Distinct gene expression signatures induced by viral transactivators of different HTLV-1 subgroups that confer a different risk of HAM/TSP

Diversity of Human T-Lymphotropic Virus Type 1 Cosmopolitan Subtype (HTLV-1a) Circulating in Infected Residents in Portugal

Human T-cell lymphotropic virus type 1 (HTLV-1) prevalence in Portugal is low and mainly affects immigrants from endemic areas where human immunodeficiency virus (HIV) infection represents a public health problem. Despite the majority of HTLV-1-infected individuals remains asymptomatic, severe pathologies may develop after prolonged viral persistence, namely an aggressive form of leukemia. An increased mortality rate and faster progression to death is often related to HTLV-1/HIV coinfection. Nevertheless, studies showed that some antiretrovirals used in HIV treatment lead to a positive immune response against HTLV-1. This study aimed to analyze epidemiological and clinical data, and to assess the diversity of HTLV-1 strains circulating in infected residents diagnosed in the Portuguese national reference laboratory between 2010 and 2021. Long terminal repeat and env proviral sequences derived from 20 individuals were used to generate phylogenetic trees along with multiples reference sequences from different geographic origins retrieved from the database. Three samples belong to Portuguese natives and 17 belong to immigrants: 15 from several countries of Africa, 1 from South America, and 1 from Europe; 6 patients (30%, mean age 40.3 years) showed HTLV-1-related diseases, and 6 (30%, mean age 45.2 years) were coinfected with HIV/AIDS. The results show that the Cosmopolitan subtype is circulating in Portugal, with 10 sequences being classified as subgroup A, that include Portuguese and natives from S. Tomé and Príncipe with a mean age of 39.4 years, and 10 sequences that segregated into the Senegal cluster derived from natives born in Guinea-Bissau with a mean age of 43.5 years. A high proportion of HTLV-1-related diseases and HIV/AIDS coinfection was observed. Risk behavior practices and the absence of specific control measures, including diagnostic and treatment, may contribute to a silent dissemination of a broad diversity of HTLV-1 strains and, therefore, the increased rate of progression to debilitating diseases. In this manner, an early diagnostic and a molecular surveillance of HTLV-1 transmission remains necessary in Portugal.

Geographic characteristics of HTLV-1 molecular subgroups and genetic substitutions in East Asia: Insights from complete genome sequencing of HTLV-1 strains isolated in Taiwan and Japan

BACKGROUND

Although Japan is a major endemic area for human T-lymphotropic virus type 1 (HTLV-1) and the virus has been well-studied in this region, there is limited research on HTLV-1 in surrounding regions. In this study, we determined the complete genome sequences of HTLV-1 strains isolated from Taiwan and Japan and investigated the geographic characteristics of molecular subgroups and substitution mutations to understand the spread of HTLV-1 and its correlation with human migration.

METHODOLOGY/PRINCIPAL FINDINGS

The complete genome sequences of 26 HTLV-1 isolates from Taiwan were determined using next-generation sequencing and were compared with those of 211 isolates from Japan in terms of subgroup and genetic mutations. In total, 15/26 (58%) isolates from Taiwan belonged to the transcontinental subgroup and 11/26 (42%) isolates belonged to the Japanese subgroup. The transcontinental subgroup was significantly more prevalent among Taiwanese isolates than Japanese isolates (58% vs 18%, P < 0.0001). The mutation rate for the complete HTLV-1 sequence was as low as 0.2%. On examining individual base substitutions, the G-to-A mutation was predominant. Bayesian phylogenetic tree analysis estimated the time to the most recent common ancestor for the transcontinental and Japanese subgroups to be 28447 years. The transcontinental subgroups from Taiwan and Japan appeared to form clusters according to their respective regions.

CONCLUSIONS/SIGNIFICANCE

The transcontinental subgroup of HTLV-1 is predominant in Taiwan, while the Japanese subgroup is common in Japan. The difference in subgroup distribution may be attributed to the initial spread of the transcontinental subgroup in East Asia, followed by the influx of the Japanese subgroup.

