Adult T-cell Leukemia/lymphoma Cells Research Articles

Abstract 3965: A cytolytic effector CD8+ T cell response is associated with remission in adult T-cell leukemia/lymphoma

Abstract Introduction: Adult T-cell leukemia/lymphoma (ATLL) is a rare blood cancer that develops in 3-5% of human T-lymphotropic virus-1 (HTLV1) carriers when the combination of viral oncoproteins and somatic mutations lead to malignant transformation of HTLV1 infected CD4+ T cells. ATLL has the worst overall survival among peripheral T cell lymphomas and remains a fatal disease despite efforts to improve outcomes over the last 35 years. First-line combination chemotherapy rarely achieves a durable response and two immune-modulating treatments (α-CCR4 and α-PD-1 monoclonal antibodies) failed in clinical trials. These findings highlight an urgent need to improve our understanding of the functional state of host immunity in ATLL patients. A host immune response against HTLV1 is pivotal in preventing ATLL development. Malignant ATLL cells can escape immune surveillance by preventing antigen presentation and engaging immune checkpoints. The prospect of an ATLL clone inducing systemic suppression was suggested in the literature but has not been directly examined. Furthermore, HTLV1-specific CD8+ cytotoxic T lymphocytes (CTLs) play an important role during viral latency, yet it remains unknown if they play a clinically relevant role during ATLL treatment. Methodology: In this work, we hypothesized that malignant ATLL cells will exhibit a suppressive immune phenotype and that effective therapeutic interventions will augment anti-ATLL CTLs to promote durable remission. We implemented an immune profiling approach to analyze PBMC samples from ATLL patients. Specifically, we developed a powerful 30-marker spectral flow panel to discriminate malignant ATLL cells from non-transformed lymphocytes (T, B, and NK cells) and monitor the expression of key transcription factors and markers associated with proliferation, cytolysis, and exhaustion. We analyzed diagnostic samples from the Montefiore-Einstein ATLL Biobank and samples collected during a phase 2 clinical trial aimed to assess the efficacy of a promising Belinostat/Zidovudine/Interferon-α combination therapy against ATLL (NCT02737046). Results: Our findings reveal that malignant ATLL cells exhibit an immune phenotype associated with robust immunosuppression and yet distinct from other suppressive immune cells (i.e., regulatory T cells). Additionally, we discovered that ATLL patient samples contained a unique population of phenotypically exhausted CD8+ T cells, the proportion of which was drastically reduced in patients under remission. Remarkably, a decrease in this exhausted subset correlated with the expansion of highly cytolytic CD8+ CTLs. Conclusion: Altogether, our findings suggest that ATLL cells may drive CD8+ CTLs into exhaustion to achieve immune evasion and that a robust anti-ATLL CTL response actively contributes to a remission state. Citation Format: Erik Guillen, Eric Liu, Yanhua Wang, Aditi Shastri, Alejandro Sica, Amit Verma, Xingxing Zhang, Juan Carlos Ramos, Hilda Ye, Gregoire Lauvau. A cytolytic effector CD8+ T cell response is associated with remission in adult T-cell leukemia/lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3965.

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)-β/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-β/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-β/Smad pathway. Antisense factors in each virus, differently adapted to control host cellular functions through A3G, seem to dictate the pathogenesis.

Inhibition of PRMT5/MEP50 Arginine Methyltransferase Activity Causes Cancer Vulnerability in NDRG2low Adult T-Cell Leukemia/Lymphoma.

N-myc downstream-regulated gene 2 (NDRG2), which is a tumour suppressor, is frequently lost in many types of tumours, including adult T-cell leukaemia/lymphoma (ATL). The downregulation of NDRG2 expression is involved in tumour progression through the aberrant phosphorylation of several important signalling molecules. We observed that the downregulation of NDRG2 induced the translocation of protein arginine methyltransferase 5 (PRMT5) from the nucleus to the cytoplasm via the increased phosphorylation of PRMT5 at Serine 335. In NDRG2low ATL, cytoplasmic PRMT5 enhanced HSP90A chaperone activity via arginine methylation, leading to tumour progression and the maintenance of oncogenic client proteins. Therefore, we examined whether the inhibition of PRMT5 activity is a drug target in NDRG2low tumours. The knockdown of PRMT5 and binding partner methylsome protein 50 (MEP50) expression significantly demonstrated the suppression of cell proliferation via the degradation of AKT and NEMO in NDRG2low ATL cells, whereas NDRG2-expressing cells did not impair the stability of client proteins. We suggest that the relationship between PRMT5/MEP50 and the downregulation of NDRG2 may exhibit a novel vulnerability and a therapeutic target. Treatment with the PRMT5-specific inhibitors CMP5 and HLCL61 was more sensitive in NDRG2low cancer cells than in NDRG2-expressing cells via the inhibition of HSP90 arginine methylation, along with the degradation of client proteins. Thus, interference with PRMT5 activity has become a feasible and effective strategy for promoting cancer vulnerability in NDRG2low ATL.

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.

IMiD/CELMoD-induced growth suppression of adult T-cell leukemia/lymphoma cells via cereblon through downregulation of target proteins and their downstream effectors.

