MicroRNA (miRNA) dysregulation is a hallmark of cutaneous T-cell lymphoma (CTCL), an often-fatal malignancy of skin-homing CD4 T cells for which there are few effective therapies. The role of microRNAs (miRs) in controlling epigenetic modifier-dependent transcriptional regulation in CTCL is unknown. In this study, we characterize a novel miR dysregulation that contributes to overexpression of the epigenetic reader bromodomain-containing protein 4 (BRD4). We used patient CD4 T cells to show diminished levels of miR-29b compared with healthy donor cells. Patient cells and miR-29b mouse cells revealed an inverse relationship between miR-29b and BRD4, the latter of which is overexpressed in these cells. Chromatin immunoprecipitation and sequencing analysis revealed increased genome-wide BRD4 occupancy at promoter and enhancer regions in CD4 T cells from CTCL patients. The cumulative result of BRD4 binding was increased expression of tumor-associated genes such as and, as well as the interleukin-15 (IL-15) receptor complex, the latter enhancing IL-15 autocrine signaling. Furthermore, we confirm the in vivo relevance of this pathway in our IL-15 transgenic mouse model of CTCL by showing that interference with BRD4-mediated pathogenesis, either by restoring miR-29b levels via bortezomib treatment or by directly inhibiting BRD4 binding via JQ1 treatment, prevents progression of CTCL. We describe a novel oncogenic pathway featuring IL-15, miR-29b, and BRD4 in CTCL and suggest targeting of these components as a potentially effective therapy for CTCL patients.

Immunotherapy approaches have advanced rapidly in recent years. While the greatest therapeutic advances so far have been achieved with T cell therapies such as immune checkpoint blockade and CAR-T, recent advances in NK cell therapy have highlighted the therapeutic potential of these cells. Chronic lymphocytic leukemia (CLL), the most prevalent form of leukemia in Western countries, is a very immunosuppressive disease but still shows significant potential as a target of immunotherapy, including NK-based therapies. In addition to their antileukemia potential, NK cells are important immune effectors in the response to infections, which represent a major clinical concern for CLL patients. Here, we review the interactions between NK cells and CLL, describing functional changes and mechanisms of CLL-induced NK suppression, interactions with current therapeutic options, and the potential for therapeutic benefit using NK cell therapies.

Successes with anti-CD20 antibodies in chronic lymphocytic leukemia (CLL) and enhanced activity of Fc-engineered versus unmodified antibody therapy suggest a potentially impactful role for natural killer (NK) cells and other innate immune cells in controlling this disease. Stimulated natural killer cells have shown promise as a cellular therapy but their application has been constrained by limited expansion capacity and low cytotoxic activity against CLL cells. Here, we demonstrate that both healthy donor-derived and CLL patient-derived NK cells expand rapidly when stimulated with feeder cells expressing membrane-bound IL-21 and have potent cytotoxic activity against allogeneic or autologous CLL cells. Combination with anti-CD20 antibodies significantly enhances NK recognition and killing of CLL targets. As any CLL immune therapy would likely be given in combination, we assess commonly-used treatments and demonstrate that ibrutinib has mixed suppressive and protective effects on expanded NK cells whereas expanded NKs are highly resistant to venetoclax. We demonstrate efficacy in vivo in two xenograft mouse models of human CLL that support building upon a regimen of venetoclax and obinutuzumab with mbIL-21-expanded NK cells. Collectively, these data support development of mbIL-21-expanded NKs combined with the CD20 antibody obinutuzumab and venetoclax in the treatment of CLL.

Rare, recurrent balanced translocations occur in a variety of cancers but are often not functionally interrogated. Balanced translocations with the immunoglobulin heavy chain locus (IGH; 14q32) in chronic lymphocytic leukemia (CLL) are infrequent but have led to the discovery of pathogenic genes including CCND1, BCL2, and BCL3. Following identification of a t(X;14)(q28;q32) translocation that placed the mature T cell proliferation 1 gene (MTCP1) adjacent to the immunoglobulin locus in a CLL patient, we hypothesized that this gene may have previously unrecognized importance. Indeed, here we report overexpression of human MTCP1 restricted to the B cell compartment in mice produces a clonal CD5+/CD19+ leukemia recapitulating the major characteristics of human CLL and demonstrates favorable response to therapeutic intervention with ibrutinib. We reinforce the importance of genetic interrogation of rare, recurrent balanced translocations to identify cancer driving genes via the story of MTCP1 as a contributor to CLL pathogenesis.

