HIV-1 Infection Of Primary CD4 Research Articles

Transcriptional Interference Antagonizes Proviral Gene Expression to Promote HIV Latency

Eradication of the latent HIV reservoir remains a major barrier to curing AIDS. However, the mechanisms that direct viral persistence in the host are not well understood. Studying a model system of postintegration latency, we found that viral integration into the actively transcribed host genes led to transcriptional interference (TI) caused by the elongating RNA polymerase II (RNAPII) transcribing through the viral promoter. The resulting physical exclusion of preinitiation complex formation on the 5' long terminal repeat (LTR) promoted the silencing of HIV transcription. This block could be counteracted by inhibiting the upstream transcription or cooperatively activating viral transcription initiation and elongation. Importantly, PCR-based analysis, which detects host transcription through the 5'LTR independently of the viral integration site, revealed substantial levels of this transcription in HIV-infected primary CD4(+) T cells. Collectively, our findings suggest that TI contributes significantly to HIV latency and should be considered when attempting to purge the latent reservoir.

Silencing of HALP Decreases HIV-1 Infection of Primary CD4+ T-cells (45.4)

Abstract HIV/AIDS is an ideal candidate for a novel gene therapy approach since it is an incurable and terminal disease. We have identified a set of candidate host cell genes, associated with survival of HIV-infected T-cells. We named one of these genes, “HALP”, for “HIV-Associated Life Preserver”. Recently, we used a lentiviral vector to stably express HALP shRNA in primary human CD4 T-cells. In the absence of HIV infection, silencing of HALP appeared to have no effect on viability of these cells. As predicted, silencing of HALP markedly reduced HIV infection of primary CD4+ T-cells, as measured by the percent of p24+ cells and by supernatant p24. Published data suggest that hypoxia induces HALP expression by increasing the activity of the transcription factor, Hif-1α. HIF-1 binding sites have been identified within the HALP promoter and HALP is responsive to HIF-1 in non-immune cells. We show here that HIV-1 infection of primary CD4+ T-cells increases Hif-1α mRNA expression, as measured by real time RT-PCR. Transfection of T-cells with wild-type Hif-1α or with a mutated form of Hif that is resistant to proteolysis (Hif-DPA) also increased expression of HALP mRNA. These data are consistent with a pathway of Hif-induced HALP expression in HIV-1 infected cells, leading to a hypoxia-like stress response and, ultimately, to cell survival. Our work represents one of the first attempts to search for novel cellular genes that contribute to viral inhibition of host cell apoptosis and, thus, to viral latency. HALP represents a candidate for a host cell anti-apoptotic protein, which is triggered by HIV infection, and may provide a novel molecular target for drug use and design.

Expression of Nef Downregulates CXCR4, the Major Coreceptor of Human Immunodeficiency Virus, from the Surfaces of Target Cells and Thereby Enhances Resistance to Superinfection

Lentiviral Nef proteins are key factors for pathogenesis and are known to downregulate functionally important molecules, including CD4 and major histocompatibility complex class I (MHC-I), from the surfaces of infected cells. Recently, we demonstrated that Nef reduces cell surface levels of the human immunodeficiency virus type 1 (HIV-1) entry coreceptor CCR5 (N. Michel, I. Allespach, S. Venzke, O. T. Fackler, and O. T. Keppler, Curr. Biol. 15:714-723, 2005). Here, we report that Nef downregulates the second major HIV-1 coreceptor, CXCR4, from the surfaces of HIV-infected primary CD4 T lymphocytes with efficiencies comparable to those of the natural CXCR4 ligand, stromal cell-derived factor-1 alpha. Analysis of a panel of mutants of HIV-1(SF2) Nef revealed that the viral protein utilized the same signature motifs for downmodulation of CXCR4 and MHC-I, including the proline-rich motif P(73)P(76)P(79)P(82) and the acidic cluster motif E(66)E(67)E(68)E(69.) Expression of wild-type Nef, but not of specific Nef mutants, resulted in a perinuclear accumulation of the coreceptor. Remarkably, the carboxy terminus of CXCR4, which harbors the classical motifs critical for basal and ligand-induced receptor endocytosis, was dispensable for the Nef-mediated reduction of surface exposure. Functionally, the ability of Nef to simultaneously downmodulate CXCR4 and CD4 correlated with maximum-level protection of Nef-expressing target cells from fusion with cells exposing X4 HIV-1 envelopes. Furthermore, the Nef-mediated downregulation of CXCR4 alone on target T lymphocytes was sufficient to diminish cells' susceptibility to X4 HIV-1 virions at the entry step. The downregulation of chemokine coreceptors is a conserved activity of Nef to modulate infected cells, an important functional consequence of which is an enhanced resistance to HIV superinfection.

