Molecular epidemiology of HTLV type I in Japan: evidence for two distinct ancestral lineages with a particular geographical distribution

Genetic Alterations in Adult T-Cell Leukemia/Lymphoma: Novel Discoveries with Clinical and Biological Significance

Adult T-cell leukemia/lymphoma (ATLL) is a refractory T-cell neoplasm that develops in human T-cell leukemia virus type-I (HTLV-1) carriers. Large-scale comprehensive genomic analyses have uncovered the landscape of genomic alterations of ATLL and have identified several altered genes related to prognosis. The genetic alterations in ATLL are extremely enriched in the T-cell receptor/nuclear factor-κB pathway, suggesting a pivotal role of deregulation in this pathway in the transformation of HTLV-1-infected cells. Recent studies have revealed the process of transformation of HTLV-1-infected cells by analyzing longitudinal samples from HTLV-1 carriers and patients with overt ATLL, an endeavor that might enable earlier ATLL diagnosis. The latest whole-genome sequencing study discovered 11 novel alterations, including CIC long isoform, which had been overlooked in previous studies employing exome sequencing. Our study group performed the targeted sequencing of ATLL in Okinawa, the southernmost island in Japan and an endemic area of HTLV-1, where the comprehensive genetic alterations had never been analyzed. We found associations of genetic alterations with HTLV-1 strains phylogenetically classified based on the tax gene, an etiological virus factor in ATLL. This review summarizes the genetic alterations in ATLL, with a focus on their clinical significance, geographical heterogeneity, and association with HTLV-1 strains.

Brazilian Protocol for Sexually Transmitted Infections 2020: human T-cell lymphotropic virus (HTLV) infection

This article addresses the Human T-lymphotropic virus (HTLV). This subject comprises the Clinical Protocol and Therapeutic Guidelines for Comprehensive Care for People with Sexually Transmitted Infections, published by the Brazilian Ministry of Health. HTLV-1/2 infection is a public health problem globally, and Brazil has the largest number of individuals living with the virus. HTLV-1 causes several clinical manifestations of neoplasm (adult T-cell leukemia/lymphoma) and inflammatory nature, such as HTLV-1-associated myelopathy and other manifestations such as uveitis, arthritis, and infective dermatitis. These pathologies have high morbidity and mortality and negatively impact the quality of life of infected individuals. This review includes relevant information for health authorities professionals regarding viral transmission, diagnosis, treatment, and monitoring of individuals living with HTLV-1 and 2 in Brazil.

HTLV-1/2 transmission can occur through blood transfusion and derivatives, injectable drug use, organ transplantation, unprotected sexual intercourse, and vertical transmission.

[Brazilian Protocol for Sexually Transmitted Infections 2020: human T cell lymphotropic virus (HTLV) infection]

This manuscript is related to the chapter about human T-cell lymphotropic virus (HTLV) that is part of the Clinical Protocol and Therapeutic Guidelines for Comprehensive Care for People with Sexually Transmitted Infections, published by the Brazilian Health Ministry. HTLV-1/2 infection is a worldwide public health problem and Brazil has the largest number of individuals living with the virus. HTLV-1 causes a variety of clinical manifestations of a neoplastic nature, such as adult leukemia/T-cell lymphoma, and also of an inflammatory nature, such as HTLV-1-associated myelopathy, as well as other manifestations such as uveitis, arthritis and infective dermatitis. These pathologies have high morbidity and mortality and negatively impact the quality of life of infected individuals. This review includes relevant information for health service managers and workers regarding virus transmission modes, diagnosis, treatment and monitoring of individuals living with HTLV-1 and 2 in Brazil.

