Establishment of HTLV-I-infected cell lines from French, Guianese and West Indian patients and isolation of a proviral clone producing viral particles

Feedback Loop Regulation Between Pim Kinases and Tax Keeps HTLV-I Viral Replication in Check

The Pim family of serine/threonine kinases promote tumorigenesis by enhancing cell survival and inhibiting apoptosis. Three isoforms exist, Pim-1, -2, and -3 that are highly expressed in hematological cancers, including Pim-1 in Adult T-cell leukemia (ATL). Human T-cell leukemia virus type-1 (HTLV-I) is the etiological agent of ATL, a dismal lymphoproliferative disease known as adult T-cell leukemia. The HTLV-I virally encoded oncogene Tax promotes CD4+ T-cell transformation through disruption of DNA repair pathways and activation of survival and cellular proliferation pathways. In this study, we found Tax increases the expression of Pim-1 and Pim-3, while decreasing Pim-2 expression. Furthermore, we discovered that Pim-1, -2, and -3 bind Tax protein to reduce its expression thereby creating a feedback regulatory loop between these two oncogenes. The loss of Tax expression triggered by Pim kinases led to loss in Tax-mediated transactivation of the HTLV-I LTR and reductions in HTLV-I virus replication. Since Tax is also the immunodominant cytotoxic T cell lymphocytes (CTL) target, our data suggest that Pim kinases may play an important role in immune escape of HTLV-1-infected cells. IMPORTANCE The Pim family of protein kinases have established pro-oncogenic functions. They are often up regulated in cancer; especially leukemias and lymphomas. In addition, a role for Pim kinases in control of virus expression and viral latency is important for KSHV and HIV-1. Our data demonstrate that HTLV-I encodes viral genes that promote and maintain Pim kinase activation, which in turn may stimulate T-cell transformation and maintain ATL leukemic cell growth. HTLV-I Tax increases expression of Pim-1 and Pim-3, while decreasing expression of Pim-2. In ATL cells, Pim expression is maintained through extended protein half-life and heat shock protection. In addition, we found that Pim kinases have a new role during HTLV-I infection. Pim-1, -2, and -3 can subvert Tax expression and HTLV-I virus production. This may lead to partial suppression of the host immunogenic responses to Tax and favor immune escape of HTLV-1-infected cells. Therefore, Pim kinases have not only pro-oncogenic roles but also favor persistence of the virus-infected cell.

miR-28-3p is a cellular restriction factor that inhibits human T cell leukemia virus, type 1 (HTLV-1) replication and virus infection

Human T cell leukemia virus, type 1 (HTLV-1) replication and spread are controlled by different viral and cellular factors. Although several anti-HIV cellular microRNAs have been described, such a regulation for HTLV-1 has not been reported. In this study, we found that miR-28-3p inhibits HTLV-1 virus expression and its replication by targeting a specific site within the genomic gag/pol viral mRNA. Because miR-28-3p is highly expressed in resting T cells, which are resistant to HTLV-1 infection, we investigated a potential protective role of miR-28-3p against de novo HTLV-1 infection. To this end, we developed a new sensitive and quantitative assay on the basis of the detection of products of reverse transcription. We demonstrate that miR-28-3p does not prevent virus receptor interaction or virus entry but, instead, induces a post-entry block at the reverse transcription level. In addition, we found that HTLV-1, subtype 1A isolates corresponding to the Japanese strain ATK-1 present a natural, single-nucleotide polymorphism within the miR-28-3p target site. As a result of this polymorphism, the ATK-1 virus sequence was not inhibited by miR-28. Interestingly, genetic studies on the transmission of the virus has shown that the ATK-1 strain, which carries a Thr-to-Cys transition mutation, is transmitted efficiently between spouses, suggesting that miR-28 may play an important role in HTLV-1 transmission.

PA28γ is a novel corepressor of HTLV-1 replication and controls viral latency

The establishment of a latent reservoir by human tumor viruses is a vital step in initiating cellular transformation and represents a major shortcoming to current therapeutic strategies and the ability to eradicate virus-infected cells. Human T-cell leukemia virus type 1 (HTLV-1) establishes a lifelong infection and is linked to adult T-cell leukemia lymphoma (ATLL). Here, we demonstrate that HTLV-1 p30 recruits the cellular proteasome activator PA28γ onto the viral tax/rex mRNA to prevent its nuclear export and suppress virus replication. Interaction of p30 with a PA28γ retaining fully functional proteasome activity is required for p30's ability to repress HTLV-1. Consistently, HTLV-1 molecular clones replicate better and produce more virus particles in PA28γ-deficient cells. These results define a unique and novel role for the cellular factor PA28γ in the control of nuclear RNA trafficking and HTLV-1–induced latency. Importantly, knockdown of PA28γ expression in ATLL cells latently infected with HTLV-1 reactivates expression of viral tax/rex RNA and the Tax protein. Because Tax is the most immunogenic viral antigen and triggers strong CTL responses, our results suggest that PA28γ-targeted therapy may reactivate virus expression from latently infected cells and allow their eradication from the host.

KEY POINTS

PA28γ acts as a co-repressor of HTLV-1 p30 to suppress virus replication and is required for the maintenance of viral latency. HTLV-1 has evolved a unique function mediated by its posttranscriptional repressor p30, which is not found in HTLV-2.

