Human immunodeficiency virus-infected monocyte-derived macrophages express surface gp120 and fuse with CD4 lymphoid cells in vitro: a possible mechanism of T lymphocyte depletion in vivo

Strategies to target the central nervous system HIV reservoir

PURPOSE OF THE REVIEW

The central nervous system (CNS) is an hotspot for HIV persistence and may be a major obstacle to overcome for curative strategies. The peculiar anatomical, tissular and cellular characteristics of the HIV reservoir in the CNS may need to be specifically addressed to achieve a long-term HIV control without ART. In this review, we will discuss the critical challenges that currently explored curative strategies may face in crossing the blood-brain barrier (BBB), targeting latent HIV in brain-resident myeloid reservoirs, and eliminating the virus without eliciting dangerous neurological adverse events.

RECENT FINDINGS

Latency reversing agents (LRA), broadly neutralizing monoclonal antibodies (bNabs), chimeric antigen receptor (CAR) T-cells, and adeno-associated virus 9-vectored gene-therapies cross the BBB with varying efficiency. Although brain penetration is poor for bNAbs, viral vectors for in vivo gene-editing, certain LRAs, and CAR T-cells may reach the cerebral compartment more efficiently. All these approaches, however, may encounter difficulties in eliminating HIV-infected perivascular macrophages and microglia. Safety, including local neurological adverse effects, may also be a concern, especially if high doses are required to achieve optimal brain penetration and efficient brain cell targeting.

SUMMARY

Targeting the CNS remains a potential problem for the currently investigated HIV curing strategies. In vivo evidence on CNS effectiveness is limited for most of the investigated strategies, and additional studies should be focused on evaluating the interplay between the cerebral HIV reservoir and treatment aiming to achieve an ART-free cure.

In vivo killing of primary HIV-infected cells by peripheral-injected early memory-enriched anti-HIV duoCAR T cells

HIV-specific chimeric antigen receptor-T cell (CAR T cell) therapies are candidates to functionally cure HIV infection in people with HIV (PWH) by eliminating reactivated HIV-infected cells derived from latently infected cells within the HIV reservoir. Paramount to translating such therapeutic candidates successfully into the clinic will require anti-HIV CAR T cells to localize to lymphoid tissues in the body and eliminate reactivated HIV-infected cells such as CD4+ T cells and monocytes/macrophages. Here we show that i.v. injected anti-HIV duoCAR T cells, generated using a clinical-grade anti-HIV duoCAR lentiviral vector, localized to the site of active HIV infection in the spleen of humanized mice and eliminated HIV-infected PBMCs. CyTOF analysis of preinfusion duoCAR T cells revealed an early memory phenotype composed predominantly of CCR7+ stem cell-like/central memory T cells (TSCM/TCM) with expression of some effector-like molecules. In addition, we show that anti-HIV duoCAR T cells effectively sense and kill HIV-infected CD4+ T cells and monocytes/macrophages. Furthermore, we demonstrate efficient genetic modification of T cells from PWH on suppressive ART into anti-HIV duoCAR T cells that subsequently kill autologous PBMCs superinfected with HIV. These studies support the safety and efficacy of anti-HIV duoCAR T cell therapy in our presently open phase I/IIa clinical trial (NCT04648046).

Differential expression of HIV envelope epitopes on the surface of HIV-Infected macrophages and CD4+ T cells

HIV-infected macrophages contribute to persistence of HIV reservoirs in people living with HIV receiving antiretroviral therapy. A potential strategy to eliminate reservoirs is the use of antibody-dependent cellular cytotoxicity (ADCC) against infected cells expressing the HIV envelope (Env) protein on their surface. Designing ADCC strategies requires knowledge of exposed Env epitopes on the cell surface and identifying antibodies capable of opsonising infected cells, yet little is known regarding the ability of HIV-infected macrophages to be targeted with such strategies. Using a panel of neutralising and poorly-neutralising anti-Env antibodies we compared Env epitopes expressed on infected monocyte-derived macrophages (MDM) and autologous T cells. Our results reveal potential differences in epitope expression on macrophage- and T cell-expressed Env. Notably, HIV_BaL-infected macrophages were more susceptible to opsonisation by NIH45-46 (median = 40.4%) compared to infected T cells (13.6%; p = 0.002), which were more susceptible to opsonisation by 17b and 447.52D (88.6% and 45.6% respectively) compared to MDM (30% and 6.7%, p = 0.002 and 0.004 respectively). Furthermore, neutralising antibodies 10E8 and PGT145 were relatively ineffective at opsonising Env expressed on the surface of infected T cells or macrophages, indicating that the context in which Env is presented on infected cells may differ to that of cell-free virions.

