Detection of intracellular HIV-1 Rev protein by flow cytometry

Synthesis of fluorescence labelled aptamers for use as low-cost reagents in HIV/AIDS research and diagnostics

Aptamers are nucleic acids selected by systematic evolution of ligands by exponential enrichment. They have potential as alternatives to antibodies in medical research and diagnostics, with the advantages of being non-immunogenic and relatively inexpensive to produce. In the present study, gp120 aptamers conjugated with fluorescein isothiocyanate (FITC) were generated, which could interact with HIV-1 gp120. A previously isolated gp120 aptamer, CSIR 1.1, was conjugated with FITC by incubation with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and imidazole. The conjugation and binding to the glycoprotein were confirmed by flow cytometry. FITC conjugated aptamers showed an increase in fluorescence emission 24-fold higher than baseline, and this difference was statistically significant (P=0.0016). Compared with a commercially available biotinylated anti-gp120 antibody, detected using FITC conjugated streptavidin, the emission of fluorescence obtained from the FITC-conjugated aptamer was 8-fold higher, suggesting a stronger interaction with gp120. In addition, the FITC conjugated aptamer neutralized HIV-1 pseudoviruses with an average IC₅₀ of 21.3 nM, similar to the parent aptamer that had an IC₅₀ of 19.2 nM. However, the difference in inhibition between the two aptamers was not statistically significant (P=0.784). These results indicate that the FITC-conjugated aptamer generated in the present study could potentially be used as a low-cost reagent in HIV/AIDS research and diagnostics.

Patients with discordant responses to antiretroviral therapy have impaired killing of HIV-infected T cells

In medicine, understanding the pathophysiologic basis of exceptional circumstances has led to an enhanced understanding of biology. We have studied the circumstance of HIV-infected patients in whom antiretroviral therapy results in immunologic benefit, despite virologic failure. In such patients, two protease mutations, I54V and V82A, occur more frequently. Expressing HIV protease containing these mutations resulted in less cell death, caspase activation, and nuclear fragmentation than wild type (WT) HIV protease or HIV protease containing other mutations. The impaired induction of cell death was also associated with impaired cleavage of procaspase 8, a requisite event for HIV protease mediated cell death. Primary CD4 T cells expressing I54V or V82A protease underwent less cell death than with WT or other mutant proteases. Human T cells infected with HIV containing these mutations underwent less cell death and less Casp8p41 production than WT or HIV containing other protease mutations, despite similar degrees of viral replication. The reductions in cell death occurred both within infected cells, as well as in uninfected bystander cells. These data indicate that single point mutations within HIV protease which are selected in vivo can significantly impact the ability of HIV to kill CD4 T cells, while not impacting viral replication. Therefore, HIV protease regulates both HIV replication as well as HIV induced T cell depletion, the hallmark of HIV pathogenesis.

Although most patients infected with HIV who have persistent viral replication will experience a decline in CD4 T cell number, this is not always the case. In a small subset of patients in whom ART fails to suppress viral replication, CD4 T cell counts do not fall, for unknown reasons. We identified that these patients have an increased frequency of selected protease mutations, which we call discordance associated mutations (DAMs). While wild type protease rapidly induces cell death, protease containing DAMs have an impaired ability to induce cell death, due to a selective defect in cleavage of caspase 8. Furthermore, viruses containing DAMs replicate as efficiently as wild type, yet fail to induce infected cell death. These results demonstrate an unanticipated role of protease in determining the immunologic outcome of HIV infection in vitro and in vivo.

Multiple importins function as nuclear transport receptors for the Rev protein of human immunodeficiency virus type 1

The Rev protein of human immunodeficiency virus type 1 is an RNA-binding protein that is required for nuclear export of unspliced and partially spliced viral mRNAs. Nuclear import of human immunodeficiency virus type 1 Rev has been suggested to depend on the classic nuclear transport receptor importin beta, but not on the adapter protein importin alpha. We now show that, similar to importin alpha, Rev is able to dissociate RanGTP from recycling importin beta, a reaction that leads to the formation of a novel import complex. Besides importin beta, the transport receptors transportin, importin 5, and importin 7 specifically interact with Rev and promote its nuclear import in digitonin-permeabilized cells. A single arginine-rich nuclear localization sequence of Rev is required for interaction with all importins tested so far. In contrast to the importin beta-binding domain of importin alpha, Rev interacts with an N-terminal fragment of importin beta. Transportin contains two independent binding sites for Rev. Hence, the mode of interaction of importin beta and transportin with Rev is clearly distinct from that with their classic import cargoes. Taken together, the viral protein takes advantage of multiple cellular transport pathways for its nuclear accumulation.