Requirement of the human T-cell leukemia virus p12 and p30 products for infectivity of human dendritic cells and macaques but not rabbits

The identification of the genes necessary for human T-cell leukemia virus (HTLV-1) persistence in humans may provide targets for therapeutic approaches. We demonstrate that ablation of the HTLV-1 genes encoding p12, p30, or the HBZ protein, does not affect viral infectivity in rabbits and in this species, only the absence of HBZ is associated with a consistent reduction in virus levels. We observed reversion of the HTLV-1 mutants to the HTLV-1 wild-type genotype in none of the inoculated rabbits. In contrast, in macaques, the absence of HBZ was associated with reversion of the mutant virus to the wild-type genotype in 3 of the 4 animals within weeks from infection. Similarly, reversion to the wild type was observed in 2 of the 4 macaque inoculated with the p30 mutant. The 4 macaques exposed to the p12 knock remained seronegative, and only 2 animals were positive at a single time point for viral DNA in tissues. Interestingly, we found that the p12 and the p30 mutants were also severely impaired in their ability to replicate in human dendritic cells. These data suggest that infection of dendritic cells may be required for the establishment and maintenance of HTLV-1 infection in primate species.

In vivo genetic mutations define predominant functions of the human T-cell leukemia/lymphoma virus p12I protein

The human T-cell leukemia/lymphoma virus type 1 (HTLV-1) ORF-I encodes a 99-amino acid hydrophobic membrane protein, p12(I), that affects receptors in different cellular compartments. We report here that proteolytic cleavage dictates different cellular localization and functions of p12(I). The removal of a noncanonical endoplasmic reticulum (ER) retention/retrieval signal within the amino terminus of p12(I) is necessary for trafficking to the Golgi apparatus and generation of a completely cleaved 8-kDa protein. The 8-kDa protein in turn traffics to the cell surface, is recruited to the immunologic synapse following T-cell receptor (TCR) ligation, and down-regulates TCR proximal signaling. The uncleaved 12-kDa form of p12(I) resides in the ER and interacts with the beta and gamma(c) chains of the interleukin-2 receptor (IL-2R), the heavy chain of the major histocompatibility complex (MHC) class I, as well as calreticulin and calnexin. Genetic analysis of ORF-I from ex vivo samples of HTLV-1-infected patients reveals predominant amino acid substitutions within ORF-I that affect proteolytic cleavage, suggesting that ER-associated functions of p12(I) may contribute to the survival and proliferation of the infected T cells in the host.

Construction and characterization of a full-length infectious simian T-cell lymphotropic virus type 3 molecular clone

Together with their simian T-cell lymphotropic virus (STLV) equivalent, human T-cell lymphotropic virus type 1 (HTLV-1), HTLV-2, and HTLV-3 form the primate T-cell lymphotropic virus (PTLV) group. Over the years, understanding the biology and pathogenesis of HTLV-1 and HTLV-2 has been widely improved by the creation of molecular clones. In contrast, so far, PTLV-3 experimental studies have been restricted to the overexpression of the tax gene using reporter assays. We have therefore decided to construct an STLV-3 molecular clone. We generated a full-length STLV-3 proviral clone (8,891 bp) by PCR amplification of overlapping fragments. This STLV-3 molecular clone was then transfected into 293T cells. Reverse transcriptase PCR experiments followed by sequence analysis of the amplified products allowed us to establish that both gag and tax/rex mRNAs were transcribed. Western blotting further demonstrated the presence of the STLV-3 p24gag protein in the cell culture supernatant from transfected cells. Transient transfection of 293T cells and of 293T-long terminal repeat-green fluorescent protein cells with the STLV-3 clone promoted syncytium formation, a hallmark of PTLV Env expression, as well as the appearance of fluorescent cells, also demonstrating that the Tax3 protein was expressed. Virus particles were visible by electron microscopy. These particles are infectious, as demonstrated by our cell-free-infection experiments with purified virions. All together, our data demonstrate that the STLV-3 molecular clone is functional and infectious. This clone will give us a unique opportunity to study in vitro the different pX transcripts and the putative presence of antisense transcripts and to evaluate the PTLV-3 pathogenicity in vivo.

SYBR Green-based quantitation of human T-lymphotropic virus type 1 proviral load in Peruvian patients with neurological disease and asymptomatic carriers: influence of clinical status, sex, and familial relatedness

To evaluate the human T-lymphotropic virus type 1 (HTLV-1) proviral DNA load in patients with HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and asymptomatic HTLV-1 carriers, a SYBR Green-based real-time quantitative polymerase chain reaction (qPCR) assay was developed. HTLV-1 proviral DNA in peripheral blood mononuclear cells (PBMCs) was quantified using primers targeting the pX region and the HTLV-1 copy number normalized to the amount of ERV-3 (Endogenous Retrovirus 3) cellular DNA. Thirty-three asymptomatic HTLV-1 carriers (ACs) and 39 patients with HAM/TSP were enrolled. Some participants were relatives of HAM/TSP cases (16 ACs and 7 patients with HAM/TSP). On multiple linear regression analysis, the authors found a significant association between clinical status and HTLV-1 proviral load (P < .01), but only among women. ACs showed a median proviral load of 561 copies per 104 PBMCs (interquartile range: 251-1623). In HAM/TSP patients, the median proviral load was 1783 (1385-2914). ACs related to HAM/TSP patients presented a relatively high proviral load (median 1152); however, the association between relatedness to a HAM/TSP patient and proviral load was not significant (P = .1). In HAM/TSP patients, no association was found between proviral load and disease duration, progression or severity. The fact that the effect of HAM/TSP upon the HTLV-1 proviral load differed between sexes and the finding of a high proviral load among asymptomatic relatives of HAM/TSP patients suggest that not yet identified genetic or environmental factors influence the pathogenesis of HTLV-1 infection.

