Diagnóstico de la infección por el virus linfotrópico de los linfocitos T humano y estrategias para ampliar el tamizaje conexo en el contexto de la salud maternoinfantil. Informe de la reunión (virtual) celebrada el 7 de julio del 2023

En los últimos años, la OPS ha estado colaborando con diferentes interesados directos —como especialistas en VLTH‑1, gerentes de programas de salud y personas con infección por el VLTH‑1— a fin de definir prioridades y delinear estrategias eficaces para hacer frente a esta infección desatendida. Una de las prioridades definidas por los interesados directos es la prevención de la transmisión maternoinfantil del VLTH‑1. Sin embargo, para que sea posible prevenir la transmisión vertical, las embarazadas con infección por el VLTH‑1 deben conocer su estado serológico respecto a esta infección. En la Región de las Américas, la cobertura del tamizaje del VLTH‑1 en donantes de sangre es alta, aunque el tamizaje prenatal sigue siendo limitado. Los países siguen encontrando obstáculos para implantar el uso de las pruebas de diagnóstico de la infección por el VLTH. No hay directrices internacionales para el diagnóstico de la infección por el VLTH‑1 y la orientación nacional puede variar de un país a otro. En este contexto, la OPS organizó un taller para debatir sobre el diagnóstico de la infección por el VLTH‑1, en particular en el contexto de la salud maternoinfantil. En la Región de las Américas se observa un interés cada vez mayor por el tamizaje prenatal de la infección por el VLTH‑1 y algunos países como Chile, Brasil, Santa Lucía y Colombia transmitieron su experiencia durante el taller. Entre las buenas prácticas figuran el programa para prevenir la transmisión maternoinfantil del VLTH‑1, integrado en la iniciativa ETMI Plus, en Santa Lucía; la estrecha colaboración entre la sociedad civil, expertos en la infección por el VLTH‑1 y responsables de las políticas en Brasil; iniciativas para aumentar la concientización sobre la infección por el VLTH‑1 en la Región; y la elaboración de directrices clínicas sobre la infección por el VLTH por distintos países de la Región. Se determinaron diversas prioridades, como aumentar la concientización acerca de la infección por el VLTH, elaborar directrices y capacitación de apoyo para los profesionales de la salud, fortalecer la colaboración entre países y promover la inclusión de la infección por el VLTH en los programas de eliminación.

The diagnosis of human T lymphotropic virus (HTLV) and strategies to expand HTLV screening in the context of maternal and child health. Meeting Report (virtual), 7 July 2023

In recent years, PAHO has been engaging with different stakeholders, including HTLV‑1 specialists, health managers and people living with HTLV-1 to define priorities and to delineate effective strategies to tackle this neglected infection. One of the priorities identified by stakeholders is the prevention of HTLV-1 mother-to-child transmission. However, to be able to prevent vertical transmission, pregnant women living with HTLV-1 must be aware of their status. The coverage of HTLV-1 screening of blood donors is high in the region, but antenatal screening is still limited. Countries still face barriers to implement diagnostic tests for HTLV. There are no international guidelines for HTLV-1 diagnostics and national guidance may vary between countries. In this context, PAHO promoted a workshop to discuss the diagnosis of HTLV-1 infection, particularly in the context of maternal and child health. Increased interest on HTLV-1 antenatal screening has been observed in the region and countries such as Chile, Brazil, Saint Lucia and Colombia shared their experience during the workshop. Good practices included the program to prevent HTLV-1 mother-to-child transmission, that is integrated with the EMTCT Plus initiative in Saint Lucia, strong collaboration between civil society, HTLV-1 experts and policy-makers in Brazil, initiatives to increase awareness about HTLV-1, and the construction of HTLV clinical guidelines by different countries in the Region. Priorities identified include increasing awareness about HTLV, developing guidelines and support training of health-care workers, strengthening the collaboration between countries, and promoting the inclusion of HTLV into elimination programs.