Adult T-cell leukemia/lymphoma (ATL) is an aggressive T-cell neoplasia associated with human T-cell leukemia virus type 1 (HTLV-1) infection and has an extremely poor prognosis. Lenalidomide (LEN; a second-generation immunomodulatory drug [IMiD]) has been employed as an additional therapeutic option for ATL since 2017, but its mechanism of action has not been fully proven, and recent studies reported emerging concerns about the development of second primary malignancies in patients treated with long-term IMiD therapy. Our purpose in this study was to elucidate the IMiD-mediated anti-ATL mechanisms. Thirteen ATL-related cell lines were divided into LEN-sensitive or LEN-resistant groups. CRBN knockdown (KD) led to a loss of LEN efficacy and IKZF2-KD-induced LEN efficacy in resistant cells. DNA microarray analysis demonstrated distinct transcriptional alteration after LEN treatment between LEN-sensitive and LEN-resistant ATL cell lines. Oral treatment of LEN for ATL cell-transplanted severe combined immunodeficiency (SCID) mice also indicated clear suppressive effects on tumor growth. Finally, a novel cereblon modulator (CELMoD), iberdomide (IBE), exhibited a broader and deeper spectrum of growth suppression to ATL cells with efficient IKZF2 degradation, which was not observed in other IMiD treatments. Based on these findings, our study strongly supports the novel therapeutic advantages of IBE against aggressive and relapsed ATL.

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

AbstractAdult 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.

Development of Innate-Immune-Cell-Based Immunotherapy for Adult T-Cell Leukemia-Lymphoma.

γδ T cells and natural killer (NK) cells have attracted much attention as promising effector cell subsets for adoptive transfer for use in the treatment of malignant and infectious diseases, because they exhibit potent cytotoxic activity against a variety of malignant tumors, as well as virus-infected cells, in a major histocompatibility complex (MHC)-unrestricted manner. In addition, γδ T cells and NK cells express a high level of CD16, a receptor required for antibody-dependent cellular cytotoxicity. Adult T-cell leukemia-lymphoma (ATL) is caused by human T-lymphotropic virus type I (HTLV-1) and is characterized by the proliferation of malignant peripheral CD4+ T cells. Although several treatments, such as chemotherapy, monoclonal antibodies, and allogeneic hematopoietic stem cell transplantation, are currently available, their efficacy is limited. In order to develop alternative therapeutic modalities, we considered the possibility of infusion therapy harnessing γδ T cells and NK cells expanded using a novel nitrogen-containing bisphosphonate prodrug (PTA) and interleukin (IL)-2/IL-18, and we examined the efficacy of the cell-based therapy for ATL in vitro. Peripheral blood samples were collected from 55 patients with ATL and peripheral blood mononuclear cells (PBMCs) were stimulated with PTA and IL-2/IL-18 for 11 days to expand γδ T cells and NK cells. To expand NK cells alone, CD3+ T-cell-depleted PBMCs were cultured with IL-2/IL-18 for 10 days. Subsequently, the expanded cells were examined for cytotoxicity against ATL cell lines in vitro. The proportion of γδ T cells in PBMCs was markedly low in elderly ATL patients. The median expansion rate of the γδ T cells was 1998-fold, and it was 12-fold for the NK cells, indicating that γδ T cells derived from ATL patients were efficiently expanded ex vivo, irrespective of aging and HTLV-1 infection status. Anti-CCR4 antibodies enhanced the cytotoxic activity of the γδ T cells and NK cells against HTLV-1-infected CCR4-expressing CD4+ T cells in an antibody concentration-dependent manner. Taken together, the adoptive transfer of γδ T cells and NK cells expanded with PTA/IL-2/IL-18 is a promising alternative therapy for ATL.

Whole-genome CRISPR screening identifies molecular mechanisms of PD-L1 expression in adult T-cell leukemia/lymphoma

AbstractAdult T-cell leukemia/lymphoma (ATLL) is an aggressive T-cell malignancy with a poor prognosis and limited treatment options. Programmed cell death ligand 1(PD-L1) is recognized to be involved in the pathobiology of ATLL. However, what molecules control PD-L1 expression and whether genetic or pharmacological intervention might modify PD-L1 expression in ATLL cells are still unknown. To comprehend the regulatory mechanisms of PD-L1 expression in ATLL cells, we performed unbiased genome-wide clustered regularly interspaced short palindromic repeat (CRISPR) screening in this work. In ATLL cells, we discovered that the neddylation-associated genes NEDD8, NAE1, UBA3, and CUL3 negatively regulated PD-L1 expression, whereas STAT3 positively did so. We verified, in line with the genetic results, that treatment with the JAK1/2 inhibitor ruxolitinib or the neddylation pathway inhibitor pevonedistat resulted in a decrease in PD-L1 expression in ATLL cells or an increase in it, respectively. It is significant that these results held true regardless of whether ATLL cells had the PD-L1 3' structural variant, a known genetic anomaly that promotes PD-L1 overexpression in certain patients with primary ATLL. Pevonedistat alone showed cytotoxicity for ATLL cells, but compared with each single modality, pevonedistat improved the cytotoxic effects of the anti–PD-L1 monoclonal antibody avelumab and chimeric antigen receptor (CAR) T cells targeting PD-L1 in vitro. As a result, our work provided insight into a portion of the complex regulatory mechanisms governing PD-L1 expression in ATLL cells and demonstrated the in vitro preliminary preclinical efficacy of PD-L1–directed immunotherapies by using pevonedistat to upregulate PD-L1 in ATLL cells.

