The immune control and cell-to-cell spread of human T-lymphotropic virus type 1

HTLV-1/-2 and HIV-1 co-infections: retroviral interference on host immune status

The human retroviruses HIV-1 and HTLV-1/HTLV-2 share similar routes of transmission but cause significantly different diseases. In this review we have outlined the immune mediated mechanisms by which HTLVs affect HIV-1 disease in co-infected hosts. During co-infection with HIV-1, HTLV-2 modulates the cellular microenvironment favoring its own viability and inhibiting HIV-1 progression. This is achieved when the HTLV-2 proviral load is higher than that of HIV-1, and thanks to the ability of HTLV-2 to: (i) up-regulate viral suppressive CCL3L1 chemokine expression; (ii) overcome HIV-1 capacity to activate the JAK/STAT pathway; (iii) reduce the activation of T and NK cells; (iv) modulate the host miRNA profiles. These alterations of immune functions have been mainly attributed to the effects of the HTLV-2 regulatory protein Tax and suggest that HTLV-2 exerts a protective role against HIV-1 infection. Contrary to HIV-1/HTLV-2, the effect of HIV-1/HTLV-1 co-infection on immunological and pathological conditions is still controversial. There is evidence that indicates a worsening of HIV-1 infection, while other evidence does not show clinically relevant effects in HIV-positive people. Possible differences on innate immune mechanisms and a particularly impact on NK cells are becoming evident. The differences between the two HIV-1/HTLV-1 and HIV-1/HTLV-2 co-infections are highlighted and further discussed.

Human T-lymphotropic virus type 1 non-structural proteins: Requirements for latent infection

It has been more than 30 years since the discovery of human T-lymphotropic virus type 1 (HTLV-1), the first human retrovirus identified. Human T-lymphotropic virus type 1 infects 15-20 million people worldwide causing two major diseases: adult T-cell leukemia/lymphoma and HTLV-1-associated myelopathy/tropical spastic paraparesis. Human T-lymphotropic virus type 1 establishes several decades of latent infection, during which viral-host interaction determines disease segregation. This review highlights non-structural proteins that are encoded on the viral genome and manage latent infection. Latent infection is a key in HTLV pathology, so that effective inhibition of these proteins might lead to successful disease management.

Effects of exogenous interleukin-7 on CD8(+) T-cell survival and function in human T-cell lymphotropic virus type 1 infection

Interleukin-7 (IL-7) mediates T-cell homeostasis through its effects on T-cell development, survival and function. In human T-cell lymphotropic virus type 1 (HTLV-1) infection, which is causally implicated in adult T-cell leukemia (ATL), the efficiency with which CD8(+) cytotoxic T-lymphocytes (CTLs) clear HTLV-1-infected cells mediates viral control and may be related to disease progression. We report here that CD127 expression in CD8(+) T-cells is independently related to disease status, and that exogenous IL-7 enhances CD8(+) T-cell survival and clearance of HTLV-1 infected cells in vitro. We conclude that CD127 down-regulation may be associated with disease status in HTLV-1 infection, and propose that exogenous IL-7 may be useful immunotherapy or cytokine adjuvant for an anti-ATL therapeutic vaccine.

Molecular characterization of HTLV-1 gp46 glycoprotein from health carriers and HAM/TSP infected individuals

BACKGROUND

Human T-cell Leukemia Virus type 1 (HTLV-1) is the etiological agent of tropical spastic paraparesis/HTLV-associated myelopathy (HAM/TSP) that can be identified in around 0.25%-3.8% of the infected population. Disease progression can be monitored by the proviral load and may depend on genetic factors, however, it is not well understood why some HTLV-1 infected people develop the disease while others do not. The present study attempts to assess the molecular diversity of gp46 glycoprotein in HAM/TSP patients and Health Carrier (HC) individuals.

METHODS

Blood samples were collected from 10 individuals, and DNA was extracted from PBMCs to measure the HTLV-1 proviral load. The gp46 coding sequences were amplified PCR, cloned and sequenced. The molecular characterization was performed using bioinformatics tools.

RESULTS

The median HTLV-1 proviral load of HC (n = 5) and HAM/TSP (n = 5) patients was similar (average 316,227 copies/106 PBMCs). The gp46 molecular characterization of 146 clones (70 HC and 76 HAM/TSP) revealed an overall diversity, within HC and HAM/TSP clones, of 0.4% and 0.6%, respectively. Five frequent mutations were detected among groups (HAM/TSP and HC clone sequences). A single amino acid (aa) substitution (S35L) was exclusive for the HC group, and three gp46 substitutions (F14S, N42H, G72S) were exclusive for the HAM/TSP group. The remaining frequent mutation (V247I) was present in both groups (p = 0.0014). The in silico protein analysis revealed that the mutated alleles F14S and N42H represent more hydrophilic and flexible protein domains that are likely to be less antigenic. The Receptor Binding Domain is quite variable in the HAM/TSP group. Two other domains (aa 53-75 and 175-209) that contain multiple linear T-cell epitopes showed genetic diversity in both HAM/TSP and HC groups. Further analysis revealed 27 and 13 T-cell epitopes for class I HLA alleles and class II HLA alleles, when analyzing the entire gp46.

CONCLUSIONS

The most common gp46 mutations were not associated clinical status because they were found in only one individual, except for the V247I mutation, that was found at viral clones from HAM/TSP ad HC individuals. Because of this, we cannot associate any of the gp46 found mutations with the clinical profile.

Cell-to-cell transmission can overcome multiple donor and target cell barriers imposed on cell-free HIV

Virus transmission can occur either by a cell-free mode through the extracellular space or by cell-to-cell transmission involving direct cell-to-cell contact. The factors that determine whether a virus spreads by either pathway are poorly understood. Here, we assessed the relative contribution of cell-free and cell-to-cell transmission to the spreading of the human immunodeficiency virus (HIV). We demonstrate that HIV can spread by a cell-free pathway if all the steps of the viral replication cycle are efficiently supported in highly permissive cells. However, when the cell-free path was systematically hindered at various steps, HIV transmission became contact-dependent. Cell-to-cell transmission overcame barriers introduced in the donor cell at the level of gene expression and surface retention by the restriction factor tetherin. Moreover, neutralizing antibodies that efficiently inhibit cell-free HIV were less effective against cell-to-cell transmitted virus. HIV cell-to-cell transmission also efficiently infected target T cells that were relatively poorly susceptible to cell-free HIV. Importantly, we demonstrate that the donor and target cell types influence critically the extent by which cell-to-cell transmission can overcome each barrier. Mechanistically, cell-to-cell transmission promoted HIV spread to more cells and infected target cells with a higher proviral content than observed for cell-free virus. Our data demonstrate that the frequently observed contact-dependent spread of HIV is the result of specific features in donor and target cell types, thus offering an explanation for conflicting reports on the extent of cell-to-cell transmission of HIV.

