Selective cytotoxicity of AIDS virus infection towards HTLV-I-transformed cell lines

Anti-HIV-1 potency of the CRISPR/Cas9 system insufficient to fully inhibit viral replication

The range of genome-editing tools has recently been expanded. In particular, an RNA-guided genome-editing tool, the clustered regularly interspaced short palindromic repeat (CRISPR)-associated 9 (Cas9) system, has many applications for human diseases. In this study, guide RNA (gRNA) to target gag, pol and a long terminal repeat of HIV-1 was designed and used to generate gRNA-expressing lentiviral vectors. An HIV-1-specific gRNA and Cas9 were stably dually transduced into a highly HIV-1-susceptible human T-cell line and the inhibitory ability of the anti-HIV-1 CRISPR/Cas9 lentiviral vector assessed. Although clear inhibition of the early phase of HIV-1 infection was observed, as evaluated by a VSV-G-pseudotyped HIV-1 reporter system, the anti-HIV-1 potency in multiple rounds of wild type (WT) viral replication was insufficient, either because of generation of resistant viruses or overcoming of the activity of the WT virus. Thus, there are potential difficulties that must be addressed when considering anti-HIV-1 treatment with the CRISPR/Cas9 system alone.

Synthesis and Anti-HIV Activity of Novel 4'-Trifluoromethylated 5'-Deoxycarbocyclic Nucleoside Phosphonic Acids

Efficient synthetic route to novel 4'-trifluoromethylated 5'-deoxycarbocyclic nucleoside phosphonic acids was described from α-trifluoromethyl-α,β-unsaturated ester. Coupling of purine nucleosidic bases with cyclopentanol using a Mitsunobu reaction gave the nucleoside intermediates which were further phosphonated and hydrolyzed to reach desired nucleoside analogs. Synthesized nucleoside analogs were tested for anti-HIV activity as well as cytotoxicity. Adenine analog 22 shows significant anti-HIV activity (EC50 = 8.3 μM) up to 100 μM.

Synthesis and Anti-HIV Activity of Novel 2'-Deoxy-2'-β-Fluoro-Threosyl Nucleoside Phosphonic Acid Analogues

Novel 2'-deoxy-2'-β-fluoro-threose purine phosphonic acid analogues were designed and racemically synthesized from 2-propanone-1,3-diacetate. Condensation successfully proceeded from a glycosyl donor 9 under Vorbrüggen conditions. Cross-metathesis of vinyl analogues 13 and 23 with diethyl vinylphosphonate yielded the desired nucleoside phosphonate analogues 14 and 24, respectively. Ammonolysis and hydrolysis of phosphonates yielded the nucleoside phosphonic acid analogues 16, 19, 26, and 29. The synthesized nucleoside analogues were subjected to antiviral screening against human immunodeficiency virus (HIV)-1. Adenine analogue 18 exhibited weak in vitro activities against human immunodeficiency virus (HIV)-1.

Aspects of successful drug discovery and development

Despite landmark achievements (e.g. >20 new anti-HIV drugs), a number of important therapeutic challenges remain. Although an expanding array of new drug discovery technologies has become available, drug research and development (R&D) productivity in general is still low. The establishment of close functional links between specialists active in early discovery, development and the clinic can thereby contribute to overall efficiency and higher success rates of new drug candidates. One of the more qualitative discovery challenges is to improve the predictability of early stage research models in term of in vivo drug efficacy. A cell-based model using viral replication in human T cells (MT-4) is used as an example from the HIV field to highlight the role of cell-based assays as tools for new target discovery, lead finding and optimization. The development of the next generation HIV non-nucleoside reverse transcriptase inhibitors (NNRTIs) TMC125 and TMC278 and the protease inhibitor (PI) TMC114 (Prezista), further point to new fundamental strategies to combat and prevent antiviral drug resistance and to the importance of incorporating clinical and pharmaceutical aspects into lead finding and optimization, drug design and drug candidate selection. A more parallel-oriented drug discovery strategy is thus portrayed that harnesses some 'evolutionary' principles in combination with technologies that are currently rationalizing drug discovery.

Infection of CD4+ primary T cells and cell lines, generation of chronically infected cell lines, and induction of HIV expression

Acute infection of most primary cells and cell lines with HIV depends upon the sequential engagement of CD4 (primary receptor) and a chemokine coreceptor (usually CCR5 or CXCR4) by gp120 Env. Chronically infected cell lines and clones are currently used as sources of virus for infecting other cell types, as "factories" for large-scale production of virions or viral components, and as model systems for studies of regulation of virus expression. This unit provides detailed protocols for acute in vitro HIV infection of primary T cell blasts, interleukin-2-stimulated PBMC, and resting PBMC. The unit also contains information on how to determine the chemokine coreceptor usage of the virus for experimental infections. The use of cell lines as targets of acute infection is also described. Finally, protocols for generating and studying chronically HIV-infected cell lines are provided.

