Sequence variations in LTR and env regions of HTLV-I do not discriminate between the virus from patients with HTLV-I-associated myelopathy and adult T-cell leukemia

An HTLV-1 envelope mRNA vaccine is immunogenic and protective in New Zealand rabbits

Human T-cell leukemia virus type 1 (HTLV-1) is a retrovirus responsible for adult T-cell leukemia/lymphoma, a severe and fatal CD4+ T-cell malignancy. Additionally, HTLV-1 can lead to a chronic progressive neurodegenerative disease known as HTLV-1-associated myelopathy/tropical spastic paraparesis. Unfortunately, the prognosis for HTLV-1-related diseases is generally poor, and effective treatment options are limited. In this study, we designed and synthesized a codon optimized HTLV-1 envelope (Env) mRNA encapsulated in a lipid nanoparticle (LNP) and evaluated its efficacy as a vaccine candidate in an established rabbit model of HTLV-1 infection and persistence. Immunization regimens included a prime/boost protocol using Env mRNA-LNP or control green fluorescent protein (GFP) mRNA-LNP. After immunization, rabbits were challenged by intravenous injection with irradiated HTLV-1 producing cells. Three rabbits were partially protected and three rabbits were completely protected against HTLV-1 challenge. These rabbits were then rechallenged 15 weeks later, and two rabbits maintained sterilizing immunity. In Env mRNA-LNP immunized rabbits, proviral load and viral gene expression were significantly lower. After viral challenge in the Env mRNA-LNP vaccinated rabbits, an increase in both CD4+/IFN-γ+ and CD8+/IFN-γ+ T-cells was detected when stimulating with overlapping Env peptides. Env mRNA-LNP elicited a detectable anti-Env antibody response after prime/boost vaccination in all animals and significantly higher levels of neutralizing antibody activity. Neutralizing antibody activity was correlated with a reduction in proviral load. These findings hold promise for the development of preventive strategies and therapeutic interventions against HTLV-1 infection and its associated diseases.IMPORTANCEmRNA vaccine technology has proven to be a viable approach for effectively triggering immune responses that protect against or limit viral infections and disease. In our study, we synthesized a codon optimized human T-cell leukemia virus type 1 (HTLV-1) envelope (Env) mRNA that can be delivered in a lipid nanoparticle (LNP) vaccine approach. The HTLV-1 Env mRNA-LNP produced protective immune responses against viral challenge in a preclinical rabbit model. HTLV-1 is primarily transmitted through direct cell-to-cell contact, and the protection offered by mRNA vaccines in our rabbit model could have significant implications for optimizing the development of other viral vaccine candidates. This is particularly important in addressing the challenge of enhancing protection against infections that rely on cell-to-cell transmission.

Vaccination with short-term-cultured autologous PBMCs efficiently activated STLV-1-specific CTLs in naturally STLV-1-infected Japanese monkeys with impaired CTL responses

A small proportion of human T-cell leukemia virus type-1 (HTLV-1)-infected individuals develop adult T-cell leukemia/lymphoma, a chemotherapy-resistant lymphoproliferative disease with a poor prognosis. HTLV-1-specific cytotoxic T lymphocytes (CTLs), potential anti-tumor/virus effectors, are impaired in adult T-cell leukemia/lymphoma patients. Here, using Japanese monkeys naturally infected with simian T-cell leukemia/T-lymphotropic virus type-1 (STLV-1) as a model, we demonstrate that short-term-cultured autologous peripheral blood mononuclear cells (PBMCs) can serve as a therapeutic vaccine to activate such CTLs. In a screening test, STLV-1-specific CTL activity was detectable in 8/10 naturally STLV-1-infected monkeys. We conducted a vaccine study in the remaining two monkeys with impaired CTL responses. The short-term-cultured PBMCs of these monkeys spontaneously expressed viral antigens, in a similar way to PBMCs from human HTLV-1 carriers. The first monkey was subcutaneously inoculated with three-day-cultured and mitomycin C (MMC)-treated autologous PBMCs, and then boosted with MMC-treated autologous STLV-1-infected cell line cells. The second monkey was inoculated with autologous PBMC-vaccine alone twice. In addition, a third monkey that originally showed a weak STLV-1-specific CTL response was inoculated with similar autologous PBMC-vaccines. In all three vaccinated monkeys, marked activation of STLV-1-specific CTLs and a mild reduction in the STLV-1 proviral load were observed. Follow-up analyses on the two monkeys vaccinated with PBMCs alone indicated that STLV-1-specific CTL responses peaked at 3-4 months after vaccination, and then diminished but remained detectable for more than one year. The significant reduction in the proviral load and the control of viral expression were associated with CTL activation but also diminished 6 and 12 months after vaccination, respectively, suggesting the requirement for a booster. The vaccine-induced CTLs in these monkeys recognized epitopes in the STLV-1 Tax and/or Envelope proteins, and efficiently killed autologous STLV-1-infected cells in vitro. These findings indicated that the autologous PBMC-based vaccine could induce functional STLV-1-specific CTLs in vivo.

Association Between HTLV-1 Genotypes and Risk of HAM/TSP

Human T-cell leukemia virus type 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a neurological disorder presenting with spastic paraparesis, sphincter dysfunction, and mild sensory disturbance in the lower extremities, which develops in a small minority of HTLV-1-infected individuals. HTLV-1-specific T cells are efficiently activated through dedicated human leukocyte antigen-mediated mechanisms, a process considered deeply involved with its pathogenesis. It has been reported that the lifetime risk of developing HAM/TSP differs between ethnic groups, and there is an association between HTLV-1 tax gene subgroups (i.e., tax subgroup-A or -B), which correspond to HTLV-1 “cosmopolitan subtype 1a subgroup A (i.e., transcontinental subgroup)” and “cosmopolitan subtype 1a subgroup B (i.e., Japanese subgroup),” respectively, and the risk of HAM/TSP in the Japanese population. These findings suggest that a given host’s susceptibility to HAM/TSP is deeply connected with both differences in genetically determined components of the host immune response and HTLV-1 subgroup. Therefore, it is crucial for ongoing work to focus on developing novel treatments and preventative approaches for HAM/TSP. In this review, based on an overview of the topic and our latest research findings, the role of the HTLV-1 subgroup on the effects of virus–host interactions in the pathogenesis of HAM/TSP is discussed.

