Development of reference material with assigned value for human T-cell leukemia virus type 1 quantitative PCR in Japan

Advances in the treatment of human T-cell lymphotropic virus type-I associated myelopathy

INTRODUCTION

Nearly 2-3% of those 10 to 20 million individuals infected with the Human T-cell lymphotropic virus type-1 (HTLV-1); are predisposed to developing HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). It is a neuro-inflammatory disease; differentiated from multiple sclerosis based on the presence of typical neurologic symptoms, confirmation of HTLV-1 infection, and other molecular biomarkers.

AREAS COVERED

A brief review of the epidemiology, host immune responses, and molecular pathogenesis of HAM/TSP is followed by detailed discussions about the host-related risk factors for developing HAM/TSP and success/failure stories of the attempted management strategies.

EXPERT OPINION

Currently, there is no effective treatment for HAM/TSP. Anti-retroviral therapy, peculiar cytokines (IFN-α), some anti-oxidants, and allograft bone marrow transplantation have been used for treating these patients with limited success. Under current conditions, asymptomatic carriers should be examined periodically by a neurologist for early signs of spinal cord injury. Then it is crucial to determine the progress rate to adapt the best management plan for each patient. Corticosteroid therapy is most beneficial in those with acute myelitis. However, slow-progressing patients are best managed using a combination of symptomatic and physical therapy. Additionally, preventive measures should be taken to decrease further spread of HTLV-1 infection.

Potential role of HTLV-1 Tax-specific cytotoxic t lymphocytes expressing a unique t-cell receptor to promote inflammation of the central nervous system in myelopathy associated with HTLV-1

Human T-lymphotropic virus 1 (HTLV-1) infection causes two serious diseases: adult T-cell leukemia/lymphoma (ATL) and HTLV-1-associated myelopathy (HAM). Immunological studies have revealed that HTLV-1 Tax-specific CD8⁺ cytotoxic T-cells (Tax-CTLs) in asymptomatic carriers (ACs) and ATL patients play an important role in the elimination of HTLV-1-infected host cells, whereas Tax-CTLs in HAM patients trigger an excessive immune response against HTLV-1-infected host cells infiltrating the central nervous system (CNS), leading to local inflammation. Our previous evaluation of HTLV-1 Tax_301-309 (SFHSLHLLF)-specific Tax-CTLs (Tax_301-309-CTLs) revealed that a unique T-cell receptor (TCR) containing amino acid (AA)-sequence motif PDR, was shared among HLA-A*24:02⁺ ACs and ATL patients and behaved as an eliminator by strong activity against HTLV-1. However, it remains unclear whether PDR⁺Tax_301-309-CTLs also exist in HLA-A*24:02⁺ HAM patients and are involved in the pathogenesis of HAM. In the present study, by high-throughput TCR repertoire analysis technology, we revealed TCR repertoires of Tax_301-309-CTLs in peripheral blood (PB) of HLA-A*24:02⁺ HAM patients were skewed, and a unique TCR-motif PDR was conserved in HAM patients (10 of 11 cases). The remaining case dominantly expressed (-DR, P-R, and PD-), which differed by one AA from PDR. Overall, TCRs with unique AA-sequence motifs PDR, or (-DR, P-R, and PD-) accounted for a total of 0.3-98.1% of Tax_301-309-CTLs repertoires of HLA-A*24:02⁺ HAM patients. Moreover, TCR repertoire analysis of T-cells in the cerebrospinal fluid (CSF) from four HAM patients demonstrated the possibility that PDR⁺Tax_301-309-CTLs and (-DR, P-R, and PD-)⁺Tax_301-309-CTLs efficiently migrated and accumulated in the CSF of HAM patients fostering increased inflammation, although we observed no clear significant correlation between the frequencies of them in PB and the levels of CSF neopterin, a known disease activity biomarker of HAM. Furthermore, to better understand the potential function of PDR⁺Tax_301-309-CTLs, we performed immune profiling by single-cell RNA-sequencing of Tax_301-309-CTLs, and the result showed that PDR⁺Tax_301-309-CTLs up-regulated the gene expression of natural killer cell marker KLRB1 (CD161), which may be associated with T-cell activation and highly cytotoxic potential of memory T-cells. These findings indicated that unique and shared PDR⁺Tax_301-309-CTLs have a potential role in promoting local inflammation within the CNS of HAM patients.