Hematologic recovery in mice transplanted with bone marrow stem cells expressing anti-human immunodeficiency virus genes

We have used a mouse bone marrow transplantation (BMT) model to study the safety of retrovirus-mediated transfer of anti-HIV genes (RevM10 and HIV-1 pol antisense) into hematopoietic stem/progenitor cells (HSPCs). In particular, we have monitored the hematologic recovery post-BMT and transgene expression in myeloid and lymphoid lineages, and analyzed tissue sections for evidence of any transgene-related pathological condition. Expression of anti-HIV genes had no effect on kinetics of hematologic recovery post-BMT. The average time to reach 20% of normal cell counts was 15-17 days for white blood cells and 12-14 days for platelets, and the average time to reach complete recovery was 42-56 days for leukocytes and 104-161 days for platelets. Hematocrit levels were not significantly affected by irradiation and transplantation procedures. Donor chimerism was uniformly > or =90% in all transplanted animals. At 4-5 weeks post-BMT transgene expression was detected in peripheral blood leukocytes in 100% of the animals and ranged from 4.5 to 44.7%. In a majority of the animals the percentage of transgene-expressing cells in circulation decreased over time but remained detectable for the length of the study (>6 months). Expression was detected in all analyzed cell lineages (RBCs, platelets, monocytes, granulocytes, and T and B cells). Relative counts of various leukocytes (Mac1+ monocytes, Gr1+ granulocytes, CD3+ T cells, and B220+ B cells) were normal. There were no treatment-related histopathological changes in a wide range of tissues examined. In addition, there were no treatment effects on differential leukocyte counts, and morphology of peripheral blood and bone marrow brush smears. In summary, transfer and expression of the RevM10 and the HIV-1 antisense genes into hematopoietic stem/progenitor cells in vivo appears safe. We propose that the mouse bone marrow transplantation model could be used to evaluate some safety aspects of HSPC-based gene therapies.

Induction of MHC Class I Expression on Immature Thymocytes in HIV-1-Infected SCID-hu Thy/Liv Mice: Evidence of Indirect Mechanisms

The SCID-hu Thy/Liv mouse and human fetal thymic organ culture (HF-TOC) models have been used to explore the pathophysiologic mechanisms of HIV-1 infection in the thymus. We report here that HIV-1 infection of the SCID-hu Thy/Liv mouse leads to the induction of MHC class I (MHCI) expression on CD4+CD8+ (DP) thymocytes, which normally express low levels of MHCI. Induction of MHCI on DP thymocytes in HIV-1-infected Thy/Liv organs precedes their depletion and correlates with the pathogenic activity of the HIV-1 isolates. Both MHCI protein and mRNA are induced in thymocytes from HIV-1-infected Thy/Liv organs, indicating induction of MHCI gene expression. Indirect mechanisms are involved, because only a fraction (<10%) of the DP thymocytes were directly infected by HIV-1, although the majority of DP thymocytes are induced to express high levels of MHCI. We further demonstrate that IL-10 is induced in HIV-1-infected thymus organs. Similar HIV-1-mediated induction of MHCI expression was observed in HF-TOC assays. Exogenous IL-10 in HF-TOC induces MHCI expression on DP thymocytes. Therefore, HIV-1 infection of the thymus organ leads to induction of MHCI expression on immature thymocytes via indirect mechanisms involving IL-10. Overexpression of MHCI on DP thymocytes can interfere with thymocyte maturation and may contribute to HIV-1-induced thymocyte depletion.