Genome-Wide CRISPR Screen Identifies ZNF451 Regulating Sensitivity to Topoisomerase 2 Inhibitors in Peripheral T-Cell Lymphoma Cells

Introduction: Despite the recent therapeutic developments for peripheral T-cell lymphomas (PTCLs), their prognosis remains dismal. Topoisomerase 2 inhibitors (TOP2i), which increase the amount of TOP2-DNA covalent complex and block DNA double-strand break repair, have long been used as key drugs in the treatment of PTCLs. The molecular mechanisms underlying sensitivity to TOP2i remain to be fully elucidated. Methods: To elucidate the cell-intrinsic genes affecting TOP2i sensitivity in PTCL cells, we performed whole-genome loss-of-function CRISPR screenings in adult T-cell leukemia/lymphoma (ATLL) cell lines. ST1 and KK1 cells were transduced with the Brunello CRISPR knockout pooled library targeting 19,114 genes (4 sgRNAs/gene) followed by puromycin selection. The transduced cells were then treated with etoposide (ETP), doxorubicin (DOX) or DMSO control for 8 days. The MAGeCK algorithm was used to rank the sgRNAs responsible for TOP2i sensitivity. Among the top 500 enriched genes, we further selected the those with at least 2 sgRNAs with a log2 fold change (TOP2i/DMSO) &amp;lt; -0.5 or &amp;gt;0.5 in both ST1 and KK1 cells as genes whose knockout conferred TOP2i sensitivity or resistance, respectively. Results: Using the whole genome loss-of-function CRISPR screen, we identified 3 genes and 2 genes whose knockout conferred ETP sensitivity and resistance, respectively. TOP2A, a known ETP target, was ranked as a top gene for ETP resistance, confirming the reliability of our screenings (Fig. 1). In the same way we also extracted 3 genes whose knockout conferred DOX sensitivity. Interestingly, zinc finger protein 451 (ZNF451) was identified as an overlapping gene whose knockout conferred sensitivity in both screens for ETP and DOX. ZNF451 is an E3 SUMO ligase and was previously reported to be an endogenous DNA repair factor for TOP2i-induced DNA double-strand breaks (Schellenberg et al. Science 2017). The role of ZNF451 in PTCL cells has not been previously reported, prompting us to focus on ZNF451 in further analyses. For a confirmatory experiments, we transduced sgRNAs targeting ZNF451 (sgZNF451) in ATLL cell lines. To see the knockout efficiencies of the sgZNF451, we performed immunoblot analysis by using anti-ZNF451 antibody and found three bands with different levels of reduction. To ensure whether the bands detected by the anti-ZNF451 antibody represented endogenous ZNF451 protein, we engineered the ATLL cell line with an HA-tag at the 5' UTR of the endogenous ZNF451 gene locus by CRISPR-mediated knock-in. Immunoblot analysis of sgZNF451-transduced engineered cells expressing HA-tag-ZNF451 by using anti-HA antibody showed almost the same pattern of the bands as shown in the blot by anti-ZNF451 antibody. Thus, we confirmed that sgZNF451 worked efficiently and concluded that post-transcriptional modification affected the stability of ZNF451 protein in ATLL cells. Next, we investigated the role of ZNF451 on cell viability. While sgZNF451-transduced ATLL cells did not differ from control sgRNA-transduced cells in terms of cellular proliferation under normal culture conditions, sgZNF451-transduced ATLL cells showed increased sensitivity to both ETP and DOX compared to control cells with statistical significance, confirming our screening results (Fig. 2). Importantly, sgZNF451-mediated sensitization to ETP and DOX was found not only in ATLL cells but also in other PTCL cell lines including ALK-positive and ALK-negative anaplastic large cell lymphoma (ALCL). Mechanistically, apoptosis and G2/M cell cycle arrest were induced at significantly higher frequencies by ETP treatment in ZNF451 knocked out cells compared to control cells. Given the role of ZNF451 in TOP2i sensitivity in PTCL cells, we investigated whether ZNF451 expression levels stratify the prognosis of PTCL patients treated with CHOP-like regimens. To test this, FFPE samples from 45 PTCL-NOS patients were used for Q-PCR analysis of ZNF451 mRNA but we did not find any correlation between the ZNF451 expression and prognosis. Conclusions: We performed unbiased genome-wide CRISPR/Cas9 library screens and identified ZNF451 as an important regulator of sensitivity to TOP2i in PTCL cells. Further studies are needed to determine whether measuring ZNF451 protein levels can be used as a biomarker in PTCL patients who are treated with TOP2i.

