain macrophages mediated by the mannose receptor

Although protein receptors on the plasma membrane involved in the initial steps of productive HIV-1 infection have been well characterized, little is known about interactions between cellular carbohydrate receptors and HIV-1. Here, we report the involvement of a carbohydrate receptor, the macrophage mannose receptor (MR), and its role in supporting HIV-1 binding and entry. HIV-1 can enter the cytoplasm of human macrophages and microglia as well as murine macrophages by MR, although no subsequent viral replication was observed. Correspondingly, HIV-1 entry into Cos-7 cells after induction of expression of MR by transfection with MR-cDNA did not demonstrate viral replication. Our studies suggest that whereas MR may serve as a binding and an entry site, the MR-mediated pathway does not lead to productive HIV-1 infection. In addition, we report that recombinant HIV-1 gp120 blocks MR-mediated phagocytosis in human and murine alveolar macrophages and microglial cells. Therefore, characterization of the HIV-1 noninfectious MR-mediated phagocytic pathway may foster advances in HIV-1 vaccine design and an improved understanding of HIV-1/AIDS pathogenesis and host defenses.

Replication-competent Vectors and Empty Virus-like Particles: New Retroviral Vector Designs for Cancer Gene Therapy or Vaccines

Replication-defective vectors based on murine oncoretroviruses were the first gene transfer vectors to be used in successful gene therapies. Despite this achievement, they have two major drawbacks: insufficient efficacy for in vivo gene transfer and insertional mutagenesis. Attempts to overcome these problems have led to two retroviral vector designs of principally opposite character: replication-competent vectors transducing largely intact genomes and genome-free vectors. Replication-competent retroviral vectors have achieved dramatically improved efficacy for in vivo cancer gene therapy and genome-free retroviral vectors expressing different kinds of antigens have proven excellent as immunogens. Current developments aim to improve the safety of the replication-competent vectors and to augment the production efficiency of the genome-free vectors by expression from heterologous viral or non-viral vectors. Together with the continuous advances of classical defective retroviral vectors for ex vivo gene therapy, these developments illustrate that, due to their tremendous design versatility, retroviral vectors remain important vectors for gene therapy applications.

Involvement of Src and Syk Tyrosine Kinases in HIV-1 Transfer from Dendritic Cells to CD4+T Lymphocytes

Dendritic cells (DCs) are considered as key mediators of the early events in HIV-1 infection at mucosal sites. Although several aspects of the complex interactions between DCs and HIV-1 have been elucidated, there are still basic questions that remain to be answered about DCs/HIV-1 interplay. In this study, we examined the contribution of nonreceptor TKs in the known ability of DCs to efficiently transfer HIV-1 to CD4(+) T cells in trans. Experiments performed with specific inhibitors of Src and Syk family members indicate that these tyrosine kinases (TKs) are participating to HIV-1 transfer from immature monocyte-derived DCs (IM-MDDCs) to autologous CD4(+) T cells. Experiments with IM-MDDCs transfected with small interfering RNAs targeting Lyn and Syk confirmed the importance of these nonreceptor TKs in HIV-1 transmission. The Src- and Syk-mediated effect on virus transfer was linked with infection of IM-MDDCs in cis-as monitored by quantifying integrated viral DNA and de novo virus production. The process of HIV-1 transmission from IM-MDDCs to CD4(+) T cells was unaffected following treatment with protein kinase C and protein kinase A inhibitors. These data suggest that Src and Syk TKs play a functional role in productive HIV-1 infection of IM-MDDCs. Additional work is needed to facilitate our comprehension of the various mechanisms underlying the exact contribution of Src and Syk TKs to this phenomenon.

A dendritic cell-based vaccine for treating HIV infection: background and preliminary results

Antibody response against human immunodeficiency virus-1 (HIV) is ineffective and cellular immune response is not strong enough to achieve the complete suppression or at least a strong control of viral replication in HIV- infected patients. In 2001, we showed in vitro that dendritic cells (DCs) of HIV-infected patients loaded with autologous HIV chemically inactivated by aldrithiol-2 were capable of raising an HIV-specific cellular immune response powerful enough to allow the destruction of autologous HIV- infected CD4 T cells. In 2003, we showed that simian immunodeficiency virus (SIV)-infected macaques vaccinated with inactivated SIV-loaded autologous DCs raised a strong SIV-specific cellular response. Ten months after vaccination, plasma viral load of 7 out of the 10 vaccinated monkeys remained 1000-fold lower than initially. In December 2004, we published results observed in 18 untreated HIV-infected patients vaccinated with autologous monocyte-derived DCs loaded with autologous inactivated HIV. A year following vaccination, 8 patients had a plasma viral load decrease >90%; among them, 4 had viral load <1000 copies mL(-1). Moreover, by one year, the viral load decline of the 18 patients was significantly correlated with their percentage of HIV-1-gag-specific CD8(+) T cells expressing perforin and that of HIV-1-specific CD4(+) T(H)1 cells. This is the first demonstration of the capacity of a therapeutic vaccine to induce an effective HIV-specific T cell response associated with sustained viral suppression in untreated viremic patients. The manipulation of antigen presenting cells to elicit virus-specific cellular responses is a promising tool to control persistant viral infections.

Dendritic-cell interactions with HIV: infection and viral dissemination

Dendritic cells (DCs) are crucial for the generation and the regulation of adaptive immunity. Because DCs have a pivotal role in marshalling immune responses, HIV has evolved ways to exploit DCs, thereby facilitating viral dissemination and allowing evasion of antiviral immunity. Defining the mechanisms that underlie cell-cell transmission of HIV and understanding the role of DCs in this process should help us in the fight against HIV infection. This Review highlights the latest advances in our understanding of the interactions between DCs and HIV, focusing on the mechanisms of DC-mediated viral dissemination.