Diagnóstico de infecção por vírus linfotrópico de células T humanas e estratégias para expandir a triagem relacionada no contexto da saúde materno-infantil Relatório da reunião (virtual) realizada em 7 de julho de 2023

Nos últimos anos, a OPAS vem colaborando com diferentes partes interessadas, como especialistas em HTLV‑1, administradores de saúde e pessoas vivendo com HTLV‑1, a fim de definir prioridades e delinear estratégias efetivas para combater essa infecção negligenciada. Uma das prioridades identificadas pelas partes interessadas é a prevenção da transmissão materno-infantil do HTLV‑1. No entanto, para poder prevenir a transmissão materno-infantil, as gestantes vivendo com HTLV‑1 precisam estar cientes do próprio estado sorológico. A cobertura da triagem de HTLV‑1 em doadores de sangue é alta na Região das Américas, mas a triagem pré-natal continua limitada. Os países continuam enfrentando barreiras para implementar testes diagnósticos de HTLV. Não há diretrizes internacionais para o diagnóstico do HTLV‑1, e as orientações nacionais podem variar entre países. Nesse contexto, a OPAS organizou uma oficina para discutir o diagnóstico da infecção pelo HTLV‑1, particularmente no contexto da saúde materno-infantil. Tem-se observado maior interesse na triagem pré-natal do HTLV‑1 na Região, e países como Chile, Brasil, Santa Lúcia e Colômbia compartilharam suas experiências durante a oficina. Exemplos de boas práticas incluíram um programa para prevenir a transmissão materno-infantil do HTLV‑1 que está integrado à iniciativa EMTCT Plus em Santa Lúcia; uma forte colaboração entre sociedade civil, especialistas em HTLV‑1 e formuladores de políticas no Brasil; iniciativas para aumentar a conscientização sobre o HTLV‑1 na Região; e a elaboração de protocolos clínicos para o HTLV em diferentes países da Região. As prioridades identificadas incluem aumentar a conscientização sobre o HTLV, desenvolver diretrizes e apoiar a capacitação de profissionais de saúde, fortalecer a colaboração entre os países e promover a inclusão do HTLV nos programas de eliminação.

The impact of HTLV-1 expression on the 3D structure and expression of host chromatin.

A typical HTLV-1-infected individual carries >104 different HTLV-1-infected T cell clones, each with a single-copy provirus integrated in a unique genomic site. We previously showed that the HTLV-1 provirus causes aberrant transcription in the flanking host genome and, by binding the chromatin architectural protein CTCF, forms abnormal chromatin loops with the host genome. However, it remained unknown whether these effects were exerted simply by the presence of the provirus or were induced by its transcription. To answer this question, we sorted HTLV-1-infected T-cell clones into cells positive or negative for proviral plus-strand expression, and then quantified host and provirus transcription using RNA-seq, and chromatin looping using quantitative chromosome conformation capture (q4C), in each cell population. We found that proviral plus-strand transcription induces aberrant transcription and splicing in the flanking genome but suppresses aberrant chromatin loop formation with the nearby host chromatin. Reducing provirus-induced host transcription with an inhibitor of transcriptional elongation allows recovery of chromatin loops in the plus-strand-expressing population. We conclude that aberrant host transcription induced by proviral expression causes temporary, reversible disruption of chromatin looping in the vicinity of the provirus.

HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP): Case based discussion of risk factors, clinical, and therapeutic considerations.

HTLV-1 is a retrovirus virus that infects CD4+ T cells. Most people with HTLV-1 infection remain asymptomatic but some may develop conditions such as HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP) or adult T-cell leukemia/lymphoma. HAM/TSP is characterized by progressive spasticity and weakness of the lower extremities, as well as loss of bladder control and sensory disturbances. The risk of developing HAM/TSP is associated with the duration of infection and the proviral load. There is currently no cure for the disease but medications can help manage symptoms and slow the progression of the disease. This is the case of a 66-year-old female who presented with nonspecific symptoms of weakness and spasticity in a hospital in Connecticut and was subsequently diagnosed with HAM/TSP. The patient's diagnosis highlights the importance of considering diseases previously confined to specific endemic regions in a globalized world where increased emigration and population mixing can occur. Early identification and management of such cases is essential for optimizing patient outcomes and quality of life.