IL-10-mediated signals act as a switch for lymphoproliferation in Human T-cell leukemia virus type-1 infection by activating the STAT3 and IRF4 pathways

Human T-cell leukemia virus type-1 (HTLV-1) causes two distinct diseases, adult T-cell leukemia/lymphoma (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Since there are no disease-specific differences among HTLV-1 strains, the etiological mechanisms separating these respective lymphoproliferative and inflammatory diseases are not well understood. In this study, by using IL-2-dependent HTLV-1-infected T-cell lines (ILTs) established from patients with ATL and HAM/TSP, we demonstrate that the anti-inflammatory cytokine IL-10 and its downstream signals potentially act as a switch for proliferation in HTLV-1-infected cells. Among six ILTs used, ILTs derived from all three ATL patients grew much faster than those from three HAM/TSP patients. Although most of the ILTs tested produced IFN-γ and IL-6, the production of IL-10 was preferentially observed in the rapid-growing ILTs. Interestingly, treatment with exogenous IL-10 markedly enhanced proliferation of the slow-growing HAM/TSP-derived ILTs. The IL-10-mediated proliferation of these ILTs was associated with phosphorylation of STAT3 and induction of survivin and IRF4, all of which are characteristics of ATL cells. Knockdown of STAT3 reduced expression of IL-10, implying a positive-feedback regulation between STAT3 and IL-10. STAT3 knockdown also reduced survivin and IRF4 in the IL-10- producing or IL-10- treated ILTs. IRF4 knockdown further suppressed survivin expression and the cell growth in these ILTs. These findings indicate that the IL-10-mediated signals promote cell proliferation in HTLV-1-infected cells through the STAT3 and IRF4 pathways. Our results imply that, although HTLV-1 infection alone may not be sufficient for cell proliferation, IL-10 and its signaling pathways within the infected cell itself and/or its surrounding microenvironment may play a critical role in pushing HTLV-1-infected cells towards proliferation at the early stages of HTLV-1 leukemogenesis. This study provides useful information for understanding of disease mechanisms and disease-prophylactic strategies in HTLV-1 infection.

HTLV-1 clonality in adult T-cell leukaemia and non-malignant HTLV-1 infection

Human T lymphotropic virus type 1 (HTLV-1) causes a range of chronic inflammatory diseases and an aggressive malignancy of T lymphocytes known as adult T-cell leukaemia/lymphoma (ATLL). A cardinal feature of HTLV-1 infection is the presence of expanded clones of HTLV-1-infected T cells, which may persist for decades. A high viral burden (proviral load) is associated with both the inflammatory and malignant diseases caused by HTLV-1, and it has been believed that the oligoclonal expansion of infected cells predisposes to these diseases. However, it is not understood what regulates the clonality of HTLV-1 in vivo, that is, the number and abundance of HTLV-1-infected T cell clones. We review recent advances in the understanding of HTLV-1 infection and disease that have come from high-throughput quantification and analysis of HTLV-1 clonality in natural infection.

The roles of acquired and innate immunity in human T-cell leukemia virus type 1-mediated diseases

Human T-cell leukemia virus type 1 (HTLV-1) causes adult T-cell leukemia (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis in small subsets of HTLV-1 carriers. HTLV-1-specific T-cell responses play critical roles in anti-viral and anti-tumor host defense during HTLV-1 infections. Some HTLV-1 carriers exhibit selective loss or anergy of HTLV-1-specific T-cells at an asymptomatic stage. This is also observed in ATL patients and may therefore be an underlying risk factor of ATL in combination with elevated proviral loads. HTLV-1-specific T-cells often recognize the viral oncoprotein Tax, indicating expression of Tax protein in vivo, although levels of HTLV-1 gene expression are known to be very low. A type-I interferon (IFN) response can be induced by HTLV-1-infected cells and suppresses HTLV-1 expression in vitro, suggesting a role of type-I IFN response in viral suppression and pathogenesis in vivo. Both acquired and innate immune responses control the status of HTLV-1-infected cells and could be the important determinants in the development of HTLV-1-mediated malignant and inflammatory diseases.

Correlation between LTR point mutations and proviral load levels among human T cell lymphotropic virus type 1 (HTLV-1) asymptomatic carriers

Background

In vitro studies have demonstrated that deletions and point mutations introduced into each 21 bp imperfect repeat of Tax-responsive element (TRE) of the genuine human T-cell leukemia virus type I (HTLV-1) viral promoter abolishes Tax induction. Given these data, we hypothesized that similar mutations may affect the proliferation of HTLV-1i

nfected cells and alter the proviral load (PvL). To test this hypothesis, we conducted a cross-sectional genetic analysis to compare the near-complete LTR nucleotide sequences that cover the TRE1 region in a sample of HTLV-1 asymptomatic carriers with different PvL burden.

Methods

A total of 94 asymptomatic HTLV-1 carriers with both sequence from the 5' long terminal repeat (LTR) and a PvL for Tax DNA measured using a sensitive SYBR Green real-time PCR were studied. The 94 subjects were divided into three groups based on PvL measurement: 31 low, 29 intermediate, and 34 high. In addition, each group was compared based on sex, age, and viral genotypes. In another analysis, the median PvLs between individuals infected with mutant and wild-type viruses were compared.

Results

Using a categorical analysis, a G232A substitution, located in domain A of the TRE-1 motif, was detected in 38.7% (12/31), 27.5% (8/29), and 61.8% (21/34) of subjects with low, intermediate, or high PvLs, respectively. A significant difference in the detection of this mutation was found between subjects with a high or low PvL and between those with a high or intermediate PvL (both p < 0.05), but not between subjects with a low or intermediate PvL (p > 0.05). This result was confirmed by a non-parametric analysis that showed strong evidence for higher PvLs among HTLV-1 positive individuals with the G232A mutation than those without this mutation (p < 0.03). No significant difference was found between the groups in relation to age, sex or viral subtypes (p > 0. 05).

Conclusions

The data described here show that changes in domain A of the HTLV-1 TRE-1 motif resulting in the G232A mutation may increase HTLV-1 replication in a majority of infected subjects.

Immunologic control of human T-cell leukemia virus type I and adult T-cell leukemia

Host T-cell responses to human T-cell leukemia virus type I (HTLV-I) control the expansion of HTLV-I-infected cells and are determinants of the equilibrium proviral load in vivo. Insufficient T-cell responses are regarded as an immunologic risk factor for adult T-cell leukemia (ATL) because they allow increased proviral loads, which represent an epidemiologic risk factor for ATL. ATL cells from approximately half of ATL cases retain the ability to express HTLV-I Tax, a major target antigen of HTLV-I-specific cytotoxic T-lymphocytes (CTL), whereas Tax-specific CTL in ATL patients are inactive. Tax-specific CTL responses are strongly activated after hematopoietic stem cell transplantation in some ATL patients in long-term remission, indicating that HTLV-I Tax is expressed in vivo rather than being silent, and that the donor-derived T-cell system can recognize it. These findings strongly suggest that reactivation of Tax-specific CTL by vaccines may be promising for prophylaxis of ATL in the high-risk group of HTLV-I carriers and for therapy of ATL in patients whose tumor cells are capable of expressing Tax.

Enhanced replication of human T-cell leukemia virus type 1 in T cells from transgenic rats expressing human CRM1 that is regulated in a natural manner

Human T-cell leukemia virus type 1 (HTLV-1) is the etiologic agent of adult T-cell leukemia (ATL). To develop a better animal model for the investigation of HTLV-1 infection, we established a transgenic (Tg) rat carrying the human CRM1 (hCRM1) gene, which encodes a viral RNA transporter that is a species-specific restriction factor. At first we found that CRM1 expression is elaborately regulated through a pathway involving protein kinase C during lymphocyte activation, initially by posttranscriptional and subsequently by transcriptional mechanisms. This fact led us to use an hCRM1-containing bacterial artificial chromosome clone, which would harbor the entire regulatory and coding regions of the CRM1 gene. The Tg rats expressed hCRM1 protein in a manner similar to expression of intrinsic rat CRM1 in various organs. HTLV-1-infected T-cell lines derived from these Tg rats produced 100- to 10,000-fold more HTLV-1 than did T cells from wild-type rats, and the absolute levels of HTLV-1 were similar to those produced by human T cells. We also observed enhancement of the dissemination of HTLV-1 to the thymus in the Tg rats after intraperitoneal inoculation, although the proviral loads were low in both wild-type and Tg rats. These results support the essential role of hCRM1 in proper HTLV-1 replication and suggest the importance of this Tg rat as an animal model for HTLV-1.