Suppression of HIV-1 infection in primary CD4 T cells transduced with a self-inactivating lentiviral vector encoding a membrane expressed gp41-derived fusion inhibitor

Peptidomimetics of HIV-1 gp41 sequences required for membrane fusion are potent inhibitors of HIV-1 entry. We hypothesize that expression of a membrane-bound gp41-derived fusion inhibitor will confer HIV-1 resistance to primary CD4 T cells. Efficient gene delivery and stable expression of a membrane-bound gp41-derived fusion inhibitor to primary CD4 T cells was accomplished using a self-inactivating lentiviral vector. A potent antiviral effect was observed when transduced CD4 T cells were challenged with a highly virulent CXCR4-tropic strain of HIV-1. Production of soluble p24 in the supernatant was inhibited 100-fold, and cytopathic effects were evident early in non-transduced cells and absent in transduced cells. Expression of the gp41 sequences was not detrimental to CD4 cells as transduced CD4 T cells exhibited a population doubling time that was equivalent to T cells transduced with a control vector. Results from this study support the rationale to use this lentiviral vector targeted at HIV entry as a potential gene therapy for HIV infection.

Protection from HIV-1 Infection of Primary Cd4 T Cells by Ccr5 Silencing is Effective for the Full Spectrum of Ccr5 Expression

Stable gene silencing by RNA interference (RNAi) can be achieved by expression of small hairpin RNAs (shRNAs) from RNA polymerase III promoters. We have tested lentiviral vectors expressing shRNAs targetting CCR5 in primary CD4 T cells from donors representing various CCR5 and CCR2 genetic backgrounds covering the full spectrum of CCR5 expression levels and permissiveness for HIV-1 infection. A linear decrease in CCR5 expression resulted in a logarithmic decrease in cellular infection, giving up to three logs protection from HIV-1 infection in vitro. Protection was maintained at very high multiplicity of infection. This and other recent reports on RNAi should open a debate about the use of RNAi gene therapy for HIV infection.

Productive HIV-1 Infection of Primary CD4+ T Cells Induces Mitochondrial Membrane Permeabilization Leading to a Caspase-independent Cell Death

We have explored in vitro the mechanism by which human immunodeficiency virus, type 1 (HIV-1) induces cell death of primary CD4+ T cells in conditions of productive infection. Although HIV-1 infection primed phytohemagglutinin-activated CD4+ T cells for death induced by anti-CD95 antibody, T cell death was not prevented by a CD95-Fc decoy receptor, nor by decoy receptors of other members of the TNFR family (TNFR1/R2, TRAILR1/R2/OPG, TRAMP) or by various blocking antibodies, suggesting that triggering of death receptors by their cognate ligands is not involved in HIV-induced CD4 T cell death. HIV-1 induced CD4 T cell shrinkage, cell surface exposure of phosphatidylserine, loss of mitochondrial membrane potential (Deltapsim), and mitochondrial release of cytochrome c and apoptosis-inducing factor. A typical apoptotic phenotype (nuclear chromatin condensation and fragmentation) only occurred in around half of the dying cells. Treatment with benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone, a broad spectrum caspase inhibitor, prevented nuclear chromatin condensation and fragmentation in HIV-infected CD4+ T cells and in a cell-free system (in which nuclei were incubated with cytoplasmic extracts from the HIV-infected CD4+ T cells). Nevertheless, benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone did not prevent mitochondrial membrane potential loss and cell death, suggesting that caspases are dispensable for HIV-mediated cell death. Our findings suggest a major role of the mitochondria in the process of CD4 T cell death induced by HIV, in which targeting of Bax to the mitochondria may be involved.