Human T-cell leukemia virus type 1 infection among Japanese immigrants and their descendants living in Southeast Brazil: A call for preventive and control responses

Human T-cell leukemia virus type 1 (HTLV-1) has worldwide distribution and is considered endemic in southwestern Japan. HTLV-1 infection has been associated with adult T-cell leukemia/lymphoma (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) besides other diseases. This cross-sectional study aimed to investigate the prevalence, risk factors and molecular characterization of HTLV-1, among the world’s largest population of Japanese immigrants and their descendants outside of Japan, in São Paulo, Southeast Brazil, as well as to analyze the phylogenetic relationship among isolates of HTLV-1. From July to December 2017, 2,139 individuals from five Japanese associations were interviewed and submitted to blood collection. All serum samples were first tested for the presence of anti-HTLV-1/2 antibodies by ELISA and then peripheral blood from individuals with positive serological results were analyzed for the presence of HTLV-1 5’LTR proviral DNA. Partial sequencing of the 5’LTR region of HTLV-1 proviral DNA was performed by Sanger. The prevalence of HTLV-1 infection was 5.1% (CI 95%: 4.2–6.0). In the multiple logistic regression model, HTLV-1 infection was associated with age ≥ 45 years, female sex, being first and second-generation Japanese immigrants, and having sexual partners with history of blood transfusion. The phylogenetic analysis revealed that all HTLV-1 were classified as Cosmopolitan (1a) subtype. Of them, 47.8% were classified as Transcontinental (A) subgroup and 52.2% as belonging to the Japanese (B) subgroup. Although most HTLV-1-infected patients were asymptomatic (97.3%), blurred vision was associated with HTLV-1 infection. The high prevalence of HTLV-1 infection found in this studied population and especially the intra- and interfamily HTLV-1 transmission presents an urgent call for preventive and control responses of this infection in Brazil.

What is the prevalence of HTLV-1 among the largest world population of Japanese immigrants and their descendants outside Japan? There are approximately 1.5 million people of Japanese descent in Brazil and most of them living in São Paulo state, Southeast Brazil. The prevalence of HTLV-1 infection was 5.1% among 2,139 individuals from five Japanese associations in São Paulo. The prevalence of 5.1% (95% CI: 4.2–6.0) of HTLV-1 infection found in this study is higher than those observed in other studies conducted in HTLV-1 endemic areas and in specific groups at high risk from Brazil. Among HTLV-infected individuals, the majority (86.2%) were unaware of their HTLV diagnosis. The HTLV-1 infection was associated with the age ≥ 45 years, being the first and second generation of Japanese immigrants, and having sexual partners with a history of blood transfusion. Epidemiological data, along with molecular results also demonstrated high occurrence of similar sequences transmitted intra- and interfamily. The high prevalence of HTLV-1 infection found in this studied population presents an urgent call for preventive and control responses of this infection in Brazil.

The challenge of describing the epidemiology of HTLV in the Amazon region of Brazil

HTLV-1 was the first described human retrovirus and was soon found to be associated with severe clinical diseases, including a devastating lymphoma/leukemia and other inflammatory diseases. Although HTLV-2 is not usually pathogenic, it is widely distributed among native Indian populations in Brazil, particularly in the Amazon region of the country. Presently, HTLV spreads mainly by the sexual route and from mother to child, and virus persistence is an active biological factor aiding its transmission. Recently, the use of illicit drugs has been shown to be an additional risk factor, showing the influence of new habits on the epidemiology of HTLV in the region. Despite the detection of the virus in several different populations in the Amazon region of Brazil for almost 30 years, the exact prevalence of HTLV-1/2 is not well defined. The original biases in sampling and the selection of epidemiologically unsuitable populations were commonly repeated in most prevalence studies, generating unreliable and conflicting figures that do not represent the actual prevalence of HTLV. The improvements in clinical and laboratory facilities have resulted in the description of several clinical manifestations that were previously unknown in the region. The extent of the spread of the virus must be defined in this region, which is the largest geographical area of the country. As prophylaxis advances toward the use of vaccines against HTLV-1, it is important to determine who is at risk of being infected and developing a disease to successfully implement preventive measures, particularly as proposals are made to eradicate the virus among humans.

Molecular epidemiology, genetic variability and evolution of HTLV-1 with special emphasis on African genotypes