Proviral load and immune markers associated with human T-lymphotropic virus type 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) in Peru

Human T-lymphotropic virus type 1 (HTLV-1) is the aetiological agent of HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The objective of this study is to identify which ex vivo and in vivo markers are associated independently with HAM/TSP in a Peruvian population. Eighty-one subjects (33 men/48 women) were enrolled: 35 presented with HAM/TSP, 33 were asymptomatic HTLV-1 carriers (ACs) and 13 were HTLV-1-seronegative controls (SCs). Ex vivo markers included T cell proliferation and Th1 [interferon (IFN)-gamma], Th2 [interleukin (IL)-4, IL-5], proinflammatory [tumour necrosis factor (TNF)-alpha] and anti-inflammatory (IL-10) cytokine production in non-stimulated peripheral blood mononuclear cell (PBMC) cultures. In vivo CD4(+) T cell count, markers of Th1 [interferon-inducible protein (IP)-10] and Th2 (sCD30) activity in plasma and HTLV-1 proviral load in PBMCs were also evaluated. In univariate analysis, several markers, including T cell proliferation, IFN-gamma, IP-10, sCD30 and proviral load were associated with HAM/TSP, but in a multiple logistic regression analysis only the proviral load remained associated significantly with disease manifestation [adjusted OR 9.10 (1.24-66.91)]. Our findings suggest that HAM/TSP is associated primarily with proviral load, whereas the observed association with some immune markers seems secondary.

Human T-cell leukemia virus type I p30 nuclear/nucleolar retention is mediated through interactions with RNA and a constituent of the 60 S ribosomal subunit

Human T-cell leukemia virus type I is the etiological agent of adult T-cell leukemia/lymphoma, an aggressive and fatal lymphoproliferative malignancy. The virus has evolved strategies to escape immune clearance by remaining latent in most infected cells in vivo. We demonstrated previously that virally encoded p30 protein is a potent post-transcriptional inhibitor of virus replication (Nicot, C., Dundr, M., Johnson, J. M., Fullen, J. R., Alonzo, N., Fukumoto, R., Princler, G. L., Derse, D., Misteli, T., and Franchini, G. (2004) Nat. Med. 10, 197-201). p30 is unable to shuttle out of the nucleus in heterokaryon assays, suggesting the existence of specific retention signals. Because suppression of virus replication relies on nuclear retention of the tax/rex mRNA by p30, determining the retention features of p30 will offer hints to break latency in infected cells and insights into new therapeutic approaches. In this study, we used live cell imaging technologies to study the kinetics of p30 and to delineate its retention signals and their function in virus replication. Notably, this is the first study to identify p30 nucleolar retention domains. Using mutants of p30 that localized in different cellular compartments, we show that post-transcriptional control of virus replication by p30 occurs in the nucleoplasm. We further demonstrate that p30 nuclear/nucleolar retention is dependent upon de novo RNA transcripts and interactions with components of the ribosomal machinery.

Human T-cell leukemia/lymphoma virus type 1 nonstructural genes and their functions

The human T-cell leukemia/lymphoma virus (HTLV) genome, in addition to the structural Gag and Env proteins and retroviral enzymes, carries a region at its 3' end originally designated pX. To date, we know that this region encodes two essential transcriptional and post-transcriptional positive regulators of viral expression, the Tax and Rex proteins, respectively (reviewed elsewhere in this issue). Here, we will review current knowledge of the functions of three additional proteins encoded in the pX region, p12I, p13II, and p30II.

In vitro photochemical inactivation of cell-associated human T-cell leukemia virus Type I and II in human platelet concentrates and plasma by use of amotosalen

BACKGROUND

Human T-cell leukemia virus Types I and II (HTLV-I and HTLV-II), blood-borne retroviruses found worldwide, can cause leukemia, immunosuppression, and severe neurologic diseases. In most countries, HTLV-I and -II screening is not performed systematically for blood donations. A new photochemical treatment (PCT) with a synthetic psoralen was developed to inactivate most pathogens in platelet (PLT) concentrates or plasma and to improve the safety of blood donations.

STUDY DESIGN AND METHODS

Cell-associated HTLV-I or -II (10(6)/mL) was inoculated in full-size fresh PLT concentrates or fresh frozen plasma and treated with 150 micromol per L amotosalen (S-59) and different doses of long-wavelength ultraviolet A (UVA) light. The residual viral titer in the treated samples was assessed by a cocultivation assay on indicator cells.

RESULTS

The inactivation obtained at a 3.0 J per cm2 UVA dose was greater than 5.2 log foci-forming units (FFUs) per mL for HTLV-I and 4.6 log FFUs per mL for HTLV-II in presence of human PLT concentrates and greater than 4.5 log FFUs per mL for HTLV-I and 5.7 log FFUs per mL for HTLV-II in the presence of human plasma. The residual infectivity was very low and shown as the limit of detection of the cocultivation assay.

CONCLUSION

In human plasma or PLT concentrates, the retroviruses HTLV-I and -II were strongly sensitive to the PCT with 150 micromol per L amotosalen (S-59) and a 3.0 J per cm2 UVA dose. This high efficiency for photoinactivation of these retroviruses opens a possibility of improving the safety of PLTs or plasma transfusion in the future.

