Human T-cell leukemia viruses: epidemiology, biology, and pathogenesis

The human T-cell lymphotropic viruses type I and type II are closely related human retroviruses that have similar biological properties, genetic organization and tropism for T lymphocytes. Along with the simian T-cell lymphoma virus type I, they define the group of retroviruses known as the primate T-cell leukemia/lymphoma viruses. Initially identified in 1980, the human T-cell lymphotropic virus type I has been implicated as the etiologic agent of adult T-cell leukemia/lymphoma and of a degenerative neurologic disorder known as tropical spastic paraparesis or human T-cell lymphotropic virus type I-associated myelopathy. The intriguing link between human T-cell lymphotropic virus type, T-cell malignancy, and a totally unrelated and non-overlapping neurological disorder suggests divergent and unique pathogenetic mechanisms. This review will address the epidemiology, molecular biology, and pathogenesis of human T-cell leukemia viruses.

Prevalence of human retroviral infection in Quillabamba and Cuzco, Peru: a new endemic area for human T cell lymphotropic virus type 1

An epidemiologic study was conducted to determine the prevalence of retroviral infections among people of Qucchua origin in Cuzco and Quillabamba, Peru. The study volunteers included individuals at low and at high risk for retroviral infections. Each volunteer was interviewed to obtain clinical and epidemiologic data, and to identify risk behaviors for infection. The serum was tested for human immunodeficiency virus type 1 (HIV-1) and human T cell lymphotropic virus types 1/2 (HTLV-1/2) by standard enzyme-linked immunosorbent and Western blot assays. Among a total of 370 volunteers enrolled in the study, 276 were women and 94 were men whose ages ranged between 15 and 49 years. Infection with HTLV-1 was demonstrated in 5.1% (19 of 370), and one of these, a homosexual, was also positive for HIV-1; none had HTLV-2. Overall, the rate of HTLV-1 infection was 5.3% (5 of 94) for males and 5% (14 of 276) for females. Among the low risk group of 211 healthy pregnant women, five (2.3%) were positive for HTLV-1. The rate of HTLV-1 infection in this group was significantly correlated with a history of dental surgery, as well as other surgical procedures, and a history of jaundice. Among the volunteers who practiced risk behavior(s) for retroviral infections, the positive rates for HTLV-1 were 13.7% (7 of 51) for female sex workers, 6.2% (3 of 48) for homosexuals and/or bisexuals, 8.5% (4 of 47) for patients with sexually transmitted diseases (STDs), and 0.0% (0 of 13) for promiscuous heterosexual males. In female sex workers. HTLV-1 infection was found to be significantly associated with age, a history of STDs or genital ulcers, sexual intercourse during menses, and vaginal douching (P < 0.05). A low prevalence of HIV-1 infection indicates that the virus has not yet spread significantly in these areas.

Common origin of human T-lymphotropic virus type-I from Iran, Kuwait, Israel, and La Réunion Island

We found previously that Kuwaiti HTLV-I isolates had two nucleotide substitutions in the most frequently sequenced regions of HTLV-I genome, namely: T-->C 4783 in the pol and T-->C 6569 the env genes. These substitutions were observed rarely in other HTLV-I isolates and seemed to be good markers of the HTLV-I lineage, the "epicentre" of which was located in Mashhad, Iran. To test this hypothesis we sequenced the fragments of HTLV-I genome including sites 4783 and 6569 from seven isolates obtained from the Iranians either living in (five isolates) or originating from (two isolates) Mashhad. RFLP-based tests were also designed and used for typing of the substitutions. All seven isolates were positive for T-->C 4783 and six, from which env fragment was amplifiable, were also positive for T-->C 6569. It is highly probable that all the isolates from Mashhadi Jews belong to the same HTLV-I lineage, although they were not typed yet for the presence of T-->C 6569 substitution. Only 2 "non-Middle Eastern" HTLV-1, both from La Réunion Island were positive for both of the substitutions. Another possible member of Mashhadi lineage of HTLV-I is one isolate from southern India and two isolates from the American Indians, British Columbia, Canada. The determination of the T-->C 4783 and T-->C 6569 markers in HTLV-I isolates of different geographical/ethnic origin may be useful for the reconstruction of the routes of HTLV-I spread from the Middle East and/or Indian subcontinent to other regions of the world and, possibly, for gaining insights into the origin of HTLV-I in Asia.

