Sex-specific mortality from adult T-cell leukemia among carriers of human T-lymphotropic virus type I

Cabotegravir, the Long-Acting Integrase Strand Transfer Inhibitor, Potently Inhibits Human T-Cell Lymphotropic Virus Type 1 Transmission in vitro

Human T-cell lymphotropic virus type 1 (HTLV-1) is a deltaretrovirus most prevalent in southwestern Japan, sub-Saharan Africa, Australia, South America, and the Caribbean. Latest figures approximate 10 million people worldwide to be infected with HTLV-1. This is likely a significant underestimation due to lack of screening in endemic areas and absence of seroconversion symptoms. The two primary diseases associated with HTLV-1 infection are adult T cell leukaemia-lymphoma, a malignant and, sometimes, aggressive cancer; and HTLV-1 associated myelopathy/tropical spastic paraparesis, a debilitating neurological degenerative disease. Unfortunately, despite the poor prognosis, there is currently no effective treatment for HTLV-1 infection. We previously showed that integrase strand transfer inhibitors (INSTIs) clinically used for human immunodeficiency virus type 1 (HIV-1) prophylaxis and treatment are also effective against HTLV-1 transmission in vitro. In 2021 a new INSTI, cabotegravir, was approved by the FDA for HIV-1 treatment. We thus set out to evaluate its efficacy against HTLV-1 infection in vitro. Strand transfer assays performed using recombinant HTLV-1 integrase treated with increasing concentrations of cabotegravir, effectively inhibited strand transfer activity, displaying an IC50 of 77.8 ± 22.4 nM. Furthermore, cabotegravir blocked HTLV-1 transmission in tissue culture; we determined an EC50 of 0.56 ± 0.26 nM, similar to bictegravir. Alu-PCR confirmed the block in integration. Thus, there are four INSTIs and one reverse transcriptase inhibitor approved by the FDA for HIV-1 treatment, that potently block HTLV-1 infection in vitro. This should strongly encourage the establishment of a new standard of HTLV-1 treatment - particularly for pre-exposure prophylaxis and prevention of mother-to-child transmission.

Sexual Dimorphism and Gender in Infectious Diseases

Epidemiological studies and clinical observations show evidence of sexual dimorphism in infectious diseases. Women are at less risk than men when it comes to developing most infectious diseases. However, understanding these observations requires a gender approach that takes into account an analysis of both biological and social factors. The host’s response to infection differs in males and females because sex differences have an impact on hormonal and chromosomal control of immunity. Estradiol appears to confer protective immunity, while progesterone and testosterone suppress anti-infectious responses. In addition, genetic factors, including those associated with sex chromosomes, also affect susceptibility to infections. Finally, differences in occupational activities, lifestyle, and comorbidities play major roles in exposure to pathogens and management of diseases. Hence, considering sexual dimorphism as a critical variable for infectious diseases should be one of the steps taken toward developing personalized therapeutic approaches.

Adult T-cell leukemia/lymphoma incidence rate in French Guiana: a prospective cohort of women infected with HTLV-1

Adult T-cell leukemia/lymphoma (ATL) is an aggressive malignancy caused by the human T-cell leukemia virus type 1 (HTLV-1). The incidence of ATL among HTLV-1 carriers remains largely unknown in endemic countries other than Japan as very few prospective studies have been performed. We assessed the ATL incidence rate among HTLV-1 infected women in a prospective cohort in French Guiana. This is the first prospective study to assess the ATL incidence rate in an area of South America where HTLV-1 prevalence is high. Patients were enrolled between 1991 and 2005, and follow-up continued until April 2018. In the general hospital in Saint-Laurent-du-Maroni, 307 pregnant women were diagnosed with HTLV-1 infection, and 268 of them were observed for a median of 16.7 years. During follow-up, 9 ATL incident cases occurred resulting in an ATL incidence rate of 2.03 per 1000 HTLV-1 carrier-years (95% confidence interval, 0.93-3.85 per 1000 HTLV-1 carrier-years). The median age at diagnosis was 47.4 years, and median survival from diagnosis was low at 3.5 months. The ATL incidence rate was elevated for a study population consisting mostly of young people, which could either be a general feature in South America or could be specific to the Noir Marron population that constituted most of the cohort.

