6 Human T-cell leukaemia virus

6 Human T-cell leukaemia virus GENOVEFFA FRANCHINI HOWARD STREICHER

The human T-cell leukaemia virus type I (HTLV-I) (Poiesz et al, 1980; Miyoshi et al, 1981; Gallo, 1986) is the aetiological agent of adult T-cell leukaemia (ATL) and tropical spastic paraparesis/HTLV-I-associated myelopathy (TSP/HAM). HTLV-I was the first retrovirus to be associated with human disease. HTLV-I was isolated in the late 1970s (1978) from an American black patient with an aggressive cutaneous T-cell lymphoma (CTCL) (Poiesz et al, 1980). In 1977, a cluster of a distinct type of T-cell leukaemia involving CD4 ÷ cells, designated ATL, was described in Japan (Takatsuki et al, 1977). As an example of timely convergent research in medicine, almost immediately HTLV-I was causally linked to ATL (Catovsky et al, 1982; Hinuma et al, 1982; Kalyanaraman et at, 1982; Robert-Guroff et al, 1982). In 1985, another seroepidemiological association was observed between HTLV-I and a chronic progressive myelopathy occurring in tropical areas where HTLV-I was endemic (Gessain et al, 1985); this clinical syndrome was originally designated TSP. Soon after, several cases of a disease with clinical features similar to TSP were described in HTLV-I infected individuals in Japan (Osame et al, 1986), the Caribbean (Rodgers-Johnson et al, 1985), Africa, South America and the southwest Pacific Islands. The progressive myelopathy of the tropics was then designated by TSP/HAM.

VIROLOGY AND CELL BIOLOGY Retroviruses are classified in the family of Retroviridae which includes three subfamilies: Oncovirinae, Lentivirinae and Spumavirinae. HTLV-I is a member of the Oncovirinae family. As with other retroviruses, the HTLV-I replicative cycle occurs through reverse transcription of the viral RNA, a process that yields double-stranded viral DNA which then integrates (as provirus) into the host cellular DNA. Viral progeny are generated by the transcription of proviral DNA. Mature virions (70-80 nm in size) are made of a dense round core (gag proteins) that contains the diploid singlestranded RNA genome and is surrounded by envelope glycoproteins (Figure 1). HTLV-I is closely related to the simian T-cell leukaemia viruses Bailli~re's Clinical Haematology-Vol. 8, No. 1, March 1995 ISBN 0--7020-1857-0

131 Copyright © 1995, by Bailli~re Tindall All rights of reproduction in any form reserved

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G. FRANCHINI AND H. STREICHER

Figure 1. HTLV-I virions. The electronmicrograph shown above displays the presence of mature HTLV-I virions (75 000 × magnification) produced by an infected T-cell (courtesy of Dr Kramasky).

(STLV), which share between 85 and 97% of their nucleotide sequence with the HTLV-I prototype. STLVs have been identified in several monkey species and in the great apes (Miyoshi et al, 1982; Becker et al, 1985; Botha et al, 1985; Watanabe et al, 1985, 1986; Blakeslee et al, 1987; Ishikawa et al, 1987; Daniel et al, 1988; Koralnik et al, 1993; Saksena et al, 1994). These viruses are not only genetically and immunologically closely related, but they also share similar biological features. A second human oncornavirus, HTLV-II, also isolated within the last decade from a patient with a rare form of T-cell hairy cell leukaemia (Kalyanaraman et al, 1982), is 70% identical in nucleotide sequence to HTLV-I (Gelmann et al, 1984; Shimotohno et al, 1985) and to STLV and has similar biological properties to HTLV-I in vitro. However, until recently there has been no clear association of HTLV-II with human disease. There is a recent case report of progressive myelopathy

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resembling TSP/HAM in a patient who was infected by HTLV-II (Jacobson et al, 1993). More case descriptions will be required to establish a role for HTLV-II in TSP/HAM. EPIDEMIOLOGY AND PHYLOGENESIS OF HTLV AND STLVs

HTLV-! infection is lifelong. The virus is transmitted at birth by breast feeding and later in life through sexual contacts or blood transfusions (Blattner, 1989). Japan, the Caribbean Basin, southeastern USA and Africa are endemic areas for HTLV-I infection. The detection of HTLV-I in black Americans, as well as in the black populations of the West Indies, led to speculation that HTLV-I might have been disseminated by the slave trade and that HTLV-I brought to southern Japan by Portuguese slave traders (Galto et al, 1983). Against this hypothesis is the high prevalence of serum antibodies against HTLV-I in two Japanese ethnic groups, the Ainu of Hokkaido and Ryukyuans in Okinawa, who are descendants of ancient Mongoloid populations from central Asia (Ishida et al, 1985). Recent reports addressed this issue by performing extensive molecular (Gray et al, 1990; Gessain et al, 1991, 1992, 1994; Komurian et al, 1991; Paine et al, 1991; Schulz et al, 1991), epidemiology, and phylogenetic analyses of HTLV-I isolates from throughout the world. The results demonstrated the existence in nature of at least four different HTLV-I subtypes: (i) the cosmopolitan HTLV-I group, including most HTLV-I from the Americas, West Africa, Europe and Japan with an average nucleotide difference among them of approximately 2%; (ii) HTLV-I from equatorial Zaire (Gessain et al, 1992) constituting a quasispecies, as discrete differences can be found among genotypes present in the same host (members of this group of viruses also differ from the cosmopolitan HTLV-I by 3%); (iii) HTLV-I variants from Melanesia and Australia (Bastian et al, 1991; Gessain et al, 1991; Yanagihara et al, t991a,b), another quasispecies whose members differ among themselves by approximately 4% from the two other HTLV-I groups by 8%; and (iv) HTLV-II, which can be divided genetically into two subgroups, A and B (Hall et al, 1992), and differ from all HTLV-I by approximately 30% (Figure 2). The existence of closely related retroviruses in nonhuman primates (STLV) suggested that these animal species might represent natural reservoirs of HTLV-I; if so, HTLV-I infection of humans could be considered a zoonosis. Comparison of the sequences of the envelope gene of STLV and HTLV by computer analysis support the hypothesis of horizontal transmission of STLV and HTLV (Figure 2). The geographic origin of the animal rather than its species correlated best with STLV-I genetic homogeneity (Koralnik et al, 1994). Furthermore, the finding of STLV-I strains highly related to HTLV-I in chimpanzees (cluster z), whose natural habitat is the Zairian basin and surrounding areas, clearly, suggested that horizontal transmission might have occurred there. Human and nonhuman primates were in close contact for thousands of years during the glacial era in the

