Highly Attenuated Infection With a Vpr-Deleted Molecular Clone of Human Immunodeficiency Virus-1

A 48-year-old woman was infected with a vpr-defective human immunodeficiency virus (HIV)-1 molecular clone. Seroconversion was markedly delayed, and without treatment she had durably suppressed viremia and normal T-cell levels. Neutralizing antibody and CD8+ T-cell immune responses against HIV-1 were unremarkable. Viral sequences confirmed the source but evolved defective nef, suggesting an unknown mechanistic link to vpr. There were subtle qualitative defects in T and B cells. To our knowledge, this is the only case of human infection with a characterized defective HIV-1 molecular clone, which furthermore recapitulated live-attenuated vaccination in macaque models of HIV-1 vaccine research.

Human immunodeficiency virus (HIV) type 1 Vpr induces differential regulation of T cell costimulatory molecules: Direct effect of Vpr on T cell activation and immune function

Human immunodeficiency virus type 1 (HIV-1) viral proteins disrupt the normal host cellular immune pathways thus exploiting the cellular machinery for replication, survival and to escape host immune attack. Here we evaluated the direct effects of HIV-1 Vpr-mediated immune modulation of infected T cells. Vpr specifically downregulated the expression of CD28 and increased the expression of CTLA-4, whereas no significant difference in the expression of CD25 and HLA-DR was observed. Interferon gamma (IFN-gamma) production in T cells was evaluated as a measure of the downstream effector functions. Results indicate that Vpr significantly inhibited IFN-gamma production and this may, in part, due to Vpr's ability to inhibit the nuclear translocation of NF-kappaB, and its transcriptional regulation. Together these results support that HIV-1 Vpr selectively dysregulates the immune functions at multiple levels and exerts its inhibitory effects in the presence of other viral proteins.

Immunodetection of human immunodeficiency virus type 1 (HIV-1) Vpr in brain tissue of HIV-1 encephalitic patients

Human immunodeficiency virus (HIV) encephalitis (HIVE), the most severe neurological complication associated with HIV-1 infection, leads to the onset of HIV-1-associated dementia (HAD). Several HIV-1 viral proteins have been implicated in HIVE-associated neurodegeneration. HIV-1 viral protein R (Vpr), a virion associated gene product known to induce apoptosis in nonproliferating cells, including neurons, is thought to contribute to the neuropathogenesis associated with HIVE. Though current research suggests that Vpr plays a significant role in neuropathogenesis, the presence of Vpr in the brain tissue of HIVE patients has not been assessed. Using a panel of HIVE patient brain tissue, the authors have shown that Vpr is present in detectable amounts in both the basal ganglia and frontal cortex of all HIVE brain tissue samples tested. Double immunofluorescence indicated that Vpr was found in the macrophages and neurons, but not in the astrocytes, of HIVE patients. These results for the first time show the presence of Vpr in vivo and further support the role of Vpr in neuropathogenesis.

Development and characterization of ten monoclonal anti-Vpr antibodies

HIV-1 Vpr is a 96-amino acid auxiliary protein that performs numerous activities during viral infection. In the present study, 10 antibodies were generated after mice immunization with either the N- or the C-terminus domain of Vpr, respectively, Vpr(1-51) and Vpr(52-96). ELISA and immunoblot experiments using pure synthetic overlapping Vpr peptides suggested that these anti-Vpr antibodies could be classified into five groups and that they recognized conformational or linear Vpr epitopes. Further analysis revealed the effect of C-terminal arginine mutations on the antibody binding. Two of the antibodies precipitated Vpr expressed after transfection of a Vpr-encoding vector in human cells. More importantly, one of them was able to detect Vpr in HIV-1-infected U1 cells and in HIV-1-infected human PBMC. Surface plasmon resonance experiments demonstrated that some of these antibodies prevented the interaction between Vpr and one of its cellular partners, the adenine nucleotide translocator. Thus, these anti-Vpr monoclonal antibodies may be useful to any laboratory working on the molecular mechanism of HIV-1 infection.

A suboptimal 5' splice site downstream of HIV-1 splice site A1 is required for unspliced viral mRNA accumulation and efficient virus replication

Background

Inefficient alternative splicing of the human immunodeficiency virus type 1(HIV-1) primary RNA transcript results in greater than half of all viral mRNA remaining unspliced. Regulation of HIV-1 alternative splicing occurs through the presence of suboptimal viral 5' and 3' splice sites (5' and 3'ss), which are positively regulated by exonic splicing enhancers (ESE) and negatively regulated by exonic splicing silencers (ESS) and intronic splicing silencers (ISS). We previously showed that splicing at HIV-1 3'ss A2 is repressed by ESSV and enhanced by the downstream 5'ss D3 signal. Disruption of ESSV results in increased vpr mRNA accumulation and exon 3 inclusion, decreased accumulation of unspliced viral mRNA, and decreased virus production.

