Natural killer (NK) cells in HTLV-I-associated myelopathy/tropical spastic paraparesis-decrease in NK cell subset populations and activity in HTLV-I seropositive individuals

Comprehensive Insight into the Functional Roles of NK and NKT Cells in HTLV-1-Associated Diseases and Asymptomatic Carriers

Human T cell leukemia virus type 1 (HTLV-1) is the first human oncogenic retrovirus to be discovered and causes two major diseases: a progressive neuro-inflammatory disease, termed HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP), and an aggressive malignancy of T lymphocytes known as adult T cell leukemia (ATL). Innate and acquired immune responses play pivotal roles in controlling the status of HTLV-1-infected cells and such, the outcome of HTLV-1 infection. Natural killer cells (NKCs) are the effector cells of the innate immune system and are involved in controlling viral infections and several types of cancers. The ability of NKCs to trigger cytotoxicity to provide surveillance against viruses and cancer depends on the balance between the inhibitory and activating signals. In this review, we will discuss NKC function and the alterations in the frequency of these cells in HTLV-1 infection.

Unraveling the dynamic mechanisms of natural killer cells in viral infections: insights and implications

Viruses pose a constant threat to human well-being, necessitating the immune system to develop robust defenses. Natural killer (NK) cells, which play a crucial role in the immune system, have become recognized as vital participants in protecting the body against viral infections. These remarkable innate immune cells possess the unique ability to directly recognize and eliminate infected cells, thereby contributing to the early control and containment of viral pathogens. However, recent research has uncovered an intriguing phenomenon: the alteration of NK cells during viral infections. In addition to their well-established role in antiviral defense, NK cells undergo dynamic changes in their phenotype, function, and regulatory mechanisms upon encountering viral pathogens. These alterations can significantly impact the effectiveness of NK cell responses during viral infections. This review explores the multifaceted role of NK cells in antiviral immunity, highlighting their conventional effector functions as well as the emerging concept of NK cell alteration in the context of viral infections. Understanding the intricate interplay between NK cells and viral infections is crucial for advancing our knowledge of antiviral immune responses and could offer valuable information for the creation of innovative therapeutic approaches to combat viral diseases.

The CD56-CD16+ NK cell subset in chronic infections

Long-term human diseases can shape the immune system, and natural killer (NK) cells have been documented to differentiate into distinct subsets specifically associated with chronic virus infections. One of these subsets found in large frequencies in HIV-1 are the CD56-CD16+ NK cells, and this population's association with chronic virus infections is the subject of this review. Human NK cells are classically defined by CD56 expression, yet increasing evidence supports the NK cell status of the CD56-CD16+ subset which we discuss herein. We then discuss the evidence linking CD56-CD16+ NK cells to chronic virus infections, and the potential immunological pathways that are altered by long-term infection that could be inducing the population's differentiation. An important aspect of NK cell regulation is their interaction with human leukocyte antigen (HLA) class-I molecules, and we highlight work that indicates both virus and genetic-mediated variations in HLA expression that have been linked to CD56-CD16+ NK cell frequencies. Finally, we offer a perspective on CD56-CD16+ NK cell function, taking into account recent work that implies the subset is comparable to CD56+CD16+ NK cell functionality in antibody-dependent cell cytotoxicity response, and the definition of CD56-CD16+ NK cell subpopulations with varying degranulation capacity against target cells.

CD56-negative NK cells: Frequency in peripheral blood, expansion during HIV-1 infection, functional capacity, and KIR expression

Human NK cells are usually defined as CD3-CD56+ lymphocytes. However, a CD56-CD16+ (CD56neg) lymphocyte population that displays NK-associated markers expands during chronic viral infections such as HIV-1 and HCV, and, to lesser extent, in herpesvirus infections. This CD56neg NK cell subset has been understudied because it requires the exclusion of other lymphocytes to accurately identify its presence. Many questions remain regarding the origin, development, phenotype, and function of the CD56neg NK cell population. Our objective was to determine the frequency of this NK subset in healthy controls and its alteration in viral infections by performing a meta-analysis. In addition to this, we analyzed deposited CyTOF and scRNAseq datasets to define the phenotype and subsets of the CD56neg NK cell population, as well as their functional variation. We found in 757 individuals, from a combined 28 studies and 6 datasets, that the CD56neg subset constitutes 5.67% of NK cells in healthy peripheral blood, while HIV-1 infection increases this population by a mean difference of 10.69%. Meta-analysis of surface marker expression between NK subsets showed no evidence of increased exhaustion or decreased proliferation within the CD56neg subset. CD56neg NK cells have a distinctive pattern of KIR expression, implying they have a unique potential for KIR-mediated education. A perforin-CD94-NKG2C-NKp30- CD56neg population exhibited different gene expression and degranulation responses against K562 cells compared to other CD56neg cells. This analysis distinguishes two functionally distinct subsets of CD56neg NK cells. They are phenotypically diverse and have differing capacity for education by HLA class-I interactions with KIRs.

Interaction of perforin and granzyme B and HTLV-1 viral factors is associated with Adult T cell Leukemia development

Objective(s):

Human T cell leukaemia virus type 1 (HTLV-1) is associated with adult T cell leukaemia (ATL), a malignant lymphoproliferative disease that infects CD4 T cells. It is not clear why the majority of HTLV-1-infected individuals remain asymptomatic carries (ACs) and a minority develop ATL. Cellular immune response has a critical role in ATL and destroys malignant and HTLV-1-infected cells. Perforin and granzyme have important functional roles in apoptosis and destruction of infected cells. In the present study we examined the role of perforin and granzyme in ATL patients and ACs.