Effect of scaffold attachment region on transgene expression in retrovirus vector-transduced primary T cells and macrophages

The scaffold attachment region of the human interferon beta gene (IFN-SAR) inserted into a retroviral vector improved transgene expression in human primary CD4+ and CD8+ T cells, and in primary monocytemacrophages. In T cells, expression of the Maloney murine leukemia virus (Mo-MuLV)-based retroviral vectors was high in activated cells but low in resting cells. Addition of the IFN-SAR sequence enhanced vector expression 2- to 10-fold, and the effect was particularly pronounced in resting T cells. In CD33+CD14+CD4+ monocyte-macrophages derived from transduced hematopoietic stem/progenitor cells (HSPCs) in vitro, the IFN-SAR enhanced vector expression three- to sixfold. We have used the IFN-SAR-containing vectors to express the RevM10 gene, a trans-dominant mutant of the human immunodeficiency virus type 1 (HIV-1) rev gene. Compared with a standard retroviral vector, the IFN-SAR-containing vector was significantly (p < 0.01) more potent at inhibiting HIV-1 replication in infected CD4+ peripheral blood lymphocytes. In monocytes, however, addition of the IFN-SAR did not significantly improve antiviral efficacy. To understand better the reason for the strong effect of the SAR on antiviral efficacy in T cells we have studied the expression of HIV, Mo-MuLV, and Mo-MuLV + SAR vectors in resting and activated cells. While the expression of all three vectors was lower in resting compared with activated cells, the kinetics of the decrease in expression were fastest for the Mo-MuLV vector, followed by the HIV vector and then the Mo-MuLV + SAR vector. Thus, higher level expression of the Mo-MuLV + SAR vector relative to wild-type HIV at all stages of T cell activation is the most likely explanation for the strong antiviral efficacy. Overall, this study demonstrates the utility of the IFN-SAR sequence for achieving high-level retroviral vector expression in lymphoid and myeloid hematopoietic cells.

Flow cytometric quantification of HIV-1 Tat protein in tat-transfected Jurkat T cell lines

The transactivator Tat protein represents a pivotal factor for the replication of human immunodeficiency virus type 1 (HIV-1). In this report, we describe a flow cytometry procedure designed to quantify the intracellular content of Tat protein in Jurkat CD4+ T lymphoblastoid cell lines, stably transfected with plasmids expressing full-length Tat protein. Various expression vectors were compared for their effectiveness to yield Tat protein in Jurkat cells, and several technical parameters were analyzed to optimize the assay. This method offers a quick and efficient approach to select stably transfected cell lines expressing different levels of specific protein.

Production and flow cytometric application of a monoclonal anti-glucocorticoid receptor antibody

Detection and monitoring the expression and level of intracellular glucocorticoid receptor (GCR) is necessary in many clinical and experimental situations. Binding of radioactive steroids (3H dexamethasone) to the cytosolic fractions of cells has been recently used. However, it is an expensive, time-consuming technique difficult to use in routine diagnostics. In this article we describe a novel, simple method for GCR detection, using a FITC-conjugated anti-GCR monoclonal antibody (mAb) for flow cytometric measurements in permeabilized cells. The monoclonal antibody was raised against a conserved sequence (150-176 amino acids) of the regulatory part of the receptor. Synthetic peptide (called APTEK-26) fragment of the receptor conjugated to different carriers (TG, BSA) was used for immunization and screening of the hybridomas. The a-GCR 8E9, 3C8 and 5E4 clones (IgG1) were further characterized by immunoserological methods for their reactivity against overlapping synthetic peptide fragments of the receptor and by Western blot technique on cytosolic fraction of HEP G2 cells (containing the GCR). Furthermore the mAbs could be used for the FACS based detection of GCR, despite its low number of antigen structure within the cells. Solving the problem of nonspecific binding of the secondary antibodies we used our high affinity IgG1 a-GCR mAbs directly labeled with the fluorescent dye FITC. The fluorescent labeling of the GCRs in HEP G2 cell line and human peripheral blood mononuclear cells (PBMC) were demonstrated by flow cytometric analysis after fixation with 4% paraformaldehyde and permeabilization with saponin. Competition with molar excess of unlabelled antibodies and with the GCR peptide fragment confirmed the specific binding of the 8E9 and 5E4 mAbs to the GCRs. Monitoring the GCR level by flow cytometry would be useful in clinical diagnostics, e.g., in steroid-treated patients and in steroid-resistant states.