Inefficient human immunodeficiency virus replication in mobile lymphocytes

Cell-to-cell viral transfer facilitates the spread of lymphotropic retroviruses such as human immunodeficiency virus (HIV) and human T-cell leukemia virus (HTLV), likely through the formation of "virological synapses" between donor and target cells. Regarding HIV replication, the importance of cell contacts has been demonstrated, but this phenomenon remains only partly characterized. In order to alter cell-to-cell HIV transmission, we have maintained cultures under continuous gentle shaking and followed viral replication in this experimental system. In lymphoid cell lines, as well as in primary lymphocytes, viral replication was dramatically reduced in shaken cultures. To document this phenomenon, we have developed an assay to assess the relative contributions of free and cell-associated virions in HIV propagation. Acutely infected donor cells were mixed with carboxyfluorescein diacetate succinimidyl ester-labeled lymphocytes as targets, and viral production was followed by measuring HIV Gag expression at different time points by flow cytometry. We report that cellular contacts drastically enhance productive viral transfer compared to what is seen with infection with free virus. Productive cell-to-cell viral transmission required fusogenic viral envelope glycoproteins on donor cells and adequate receptors on targets. Only a few syncytia were observed in this coculture system. Virus release from donor cells was unaffected when cultures were gently shaken, whereas virus transfer to recipient cells was severely impaired. Altogether, these results indicate that cell-to-cell transfer is the predominant mode of HIV spread and help to explain why this virus replicates so efficiently in lymphoid organs.

Development and implementation of a direct detection, quantitation and validation system for class I MHC self-peptide epitopes

Gene and protein expression studies demonstrate that viral-infected and malignant cells undergo a complex series of transcriptional and translational changes. As class I MHC molecules reflect the proteome (and changes therein) by presenting intracellular peptide epitopes, the development of a direct discovery and validation technology for the identification of these epitopes is needed. We developed our technology using HIV-1-infected cells as a model. A combination of hollow fiber class I HLA protein production and mass spectrometric epitope analysis indicated a 3-fold increase in the host-peptide VLMTEDIKL(720-728), [eIF4G((720))] presented by the HLA-A*0201 of HIV-1-infected cells. This peptide is derived from the host-protein translation of eukaryotic initiation factor 4-gamma (eIF4G) that plays a pivotal role in cellular protein synthesis. Direct confirmation of expression of this self-encoded antigen was performed through development of a T cell receptor mimic (TCRm) monoclonal antibody (mAb). The resulting 4F7 TCRm demonstrated specific recognition of the eIF4G((720))-A*0201 complex. Staining of normal PBMCs with 4F7 showed only low levels of endogenous eIF4G((720)) presentation by HLA-A*0201, while 4F7 staining of HIV-1-infected PBMCs revealed an approximately 3-fold increase in eIF4G((720))-A*0201. The MHC-peptide complex was initially detectable by 4F7 at 3 days post-infection, with a steady increase through day 8. We therefore demonstrate the successful development and implementation of an integrated discovery and validation technology system for direct identification and confirmation of class I MHC-peptide epitopes on cells.

Induction of primary anti-HIV CD4 and CD8 T cell responses by dendritic cells transduced with self-inactivating lentiviral vectors

In this study, we demonstrate that a minimal self-inactivating (SIN) lentiviral vector (LV) that does not encode any human immunodeficiency virus (HIV) genes is able to induce HIV-specific CD4 and CD8 T cell responses after transduction of dendritic cells (DCs). The LV-DC-primed T cells displayed HIV-specific lytic degranulation, as illustrated by acquisition of CD107a/b expression on the cell surface and up-regulation of active caspase 3. HIV-specific cytotoxic T lymphocyte (CTL) response was consistently detected using different assays, and T cell receptors specific to three prominent HIV epitopes, SL9 (Gag peptide: SLYNTVATL), IV9 (Pol peptide: ILKEPVHGV), and MA10 (In peptide: MASDFNLPPV) were detected using HLA-A0201 peptide-tetramers. These results demonstrate that DCs transduced with the minimal SIN-LV can efficiently induce HIV-specific CD4 and CD8 T cell responses. Since LVs are popular gene transfer tools, our results have fundamental implications for future LV applications and DC vaccine development.

Dendritic cells and HIV-specific CD4+ T cells: HIV antigen presentation, T-cell activation, and viral transfer

Human immunodeficiency virus (HIV)-specific CD4+ lymphocytes are preferentially infected in HIV-positive individuals. To study this preferential infection, we have derived several HIV-specific (HS) CD4+ clones. We show that in dendritic cells (DCs), HIV virion capture led to major histocompatibility complex class-II (MHC-II)-restricted viral antigen presentation and to activation of HS cells. In contrast, neither cell-free virions nor infected lymphocytes activated HS cells. In DCs, the dendritic cell-specific intercellular adhesion molecule 3-grabbing nonintegrin (DC-SIGN/CD209), which internalizes virions, promoted MHC-II presentation of HIV antigens. Activation of HS cells by HIV-exposed DCs triggered an efficient viral spread in lymphocytes. CD4+ clones with irrelevant antigenic specificities were not activated by HIV-exposed DCs and poorly supported viral replication under this setting. Our results unravel the mechanisms of MHC-II-restricted HIV antigen presentation by DCs and describe how HIV gains access to the very cells designed by the immune system to counteract this pathogen.