Evolution of retrovirus-infected premalignant T-cell clones prior to adult T-cell leukemia/lymphoma diagnosis

Adult T-cell leukemia/lymphoma (ATL) is an aggressive hematological malignancy caused by human T-cell leukemia virus type-1 (HTLV-1). ATL is preceded by decades of chronic HTLV-1 infection, and the tumors carry both somatic mutations and proviral DNA integrated into the tumor genome. In order to gain insight into the oncogenic process, we used targeted sequencing to track the evolution of the malignant clone in 6 individuals, 2 to 10 years before the diagnosis of ATL. Clones of premalignant HTLV-1-infected cells bearing known driver mutations were detected in the blood up to 10 years before individuals developed acute and lymphoma subtype ATL. Six months before diagnosis, the total number and variant allele fraction of mutations increased in the blood. Peripheral blood mononuclear cells from premalignant cases (1 year prediagnosis) had significantly higher mutational burden in genes frequently mutated in ATL than did high-risk, age-matched HTLV-1 carriers who remained ATL-free after a median of 10 years of follow-up. These data show that HTLV-1-infected T-cell clones carrying key oncogenic driver mutations can be detected in cases of ATL years before the onset of symptoms. Early detection of such mutations may enable earlier and more effective intervention to prevent the development of ATL.

Mother-to-Child HTLV-1 Transmission: Unmet Research Needs

Mother-to-child transmission (MTCT) of Human T-cell lymphotropic virus type 1 (HTLV-1) causes lifelong infection. At least 5–10 million individuals worldwide are currently living with HTLV-1. Studies of regional variation are required to better understand the contribution of MTCT to the global burden of infection. Although most infected individuals remain asymptomatic ∼10% develop high morbidity, high mortality disease. Infection early in life is associated with a higher risk of disease development. Adult T-cell leukemia (ATL), which is caused by HTLV-1 and has a median survival of 8 months is linked to MTCT, indeed evidence of ATL following infection as an adult is sparse. Infective dermatitis also only occurs following neonatal infection. Whilst HTLV-1-associated myelopathy (HAM) follows sexual and iatrogenic infection approximately 30% of patients presenting with HAM/TSP acquired the infection through their mothers. HAM/TSP is a disabling neurodegenerative disease that greatly impact patient’s quality of life. To date there is no cure for HTLV-1 infection other than bone marrow transplantation for ATL nor any measure to prevent HTLV-1 associated diseases in an infected individual. In this context, prevention of MTCT is expected to contribute disproportionately to reducing both the incidence of HTLV-1 and the burden of HTLV-1 associated diseases. In order to successfully avoid HTLV-1 MTCT, it is important to understand all the variables involved in this route of infection. Questions remain regarding frequency and risk factors for in utero peri-partum transmission whilst little is known about the efficacy of pre-labor cesarean section to reduce these infections. Understanding the contribution of peripartum infection to the burden of disease will be important to gauge the risk-benefit of interventions in this area. Few studies have examined the impact of HTLV-1 infection on fertility or pregnancy outcomes nor the susceptibility of the mother to infection during pregnancy and lactation. Whilst breast-feeding is strongly associated with transmission and avoidance of breast-feeding a proven intervention little is known about the mechanism of transmission from the breast milk to the infant and there have been no clinical trials of antiretroviral therapy (ARV) to prevent this route of transmission.