Materials and Methods:

Peripheral blood mononuclear cells (PBMCs) were isolated from ATL patients and ACs by using Ficoll-hypaque density centrifugation. RNA was extracted and cDNA was synthesized. A real-time PCR TaqMan method was designed and optimized for evaluation of perforin, granzyme, tax, and HBZ gene expression. HTLV-1 proviral load (PVL) was quantified in patients with ATL and ACs.

Results:

The mRNA expression of tax and HBZ was significantly higher in ATL patients than ACs (P=0.011 and P=0.0001,respectively). The HTLV-1 PVL was higher in ATL patients compared to with AC group (P=0.015). There was a significant increase in perforin gene expression in ACs compared with ATL patients (P=0.002). Furthermore, the expression of granzyme was also higher in ACs compared with ATL patients, and significant differences were observed between the two groups (P=0.036).

Conclusion:

Low expression of perforin and granzyme in ATL patients seems to influence the efficiency of CTL function and destruction of HTLV-1-infected cells, which might contribute to the disease pathogenesis.

An insight to HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) pathogenesis; evidence from high-throughput data integration and meta-analysis

BACKGROUND

Human T-lymphotropic virus 1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a progressive disease of the central nervous system that significantly affected spinal cord, nevertheless, the pathogenesis pathway and reliable biomarkers have not been well determined. This study aimed to employ high throughput meta-analysis to find major genes that are possibly involved in the pathogenesis of HAM/TSP.

RESULTS

High-throughput statistical analyses identified 832, 49, and 22 differentially expressed genes for normal vs. ACs, normal vs. HAM/TSP, and ACs vs. HAM/TSP groups, respectively. The protein-protein interactions between DEGs were identified in STRING and further network analyses highlighted 24 and 6 hub genes for normal vs. HAM/TSP and ACs vs. HAM/TSP groups, respectively. Moreover, four biologically meaningful modules including 251 genes were identified for normal vs. ACs. Biological network analyses indicated the involvement of hub genes in many vital pathways like JAK-STAT signaling pathway, interferon, Interleukins, and immune pathways in the normal vs. HAM/TSP group and Metabolism of RNA, Viral mRNA Translation, Human T cell leukemia virus 1 infection, and Cell cycle in the normal vs. ACs group. Moreover, three major genes including STAT1, TAP1, and PSMB8 were identified by network analysis. Real-time PCR revealed the meaningful down-regulation of STAT1 in HAM/TSP samples than AC and normal samples (P = 0.01 and P = 0.02, respectively), up-regulation of PSMB8 in HAM/TSP samples than AC and normal samples (P = 0.04 and P = 0.01, respectively), and down-regulation of TAP1 in HAM/TSP samples than those in AC and normal samples (P = 0.008 and P = 0.02, respectively). No significant difference was found among three groups in terms of the percentage of T helper and cytotoxic T lymphocytes (P = 0.55 and P = 0.12).

CONCLUSIONS

High-throughput data integration disclosed novel hub genes involved in important pathways in virus infection and immune systems. The comprehensive studies are needed to improve our knowledge about the pathogenesis pathways and also biomarkers of complex diseases.

Functional capacity of natural killer cells in HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP) patients

Background

Natural killer (NK) cells are part of the innate immune system and provide surveillance against viruses and cancers. The ability of NK cells to kill virus-infected cells depends on the balance between the effects of inhibitory and activating NK cell receptors. This study aimed to investigate the phenotypic profile and the functional capacity of NK cells in the context of HTLV-1 infection.

Methods

This cross-sectional study sequentially recruited HTLV-1 infected individuals with HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP) and asymptomatic HTLV-1 (AS) from the Integrated and Multidisciplinary HTLV Center in Salvador, Brazil. Blood samples from healthy blood donors served as controls. NK cell surface receptors (NKG2D, KIR2DL2/KIR2DL3, NKp30, NKG2A, NKp46, TIM-3 and PD-1), intracellular cytolytic (Granzyme B, perforin) and functional markers (CD107a for degranulation, IFN-γ) were assayed by flow cytometry in the presence or absence of standard K562 target cells. In addition, cytotoxicity assays were performed in the presence or absence of anti-NKp30.

Results

The frequency of NKp30⁺ NK cells was significantly decreased in HAM/TSP patients [58%, Interquartile Range (IQR) 30–61] compared to controls (73%, IQR 54–79, p = 0.04). The production of cytolytic (perforin, granzyme B) and functional markers (CD107a and IFN-γ) was higher in unstimulated NK cells from HAM/TSP and AS patients compared to controls. By contrast, stimulation with K562 target cells did not alter the frequency of CD107a⁺ NK cells in HAM/TSP subjects compared to the other groups. Blockage of the NKp30 receptor was shown to decrease cytotoxic activity (CD107a) and IFN-γ expression only in asymptomatic HTLV-1-infected individuals.

Conclusions

NK cells from individuals with a diagnosis of HAM/TSP present decreased expression of the activating receptor NKp30, in addition to elevated degranulation activity that remained unaffected after blocking the NKp30 receptor.