Cellular immune response to HTLV-1

There is strong evidence at the individual level and the population level that an efficient cytotoxic T lymphocyte (CTL) response to HTLV-1 limits the proviral load and the risk of associated inflammatory diseases such as HAM/TSP. This evidence comes from host population genetics, viral genetics, DNA expression microarrays and assays of lymphocyte function. However, until now there has been no satisfactory and rigorous means to define or to measure the efficiency of an antiviral CTL response. Recently, methods have been developed to quantify lymphocyte turnover rates in vivo and the efficiency of anti-HTLV-1 CTLs ex vivo. Data from these new techniques appear to substantiate the conclusion that variation between individual hosts in the rate at which a single CTL kills HTLV-1-infected lymphocytes is an important determinant, perhaps the decisive determinant, of the proviral load and the risk of HAM/TSP. With these experimental data, it is becoming possible to refine, parameterize and test mathematical models of the immune control of HTLV-1, which are a necessary part of an understanding of this complex dynamic system.

Tumor immunity against adult T-cell leukemia

Human T-cell leukemia virus type-I (HTLV-I) causes adult T-cell leukemia (ATL) in a small population of infected individuals after a long incubation period. Although the process of clonal evolution of ATL cells may involve multiple steps, ATL cells from half of the ATL cases still retain the ability to express HTLV-I Tax, a key molecule of HTLV-I leukemogenesis. A recent finding of reactivation of Tax-specific cytotoxic T lymphocytes (CTL) in ATL patients after hematopoietic stem cell transplantation suggests the presence of Tax expression in vivo and potential contribution of the CTL to antitumor immunity. This is consistent with the results of a series of animal experiments indicating that Tax-specific CTL limit the growth of HTLV-I-infected cells in vivo, although the animal model mimics only an early phase of HTLV-I infection and leukemogenesis. Establishment of an insufficient HTLV-I-specific T-cell response and an increased viral load in orally HTLV-I-infected rats suggests that host HTLV-I-specific T-cell response at a primary HTLV-I infection can be a critical determinant of persistent HTLV-I levels thereafter. These findings indicate that Tax-targeted vaccines may be effective for prophylaxis of ATL in a high-risk group, and also for therapy of ATL in at least half the cases.

Immunological risks of adult T-cell leukemia at primary HTLV-I infection

A small percentage of human T-cell leukemia virus type-I (HTLV-I)-infected individuals develop adult T-cell leukemia (ATL). In animal experiments, inoculation of HTLV-I via the oral route, which is the main route of mother-to-child viral transmission in humans as a result of breastfeeding, induced host HTLV-I-specific T-cell unresponsiveness and resulted in increased viral load. This strongly suggested that the known epidemiological risk factors for ATL (i.e. vertical HTLV-I infection and elevated viral load) are linked by an insufficient HTLV-I-specific T-cell response. Recent findings on the anti-tumor effects of Tax-targeted vaccination in rats and the reactivation of Tax-specific T cells in ATL patients as a result of hematopoietic stem cell transplantation imply promising immunological approaches for the prophylaxis and therapy of ATL.

Repression of tax expression is associated both with resistance of human T-cell leukemia virus type 1-infected T cells to killing by tax-specific cytotoxic T lymphocytes and with impaired tumorigenicity in a rat model

Human T-cell leukemia virus type 1 (HTLV-1) causes adult T-cell leukemia (ATL). Although the viral transactivation factor, Tax, has been known to have apparent transforming ability, the exact function of Tax in ATL development is still not clear. To understand the role of Tax in ATL development, we introduced short-interfering RNAs (siRNAs) against Tax in a rat HTLV-1-infected T-cell line. Our results demonstrated that expression of siRNA targeting Tax successfully downregulated Tax expression. Repression of Tax expression was associated with resistance of the HTLV-1-infected T cells to Tax-specific cytotoxic-T-lymphocyte killing. This may be due to the direct effect of decreased Tax expression, because the Tax siRNA did not alter the expression of MHC-I, CD80, or CD86. Furthermore, T cells with Tax downregulation appeared to lose the ability to develop tumors in T-cell-deficient nude rats, in which the parental HTLV-1-infected cells induce ATL-like lymphoproliferative disease. These results indicated the importance of Tax both for activating host immune response against the virus and for maintaining the growth ability of infected cells in vivo. Our results provide insights into the mechanisms how the host immune system can survey and inhibit the growth of HTLV-1-infected cells during the long latent period before the onset of ATL.

Human T cell leukemia virus type I-induced disease: pathways to cancer and neurodegeneration

Retroviral infection is associated with a number of pathologic abnormalities, including a variety of cancers, immunologic diseases, and neurologic disorders. Shortly after its discovery in 1980, human T cell leukemia virus type I (HTLV-I) was found to be the etiologic agent of both adult T cell leukemia (ATL) and HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP), a neurologic disease characterized by demyelinating lesions in both the brain and the spinal cord. Approximately 5-10% of HTLV-I-infected individuals develop either ATL or HAM/TSP. Interestingly, the two diseases have vastly different pathologies and have rarely been found to occur within the same individual. While a number of host and viral factors including virus strain, viral load, and HLA haplotype have been hypothesized to influence disease outcome associated with HTLV-I infection, the relative contributions of such factors to disease pathogenesis have not been fully established. Recent research has suggested that the route of primary viral infection may dictate the course of disease pathogenesis associated with HTLV-I infection. Specifically, mucosal exposure to HTLV-I has been associated with cases of ATL, while primary viral infection based in the peripheral blood has been correlated with progression to HAM/TSP. However, the cellular and molecular mechanisms regulating disease progression resulting from primary viral invasion remain to be elucidated. Although a variety of factors likely influence these mechanisms, the differential immune response mounted by the host against the incoming virus initiated in either the peripheral blood or the mucosal compartments likely plays a key role in determining the outcome of HTLV-I infection. It has been proposed that the route of infection and size of the initial viral inoculum allows HTLV-I to infect different target cell populations, in turn influencing the breadth of the immune response mounted against HTLV-I and affecting disease pathogenesis. A model of HTLV-I-induced disease progression is presented, integrating information regarding the role of several host and viral factors in the genesis of both neoplasia and neurologic disease induced following HTLV-I infection, focusing specifically on differential viral invasion into the bone marrow (BM) and the influence of this event on the virus-specific CD8(+) cytotoxic T lymphocyte (CTL) response that is initiated following HTLV-I infection.