Results

Here we show that optimization of the 5'ss D2 signal results in increased splicing at the upstream 3'ss A1, increased inclusion of exon 2 into viral mRNA, decreased accumulation of unspliced viral mRNA, and decreased virus production. Virus production from the 5'ss D2 and ESSV mutants was rescued by transient expression of HIV-1 Gag and Pol. We further show that the increased inclusion of either exon 2 or 3 does not significantly affect the stability of viral mRNA but does result in an increase and decrease, respectively, in HIV-1 mRNA levels. The changes in viral mRNA levels directly correlate with changes in tat mRNA levels observed upon increased inclusion of exon 2 or 3.

Conclusion

These results demonstrate that splicing at HIV-1 3'ss A1 is regulated by the strength of the downstream 5'ss signal and that suboptimal splicing at 3'ss A1 is necessary for virus replication. Furthermore, the replication defective phenotype resulting from increased splicing at 3'ss A1 is similar to the phenotype observed upon increased splicing at 3'ss A2. Further examination of the role of 5'ss D2 and D3 in the alternative splicing of 3'ss A1 and A2, respectively, is necessary to delineate a role for non-coding exon inclusion in HIV-1 replication.

HIV-1 Viral Protein-R (VPR) Protects against Lethal Superantigen Challenge While Maintaining Homeostatic T Cell Levels in Vivo

The HIV-1 accessory protein Vpr exhibits many interesting features related to macrophage and T cell biology. As a viral protein or as a soluble molecule it can suppress immune cell activation and cytokine production in vitro in part by targeted inhibition of NF-kappaB. In this regard we sought to test its effects in vivo on an NF-kappaB-dependent immune pathway. We examined the activity of Vpr in a lethal toxin-mediated challenge model in mice. Intravenous delivery of Vpr was sufficient to protect mice from lethal challenge with staphylococcal endotoxin B (SEB). Furthermore, Vpr protected host CD4+ T cells from in vivo depletion likely by preventing induction of AICD of SEB-exposed cells in a post-toxin-binding fashion. Understanding the biology of Vpr's activities in this model may allow for new insight into potential mechanisms of hyperinflammatory disease and into Vpr pathobiology in the context of HIV infection.

HIV and inflammation

A main feature of HIV infection is the expression of several proinflammatory cytokines. Proinflammatory cytokines expressed as soluble factors or membrane-bound molecules regulate both HIV replication and T cell apoptosis. Proinflammatory cytokines have key roles in the HIV lifecycle, especially at the level of transcription, favouring the ability of HIV to establish latent reservoirs. In addition, proinflammatory cytokines are involved in both CD4+ T cell and CD8+ T cell apoptosis, resulting in immune suppression. Moreover, several HIV proteins such as Nef, Tat, and Vpr hijack proinflammatory cytokine signaling, further underlining the potential importance of inflammation in HIV pathogenesis. In vivo chronic inflammatory conditions have been correlated to increased levels of viremia and accelerated disease progression. This article raises the possibility that inflammation plays a crucial role in both immune suppression and the formation of viral reservoirs during HIV infection. Understanding the role of inflammation in HIV infection could lead to new therapeutic strategies that could ultimately enhance immune restoration and limit the formation of viral reservoirs in HIV-infected patients.

The majority of currently circulating human immunodeficiency virus type 1 clade B viruses fail to prime cytotoxic T-lymphocyte responses against an otherwise immunodominant HLA-A2-restricted epitope: implications for vaccine design

Human immunodeficiency virus type 1 (HIV-1) mutates to escape immune selection pressure, but there is little evidence of selection mediated through HLA-A2, the dominant class I allele in persons infected with clade B virus. Moreover, HLA-A2-restricted responses are largely absent in the acute phase of infection as the viral load is being reduced, suggesting that circulating viruses may lack immunodominant epitopes targeted through HLA-A2. Here we demonstrate an A2-restricted epitope within Vpr (Vpr59-67) that is targeted by acute-phase HIV-1-specific CD8+ T cells, but only in a subset of persons expressing HLA-A2. Individuals in the acute stage of infection with viruses containing the most common current sequence within this epitope (consensus sequence) were unable to mount epitope-specific T-cell responses, whereas subjects infected with the less frequent I60L variant all developed these responses. The I60L variant epitope was a stronger binder to HLA-A2 and was recognized by epitope-specific T cells at lower peptide concentrations than the consensus sequence epitope. These data demonstrate that HLA-A2 is capable of contributing to the acute-phase cytotoxic T-lymphocyte response in infected subjects, but that most currently circulating viruses lack a dominant immunogenic epitope presented by this allele, and suggest that immunodominant epitopes restricted by common HLA alleles may be lost as the epidemic matures.