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equatorial regions (Barraclough, 1979) (Figure 3), before the occurrence of migration and colonization in other parts of the world. The finding that the Asian STLV clustered with the HTLV-I from Melanesia, although based on a relatively small number of HTLV and STLV isolates, also suggested that perhaps the HTLV identified in humans in remote populations of Papua New Guinea, the Solomon Islands and Australia, as well as HTLV-II, originated from nonhuman primate species in Asia. A common ancestor for HTLV-I and HTLV-II existed, probably in nonhuman primates rather than in humans; STLV-I infection of nonhuman primates would then have predated infection of humans. Subsequent migration of infected human populations may have contributed to the dissemination of these oncornaviruses throughout the world (Gessain et al, 1992). MOLECULAR AND BIOLOGICAL FEATURES OF HTLV-I

HTLV-I infects and transforms CD4 + T-cells (Miyoshi et al, 1981; Yamamoto et al, 1982; Markham et al, 1983; Popovic et al, 1983). An isolated report indicated that HTLV-I can also transform B-cells (Longo et al, 1984), but a parallel study (Franchini et al, 1985) of the same patient's B-cells showed coinfection by HTLV-I and Epstein-Barr virus. In any event, HTLV-I tropism is not limited to T-cells and macrophages (Miyoshi et al, 1981; Markham et al, 1983; Watanabe et al, 1985; Hoffman et al, 1992; Koralnik et al, 1992a) but extends to malignant fibroblasts of different animal species. The viral receptor, which has been mapped to human chromosome 17 (Sommerfelt et al, 1988), is thought to be present on the surface of many different cell types (Gavalchin et al, 1993). The organization of the 10kb HTLV-I genome, LTR-gag-pol-env pX LTR, is similar to other animal oncornaviruses except for the presence of a large region called pX preceding the 3' LTR (Seiki et al, 1983). This region contains at least four open reading frames (off), designated by Roman numbers I-IV (Figures 4 and 5). The genetic complexity of HTLV-I is increased by alternative splicing of the genomic mRNAs (Figure 4) (Berneman et al, 1992; Ciminale et al, 1992; Koralnik et al, 1992b). The

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same doubly spliced polycistronic mRNA encodes: (1) the nuclear p40m"x protein, a transcriptional activator of viral expression (Sodroski et al, 1984; Felber et al, 1985); (2) the nuclear p27 ~e× protein, the post-transcriptional regulator of structural gene expression (Inoue et al, 1987; Hidaka et al, 1988); and (3) the p21 Rex proteins of unknown function (Kiyokawa et al, 1985). The p21 Rex protein can also be encoded by a single-spliced mRNA (Figure 5) (Berneman et al, 1992; Koralnik et al, 1992b). These regulatory proteins are encoded by frames I11 and IV. The Rex protein either stabilizes or facilitates the transport from nucleolus to cytoplasm of unspliced genomic mRNA, thereby allowing the expression of core proteins as well as providing genomic R N A for viral progeny. Rex also exerts its function on the single-spliced envelope mRNA. Production of a new virus is strictly dependent on Rex function. Rex binds in vitro to a Rex responsive element located in the R/U3 region of the viral long terminal repeat (LTR) (Hanly et al, 1989; Bar-Shira et al, 1991). LTR RNA is rich in secondary structures, and the binding site of the Rex proteins has been localized to a stem loop region within this RNA fragment. Mutations within the LTR or interference with the Rex protein function or the R R E structure could induce viral latency, for these reasons the Rex protein and R R E are good candidates for antiviral therapy. The Tax protein is also indispensable for viral replication because it activates proviral expression. Tax activates a 21 bp repeat D N A sequence in the U3 region of the viral LTR, and its action is mediated by cellular transcriptional factor (NFKB) (Leung and Nabel, 1988; Lowenthal et al, 1988; Lindholm et al, 1993). Tax protein binds physically to transcriptional factors (Suzuki et al, 1993). Because of its interaction with cellular factors, Tax can up-regulate not only viral genes but also cellular genes. Tax protein can be released in the supernatant by infected cells and its internalization by other cells resulting in general T-cell proliferation in culture (Lindholm et al, 1993). The ability of a viral transactivator to interfere with cellular gene expression in vitro (reviewed in Gitlin et al (1993)), not only in infected cells but at a distance (Marriott et al, 1992), could play an important pathogenic role in

