Isolation of an HTLV-1-like retrovirus from patients with tropical spastic paraparesis

Establishment of a novel human T-cell leukemia virus type 1 infection model using cell-free virus

The primary mode of infection by human T-cell leukemia virus type 1 (HTLV-1) is cell-to-cell transmission during contact between infected cells and target cells. Cell-free HTLV-1 infections are known to be less efficient than infections with other retroviruses, and transmission of free HTLV-1 is considered not to occur in vivo. However, it has been demonstrated that cell-free HTLV-1 virions can infect primary lymphocytes and dendritic cells in vitro, and that virions embedded in biofilms on cell membranes can contribute to transmission. The establishment of an efficient cell-free HTLV-1 infection model would be a useful tool for analyzing the replication process of HTLV-1 and the clonal expansion of infected cells. We first succeeded in obtaining supernatants with high-titer cell-free HTLV-1 using a highly efficient virus-producing cell line. The HTLV-1 virions retained the structural characteristics of retroviruses. Using this cell-free infection model, we confirmed that a variety of cell lines and primary cultured cells can be infected with HTLV-1 and demonstrated that the provirus was randomly integrated into all chromosomes in the target cells. The provirus-integrated cell lines were HTLV-1-productive. Furthermore, we demonstrated for the first time that cell-free HTLV-1 is infectious in vivo using a humanized mouse model. These results indicate that this cell-free infection model recapitulates the HTLV-1 life cycle, including entry, reverse transcription, integration into the host genome, viral replication, and secondary infection. The new cell-free HTLV-1 infection model is promising as a practical resource for studying HTLV-1 infection.IMPORTANCECo-culture of infected and target cells is frequently used for studying HTLV-1 infection. Although this method efficiently infects HTLV-1, the cell mixture is complex, and it is extremely difficult to distinguish donor infected cells from target cells. In contrast, cell-free HTLV-1 infection models allow for more strict experimental conditions. In this study, we established a novel and efficient cell-free HTLV-1 infection model. Using this model, we successfully evaluated the infectivity titers of cell-free HTLV-1 as proviral loads (copies per 100 cells) in various cell lines, primary cultured cells, and a humanized mouse model. Interestingly, the HTLV-1-associated viral biofilms played an important role in enhancing the infectivity of the cell-free infection model. This cell-free HTLV-1 infection model reproduces the replication cycle of HTLV-1 and provides a simple, powerful, and alternative tool for researching HTLV-1 infection.

Conservation of a Neutralization Epitope of Human T-cell Leukemia Virus Type 1 (HTLV-1) among Currently Endemic Clinical Isolates in Okinawa, Japan

Approximately one-tenth of the 10 million individuals living with human T-cell leukemia virus type-1 (HTLV-1) worldwide live in Japan. Most of these infected individuals live in the southwest region of Japan, including Okinawa prefecture; however, currently no prophylactic vaccine against HTLV-1 infection is available. For preventing the HTLV-1 spread, we previously generated a humanized monoclonal antibody (hu-LAT-27) that mediates both neutralization and antibody-dependent cellular cytotoxicity (ADCC). The neutralization epitope of LAT-27 is a linear amino acid sequence from residue 191 to 196 (Leu-Pro-His-Ser-Asn-Leu) of the HTLV-1 envelope gp46 protein. Here, we found that the LAT-27 epitope is well conserved among HTLV-1 clinical isolates prevalent in Okinawa. The hu-LAT-27 treatment inhibited syncytium formation by these clinical HTLV-1 isolates. Although an amino acid substitution at residue 192 in the LAT-27 epitope from proline to serine was found in a few HTLV-1 isolates, hu-LAT-27 could still react with a synthetic peptide carrying this amino acid substitution. These findings demonstrate the wide spectrum of hu-LAT-27 reactivity, suggesting that hu-LAT-27 may be a candidate drug for prophylactic passive immunization against HTLV-1 infection.

Heat Shock Enhances the Expression of the Human T Cell Leukemia Virus Type-I (HTLV-I) Trans-Activator (Tax) Antigen in Human HTLV-I Infected Primary and Cultured T Cells

The environmental factors that lead to the reactivation of human T cell leukemia virus type-1 (HTLV-I) in latently infected T cells in vivo remain unknown. It has been previously shown that heat shock (HS) is a potent inducer of HTLV-I viral protein expression in long-term cultured cell lines. However, the precise HTLV-I protein(s) and mechanisms by which HS induces its effect remain ill-defined. We initiated these studies by first monitoring the levels of the trans-activator (Tax) protein induced by exposure of the HTLV-I infected cell line to HS. HS treatment at 43 °C for 30 min for 24 h led to marked increases in the level of Tax antigen expression in all HTLV-I-infected T cell lines tested including a number of HTLV-I-naturally infected T cell lines. HS also increased the expression of functional HTLV-I envelope gp46 antigen, as shown by increased syncytium formation activity. Interestingly, the enhancing effect of HS was partially inhibited by the addition of the heat shock protein 70 (HSP70)-inhibitor pifithlin-μ (PFT). In contrast, the HSP 70-inducer zerumbone (ZER) enhanced Tax expression in the absence of HS. These data suggest that HSP 70 is at least partially involved in HS-mediated stimulation of Tax expression. As expected, HS resulted in enhanced expression of the Tax-inducible host antigens, such as CD83 and OX40. Finally, we confirmed that HS enhanced the levels of Tax and gp46 antigen expression in primary human CD4⁺ T cells isolated from HTLV-I-infected humanized NOD/SCID/γc null (NOG) mice and HTLV-I carriers. In summary, the data presented herein indicate that HS is one of the environmental factors involved in the reactivation of HTLV-I in vivo via enhanced Tax expression, which may favor HTLV-I expansion in vivo.

Human T-cell Lymphotropic Viruses: Review and Prospects for Antiviral Therapy

The human T-cell lymphotropic viruses types I and II (HTLV-I, II) pose challenges to researchers and clinicians who seek to unveil mechanisms of viral transformation and pathogenesis. HTLV-I infection in humans is associated with a wide array of primary and secondary diseases ranging from mild immunosuppression to adult T-cell leukaemia/lymphoma and HTLV-associated myelopathy/tropical spastic paraparesis (HAM/TSP), a neurological degenerative syndrome. As retroviruses, HTLV-I and II share similar replicative cycles with human immunodeficiency virus (HIV), the causative agent of acquired immunodeficiency syndrome. However, in contrast to HIV-I which destroys CD4+ T cells, HTLV-I and II can preferentially transform a CD4+ T-cell subset to an unrestricted growth state.

HTLV-I and II, along with simian T-lymphotropic virus (STLV) and bovine leukaemia virus (BLV), form a phylogenetic group which is distinct from ungulate, non-human primate and human lentiviruses such as visna, simian immunodeficiency virus (SIV), and human immunodeficiency viruses types 1 and 2. The proviral genome of HTLV-I is flanked at the 5′ and 3′ ends by long terminal repeats (LTR) and is further subdivided into structural gag and env genes, a pro gene encoding an aspartyl protease, a pol gene which encodes reverse transcriptase and endonuclease, and the regulatory gene elements tax and rex. Regions within the LTR contain recognition sites for cellular proteins and the tax gene product that collectively promote viral expression. Tax-mediated activation of cellular genes involved in growth and differentiation is suspected to play a dominant role in the leukaemogenic process associated with HTLV-I infection. Differential rex-regulated splicing of viral message gives rise to transcripts encoding the polyprotein precursor gag-pro-pol (unspliced), envelope (single spliced), or tax/rex (doubly spliced). The 100nm HTLV virion contains an electron-dense core surrounding a divalent-single stranded DNA genome. This core is in turn enclosed by concentric shells of matrix protein and an outer lipid bilayer, the latter acquired as the virus buds from the surface of the infected cell. Envelope glycoproteins associated with the outside of this lipid bilayer can interact with viral receptors on cells and mediate virus entry. Antiviral strategies have been directed at inhibiting viral entry into cells (sulphated and non-sulphated polysaccharides, vaccines), blocking of viral replication (AZT, suramin), intracellular immunization (transdominant repression of rex), and elimination of virus infected cells (IL-2 receptor-directed toxins). Serological screening of the blood supply and curtailing breast feeding of children by HTLV-I + mothers have likely had a major impact in preventing HTLV-I infection.