Molecular analysis of HTLV-I and HTLV-II isolates from Italian blood donors, intravenous drug users and prisoners

Using molecular methods three or five major variants of HTLV-I have been identified; moreover two subtypes of HTLV-II defined as HTLV-IIa and HTLV-IIb with six variants within each of these groups have been described. In the present study we analysed proviral DNA obtained from the peripheral blood mononuclear cells (PBMCs) of a significant group of Italian intravenous drug users (IVDUs), prison inmates and blood donors (BDs) who were HTLV antibody positive. Restriction fragment length polymorphism (RFLP) of amplified LTR region with ApaI, NdeI, DraI, SacI and MaeIII endonucleases was used to define the HTLV-I subtypes, while the different variants of HTLV-IIa and -IIb were defined by RFLP of the LTR region with the AvaII, BglI, SauI, XhoI and BanII endonucleases. The four HTLV-I isolated from BDs were characterized as C type. All the 11 HTLV-II detected in the IVDUs were HTLV-IIb4, while among the prisoners one HTLV-IIb5 and five HTLV-IIb4 were found. Interestingly, in the BDs group two HTLV-IIa0 and one HTLV-IIb4 were detected. It should also be noted that 82% of the IVDUs and 50% of the prisoners were coinfected with HIV, while all the BDs were HIV negative. These data indicate that HTLV-IIb4 is the predominant genotype in Italian IVDUs and prisoners, while the significant variability observed in the BD HTLV-II isolates could be due to the different source of infection among this group.

Primary prevention of HTLV-1 in Japan

The Nagasaki Prefecture, Japan (population: 1.5 million), is one of the hot endemic foci of Human T-lymphotropic virus type 1 (HTLV-1). Prevalence of HTLV-1 carriers are approximately 10% in the age group over 40 years old (40,000 individuals), approximately 10 times of the national average. Annual registry of adult T-cell leukemia (ATL) in the Prefecture is approximately 60 cases (estimated incidence: 100 cases), or a half percent of total deaths. A effective measure to control the endemic cycle of HTLV-1 has been imperative, since practical ways to prevent or control ATL are not available. A prefecture wide intervention at Nagasaki by refrain from breast-feeding blocked approximately 80% of mother-to-child transmission of HTLV-1.

Pathogenesis and prevention of HTLV-1-associated diseases

HTLV-1 is an important factor involved in various diseases including adult T-cell leukemia/lymphoma and HTLV-1 associated myelopathy/tropical spastic paraparesis. Amount of HTLV-1 provirus integrated in human peripheral blood mononuclear cells might be a candidate for a risk factor in the manifestation of HTLV-1 associated diseases. Experimental animal models would be useful to dissect the pathogenesis of HTLV-1 associated diseases. We present rat and mouse models of HTLV-1 infection. Using these animal models, we could clarify the intrauterine transmission of HTLV-1, and have found that both genetic background and HTLV-1 infection are important in pathogenesis of HAM/TSP-like rats. We also discuss the preventive measures of HTLV-1 transmission by use of antisense oligonucleotides.

HTLV-1 uveitis (HU)

We reported HTLV-1 uveitis (HU) as the third distinct clinical entity associated with HTLV-1 infection. Uveitis has advantages for studying the pathogenetic mechanisms of inflammatory diseases caused by HTLV-1, since observation of the disease process is relatively easy and clinical samples from the lesion can be obtained. Results of our clinical, virological and epidemiological studies of HU patients will be first summarized. Then we present results on in vitro studies that showed transactivation of HTLV-1 LTR by thyroid hormone and discuss the significance in the context of pathogenesis of HTLV-1-related inflammatory diseases.