HTLV-1 infection: what determines the risk of inflammatory disease?

Human T-lymphotropic virus type 1 (HTLV-1) is an exogenous retrovirus that persists lifelong in the infected host. Infection has been linked to a spectrum of diverse diseases: adult T cell leukemia, encephalomyelopathy, and predisposition to opportunistic bacterial and helminth infections. Applications of new technologies and biological concepts to the field have provided new insights into viral persistence and pathogenesis in HTLV-1 infection. Here, we summarize the emerging concepts of dynamic HTLV-1-host interactions and propose that chronic interferon (IFN) production causes tissue damage in HTLV-1-associated inflammatory diseases.

[HTLV-1-associated myelopathy/tropical spastic paraparesis: a differential diagnosis in multiple sclerosis]

Human T-cell lymphotropic virus 1 (HTLV-1) associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a neurological disease caused by infection with HTLV-1. The disorder is very rare in Europe but endemic in many parts of the world. The pathogenesis is not clearly characterized but is based on a possibly immune-mediated injury of the cervicothoracic spinal cord. Clinically, HAM/TSP constitutes a slowly progressive spastic paraparesis associated with bladder dysfunction and often mimics the course of autoimmune and neurodegenerative diseases. The diagnosis is based on typical symptoms as well as detection of HTLV-1 specific antibodies and proviral HTLV-1 DNA or HTLV-1 RNA. The therapy is limited to symptomatic treatment. Transmission of HTLV-1 can occur vertically by breast feeding, through sexual contact or via infected blood products. Based on a clinical case report, we present here a current review on the pathophysiology, epidemiology, clinical manifestations, diagnosis and treatment of HAM/TSP.

Interleukin-18 and interferon-gamma polymorphisms are implicated on proviral load and susceptibility to human T-lymphotropic virus type 1 infection

Interleukin-18 (IL-18) and interferon-gamma (IFN-γ) exert important functions in both innate and adaptive immune responses against intracellular pathogens and viruses. Previous studies suggested that host genetic factors, including cytokines gene polymorphisms, could be involved in the pathogenesis of human T-cell leukemia virus type 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Thus, we analyzed -137C/G and -607A/C of the IL-18 promoter and +874T/A of the IFN-γ in DNA samples from 98 HTLV-1-infected individuals exhibiting or not clinical symptoms and 150 healthy control individuals. The IL-18 promoter -607CC genotype was significantly lower in HTLV-1 asymptomatic carriers (HAC) and HTLV-1-infected individuals (HAC + HAM/TSP) than healthy control group. In contrast, the -607AC genotype was significantly higher in HAC and HTLV-1-infected individuals group compared to the healthy control group. The -137G/-607A IL-18 haplotype was higher in infected group than healthy control group, and the -137C/-607C IL-18 haplotype was increased in the healthy control group compared to the others. Finally, the IFN-γ polymorphism analysis showed that the HTLV-1-infected individuals with +874AT genotype presented higher proviral load than +874AA genotype. These data indicate that the IL-18-607AC genotype and -137G/-607A haplotype could be a risk factor for HTLV-1 infection, whereas the protective effect could be conferred by -607CC genotype and -137C/-607C haplotype. Also, the IFN-γ could be implicated on the proviral load levels.

HTLV-1 Tax mediated downregulation of miRNAs associated with chromatin remodeling factors in T cells with stably integrated viral promoter

RNA interference (RNAi) is a natural cellular mechanism to silence gene expression and is predominantly mediated by microRNAs (miRNAs) that target messenger RNA. Viruses can manipulate the cellular processes necessary for their replication by targeting the host RNAi machinery. This study explores the effect of human T-cell leukemia virus type 1 (HTLV-1) transactivating protein Tax on the RNAi pathway in the context of a chromosomally integrated viral long terminal repeat (LTR) using a CD4⁺ T-cell line, Jurkat. Transcription factor profiling of the HTLV-1 LTR stably integrated T-cell clone transfected with Tax demonstrates increased activation of substrates and factors associated with chromatin remodeling complexes. Using a miRNA microarray and bioinformatics experimental approach, Tax was also shown to downregulate the expression of miRNAs associated with the translational regulation of factors required for chromatin remodeling. These observations were validated with selected miRNAs and an HTLV-1 infected T cells line, MT-2. miR-149 and miR-873 were found to be capable of directly targeting p300 and p/CAF, chromatin remodeling factors known to play critical role in HTLV-1 pathogenesis. Overall, these results are first in line establishing HTLV-1/Tax-miRNA-chromatin concept and open new avenues toward understanding retroviral latency and/or replication in a given cell type.

Detection of HTLV-1 in the Labial Salivary Glands of Patients with Sjögren’s Syndrome: A Distinct Clinical Subgroup?

Objective.

To examine whether patients with Sjögren’s syndrome (SS) can be distinguished based on the expression of human T cell lymphotrophic virus type I (HTLV-1) and, if so, whether the subgroups differ in their clinical features and serological measures.

Methods.

Polymerase chain reaction (PCR) and nested PCR were used to amplify viral DNA from peripheral blood mononuclear cells (PBMC) in 53 patients with SS, using primers from the HTLV-1 pX, p19, pol, and tax regions. Minor salivary gland biopsy specimens from 33 patients with SS were examined for the presence of HTLV-1 p19 or tax proteins immunohistochemically. The sociodemographic, glandular, and extraglandular manifestations, and laboratory findings including autoantibodies, complement, and immunoglobulin levels, were analyzed.

Results.

