Development of leukemia in mice transgenic for the tax gene of human T-cell leukemia virus type I.

The human T-cell leukemia virus type I Tax protein trans-activates several cellular genes implicated in T-cell replication and activation. To investigate its leukemogenic potential, Tax was targeted to the mature T-lymphocyte compartment in transgenic mice by using the human granzyme B promoter. These mice developed large granular lymphocytic leukemia, demonstrating that expression of Tax in the lymphocyte compartment is sufficient for the development of leukemia. Furthermore, these observations suggest that human T-cell leukemia virus infection may be involved in the development of large granular lymphocytic leukemia.     

Cell-type-specific transactivation of the parathyroid hormone-related protein gene promoter by the human T-cell leukemia virus type I (HTLV- I) tax and HTLV-II tax proteins

The human T-cell leukemia virus type I (HTLV-I) and HTLV-II Tax proteins are potent transactivators of viral and cellular gene expression. Using deletion mutants, the downstream parathyroid hormone- related protein (PTHrP) promoter is shown to be responsive to both HTLV- I and HTLV-II Tax as well as the AP1/c-jun proto-oncogene. Transactivation of PTHrP by Tax was seen in T cells but not in B-cell lines or fibroblasts. A carboxy terminal Tax deletion mutant was deficient in transactivation of both the PTHrP and IL2R alpha promoters but not the HTLV-I long terminal repeat (LTR). Exogenous provision of NFkB rescued IL2R alpha expression but not the PTHrP promoter. Thus, HTLV-I Tax, HTLV-II Tax, and c-jun transactivate PTHrP and may contribute to the pathogenesis of hypercalcemia in adult T-cell leukemia.     

Infection of human endothelial cells by human T-cell leukemia virus type I.

The effects of the human T-cell leukemia virus type I (HTLV-I) on cultured human endothelial cells were evaluated. Coculture of endothelial monolayers with either irradiated HTLV-producing lymphocytes or cell-free virus resulted in the production of multinucleated syncytia. The development of syncytia was inhibited by sera from patients with adult T-cell leukemia/lymphoma (ATLL). HTLV antigens were present on endothelial syncytia passaged in culture for greater than 3 months as detected by an anti-p19 monoclonal antibody, which detects a core protein of HTLV-I, and by ATLL sera. Moreover, these HTLV-infected endothelial cells were then able to infect and transform normal cord blood T lymphocytes with HTLV. These studies demonstrate that human endothelial cells are susceptible to productive HTLV-I infection in vitro and may have relevance for the spectrum of human disease associated with this family of retroviruses.     

Stable expression of the tax gene of type I human T-cell leukemia virus in human T cells activates specific cellular genes involved in growth.

Stable expression of the 40-kDa transactivator protein (Tax) from the type I human T-cell leukemia virus (HTLV-I) in Jurkat T cells leads to the activation and sustained expression of certain cellular genes that are transiently induced during normal T-cell growth. Cellular genes induced by Tax include those encoding the alpha subunit of the high-affinity interleukin 2 receptor (Tac), interleukin 2, and granulocyte/macrophage colony-stimulating factor. Tax induction of the interleukin 2 gene is synergistically amplified by mitogens that augment cytoplasmic levels of calcium. These changes in the pattern of cellular gene expression reflect a specific action of Tax, as they are undetectable in isogenically matched control cell lines expressing antisense tax cDNA. The spectrum of cellular genes regulated by Tax appears to be restricted: several other T-cell genes, either inducibly or constitutively expressed, are unaffected by this viral protein. These cell lines constitutively expressing Tax provide valuable reagents to explore the molecular basis for Tax action and to delineate the full spectrum of cellular genes regulated by this retroviral gene product.     

Adult T-cell leukemia/lymphoma not associated with human T-cell leukemia virus type I.

We describe five patients with adult T-cell leukemia/lymphoma (ATL) with neither integration of human T-cell leukemia virus type I (HTLV-I) into their leukemia cells nor anti-HTLV-I antibody in their sera. These findings indicate that HTLV-I may not have been involved in leukemogenesis in these patients. The clinicohematological, cytopathological, and immunological features of HTLV-I-negative ATL were exactly the same as those of HTLV-I-associated ATL. Leukemia cells with pleomorphic nuclei, generalized lymphadenopathy, hepatosplenomegaly, skin lesions, hypercalcemia, and elevated lactate dehydrogenase levels, all of which are characteristic features of typical ATL, were also seen in these patients with HTLV-I-negative ATL. Leukemia cells expressed T3, T4, and pan-T-cell antigens in three cases, and T3 and pan-T-cell antigens in two. All five patients had lived in ATL-nonendemic areas. The finding of HTLV-I-negative ATL suggests that factor(s) other than HTLV-I infection may be involved in ATL leukemogenesis.     