The Role of NK Cells in the Control of Viral Infection in HTLV-1 Carriers

The cytotoxic activities of CD8⁺ T cells have been considered the main defense mechanism against the human T lymphotropic virus type 1 (HTLV-1). As with CD8⁺ T cells, NK cells can perform cytotoxic degranulation with production of cytotoxic mediators, such as perforins and granzymes. NK cells are also responsible for antibody-dependent cellular cytotoxicity (ADCC) against infected cells, but few studies have evaluated the role of NK cells in HTLV-1 infection. The aim of this study was to characterize the subsets and measure the frequency of NK cells in HTLV-1 carriers (HC) and in patients with HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and correlate these findings with the proviral load and development of HAM/TSP. The diagnosis of HTLV-1 infection was performed with a detection antibody against viral antigens by ELISA and confirmed by Western blot. Phenotypic characterization of NK cells was performed by flow cytometry. The frequencies of CD56⁺, CD56⁺CD3⁻, CD56⁺CD16⁺, and CD56^dim cells were decreased in HAM/TSP patients. The frequency of CD56⁺CD3⁻ cells was inversely correlated with proviral load in HC but not in HAM/TSP patients. HAM/TSP patients showed decreased frequency of CD56⁺ and CD56^dim cells expressing CD16, the main receptor for ADCC. These data indicate that NK cells may play a key role in the control of HTLV-1 infection by preventing the progression of HC to HAM/TSP.

Human T cell leukemia virus type 1 and Zika virus: tale of two reemerging viruses with neuropathological sequelae of public health concern

Human T cell leukemia virus type 1 (HTLV-1) and Zika virus (ZIKV) have been considered neglected viruses of low public health concern until recently when incidences of HTLV-1 and ZIKV were observed to be linked to serious immune-related disease and neurological complications. This review will discuss the epidemiology, genomic evolution, virus-host interactions, virulence factors, neuropathological sequelae, and current perspectives of these reemerging viruses. There are no FDA-approved therapeutics or vaccines against these viruses, and as such, it is important for clinical trials to focus on developing vaccines that can induce cell-mediated immune response to confer long-term protective immunity. Furthermore, attention should be paid to reducing the transmission of these viruses through unprotected sex, infected blood during sharing of contaminated needles, donated blood and organs, and vertical transmission from mother to baby via breastfeeding. There is an urgent need to re-evaluate repurposing current antiviral therapies as well as developing novel antiviral agents with enhanced efficacy due to the high morbidity rate associated with these two reemerging chronic viral diseases.

Human T-cell leukaemia virus type 1: parasitism and pathogenesis

Human T-cell leukaemia virus type 1 (HTLV-1) causes not only adult T-cell leukaemia-lymphoma (ATL), but also inflammatory diseases including HTLV-1-associated myelopathy/tropical spastic paraparesis. HTLV-1 transmits primarily through cell-to-cell contact, and generates abundant infected cells in the host in order to survive and transmit to a new host. The resulting high proviral load is closely associated with the development of ATL and inflammatory diseases. To increase the number of infected cells, HTLV-1 changes the immunophenotype of infected cells, induces proliferation and inhibits apoptosis through the cooperative actions of two viral genes, tax and HTLV-1 bZIP factor (HBZ). As a result, infected cells survive, proliferate and infiltrate into the tissues, which is critical for transmission of the virus. Thus, the strategy of this virus is indivisibly linked with its pathogenesis, providing a clue for prevention and treatment of HTLV-1-induced diseases.

This article is part of the themed issue ‘Human oncogenic viruses’.

How does HTLV-1 cause adult T-cell leukaemia/lymphoma (ATL)?

A typical person infected with the retrovirus human T-lymphotropic virus type 1 (HTLV-1) carries tens of thousands of clones of HTLV-1-infected T lymphocytes, each clone distinguished by a unique integration site of the provirus in the host genome. However, only 5% of infected people develop the malignant disease adult T cell leukaemia/lymphoma, usually more than 50 years after becoming infected. We review the host and viral factors that cause this aggressive disease.

HTLV-1-associated myelopathy/tropical spastic paraparesis

Human T-lymphotropic virus 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a progressive disease of the CNS that causes weakness or paralysis of the legs, lower back pain and urinary symptoms. HAM/TSP was first described in Jamaica in the nineteenth century, but the aetiology of the condition, infection with the retrovirus HTLV-1, was only identified in the 1980s. HAM/TSP causes chronic disability and, accordingly, imposes a substantial health burden in areas where HTLV-1 infection is endemic. Since the discovery of the cause of HAM/TSP, considerable advances have been made in the understanding of the virology, immunology, cell biology and pathology of HTLV-1 infection and its associated diseases. However, progress has been limited by the lack of accurate animal models of the disease. Moreover, the treatment of HAM/TSP remains highly unsatisfactory: antiretroviral drugs have little impact on the infection and, although potential disease-modifying therapies are widely used, their value is unproved. At present, clinical management is focused on symptomatic treatment and counselling. Here, we summarize current knowledge on the epidemiology, pathogenesis and treatment of HAM/TSP and identify areas in which further research is needed. For an illustrated summary of this Primer, visit: http://go.nature.com/tjZCFM.