Synaptic Plasticity and Neurological Disorders in Neurotropic Viral Infections

Based on the type of cells or tissues they tend to harbor or attack, many of the viruses are characterized. But, in case of neurotropic viruses, it is not possible to classify them based on their tropism because many of them are not primarily neurotropic. While rabies and poliovirus are considered as strictly neurotropic, other neurotropic viruses involve nervous tissue only secondarily. Since the AIDS pandemic, the interest in neurotropic viral infections has become essential for all clinical neurologists. Although these neurotropic viruses are able to be harbored in or infect the nervous system, not all the neurotropic viruses have been reported to cause disrupted synaptic plasticity and impaired cognitive functions. In this review, we have discussed the neurotropic viruses, which play a major role in altered synaptic plasticity and neurological disorders.

Elimination of human T cell leukemia virus type-1-infected cells by neutralizing and antibody-dependent cellular cytotoxicity-inducing antibodies against human t cell leukemia virus type-1 envelope gp46

Human T cell leukemia virus type-1 (HTLV-1) is prevalent worldwide with foci of high prevalence. However, to date no effective vaccine or drug against HTLV-1 infection has been developed. In efforts to define the role of antibodies in the control of HTLV-1 infection, we capitalized on the use of our previously defined anti-gp46 neutralizing monoclonal antibody (mAb) (clone LAT-27) and high titers of human anti-HTLV-1 IgG purified from HAM/TSP patients (HAM-IgG). LAT-27 and HAM-IgG completely blocked syncytium formation and T cell immortalization mediated by HTLV-1 in vitro. The addition of these antibodies to cultures of CD8(+) T cell-depleted peripheral blood mononuclear cells (PBMCs) from HAM/TSP patients at the initiation of culture not only decreased the numbers of Tax-expressing cells and the production of HTLV-1 p24 but also inhibited the spontaneous immortalization of T cells. Coculture of in vitro-HTLV-1-immortalized T cell lines with autologous PBMCs in the presence of LAT-27 or HAM-IgG, but not an F(ab')2 fragment of LAT-27 or nonneutralizing anti-gp46 mAbs, resulted in depletion of HTLV-1-infected cells. A 24-h (51)Cr release assay showed the presence of significant antibody-dependent cellular cytotoxicity (ADCC) activity in LAT-27 and HAM-IgG, but not F(ab')2 of LAT-27, resulting in the depletion of HTLV-1-infected T cells by autologous PBMCs. The depletion of natural killer (NK) cells from the effector PBMCs reduced this ADCC activity. Altogether, the present data demonstrate that the neutralizing and ADCC-inducing activities of anti-HTLV-1 antibodies are capable of reducing infection and eliminating HTLV-1-infected cells in the presence of autologous PBMCs.

Role of Nucleocytoplasmic RNA Transport during the Life Cycle of Retroviruses

Retroviruses have evolved mechanisms for transporting their intron-containing RNAs (including genomic and messenger RNAs, which encode virion components) from the nucleus to the cytoplasm of the infected cell. Human retroviruses, such as human immunodeficiency virus (HIV) and human T cell leukemia virus type 1 (HTLV-1), encode the regulatory proteins Rev and Rex, which form a bridge between the viral RNA and the export receptor CRM1. Recent studies show that these transport systems are not only involved in RNA export, but also in the encapsidation of genomic RNA; furthermore, they influence subsequent events in the cytoplasm, including the translation of the cognate mRNA, transport of Gag proteins to the plasma membrane, and the formation of virus particles. Moreover, the mode of interaction between the viral and cellular RNA transport machinery underlies the species-specific propagation of HIV-1 and HTLV-1, forming the basis for constructing animal models of infection. This review article discusses recent progress regarding these issues.

Entry of human T-cell leukemia virus type 1 is augmented by heparin sulfate proteoglycans bearing short heparin-like structures

Three molecules have been identified as the main cellular factors required for binding and entry of human T-cell leukemia virus type 1 (HTLV-1): glucose transporter 1 (GLUT1), heparan sulfate (HS), and neuropilin 1 (NRP-1). However, the precise mechanism of HTLV-1 cell tropism has yet to be elucidated. Here, we examined the susceptibilities of various human cell lines to HTLV-1 by using vesicular stomatitis virus pseudotypes bearing HTLV-1 envelope proteins. We found that the cellular susceptibility to HTLV-1 infection did not correlate with the expression of GLUT1, HS, or NRP-1 alone. To investigate whether other cellular factors were responsible for HTLV-1 susceptibility, we conducted expression cloning. We identified two HS proteoglycan core proteins, syndecan 1 and syndecan 2, as molecules responsible for susceptibility to HTLV-1. We found that treatment of syndecan 1-transduced cells (expressing increased HS) with heparinase, a heparin-degradative enzyme, reduced HTLV-1 susceptibility without affecting the expression levels of HS chains. To further elucidate these results, we characterized the expression of HS chains in terms of the mass, number, and length of HS in several syndecan 1-transduced cell clones as well as human cell lines. We found a significant correlation between HTLV-1 susceptibility and the number of HS chains with short chain lengths. Our findings suggest that a combination of the number and the length of HS chains containing heparin-like regions is a critical factor which affects the cell tropism of HTLV-1.

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.

Role of resident CNS cell populations in HTLV-1-associated neuroinflammatory disease

Human T cell leukemia virus type 1 (HTLV-1), the first human retrovirus discovered, is the etiologic agent for a number of disorders; the two most common pathologies include adult T cell leukemia (ATL) and a progressive demyelinating neuroinflammatory disease, HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The neurologic dysfunction associated with HAM/TSP is a result of viral intrusion into the central nervous system (CNS) and the generation of a hyperstimulated host response within the peripheral and central nervous system that includes expanded populations of CD4+ and CD8+ T cells and proinflammatory cytokines/chemokines in the cerebrospinal fluid (CSF). This robust, yet detrimental immune response likely contributes to the death of myelin producing oligodendrocytes and degeneration of neuronal axons. The mechanisms of neurological degeneration in HAM/TSP have yet to be fully delineated in vivo and may involve the immunogenic properties of the HTLV-1 transactivator protein Tax. This comprehensive review characterizes the available knowledge to date concerning the effects of HTLV-1 on CNS resident cell populations with emphasis on both viral and host factors contributing to the genesis of HAM/TSP.

In vivo T lymphocyte dynamics in humans and the impact of human T-lymphotropic virus 1 infection

Human T-lymphotropic virus type 1 (HTLV-1) is a persistent CD4+ T-lymphotropic retrovirus. Most HTLV-1-infected individuals remain asymptomatic, but a proportion develop adult T cell leukemia or inflammatory disease. It is not fully understood how HTLV-1 persists despite a strong immune response or what determines the risk of HTLV-1-associated diseases. Until recently, it has been difficult to quantify lymphocyte kinetics in humans in vivo. Here, we used deuterated glucose labeling to quantify in vivo lymphocyte dynamics in HTLV-1-infected individuals. We then used these results to address four questions. (i) What is the impact of HTLV-1 infection on lymphocyte dynamics? (ii) How does HTLV-1 persist? (iii) What is the extent of HTLV-1 expression in vivo? (iv) What features of lymphocyte kinetics are associated with HTLV-1-associated myelopathy/tropical spastic paraparesis? We found that CD4+CD45RO+ and CD8+CD45RO+ T lymphocyte proliferation was elevated in HTLV-1-infected subjects compared with controls, with an extra 10(12) lymphocytes produced per year in an HTLV-1-infected subject. The in vivo proliferation rate of CD4+CD45RO+ cells also correlated with ex vivo viral expression. Finally, the inflammatory disease HTLV-1-associated myelopathy/tropical spastic paraparesis was associated with significantly increased CD4+CD45RO+ cell proliferation. We suggest that there is persistent viral gene expression in vivo, which is necessary for the maintenance of the proviral load and determines HTLV-1-associated myelopathy/tropical spastic paraparesis risk.

HPRT mutations, TCR gene rearrangements, and HTLV-1 integration sites define in vivo T-cell clonal lineages

HPRT mutations in vivo in human T-lymphocytes are useful probes for mechanistic investigations. Molecular analyses of isolated mutants reveal their underlying mutational changes as well as the T-cell receptor (TCR) gene rearrangements present in the cells in question. The latter provide temporal reference points for other perturbations in the in vivo clones as well as evidence of clonal relationships among mutant isolates. Immunological studies and investigations of genomic instability have benefited from such analyses. A method is presented describing a T-cell lineage analysis in a patient with HTLV-1 infection. Lineage reconstruction of an in vivo proliferating HPRT mutant clone allows timing of the integration event to a postthymic differentiated cell prior to the occurrence of HPRT mutations.