Human T cell leukemia virus (HTLV-1) is an oncoretrovirus that infects at least 10 million people worldwide. HTLV-1 exhibits a remarkable genetic stability, however, viral strains have been classified in several genotypes and subgroups, which often mirror the geographic origin of the viral strain. The Cosmopolitan genotype HTLV-1a, can be subdivided into geographically related subgroups, e.g. Transcontinental (a-TC), Japanese (a-Jpn), West-African (a-WA), North-African (a-NA), and Senegalese (a-Sen). Within each subgroup, the genetic diversity is low. Genotype HTLV-1b is found in Central Africa; it is the major genotype in Gabon, Cameroon and Democratic Republic of Congo. While strains from the HTLV-1d genotype represent only a few percent of the strains present in Central African countries, genotypes -e, -f, and -g have been only reported sporadically in particular in Cameroon Gabon, and Central African Republic. HTLV-1c genotype, which is found exclusively in Australo-Melanesia, is the most divergent genotype. This reflects an ancient speciation, with a long period of isolation of the infected populations in the different islands of this region (Australia, Papua New Guinea, Solomon Islands and Vanuatu archipelago). Until now, no viral genotype or subgroup is associated with a specific HTLV-1-associated disease. HTLV-1 originates from a simian reservoir (STLV-1); it derives from interspecies zoonotic transmission from non-human primates to humans (ancient or recent). In this review, we describe the genetic diversity of HTLV-1, and analyze the molecular mechanisms that are at play in HTLV-1 evolution. Similar to other retroviruses, HTLV-1 evolves either through accumulation of point mutations or recombination. Molecular studies point to a fairly low evolution rate of HTLV-1 (between 5.6E−7 and 1.5E−6 substitutions/site/year), supposedly because the virus persists within the host via clonal expansion (instead of new infectious cycles that use reverse transcriptase).

Phylogeography of Human T-lymphotropic Virus Type 1 (HTLV-1) Lineages Endemic to Japan

We conducted phylogenetic analyses and an estimation of coalescence times for East Asian strains of HTLV-1. Phylogenetic analyses showed that the following three lineages exist in Japan: "JPN", primarily comprising Japanese isolates; "EAS", comprising Japanese and two Chinese isolates, of which one originated from Chengdu and the other from Fujian; and "GLB1", comprising isolates from various locations worldwide, including a few Japanese isolates. It was estimated that the JPN and EAS lineages originated as independent lineages approximately 3,900 and 6,000 years ago, respectively. Based on archaeological findings, the "Out of Sunda" hypothesis was recently proposed to clarify the source of the Jomon (early neolithic) cultures of Japan. According to this hypothesis, it is suggested that the arrival of neolithic people in Japan began approximately 10,000 years ago, with a second wave of immigrants arriving between 6,000 and 4,000 years ago, peaking at around 4,000 years ago. Estimated coalescence times of the EAS and JPN lineages place the origins of these lineages within this 6,000-4,000 year period, suggesting that HTLV-1 was introduced to Japan by neolithic immigrants, not Paleo-Mongoloids. Moreover, our data suggest that the other minor lineage, GLB1, may have been introduced to Japan by Africans accompanying European traders several centuries ago, during or after "The Age of Discovery." Thus, the results of this study greatly increase our understanding of the origins and current distribution of HTLV-1 lineages in Japan and provide further insights into the ethno-epidemiology of HTLV-1.

Distribution of Two Subgroups of Human T-Lymphotropic Virus Type 1 (HTLV-1) in Endemic Japan

Endemic areas of human T-lymphotropic virus type 1 (HTLV-1) have been reported in Japan as well as tropical Africa, Central and South America and Melanesia. The existence of two subgroups, i.e., the transcontinental and Japanese subgroups, was reported in Japan. In the present study, we provide data on the ratio of the two subgroups in each endemic area and infection foci and examine the distribution of HTLV-1 in Japan and neighboring areas. A 657 bp fragment of env region of HTLV-1 proviral genome was successfully amplified for 183 HTLV-1 positive DNA samples. The subgroup determination was done by RFLP reactions using endonucleases HpaI and HinfI. The northern part of mainland Kyushu, represented by Hirado and Kumamoto, was monopolized by the Japanese subgroup, while the transcontinental subgroup ranged from 20 to 35% in the Pacific coast areas of Shikoku (Kochi), the Ryukyu Archipelago (Kakeroma and Okinawa) and Taiwan. An interesting finding in the present study is the presence of the transcontinental subgroup in Kochi, suggesting the endemicity of the transcontinental subgroup along the Kuroshio Current.