Gene expression study of host-human T-cell leukaemia virus type 1 (HTLV-1) interactions: adult T-cell leukaemia/lymphoma (ATLL)

BACKGROUND

In HTLV-1-associated malignant disease, adult T-cell leukaemia/lymphoma (ATLL), the interaction of virus and host was evaluated at the chemokines gene expression level. Also, IL-1β and Caspase-1 expressions were evaluated to investigate the importance of pyroptosis in disease development and progression.

METHODS AND RESULTS

The expression of host CCR6 and CXCR-3 and the HTLV-1 proviral load (PVL), Tax, and HBZ were assessed in 17 HTLV-1 asymptomatic carriers (ACs) and 12 ATLL patients using the reverse transcription-quantitative polymerase chain reaction (RT-qPCR), TaqMan method. Moreover, RT-qPCR, SYBR Green assay were performed to measure Caspase-1 and IL-1β expression. HTLV-1-Tax did not express in 91.5% of the ATLLs, while HBZ was expressed in all ATLLs. The expression of CXCR3 dramatically decreased in ATLLs compared to ACs (p = 0.001). The expression of CCR6 was lower in ATLLs than ACs (p = 0.04). The mean of PVL in ATLL patients was statistically higher than ACs (p = 0.001). Furthermore, the expression of the IL-1β between ATLLs and ACs was not statistically significant (p = 0.4). In contrast, there was a meaningful difference between Caspase-1 in ATLLs and ACs (p = 0.02).

CONCLUSIONS

The present study indicated that in the first stage of ATLL malignancy toward acute lymphomatous, CXCR3 and its progression phase may target the pyroptosis process. Mainly, HBZ expression could be a novel therapeutic target.

HTLV-1 Infection and Pathogenesis: New Insights from Cellular and Animal Models

Since the discovery of the human T-cell leukemia virus-1 (HTLV-1), cellular and animal models have provided invaluable contributions in the knowledge of viral infection, transmission and progression of HTLV-associated diseases. HTLV-1 is the causative agent of the aggressive adult T-cell leukemia/lymphoma and inflammatory diseases such as the HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP). Cell models contribute to defining the role of HTLV proteins, as well as the mechanisms of cell-to-cell transmission of the virus. Otherwise, selected and engineered animal models are currently applied to recapitulate in vivo the HTLV-1 associated pathogenesis and to verify the effectiveness of viral therapy and host immune response. Here we review the current cell models for studying virus–host interaction, cellular restriction factors and cell pathway deregulation mediated by HTLV products. We recapitulate the most effective animal models applied to investigate the pathogenesis of HTLV-1-associated diseases such as transgenic and humanized mice, rabbit and monkey models. Finally, we summarize the studies on STLV and BLV, two closely related HTLV-1 viruses in animals. The most recent anticancer and HAM/TSP therapies are also discussed in view of the most reliable experimental models that may accelerate the translation from the experimental findings to effective therapies in infected patients.

Extracellular vesicles from HTLV-1 infected cells modulate target cells and viral spread

BACKGROUND

The Human T-cell Lymphotropic Virus Type-1 (HTLV-1) is a blood-borne pathogen and etiological agent of Adult T-cell Leukemia/Lymphoma (ATLL) and HTLV-1 Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP). HTLV-1 has currently infected up to 10 million globally with highly endemic areas in Japan, Africa, the Caribbean and South America. We have previously shown that Extracellular Vesicles (EVs) enhance HTLV-1 transmission by promoting cell-cell contact.