Expansion of human T-cell leukemia virus type 1 (HTLV-1) reservoir in orally infected rats: inverse correlation with HTLV-1-specific cellular immune response

Adult T-cell leukemia (ATL) occurs in a small population of human T-cell leukemia virus type 1 (HTLV-1)-infected individuals. Although the critical risk factor for ATL development is not clear, it has been noted that ATL is incidentally associated with mother-to-child infection, elevated proviral loads, and weakness in HTLV-1-specific T-cell immune responses. In the present study, using a rat system, we investigated the relationships among the following conditions: primary HTLV-1 infection, a persistent HTLV-1 load, and host HTLV-1-specific immunity. We found that the persistent HTLV-1 load in orally infected rats was significantly greater than that in intraperitoneally infected rats. Even after inoculation with only 50 infected cells, a persistent viral load built up to considerable levels in some orally infected rats but not in intraperitoneally infected rats. In contrast, HTLV-1-specific cellular immune responses were markedly impaired in orally infected rats. As a result, a persistent viral load was inversely correlated with levels of virus-specific T-cell responses in these rats. Otherwise very weak HTLV-1-specific cellular immune responses in orally infected rats were markedly augmented after subcutaneous reimmunization with infected syngeneic rat cells. These findings suggest that HTLV-1-specific immune unresponsiveness associated with oral HTLV-1 infection may be a potential risk factor for development of ATL, allowing expansion of the infected cell reservoir in vivo, but could be overcome with immunological strategies.

Correlation of major histocompatibility complex class I downregulation with resistance of human T-cell leukemia virus type 1-infected T cells to cytotoxic T-lymphocyte killing in a rat model

Human T-cell leukemia virus type 1 (HTLV-1) causes adult T-cell leukemia (ATL) in infected individuals after a long incubation period. Despite the apparent transforming ability of HTLV-1 under experimental conditions, most HTLV-1 carriers are asymptomatic. These facts suggest that HTLV-1 is controlled by host immunity in most carriers. To understand the interplay between host immunity and HTLV-1-infected cells, in this study, we isolated several HTLV-1 Tax-specific cytotoxic T-lymphocyte (CTL) lines from rats inoculated with Tax-coding DNA and investigated the long-term effects of the CTL on syngeneic HTLV-1-infected T cells. Our results demonstrated that long-term mixed culture of these CTL and the virus-infected T cells led to the emergence of CTL-resistant HTLV-1-infected cells. Although the Tax expression level in these resistant cells was equivalent to that in the parental cells, expression of surface major histocompatibility complex class I (MHC-I) was significantly downregulated in the resistant cells. Downregulation of MHC-I was more apparent in RT1.A(l), which presents a Tax epitope recognized by the CTL established in this study. Moreover, peptide pulsing resulted in killing of the resistant cells by CTL, indicating that resistance was caused by a decreased epitope density on the infected cell surface. This may be one of the mechanisms for persistence of HTLV-1-infected cells that evade CTL lysis and potentially develop ATL.

Nucleotide sequence analysis of human T-cell lymphotropic virus type I pX and LTR regions from patients with sicca syndrome

Human T-cell lymphotropic virus type I (HTLV-I) is associated with adult T-cell leukemia (ATL) and tropical spastic paraparesis/HTLV-I-associated myelopathy (TSP/HAM). Other inflammatory disorders may occur in HTLV-I-infected patients, such as sicca syndrome resembling Sjögren's syndrome. The sicca syndrome may be the unique clinical manifestation of HTLV-I infection, but is associated frequently with TSP/HAM, which could suggest that sicca syndrome might be an early event in disease progression to TSP/HAM in some cases. We investigated whether peculiar pX and LTR mutations could be related to sicca syndrome, or might argue the existence of clinical progression to TSP/HAM. pX, especially pX(I), pX(II), and pX(IV) ORFs corresponding to Tax cytotoxic T-lymphocyte epitopes, and LTR regions from Caribbean patients who have sicca syndrome with or without TSP/HAM, ATL patients, and healthy carriers were sequenced. The sequences were aligned and compared with ATK-1 prototype and published sequences. LTR sequences exhibited 1.5-2.4% of divergence with ATK-1. pX-sequenced regions showed a lower homology within p12(I) encoding sequences. Only few mutations were found within functionally important regions, but were not associated specifically with the clinical status. Finally, no mutations that could be related to sicca syndrome or argue the existence of clinical progression to TSP/HAM were found. It would be of interest to study the clinical evolution of HTLV-I-sicca syndrome in patients and to determine HTLV-I sequences from peripheral blood and salivary glands at different stages.

Induction of adult T-cell leukemia-like lymphoproliferative disease and its inhibition by adoptive immunotherapy in T-cell-deficient nude rats inoculated with syngeneic human T-cell leukemia virus type 1-immortalized cells

Human T-cell leukemia virus type 1 (HTLV-1) has been shown to be the etiologic agent of adult T-cell leukemia (ATL), but the in vivo mechanism by which the virus causes the malignant transformation is largely unknown. In order to investigate the mechanisms of HTLV-1 leukemogenesis, we developed a rat model system in which ATL-like disease was reproducibly observed, following inoculation of various rat HTLV-1-immortalized cell lines. When previously established cell lines, F344-S1 and TARS-1, but not TART-1 or W7TM-1, were inoculated, systemic multiple tumor development was observed in adult nude (nu/nu) rats. FPM1 cells, newly established from a heterozygous (nu/+) rat syngeneic to nu/nu rats, caused transient tumors only at the injection site in adult nu/nu rats, but could progressively grow in newborn nu/nu rats and metastasize in lymph nodes. The derivative cell line (FPM1-V1AX) serially passed through newborn nu/nu rats acquired the potency to grow in adult nu/nu rats. These results indicated that only some with additional changes but not all of the in vitro HTLV-1-immortalized cell lines possessed in vivo tumorigenicity. Using the syngeneic system, we further showed the inhibition of tumor development by transferring splenic T cells from immunized rats, suggesting the involvement of T cells in the regression of tumors. This novel and reproducible nude rat model of human ATL would be useful for investigation of leukemogenesis and antitumor immune responses in HTLV-1 infection.

Pathogenesis and treatment of HTLV-I associated myelopathy

That HTLV-I is not a latent infection is indicated by the detection of mRNA in the peripheral blood and CNS of patients with HTLV-I infection and by the persisting humoral and cellular immune responses. Indeed the frequency of anti-HTLV CTL is extremely high. The reduction in anti-TAX CTL frequency following reduction in proviral load suggests that removal of viral antigen may result in a reduced inflammatory response at least in peripheral blood and although the clinical data should be interpreted with caution, perhaps in the CNS. Patients with more advanced disease, and possibly fixed deficits may not benefit from either anti-inflammatory or antiretroviral treatment. The patients with most to gain are those with least deficit in whom early diagnosis and treatment will depend on raising awareness of HTLV-I beyond the neurological community. Many patients with HAM first present to a urologist or gynaecologist with bladder dysfunction or may have been seen in the genitourinary clinical with impotence or positive treponemal serology, which in the older patient is often the result of childhood infection with Treponema pallidum pertenue. Investigation of these patients should include HTLV-I serology and further investigation of HTLV-I positive patients should include proviral load measurements as well as markers of inflammation. Treatments whether antiviral or anti-inflammatory should be assessed for their effect on both as well as a clinical response.