Relative anti-HIV-1 efficacy of lamivudine and emtricitabine in vitro is dependent on cell type

OBJECTIVE

To assess the relative in vitro potency of the antiviral agents emtricitabine (FTC), lamivudine (3TC), and zidovudine (ZDV) in peripheral blood mononuclear cells (PBMCs), monocyte-derived macrophages, and MT-4 cells infected with HIV-1. DESIGN In vitro evaluation of the test compounds against M-tropic or T-tropic laboratory strains of HIV-1 and against clinical HIV-1 isolates from antiretroviral therapy-naive subjects using PBMCs, monocyte-derived macrophages, and MT-4 cells.

METHODS

Standard methods for assessing antiviral potency based on 50% inhibitory concentrations using propidium iodide staining of host cell DNA to assess cytopathic effects or measurement of HIV-1 reverse transcriptase activity to assess inhibition of viral replication.

RESULTS

There were no significant differences in potency between 3TC and FTC in assays with HIV-1(IIIB)-infected PBMCs or HIV-1(Ba-L) -infected monocyte-derived macrophages, which are primary cell types for HIV-1 infection in vivo. In agreement with earlier reports, FTC was approximately fourfold more active than 3TC in assays in the transformed T-cell line MT-4 infected with HIV-(1IIIB), whereas ZDV was more active than FTC. 3TC, FTC, and ZDV were equally active against a panel of eight primary HIV-1 isolates from antiretroviral-naive subjects in PBMCs. These results demonstrate the in vitro similarity of 3TC and FTC activity in primary cells. The variability in potency depending on cell types and viral strains underscores our observation that antiviral effects in vitro are not reliable predictors of in vivo clinical activity.

Role of cell surface glycosaminoglycans of human T cells in human immunodeficiency virus type-1 (HIV-1) infection

To investigate the role of cell surface glycosaminoglycans (GAGs), including heparan sulfate (HS), on HIV-1 infection in human T cells, HIV-1 binding and infection were determined after treatment of T-cell lines and CD4+ T cells from normal peripheral blood mononuclear cells (PBMC) with GAG-degrading enzyme or a GAG metabolic sulfation inhibitor. Heparitinase I (hep I) and sodium chlorate prevented binding of HIV-1/IIIB to MT-4 cells as revealed by indirect immunofluorescence procedures, thereby inhibiting infection. Hep I was less effective in the binding inhibition of the macrophage-tropic strain HIV-1/SF162 than that of the T-cell line-tropic strain HIV-1/IIIB. The binding of HIV-1/SF162 was about 100-fold less dependent on cell surface HS than HIV-1/IIIB. Human HTLV-I positive T-cell lines expressed more HS than HTLV-I negative T-cell lines or normal CD4+ T cells when stained with anti-HS mAbs against either native or heparitinase-treated HS. With the exception of endo-beta-galactosidase (endo-beta-gal), GAG-degrading enzymes, including hep I, chondroitinase ABC (chon ABC), chondroitinase AC II (chon AC II) and keratanase, did not prevent the binding of HIV-1/IIIB to CD4+ T cells from normal PBMC. These results indicate that the cell surface HS of human T cells participates in HIV-1 infection by facilitating HIV-1/IIIB binding to MT-4 cells. In particular, the sulfation of HS chains is critical. Since the expression of cell surface HS varies among T cells, which are not consistently sensitive to hep I treatment in HIV-1 binding inhibition, other GAG-like molecules may also be involved.

Discovery and in vitro development of AIDS antiviral drugs as biopharmaceuticals

The goal of developing an effective drug against HIV-1 and AIDS has been approached by several routes, with enough encouraging results to stimulate further efforts. Compounds active against HIV-1 have been discovered for many of the functions in the reproductive cycle recognized as virus-specific targets. Discoveries have been made in cell-based assays as well as mechanistic assays, and the value of both types of assays in the drug discovery process has been discussed. Although the final test of a drug's efficacy comes in the clinical experience, submission of an antiviral compound to an in vitro developmental gauntlet can save much time, effort, expense, and human resource in the in vivo developmental regimen required prior to human use. Emergence of viral resistance to drugs in several structural classes has compromised their clinical efficacy, suggesting that development of other potential drugs in those classes may not be good investments. Strains of HIV-1 resistant to specific compound classes are used to categorize new active discoveries for possible developmental exclusion, and defining the mechanism of action of such a new compound may confirm the discouraging judgement. On the other hand, novel compounds which exhibit a broad range of activity in drug-resistant and other HIV-1 strains deserve greater scrutiny. Clinicians most likely will be hesitant to treat patients with compounds shown to act on virus-cell surface interactions, given the failure in the past of several such compounds in clinical studies. But a compound shown to have a unique and novel mechanism of action will be looked upon more favorably, and surviving other tests of potency, solubility, and stability will be unhesitatingly presented for in vivo development. The partial successes of drugs currently in clinical use against AIDS offers great encouragement that other more-effective, less-toxic drugs will be found. Exquisite techniques for identifying new targets on virus gene products, the selection of compounds on activity paradigms, and the enormous variety of compounds becoming available through synthesis libraries, all offer opportunities for anti-HIV drug discovery, which, in our view, cannot fail to present potent antiviral compounds which will survive the rigorous preclinical and clinical tests leading to a drug effective against AIDS.