The evolution of sex-specific virulence in infectious diseases

Fatality rates of infectious diseases are often higher in men than women. Although this difference is often attributed to a stronger immune response in women, we show that differences in the transmission routes that the sexes provide can result in evolution favouring pathogens with sex-specific virulence. Because women can transmit pathogens during pregnancy, birth or breast-feeding, pathogens adapt, evolving lower virulence in women. This can resolve the long-standing puzzle on progression from Human T-cell Lymphotropic Virus Type 1 (HTLV-1) infection to lethal Adult T-cell Leukaemia (ATL); a progression that is more likely in Japanese men than women, while it is equally likely in Caribbean women and men. We argue that breastfeeding, being more prolonged in Japan than in the Caribbean, may have driven the difference in virulence between the two populations. Our finding signifies the importance of investigating the differences in genetic expression profile of pathogens in males and females.

Many infectious diseases are more likely to progress to serious illness or death in men than in women, which has been attributed to a stronger immune response in women. Here, the authors propose that pathogen transmission from mother to child favours the evolution of lower virulence in women, and argue that the higher risk of HTLV-1 infection progressing to leukaemia in Japanese men is due to prolonged breastfeeding in Japan.

Role of the HTLV-1 viral factors in the induction of apoptosis

Adult T-cell leukemia (ATL) and HTLV-1-associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP) are the two main diseases that are caused by the HTLV-1 virus. One of the features of HTLV-1 infection is its resistance against programmed cell death, which maintains the survival of cells to oncogenic transformation and underlies the viruses' therapeutic resistance. Two main genes by which the virus develops cancer are Tax and HBZ; playing an essential role in angiogenesis in regulating viral transcription and modulating multiple host factors as well as apoptosis pathways. Here we have reviewed by prior research how the apoptosis pathways are suppressed by the Tax and HBZ and new drugs which have been designed to deal with this suppression.

Evaluation of the natural perinatal transmission of bovine leukaemia virus

The perinatal transmission of bovine leukaemia virus (BLV) plays a critical role in the spread and persistence of BLV infection in cattle herds. The purpose of this study was to examine the frequency of perinatal infections in an area in Japan and investigate some risk factors associated with infection. Altogether, 129 calves born to BLV-infected cows in a herd in Japan were tested for infection immediately after birth and again at one month of age using nested PCR. Twenty-four calves (18.6 per cent) were infected with BLV, of which 14 (10.8 per cent) and 10 (7.7 per cent) calves were infected via the transplacental and the birth canal routes, respectively. Maternal viral loads, breed, the presence or absence of assistance during parturition and the number of births per dam were evaluated to investigate risk factors associated with infection. Maternal viral load was significantly correlated with the frequency of perinatal infection, and more than 40 per cent of newborn calves born to dams with high viral loads were infected with BLV. The results of this study could contribute towards developing effective eradication programmes by providing necessary data for replacement of breeding cow in the field.

Expansion in CD39⁺ CD4⁺ immunoregulatory t cells and rarity of Th17 cells in HTLV-1 infected patients is associated with neurological complications

HTLV-1 infection is associated with several inflammatory disorders, including the neurodegenerative condition HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). It is unclear why a minority of infected subjects develops HAM/TSP. CD4⁺ T cells are the main target of infection and play a pivotal role in regulating immunity to HTLV and are hypothesized to participate in the pathogenesis of HAM/TSP. The CD39 ectonucleotidase receptor is expressed on CD4⁺ T cells and based on co-expression with CD25, marks T cells with distinct regulatory (CD39⁺CD25⁺) and effector (CD39⁺CD25⁻) function. Here, we investigated the expression of CD39 on CD4⁺ T cells from a cohort of HAM/TSP patients, HTLV-1 asymptomatic carriers (AC), and matched uninfected controls. The frequency of CD39⁺ CD4⁺ T cells was increased in HTLV-1 infected patients, regardless of clinical status. More importantly, the proportion of the immunostimulatory CD39⁺CD25⁻ CD4⁺ T-cell subset was significantly elevated in HAM/TSP patients as compared to AC and phenotypically had lower levels of the immunoinhibitory receptor, PD-1. We saw no difference in the frequency of CD39⁺CD25⁺ regulatory (Treg) cells between AC and HAM/TSP patients. However, these cells transition from being anergic to displaying a polyfunctional cytokine response following HTLV-1 infection. CD39⁻CD25⁺ T cell subsets predominantly secreted the inflammatory cytokine IL-17. We found that HAM/TSP patients had significantly fewer numbers of IL-17 secreting CD4⁺ T cells compared to uninfected controls. Taken together, we show that the expression of CD39 is upregulated on CD4⁺ T cells HAM/TSP patients. This upregulation may play a role in the development of the proinflammatory milieu through pathways both distinct and separate among the different CD39 T cell subsets. CD39 upregulation may therefore serve as a surrogate diagnostic marker of progression and could potentially be a target for interventions to reduce the development of HAM/TSP.