Human T-cell leukaemia virus type I is highly sensitive to UV-C light

The biological characteristics of human T-cell leukaemia virus type I (HTLV-I) are not yet well understood. UV light C (UV-C) sensitivity of HTLV-I was studied using a newly established infectivity assay: infection with cell-free HTLV-I dose-dependently induced syncytial plaques in cat cells transduced with the tax1 gene of HTLV-I. HTLV-I was inactivated by a much lower UV dose than bovine leukaemia virus (BLV). The D(10) (10 % survival dose) of HTLV-I was about 20 J m(-2), while that of BLV was about 180 J m(-2), which was similar to the reported D(10) of BLV. The UV sensitivity of HTLV-I and BLV was also examined by detecting viral DNA synthesis 24 h after infection. The D(10) values determined by PCR using the gag primers for HTLV-I and BLV were close to those determined by the infectivity assays. Further PCR analyses were then performed to determine D(10) values using several different primers located between the 5'-long terminal repeat (5'-LTR) and the tax1 gene. The difference in UV sensitivity between HTLV-I and BLV was detected very early during replication, even during reverse transcription of the 5'-LTR of irradiated viruses, and became more prominent as reverse transcription proceeded towards the tax1 gene. Chimeric mouse retroviruses that contain the LTR-tax1 fragments of HTLV-I and BLV were made and hardly any difference in UV sensitivity was detected between them, suggesting that the difference was not determined by the linear RNA sequences of HTLV-I and BLV. HTLV-I was found to be much more sensitive than other retroviruses to UV.

Alpha interferon inhibits human T-cell leukemia virus type 1 assembly by preventing Gag interaction with rafts

Alpha-2a interferon (IFN-alpha2a) has beneficial clinical effects on human T-cell leukemia virus type 1 (HTLV-1) infection, but its antiviral mechanism of action is unknown. Antiviral effects of IFN-alpha2a were studied in 293T cells expressing HTLV-1 proviral DNA and in HTLV-1-infected cells (HOS/PL, MT2, and HUT102). In 293T cells, an 50% inhibitory concentration of 10 U of IFN-alpha2a/ml was determined by p19 antigen ELISA. Analysis of IFN-treated cells demonstrated no defect in viral protein synthesis but did show a decrease in the level of released virus, as determined by immunoblot assays. Electron microscopy studies of IFN-treated cells revealed neither a defect in the site of virus budding nor tethering of virus particles at the plasma membrane, thus arguing against an effect on virus release. Cell fractionation studies and confocal microscopy showed no effect of IFN on Gag association with membranes. However, the level of Gag association with lipid rafts was decreased, suggesting a role of IFN in inhibiting HTLV-1 assembly.

T-Cell Control by Human T-Cell Leukemia/Lymphoma Virus Type 1

Human T-cell leukemia/lymphoma virus type 1 (HTLV-1) causes neoplastic transformation of human T-cells in a small number of infected individuals several years from infection. Collective evidence from in vitro studies indicates that several viral proteins act in concert to increase the responsiveness of T-cells to extracellular stimulation, modulate proapoptotic and antiapoptotic gene signals, enhance T-cell survival, and avoid immune recognition of the infected T-cells. The virus promotes T-cell proliferation by usurping several signaling pathways central to immune T-cell function, such as antigen stimulation and receptor-ligand interaction, suggesting that extracellular signals are important for HTLV-1 oncogenesis. Environmental factors such as chronic antigen stimulation may therefore be of importance, as also suggested by epidemiological data. Thus genetic and environmental factors together with the virus contribute to disease development. This review focuses on current knowledge of the mechanisms regulating HTLV-1 replication and the T-cell pathways that are usurped by viral proteins to induce and maintain clonal proliferation of infected T-cells. The relevance of these laboratory findings is related to clonal T-cell proliferation and adult T-cell leukemia/lymphoma development in vivo.

Role of endogenous retroviruses in autoimmune diseases

Endogenous retroviruses (ERVs) correspond to the integrated proviral form of infectious retroviruses that are trapped within the genome by mutations. Endogenous retroviruses represent a key molecular link between the host genome and infectious viral particles. Proteins encoded by ERVs are recognized by antiviral immune responses and become targets of autoreactivity. Activation of ERVs, such as human ERV-K or a human T-cell lymphotropic virus-related endogenous sequence, may also mediate pathogenicity of Epstein-Barr virus. Endogenous retrovirus peptides can directly regulate immune responses. Thus, molecular mimicry and immunomodulation by ERVs may account for self-reactivity and abnormal T- and B-cell functions in autoimmune disorders.

Seizing of T Cells by Human T-Cell Leukemia⧸Lymphoma Virus Type 1

Human T-cell leukemia/lymphoma virus type 1 (HTLV-1) causes neoplastic transformation of human T-cells in a small number of infected individuals several years from infection. Several viral proteins act in concert to increase the responsiveness of T-cells to extracellular stimulation, modulate proapoptotic and antiapoptotic gene signals, enhance T-cell survival, and avoid immune recognition of the infected T-cells. The virus promotes T-cell proliferation by usurping several signaling pathways central to immune T-cell function. Viral proteins modulate the downstream effects of antigen stimulation and receptor-ligand interaction, suggesting that extracellular signals are important for HTLV-1 oncogenesis. Environmental factors such as chronic antigen stimulation are therefore important, as also suggested by epidemiological data. The ability of a given individual to respond to specific antigens is determined genetically. Thus, genetic and environmental factors, together with the virus, contribute to disease development. As in the case of other virus-associated cancers, HTLV-1-induced leukemia/lymphoma can be prevented by avoiding viral infection or by intervention during the asymptomatic phase with approaches able to interrupt the vicious cycle of virus-induced proliferation of a subset of T-cells. This review focuses on current knowledge of the mechanisms regulating HTLV-1 replication and the T-cell pathways that are usurped by viral proteins to induce and maintain clonal proliferation of infected T-cells in vitro. The relevance of these laboratory findings will be related to clonal T-cell proliferation and adult T-cell leukemia/lymphoma development in vivo.

Retroviral proteins that target the major histocompatibility complex class I

The human T-cell leukemia virus type 1 (HTLV-1) and human immunodeficiency virus type 1 (HIV-1) retroviruses are two evolutionary distinct human pathogens. HTLV-1 is the etiologic agent of two diverse diseases: adult T-cell leukemia/lymphoma, as well as the neurologic disorder tropical spastic paraparesis/HTLV-1-associated myelopathy. HTLV-1 is the only retrovirus known to be the etiologic agent of human cancer. HTLV-2, the other known oncovirus, is not apparently associated with human cancer. While HTLV-1 transforms T-cells in vitro, HIV kills CD4+ T-cells and is the etiological agent of human acquired immunodeficiency syndrome, characterized by a progressive loss of CD4+ cells, weakening of the immune system, and susceptibility to opportunistic infections and cancer. HTLV-1 and HIV-1 both cause lifelong infections, which suggests that they have evolved mechanism(s) to evade detection by the host's immune response; particularly to evade cytotoxic T-lymphocytes, which play a major role in cellular immunity against viruses and will be the focus of this review.

