Altered cytokine expression in T lymphocytes from human immunodeficiency virus Tat transgenic mice

Murine Models of Chronic Viral Infections and Associated Cancers

Viruses are now recognized as bona fide etiologic factors of human cancer. Carcinogenic viruses include Epstein– Barr virus (EBV), high-risk human papillomaviruses (HPVs), hepatitis B virus (HBV), hepatitis C virus (HCV), human T-cell leukemia virus type 1 (HTLV-1), human immunodeficiency virus type 1 (HIV-1, indirectly), and several candidate human cancer viruses. It is estimated that 15% of all human tumors worldwide are caused by viruses. Tumor viruses establish long-term persistent infections in humans, and cancer is an accidental side effect of viral replication strategies. Viruses are usually not complete carcinogens, supporting the concept that cancer results from the accumulation of multiple cooperating events, in which human cancer viruses display different, often opposing roles. The laboratory mouse Mus musculus is one of the best in vivo experimental systems for modeling human pathology, including viral infections and cancer. However, mice are unsusceptible to infection with the known carcinogenic viruses. Many murine models were developed to overcome this limitation and to address various aspects of virus-associated carcinogenesis, from tumors resulting from xenografts of human tissues and cells, including cancerous and virus infected, to genetically engineered mice susceptible to viral infections and associated cancer. The review considers the main existing models, analyzes their advantages and drawbacks, describes their applications, outlines the prospects of their further development.

SARS-CoV-2-specific T cells in infection and vaccination

During viral infections, antibodies and T cells act together to prevent pathogen spread and remove virus-infected cells. Virus-specific adaptive immunity can, however, also trigger pathological processes characterized by localized or systemic inflammatory events. The protective and/or pathological role of virus-specific T cells in SARS-CoV-2 infection has been the focus of many studies in COVID-19 patients and in vaccinated individuals. Here, we review the works that have elucidated the function of SARS-CoV-2-specific T cells in patients and in vaccinated individuals. Understanding whether SARS-CoV-2-specific T cells are more linked to protection or pathogenesis is pivotal to define future therapeutic and prophylactic strategies to manage the current pandemic.

Activation or exhaustion of CD8+ T cells in patients with COVID-19

In addition to CD4⁺ T cells and neutralizing antibodies, CD8⁺ T cells contribute to protective immune responses against SARS-CoV-2 in patients with coronavirus disease 2019 (COVID-19), an ongoing pandemic disease. In patients with COVID-19, CD8⁺ T cells exhibiting activated phenotypes are commonly observed, although the absolute number of CD8⁺ T cells is decreased. In addition, several studies have reported an upregulation of inhibitory immune checkpoint receptors, such as PD-1, and the expression of exhaustion-associated gene signatures in CD8⁺ T cells from patients with COVID-19. However, whether CD8⁺ T cells are truly exhausted during COVID-19 has been a controversial issue. In the present review, we summarize the current understanding of CD8⁺ T-cell exhaustion and describe the available knowledge on the phenotypes and functions of CD8⁺ T cells in the context of activation and exhaustion. We also summarize recent reports regarding phenotypical and functional analyses of SARS-CoV-2-specific CD8⁺ T cells and discuss long-term SARS-CoV-2-specific CD8⁺ T-cell memory.

Advances in Transgenic Mouse Models to Study Infections by Human Pathogenic Viruses

Medical research is changing into direction of precision therapy, thus, sophisticated preclinical models are urgently needed. In human pathogenic virus research, the major technical hurdle is not only to translate discoveries from animals to treatments of humans, but also to overcome the problem of interspecies differences with regard to productive infections and comparable disease development. Transgenic mice provide a basis for research of disease pathogenesis after infection with human-specific viruses. Today, humanized mice can be found at the very heart of this forefront of medical research allowing for recapitulation of disease pathogenesis and drug mechanisms in humans. This review discusses progress in the development and use of transgenic mice for the study of virus-induced human diseases towards identification of new drug innovations to treat and control human pathogenic infectious diseases.