Genomic cloning and complete sequence analysis of a highly divergent African human immunodeficiency virus isolate

Analysis of the complete sequence of a human immunodeficiency virus (HIV) isolate (Ant70) obtained from a Cameroonian patient indicates that this virus is the most divergent strain within the HIV-1 family hitherto described. Comparison of the Pol protein, usually highly conserved within the HIV-1 family, shows only about 73% similarity with the HIVmm isolate, whereas for the more variable proteins such as envelope, similarities of 50% or lower are found. The principal neutralizing determinant (V3 loop) and the immunodominant region within gp41 also contain some unusual substitutions, which may have implications for protein function as well as for serological assays based on these regions. Phylogenetic analyses show that this isolate occupies a unique position relative to the human HIV-1 isolates and the recently described SIVcpz virus, indicating that this Cameroonian isolate may provide us with new insights into the origins of the HIV-1 family.

HIV-1 infection of the trophoblast cell line BeWo: a study of virus uptake

An in vitro model has made it possible to demonstrate HIV transmission from infected lymphocytes to placental trophoblast cells via endocytosis. Upon addition to cultured trophoblast cells (BeWo), chronically HIV-infected lymphocytic cells (MOLT-4) adhered to the epithelial cells via a complex of newly induced microvilli. Though viruses were infrequently seen in the infected lymphocytic cell line, mature virions appeared promptly and profusely in the interstices between the interdigitating microvilli of the two cell types. Virions appeared to bud from the lymphocyte donor cells at the point of cell-to-cell contact and were rapidly taken up by the trophoblast cells via an endocytic mechanism involving coated pits, endosomes, and lysosomes. Electron microscopic observations suggest that HIV may later escape into the trophoblast cytoplasm by fusing with the endosome membrane or by lysing the lysosome membrane. Coincubation for 1 h was sufficient to establish HIV infection in the trophoblast cell line. Four weeks after thoroughly washing out the donor lymphocytic cells, HIV RNA was demonstrated in clusters of BeWo cells by in situ hybridization, and p24 antigen was localized with immunocytochemistry. Soluble CD4 did not block infection as measured by p24 ELISA. The HIV infection was productive and chronic as demonstrated by cocultivating the BeWo cells with indicator lymphocytes 4 weeks after the initial infection. This study, demonstrating a mechanism of HIV transmission, expands upon previous observations that trophoblast cell lines lacking the CD4 viral receptor can nevertheless be infected by HIV and can support productive infection.

Soluble IL-2 receptor and tumour necrosis factor-alpha in plasma of haemophilia patients infected with HIV

We measured plasma concentrations of soluble receptors for IL-2 (sIL-2R) and tumour necrosis factor-alpha (TNF-alpha) in 149 haemophilia patients. Soluble IL-2R levels were elevated in 37% of 62 HIV-seronegative patients (mean 570 +/- 27 U/ml versus 361 +/- 17 U/ml in the control group, P less than 0.0001), in 78% of 68 HIV-seropositive patients (928 +/- 49 U/ml, P less than 0.0001), and in 95% of 19 AIDS/ARC patients (1578 +/- 199 U/ml, P less than 0.0001 compared with controls and with HIV-seronegative patients; P less than 0.005 compared with HIV-seropositive asymptomatic patients). A negative correlation was observed between sIL-2R, relative and absolute numbers of CD4+ cells (P less than 0.0001), and CD4/CD8 ratios (P less than 0.0001). There was also a negative correlation between sIL-2R in plasma and the cellular expression of IL-2R (P less than 0.001). We found a significant association of sIL-2R and plasma neopterin (P less than 0.0001). With progression of the disease from HIV-seronegative to seropositive without symptoms and to full manifestation of AIDS/ARC, sIL-2R plasma levels increased. The highest levels were found at the time of diagnosis of AIDS/ARC, but the levels decreased again during the following 18 months. Eight per cent of HIV-seronegative patients, 32% of HIV-seropositive patients, and 24% of patients with AIDS/ARC had increased plasma TNF-alpha. We conclude that sIL-2R and TNF-alpha plasma levels are elevated in HIV-infected haemophilia patients and that sIL-2R is a marker for disease progression from asymptomatic HIV-seropositive to AIDS/ARC.