NK cells and virus-related cancers

Natural killer (NK) cells become activated during viral infections and can play roles in such infections by attacking virus-infected cells or by regulating adaptive immune responses. Experimental models suggest that NK cells may also have the capacity to restrain virus-induced cancers. Here, we discuss the seven viruses linked to human cancers and the evidence of NK cell involvement in these systems.

Neuroimmunological aspects of human T cell leukemia virus type 1-associated myelopathy/tropical spastic paraparesis

Human T cell leukemia virus type 1 (HTLV-1) is a human retrovirus etiologically associated with adult T cell leukemia/lymphoma and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Only approximately 0.25-4 % of infected individuals develop HAM/TSP; the majority of infected individuals remain lifelong asymptomatic carriers. Recent data suggest that immunological aspects of host-virus interactions might play an important role in the development and pathogenesis of HAM/TSP. This review outlines and discusses the current understanding, ongoing developments, and future perspectives of HAM/TSP research.

Clinical pathophysiology of human T-lymphotropic virus-type 1-associated myelopathy/tropical spastic paraparesis

Human T-lymphotropic virus type 1 (HTLV-1), a human retrovirus, is the causative agent of a progressive neurological disease termed HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). HAM/TSP is a chronic inflammatory disease of the central nervous system and is characterized by unremitting myelopathic symptoms such as spastic paraparesis, lower limb sensory disturbance, and bladder/bowel dysfunction. Approximately 0.25-3.8% of HTLV-1-infected individuals develop HAM/TSP, which is more common in women than in men. Since the discovery of HAM/TSP, significant advances have been made with respect to elucidating the virological, molecular, and immunopathological mechanisms underlying this disease. These findings suggest that spinal cord invasion by HTLV-1-infected T cells triggers a strong virus-specific immune response and increases proinflammatory cytokine and chemokine production, leading to chronic lymphocytic inflammation and tissue damage in spinal cord lesions. However, little progress has been made in the development of an optimal treatment for HAM/TSP, more specifically in the identification of biomarkers for predicting disease progression and of molecular targets for novel therapeutic strategies targeting the underlying pathological mechanisms. This review summarizes current clinical and pathophysiological knowledge on HAM/TSP and discusses future focus areas for research on this disease.

Immunopathogenesis of human T-cell leukemia virus type-1-associated myelopathy/tropical spastic paraparesis: recent perspectives

Human T-cell leukemia virus type-1 (HTLV-1) is a replication-competent human retrovirus associated with two distinct types of disease only in a minority of infected individuals: the malignancy known as adult T-cell leukemia (ATL) and a chronic inflammatory central nervous system disease HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). HAM/TSP is a chronic progressive myelopathy characterized by spastic paraparesis, sphincter dysfunction, and mild sensory disturbance in the lower extremities. Although the factors that cause these different manifestations of HTLV-1 infection are not fully understood, accumulating evidence from host population genetics, viral genetics, DNA expression microarrays, and assays of lymphocyte function suggests that complex virus-host interactions and the host immune response play an important role in the pathogenesis of HAM/TSP. Especially, the efficiency of an individual's cytotoxic T-cell (CTL) response to HTLV-1 limits the HTLV-1 proviral load and the risk of HAM/TSP. This paper focuses on the recent advances in HAM/TSP research with the aim to identify the precise mechanisms of disease, in order to develop effective treatment and prevention.

Systems biology approaches reveal a specific interferon-inducible signature in HTLV-1 associated myelopathy

Human T-lymphotropic virus type 1 (HTLV-1) is a retrovirus that persists lifelong in the host. In ∼4% of infected people, HTLV-1 causes a chronic disabling neuroinflammatory disease known as HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The pathogenesis of HAM/TSP is unknown and treatment remains ineffective. We used gene expression microarrays followed by flow cytometric and functional assays to investigate global changes in blood transcriptional profiles of HTLV-1-infected and seronegative individuals. We found that perturbations of the p53 signaling pathway were a hallmark of HTLV-1 infection. In contrast, a subset of interferon (IFN)-stimulated genes was over-expressed in patients with HAM/TSP but not in asymptomatic HTLV-1 carriers or patients with the clinically similar disease multiple sclerosis. The IFN-inducible signature was present in all circulating leukocytes and its intensity correlated with the clinical severity of HAM/TSP. Leukocytes from patients with HAM/TSP were primed to respond strongly to stimulation with exogenous IFN. However, while type I IFN suppressed expression of the HTLV-1 structural protein Gag it failed to suppress the highly immunogenic viral transcriptional transactivator Tax. We conclude that over-expression of a subset of IFN-stimulated genes in chronic HTLV-1 infection does not constitute an efficient host response but instead contributes to the development of HAM/TSP.

Infection with the Human T Lymphotropic virus is widespread in the tropics and subtropics, where it causes a chronic disabling disease of the nervous system abbreviated as HAM/TSP. There is no effective treatment available for HAM/TSP, because it is not understood how the virus causes the neuronal damage that results in the clinical symptoms of weakness and paralysis of the legs. Here, we compared the frequencies of cell populations and gene expression profiles from diseased and asymptomatic HTLV-1 carriers to identify abnormalities in biological pathways that cause HAM/TSP. We discovered a distinct group of genes that is over-expressed in white blood cells in patients with HAM/TSP, but not asymptomatic HTLV-1 carriers or patients with the clinically similar disease multiple sclerosis. The expression of these genes is induced by interferons, a group of anti-viral proteins that are usually beneficial to the host but can also cause inflammation. We also found that interferons did not efficiently suppress HTLV-1 protein expression in vitro. We conclude that interferons do not control chronic HTLV-1 infection but instead contribute to the development of HAM/TSP. Our study provides new insights into the development of HTLV-1-associated diseases and opens new areas of therapeutic intervention.