Short-term breast-feeding may reduce the risk of vertical transmission of HTLV-I. The Tsushima ATL Study Group

To establish a desirable preventive measure against mother-to-child transmission of HTLV-I through breast milk, we conducted a prospective study to investigate the seroconversion rate among children born to HTLV-I carrier mothers on two highly HTLV-I-endemic islands where 8% of pregnant women carry HTLV-I. Between 1985 to 1991, 428 pregnant women were found to be positive against anti-HTLV-I antibody and were advised not to breast-feed their newborn babies. Among them, 212 women (50%) accepted this advice and the other mothers proceeded to breast-feed. Results were obtained from 277 children born to HTLV-I carrier mothers and were followed up until more than 30 months of age. When the seroconversion rate was analyzed by feeding manner, short-term breast-feeders (< or = 6 months) showed a statistically significant lower seroconversion rate than long-term breast-feeders (2/51; 3.9% vs. 13/64; 20.3%, p < 0.05). On the other hand, four out of 162 bottle-fed children (2.5%) became positive. It is hypothesized that maternal HTLV-I antibody may protect babies from HTLV-I infection through breast milk during the first 6 months.

Serologic survey for HTLV-I in Kanagawa Prefecture

To investigate the seroprevalence of HTLV-I in Kanagawa Prefecture (central Japan), we tested the sera of 8,264 healthy volunteers and 2,414 pregnant women. Of the 8,264 healthy volunteers, 66 (0.80%) were seropositive. The seroprevalence of HTLV-I in the pregnant women was 14/2,414 (0.58%), and this rate was almost identical to that in the healthy female volunteers 15 to 44 years of age (0.59%). These figures indicate that the seroprevalence of HTLV-I in Kanagawa Prefecture is very low and that sexual contact may not be an important contributory factor.

[A seroepidemiological survey: antibody to HTLV-1 in sera from various populations in Guangdong Province]

A seroepidemiological survey of HTLV-1 infection in Guangdong Province was reported. 2224 serum samples from various populations were collected and antibodies to HTLV-1 in sera were detected with indirect immunofluorescent assay. Total seropositive rate was 1.57% (35/2224). The antibody positive rates of HTLV-1 in sera from healthy individuals (n = 1810), blood donors (n = 248), patients with T cell leukemia (n = 109) and patients with neurological diseases (n = 57) were 1.27%, 0.40 %, 7.30% and 5.26% respectively. There was a significant difference between the patients with T cell leukemia and the healthy individuals (P<0.005).

Significance of indeterminate reactivity to human T-cell lymphotropic virus in western blot analysis of individuals at risk

Current tests to confirm human T-cell lymphotropic virus (HTLV) infection in individuals at risk of retroviral infection commonly yield indeterminate results. To assess the significance of HTLV-seroindeterminate reactivities in a high-risk population, 16 at-risk individuals who had this serologic pattern by Western blot were studied using a polymerase chain reaction (PCR) assay. Human T-cell lymphotropic virus type II infection was confirmed by the presence of virus-specific nucleic acid in four patients. However, PCR analysis was negative in the remaining 12 individuals. These results indicate strongly that all specimens from at-risk individuals with nondiagnostic HTLV reactivity by current Western blot assay should continue to be considered inconclusive, requiring further testing by more sensitive tests.

International forum: Saudi Arabia. Donor screening for HTLV-I in Saudi Arabia: is it cost effective?

After screening over 100,000 blood donations for the presence of anti-HTLV-I antibodies, a final prevalence of 0.0038% was established in a multinational donor population. Among 38,201 donations by Saudi Arabian donors, the prevalence was found to be 0.0052%. Fifty-eight donors were found to be repeat reactive in the EIA screen test, but only 6.9% of these (n = 4) were truly infected with HTLV-I as judged by the Western blot result. These results indicate that Saudi Arabia is non-endemic for HTLV-I as well as HTLV-II. The cost effectiveness of screening for HTLV-I in healthy blood donors from this area is highly questionable. Calculations point to a final risk of a case of post-transfusion HTLV-I associated disease of approximately one per 100 years at the current level of activity.

Human T cell lymphotropic virus type I does not increase human immunodeficiency virus viral load in vivo

Human T lymphotropic virus type I (HTLV-I) can increase human immunodeficiency virus (HIV) replication in vitro, and several studies suggest that HTLV-I accelerates the progression of HIV infection. To determine whether HTLV-I enhances HIV replication in vivo, a case-control study was done of serum HIV viral load, using polymerase chain reaction, in 23 subjects with HTLV-I/HIV coinfection and 92 control subjects with HIV single infection. The geometric mean serum RNA level was 11,482 copies/mL in the coinfected group and 13,804 in the single-infection group (P = .57), a result that did not change after adjustment for zidovudine use and CD4 cell count. Among subjects with advanced HIV infection, there was a trend toward higher viral load among singly infected subjects. HTLV-I did not appear to increase HIV plasma RNA levels in subjects with coinfection. These results do not provide a biologic basis for the hypothesis that HTLV-I accelerates the course of HIV infection.