Transplantation of allogeneic hematopoietic stem cells for adult T-cell leukemia: a nationwide retrospective study

Allogeneic hematopoietic stem cell transplantation (HSCT) is increasingly used as a curative option for adult T-cell leukemia (ATL), an intractable mature T-cell neoplasm causally linked with human T-cell leukemia virus type I (HTLV-I). We compared outcomes of 386 patients with ATL who underwent allogeneic HSCT using different graft sources: 154 received human leukocyte antigen (HLA)–matched related marrow or peripheral blood; 43 received HLA-mismatched related marrow or peripheral blood; 99 received unrelated marrow; 90 received single unit unrelated cord blood. After a median follow-up of 41 months (range, 1.5-102), 3-year overall survival for entire cohort was 33% (95% confidence interval, 28%-38%). Multivariable analysis revealed 4 recipient factors significantly associated with lower survival rates: older age (> 50 years), male sex, status other than complete remission, and use of unrelated cord blood compared with use of HLA-matched related grafts. Treatment-related mortality rate was higher among patients given cord blood transplants; disease-associated mortality was higher among male recipients or those given transplants not in remission. Among patients who received related transplants, donor HTLV-I seropositivity adversely affected disease-associated mortality. In conclusion, allogeneic HSCT using currently available graft source is an effective treatment in selected patients with ATL, although greater effort is warranted to reduce treatment-related mortality.

Age and gender specific prevalence of HTLV-1

BACKGROUND

The seroprevalence of Human T-cell Leukemia Virus Type 1 (HTLV-1) is female predominant despite the higher incidence of Adult T-cell Leukemia (ATL) in males. If the mother-to-child transmission of HTLV-1 is more common for male infants than in female infants, longer exposure to the virus for males may explain the paradoxically higher incidence of ATL.

OBJECTIVES

To test the hypothesis that the seroprevalence of HTLV-1 is male predominant during adolescence.

STUDY DESIGN

The presence of HTLV-1 antibody in 272,043 blood samples donated to a regional blood bank in an HTLV-1 high-endemic region was assessed.

RESULTS

The entire population of female donors had a significantly higher seroprevalence compared to males (2.05% and 1.80%, respectively, p<0.0001). However, compared with male donors, the carrier rate for female donors was lower for the youngest subgroup (16-19 years, p=0.0011); was similar for the next two age subgroups (20-29 years and 30-39 years); and was significantly higher for the last two age subgroups (40-49 years and over 50-64 years, both p<0.0001). In general, older age subgroups led to higher seroprevalence in both genders.

CONCLUSIONS

HTLV-1 infection is more common for males until after age 20, when male to female sexual transmission becomes likely. This suggests that mother-to-child transmission is more common for males.

Impaired Tax-specific T-cell responses with insufficient control of HTLV-1 in a subgroup of individuals at asymptomatic and smoldering stages