Ripasudil as a Potential Therapeutic Agent in Treating Secondary Glaucoma in HTLV-1-Uveitis: An In Vitro Analysis.

Human T-cell leukemia virus type 1 (HTLV-1), a virus that affects 5-10 million people globally, causes several diseases, including adult T-cell leukemia-lymphoma and HTLV-1-associated uveitis (HU). HU is prevalent in Japan and often leads to secondary glaucoma, which is a serious complication. We investigated the efficacy of ripasudil, a Rho-associated coiled coil-forming protein kinase inhibitor, in alleviating changes in human trabecular meshwork cells (hTM cells) infected with HTLV-1. HTLV-1-infected hTM cells were modeled in vitro using MT-2 cells, followed by treatment with varying concentrations of ripasudil. We assessed changes in cell morphology, viability, and inflammatory cytokine levels, as well as NF-κB activation. The results showed that ripasudil treatment changed the cell morphology, reduced the distribution of F-actin and fibronectin, and decreased the levels of certain inflammatory cytokines, such as interleukin (IL)-6, IL-8, and IL-12. However, ripasudil did not significantly affect NF-κB activation or overall cell viability. These findings suggest that ripasudil has the potential to treat secondary glaucoma in patients with HU by modulating cytoskeletal organization and alleviating inflammation in HTLV-1-infected hTM cells. This study lays the foundation for further clinical studies exploring the effectiveness of ripasudil for the treatment of secondary glaucoma associated with HU.

Proteomic analysis of adult T-cell leukemia/lymphoma: A biomarker identification strategy based on preparation and in-solution digestion methods of total proteins.

Adult T-cell leukemia/lymphoma (ATL), caused by human T-cell leukemia virus type-1 (HTLV-1) infection, is a malignant hematologic cancer that remains difficult to cure. We herein established a biomarker identification strategy based on the total cell proteomics of cultured ATL cells to search for novel ATL biomarkers. Four protocols with a combination of selected conditions based on lysis buffers and addition agents for total cell proteomics were used for a differential analysis between the ATL cell group (consisting of 11 cell lines), HTLV-1-infected cell group (consisting of 6 cell lines), and HTLV-1-negative cell group (consisting of 6 cell lines). In the analysis, we identified 24 and 27 proteins that were significantly increased (ratio ≥2.0, p < 0.05) and decreased (ratio ≤ 0.5, p < 0.05), respectively, in the ATL group. Previously reported CCL3 and CD30/TNFRSF8 were confirmed to be among significantly increased proteins. Furthermore, correlation analysis between identified proteins and Tax suggested that RASSF2 and GORASP2 were candidates of novel Tax-regulated factors. The biomarker identification strategy established herein is expected to contribute to the identification of biomarkers for ATL and other diseases.

Evaluating a Retro-Inverso Type Inhibitor of HTLV-1 Protease as a Competitive Inhibitor.

The inhibition mode of a retro-inverso (RI) inhibitor containing a hydroxyethylamine dipeptide isostere against the human T-cell leukemia virus type-1 (HTLV-1) protease was examined. Enzymatic evaluation of the RI-modified inhibitor containing a D-allo-Ile residue revealed that HTLV-1 was competitively inhibited. IC50 values of the RI-modified inhibitor and pepstatin A, a standard inhibitor of aspartic proteases, were nearly equivalent.

HTLV in Sweden.

