Lucy Cook

HTLV-1: persistence and pathogenesis.

ContentsIntroduction. . 131HTLV-1 pathogenesis 132HTLV-1 and disease. . . 132ATL 132HAM/TSP . . 132Determinants of proviral load 132Integration and clonal expansion . . 132CD8þ T cell lysis 133The immune response to HTLV-1. . . 133Determinants of protective immunity 133Immunodominance 134‘‘Innate’’ receptors enhance the HLA class I-restricted response 135Persistence in the face of a strong immune response 136Immunogenicity of HTLV-I-infected cells 136Slow clearance of Tax-expressing cells in vivo 137Concluding remarks 137Is HBZ a viable target for HTLV-I vaccine design? 137Why is CTL killing low in vivo? 137How do KIRs affect the outcome of HTLV-1 infection? . . 137References . . . 137

HTLV-1-infected T cells contain a single integrated provirus in natural infection

Human T lymphotropic virus type 1 (HTLV-1) appears to persist in the chronic phase of infection by driving oligoclonal proliferation of infected T cells. Our recent high-throughput sequencing study revealed a large number (often > 10(4)) of distinct proviral integration sites of HTLV-1 in each host that is greatly in excess of previous estimates. Here we use the highly sensitive, quantitative high-throughput sequencing protocol to show that circulating HTLV-1(+) clones in natural infection each contain a single integrated proviral copy. We conclude that a typical host possesses a large number of distinct HTLV-1-infected T-cell clones.

HTLV-1 clonality in adult T-cell leukaemia and non-malignant HTLV-1 infection

Human T lymphotropic virus type 1 (HTLV-1) causes a range of chronic inflammatory diseases and an aggressive malignancy of T lymphocytes known as adult T-cell leukaemia/lymphoma (ATLL). A cardinal feature of HTLV-1 infection is the presence of expanded clones of HTLV-1-infected T cells, which may persist for decades. A high viral burden (proviral load) is associated with both the inflammatory and malignant diseases caused by HTLV-1, and it has been believed that the oligoclonal expansion of infected cells predisposes to these diseases. However, it is not understood what regulates the clonality of HTLV-1 in vivo, that is, the number and abundance of HTLV-1-infected T cell clones. We review recent advances in the understanding of HTLV-1 infection and disease that have come from high-throughput quantification and analysis of HTLV-1 clonality in natural infection.

Strongyloidiasis and infective dermatitis alter human T lymphotropic virus-1 clonality in vivo.

Human T-lymphotropic Virus-1 (HTLV-1) is a retrovirus that persists lifelong by driving clonal proliferation of infected T-cells. HTLV-1 causes a neuroinflammatory disease and adult T-cell leukemia/lymphoma. Strongyloidiasis, a gastrointestinal infection by the helminth Strongyloides stercoralis, and Infective Dermatitis associated with HTLV-1 (IDH), appear to be risk factors for the development of HTLV-1 related diseases. We used high-throughput sequencing to map and quantify the insertion sites of the provirus in order to monitor the clonality of the HTLV-1-infected T-cell population (i.e. the number of distinct clones and abundance of each clone). A newly developed biodiversity estimator called “DivE” was used to estimate the total number of clones in the blood. We found that the major determinant of proviral load in all subjects without leukemia/lymphoma was the total number of HTLV-1-infected clones. Nevertheless, the significantly higher proviral load in patients with strongyloidiasis or IDH was due to an increase in the mean clone abundance, not to an increase in the number of infected clones. These patients appear to be less capable of restricting clone abundance than those with HTLV-1 alone. In patients co-infected with Strongyloides there was an increased degree of oligoclonal expansion and a higher rate of turnover (i.e. appearance and disappearance) of HTLV-1-infected clones. In Strongyloides co-infected patients and those with IDH, proliferation of the most abundant HTLV-1+ T-cell clones is independent of the genomic environment of the provirus, in sharp contrast to patients with HTLV-1 infection alone. This implies that new selection forces are driving oligoclonal proliferation in Strongyloides co-infection and IDH. We conclude that strongyloidiasis and IDH increase the risk of development of HTLV-1-associated diseases by increasing the rate of infection of new clones and the abundance of existing HTLV-1+ clones.

Management of paraproteinaemia.

A paraprotein is a monoclonal immunoglobulin or light chain present in the blood or urine; it is produced by a clonal population of mature B cells, most commonly plasma cells. In individuals aged >50 years the incidence of a paraprotein is 3.2%. Plasma cell disorders can be considered as a spectrum of conditions ranging from monoclonal gammopathy of undetermined significance (MGUS), through asymptomatic, to symptomatic myeloma. MGUS is defined by a low level of paraprotein <30 g/l, bone marrow plasma cells <10% and the absence of myeloma related organ or tissue damage (predominantly renal, skeletal or bone marrow impairment.) MGUS requires no therapy and the overall risk of progression to myeloma is 1% per year. Myeloma remains incurable with a median survival of 3–4 years; autologous stem cell transplant can prolong survival, if appropriate. Thalidomide in combination with dexamethasone has an emerging role in the treatment of myeloma.