The Mtb-HIV syndemic interaction: why treating M. tuberculosis infection may be crucial for HIV-1 eradication

Accelerated tuberculosis and AIDS progression seen in HIV-1 and Mycobacterium tuberculosis (Mtb)-coinfected individuals indicates the important interaction between these syndemic pathogens. The immunological interaction between HIV-1 and Mtb has been largely defined by how the virus exacerbates tuberculosis disease pathogenesis. Understanding of the mechanisms by which pre-existing or subsequent Mtb infection may favor the replication, persistence and progression of HIV, is less characterized. We present a rationale for the critical consideration of ‘latent’ Mtb infection in HIV-1 prevention and cure strategies. In support of this position, we review evidence of the effect of Mtb infection on HIV-1 acquisition, replication and persistence. We propose that ‘latent’ Mtb infection may have considerable impact on HIV-1 pathogenesis and the continuing HIV-1 epidemic in sub-Saharan Africa.

Splenic Damage during SIV Infection: Role of T-Cell Depletion and Macrophage Polarization and Infection

The effects of HIV infection on spleen and its cellular subsets have not been fully characterized, particularly for macrophages in which diverse populations exist. We used an accelerated SIV-infected macaque model to examine longitudinal effects on T-cell and macrophage populations and their susceptibilities to infection. Substantial lymphoid depletion occurred, characterized by follicular burn out and a loss of CD3 T lymphocytes, which was associated with cellular activation and transient dysregulations in CD4/CD8 ratios and memory effector populations. In contrast, the loss of CD68 and CD163(+)CD68(+) macrophages and increase in CD163 cells was irreversible, which began during acute infection and persisted until terminal disease. Mac387 macrophages and monocytes were transiently recruited into spleen, but were not sufficient to mitigate the changes in macrophage subsets. Type I interferon, M2 polarizing genes, and chemokine-chemokine receptor signaling were up-regulated in spleen and drove macrophage alterations. SIV-infected T cells were numerous within the white pulp during acute infection, but were rarely observed thereafter. CD68, CD163, and Mac387 macrophages were highly infected, which primarily occurred in the red pulp independent of T cells. Few macrophages underwent apoptosis, indicating that they are a long-lasting target for HIV/SIV. Our results identify macrophages as an important contributor to HIV/SIV infection in spleen and in promoting morphologic changes through the loss of specific macrophage subsets that mediate splenic organization.

Human Immunodeficiency Virus Infection and Host Defense in the Lungs

Immunosuppression associated with human immunodeficiency virus (HIV) infection impacts all components of host defense against pulmonary infection. Cells within the lung have altered immune function and are important reservoirs for HIV infection. The host immune response to infected lung cells further compromises responses to a secondary pathogenic insult. In the upper respiratory tract, mucociliary function is impaired and there are decreased levels of salivary immunoglobulin A. Host defenses in the lower respiratory tract are controlled by alveolar macrophages, lymphocytes, and polymorphonuclear leukocytes. As HIV infection progresses, lung CD4 T cells are reduced in number causing a lack of activation signals from CD4 T cells and impaired defense by macrophages. CD8 T cells, on the other hand, are increased in number and cause lymphocytic alveolitis. Specific antibody responses by B-lymphocytes are decreased and opsonization of microorganisms is impaired. These observed defects in host defense of the respiratory tract explain the susceptibility of HIV-infected persons for oropharyngeal candidiasis, bacterial pneumonia, Pneumocystis pneumonia, and other opportunistic infections.

Eradication of HIV-1 from the macrophage reservoir: an uncertain goal?