Inactivation of viruses in platelet concentrates by photochemical treatment with amotosalen and long-wavelength ultraviolet light

BACKGROUND

Viral contamination of platelet (PLT) concentrates can result in transfusion-transmitted diseases. A photochemical treatment (PCT) process with amotosalen-HCl and long-wavelength ultraviolet light (UVA), which cross-links nucleic acids, was developed to inactivate viruses and other pathogens in PLT concentrates.

STUDY DESIGN AND METHODS

High titers of pathogenic or blood-borne viruses, representing 10 different families, were added to single-donor PLT concentrates containing 3.0 x 10(11) to 6.0 x 10(11) PLTs in approximately 300 mL of 35 percent plasma and 65 percent PLT additive solution (InterSol). After PCT with 150 micromol per L amotosalen and 3 J per cm(2) UVA, residual viral infectivity was assayed by sensitive cell culture or animal systems.

RESULTS

Enveloped viruses were uniformly sensitive to inactivation by PCT whereas nonenveloped viruses demonstrated variable inactivation. Log reduction of enveloped viruses for cell-free HIV-1 was >6.2; for cell-associated HIV-1, >6.1; for clinical isolate HIV-1, >3.4; for clinical isolate HIV-2, >2.5; for HBV, >5.5; for HCV, >4.5; for DHBV, >6.2; for BVDV, >6.0; for HTLV-I, 4.2; for HTLV-II, 4.6; for CMV, >5.9; for WNV, >5.5; for SARS-HCoV, >5.8; and for vaccinia virus, >4.7. Log reduction of nonenveloped viruses for human adenovirus 5 was >5.2; for parvovirus B19, 3.5->5.0; for bluetongue virus, 5.6-5.9; for feline conjunctivitis virus, 1.7-2.4; and for simian adenovirus 15, 0.7-2.3.

CONCLUSION

PCT inactivates a broad spectrum of pathogenic, blood-borne viruses. Inactivation of viruses in PLT concentrates with amotosalen and UVA offers the potential to prospectively prevent the majority of PLT transfusion-associated viral diseases.

HTLV-1-encoded p30II is a post-transcriptional negative regulator of viral replication

Human T-cell leukemia/lymphoma virus type 1 (HTLV-1) persists despite a vigorous virus-specific host immune response, and causes adult T-cell leukemia and lymphoma in approximately 2% of infected individuals. Here we report that HTLV-1 has evolved a genetic function to restrict its own replication by a novel post-transcriptional mechanism. The HTLV-1-encoded p30(II) is a nuclear-resident protein that binds to, and retains in the nucleus, the doubly spliced mRNA encoding the Tax and Rex proteins. Because Tex and Rex are positive regulators of viral gene expression, their inhibition by p30(II) reduces virion production. p30(II) inhibits virus expression by reducing Tax and Rex protein expression.

PPPYVEPTAP motif is the late domain of human T-cell leukemia virus type 1 Gag and mediates its functional interaction with cellular proteins Nedd4 and Tsg101 [corrected]

The human T-cell leukemia virus type 1 (HTLV-1) Gag polyprotein contains two adjacent proline-rich motifs (sequence PPPYVEPTAP) in the C terminus of the matrix domain [corrected]. Proline-to-alanine mutations were introduced into either or both motifs of HTLV-1 to determine the effect on the release of HTLV-1 virus-like particles from 293T cells. The release of both single mutants was significantly reduced, whereas a double mutation in both motifs abolished the release of the HTLV-1 particles. Two-hybrid and in vitro binding assays showed that the HTLV-1 Gag polyprotein binds both Tsg101 and Nedd4 proteins. The interaction with HTLV-1 Gag required the central WW domain of Nedd4 and the ubiquitin enzyme variant (UEV) domain of Tsg101. We expressed various fragments of Nedd4 and Tsg101 proteins in 293T cells and tested for their ability to interfere with virion release mediated by the HTLV-1 Gag-Pro polyprotein. Fragments consisting of the N-terminal UEV domain of Tsg101 and the central WW and C-terminal Hect domains of Nedd4 protein all caused transdominant inhibition of HTLV-1 particle release. Similarly, inhibition of the proteasome significantly decreased HTLV-1 particle release. Furthermore, the WW domain overexpression caused an early arrest of HTLV-1 particle morphogenesis before the membrane is deformed into the typical half-shell structure. This result suggests that Nedd4 is involved early in budding of HTLV-1.

Seizing of T Cells by Human T-Cell Leukemia⧸Lymphoma Virus Type 1

Human T-cell leukemia/lymphoma virus type 1 (HTLV-1) causes neoplastic transformation of human T-cells in a small number of infected individuals several years from infection. Several viral proteins act in concert to increase the responsiveness of T-cells to extracellular stimulation, modulate proapoptotic and antiapoptotic gene signals, enhance T-cell survival, and avoid immune recognition of the infected T-cells. The virus promotes T-cell proliferation by usurping several signaling pathways central to immune T-cell function. Viral proteins modulate the downstream effects of antigen stimulation and receptor-ligand interaction, suggesting that extracellular signals are important for HTLV-1 oncogenesis. Environmental factors such as chronic antigen stimulation are therefore important, as also suggested by epidemiological data. The ability of a given individual to respond to specific antigens is determined genetically. Thus, genetic and environmental factors, together with the virus, contribute to disease development. As in the case of other virus-associated cancers, HTLV-1-induced leukemia/lymphoma can be prevented by avoiding viral infection or by intervention during the asymptomatic phase with approaches able to interrupt the vicious cycle of virus-induced proliferation of a subset of T-cells. This review focuses on current knowledge of the mechanisms regulating HTLV-1 replication and the T-cell pathways that are usurped by viral proteins to induce and maintain clonal proliferation of infected T-cells in vitro. The relevance of these laboratory findings will be related to clonal T-cell proliferation and adult T-cell leukemia/lymphoma development in vivo.