The HTLV-1 tax gene was detected in PBMC samples from 2 of 53 patients (3.8%), whereas the HTLV-1 pX, p19, and pol genes were not expressed. As well, 100% of PBMC samples from 4 family members of patients in whom the tax gene was detected also expressed the tax gene. Immunohistochemical staining for HTLV-1 p19 and tax was seen in 10 out of 33 (30.3%) patients with SS each. Overall, 14 (42.4%) patients expressed HTLV-1 p19 or tax proteins, and they had lower rheumatoid factor and C3 levels (p = 0.015 and p = 0.005, respectively) and higher lymphocyte counts (p = 0.016). The prevalence of glandular and extraglandular manifestations did not differ between the HTLV-1-positive and negative patients.

Conclusion.

Our findings suggest that HTLV-1 in the salivary glands is involved in the pathogenesis of a subpopulation of SS, and HTLV-1-associated SS might have different immunological patterns than idiopathic SS.

Differential role of PKC-induced c-Jun in HTLV-1 LTR activation by 12-O-tetradecanoylphorbol-13-acetate in different human T-cell lines

We have previously shown that TPA activates HTLV-1 LTR in Jurkat T-cells by inducing the binding of Sp1-p53 complex to the Sp1 site residing within the Ets responsive region 1 (ERR-1) of the LTR and that this activation is inhibited by PKCalpha and PKCepsilon. However, in H9 T-cells TPA has been noted to activate the LTR in two consecutive stages. The first stage is activation is mediated by PKCetta and requires the three 21 bp TRE repeats. The second activation mode resembles that of Jurkat cells, except that it is inhibited by PKCdelta. The present study revealed that the first LTR activation in H9 cells resulted from PKCetta-induced elevation of non-phosphorylated c-Jun which bound to the AP-1 site residing within each TRE. In contrast, this TRE-dependent activation did not occur in Jurkat cells, since there was no elevation of non-phosphorylated c-Jun in these cells. However, we found that PKCalpha and PKCepsilon, in Jurkat cells, and PKCetta and PKCdelta, in H9 cells, increased the level of phosphorylated c-Jun that interacted with the Sp1-p53 complex. This interaction prevented the Sp1-p53 binding to ERR-1 and blocked, thereby, the ERR-1-mediated LTR activation. Therefore, this PKC-inhibited LTR activation started in both cell types after depletion of the relevant PKCs by their downregulation. In view of these variable activating mechanisms we assume that there might be additional undiscovered yet modes of HTLV-1 LTR activation which vary in different cell types. Moreover, in line with this presumption we speculate that in HTLV-1 carriers the LTR of the latent provirus may also be reactivated by different mechanisms that vary between its different host T-lymphocyte subclones. Since this reactivation may initiate the ATL process, understanding of these mechanisms is essential for establishing strategies to block the possibility of reactivating the latent virus as preventive means for ATL development in carriers.

Human T-lymphotropic virus 1 (HTLV-1) infection--dermatological implications

Human T-lymphotropic virus type 1 (HTLV-1) is a type C retrovirus primarily endemic to Japan, Central and South America, the Middle East, regions of Africa, and the Caribbean. Currently, an estimated 10-20 million people worldwide are infected with this virus. Although the majority of infected individuals remain asymptomatic, HTLV-1 is the causative agent of a number of disorders, notably adult T-cell leukemia/lymphoma (ATLL) and a progressive demyelinating neurological disorder, HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). In addition to ATLL and HAM/TSP, HTLV-1 has been associated with a spectrum of skin disorders, such as infective dermatitis associated with HTLV-1, crusted scabies, and leprosy. The understanding of the interaction between virus and host response has improved markedly, but there are still few treatment options.

Human T-cell leukemia viruses are highly unstable over a wide range of temperatures

The biological properties of human T-cell leukemia virus type I (HTLV-I) and HTLV type II (HTLV-II) are not well elucidated as cell-free viruses. We established new assay systems to detect the infectivity of cell-free HTLVs and examined the stability of cell-free HTLVs at different temperatures. HTLVs lost infectivity more rapidly than did bovine leukemia virus (BLV), which is genetically related to HTLVs. The half-lives of three HTLV-I strains (two cosmopolitan strains and one Melanesian strain) at 37 °C were approximately 0.6 h, whereas the half-life of a BLV strain was 8.5 h. HTLV-I rapidly lost infectivity unexpectedly at 0 and 4 °C. We examined the stability of vesicular stomatitis virus pseudotypes with HTLV-I, HTLV-II or BLV Env proteins, and the Env proteins of HTLVs were found to be more unstable at 4 and 25 °C than the Env proteins of the BLV. Over the course of the viral life cycle, heat treatment inhibited HTLV-I infection at the phase of attachment to the host cells, and inhibition was more marked upon entry into the cells. The HTLV-I Env surface (SU) protein (gp46) was easily released from virions during incubation at 37 °C. However, this release was inhibited by pre-treatment of the virions with N-ethylmaleimide, suggesting that the inter-subunit bond between gp46 SU and gp21 transmembrane (TM) proteins is rearranged by disulfide bond isomerization. HTLVs are highly unstable over a wide range of temperatures because the disulfide bonds between the SU and TM proteins are labile.

Short communication an interferon-γ ELISPOT assay with two cytotoxic T cell epitopes derived from HTLV-1 tax region 161-233 discriminates HTLV-1-associated myelopathy/tropical spastic paraparesis patients from asymptomatic HTLV-1 carriers in a Peruvian population

HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a chronic and progressive disorder caused by the human T-lymphotropic virus type 1 (HTLV-1). In HTLV-1 infection, a strong cytotoxic T cell (CTL) response is mounted against the immunodominant protein Tax. Previous studies carried out by our group reported that increased IFN-γ enzyme-linked immunospot (ELISPOT) responses against the region spanning amino acids 161 to 233 of the Tax protein were associated with HAM/TSP and increased HTLV-1 proviral load (PVL). An exploratory study was conducted on 16 subjects with HAM/TSP, 13 asymptomatic carriers (AC), and 10 HTLV-1-seronegative controls (SC) to map the HAM/TSP-associated CTL epitopes within Tax region 161-233. The PVL of the infected subjects was determined and the specific CTL response was evaluated with a 6-h incubation IFN-γ ELISPOT assay using peripheral blood mononuclear cells (PBMCs) stimulated with 16 individual overlapping peptides covering the Tax region 161-233. Other proinflammatory and Th1/Th2 cytokines were also quantified in the supernatants by a flow cytometry multiplex assay. In addition, a set of human leukocyte antigen (HLA) class I alleles that bind with high affinity to the CTL epitopes of interest was determined using computational tools. Univariate analyses identified an association between ELISPOT responses to two new CTL epitopes, Tax 173-185 and Tax 181-193, and the presence of HAM/TSP as well as an increased PVL. The HLA-A*6801 allele, which is predicted to bind to the Tax 181-193 peptide, was overpresented in the HAM/TSP patients tested.