Simian immunodeficiency virus Vpr/Vpx proteins kill bystander noninfected CD4+ T-lymphocytes by induction of apoptosis

The depletion of CD4+ T-lymphocytes central to the immunodeficiency in acquired immunodeficiency syndrome (AIDS) is largely mediated by apoptosis of both infected and uninfected cells, but the mechanisms involved and the viral proteins responsible are still poorly characterized. It has recently been suggested that, in human and simian immunodeficiency virus (HIV) and SIV, Vpr is a major modulator of apoptosis in infected cells. Recently, we have reported on a chimera of caprine arthritis-encephalitis virus (CAEV) carrying vpr/vpx genes from SIVmac239, which is replication competent in goat macrophages but not in lymphocytes or human cells. Despite infection being restricted to macrophages, inoculation of primary goat peripheral blood mononuclear cells (PBMCs) with this chimera induced apoptosis in the lymphocyte population. In addition, when infected goat synovial membrane (GSM) cells were co-cultured with human CD4+ T lymphocyte SupT1 cell line, these CD4+ T cells showed increased apoptosis. The parental CAEV induced no significant apoptosis in goat PBMC cultures or in co-cultures with human SupT1 lymphocytes. This indicates that SIV Vpr/Vpx proteins indeed mediate apoptosis of T-lymphocytes and, moreover, do so without the need for active infection of these cells. Moreover, this apoptosis was observed when SupT1s were cocultured in direct contact, but not in absence of contact with CAEV-pBSCAvpxvpr-infected GSM cells. In view of these data, we propose that SIV Vpx/Vpr activate cell-to-cell contact-dependent extracellular signaling pathways to promote apoptotic death of uninfected bystander T-lymphocytes. Understanding this mechanism might bring insight for intervening in the loss of CD4+ T lymphocytes in the SIV infection model and in human AIDS.

Antibody reactivity to HIV-1 Vpu in HIV-1/AIDS patients on highly active antiretroviral therapy

Human immunodeficiency virus type 1 (HIV-1) Vpu protein promotes both extracellular release of viral particles and degradation of CD4 in the endoplasmic reticulum. The correlation of anti-Vpu antibody (Ab) reactivity to Vpu and AIDS disease progression was studied in 162 HIV-1/AIDS patients after they had received highly active antiretroviral therapy (HAART) for 1 year. Anti-Vpu Ab reactivity was analyzed by Western blot using a recombinant Vpu protein. Results showed that at baseline (prior to initiation of HAART), 31.5% of patients (51/162) had anti-Vpu Ab. The proportion of anti-Vpu Ab in patients with CD4 counts > or =500, 200-500 and <200/mm(3) were 40.6, 34.7 and 14.3%, respectively (chi(2) test, p < 0.05). In addition, decreasing levels of anti-Vpu Ab reactivity were significantly correlated with increasing levels of HIV-1 viral load. After receiving HAART for 1 year, 7 of 111 anti-Vpu Ab-negative patients (6.3%) seroconverted (- --> + group) and 8 of 51 anti-Vpu Ab-positive (15.7%) patients became negative (+ --> - group). Among 104 anti-Vpu Ab-negative patients, 40 were selected for analysis of the VPU gene. All of them had an intact VPU gene. Patients were further divided into four groups according to their anti-Vpu Ab serostatus and anti-HIV-1 Ab was measured. The results showed that only the anti-Vpu Ab seroconverted group (- --> +) had increased serum levels of anti-HIV-1 Abs after 1 year of HAART, while the other three groups (+ --> +, - --> - and + --> -) had decreased serum levels of anti-HIV-1 Abs after 1 year of HAART (p < 0.05). In conclusion, the presence of anti-Vpu Ab is associated with improved prognosis following HIV-1 infection, and seroconversion of anti-Vpu Ab in patients on HAART indicates significant recovery of immunity.