Human immunodeficiency virus type 1 (HIV-1) establishes latency in resting memory CD4+ T cells and cells of myeloid lineage. In contrast to the T cells, cells of myeloid lineage are resistant to the HIV-1 induced cytopathic effect. Cells of myeloid lineage including macrophages are present in anatomical sanctuaries making them a difficult drug target. In addition, the long life span of macrophages as compared to the CD4+ T cells make them important viral reservoirs in infected individuals especially in the late stage of viral infection where CD4+ T cells are largely depleted. In the past decade, HIV-1 persistence in resting CD4+ T cells has gained considerable attention. It is currently believed that rebound viremia following cessation of combination anti-retroviral therapy (cART) originates from this source. However, the clinical relevance of this reservoir has been questioned. It is suggested that the resting CD4+ T cells are only one source of residual viremia and other viral reservoirs such as tissue macrophages should be seriously considered. In the present review we will discuss how macrophages contribute to the development of long-lived latent reservoirs and how macrophages can be used as a therapeutic target in eradicating latent reservoir.

HIV reservoir dynamics in the face of highly active antiretroviral therapy

Upon discontinuation of highly active antiretroviral therapy (HAART), human immunodeficiency virus (HIV)-infected individuals experience a brisk rebound in blood plasma viremia due to the exodus of HIV from various body reservoirs. Assessment of HIV dynamics during HAART and following treatment discontinuation is essential to better understand HIV persistence. Here we will first provide a brief overview of the molecular mechanisms involved in HIV reservoir formation and persistence. After a summary of HAART-mediated HIV decay within peripheral blood, we discuss findings from clinical studies examining the effects of HAART initiation and interruption on HIV reservoir dynamics in major anatomical compartments, including lymph nodes and spleen, gut associated lymphoid tissue, reproductive organs, the central nervous system, and the lungs. Features contributing to these reservoirs as distinct compartments, including anatomical features, the presence of drug transporters, and the effect of co-infection, are also discussed.

Cell-to-cell transfer of HIV infection: implications for HIV viral persistence

A major research priority for HIV eradication is the elucidation of the events involved in HIV reservoir establishment and persistence. Cell-to-cell transmission of HIV represents an important area of study as it allows for the infection of cell types which are not easily infected by HIV, leading to the establishment of long-lived viral reservoirs. This phenomenon enables HIV to escape elimination by the immune system. This process may also enable HIV to escape suppressive effects of anti-retroviral drugs. During cell-to-cell transmission of HIV, a dynamic series of events ensues at the virological synapse that promotes viral dissemination. Cell-to-cell transmission involves various types of cells of the immune system and this mode of transmission has been shown to have an important role in sexual and mother-to-child transmission of HIV and spread of HIV within the central nervous system and gut-associated lymphoid tissues. There is also evidence that cell-to-cell transmission of HIV occurs between thymocytes and renal tubular cells. Herein, following a brief review of the processes involved at the virological synapse, evidence supporting the role for cell-to-cell transmission of HIV in the maintenance of the HIV reservoir will be highlighted. Therapeutic considerations and future directions for this area of research will also be discussed.

The macrophage: a therapeutic target in HIV-1 infection

Human immunodeficiency virus (HIV) is still a serious global health concern responsible for more than 25 million deaths in last three decades. More than 34 million people are living with HIV infection. Macrophages and CD4+ T cells are the principal targets of HIV-1. The pathogenesis of HIV-1 takes different routes in macrophages and CD4+ T cells. Macrophages are resistant to the cytopathic effect of HIV-1 and produce virus for longer periods of time. In addition, macrophages being present in every organ system thus can disseminate virus to the different anatomical sites leading to the formation of viral sanctuaries. Complete cure of HIV-1 needs better understanding of viral pathogenesis in these reservoirs and implementation of knowledge into robust therapeutic products. In this review we will focus on the unique relationship between HIV-1 and macrophages. Furthermore, we will describe how successful antiretroviral therapy (ART) is in suppressing HIV and novel molecular and cellular strategies against HIV-1 in macrophages.