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the infected host. In vitro, the Tax protein has been shown to upregulate an important growth factor for T-cells, interleukin 2 (IL-2), as well as growth factor receptors: the IL-2 receptor a (IL-2Re0 chain, the receptor for granulocyte-macrophage colony stimulating factor, and the c-los oncogene (Fujisawa et al, 1986, 1989; Greene et al, 1986; Inoue et al, 1986; Cross et al, 1987; Leung and Nabel, 1988; Lowenthal et al, 1988; Tendler et al, 1990; Lindholm et al, 1993). Transcriptional transactivation by p40 a'axof the IL-2 and ]L-2RoL chain could be the initiating event in T-cell transformation in vitro by paracrine/autocrine mechanisms, like simultaneous expression of a ligand and its receptor (IL-2, IL-2R) (Figure 6). Recently, several novel viral mRNAs encoded by orfs I and II have been identified. As shown in Figures 4 and 5, these mRNAs encode the p12' membrane associated protein, the p13" nuclear protein, and the p30" nucleolar protein (Ciminale et al, 1992; Koralnik et al, 1993). mRNAs for all these proteins have been found in samples from HTLV-I infected individuals (Table 1) (Berneman et al, 1992; Koralnik et al, 1992b). The p12' protein encoded by the HTLV-I off I (Koralnik et al, 1994) is a weak oncogene (Franchini et al, 1993). The p12' protein is a small, hydrophobic, membrane-associated protein with some structural similarity to bovine papillomavirus type 1 (BPV-1) E5 oncoprotein, and it potentiates E5 transforming activity in C127 mouse cells (Franchini et al, 1993). Both p12' and E5 proteins physically bind to the 16kDa subunit of the H + vacuolar ATPase (Goldstein et al, 1991, 1992; Franchini et al, 1993), a proton pump ubiquitous in cellular organelles that regulates acidification in the cellular vacuolar system (Finbow et al, 1991). The biological significance of these protein interactions is presently unclear. However, the p12' protein has been shown to physically interact with the t3 and ~/but not c~chains of the IL-2R (Mulloy et al, in preparation),

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hypothesisdepictedin the secondpart of the figureawaitsfurtherexperimentalconfirmation.

139

HUMAN T-CELL LEUKAEMIA VIRUS Table 1. Proteins encoded by the HTLV-I pX region.

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Function Cell transformation

Unknown Unknown Post-transcriptional transactivator Unknown Transcriptional transactivator; cell transformation

suggesting possible involvement with IL-2R signalling and T-cell transformation. Changes in the pH of cellular organelles might influence the internalization and degradation of receptor-ligand complexes. In a mouse model of leukaemia, induced by the spleen focus-forming virus (SFFV). an aberrant form, the viral envelope (gp55) induces cell growth by binding to the erythropoietin receptor (D'Andrea, 1992; Ruscetti, 1993; Chapter 10 of this book). The mechanism of HTLV-I transformation in vitro and in vivo is still poorly understood. As previously described, the HTLV-I transactivator protein p40 wax has been shown to transcriptionally activate several cellular genes, the expression of which is relevant to T-cell activation and proliferation. HTLV-I immortalization and transformation of T-cells in vitro are associated with alteration in the expression of a cascade of specific cellular kinases triggered by the IL-2/IL-2R interaction (Ohta et al, 1990; Nakamura et al, 1991; Wildin et al, 1991). However, IL-2 production by infected cells is not required to maintain T-cell growth after transformation. IL-2 mRNA is not expressed at detectable levels in transformed T-cells in vitro (Arya et al, 1984). The Tax protein has also been shown to directly transform rat fibroblasts in vitro (Tanaka et al, 1990), and under some conditions Tax immortalizes T-cells in vitro (Grassman et al, 1989). However, Tax appears to be insufficient to induce ligand (IL-2), independent growth of human T-cells (Akagi and Shimotohno, 1993). Therefore, the cooperation of other oncogenes of cellular or viral origin (like the p12' protein) in cell transformation may be required (Figure 6). HTLV-1 proteins might act at different levels in the complex pathway of T-cell proliferation (Figure 6). HTLV-I-ASSOCIATED DISEASES ATL

HTLV-I was first detected in cultured T-ceU lines from a patient with an acute form of CTCL. The similarity of the clinical picture of sporadic cases of T-cell leukaemia associated with HTLV-I to a newly described T-cell malignancy, ATL, endemic in southern Japan, prompted a search for HTLV-I sequences

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G. FRANCHINI A N D H . STREICHER

in the leukaemic cell DNA of these patients. The clinical features of ATL (Takatsuki et al, 1977) include the appearance in the blood of morphologically unique T-cells with lobulated nuclei (Figure 7), minimal bone marrow involvement, extensive peripheral lymphadenopathy, hepatosplenomegaly without thymic enlargement, and frequently skin infiltration. Lytic bone lesions and hypercalcaemia are often present at the onset of the disease: hypercalcaemia occurs in about 50% of patients and attempts to control calcium levels may dominate the acute clinical course. The mechanism of hypercalcaemia appears to be a paraneoplastic syndrome associated with the production of parathyroid hormone-related peptide (PTH-rP) like hormone (Watanabe et al, 1990) as in other malignancies. The histopathotogical classification of ATL is similar to that of other T-cell lymphomas (Jaffe et al, 1984). Opportunistic infections, including Pneumocystis carinii pneumonia, fungal infections, and particularly Strongyloides stercoraIis are frequent in ATL. Indeed, some patients have recurrent opportunistic infections similar

Figure 7. TypicalT-cells with lobulated nuclei found in the peripheral blood of an HTLV-I infected patient.

