Adhesion-dependent growth of primary adult T cell leukemia cells with down-regulation of HTLV-I p40Tax protein: a novel in vitro model of the growth of acute ATL cells

Short Communication: Human Bone Marrow Stromal Cells Exhibit Immunosuppressive Effects on Human T Lymphotropic Virus Type 1 T Lymphocyte from Infected Individuals

Human multipotent mesenchymal stromal cells (MSCs) display immunoregulatory functions that can modulate innate and adaptive cellular immune responses. The suppressive and immunomodulatory activities of MSCs occur through the action of soluble factors that are constitutively produced and released by these cells or, alternatively, after MSC induction by stimuli of inflammatory microenvironments. However, to date the contribution of MSCs in the inflammatory microenvironment resulting from viral infection is unknown. In our study, we evaluated the MSC immunosuppressive effect on human T lymphotropic virus type 1 (HTLV-1) infected T lymphocytes. To evaluate if MSC immunoregulation can influence the proliferation of HTLV-1 infected T lymphocytes, we compared the proliferation of lymphocytes obtained from HTLV-1 infected and healthy individuals cocultured in the presence of MSCs. It was observed that the lymphoproliferative inhibition by MSCs on infected lymphocytes was similar compared to the cells obtained from healthy individuals. In addition, this suppressive effect was related to a significant increase of indoleamine-2,3-dioxygenase and prostaglandin E2 gene expression (p ≤ .05). Furthermore, the HTLV-1 pol gene was less expressed after coculturing with MSCs, suggesting that the MSC immunoregulation can have effective suppression on HTLV-1 infected T cells. In conclusion, this study suggests that MSCs could be involved in the immunomodulation of the HTLV-1 infected T lymphocytes.

CD30 Characterizes Polylobated Lymphocytes and Disease Progression in HTLV-1-Infected Individuals

Purpose: Although expression of CD30 is reported in a subset of adult T-cell leukemia/lymphoma cases, its clinicopathologic significance is poorly understood. We aimed to characterize CD30-positive cells and clarify their tumorigenic role in human T-cell lymphotropic virus type 1 (HTLV-1)-infected cells.Experimental Design: CD30-positive peripheral blood mononuclear cells from individuals with differing HTLV-1 disease status were characterized, and the role of CD30 signaling was examined using HTLV-1-infected cell lines and primary cells.Results: CD30-positive cells were detected in all samples examined, and the marker was coexpressed with both CD25 and CD4. This cell population expanded in accordance with disease progression. CD30-positive cells showed polylobation, with some possessing "flower cell" features, active cycling, and hyperploidy. CD30 stimulation of HTLV-1-infected cell lines induced these features and abnormal cell division, with polylobation found to be dependent on the activation of PI3K. The results thus link the expression of CD30, which serves as a marker for HTLV-1 disease status, to an active proliferating cell fraction featuring polylobation and chromosomal aberrations. In addition, brentuximab vedotin, an anti-CD30 monoclonal antibody conjugated with auristatin E, was found to reduce the CD30-positive cell fraction.Conclusions: Our results indicate that CD30-positive cells act as a reservoir for tumorigenic transformation and clonal expansion during HTLV-1 infection. The CD30-positive fraction may thus be a potential molecular target for those with differing HTLV-1 disease status. Clin Cancer Res; 24(21); 5445-57. ©2018 AACR.

A Preclinical Model for the ATLL Lymphoma Subtype With Insights Into the Role of Microenvironment in HTLV-1-Mediated Lymphomagenesis

Adult T cell Leukemia/Lymphoma (ATLL) is a mature T cell malignancy associated with Human T cell Leukemia Virus type 1 (HTLV-1) infection. Among its four main clinical subtypes, the prognosis of acute and lymphoma variants remains poor. The long latency (3–6 decades) and low incidence (3–5%) of ATLL imply the involvement of viral and host factors in full-blown malignancy. Despite multiple preclinical and clinical studies, the contribution of the stromal microenvironment in ATLL development is not yet completely unraveled. The aims of this study were to investigate the role of the host microenvironment, and specifically fibroblasts, in ATLL pathogenesis and to propose a murine model for the lymphoma subtype. Here we present evidence that the oncogenic capacity of HTLV-1-immortalized C91/PL cells is enhanced when they are xenotransplanted together with human foreskin fibroblasts (HFF) in immunocompromised BALB/c Rag2^-/-γ_c^-/- mice. Moreover, cell lines derived from a developed lymphoma and their subsequent in vivo passages acquired the stable property to induce aggressive T cell lymphomas. In particular, one of these cell lines, C91/III cells, consistently induced aggressive lymphomas also in NOD/SCID/IL2Rγ_c KO (NSG) mice. To dissect the mechanisms linked to this enhanced tumorigenic ability, we quantified 45 soluble factors released by these cell lines and found that 21 of them, mainly pro-inflammatory cytokines and chemokines, were significantly increased in C91/III cells compared to the parental C91/PL cells. Moreover, many of the increased factors were also released by human fibroblasts and belonged to the known secretory pattern of ATLL cells. C91/PL cells co-cultured with HFF showed features reminiscent of those observed in C91/III cells, including a similar secretory pattern and a more aggressive behavior in vivo. On the whole, our data provide evidence that fibroblasts, one of the major stromal components, might enhance tumorigenesis of HTLV-1-infected and immortalized T cells, thus throwing light on the role of microenvironment contribution in ATLL pathogenesis. We also propose that the lymphoma induced in NSG mice by injection with C91/III cells represents a new murine preclinical ATLL model that could be adopted to test novel therapeutic interventions for the aggressive lymphoma subtype.