Virion-associated trans-regulatory protein of human T-cell leukemia virus type I.

Western blot analysis of HTLV-I virus particles from HUT-102 cells revealed a 40-kD protein strongly reactive with Tax-specific rabbit antisera. This protein subsequently was isolated from density gradient purified virions by preparative sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), purified from comigrating Gag and human cellular proteins by reversed-phase high-performance liquid chromatography (HPLC) and identified as the tax-encoded gene product by amino acid composition analysis. Among extracellular virions from five HTLV-I producing cell lines, only those from HUT-102 and C10MJ cells contained a detectable Tax protein, although all cells expressed Tax mRNA and protein intracellularly. To investigate the diagnostic implications of virion-associated Tax protein, sera from HTLV-I-infected individuals were compared on HUT-102 and MT-2 virus Western blots. The seroprevalence of antibodies to Tax, but not Gag or Env proteins, was substantially higher among adult T-cell leukemia and tropical spastic paraparesis patients using HUT-102 viral proteins. Thus, immunoassays utilizing HUT-102 virus are most sensitive for detection of Tax-reactive antibodies.     

Serological cross-reactivity between envelope gene products of type I and type II human T-cell leukemia virus.

People exposed to type I human T-cell leukemia virus (HTLV-I) develop antibodies to an antigen at the surface of virus-infected cells, designated human T-cell leukemia virus membrane antigen (HTLV-MA). In an earlier study, we demonstrated that the major component of HTLV-MA is gp61, a glycoprotein encoded by the HTLV env gene. In the current study, we found that human antibodies that react with HTLV-MA on cells infected with HTLV-I react equally well with HTLV-MA on C3-44/MO, a target cell infected with type II HTLV. A glycoprotein with an approximate size of 67 kDa, gp67, was identified in C3-44/MO using immunoprecipitation and NaDodSO4/PAGE analysis. The positions of serine and cysteine residues were determined in the amino terminus of gp67 by radiolabel sequencing analysis. Comparison with the amino acid sequence deduced from the primary nucleotide sequence of HTLV-IIMO virus reveals that gp67 is also encoded, at least in part, by the env gene. The gp67 of HTLV-IIMO, like the env gene product of HTLV-ICR, gp61, is recognized both by antibodies from a HTLV-IIMO-infected patient with a variant form of hairy cell leukemia, and by antibodies from patients with HTLV-I-associated adult T-cell leukemia/lymphoma. These results indicate that, despite the divergence between HTLV-I and HTLV-II, the major env gene products of the two types of HTLV are conserved to the degree that they are serologically cross-reactive.     

T-cell activation by autologous human T-cell leukemia virus type I-infected T-cell clones.

A unique feature of both human T-cell leukemia virus type I (HTLV-I) carriers and subjects with HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP), a chronic inflammatory disease of the nervous system, is the presence of large numbers of activated T cells that spontaneously proliferate in vitro. We have investigated the mechanisms of T-cell activation by HTLV-I in freshly isolated blood T cells and in naturally infected T-cell clones obtained by direct single-cell cloning from patients with HAM/TSP. Both CD4+ and CD8+ HTLV-I-infected T-cell clones showed the unusual ability to proliferate in the absence of exogenous interleukin 2 (IL-2). Nevertheless, HTLV-I-infected clones were not transformed, as they required periodic restimulation with phytohemagglutinin and feeder cells for long-term growth. Irradiated or fixed HTLV-I-infected clones were found to induce the proliferation of blood T cells when cocultured, which we refer to as THTLV-1-T cell activation. This THTLV-1-T cell-mediated activation was blocked by monoclonal antibodies (mAbs) against CD2/lymphocyte function-associated molecule 3 (LFA-3), LFA-1/intercellular cell-adhesion molecule (ICAM), and the IL-2 receptor but not by mAbs against class I or class II major histocompatibility complex molecules, HTLV-I gp46, or a high-titer HAM/TSP serum. Spontaneous proliferation of blood T cells from HAM/TSP patients could also be inhibited by mAbs to CD2/LFA-3, LFA-1/ICAM and to the IL-2 receptor (CD25). These results show at the clonal level that HTLV-I infection induces T-cell activation and that such activated T cells can in turn stimulate noninfected T cells by cognate THTLV-1-T cell interactions involving the CD2 pathway.     

Gastric lymphoma associated with human T-cell leukemia virus type I

A 41-year-old woman presented with a gastric lymphoma. A total gastrectomy was performed, and the tumor was found to consist of T cells of the helper/inducer (E+, Leu-1+, Leu-2a-, Leu-3a+) phenotype. The patient was seropositive for T-cell leukemia virus type I, and the tumor cells contained the proviral genome.     