North American Adult T-Cell Leukemia/Lymphoma Has Frequent Mutations in CCR4 and Responds in Vitro to a Small Molecule CCR4 Antagonist, CCR4-351

Adult T-cell leukemia/lymphoma (ATLL) is a rare and aggressive disease of malignant CD4+ T cells that develops in human T-lymphotropic virus-1 (HTLV-1) carriers. Patients diagnosed with ATLL have the worst survival among all peripheral T-cell lymphomas. There is an urgent need for in-depth understanding of its pathogenesis and development of new treatment strategies. We and others have shown that ATLLs diagnosed in the Japanese (J-ATLL) and North American (NA-ATLL) patients have differences in clinical characteristics and immune-genetic landscape. Among the most frequently mutated genes in J-ATLL cohorts is CCR4, a chemokine receptor that is targeted by C-terminal truncation mutations in one third of the cases. These mutations result in a more stabilized surface CCR4 and have been reported to cause elevated Akt activation following chemokine stimulation. Since our previous targeted exon sequencing study did not include CCR4, this work was initiated to assess CCR4 mutation frequency in NA-ATLL cases and to evaluate the preclinical activity of a small molecule CCR4 antagonist. This is because, although an anti-CCR4 mAb, mogamulizumab, has been approved in Japan to treat ATLL, this therapy failed in a Phase 2 trial among patients outside of Japan. Thus, mogamulizumab is not available as a routine treatment for NA-ATLL patients. We compiled CCR4 gene status data from bulk RNA-seq (n=10) and whole genome sequencing (WGS) analysis (n = 10). Out of a total of 17 NA-ATLL cases, 8 (47.1%) carried CCR4 gene alterations that included in-frame and frameshift indels, as well as nonsense mutations targeted to the C-terminus cytoplasmic tail and also the trans-membrane domain. In subtype analysis, 6 out 14 acute cases (42.9%) and 2 out of 3 (66.7%) of chronic cases carried at least one copy of mutated CCR4 gene, indicating that the mutation frequency in NA-ATLL is possibly even higher than that reported for the Japanese cohorts ( Figure 1). We then evaluated cell surface CCR4 expression using flow cytometry. The primary ATLL cells (CD4 +CD7 -CD8 -) from all 7 diagnostic samples uniformly express markedly increased levels of CCR4 relative to healthy control CD4 T cells. Interestingly, CCR4 expression among 8 ATLL cell lines is highly variable, implying that in vivo, tumor microenvironment factors may also contribute to sustained CCR4 upregulation in addition to the influence from the HTLV-1 oncoprotein, HBZ. FLX475 is an orally active small molecule CCR4 antagonist that is currently in a Phase 1/2 study (NCT03674567) in several types of advanced cancer including EBV+ NK/T cell lymphoma. So far, favorable clinical antitumor activity has been observed that includes complete responses with FLX475 monotherapy and encouraging combination activity (Lin C.-C. et al ESMO-IO 2022 Dec; #187P). Using several CCR4-positive cell lines, we examined in vitro anti-ATLL activity of CCR4-351, a CCR4 antagonist that is a highly related analog of FLX475. CCR4 is the exclusive homing receptor for two chemokine molecules, CCL17 and CCL22. In a transwell assay, both chemokines can elicit strong chemotaxis activity in a J-ATLL cell line ED40515(+). However, only CCL22 but not CCL17 can induce significant chemotaxis in two NA-ATLL cell lines, ATL#13 and ATL#29. The exact cause of this difference between these cell lines awaits future studies. In these transwell-based assays, CCR4-351 exhibited potent chemotaxis inhibitory activity with IC 50 values ranging from 7-60 nM ( Figure 2). In addition, when the cell lines were cultured under growth factor-deprivation conditions, CCR4-351 treatment caused a mild reduction in total cell viability, suggesting an additional anti-ATLL mechanism of action. In summary, in this first study of the CCR4 pathway status in NA-ATLL, we found that nearly half of the cases in our ATLL cohort carried a mutated CCR4 gene. Contrary to primary ATLL cells, ATLL cell lines exhibit a wide variation in CCR4 expression. CCL22 but not CCL17 induced strong chemotaxis behavior in NA-ATLL cell lines, which was potently inhibited by a small molecule CCR4 antagonist, CCR4-351. Since extramedullary presentation is frequently seen in NA-ATLL and central nervous system involvement is an adverse prognostic feature, inhibiting chemotaxis with a CCR4 antagonist such as FLX475 may be an effective therapeutic approach.

Single-Cell RNA Sequencing Revealed the YY1/EZH2/MLH1 Axis As a Possible Therapeutic Target of Intractable Adult T-Cell Leukemia