RESULTS

Here, we separated EVs into subpopulations using differential ultracentrifugation (DUC) at speeds of 2 k (2000×g), 10 k (10,000×g), and 100 k (100,000×g) from infected cell supernatants. Proteomic analysis revealed that EVs contain the highest viral/host protein abundance in the 2 k subpopulation (2 k > 10 k > 100 k). The 2 k and 10 k populations contained viral proteins (i.e., p19 and Tax), and autophagy proteins (i.e., LC3 and p62) suggesting presence of autophagosomes as well as core histones. Interestingly, the use of 2 k EVs in an angiogenesis assay (mesenchymal stem cells + endothelial cells) caused deterioration of vascular-like-tubules. Cells commonly associated with the neurovascular unit (i.e., astrocytes, neurons, and macrophages) in the blood-brain barrier (BBB) showed that HTLV-1 EVs may induce expression of cytokines involved in migration (i.e., IL-8; 100 k > 2 k > 10 k) from astrocytes and monocyte-derived macrophages (i.e., IL-8; 2 k > 10 k). Finally, we found that EVs were able to promote cell-cell contact and viral transmission in monocytic cell-derived dendritic cell. The EVs from both 2 k and 10 k increased HTLV-1 spread in a humanized mouse model, as evidenced by an increase in proviral DNA and RNA in the Blood, Lymph Node, and Spleen.

CONCLUSIONS

Altogether, these data suggest that various EV subpopulations induce cytokine expression, tissue damage, and viral spread.

Genetic profile of adult T-cell leukemia/lymphoma in Okinawa: Association with prognosis, ethnicity, and HTLV-1 strains

Genetic alterations in adult T‐cell leukemia/lymphoma (ATLL), a T‐cell malignancy associated with HTLV‐1, and their clinical impacts, especially from the perspective of viral strains, are not fully elucidated. We employed targeted next‐generation sequencing and single nucleotide polymorphism array for 89 patients with ATLL in Okinawa, the southernmost islands in Japan, where the frequency of HTLV‐1 tax subgroup‐A (HTLV‐1‐taxA) is notably higher than that in mainland Japan, where most ATLL cases have HTLV‐1‐taxB, and compared the results with previously reported genomic landscapes of ATLL in mainland Japan and the USA. Okinawan patients exhibited similar mutation profiles to mainland Japanese patients, with frequent alterations in TCR/NF‐ĸB (eg, PRKCB, PLCG1, and CARD11) and T‐cell trafficking pathways (CCR4 and CCR7), in contrast with North American patients who exhibited a predominance of epigenome‐associated gene mutations. Some mutations, especially GATA3 and RHOA, were detected more frequently in Okinawan patients than in mainland Japanese patients. Compared to HTLV‐1‐taxB, HTLV‐1‐taxA was significantly dominant in Okinawan patients with these mutations (GATA3, 34.1% vs 14.6%, P = .044; RHOA, 24.4% vs 6.3%, P = .032), suggesting the contribution of viral strains to these mutation frequencies. From a clinical viewpoint, we identified a significant negative impact of biallelic inactivation of PRDM1 (P = .027) in addition to the previously reported PRKCB mutations, indicating the importance of integrated genetic analysis. This study suggests that heterogeneous genetic abnormalities in ATLL depend on the viral strain as well as on the ethnic background. This warrants the need to develop therapeutic interventions considering regional characteristics.

Extracellular Vesicles in HTLV-1 Communication: The Story of an Invisible Messenger

Human T-cell lymphotropic virus type 1 (HTLV-1) infects 5-10 million people worldwide and is the causative agent of adult T-cell leukemia/lymphoma (ATLL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) as well as other inflammatory diseases. A major concern is that the most majority of individuals with HTLV-1 are asymptomatic carriers and that there is limited global attention by health care officials, setting up potential conditions for increased viral spread. HTLV-1 transmission occurs primarily through sexual intercourse, blood transfusion, intravenous drug usage, and breast feeding. Currently, there is no cure for HTLV-1 infection and only limited treatment options exist, such as class I interferons (IFN) and Zidovudine (AZT), with poor prognosis. Recently, small membrane-bound structures, known as extracellular vesicles (EVs), have received increased attention due to their potential to carry viral cargo (RNA and proteins) in multiple pathogenic infections (i.e., human immunodeficiency virus type I (HIV-1), Zika virus, and HTLV-1). In the case of HTLV-1, EVs isolated from the peripheral blood and cerebral spinal fluid (CSF) of HAM/TSP patients contained the viral transactivator protein Tax. Additionally, EVs derived from HTLV-1-infected cells (HTLV-1 EVs) promote functional effects such as cell aggregation which enhance viral spread. In this review, we present current knowledge surrounding EVs and their potential role as immune-modulating agents in cancer and other infectious diseases such as HTLV-1 and HIV-1. We discuss various features of EVs that make them prime targets for possible vehicles of future diagnostics and therapies.