Comparative analyses of intracellularly expressed antisense RNAs as inhibitors of human immunodeficiency virus type 1 replication

The antiviral activities of intracellularly expressed antisense RNAs complementary to the human immunodeficiency virus type 1 (HIV-1) pol, vif, and env genes and the 3' long terminal repeat (LTR) sequence were evaluated in this comparative study. Retroviral vectors expressing the antisense RNAs as part of the Moloney murine leukemia virus LTR promoter-directed retroviral transcript were constructed. The CD4+ T-cell line CEM-SS was transduced with retroviral constructs, and Northern blot analyses showed high steady-state antisense RNA expression levels. The most efficient inhibition of HIV-1 replication was observed with the env antisense RNA, followed by the pol complementary sequence, leading to 2- to 3-log10 reductions in p24 antigen production even at high inoculation doses (4 x 10(4) 50% tissue culture infective doses) of the HIV-1 strain HXB3. The strong antiviral effect correlated with a reduction of HIV-1 steady-state RNA levels, and with intracellular Tat protein production, suggesting that antisense transcripts act at an early step of HIV-1 replication. A lower steady-state antisense RNA level was detected in transduced primary CD4+ lymphocytes than in CEM-SS cells. Nevertheless, replication of the HIV-1 JR-CSF isolate was reduced with both the pol and env antisense RNA. Intracellularly expressed antisense sequences demonstrated more pronounced antiviral efficacy than the transdominant RevM10 protein, making these antisense RNAs a promising gene therapy strategy for HIV-1.

Inhibition of human immunodeficiency virus type 1 replication in myelomonocytic cells derived from retroviral vector-transduced peripheral blood progenitor cells

Monocytes and macrophages (Mo/Mphi) contribute to the pathogenesis of human immunodeficiency virus type 1 (HIV-1) infection. A successful hematopoietic stem/progenitor cell (HSPC)-based gene therapy strategy for HIV-1 disease must protect Mo/Mphi as well as T cells from HIV-1-related pathology. In this report, we demonstrate that RevM10-transduced HSPCs isolated from cytokine-mobilized peripheral blood give rise to Mo/Mphi suppressing replication of Mphi-tropic HIV-1 isolates. A Moloney murine leukemia virus (MoMLV)-based retroviral vector encoding a bicistronic mRNA co-expressing RevM10 and the murine CD8alpha' chain (Lyt2) was used to transduce HSPCs. Following transduction, these cells were expanded and differentiated by short-term culture in methylcellulose containing various cytokines. In vitro differentiated Mo/Mphi were enriched by fluorescence activated cell sorting (FACS) for the co-expressed transgene (Lyt2) and myelomonocytic (CD33, CD14) surface markers. HIV-1 replication of two Mphi-tropic isolates (JR-FL, BaL) was inhibited in Mo/Mphi expressing RevM10 and Lyt2 relative to control cells expressing only Lyt2 but no functional RevM10 gene product. Cell proliferation and expression of lineage-specific surface markers was not altered in transduced, in vitro differentiated Mo/Mphi cells. This study supports the feasibility of HSPC-based gene therapy as a future treatment for HIV-1 disease.

RevM10-expressing T cells derived in vivo from transduced human hematopoietic stem-progenitor cells inhibit human immunodeficiency virus replication

A key feature of the pathogenesis of human immunodeficiency virus type 1 (HIV-1) infection is the gradual loss of CD4-positive T cells. A number of gene therapy strategies have been designed with the intent of inhibiting HIV replication in mature T cells. As T cells are products of hematolymphoid differentiation, insertion of antiviral genes into hematopoietic stem cells could serve as a vehicle to confer long-term protection in progeny T cells derived from transduced stem cells. One such "cellular immunization" strategy utilizes the gene coding for the HIV-1 rev trans-dominant mutant protein RevM10 which has been demonstrated to inhibit HIV-1 replication in T-cell lines and in primary T cells. In this study, we used a Moloney murine leukemia virus-based retrovirus encoding a bicistronic message coexpressing RevM10 and the murine CD8-alpha' chain (Lyt2). This vector allows rapid selection of transgene-expressing cells as well as quantitation of transgene expression. We demonstrate that RevM10-transduced CD34-enriched hematopoietic progenitor-stem cells (HPSC) isolated from human umbilical cord blood or from granulocyte colony-stimulating factor-mobilized peripheral blood can give rise to mature thymocytes in the SCID-hu thymus/liver mouse model. The phenotypic distribution of HPSC-derived thymocytes is normal, and expression of the transgene can be detected by flow cytometric analysis. Moreover, we demonstrate that RevM10 can inhibit HIV replication in T cells derived from transduced HPSC after expansion in vitro. This is the first demonstration of anti-HIV efficacy in T cells derived from transduced human HPSC.