Oral administration of human T-cell leukemia virus type 1 induces immune unresponsiveness with persistent infection in adult rats

The major route of human T-cell leukemia virus type 1 (HTLV-1) infection is mother-to-child transmission caused by breast-feeding. We investigated the host immune responses to orally established persistent HTLV-1 infection in adult rats. HTLV-1-producing MT-2 cells were inoculated into immunocompetent adult rats either orally, intravenously, or intraperitoneally. HTLV-1 proviruses were detected in the peripheral blood and several organs for at least 12 weeks. Transmission of HTLV-1 to these animals was confirmed by analysis of HTLV-1 flanking regions. Despite persistent HTLV-1 presence, none of the orally inoculated rats produced detectable levels of anti-HTLV-1 antibodies, whereas all intravenously or intraperitoneally inoculated rats showed significant anti-HTLV-1 antibody responses. T-cell proliferative responses against HTLV-1 were also absent in orally inoculated rats. Our findings suggest that gastrointestinal exposure of adult rats to HTLV-1-infected cells induces persistent HTLV-1 infection in the absence of both humoral and cellular immune responses against HTLV-1. This immune unresponsiveness at primary infection may subsequently affect the host defense ability against HTLV-1.

Physical and functional interaction between the human T-cell lymphotropic virus type 1 Tax1 protein and the CCAAT binding protein NF-Y

Tax1, a potent activator of human T-cell lymphotropic virus type 1 (HTLV-1) transcription, has been shown to modulate expression of many cellular genes. Tax1 does not bind DNA directly but regulates transcription through protein-protein interactions with sequence-specific transcription factors. Using the yeast two-hybrid system to screen for proteins which interact with Tax1, we isolated the B subunit of the CCAAT binding protein NF-Y from a HeLa cDNA library. The interaction of Tax1 with NF-YB was specific in that NF-YB did not interact with a variety of other transcription factors, including human immunodeficiency virus Tat, human papillomavirus E6, and Bicoid, or with the M7 (amino acids 29CP-AS) Tax1 mutant. However, NF-YB did interact with the C-terminal Tax1 mutants M22 (130TL-AS) and M47 (319LL-RS). We also show that in vitro-translated NF-YB specifically bound to a glutathione S-transferase-Tax1 fusion protein. Further, Tax1 coimmunoprecipitated with NF-Y from nuclear extracts of HTLV-1-transformed cells, providing evidence for in vivo interaction of Tax1 and NF-YB. We further demonstrate that Tax1 specifically activated the NF-Y-responsive DQbeta promoter, as well as a minimal promoter which contains only the Y-box element. In addition, mutation of the Y-box element alone abrogated Tax1-mediated activation. Taken together, these data indicate that Tax1 interacts with NF-Y through the B subunit and that this interaction results in activation of the major histocompatibility complex class II promoter. Through activation of this and other NF-Y driven promoters, the Tax1-NF-Y interaction may play a critical role in causing cellular transformation and HTLV-1 pathogenesis.

A source of glycosylated human T-cell lymphotropic virus type 1 envelope protein: expression of gp46 by the vaccinia virus/T7 polymerase system

Heterologous expression of the human T-cell lymphotropic virus type 1 (HTLV-1) envelope surface glycoprotein (gp46) in a vaccinia virus/T7 polymerase system resulted in the production of authentic recombinant gp46. Five differentially glycosylated forms of the surface envelope protein were produced by this mammalian system, as demonstrated by tunicamycin inhibition of N-glycosylation and N-glycan removal with endoglycosidase H and glycopeptidase F. These studies revealed that all four potential N-glycosylation sites in gp46 were used for oligosaccharide modification and that the oligosaccharides were mannose-rich and/or hybrid in composition. Conformational integrity of the recombinant HTLV-1 envelope protein was determined by the ability to bind to various HTLV-1-infected human sera and a panel of conformational-dependent human monoclonal antibodies under nondenaturing conditions. Furthermore, this recombinant gp46 was recognized by a series of HTLV-2-infected human sera and sera from a Pan paniscus chimpanzee infected with the distantly related simian T-cell lymphotropic virus STLVpan-p. Maintenance of highly conserved conformational epitopes in the recombinant HTLV-1 envelope protein structure suggests that it may serve as a useful diagnostic reagent and an effective vaccine candidate.

Envelope gene sequences of human T-lymphotropic virus type 1 in Taiwan

Three major types of HTLV-1 had been proposed, the Melanesian type, the Zairian type, and the cosmopolitan type, which was further divided into subtypes A, B and C, according to the phylogenetic tree constructed from LTR sequences of current HTLV-isolates. In this study, the envelope gene sequences of HTLV-1 from 9 Taiwanese were analyzed. Based on the phylogenetic tree constructed by unweighted pair group method and the sequence homology analysis by GCG computer programs, the envelope gene sequences of HTLV-1 proviruses from these 9 Taiwanese belonged to subtype A or subtype B of the cosmopolitan type and were closely related to HTLV-1 from Japan. Twelve subtype-specific nucleotide variations were deduced from the comparison of complete or partial envelope gene sequences of 16 HTLV-1 isolates of known subtypes as well as those of 9 Taiwanese. These data provided the basis for subtyping the cosmopolitan type of HTLV-1 by amplification of envelope gene sequences and restriction fragment length polymorphism studies. A more extensive survey based upon this proposal was warranted.

Human T lymphotropic virus type II (HTLV-II): epidemiology, molecular properties, and clinical features of infection

Human T lymphotropic virus, type II (HTLV-II), infection has been shown to be endemic in a number of American Indian populations, and high rates of infection have also been documented in intravenous drug abusers in urban areas throughout the world. Although the role of HTLV-II in human disease has yet to be clearly defined, there is accumulating evidence that like HTLV-I, infection may also be associated with rare lymphoproliferative and neurological disorders. In this article we review and summarize the epidemiology, molecular properties and clinical features of HTLV-II infection.

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%.

Human T cell leukemia virus type I (HTLV-I) molecular genotypes and disease outcome

The approach taken in our laboratory to determine viral markers associated with human T cell leukemia virus type I (HTLV-I) disease induction was to compare viral genomes and host immune responses from HTLV-I-infected patients from two geographical areas with significant differences in the incidence rate of tropical spastic paraparesis/HTLV-I-associated myelopathy (TSP/HAM), Tumaco, Colombia, and Kyushu Island, Japan. These studies showed that TSP/HAM patients have higher antibody levels against viral antigens and a higher proviral load compared to asymptomatic carriers and adult T cell leukemia (ATL) patients. A mutation in the tax gene was found to be associated with TSP/HAM, which in turn correlates with a higher transactivation activity of Tax. In addition, we found that HTLV-I-infected individuals contain infected cells that are clonally expanded. The genomic structure of these expanded clones shows that defective proviruses are present in asymptomatic carriers. A predilection in the defectiveness, however, was found to correlate with the presence (Cosmopolitan molecular genotype) or absence of the tax mutation (Japanese molecular genotype). Our results suggest that defective proviruses retaining structural genes might be a risk factor for TSP/HAM development. Contrary, defective proviruses retaining regulatory genes in the pX region could be a risk factor for ATL development. The molecular mechanism by which these defective proviruses is generated and expressed should give new insight into HTLV-I pathogenesis.