Human T-lymphotropic virus type 1 (HTLV-1) and cellular immune response in HTLV-1-associated myelopathy/tropical spastic paraparesis

Human T-lymphotropic virus type 1 (HTLV-1) is associated with adult T cell leukemia/lymphoma and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). HAM/TSP is an inflammatory disease of the spinal cord and clinically characterized by progressive spastic paraparesis, urinary incontinence, and mild sensory disturbance. The interaction between the host immune response and HTLV-1-infected cells regulates the development of HAM/TSP. HTLV-1 preferentially infects CD4⁺ T cells and is maintained by proliferation of the infected T cells. HTLV-1-infected cells rarely express viral antigens in vivo; however, they easily express the antigens after short-term culture. Therefore, such virus-expressing cells may lead to activation and expansion of antigen-specific T cell responses. Infected T cells with HTLV-1 and HTLV-1-specific CD8⁺ cytotoxic T lymphocytes invade the central nervous system and produce various proinflammatory cytokines and chemokines, leading to neuronal damage and degeneration. Therefore, cellular immune responses to HTLV-1 have been considered to play important roles in disease development of HAM/TSP. Recent studies have clarified the viral strategy for persistence in the host through genetic and epigenetic changes by HTLV-1 and host immune responses including T cell function and differentiation. Newly developed animal models could provide the opportunity to uncover the precise pathogenesis and development of clinically effective treatment. Several molecular target drugs are undergoing clinical trials with promising efficacy. In this review, we summarize recent advances in the immunopathogenesis of HAM/TSP and discuss the perspectives of the research on this disease.

The Role of Chemokines in the Pathogenesis of HTLV-1

Human T cell leukemia virus type 1 (HTLV-1) is a human retrovirus that is associated with two main diseases: HTLV-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and adult T cell leukemia/lymphoma (ATL). Chemokines are highly specialized groups of cytokines that play important roles in organizing, trafficking, homing, and in the migration of immune cells to the bone marrow, lymphoid organs and sites of infection and inflammation. Aberrant expression or function of chemokines, or their receptors, has been linked to the protection against or susceptibility to specific infectious diseases, as well as increased the risk of autoimmune diseases and malignancy. Chemokines and their receptors participate in pathogenesis of HTLV-1 associated diseases from inflammation in the central nervous system (CNS) which occurs in cases of HAM/TSP to T cell immortalization and tissue infiltration observed in ATL patients. Chemokines represent viable effective prognostic biomarkers for HTLV-1-associated diseases which provide the early identification of high-risk, treatment possibilities and high-yielding clinical trials. This review focuses on the emerging roles of these molecules in the outcome of HTLV-1-associated diseases.

EOS, an Ikaros family zinc finger transcription factor, interacts with the HTLV-1 oncoprotein Tax and is downregulated in peripheral blood mononuclear cells of HTLV-1-infected individuals, irrespective of clinical statuses

BACKGROUND

EOS plays an important role in maintaining the suppressive function of regulatory T cells (Tregs), and induces a regulated transformation of Tregs into T helper-like cells, which are capable of secreting proinflammatory cytokines in response to specific inflammatory signals. Meanwhile, significant reduction in Treg activity along with production of proinflammatory cytokines has been reported in patients with HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP).

METHODS

In this study, to examine whether there is an alteration in EOS expression in peripheral blood mononuclear cells (PBMCs) derived from HTLV-1-infected individuals especially HAM/TSP, we investigated the expression of HTLV-1 tax genotype, proviral load (PVL), and the mRNA expression of tax, HBZ and EOS in HTLV-1 infected individuals including adult T-cell leukemia/lymphoma (ATL), HAM/TSP, or asymptomatic carriers. The expression levels of EOS mRNA and protein in various HTLV-1-infected or uninfected human T-cell lines were also investigated.