Treatment intensification has no effect on the HIV-1 central nervous system infection in patients on suppressive antiretroviral therapy

BACKGROUND

Antiretroviral treatment (ART) significantly reduces cerebrospinal fluid (CSF) HIV-1 RNA levels and residual viremia is less frequently found in CSF than in blood. However, persistent intrathecal immunoactivation is common, even after several years of ART. To investigate whether low-level CSF viremia and residual immunoactivation within the central nervous system (CNS) derive from ongoing local viral replication, we conducted a study of treatment intensification in patients on effective ART.

METHODS

Ten patients on ART with plasma HIV RNA <50 copies per milliliter for >18 months were included. Intensification was given for in total 8 weeks: 4 weeks with maraviroc or lopinavir/ritonavir (good CNS penetration), and 4 weeks with enfuvirtide (poor CNS penetration). Lumbar punctures were performed 4 weeks before, at intensification commencement, at switchover after 4 weeks, at the conclusion of, and 4 weeks after the intensification period.

RESULTS

No significant changes in HIV RNA, neopterin, β2-microglobulin, immunoglobulin G index, albumin ratio, and CD4(+) T-cell count were observed, either in CSF or blood, neither before, during, nor after the intensification periods.

CONCLUSIONS

ART intensification did not reduce residual CSF HIV RNA levels or intrathecal immunoactivation in patients on ART. These findings do not support an ongoing viral replication in CNS.

Antiretroviral release from poly(DL-lactide-co-glycolide) nanoparticles in mice

OBJECTIVES

Free ritonavir, lopinavir and efavirenz injected intraperitoneally were compared with antiretroviral (AR) nanoparticles (NPs).

METHODS

This is a prospective study in BALB/c mice comparing the pharmacokinetics of free drugs with AR NPs. All animals received free drugs or AR NPs (20 mg/kg) in PBS. In vitro replication assays were used for determination of the anti-HIV efficacy of NP formulations. At specific times (free drugs 0.08, 0.125, 0.25, 0.33, 1, 2 and 3 days; AR NPs 0.125, 0.33, 1, 2, 4, 7, 14, 21, 28, 35 and 42 days) mice were euthanized and serum and organs were harvested for determination of AR concentrations by HPLC. Single treatment of monocyte-derived macrophages (MDMs) infected with HIV-1(ada) compared AR NPs (0.005-0.05 mg/mL) with free efavirenz or lopinavir/ritonavir (0.01-0.1 mg/mL), blank NPs and controls. Results are presented as means ± SEM.

RESULTS

Serum free AR drug concentrations peaked 4 h post-injection (ritonavir 3.9 ± 3.05, lopinavir 3.4 ± 2.5 and efavirenz 1.8 ± 0.63 µg/mL) and were eliminated by 72 h. Poly(dl-lactide-co-glycolide) NP animals had detectable ritonavir, lopinavir and efavirenz concentrations in all tissues for 28 days. Treatment of MDMs with AR NPs resulted in sustained inhibition of HIV-1(ada) replication.

CONCLUSIONS

AR drug concentrations from NPs are sustained for 28 days in vivo and anti-HIV inhibition was comparable to that of free drugs in vitro and could be a sustained treatment for delivery of AR drugs.

Cellular reservoirs of HIV-1 and their role in viral persistence

A major obstacle in human immunodeficiency virus type 1 (HIV-1) eradication is the ability of the virus to remain latent in a subpopulation of the cells it infects. Latently infected cells can escape the viral immune response and persist for long periods of time, despite the presence of successful highly active antiretroviral therapy (HAART). Given the appropriate stimulus, latently infected cells can reactivate and start producing infectious virions. The susceptibility of these cell populations to HIV-1, their life span, their proliferative capacity, and their ability to periodically produce infectious virus subsequent to alterations in cellular physiology and/or immunologic controls are critical issues which determine the contribution of these cells to viral persistence. Memory CD4+ T cells due to the long life span, which may be several years, and their ability to reactivate upon encounter with their cognate antigen or other stimulation, are considered a critical reservoir for maintenance of latent HIV-1 proviral DNA. Cells of the monocyte-macrophage lineage, which originate in the bone marrow (BM), are of particular importance in HIV-1 persistence due to their ability to cross the blood-brain barrier (BBB) and spread HIV-1 infection in the immunoprivileged central nervous system (CNS). Hematopoietic progenitor cells (HPCs) are also a potential HIV-1 reservoir, as several studies have shown that CD34+ HPCs carrying proviral DNA can be found in vivo in a subpopulation of HIV-1-infected patients. The ability of HPCs to proliferate and potentially generate clonal populations of infected cells of the monocyte-macrophage lineage may be crucial in HIV-1 dissemination. The contribution of these and other cell populations in HIV-1 persistence, as well as the possible strategies to eliminate latently infected cells are critically examined in this review.