Eltrombopag – a novel approach for the treatment of chronic immune thrombocytopenic purpura: review and safety considerations

Eltrombopag is one of a number of novel agents recently developed for use in the treatment of patients with immune thrombocytopenia (ITP). Rather than preventing destruction of platelets, these agents increase the production of platelets, presumably overwhelming the immune system resulting in normal platelet counts in individuals refractory to or dependent on other therapies. These treatments are well tolerated and in randomized controlled trials show an improvement in platelet counts and a reduction in bleeding in refractory patients. This article summarizes the development of this new class of drug and evaluates the safety and efficacy of eltrombopag in patients with ITP.

The impact of HTLV-1 on the cellular genome

Human T-lymphotropic virus type-1 (HTLV-1) is the causative agent of adult T-cell leukaemia/lymphoma (ATL), an aggressive CD4+ T-cell malignancy. The mechanisms of leukaemogenesis in ATL are incompletely understood. Insertional mutagenesis has not previously been thought to contribute to the pathogenesis of ATL. However, the recent discovery that HTLV-1 binds the key chromatin architectural protein CTCF raises the hypothesis that HTLV-1 deregulates host gene expression by causing abnormal chromatin looping, bringing the strong HTLV-1 promoter-enhancer near to host genes that lie up to 2Mb from the integrated provirus. Here we review current opinion on the mechanisms of oncogenesis in ATL, with particular emphasis on the local and distant impact of HTLV-1 on the structure and expression of the host genome.

T Cell Receptor Vβ Staining Identifies the Malignant Clone in Adult T cell Leukemia and Reveals Killing of Leukemia Cells by Autologous CD8+ T cells.

There is growing evidence that CD8+ cytotoxic T lymphocyte (CTL) responses can contribute to long-term remission of many malignancies. The etiological agent of adult T-cell leukemia/lymphoma (ATL), human T lymphotropic virus type-1 (HTLV-1), contains highly immunogenic CTL epitopes, but ATL patients typically have low frequencies of cytokine-producing HTLV-1-specific CD8+ cells in the circulation. It remains unclear whether patients with ATL possess CTLs that can kill the malignant HTLV-1 infected clone. Here we used flow cytometric staining of TCRVβ and cell adhesion molecule-1 (CADM1) to identify monoclonal populations of HTLV-1-infected T cells in the peripheral blood of patients with ATL. Thus, we quantified the rate of CD8+-mediated killing of the putative malignant clone in ex vivo blood samples. We observed that CD8+ cells from ATL patients were unable to lyse autologous ATL clones when tested directly ex vivo. However, short in vitro culture restored the ability of CD8+ cells to kill ex vivo ATL clones in some donors. The capacity of CD8+ cells to lyse HTLV-1 infected cells which expressed the viral sense strand gene products was significantly enhanced after in vitro culture, and donors with an ATL clone that expressed the HTLV-1 Tax gene were most likely to make a detectable lytic CD8+ response to the ATL cells. We conclude that some patients with ATL possess functional tumour-specific CTLs which could be exploited to contribute to control of the disease.

Treatment of adult T-cell leukaemia/lymphoma: is the virus a target?

Purpose of review To discuss current understanding of the mechanisms of human T-lymphotropic virus type-1 (HTLV-1) tumorigenesis and current and potential treatment strategies for adult T-cell leukaemia/lymphoma (ATL), an aggressive malignant disease of CD4+ cells caused by HTLV-1. Recent findings Treatment of the aggressive subtypes of ATL remains inadequate, with little improvement in overall survival in the 30 years since HTLV-1 was discovered. Detailed analysis of the clonal expansion of HTLV-1 has provided new insight into pathogenesis. Most HTLV-1-infected cells, including ATL, express CCR4 which can be targeted. Reports of antitumour effects with allogeneic bone marrow transplantation provide a rationale for novel immunotherapy approaches. Progress has been made in the indolent subtypes of ATL with the use of ‘antiviral’ therapies. Summary ATL has poor prognosis. There is a major, urgent, unmet clinical need to identify HTLV carriers who will develop ATL to develop biomarkers of transforming disease and disease progression and to provide novel treatment approaches within the context of clinical trials. Several strategies now include putative or actual antiviral therapy. Potentially, the risk of ATL would be reduced by eliminating some or all infected clones. HTLV-1 infection, and hence ATL, can be prevented by antenatal HTLV-1 screening.

Circularised 1 and 2 LTR DNA circles are present in freshly- and chronically-infected cell lines and patient PBMCs, indicating ongoing reverse transcriptase usage

Background After cell entry, HTLV-1 RNA is reverse transcribed and integrated into the host genome using its own reverse transcriptase (RT) and integrase (IN) enzymes. However, some unintegrated DNA circularises into 1 or 2 LTR DNA. Little is known about these unintegrated HTLV-1 DNA circles. Similar to HIV an inhibition of RT should decrease, and an inhibition of IN increase the 1/2 LTR DNA levels.