Mechanism of HIV spread from lymphocytes to epithelia

Contact of human immunodeficiency virus (HIV)-infected MOLT-4 lymphocytes with epithelial cells derived from small intestine (I407; Intestine 407) resulted in a rapid polar budding of viral particles into an enclosed space formed by interdigitating microvilli of the contacting cells. Electron microscopy showed that released HIV was taken up into the mucosal cell via three independent mechanisms: (1) phagocytosis, (2) coated pits, and (3) direct fusion. Morphological evidence suggests that internalized HIV may escape into the cytoplasm of the target cell by uncoating at the endosomal membrane. Based on CD4 antibody binding and CD4 antibody blocking experiments, HIV entry does not appear to be mediated by a viral CD4 receptor. Productivity of I407 infection was confirmed by virus isolation from cocultured MT-4 lymphocytic cells, reverse transcriptase assay, p24 antigen ELISA, in situ HIV mRNA hybridization, and Southern dot blot analysis. Contrary to infection with free virus, the cell-to-cell infection was not blocked by anti-gp120 or antiviral serum from HIV-positive individuals. It appears that HIV transmission within the confined space between contacting cells enables HIV to evade immune protection provided by neutralizing antibodies. Our results reveal a mechanism of HIV infection of epithelial cells which is triggered by cell-cell contact. Furthermore, these observations offer an insight into the cellular sequence of events which may take place during sexual transmission of HIV across an intact epithelial barrier.

Human immunodeficiency virus type 1 vif, vpr, and vpu mutants can produce persistently infected cells

A series of human immunodeficiency virus type 1 (HIV-1) mutants in vif, vpr, vpu, and nef were constructed from an infectious plasmid (pNL 432) containing the full-length HIV-1 DNA by frameshift mutations. The capacities for replication and cell killing of these mutant viruses were examined in a clonal cell line (M 10) isolated from HTLV-I-transformed MT-4 cells. In all cases, the mutant viruses replicated, expressed HIV-1 antigens, and induced drastic cytopathic effects. However, some M 10 cells survived infection with vif, vpr, and vpu mutant viruses and became persistently HIV-1-infected, whereas no cells survived infection with the nef mutant as well as the wild-type virus. The HIV-1 particles produced from the surviving cells after infection with the vif, vpr, or vpu mutant viruses were fully replicative in M 10 cells without apparent cytopathic effects.

Accumulation of p60lck in HTLV-I-transformed T cell lines detected by an anti-lck monoclonal antibody, MOL 171

The lck gene encodes a protein tyrosine kinase of nonreceptor type, p56lck, whose expression occurs almost exclusively in T lymphocytes. MOL 171, an anti-p56lck monoclonal antibody, was produced by using a 25-amino-acid synthetic polypeptide as the antigen, its structure corresponding to the N-terminal region deduced from the lck cDNA sequence. Immunoblot analysis with MOL 171 showed the accumulation of 60 kD form of Lck protein, p60lck, and the decrease of p56lck in human T cell leukemia virus type I (HTLV-I)-transformed T cell lines. Another anti-Lck monoclonal antibody, MOL 294, raised by using a synthetic peptide corresponding to the C-terminal region deduced from the lck cDNA sequence, also detected the accumulation of p60lck in those HTLV-I-transformed T cell lines. The appearance of p60lck with the decrease of p56lck in normal T lymphocytes after stimulation suggested the origin of p60lck in HTLV-I-transformed T cells.

Differential expression of two lck transcripts directed from the distinct promoters in HTLV-I+ and HTLV-I- T-cells

The lck gene encodes a lymphocyte-specific tyrosine protein kinase, p56lck, the expression of which is almost exclusive in T-cells. The expression of lck in human T-cell leukemia virus type I (HTLV-I)-transformed T-cell lines is closely associated with interleukin-2 (IL-2) dependence for their growth. That is, IL-2-dependent HTLV-I-transformed cell lines contain the lck message abundantly as HTLV-I-negative T-cell lines, whereas IL-2-independent HTLV-I-transformed cell lines express either no or little lck mRNA, although they are derived from T-cells. The lck gene contains 2 distinct promoters which direct 2 types of lck transcript with different 5' untranslated regions. In this study, we show that HTLV-I-transformed IL-2-dependent T-cell lines contain the upstream promoter-initiated lck transcript exclusively, in contrast to HTLV-I-negative transformed T-cell lines which express the down-stream promoter- as well as the upstream promoter-initiated lck transcript. In addition, lck mRNA disappears transiently in IL-2-dependent HTLV-I-transformed T-cell lines after stimulation for T-cell activation, which is also observed in peripheral blood T lymphocytes. These results indicate that the disappearance of lck mRNA in HTLV-I-transformed, IL-2-independent cell lines is caused by a mechanism which down-regulates the upstream promoter-initiated lck transcript and this IL-2-independent state may represent a further "activated" condition of the IL-2-dependent state by the stimulation which mediates T-cell activation.