Dendritic cells and HIV infection: activating dendritic cells to boost immunity

Dendritic cells (DCs) are white blood cells that coordinate innate and adaptive immunity. They are distributed within epithelia and mucosal-associated lymphoid tissues, positioned to entrap incoming pathogens or vaccines. Human immunodeficiency virus (HIV) and the non-human primate equivalent (SIV) exploit DCs to amplify infection, underscoring the need to harness strategies that promote presentation of virus by DCs to stimulate potent anti-viral immunity instead of virus transmission. Two main subsets of DCs need to be considered: myeloid (MDC) and plasmacytoid (PDC) subsets. Using the SIV-macaque system to advance oral vaccine research, we examined macaque PDC and MDC biology, identifying ways to activate DCs and boost antiviral immunity. Immunostimulatory oligodeoxyribonucleotides (ISS-ODNs) stimulated PDC/MDC mixtures to up-regulate co-stimulatory molecule expression and to secrete both IFN-alpha and IL-12. Additionally, ISS-ODNs augmented SIV-specific IFN-gamma responses induced by virus-bearing DCs. ISS-ODN-driven DC activation is being pursued to improve oral/nasopharyngeal mucosal vaccines and therapies against HIV.

HIV-1 selectively infects a subset of nonmaturing BDCA1-positive dendritic cells in human blood

The infection of cultured monocyte-derived dendritic cells (DCs) with HIV-1 involves CD4 and CCR5 receptors, while transmission to T cells is enhanced at least in part by the lectin DC-SIGN/CD209. In the present study, we studied BDCA-1+ myeloid DCs isolated directly from human blood. These cells express CD4 and low levels of CCR5 and CXCR4 coreceptors, but not DC-SIGN. The myeloid DCs replicate two R5 viruses, BaL and YU2, and transfer infection to activated T cells. The virus productively infects a small fraction of the blood DCs that fail to mature in culture, as indicated by the maturation markers CD83 and DC-LAMP/CD208, and the expression of high CD86 and MHC class II, in contrast to many noninfected DCs. A greater proportion of BDCA-1+ DCs are infected when the virus is pseudotyped with the vesicular stomatitis envelope VSV-G (5-15%), as compared with the R5 virus (0.3-3.5%), indicating that HIV-1 coreceptors may limit the susceptibility of DCs to become infected, or the endocytic route of viral entry used by HIV/vesicular stomatitis virus enhances infectivity. When infected and noninfected cells are purified by cell sorting, the former uniformly express HIV p24 gag and are virtually inactive as stimulators of the allogeneic MLR, in contrast to potent stimulation by noninfected DCs from the same cultures. These results point to two roles for a small fraction of blood DCs in HIV-1 pathogenesis: to support productive infection and to evade the direct induction of T cell-mediated immunity.

Molecular and biological characterization of simian-human immunodeficiency virus-like particles produced by recombinant fowlpox viruses

Virus-like particles (VLPs) mimicking the simian-human immunodeficiency virus SHIV89.6P (VLPSHIV) were produced by co-infection of Vero cells with fowlpox SIVgag/pol (FPgag/polSIV) and fowlpox HIV-1env89.6P (FPenv89.6P) recombinant viruses. As a necessary prerequisite for a more efficient vaccine approach, ultrastructural, functional and molecular characterizations of VLP(SHIV) were performed in the SHIV-macaque model to verify the similarity of these particles to SHIV89.6P. Here we show that VLPSHIV can infect T cells by fusion without replication, as demonstrated by the absence of new viral progeny in VLPSHIV-infected C8166 cells. Biochemical characterization showed identical protein profiles of VLPSHIV and SHIV89.6P, and ultrastructural analysis of Vero cells releasing VLPSHIV also confirmed the morphological similarity of these pseudovirions to SHIV89.6P particles. Viral mRNAs were also found packaged inside the core of VLPSHIV by RT-PCR and reverse transcriptase assays.

Cell death induced by the herpes simplex virus-1 thymidine kinase delivered by human immunodeficiency virus-1-based virus-like particles

HIV-1 Nef incorporates into virions at low levels, likely about 10 molecules per viral particle. Here, we describe a Nef mutant (Nef7) apparently showing more than 100-fold higher efficiency of virion incorporation. Interestingly, Nef7 can act as a cargo molecule for protein delivery into the cells, as its virion incorporation appeared conserved even upon C-terminal fusion with proteins of up to 30 kDa. This was demonstrated first by assessing the intracellular fluorescence of cells challenged with lentivirus-based virus-like particles (VLPs) pseudotyped with the vesicular stomatitis virus envelope glycoprotein (VSV-G) and incorporating Nef7 fused with the green fluorescent protein. Furthermore, the biologic activity of products delivered by Nef7-based VLPs was demonstrated by tagging Nef7 with the herpes simplex virus-1 thymidine kinase (HSV-1 TK). In fact, we observed that both cell lines and primary human macrophages challenged with (VSV-G) Nef7/TK VLPs died after 5 to 7 days of treatment with ganciclovir (GCV). In sum, our findings support the notion that Nef7-based VLPs can be considered platforms for original systems of protein delivery. In particular, the here- described Nef7/TK VLPs represent a first applicative example opening the way toward new HSV-1 TK/GCV-based cell suicide therapies circumventing cell gene engineering procedures.