Antibody fragments selected by phage display against the nuclear localization signal of the HIV-1 Vpr protein inhibit nuclear import in permeabilized and intact cultured cells

The HIV-1 Vpr protein harbors a nuclear localization signal in its N-terminal domain. A peptide bearing this domain and which is designated VprN has been used as a target to screen a phage display single chain Fv (scFv) library. Here we report the isolation of anti-VprN scFv fragments from this library. The purified scFv fragments were able to bind the VprN peptide in an ELISA-based system and to inhibit VprN-mediated nuclear import in permeabilized as well as in intact microinjected cells. Furthermore, the anti-VprN scFv fragments recognized the full-length recombinant Vpr protein and inhibited its nuclear import. The same scFv fragments did not inhibit nuclear import mediated by the nuclear localization signal of the SV40 large T-antigen demonstrating a specific effect. The use of the described inhibitory anti-VprN scFv fragments to study nuclear import of viral karyophilic proteins and their therapeutic potential is discussed.

Antibodies to Tat and Vpr in the GRIV cohort: differential association with maintenance of long-term non-progression status in HIV-1 infection

The HIV-1 regulatory protein Tat and the accessory protein Vpr are thought to stimulate viral replication and contribute to viral pathogenesis as extracellular proteins. Humoral immune responses to these early viral proteins may therefore be beneficial. We examined serum anti-Tat and anti-Vpr IgG by ELISA in the GRIV cohort of HIV-1 seropositive slow/non-progressors (NP) and fast-progressors (FP), and in seronegative controls. Based on information obtained during a brief follow-up period (median = 20 months), NPs were sub-grouped as those maintaining non-progression status and therefore stable (NP-S), and those showing signs of disease progression (NP-P). As the primary comparison, initial serum anti-Tat and anti-Vpr IgG (prior to follow-up) were analyzed in the NP sub-groups and in FPs. Anti-Tat IgG was significantly higher in stable NP-S compared to unstable NP-P (P = 0.047) and FPs (P < 0.0005); the predictive value of higher anti-Tat IgG for maintenance of non-progression status was 92% (P = 0.029). In contrast, no-difference was observed in anti-Vpr IgG between NP-S and NP-P, although both were significantly higher than FPs (P </= 0.001). Serum anti-Tat IgG mapped to linear epitopes within the amino-terminus, the basic domain and the carboxy-terminal region of Tat in stable NP-S. Similar epitopes were identified in patients immunized with the Tat-toxoid in a Phase I study in Milan. High titer serum anti-Tat IgG from both GRIV and Milan cohorts cross-reacted in ELISA with Tat from diverse viral isolates, including HIV-1 subtype-E (CMU08) and SIVmac251 Tat; a correlation was observed between anti-Tat IgG titers and cross-reactivity. These results demonstrate that higher levels of serum anti-Tat IgG, but not anti-Vpr IgG, are associated with maintenance of non-progression status in HIV-1 infection. Evidence that vaccination with the Tat toxoid induces humoral immune responses to Tat similar to those observed in stable non-progressors is encouraging for vaccine strategies targeting Tat.

Recombinant Vpr (rVpr) causes augmentation of HIV-1 p24 Ag level in U1 cells through its ability to induce the secretion of TNF

We have found that an HIV-1 accessory gene product Vpr enhanced HIV-1 reproduction in U1 cells chiefly by the induction of TNF, a proinflammatory cytokine, which was also known to be an activator of HIV-1 reproduction. We have generated the functional HIV-1 accessory gene product Vpr in bacterial cells. Vpr was generated in an Escherichia coli system (rVpr), purified with antibodies (Ab) to the 16 C-terminal amino acids of Vpr. The purified rVpr of 15 kDa was examined for its ability to upregulate HIV-1 reproduction in U1 cells, which is a reported function of the authentic Vpr. rVpr upregulated HIV-1 reproduction in U1 cells in a dose-dependent manner and induced the secretion of TNF. The upregulation of HIV-1 by rVpr was completely inhibited not only by anti-Vpr antibodies but also by anti-TNF antibody. These findings suggested that Vpr caused an HIV-1 reproduction in U1 cells through the induction of TNF.