Impaired function of circulating HIV-specific CD8+ T cells in chronic human immunodeficiency virus infection

AbstractThe functional status of circulating human immunodeficiency (HIV)-specific CD8 T cells in chronically infected subjects was evaluated. By flow cytometry, only 5 of 7 subjects had detectable CD8 T cells that produced IFN-γ after stimulation with HIV-infected primary CD4 T cells. In 2 subjects, the frequency of IFN-γ–producing cells increased 4-fold when IL-2 was added to the culture medium; in another subject, IFN-γ–producing cells could be detected only after IL-2 was added. IFN-γ–producing cells ranged from 0.4% to 3% of CD8 T cells. Major histocompatibility complex–peptide tetramer staining, which identifies antigen-specific T cells irrespective of function, was used to evaluate the proportion of HIV-specific CD8 T cells that may be nonfunctional in vivo. CD8 T cells binding to tetramers complexed to HIV gag epitope SLYNTVATL and reverse transcriptase epitope YTAFTIPSI were identified in 9 of 15 and 5 of 12 HLA-A2–expressing seropositive subjects at frequencies of 0.1% to 1.1% and 0.1 to 0.7%, respectively. Freshly isolated tetramer-positive cells expressed a mixed pattern of memory and effector markers. On average, IFN-γ was produced by less than 25% of tetramer-positive CD8 T cells after stimulation with the relevant gag or reverse transcriptase peptide. In all subjects tested, freshly isolated CD8 T cells were not cytolytic against peptide-pulsed B lymphoblastoid cell line or primary HIV-infected CD4 T-cell targets. Exposure to IL-2 enhanced the cytotoxicity of CD8 T cells against primary HIV-infected CD4 targets in 2 of 2 subjects tested. These results suggest that a significant proportion of HIV-specific CD8 T cells may be functionally compromised in vivo and that some function can be restored by exposure to IL-2.

Impaired function of circulating HIV-specific CD8+ T cells in chronic human immunodeficiency virus infection

The functional status of circulating human immunodeficiency (HIV)-specific CD8 T cells in chronically infected subjects was evaluated. By flow cytometry, only 5 of 7 subjects had detectable CD8 T cells that produced IFN-gamma after stimulation with HIV-infected primary CD4 T cells. In 2 subjects, the frequency of IFN-gamma-producing cells increased 4-fold when IL-2 was added to the culture medium; in another subject, IFN-gamma-producing cells could be detected only after IL-2 was added. IFN-gamma-producing cells ranged from 0.4% to 3% of CD8 T cells. Major histocompatibility complex-peptide tetramer staining, which identifies antigen-specific T cells irrespective of function, was used to evaluate the proportion of HIV-specific CD8 T cells that may be nonfunctional in vivo. CD8 T cells binding to tetramers complexed to HIV gag epitope SLYNTVATL and reverse transcriptase epitope YTAFTIPSI were identified in 9 of 15 and 5 of 12 HLA-A2-expressing seropositive subjects at frequencies of 0.1% to 1.1% and 0.1 to 0.7%, respectively. Freshly isolated tetramer-positive cells expressed a mixed pattern of memory and effector markers. On average, IFN-gamma was produced by less than 25% of tetramer-positive CD8 T cells after stimulation with the relevant gag or reverse transcriptase peptide. In all subjects tested, freshly isolated CD8 T cells were not cytolytic against peptide-pulsed B lymphoblastoid cell line or primary HIV-infected CD4 T-cell targets. Exposure to IL-2 enhanced the cytotoxicity of CD8 T cells against primary HIV-infected CD4 targets in 2 of 2 subjects tested. These results suggest that a significant proportion of HIV-specific CD8 T cells may be functionally compromised in vivo and that some function can be restored by exposure to IL-2.

Viral-Specific Cytotoxic T Lymphocytes Lyse Human Immunodeficiency Virus–Infected Primary T Lymphocytes by the Granule Exocytosis Pathway

Cytotoxic T lymphocytes (CTL) lyse antigen-bearing target cells by two distinct pathways. Whereas granule exocytosis targets any antigen-bearing cell, fas-mediated cytotoxicity kills only fas-expressing cells and does not require antigen expression. Fas pathway activation can potentially lead to lysis of uninfected bystander cells. We examined the relative usage of the two pathways by CTL clones and cell lines directed against four different human immunodeficiency virus (HIV) proteins in lysing primary HIV-infected targets. Although fas was expressed on HIV-infected primary CD4+ T cells, their lysis by antigen-specific CD8+ CTL was only by the granule pathway. Fas ligand (fasL) was not detectable on antigen-specific CD8 clones, T-cell lines, or circulating HIV-specific CD8 T cells from HIV-infected donors, stained with a tetrameric HLA-A2-HIV-peptide complex. FasL expression by HIV-specific CTL clones was not activated by exposure to HIV-presenting cells, but was after unphysiological stimulation with phorbol myristate acetate (PMA). CTL clones did not lyse bystander Jurkat cells, but HIV-infected primary CD4+ T cells lysed uninfected bystander cells by the fas-mediated pathway. These results suggest that HIV-specific CD8+ CTL do not cause HIV immunopathology by lysing bystander cells. On the contrary, fas-mediated lysis of uninfected cells by HIV-infected cells may contribute to CD4 decline.