Sweden is a country with a low prevalence of human lymphotropic T-cell virus (HTLV) infection, estimated at < 0.005%, but the infection rate is notably higher in specific risk groups such as HTLV-2 among intravenous drug users (IVDU) and people originating from HTLV-1 highly endemic areas. Thus, in the most recent study from 2012, the prevalence of HTLV-2 among IVDU in Stockholm was 3.2%. However, much of the epidemiological data on HTLV in Sweden stems from studies conducted primarily between the 1990s and 2007, and the impact of migration to Sweden during the past 15 years has not been evaluated. Despite Sweden's status as a country with generally low prevalence of HTLV, it is prudent to anticipate and prepare for several potential challenges associated with HTLV infection in the future. Proactive measures to enhance awareness, alongside strategies to curtail transmission and mitigate complications, are crucial for addressing this relatively rare, but significant health issue. In this work, we review the current epidemiological knowledge about HTLV in Sweden and discuss future Swedish perspectives.

Vulnerability to APOBEC3G linked to the pathogenicity of deltaretroviruses.

Human retroviruses are derived from simian ones through cross-species transmission. These retroviruses are associated with little pathogenicity in their natural hosts, but in humans, HIV causes AIDS, and human T-cell leukemia virus type 1 (HTLV-1) induces adult T-cell leukemia-lymphoma (ATL). We analyzed the proviral sequences of HTLV-1, HTLV-2, and simian T-cell leukemia virus type 1 (STLV-1) from Japanese macaques (Macaca fuscata) and found that APOBEC3G (A3G) frequently generates G-to-A mutations in the HTLV-1 provirus, whereas such mutations are rare in the HTLV-2 and STLV-1 proviruses. Therefore, we investigated the mechanism of how HTLV-2 is resistant to human A3G (hA3G). HTLV-1, HTLV-2, and STLV-1 encode the so-called antisense proteins, HTLV-1 bZIP factor (HBZ), Antisense protein of HTLV-2 (APH-2), and STLV-1 bZIP factor (SBZ), respectively. APH-2 efficiently inhibits the deaminase activity of both hA3G and simian A3G (sA3G). HBZ and SBZ strongly suppress sA3G activity but only weakly inhibit hA3G, suggesting that HTLV-1 is incompletely adapted to humans. Unexpectedly, hA3G augments the activation of the transforming growth factor (TGF)-ß/Smad pathway by HBZ, and this activation is associated with ATL cell proliferation by up-regulating BATF3/IRF4 and MYC. In contrast, the combination of APH-2 and hA3G, or the combination of SBZ and sA3G, does not enhance the TGF-ß/Smad pathway. Thus, HTLV-1 is vulnerable to hA3G but utilizes it to promote the proliferation of infected cells via the activation of the TGF-ß/Smad pathway. Antisense factors in each virus, differently adapted to control host cellular functions through A3G, seem to dictate the pathogenesis.

Purification Method of Extracellular Vesicles Derived from Human T-Cell Leukemia Virus Type 1-Infected Cells without Virions.

To mediate intercellular communication, cells produce extracellular vesicles (EVs). These EVs transport many biomolecules such as proteins, nucleic acids, and lipids between cells and regulate pathophysiological actions in the recipient cell. However, EVs and virus particles produced from virus-infected cells are of similar size and specific gravity; therefore, the separation and purification of these two particles is often controversial. When analyzing the physiological functions of EVs from virus-infected cells, the presence or absence of virus particle contamination must always be verified. The human T-cell leukemia virus type 1 (HTLV-1)-infected cell line, MT-2, produces EVs and virus particles. Here, we validated a method for purifying EVs from MT-2 cell culture supernatants while avoiding HTLV-1 viral particle contamination. EV fractions were collected using a combination of immunoprecipitation with Tim-4, which binds to phosphatidylserine, and polymer precipitation. The HTLV-1 viral envelope protein, gp46, was not detected in the EV fraction. Proteomic analysis revealed that EV-constituted proteins were predominant in this EV fraction. Furthermore, the EVs were found to contain the HTLV-1 viral genome. The proposed method can purify EVs while avoiding virus particle contamination and is expected to contribute to future research on EVs derived from HTLV-1-infected cells.