Background: Due to clinical heterogeneity of adult T-cell leukemia/lymphoma (ATL) and its diverse genetic abnormality, common therapeutic targets of ATL remains unclear. Whereas the YY1/EZH2 axis regulates global epigenetic modification of genes in ATL, its downstream target genes have not been fully elucidated. Meanwhile, DNA mismatch repair proteins may be targeted in ATL. Here we explored underlying molecular axes for ATL progression through comprehensive single-cell RNA-sequencing (sc-RNA-seq). Methods: Peripheral blood of 42 ATL patients and asymptomatic HTLV-1 carriers in addition to two cell lines of ATL43T and ED+ were subjected to the following analyses. Molecular markers associated with their clinical phenotypes were extracted through sc-RNA-seq analysis. Expression levels of DNA mismatch repair proteins (MLH1, MSH2) and target molecules were validated by flow cytometry. Finally, their function was verified through lentiviral shRNA-dependent knockdown and molecular-targeting reagents. Results: While the frequencies of CADM1+ cells among CD4+ T cells were generally correlated with HTLV-1 proviral loads (R = 0.76, p &amp;lt; 0.001), substantial CADM1+ cells were detected but did not increase in some long-remitted cases; thus, CADM1+ cells are biologically heterogeneous. sc-RNA-seq of CADM1+ cells of four ATL cases identified a cluster of CD48-deficient cells. in silico promoter analysis of the cluster extracted a transcription factor YY1 as a candidate for common master regulators. EZH2 and the putative driver genes (CELF2, PTPRC, CBLB, ATXN1, IKZF2) were identified as differentially expressed genes (DEGs) in the cluster. The EZH2-overexpressed cluster was increased in acute-type ATL compared with remitted ATL and smoldering-type ATL. Interestingly, the cluster increased moderately in the other smoldering-type ATL, which required UVB irradiation due to intractable skin lesion. Given that YY1 and EZH2 were up-regulated in acute-type ATL, the cluster may represent tumor aggressiveness. Furthermore, biphasic expression of YY1/EZH2 was observed in 2 acute-type ATL, which indicates that the EZH2 high ATL cells confer malignant signature. In-house analysis on microarray dataset GSE55851 specified the MLH1 associated with YY1/EZH2. MLH1 within CADM1+ fraction was down-regulated in ATL patients with remission (n = 7) but maintained in progressive ATL (n = 6) (p &amp;lt; 0.05). Lentiviral shYY1 knockdown resulted in down-regulation of MLH1 in both ATL43T and ED+ (p &amp;lt; 0.01). The EZH1/2 inhibitor valemetostat down-regulated EZH2 (p = 0.018) and MLH1 (p = 0.014) in primary ATL cells. Finally, knockdown of either YY1 or MLH1 suppressed proliferation of ATL43T and ED+ (p &amp;lt; 0.0001). Conclusions: Our findings indicate that down-regulation of MLH1 through YY1/EZH2 inhibition plays a key role in the treatment of aggressive ATL.

Acetyl Transferase EP300 Deficiency Leads to Chronic Replication Stress in Adult T-Cell Leukemia/Lymphoma

Mutations in the epigenetic regulator and global transcriptional activator, E1A binding protein (EP300), is being increasingly reported in aggressive hematological malignancies including adult T-cell leukemia/lymphoma (ATLL). However, the mechanistic contribution of EP300 dysregulation to cancer initiation and progression are currently unknown. Independent inhibition of EP300 in human cells results in the differential expression of genes involved in regulating the cell cycle, DNA replication and DNA damage response. Nevertheless, specific function played by EP300 in DNA replication initiation, progression and replication fork integrity has not been studied. Here, using ATLL cells as a disease model to study EP300 deficiency and an EP300-selective PROTAC degrader, as a pharmacologic tool, we reveal that EP300-mutated cells display prolonged cell cycle kinetics, due to pronounced dysregulations in DNA replication dynamics leading to persistent genomic instability. Aberrant DNA replication in EP300-mutated cells is characterized by elevated replication origin firing due to increased replisome pausing genome-wide. We demonstrate that EP300 deficiency results in nucleolytic degradation of nascently synthesized DNA at stalled forks due to a prominent defect in fork stabilization and protection. This in turn results in the accumulation of single stranded DNA gaps at collapsed replication forks, in EP300-deficient cells. Inhibition of Mre11 nuclease rescues the ssDNA accumulation indicating a dysregulation in downstream mechanisms that restrain nuclease activity at stalled forks. Importantly, we find that the absence of EP300 results in decreased expression of BRCA2 protein expression and a dependency on POLD3-mediated error-prone replication restart mechanisms. The overall S-phase abnormalities observed lead to under-replicated DNA in G2/M that instigates mitotic DNA synthesis. This in turn is associated with mitotic segregation defects characterized by elevated micronuclei formation, transmission of unrepaired inherited DNA lesions in the subsequent G1-phase and accumulation of cytosolic DNA in EP300-deficient cells. However, EP300 deficient cells show a significant defect in innate immune system activation. Altogether these results suggest that mutations in EP300 cause chronic DNA replication stress, persistent genomic instability and innate immune system evasion underlie aggressive chemo-resistant tumorigenesis in humans.