HIV-1 protein Vpr suppresses IL-12 production from human monocytes by enhancing glucocorticoid action: potential implications of Vpr coactivator activity for the innate and cellular immunity deficits observed in HIV-1 infection

The HIV-1 protein Vpr has glucocorticoid receptor coactivator activity, potently increasing the sensitivity of glucocorticoid target tissues to cortisol. Patients with AIDS and normal cortisol secretion have manifestations compatible with glucocorticoid hypersensitivity of the immune system, such as suppression of innate and cellular immunities. The latter can be explained by glucocorticoid-induced inhibition of cytokine networks regulating innate and Th1-driven cellular immunity. We demonstrated that extracellularly administered Vpr protein dose-dependently potentiated glucocorticoid-induced suppression of both mRNA expression and secretion of IL-12 subunit p35 and IL-12 holo-protein, but not IL-12 subunit p40 or IL-10, by human monocytes/macrophages stimulated with LPS or heat-killed, formalin-fixed Staphylococcus aureus (Cowan strain 1). This effect was inhibited by the glucocorticoid receptor antagonist RU 486. Also, Vpr changed the expression of an additional five glucocorticoid-responsive genes in the same direction as dexamethasone and was active in potentiating the trans-activation, but not the trans-repression, properties of the glucocorticoid receptor on nuclear factor kappaB- or activating protein 1-regulated simple promoters. Thus, extracellular Vpr enhances the suppressive actions of the ligand-activated glucocorticoid receptor on IL-12 secretion by human monocytes/macrophages. Through this effect, Vpr may contribute to the suppression of innate and cellular immunities of HIV-1-infected individuals and AIDS patients.

Vpr- and Nef-dependent induction of RANTES/CCL5 in microglial cells

Microglia are pivotal in the pathogenesis of AIDS dementia, as they serve as the major target of HIV infection in the CNS. In addition, activation of microglia correlates best with clinical dementia. Although the beta-chemokine RANTES/CCL5 is important in modulating HIV infection as well as cellular activation, no information is available regarding how its expression is regulated in microglia by HIV-1. Here we report that RANTES/CCL5 expression is induced in microglia by HIV-1, but that this requires infection by HIV-1. This conclusion was supported by (1) the delayed kinetics coinciding with viral replication; (2) the lack of effect of X4 viruses; (3) inhibition by the reverse transcriptase inhibitor AZT, and (4) the lack of effect of cytokine antagonists or antibodies. Interestingly, RANTES/CCL5 production was dependent on the viral accessory protein Vpr, in addition to Nef, demonstrating a novel role for Vpr in chemokine induction in primary macrophage-type cells. Furthermore, the specific p38 MAP kinase inhibitor SB203580 augmented chemokine expression in microglia, indicating a negative role played by p38. These data suggest unique features of RANTES/CCL5 regulation by HIV-1 in human microglial cells.

Inclusion of Vpr accessory gene in a plasmid vaccine cocktail markedly reduces Nef vaccine effectiveness in vivo resulting in CD4 cell loss and increased viral loads in rhesus macaques

We compared the immunogenicity of plasmid vaccines containing multiple human immunodeficiency virus (HIV) antigens and found that covaccination with plasmids expressing HIV-1 14 kDa vpr gene product profoundly reduces antigen-specific CD8-mediated cytotoxic T-cell activity (CTL). Interestingly, Th1 type responses against codelivered antigens (pGag-Pol, pNef, etc.) encoded by the plasmid vaccines were suppressed. This suggested that vpr might compromise CD8 T-cell immunity in vivo during infection. A pilot primate vaccine study was designed to test the hypothesis to compare the following groups: unvaccinated controls, animals vaccinated without simean immunodeficiency virus (SIV)-Nef antigen plasmid, and animals covaccinated with the identical plasmid antigen and a plasmid construct encoding SIV Vpr/Vpx. Animals were subsequently challenged intrarectally with pathogenic SIVmac251 after the final vaccination of a multiple immunization protocol. Control animals were all infected and exhibited high viral loads and rapid CD4+ T-cell loss. In contrast, the Nef plasmid-vaccinated animals were also infected but exhibited preservation of CD4+ T-cells and a multilog reduction in viral load compared with controls. Animals covaccinated multiple times with the Nef vaccine and pVpr/Vpx plasmid suffered rapid and profound loss of CD4+ T-cells. These results have important implications for the design of multicomponent and particle vaccines for HIV-1 as well as for our understanding of HIV/SIV pathogenesis in vivo.