Nucleotide sequence and restriction fragment length polymorphism analysis of the long terminal repeat of human T cell leukemia virus type II

Molecular studies have demonstrated the existence of two major subtypes of human T cell leukemia virus type II: HTLV-IIa and HTLV-IIb. In attempts to further classify this family of viruses we have carried out nucleotide sequence and restriction fragment length polymorphism (RFLP) analysis of the long terminal repeat (LTR), a region that has been shown in previous studies to have the greatest intra- and intersubtype genomic divergence. Analysis of the nucleotide sequences suggested the existence of distinct phylogenetic groups in each subtype and, on the basis of predicted differences in restriction endonuclease sites, RFLP analysis allowed the identification of four groups within the IIa subtype (a1-a4) and six within the IIb subtype (b1-b6). Nucleotide sequence analysis also suggested the possible existence of HTLV-II quasispecies. However, this appeared not to be significant, and preliminary studies suggest that these would not be expected to influence the results of RFLP analysis appreciably. The validity of the RFLP method was demonstrated in an analysis of 36 randomly chosen samples from HTLV-II seropositive blood donors from the New York City Blood Center, where it could be shown that all could be successfully classified. Moreover, the RFLP analysis correctly matched the viruses in donors and recipients of contaminated blood in four situations in which HTLV-II was inadvertently transmitted by transfusion. RFLP analysis of the LTR appears to be a rapid and reliable method by which to identify HTLV-II infection. This should prove useful in studies of the epidemiology and the characterization of viruses present both in nonindigenous and indigenous populations.

Mechanisms of Tax Regulation of Human T Cell Leukemia Virus Type I Gene Expression

During the last several years, the human T cell leukemia virus type I (HTLV-I) has become recognized as an important cause for public health concern throughout the world. HTLV-I is the causative agent of a variety of clinical diseases, including an aggressive lymphoproliferative disorder named adult T cell leukemia. HTLV-I induces pathogenicity in the infected host cell through the synthesis of a virally encoded protein called Tax. Expression of Tax is critical to the life cycle of the virus, as the protein greatly increases the efficiency of HTLV-I gene transcription and replication. Furthermore, Tax has been shown to deregulate the transcription of many cellular genes, leading to the hypothesis that the presence of Tax promotes unchecked growth in the HTLV-I-infected cell. The mechanism of Tax trans-activation of HTLV-I gene expression is not known. Tax does not bind directly to the Tax-responsive promoter elements of the virus, but appears to function through interaction with certain cellular DNA binding proteins, including activating transcription factor 2 and cAMP response element binding protein that recognize these sequences. This review summarizes some of the recent work in the field aimed at elucidating the mechanism of Tax trans-activation of HTLV-I gene expression. Copyright 1995 S. Karger AG, Basel

Familial transmission and minimal sequence variability of human T-lymphotropic virus type I (HTLV-I) in Zaire

Our group previously reported a strong familial clustering of HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP) in Zaire, suggesting a familial transmission of the virus together with the presence of cofactors. In the present study among 84 relatives of 16 HTLV-I-positive or HAM/TSP index cases, we found that all 15 seropositive children had a seropositive mother and that all 15 children with a seropositive father but a seronegative mother were seronegative. Lymphocytes of 17 relatives from 2 families with a familial HTLV-I-associated neuropathy were tested in 2 polymerase chain reaction (PCR) assays amplifying pol and tax/rex gene fragments. The 10 seropositive individuals were PCR positive for HTLV-I and the 7 seronegatives were negative in both PCR assays. The PCR results showed no evidence for a long lag period between infection with HTLV-I and seroconversion. The HTLV-I long terminal repeat (LTR) of these 10 individuals, related in the first to the fourth degree, was amplified and sequenced. Identical sequences were found within the families except for one woman infected with two variants, one being the familial strain and the other a mutated one with a single nucleotide substitution in the 755 sequenced nucleotides of the LTR region. The family strain and the mutant were both present in two samples taken 1 year apart. Together, the HTLV-I serology, PCR, and sequencing results point toward mother-to-child transmission as the main mode of HTLV-I infection in this population. Comparison of the LTR sequences of the two families with other HTLV-I strains from different geographical regions shows that the Zairean HTLV-I strains form a separate cluster.(ABSTRACT TRUNCATED AT 250 WORDS)

Subtype analysis of HTLV-1 in patients with HTLV-1 uveitis

The hypothesis that HTLV-1 uveitis, a recently identified disease entity associated with human T-cell leukemia virus type I (HTLV-1), is caused by a specific subtype of the virus was tested. The nucleotide sequences of the long terminal repeat of HTLV-1 from five patients with HTLV-1 uveitis (HU) and four with adult T-cell leukemia were phylogenetically analyzed. Our results showed that both subtypes which had been identified in Japan were associated with HU, indicating that there was no difference in pathogenicity between these phylogenetic subtypes. One of the subtypes was more frequently isolated in Okinawa than in Kyushu, suggesting a bias in the prevalence of each subtype among the inhabitants of these two areas of Japan.

Identification of functional regions in the human T-cell leukemia virus type I SU glycoprotein

Single conservative and nonconservative amino acid substitutions were introduced into the gp45 external envelope protein (SU) of human T-cell leukemia virus type I (HTLV-I). The mutated amino acids were those identified as being conserved in HTLV-I, HTLV-II, and simian T-cell leukemia virus type I (but not in bovine leukemia virus). The mutated envelopes were tested for intracellular maturation and for function. Mutants with three major phenotypes could be defined: (i) 9 mutants with a wild-type phenotype, which included most of the conservative amino acid changes (five of seven) distributed throughout the SU protein; (ii) 8 mutants with affected intracellular maturation, 6 of which define a region in the central part of the SU protein essential for correct folding of the protein; and (iii) 13 mutants with normal intracellular maturation but impaired syncytium formation. These mutations likely affect the receptor binding step or postbinding events required for fusion. Five of these mutations are located between amino acids 75 and 101 of the SU protein, in the amino-terminal third of the molecule. The other mutations involve positions 170, 181, 195, 197, 208, 233, and 286, suggesting that two other domains, one central and one carboxy terminal, are involved in HTLV-I envelope functions.