How do socioeconomic determinants of health affect the likelihood of living with HTLV-1 globally? A systematic review with meta-analysis.

Introduction: Human T Lymphotropic Virus type 1 (HTLV-1) is a neglected retrovirus associated with many clinical disorders, most notably Adult T-cell Leukemia/Lymphoma and HTLV-1-Associated Myelopathy (HAM). Found in endemic clusters across the world, high prevalence has been reported in minoritized groups who suffer from health inequities. This study investigates the association between HTLV-1 prevalence and the following socioeconomic determinants of health: education, income, and employment, which are markers of health inequity. Methods: A systematic review was conducted by searching the following databases: Ovid/Medline, Embase, Global Health Database, Web of Science, LILACS and SciELO. Primary studies in English, Spanish and Portuguese mentioning HTLV-1 and one of education, income and/or employment were included. A random-effects meta-analysis was performed, and odds ratios (OR) were calculated to determine the association between these socioeconomic determinants of health and HTLV-1 prevalence. Results: 42 studies were included. The likelihood of having HTLV-1 was higher in individuals with less than completed primary education compared to those who completed primary education (OR 1.86 [95% CI 1.34-2.57]; p < 0.01). This may be because individuals with low education have reduced access to and understanding of health information, thus increasing the prevalence of risk factors associated with HTLV-1 infection. No other determinants were found to be statistically significant. Conclusion: Fewer years of schooling are associated with increased likelihood of contracting HTLV-1. Therefore, health promotion materials and public health policies regarding HTLV-1 must consider those with lower educational levels to effectively reduce disease transmission. Systematic review registration: https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=335004, identifier (CRD42022335004).

Mycophenolate mofetil for the long-term treatment of HTLV-1 associated myelopathy: A case report.

Human T-cell leukemia virus type 1 (HTLV-1) can cause HTLV-1 Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP). Current treatment options for HAM/TSP are limited. We present a woman with rapidly-progressive HAM/TSP with significant, sustained clinical improvement following initiation of mycophenolate mofetil (MMA). Peripheral blood mononuclear cells from the patient, her asymptomatic carrier husband and eight healthy controls were isolated. Frequencies of T-cell populations upon exposure to low and high MMA concentrations and differences in proliferation were analyzed using flow cytometry and a CSFE-proliferation assay. Characterization of T-cell function and proliferation showed higher levels of GranzymeB in HTLV-1+ donors. The improvement and stability of symptoms in this patient with HAM/TSP following MMA initiation requires further study as a potential treatment for HAM/TSP.

Stem cell therapy for HTLV-1 induced adult T-cell leukemia/lymphoma (ATLL): A comprehensive review.

Adult T-cell leukemia/lymphoma (ATLL) is a rare and aggressive form of cancer associated with human T-cell lymphotropic virus type 1 (HTLV-1) infection. The emerging field of stem cell therapies for ATLL is discussed, highlighting the potential of hematopoietic stem cell transplantation (HSCT) and genetically modified stem cells. HSCT aims to eradicate malignant T-cells and restore a functional immune system through the infusion of healthy donor stem cells. Genetically modified stem cells show promise in enhancing their ability to target and eliminate ATLL cells. The article presents insights from preclinical studies and limited clinical trials, emphasizing the need for further research to establish the safety, efficacy, and long-term outcomes of stem cell therapies for ATLL and challenges associated with these innovative approaches are also explored. Overall, stem cell therapies hold significant potential in revolutionizing ATLL treatment, and ongoing clinical trials aim to determine their benefits in larger patient populations.

Screening for HTLV-1 infection should be expanded in Europe.