Bovine leukemia virus SU protein interacts with zinc, and mutations within two interacting regions differently affect viral fusion and infectivity in vivo

Bovine leukemia virus (BLV) and human T-cell lymphotropic virus type 1 (HTLV-1) belong to the genus of deltaretroviruses. Their entry into the host cell is supposed to be mediated by interactions of the extracellular (SU) envelope glycoproteins with cellular receptors. To gain insight into the mechanisms governing this process, we investigated the ability of SU proteins to interact with specific ligands. In particular, by affinity chromatography, we have shown that BLV SU protein specifically interacted with zinc ions. To identify the protein domains involved in binding, 16 peptides distributed along the sequence were tested. Two of them appeared to be able to interact with zinc. To unravel the role of these SU regions in the biology of the virus, mutations were introduced into the env gene of a BLV molecular clone in order to modify residues potentially interacting with zinc. The fusogenic capacity of envelope mutated within the first zinc-binding region (104 to 123) was completely abolished. Furthermore, the integrity of this domain was also required for in vivo infectivity. In contrast, mutations within the second zinc-binding region (218 to 237) did not hamper the fusogenic capacity; indeed, the syncytia were even larger. In sheep, mutations in region 218 to 237 did not alter infectivity or viral spread. Finally, we demonstrated that the envelope of the related HTLV-1 was also able to bind zinc. Interestingly, zinc ions were found to be associated with the receptor-binding domain (RBD) of Friend murine leukemia virus (Fr-MLV) SU glycoprotein, further supporting their relevance in SU structure. Based on the sequence similarities shared with the Fr-MLV RBD, whose three-dimensional structure has been experimentally determined, we located the BLV zinc-binding peptide 104-123 on the opposite side of the potential receptor-binding surface. This observation supports the hypothesis that zinc ions could mediate interactions of the SU RBD either with the C-terminal part of SU, thereby contributing to the SU structural integrity, or with a partner(s) different from the receptor.

Cell-free human T-cell leukemia virus type 1 binds to, and efficiently enters mouse cells

Human T-cell leukemia virus type 1 (HTLV-1) is an etiologic agent of adult T-cell leukemia / lymphoma and other HTLV-1-associated diseases. However, the interaction between HTLV-1 and T cells in the pathogenesis of these diseases is poorly understood. Mouse cells have been reported to be resistant to cell-free HTLV-1 infection. However, we recently reported that HTLV-1 DNA could be observed 24 h after cell-free HTLV-1 infection of mouse cell lines. To understand HTLV-1 replication in these cells in detail, we concentrated the virus produced from c77 feline kidney cell line and established an efficient infection system. The amounts of adsorption of HTLV-1 are larger in mouse T cell lines, EL4 and RLm1, than those in human T cell lines, Molt4 and HUT78, and are similar to that in human kidney cell line, 293T. Unexpectedly, however, the amounts of entry of HTLV-1 are about 10-fold larger in the two mouse cell lines than those in the three human cell lines employed. Moreover, viral DNA was detectable from 1 h in EL4 and RLm1 cells, but only from 2 - 3 h in 293T, Molt4 and HUT78 cells. However, the amount of viral DNA in EL4 cells became smaller than that in Molt4 cells. HTLV-1 expression could be detected until day 1 - 2 in RLm1 and EL4 cells, and until day 4 in Molt4 cells. Our results suggest that mouse cell experiments would give useful information to dissect the early steps of cell-free HTLV-1 infection.

Monoclonally integrated HTLV type 1 in epithelial cancers from rabbits infected with an HTLV type 1 molecular clone

In addition to T cell leukemias and lymphomas, human T cell leukemia virus type 1 (HTLV-1) infection has been associated with nonhematologic malignancies and described as the cause of one case of small-cell lung carcinoma. Infected primary epithelial cells have been isolated from sweat gland and oral mucosae of HTLV-1-infected human patients. In the present study, epithelial neoplasms developed in two rabbits experimentally infected with a molecular clone of HTLV-1 (strain K30p). Serologic detection of anti-HTLV-1 and isolation of virus from blood lymphocytes at multiple time points postinjection established a course of chronic asymptomatic infection in both. One rabbit, infected for 5.5 years after intramuscular injection of HTLV-1 DNA, developed a thymoma having features of medullary differentiation. HTLV-1 provirus was detected in both thymocytes and neoplastic epithelium isolated discretely from the thymoma by laser capture microdissection. These findings provide the first experimental evidence of HTLV-1 disease after infection by HTLV-1 DNA injection. Endometrial adenocarcinoma occurred in a second rabbit 2.5 years after its inoculation with cell-associated virus. In this second case, an epithelial cell line derived ex vivo from a metastatic lesion produced virus in culture. In tumors from each of the two rabbits, the neoplastic epithelium was infected and harbored monoclonally integrated HTLV-1 provirus. Although monoclonal provirus integration alone does not establish retroviral cause of carcinogenesis unequivocally, these and other accumulating data indicate that there may be a role for HTLV-1 in diseases associated with infection of epithelia, including some epithelial cancers.

Human T cell leukemia virus type I and neurologic disease: events in bone marrow, peripheral blood, and central nervous system during normal immune surveillance and neuroinflammation

Human T cell lymphotropic/leukemia virus type I (HTLV-I) has been identified as the causative agent of both adult T cell leukemia (ATL) and HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Although the exact sequence of events that occur during the early stages of infection are not known in detail, the initial route of infection may predetermine, along with host, environmental, and viral factors, the subset of target cells and/or the primary immune response encountered by HTLV-I, and whether an HTLV-I-infected individual will remain asymptomatic, develop ATL, or progress to the neuroinflammatory disease, HAM/TSP. Although a large number of studies have indicated that CD4(+) T cells represent an important target for HTLV-I infection in the peripheral blood (PB), additional evidence has accumulated over the past several years demonstrating that HTLV-I can infect several additional cellular compartments in vivo, including CD8(+) T lymphocytes, PB monocytes, dendritic cells, B lymphocytes, and resident central nervous system (CNS) astrocytes. More importantly, extensive latent viral infection of the bone marrow, including cells likely to be hematopoietic progenitor cells, has been observed in individuals with HAM/TSP as well as some asymptomatic carriers, but to a much lesser extent in individuals with ATL. Furthermore, HTLV-I(+) CD34(+) hematopoietic progenitor cells can maintain the intact proviral genome and initiate viral gene expression during the differentiation process. Introduction of HTLV-I-infected bone marrow progenitor cells into the PB, followed by genomic activation and low level viral gene expression may lead to an increase in proviral DNA load in the PB, resulting in a progressive state of immune dysregulation including the generation of a detrimental cytotoxic Tax-specific CD8(+) T cell population, anti-HTLV-I antibodies, and neurotoxic cytokines involved in disruption of myelin-producing cells and neuronal degradation characteristic of HAM/TSP.

New approach for generation of neutralizing antibody against human T-cell leukaemia virus type-I (HTLV-I) using phage clones

We have screened a phage peptide library to address whether clones binding to a monoclonal antibody (mAb) could be isolated and if the selected phage particles would be able to elicit an in vivo immune response against the original antigen. A phage peptide library, consisting of seven random amino acids inserted in the minor coat protein (pIII), was screened for specific binding to a rat mAb LAT-27, which is capable of neutralizing human T-cell leukaemia virus type-I (HTLV-I) by binding to its envelope gp46 epitope, (amino acids LPHSNL). Total 37 clones were selected from the library and one clone named 4-2-22 was tested for its immunogenicity in three rabbits. The all rabbit immune sera showed strong binding activity to a gp46 peptide carrying the neutralization sequence, stained gp46-expressing cells and neutralized HTLV-I in vitro as determined by cell fusion inhibition assay. These results show that the selected phage clone was capable of mimicking the epitope recognized by a HTLV-I neutralizing mAb, and it can be used as an immunogen to induce protective immune response against HTLV-I. Thus, the present methodology could be one of the approaches to develop vaccines against infectious agents in a simple and inexpensive way.

Rat CRM1 is responsible for the poor activity of human T-cell leukemia virus type 1 Rex protein in rat cells

Rat models of human T-cell leukemia virus type 1 (HTLV-1)-related diseases such as adult T-cell leukemia and HTLV-1-associated myelopathy/tropical spastic paraparesis have been reported. However, these models do not completely reproduce human diseases partly because HTLV-1 replicates poorly in rats. We investigated here the possible reason for this. We found that the activity of Rex in rat cells is quite low compared to that in human cells. As Rex function depends largely on the CRM1 protein, whose human type (human CRM1 [hCRM1]) directly binds to Rex and exports it from the nucleus to the cytoplasm, we assessed whether rat CRM1 (rCRM1) could act as well as hCRM1 as a cofactor for Rex activity. We first cloned a cDNA encoding rCRM1 and found that both rCRM1 and hCRM1 could bind to and export Rex protein to the cytoplasm with similar efficiencies. However, unlike hCRM1, rCRM1 could hardly support Rex function because of its poor ability in inducing the Rex-Rex interaction required for RNA export into the cytoplasm. These observations suggest that the poor ability of rCRM1 to act as a cofactor for Rex function may be responsible for the poor replication of HTLV-1 in rats.