Interleukin-1 alpha produced by human T-cell leukaemia virus type I-infected T cells induces intercellular adhesion molecule-1 expression on lung epithelial cells

The pathogenic mechanism of human T-cell leukaemia virus type I (HTLV-I)-related pulmonary disease, which involves overexpression of intercellular adhesion molecule-1 (ICAM-1) in lung epithelial cells, was investigated. The supernatant of HTLV-I-infected Tax(+) MT-2 and C5/MJ cells induced ICAM-1 expression on A549 cells, a human tumour cell line with the properties of alveolar epithelial cells. Neutralization of ICAM-1 partially inhibited HTLV-I-infected T-cell adhesion to A549 cells. Analysis of the ICAM-1 promoter showed that the nuclear factor-kappa B-binding site was important for supernatant-induced ICAM-1 expression. Induction of interleukin (IL)-1 alpha (IL-1α) expression in MT-2 and C5/MJ cells was observed compared with uninfected controls and HTLV-I-infected Tax-negative cell lines. The significance of IL-1α as a soluble messenger was supported by blocking the biological activities of MT-2 supernatant with an IL-1α-neutralizing mAb. Moreover, Tax and IL-1α expression was demonstrated in the bronchoalveolar lavage cells of patients with HTLV-I-related pulmonary disease. Immunohistochemistry confirmed ICAM-1 and IL-1α expression in lung epithelial cells and lymphocytes of patients with HTLV-I-related pulmonary diseases, and in a transgenic mouse model of Tax expression. These results suggest that IL-1α produced by HTLV-I-infected Tax(+) T cells is crucial for ICAM-1 expression in lung epithelial cells and subsequent adhesion of lymphocytes in HTLV-I-related pulmonary diseases.

Programmed death-1 (PD-1)/PD-1 ligand pathway-mediated immune responses against human T-lymphotropic virus type 1 (HTLV-1) in HTLV-1-associated myelopathy/tropical spastic paraparesis and carriers with autoimmune disorders

Human T-lymphotropic virus-1 (HTLV-1) causes HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and adult T-cell leukemia-lymphoma in individuals with dysfunctional immune responses. In this study, to characterize the HTLV-1-specific cytotoxic T lymphocyte (CTL) populations in asymptomatic HTLV-1 carriers (ACs), HAM/TSP patients, and carriers with autoimmune disorders (CAIDs), we examined the role of programmed death-1 and its ligand (PD-1/PD-L1) in HTLV-1-specific CTL functions using an HTLV-1 Tax/HLA-A*0201 tetramer and an HTLV-1 Tax/HLA-A*2402 tetramer. Interestingly, the percentage of HTLV-1 Tax301-309/HLA-A*2402 tetramer(+)CD8(+) cells expressing PD-1 in ACs was significantly higher than the percentage of HTLV-1 Tax11-19/HLA-A*0201 tetramer(+)CD8(+) cells expressing PD-1. PD-1 expression was significantly downregulated on HTLV-1-specific CTLs in HAM/TSP compared with ACs. PD-L1 expression was observed in a small proportion of unstimulated lymphocytes from ACs and was greater in ACs than in HAM/TSP and CAIDs after short-term culture. Furthermore, CTL degranulation was impaired in HAM/TSP, whereas anti-PD-L1 blockade significantly increased CTL function in ACs. Downregulation of PD-1 on HTLV-1-specific CTLs and loss of PD-L1 expression in HAM/TSP and CAIDs, along with impaired function of HTLV-1-specific CTLs in HAM/TSP, may underlie the apparently dysfunctional immune response against HTLV-1.

Stable and transient periodic oscillations in a mathematical model for CTL response to HTLV-I infection

The cytotoxic T lymphocyte (CTL) response to the infection of CD4+ T cells by human T cell leukemia virus type I (HTLV-I) has previously been modelled using standard response functions, with relatively simple dynamical outcomes. In this paper, we investigate the consequences of a more general CTL response and show that a sigmoidal response function gives rise to complex behaviours previously unobserved. Multiple equilibria are shown to exist and none of the equilibria is a global attractor during the chronic infection phase. Coexistence of local attractors with their own basin of attractions is the norm. In addition, both stable and unstable periodic oscillations can be created through Hopf bifurcations. We show that transient periodic oscillations occur when a saddle-type periodic solution exists. As a consequence, transient periodic oscillations can be robust and observable. Implications of our findings to the dynamics of CTL response to HTLV-I infections in vivo and pathogenesis of HAM/TSP are discussed.

Decreased infectivity of a neutralization-resistant equine infectious anemia virus variant can be overcome by efficient cell-to-cell spread

Two variants of equine infectious anemia virus (EIAV) that differed in sensitivity to broadly neutralizing antibody were tested in direct competition assays. No differences were observed in the growth curves and relative fitness scores of EIAVs of principal neutralizing domain variants of groups 1 (EIAV(PND-1)) and 5 (EIAV(PND-5)), respectively; however, the neutralization-resistant EIAV(PND-5) variant was less infectious in single-round replication assays. Infectious center assays indicated similar rates of cell-to-cell spread, which was approximately 1,000-fold more efficient than cell-free infectivity. These data indicate that efficient cell-to-cell spread can overcome the decreased infectivity that may accompany immune escape and should be considered in studies assessing the relative levels of fitness among lentivirus variants, including HIV-1.