Clinical Course of Adult T-Cell Leukemia-Lymphoma with Central Nervous System Involvement

Background: Adult T-cell leukemia-lymphoma (ATL) is a peripheral T-cell lymphoma with a highly diverse clinical presentation. Although central nervous system (CNS) involvement is common, the detailed clinical presentation of CNS-ATL needs to be clarified. Objective: This study aims to clarify the clinical course of ATL with CNS involvement. CNS involvement was classified according to the criteria of JALSG202 for acute lymphocytic leukemia as follows: Grade I: no symptoms and cerebrospinal fluid (CSF)cell count less than 5/μl and presence of abnormal lymphocytes; Grade II: asymptomatic and CSF cell count 5-50/μl and presence of abnormal lymphocytes; Grade III: symptomatic or CSF cell counts &amp;gt; 50 cells/μl and presence of abnormal lymphocytes. Results: The analysis included 213 cases of ATL treated at Kagoshima University Hospital from 2002 to 2021. Of these aggressive ATL cases, the clinical subtypes at initial presentation were as follows: acute type 109, lymphoma type 54, chronic type 30, smoldering type 18, and 2 cases were unclassifiable. The median age of the patients was 63 years, and 96 cases (45.1%) were women. Sixty patients had received allogeneic hematopoietic stem cell transplants. During the clinical course, 28 patients (13.1%) with a median age of 61 years and 13 women（46.4%）had CNS involvement. Two cases were classified as Grade I, six as Grade II, and 20 as Grade III. Among them, nine patients (4.2%) showed neurological symptoms at the initial ATL diagnosis, and 1 patient presented with neurological findings at the time of chronic to acute transformation. Of the remaining 203 patients, prophylactic intrathecal chemotherapy was administered in 101 cases, at which time CNS involvement was diagnosed in 9 cases (8.9%). Three patients developed symptomatic involvement while responding to chemotherapy. One patient developed symptomatic involvement when refractory to chemotherapy. Four cases were CNS recurrence with systemic disease progression after remission. Two cases were identified as primary CNS-ATL. The simplified ATL-PI (Prognostic Index) at initial ATL diagnosis for the 28 patients with CNS involvement revealed four cases with high-risk, thirteen with intermediate-risk, two with low-risk, six not eligible due to indolent ATL subtypes, and three cases with unknown risk. The incidence of CNS involvement by ATL subtype was 17.8% (19/107) for acute type, 1.8% (1/54) for lymphoma type, 16.7% (5/30) for chronic type, and 0% for smoldering type (excluding 1 case of unknown subtype and 2 cases of primary CNS-ATL) at ATL diagnosis. At the diagnosis of CNS involvement, 15 (53.6％) patients showed at least 5% of ATL cells in the peripheral blood. During a median observation period of 429 days, the 1-year cumulative incidence of CNS involvement was 12.3% (95% CI 8.3-17.1%). High-dose methotrexate-based therapy was administered to 5 patients with CNS involvement, which had a certain effect on CNS lesions but had limited efficacy for other lesions. All of these cases were treated with concomitant intrathecal chemotherapy. The 2-year overall survival rate after diagnosis of CNS involvement was 16.9% (95% CI 4.9-35.2%). The CNS-IPI (International Prognostic Index) did not predict CNS involvement in ATL. Conclusions: This is the largest study to examine the clinical course of CNS involvement of ATL. The 1-year cumulative incidence of CNS involvement was 12.3%, indicating that CNS involvement is an early complication after diagnosis of aggressive ATL, especially in leukemic subtypes. The prognosis after the diagnosis of CNS involvement was also clarified. The high frequency of CNS involvement during prophylactic intrathecal chemotherapy in patients with ATL without neurological symptoms suggests that it is an important clinical question that needs to be addressed.

Conferone, a coumarin from Ferula flabelliloba, induced toxic effects on adult T-cell leukemia/lymphoma cells.

Adult T-cell leukemia/lymphoma (ATL) is a lymphoid malignancy caused by HTLV-1 infection, with distinct geographical distribution. Despite advances in cancer treatment, the average survival rate of ATL is low. Conferone is a natural coumarin extracted from Ferula species with a wide range of pharmaceutical effects. In search for a novel chemotherapeutic agent, we investigated the cytotoxicity of conferone on ATL cells. To obtain conferone, the methanolic extract of the roots of F. flabelliloba was subjected to silica gel column chromatography, followed by 1H- and 13C-NMR to confirm its structure. For cytotoxicity assay, MT-2 cells were treated with different concentrations of conferone (2.5, 5, 10, 20, and 40 µM) for 24, 48, and 72 h, and viability was evaluated by a colorimetric assay using alamarBlue. Cell cycle was analyzed by PI staining and flow cytometry, and qPCR was used to study the expression of candidate genes. Obtained findings indicated that conferone induced considerable cytotoxic effects on MT-2 cells in a time- and dose-dependent manner. In addition, accumulation of cells in the sub-G1 phase of the cell cycle was detected upon conferone administration. Moreover, conferone reduced the expression of CDK6, c-MYC, CFLIPL, and NF-κB (Rel-A) in MT-2 cells. Accordingly, conferone could be considered as a potent agent against ATL, although complementary investigations are required to define more precisely its mechanism of action.

CDK9 Inhibitor Induces Apoptosis, Autophagy, and Suppression of Tumor Growth in Adult T-Cell Leukemia/Lymphoma.