Human T-lymphotropic virus type 1 (HTLV-1) genetic typing in Kakeroma Island, an island at the crossroads of the ryukyuans and Wajin in Japan, providing further insights into the origin of the virus in Japan

Peripheral blood samples were collected from 23 human T-lymphotropic virus type-1 (HTLV-1) carriers residing in Kakeroma Island, Japan (Kagoshima Prefecture, Oshima County, Setouchi Town), one of the most highly endemic areas in Japan. The samples were subjected to amplification by PCR and sequencing of the Long Terminal Repeat in order to reconstruct a phylogenetic tree of HTLV-1 isolates. Restriction Fragment Length Polymorphism (RFLP) analysis of env region was also conducted for subgrouping of HTLV-1. Although one sample could not be amplified by PCR, and three more could not be sequenced due to the existence of conspicuous nonspecific bands or repeated sequences, the phylogenetic analysis revealed that the remaining 19 isolates obtained from Kakeroma Island belonged to either the Transcontinental or the Japanese subgroups of the Cosmopolitan subtype, one of the three major subtypes. The RFLP data corresponded closely with the typing data throughout the sequencing. The proportion of the Transcontinental subgroup among the isolates was 26.3% (5 of 19) by sequence analysis and 27.3% (6 of 22) by RFLP. Unlike in Taiwan, China and Okinawa, the Japanese subgroup was dominant in Kakeroma Island. The analysis would also suggest that the Japanese subgroup seems not to have derived from the Transcontinental subgroup, but rather that the Transcontinental subgroup came to Japan first and was followed later by the Japanese one.

Peripheral T-cell lymphomas, unspecified (or not otherwise specified): a review

Peripheral T-cell lymphomas (PTCL) comprises a heterogeneous group of haematological tumours, which originate from mature T-cells, and constitute less than 15% of all non-Hodgkin's lymphomas (NHLs) in adults. The current WHO classification recognizes nine distinct clinicopathologic peripheral T-cell NHLs, being the 'unspecified variant' (PTCL-U) the most common subtype. These neoplasms often present in advanced stage at diagnosis, and most commonly have an aggressive clinical course requiring prompt treatment. The rarity of these tumours requires additional studies to better understand their biology and search for new therapies which may hopefully improve the dismal outcome of most patients. This review aims to describe the pathobiological aspects as well the clinical characteristics and current therapeutic strategies of the PTCLs, with special attention to the group of PTCL-U.

Hypothetical HTLV-I induction by ionizing radiation

Some laboratories have reported HTLV-I genome integration in cancer patients diagnosed with neoplasms of cervix and uterus. Usually, cancer patients undergo radiotherapy besides chemotherapy and surgery. It is hypothesized that radiation exposure would induce HTLV-I genome generation/activation, nevertheless there is not any report on experimental procedures trying to demonstrate HTLV-I gene expression in cells exposed to ionizing radiation. Anyway, earlier experimental works by Lieberman and Kaplan in 1959 succeeded to isolate retroviral particles, the radiation leukemia virus (RadLV), from thymic lymphomas of X-ray-irradiated C57BL/Ka mice, assuming that RadLV activated in the host by ionizing radiation, is released and transported to the thymus, where lymphoblasts, generated during the postradiation recovery phase, constitute an optimal target cell population for both replication of and eventual transformation by virus. Recent studies claim that besides RadLV, another retrovirus (RadLV-0) also induced by ionizing radiation is expressed and would be responsible for transformed cells of bone marrow origin. Epidemiological studies coincidentally point out to high incidence of HTLV-I infection in geographic areas displaying significant levels of radioactivity contamination as in Central Africa, Japan Islands and Mururoa Atoll. In our research work, we detected HTLV-I antibodies and viral genome integration in cancer patients of cervix and uterus and health care workers, whose had been exposed to ionizing radiation during radiotherapeutic procedures. Recombinational events among endogenous retrovirus and other retrogenic elements in the host cell genome under the bombardment of ionizing radiation from different sources could have optimized the phenomena occurrence or even ignited them to happen, generating HTLV-I genome, related viral peptides and virions. Therefore, it is feasible that exposure to ionizing radiation during therapeutic procedures could generate HTLV-I genome or induce the virus to be expressed in cells of cancer patients submitted to radiotherapy as also in healthy subjects under the same conditions, in artificial or natural radiation environment.