Antibodies to the envelope glycoprotein of human T cell leukemia virus type 1 robustly activate cell-mediated cytotoxic responses and directly neutralize viral infectivity at multiple steps of the entry process

Infection of human cells by human T cell leukemia virus type 1 (HTLV-1) is mediated by the viral envelope glycoproteins. The gp46 surface glycoprotein binds to cell surface receptors, including heparan sulfate proteoglycans, neuropilin 1, and glucose transporter 1, allowing the transmembrane glycoprotein to initiate fusion of the viral and cellular membranes. The envelope glycoproteins are recognized by neutralizing Abs and CTL following a protective immune response, and therefore, represent attractive components for a HTLV-1 vaccine. To begin to explore the immunological properties of potential envelope-based subunit vaccine candidates, we have used a soluble recombinant surface glycoprotein (gp46, SU) fused to the Fc region of human IgG (sRgp46-Fc) as an immunogen to vaccinate mice. The recombinant SU protein is highly immunogenic and induces high titer Ab responses, facilitating selection of hybridomas that secrete mAbs targeting SU. Many of these mAbs recognize envelope displayed on the surface of HTLV-1-infected cells and virions and several of the mAbs robustly antagonize envelope-mediated membrane fusion and neutralize pseudovirus infectivity. The most potently neutralizing mAbs recognize the N-terminal receptor-binding domain of SU, though there is considerable variation in neutralizing proficiency of the receptor-binding domain-targeted mAbs. By contrast, Abs targeting the C-terminal domain of SU tend to lack robust neutralizing activity. Importantly, we find that both neutralizing and poorly neutralizing Abs strongly stimulate neutrophil-mediated cytotoxic responses to HTLV-1-infected cells. Our data demonstrate that recombinant forms of SU possess immunological features that are of significant utility to subunit vaccine design.

A new role for the HTLV-1 p8 protein: increasing intercellular conduits and viral cell-to-cell transmission

Retroviruses like HIV-1 and HTLV-1 can be transmitted efficiently by direct contact between infected and target cells. For HIV-1, various modes of cell-to-cell transfer have been reported, including virological synapses, polysynapses, filopodial bridges, and nanotube-like structures. So far, only synapses and biofilms have been described for HTLV-1 transmission. Recently, Van Prooyen et al. [1] identified an additional mode of HTLV-1 transmission through cellular conduits induced by the viral accessory protein p8.

Monocytes from HTLV-1–infected patients are unable to fully mature into dendritic cells

Human T-cell lymphotropic virus type 1 (HTLV-1) is a causative agent of adult T-cell leukemia and HTLV-1–associated myelopathy/tropical spastic paraparesis. HTLV-1–associated myelopathy/tropical spastic paraparesis is a chronic inflammatory disease characterized by loss of motor movement in response to spinal marrow cell destruction by T lymphocytes. To perform their cellular function, T cells need to be activated by antigen-presenting cells, such as dendritic cells (DCs). The aim of this work was to analyze DC differentiation and activation from monocytes of HTLV-1–infected individuals. We demonstrated that monocytes from HTLV-1–infected patients who had been stimulated to differentiate had an impaired loss of CD14 expression, expressed low levels of CD1a, and maintained secretion of tumor necrosis factor-α compared with monocytes from noninfected donors. We further evaluated DC activation by tumor necrosis factor-α. We observed that in response to activation, DCs that were derived from noninfected donors had an increase in the percentage of CD83+, CD86+, and human leukocyte antigen-DR+ cells, whereas in DCs derived from HTLV-1–infected patients, the percentage of CD83+, CD86+, and human leukocyte antigen-DR+ cells remained similar to that of nonactivated cells. Moreover, these cells had an impaired capacity to stimulate allogeneic T lymphocytes. We demonstrated that DC maturation was altered in HTLV-1–infected patients, which could contribute to the development of HTLV-1–associated diseases.

Antiretroviral activity of thiosemicarbazone metal complexes

Thiosemicarbazones display a wide antimicrobial activity by targeting bacteria, fungi, and viruses. Here, we report our studies on the antiviral activity of two thiosemicarbazone metal complexes, [bis(citronellalthiosemicarbazonato)nickel(II)] and [aqua(pyridoxalthiosemicarbazonato)copper(II)] chloride monohydrate, against the retroviruses HIV-1 and HTLV-1/-2. Both compounds exhibit antiviral properties against HIV but not against HTLVs . In particular, the copper complex shows the most potent anti-HIV activity by acting at the post-entry steps of the viral cycle.

Highly active antiretroviral treatment against STLV-1 infection combining reverse transcriptase and HDAC inhibitors

Approximately 3% of all human T-lymphotropic virus type 1 (HTLV-1)–infected persons will develop a disabling inflammatory disease of the central nervous system known as HTLV-1–associated myelopathy/tropical spastic paraparesis, against which there is currently no efficient treatment. As correlation exists between the proviral load (PVL) and the clinical status of the carrier, it is thought that diminishing the PVL could prevent later occurrence of the disease. We have conducted a study combining valproate, an inhibitor of histone deacetylases, and azidothymidine, an inhibitor of reverse transcriptase, in a series of baboons naturally infected with simian T-lymphotropic virus type 1 (STLV-1), whose PVL was equivalent to that of HTLV-1 asymptomatic carriers. We show that the combination of drugs caused a strong decrease in the PVL and prevented the transient rise in PVL that is seen after treatment with histone deacetylases alone. We then demonstrate that the PVL decline was associated with an increase in the STLV-1–specific cytotoxic T-cell population. We conclude that combined treatment with valproate to induce viral expression and azidothymidine to prevent viral propagation is a safe and effective means to decrease PVL in vivo. Such treatments may be useful to reduce the risk of HAM/TSP in asymptomatic carriers with a high PVL.

Intra- and inter-laboratory variability in human T-cell leukemia virus type-1 proviral load quantification using real-time polymerase chain reaction assays: a multi-center study

Human T-cell leukemia virus type-1 (HTLV-1) proviral load (VL) is an important determinant of viral pathogenesis and malignant evolution. Although VL has been quantified by in-house real-time quantifiable polymerase chain reaction (qPCR) technology, little is known about the harmonization among different VL assay systems. We evaluated intra- and inter-laboratory variability of VL measured at six laboratories using the same DNA samples seropositive for HTLV-1 in a two-step manner. The first study measured 60 samples by original in-house assays, finding that the median intra- and inter-laboratory coefficient of variation (CV) was 44.9% (range, 25.4-71.8%) and 59.9% (34.2-93.4%), respectively. The inter-laboratory correlation coefficients ranged from 0.760 to 0.875, indicating that VL were measured with good precision in each laboratory, but inter-laboratory regression slopes differed from 0.399 to 2.206, indicating that VL were measured with a wide variation between laboratories. To examine the effect of standardization of reference materials (RM) on the VL variability, we performed a second study using only 20 samples by substituting RM for plasmid including the HTLV-1 pX region. The median inter-laboratory CV for raw pX copy number was reduced significantly from 66.9% to 35.7%, whereas the median CV for the internal control remained almost unchanged, resulting in no improvement in inter-laboratory CV for VL. This indicates that each in-house assay system worked well with good precision, but standardizing RM alone was insufficient for harmonization. The relevant choice of not only RM, but also internal control genes for data normalization is expected to be realistic to standardize HTLV-1 VL measurement.