Covert human immunodeficiency virus replication in dendritic cells and in DC-SIGN-expressing cells promotes long-term transmission to lymphocytes

HIV-1 virions are efficiently captured by monocyte-derived immature dendritic cells (iDCs), as well as by cell lines expressing the lectin DC-SIGN. Viral infectivity can be retained for several days, and even enhanced, before transmission to CD4+ lymphocytes. The role of DC-SIGN in viral retention and enhancement of infection is not fully understood and varies according to the cell line expressing the lectin. We studied here the mechanisms underlying this process. We focused our study on X4-tropic human immunodeficiency virus (HIV) strains, since they were widely believed not to replicate in iDCs. However, we first show that X4 HIV replicates covertly and slowly in iDCs. This is also the case in Raji-DC-SIGN cells, which are classically used to study HIV transmission. We used either single-cycle or replicative HIV and measured viral RT and replication to further demonstrate that transfer of incoming virions from iDCs or DC-SIGN+ cells occurs only on the short-term (i.e., a few hours after viral exposure). There is no long-term storage of original HIV particles in these cells. A few days after viral exposure, replicative viruses, and not single-cycle virions, are transmitted to CD4+ cells. The cell-type-dependent activity of DC-SIGN reflects the ability of HIV to replicate covertly in some cells, and not in others.

Pseudovirion particle production by live poxvirus human immunodeficiency virus vaccine vector enhances humoral and cellular immune responses

Live-vector-based human immunodeficiency virus (HIV) vaccines are an integral part of a number of HIV vaccine regimens currently under evaluation. Live vectors that carry an intact gag gene are capable of eliciting HIV pseudovirion particle formation from infected host cells. The impact of pseudovirion particle formation on the immune response generated by live HIV vaccine vectors has not been established. In this study, a canarypox HIV vaccine candidate vector expressing HIV gag and env genes, vCP205, was modified by the introduction of a glycine-to-alanine coding change in the N-terminal myristylation site of gag to create Myr- vCP205. This substitution effectively eliminated particle formation without altering the level of protein production. vCP205 and Myr- vCP205 were then directly compared for the ability to induce HIV-specific immune responses in mice. The particle-competent vector vCP205 elicited higher levels of CD8+ T-cell responses, as indicated by gamma interferon enzyme-linked immunospot (ELISPOT) assay and intracellular cytokine staining. Humoral responses to Gag and Env were also markedly higher from animals immunized with the particle-competent vector. Furthermore, HIV-specific CD4+ T-cell responses were greater among animals immunized with the particle-competent vector. Using a human dendritic cell model of antigen presentation in vitro, vCP205 generated greater ELISPOT responses than Myr- vCP205. These results demonstrate that pseudovirion particle production by live-vector HIV vaccines enhances HIV-specific cellular and humoral immune responses.

Loss of reactivity of vaccine-induced CD4 T cells in immunized monkeys after SIV/HIV challenge

BACKGROUND

Immunization protocols involving priming with DNA and boosting with recombinant live virus vectors such as recombinant modified Vaccinia Ankara (rMVA) are considered as vaccine candidates against HIV. Such protocols improve the outcome of simian/human immunodeficiency virus (SHIV) pathogenic challenge in Rhesus monkeys.

OBJECTIVES

To investigate the fate of vaccine-induced T cells after a mucosal SHIV challenge.

METHODS

We immunized Rhesus monkeys (Macaca mulatta) by DNA priming followed by rMVA boost. After intrarectal challenge with SHIV 89.6P, immunized animals demonstrated early control of viral replication and stable CD4 T-cell counts. We monitored T-cell responses by measuring IFN-gamma secretion and proliferation.

RESULTS

Immunization induced strong and sustained SHIV-specific CD4 and CD8 T-cell responses. CD8 T-cell responses were recalled during acute infection, whereas none of the vaccine-induced SHIV-specific CD4 T-cell responses were recalled. Moreover, most of the CD4 T-cell responses became undetectable in peripheral blood or lymph nodes even after in-vitro peptide stimulation. In contrast, we persistently detected CD4 T-cell responses specific for control recall antigens in infected animals.

CONCLUSION

SHIV 89.6P challenge results in a lack of reactivity of vaccine-induced SHIV-specific CD4 T cells. These results may have important implications in the AIDS vaccine field, especially for the evaluation of new vaccine candidates, both in preventive and therapeutic trials.

Elimination of retroviral infectivity by N-ethylmaleimide with preservation of functional envelope glycoproteins

The zinc finger motifs in retroviral nucleocapsid (NC) proteins are essential for viral replication. Disruption of these Cys-X2-Cys-X4-His-X4-Cys zinc-binding structures eliminates infectivity. To determine if N-ethylmaleimide (NEM) can inactivate human immunodeficiency virus type 1 (HIV-1) or simian immunodeficiency virus (SIV) preparations by alkylating cysteines of NC zinc fingers, we treated infectious virus with NEM and evaluated inactivation of infectivity in cell-based assays. Inactivation was rapid and proportional to the NEM concentration. NEM treatment of HIV-1 or SIV resulted in extensive covalent modification of NC and other internal virion proteins. In contrast, viral envelope glycoproteins, in which the cysteines are disulfide bonded, remained intact and functional, as assayed by high-performance liquid chromatography, fusion-from-without analyses, and dendritic cell capture. Quantitative PCR assays for reverse transcription intermediates showed that NEM and 2,2'-dipyridyl disulfide (aldrithiol-2), a reagent which inactivates retroviruses through oxidation of cysteines in internal virion proteins such as NC, blocked HIV-1 reverse transcription prior to the formation of minus-strand strong-stop products. However, the reverse transcriptase from NEM-treated virions remained active in exogenous template assays, consistent with a role for NC in reverse transcription. Since disruption of NC zinc finger structures by NEM blocks early postentry steps in the retroviral infection cycle, virus preparations with modified NC proteins may be useful as vaccine immunogens and probes of the role of NC in viral replication.