Plasma proteome analysis in HTLV-1-associated myelopathy/tropical spastic paraparesis

Background

Human T lymphotropic virus Type 1 (HTLV-1) causes a chronic inflammatory disease of the central nervous system known as HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM) which resembles chronic spinal forms of multiple sclerosis (MS). The pathogenesis of HAM remains uncertain. To aid in the differential diagnosis of HAM and to identify pathogenetic mechanisms, we analysed the plasma proteome in asymptomatic HTLV-1 carriers (ACs), patients with HAM, uninfected controls, and patients with MS. We used surface-enhanced laser desorption-ionization (SELDI) mass spectrometry to analyse the plasma proteome in 68 HTLV-1-infected individuals (in two non-overlapping sets, each comprising 17 patients with HAM and 17 ACs), 16 uninfected controls, and 11 patients with secondary progressive MS. Candidate biomarkers were identified by tandem Q-TOF mass spectrometry.

Results

The concentrations of three plasma proteins - high [β2-microglobulin], high [Calgranulin B], and low [apolipoprotein A2] - were specifically associated with HAM, independently of proviral load. The plasma [β2-microglobulin] was positively correlated with disease severity.

Conclusions

The results indicate that monocytes are activated by contact with activated endothelium in HAM. Using β2-microglobulin and Calgranulin B alone we derive a diagnostic algorithm that correctly classified the disease status (presence or absence of HAM) in 81% of HTLV-1-infected subjects in the cohort.

HTLV-1 and innate immunity

Innate immunity plays a critical role in the host response to a viral infection. The innate response has two main functions. First, it triggers effector mechanisms that restrict the infection. Second, it primes development of the adaptive response, which completes the elimination of the pathogen or of infected cells. In vivo, HTLV-1 infects T lymphocytes that participate in adaptive immunity but also monocytes and dendritic cells that are major players in innate immunity. Herein, we will review the interplay between HTLV-1 and innate immunity. Particular emphasis is put on HTLV-1-induced alteration of type-I interferon (IFN-I) function. In vitro, the viral Tax protein plays a significant role in the alteration of IFN synthesis and signaling. Despite this, IFN-I/AZT treatment of Adult T-cell Leukemia/Lymphoma (ATLL) patients leads to complete remission. We will discuss a model in which exogenous IFN-I could act both on the microenvironment of the T-cells to protect them from infection, and also on infected cells when combined with other drugs that lead to Tax down-regulation/degradation.

Human T cell leukemia virus type 1 infection drives spontaneous proliferation of natural killer cells

Most human T cell leukemia virus type 1 (HTLV-1) infected subjects remain asymptomatic throughout their lives, with a few individuals developing HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP) or adult T cell leukemia. Lymphocytes from about half of HTLV-1 infected subjects spontaneously proliferate in vitro, and how this phenomenon relates to symptomatic disease outcome and viral burden is poorly understood. Spontaneous proliferation was measured in lymphocyte subsets, and these findings were correlated with HTLV-1 proviral load and Tax expression in PBMCs. We found that in addition to previously described vigorous CD8+ T cell spontaneous proliferation, natural killer (NK) cells spontaneously proliferated to a similar high level, resulting in expansion of CD56-expressing NK cells. Spontaneous NK cell proliferation positively correlated with HTLV-1 proviral load but not with Tax expression or the presence of HAM/TSP. The strongest correlate with clinical outcome in this cohort was the ability of cells to express Tax, while HTLV-1 proviral load was more closely related to spontaneous NK cell proliferation. These results demonstrate that spontaneous proliferation, Tax expression, and proviral load are inter-related but not equivalent, and that spontaneous lymphocyte proliferation is not restricted to T cells, the targets of HTLV-1 infection.

Role of killer cell immunoglobulin-like receptor gene content and human leukocyte antigen-C group in susceptibility to human T-lymphotropic virus 1-associated myelopathy/tropical spastic paraparesis in Peru

Human T-lymphotropic virus 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) affects approximately 5% of HTLV-1-infected individuals. It is poorly understood why only some infected subjects develop this disease, but host genetic factors may determine susceptibility. The innate immune system may influence disease outcome in HTLV-1-infected individuals because of its role in early immune responses to viral infections. Variation in genes encoding killer cell immunoglobulin-like receptors (KIR) and their human leukocyte antigen (HLA) molecule ligands may affect the risk of HAM/TSP. We performed a two-stage case-control study to examine the distribution of KIR genes and HLA-Cw groups in Peruvian HTLV-1-infected HAM/TSP individuals and asymptomatic carriers. We also tested for epistatic effects between specific KIR genes and HLA-Cw groups. In the first stage, we found several trends toward association with HAM/TSP or proviral load (PVL). However, these results were not replicated in the second stage. In conclusion, this is the first report on KIR gene frequencies in the Peruvian population and may be of significance in hematopoietic stem-cell transplants. Our study did not reveal significant associations between KIR genes and HLA-Cw groups and HAM/TSP or PVL. However, because our study was powered to detect only larger effects, additional studies using larger cohorts are needed.