Production of infectious particles from defective human immunodeficiency virus type 1 (HIV-1)-producing cell clones by superinfection with infectious HIV-1

A total of 81 cell clones persistently infected with the LAV-1 or HTLV-IIIB strain of human immunodeficiency virus type 1 (HIV-1) was isolated from cells which were obtained by serial passage of some proliferating MT-4 cells after a drastic cytolysis of most cells by HIV-1-infection. These cell clones were classified into 8 types (I to VIII) in terms of the expression of HIV-1 antigens, syncytium formation capacity, and reverse transcriptase activity and infectivity of virus particles in the culture fluid. Type I cell clones were producers of infectious HIV-1 particles, while types II to VIII cell clones did not produce infectious HIV-1 or were producers of uninfectious defective HIV-1 particles. Immunoprecipitation followed by SDS-polyacrylamide gel electrophoresis (PAGE) showed that the gag precursor protein in L-2 cell clone (type IV) was not cleaved to mature gag proteins, while the env precursor protein on L-3 cell clone (type III) was not cleaved to mature env protein. H-7 cell clone (type VIII) did not express any HIV-1 antigen. All these cell clones after the superinfection with infectious HIV-1 synthesized intact gag and env proteins, which were, at least in part, related to the HIV-1 genome persistently present in the cell clones before the superinfection, resulting in production of infectious HIV-1. For example, it was found that L-2 cell clone contained a single copy of the LAV-1 genome per haploid cell and produced doughnut-shaped particles. On the other hand, the cell clone isolated from the L-2 cell clone superinfected with infectious HTLV-IIIB contained the integrated HTLV-IIIB genome in addition to the LAV-1 genome present before the superinfection, and produced intact HIV-1 particles in addition to doughnut-shaped particles from a single cell. These results indicate that complementation and/or genetic recombination events in the superinfected cells may account for the production of infectious intact HIV-1 virions.

Production of tumor necrosis factors by human T cell lines infected with HTLV-1 may cause their high susceptibility to human immunodeficiency virus infection

The production of tumor necrosis factor (TNF)-alpha and TNF-beta by various human hematopoietic cell lines was quantitatively examined using a highly sensitive radioimmunoassay specific to TNF-alpha, or a cytolytic assay performed with mouse L929 cells. It was found that the HTLV-1-infected T cell lines examined produced large amounts of both TNF-alpha and TNF-beta. In particular, interleukin-2 (IL-2)-dependent cell lines produced large amounts of TNF-alpha. In contrast, human cell lines not infected with HTLV-1 essentially did not produce either of the TNFs. It was also found that the high production of TNF-alpha by HTLV-1-infected cells partially correlated to their high sensitivity to human immunodeficiency virus (HIV) infection. Treatment of MT-4 cells, one of the most HIV-sensitive HTLV-1-infected cell lines, with antibody specific to TNF-alpha reduced their sensitivity to HIV infection.

The phorbol ester TPA strongly inhibits HIV-1-induced syncytia formation but enhances virus production: possible involvement of protein kinase C pathway

Cocultivation of MOLT-4 and MOLT-4/HIVHTLV-IIIB cells with more than 0.01 ng/ml of 12-O-tetradecanoylphorbol-13-acetate (TPA) for 20 hr strikingly inhibited HIV-induced syncytia formation resulting from cell to cell infection. Interestingly, the production of HIV-specific p24 antigen in the culture fluid was significantly enhanced by TPA. TPA down-modulated the expression of CD4. CD4 is essential for syncytia formation through interaction with viral envelope protein gp120 on the surface of MOLT-4 cells. The effects of TPA on syncytia formation and on CD4 expression were specifically interfered with by nontoxic doses of blockers of protein kinase C (PKC) such as staurosporine and H7. These data suggest that (1) TPA inhibits HIV-induced syncytia formation through down-modulation of CD4 molecules on the surface of MOLT-4 cells and (2) PKC may play an important role in cell to cell as well as in cell-free infection of HIV.

Isolation and partial characterization of an unusual human immunodeficiency retrovirus from two persons of west-central African origin

An unusual human retrovirus was isolated from two patients with persistent generalized lymphadenopathy who originate from West-Central Africa and are currently residing in Belgium. Although the virus shared a number of the same biological and morphological properties as human immunodeficiency retrovirus type 1 (HIV-1) and HIV-2, significant antigenic differences could be demonstrated. Several of the viral proteins also differed in molecular weight from the corresponding HIV-1 and HIV-2 proteins. Partial chemical cleavage of the most highly conserved viral proteins resulted in patterns which differed from those of HIV-1 and HIV-2. Furthermore, nucleic acid hybridization experiments were capable of discriminating between the virus types. Sequence analysis of the viral U3 region revealed a unique enhancer organization not found in other immunodeficiency viruses. The data indicated that the new isolate is more closely related to HIV-1 than to HIV-2 but clearly differs in a number of important respects.

Photodynamic inactivation of simian immunodeficiency virus

A photodynamic flow system employing a dihematoporphyrin ether (DHE) was tested for its ability to inactivate the in vitro infectivity of simian immunodeficiency virus (SICMac) at 630 +/- 5 nm with a light fluence of 5 J/cm2. Cell-free SIVMac was inactivated by photoactivated hematoporphyrin derivative in a dose-dependent fashion. Since SIVMac is closely related to human immunodeficiency virus type 2 (HIV-2) and we have previously reported the successful photodynamic inactivation of HIV-1 in cell-free medium as well as in whole human blood, this technology has the potential for the eradication of transfusion-associated acquired immunodeficiency diseases caused by the above-mentioned retroviruses.

