Tissue expression pattern directed in transgenic mice by the LTR of an HTLV-I provirus isolated from a case of tropical spastic paraparesis

Imaging spontaneous tumorigenesis: inflammation precedes development of peripheral NK tumors

Early events in tumor development are spontaneous, microscopic, and affected by the microenvironment. We developed a mouse model of spontaneous lymphoma in which malignant transformation is coupled with light emission that can be detected noninvasively using bioluminescent imaging. The human T-cell leukemia virus (HTLV) type 1 transcriptional transactivator Tax is an oncogene sufficient to produce lymphoma in transgenic animal models. Using the granzyme B promoter to restrict Tax expression to the mature natural killer (NK)/T-cell compartment, we have reproduced many elements of HTLV-associated adult T-cell leukemia/lymphoma. Tax activates signaling cascades associated with transformation, inflammation, and tumorigenesis. Here, we report that Tax-mediated activation of luciferase in long terminal repeat-luciferase (LTR-LUC) mice serves as a reporter for imaging these processes in vivo. Using bioluminescent imaging (BLI), we discovered that microscopic intraepithelial lesions precede the onset of peripheral subcutaneous tumors, tumorigenesis progresses through early reversible stages, and Tax is sufficient for inducing tumors. Based on these findings, we propose that Tax expression in activated lymphocytes initiates a cascade of events that leads to NK/T cell recruitment, activation, and transformation. The use of BLI expands our ability to interrogate the role of Tax in tumorigenesis in vivo and has made the association of inflammation with tumor initiation amenable for study.

Reduction of human T-cell leukemia virus type-1 infection in mice lacking nuclear factor-kappaB-inducing kinase

Human T-cell lymphotropic virus type 1 (HTLV-1) causes adult T-cell leukemia and inflammatory disorders. Aberrant activation of nuclear factor-kappaB (NF-kappaB) has been linked to HTLV-1 pathogenesis and to various kinds of cancers, including adult T-cell leukemia. NF-kappaB-inducing kinase (NIK) is critical for non-canonical activation of NF-kappaB and for the development of lymphoid organs. HTLV-1 activates NF-kappaB by the non-canonical pathway, but examination of the role of NIK in proliferation of HTLV-1-infected cells in vivo has been hindered by lack of a suitable animal model. Alymphoplasia (aly/aly) mice bear a mutation of NIK, resulting in defects in the development of lymphoid organs and severe deficiencies in both humoral and cell-mediated immunity. In the present study we therefore used a mouse model of HTLV-1 infection with aly/aly mice. The number of HTLV-1-infected cells in the reservoir organs in aly/aly mice was significantly smaller than in the control group 1 month after infection. In addition, aly/aly mice did not maintain provirus for 1 year and antibodies against HTLV-1 were undetectable. These results demonstrate that the absence of functional NIK impairs primary HTLV-1 proliferation and abolishes the maintenance of provirus. Interestingly, clonal proliferation of HTLV-1-infected mouse cells was not detected in aly/aly mice, which is consistent with the lack of HTLV-1 persistence. These observations imply that the clonal proliferation of HTLV-1-infected cells in secondary lymphoid organs might be important for HTLV-1 persistence.

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.

Experimental HTLV-I infection and associated myelopathy

HTLV-I infection and associated myelopathy has been reproduced experimentally in vitro and in vivo and these studies have shown the possibility of creating several lines of infective cells and of detecting minor and major clinical expressions of HTLV-I associated myelopathy in rabbits and rats.

HTLV-I transgenic models: an overview

Human T cell leukemia virus type I (HTLV-I) is the agent of a wide spectrum of human diseases. The mechanisms by which a single virus can cause neurodegenerative disorders as well as leukemia is still a matter of debate. Transgenic mice have been used to assess the contribution of different viral elements in viral tropism as well as on cell transformation in vivo. In particular, transgenic models were generated to study the tissue specificity of expression directed by the viral long terminal repeat and the pathological effects induced by the Tax protein of HTLV-I. These models have led to a description of the cell types able to support the viral expression in vivo, and the use of Tax-transgenic mice has demonstrated that this protein is oncogenic and able to induce muscular atrophy and arthropathies. Finally, these models could provide a useful system to study therapeutic approaches for HTLV-I-associated diseases.