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to those in HIV infected cases. The nature of the immune defect in ATL is unknown but could be mediated by soluble factors produced by HTLV-I infected cells, since supernatants from T-cell infected culture are immunosuppressive for uninfected T-ceUs. In its classic presentation, ATL is a rapidly progressive and usually fatal disease (Yamaguchi, 1994). Average survival beyond the acute episode is approximately 6 months and is not markedly increased by any currently available combination of antileukaemic drugs (Centers for Disease Control and Prevention and the USPHS Working Group, 1993). The diagnosis of ATL includes at least four different clinical subtypes: acute, chronic, lymphomatous, and smouldering, depending on the clinical course, the extent of disease, and the serum calcium level (Yamaguchi et al, 1983; Shimoyama et al, 1984-1987; Takatsuki et al, 1985; Yamaguchi, 1994). In all these variants the provirus is clonally integrated in the DNA of the patients peripheral blood mononuclear cells (PBMC) (Wong-Staal et al, 1983; Yoshida et al, 1984). The appearance of a T-cell clone with the HTLV-I provirus appears to be an event that precedes malignant disease (Yamaguchi et al, 1988), but only about 10% of patients with detectable monoclonal T-cell populations in the peripheral blood will develop overt ATL during a 5 year follow-up period. Patients with detectable monoclonal or oligoclonal populations and elevated PBMCs are at increased risk of developing the acute disease. As the lifetime rate of malignancy is approximately 4-5% among HTLV-I infected individuals (Tokudome et al, 1989), most individuals found to be HTLV-I seropositive will be asymptomatic, The average time interval between infection and malignancy is about 20-30 years. While leukaemic cells do not express viral mRNA, as judged by Northern blot analysis (Franchini et al, 1984) and viral antigen expression, they constitutively express high affinity IL-2R which can be targeted by the monoclonal antibody anti-Tac (Waldmann et al, 1993). Invariably a high number of IL-2R o~chains is found not only on the surface of ATL cells but also in the sera of ATL patients (Yamaguchi et al, 1989). The use of anti-Tac alone or armed with radioactive yttrium as a therapy in ATL patients has resulted in partial responses, including normalization of hypercalcaemia and remission of immunosuppression. Incomplete responses may be due to the host production of antibodies against the mouse antibody. Humanized anti-Tac antibody is currently in clinical trials at the National Institutes of Health. For conventional chemotherapy treatment of ATL see Tsukasaki et al (1993) and Yamaguchi (1994). Other non-malignant HTLV-I-associated diseases The most frequent disease associated with HTLV-I infection other than ATL is a progressive form of myelopathy called TSP/HAM (for recent reviews see Gessain and Gout (1992) and Hollsberg and Hailer (1993)). TSP/HAM presents with spasticity and weakness of lower limbs, paraplegia, sphincter disturbances, and various degrees of sensory loss. Occasionally, peripheral nerves are involved. Signs of meningomyelitis like funicular

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demyelination axonal loss, perivascular cuffing, and gliosis are found in the lower thoracic spinal cord. In affected individuals there is a strong humoral and cellular immune response to viral antigens. In several patients a vigorous cell mediated immune response against the Tax protein has been described and invoked as an important pathogenetic step in disease development (Jacobson et al, 1990; Kannagi et al, 199i). In most TSP/HAM cases, HTLV-I is polyclonally integrated in the D N A of patients' PBMC as well as T-cells recovered from the spinal fluid. Short-term improvement after immunosuppressive treatment with steroids is consistent with a possible immune pathogenetic mechanism. Other disorders associated with HTLV-I infection include arthropathy, also not uncommonly found in TSP/HAM (Nishioka et al, 1989) and ATL. In an experimental transgenic mouse model, generated with the entire HTLV-I genome, chronic arthritis with synovial inflammation and articular erosion were major signs of disease (Iwakura et al, 1991). Several cases of HTLV-I-associated uveitis have also been reported and the presence of HTLV-I has been demonstrated in the DNA of T-cells obtained from the anterior chamber of the eye (Mochizuki et al, 1992). Polymyositis and infectious dermatitis have also been associated with HTLV-I in endemic areas.

SUMMARY

HTLV-I has a complex and finely regulated mechanism of replication, which can be used as a model to study both cellular and viral regulation pathways in T-cells. Understanding of the underlying mechanisms involved in the pleiotropic effects of HTLV-I in the host represents a real challenge. Immunological regulation likely plays a central role in HTLV-I induced neurological disease, uveitis, and perhaps arthritis, implicating the importance of host factors as well. Viral proteins, including tax and p12' might play a role in T-cell proliferation, but the event(s) that result in the late leukaemic phase are unknown. The lack of effective therapy against HTLV-I-induced leukaemia renders prevention of viral infection the best means to eliminate HTLV-I associated diseases. Elimination or reduction of breast feeding from seropositive mothers in Japan has already produced encouraging results. In developing countries, probably only a vaccine will prevent the spread of HTLV-I infection. The molecular epidemiology of HTLV and STLV will help understand not only the phylogeny of these viruses but also the migration of human populations in the past. Episodes of horizontal transmission in the past and probably the present, indicates that nonhunlan primates are the natural reservoir of HTLVs. New related viruses will likely be discovered in monkeys (and humans) in the future.

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Acknowledgements The authors are grateful to Dr Mary Klotman for critical reading of the manuscript and Linda Anderson for her editorial assistance.