RESULTS

EOS was highly expressed at the protein level in most HTLV-1 infected T-cell lines, and was augmented after the HTLV-1 regulatory factor Tax was induced in a Tax-inducible JPX-9 cell line. Immunoprecipitation experiments demonstrated a physical interaction between EOS and the viral regulatory protein Tax, but not HBZ. Meanwhile, there was a significant decrease in EOS mRNA levels in PBMCs of HTLV-1 infected individuals irrespective of their clinical statuses. We found an inverse correlation between EOS mRNA levels and HTLV-1 PVL in ATL patients, and positive correlations between both EOS mRNA load and PVL, and EOS and HBZ mRNA load in HAM/TSP patients, whereas this correlation was not observed in other clinical statuses.

CONCLUSIONS

These findings suggest that both Tax and HBZ can alter the expression of EOS through undetermined mechanisms, and dysregulated expression of EOS in PBMCs of HTLV-1 infected individuals may contribute to the pathological progression of HTLV-1-associated diseases, such as ATL and HAM/TSP.

HTLV-1 Extracellular Vesicles Promote Cell-to-Cell Contact

Human T-cell leukemia virus-1 (HTLV-1) is a neglected and incurable retrovirus estimated to infect 5 to 10 million worldwide. Specific indigenous Australian populations report infection rates of more than 40%, suggesting a potential evolution of the virus with global implications. HTLV-1 causes adult T-cell leukemia/lymphoma (ATLL), and a neurological disease named HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP). Even though HTLV-1 transmission primarily occurs from cell-to-cell, there is still a gap of knowledge regarding the mechanisms of viral spread and disease progression. We have recently shown that Extracellular Vesicles (EVs) ubiquitously produced by cells may be used by HTLV-1 to transport viral proteins and RNA, and elicit adverse effects on recipient uninfected cells. The viral proteins Tax and HBZ are involved in disease progression and impairment of autophagy in infected cells. Here, we show that activation of HTLV-1 via ionizing radiation (IR) causes a significant increase of intracellular Tax, but not EV-associated Tax. Also, lower density EVs from HTLV-1-infected cells, separated by an Iodixanol density gradient, are positive for gp61+++/Tax+++/HBZ+ proteins (HTLV-1 EVs). We found that HTLV-1 EVs are not infectious when tested in multiple cell lines. However, these EVs promote cell-to-cell contact of uninfected cells, a phenotype which was enhanced with IR, potentially promoting viral spread. We treated humanized NOG mice with HTLV-1 EVs prior to infection and observed an increase in viral RNA synthesis in mice compared to control (EVs from uninfected cells). Proviral DNA levels were also quantified in blood, lung, spleen, liver, and brain post-treatment with HTLV-1 EVs, and we observed a consistent increase in viral DNA levels across all tissues, especially the brain. Finally, we show direct implications of EVs in viral spread and disease progression and suggest a two-step model of infection including the release of EVs from donor cells and recruitment of recipient cells as well as an increase in recipient cell-to-cell contact promoting viral spread.

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.

Neuroimmunology of Human T-Lymphotropic Virus Type 1-Associated Myelopathy/Tropical Spastic Paraparesis

Human T-lymphotropic virus type 1 (HTLV-1) is the etiologic agent of both adult T-cell leukemia/lymphoma and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). HAM/TSP is clinically characterized by chronic progressive spastic paraparesis, urinary incontinence, and mild sensory disturbance. Given its well-characterized clinical presentation and pathophysiology, which is similar to the progressive forms of multiple sclerosis (MS), HAM/TSP is an ideal system to better understand other neuroimmunological disorders such as MS. Since the discovery of HAM/TSP, large numbers of clinical, virological, molecular, and immunological studies have been published. The host-virus interaction and host immune response play an important role for the development with HAM/TSP. HTLV-1-infected circulating T-cells invade the central nervous system (CNS) and cause an immunopathogenic response against virus and possibly components of the CNS. Neural damage and subsequent degeneration can cause severe disability in patients with HAM/TSP. Little progress has been made in the discovery of objective biomarkers for grading stages and predicting progression of disease and the development of molecular targeted therapy based on the underlying pathological mechanisms. We review the recent understanding of immunopathological mechanism of HAM/TSP and discuss the unmet need for research on this disease.