Insights on the pathogenicity of human T-lymphotropic/leukemia virus types I and II

40 years of the human T-cell leukemia virus: past, present, and future

It has been nearly 40 years since human T-cell leukemia virus-1 (HTLV-1), the first oncogenic retrovirus in humans and the first demonstrable cause of cancer by an infectious agent, was discovered. Studies indicate that HTLV-1 is arguably one of the most carcinogenic agents to humans. In addition, HTLV-1 causes a diverse array of diseases, including myelopathy and immunodeficiency, which cause morbidity and mortality to many people in the world, including the indigenous population in Australia, a fact that was emphasized only recently. HTLV-1 can be transmitted by infected lymphocytes, from mother to child via breast feeding, by sex, by blood transfusion, and by organ transplant. Therefore, the prevention of HTLV-1 infection is possible but such action has been taken in only a limited part of the world. However, until now it has not been listed by the World Health Organization as a sexually transmitted organism nor, oddly, recognized as an oncogenic virus by the recent list of the National Cancer Institute/National Institutes of Health. Such underestimation of HTLV-1 by health agencies has led to a remarkable lack of funding supporting research and development of treatments and vaccines, causing HTLV-1 to remain a global threat. Nonetheless, there are emerging novel therapeutic and prevention strategies which will help people who have diseases caused by HTLV-1. In this review, we present a brief historic overview of the key events in HTLV-1 research, including its pivotal role in generating ideas of a retrovirus cause of AIDS and in several essential technologies applicable to the discovery of HIV and the unraveling of its genes and their function. This is followed by the status of HTLV-1 research and the preventive and therapeutic developments of today. We also discuss pending issues and remaining challenges to enable the eradication of HTLV-1 in the future.

Tax-1 and Tax-2 similarities and differences: focus on post-translational modifications and NF-κB activation

Although human T cell leukemia virus type 1 and 2 (HTLV-1 and HTLV-2) share similar genetic organization, they have major differences in their pathogenesis and disease manifestation. HTLV-1 is capable of transforming T lymphocytes in infected patients resulting in adult T cell leukemia/lymphoma whereas HTLV-2 is not clearly associated with lymphoproliferative diseases. Numerous studies have provided accumulating evidence on the involvement of the viral transactivators Tax-1 versus Tax-2 in T cell transformation. Tax-1 is a potent transcriptional activator of both viral and cellular genes. Tax-1 post-translational modifications and specifically ubiquitylation and SUMOylation have been implicated in nuclear factor-kappaB (NF-κB) activation and may contribute to its transformation capacity. Although Tax-2 has similar protein structure compared to Tax-1, the two proteins display differences both in their protein–protein interaction and activation of signal transduction pathways. Recent studies on Tax-2 have suggested ubiquitylation and SUMOylation independent mechanisms of NF-κB activation. In this present review, structural and functional differences between Tax-1 and Tax-2 will be summarized. Specifically, we will address their subcellular localization, nuclear trafficking and their effect on cellular regulatory proteins. A special attention will be given to Tax-1/Tax-2 post-translational modification such as ubiquitylation, SUMOylation, phosphorylation, acetylation, NF-κB activation, and protein–protein interactions involved in oncogenecity both in vivo and in vitro.

Inhibitory effect of chondroitin sulfate type E on the binding step of human T-cell leukemia virus type 1

Cell surface heparan sulfate proteoglycans (HSPGs) are involved in the binding and entry of human T-cell leukemia virus type 1 (HTLV-1) into host cells, while sulfated polysaccharides such as heparin inhibit HTLV-1 infection. Chondroitin sulfate proteoglycans (CSPGs) are classified as another major type of proteoglycans. Here, we examined the effect of four types of chondroitin sulfate (CS) on HTLV-1 infection. Accordingly, a human T cell line, MOLT-4, was inoculated with cell-free HTLV-1 in the presence or absence of soluble CS, and the synthesis of reverse-transcribed HTLV-1 DNA within cells 20 h after inoculation was detected using polymerase chain reaction (PCR). Among the four types of CS (A, C, D, and E), the E type (CSE), which was derived from the squid cartilage, exhibited anti-HTLV-1 activity. Furthermore, we observed that CSE directly interacted with recombinant HTLV-1 envelope (Env) proteins and inhibited the binding of HTLV-1 virions to MOLT-4 cells, indicating that the interaction between Env and CSE plays a significant role in its anti-HTLV-1 activity. In addition, CSE inhibited syncytium formation that was induced by HTLV-1-producing cells. When CSE was mixed with the synthetic fusion inhibitor peptide corresponding to the ectodomain of the Env transmembrane subunit (TM) gp21, the HTLV-1 infection was further inhibited when compared with the inhibitory effect of each compound alone. Thus, further elucidation of the in vitro antiviral mechanism of CSE shown in this study will lead to the development of CSE-like molecules for the entry inhibition of HTLV-1.