Genetic and phylogenetic analyses of human T-cell lymphotropic virus type I variants from Melanesians with and without spastic myelopathy

Molecular variants of human T-cell lymphotropic virus type I (HTLV-I) have been isolated recently from lifelong residents of remote Melanesian populations, including a Solomon Islander with tropical spastic paraparesis/HTLV-I-associated myelopathy (TSP/HAM) or HTLV-I myeloneuropathy. To clarify the genetic heterogeneity and molecular epidemiology of disease-associated strains of HTLV-I, we enzymatically amplified, then directly sequenced representative regions of the gag, pol, env, and pX genes of HTLV-I strains from Melanesians with and without TSP/HAM, and aligned and compared these sequences with those of HTLV-I strains from patients with TSP/HAM or adult T-cell leukemia/lymphoma and from asymptomatic carriers from widely separated and culturally disparate populations. Overall, the HTLV-I variant from the Solomon Islander with TSP/HAM, like HTLV-I strains from asymptomatically infected Melanesians, diverged by approx 7% from cosmopolitan HTLV-I strain. No disease-specific viral sequences were found. Gene phylogenies, as determined by the unweighted pair-group method of assortment and by the maximum parsimony method, indicated that the Melanesian and cosmopolitan strains of HTLV-I have evolved along separate geographically dependent lineages, one comprised of HTLV-I strains from Papua New Guinea and the Solomon Islands, and the other composed of virus strains from Japan, India, the Caribbean, Polynesia, the Americas, and Africa. The total absence of nonhuman primates in Papua New Guinea and the Solomon Islands precludes any possibility that the Melanesian HTLV-I strains have evolved recently from the simian homolog of HTLV-I.

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.

Human T-cell leukaemia virus type I and neurological disease

Tropical spastic paraparesis is thought to be caused either directly by human T-cell leukaemia virus type I (HTLV-1), or by the immune response to the virus. Recent work has identified differences between tropical spastic paraparesis patients and healthy carriers of HTLV-I, both in the virus and in the host's T-cell response to the virus. These differences may provide clues to the pathogenesis of tropical spastic paraparesis.

Human T-cell leukemia virus type I-induced proliferation of human immature CD2+CD3- thymocytes

The mitogenic activity of human T-cell leukemia virus type I (HTLV-I) is triggering the proliferation of human resting T lymphocytes through the induction of the interleukin-2 (IL-2)/IL-2 receptor autocrine loop. This HTLV-I-induced proliferation was found to be mainly mediated by the CD2 T-cell antigen, which is first expressed on double-negative lymphoid precursors after colonization of the thymus. Thus, immature thymocytes express the CD2 antigen before that of the CD3-TCR complex. We therefore investigated the responsiveness of these CD2+CD3- immature thymocytes and compared it with that of unseparated thymocytes, containing a majority of the CD2+CD3+ mature thymocytes, and that of the CD2-CD3- prothymocytes. Both immature and unseparated thymocytes were incorporating [3H]thymidine in response to the virus, provided that they were cultivated in the presence of submitogenic doses of phytohemagglutinin. In contrast, the prothymocytes did not proliferate. Downmodulation of the CD2 molecule by incubating unseparated and immature thymocytes with a single anti-CD2 monoclonal antibody inhibited the proliferative response to HTLV-I. These results clearly underline that the expression of the CD2 molecule is exclusively required in mediating the proliferative response to the synergistic effect of phytohemagglutinin and HTLV-I. Immature thymocytes treated with a pair of anti-CD2 monoclonal antibodies were shown to proliferate in response to HTLV-I, even in the absence of exogenous IL-2. We further verified that the proliferation of human thymocytes is consecutive to the expression of IL-2 receptors and the synthesis of IL-2. These observations provide evidence that the mitogenic stimulus delivered by HTLV-I is more efficient than that provided by other conventional mitogenic stimuli, which are unable to trigger the synthesis of endogenous IL-2. Collectively, these results show that the mitogenic activity of HTLV-I is able to trigger the proliferation of cells which are at an early stage of T-cell development. They might therefore represent target cells in which HTLV-I infection could favor the initiation of the multistep lymphoproliferative process leading to adult T-cell leukemia.

Nucleotide sequence analysis of human T cell leukemia virus, type II (HTLV-II) isolates

A study by Hall et al. (J Virol 1992;66:2456-2463; Ref. 11) has suggested the existence of two closely related molecular subtypes of HTLV-II, which were tentatively designated HTLV-IIa and HTLV-IIb. To confirm this nucleotide sequence analysis of 986 bp of the env gene region encoding the entire surface glycoprotein, gp46, and the amino terminus of the transmembrane glycoprotein, gp21, of 10 HTLV-II isolates was carried out. The results clearly established the existence of two subtypes and demonstrated a 4.3% divergence in sequence in this region. Analysis of other gene regions of the provirus, including the pol (1544 bp), gag (448 bp), and the entire LTR (743 bp) of two representative isolates of each subtype, showed a sequence divergence of 3.8 to 5.7%, with greatest divergence occurring in the LTR. In addition to single nucleotide changes, the gag regions encoding the structural protein, p19, of the HTLV-IIb isolates were also found to have a 66-bp deletion that would be expected to result in a p19 protein having a 22-amino acid deletion in the carboxy-terminus region. Attempts to exploit this to differentiate the two subtypes serologically were unsuccessful in that recombinant p19 proteins of both subtypes were found to be antigenically cross-reactive. The finding of two molecular subtypes of HTLV-II may have important implications for a better understanding of the biological and pathogenic properties of the virus, and will be useful in characterizing the viruses present in endemic foci in American Indian populations.

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.

LTR sequence and phylogenetic analyses of a newly discovered variant of HTLV-I isolated from the Hagahai of Papua New Guinea

A 631-bp region of the long terminal repeat (LTR) of a variant of human T-cell lymphoma/leukemia virus type I (HTLV-I), isolated from a healthy member of a remote, recently contacted group (Hagahai) in Papua New Guinea, was sequenced and compared to LTR sequences of other members of the primate T-cell lymphoma virus group (PTLV), including HTLV-I, simian T-cell lymphoma virus (STLV-I) and HTLV-II. Sequence analysis of the LTR of this New Guinean isolate, designated as HTLV-I(PNG-1), indicated a sequence divergence of 8.4% to 10.4% from prototype Japanese HTLV-I(ATK) and other HTLV-I and STLV-I isolates and 48.6% diversity from HTLV-II. Few mutations were found in the core elements of the transcriptional enhancer regions, the TATA box promoter, and the polyadenylation signal and site. Further, the observed changes did not significantly alter the inferred stability of the Rex response element, a stem loop structure critical for polyadenylation and Rex protein binding. Dendograms based on LTR sequences indicated that the strain of virus that evolved into HTLV-I(PNG-1) diverged from the other PTLV in the distant past, just after the progenitors of STLV-I from Asia, but before the ancestors of STLV-I from Africa. By contrast, other HTLV-I isolates were found to represent strains of virus that have diverged more recently and clustered primarily according to their geographical origin. These data confirm that HTLV-I(PNG-1) is a new and distinct variant of the PTLV group. Also, our analyses suggest that both HTLV-I and STLV-I may have originated in the Indo-Malay region and eventually spread to Africa and then to the New World and Japan with horizontal transmission between man and nonhuman primates possibly occurring over thousands of years.