Vpr is preferentially targeted by CTL during HIV-1 infection

The HIV-1 accessory proteins Vpr, Vpu, and Vif are essential for viral replication, and their cytoplasmic production suggests that they should be processed for recognition by CTLs. However, the extent to which these proteins are targeted in natural infection, as well as precise CTL epitopes within them, remains to be defined. In this study, CTL responses against HIV-1 Vpr, Vpu, and Vif were analyzed in 60 HIV-1-infected individuals and 10 HIV-1-negative controls using overlapping peptides spanning the entire proteins. Peptide-specific IFN-gamma production was measured by ELISPOT assay and flow-based intracellular cytokine quantification. HLA class I restriction and cytotoxic activity were confirmed after isolation of peptide-specific CD8(+) T cell lines. CD8(+) T cell responses against Vpr, Vpu, and Vif were found in 45%, 2%, and 33% of HIV-1-infected individuals, respectively. Multiple CTL epitopes were identified in functionally important regions of HIV-1 Vpr and Vif. Moreover, in infected individuals in whom the breadth of HIV-1-specific responses was assessed comprehensively, Vpr and p17 were the most preferentially targeted proteins per unit length by CD8(+) T cells. These data indicate that despite the small size of these proteins Vif and Vpr are frequently targeted by CTL in natural HIV-1 infection and contribute importantly to the total HIV-1-specific CD8(+) T cell responses. These findings will be important in evaluating the specificity and breadth of immune responses during acute and chronic infection, and in the design and testing of candidate HIV vaccines.

Simultaneous positive and purifying selection on overlapping reading frames of the tat and vpr genes of simian immunodeficiency virus

Tat-specific cytotoxic T cells have previously been shown to exert positive Darwinian selection favoring amino acid replacements of an epitope of simian immunodeficiency virus (SIV). The region of the tat gene encoding this epitope falls within a region of overlap between the tat and vpr reading frames, and nonsynonymous nucleotide substitutions in the tat reading frame were found to occur disproportionately in such a way as to cause synonymous changes in the vpr reading frame. Comparison of published complete SIV genomes showed Tat to be the least conserved at the amino acid level of nine proteins encoded by the virus, while Vpr was one of the most conserved. Numerous parallel amino acid changes occurred within the Tat epitope independently in different monkeys, and purifying selection on the vpr reading frame, by limiting acceptable nonsynonymous substitutions in the tat reading frame, evidently has enhanced the probability of parallel evolution.

T cell apoptosis causes peripheral T cell depletion in mice transgenic for the HIV-1 vpr gene

Vpr, an accessory protein of HIV, is known to affect viral replication as well as cell growth, differentiation, and apoptosis in vitro. To investigate its pathogenicity in vivo, we have produced mice transgenic for the HIV-1 vpr gene with the CD4 enhancer/promoter. Interestingly, apoptotic death of T lymphocytes was enhanced in those mice, causing marked reduction of T cells in lymphatic organs and peripheral blood. Involvement of Bcl-x, Bax, and Caspase-1, but not of the Fas-Fas ligand system, was suggested in the apoptotic processes. These observations suggest that Vpr is involved in the pathogenesis of T cell depletion in HIV-infected people.

Identification of novel HLA-A2-restricted human immunodeficiency virus type 1-specific cytotoxic T-lymphocyte epitopes predicted by the HLA-A2 supertype peptide-binding motif

Virus-specific cytotoxic T-lymphocyte (CTL) responses are critical in the control of human immunodeficiency virus type 1 (HIV-1) infection and will play an important part in therapeutic and prophylactic HIV-1 vaccines. The identification of virus-specific epitopes that are efficiently recognized by CTL is the first step in the development of future vaccines. Here we describe the immunological characterization of a number of novel HIV-1-specific, HLA-A2-restricted CTL epitopes that share a high degree of conservation within HIV-1 and a strong binding to different alleles of the HLA-A2 superfamily. These novel epitopes include the first reported CTL epitope in the Vpr protein. Two of the novel epitopes were immunodominant among the HLA-A2-restricted CTL responses of individuals with acute and chronic HIV-1 infection. The novel CTL epitopes identified here should be included in future vaccines designed to induce HIV-1-specific CTL responses restricted by the HLA-A2 superfamily and will be important to assess in immunogenicity studies in infected persons and in uninfected recipients of candidate HIV-1 vaccines.

Generation of monoclonal antibodies specifically directed against the proximal zinc finger of HIV type 1 NCp7

The HIV-1 NCp7 contains two spatially close zinc fingers, required for the production of infectious particles. To investigate in more detail the function of the zinc finger domain, monoclonal antibodies were generated with a cyclic analog of the NCp7 proximal zinc finger. This analog was shown to bind zinc ions and to preserve the highly folded structure of the native peptide (Dong C-Z et al.: J Am Chem Soc 1995;117:2726-2731). We report here two monoclonal antibodies (2B10 and 4D3), which are the first monoclonal antibodies directed against CCHC NCp7 zinc fingers. Dot-blot experiments revealed that a few nanograms of synthetic NCp7 can be detected on a nitrocellulose membrane. Whereas 2B10 appears specific for an epitope located in sequence 19-27 of NCp7, 4D3 appears to be structurally specific. Immunocomplex affinities were evaluated, using BIAcore technology, to be up to 1 and 10 nM, respectively, for 2B10 and 4D3 in 100 mM NaCl. These antibodies were able to recognize NCp7 in the Gag polyprotein precursor and were shown to immunoprecipitate NCp7 from a cell supernatant. Moreover, NCp7-Vpr interaction mediated by the zinc fingers is inhibited by 2B10, emphasizing the role of these domains in the protein-protein complex. These results indicate that 2B10 and 4D3 behave as useful tools for studying both NC protein functions during the course of virion morphogenesis and the role played by its zinc finger domain at various steps in the retroviral life cycle.