Multiple stable periodic oscillations in a mathematical model of CTL response to HTLV-I infection

Stable periodic oscillations have been shown to exist in mathematical models for the CTL response to HTLV-I infection. These periodic oscillations can be the result of mitosis of infected target CD4(+) cells, of a general form of response function, or of time delays in the CTL response. In this study, we show through a simple mathematical model that time delays in the CTL response process to HTLV-I infection can lead to the coexistence of multiple stable periodic solutions, which differ in amplitude and period, with their own basins of attraction. Our results imply that the dynamic interactions between the CTL immune response and HTLV-I infection are very complex, and that multi-stability in CTL response dynamics can exist in the form of coexisting stable oscillations instead of stable equilibria. Biologically, our findings imply that different routes or initial dosages of the viral infection may lead to quantitatively and qualitatively different outcomes.

Increased all-cause and cancer mortality in HTLV-II infection

BACKGROUND

Human T-lymphotropic virus (HTLV)-I and HTLV-II cause chronic human retroviral infections, but few studies have examined the impact of either virus on survival among otherwise healthy individuals. The authors analyzed all-cause and cancer mortality in a prospective cohort of 155 HTLV-I, 387 HTLV-II, and 799 seronegative subjects.

METHODS

Vital status was ascertained using death certificates, the US Social Security Death Index or family report, and causes of death were grouped into 9 categories. Hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated using Cox proportional hazards models.

RESULTS

After a median follow-up of 15.9 years, there were 105 deaths: 22 HTLV-I, 41 HTLV-II, and 42 HTLV-seronegative. Cancer was the predominant cause of death, resulting in 8 HTLV-I, 17 HTLV-II, and 15 HTLV-seronegative deaths. After adjustment for confounding, HTLV-I status was not significantly associated with increased all-cause mortality, though there was a positive trend (HR: 1.6, 95% CI: 0.8 to 3.1). HTLV-II status was strongly associated with increased all-cause (HR: 2.4, 95% CI: 1.4 to 4.4) and cancer mortality (HR: 3.8, 95% CI: 1.6 to 9.2).

CONCLUSIONS

The observed associations of HTLV-II with all-cause and cancer mortality could reflect biological effects of HTLV-II infection, residual confounding by socioeconomic status or other factors, or differential access to health care and cancer screening.

Transformation of breast milk macrophages by HTLV-I: implications for HTLV-I transmission via breastfeeding

Human T cell leukemia virus type I (HTLV-I), a causative agent of adult T-cell leukemia (ATL), is transmitted from mother to child predominantly by breastfeeding. The source of HTLV-I-infected cells in breast milk has been thought to be T cells, however, the majority of cells in breast milk are CD14(+) macrophages but not CD3(+) T lymphocytes, and no data are available regarding HTLV-I transmission through breast milk macrophages (BrMMpsi). To explore the potential of BrMMpsi as a possible source of infection in mother to child transmission (MTCT) of HTLV-I, an immortalized cell line (HTLV-BrMMpsi) has been established from BrMMpsi by infection with HTLV-I. HTLV-BrMMpsi retained macrophage characteristics and did not express a complete dendritic cell (DC) phenotype; nevertheless, HTLV-BrMMpsi efficiently promoted T cell proliferation in primary allogeneic mixed lymphocyte reaction (MLR) like DC. Moreover, HTLV-I infection could be transmitted from HTLV-BrMMpsi to activated T cells in the peripheral blood. These findings suggested that BrMMpsi might be an appropriate HTLV-I reservoir involved in MTCT transmission via breastfeeding.

The Role of Lipids in Retrovirus Replication

Retroviruses undergo several critical steps to complete a replication cycle. These include the complex processes of virus entry, assembly, and budding that often take place at the plasma membrane of the host cell. Both virus entry and release involve membrane fusion/fission reactions between the viral envelopes and host cell membranes. Accumulating evidence indicates important roles for lipids and lipid microdomains in virus entry and egress. In this review, we outline the current understanding of the role of lipids and membrane microdomains in retroviral replication.

Virus cell-to-cell transmission

Viral infections spread based on the ability of viruses to overcome multiple barriers and move from cell to cell, tissue to tissue, and person to person and even across species. While there are fundamental differences between these types of transmissions, it has emerged that the ability of viruses to utilize and manipulate cell-cell contact contributes to the success of viral infections. Central to the excitement in the field of virus cell-to-cell transmission is the idea that cell-to-cell spread is more than the sum of the processes of virus release and entry. This implies that virus release and entry are efficiently coordinated to sites of cell-cell contact, resulting in a process that is distinct from its individual components. In this review, we will present support for this model, illustrate the ability of viruses to utilize and manipulate cell adhesion molecules, and discuss the mechanism and driving forces of directional spreading. An understanding of viral cell-to-cell spreading will enhance our ability to intervene in the efficient spreading of viral infections.