The macrophage origin of the HIV-expressing multinucleated giant cells in hyperplastic tonsils and adenoids

Replication and storage of virus are characteristic features of hyperplastic lymphoid tissues in HIV infection. In opportunistic infections, HIV is synthesized by phagocytic mononuclear and Langhans'-type multinucleated macrophages that coexpress the dendritic cell-associated S-100 and p55 antigens. However, similar cells in hyperplastic tonsils and adenoids from HIV+ individuals were alternatively identified as macrophages or, on the basis of the same S-100 and p55 staining, as dendritic cells. To consider establishing the role of these HIV-rich cells in HIV disease, it is important to reconcile this apparent discrepancy in identity. Hyperplastic tonsils and adenoid specimens were analyzed by HIV RNA in situ hybridization (ISH), light and transmission electron microscopy (TEM), and immunohistochemistry (IHC) (HIV Gag p24 protein, S-100, p55, CD68, HAM56, lysozyme, alpha-1-anti-trypsin, and alpha-1-anti-chymotrypsin). In HIV+ pediatric and adult surgical specimens (n = 11), the giant cells and their mononuclear counterpart were positive for both macrophage and p55 and S-100 IHC markers. In addition, TEM, p24 IHC, and ISH showed HIV expression by cells with typical features of macrophages. Furthermore, these cells were not unique to HIV+ specimens, being seen in 20% of hyperplastic T&A surgical specimens (n = 57) lacking HIV as well as in several types of granulomatous processes, such as sarcoidosis. These cells appear to represent an activated phenotype that can develop independent of HIV, but that may represent a viral host in HIV-infected individuals. Thus, the giant and mononuclear cells that produce striking amounts of HIV in tonsils and adenoids are of macrophage origin, yet, as in opportunistic infections, share dendritic cell-associated antigens, reflecting a common CD34+ bone marrow progenitor.

Increased CD4-positive monocytes in HIV-infected haemophilic patients

The monocyte-macrophage system is known to play a central role in HIV infection, and expression of CD4 on the surface of monocytes/macrophages is important, since this molecule is a key factor for the entrance of HIV into susceptible cells. In this paper we evaluated the expression of CD4 in monocytes of haemophilic patients (He) who had been infected with HIV (HIV + He) through transfusion of contaminated plasma concentrates. Thirty seropositive patients (HIV + He), 10 seronegative He patients (HIV-He) and 20 voluntary normal blood donors were studied. Phenotypic evaluation of monocytes was performed by flow cytometry of peripheral blood stained with anti-CD45, -CD3, -CD4 and -CD14 monoclonal antibodies. The percentage of CD4 monocytes was increased in all HIV+ patients groups, but it was highest in those belonging to Groups III and IV A of the CDC classification. Furthermore, the median of fluorescence intensity of CD4+ monocytes from individual patients was shifted to the right, indicating expression of increased numbers of CD4 molecules on the cell membrane of monocytes. This could in turn favour HIV infection and viral persistence, facilitating in vivo dissemination of the virus.