Human T-cell leukemia virus type-1 (HTLV-1)-specific T-cell immunity, a potential antitumor surveillance system in vivo, is impaired in adult T-cell leukemia (ATL). In this study, we aimed to clarify whether the T-cell insufficiency in ATL is present before the disease onset or occurs as a consequence of the disease. We investigated T-cell responses against Tax protein in peripheral blood mononuclear cells (PBMCs) from individuals at earlier stages of HTLV-1-infection, including 21 asymptomatic HTLV-1 carriers (ACs) and four patients with smoldering-type ATL (sATL), whose peripheral lymphocyte count was in normal range. About 30% of samples tested showed clear Tax-specific interferon (IFN)-gamma producing responses. Proviral loads in this group were significantly lower than those in the other less-specific response group. The latter group was further divided to two subgroups with or without emergence of Tax-specific responses following depletion of CC chemokine receptor 4 (CCR4)(+) cells that contained HTLV-1-infected cells. In the PBMCs with Tax-specific responses, CD8(+) cells efficiently suppressed HTLV-1 p19 production in culture. The remaining group without the emergence of Tax-specific response after CCR4(+) cell-depletion included at least two sATL and one AC samples, which spontaneously produced HTLV-1 p19 in culture, where tetramer-binding, Tax-specific cytotoxic T-lymphocytes were either undetectable or unresponsive. Our results indicated that HTLV-1-specific T-cell responsiveness widely differed among HTLV-1 carriers, and that impairment of HTLV-1-specific T-cell responses was observed not only in advanced ATL patients but also in a subpopulation at earlier stages, which was associated with insufficient control of HTLV-1.

Hematologic and biochemical changes associated with human T lymphotropic virus type 1 infection in Jamaica: a report from the population-based blood donors study

OBJECTIVE

We investigated changes in hematologic and biochemical parameters associated with human T lymphotropic virus type 1 (HTLV-1) infection, antibody titer, and provirus load. Additionally, on a subset of participants, we assessed the epidemiologic relationship of HTLV-1 with Strongyloides stercoralis.

METHODS

Among volunteer blood donors in Jamaica, HTLV-1 carriers (n=482) were frequency matched with HTLV-1 negative subjects (n=355) by age (+/-5 years), sex, and date of blood donation (+/-3 months). HTLV-1 antibody titer, provirus load, S. stercoralis IgG antibodies, complete blood cell count, blood chemistry, and urinalysis parameters were measured.

RESULTS

HTLV-1 carriers, compared with HTLV-1-negative individuals, had elevated levels of cleaved lymphocytes (24.5% vs. 16.4%), any lymphocyte abnormalities (atypical, cleaved, and reactive lymphocytes combined, 45.7% vs. 35.4%), and gamma-glutamyl transferase levels (21.2 vs. 19.6 IU/L), as well as lower eosinophil count (2.6% vs. 3.1%). Among carriers, HTLV-1 antibody titer (n=482) was inversely correlated with mean corpuscular volume (r=-0.10) and positively correlated with levels of total protein (r=0.16), phosphorus (r=0.12), and lactate dehydrogenase (r=0.24). HTLV-1-provirus load (n=326) was higher among carriers with cleaved lymphocytes and any lymphocyte abnormalities. Provirus load was inversely correlated with hemoglobin (r=-0.11), mean corpuscular volume (r=-0.15), neutrophil (r=-0.12), and eosinophil (r=-0.19) levels and was positively correlated with lactate dehydrogenase levels (r=0.12). Provirus load was significantly higher among male than female subjects. S. stercoralis antibodies were detected in 35 (12.1%) of 288 participants but were not associated with HTLV-1 status, antibody titer, or provirus load.

CONCLUSIONS

Markers of HTLV-1 infection (infection status, antibody titer, and provirus load) are associated with hematologic and biochemical alterations, such as lymphocyte abnormalities, anemia, decreased eosinophils, and elevated lactate dehydrogenase levels.

Anti-HTLV-1 tax antibody and tax-specific cytotoxic T lymphocyte are associated with a reduction in HTLV-1 proviral load in asymptomatic carriers