Hematopoietic Stem Cell–Based Gene Therapy for Acquired Immunodeficiency Syndrome: Efficient Transduction and Expression of RevM10 in Myeloid Cells In Vivo and In Vitro

Gene delivery via the hematopoietic stem cell (HSC) offers an attractive means to introduce antiviral genes into both T cells and macrophages for acquired immunodeficiency syndrome (AIDS) gene therapy. An amphotropic retroviral vector encoding a bicistronic gene coexpressing RevM10 and the murine CD8α′ chain (lyt2) was developed to transduce HSC/progenitor cells. After transduction of CD34+ cells isolated from human umbilical cord blood, the lyt2 molecule detected by flow cytometry was used to monitor the level of gene transduction and expression and to enrich RevM10-expressing cells by cell sorting without drug selection. Using this quantitative method, high levels of gene transduction and expression (around 20%) were achieved by high-speed centrifugation of CD34+ cells with the retroviral supernatant (spinoculation). After reconstitution of human bone marrow implanted in SCID mice (SCID-hu bone) with the transduced HSC/progenitor cells, a significant number of donor-derived CD14+ bone marrow cells were found to express the RevM10/lyt2 gene. Finally, replication of a macrophage-tropic human immunodeficiency virus–type 1 (HIV-1) isolate was greatly inhibited in the lyt2+/CD14+ cells differentiated from transduced CD34+ cells after the enrichment of lyt2+ population. Thus, the RevM10 gene did not appear to inhibit the differentiation of HSC/progneitor cells into monocytes/macrophages. The level of retrovirus-mediated RevM10 expression in monocytes/macrophages derived from transduced HSCs is sufficient to suppress HIV-1 replication.

Intracellular expression of RNA transcripts complementary to the human immunodeficiency virus type 1 gag gene inhibits viral replication in human CD4+ lymphocytes

Intracellular expression of antisense transcripts was evaluated for its potential to interfere with human immunodeficiency virus type 1 (HIV-1) replication. Retroviral vectors encoding HIV-1 psi-gag complementary sequences downstream of a selectable gene (neo, puromycin gene, or Lyt2 gene) were stable and yielded high titers. Human CEMSS T cells were transduced with amphotropic retroviral vectors to express RNA complementary to the psi-gag sequence of HIV-1. Replication of laboratory-adapted HIV-1 strains was inhibited by more than 1 order of magnitude (log10) in these transduced cells even at high inoculation doses (4 x 10(4) 50% tissue culture infective doses). Antisense-mediated anti-HIV efficacy was further demonstrated by survival of CD4+ cells in these cultures relative to controls. The level of anti-HIV-1 activity of the psi-gag antisense sequence correlated with the length of the antisense transcript. Maximal anti-HIV efficacy was observed with complementary sequence more than 1,000 nucleotides long, whereas transcripts less than 400 nucleotides long failed to inhibit HIV-1 replication. Expression of psi-gag antisense RNA also reduced HIV-1 JR-CSF replication 10-fold in primary CD4+ lymphocytes. These results obtained with a T-cell line and primary peripheral blood lymphocytes indicate the potential of long antisense RNAs as an efficient anti-HIV-1 therapeutic agent for gene therapy.

Intracellular expression of human immunodeficiency virus type 1 (HIV-1) protease variants inhibits replication of wild-type and protease inhibitor-resistant HIV-1 strains in human T-cell lines

The enzymatic activity of the human immunodeficiency type 1 (HIV-1) protease (PR) is crucial to render HIV-1 virions mature and infectious. Hence, genetic intervention strategies based on trans-dominant (td) variants of the HIV-1 PR might be an alternative to current pharmacological and gene therapy regimens for AIDS. CD4-positive human CEM-SS T-cell lines were generated which constitutively expressed HIV-1 td PR variants. HIV-1 infection experiments demonstrated severely reduced HIV-1 replication in these td PR CEM-SS cell lines compared with control T cells expressing wild-type PR. Furthermore, replication of an HIV-1 isolate bearing a PR inhibitor-resistant PR was blocked, showing that genetic intervention strategies based on td PRs can be effective against HIV-1 isolates containing PR inhibitor-resistant mutants.