HTLV-1 targets human placental trophoblasts in seropositive pregnant women

Human T cell leukemia virus type 1 (HTLV-1) is mainly transmitted vertically through breast milk. The rate of mother-to-child transmission (MTCT) through formula feeding, although significantly lower than through breastfeeding, is approximately 2.4%-3.6%, suggesting the possibility of alternative transmission routes. MTCT of HTLV-1 might occur through the uterus, birth canal, or placental tissues; the latter is known as transplacental transmission. Here, we found that HTLV-1 proviral DNA was present in the placental villous tissues of the fetuses of nearly half of pregnant carriers and in a small number of cord blood samples. An RNA ISH assay showed that HTLV-1-expressing cells were present in nearly all subjects with HTLV-1-positive placental villous tissues, and their frequency was significantly higher in subjects with HTLV-1-positive cord blood samples. Furthermore, placental villous trophoblasts expressed HTLV-1 receptors and showed increased susceptibility to HTLV-1 infection. In addition, HTLV-1-infected trophoblasts expressed high levels of viral antigens and promoted the de novo infection of target T cells in a humanized mouse model. In summary, during pregnancy of HTLV-1 carriers, HTLV-1 was highly expressed in placental villous tissues, and villous trophoblasts showed high HTLV-1 sensitivity, suggesting that MTCT of HTLV-1 occurs through the placenta.

A new diagnostic algorithm using biopsy specimens in adult T-cell leukemia/lymphoma: combination of RNA in situ hybridization and quantitative PCR for HTLV-1

Histopathological distinction between adult T-cell leukemia/lymphoma (ATLL) and other T-cell neoplasms is often challenging. The current gold standard for the accurate diagnosis of ATLL is the Southern blot hybridization (SBH) assay, which detects clonal integration of human T-cell leukemia virus type I (HTLV-1) provirus. However, SBH cannot be performed with small biopsy or formalin-fixed paraffin-embedded (FFPE) tissue samples because this assay requires a large amount of DNA without degradation. Here we developed a new diagnostic algorithm for the accurate diagnosis of ATLL using FFPE samples. This method combines two HTLV-1 detection assays, namely, ultrasensitive RNA in situ hybridization using RNAscope for HTLV-1 bZIP factor (HBZ-RNAscope), and quantitative PCR targeting the tax gene (tax-qPCR). We analyzed 119 FFPE tissue specimens (62 ATLL, and 57 non-ATLL, including 41 HTLV-1 carriers) and compared them with the SBH results using the corresponding fresh-frozen samples. As a result, tax-qPCR had a higher ATLL identification rate than HBZ-RNAscope (88% [52/59], and 63% [39/62], respectively). However, HBZ-RNAscope clearly visualized the localization of HTLV-1-infected tumor cells and its identification rate increased to 94% (17/18) when the analysis was limited to samples up to 2 years old, indicating its usefulness in the daily diagnosis. The diagnostic algorithm combining these two assays successfully evaluated 94% (112/119) of samples and distinguished ATLL from non-ATLL cases including HTLV-1 carriers with 100% sensitivity and specificity. This method is expected to replace SBH and increase the accuracy of the diagnosis of ATLL.

Estimation of the window period of human T-cell leukemia virus type 1 and 2 tests by a lookback study of seroconverters among Japanese voluntary blood donors

BACKGROUND

Japan is endemic for human T-cell leukemia virus type 1 (HTLV-1), and the horizontal transmission of HTLV-1 is often reported. However, the window period (WP) for serologic or molecular screening is unclear.

STUDY DESIGN AND METHODS

Results for anti-HTLV-1 screening and confirmatory tests obtained from 648 591 repeated blood donors in the Kyushu district, one of the most endemic areas of HTLV-1 in the world, were evaluated. A lookback study was conducted for seroconverters.

RESULTS

During 2012 to 2019, 436 seroconverters (155 men, 281women) were identified with use of a screening chemiluminescence enzyme-immunoassay (CLEIA) and multiple confirmatory tests. Because the period between the latest seronegative donation and seroconversion was highly variable (2.1-276.7 months), 19 cases that seroconverted within 6 months were subjected to the analysis. The WP of the particle agglutination assay and CLEIA was estimated to be 2.2 ± 0.6 and 2.6 ± 1.7 months, respectively. The WP of the indirect immunofluorescence assay was 4.8 ± 6.5 months. Although the WP of western blotting was estimated to be 6.3 ± 8.7 months, four cases were still indeterminate through the study period. Chemiluminescence and line immunoassays, the current screening and confirmatory tests used in the Japanese blood program, showed the shortest WP of 2.2 ± 0.6 months. The WP of real-time polymerase chain reaction for HTLV-1 was estimated to be 4.1 ± 7.8 months.

CONCLUSIONS

The WP in commercially available testing systems for HTLV-1/2 was determined for natural infection among repeated blood donors. Considering the HTLV-1 WP will help increase transfusion safety and facilitate the accurate diagnosis of HTLV-1 infection.