Adult T-cell leukemia: molecular basis for clonal expansion and transformation of HTLV-1-infected T cells

Adult T-cell leukemia (ATL) is an aggressive T-cell malignancy caused by human T-cell leukemia virus type 1 (HTLV-1) that develops through a multistep carcinogenesis process involving 5 or more genetic events. We provide a comprehensive overview of recently uncovered information on the molecular basis of leukemogenesis in ATL. Broadly, the landscape of genetic abnormalities in ATL that include alterations highly enriched in genes for T-cell receptor-NF-κB signaling such as PLCG1, PRKCB, and CARD11 and gain-of function mutations in CCR4 and CCR7 Conversely, the epigenetic landscape of ATL can be summarized as polycomb repressive complex 2 hyperactivation with genome-wide H3K27 me3 accumulation as the basis of the unique transcriptome of ATL cells. Expression of H3K27 methyltransferase enhancer of zeste 2 was shown to be induced by HTLV-1 Tax and NF-κB. Furthermore, provirus integration site analysis with high-throughput sequencing enabled the analysis of clonal composition and cell number of each clone in vivo, whereas multicolor flow cytometric analysis with CD7 and cell adhesion molecule 1 enabled the identification of HTLV-1-infected CD4+ T cells in vivo. Sorted immortalized but untransformed cells displayed epigenetic changes closely overlapping those observed in terminally transformed ATL cells, suggesting that epigenetic abnormalities are likely earlier events in leukemogenesis. These new findings broaden the scope of conceptualization of the molecular mechanisms of leukemogenesis, dissecting them into immortalization and clonal progression. These recent findings also open a new direction of drug development for ATL prevention and treatment because epigenetic marks can be reprogrammed. Mechanisms underlying initial immortalization and progressive accumulation of these abnormalities remain to be elucidated.

Protective roles of epithelial cells in the survival of adult T-cell leukemia/lymphoma cells

Adult T-cell leukemia/lymphoma (ATL) is a highly invasive and intractable T-cell malignancy caused by human T-cell leukemia virus-1 infection. We demonstrate herein that normal tissue-derived epithelial cells (NECs) exert protective effects on the survival of leukemic cells, which may partially account for high resistance to antileukemic therapies in patients with ATL. Viral gene-silenced, ATL-derived cell lines (ATL cells) dramatically escaped from histone deacetylase inhibitor-induced apoptosis by direct co-culture with NECs. Adhesions to NECs suppressed p21(Cip1) expression and increased a proportion of resting G0/G1 phase cells in trichostatin A (TSA)-treated ATL cells. ATL cells adhering to NECs down-regulated CD25 expression and enhanced vimentin expression, suggesting that most ATL cells acquired a quiescent state by cell-cell interactions with NECs. ATL cells adhering to NECs displayed highly elevated expression of the cancer stem cell marker CD44. Blockade of CD44 signaling diminished the NEC-conferred resistance of ATL cells to TSA-induced apoptosis. Co-culture with NECs also suppressed the expression of NKG2D ligands on TSA-treated ATL cells, resulting in decreased natural killer cell-mediated cytotoxicity. Combined evidence suggests that interactions with normal epithelial cells augment the resistance of ATL cells to TSA-induced apoptosis and facilitate immune evasion by ATL cells.

Stromal cell-mediated suppression of human T-cell leukemia virus type 1 expression in vitro and in vivo by type I interferon

Human T-cell leukemia virus type 1 (HTLV-1) causes adult T-cell leukemia (ATL), HTLV-1-associated myelopathy/tropical spastic paraparesis, and other inflammatory diseases. Despite such severe outcomes of HTLV-1 infection, the level of HTLV-1 expression in vivo is very low and rapidly increases after transfer of cells to culture conditions. The mechanisms of this phenomenon have remained obscure. In the present study, we found that human and mouse stromal cells, such as epithelial cells and fibroblasts, suppressed HTLV-1 expression in ATL and non-ATL HTLV-1-infected cells. HTLV-1 mRNA and proteins in HTLV-1-infected cells markedly decreased upon coculture with human epithelial-like cells (HEK293T) or mouse embryo fibroblasts (NIH 3T3). When infected cells were reisolated from the cocultures, viral expression was restored to the original level over the following 48 h. Spontaneous induction of HTLV-1 expression in primary ATL cells in the first 24 h of culture was also inhibited by coculture with HEK293T cells. Coculture of HTLV-1-infected cells and HEK293T cells induced type I interferon responses, as detected by beta interferon (IFN-beta) promoter activation and IFN-stimulated gene upregulation. HEK293T-mediated suppression of HTLV-1 expression was partly inhibited by antibodies to human IFN-alpha/beta receptor. NIH 3T3-mediated suppression was markedly abrogated by neutralizing antibodies to mouse IFN-beta. Furthermore, viral expression in HTLV-1-infected cells was significantly suppressed when the infected cells were intraperitoneally injected into wild-type mice but not IFN regulatory factor 7 knockout mice that are deficient of type I IFN responses. These findings indicate that the innate immune system suppresses HTLV-1 expression in vivo, at least through type I IFN.