Long Terminal Repeat Circular DNA as Markers of Active Viral Replication of Human T Lymphotropic Virus-1 in Vivo.

Clonal expansion of human T-lymphotropic virus type-1 (HTLV-1) infected cells in vivo is well documented. Unlike human immunodeficiency virus type 1 (HIV-1), HTLV-1 plasma RNA is sparse. The contribution of the "mitotic" spread of HTLV-1 compared with infectious spread of the virus to HTLV-1 viral burden in established infection is uncertain. Since extrachromosomal long terminal repeat (LTR) DNA circles are indicators of viral replication in HIV-1 carriers with undetectable plasma HIV RNA, we hypothesised that HTLV-1 LTR circles could indicate reverse transcriptase (RT) usage and infectious activity. 1LTR and 2LTR DNA circles were measured in HTLV-1 cell lines and peripheral blood mononuclear cells (PBMC) of asymptomatic carriers (ACs) and patients with HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) or adult T cell leukaemia/lymphoma (ATLL). 1LTR DNA circles were detected in 14/20 patients at a mean of 1.38/100 PBMC but did not differentiate disease status nor correlate with HTLV-1 DNA copies. 2LTR DNA circles were detected in 30/31 patients and at higher concentrations in patients with HTLV-1-associated diseases, independent of HTLV-1 DNA load. In an incident case the 2LTR DNA circle concentration increased 2.1 fold at the onset of HAM/TSP compared to baseline. Detectable and fluctuating levels of HTLV-1 DNA circles in patients indicate viral RT usage and virus replication. Our results indicate HTLV-1 viral replication capacity is maintained in chronic infection and may be associated with disease onset.

Human T cell lymphotropic virus type 1 viral load variability and long-term trends in asymptomatic carriers and in patients with human T cell lymphotropic virus type 1-related diseases.

Human T cell lymphotropic virus type 1 (HTLV-1) proviral load (PVL) in peripheral blood mononuclear cells (PBMCs) is high in patients with adult T cell leukemia/lymphoma or HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and in some asymptomatic carriers, but fluctuates. Our objectives were to document ranges of HTLV PVL across a broader spectrum of diseases and tissues, to quantify the normal range of intrapatient PVL variability, and to identify which PVL values and changes deserve further investigation. PVL was measured in 191 patients with HTLV-1-associated diseases and in 211 asymptomatic carriers, using real-time quantitative PCR. The intraassay variability increases as viral load decreases: 8% at high load, 17% at medium load, and 33% at low load. The interassay variability is not different from the intraassay. Mean intrapatient CV is 65% (SD 21) in asymptomatic carriers and 59% (SD 22) in HAM/TSP. PVL values varied widely between individuals, but were relatively constant within individuals. High PVL in cerebrospinal fluid (CSF) and lymph nodes (LN) was associated with disease but 57% of asymptomatic carriers had a PVL greater than 1% in PBMCs. Our results suggest that (1) PVL changes falling outside a coefficient of variation of 100% require more detailed assessment, (2) asymptomatic carriers with PVL higher than 10% should undergo more frequent clinical and laboratory monitoring, and (3) HTLV-1 PVL in blood and tissue is helpful in the diagnosis and monitoring of HTLV-1 infection.

Susceptibility of primary HTLV-1 isolates from patients with HTLV-1-associated myelopathy to reverse transcriptase inhibitors.