Genetic variability and molecular epidemiology of human and simian T cell leukemia/lymphoma virus type I

In the past few years, numerous investigators have demonstrated that human T cell leukemia/lymphoma virus type I (HTLV-I) possesses a great genetic stability, and recent data indicate that viral amplification via clonal expansion of infected cells, rather than by reverse transcription, could explain this remarkable genetic stability. In parallel, the molecular epidemiology of HTLV-I proviruses showed that the few nucleotide changes observed between isolates were specific for the geographical origin of the patients but not for the type of the associated pathologies (adult T cell leukemia/lymphoma, tropical spastic paraparesis/HTLV-I-associated myelopathy). Thus, based on sequence and/or restriction fragment length polymorphism analysis of more than 250 HTLV-I isolates originating from the main viral endemic areas, three major molecular geographical subtypes (or genotypes) emerged, strongly supported by phylogenetic analysis (high bootstrap values). Each of these genotypes (Cosmopolitan, Central African, and Melanesian) appeared to arise from ancient interspecies transmission between monkeys infected with simian T cell leukemia/lymphoma virus type I and humans. Furthermore, careful sequences analyses indicate that, within (or alongside) these three main genotypes, there are molecular subgroups defined clearly by several specific mutations but not always supported by phylogenetic analyses. Thus in Japan, there is evidence for two ancestral HTLV-I lineages: the classical Cosmopolitan genotype, representing approximately 25% of the HTLV-I present in Japan and clustering in the southern islands; and a related subgroup that we called the Japanese group. Similarly, within the Central African cluster, there are molecular subgroups defined by specific substitutions in either the env or the long terminal repeat. Furthermore, recent data from our laboratory indicate the presence of a new molecular phylogenetic group (fourth genotype) found among inhabitants of Central Africa, particularly in Pygmies. While geographical subtypes vary from 2 to 8% between themselves, HTLV-I quasi-species present within an individual appear to be much lower, with a variability of < 0.5%.

Transactivation of human T-cell leukemia virus type 1 by herpes simplex virus type 1

HTLV-1 transcription depends upon activation by the HTLV-1 tax gene product. In addition, various substances and cellular transcription factors are also known to activate the HTLV-1 long terminal repeat (LTR)-mediated transcription in the absence of Tax. In this work we demonstrate that infection of either Jurkat or 293 cell lines with herpes simplex I (HSV-1), a widespread infectious virus of humans, activates HTLV-1 LTR-mediated gene expression. Further investigation revealed that each of the immediate-early (IE) gene products--ICPO, ICP4, and ICP27--of HSV-1 transactivates the HTLV-1 LTR-mediated gene expression in the absence of Tax. The HSV-1 activation is additive to Tax activation in its presence in the cell. Three 21 base repeats upstream of the TATA box are known as the TAX responsive elements (TRE). Recombinant HTLV-1 minimal promoter composed of the HTLV-1 TATA box fused to a synthetic 21 base TRE is responsive to Tax but not to HSV-1 activation. It thus can be concluded that HSV-1 IE gene products and Tax transactivates HTLV-1 LTR mediated gene expression through different transcription complexes. The results presented in this work may point to one possible way for the transition of HTLV-1 from a quiescent to an actively replicating stage.