HTLV-associated myelopathy in a cohort of HTLV-I and HTLV-II-infected blood donors. The REDS investigators

OBJECTIVE

HTLV-I-associated myelopathy (HAM) is a slowly progressive spastic paraparesis caused by infection with human T-lymphotropic virus type I (HTLV-I). The prevalence of HAM among those infected with HTLV-I is poorly defined, and the association of a similar myelopathy with HTLV-II infection has not been confirmed.

DESIGN

Cross-sectional examination of HTLV-I, HTLV-II, and control subjects from the baseline visit of a cohort study. SETTING/ SUBJECTS: Persons testing HTLV seropositive at the time of blood donation at five U.S. blood centers, their seropositive sex partners, and a matched control group of HTLV seronegative blood donors.

MEASUREMENTS

HTLV-I and HTLV-II were differentiated by serology and/or polymerase chain reaction. All subjects received systematic neurologic screening examinations.

RESULTS

A diagnosis of myelopathy was confirmed in four of 166 HTLV-I subjects (2.4%, 95% confidence interval 0.7%, 6.1%) and in one of 404 HTLV-II subjects (0.25%, 95% confidence interval 0.0%, 0.6%). None of the 798 controls had a similar myelopathy, although one had longstanding typical multiple sclerosis.

CONCLUSIONS

Our data also suggest that HAM occurs more frequently among HTLV-I-infected subjects than reported by previous studies. The HTLV-II infected myelopathy patient identified in this cohort, together with three other case reports in the literature, implies a pathogenic role for this human retrovirus. The diagnosis of HTLV-associated myelopathy should be considered in cases of spastic paraparesis or neurogenic bladder when risk factors for HTLV-I or HTLV-II infection are present.

Is HTLV-1 status another antenatal screening test that we need?

Human T-lymphocytic virus type 1 (HTLV-1) carriage is associated with a 2% to 5% lifetime risk of developing a severe, if not fatal, disease. In our Inner London antenatal population, we found that the carrier rate was 0.3%. The antenatal transmission rate is known to be very low, but if the infant is breastfed the transmission rate is up to 25%. It is therefore possible to interrupt the transmission cycle by advising against breastfeeding. The ethical and fiscal issues surrounding antenatal testing are addressed.

Retroviral coinfections at a New Orleans HIV outpatient clinic

The purpose of the study was to determine the seroprevalence of human T-lymphotropic virus types I and II (HTLV-I and HTLV-II) infections in an outpatient clinic population of human immunodeficiency virus (HIV)-1 infected persons as well as to identify the demographic and clinical characteristics and laboratory results associated with HTLV-I/II infections. During 1993-1995, 854 patients were tested for HTLV-I/II infection on entry into the clinic, of whom 25 were infected with HTLV-I and 35 with HTLV-II. Multivariate analysis revealed that patients with coinfections were more likely to be black, aged over 35 years, and have a history of injection drug use. HIV-1/HTLV-I coinfections were associated with higher median CD8 counts on entry (p < 0.05), and HIV-1/HTLV-II coinfections were associated with higher median percent CD4 counts (p < 0.05) compared with patients infected with HIV only. Coinfection was not associated with an increased diagnosis of AIDS. These findings indicate that HIV-1/HTLV-I/II coinfections are frequently diagnosed and are associated with unique immune phenotypes. Given the lack of information regarding the influence of dual infection on clinical status, differentiation of HTLV-I from HTLV-II infections may be important in understanding the clinical significance of retroviral coinfections.