Recombinant HIV-1 Pr55gag virus-like particles: potent stimulators of innate and acquired immune responses

Several previous reports have clearly demonstrated the strong effectiveness of human immunodeficiency virus (HIV) Gag polyprotein-based virus-like particles (VLP) to stimulate humoral and cellular immune responses in complete absence of additional adjuvants. Yet, the mechanisms underlying the strong immunogenicity of these particulate antigens are still not very clear. However, current reports strongly indicate that these VLP act as "danger signals" to trigger the innate immune system and possess potent adjuvant activity to enhance the immunogenicity of per se only weakly immunogenic peptides and proteins. Here, we review the current understanding of how various particle-associated substances and other impurities may contribute to the observed immune-activating properties of these complex immunogens.

Efficient priming of simian/human immunodeficiency virus (SHIV)-specific T-cell responses with DNA encoding hybrid SHIV/hepatitis B surface antigen particles

Recent efforts to design an human immunodeficiency virus type 1 (HIV-1) vaccine candidate have focused on means of eliciting anti-viral T-cell responses. We tried to improve the immunogenicity of DNA vaccines by designing hybrid DNA constructs encoding hepatitis B surface antigen (HBsAg) fused to antigenic domains of simian/human immunodeficiency virus (SHIV 89.6P). Immunisation with hybrid DNA induced both effector and long-lasting precursor T-cells. Following boosting with a recombinant modified vaccinia Ankara (rMVA) producing full-length SIV and HIV antigens, it appeared that priming with hybrid DNA had increased virus-specific T-cell responses in terms of both the number of virus-specific IFN-gamma-secreting T-cells and virus-specific lymphoproliferation. After intrarectal challenge with SHIV 89.6P, immunised animals demonstrated early control of SHIV 89.6P replication and stable CD4+ T-cell counts.

Therapeutic dendritic-cell vaccine for chronic HIV-1 infection

We present the results of a preliminary investigation of the efficacy of a therapeutic dendritic cell (DC)-based vaccine for HIV-1. We immunized 18 chronically HIV-1-infected and currently untreated individuals showing stable viral loads for at least 6 months with autologous monocyte-derived DCs loaded with autologous aldrithiol-2-inactivated HIV-1. Plasma viral load levels were decreased by 80% (median) over the first 112 d following immunization. Prolonged suppression of viral load of more than 90% was seen in 8 individuals for at least 1 year. The suppression of viral load was positively correlated with HIV-1-specific interleukin-2 or interferon-gamma-expressing CD4(+) T cells and with HIV-1 gag-specific perforin-expressing CD8(+) effector cells, suggesting that a robust virus-specific CD4(+) T-helper type 1 (T(H)1) response is required for inducing and maintaining virus-specific CD8(+) effectors to contain HIV-1 in vivo. The results suggest that inactivated whole virus-pulsed DC vaccines could be a promising strategy for treating people with chronic HIV-1 infection.

HIV-1 and the hijacking of dendritic cells: a tug of war

Dendritic cells are critical for host immunity and are involved both in the innate and adaptive immune responses. They are among the first cells targeted by HIV-1 in vivo at mucosal sites. Dendritic cells can sequester HIV-1 in endosomal compartments for several days and transmit infectious HIV-1 to interacting T cells in the lymph node, which is the most important site for viral replication and spread. Initially, the cellular immune response developed against HIV-1 is strong, but eventually it fails to control and resolve the infection. The most dramatic effect seen on the immune system during untreated HIV-1 infection is the destruction of helper CD4(+) T cells, which leads to subsequent immune deficiency. However, the immunomodulatory effects of HIV-1 on different dendritic cell subpopulations may also play an important role in the pathogenesis of HIV-1. This review discusses the effects HIV-1 exerts on dendritic cells in vivo and in vitro, including the binding and uptake of HIV by dendritic cells, the formation of infectious synapses, infection, and the role of dendritic cells in HIV-1 pathogenesis.

Virus infection of dendritic cells: portal for host invasion and host defense

Dendritic cells (DCs) act as a portal for virus invasion and as the most potent antigen-presenting cells in antiviral host defense. Human immunodeficiency virus (HIV)-1 has served as the paradigm for virus interaction with DCs. HIV-1 infection of DCs via its primary CD4 receptor and secondary chemokine receptors leads to full virus replication (cis infection), whereas binding to C-type lectin receptors results both in cis replication, as well as transfer and replication of virus in CD4(pos) T cells (trans infection). DCs respond to this invasion by processing viral proteins through MHC class I and II pathways and undergoing a maturation that enhances their presentation of antigen to T cells for induction of adaptive antiviral immunity. HIV-1 and other viruses have evolved mechanisms to subvert this immune function. Engineering of DCs with various forms of viral immunogens and co-treatment with cytokines and chemokines is being used as an immunotherapy for HIV-1 and other viral infections.

Loading of MHC class I and II presentation pathways by exogenous antigens: a quantitative in vivo comparison

The MHC class I pathway is usually fueled by endogenous Ags, while exogenous Ags reach the MHC class II pathway. Although exogenous epitopes may also enter the MHC class I pathway, quantification of the efficiency of the process has remained a difficult task. In an attempt of such a quantification, we directly compared the amount of exogenous virus-like particles required for induction of cytotoxic T cell responses by cross-priming with the amount of virus-like particles required for induction of Th cell responses by the conventional route of MHC class II loading as an internal standard. Surprisingly, we found that cross-presentation of peptides derived from exogenous Ags on MHC class I molecules is of only marginally lower efficiency ( approximately 1- to 10-fold) than the classical MHC class II pathway in vitro and in vivo. Thus, Ag quantities required for cross-presentation and cross-priming are similar to those required for fueling the MHC class II pathway.