Sequence heterogeneity of HTLV-I proviral DNA in the central nervous system of patients with HTLV-I-associated myelopathy

The nucleotide sequence of human T-lymphotropic virus type I (HTLV-I) in central nervous system tissue was determined in 3 autopsy cases with HTLV-I-associated myelopathy (HAM)/tropical spastic paraparesis (TSP) and 1 seropositive carrier without HAM/TSP but with multiple sclerosis. All HAM/TSP samples (3 spinal cords and 2 brains) and the sample from the seropositive carrier without HAM/TSP (brain) were positive for HTLV-I env (5146-6681), pX5' (6549-7494), and pX3' (7354-8276) regions by the two-step polymerase chain reaction method. A nucleotide sequence analysis of the pX5' and pX3' polymerase chain reaction products from nucleotides 6631 to 8259 revealed heterogeneity of the HTLV-I genome in all cases. It is notable that 13 of 50 clones derived from the pX3' polymerase chain reaction products were defective in the tax open reading frame while 7 were defective in the rex open reading frame in the HAM/TSP samples. All 17 clones from 1 HAM/TSP case were defective in the pX open reading frame II. One nucleotide insertion at 7784 creating a frame shift in both tax and rex was seen in all 3 HAM/TSP cases but not in the HTLV-I carrier without HAM/TSP. The pX-defective mutants found frequently in the central nervous system may contribute to the neural damage, since the pX gene products are essential for the transactivation of various cellular genes as well as for viral replication.

Identification of human T-cell lymphotropic virus type I 21-base-pair repeat-specific and glial cell-specific DNA-protein complexes

The human T-cell lymphotropic virus type I (HTLV-I)-encoded protein, Tax, is capable of trans-activating HTLV-I transcription by interacting with specific sequences in the HTLV-I long terminal repeat (LTR) which comprise an inducible enhancer containing three imperfect tandem repeats of a 21-bp sequence. There is no evidence that purified Tax can bind to DNA in the absence of cellular factors, suggesting that Tax most likely regulates transcription via interaction with cellular factors. Since HTLV-I is a documented agent of adult T-cell leukemia and tropical spastic paraparesis, disorders of the immune and nervous systems, respectively, characterization of cellular factors of lymphoid and neuroglial origin which interact with the 21-bp repeat elements is essential to understanding of the mechanisms involved in basal and Tax-mediated transcription in cells of immune and nervous system origin. Utilizing electrophoretic mobility shift (EMS) analyses, we have detected both 21-bp repeat-specific and glial cell-specific DNA-protein complexes. Several 21-bp repeat-specific DNA-protein complexes were detected when nuclear extracts derived from cells of lymphoid (Jurkat, SupT1, and H9), neuronal (IMR-32 and SK-N-MC), and glial (U-373 MG, Hs683, and U-118) origin were used in reactions with each of the three 21-bp repeat elements. In addition, a glial cell-specific DNA-protein complex was detected when nuclear extracts derived from U-373 MG, Hs683, and U-118 glial cell lines reacted with the promoter-distal and central 21-bp repeat elements. Furthermore, EMS analyses performed with nuclear extracts derived from lymphocytic and glial cell origin and a 223-bp fragment of the HTLV-I long terminal repeat encompassing the three 21-bp repeat elements (designated Tax-responsive elements 1 and 2, TRE-1/-2) have also resulted in the detection of glial cell type-specific DNA-protein complexes. Competition EMS analyses with oligonucleotides containing transcription factor binding site sequences indicate the involvement of a cyclic AMP response element binding protein in the formation of DNA-protein complexes which form with all three 21-bp repeat elements and the glial cell-specific DNA-protein complex as well as the involvement of Sp1 or an Sp1-related factor in the formation of the 21-bp repeat III-specific DNA-protein complexes.

The presence of HTLV-I proviral DNA in the central nervous system of patients with HTLV-I-associated myelopathy/tropical spastic paraparesis

Human T-lymphotropic virus type 1 (HTLV-I) is a pathogenic retrovirus associated with a chronic progressive myelopathy, termed HTLV-I-associated myelopathy (HAM)/tropical spastic paraparesis (TSP), as well as adult T-cell leukemia (ATL). A chronic inflammatory process has been implicated in HAM/TSP by a pathological study, but the exact mechanism still remains unknown. To understand better the complex mechanism of disease induction by HTLV-I, I studied the spreading pattern of HTLV-I in both peripheral blood mononuclear cells (PBMNCs) and central nervous system (CNS) tissues in patients with HAM/TSP using a quantitative polymerase chain reaction (PCR) method. My results indicated the primary event to be the efficient replication of HTLV-I in vivo, whereas HTLV-I is likely to be present in the constituent cells of the CNS in addition to the infiltrating mononuclear cells.