Increased HTLV-I proviral load and preferential expansion of HTLV-I Tax-specific CD8+ T cells in cerebrospinal fluid from patients with HAM/TSP

To date, high human T-cell lymphotropic virus type I proviral load in patients with human T-cell lymphotropic virus type I-associated myelopathy/tropical spastic paraparesis has been reported and is thought to be related to the pathogenesis of human T-cell lymphotropic virus type I-associated myelopathy/tropical spastic paraparesis. However, the proviral load in cerebrospinal fluid has not been well investigated. We measured human T-cell lymphotropic virus type I proviral load in cerebrospinal fluid cells from human T-cell lymphotropic virus type I-associated myelopathy/tropical spastic paraparesis patients using real-time quantitative polymerase chain reaction (TaqMan). Human T-cell lymphotropic virus type I proviral load in cerebrospinal fluid cells were significantly higher than that of the matched peripheral blood mononuclear cells, and a high ratio of human T-cell lymphotropic virus type I proviral load in cerebrospinal fluid cells to peripheral blood mononuclear cells were observed in patients with short duration of illness. Human T-cell lymphotropic virus type I Tax-specific CD8+ T cells, as detected by peptide-loaded HLA tetramers, accumulated in cerebrospinal fluid compared with that in peripheral blood mononuclear cells, while the frequency of cytomegalovirus-specific CD8+ T cells in cerebrospinal fluid was reduced. These observations suggest that accumulation of both human T-cell lymphotropic virus type I-infected cells and preferential expansion of human T-cell lymphotropic virus type I-specific CD8+ cells in cerebrospinal fluid may play a role in the pathogenesis of human T-cell lymphotropic virus type I-associated myelopathy/tropical spastic paraparesis.

Free major histocompatibility complex class I heavy chain is preferentially targeted for degradation by human T-cell leukemia/lymphotropic virus type 1 p12(I) protein

Human T-cell leukemia virus type 1 (HTLV-1) establishes a persistent infection in the host despite a vigorous virus-specific immune response. Here we demonstrate that an HTLV-1-encoded protein, p12(I), resides in the endoplasmic reticulum (ER) and Golgi and physically binds to the free human major histocompatibility complex class I heavy chains (MHC-I-Hc) encoded by the HLA-A2, -B7, and -Cw4 alleles. As a result of this interaction, the newly synthesized MHC-I-Hc fails to associate with beta(2)-microglobulin and is retrotranslocated to the cytosol, where it is degraded by the proteasome complex. Targeting of the free MHC-I-Hc, and not the MHC-I-Hc-beta(2)-microglobulin complex, by p12(I) represents a novel mechanism of viral interference and disrupts the intracellular trafficking of MHC-I, which results in a significant decrease in surface levels of MHC-I on human T-cells. These findings suggest that the interaction of p12(I) with MHC-1-Hc may interfere with antigen presentation in vivo and facilitate escape of HTLV-1-infected cells from immune recognition.

Molecular biology and pathogenesis of the human T-cell leukaemia/lymphotropic virus Type-1 (HTLV-1)

Retroviruses are associated with a variety of diseases, including immunological and neurological disorders, and various forms of cancer. In humans, the Human T-cell Leukaemia/Lymphotropic virus type 1 (HTLV-1), which belongs to the Oncovirus family, is the aetiological agent of two diverse diseases: Adult T-cell leukaemia/lymphoma (ATLL) (Poiesz et al. 1980; Hinuma et al. 1981; Yoshida et al. 1982), as well as the neurological disorder tropical spastic paraparesis/HTLV-1-associated myelopathy (TSP/HAM) (Gessain et al. 1985; Rodgers-Johnson et al. 1985; Osame et al. 1986). HTLV-1 is the only human retrovirus known to be the aetiological agent of cancer. A genetically related virus, HTLV-2, has been identified and isolated (Kalyanaraman et al. 1982). However, there has been no demonstration of a definitive aetiological role for HTLV-2 in human disease to date. Simian T-cell lymphotropic viruses types 1 and 2 (STLV-1 and -2) and bovine leukaemia virus (BLV) have also been classified in same group, Oncoviridae, based upon their similarities in genetic sequence and structure to HTLV-1 and -2 (Burny et al. 1988; Dekaban et al. 1995; Slattery et al. 1999). This article will focus on HTLV-1, reviewing its discovery, molecular biology, and its role in disease pathogenesis.

Passage of human T-cell leukemia virus type-1 during progression to cutaneous T-cell lymphoma results in myelopathic disease in an HTLV-1 infection model

Studies comparing functional differences in human T-cell leukemia virus type 1 (HTLV-1) clones that mediate distinct outcomes in experimentally infected rabbits, resulted in a dermatopathic smoldering adult T-cell leukemia/lymphoma following chronic infection with HTLV-1 strain RH/K34. During the 3.5 years' follow-up, HTLV-1 skin disease progressed to cutaneous T-cell lymphoma. When infection was passed to several naive rabbits, progressive paraparesis due to myelopathic neurodegeneration, analogous to HTLV-associated myelopathy, resulted in one of 4 transfusion recipients. Similar proviral loads were detected in the two diseases, regardless of stage of progression or tissue compartment of infection. Complete proviral sequences obtained from the donor and affected recipient aligned identically with each other and with the inoculated virus clone. Existence of disparate pathogenic outcomes following infectious transmission further extends the analogy of using rabbits to model human infection and disease. Although the experimental outcomes shown are limited by numbers of animals affected, they mimic the infrequency of HTLV-1 disease and authenticate epidemiological evidence of virus sequence stability regardless of disease phenotype. The findings suggest that further investigation of a possible role for HTLV-1 in some forms of cutaneous T-cell lymphoma is warranted.

RNA polymerase III transcription: its control by tumor suppressors and its deregulation by transforming agents

The level of RNA polymerase (pol) III transcription is tightly linked to the rate of growth; it is low in resting cells and increases following mitogenic stimulation. When mammalian cells begin to proliferate, maximal pol III activity is reached shortly before the G1/S transition; it then remains high throughout S and G2 phases. Recent data suggest that the retinoblastoma protein RB and its relatives p107 and p130 may be largely responsible for this pattern of expression. During G0 and early G1 phase, RB and p130 bind and repress the pol III-specific factor TFIIIB; shortly before S phase they dissociate from TFIIIB, allowing transcription to increase. At the end of interphase, when cells enter mitosis, pol III transcription is again suppressed; this mitotic repression is achieved through direct phosphorylation of TFIIIB. Thus, pol III transcription levels fluctuate as mammalian cells cycle, being high in S and G2 phases and low during mitosis and early G1. In addition to this cyclic regulation, TFIIIB can be bound and repressed by the tumor suppressor p53. Conversely, it is a target for activation by several viruses, including SV40, HBV, and HTLV-1. Some viruses also increase the activity of a second pol III-specific factor called TFIIIC. A large proportion of transformed and tumor cell types express abnormally high levels of pol III products. This may be explained, at least in part, by the very high frequency with which RB and p53 become inactivated during neoplastic transformation; loss of function of these cardinal tumor suppressors may release TFIIIB from key restraints that operate in normal cells.

Inhibition of cell-free human T-cell leukemia virus type 1 infection at a postbinding step by the synthetic peptide derived from an ectodomain of the gp21 transmembrane glycoprotein

To investigate the roles of human T-cell leukemia virus type 1 (HTLV-1) envelope (Env) proteins gp46 and gp21 in the early steps of infection, the effects of the 23 synthetic peptides covering the entire Env proteins on transmission of cell-free HTLV-1 were examined by PCR and by the plaque assay using a pseudotype of vesicular stomatis virus (VSV) bearing the Env of HTLV-1 [VSV(HTLV-1)]. The synthetic peptide corresponding to amino acids 400 to 429 of the gp21 Env protein (gp21 peptide 400-429, Cys-Arg-Phe-Pro-Asn-Ile-Thr-Asn-Ser-His-Val-Pro-Ile-Leu-Gln-Glu-Arg-P ro-Pro-Leu-Glu-Asn-Arg-Val-Leu-Thr-Gly-Trp-Gly-Leu) strongly inhibited infection of cell-free HTLV-1. By using the mutant peptide, Asn407, Ser408, and Leu413, -419, -424, and -429 were confirmed to be important amino acids for neutralizing activity of the gp21 peptide 400-429. Addition of this peptide before or during adsorption of HTLV-1 at 4 degrees C did not affect its entry. However, HTLV-1 infection was inhibited about 60% when the gp21 peptide 400-429 was added even 30 min after adsorption of HTLV-1 to cells, indicating that the amino acid sequence 400 to 429 on the gp21 Env protein plays an important role at the postbinding step of HTLV-1 infection. In contrast, a monoclonal antibody reported to recognize the gp46 191-196 peptide inhibited the infection of HTLV-1 at the binding step.