Clinicopathological and virological analyses of familial human T-lymphotropic virus type I–associated polyneuropathy

Human T-lymphotropic virus type I (HTLV-I) is known to be the causative agent of the chronic myelopathy, HTLV-I--associated myelopathy (HAM), and on rare occasions infection is also associated with the development of polyneuropathy. Here the authors present an HTLV-I--positive family of whom four members developed a chronic demyelinating polyneuropathy without HAM. Four female patients in a family from Hokkaido in Japan developed distal dominant paresthesia and muscle weakness in the second and third decades of their life. Neurological findings at ages ranging from 50 to 65 years included mild painful sensorimotor disturbances with atrophy of the distal parts of the extremities but without pyramidal signs or hyperactive tendon reflexes. Magnetic resonance imaging (MRI) findings of brain and spinal cord were unremarkable. Serum HTLV-I antibody levels were elevated at 1:8192 to 1:32,768, whereas those in cerebrospinal fluid were low at 1:4 to 1:8. Electrophysiological studies revealed polyphasic compound muscle action potentials with denervation potentials on nerve conduction studies and neurogenic patterns by electromyography, which were consistent with signs of chronic motor dominant demyelinating polyneuropathy. Sural nerve biopsy showed decreased myelinated fibers, occurrence of globule formation, myelin ovoid and remyelinated fibers, and an infiltration of CD68-positive macrophages with occasional CD4-positive T cells in the nerve fascicles. The polyneuropathy was responsive to steroid therapy. Analyses of serological human leukocyte antigen (HLA) types indicated that none of the patients possessed a high-risk HLA type known to be associated with adult T-cell leukemia (ATL), whereas they did have high responsive alleles to HTLV-I env similar to that observed in HAM. Nucleotide sequence analysis of the HTLV-I tax region demonstrated the B subgroup in all patients. This study suggests that HTLV-I infection can result in the development of a familial form of polyneuropathy that is associated with distinct HLA class I alleles, which might possibly involve a distinct virus subtype.

Phylogenetic characterization of a new HTLV type 1 from the Ainu in Japan

Human T cell leukemia virus type 1 (HTLV-1) is endemic among three ethnically distinguishable populations in Japan (the Ainu, Ryukyuans, and Wajin), which, together, account for most of the population in Japan. While much is known about the phylogeny of the Ryukyuan and Wajin strains of HTLV-1, only one Ainu strain has been phylogenetically analyzed. We report here a new HTLV-1 strain from the Ainu. The new isolate (U8306), as well as the previously reported isolate, are members of the Cosmopolitan group and further belong to the Transcontinental subgroup. This subgroup also predominates among the Ryukyuans, whereas the Japanese subgroup is the major subgroup among the Wajin. The predominance of subgroup A in the Ainu and Ryukyuans suggests that they share a common origin of HTLV-1.

First seroepidemiological study and phylogenetic characterization of human T-cell lymphotropic virus type I and II infection among Amerindians in French Guiana

We investigated the serological, epidemiological and molecular aspects of human T-cell lymphotropic virus type I and II (HTLV-I/II) infection in the Amerindian populations of French Guiana by testing 847 sera. No HTLV-II antibodies were detected, but five individuals (0.59%) were seropositive for HTLV-I. Analysis of the nucleotide sequences of 522 bp of the env gene and the compete LTR showed that all of the strains from French Guiana belonged to the cosmopolitan subtype A. The similarities were greater between Amerindian and Creole strains than between Amerindian and Noir-Marron strains or than between Creole and Noir-Marron strains. Phylogenetic analysis showed two clusters: one of strains from Amerindians and Creoles, which belong to the transcontinental subgroup, and the other of strains from Noirs-Marrons, belonging to the West African subgroup. Our results suggest that the Amerindian HTLV-I strains are of African origin.

Identification and phylogenetic characterization of a human T-cell leukaemia virus type I isolate from a native inhabitant (Rapa Nui) of Easter Island

Human T-cell leukaemia virus type I (HTLV-I) is endemic in Melanesia, one of the three ethnogeographic regions of the Pacific; in the other two regions, Polynesia and Micronesia, the incidence of the virus is relatively low. In an effort to gain new insights into the prevalence of HTLV-I in the Pacific region, we did a seroepidemiological survey on Easter Island, which is located on the eastern edge of Polynesia. Of 138 subjects surveyed, including 108 Rapa Nui (the native inhabitants of this island), we identified one HTLV-I-seropositive Rapa Nui. The new HTLV-I isolate derived from this carrier (E-12) was phylogenetically analysed to ascertain the origin and past dissemination of HTLV-I in the island. The analysis demonstrated that isolate E-12 belongs to subgroup A of the Cosmopolitan group, and that it differs from HTLV-Is found in Melanesia, which are highly divergent variants. In subgroup A, E-12 grouped with South American HTLV-Is including those from Amerindians. This result suggests that this isolate originated in South America rather than in Melanesia.