Adult T-cell leukemia/lymphoma (ATL) is a hematopoietic malignancy with a poor prognosis that develops in approximately 5% of human T-cell leukemia virus type 1 (HTLV-1) carriers. Cyclin-dependent kinase 9 (CDK9), together with Cyclin T, forms a transcription elongation factor, positive transcription elongation factor b (P-TEFb). P-TEFb promotes transcriptional elongation by phosphorylating the second serine (Ser2) of the seven amino acid repeat sequence in the C-terminal domain of RNA polymerase II (RNAP II). CDK9 inhibitors suppress cell proliferation by inducing apoptosis in chronic lymphocytic leukemia and breast cancer but there are no reports on autophagy of CDK9 inhibitors. Here, we investigated the effect of LY2857785, a novel CDK9 selective inhibitor, on cell death in ATL-related cell lines in vitro, freshly isolated cells from ATL patients ex vivo, and on ATL tumor xenografts in NOD/SCID mice in vivo. LY2857785 significantly reduced cell viability and induced apoptosis, as shown by annexin V-positive cells, cleaved poly(ADP-ribose) polymerase (PARP), and cleaved caspase-3, and suppressed the levels of anti-apoptotic protein myeloid cell leukemia-1 (MCL-1). LY2857785 decreased RNAP II Ser2 phosphorylation and downstream c-Myc protein levels. Interestingly, LY2857785 also increased microtubule-associated proteins 1A/1B light chain 3B (LC3)-II binding to autophagosome membranes. Furthermore, LY2857785 decreased the viability of freshly isolated ATL cells and induced apoptosis. Finally, LY2857785 significantly decreased the growth of ATL tumor xenografts. These results suggest that LY2857785 induces cell death of ATL cells by MCL-1-dependent apoptosis and autophagy and has anti-tumor activity.

YAP suppresses human T-cell leukemia virus type 1 transcription.

Human T-cell leukemia virus type 1 (HTLV-1) is an oncogenic retrovirus that causes adult T-cell leukemia/lymphoma (ATL). HTLV-1 encodes Tax protein that activates transcription from viral long terminal repeats (LTR). Multiple cofactors are involved in the regulation of HTLV-1 transcription via association with Tax. Yes-associated protein (YAP), which is the key effector of Hippo pathway, is elevated and activated in ATL cells. In this study, we reported that YAP protein suppressed Tax activation of HTLV-1 5' LTR but not 3' LTR. The activation of the 5' LTR by Tax was potentiated when YAP was depleted. Moreover, overexpression of YAP repressed HTLV-1 plus-strand viral gene expression and virion production, whereas compromising YAP by RNA inference augmented the expression of HTLV-1 protein. As mechanisms of YAP-mediated viral transcription inhibition, we found that YAP interacted with Tax, and prevented the association between Tax and p300. It finally led to the inhibition of recruitment of Tax to the Tax-responsive element in the 5' LTR of HTLV-1. Taken together, our results demonstrate the negative regulatory function of YAP in Tax activation of HTLV-1 transcription. It may achieve sufficient transcriptional repression to maintain persistent infection and long-term latency of HTLV-1 in the host cells.

The development of adult T cell leukemia/lymphoma in renal transplant recipients: report of two cases with literature review

BackgroundsTherefore, reports on the risk of HTLV-1-related diseases in organ transplantation have increased in recent years, and the management of HTLV in renal transplantation remains a challenge.Patients and methodsWe retrospectively analyzed four HTLV-1-positive recipients or donors among 89 renal transplantation cases from 2006 to 2021.ResultsAmong the four HTLV-1-positive recipients, two patients developed adult T cell leukemia/lymphoma (ATL) derived from recipients at approximately 3 years (1016 days and 1195 days) after renal transplantation. Case 1 developed lymphoma-type ATL (an extranodal primary cutaneous variant), including skin and pulmonary lesions. The patient achieved CR with FK tapering and CHOP therapy following cord blood stem cell transplantation. However, the patient died 101 days after ATL development because of a severe fungal infection. Case 2 developed acute-type ATL with an unusual phenotype of CD4+8+30+. The patient was treated with FK tapering and palliative therapy because of poor PS. Notably, in case 1, histopathological findings showed high numbers of PD-1-positive TIL cells in ATL, suggesting exhausted T cells and a correlation with the early onset of ATL. Furthermore, in Case 2, histopathological findings revealed CD 30 expression in ATL cells, suggesting the importance of CD 30 in ATL development. Importantly, case 2 showed typical driver mutations, including CCR4 truncation mutations of the C-terminal, TBL1XR1 mutation, and TP53 mutation in the splice site. Notably, our present study and our previous study on renal transplantation strongly indicated that two out of two and one out of 59 “recipient” positive cases developed ATL, respectively. Furthermore, our previous nationwide study 4 out of 10 “donor” positive cases developed HAM. These findings showed that ATL may be derived from HTLV-I+ recipient cells and HAM may be derived from HTLV-1+ donor cells, although the precise mechanism remains unknown.ConclusionsThus, early onset and rapid progression of ATL with poor outcomes should be considered in HTLV-1 endemic areas. Furthermore, immunological or genetic mechanisms may be related to the development of ATL after renal transplantation. We believe that the mechanism of onset of ATL after transplantation may be important when considering the immune environment of ATL itself.

Therapeutic efficacy of the resorcylic acid lactone LL-Z1640-2 for adult T-cell leukaemia/lymphoma.