Previous studies have suggested that higher anti-human T-lymphotropic virus 1 (HTLV-1) antibody titer and lower anti-HTLV-1 Tax antibody reactivity are risk factors for adult T-cell leukemia/lymphoma. In the present study, we analyzed the relationships between these factors and clarified their significance. Forty-five carriers were examined for anti-HTLV-1 and anti-Tax antibody by ELISA. In addition, 43 of the 45 carriers with HLA-A*0201 and/or A*2402 were examined for frequency of Tax-specific cytotoxic T lymphocytes (CTLs) using HTLV-1/HLA tetramers, and 44 were examined for proviral load by real-time PCR. The relationships between these factors were analyzed statistically. The frequencies of Tax11-19 and Tax301-309-specific CTLs were significantly higher in the anti-Tax antibody-positive group as compared with the antibody-negative group (P = 0.002 and 0.033, respectively). Anti-HTLV-1 antibody titer had a positive correlation with proviral load (P = 0.019), whereas anti-Tax antibody did not show a significant correlation. Higher frequencies of both Tax11-19 and Tax301-309-specific CTLs are related to a reduction in proviral load (P = 0.017 and 0.015, respectively). Synergistic interactions of humoral and cellular immunity against Tax protein were demonstrated in HTLV-1 carriers. Tax-specific CTL may reduce HTLV-1 proviral load to prevent asymptomatic carriers from developing adult T-cell leukemia/lymphoma.

Antibody to the central region of human T-lymphotropic virus type 1 gp46 is associated with the progression of adult T-cell leukemia

Human T-cell lymphotropic virus type 1 (HTLV-1) is an etiologic agent of adult T-cell leukemia/lymphoma (ATL). HTLV-1 is spread by cell-to-cell transmission via the gp46-197 region, Asp197 to Leu216, on the envelope protein gp46. In the present study, we revealed a positive correlation between the appearance of an antibody recognizing the gp46-197 region (anti-gp46-197 antibody) and the severity of ATL. The prevalence and titer of the anti-gp46-197 antibody were found to be elevated along with the progression of ATL. In serial samples obtained from a single patient, the anti-gp46-197 antibody was detected before treatment in acute phase, then diminished after allogeneic bone marrow transplantation, to which the patient had a complete response. However, the antibody appeared again before a relapse, along with an increase of the serum-soluble interleukin-2 receptor level and proviral load. The results from the other six patients also indicate that seroconversion of this antibody was synchronized with the deterioration of ATL. Taken together, the findings indicate that the anti-gp46-197 antibody may be a novel beacon for gauging the efficacy of therapeutic approaches to ATL, and a survey of this antibody would be useful for identifying asymptomatic carriers infected with HTLV-1 who are at high risk of developing ATL.

Reduction of human T-cell leukemia virus type 1 (HTLV-1) proviral loads in rats orally infected with HTLV-1 by reimmunization with HTLV-1-infected cells

Human T-cell leukemia virus type 1 (HTLV-1) persistently infects humans, and the proviral loads that persist in vivo vary widely among individuals. Elevation in the proviral load is associated with serious HTLV-1-mediated diseases, such as adult T-cell leukemia and HTLV-1-associated myelopathy/tropical spastic paraparesis. However, it remains controversial whether HTLV-1-specific T-cell immunity can control HTLV-1 in vivo. We previously reported that orally HTLV-1-infected rats showed insufficient HTLV-1-specific T-cell immunity that coincided with elevated levels of the HTLV-1 proviral load. In the present study, we found that individual HTLV-1 proviral loads established in low-responding hosts could be reduced by the restoration of HTLV-1-specific T-cell responses. Despite the T-cell unresponsiveness for HTLV-1 in orally infected rats, an allogeneic mixed lymphocyte reaction in the splenocytes and a contact hypersensitivity response in the skin of these rats were comparable with those of naive rats. HTLV-1-specific T-cell response in orally HTLV-1-infected rats could be restored by subcutaneous reimmunization with mitomycin C (MMC)-treated syngeneic HTLV-1-transformed cells. The reimmunized rats exhibited lower proviral loads than untreated orally infected rats. We also confirmed that the proviral loads in orally infected rats decreased after reimmunization in the same hosts. Similar T-cell immune conversion could be reproduced in orally HTLV-1-infected rats by subcutaneous inoculation with MMC-treated primary T cells from syngeneic orally HTLV-1-infected rats. The present results indicate that, although HTLV-1-specific T-cell unresponsiveness is an underlying risk factor for the propagation of HTLV-1-infected cells in vivo, the risk may potentially be reduced by reimmunization, for which autologous HTLV-1-infected cells are a candidate immunogen.