Augmentation of human immunodeficiency virus type 1 gene expression by tumor necrosis factor alpha

It is now well established that cytokines are involved in the regulation of gene expression from HIV-1 LTR. The present study provides evidence that TNF-alpha stimulates HIV-1 gene expression and that the enhancer sequence within the HIV-1 LTR is involved in the stimulation. These results support the idea that immunologic stimulation and infection may trigger the development of clinical AIDS in individuals latently infected with HIV-1.

Rapid and automated tetrazolium-based colorimetric assay for the detection of anti-HIV compounds

A rapid, sensitive and automated assay procedure was developed for the in vitro evaluation of anti-HIV agents. An HTLV-I transformed T4-cell line, MT-4, which was previously shown by Koyanagi et al. (1985) to be highly susceptible to, and permissive for, HIV infection, served as the target cell line. Inhibition of the HIV-induced cytopathic effect was used as the end point. The viability of both HIV- and mock-infected cells was assessed spectrophotometrically via the in situ reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). The procedure was optimized as to make optimal use of multichannel pipettes, microprocessor-controlled dispensing and optical density reading. The absorbance ratio of the mock-infected control to the HIV-infected samples was about 20. This allowed an accurate determination of the 50% effective doses, as demonstrated for 3'-azido-2',3'-dideoxythymidine (AZT), 2',3'-dideoxycytidine (ddCyd), dextran sulfate and heparin. The technique significantly reduced labor time as compared to the trypan blue exclusion method, and permits the evaluation of large numbers of compounds for their anti-HIV activity.

A microtiter cell-culture assay for the determination of anti-human immunodeficiency virus neutralizing antibody activity

A microtiter cell-culture assay is described for measuring neutralizing antibody activity directed against the human immunodeficiency virus (HIV). The assay relies upon inhibition of HIV-mediated cell killing of infected MT-4 lymphoid cells. The assay exhibits comparable sensitivity to two other methods used for such measurements, is relatively rapid, may be adapted for screening large numbers of samples and involves minimal handling of infectious virus.

Defective human immunodeficiency virus (HIV) particles produced by cloned cells of HTLV-I-carrying MT-4 cells persistently infected with HIV

Persistently HIV-infected cell lines were isolated from surviving and proliferating cells after infection of HTLV-I-carrying MT-4 cells with cell-free human immunodeficiency virus (HIV); HTLV-IIIB and LAV. The media of the cloned cell cultures did not cause HIV infection of MT-4, MOLT-4, TALL-1, or HL-60 cells. Most of the constituents of the virus in the media were env proteins and many defective doughnut-shaped particles released from the cells were identified by electron microscopy.

Effect of culture supernatant of MT-2 cells on human immunodeficiency virus-producing cells, MOLT-4/HIVHTLV-IIIB cells

The effect of culture supernatant of MT-2 cells on human immunodeficiency virus (HIV)-producing cells, MOLT-4/HIVHTLV-IIIB cells, was examined. As compared to the effect on MOLT-4 cells, parent cells not infected with HIV, a selective cytotoxic/cytostatic effect on MOLT-4/HIVHTLV-IIIB cells was observed 4 days after treatment with up to 640-fold-diluted MT-2 supernatant. Furthermore, under similar conditions, a 2- to 6-fold increase in the number of HIV particles was detected in the culture of MOLT-4/HIVHTLV-IIIB cells 6 hr after treatment. Complete blocking of these effects by anti-lymphotoxin monoclonal antibody, but not by anti-tumor necrosis factor antibody, indicates that these effects of MT-2 supernatant on MOLT-4/HIVHTLV-IIIB cells are attributable to a lymphotoxin-related cytotoxic factor.

Persistent coinfection of T lymphocytes with HTLV-II and HIV and the role of syncytium formation in HIV-induced cytopathic effect

We previously demonstrated a high permissiveness of HTLV-II-transformed T lymphocytes (C3) to human immunodeficiency virus (HIV) infection in vitro, and that this infection results in the lysis of cells (D.C. Montefiori and W.M. Mitchell (1986) Virology 155, 726-731). We now show that a small percentage of HIV-infected C3 cells resist cell lysis, grow continuously in culture, and express antigens of both viruses. High levels of reverse transcriptase activity found in the culture fluid of these coinfected cells were associated with the presence of fully infectious HIV and an absence of detectable infectious HTLV-II. Virus production in C3 cells coinfected with the HIV isolate HTLV-III was approximately threefold greater than in C3 cells coinfected with the HIV isolate LAV, a result which suggests that HIV genomic diversity may give rise to differences in replicative capacities. Lysis resistance was found to be a cellular-determined function in that HIV produced in cultures of C3/HTLV-III cells retained the capacity to elicit a lytic response upon repeated infection. Small syncytia (less than five nuclei) were rarely observed in cultures of C3 and nonlytic C3/HIV cells, whereas large syncytia (more than five nuclei) were in abundance during the lytic phase of coinfection, a result which supports a role for syncytium formation in the mechanism of HIV-induced cytopathic effects. The results of these studies further demonstrate that there exists a lack of viral interference by HTLV-II infection, and that HTLV-II-transformed lymphocytes could act as a chronic reservoir for HIV in vivo.