Epitope-tagging approach to determine the stoichiometry of the structural and nonstructural proteins in the virus particles: amount of Vpr in relation to Gag in HIV-1

We used an epitope-tagging approach to determine the ratio of Gag (structural) to Vpr (nonstructural) in the virus particles directed by human immunodeficiency virus type 1. For this purpose, chimeric Gag and Vpr expression plasmids were constructed with the Flag epitope (DYKDDDDK), and the sequences corresponding to the chimeric protein were introduced into human immunodeficiency virus type 1 proviral DNA (NL4-3) to determine the ratio in the virus particles when these proteins are expressed in cis. In addition, NL4-3 DNA was modified to disrupt Vpr synthesis to determine the extent of incorporation of Vpr-FL when it is expressed in trans through a heterologous promoter. The analysis of virus particles generated by transfection of proviral DNA into RD cells indicated that (1) the ratio of Gag to Vpr in virus particles, when Vpr-FL is expressed in cis (in the context of proviral DNA), is in the range of 150-200:1 (14-18 molecules of Vpr per virion) and (2) the expression of Vpr-FL in trans showed efficient incorporation with a Gag to Vpr ratio of 5-7:1 (392-550 molecules of Vpr). These results suggest that the presence of the same epitope on different viral proteins may provide an accurate comparison of these proteins in the virus particles.

Packageable antiviral therapeutics against human immunodeficiency virus type 1: virion-targeted virus inactivation by incorporation of a single-chain antibody against viral integrase into progeny virions

To determine their activities as an antiviral agent packageable within virions and suitable for continued expression in cells, we tested a single-chain antibody (scAb) against human immunodeficiency virus type 1 (HIV-1) integrase and its three fusion proteins: fused to viral protein R (scab-Vpr), a double-cassette of the WXXF motif binding to Vpr (scAb-WXXF), and viral major capsid protein (scAb-CA), respectively. Cotransfection of human 293T cells with expression plasmid for scAb-Vpr or -WXXF along with HIV-1 clone pLAI resulted in the production of a normal amount of progeny virions with infectivity decreased by more than 10(3)-fold. Immunoblot analyses showed that scAb-Vpr or -WXXF was associated with virions, whereas scAb or scAb-CA was not, suggesting that scAb-Vpr or -WXXF was incorporated into virions. The incorporation of scAb-WXXF appeared to be Vpr dependent, because the fusion protein was associated with the wild-type but not with Vpr-truncated HIV-1 virions. Since G418-selected HeLa clones carrying expression plasmid for scAb-WXXF were obtained much more frequently than those for scAb-Vpr, scAb-WXXF was inferred to be less toxic to cells than scAb-Vpr. These results suggest that scAb-WXXF may serve as a novel class of antiviral therapeutic that inactivates progeny HIV virions from within.

Protection of macaques against a SHIV with a homologous HIV-1 Env and a pathogenic SHIV-89.6P with a heterologous Env by vaccination with multiple gene-deleted SHIVs

To evaluate the potential of SHIVs as anti-HIV-1 live vaccines, we constructed two gene-deleted SHIVs, designated SHIV-drn and SHIV-dxrn. The former lacks vpr/nef and the latter lacks vpx/vpr/nef. Four macaques that had been vaccinated with SHIV-drn were challenged with SHIV-NM-3rN, which has an HIV-1 Env that is the same as that of SHIV-drn. No challenge virus was detected by DNA PCR in, or recovered from, two of the macaques. In the other two, challenge virus was detected once and twice, respectively. Plasma viral loads were much lower than those in unvaccinated controls. Another four macaques were vaccinated with SHIV-dxrn. These macaques showed resistance but less than that of SHIV-drn-vaccinated macaques. When the two SHIV-drn-vaccinated macaques were challenged with pathogenic SHIV-89.6P, which has an HIV-1 Env that is antigenically different from that of SHIV-drn, replication of the challenge virus was restricted, and the usual decrease in the number of CD4(+) cells was prevented. In this protection, it is noteworthy that protection involved not only neutralizing antibodies and killer cell activity, but also other unknown specific and nonspecific immunity elicited by the infection.