Neuroimmunity of HTLV-I Infection

Human T-lymphotrophic virus type I (HTLV-I) is an oncogenic retrovirus and its infection is associated with a variety of human diseases including HTLV-I-associated myelopathy/tropic spastic paraparesis (HAM/TSP). Large numbers of epidemiological, virological, immunological, and clinical studies on HTLV-I- and HTLV-I-associated diseases have been published, although the pathogenesis of HAM/TSP remains to be fully understood. In the last several years, researchers have shown that several key factors are important in HTLV-I-associated neurologic disease including high HTLV-I proviral load and a strong immune response to HTLV-I. Here, we review pathophysiological findings on HAM/TSP and focus on viral-host immune responses to the virus in HTLV-I infected individuals. In particular, the role of HTLV-I-specific CD8+ T cell response is highlighted.

Immunogenetics and the Pathological Mechanisms of Human T-Cell Leukemia VirusType 1- (HTLV-1-)Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP)

Human T-cell leukemia virus type 1 (HTLV-1) is a replication-competent human retrovirus associated with two distinct types of disease only in a minority of infected individuals: the malignancy known as adult T-cell leukemia (ATL) and a chronic inflammatory central nervous system disease HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Although the factors that cause these different manifestations of HTLV-1 infection are not fully understood, accumulating evidence suggests that complex virus-host interactions play an important role in determining the risk of HAM/TSP. This review focuses on the role of the immune response in controlling or limiting viral persistence in HAM/TSP patients, and the reason why some HTLV-1-infected people develop HAM/TSP whereas the majority remains asymptomatic carriers of the virus.

A prospective uncontrolled trial of fermented milk drink containing viable Lactobacillus casei strain Shirota in the treatment of HTLV-1 associated myelopathy/tropical spastic paraparesis

Ten patients with human T-cell lymphotropic virus type-1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) were treated in an uncontrolled preliminary trial by oral administration of viable Lactobacillus casei strain Shirota (LcS) containing fermented milk. HTLV-1 provirus load, motor function, neurological findings, and immunological parameters were evaluated after 4 weeks. Although LcS did not change the frequencies or absolute numbers of all the examined cell surface phenotypes of peripheral blood mononuclear cells, NK cell activity was significantly increased after 4 weeks of oral administration of LcS preparation. Improvements in spasticity (modified Ashworth Scale scores) and urinary symptoms were also seen after LcS treatment. No adverse effect was observed in all the 10 patients throughout the study period. Our results indicated that LcS may be a safe and beneficial agent for the treatment of HAM/TSP; therefore randomized controlled studies are warranted.

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.

Cell-mediated immune response to human T-lymphotropic virus type I

Human T-lymphotropic virus type I (HTLV-I) is a retrovirus that causes persistent infection in many populations in tropical and subtropical regions. HTLV-I chronically activates the cell-mediated arm of the host adaptive immune response. There has been much debate about the role of the immune response in determining the outcome of HTLV-I infection: most seropositive individuals remain lifelong asymptomatic carriers of the virus, whereas a small proportion-usually those with higher equilibrium proviral loads-develop an inflammatory disease of the central nervous system known as HAM/TSP. Here we discuss the cell-mediated immune response to HTLV-I infection. We summarize recent data on the HTLV-I-specific CD4(+) cell response and explore its potential role in HAM/TSP pathogenesis. We also explore the controversy surrounding the role of the CD8(+) cell response in controlling HTLV-I infection and/or contributing to HAM/TSP disease, highlighting recent studies of T cell gene expression profiles and a newly developed assay of CD8(+) cell functional efficiency. Finally, we introduce a possible role for cellular innate immune effectors in HTLV-I infection.

The CC Chemokine Receptor 4 as a Novel Specific Molecular Target for Immunotherapy in Adult T-Cell Leukemia/Lymphoma

Adult T-cell leukemia/lymphoma (ATLL) is a peripheral T-cell neoplasm with dismal prognosis, and no optimal therapy has been developed. We tested the defucosylated chimeric anti-CC chemokine receptor 4 (CCR4) monoclonal antibody, KM2760, to develop a novel immunotherapy for this refractory tumor. In the presence of peripheral blood mononuclear cells (PBMCs) from healthy adult donors, KM2760 induced CCR4-specific antibody-dependent cellular cytotoxicity (ADCC) against CCR4-positive ATLL cell lines and primary tumor cells obtained from ATLL patients. We next examined the KM2760-induced ADCC against primary ATLL cells in an autologous setting. Antibody-dependent cellular cytotoxicity mediated by autologous effector cells was generally lower than that mediated by allogeneic control effector cells. However, a robust ADCC activity was induced in some cases, which was comparable with that mediated by allogeneic effector cells. It suggests that the ATLL patients' PBMCs retain substantial ADCC-effector function, although the optimal conditions for maximal effect have not yet been determined. In addition, we also found a high expression of FoxP3 mRNA and protein, a hallmark of regulatory T cells, in ATLL cells, indicating the possibility that ATLL cells originated from regulatory T cells. KM2760 reduced FoxP3 mRNA expression in normal PBMCs along with CCR4 mRNA by lysis of CCR4+ T cells in vitro. Our data suggest not only that the CCR4 molecule could be a suitable target for the novel antibody-based therapy for patients with ATLL but also that KM2760 may induce effective tumor immunity by reducing the number of regulatory T cells.