REFERENCES Akagi Y & Shimotohno K (1993) Proliferative response of Taxi-transduced primary human T cells to anti-CD3 antibody stimulation by an interleukin-2-independent pathway. Journal of Virology 67:1211-1217. Arya SK, Wong-Staal F & Gallo RC (1984) T-cell growth factor gene: Lack of expression in human T-cell leukemia-lymphoma virus-infected cells. Science 223: 1086-108% Barraclough G (1979) Man and the ice age. In Barraclough G (ed.) The TimeAtlas of World History, pp 36-37. l o n d o n : Times Book Ltd. Bar-Shira A, Panet A & Honigman A (1991) A n RNA secondary structure juxtaposes two remote genetic signals for human T-cell leukemia virus type I R N A 3'- end processing. Journal of Virology 65: 5165-5169. Bastian IB, Gardner J, Webb D et al (1991) Isolation of an HTLV-I strain from Australian Aboriginals. 4th International Conference on Human Retrovirology: HTLV. Montego Bay, Jamaica. Becker WB, Becker MLB, Homma T et al (1985) Serum antibodies to human T-cell leukaemia virus type I in different ethnic groups and in non-human primates in South Africa. South Africa Medical Journal 67: 445-449. Berneman ZN, Gartenhaus RB, Reitz MS Jr et al (1992) Expression of alternatively spliced human T-lymphotropic virus type I (HTLV-I) pX mRNA in infected cell lines and in primary uncultured cells from patients with adult T-cell leukemia/lymphoma and healthy carriers. Proceedings of the National Academy of Sciences of the USA 89: 3005-3009. Blakeslee JR Jr, McClure HM, Anderson DC et al (1987) Chronic fatal disease in gorillas seropositive for simian T-lymphotropic virus I antibodies. Cancer Letters 37: 1-6. Blattner WA (1989) Retroviruses in viral infection of human epidemiology and control. In Evans AS (ed.) Retroviruses, pp 545-592. New York: Plenum Press. Botha MC, Jones M, DeKlerk WA & Yamamoto N (1985) Spread and distribution of human T-ceU leukaemia virus type I-reactive antibody among baboons and monkeys in the northern and eastern Transvaal. South Africa Medical Journal 67: 665-668. Catovsky D, Rose M, Gootden AWG et al (1982) Adult T-cell lymphoma-teukemia in blacks from the West Indies. Lancet i: 639-643. Centers for Disease Contro~ and Prevention and the USPHS Working Group (1993) Guidelines for counseling persons with human T-lymphotropic virus type I (HTLV-I) and type II (HTLV-II). Annals of lnternal Medicine 118: 448-454. Ciminale V, Pavlakis GN, Derse D et al (1992) Complex splicing in the human T-cell leukemia virus (HTLV) family of retroviruscs: novel mRNAs and proteins produced by HTLV-I. Journal of Virology 66: 1737-1745. Cross SL, Feinberg MB, Wolf JB et al (1987) Regulation of the human interleukin-2 receptor c~-chain promoter: activation of a non-functional promoter by the transactivator gene of HTLV-1. Cell 49: 47-56. D'Andrea AD (1992) The interaction of erythropoietin receptor and gp55. CancerSurveys 15: 19-36. Daniel MD, Letvin NL, Sehgal PK et al (1988) Prevalence of antibodies to 3 retroviruses in a captive colony of macaque monkeys. International Journal of Cancer 41: 601-608. Felber BK, Paskatis H, Wong-Staal F & Pavlakis GN (1985) qqae pX protein of HTLV-I is a transcriptional activator of its long terminal repeats. Science 229: 675-679. Finbow ME, Pitts JD, Goldstein DJ et al (1991) The E5 oncoprotein target: A 16kDa channel-forming protein with diverse functions. Molecular Carcinogenesis 4: 441-444. Franchini G, Wong-Staal F & Gallo RC (1984) Human T cell leukemia virus (HTLV-I) transcripts in fresh and cultured ceils of patients with adult T cell leukemia. Proceedings of the National Academy of Sciences of the USA 81: 6207-6211.

144

G. FRANCHINI AND H. STREICHER

Franchini G, Mann DL, Popovic M e t al (1985) HTLV-I infection of T and B cells of a patient with adult T cell leukemia-lymphoma (ATLL) and transmission of HTEV-I from B cells to normal T cells. Leukemia Research 9: 1305-1314. Franchini G, Mulloy JC, Koralnik IJ et al (1993) The human T-cell leukemia/lymphotropic virus type I p12' protein cooperates with the E5 oncoprotein of bovine papillomavirus in cell transformation and binds the 16kd subunit of vacuolar H+ATPase. Journal of Virology 67: 7701-7704. Fujisawa J, Seiki M, Sato M & Yoshida M (1986) A transcriptional enhancer sequence of HTLV-I is responsible for transactivation mediated by p40 chi HTLV-I. European Molecular Biology Organization Journal 5: 713--718. Fujisawa J, Toita M & Yoshida M e t al (1989) A unique enhancer element for the trans activator (p4Otax) of human T-cell leukemia virus type I that is distinct from cyclic AMPand 12-O-tetradecanoylphorbol-13-acetate-responsive elements. Journal of Virology 63: 3234-3239. Gallo RC (1986) The first human retrovirus. Scientific American 255: 88-98. Gallo RC, Sliski A & Wong-Staal F (1983) Origin of human T-cell leukaemia-lymphoma virus. Lancet ii: 962-963. Gavalchin J, Fan N, Lane MJ et al (1993) Identification of a putative cellular receptor for HTLV-I by a monoclonal antibody, Mab 34-23. Virology 194: I-9. Gelmann EP, Franchini G, Manzari V e t al (I984) Molecular cloning of a unique human T-celt leukemia virus HTLV-IIMo. Proceedings of the National Academy of Sciences of the USA 81: 993-997. Gessain A & Gout O (1992) Chronic myelopathy associated with human T-lymphotropic virus type I (HTLV-I). Annals oflnternal Medicine 117: 933-946. Gessain A, Barin F. Vernant J-C et al (1985) Antibodies to human T-lymphotropic virus type I in patients with tropical spastic paraparesis. Lancet 2: 407-410. Gessain A, Yanagihara R, Franchini G e t al (1991) Highly divergent molecular variants of human T-lymphotropic virus type I from isolated populations in Papua New Guinea and the Solomon Islands. Proceedings of lhe National Academy of Sciences of the USA 88: 7694-7698. Gessain A, Gallo RC & Franchini G (1992) Low degree of human T-ceU leukemia/lymphomas virus type I genetic drift in vivo as a means of monitoring viral transmission and movement of ancient human populations. Journal of Virology 66: 2288-2295. Gessain A, Koralnik IJ, Fullen F et al (1994) Phylogenetic study of ten new HTLV-I strains from the Americas. AIDS Research and Human Retroviruses 10: 103-106. Gitlin SD, Dittmer J, Reid RL & Brady JN (1993) The molecular biology of human T-cell leukemia viruses. In Cullen B (ed.) Frontiers in Molecular Biology, pp 156-192. Oxford: Oxford University Press (IRL Books). Goldstein DJ, Finbow ME, Andresson T et al (1991) The bovine papillomavirus E5 oncoprotein binds to the 16 kilodalton component of vacuolar H+-ATPases. Nature 352: 347-349. Goldstein DJ, Andresson T, Sparkowski JJ & Schlegel R (1992) The BPV-1 E5 protein, the 16 kDa membrane pore-forming protein and the PDGF receptor exist in a complex that is dependent on hydrophobic transmembrane interactions. European Molecular Biology Organization Journal 11: 4851~1859. Grassmann R, Dengler C, Muller-Fleckenstein I e t al (t989) Transformation to continuous growth of primary human T-lymphocytes by human T-cell leukemia virus type X-region genes transduced by a herpesvirus simian vector. Proceedings of the NationalAcademy of Sciences of the USA 86: 3351-3355. Gray GS, White M, Bartman T & Mann D (1990) Envelope gene sequence of HTLV-I isolate MT-2 and its comparison with other HTLV-I isolates. Virology 177: 391-395. Greene WC, Leonard WJ, Wano Y e t al (1986) Trans-activator gene of HTLV-II induces IL-2 receptor and IL-2 cellular gene expression. Science 232: 877-880. Hall WW, Takahashi H, Liu C et al (1992) Multiple isolates and characteristics of human T-cell leukemia virus type II. Journal of Virology 66: 2456-2463. Hanly SM, Rimsky LT & Malim MH (1989) Comparative analysis of the HTLV-I rex and HIV-1 rev trans-regulatory proteins and their R N A response elements. Genes and Development 3: t534-1540. Hidaka N, Inoue N, Yoshida M & Seiki M (1988) Posttranscriptional regulator (rex) of HTLV-I