Adult T-cell leukaemia/lymphoma (ATL) remains incurable. The NF-κB and interferon regulatory factor 4 (IRF4) signalling pathways are among the critical survival pathways for the progression of ATL. TGF-β-activated kinase 1 (TAK1), an IκB kinase-activating kinase, triggers the activation of NF-κB. The resorcylic acid lactone LL-Z1640-2 is a potent irreversible inhibitor of TAK1/extracellular signal-regulated kinase 2 (ERK2). We herein examined the therapeutic efficacy of LL-Z1640-2 against ATL. LL-Z1640-2 effectively suppressed the in vivo growth of ATL cells. It induced in vitro apoptosis and inhibited the nuclear translocation of p65/RelA in ATL cells. The knockdown of IRF4 strongly induced ATL cell death while downregulating MYC. LL-Z1640-2 as well as the NF-κB inhibitor BAY11-7082 decreased the expression of IRF4 and MYC at the protein and mRNA levels, indicating the suppression of the NF-κB-IRF4-MYC axis. The treatment with LL-Z1640-2 also mitigated the phosphorylation of p38 MAPK along with the expression of CC chemokine receptor 4. Furthermore, the inhibition of STAT3/5 potentiated the cytotoxic activity of LL-Z1640-2 against IL-2-responsive ATL cells in the presence of IL-2. Therefore, LL-Z1640-2 appears to be an effective treatment for ATL. Further studies are needed to develop more potent compounds that retain the active motifs of LL-Z1640-2.

EZH1/2 dual inhibitors suppress HTLV-1-infected cell proliferation and hyperimmune response in HTLV-1-associated myelopathy.

Human T-cell leukemia virus type 1 (HTLV-1) causes HTLV-1-associated myelopathy (HAM), adult T-cell leukemia/lymphoma (ATL), HTLV-1-associated uveitis, and pulmonary diseases. Although both HAM and ATL show proliferation of infected cells, their pathogeneses are quite different. In particular, the pathogenesis of HAM is characterized by hyperimmune responses to HTLV-1-infected cells. Recently, we demonstrated the overexpression of histone methyltransferase EZH2 in ATL cells and the cytotoxic effects of EZH2 inhibitors and EZH1/2 dual inhibitors on these cells. However, these phenomena have never been studied in HAM. Furthermore, what effect these agents have on the hyperimmune response seen in HAM is completely unknown. In this study, we investigated histone methyltransferase expression levels in infected cell populations (CD4+ and CD4+CCR4+ cells) from patients with HAM using microarray and RT-qPCR analyses. Next, using an assay system that utilizes the spontaneous proliferation characteristic of peripheral blood mononuclear cells derived from patients with HAM (HAM-PBMCs), we investigated the effects of EZH2 selective inhibitors (GSK126 and tazemetostat) and EZH1/2 dual inhibitors (OR-S1 and valemetostat, also known as DS-3201), particularly on cell proliferation rate, cytokine production, and HTLV-1 proviral load. We also examined the effect of EZH1/2 inhibitors on the proliferation of HTLV-1-infected cell lines (HCT-4 and HCT-5) derived from patients with HAM. We found elevated expression of EZH2 in CD4+ and CD4+CCR4+ cells from patients with HAM. EZH2 selective inhibitors and EZH1/2 inhibitors significantly inhibited spontaneous proliferation of HAM-PBMC in a concentration-dependent manner. The effect was greater with EZH1/2 inhibitors. EZH1/2 inhibitors also reduced the frequencies of Ki67+ CD4+ T cells and Ki67+ CD8+ T cells. Furthermore, they reduced HTLV-1 proviral loads and increased IL-10 levels in culture supernatants but did not alter IFN-γ and TNF-α levels. These agents also caused a concentration-dependent inhibition of the proliferation of HTLV-1-infected cell lines derived from patients with HAM and increased annexin-V(+)7-aminoactinomycin D(-) early apoptotic cells. This study showed that EZH1/2 inhibitors suppress HTLV-1-infected cell proliferation through apoptosis and the hyperimmune response in HAM. This indicates that EZH1/2 inhibitors may be effective in treating HAM.

Primary cells from patients with adult T cell leukemia/lymphoma depend on HTLV-1 Tax expression for NF-κB activation and survival

Adult T cell leukemia/lymphoma (ATL) is an aggressive malignancy secondary to chronic infection with human T cell leukemia virus type 1 (HTLV-1). The viral oncoprotein Tax initiates T cell transformation through activation of critical cellular pathways, including NF-κB. Unexpectedly, Tax protein is not detectable in most ATL cells, in contrast to the HTLV-1 HBZ protein which antagonizes Tax effects. Here, we demonstrate that primary ATL cells from patients with acute or chronic ATL express very low levels of Tax mRNA and protein. Critically, survival of these primary ATL cells is dependent on continued Tax expression. Mechanistically, Tax extinction results in reversal of NF-κB activation, P53/PML activation and apoptosis. Tax drives interleukin-10 (IL-10) expression and recombinant IL-10 rescues the survival of tax-depleted primary ATL cells. These results demonstrate the critical role of continued Tax and IL-10 expression for the survival of primary ATL cells, highlighting their relevance as therapeutic targets.