Effects of HIV-1 on the surface expression of LFA-1 on cultured monocytes

CD11a, the alpha chain of LFA-1, which is a member of the LeuCAM family of integrins, has been implicated in the formation of HIV-induced syncytia and may contribute to the depletion of CD4-positive lymphocytes seen in patients with HIV infection. In this study, we examined the effects of HIV-1 infection on the expression of CD11a on cultured monocyte-derived macrophages (MDMs). Monocytes isolated from peripheral blood and maintained in suspension culture were infected in vitro with a monocytotropic variant of HIV-1 (Ba-L). Surface expression of CD11a, measured by indirect immunofluorescence and flow cytometry, was significantly higher on HIV-infected cells than on mock-infected cells from the same donor. Upregulation of CD11a expression was unaffected by the HIV reverse transcriptase inhibitor, zidovudine, indicating that it did not depend on reverse transcription. A step before reverse transcription, such as viral binding, appears sufficient to trigger an increase in CD11a expression. This hypothesis is supported by our findings of soluble recombinant CD4 inhibition of HIV-induced CD11a upregulation. It is possible that induction of a cytokine network by HIV underlies this effect, given our findings that exposure of uninfected MDMs to granulocyte-macrophage colony-stimulating factor (GM-CSF) specifically increased CD11a expression and that HIV-infected MDMs secreted more GM-CSF than mock-infected cells.

Role of macrophages in the pathogenesis of human immunodeficiency virus (HIV) infection

There are a number of machanisms by which HIV-infected macrophages contribute to the pathogenesis of the Acquired Immunodeficiency Syndrome (AIDS). Macrophage-tropic strains of HIV are present at the time of infection, and persist throughout the course of infection, despite the emergence of T cell tropic quasispecies. As HIV causes chronic infection of macrophages with only minimal cytopathology, these cells can provide an important viral reservoir in HIV-infected persons. Macrophages are more susceptible to HIV infection than freshly isolated monocytes. HIV-infected macrophages can contribute to CD4 T lymphocyte depletion through a gp120-CD4 dependent fusion process with uninfected CD4-expressing T cells. Increasing data support the role of HIV-infected macrophages and microglia in the pathogenesis of HIV-related encephalopathy and AIDS-related dementia through the production of neurotoxins. HIV infection of macrophages in vitro results in impairment of many aspects of their function. Reduced phagocytic capacity for certain opportunistic pathogens, including Toxoplasma gondii and Candida albicans, may be responsible for reactivation of these pathogens in persons with advanced HIV infection, although the mechanisms underlying reactivation of infections and susceptibility to disease from new infections are likely to be multifactorial. Our studies showing defective phagocytosis and killing provide additional information that contribute to our understanding of the pathogenesis of AIDS. Studies of in vitro efficacy of potential antiretroviral therapies should be performed in both primary lymphocyte and monocyte cultures, given the importance of both of these cell populations to HIV pathogenesis and their differing biology.

Analysis of trans-dominant mutants of the HIV type 1 Rev protein for their ability to inhibit Rev function, HIV type 1 replication, and their use as anti-HIV gene therapeutics

The HIV-1 rev gene product facilitates the transport of singly spliced and unspliced HIV-1 transcripts and is necessary for productive HIV-1 infection. On the basis of the previously described trans-dominant Rev mutant M10, four point mutants and one frameshift mutant of the Rev protein were constructed. The mutants were inserted into retroviral expression vectors and analyzed for their ability to inhibit Rev-mediated gene expression. Transient transfection systems were used to screen these new mutants, and each was shown to inhibit expression of a Rev-dependent CAT reporter plasmid. Inhibition of HIV-1 envelope gene expression was tested in the HeLa-T4 cell line and was also shown to be inhibited by the trans-dominant Rev mutants. Retroviral vector producer cell lines were constructed and used to transduce Rev trans-dominant genes into the human T-cell line SupT1. The engineered SupT1 cell lines were then challenged with HIV-1 IIIB and HIV-1 expression was monitored by Northern blot analysis and in situ hybridization. SupT1 cells expressing either a Rev point mutant or the frameshift mutant showed greatly reduced HIV-1 mRNA accumulation and the Rev-dependent singly spliced and unspliced HIV-1 mRNAs were reduced. The kinetics of viral replication following challenge of Rev trans-dominant-engineered SupT1 cells with both HIV-1 IIIB and MN strains was significantly reduced and cells were protected from viral lysis. Viruses that emerge late in infection from Rev trans-dominant-engineered cultures are not resistant to Rev-mediated inhibition. Last, trans-dominant Rev-mediated protection of human CD4+ lymphocytes from challenge with primary HIV-1 patient isolates confirms the potential utility of this system as an anti-HIV-1 gene therapy approach.