Genomic Evolution, Patterns of Global Dissemination, and Interspecies Transmission of Human and Simian T-cell Leukemia/Lymphotropic Viruses

Using both env and long terminal repeat (LTR) sequences, with maximal representation of genetic diversity within primate strains, we revise and expand the unique evolutionary history of human and simian T-cell leukemia/lymphotropic viruses (HTLV/STLV). Based on the robust application of three different phylogenetic algorithms of minimum evolution–neighbor joining, maximum parsimony, and maximum likelihood, we address overall levels of genetic diversity, specific rates of mutation within and between different regions of the viral genome, relatedness among viral strains from geographically diverse regions, and estimation of the pattern of divergence of the virus into extant lineages. Despite broad genomic similarities, type I and type II viruses do not share concordant evolutionary histories. HTLV-I/STLV-I are united through distinct phylogeographic patterns, infection of 20 primate species, multiple episodes of interspecies transmission, and exhibition of a range in levels of genetic divergence. In contrast, type II viruses are isolated from only two species (Homo sapiens and Pan paniscus) and are paradoxically endemic to both Amerindian tribes of the New World and human Pygmy villagers in Africa. Furthermore, HTLV-II is spreading rapidly through new host populations of intravenous drug users. Despite such clearly disparate host populations, the resultant HTLV-II/STLV-II phylogeny exhibits little phylogeographic concordance and indicates low levels of transcontinental genetic differentiation. Together, these patterns generate a model of HTLV/STLV emergence marked by an ancient ancestry, differential rates of divergence, and continued global expansion.

Community-based molecular epidemiology of HTLV type I in Taiwan and Kinmen: implication of the origin of the cosmopolitan subtype in northeast Asia

To understand the possible origin and dissemination of HTLV-I infection in northeast Asia, community-based molecular epidemiological studies were conducted on the Kinmen Islands (off the coast of Fukien Province, China) and in Taiwan. A total of 3831 Taiwanese from 3 townships (Pu-Li, Chu-Dung, and Pu-Tze) and 993 aborigines from 4 tribes in Taiwan participated in this study. The prevalence rates of HTLV-I infection in adult residents from Pu-Li, Chu-Dung, and Pu-Tze were 0.82, 1.72, and 1.63%, respectively. None of the aborigines had HTLV-I infection. Previously, 0.73% of the adult population of Kin-Hu, Kinmen were found to have HTLV-I infection. Peripheral blood mononuclear cells were collected from HTLV-I carriers identified both in Taiwan and Kinmen and the HTLV-I LTR sequences were PCR amplified, subcloned, and sequenced for phylogenetic tree analysis. The results showed that all 6 HTLV-I isolates from Kinmen and 13 of 18 (72.2%) isolates from Taiwan were group a (transcontinental) of Cosmopolitan subtype, while 5 of 18 (27.8%) isolates from Taiwan were group b (Japanese) of Cosmopolitan subtype. Since all of the HTLV-I-infected persons were descendants of immigrants from mainland China, the origin of the Cosmopolitan subtype in Taiwan and Kinmen may not have been Japan, as previously theorized, but China, possibly the result of the migration of an infected population in the past several centuries.