Low degree of human T-cell leukemia/lymphoma virus type I genetic drift in vivo as a means of monitoring viral transmission and movement of ancient human populations

We have studied the genetic variation of human T-cell leukemia/lymphoma virus type I (HTLV-I) isolates in the same individuals over time, as well as of HTLV-I isolates from various parts of the world. The viral DNA fragment studied encodes the carboxy terminus of gp46 and almost all of gp21, both of which are envelope glycoproteins. Samples were obtained from native inhabitants of five African countries, two South American countries, China, the French West Indies, and Haiti and included 14 patients with tropical spastic paraparesis/HTLV-I-associated myelopathy, 10 patients with adult T-cell leukemia, 1 patient with T-cell non-Hodgkin's lymphoma, and 3 healthy HTLV-I-seropositive individuals. DNA analyses of HTLV-I sequences demonstrated that (i) little or no genetic variation occurred in vivo in the same individual or in different hosts from the same region carrying the same virus, regardless of their clinical statuses; (ii) changes in nucleotide sequences in some regions of the HTLV-I genome were diagnostic of the geographical origin of the viruses; (iii) HTLV-I sequences from West African countries (Mauritania and Guinea Bissau) and some from the Ivory Coast and Central African Republic were virtually identical to those from the French West Indies, Haiti, French Guyana, and Peru, strongly suggesting that at least some HTLV-I strains were introduced into the New World through infected individuals during the slave trade events; and (iv) the Zairian HTLV-I isolates represent a separate HTLV-I cluster, in which intrastrain variability was also observed, and are more divergent from the other HTLV-I isolates. Because of the low genetic variability of HTLV-I in vivo, the study of the proviral DNA sequence in selected populations of infected individuals will increase our knowledge of the origin and evolution of HTLV-I and might be useful in anthropological studies.

Multiple isolates and characteristics of human T-cell leukemia virus type II

Human T-cell leukemia (or lymphotropic) virus type II (HTLV-II) was isolated from eight HTLV-seropositive patients, six of whom were also infected with human immunodeficiency virus, by cocultivation of peripheral blood mononuclear cells (PBMCs) with BJAB, a continuous B-cell line. Restriction endonuclease mapping of the proviruses demonstrated consistent differences among isolates, and two distinct physical map patterns were observed. The results suggest the existence of two closely related molecular subtypes of HTLV-II, which are tentatively designated HTLV-IIa and HTLV-IIb. This finding was supported by preliminary nucleotide sequence analysis of the env gene region encoding the transmembrane glycoprotein gp21, which showed consistent differences between the two proposed virus subtypes. Exploitation of differences in restriction endonuclease sites allowed polymerase chain reaction amplification to detect and differentiate the two subtypes in fresh PBMCs of HTLV-seropositive intravenous drug abusers (IVDAs). The results of these studies confirm that HTLV-II infection is the prominent HTLV infection in seropositive IVDAs and also show that infection with both subtypes occurs. The finding of genetic heterogeneity in the HTLV-II group of viruses may have important implications for studies on its role in human disease and will be useful in characterizing the viruses present in newly discovered endemic foci in New World indigenous populations.

Evolutionary insights on the origin of human T-cell lymphoma/leukemia virus type I (HTLV-I) derived from sequence analysis of a new HTLV-I variant from Papua New Guinea

Recent studies have established the presence of human T-cell lymphoma/leukemia virus type I (HTLV-I) in Melanesia. An HTLV-I strain, PNG-1, has now been isolated from a healthy member of the Hagahai, a remote, recently contacted group in Papua New Guinea. To further characterize PNG-1, we employed polymerase chain reaction amplification with subsequent cloning and sequencing of amplified products. Sequence analyses of amplified regions of pol, env, and pX genes of this variant indicate marked heterogeneity (approximately 7%) from prototype HTLV-I. Based on available sequence data, PNG-1 is distinct from all other known HTLV-I strains and diverges from the common ancestor of HTLV-I prior to prototype isolates. The data also suggest, therefore, that HTLV-I originated in the Indo-Malay region rather than Africa.

Geographical subtypes demonstrated by RFLP following PCR in the LTR region of HTLV-I

It has been demonstrated that specific mutations, localized in the long terminal repeat (LTR) region of HTLV-I, allowed to propose the existence of three HTLV-I subtypes. Because some of these mutations created or suppressed the restriction sites for ApaI, NdeI, DraI, SacI, MaeIII, and MaeII enzymes, these endonucleases were used for characterization of further 30 HTLV-I isolates. Seventeen proviral DNA from Japan, five from the Caribbean, one each from French Guyana, the United States, and China, two from Ivory Coast, and three from Zaire were tested. The DNA used were extracted from 26 in vivo peripheral blood mononuclear cell samples and from four cell lines obtained from two Japanese, one Chinese, and one North American patients. Digestions were performed on amplified DNA of the LTR region (nucleotides 31-768). The results confirm the existence of three subtypes of HTLV-I according to LTR sequences. Subtype I was observed only in patients from the Ivory Coast and Zaire. Subtype II was found in the patient from the French West Indies, and in 33% of the samples from Japan. Subtype III was most often observed in the Japanese but also in the Zairian patients.

Human T-cell leukemia virus type I envelope protein maturation process: requirements for syncytium formation

The human T-cell leukemia virus type I (HTLV-I) envelope protein is synthesized as a gp61 precursor product cleaved into two mature proteins, a gp45 exterior protein and a gp20 anchoring the envelope at the cell membrane. Using N-glycosylation inhibitors and site-directed mutagenesis of the potential glycosylation sites, we have studied the HTLV-I envelope intracellular maturation requirements for syncytium formation. We show here that experimental conditions resulting in the absence of precursor cleavage (tunicamycin, monensin treatments, and use of inhibitors of the reticulum steps of the N glycosylations) also result in no cell surface expression of envelope protein. The lack of syncytium formation observed in these cases is thus explained by incorrect intracellular transport. When the precursor is cleaved in the Golgi stack (no treatment or treatment with inhibitors of the Golgi steps of the N glycosylations), it is transported to the cell surface in all the cases examined. Syncytium formation is markedly reduced, however, when Golgi glycosylations are incorrect, which shows that the sugar moieties are involved in the envelope functions. Site-directed mutagenesis demonstrates that each of the five potential glycosylation sites is actually glycosylated. Glycosylation of sites 1 and 5 is required for normal maturation, whereas that of sites 2, 3, and 4 is dispensable. Glycosylation of each site, however, is required for normal syncytium formation. Altogether, the restraints exerted by the cell for the HTLV-I envelope to be transported and functional are very high, which might play a role in the observed conservation of the envelope amino acid sequence between various strains.

DNA sequence analysis of the gene encoding the HTLV-I p21e transmembrane protein reveals inter- and intraisolate genetic heterogeneity

DNA sequence analysis was performed on a 235-bp region of the p21 e transmembrane protein gene of the human T-cell lymphoma/leukemia virus type I (HTLV-I) which encompassess the putative immunosuppressive peptide. Polymerase chain reaction-based amplification was used to generate multiple molecular clones from isolates derived from fresh or cultured cells from 19 individuals. A dendrogram was constructed using the p21e DNA sequence information to compare the sequences among isolates in the current study and other previously published HTLV-I isolates including strains from Africa and Papua New Guinea. Examination of multiple clones from individual isolates revealed the presence of multiple genotypes in patients with tropical spastic paraparesis/HTLV-I-associated myelopathy and adult T-cell leukemia/lymphoma. These findings suggest that HTLV-I, like HIV, may be present as a quasispecies in vivo. Our studies, however, failed to identify specific sequence motifs that segregated exclusively with the lymphoproliferative or neurological forms of the disease.