Human T-cell lymphotropic virus type 1 (HTLV-1) infection is spreading globally at an uncertain speed. Sexual, mother-to-child, and parenteral exposure are the major transmission routes. Neither vaccines nor antivirals have been developed to confront HTLV-1, despite infecting over 10 million people globally and causing life-threatening illnesses in 10% of carriers. It is time to place this long-neglected disease firmly into the 2030 elimination agenda. Current evidence supports once-in-life testing for HTLV-1, as recommended for HIV, hepatitis B and C, along with targeted screening of pregnant women, blood donors, and people who attended clinics for sexually transmitted infections (STIs). Similar targeted screening strategies are already being performed for Chagas disease in some Western countries in persons from Latin America. Given the high risk of rapid-onset HTLV-1-associated myelopathy, universal screening of solid organ donors is warranted. To minimize organ wastage, however, the specificity of HTLV screening tests must be improved. HTLV screening of organ donors in Europe has become mandatory in Spain and the United Kingdom. The advent of HTLV point-of-care kits would facilitate testing. Finally, increasing awareness of HTLV-1 will help those living with HTLV-1 to be tested, clinically monitored, and informed about transmission-preventive measures.

Geographic characteristics of HTLV-1 molecular subgroups and genetic substitutions in East Asia: Insights from complete genome sequencing of HTLV-1 strains isolated in Taiwan and Japan.

BACKGROUND: Although Japan is a major endemic area for human T-lymphotropic virus type 1 (HTLV-1) and the virus has been well-studied in this region, there is limited research on HTLV-1 in surrounding regions. In this study, we determined the complete genome sequences of HTLV-1 strains isolated from Taiwan and Japan and investigated the geographic characteristics of molecular subgroups and substitution mutations to understand the spread of HTLV-1 and its correlation with human migration. METHODOLOGY/PRINCIPAL FINDINGS: The complete genome sequences of 26 HTLV-1 isolates from Taiwan were determined using next-generation sequencing and were compared with those of 211 isolates from Japan in terms of subgroup and genetic mutations. In total, 15/26 (58%) isolates from Taiwan belonged to the transcontinental subgroup and 11/26 (42%) isolates belonged to the Japanese subgroup. The transcontinental subgroup was significantly more prevalent among Taiwanese isolates than Japanese isolates (58% vs 18%, P < 0.0001). The mutation rate for the complete HTLV-1 sequence was as low as 0.2%. On examining individual base substitutions, the G-to-A mutation was predominant. Bayesian phylogenetic tree analysis estimated the time to the most recent common ancestor for the transcontinental and Japanese subgroups to be 28447 years. The transcontinental subgroups from Taiwan and Japan appeared to form clusters according to their respective regions. CONCLUSIONS/SIGNIFICANCE: The transcontinental subgroup of HTLV-1 is predominant in Taiwan, while the Japanese subgroup is common in Japan. The difference in subgroup distribution may be attributed to the initial spread of the transcontinental subgroup in East Asia, followed by the influx of the Japanese subgroup.

HTLV-1 induces an inflammatory CD4+CD8+ T cell population in HTLV-1-associated myelopathy.

Human T cell leukemia virus type 1 (HTLV-1) is a retrovirus with preferential CD4+ T cell tropism that causes a range of conditions spanning from asymptomatic infection to adult T cell leukemia and HTLV-1-associated myelopathy (HAM), an inflammatory disease of the CNS. The mechanisms by which HTLV-1 induces HAM are poorly understood. By directly examining the ex vivo phenotype and function of T cells from asymptomatic carriers and patients with HAM, we show that patients with HAM have a higher frequency of CD4+CD8+ double-positive (DP) T cells, which are infected with HTLV-1 at higher rates than CD4+ T cells. Displaying both helper and cytotoxic phenotypes, these DP T cells are highly proinflammatory and contain high frequencies of HTLV-1-specific cells. Mechanistically, we demonstrate that DP T cells arise by direct HTLV-1 infection of CD4+ and CD8+ T cells. High levels of CD49d and CXCR3 expression suggest that DP T cells possess the ability to migrate to the CNS, and when cocultured with astrocytes, DP T cells induce proinflammatory astrocytes that express high levels of CXCL10, IFN-γ, and IL-6. These results demonstrate the potential of DP T cells to directly contribute to CNS pathology.