H U M A N T-CELL LEUKAEMIA VIRUS

145

initiates expression of viral structural proteins but suppresses expression of regulatory proteins. European Molecular Biology Organization Journal 7: 519-523. Hinuma Y, Komoda H, Chosa T e t al (1982) Antibodies to adult T-cell leukemia-virus associated antigen (ATLA) in sera from patients with ATL and controls in Japan: a nation-wide sero-epidemiologic study. International Journal of Cancer 29: 631-635. Hoffman PM, Dhib-Jalbut S, Mikovits JA et al (1992) Human T-cell leukemia virus type I infection of monocytes and microglial cells in primary human cultures. Proceedings of the National Academy of Sciences of the USA 89: 11784-11788. Hollsberg P & Haffer DA (1993) Seminars in medicine of the Beth Israel Hospital, Boston: Pathogenesis of diseases induced by human lymphotropic virus type I infection. New England Journal of Medicine 382" 1173-1182. Inoue JI, Seiki M, Taniguchi T e t al (1986) Induction of interleukin 2 receptor gene expression by p40 ~ encoded by human T-cell leukemia virus type I. European Molecular Biology Organization Journal 5: 2883-2888. Inoue JI, Seiki M, Taniguchi T et al (1987) Transcriptional (p40 ×) and post-transcriptional (p24 x-lu) regulators are required for the expression and replication of human T-cell leukemia virus type I genes. Proceedings of the National Academy of Sciences of the USA 84: 3653-3657. Ishida T, Yamamoto K, Omoto K et al (1985) The prevalence of human retroviruses in native Japanese: evidence for a possible ancient origin. Journal oflnfectious Diseases II: 153157. Ishikawa K, Fukasawa M, Tsujimoto H et al (1987) Serological survey and virus isolation of simian T-cell leukemia/T-lymphotropic virus type I (STLV-I) in non-human primates in their native countries. International Journal of Cancer 40: 233-239. Iwakura Y, Tosu M, Yoshida E e t al (1991) Induction of inflammatory arthropathy resembling rheumatoid arthritis in mice transgenic for HTLV-I. Science 253: 1026-1030. Jacobson S, Shida H, MacFarlin DE et al (1990) Circulating CD8 ÷ cytotoxic T cells directed against HTLV-I-infected cells. Nature 348: 245-248. Jacobson S, Lehky T, Nishimura M e t al (1993) Isolation of HTLV-II from a patient with chronic progressive neurological disease clinically indistinguishable from HTLV-Iassociated myelopathy/tropical spastic paraparesis. Annals of Neurology 33: 392-396. Jaffe ES, Blattner WA, Blayney DW et al (1984) The pathologic spectrum of adult T-cell leukemia/lymphoma in the U.S. American Journal of Surgical Pathology 8: 263-275. Kalyanaraman VS, Sarngadharan MG, Robert-Guroff M et al (1982) A new subtype of human T-cell leukemia virus (HTLV-II) associated with a T-cell variant of hairy cell leukemia. Science 218: 571-573. Kannagi M, Harada S, Maruyama I e t al (1991) Predominant recognition of human T cell leukemia virus type I (HTLV-I) p X gene products by human CD8 ÷ cytotoxic T cells directed against HTLV-I-infected cells. International Immunology 3: 761-767. Kiyokawa T, Seiki M, Iwashita Set al (1985) p27X m and p21X hI, proteins encoded by the pX sequence of human T-cell leukemia virus type I. Proceedings of the National Academy of Sciences of the USA 82: 8359-8363. Komurian F, Peloquin F & de The G (1991) In vivo genomic variability of human T-cell leukemia virus type I depends more upon geography than upon pathologies. Journal of Virology 65: 3770-3778. Koralnik IJ, Letup JF Jr, Gallo RC & Franchini G (1992a) In vitro infection of human macrophages by human T-cell leukemia/lymphotropic virus type I (HTLV-I). AIDS Research and Human Retroviruses 8: 1845-1849. Koratnik IJ, Gessain A, Klotman ME et al (1992b) Protein isoforms encoded by the pX region of human T-cell leukemia/lymphotropic virus type I. Proceedings of the NationalAcademy of Sciences of the USA 89: 8813-8817. Koralnik I J, Fullen J & Franchini G (1993) The p12', p13", and p30"proteins encoded by human T-cell leukemia/lymphotropic virus type I open reading frames I and II are localized in three different cellular compartments. Journal of Virology 67: 2360-2366. Koralnik IJ, Boeri E, Saxinger WC et al (1994) Phylogenetic associations of human simian T-cell leukemia/lymphotropic virus type I strains: evidence for interspecies transmission. Journal of Virology 68: 2693-2707. Leung K & Nabel GJ (1988) HTLV-l transactivator induces interleukin-2 receptor expression through an NF-kappa B-like factor. Nature 333: 776-778.