Two-step nature of human T-cell leukemia virus type 1 replication in experimentally infected squirrel monkeys (Saimiri sciureus)

After experimental infection of squirrel monkeys (Saimiri sciureus) with human T-cell leukemia virus type 1 (HTLV-1)-infected cells, the virus is transcribed only transiently in circulating blood, spleen, and lymph nodes. Stable disappearance of viral expression occurs at 2 to 3 weeks after inoculation. This coincides with the development of the anti-HTLV-1 immune response and persistent detection of the provirus in peripheral blood mononuclear cells (PBMCs). In this study, the HTLV-1 replication pattern was analyzed over time in PBMCs and various organs from two HTLV-1-infected squirrel monkeys. Real-time quantitative PCR confirmed that PBMCs and lymphoid organs constitute the major reservoirs for HTLV-1. The PCR amplification of HTLV-1 flanking sequences from PBMCs evidenced a pattern of clonal expansion of infected cells identical to that observed in humans. Dissemination of the virus in body compartments appeared to result from cellular transport of the integrated provirus. The circulating proviral burden increased as a function of time in one animal studied over a period of 4 years. The high proviral loads observed in the last samples resulted from the accumulation of infected cells via the extensive proliferation of a restricted number of persistent clones on a background of polyclonally expanded HTLV-1-positive cells. Therefore, HTLV-1 primary infection in squirrel monkeys is a two-step process involving a transient phase of reverse transcription followed by persistent multiplication of infected cells. This suggests that the choice of the target for blocking HTLV-1 replication might depend on the stage of infection.

Distinct p300-responsive mechanisms promote caspase-dependent apoptosis by human T-cell lymphotropic virus type 1 Tax protein

The dysregulation of cellular apoptosis pathways has emerged as a critical early event associated with the development of many types of human cancers. Numerous viral and cellular oncogenes, aside from their inherent transforming properties, are known to induce programmed cell death, consistent with the hypothesis that genetic defects are required to support tumor survival. Here, we report that nuclear expression of the CREB-binding protein (CBP)/p300-binding domain of the human T-cell lymphotropic virus type 1 (HTLV-1) transactivator, Tax, triggers an apoptotic death-inducing signal during short-term clonal analyses, as well as in transient cell death assays. Coexpression of the antiapoptotic factor Bcl-2 increased serum stimulation; incubation with the chemical caspase inhibitor z-Val-Ala-DL-Asp fluoromethylketone antagonized Tax-induced cell death. The CBP/p300-binding defective Tax mutants K88A and V89A exhibited markedly reduced cytotoxic effects compared to the wild-type Tax protein. Importantly, nuclear expression of the minimal CBP/p300-binding peptide of Tax induced apoptosis in the absence of Tax-dependent transcriptional activities, while its K88A counterpart did not cause cell death. Further, Tax-mediated apoptosis was effectively prevented by ectopic expression of the p300 coactivator. We also report that activation of the NF-kappaB transcription pathway by Tax, under growth arrest conditions, results in apoptosis that occurs independent of direct Tax coactivator effects. Our results allude to a novel pivotal role for the transcriptional coactivator p300 in determining cell fate and raise the possibility that dysregulated coactivator usage may pose an early barrier to transformation that must be selectively overcome as a prerequisite for the initiation of neoplasia.

Lymphoid organs as a major reservoir for human T-cell leukemia virus type 1 in experimentally infected squirrel monkeys (Saimiri sciureus): provirus expression, persistence, and humoral and cellular immune responses

The aim of this study was to investigate the distribution of human T-cell leukemia virus type 1 (HTLV-1) in various organs of serially sacrificed squirrel monkeys (Saimiri sciureus) in order to localize the reservoir of the virus and to evaluate the relationship between viral expression and the humoral or cellular immune response during infection. Six squirrel monkeys infected with HTLV-1 were sacrificed 6, 12, and 35 days and 3, 6, and 26 months after inoculation, and 20 organs and tissues were collected from each animal. PCR and reverse transcription-PCR (RT-PCR) were performed with gag and tax primers. Proviral DNA was detected by PCR in peripheral blood mononuclear cells (PBMCs) of monkeys sacrificed 6 days after inoculation and in PBMCs, spleens, and lymph nodes of monkeys sacrificed 12 and 35 days and 3, 6, and 26 months after inoculation. Furthermore, tax/rex mRNA was detected by RT-PCR in the PBMCs of two monkeys 8 to 12 days after inoculation and in the spleens and lymph nodes of the monkey sacrificed on day 12. In this animal, scattered HTLV-1 tax/rex mRNA-positive lymphocytes were detected by in situ hybridization in frozen sections of the spleen, around the germinal centers and close to the arterial capillaries. Anti-HTLV-1 cell-mediated immunity was evaluated at various times after inoculation. Anti-p40(Tax) and anti-Env cytolytic T-cell responses were detected 2 months after infection and remained detectable thereafter. When Tax peptides were used, this response appeared to be directed against various Tax epitopes. Our results indicate that squirrel monkeys represent a promising animal model for studying the early events of HTLV-1 infection and for evaluating candidate vaccines against HTLV-1.