The seroprevalence of HTLV-I in patients with ocular diseases, pregnant women and healthy volunteers in the Kanto district, central Japan

HTLV-I has been shown to be related to the development of inflammatory diseases in various organs such as the eyes, lungs and joints. In south-west Japan where HTLV-I is highly endemic, the term 'HTLV-I associated complex' has been approved. To investigate the seroprevalence of HTLV-I in the Kanto district in central Japan, we have estimated the frequency of seropositivity to HTLV-I in 2,110 patients with various ocular diseases and 2,683 pregnant women, in addition to 5,336 healthy volunteers. Of the healthy volunteers, only 42 (0.79%) were seropositive, and the HTLV-I seroprevalence in pregnant women was also only 16/2,683 (0.60%) which was almost equal to that in female healthy volunteers aged 15-44 years (0.59%). In patients with various ocular diseases, however, there was significantly higher seroprevalence of HTLV-I (2.32%) compared with healthy volunteers in each sex (male: p = 0.0029; female: p = 0.000023). These results suggest that the seroprevalence of HTLV-I in the Kanto district is much lower than in south-west Japan. On the other hand, HTLV-I infection was shown to be correlated to ocular diseases also in the Kanto district. In particular, we found a higher seroprevalence of HTLV-I in patients with inflammatory ocular disease, such as endogenous uveitis, episcleritis, retinitis pigmentosa and degenerative choroiditis. This possibly suggests a causative role of HTLV-I in the development of these inflammatory ocular diseases also where HTLV-I is not endemic.

HTLV-I seroprevalence in the Sultanate of Oman

2329 subjects (blood donors and patients) from various areas of the Sultanate of Oman were investigated for the presence of HTLV-I antibody by as enzyme immunoassay (EIA) method. 10 subjects (0.4%), including 9/1586 blood donors (0.6%) and 1/165 patients with sexually transmitted diseases (0.6%), were found to be EIA seropositive with a regional variation in seroprevalence of 0-14%. 6/9 EIA seropositive samples from blood donors yielded 'indeterminate' results on Western immunoblot analysis (WBA). A much larger survey with additional confirmatory assays such as a radioimmunoprecipitation assay (RIPA), should provide a more conclusive picture of the prevalence of this retroviral infection in the Sultanate.

Breast milk is not a significant source for early Epstein-Barr virus or human herpesvirus 6 infection in infants: a seroepidemiologic study in 2 endemic areas of human T-cell lymphotropic virus type I in Japan

In order to evaluate the possibility of Epstein-Barr virus (EBV) and human herpesvirus 6 (HHV-6) transmission via breast milk, a total of 331 serum specimens collected from bottle-fed and breast-fed children and their mothers, in 2 endemic areas of human T-cell lymphotropic virus type I (HTLV-I) in Japan, were assayed for antibodies to EBV and HHV-6. The seroprevalences of EBV and HHV-6 were over 95% both in the mothers of bottle-fed children and in those of breast-fed children. The seroprevalence of EBV at 12-23 months of age was 54.5% (36/66) and 55.8% (24/43) in breast-fed children and bottle-fed children, respectively. The seroprevalence of HHV-6 at 12-23 months of age was 90.9% (60/66) and 93.0% (40/43) in breast-fed children and bottle-fed children, respectively. No difference was observed between the seroprevalences of EBV and HHV-6 in breast-fed and bottle-fed children at 12-23 months of age. Our seroepidemiologic data indicate that breast milk is not a significant source of early EBV or HHV-6 infection in infancy.

Correlation between human T cell lymphotropic virus type-1 and Strongyloides stercoralis infections and serum immunoglobulin E responses in residents of Okinawa, Japan

To clarify the relationship between Strongyloides stercoralis, infection with human T cell lymphotropic virus type-1 (HTLV-1), and serum immunoglobulin E (IgE) levels, epidemiologic investigations of these two infections were conducted in inhabitants of Okinawa, a subtropical zone in Japan. Blood and feces samples were taken from 1,347 healthy inhabitants (554 males and 793 females). Antibody to HTLV-1 was measured by particle agglutination, enzyme-linked immunosorbent assay, and Western blotting. The presence of Strongyloides was determined by direct detection of rhabditiform larvae in fresh stool on agar-plate cultures. Serum IgE levels in 127 inhabitants were measured by a fluoroenzyme immunoassay. Antibody to HTLV-1 was detected in 23.0% of the blood samples and was more frequent in females (25.1%) than in males (20.0%) (P < 0.05). Strongyloides were detected in 21.9% of the feces samples and were more frequent in males (31.9%) than in females (14.9%) (P < 0.001). The prevalence of both infections increased with age, especially in persons 50 years of age and older: The prevalence of Strongyloides infection was significantly higher in HTLV-1 carriers (31.6%) than in those without HTLV-1 infection (P < 0.001). The level of IgE was low in HTLV-1 carriers, and significantly lower in HTLV-1 carriers than in noncarriers among inhabitants with Strongyloides infection. Both HTLV-1 and Strongyloides infections are endemic in the area studied.