GLI2 regulates TGF-β1 in human CD4+ T cells: implications in cancer and HIV pathogenesis

Elevated levels of the immunoregulatory cytokine TGF-β1 in cancer and HIV infection have been linked to the suppression of protective immune responses. The transcriptional regulation of TGF-β1 is complex and still not completely understood. We report here for the first time that the transcription factor GLI2 regulates the expression of TGF-β1 in human CD4⁺ T cells. In silico screening revealed five novel putative GLI binding sites in the human TGF-β1 promoter. At least two of these sites within the human TGF-β1 promoter are regulated by the GLI2 activator as knockdown of GLI2 in regulatory CD4⁺CD25^hi T cells, high producers of TGF-β1, significantly decreased TGF-β1 transcription. Additionally, naïve CD4⁺ T cells, low producers of TGF-β1, increased their basal level of TGF-β1 mRNA following lentiviral infection with GLI2. The transcriptional regulation of TGF-β1 by GLI2 is a new extension to Sonic Hedgehog (SHH) and TGF-β1 cross-regulation and may provide insight into the detrimental elevation of TGF-β1 leading to pathogenesis in cancer and HIV infection.

HIV-1 Tat increases oxidant burden in the lungs of transgenic mice

Chronic human immunodeficiency virus infection is associated with higher incidence of pulmonary complications including hypertension, vasculopathy, lymphocytic alveolitis, and interstitial pneumonitis not attributed to either opportunistic infections or presence of the virus. The Tat (transactivator of transcription) protein, a required transactivator for expression of full-length viral genes, is pleiotropic and influences expression of cellular inflammatory genes. Tat-dependent transactivation of cellular genes requires specific mediators, including NF-κB, widely recognized as sensitive to changes in cellular oxidant burden. We hypothesized that overproduction of Tat leads to increased oxidant burden and to alterations in basal inflammatory status as measured by NF-κB activation. We engineered transgenic mouse lines that express Tat (86-amino-acid isoform) in the lung under the control of the surfactant protein C promoter. Tat-transgenic mice exhibit increased pulmonary cellular infiltration, increased nitrotyrosine and carbonyl protein modifications, and increased levels of NF-κB, MnSOD, and thioredoxin-interacting protein. These data indicate that Tat increases oxidant burden and resets the threshold for inflammation, which may increase susceptibility to secondary injuries.

Adult AIDS-like disease in a novel inducible human immunodeficiency virus type 1 Nef transgenic mouse model: CD4+ T-cell activation is Nef dependent and can occur in the absence of lymphophenia

CD4C/HIV(nef) transgenic (Tg) mice express Nef in CD4+ T cells and in the cells of the macrophage/monocyte/dendritic lineage, and they develop an AIDS-like disease similar to human AIDS. In these mice, Nef is constitutively expressed throughout life. To rule out the contribution of any developmental defects caused by early expression of Nef, we generated inducible human immunodeficiency virus type 1 (HIV-1) Nef Tg mice by using the tetracycline-inducible system. Faithful expression of the Nef transgene was induced in (CD4C/rtTA x TRE/HIV(Nef)) or (CD4C/rtTA2S-M2 x TRE/HIV(Nef)) double-Tg mice upon doxycycline (DOX) treatment in drinking water. Long-term treatment of these mice with DOX also led to loss, apoptosis, and activation of CD4+ T cells, this latter phenotype being observed even with low levels of Nef. These phenotypes could be transferred by bone marrow (BM) transplantation, indicating a hematopoietic cell autonomous effect. In addition, in mixed Tg:non-Tg BM chimeras, only Tg and not non-Tg CD4+ T cells exhibited an effector/memory phenotype in the absence of lymphopenia. Finally, the DOX-induced double-Tg mice developed nonlymphoid organ diseases similar to those of CD4C/HIV(Nef) Tg mice and of humans infected with HIV-1. These results show for the first time that adult mice are susceptible to the detrimental action of Nef and that Nef-mediated T-cell activation can be independent of lymphopenia. These Tg mice represent a unique model which is likely to be instrumental for understanding the cellular and molecular pathways of Nef action as well as the main characteristics of immune reconstitution following DOX withdrawal.