HTLV-I Tax transrepresses the human c-Myb promoter independently of its interaction with CBP or p300

The c-Myb proto-oncogene is preferentially expressed in hematopoietic lineages, and highly expressed in several leukemia types. The Human T-cell Leukemia Virus Type I (HTLV-I) is the etiological agent of Adult T-cell Leukemia/Lymphoma (ATLL). A previous report suggested that Tax, the viral transactivator, is able to suppress the transactivation potential of c-Myb protein by competing for recruitment of CBP. We tested whether such a competition could affect transcription from the c-Myb promoter in Tax expressing T-cells. Using several c-Myb promoter reporter constructs carrying mutations in various regions, we demonstrate that Tax suppression of c-Myb transactivation results in transrepression of the c-Myb promoter through the Myb responsive elements in Jurkat T-cells. The ability of Tax mutants M22, M47 and V89A to interact with the full-length CBP and p300 proteins in vitro, and their ability to repress the c-Myb promoter, was then evaluated. Although both M47 and M22 bind to CBP and p300 to a similar extent, only M47 was able to repress the c-Myb promoter, suggesting that competition for CBP/p300 binding was not the mechanism underlying Tax's effect. This concept was further supported by the fact that the Tax mutant V89A transrepresses the c-Myb promoter efficiently in spite of an impaired binding to CBP and p300. Therefore, Tax-mediated repression of the c-Myb promoter appears to be independent from a direct competition between c-Myb and Tax for recruitment of CBP/p300. Interestingly, a decreased transcription from the endogenous c-Myb promoter was observed in several HTLV-I transformed T-cell lines. Finally, the ability of Tax to directly repress the endogenous c-Myb promoter was demonstrated in a Jurkat cell line stably transfected with a tax gene driven by a cadmium-inducible promoter.

Expression, purification and biological properties of the carboxyl half part of the HTLV-I surface envelope glycoprotein

The carboxyl half of the surface envelope protein of HTLV-I contains the major immunodominant and neutralizable domains. Using two affinity chromatography steps and a combination of high salt concentration and non-ionic detergent, we purified this part of the envelope protein from Escherichia coli. Analysis of some immmunological and biological properties of this protein indicated that it was folded in a way that preserved the correct structure of this domain of the HTLV-I envelope protein. It could be utilized in structural studies to further understand the mechanisms of HTLV-I entry and to better define the component(s) of an effective vaccine.

Amino acid changes at positions 173 and 187 in the human T-cell leukemia virus type 1 surface glycoprotein induce specific neutralizing antibodies

The nucleotide sequence of human T-cell leukemia virus type 1 (HTLV-1) is highly conserved, most strains sharing at least 95% sequence identity. This sequence conservation is also found in the viral env gene, which codes for the two envelope glycoproteins that play a major role in the induction of a protective immune response against the virus. However, recent reports have indicated that some variations in env sequences may induce incomplete cross-reactivity between HTLV-1 strains. To identify the amino acid changes that might be involved in the antigenicity of neutralizable epitopes, we constructed expression vectors coding for the envelope glycoproteins of two HTLV-1 isolates (2060 and 2072) which induced human antibodies with different neutralization patterns. The amino acid sequences of the envelope glycoproteins differed at four positions. Vectors coding for chimeric or point-mutated envelope proteins were derived from 2060 and 2072 HTLV-1 env genes. Syncytium formation induced by the wild-type or mutated envelope proteins was inhibited by human sera with different neutralizing specificities. We thus identified two amino acid changes, I173-->V and A187-->T, that play an important role in the antigenicity of neutralizable epitopes located in this region of the surface envelope glycoprotein.

Influence of amino acid substitutions on antigenicity of immunodominant regions of the HTLV type I envelope surface gylcoprotein: a study using monoclonal antibodies raised against relevant peptides

By the use of sera of human T cell leukemia virus type I (HTVL-I)-infected individuals it was shown that amino acid substitutions at positions 192 (proline to serine) and 250 (serine to proline) in major immunodominant regions (175-199 and 239-261) of the surface envelope glycoprotein (gp46) of the virus may influence the humoral response. Since human sera are polyclonal in nature, one cannot readily discriminate between an immunoglobulin-specific recognition and multiple bindings of diverse antibodies. To overcome this difficulty we generated murine monoclonal antibodies to synthetic peptides mimicking all or portions of these gp46 regions. The reactivity of some of these antibodies to synthetic peptides harboring (or not harboring) the preceding amino acid substitutions at position 192 or 250, to denatured gp46 by Western blotting, and to live (variously substituted) HTLV-I-infected cells, combined with blocking experiments with various peptides, allow us to conclude that the major epitopes (positions 183-191, 190-197, 190-199, and 246-252) in the two immunodominant regions may elicit different antibody responses according to their sequences. It is worth noting that in a reporter gene inhibition assay, it was found that a neutralizing monoclonal antibody (MF1), the epitope for which is located between residues 190 and 197, had a high level of activity when cells (2060) harboring a gp46 with proline at position 192 were used and had no activity toward cells (1010) with a serine at this position. Therefore our results establish that certain amino acid substitutions of gp46 may drastically affect the antigenicity of the molecule and the biological activity of the antibodies elicited.

HTLV-I associated sicca syndrome in Guadeloupe: lack of relation with a peculiar encoding sequence of surface envelope glycoprotein

We previously reported a strikingly high prevalence of ocular diseases in HTLV-I infected patients in Guadeloupe (Caribbean basin). We sequenced the surface envelope encoding region of 7 HTLV-I proviruses from guadeloupean patients (5 with sicca syndrome, 2 with TSP/HAM). No relation between sequence and disease was observed. These 7 sequences are the first described from Guadeloupe.