Gene-mutated HIV-1/SIV chimeric viruses as AIDS live attenuated vaccines for potential human use

To develop an AIDS vaccine for human use as well as a suitable animal model for AIDS research, we constructed a series of HIV-1/SIVmac chimeric viruses (SHIVs). We successfully generated a SHIV (designated as NM-3rN) having the HIV-1 env gene, which enabled the evaluation of the efficacy of HIV-1 Env-targeted vaccines in macaque monkeys instead of chimpanzees. Two NM-3rN derivatives (NM-3 and NM-3n) induced long-term anti-virus immunities without manifesting the disease. The monkeys vaccinated with NM-3 or NM-3n became resistant to a challenge inoculation with NM-3rN. Serum from a monkey vaccinated with NM-3 neutralized not only the parental HIV-1 (NL432), but also an antigenically different HIV-1 (MN). In vivo experiments confirmed the heterologous protection against an SHIV having the HIV-1 (MN) env. In addition to specific immunity including neutralizing antibodies and cytotoxic T lymphocyte activity, nonspecific immunity such as natural killer activity is associated with this protection. These data suggest that the live vaccine has the ability to protect individuals against various types of HIVs. These SHIVs should contribute to the development of future anti-HIV-1 live vaccines in humans.

Protection of monkeys vaccinated with vpr- and/or nef-defective simian immunodeficiency virus strain mac/human immunodeficiency virus type 1 chimeric viruses: a potential candidate live-attenuated human AIDS vaccine

Two simian immunodeficiency virus strain mac (SIVmac)/human immunodeficiency virus type 1(HIV-1) chimeric viruses (SHIVs), designated NM-3 and NM-3n, with env derived from HIV-1 and defective vpr (plus defective nef for NM-3), were inoculated into seven macaques. These macaques were transiently or persistently infected and most of them produced long-lasting neutralizing antibodies and Env-specific killer T cells to HIV-1 with no AIDS-like symptoms. When they were challenged with another SHIV with intact vpr and nef (designated NM-3rN), all were protected as judged by virus recovery, DNA detection by PCR and antibody responses. Anti-HIV-1 Env-specific killer T cells were considered to have played a major role in this protection, but a non-specific defence mechanism as well as specific immunity also appeared to be involved. Thus, these two non-pathogenic SHIVs induced long-lasting protective immunities in macaques, suggesting the possibility of gene-defective SHIVs as attenuated live vaccines for human use.

Induction of neutralizing antibodies against human immunodeficiency virus type 1 using synthetic peptide constructs containing an immunodominant T-helper cell determinant from vpr

Identification of immunodominant T-helper-cell determinants after natural infection is an important step in the design of immunogens for potential use in vaccination. Using cells from human immunodeficiency virus type 1 (HIV-1)-infected individuals and a panel of peptides encompassing the sequence of the regulatory protein vpr from HIV-1, we identified the T-helper determinant QLLFIHFRIGCRHSR, which is active in 37.5% of these individuals. To gain insight on the efficacy of this peptide in helping induce neutralizing antibodies against a B-cell determinant (BD), we synthesized constructs containing B- and T-cell determinants and tested them in BALB/c mice, the highest responders to the T-cell determinant moiety among several strains tested. These immunogens induced antibodies against two chosen B-cell determinants from HIV-1IIIB gp160 (amino acids 310-322 from the V3 loop of gp120 and 736-751 from gp41) that were able to neutralize HIV-1 infection in vitro. The highest neutralization titer against HIV-1IIIB was obtained by immunization with the homopolymer of the construct containing the T-cell epitope from vpr and the B-cell epitope from the V3 loop. We believe that the immunodominant T-cell determinant from vpr is a promising epitope to consider in the design of future peptide vaccines.

A synthetic protein corresponding to the entire vpr gene product from the human immunodeficiency virus HIV-1 is recognized by antibodies from HIV-infected patients

The 95 amino acid-protein encoded by the non-structural vpr gene of the human immunodeficiency virus type 1 (LAV-1BRU isolate) was chemically synthesized by solid phase methodology. The synthetic vpr protein was characterized by amino acid analysis, sequence analysis, RP-HPLC, and urea-SDS PAGE. Using a radioimmunoassay, antibodies to the synthetic protein were detected in sera of 25% of HIV 1-seropositive patients tested. Western blot analysis suggested that the antibodies preferentially recognize the dimeric form of vpr.