Development of a cytotoxic T-cell assay in rabbits to evaluate early immune response to human T-lymphotropic virus type 1 infection

Human T-lymphotropic virus type 1 (HTLV-1) infection causes adult T-cell lymphoma/leukemia (ATL) following a prolonged clinical incubation period, despite a robust adaptive immune response against the virus. Early immune responses that allow establishment of the infection are difficult to study without effective animal models. We have developed a cytotoxic T-lymphocyte (CTL) assay to monitor the early events of HTLV-1 infection in rabbits. Rabbit skin fibroblast cell lines were established by transformation with a plasmid expressing simian virus 40 (SV40) large T antigen and used as autochthonous targets (derived from same individual animal) to measure CTL activity against HTLV-1 infection in rabbits. Recombinant vaccinia virus (rVV) constructs expressing either HTLV-1 envelope surface unit (SU) glycoprotein 46 or Tax proteins were used to infect fibroblast targets in a (51)Cr-release CTL assay. Rabbits inoculated with Jurkat T cells or ACH.2 cells (expressing ACH HTLV-1 molecule clone) were monitored at 0, 2, 4, 6, 8, 13, 21, and 34 wk post-infection. ACH.2-inoculated rabbits were monitored serologically and for viral infected cells following ex vivo culture. Proviral load analysis indicated that rabbits with higher proviral loads had significant CTL activity against HTLV-1 SU as early as 2 wk post-infection, while both low- and high-proviral-load groups had minimal Tax-specific CTL activity throughout the study. This first development of a stringent assay to measure HTLV-1 SU and Tax-specific CTL assay in the rabbit model will enhance immunopathogenesis studies of HTLV-1 infection. Our data suggest that during the early weeks following infection, HTLV-1-specific CTL responses are primarily targeted against Env-SU.

Evaluation of host genetic and viral factors as surrogate markers for HTLV-1-associated myelopathy/tropical spastic paraparesis in Peruvian HTLV-1-infected patients

Human T-lymphotropic virus 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a complication that affects up to 5% of HTLV-1-infected individuals. Several host genetic and viral factors have been associated with the risk of HAM/TSP. The aim of this study was to evaluate the performance of a prognostic model for HAM/TSP developed in Japan in a Peruvian population of 71 HAM/TSP patients and 94 asymptomatic carriers (ACs). This model included age, proviral load (PVL), the presence of HLA-A*02 and HLA-Cw*08 alleles, SDF-1 +801, and TNF-alpha -863 polymorphisms, and viral subgroup. We describe frequencies for the four host genetic markers and demonstrate the presence of the HTLV-1 tax B subgroup in Peru. Using cross-validation, we show that the predictive ability of the prognostic model, as characterized by the area under the receiver-operating characteristic curve (AUC), does not differ from a model containing PVL only (both AUC = 0.74). We found some suggestive evidence of a protective effect of the HLA-A*02 allele but failed to replicate the associations with the other three genetic markers and with viral subgroup. A logistic model containing PVL, age, gender, and HLA-A*02 provided the best predictive ability in the Peruvian cohort (AUC = 0.79). J. Med. Virol. 82:460-466, 2010. (c) 2010 Wiley-Liss, Inc.

Diagnostic tool based on an HTLV-1-Tax expression system in eukaryotic cells using a poxvirus vector

Human T-lymphotropic virus 1 (HTLV-1) induces an immune-mediated inflammatory disease affecting the nervous system that eventually is accompanied by ocular, rheumatic and dermatologic manifestations (HTLV-1 associated myelopathy/tropical spastic paraparesis, or HAM/TSP). Proviral load and HTLV-1 protein expression, mainly of Tax, is correlated with disease progression and induction of host-virus equilibrium breakdown that, reportedly, involves the presence of Tax-specific cytotoxic T lymphocytes (CTL), T regulatory cells and anti-Tax antibodies. Based on knowledge of anti-Tax antibodies as markers of disease progression, the objectives of this study were both to design an infection/transfection system using the Vaccinia virus and a tax-encoding plasmid for the expression of Tax protein as well as to use this cell support to evaluate anti-Tax IgG by flow cytometry. The flow cytometry assay was standardized using pooled sera from each test group (negative, asymptomatic and HAM/TSP patients). The HAM/TSP group presented higher IgG anti-Tax reactivity (above 70%) than the asymptomatic group (nearly 40% reactivity). The data indicate that the infection/transfection system is useful for assessing Tax expression. This is a promising assay for use as a diagnostic tool to detect IgG anti-Tax and monitor HTLV-1 infected individuals.

Surface Transmission or Polarized Egress? Lessons Learned from HTLV Cell-to-Cell Transmission

Commentary on Pais-Correia, A.M.; Sachse, M.; Guadagnini, S.; Robbiati, V.; Lasserre, R.; Gessain, A.; Gout, O.; Alcover, A.; Thoulouze, M.I. Biofilm-like extracellular viral assemblies mediate HTLV-1 cell-to-cell transmission at virological synapses. Nat. Med.2010, 16, 83–89.

Assembly of the murine leukemia virus is directed towards sites of cell-cell contact

We have investigated the underlying mechanism by which direct cell-cell contact enhances the efficiency of cell-to-cell transmission of retroviruses. Applying 4D imaging to a model retrovirus, the murine leukemia virus, we directly monitor and quantify sequential assembly, release, and transmission events for individual viral particles as they happen in living cells. We demonstrate that de novo assembly is highly polarized towards zones of cell-cell contact. Viruses assembled approximately 10-fold more frequently at zones of cell contact with no change in assembly kinetics. Gag proteins were drawn to adhesive zones formed by viral Env glycoprotein and its cognate receptor to promote virus assembly at cell-cell contact. This process was dependent on the cytoplasmic tail of viral Env. Env lacking the cytoplasmic tail while still allowing for contact formation, failed to direct virus assembly towards contact sites. Our data describe a novel role for the viral Env glycoprotein in establishing cell-cell adhesion and polarization of assembly prior to becoming a fusion protein to allow virus entry into cells.

Targeting host factors: a novel rationale for the management of hepatitis C virus

Hepatitis C is recognized as a major threat to global public health. The current treatment of patients with chronic hepatitis C is the addition of ribavirin to interferon-based therapy which has limited efficacy, poor tolerability, and significant expense. New treatment options that are more potent and less toxic are much needed. Moreover, more effective treatment is an urgent priority for those who relapse or do not respond to current regimens. A major obstacle in combating hepatitis C virus (HCV) infection is that the fidelity of the viral replication machinery is notoriously low, thus enabling the virus to quickly develop mutations that resist compounds targeting viral enzymes. Therefore, an approach targeting the host cofactors, which are indispensable for the propagation of viruses, may be an ideal target for the development of antiviral agents because they have a lower rate of mutation than that of the viral genome, as long as they have no side effects to patients. Drugs targeting, for example, receptors of viral entry, host metabolism or nuclear receptors, which are factors required to complete the HCV life cycle, may be more effective in combating the viral infection. Targeting host cofactors of the HCV life cycle is an attractive concept because it imposes a higher genetic barrier for resistance than direct antiviral compounds. However the principle drawback of this strategy is the greater potential for cellular toxicity.