Different HTLV-I neutralization patterns among sera of patients infected with cosmopolitan HTLV-I

To determine if sequence variations observed in cosmopolitan HTLV-I interfered with viral recognition by neutralizing antibodies, we evaluated the neutralization potential of sera from persons infected by HTLV-I of this clade selected for amino acid changes in their eny glycoproteins. Each serum was used to neutralize three previously described HTLV-I isolates, 2060, 2072, and 1010, that possess amino acid env sequences differing at several positions, one of them being located in the immunodominant and neutralizable domain (aa 187-199). The results obtained in syncytia and/or reporter gene inhibition assays showed that the neutralization pattern of the sera clearly differed and could be classified in three categories. Five sera completely neutralized the three viruses with an equivalent titer, two sera gave a maximum inhibition, with higher ID50 on the 2072 virus than on the 2060 or 1010 viruses, and three sera had a stronger neutralization potential toward the 1010 virus than toward the 2060 virus. One of these sera partially neutralized the virus produced by 2072 cells, whereas neutralizing antibodies in the other two recognized the neutralizable epitopes on the 1010 or 2072 viruses equally well. Identification of amino acid sequences involved in induction of neutralizing antibodies with different recognition capacities could help identify new neutralizable epitopes of HTLV-I envelope glycoproteins and to better define the component(s) of an effective vaccine.

Activation of Bcl-2 expression in human endothelial cells chronically expressing the human T-cell lymphotropic virus type I

Programmed cell death (PCD) characteristically involves chromatin condensation, membrane blebbing, and DNA oligonucleosomal fragmentation. These events, collectively referred to as apoptosis, represent an active cell suicide mechanism that eliminates cellular threats including potentially cancerous or virus-infected cells. Various types of programmed cell death can be blocked by the proto-oncogene Bcl-2. Levels of this protein are consistently low or undetectable in human endothelial cells (EC), which are important for immunoregulation through their interactions with circulating lymphocytes and are potential targets for infection by virus-bearing T-cells. Accumulating evidence suggests that EC may be infected in vivo to play an important role in HTLV-I-associated neuromyelopathy. In the present study, we report the establishment and characterization of human endothelial cell lines stably transfected with an HTLV-I-derived molecular clone. We observed constitutive expression of HTLV-I genes coinciding with activated Bcl-2 expression. Transient transfection of EC with the viral transactivator Tax and a reporter construct Bcl-2 promoter-CAT did not result in a significant increase in CAT activity and suggests that, in EC, expression of a second viral protein might be required for Bcl-2 activation. Further, Tax-induced apoptosis in rat fibroblasts has been shown to be blocked by Bcl-2 expression. Thus, HTLV-I-mediated induction of Bcl-2 expression in EC may provide protection against viral-induced apoptosis or extend cellular survival and create a reservoir for viral gene expression.

Examining the molecular genetics of HTLV-I with an infectious molecular clone of the virus and permissive cell culture systems

Infectious molecular clones of HTLV-I proviruses have only recently been reported. The long wait for such provirus clones reflects the difficulties inherent in propagating HTLV-I in vitro, and thus a rigorous demonstration of infectivity has awaited improved cell culture systems and sensitive detection techniques for HTLV-I. An intact HTLV-I provirus, originating from an American ATL patient, was subcloned into a plasmid vector and was designated pCS-HTLV. Transient transfections of mammalian cells with pCS-HTLV resulted in the synthesis of viral proteins and mRNAs which were assembled into virions that had physical and morphological characteristics typical of HTLV-I particles. The ability of these virus particles to infect cells, replicate, and produce infectious progeny was demonstrated initially in short term, cell-free infection assays by monitoring the expression of specific viral mRNAs. These studies have been extended in cell culture systems that support continuous virus production. Primary T-lymphocytes have been infected either with cell-free supernatant fluids from, or by coculture with, cells transiently transfected with pCS-HTLV, giving rise to continuous, IL-2-dependent cell lines that have been in culture for >1 year. Furthermore, fetal rhesus lung cells (FRhL) were shown to be permissive for HTLV-I replication and sustained virus expression after infection with pCS-HTLV. Continuous FRhL cell lines now have been established that express various HTLV-I proviruses and mutants. These provirus clones and cell lines provide us with the means to address long-standing questions dealing with the biology of HTLV-I.

Stochastic events in the amplification of HTLV-I integration sites by linker-mediated PCR

Human T-cell leukaemia virus type I (HTLV-I) proviral integration sites from an asymptomatic carrier and from the MT4 cell line were analysed by linker-mediated PCR (LMPCR) and inverse PCR (IPCR). LMPCR was more sensitive, allowing detection of a greater number of integrated proviruses. Reconstruction experiments using a cloned integrated HTLV-1 provirus indicated that > 100 copies were necessary to be detected frequently by LMPCR. To circumvent this problem, the LMPCR analysis was performed approximately 20 times per sample. Thus, for the MT4 cell line, the seven major integration sites were accompanied by approximately 20 clones of lesser frequency. For an asymptomatic HTLV-I carrier, nine integration sites were identified in a single amplfication, while a further 9 followed from 14 additional reactions. These findings show that there is a stochastic element to sampling HTLV-I integration sites by LMPCR, which tends to underestimate the actual number of HTLV-I bearing clones. Accordingly, those detected in at least two reactions represent the most abundant clones.