Cyclic nucleotide phosphodiesterases (PDE) 3 and 4 in normal, malignant, and HTLV-I transformed human lymphocytes

Intracellular cyclic AMP, determined in part by cyclic nucleotide phosphodiesterases (PDEs), regulates proliferation and immune functions in lymphoid cells. Total PDE, PDE3, and PDE4 activities were measured in phytohemagglutinin (PHA)-activated peripheral blood mononuclear cells (PBMC-PHA), normal natural killer (NK) cells, Jurkat and Kit225-K6 leukemic T-cells, T-cell lines transformed with human T-lymphotropic virus (HTLV)-I (a retrovirus that causes adult T-cell leukemia/lymphoma) and HTLV-II (a nonpathogenic retrovirus), normal B-cells, and B-cells transformed with Epstein-Barr virus (EBV). All cells exhibited PDE3 and PDE4 activities but in different proportions. In EBV-transformed B cells, PDE4 was much higher than PDE3. HTLV-I+ T-cells differed significantly from other T-lymphocyte-derived cells in also having a higher proportion of PDE4 activities, which apparently were not related to selective induction of any one PDE4 mRNA (judged by reverse transcription-polymerase chain reaction) or expression of the HTLV-I regulatory protein Tax. In MJ cells (an HTLV-I+ T-cell line), Jurkat cells, and PBMC-PHA cells, the tyrosine kinase inhibitor herbimycin A strongly inhibited PDE activity. Growth of MJ cells was inhibited by herbimycin A and a protein kinase C (PKC) inhibitor, and was arrested in G1 by rolipram, a specific PDE4 inhibitor. Proliferation of several HTLV-I+ T-cell lines, PBMC-PHA, and Jurkat cells was inhibited differentially by forskolin (which activates adenylyl cyclase), the selective PDE inhibitors cilostamide and rolipram, and the nonselective PDE inhibitors pentoxifylline and isobutyl methylxanthine. These results suggest that PDE4 isoforms may be functionally up-regulated in HTLV-I+ T-cells and may contribute to the virus-induced proliferation, and that PDEs could be therapeutic targets in immune/inflammatory and neoplastic diseases.

HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) pathogenesis hypothesis. A shift of homologous peptides pairs, central nervous system (CNS)/HTLF-1, HTLV-1/thymus, thymus/CNS, in a thymus-like CNS environment, underlies the pathogenesis of HAM/TSP

Determinants shared by thymus, brain and HTLV-1 induce lymphocytic neurotropism and demyelinization in HAM/TSP, within the framework thymus-like brain environment. The disease evolves in two phases. The first phase of the disease would be dependent on CD4 T-lymphocytes specific for thymic autoantigens, reactivated by viral antigens homologous to thymus and CNS autoantigens. During this phase, demyelinization could be due initially to a stop in the synthesis of myelin following an altered expression of adhesion proteins at the surface of oligodendrocytes and neurons. The second phase, which covers the inflammatory and chronic character of the disease, would be dependent, on the one hand, on CD8 T-lymphocytes specific for viral peptides, and on the other hand, on CD8 T-lymphocytes specific for peptides arising from the cell-proteases induced progressive proteolysis of protein components from the myelin layers and other protein components of the CNS. Non-specific inflammatory and non-inflammatory cytokines keep the activation going of the different cellular types. The thoracic spinal cord cell-location specificity would be linked to a peptidic coherence between HTLV-1 (significant agent), thymus and thoracic spinal cord antigens, genetically peculiar to HAM/TSP patients.

Seroprevalence of HTLV-I and HTLV-II among a cohort of HIV-infected women and women at risk for HIV infection. Women's Interagency HIV Study

OBJECTIVES

To determine the seroprevalence of, and risk factors for, HTLV-I and HTLV-II infection among HIV-infected women and women at high risk for HIV infection.

DESIGN

Cross-sectional analysis of baseline data for women enrolled in the prospective Women's Interagency HIV Study (WIHS).

METHODS

From October 1994 through November 1995, 2657 women from five metropolitan areas in the United States (Chicago, Los Angeles, New York City [two sites], Northern California, and Washington DC) were enrolled in WIHS. An interview-based survey collected data on demographics, behavior, and medical history. HTLV-I and HTLV-II determinations were made using a combined HTLV-I/HTLV-II indirect immunofluorescent antibody (IFA) screening test, an IFA titration specificity test, and individual HTLV-I and HTLV-II confirmatory Western blots. Fisher's exact tests and logistic regression were used to determine univariate and multivariate independent predictors for HTLV-II infection.

RESULTS

Of 2625 women enrolled in WIHS with confirmed HIV results, 2487 (95%) were tested for HTLV-I and HTLV-II. Of these, 241 (10%) were HTLV-II-seropositive and 13 (0.5%) were HTLV-I-seropositive. On multivariate analysis, independent predictors of HTLV-II infection included injection drug use (OR = 5.2; p < .001), black race (OR = 3.6; p < 0.001), age >35 years (OR = 3.3; p < .001) and a history of sex with a male injecting drug user (OR = 1.9; p < .001). Among women infected with HIV, the seroprevalence of HTLV-II was 11% compared with 6% for women at risk for HIV but not infected (p < .001). However, HIV was not an independent predictor of HTLV-II infection in multivariate analysis.

CONCLUSIONS

This cross-sectional analysis confirms that HTLV-II is found commonly in HIV-infected women and uninfected women at risk for HIV in major urban areas throughout the United States and that HTLV-II is far more common than HTLV-I in these populations. Although injecting drug use is most strongly associated with HTLV-II infection, sexual transmission likely contributes to the high HTLV-II seroprevalence in this cohort.

Reduction in HTLV-I proviral load and spontaneous lymphoproliferation in HTLV-I-associated myelopathy/tropical spastic paraparesis patients treated with humanized anti-Tac

Human T-lymphotropic virus type I (HTLV-I)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a neurological disease that results from an interaction of retroviral infection and immune activation. In this study, five doses (1 mg/kg) of humanized anti-Tac antibody were administered to 9 HAM/TSP patients at weeks 0, 2, 6, 10, and 14. Preliminary immunological studies on HAM/TSP patients treated with humanized anti-Tac indicate that there is a selective down-regulation of activated T cells and a decrease in the HTLV-I viral load in peripheral blood lymphocytes, most likely through the selective removal of HTLV-I-infected, activated CD4+ lymphocytes.

Identification of membrane antigens important for adsorption of human T-cell leukaemia virus type I

We isolated three monoclonal antibodies (mAbs), H3e, H11b and H16h, which were capable of inhibiting syncytium formation induced in a human T-cell line MOLT-4 or a human glioma line U251 MG by coculture with human T-cell leukaemia virus type I (HTLV-I)-positive human T-cell lines. The mAbs partially inhibited the plating of pseudotypes of vesicular stomatitis virus (VSV) bearing envelope antigens of HTLV-I. Formation of proviral DNA was also inhibited when indicator cells were treated with the mAbs before adsorption of HTLV-I, but not after its adsorption. They did not inhibit syncytium formation induced by human immunodeficiency virus type 1. Flow cytometry revealed that H16h hardly reacted with various HTLV-I-positive T cells, while H3e and H11b reacted with HTLV-I-positive human cells as well as HTLV-I-negative human cells. H11b and H16h immunoprecipitated the membrane antigen with a molecular weight of 20 and 110-130 kDa, respectively. Western blot analysis showed that H3e, H11b and H16h bound to the protein of 20, 20 and 110-130 kDa, respectively. Thus, these findings suggest that the 20- and 110-130-kDa cell surface proteins may play a role at the early stage of HTLV-I infection.