Complement and antibodies: a dangerous liaison in HIV infection?

Due to ongoing recombination and mutations, HIV permanently escapes from neutralizing antibody (nAb) responses of the host. By the masking of epitopes or shedding of gp120, HIV-1 further impedes an efficient neutralization by Abs. Therefore, nAbs responses of the host are chasing behind a rapidly evolving virus and mainly non-neutralizing antibodies (non-nAbs) are present in the host. At the same time, complement deposition on immune-complexed HIV may counteract the immune response by enhancing the infection. On the other hand, complement-mediated lysis is a putative effector mechanism to control viral replication. Here we review the complex interplay between complement, neutralizing and non-neutralizing Abs during HIV infection and discuss the contribution of Abs and complement in blocking versus enhancing the course of infection.

HIV-1 at the immunological and T-lymphocytic virological synapse

Cell-cell transmission of human immunodeficiency virus type 1 (HIV-1) is considered the most effective mode of viral spread in T-lymphocyte cultures. Evidence has accumulated that HIV-1 assembles polarized synaptic-like structures, referred to as virological synapses, as specialized sites of viral transfer. Interestingly, it was recently also discovered that HIV-1 impairs the formation of the structurally similar immunological synapse, thereby modulating exogenous T-lymphocyte stimulation to yield an optimal activation state for productive HIV-1 infection. The careful dissection of these opposing effects will contribute to our understanding of retroviral spread and cellular signal transduction machineries.

Basic residues are critical to the activity of peptide inhibitors of human T cell leukemia virus type 1 entry

A synthetic peptide based on the leash and alpha-helical region (LHR) of human T cell leukemia virus type 1 envelope is a potent inhibitor of viral entry into cells. The inhibitory peptide targets a triple-stranded coiled-coil motif of the fusion-active transmembrane glycoprotein and in a trans-dominant negative manner blocks resolution to the trimer-of-hairpins form. The LHR-mimetic is, therefore, functionally analogous to the C34/T20-type inhibitors of human immunodeficiency virus. Previous attempts to shorten the bioactive peptide produced peptides with severely attenuated activity. We now demonstrate that truncated peptides often suffer from poor solubility and impaired coiled coil binding properties, and we identify features that are critical to peptide function. In particular, the alpha-helical region of the LHR-mimetic is necessary but not sufficient for inhibitory activity. Moreover, two basic residues are crucial for coiled-coil binding and efficient inhibition of membrane fusion. By retaining these basic residues and a region of main chain peptide contacts with the coiled coil, a core LHR-mimetic was obtained that retains both the inhibitory properties and solubility profile of the parental peptide. Variants of the core peptide inhibit both membrane fusion and infection of cells by free viral particles, but unexpectedly, infection by virions was more susceptible to inhibition by low activity inhibitors than syncytium formation. The core inhibitor provides a valuable lead in the search for smaller more bio-available peptides and peptido-mimetics that possess anti-viral activity. Such molecules may be attractive candidates for therapeutic intervention in human T cell leukemia virus type 1 infections.

Manifestações cutâneas da infecção e das doenças relacionadas ao vírus linfotrópico de células T humanas do tipo 1

O vírus linfotrópico de células T humanas tipo 1 (HTLV-1) é um retrovírus encontrado em todo o mundo e, no Brasil, tem distribuição heterogênea com várias regiões consideradas de alta prevalência. Está relacionado com doenças graves e/ou incapacitantes, como a leucemia/linfoma de células T do adulto, com a doença neurológica conhecida como mielopatia associada ao HTLV-1/paraparesia espástica tropical, com a uveíte associada ao HTLV-1 e com a dermatite infecciosa. O risco para o aparecimento dessas doenças depende, principalmente, de fatores genéticos, da forma como a infecção foi adquirida e da carga proviral. Estima-se que até 10% dos infectados possam desenvolver alguma doença relacionada ao vírus ao longo da vida. O comprometimento da pele tem sido descrito tanto nas doenças relacionadas ao HTLV-1 quanto nos indivíduos portadores assintomáticos. Vários mecanismos são propostos para explicar as lesões da pele, seja pela presença direta do vírus em células, pela imunossupressão ou por resposta inflamatória que a infecção pelo vírus poderia desencadear. Dentre as manifestações dermatológicas mais freqüentes destacam-se a xerose, as dermatofitoses e as infecções bacterianas recorrentes. Neste artigo são revistos os principais aspectos referentes à infecção e às doenças relacionadas ao HTLV- 1, com ênfase na discussão das manifestações dermatológicas observadas nesse contexto.

Human T-cell leukemia virus type I infects human lung epithelial cells and induces gene expression of cytokines, chemokines and cell adhesion molecules

Background

Human T-cell leukemia virus type I (HTLV-I) is associated with pulmonary diseases, characterized by bronchoalveolar lymphocytosis, which correlates with HTLV-I proviral DNA in carriers. HTLV-I Tax seems to be involved in the development of such pulmonary diseases through the local production of inflammatory cytokines and chemokines in T cells. However, little is known about induction of these genes by HTLV-I infection in lung epithelial cells.

Results

We tested infection of lung epithelial cells by HTLV-I by coculture studies in which A549 alveolar and NCI-H292 tracheal epithelial cell lines were cocultured with MT-2, an HTLV-I-infected T-cell line. Changes in the expression of several cellular genes were assessed by reverse transcription-polymerase chain reaction, enzyme-linked immunosorbent assay and flow cytometry. Coculture with MT-2 cells resulted in infection of lung epithelial cells as confirmed by detection of proviral DNA, HTLV-I Tax expression and HTLV-I p19 in the latter cells. Infection was associated with induction of mRNA expression of various cytokines, chemokines and cell adhesion molecule. NF-κB and AP-1 were also activated in HTLV-I-infected lung epithelial cells. In vivo studies showed Tax protein in lung epithelial cells of mice bearing Tax and patients with HTLV-I-related pulmonary diseases.

Conclusion

Our results suggest that HTLV-I infects lung epithelial cells, with subsequent production of cytokines, chemokines and cell adhesion molecules through induction of NF-κB and AP-1. These changes can contribute to the clinical features of HTLV-I-related pulmonary diseases.