Establishment of a novel diagnostic test algorithm for human T-cell leukemia virus type 1 infection with line immunoassay replacement of western blotting: a collaborative study for performance evaluation of diagnostic assays in Japan

BACKGROUND

The reliable diagnosis of human T-cell leukemia virus type 1 (HTLV-1) infection is important, particularly as it can be vertically transmitted by breast feeding mothers to their infants. However, current diagnosis in Japan requires a confirmatory western blot (WB) test after screening/primary testing for HTLV-1 antibodies, but this test often gives indeterminate results. Thus, this collaborative study evaluated the reliability of diagnostic assays for HTLV-1 infection, including a WB-based one, along with line immunoassay (LIA) as an alternative to WB for confirmatory testing.

RESULTS

Using peripheral blood samples from blood donors and pregnant women previously serologically screened and subjected to WB analysis, we analyzed the performances of 10 HTLV-1 antibody assay kits commercially available in Japan. No marked differences in the performances of eight of the screening kits were apparent. However, LIA determined most of the WB-indeterminate samples to be conclusively positive or negative (an 88.0% detection rate). When we also compared the sensitivity to HTLV-1 envelope gp21 with that of other antigens by LIA, the sensitivity to gp21 was the strongest. When we also compared the sensitivity to envelope gp46 by LIA with that of WB, LIA showed stronger sensitivity to gp46 than WB did. These findings indicate that LIA is an alternative confirmatory test to WB analysis without gp21. Therefore, we established a novel diagnostic test algorithm for HTLV-1 infection in Japan, including both the performance of a confirmatory test where LIA replaced WB on primary test-reactive samples and an additional decision based on a standardized nucleic acid detection step (polymerase chain reaction, PCR) on the confirmatory test-indeterminate samples. The final assessment of the clinical usefulness of this algorithm involved performing WB analysis, LIA, and/or PCR in parallel for confirmatory testing of known reactive samples serologically screened at clinical laboratories. Consequently, LIA followed by PCR (LIA/PCR), but neither WB/PCR nor PCR/LIA, was found to be the most reliable diagnostic algorithm.

CONCLUSIONS

Because the above results show that our novel algorithm is clinically useful, we propose that it is recommended for solving the aforementioned WB-associated reliability issues and for providing a more rapid and precise diagnosis of HTLV-1 infection.

Mortality and risk of progression to adult T cell leukemia/lymphoma in HTLV-1-associated myelopathy/tropical spastic paraparesis

HTLV-1 manifests many diseases, which cause morbidity and mortality in 5∼10% of infected individuals, including the fatal adult T cell leukemia/lymphoma (ATLL) and debilitating myelopathy (HAM/TSP). However, the rarity of these diseases had made it prohibitory to conduct large-scale prospective observational studies. This work enabled calculating the standard mortality ratio of HAM/TSP patients and also identified ATLL as one of the major causes of death among these patients. We also identified the features that lead HAM/TSP patients to develop ATLL: having dominant clonal expansion of HTLV-1–infected cells with ATLL-associated somatic mutations. Furthermore, this manuscript describes genomic changes occurring in HAM/TSP patients at the actual time of their ATLL transformation.

Human T cell leukemia virus 1 (HTLV-1) causes the functionally debilitating disease HTLV-1–associated myelopathy/tropical spastic paraparesis (HAM/TSP) as well as adult T cell leukemia lymphoma (ATLL). Although there were concerns that the mortality of HAM/TSP could be affected by the development of ATLL, prospective evidence was lacking in this area. In this 5-y prospective cohort study, we determined the mortality, prevalence, and incidence of ATLL in 527 HAM/TSP patients. The standard mortality ratio of HAM/TSP patients was 2.25, and ATLL was one of the major causes of death (5/33 deaths). ATLL prevalence and incidence in these patients were 3.0% and 3.81 per 1,000 person-y, respectively. To identify patients at a high risk of developing ATLL, flow cytometry, Southern blotting, and targeted sequencing data were analyzed in a separate cohort of 218 HAM/TSP patients. In 17% of the HAM/TSP patients, we identified an increase in T cells positive for cell adhesion molecule 1 (CADM1), a marker for ATLL and HTLV-1–infected cells. Genomic analysis revealed that somatic mutations of HTLV-1–infected cells were seen in 90% of these cases and 11% of them had dominant clone and developed ATLL in the longitudinal observation. In this study, we were able to demonstrate the increased mortality in patients with HAM/TSP and a significant effect of ATLL on their prognosis. Having dominant clonal expansion of HTLV-1–infected cells with ATLL-associated somatic mutations may be important characteristics of patients with HAM/TSP who are at an increased risk of developing ATLL.