Molecular subtyping of human T-lymphotropic virus type I (HTLV-I) by a nested polymerase chain reaction-restriction fragment length polymorphism analysis of the envelope gene: two distinct lineages of HTLV-I in Taiwan

The major type of human T-lymphotropic virus type I (HTLV-I), generally referred to as the cosmopolitan type, has been grouped into three subtypes (A, B, and C) by phylogenetic analysis of the long terminal repeat sequences of the viral genome. Twelve subtype-specific nucleotide variations have been deduced by comparison between the envelope (env) sequences of 16 HTLV-I strains with defined subtypes and 9 Taiwanese HTLV-I strains. To gain further insights into the molecular epidemiology of HTLV-I and the origin of this virus in Taiwan, a rapid method of identification for the cosmopolitan subtypes was developed by using a nested polymerase chain reaction (PCR) and subsequent restriction fragment length polymorphism (RFLP) studies using the two subtype B-specific and four subtype C-specific nucleotides located within the positions 5708 to 6320 of the envgene. The nested PCR-RFLP method was used to subtype HTLV-I from four virus-positive cell lines derived from 1 Japanese and 3 North American patients, as well as 41 blood-unrelated Taiwan Chinese. The sequences of PCR products were determined and the six positions of subtype-specific nucleotide variations were examined. The sequence data completely supported the subtyping data via the nested PCR-RFLP method. The results demonstrated that, as is the case in Japan, at least two distinct cosmopolitan subtypes (A and B) of HTLV-I were present in Taiwan, but the more prevalent subtype in Taiwan is A in contrast to subtype B in Japan. Furthermore, rapid subtyping could facilitate molecular epidemiological studies of HTLV-I infection and linkage between HTLV-I subtypes and virus-associated diseases.

Determination of the true prevalence of infection with the human T-cell lymphotropic viruses (HTLV-I/II) may require a combination of biomolecular and serological analyses

Infection with the human T-cell lymphotropic virus types I and II (HTLV-I/II) usually is determined by tests that detect antibodies to the viral structural proteins. However, recent studies revealed that patients with mycosis fungoides have proviral DNA sequences related to the HTLV transactivating-transforming gene tax, without having antibodies to the virus. These results raised the possibility that the prevalence of HTLV infection in the general population of the United States also may be underestimated. To reassess the prevalence of HTLV-I/II infection effectively, a population at increased risk for infection (i.e., a cohort of injection drug users [IDUs]) was studied. Paired sera and peripheral blood mononuclear cells (PBMCs) from 81 IDUs were subjected to testing by Western blot analysis for antibodies to the viral structural proteins gag and env and by polymerase chain reaction (PCR) Southern analysis to detect gag, pol and tax proviral DNA sequences. Western blot assays showed 1 of 81 IDUs to be positive for HTLV-I, 14 to be positive for antibodies to HTLV-II, and 3 to be HTLV-serotype indeterminate. When whole-cell lysates of PBMCs from these individuals were subjected to PCR and Southern analysis. 39 of 81 were found to have HTLV-related sequences. A total of nine IDUs were found to be infected with HTLV-I, a figure nearly 10 times higher than that estimated by serology alone. Bio-molecular analysis showed HTLV-II-specific proviral sequences in 21 IDUs. Three individuals were seropositive for HTLV-II but lacked PCR evidence of gag, pol and tax sequences. Thus, the overall prevalence of HTLV infection among this cohort was 59% (43 of 81) (i.e., more than twice the frequency predicted by serology, 18 of 81 or 22%). These results indicate that it may be necessary to incorporate biomolecular as well as serological methodologies to identify all persons infected with these retroviruses.