Routine screening for chronic human immunodeficiency virus infection: why don't the guidelines agree?

Infection with human immunodeficiency virus remains a major public health problem in the United States. Prominent guidelines from the U.S. Preventive Services Task Force and the Centers for Disease Control and Prevention differ in their recommendations on whether and how to screen adults and adolescents not known to be at higher risk. These discrepancies have led to controversy and debate as well as confusion among clinicians. This article reviews principles of screening, explains specific issues related to screening for human immunodeficiency virus, reviews the discrepancies between the US Preventive Services Task Force and the Centers for Disease Control and Prevention guidelines and the methods used in each guideline, and describes potential reasons for the discrepancies. The case of screening for human immunodeficiency virus illustrates how discrepancies between guidelines may be related to different guideline development methods as well as the different perspectives of the guideline development groups.

Highly enhanced expression of CD70 on human T-lymphotropic virus type 1-carrying T-cell lines and adult T-cell leukemia cells

Human T-lymphotropic virus type 1 (HTLV-1) is the etiologic agent of adult T-cell leukemia (ATL). In Japan, the number of HTLV-1 carriers is estimated to be 1.2 million and more than 700 cases of ATL have been diagnosed every year. Considering the poor prognosis and lack of curative therapy of ATL, it seems mandatory to establish an effective strategy for the treatment of ATL. In this study, we attempted to identify the cell surface molecules that will become suitable targets of antibodies for anti-ATL therapy. The expression levels of approximately 40,000 host genes of three human T-cell lines carrying HTLV-1 genomes were analyzed by oligonucleotide microarray and compared with the expression levels of the genes in an HTLV-1-negative T-cell line. The HTLV-1-carrying T-cell lines used for experiments had totally different expression patterns of viral genome. Among the genes evaluated, the expression levels of 108 genes were found to be enhanced more than 10-fold in all of the T-cell lines examined and 11 of the 108 genes were considered to generate the proteins expressed on the cell surface. In particular, the CD70 gene was upregulated more than 1,000-fold and the enhanced expression of the CD70 molecule was confirmed by laser flow cytometry for various HTLV-1-carrying T-cell lines and primary CD4(+) T cells isolated from acute-type ATL patients. Such expression was not observed for primary CD4(+) T cells isolated from healthy donors. Since CD70 expression is strictly restricted in normal tissues, such as highly activated T and B cells, CD70 appears to be a potential target for effective antibody therapy against ATL.

The human T-cell leukemia virus type 1 (HTLV-1): New insights into the clinical aspects and molecular pathogenesis of adult t-cell leukemia/lymphoma (ATLL) and tropical spastic paraparesis/HTLV-associated myelopathy (TSP/HAM)

Human T-cell leukemia virus type 1 (HTLV-1) was the first human retrovirus to be identified in the early 1980s. The isolation and identification of a related virus, HTLV-2, and the distantly related human immunodeficiency virus (HIV) immediately followed. Of the three retroviruses, two are associated definitively with specific diseases, HIV, with acquired immune deficiency syndrome (AIDS) and HTLV-1, with adult T-cell leukemia/lymphoma (ATLL) and tropical spastic paraparesis/HTLV-1-associated myelopathy (TSP/HAM). While an estimated 10-20 million people worldwide are infected with HTLV-I, infection is endemic in the Caribbean, parts of Africa, southwestern Japan, and Italy. Approximately 4% of HTLV-I infected individuals develop ATLL, a disease with a poor prognosis. The clinical manifestations of infection and the current biology of HTLV viruses with emphasis on HTLV-1 are discussed in detail. The implications for improvements in diagnosis, treatment, intervention, and vaccination are included, as well as a discussion of the emergence of HTLV-1 and -2 as copathogens among HIV-1-infected individuals.

Human T-cell lymphotropic-I-associated leukemia/lymphoma

Human T-cell lymphotropic virus-I (HTLV-I)-related adult T-cell leukemia/lymphoma (ATL) is a model disease for proof of viral oncogenesis. HTLV-I infection is endemic in southern Japan and the Caribbean basin, and occurs sporadically in Africa, Central and South America, the Middle East, and the southeastern United States. ATL occurs in only 2% to 4% of HTLV-I-infected people [1-3]. When it does occur, it is usually aggressive and difficult to treat; most people survive for less than 1 year [1-3]. Combination chemotherapy with cytotoxic agents has yielded complete response rates of 20% to 45%, but responses usually last only a few months [3]. Recently, novel treatments, such as monoclonal antibodies directed at the interleukin-2 receptor and the combination of interferon alfa and zidovudine, have been shown to be active in the treatment of patients with ATL. A small percentage of patients achieve long-lasting remissions [2,3].