Noninfectious X4 but not R5 human immunodeficiency virus type 1 virions inhibit humoral immune responses in human lymphoid tissue ex vivo

Ex vivo human immunodeficiency virus type 1 (HIV-1) infection of human lymphoid tissue recapitulates some aspects of in vivo HIV-1 infection, including a severe depletion of CD4(+) T cells and suppression of humoral immune responses to recall antigens or to polyclonal stimuli. These effects are induced by infection with X4 HIV-1 variants, whereas infection with R5 variants results in only mild depletion of CD4(+) T cells and no suppression of immune responses. To study the mechanisms of suppression of immune responses in this ex vivo system, we used aldrithiol-2 (AT-2)-inactivated virions that have functional envelope glycoproteins but are not infectious and do not deplete CD4(+) T cells in human lymphoid tissues ex vivo. Nevertheless, AT-2-inactivated X4 (but not R5) HIV-1 virions, even with only a brief exposure, inhibit antibody responses in human lymphoid tissue ex vivo, similarly to infectious virus. This phenomenon is mediated by soluble immunosuppressive factor(s) secreted by tissue exposed to virus.

Potent neutralizing serum immunoglobulin A (IgA) in human immunodeficiency virus type 2-exposed IgG-seronegative individuals

The mechanisms behind the resistance to human immunodeficiency virus type 2 (HIV-2) infection are still not fully understood. In the present study, we explored the HIV-2-specific humoral serum immunoglobulin A (IgA) immune response in HIV-2-exposed IgG-seronegative (EGSN) individuals. Serum samples from heterosexual EGSN individuals and their known HIV-2-infected partners, as well as controls originating from Guinea-Bissau in Africa, were studied. Antibody reactivity to native and recombinant envelope glycoproteins was investigated, and the capacity of purified serum IgA to neutralize HIV-2(SBL6669) was tested. Our results showed that 16 of 25 EGSN samples exhibited reactivity against whole HIV-2 antigen, 6 of 25 samples reacted with recombinant gp36 (rgp36), and 3 of 25 samples were positive against HIV-2 rgp105; no reactivity to native HIV-2 gp125 was detected. Purified serum IgA antibodies from both EGSN and HIV-2-positive individuals, but not that from the negative controls, exhibited neutralization of HIV-2(SBL6669). The most potent neutralization activity was exhibited by IgA purified from EGSN compared to infected individuals' IgA. The antigenic pattern of the HIV-2-positive partners showed that all serum IgA samples were reactive to whole HIV-2 antigen, and 14 of 15 reacted with rgp36. For rgp105 and gp125, 5 of 15 and 4 of 15 samples exhibited binding, respectively. The serum of the EGSN group had a higher mean IgA concentration than that of the negative controls (P < 0.05). Thus, we describe HIV-2-specific serum IgA antigen reactivity and show a more potent serum IgA-mediated HIV-2-neutralizing activity in EGSN individuals than in HIV-2-infected patients.

Human immunodeficiency virus type 1 activates plasmacytoid dendritic cells and concomitantly induces the bystander maturation of myeloid dendritic cells

In this study, we analyzed the phenotypic and physiological consequences of the interaction of plasmacytoid dendritic cells (pDCs) with human immunodeficiency virus type 1 (HIV-1). pDCs are one cellular target of HIV-1 and respond to the virus by producing alpha/beta interferon (IFN-alpha/beta) and chemokines. The outcome of this interaction, notably on the function of bystander myeloid DC (CD11c+ DCs), remains unclear. We therefore evaluated the effects of HIV-1 exposure on these two DC subsets under various conditions. Blood-purified pDCs and CD11c+ DCs were exposed in vitro to HIV-1, after which maturation markers, cytokine production, migratory capacity, and CD4 T-cell stimulatory capacity were analyzed. pDCs exposed to different strains of infectious or even chemically inactivated, nonreplicating HIV-1 strongly upregulated the expression of maturation markers, such as CD83 and functional CCR7, analogous to exposure to R-848, a synthetic agonist of toll-like receptor-7 and -8. In addition, HIV-1-activated pDCs produced cytokines (IFN-alpha and tumor necrosis factor alpha), migrated in response to CCL19 and, in coculture, matured CD11c+ DCs, which are not directly activated by HIV. pDCs also acquired the ability to stimulate naïve CD4+ T cells, albeit less efficiently than CD11c+ DCs. This HIV-1-induced maturation of both DC subsets may explain their disappearance from the blood of patients with high viral loads and may have important consequences on HIV-1 cellular transmission and HIV-1-specific T-cell responses.