146

G. FRANCHINI AND H. STREICHER

Lindholm PF, Kashanchi F & Brady JN (1993) Transcriptional regulation in the human retrovirus HTLV-I. Virology 4: 53--60. Longo DL, Getmann EP, Cossman J e t al (1984) Isolation of HTLV-I transformed B lymphocytes clone from a patient with HTLV-associated adult T-cell leukemia. Nature 310: 5O5-506. Lowenthal JW, Bohnlein E, Baltard DW & Green WC (1988) Regulation of interleukin 2 receptor alpha subunit (Tac or CD25 antigen) gene expression: binding of inducible nuclear proteins to discrete promoter sequences correlates with transcriptional activation. Proceedings of the National Academy of Sciences of the USA 85: 4468-4472. Markham PD, Salahuddin SZ, Katyanaraman VS et al (1983) Infection and transformation of fresh human umbilical cord blood cells by multiple sources of human T-cell leukemialymphoma virus (HTLV). International Journal of Cancer 31: 413--420. Marriott SF, Trinh D & Brady JN (1992) Activation of interleukin 2 receptor alpha expression by extracellular HTLV-I Tax~ protein: a potential role in HTLV-I pathogenesis. Oncogene 7: 1749-1754. Miyoshi I, Kubonishi I, Yoshimoto S e t al (1981) Type C virus particles in a cord T cell line derived by co-cultivating normal human cord leukocytes and human leukaemic T cells. Nature 294: 770-771. Miyoshi I, Yoshimoto S, Fujishita Met al (1982) Natural adult T-cell leukemia virus infection in Japanese monkeys. Lancet ii: 658. Mochizuki M, Watanabe T, Yamaguchi K et al (1992) HTLV-I uveitis: a distinct clinical entity caused by HTLV-I. Japanese Journal of Cancer Research 83: 236-239, Nakamura K, Koga Y, Yoshida H et al (1991) Differential expression of two lck transcripts directed from the distinct promoters in HTLV-I + and HTLV-I T-cells. International Journal of Cancer 48: 789-793. Nishioka K, Maruyama I, Sato Set al (1989) Chronic inflammatory arthropathy associated with HTLV-I. Lancet i: 441. Ohta M, Morita T, Shimotohno K et al (1990) lck suppresses gene expression from various promoters including human T-cell leukemia virus type I promoter. Japanese Journal of Cancer Research 81: 440-444, Osame M, Usuku K, Izumo Set al (1986) HTLV-I associated myelopathy, a new clinical entity. Lancet 1:1031-1032 (letter). Paine E, Garcia J, Philpott TC et al (1991) Limited sequence variation in human Tlymphotropic virus type 1 isolates from North America and African patients. Virology 182: 111-123.

Poiesz BJ, Ruscetti FW, Gazdar AF et al (1980) Detection and isolation of type C retrovirus particles from fresh and cultured lymphocytes of a patient with cutaneous T-cell lymphoma. Proceedings of the National Academy of Sciences of the USA 77: 7415-7419. Popovic M, Lange-Wantzin G, Sarin PS et al (t983) Transformation of human umbilical cord blood T-cells by human T-cell leukemia/lymphoma virus. Proceedings of the National Academy of Sciences of the USA 80: 5402-5406, Robert-Guroff M, Nakao Y, Notake K et al (1982) Natural antibodies to human retrovirus HTLV in a cluster of Japanese patients with adult T cell leukemia. Science 215: 975-978. Rodgers-Johnson P, Gajdusek DC, Morgan Ost C et al (1985) HTLV-I and HTLV-III antibodies and tropical spastic paraparesis. Lancet 2:1247-1249 (letter). Ruscetti SK (1993) Friend spleen focus-forming virus. In Young N (ed.) Viruses in Hematopoiesis, pp 289-313. New York: Marcel Dekker. Saksena NK, Herve V, Durand JP et aI (I994) Seroepidemiologic, molecular and phylogenetic analyses of simian T-cell leukemia viruses (SLTV-I) from various naturally infected monkey species from central and western Africa, Virology 198: 297-310, Schulz TF, Calabro ML, Hoad JG et al (1991) HTLV-I envelope sequences from Brazil, the Caribbean, and Romania: clustering of sequences according to geographic origin and variability in an antibody epitope. Virology 184: 483-491. Seiki M, Hattori S~ Hirayama Y & Yoshida M (1983) Human adult T-cell leukemia virus: complete nucleotide sequence of the provirus genome integrated in leukemia cell DNA. Proceedings of the National Academy of Sciences of the USA 80: 3618-3622. Shimotohno K, Takahasbi Y, Shimizu N e t al (1985) Complete nucleotide sequence of an infectious clone of human T-cell leukemia virus type II: An open reading frame for the protease gene. Proceedings of the NationalAcademy of Sciences of the USA 82: 3101-3105.