Efficient replication of HTLV-III and STLV-IIImac in human Jurkat cells

High producer cell lines were established by infecting Jurkat cells with either HTLV-IIIB from H9 cells or with STLV-IIImac from HUT-78 cells. The Jurkat cells produced both viruses at least 10 times more efficiently then the original cell lines; the pelleted virus from Jurkat cells was also less contaminated with non-virion proteins. Accordingly, a higher specificity was attained in an ELISA for antibodies to HTLV-III if the antigenic activity was derived from the virus from Jurkat cells, as opposed to that from H9 cells.

Clonal selection of human immunodeficiency virus (HIV): serological differences in the envelope antigens of the cloned viruses and HIV prototypes (HTLV-III B, LAV, and ARV)

Human T-cell lymphotropic virus type III B (HTLV-III B) derived from H9/HTLV-III cells was cloned by a plaque-forming assay. Cloned viruses showed different restriction cleavage patterns, suggesting that HTLV-III B is a mixture of several viruses. Using two different neutralization assay systems, we compared the envelope antigenicity of uncloned HTLV-III B, cloned viruses, lymphadenopathy-associated virus (LAV), and acquired immune deficiency syndrome (AIDS)-associated retrovirus (ARV). A diversity of viral envelope antigens was consistently found among the strains of these AIDS-related retroviruses. These results concur with the previous finding that genomic divergence of AIDS-related viruses is located mainly in the region of the viral envelope gene. Thus, this plaque assay is useful for the clonal analysis of the virus, which is essential for comparing the envelope antigen(s) of the virus.

Sensitive and rapid assay on MT-4 cells for detection of antiviral compounds against the AIDS virus

Human immunodeficiency virus (HIV) infection of MT-4 cells, an HTLV-I-transformed T-cell line, proved to be a rapid and sensitive assay system for the detection of potential antiviral drugs effective against the acquired immune deficiency syndrome (AIDS). Four days after HIV inoculation of the MT-4 cells, viral antigen expression was monitored in parallel with indirect immunofluorescence microscopy and laser flow cytofluorography. When 3'-azido-2',3'-dideoxythymidine (AzddThd, AZT) and 2',3'-dideoxycytidine (ddCyd) were evaluated under these conditions, they inhibited viral antigen expression at a minimum (33% inhibitory) concentration of 0.0004 and 0.02 microM, respectively. Similar minimum effective concentrations were found for AzddThd and ddCyd in assays where inhibition of viral cytopathogenicity was based on cell survival. While laser flow cytofluorography could be best adapted for quantitative measurements, cell survival and reconstitution of disrupted cell aggregates gave an equally rapid and sensitive endpoint; and the latter may be ideally suited for preliminary drug screening.

Infection of the HTLV-II-bearing T-cell line C3 with HTLV-III/LAV is highly permissive and lytic

The recent discovery that HTLV-I infected T-cells have an enhanced susceptibility to HTLV-III/LAV infection with concurrent cell lysis (S. Harada, Y. Koyanagi, and N. Yamamoto (1985) Science, 229, 563-566) led us to investigate a possible role for HTLV-II infected T cells in this respect. HTLV-II-bearing C3 cells were exposed to HTLV-III/LAV and the subsequent infection monitored by indirect immunofluorescence (IIF) of cells, reverse transcriptase (RT) activity in culture fluids, and hemacytometer cell counts. HTLV-III/LAV antigen expression was detected within 2 days whereas RT activity was detected within 3 days postinfection. The presence of immunofluorescent positive cells and RT activity was accompanied by cell lysis. Double infection of C3 cells was confirmed by IIF using a goat polyclonal antibody directed against the core p24 protein for detecting HTLV-II, and high titer serum from a pre-AIDS patient for detecting HTLV-III/LAV. We conclude that HTLV-I and HTLV-II infected T-cells share an enhanced susceptibility to HTLV-III/LAV infection with the promotion of cell lysis.