The role of CTLs in persistent viral infection: cytolytic gene expression in CD8+ lymphocytes distinguishes between individuals with a high or low proviral load of human T cell lymphotropic virus type 1

The proviral load in human T cell lymphotropic virus type 1 (HTLV-1) infection is typically constant in each infected host, but varies by >1000-fold between hosts and is strongly correlated with the risk of HTLV-1-associated inflammatory disease. However, the factors that determine an individual's HTLV-1 proviral load remain uncertain. Experimental evidence from studies of host genetics, viral genetics, and lymphocyte function and theoretical considerations suggest that a major determinant of the equilibrium proviral load is the CD8+ T cell response to HTLV-1. In this study, we tested the hypothesis that the gene expression profile in circulating CD8+ and CD4+ lymphocytes distinguishes between individuals with a low proviral load of HTLV-1 and those with a high proviral load. We show that circulating CD8+ lymphocytes from individuals with a low HTLV-1 proviral load overexpressed a core group of nine genes with strong functional coherence: eight of the nine genes encode granzymes or other proteins involved in cell-mediated lysis or Ag recognition. We conclude that successful suppression of the HTLV-1 proviral load is associated with strong cytotoxic CD8+ lymphocyte activity in the peripheral blood.

Human T-lymphotropic virus type 1 (HTLV-1): persistence and immune control

The human retrovirus human T-lymphotropic virus type 1 (HTLV-1) is associated with two distinct types of disease: the malignancy known as adult T-cell leukemia and a range of chronic inflammatory conditions including the central nervous system disease HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Until recently, it was believed that HTLV-1 was largely latent in vivo. However, evidence from a number of types of experiments shows that HTLV-1 persistently expresses its genes, and that the "set point" of an individual's proviral load of HTLV-1 is mainly determined by the efficiency of that individual's cellular immune response to the virus. These conclusions have two main consequences. First, HTLV-1 may be vulnerable to antiretroviral drug therapy or immunotherapy. Second, HTLV-1 infection has become a useful system to analyze the determinants of the efficiency of the antiviral immune response.

Interferon-alpha significantly reduces cerebrospinal fluid CD4 cell subsets in HAM/TSP

We, for the first time, analyzed T cell and natural killer (NK) cell subsets in the cerebrospinal fluid (CSF) in nine patients with human T-lymphotropic virus type 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) treated with interferon-alpha (IFN-alpha). The CD4/CD8 ratio in CSF was significantly lower after the therapy, which is mainly attributable to the significant reduction in CD4+ cells, especially CD25+CD4 and CD45RO+CD4 cell subsets. Meanwhile, NK, natural T and NKT cell subsets in the CSF remained unchanged. There was no CSF lymphocyte subset significantly associated with the clinical efficacy of IFN-alpha in this small-scale study, and more patients should be analyzed to ascertain the link.

Optic-spinal form of multiple sclerosis and immune-mediated myelopathy in Japan

Optic-spinal form of multiple sclerosis (OS-MS) and HTLV-I associated myelopathy/tropical spastic paraparesis (HAM/TSP) are two immune-mediated myelopathy relatively common in Japan. (1) Transverse myelitis, once seen in 60% of MS, mostly OS-MS, 30 years ago, drastically decreased (5%) recently in Japan. In contrast, frequency of conventional form of MS (C-MS) increased during this period of time. But unlike C-MS in white patients, cerebellar hemispheric lesions are uncommon in Japanese C-MS. These findings emphasize influence of changes in exogenous factors on manifestations of MS and distinct genetic factors related to MS in Japanese and white patients. (2) To clarify the reason of high HTLV-I proviral load in HAM/TSP, we studied cellular immune surveillance against HTLV-I and found that significant cytotoxic T lymphocyte activity, and suppressed natural killer activity and antibody-dependent cell-mediated cytotoxicity in the patients. These altered immune surveillance may be associated with the spread of HTLV-I infection and the pathogenesis of HAM/TSP.

Flow cytometric differentiation of Asian and Western types of multiple sclerosis, HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and hyperIgEaemic myelitis by analyses of memory CD4 positive T cell subsets and NK cell subsets

We examined the alterations of memory CD4(+) T cell subsets bearing surface receptors linked to either Th1 or Th2 cytokine production as well as natural killer (NK) cell subsets by three color flow cytometry in the peripheral blood from 36 patients with clinically definite multiple sclerosis (MS), 27 patients with HAM/TSP, 13 patients with hyperIgEaemic myelitis who had mite antigen-specific IgE and 25 healthy controls (HC). The patients with MS were clinically classified into an optico-spinal form of MS (Asian type, MS-A) and the conventional form of MS (Western type, MS-W). MS-A showed a significant increase of CD4(+)CD45RA(-)CCR5(+) cells (Th1 cells) through the relapse and remission phases in comparison to HC, while MS-W showed a significant increase of CD4(+)CD45RO(+)CD62L(-) cells (Th1 cells) only at the relapse phase. HAM/TSP showed a significant increase of CCR5(+) and CD62L(-) memory CD4(+) T cells as well as CD30(+) memory CD4(+) T cells (Th2 cells) in comparison to HC. On the other hand, a selective increase of CD4(+)CD45RO(+)CD30(+) cells was found in hyperIgEaemic myelitis. The percentage of mature NK cells (CD3(-)CD16(+)CD56(+) cells) as well as double negative T cells (CD3(+)CD4(-)CD8(-) cells) decreased significantly in HAM/TSP in comparison to HC. Our findings therefore suggest a flow cytometric analysis of Th1/Th2-associated markers on memory CD4(+) T cells as well as NK cell subsets to be useful for differentiating various inflammatory neurologic conditions.