Human immunodeficiency virus type 1 Tat protein induces an intracellular calcium increase in human monocytes that requires DHP receptors: involvement in TNF-alpha production

HIV-1 Tat protein, acting at the cell membrane, stimulates the production by human monocytes of TNF-alpha, a cytokine implicated in both HIV-1 replication and pathogenesis. Here, we analyze, in primary human monocytes, the mechanisms involved in Tat-stimulated calcium mobilization and its relationship with TNF-alpha production. We show that the Tat protein induces a calcium signal by mobilizing calcium from extracellular stores. This calcium signal is totally blocked when cells are stimulated in the presence of DHP receptor inhibitors such as nimodipine or calcicludine, thus suggesting the implication of this L-type calcium channel. By using RT-PCR amplification, Western blot with antibodies directed against the alpha1D subunit, binding assays with specific agonists or antagonists, and inhibition with specific antisense oligonucleotides, we show that DHP receptors are expressed and functional in primary human monocytes. Interestingly, we demonstrate that Tat-induced calcium mobilization is tightly linked to TNF-alpha production, thus indicating that Tat-induced mobilization and TNF-alpha production are entirely mediated by DHP receptors, as shown by their total inhibition by nimodipine, calcicludine, or anti-alpha1D antisense oligonucleotides.

Astrocyte activation and dysfunction and neuron death by HIV-1 Tat expression in astrocytes

Human immunodeficiency virus type 1 (HIV-1) Tat protein plays an important role in HIV-associated neuropathogenesis. Astrocytosis and neuron death are two hallmarks of HIV-1 infection of the central nervous system (CNS). However, whether there is a direct link between Tat expression, astrocytosis and subsequent neuron death is not known. In this study, we expressed Tat in astrocytes and examined Tat effects on astrocyte function and subsequent neuronal survival. The results showed that Tat expression resulted in a significant increase in glial fibrillary acidic protein (GFAP) expression, a cellular marker of astrocyte activation or astrocytosis. The GFAP promoter-driven reporter gene assay showed that Tat transactivated GFAP expression at the transcriptional level. Furthermore, Tat expression markedly impaired glutamate uptake by astrocytes. Importantly, cell culture supernatants from Tat-expressing astrocytes induced dramatic neuron death. Taken together, these data provide evidence for the first time to directly link Tat expression in astrocytes to astrocytosis, astrocyte dysfunction, and subsequent neuron death. In addition, these data suggest that astrocyte dysfunction contributes, at least in part, to Tat neurotoxicity and subsequently HIV-associated neuropathogenesis.

Targeted myocardial transgenic expression of HIV Tat causes cardiomyopathy and mitochondrial damage

Cardiac effects of human immunodeficiency virus (HIV) transactivator (Tat) are unclear, but Tat decreases liver glutathione (an important mitochondrial antioxidant) when ubiquitously expressed in transgenic mice (TG). With an alpha-myosin heavy chain promoter, Tat was selectively targeted to murine cardiac myocytes. One high-expression hemizygous ((+/-)Tat(high); 12 copies) and two low-expression ((+/-)Tat(lowA,B); 2-5 copies) TG lines were created. Cardiomyopathy was documented with increased left ventricle (LV) mass, ventricular expression of atrial natriuretic factor (ANF) mRNA, mitochondrial ultrastructural defects, and myocardial depletion of glutathione. In (+/-)Tat(high) TGs, normalized LV mass (determined echocardiographically) increased 46% (90 days), 134% (240 days), and 96% (365 days) compared with wild-type littermates (WT). LV fractional shortening was decreased to 28% (90 days), 27% (240 days), and 19% (365 days). (+/-)Tat(low) LV mass was unchanged (<or=365 days). ANF in (+/-)Tat(high) ventricles (180 days) was twofold WT values. Glutathione was selectively decreased in (+/-)Tat(high) hearts (120 days). (+/-)Tat(high) hearts contained damaged mitochondria (>or=210 days); however, profound mitochondrial destruction occurred in homozygous (+/+)Tat(high) hearts (10 days) and the pups died (14 days). Tat caused cardiac dysfunction in this TG and may impact on cardiomyopathy in acquired immunodeficiency syndrome.