Establishment of HTLV-I-infected cell lines from French, Guianese and West Indian patients and isolation of a proviral clone producing viral particles

Human T-cell leukemia virus (HTLV-I) induces adult T cell leukemia/lymphoma (ATL) and a chronic neurological disease named either tropical spastic paraparesis (TSP) or HTLV-I associated myelopathy (HAM). We report here the establishment and characterization of eight HTLV-I-infected lymphoid cell lines derived either from patients with TSP (5) or from asymptomatic carriers (1). Southern blot analysis of T cell beta chain gene rearrangements indicates that all cell lines are composed of clonal populations. The same type of analysis performed with HTLV-I-specific probes showed that they harbor 1 to 5 copies of full length proviruses often associated with deleted proviruses with a restriction map for BamHI, HindIII, PstI and SacI restriction enzymes resembling those of HTLV-I previously isolated from Japan and Caribbean area. One of the cell lines, 2060, derived from a TSP patient was shown to express a relative large amount of virus easily transmissible to fresh peripheral and cord blood lymphocytes. The full length proviral genome contained in this cell line was cloned and used in transient expression experiments. We showed that the cloned provirus was able to direct the synthesis of the major structural viral proteins, the protease and the tax and rex regulatory proteins. The structural viral proteins could be assembled into free particles detected in the culture medium of transfected cells. Although the infectivity of these viral particles remains to be determined, this new clone can be employed to examine the cell types in which this TSP-derived provirus directs viral protein synthesis and eventually replicates. It should also prove of value in studies on the early cellular events induced by viral products.

Do endogenous retroviruses have etiological implications in inflammatory and degenerative nervous system diseases?

Vertebrates carry large numbers of endogenous retroviruses (ERVs) and related sequences in their genomes. These retroviral elements are inherited as Mendelian traits. Generally, ERVs are defective without the ability of being expressed as viral particles. However, ERV sequences often have a potential for expression of at least some proteins. So far, the possible biological significance of ERVs is not clear. Nonetheless, there are observations suggesting a connection between ERVs and various diseases. This is the case with murine lupus and a spinal cord disease of certain mouse strains. In the present review, we discuss possible mechanisms by which ERVs could contribute to the development of human degenerative and inflammatory nervous system diseases, including direct effects on nervous system cells and immune cells. Interactions between ERVs and infectious viruses are also discussed. Finally, we review a possible retroviral etiology of multiple sclerosis.

Nucleotide sequence analysis of HTLV-I isolated from cerebrospinal fluid of a patient with TSP/HAM: comparison to other HTLV-I isolates

Human T-cell leukemia virus type I (HTLV-I) has been associated with adult T-cell leukemia/lymphoma and the chronic neurologic disorder tropical spastic paraparesis/HTLV-I-associated myelopathy (TSP/HAM). To study the genetic structure of the virus associated with TSP/HAM, we have obtained and sequenced a partial genomic clone from an HTLV-I-positive cell line established from cerebrospinal fluid (CSF) of a Jamaican patient with TSP/HAM. This clone consisted of a 4.3-kb viral sequence containing the 5' long terminal repeat (LTR), gag, and N-terminal portion of the pol gene, with an overall 1.3% sequence variation resulting from mostly nucleotide substitutions, as compared to the prototype HTLV-I ATK-1. The gag and pol regions showed only 1.4% and 1.2% nucleotide variations, respectively. However, the U3 region of the LTR showed the highest sequence variation (3.6%), where several changes appear to be common among certain TSP/HAM isolates. Several of these changes reside within the 21-bp boundaries and the Tax-responsive element. It would be important to determine if the observed changes are sufficient to cause neurologic disorders similar to the murine leukemia virus system or simply reflect the divergent pool of HTLV-I from different geographic locations. At this time, we cannot rule out the possibility that the observed changes have either direct or indirect significance for the HTLV-I pathogenesis in TSP/HAM.