Since human T-lymphotropic virus type 1 (HTLV-1)-associated diseases are associated with a high HTLV-1 load, reducing this load may treat or prevent disease. However, despite in vitro evidence that certain nucleoside/nucleotide analogue reverse transcriptase inhibitors (NRTIs) are active against HTLV-1, in vivo results have been disappointing. We therefore assayed the sensitivity of HTLV-1 primary isolates to a panel of RT inhibitors. HTLV-1 primary isolates were obtained, pre- and post- NRTI treatment, from patients with HTLV-1-associated myelopathy. Sensitivity to azidothymidine (AZT), lamivudine (3TC), tenofovir (TDF) and three phosphonated carbocyclic 2'-oxa-3'aza nucleosides (PCOANs) was assessed in a RT inhibitor assay. With the exception of 3TC, HTLV RT from primary isolates was less sensitive to all tested inhibitors than HTLV-1 RT from MT-2 cells. HTLV-1 RT from primary isolates and from chronically infected, transformed MT-2 cells was insensitive to 3TC. Sensitivity of primary isolates to RT inhibitors was not reduced following up to 12 months of patient treatment with AZT plus 3TC. The sensitivity of HTLV-1 primary isolates to NRTIs differs from that of cell lines and may vary among patients. Failure of NRTIs to reduce HTLV-1 viral load in vivo was not due to the development of phenotypic NRTI resistance. AZT and the three PCOANs assayed all consistently inhibited primary isolate HTLV-1 RT.

In vivo expression of human T-lymphotropic virus type 1 basic leucine-zipper protein generates specific CD8+ and CD4+ T-lymphocyte responses that correlate with clinical outcome.

BACKGROUND: The roles of the human T-lymphotropic virus type 1 (HTLV-1) basic leucine zipper (HBZ) gene are not clearly understood. We examined CD8+ and CD4+ T cell responses to HBZ and compared these with Tax responses. METHOD: Interferon (IFN)-γ and interleukin (IL)-2-secreting T cells were detected by enzyme-linked immunosorbent spot (ELISpot) assays of freshly isolated peripheral blood mononuclear cells (PBMCs) stimulated with synthetic HBZ or Tax peptides. Ten patients with HTLV-1-associated myelopathy (HAM) and 20 asymptomatic HTLV-1 carriers (ACs), (10 high, 10 low viral load). RESULTS: Of 30 study participants, 17 had detectable HBZ-specific CD4+ T cells and 12 had HBZ-specific CD8+ T cell responses. Detection of Tax-specific CD4+ T cells (IL-2- or IFN-γ-secreting) did not differ by disease status, but Tax-specific CD8+ T cell responses were more commonly detected in patients with HAM. HBZ-specific CD4+ or CD8+ T cells were less likely to be detected than Tax-specific T cells. IL-2-secreting Tax-specific CD8+ T cells, and IFN-γ-secreting Tax-specific CD4+ T cells were associated with HAM. Low viral load, asymptomatic HTLV-1 carriage was associated with IL-2-secreting CD8+ T cells specific for HBZ. CONCLUSION: HBZ protein is expressed in vivo in patients with HAM and in ACs. Our results are consistent with the idea that the T cell response to HBZ plays an important part in restricting HTLV-1 viral load.

HLA class I binding of HBZ determines outcome in HTLV-1 infection.

CD8(+) T cells can exert both protective and harmful effects on the virus-infected host. However, there is no systematic method to identify the attributes of a protective CD8(+) T cell response. Here, we combine theory and experiment to identify and quantify the contribution of all HLA class I alleles to host protection against infection with a given pathogen. In 432 HTLV-1-infected individuals we show that individuals with HLA class I alleles that strongly bind the HTLV-1 protein HBZ had a lower proviral load and were more likely to be asymptomatic. We also show that in general, across all HTLV-1 proteins, CD8(+) T cell effectiveness is strongly determined by protein specificity and produce a ranked list of the proteins targeted by the most effective CD8(+) T cell response through to the least effective CD8(+) T cell response. We conclude that CD8(+) T cells play an important role in the control of HTLV-1 and that CD8(+) cells specific to HBZ, not the immunodominant protein Tax, are the most effective. We suggest that HBZ plays a central role in HTLV-1 persistence. This approach is applicable to all pathogens, even where data are sparse, to identify simultaneously the HLA Class I alleles and the epitopes responsible for a protective CD8(+) T cell response.