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.

[Anti-tumor immunity in adult T-cell leukemia]

Adult T-cell leukemia (ATL) occurs in a small population of human T-cell leukemia virus type I (HTLV-I)-infected individuals. It has been noted that ATL is incidentally associated with mother-to-child infection which occurs mainly through breast-feeding, elevated levels of proviral load, and insufficiency in HTLV-I-specific cytotoxic T lymphocyte (CTL) responses. Among these, anti-tumor potentials of HTLV-I-specific CTL have been shown in ex vivo analysis of human HTLV-I-infected individuals and also in vivo experiments by using rat models of HTLV-I-infected lymphomas. In another rat model of HTLV-I-infection, orally infected rats showed significantly higher HTLV-I proviral load but lower HTLV-I-specific cellular immune responses than in intraperitoneally infected rats. As a result, persistent viral load was inversely correlated with levels of virus-specific T-cell responses. HTLV-I-specific T-cell responses in orally infected rats recovered by re-immunization. Conversion of Tax-specific T-cell responses from low to high levels was also observed in an ATL patient who obtained complete remission after hematopoietic stem cell transplantation. These findings suggest that HTLV-I-specific immune unresponsiveness associated with oral HTLV-I infection may be a potential risk factor for development of ATL, allowing expansion of the infected cell reservoir in vivo, and that immunological strategies targeting Tax may potentially reduce the risk of ATL and induce therapeutic effects on ATL.

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.

Cutaneous type of adult T cell leukemia/lymphoma: a new entity among cutaneous lymphomas

Adult T cell leukemia/lymphoma (ATL) is a malignancy of CD4+ T cells that is endemic in certain areas in Japan. Two types of cutaneous ATL thought to originate from skin include cutaneous tumor and erythematopapule types. Patients with cutaneous ATL show neither leukemic involvement nor invasion of tumor cells into the lymph nodes for at least six months. The differential diagnosis between cutaneous ATL and mycosis fungoides is often difficult. The presence of monoclonal integration of human T lymphotropic virus-I proviral DNA in skin samples is of definitive diagnostic value in cutaneous ATL.

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.

Estradiol represses human T-cell leukemia virus type 1 Tax activation of tumor necrosis factor-alpha gene transcription

Adult T-cell leukemia is caused by human T-cell leukemia virus type I (HTLV-I). The HTLV-I Tax protein is essential for clinical manifestations because it activates viral and cellular gene transcription. Tax enhances production of tumor necrosis factor-alpha (TNF-alpha), which may lead to bone and joint destruction. Because estrogens might prevent osteoporosis by repressing TNF-alpha gene transcription, we investigated whether estrogens inhibit the transcriptional effects of Tax on the TNF-alpha promoter. Tax activated the -1044, -163, and -125 TNF-alpha promoters by 9-25-fold but not the -82 promoter, demonstrating that Tax activation requires the -125 to -82 region, known as the TNF response element (TNF-RE). Three copies of the TNF-RE upstream of the minimal thymidine kinase promoter conferred a similar magnitude of activation by Tax. We demonstrated that c-Jun, NFkappaB, p50, and p65 interact with and activate the TNF-RE by using mutational analysis of the TNF-RE, Tax mutants that selectively activate NFkappaB or the cAMP-response element binding protein/activating transcription factor pathway, and gel shift assays with nuclear extracts. Estradiol markedly repressed Tax-activated transcription of the TNF-alpha gene with estrogen receptor (ER) alpha or beta. Nuclear extracts from U2OS cells stably transfected with ER(alpha) demonstrated that ERs interact with the TNF-RE. Our studies provide evidence that ERs repress Tax-activated TNF-alpha transcription by interacting with a c-Jun and NFkappaB platform on the TNF-RE. Estrogens may ameliorate bone and inflammatory joint diseases in patients infected with HTLV-I by repressing transcription of the TNF-alpha gene.