HUMAN T-CELL LEUKAEMIA VIRUS

147

Shimoyama M & Members of the Lymphoma Study Group (1984-1987) Diagnostic criteria and classification of clinical subtypes of adult T-cell leukemia-lymphoma. British Journal of Haematology 79: 428--437. Sodroski JC, Rosen WC & Haseltine WA (1984) Transacting transcriptional activation of the long terminal repeat of human T lymphotropic viruses in infected cells. Science 225: 381-385. Sommeffelt MA, Williams BP, Clapham PR et al (1988) Human T cell leukemia viruses use a receptor determined by human chromosome 17. Science 242- 1557-1559. Suzuki T, Fujisawa J-I, Toita M & Yoshida M (1993) The trans-activator Tax of human T-cell leukemia virus type 1 (HTLV-1) interacts with cAMP-responsive element (CRE) binding and CRE modulator proteins that bind to the 21-base-pair enhancer of HTLV-1. Proceedings of the National Academy of Sciences of the USA 90: 610-614. Takatsuki K, Uchiayama T, Sagawa K & Yodoi J (1977) Adult T-cell leukemia in Japan. In Seno S, Takaku F & Irino S (eds) Topics in Hematology, pp 73-77. Amsterdam: Exccrpta Medica. Takatsuki K, Yamaguchi K, Kawano F et al (1985) Clinical diversity in adult T-cell leukemialymphoma. Cancer Research 45 (supplement): 4644S-4645S. Tanaka A, Takahashi C, Yamaoka Set al (1990) Oncogenic transformation by the tax gene of human T-cell leukemia virus type I in vitro. Proceedings of the National Academy of Sciences of the USA 87: 1071-1075. Tendler CL, Greenberg SJ, Blattner WA et a! (1990) Transactivation of interleukin 2 and its receptor induces immune activation in human T-cell lymphotropic virus type 1-associated myelopathy: pathogenic implications and a rationale for immunotherapy. Proceedings of the National Academy of Sciences of the USA 87: 5218-5222. Tokudome S, Tokunaga O, Shimamoto Y et al (1989) Incidence of adult T-cell leukemia/ lymphoma among human T-lymphotrophic virus type I carrier in Saga, Japan. Cancer Research 49: 226-228. Tsukasaki K, Ikeda S, Murata K et al (1993) Characteristics of chemotherapy-induced clinical remission in long survivors with aggressive adult T-cell leukemia/lymphoma. Leukemia Research 17: 157-166. Waldmann TA, White JD, Goldman CK et al (1993) The interleukin-2 receptor: A target for monoclonal antibody treatment of human T-cell lymphotropic virus I-induced adult T-cell leukemia. Blood 82: 1701-1712. Watanabe T, Seiki M, Tsujimoto H et al (1985) Sequence homology of the simian retrovirus genome with human T-cell leukemia virus type 1. Virology 144: 59-65. Watanabe T, Seiki M, Hirayama Y & Yoshida M (1986) Human T-cell leukemia virus type 1 is a member of the African subtype of simian viruses (STLV). Virology 148: 385-388. Watanabe T, Yamaguchi K, Takatsuki K et al (1990) Constitutive expression of parathyroid hormone-related protein (PTHrP) gene in HTLV-I carrier and adult T-cell leukemia patients which can be transactivated by HTLV-I tax gene. Journal of Experimental Medicine 172: 759-765. Wildin RS, Garvin AM, Pawar Set al (199i) Developmental regulation of lck gene expression in T lymphocytes. Journal of Experimental Medicine 173: 383-393. Wong-Staal F, Hahn B, Manzari Vet al (1983) A survey of human leukemias for sequences of a human retrovirus. Nature 302: 626-628. Yamaguchi K (1994) Human T-lymphotropic virus type I in Japan. Lancet 343: 213-216. Yamaguchi K, Nishimura Y, Kawano F et al (1983) A proposal for smoldering adult T-cell leukemia~iversity in clinical pictures of adult T-cell leukemia. Japanese Journal of Clinical Oncology 13: 189-199. Yamaguchi K, Kiyokawa T, Nakada K et al (1988) Polycl0nal integration of HTLV-I proviral DNA in lymphobytes from HTLV-I seropositive individuals: an intermediate state between the healthy carrier state and smoldering ATL. British Journal of Haematology 68: 169-174. Yamaguchi K, Nishimura Y, Kiyokawa T & Takatsuki K (1989) Elevated serum levels of soluble interleukin-2 receptors in HTLV-I associated myelopathy. Journal of Laboratory and Clinical Medicine 114: 407-410. Yamamoto N, Okada M, Koyanagi Y e t al (1982) Transformation of human leukocytes by co-cultivation with an adult T cell leukemia virus producer cell line~ Science 217: 737-739. Yanagihara R, Nerurkar VR & Ajdukiewicz AB (1991) Comparison between strains of human

148

G. FRANCHINI AND H. STREICHER

T lymphotropic virus type I isolated from inhabitants of the Solomon Islands and Papua New Guinea. Journal of Infectious Diseases 164: 443-449. Yanagihara R, Nerurkar VR, Garruto RM et al (1991b) Characterization of a variant of human T-lymphotropic virus type I isolated from a healthy member of a remote, recently contacted group in Papua New Guinea. Proceedings of the National Academy of Sciences of the USA 88: 1446-1450. Yoshida M (1994) Ten Anniversary Perspectives on AIDS. Host-HTLV Type I Interaction at the Molecular Level. AIDS Research and Human Retroviruses 10:1193-1197. Yoshida M, Seidi M, Yamaguchi K et al (1984) Monoclonal integration of HTLV in all primary tumors of adult T-cell leukemia suggests causative rote of HTLV in the disease. Proceedings of the National Academy of Sciences of the USA 81: 2534-2537.