Characterization of an infectious molecular clone of human T-cell leukemia virus type I

An infectious molecular clone of human T-cell leukemia virus type I (HTLV-I) was derived from an HTLV-I-transformed rabbit T-cell line, RH/K30, obtained by coculture of rabbit peripheral blood mononuclear cells (PBMC) with the human HTLV-I-transformed cell line MT-2. The RH/K30 cell line contained two integrated proviruses, an intact HTLV-I genome and an apparently defective provirus with an in-frame stop codon in the env gene. A genomic DNA fragment containing the intact HTLV-I provirus was cloned into bacteriophage lambda (K30 phi) and subcloned into a plasmid vector (K30p). HTLV-I p24gag protein was detected in culture supernatants of human and rabbit T-cell and fibroblast lines transfected with these clones, at levels comparable to those of the parental cell line RH/K30. Persistent expression of virus was observed in one of these lines, RL-5/K30p, for more than 24 months. Biologic characterization of this cell line revealed the presence of integrated HTLV-I provirus, spliced and unspliced mRNA transcripts, and typical extracellular type C retrovirus particles. As expected, these virus particles contained HTLV-I RNA and reverse transcriptase activity. The transfected cells also expressed surface major histocompatibility complex class II, whereas no expression of this molecule was detected in the parental RL-5 cell line. Virus was passaged by cocultivation of irradiated RL-5/K30p cells with either rabbit PBMC or human cord blood mononuclear cells, demonstrating in vitro infectivity. The virus produced in these cells was also infectious in vivo, since rabbits injected with RL-5/K30p cells became productively infected, as evidenced by seroconversion, amplification of HTLV-I-specific sequences by PCR from PBMC DNA, and virus isolation from PBMC. Availability of infectious molecular clones will facilitate functional studies of HTLV-I genes and gene products.

Clustering and clinical diversity of adult T-cell leukemia/lymphoma associated with HTLV-I in a remote black population of French Guiana

An epidemiological study was performed in French Guiana (population 115,000) to determine the prevalence and incidence of adult T-cell leukemia/lymphoma (ATL) associated with human T-cell leukemia/lymphoma virus type I (HTLV-I). From January 1990 to December 1993, all suspected cases of ATL were enrolled in this study, and their clinical, epidemiological and immunovirological features were analyzed. Out of the 19 suspected cases, 18 were considered as ATL associated with HTLV-I (8 acute forms, 8 lymphoma types and 2 smoldering cases). Before this study, only 2 ATL cases had been reported in French Guiana over a 10-year period. This demonstrates that the number of ATL cases is greatly under-estimated in most tropical HTLV-I endemic areas unless a specific disease search is performed. The mean age of the patients was 41 years. While HTLV-I antibodies were present in all cases, molecular studies demonstrated a clonal integration of HTLV-I in the tumoral cells in 7 cases out of the 9 tested. Fifteen patients died within a year of diagnosis. The crude incidence rate of ATL in French Guiana is around 3.5/100,000/year, a situation similar to that found in the Caribbean and in HTLV-I-endemic regions of Japan. However it reaches around 30/100,000/year (highest incidence ever described) in a small remote ethnic group of African origin (around 6200 inhabitants). Possible causes of ATL clustering in this ethnic group are presented.

Virions released from cells transfected with a molecular clone of human T-cell leukemia virus type I give rise to primary and secondary infections of T cells

The ability of molecular clones of human T-cell leukemia virus type I (HTLV-I) to direct the synthesis of infectious virions has not previously been demonstrated. An HTLV-I provirus originating from an adult T-cell leukemia patient was cloned into a plasmid vector and is designated pCS-HTLV. This molecular clone was shown to direct the synthesis of viral mRNA and proteins in transiently transfected cells; in addition, virus structural proteins were released into the culture medium. Viral proteins were assembled into virions that sedimented at a buoyant density characteristic of retrovirus particles and whose morphology was verified by electron microscopy. Virions concentrated from transiently transfected cell supernatants were incubated with primary cord blood lymphocytes or with transformed T-cell lines to establish that these particles were infectious. Expression of spliced, viral mRNAs in the T-cell cultures after both primary and secondary infections with cell-free virus revealed that pCS-HTLV encodes an infectious provirus.

Identification of HTLV-I- or HTLV-II-producing cells by cocultivation with BHK-21 cells stably transfected with a LTR-lacZ gene construct

The Syrian Hamster kidney cell line (BHK-21) was stably transfected with a plasmid vector containing the lacZ bacterial gene under the control of a HTLV-I-LTR promoter. In these cells termed pA18G-BHK-21, this lacZ construct is inducible by the tax protein produced by a tax expression vector. It was also shown that beta-galactosidase synthesis was detected within 48 h after cocultivation of pA18G-BHK-21 cells with HTLV-I (HUT-102, MT2, C91/PL, 2060) or HTLV-II (MoT strain) -producing cells. The number of positive cells was directly related to the number of HTLV-I or -II-infected cells seeded. In addition, the LTR transactivation observed in coculture with HTLV-I-infected cells was specifically inhibited by sera containing antibodies directed against HTLV-I proteins, but not, or only weakly, by sera containing HTLV-II antibodies. Conversely, beta-galactosidase expression induced by HTLV-II-infected cells was inhibited by sera of HTLV-II-infected individuals, but not, or only weakly, by HTLV-I-positive sera. Irrespective of the inducer cell, sera from uninfected people did not inhibit LTR-driven expression of the lacZ gene in pA18G-BHK-21 cells cocultivated with HTLV-producing cells. This assay may thus be employed profitably for the detection and quantification of both HTLV-producing cells and HTLV-specific antibodies.