The human immunodeficiency virus type 1 Vpu protein inhibits NF-kappa B activation by interfering with beta TrCP-mediated degradation of Ikappa B

The human immunodeficiency virus type 1 (HIV-1) Vpu protein binds to the CD4 receptor and induces its degradation by cytosolic proteasomes. This process involves the recruitment of human betaTrCP (TrCP), a key member of the SkpI-Cdc53-F-box E3 ubiquitin ligase complex that specifically interacts with phosphorylated Vpu molecules. Interestingly, Vpu itself, unlike other TrCP-interacting proteins, is not targeted for degradation by proteasomes. We now report that, by virtue of its affinity for TrCP and resistance to degradation, Vpu, but not a phosphorylation mutant unable to interact with TrCP, has a dominant negative effect on TrCP function. As a consequence, expression of Vpu in HIV-infected T cells or in HeLa cells inhibited TNF-alpha-induced degradation of IkappaB-alpha. Vpu did not inhibit TNF-alpha-mediated activation of the IkappaB kinase but instead interfered with the subsequent TrCP-dependent degradation of phosphorylated IkappaB-alpha. This resulted in a pronounced reduction of NF-kappaB activity. We also observed that in cells producing Vpu-defective virus, NF-kappaB activity was significantly increased even in the absence of cytokine stimulation. However, in the presence of Vpu, this HIV-mediated NF-kappaB activation was markedly reduced. These results suggest that Vpu modulates both virus- and cytokine-induced activation of NF-kappaB in HIV-1-infected cells.

Positive and negative aspects of the human immunodeficiency virus protease: development of inhibitors versus its role in AIDS pathogenesis

In this review we summarize multiple aspects of the human immunodeficiency virus (HIV) protease from both structural and functional viewpoints. After an introductory overview, we provide an up-to-date status report on protease inhibitors (PI). This proceeds from a discussion of PI structural design, to how PI are optimally utilized in highly active antiretroviral triple therapy (one PI along with two reverse transcriptase inhibitors), the emergence of PI resistance, and the natural role of secretory leukocyte PI. Then we switch to another focus: the interaction of HIV protease with other genes in acute and persistent infection, which in turn may have an effect on AIDS pathogenesis. We conclude with a discussion on future directions in HIV treatment, involving multiple-target anti-HIV therapy, vaccine development, and novel reactivation-inhibitory reagents.

Pronounced acute immunosuppression in vivo mediated by HIV Tat challenge

HIV infection is accompanied by an early immune dysfunction limiting host control of virus and likely contributing to difficulties in achieving a successful vaccine against HIV. We report here that the HIV Tat protein is strongly immunosuppressive, both immediately after immunization of mice with soluble protein (sTat), and in seroconverting humans, and propose that Tat-induced suppression cripples immune surveillance to HIV infection. We show that macrophages are sensitive to sTat stimulation at concentrations 1,000-fold lower (500 pM) than T cells, and this stimulation is accompanied by the immunosuppressive induction of Fas ligand on the macrophage. T cell proliferative defects induced by sTat in vitro can be completely (at lower concentrations of sTat) or partially (at higher concentrations) reversed by antagonists to Fas/Fas ligand interaction. We further report a method to preserve immunogenicity while inactivating Tat immunosuppression through oxidation, which advances the use of oxidized Tat as a component of an anti-HIV vaccine. These observations define additional methods to study the immunosuppressive functions of sTat that now may be rapidly applied to primary isolates from individuals with differing clinical courses. Our findings have immediate relevance for vaccine development, by describing and supporting a strategy that includes inactivated sTat in a multicomponent, anti-HIV vaccine.