HIV-1-infected monocyte-derived dendritic cells do not undergo maturation but can elicit IL-10 production and T cell regulation

Dendritic cells (DCs) undergo maturation during virus infection and thereby become potent stimulators of cell-mediated immunity. HIV-1 replicates in immature DCs, but we now find that infection is not accompanied by many components of maturation in either infected cells or uninfected bystanders. The infected cultures do not develop potent stimulating activity for the mixed leukocyte reaction (MLR), and the DCs producing HIV-1 gag p24 do not express CD83 and DC-lysosome-associated membrane protein maturation markers. If different maturation stimuli are applied to DCs infected with HIV-1, the infected cells selectively fail to mature. When DCs from HIV-1-infected patients are infected and cultured with autologous T cells, IL-10 was produced in 6 of 10 patients. These DC-T cell cocultures could suppress another immune response, the MLR. The regulation was partially IL-10-dependent and correlated in extent with the level of IL-10 produced. Suppressor cells only developed from infected patients, rather than healthy controls, and the DCs had to be exposed to live virus rather than HIV-1 gag peptides or protein. These results indicate that HIV-1-infected DCs have two previously unrecognized means to evade immune responses: maturation can be blocked reducing the efficacy of antigen presentation from infected cells, and T cell-dependent suppression can be induced.

Immunomodulation Induced by Tucaresol in HIV Infection: Results of a 16 Week Pilot Phase I/II Trial

Objective

Immune reconstitution in highly active anti-retroviral therapy (HAART)-treated individuals is incomplete and immunomodulatory compounds are needed to improve the outcome of HIV therapy. In a Phase I/II clinical trial performed on HIV-positive patients we analysed the safety and immunomodulating effects of tucaresol, a novel compound that has previously been described to enhance cell-mediated immune responses.

Patients and methods

Sixteen weeks pulse dose escalation protocol. Four groups of HIV-positive patients were enrolled: group A ( n=6): HAART, CD4+ 300–500 cells/μl, HIV RNA <80 copies/ml; group B ( n=6): HAART-naive, CD4+ <500 cells/μl, HIV RNA >10 000 copies/ml; group C ( n=3): HAART-naive, CD4+ >500 cells/μl, HIV RNA <10 000 copies/ml; and group D ( n=6): HAART, CD4+ <200 cells/μl, HIV RNA <80 copies/ml. Tucaresol was added to HAART in group A and D patients; group B patients started tucaresol with HAART, group C patients received tucaresol alone. Clinical and immunological analyses were performed at different time points.

Results

Tucaresol-related serious adverse events were observed in the first week of therapy in 2/21 patients who were viraemic when commencing treatment, but did not occur in patients on stable HAART. Tucaresol did not affect HIV viraemia whereas increases in CD4+ percentages, mainly supported by naive CD4+ cells, were observed. CD8+/28-/45RA+ cells and HIV-specific CD8+ IFNγ- and perforin-producing cells improved whereas IL-10 mRNA diminished in tucaresol-treated patients. The effects were greater with 25 mg given every other day for 1 week.

Conclusion

In HAART-receiving patients with proper virus suppression, tucaresol was not associated with serious adverse events and resulted in qualitative and quantitative stimulation of HIV-specific cytotoxic T lymphocyte activity and generation of naive T cells. These data may support further exploration of tucaresol use in reconstitution of immune system parameters in HIV patients with proper virus suppression while on HAART.

Dendritic cells cross-present HIV antigens from live as well as apoptotic infected CD4+ T lymphocytes

A better understanding of the antigen presentation pathways that lead to CD8(+) T cell recognition of HIV epitopes in vivo is needed to achieve better immune control of HIV replication. Here, we show that cross-presentation of very small amounts of HIV proteins from apoptotic infected CD4(+) T lymphocytes by dendritic cells to CD8(+) T cells is much more efficient than other known HIV presentation pathways, i.e., direct presentation of infectious virus or cross-presentation of defective virus. Unexpectedly, dendritic cells also take up actively antigens into endosomes from live infected CD4(+) T lymphocytes and cross-present them as efficiently as antigens derived from apoptotic infected cells. Moreover, live infected CD4(+) T cells costimulate cross-presenting dendritic cells in the process. Therefore, dendritic cells can present very small amounts of viral proteins from infected T cells either after apoptosis, which is frequent during HIV infection, or not. Thus, if HIV expression is transiently induced while costimulation is enhanced (for instance after IL-2 and IFNalpha immune therapy), this HIV antigen presentation pathway could be exploited to eradicate latently infected reservoirs, which are poorly recognized by patients' immune systems.

Identification of cryptic MHC I-restricted epitopes encoded by HIV-1 alternative reading frames

Human immunodeficiency virus (HIV) 1 major histocompatibility complex (MHC) I–restricted epitopes are widely believed to be derived from viral proteins encoded by primary open reading frames. However, the HIV-1 genome contains alternative reading frames (ARFs) potentially encoding small polypeptides. We have identified a panel of epitopes encoded by ARFs within the gag, pol, and env genes. The corresponding epitopic peptides were immunogenic in mice humanized for MHC-I molecules. In addition, cytotoxic T lymphocytes recognizing these epitopes were found in HIV-infected patients. These results reveal the existence of atypical mechanisms of HIV-1 epitope generation. They indicate that the repertoire of epitopes recognized by the cellular anti–HIV-1 immune response is broader than initially thought. This should be taken into account when designing vaccine strategies aimed at activating these responses.

DNA vaccines against human immunodeficiency virus type 1 in the past decade

This article reviews advances in the field of human immunodeficiency virus type 1 (HIV-1) and AIDS vaccine development over the last decade, with an emphasis on the DNA vaccination approach. Despite the discovery of HIV-1 and AIDS in humans nearly 20 years ago, there is no vaccine yet that can prevent HIV-1 infection. The focus has shifted toward developing vaccines that can control virus replication and disease progression by eliciting broadly cross-reactive T-cell responses. Among several approaches evaluated, the DNA-based modality has shown considerable promise in terms of its ability to elicit cellular immune responses in primate studies. Of great importance are efforts aimed at improvement of the potency of this modality in the clinic. The review discusses principles of DNA vaccine design and the various mechanisms of plasmid-encoded antigen presentation. The review also outlines current DNA-based vaccine strategies and vectors that have successfully been shown to control virus replication and slow disease progression in animal models. Finally, it lists recent strategies that have been developed as well as novel approaches under consideration to enhance the immunogenicity of plasmid-encoded HIV-1 antigen in various animal models.