Smoldering HTLV-1-induced T-cell lymphoma localized within the skin; a radiation-resistant tumor

BACKGROUND

Human T-cell lymphotrophic virus type 1 (HTLV-1)-induced lymphoproliferative disease occurs in approximately 3-5% of people in endemic areas who have been HTLV-1 positive for decades. Lymphoproliferative disease may present as four subtypes, including an acute adult T-cell leukemia/lymphoma (ATLL), an aggressive HTLV-1 lymphoma, chronic ATLL, and smoldering ATLL.

MATERIALS AND METHODS

A 72-year-old HTLV-1+ Haitian woman presented with a 2-year history of a cutaneous eruption localized to the right arm. The eruption had evolved into multinodular lesions over the past 6-7 months. Peripheral blood and cutaneous biopsy specimens were evaluated. Immunohistochemical studies for lymphoid markers were performed on the cutaneous biopsy material, and polymerase chain reaction (PCR) and Southern blot assay were evaluated for the presence and integration of HTLV-1 within the genome.

RESULTS

The biopsy specimen showed a pleomorphic T-cell infiltrate with epidermotrophism, and an immunohistochemical phenotype showing CD3+, CD4+, CD8-, CD25, CD30-, HLDA-DR+ cells. PCR and Southern blot assay evaluation showed a single clonal integration of HTLV-1 provirus within a monoclonal tumor cell population. The patient had no abnormal lymphoid forms on peripheral smear at presentation, and no evidence of other organ involvement.

CONCLUSIONS

Smoldering HTLV-1-induced lymphoma is uncommon even in endemic areas. In previously reported cases, the smoldering variant was accompanied by abnormal forms in the peripheral blood and/or by other signs of systemic disease. This case illustrates that smoldering disease may be localized to the skin with no detected morphologic abnormalities on peripheral smear.

The influence of human T lymphotropic virus type I infection on the outcome of cardiovascular surgery

OBJECTIVE

Human T lymphotropic virus type I infects CD4(+) T cells and affects cell-mediated immunity. Cardiopulmonary bypass transiently alters lymphocyte subsets, resulting in a reduction in CD4(+) T cells and an increase in CD8(+) T cells. We proposed that cardiovascular operations and human T lymphotropic virus type I infection may act synergistically, resulting in serious damage to cell-mediated immunity.

METHODS

A total of 517 consecutive patients who were preoperatively screened for anti-human T lymphotropic virus type I antibody and underwent cardiovascular operations with cardiopulmonary bypass were enrolled in this study. Of the 517 patients, 82 (16%) had positive test results for anti-human T lymphotropic virus type I antibody. The surgical outcome of patients with positive and negative results for anti-human T lymphotropic virus type I antibody was analyzed retrospectively.

RESULTS

There was no difference between the 2 groups with respect to early mortality. Distribution of survival curve was also not significantly different (P =.5; mean follow-up duration, 2.4 +/- 1.8 years [range, 0-9.4 years] and 3.2 +/- 2.8 years [range, 0-9.8 years]) in the groups with positive and negative antibody results, respectively). In particular, long-term follow-up did not reveal adult T-cell leukemia or human T lymphotropic virus type I-associated myelopathy, and occurrence of neoplasm did not differ between groups. Early infectious complication was, however, significantly higher in the group with positive antibody results than in the group with negative results (P =.02). Logistic regression analysis revealed human T lymphotropic virus type I infection as a significant risk for this complication (P =.04; odds ratio, 2.5; 95% confidence interval, 1. 0-5.8).

CONCLUSION

A combination of human T lymphotropic virus type I infection and cardiovascular operation is believed to increase the potential risk of infectious complications shortly after the operation. However, this synergistic effect seems to be transient and has little influence on long-term prognosis.

Molecular epidemiology of HTLV-II among United States blood donors and intravenous drug users: an age-cohort effect for HTLV-II RFLP type aO

Molecular subtyping was used to investigate the epidemiology of human T-lymphotropic virus type II (HTLV-II) in the United States. Nested polymerase chain reaction of the HTLV-II long terminal repeat region followed by restriction fragment length polymorphism (RFLP) analysis was performed on HTLV-II seropositive subjects including 97 U.S. blood donors without major risk factors for HTLV-II infection, 53 injection drug users (IDU), and 10 American Indian blood donors. Three new HTLV-II RFLP types were confirmed with DNA sequencing and phylogenetic analysis. HTLV-II RFLP type aO (Switzer classification) was associated with older age [adjusted odds ratio (OR) 1.06 per year of age, 95% confidence interval (CI) 1.02-1.09] and with Black (OR 5.24, 95% CI 1.90-14.47) and White (OR 4.43, 95% CI 1.67-11.75) race/ethnicity. These data are consistent with an age-cohort effect for HTLV-II RFLP type aO among older White and Black IDU and blood donors. This finding could be explained by an epidemic of non-aO HTLV-II RFLP types among younger persons of Hispanic and other race/ethnicity, superimposed upon endemic HTLV-II RFLP type aO among older Black and White persons.