Inhibition of HIV-1 replication by a Tat RNA-binding domain peptide analog

The peptidic compound, N-acetyl-Arg-Lys-Lys-Arg-Arg-Gln-Arg-Arg-Arg-Cys(biotin)-NH2 (Tat10-biotin), contains the 9-amino acid sequence from the basic domain of the Tat protein responsible for specific interaction with TAR RNA. The cysteine residue provides an attachment site for biotin, which acts as a cellular uptake enhancer. Tat10-biotin binds a fragment of TAR RNA (deltaTAR) avidly and specifically, as measured in an electrophoretic gel shift assay. Tat10-biotin inhibited tat gene-induced expression of a stably transfected chloramphenicol acetyl transferase (CAT) reporter gene linked to the HIV-1 long terminal repeat (LTR) in a model cell assay, but did not inhibit phorbol ester-induced expression of CAT, thereby demonstrating a Tat-dependent mechanism of inhibition. Inhibition of HIV-1 replication after acute infection of MT2 cells was demonstrated by absence of HIV-induced syncytium formation and cytotoxicity, as well as by suppression of reverse transcriptase production. These results suggest that a peptide or peptide mimetic capable of competing with the TAR RNA-binding domain of Tat protein might be useful as a therapeutic agent for AIDS.

Host factors in the pathogenesis of HIV disease

Host factors play an important role in determining rates of disease progression in human immunodeficiency virus (HIV)-infected individuals. HIV is able to subvert the host immune system by infecting CD4+ T cells that normally orchestrate immune responses and by inducing the secretion of proinflammatory cytokines that the virus can utilize to its own replicative advantage. The recognition that certain chemokine receptors serve as necessary co-factors for HIV entry into its target cells as well as the fact that ligands for these receptors can modulate the efficiency of HIV infection has expanded the number and scope of host factors that may impact the pathogenesis of HIV disease. This area of investigation will no doubt yield novel therapeutic strategies for intervention in HIV disease; however, caution is warranted in light of the enormous complexity of the pleiotropic cytokine and chemokine networks and the uncertainty inherent in manipulating these systems. HIV-infected long-term non-progressors represent an excellent model to study potential host factors involved in HIV disease pathogenesis. Genetic factors certainly have a major impact on the immune responses mounted by the host. In this regard, a polymorphism in the gene for the HIV co-receptor CC chemokine receptor 5 (CCR5), which serves as a co-receptor for macrophage (M)-tropic strains of HIV, affords a high degree of protection against HIV infection in individuals homozygous for the genetic defect and some degree of protection against disease progression in HIV-infected heterozygotes. HIV-specific immune responses, including cytotoxic T-lymphocyte (CTL) responses and neutralizing antibody responses, also appear to play salutary roles in protecting against disease progression.

Laboratory diagnostic tests for retroviral infections in dairy and beef cattle

Detection of bovine retroviruses stretches our diagnostic creativity to its limits. The nucleic acid-based, PCR-amplified assays are finding increased clinical use as the veterinary and livestock industry seek earlier detection of infection for eventual corrective management decisions. We are evolving from a point of disease diagnosis by tumor identification through conventional histopathology, to molecular diagnostics for early identification of retroviral nucleic acid (provirus). The clinical use of antibody-based assays lies in the simplicity of testing large numbers of animals, the relative sensitivity of the assays, and the low cost of testing. Although the pathogenicity of bovine leukemia virus (BLV) for cattle has been well documented, the disease potential for bovine immunodeficiency-like virus (BIV) for cattle is still being determined. Nevertheless, pressure to test for retroviral infections of livestock and, when feasible, removal of these infected animals from the herd will be increased.