Viral-Specific Cytotoxic T Lymphocytes Lyse Human Immunodeficiency Virus–Infected Primary T Lymphocytes by the Granule Exocytosis Pathway

AbstractCytotoxic T lymphocytes (CTL) lyse antigen-bearing target cells by two distinct pathways. Whereas granule exocytosis targets any antigen-bearing cell, fas-mediated cytotoxicity kills only fas-expressing cells and does not require antigen expression. Fas pathway activation can potentially lead to lysis of uninfected bystander cells. We examined the relative usage of the two pathways by CTL clones and cell lines directed against four different human immunodeficiency virus (HIV) proteins in lysing primary HIV-infected targets. Although fas was expressed on HIV-infected primary CD4+ T cells, their lysis by antigen-specific CD8+ CTL was only by the granule pathway. Fas ligand (fasL) was not detectable on antigen-specific CD8 clones, T-cell lines, or circulating HIV-specific CD8 T cells from HIV-infected donors, stained with a tetrameric HLA-A2-HIV-peptide complex. FasL expression by HIV-specific CTL clones was not activated by exposure to HIV-presenting cells, but was after unphysiological stimulation with phorbol myristate acetate (PMA). CTL clones did not lyse bystander Jurkat cells, but HIV-infected primary CD4+ T cells lysed uninfected bystander cells by the fas-mediated pathway. These results suggest that HIV-specific CD8+ CTL do not cause HIV immunopathology by lysing bystander cells. On the contrary, fas-mediated lysis of uninfected cells by HIV-infected cells may contribute to CD4 decline.

Effective Lysis of HIV-1-Infected Primary CD4+ T Cells by a Cytotoxic T-Lymphocyte Clone Directed Against a Novel A2-Restricted Reverse-Transcriptase Epitope

Most HIV-specific cytotoxic T-lymphocyte (CTL) epitopes have been identified using peptide-pulsed and recombinant vaccinia virus-infected targets. These systems may not accurately reflect the ability of epitopes to be presented by HIV-infected T cells. Recent studies suggest, in fact, that some CTL epitopes are poorly presented on HIV-infected cells. In this study, we have identified a novel A2.1-restricted HIV reverse-transcriptase (RT) epitope and investigated the presentation of this epitope by HIV-infected primary CD4+ T cells and T-cell lines. A CD8+ CTL clone, isolated from a seropositive subject that recognized a novel A2-restricted epitope KYTAFTIPSI (aa 293-302) in RT, was used for these studies. Primary CD4+ T cells and the CD4+ T-cell line T1 were infected with virus from T1-nPLAP, a cell line stably transfected with HXB-nPLAP, a molecular construct of HIV linked to a placental alkaline phosphatase (PLAP) marker gene. A uniformly infected cell population, obtained by immunomagnetic selection for PLAP expression, was used as targets in CTL assays. HIV-infected T cells were lysed by CTL recognizing this RT epitope as effectively as peptide-pulsed targets. This suggests that some RT epitopes are good targets for CTL recognition.

Human immune response to HIV-1 Nef. II. Induction of HIV-1/HIV-2 Nef cross-reactive cytotoxic T lymphocytes in peripheral blood lymphocytes of non-infected healthy individuals.

HIV-specific CD8+ cytotoxic T lymphocytes (CTL) are thought to have a beneficial role in HIV infection. In a previous report we have shown that HIV-1 Nef-specific CTL can be readily induced in peripheral blood lymphocytes of seronegative healthy young adults by in vitro stimulation with autologous Epstein-Barr virus-transformed B lymphoblastoid cell lines transfected with the HIV-1 nef gene. Here we demonstrate that these Nef-specific CTL can efficiently lyse HIV-infected primary CD4+ T lymphocytes. CTL of the blood donor tested were Nef-specific and restricted by the autologous MHC class I molecules HLA-A2 and HLA-B7. They recognized HIV-1 Nef in association with both restriction elements but HIV-2 Nef only in association with HLA-B7. The cross-reactivity of the induced effector cells together with the potent immunogenicity of Nef in healthy seronegatives further support the inclusion of Nef as a constituent of HIV vaccines.