Cerebrospinal fluid of HTLV-1 associated myelopathy patients induces axonal sproutings and Schwann cell proliferation in the rat sciatic nerve

HTLV-1 (human T-cell leukemia virus type I) associated myelopathy (HAM) is a demyelinating disease. We showed that the CSF of patients and heated CSF of normal subjects induce a segmentary demyelination in rat nerves, and potentiate trypsin in vitro. Here we further characterize the neuropathy induced by the CSF of patients. Peroneal nerves injected 5-8 days before with native or heated CSF of patients, besides extensive demyelination, presented proliferation of myelinating and nonmyelinating Schwann cells, axonal sprouting, fine fibres with a few turns of myelin, disarray of nonmedullated bundles, desmosome-like junctions, and coated pits and vesicles in Schwann cells and axons. The normal CSF was innocuous to the nerve in its native form, but after heating, it induced a neuropathy in all, similar to that elicited by the CSF of patients. Our findings indicate that the CSF of HAM patients contains a thermostable pathogen for nerves of the rat; a thermostable pathogen also occurs in the normal CSF although its activity is checked by endogenous thermolabile factors. We suggest that the pathogen present in the CSF of HAM patients participates in the disease.

Source and route of exposure influence infectivity of a molecular clone of human T cell leukemia virus type I

Infection with human T cell leukemia virus type I (HTLV-I) is typically asymptomatic, but does result in diverse diseases ranging from adult T cell leukemia to spastic neuromyelopathy. To date, differences in HTLV-I provirus structure have not been correlated with pathogenic or asymptomatic outcome of infection. Molecular clones of HTLV-I are now available and represent a powerful tool to link virus structure to pathogenesis. Present studies to explore in vivo infectivity and pathogenicity of an HTLV-I molecular clone, K30p, have utilized the rabbit as a model system. This clone was administered to neonatal or adult rabbits by several different routes and infectivity and pathogenicity were examined. Detection of antiviral humoral immune responses, presence of provirus in tissue samples, and isolation of virus in cultures of blood lymphocytes were used to establish systemic HTLV-I infection. Intramuscular, but not nervous system, exposure to K30p HTLV-I naked DNA resulted in infection. Conversely, neural exposure to T cells that had been transfected with the K30p HTLV-I DNA consistently resulted in systemic infection. Despite detection of HTLV-I provirus in brain and spinal cord of some infected rabbits, no clinical or neuropathological changes occurred. Source and route of virus exposure played a role in infectivity, but did not influence the pathogenic outcome of HTLV-I infection.

Human T-lymphocyte transformation with human T-cell lymphotropic virus type 2

Human T-cell lymphotrophic virus type 2 (HTLV-2), a common infection of intravenous drug users and subpopulations of Native Americans, is uncommon in the general population. In contrast with the closely related HTLV-1, which is associated with both leukemia and neurologic disorders, HTLV-2 lacks a strong etiologic association with disease. HTLV-2 does shares many properties with HTLV-1, including in vitro lymphocyte transformation capability. To better assess the ability of HTLV-2 to transform lymphocytes, a limiting dilution assay was used to generate clonal, transformed lymphocyte lines. As with HTLV-1, the transformation efficiency of HTLV-2 producer cells was proportionately related to the number of lethally irradiated input cells and was comparable to HTLV-1-mediated transformation efficiency. HTLV-2-infected cells were reproducibly isolated and had markedly increased growth potential compared to uninfected cells; HTLV-2 transformants required the continued presence of exogenous interleukin 2 for growth for several months and were maintained for over 2 years in culture. All HTLV-2-transformed populations were CD2 and/or CD3 positive and B1 negative and were either CD4+ or CD8+ populations or a mixture of CD4+ and CD8+ lymphocytes. Clonality of the HTLV-2 transformants was confirmed by Southern blot analysis of T-cell receptor beta chain rearrangement. Southern blot analysis revealed a range of integrated full-length genomes from one to multiple. In situ hybridization analysis of HTLV-2 integration revealed no obvious chromosomal integration pattern.

71-kilodalton heat shock cognate protein acts as a cellular receptor for syncytium formation induced by human T-cell lymphotropic virus type 1

We previously reported that the region corresponding to amino acids 197 to 216 of the gp46 surface glycoprotein (gp46-197) served as a binding domain for the interaction between gp46 and trypsin-sensitive membrane components of the target cell, leading to syncytium formation induced by human T-cell lymphotropic virus type 1 (HTLV-1)-bearing cells. Our new evidence shows that the 71-kDa heat shock cognate protein (HSC70) acts as a cellular receptor for syncytium formation. Using affinity chromatography with the peptide gp46-197, followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, we isolated three components (bands A, B, and C) from MOLT-4 cell lysate which exhibited specific interactions with gp46 and inhibitory activities for syncytium formation induced by HTLV-1-bearing cells. Band A and B components were identified as HSC70 and beta-actin, respectively, through amino acid sequencing by tandem mass spectrometry and immunostaining with specific monoclonal antibodies. Band C is likely to be a nonprotein component, because full activity for syncytium formation was seen after extensive trypsin digestion. Anti-HSC70 monoclonal antibody clearly blocked syncytium formation in a coculture of HTLV-1-bearing cells and indicator cells, whereas no inhibition was seen with anti-beta-actin monoclonal antibody. Furthermore, flow cytometric analysis indicated that anti-HSC70 antibody reacted with MOLT-4 cells. Thus, we propose that HSC70 expressed on the target cell surface acts as a cellular acceptor to gp46 exposed on the HTLV-1-infected cell for syncytium formation, thereby leading to cell-to-cell transmission of HTLV-1.

The effect of rolipram on the production of cytokines in HTLV-I infected cell lines and peripheral blood mononuclear cells of patients with HTLV-I-associated myelopathy (HAM)

Previous studies have reported that the levels of pro-inflammatory cytokines, such as TNF-alpha and IFN-gamma, are elevated in the serum as well as in the cerebrospinal fluid of HAM/TSP patients. To evaluate the effect of the phosphodiesterase type IV inhibitor, rolipram on cytokine production, peripheral blood mononuclear cells (PBMCs) of HAM/TSP patients or HTLV-I infected T-cell lines (HUT102, MT2) were cultured in the presence of different doses of rolipram. The amount of cytokines in the supernatants of the cultured cells was determined by ELISA for TNF-alpha, IFN-gamma and TGF-beta. Rolipram inhibited TNF-alpha production by HUT102 and PBMCs from all the HAM/TSP patients in a dose-dependent manner. The suppression of IFN-gamma varied and was weaker in some HAM/TSP patients compared to that of TNF-alpha. The concentration of TGF-beta in the culture supernatants was not influenced by rolipram. The levels of TNF-alpha mRNA determined by competitive PCR were not changed in the cultured cells in the presence of rolipram, suggesting that rolipram inhibits TNF-alpha production at the post-transcriptional level. These findings suggest the possible benefit of rolipram as a therapeutic agent for HAM/TSP patients.

High levels of the DNA-binding activity of E2F in adult T-cell leukemia and human T-cell leukemia virus type I-infected cells: possible enhancement of DNA-binding of E2F by the human T-cell leukemia virus I transactivating protein, Tax

Transcription factor E2F binds to cellular promoters of certain growth- and cell cycle-controlling genes and forms distinct heteromeric complexes with other nuclear proteins. It has therefore been proposed that E2F is involved in cellular proliferation control. Human T-cell leukemia virus type I (HTLV-I) is an etiological agent of adult T-cell leukemia (ATL). We show here by mobility-shift assay that E2F-containing DNA-binding complexes were detected in HTLV-I-infected T-cell lines and leukemic cells obtained from ATL patients but not in an uninfected T-cell line, Jurkat, and normal peripheral blood mononuclear cells. The Tax protein, encoded by HTLV-I, is a potent transcription activator of viral and several cellular genes. We demonstrate that expression of Tax can induce the E2F-containing DNA-binding complexes in Jurkat T cells. Thus, Tax, through enhancement of the DNA-binding activity of E2F, may be capable of regulating cellular gene expression implicated in the proliferation and transformation of T cells in ATL. This activity may be relevant to the mechanisms whereby HTLV-I which does not contain oncogenes induces neoplasia.