Thrombocytopenic purpura in a carrier of human T-cell leukemia virus type I

Thrombocytopenic purpura developed in a 64-year-old woman seropositive for human T-cell leukemia virus type I (HTLV-I). She had no underlying disorders and HTLV-I is suggested as a possible cause of her thrombocytopenia.     

Kaposi's sarcoma in human T-cell leukemia virus type I-associated adult T-cell leukemia

Kaposi's sarcoma (KS) developed in a patient with human T-cell leukemia virus type I (HTLV-I)-associated adult T-cell leukemia who was treated with a short-term course of monoclonal antibody immunotherapy. The presentation was transient and temporally related to the underlying clinical course. The association of KS in an HTLV-I infected, but not human immunodeficiency virus (HIV)-infected, individual should alert investigators to the occurrence of KS in retroviral-associated diseases other than acquired immunodeficiency disease syndrome. Recognition of the similarities and differences between HTLV-I and HIV infections may provide insights concerning the angiopathogenesis of KS.     

In vitro infection of human macrophages with human T-cell leukemia virus type 1

The tropism of the human T-cell leukemia virus type 1 (HTLV-1) for the cells of monocyte-macrophage lineage was evaluated by the coculture of blood monocyte-derived macrophages, with irradiated cells of HTLV-1 producing cell lines MT2 or C91/PL. The susceptibility to HTLV-1 was assessed by the detection of viral DNA using the polymerase chain reaction method. HTLV-1 gene expression in the cells was detected using in situ hybridization and by immunofluorescent staining of viral antigen. The presence of type C virus-like particles detected by electron microscopy and the ability to infect normal cord blood lymphocytes demonstrated that the infected macrophages produced infectious virus. These results indicate that human macrophages are susceptible in vitro to productive HTLV-1 infection, and thus might be involved in the pathogenesis of HTLV-1-related diseases.     

Establishment of human T-cell leukemia virus type I T-cell lymphomas in severe combined immunodeficient mice

Human T-cell leukemia virus type I (HTLV-I) is recognized as the etiologic agent of adult T-cell leukemia (ATL), a disease endemic in certain regions of southeastern Japan, Africa, and the Caribbean basin. Although HTLV-I can immortalize T lymphocytes in culture, factors leading to tumor progression after HTLV-I infection remain elusive. Previous attempts to propagate the ATL tumor cells in animals have been unsuccessful. Severe combined immunodeficient (SCID) mice have previously been used to support the survival of human lymphoid cell populations when inoculated with human peripheral blood lymphocytes (PBL). SCID mice were injected intraperitoneally with PBL from patients diagnosed with ATL, HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP), or from asymptomatic HTLV-I-seropositive patients. Many of these mice become persistently infected with HTLV-I. Furthermore, after human reconstitution was established in these mice, HTLV-I-infected cells displayed a proliferative advantage over uninfected human cells. Lymphoblastic lymphomas of human origin developed in animals injected with PBL from two ATL patients. The tumor cells represented outgrowth of the original ATL leukemic clone in that they had monoclonal or oligoclonal integrations of the HTLV-I provirus identical to the leukemic clone and predominantly expressed the cell surface markers, CD4 and CD25. In contrast, cell lines derived by HTLV immortalization of T cells in vitro did not persist or form tumors when inoculated into SCID mice, indicating differences between in vitro immortalized cells and ATL leukemic cells. This system represents the first small animal model to study HTLV-I tumorigenesis in vivo.     

Simian T-cell leukemia virus type I infection in captive baboons.

Human T-cell leukemia virus type (HTLV-I) is a type C retrovirus that has been linked to both adult T-cell leukemia and neurological disorders in humans. Baboons and other Old World non-human primates harbor a related virus termed simian T-cell leukemia virus type 1 (STLV-I), which may also be associated with neoplastic disease. To explore the utility of the baboon as a model for HTLV-I infection and disease, 329 baboons from a colony of 3200 at the Southwest Foundation for Biomedical Research (SFBR) were analyzed for the presence of antibodies against STLV-I. An overall seroprevalence rate of > 40% was found, with higher rates in females versus males. Furthermore, seroprevalence rates increased dramatically with age, reaching greater than 80% in animals over the age of 16. Molecular and antigenic analysis of proviral DNA isolated from both tumor tissue and a cell line isolated from a baboon with non-Hodgkin's lymphoma (NHL) indicates that STLV-I in this colony is closely related to HTLV-I. Furthermore, monoclonally integrated provirus isolated from lymphoma tissue was detected, strongly implicating STLV-I in the etiology of this malignancy. DNA primer pairs homologous to HTLV-I sequences amplified both HTLV-I and STLV-I, but not HTLV-II, providing further evidence for a close genetic relationship between baboon-derived STLV-I and HTLV-I. The detailed study of a large population of naturally infected baboons may therefore shed some light into the complex processes required for the induction of disease associated with HTLV-I infection in humans.