Antibody-dependent cell-mediated cytotoxicity (ADCC) in HTLV-I associated myelopathy/tropical spastic paraparesis (HAM/TSP)

Defects in immune surveillance mechanisms may allow increased replication of human T-lymphotropic virus type I (HTLV-I) in peripheral blood mononuclear cells in HTLV-I associated myelopathy/tropical spastic paraparesis (HAM/TSP). To explore this possibility, antibody-dependent cell-mediated cytotoxicity (ADCC) against HTLV-I infected cells in HAM/TSP and in asymptomatic HTLV-I-seropositive carriers (SPC), was studied. ADCC activity was significantly depressed in HAM/TSP compared to SPC subjects (p < 0.025) and was due to specific reduction in ADCC effector activity. On the other hand, there was no difference in antibody component of anti-HTLV-I ADCC (ADCC-Ab) activities between HAM/TSP and SPC, although patients with more severe forms of disease tended to have higher anti-HTLV-I ADCC-Ab activity. In HAM/TSP, depressed ADCC activity against HTLV-I due to reduced ADCC-effector activity may allow increased replication of HTLV-I which may implicate the development of inflammatory neuropathologic lesions of HAM/TSP.

Potential role of natural killer cells in controlling tumorigenesis by human T-cell leukemia viruses

Human T-cell leukemia virus (HTLV) is the etiologic agent of adult T-cell leukemia (ATL), a malignancy of T lymphocytes that is characterized by a long latency period after virus exposure. Intraperitoneal inoculation of severe combined immunodeficient (SCID) mice with HTLV-transformed cell lines and ATL tumor cells was employed to investigate the tumorigenic potential of HTLV type I (HTLV-I)-infected cells. In contrast to inoculation of ATL (RV-ATL) cells into SCID mice, which resulted in the formation of lymphomas, inoculation of HTLV-I- and HTLV-II-transformed cell lines (SLB-I and JLB-II cells, respectively) did not result in tumor formation. Immunosuppression of SCID mice, either by whole-body irradiation or by treatment with an antiserum, anti-asialo GM1 (alpha-AGM1), which transiently abrogates natural killer cell activity in vivo, was necessary to establish the growth of tumors derived from HTLV-transformed cell lines. PCR and flow cytometric studies reveal that HTLV-I-transformed cells are eliminated from the peritoneal cavities of inoculated mice by 3 days postinoculation; in contrast, RV-ATL cells persist and are detected until the mice succumb to lymphoma development. The differing behaviors of HTLV-infected cell lines and ATL tumor cells in SCID mice suggest that ATL cells have a higher tumorigenic potential in vivo than do HTLV-infected cell lines because of their ability to evade natural killer cell-mediated cytolysis.

Evolution of mutation rate and virulence among human retroviruses

High mutation rates are generally considered to be detrimental to the fitness of multicellular organisms because mutations untune finely tuned biological machinery. However, high mutation rates may be favoured by a need to evade an immune system that has been strongly stimulated to recognize those variants that reproduced earlier during the infection. HIV infections conform to this situation because they are characterized by large numbers of viruses that are continually breaking latency and large numbers that are actively replicating throughout a long period of infection. To be transmitted, HIVs are thus generally exposed to an immune system that has been activated to destroy them in response to prior viral replication in the individual. Increases in sexual contact should contribute to this predicament by favouring evolution toward relatively high rates of replication early during infection. Because rapid replication and high mutation rate probably contribute to rapid progression of infections to AIDS, the interplay of sexual activity, replication rate, and mutation rate helps explain why HIV-1 has only recently caused a lethal pandemic, even though molecular data suggest that it may have been present in humans for more than a century. This interplay also offers an explanation for geographic differences in progression to cancer found among infections due to the other major group of human retroviruses, human T-cell lymphotropic viruses (HTLV). Finally, it suggests ways in which we can use natural selection as a tool to control the AIDS pandemic and prevent similar pandemics from arising in the future.

Cellular immune surveillance against HTLV-I infected T lymphocytes in HTLV-I associated myelopathy/tropical spastic paraparesis (HAM/TSP)

To investigate the cellular immune surveillance against HTLV-I infected T lymphocytes in HTLV-I associated myelopathy/tropical spastic paraparesis (HAM/TSP), we studied the cytotoxic T lymphocytes (CTL) activity against an HTLV-I infected human T cell line (MT-2) and the natural killer (NK) cell activity in 15 HAM patients, 6 HTLV-I carriers, and 15 controls. The activity of CTL against MT-2 cells was found to be significantly elevated in HAM compared with that in the controls. This cytotoxicity in HAM was higher than in HTLV-I carriers, although the difference was not statistically significant. There was an HLA class I restriction in this CTL activity against MT-2 cells in HAM. On the other hand, NK cell activity was significantly lower in HAM than in controls. Cold target inhibition studies suggested that NK cells could not lyse MT-2 cells effectively. There was a positive correlation between the CTL activity against MT-2 cells and the serum antibody titers to HTLV-I in HAM.