Early protection against pathogenic virus infection at a mucosal challenge site after vaccination with attenuated simian immunodeficiency virus

Atraumatic application of attenuated SIVmac239 Delta nef vaccine to the tonsils of rhesus macaques provided protection against challenge 26 weeks later with infectious SIVmac251 applied through this route. Early events at the mucosal portal of entry of challenge virus were followed. Wild-type virus was detected in nonvaccinated controls by day 4, and then simian immunodeficiency virus (SIV) replicated vigorously at days 7 and 14. In contrast, a challenge of 10 of 10 vaccinees with SIV did not significantly raise RNA levels in the plasma or increase infected cells in lymphoid tissues, as assessed by single-cell labeling for viral RNA and nef protein. Vaccine virus was found in the tonsils of all vaccinees, but challenge virus was only detected at this portal of entry in 4 of 10 monkeys. In the tonsil, the challenge virus did not induce an expansion of perforin(+) killer cells. However, there was a significant increase in gamma delta T cells and mature dendritic cells relative to unvaccinated controls. Therefore, during tonsillar SIV Delta nef vaccination, infection is blocked early at the entry portal, which we propose is due in part to innate functions of gamma delta T and dendritic cells.

Defective Control of Latent Epstein-Barr Virus Infection in Systemic Lupus Erythematosus

EBV infection is more common in patients with systemic lupus erythematosus (SLE) than in control subjects, suggesting that this virus plays an etiologic role in disease and/or that patients with lupus have impaired EBV-specific immune responses. In the current report we assessed immune responsiveness to EBV in patients with SLE and healthy controls, determining virus-specific T cell responses and EBV viral loads using whole blood recall assays, HLA-A2 tetramers, and real-time quantitative PCR. Patients with SLE had an approximately 40-fold increase in EBV viral loads compared with controls, a finding not explained by disease activity or immunosuppressive medications. The frequency of EBV-specific CD69+ CD4+ T cells producing IFN-gamma was higher in patients with SLE than in controls. By contrast, the frequency of EBV-specific CD69+ CD8+ T cells producing IFN-gamma in patients with SLE appeared lower than that in healthy controls, although this difference was not statistically significant. These findings suggest a role for CD4+ T cells in controlling, and a possible defect in CD8+ T cells in regulating, increased viral loads in lupus. These ideas were supported by correlations between viral loads and EBV-specific T cell responses in lupus patients. EBV viral loads were inversely correlated with the frequency of EBV-specific CD69+ CD4+ T cells producing IFN-gamma and were positively correlated with the frequencies of CD69+ CD8+ T cells producing IFN-gamma and with EBV-specific, HLA-A2 tetramer-positive CD8+ T cells. These results demonstrate that patients with SLE have defective control of latent EBV infection that probably stems from altered T cell responses against EBV.

Immunodeficiency virus exploitation of dendritic cells in the early steps of infection

The unique capacity of dendritic cells (DCs) to capture and process pathogens for presentation to the immune system, combined with their capacity to express costimulatory and adhesion molecules as well as cytokines and chemokines, renders them powerful antigen-presenting cells. However, immunodeficiency viruses hijack DCs to facilitate virus dissemination while subverting effective immune activation. Depending on the activation level of the DC subset, human immunodeficiency virus can use different receptors (CD4, chemokine, and C-type lectin receptors) to bind to DCs. These aspects likely impact whether a DC is productively infected by or simply carries virus for transmission to more permissive targets. DCs efficiently transmit virus to CD4+ T cells, driving virus growth as well as providing signals to trigger virus expansion in virus-bearing CD4+ T cells. There is accumulating evidence that viral determinants (nef, tat) selectively modulate immature DC biology, fostering DC-T cell interactions and virus replication without up-regulating costimulatory molecules for effective immune function. In addition, virus-loaded, immature DCs activate CD4+ virus-specific T cells, and mature DCs stimulate CD4+ and CD8+ T cells. Thus, even if immature DCs entrap virus as it crosses the mucosae and initiate a CD4+ T cell response, this is likely insufficient to control infection. Appreciating how virus modulates DC function and what determines whether virus is processed for immune stimulation or transmitted between cells will unveil the exact role of these cells in the onset of infection and advance preventative microbicide and vaccine/therapeutic approaches.

Endogenous neosynthesis vs. cross-presentation of viral antigens for cytotoxic T cell priming

Induction of antiviral cytotoxic T lymphocytes (CTLs) has been proposed to require cross-presentation of viral antigens derived from infected extralymphatic host cells by antigen-presenting cells (APC). This postulated mechanism of cross-priming is thought to be essential for CTL responses against viruses that do not infect professional APC, e.g., because of absence of the specific virus receptor. Here, we show for the human pathogen poliovirus that naturally nonpermissive murine APC acquire viral RNA in vivo independently of the cellular virus receptor. Uptake of poliovirus or polioviral RNA initiated neosynthesis of viral antigen to an extent sufficient to prime CTLs in vivo, which were detectable 2-3 wk after infection. Our results do not only indicate that experiments studying cross-presentation and cross-priming by using potentially amplifiable or translatable materials need careful examination, but they also question the general biological importance of cross-presentation and cross-priming in antiviral CTL responses.