Molecular phylogeny of human T-cell leukemia virus type I and II of Amerindians in Colombia and Chile

Six human T-cell leukemia virus type I (HTLV-I) and eight human T-cell leukemia virus type II (HTLV-II) cases newly isolated from the South American countries of Colombia and Chile were analyzed together with the two Amerindian HTLV-I isolates previously reported. All of the HTLV-I isolates belonged to the transcontinental subgroup of the "cosmopolitan" group, and Colombian isolates, including those from native Amerindians and Negroes, formed a single tight cluster within this subgroup. The transcontinental subgroup consisted of isolates from various regions such as the Caribbean basin, India, Iran, South Africa, Sakhalin, and Japan, and included isolates from the "Ainu" and "Okinawa" people, regarded as relatively pure Japanese descended from the prehistoric "Jomon" period which began more than 10,000 years ago. This implied a dissemination of the subgroup associated with the movement of human beings in ancient times. On the other hand, all of the HTLV-II isolates from native Amerindians in Colombia and Chile belonged to the HTLV-IIb subtype which has previously been reported to be mainly endemic in certain populations of native Amerindians. The southernmost isolate from Chile, showing wide distribution of the IIb subtype in native South Amerindians and largest heterogeneity of the subtype in Colombian isolates, supported the idea that the HTLV-IIb subtype has been endemic for a long time in native Indians of South America.

Immunogenicity of variable regions of the surface envelope glycoprotein of HTLV type I and identification of new major epitopes in the 239-261 region

The reactivity of sera of 96 individuals infected with human T-cell leukemia virus type I (HTLV-I) was tested against various synthetic peptides corresponding to the gp46 immunodominant antigenic domains: residues 86-107, 175-199, and 239-261. The frequency of reactive sera was higher for 175-199 (93%) than for 239-261 (78%) or 86-107 (24%) with some variations in geographical regions and in diseases. The region 239-261 was extensively analyzed and five (linear or conformational) epitopes were found. The reactivity of sera toward functional or immunodominant domains may depend on the sequence of the infecting virus, and the role of three frequent substitutions (asparagine by tyrosine, proline by serine, and serine by proline or leucine at positions 93, 192, and 250 respectively) was established. Finally, the role of the genetic background of the host may condition the humoral immune response as individuals infected by HTLV-Is harboring the same predicted gp46 peptide sequence may recognize one, several, or all regions examined.

Molecular epidemiology of HTLV-I in the world

The geographic distribution of human T-cell lymphotropic/leukemia virus type I (HTLV-I) was initially believed to be limited to southwestern Japan, the Caribbean basin, and Africa. However, extensive searches in recent years have discovered its existence in other areas of the world as well as in isolated, ethnic populations such as South Amerindians, Australo-Melanesian aborigines, religiously segregated Jews, and Pygmies. Previous genetic analyses indicated that HTLV-I can be phylogenetically classified into three major lineages: Melanesian, Central African, and Cosmopolitan groups. Recently, more detailed characterization using long terminal repeat sequences (the most variable genomic region) has revealed that the Cosmopolitan group consists of four subtypes: (A) Transcontinental, (B) Japanese, (C) West African, and (D) North African. Most HTLV-I isolates of the same ethnic group from distant locations and those from different groups inhabiting the same area showed phylogenetic similarities. These observations indicate the present distribution of this virus should be interpreted from the anthropological backgrounds of the virus-possessing populations as well as spatial contact among them. Thus, the molecular epidemiology of HTLV-I and its simian counterpart, STLV-I, provides us with important clues for understanding not only the origin and dissemination of this retrovirus but past human movements over the globe.

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

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

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

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

Human T-lymphotropic virus type 1 in coastal natives of British Columbia: phylogenetic affinities and possible origins

Human T-lymphotropic virus type 1 (HTLV-1) infection has been discovered recently in people of Amerindian descent living in coastal areas of British Columbia, Canada. DNA sequencing combined with phylogenetic analysis and restriction fragment length polymorphism (RFLP) typing of HTLV-1 strains recovered from these British Columbia Indians (BCI) was conducted. Sequence-based phylogenetic trees distributed the BCI isolates among the Japanese subcluster (subcluster B) and the geographically widely distributed subcluster (subcluster A) of the large HTLV-1 cosmopolitan cluster. Long terminal repeat (LTR) RFLP typing revealed three distinct, equally frequent LTR cleavage patterns, two of which were of previously recognized Japanese and widely dispersed cosmopolitan types. A third, new cleavage pattern was detected which may have arisen by recombination between two other HTLV-1 genotypes. Our results suggest multiple origins for HTLV-1 in BCI, which are equally consistent with (i) a cluster of recent sporadic infections, (ii) ancient endemic vertical transmission through Amerindian lineages, or (iii) both.