Phagocytosis of individual CD4+ T cells by HIV-induced T cell syncytia

Transmission electron microscopic analysis of HIV-induced syncytia of the CD4+ SupT1 cell line has revealed profiles of whole T cells in the syncytium cytoplasm. Serial sections demonstrate that these T cells are completely enveloped by a second membrane in the syncytium cytoplasm and represent phagosomes. Pycnosis of engulfed T cell nuclei, vacuolation of the cytoplasm of engulfed T cells, and the association of engulfed T cells with dense vesicular clusters in the syncytium cytoplasm support the conclusion that they represent phagosomes. In addition, transmission electron micrographs of the syncytium surface reveal giant pseudopodial extensions wrapping around T cells, in a fashion similar to bacterial and yeast phagocytosis by professional phagocytes. These results suggest that phagocytosis is a characteristic acquired during HIV-induced syncytium formation, and that it may represent an avenue of T cell death in addition to fusion in HIV-infected SupT1 cell cultures.

The proteins of lymphocyte- and macrophage-tropic strains of simian immunodeficiency virus are processed differently in macrophages

Since the pathogenesis of SIVmac disease complex is thought to be explained by the tropism of the infecting virus for either CD4+ T-lymphocytes or macrophages or both types of cells, we compared the infection in primary macaque macrophages with molecularly cloned, lymphocyte-tropic SIVmac239 and a cloned, macrophage-tropic chimeric virus (SIVmac239/17E) whose env gene was derived from brain of a macaque (17E) dying from SIV-induced encephalopathy. SIVmac239/17E caused a productive, syncytial cytopathic infection accompanied by accumulation of virus particles within cytoplasmic vesicles of the macrophages. Pulse-chase and immune precipitation studies showed that both the viral glycoprotein precursor (gp160) and the gag precursor (p57) were cleaved into gp120 and p27, respectively, and both were released into the culture medium of infected cells, although most of the p27 remained cell associated. SIVmac239 also infected macrophages, but in comparison to SIVmac239/17E, minimal virus replication occurred. Immunocytostaining revealed that while occasional syncytia were observed in cultures, the majority of the infected cells were not associated with syncytium formation. Ultrastructural studies did not reveal the accumulation of virions within infected macrophages. Pulse-chase studies showed that both gp160 and p57 were produced but were cleaved inefficiently and only minimal amounts of gp120 and p27 were released into the culture medium, even after prolonged incubation times. The processing of proteins of the two viruses was indistinguishable in lymphocytes. Since these two viruses are identical except for changes within the env gene, these results indicate that efficient assembly and release of SIV from blood-derived macrophages is mediated by changes in the envelope glycoprotein.

Further evaluation of soluble CD4 as an anti-HIV type 1 gene therapy: demonstration of protection of primary human peripheral blood lymphocytes from infection by HIV type 1

We previously reported on the construction of retroviral vectors that produce a secreted form of the HIV-1 receptor, T cell antigen CD4 (Morgan et al., AIDS Res Hum Retroviruses 1990;6:183-191). In this article we test the ability of these sCD4-expressing retroviral vectors to protect human T-cell lines or primary T cells from HIV-1 infection. To demonstrate that protection from HIV-1 infection is mediated by the soluble nature of this protein, two coculture protection experiments were conducted. In these experiments, sCD4-expressing retroviral vectors were used to engineer mouse NIH 3T3 cells. In one coculture experiment the human SupT1 cell line was added directly to the culture of sCD4-producing NIH 3T3 cells, and in another experiment the two cell types were separated physically by a semipermeable membrane. In both coculture configurations, the T cell line was protected from HIV-1 challenge as measured by syncytium formation and indirect immunofluorescent assays. In addition, the SupT1 line was directly engineered with sCD4-expressing retroviral vectors and shown to be protected from HIV-1 challenge. As a prelude to further preclinical studies, we tested the ability of retroviral vectors to transduce primary human peripheral blood lymphocytes (PBLs). Conditions used to stimulate T cell growth resulted in significant shifts in the CD4/CD8 cell in favor of CD8 cells. Retroviral-mediated gene transfer under these conditions resulted in low levels of gene transfer (< 5%).(ABSTRACT TRUNCATED AT 250 WORDS)