Tumor promoter, TPA, enhances replication of HTLV-III/LAV

The incubation of Molt-4/HTLV-III cells, human T-lymphotropic virus type III (HTLV-III)/lymphadenopathy-associated virus (LAV)-producer cell line, with more than 0.5 ng/ml of 12-O-tetradecanoylphorbol-13-acetate (TPA) for 2 to 4 days stimulated virus-induced cell killing which resulted in a high production of HTLV-III/LAV. TPA significantly increased the number of plaque-forming viruses released from the cultures as well as viral RNA content. Interestingly, MT-4 cells freshly infected with HTLV-III/LAV treated for 4 days with 0.125 to 2.0 ng/ml of TPA were found to retain the capacity to grow, because TPA inhibited the induction of the virus-specific antigens and cytopathic effects. In contrast to the situation in infected MT-4 cells in liquid cultures, the addition of 0.125 and 0.25 ng/ml of TPA into agarose medium induced large plaques, suggesting that TPA basically enhanced the production of the virus from one infected MT-4 cell. Taken together, the data suggest that TPA enhances the replication of HTLV/III/LAV. These assay systems are shown to be useful for analyzing the induction or suppression of a virus infection by many drugs and other factors in vitro.

Effect of HTLV-III on the macromolecular synthesis in HTLV-I carrying cell line, MT-4

Upon infection of human T-cell leukemia virus type I (HTLV-I)-carrying human T-cell lines such as MT-4, HTLV-III, a probable etiologic agent of acquired immune deficiency syndrome (AIDS) caused fast and strong cytopathic effects leading ultimately to the death of the cells. Such effects were preceded by the rapid induction of HTLV-III antigens. Cell lines not infected with HTLV-I could, however, be subcultured after infection with HTLV-III, although they were also positive for HTLV-III antigens. To understand this cytopathogenicity of HTLV-III in HTLV-I bearing cells, macromolecular synthesis, including DNA synthesis and total protein synthesis, and also IL-2 receptor expression were investigated kinetically. In infected MT-4 cells DNA synthesis was markedly inhibited by HTLV-III after the HTLV-III antigen synthesis became evident. This inhibition occurred before cell damage was detected in terms of viable cell-growth, but after induction of HTLV-III antigen. Puromycin, at 40 micrograms/ml, caused no toxic changes in MT-4 cells over 3 days but prevented viral antigen synthesis and virus-induced cytopathic effect. Protein synthesis and IL-2 receptor expression were also inhibited at 4 and 5 days post infection. The degree of the effects and their kinetics suggest that they are the secondary effects of cytotoxicity by HTLV-III infection.

Prostaglandin E2, a seminal constituent, facilitates the replication of acquired immune deficiency syndrome virus in vitro

Acquired immune deficiency syndrome (AIDS)-associated virus is thought to be transmitted effectively through semen during sexual activities from male to male or from male to female. Prostaglandin (PG) E2 is one of the immunosuppressive compounds present in high concentrations in human semen. We, therefore, investigated direct effects of PGE2 and other PGs on AIDS-associated virus infection and replication in vitro. First, type III human T-lymphotropic virus (HTLV-III) was used to infect a T-cell line (MT-4) in culture. PGE2 (10 nM to 10 microM) added to the culture medium enhanced the production of infectious virus in a dose-dependent fashion. In the presence of 5 microM PGE2, 2.5-fold more virus were released from the infected MT-4 cells as compared to untreated control cells on day 3 after infection. Second, when we used an HTLV-III continuous-producer cell line (Molt-4/HTLV-III), PGE2 and PGD2 added to the culture medium increased the number of viruses released from Molt-4/HTLV-III cells. Other PGs such as PGF2 alpha and 13,14-dihydro-15-keto PGE2 did not affect the replication of HTLV-III in this system. These results indicate that some PGs including seminal PGs enhance the AIDS-associated virus replication in vitro. We propose that PGE2 in human semen might directly facilitate the infection of AIDS-associated virus and cause the efficient transmission of the virus during sexual activities.

Infection of human T-lymphotropic virus type-I (HTLV-I)-bearing MT-4 cells with HTLV-III (AIDS virus): chronological studies of early events

Early events in the infection of the human T-lymphotropic virus type-I (HTLV-I)-positive MT-4 cell line by the acquired immune deficiency syndrome (AIDS) retrovirus HTLV-III were investigated. The virus was adsorbed completely to the cells within 60 min incubation after inoculation of the virus. Then, infected MT-4 cells started to produce the HTLV-III-specific antigens between 12 and 24 hr postinfection. Synthesis of the viral antigens consisting of 120K, 46K, 24K, and 17K polypeptides was suppressed by the treatment of the virus-infected MT-4 cells with cytosine arabinoside (Ara-C) or by the treatment of the virus with anti-HTLV-III-positive sera. The progeny of the virus released from the infected MT-4 cells was titrated by a newly developed plaque-forming assay method and reverse transcriptase activity. The maximum activity of HTLV-III (3 X 10(5) PFU/ml) was observed on Days 4 and 5 p.i. Most of the viral activities in this preparation were ascribed to HTLV-III, and not to HTLV-I. No phenotypic mixing between HTLV-III and HTLV-I was discerned, although MT-4 cells were HTLV-I-producer cell line. Thus, HTLV-III-infected MT-4 cells are thought to be useful in further study of the interaction between host cells and the virus, and appear to be a good viral source for the analysis of the virus.