Trypsin-sensitive and -resistant components in human T-cell membranes required for syncytium formation by human T-cell lymphotropic virus type 1-bearing cells

Human T-cell lymphotropic virus type 1 (HTLV-1) envelope proteins play an important role in viral entry into target cells. In a syncytium formation assay consisting of a coculture of HTLV-1-bearing cells and target cells, mature gp46 and gp21 proteins each inhibited syncytium formation induced by HTLV-1-bearing cells. Experiments with 125I-labeled proteins showed that 125I-gp46 bound specifically with MOLT-4 target cells even in the presence of large amounts of gp21, whereas 125I-gp21 binding to target cells was completely blocked in the presence of large amounts of gp46. These observations suggest that HTLV-1 envelope proteins in syncytium formation interact with at least two components, which are located close to each other on the cell membrane. We isolated two components from MOLT-4 cell lysate, using Sepharose 4B columns coupled with peptides corresponding to amino acids 197 to 216 and 400 to 429, respectively, of the envelope protein. One is a trypsin digestion-sensitive component of approximately 34 to 35 kDa, which interacts specifically with gp46. The other is a nonprotein component, which interacts with gp21. This component was destroyed by sodium periodate oxidation and was partitioned into the methanol-chloroform phase. These observations suggest that these two components play an important role in HTLV-1 entry into target cells via membrane fusion.

Detection of HTLV-I in Peripheral Blood Lymphocytes from Patients with Chronic HTLV-I-Associated Myelopathy/Tropical Spastic Paraparesis and Asymptomatic Carriers by PCR-in situ Hybridization

Less than 5% of people infected with human T-lymphotropic virus type I (HTLV-I) develop HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP), a chronic progressive neurologic disease. A number of factors have been implicated in the development of HAM/TSP including heterogeneity of viral sequences, host-genetic background, viral-specific cellular immune responses and viral load. This study examined the presence of HTLV-1 tax DNA in peripheral blood lymphocytes (PBL) from 2 chronic HAM/TSP patients and 2 asymptomatic HTLV-I carriers by using PCR-in situ hybridization (PCR-ISH) for the in situ presence of proviral HTLV-I tax DNA. By this technique, rare PBL from these HTLV-I-infected individuals contained HTLV-I DNA. PCR-ISH did not detect any difference in the number of infected cells between HAM/TSP patients and asymptomatic carriers. Copyright 1997 S. Karger AG, Basel

Interaction of the human T-lymphotropic virus type 1 Tax dimer with CREB and the viral 21-base-pair repeat

Human T-lymphotropic virus type 1 Tax interacts specifically with the cellular transcription factor CREB and the viral 21-bp repeat element to form a Tax-CREB-DNA ternary complex which mediates activation of viral mRNA transcription. Analyses of Tax and Tax mutants indicate that, like CREB, Tax incorporates into the ternary complex as a dimer. The ability of Tax to form a dimer is necessary for its interaction with CREB and the 21-bp element. Analyses of several Tax mutants with amino acid substitutions spanning residues 123 to 204 indicate that intersubunit Tax dimerization correlates with its ability to assemble into the ternary complex and activate transcription. Tax also enhances the DNA binding activities of specific bZip domains in vitro. The ability of Tax to enhance DNA binding of bZip proteins can be explained in part by Tax dimerization. This activity alone is not sufficient for transactivation. A dual amino acid substitution mutant of Tax, M47 (L319R, L320S), completely abrogated for activation of the human T-lymphotropic virus type 1 long terminal repeat as a result of a defect in the transactivation domain, continues to stimulate binding of bZip proteins to DNA.

Human T-cell leukemia virus type I Tax protein transactivates RNA polymerase III promoter in vitro and in vivo

Tax protein of the human T-cell lymphotropic virus type 1 (HTLV-I) is critical for viral replication and is a potent transcriptional activator of viral and cellular polymerase II (pol II) genes. We report here that Tax is able to transactivate a classical pol III promoter, VA-I. In cotransfection experiments, Tax is shown to increase transcription of the VA-I promoter approximately 25-fold. Moreover, Tax is able to activate VA-I transcription when added exogenously to an in vitro transcription reaction. Using Tax affinity column chromatography, we demonstrate that Tax is able to deplete a HeLa cell extract for components required for transcription of VA-I. The transcriptional activity of the Tax-depleted extract can be restored by the 0.6 phosphocellulose fraction. Interestingly, a consensus binding site for cAMP-responsive element binding protein (CREB) is located upstream of the VA-I promoter, and deletion of this element results in the loss of Tax responsiveness. When this CREB binding site is replaced by a Gal-4 binding site, the VA-I promoter can be transactivated by a Gal4-Tax fusion protein. Taken together, these results suggest that Tax may activate pol III and pol II promoter through a similar mechanism involving the CREB activation pathway. It is also possible that Tax affects pol III transcription by direct interaction with a component of the pol III transcriptional machinery.

Segmental demyelination induced by cerebrospinal fluid of progressive spastic paraparesis: correlation with altered proteolytic parameters

Progressive spastic paraparesis (PSP) is a demyelinating disease of the central nervous system. We studied the ability of the cerebrospinal fluid (CSF) of patients to induce alterations in rat peroneal nerves, and to modify the proteolytic activity of trypsin in vitro. Subperineurial injection of native or heated CSF of patients induced segmental demyelination and other cytological alterations 5-7 days later, in the infiltrated zone, while proximal and distal regions were normal. The CSF of normal subjects did not induce demyelination, but upon heating, it did so. Trypsin was strongly inhibited by the normal CSF but upon heating, its inhibitory activity was replaced by a strong potentiation. In contrast, native and heated CSF of patients potentiated trypsin. Our findings indicate that (1) the normal CSF contains a thermostable factor that potentiates trypsin whose function is overruled by thermolabile protease inhibitors; (2) the CSF of PSP patients has a reduced inhibitory activity and a conserved ability to potentiate trypsin; and (3) the CSF is endowed with a pathogenic power that correlates with an unchecked potentiating activity. We propose that the imbalance of a protease system may play a role in the pathogenesis of PSP lesions.

Prevalence of HTLV type I infection in Iran: a serological and genetic study

Several publications describe the presence of the human T cell lymphotropic virus type I (HTLV-I) in Jewish individuals born in Mash-had, Iran. We report here the results of HTLV-I serological and genetic studies in the non-Jewish population of Mash-had as well as a neighboring area: Gonbad-Kavous. Seven hundred and seven serum samples from Mash-had (694 healthy individuals and 13 patients with lymphoma) and 90 from Gonbad-Kavous were tested for HTLV antibodies by gelatin particle agglutination assay (PA) and confirmatory Western blots (WBs). Seropositive rates of 3.0% (21 of 694) in Mash-had, 0% (0 of 90) in Gonbad-Kavous, and 100% (13 of 13) in lymphoma cases were observed. HTLV-I DNA sequence were amplified by polymerase chain reaction directly from the fresh PBMCs of seropositive individuals. Phylogenetic analysis of the viral DNA sequence indicated that the HTLV-I present in Mash-had belong to the HTLV-I cosmopolitan clade. Altogether, these data indicate that Mash-had, located in northeastern Iran, is a newly recognized endemic center for HTLV-I.

Infectivity of chimeric human T-cell leukemia virus type I molecular clones assessed by naked DNA inoculation

Two human T-cell leukemia virus type I (HTLV-I) molecular clones, K30p and K34p were derived from HTLV-I-infected rabbit cell lines. K30p and K34p differ by 18 bp with changes in the long terminal repeats (LTRs) as well as in the gag, pol, and rex but not tax or env gene products. Cells transfected with clone K30p were infectious in vitro and injection of the K30p transfectants or naked K30p DNA into rabbits leads to chronic infection. In contrast, K34p did not mediate infection in vitro or in vivo, although the cell line from which it was derived is fully infectious and K34p transfectants produce intact virus particles. To localize differences involved in the ability of the clones to cause infection, six chimeric HTLV-I clones were constructed by shuffling corresponding fragments containing the substitutions in the LTRs, the gag/pol region and the rex region between K30p and K34p. Cells transfected with any of the six chimeras produced virus, but higher levels of virus were produced by cells transfected with those constructs containing the K30p rex region. Virus production was transient except in cells transfected with K30p or with a chimera consisting of the entire protein coding region of K30p flanked by K34p LTRs; only the transfectants showing persistent virus production mediated in vitro infection. In vivo infection in rabbits following intramuscular DNA injection was mediated by K30p as well as by a chimera of K30p containing the K34p rex gene. Comparisons revealed that virus production was greater and appeared earlier in rabbits injected with K30p. These data suggest that several defects in the K34p clone preclude infectivity and furthermore, provide systems to explore functions of HTLV-I genes.