The importance of confirmatory assays in testing blood donors for human T-cell lymphotropic virus.

BACKGROUND AND OBJECTIVES: Serological HTLV-1/2 screening is mandatory for blood donor candidates in Brazil. Our objective was to analyse HTLV test results in blood donors submitted for screening and confirmatory assays in a Brazilian blood bank. MATERIALS AND METHODS: Retrospective analysis (2017-2022) results of chemiluminescence immunoassays and confirmatory tests for HTLV-1/2 in reactive donors were performed. During the analysed period, three sets of assays were used: (1) Architect rHTLV-I/II + HTLV Blot 2.4 (Western blot [WB]); (2) Alinity s HTLV I/II Reagent Kit + INNO-line immunoassay (LIA) HTLV I/II Score (LIA); (3) Alinity + WB. RESULTS: The analysed period comprised a total of 1,557,333 donations. The mean percentage of HTLV reactive donors using the Architect assay was 0.14%. With the change to the Alinity assay, that percentage dropped 2.3-fold (0.06%). The reactivity rate in the confirmatory tests (1064 samples) ranged from 13.5% to 30.2%, whereas 58.3%-85.9% of samples were non-reactive. The highest rates of positive (30.2%) and indeterminate (11.5%) results were seen using LIA. Considering all analysed samples, those with signal/cut-off ratio (S/CO) >50 were positive in confirmatory tests (positive predictive value, PPV = 100%), whereas samples with S/CO ≤6 are very unlikely to be truly positive (PPV = 0). CONCLUSION: The use of the Alinity assay reduced the frequency of false-positive results. Confirmatory tests are important to identify true HTLV infection in blood donors, because more than 58% of initially reactive individuals are confirmed as seronegative. Categorizing S/CO values is useful for assessing the likelihood of true HTLV-1/2 infection.

Reprogramming of pyrimidine nucleotide metabolism supports vigorous cell proliferation of normal and malignant T cells.

ABSTRACT: Adult T-cell leukemia/lymphoma (ATL) is triggered by infection with human T-cell lymphotropic virus-1 (HTLV-1). Here, we describe the reprogramming of pyrimidine biosynthesis in both normal T cells and ATL cells through regulation of uridine-cytidine kinase 2 (UCK2), which supports vigorous proliferation. UCK2 catalyzes the monophosphorylation of cytidine/uridine and their analogues during pyrimidine biosynthesis and drug metabolism. We found that UCK2 was overexpressed aberrantly in HTLV-1-infected T cells but not in normal T cells. T-cell activation via T-cell receptor (TCR) signaling induced expression of UCK2 in normal T cells. Somatic alterations and epigenetic modifications in ATL cells activate TCR signaling. Therefore, we believe that expression of UCK2 in HTLV-1-infected cells is induced by dysregulated TCR signaling. Recently, we established azacitidine-resistant (AZA-R) cells showing absent expression of UCK2. AZA-R cells proliferated normally in vitro, whereas UCK2 knockdown inhibited ATL cell growth. Although uridine and cytidine accumulated in AZA-R cells, possibly because of dysfunction of pyrimidine salvage biosynthesis induced by loss of UCK2 expression, the amount of UTP and CTP was almost the same as in parental cells. Furthermore, AZA-R cells were more susceptible to an inhibitor of dihydroorotic acid dehydrogenase, which performs the rate-limiting enzyme of de novo pyrimidine nucleotide biosynthesis, and more resistant to dipyridamole, an inhibitor of pyrimidine salvage biosynthesis, suggesting that AZA-R cells adapt to UCK2 loss by increasing de novo pyrimidine nucleotide biosynthesis. Taken together, the data suggest that fine-tuning pyrimidine biosynthesis supports vigorous cell proliferation of both normal T cells and ATL cells.