Chronic lymphocytic leukemia (CLL) transformation to aggressive lymphoma, known as Richter's Transformation (RT), has a dismal prognosis. There are limited data evaluating risk of RT in patients treated with ibrutinib. We performed a retrospective analysis to determine prognostic variables associated with development of RT and overall survival (OS) at progression after treatment with ibrutinib. We identified 559 patients with CLL treated with ibrutinib from 2010–2019. After a median follow‐up of 44.5 months from ibrutinib start, 179 patients progressed and were included in our analysis. After a median follow‐up of 20.8 months from progression, 54 out of 179 patients developed RT. Progression on treatment (hazard ratio [HR] 4.01 [1.60–10.00], p = .003), higher LDH (HR 1.80 for 2‐fold increase [1.33–2.43], p = .0001), and lymphadenopathy without lymphocytosis (HR 2.88 [1.15–7.20], p = .02) were independent prognostic variables for the development of RT at progression. Progression with lymphadenopathy without lymphocytosis continued to be an independent prognostic variable of worse OS post‐progression. In a subset analysis of 50 patients who obtained a PET‐CT at progression, the median SUVmax for patients who would develop RT was 15.2 (n = 30, range: 4.0–46.3) versus those patients who did not develop RT with a SUVmax of 7.7 (n = 20, range: 2.3–27.2) (p = .0030). Median OS from date of RT was 4.0 months, suggesting that prognosis for RT remains poor. A lymph node biopsy to rule out RT should be considered in patients who received ibrutinib who progress on treatment, have an elevated LDH, or progress with lymphadenopathy without lymphocytosis.

Prostate apoptosis response 4 (Par-4) is a tumor suppressor that prevents proliferation and induces cell death in several solid tumors. However, its role in B-cell malignancies has not been elucidated. To describe the role of Par-4 in chronic lymphocytic leukemia (CLL) pathogenesis, we developed a B-cell–specific human Par-4–overexpressing mouse model of CLL using the TCL1 leukemia model. While Par-4 transgenic mice did not display any obvious defects in B-cell development or function, disease burden as evidenced by abundance of CD19+CD5+ B cells in the peripheral blood was significantly reduced in Par-4 × TCL1 mice compared with TCL1 littermates. This conferred a survival advantage on the Par-4–overexpressing mice. In addition, a B-cell–specific knockout model displayed the opposite effect, where lack of Par-4 expression resulted in accelerated disease progression and abbreviated survival in the TCL1 model. Histological and flow cytometry–based analysis of spleen and bone marrow upon euthanasia revealed comparable levels of malignant B-cell infiltration in Par-4 × TCL1 and TCL1 individuals, indicating delayed but pathologically normal disease progression in Par-4 × TCL1 mice. In vivo analysis of splenic B-cell proliferation by 5-ethynyl-2-deoxyuridine incorporation indicated >50% decreased expansion of CD19+CD5+ cells in Par-4 × TCL1 mice compared with TCL1 littermates. Moreover, reduced nuclear p65 levels were observed in Par-4 × TCL1 splenic B cells compared with TCL1, suggesting suppressed NF-κB signaling. These findings have identified an in vivo antileukemic role for Par-4 through an NF-κB–dependent mechanism in TCL1-mediated CLL-like disease progression.

Targeting the epigenome is a promising strategy in the treatment of advanced stage cutaneous T-cell lymphoma (CTCL). CTCL is a malignancy of mature CD4+ T-cells which initially involves the skin but may progress to involve blood and visceral organs. There is no curative treatment, and drug resistance is a common problem. A hallmark feature in the development and progression of CTCL is global dysregulation of the epigenome resulting in aberrant gene expression, increased expression of oncogenes, and silencing of tumor suppressors. Bromodomain 4 (BRD4) is a master epigenetic regulator of gene expression recently identified as a survival factor in many hematologic and solid malignancies. A member of the bromodomain and extra terminal (BET) protein family, BRD4 binds chromatin in super-enhancer regions to direct downstream gene expression through interaction with co-factors such as Mediator and p-TEFb. Recently, a small molecule specific inhibitor of BRD4, JQ1, has been investigated as an anti-tumor agent. The role of BRD4, and therefore the efficacy and mechanism of JQ1 in CTCL is not known. Our group recently reported the critical role of IL-15 signaling in the development and progression of CTCL (Mishra et al, Cancer Discovery, 2016). Utilizing CTCL-derived cell lines, patient samples, and the newly characterized IL-15 transgenic mouse model of CTCL, we describe the effects of IL-15 signaling on BRD4 expression, and demonstrate for the first time regulation of IL-15 receptor expression by BRD4. We also describe the efficacy of JQ1 as an anti-tumor agent in CTCL which acts by inducing cell cycle arrest in cell lines and preventing disease progression in IL-15 transgenic mice. IL-15 signaling through its heterotrimeric receptor is a driver of oncogenesis in CTCL. Treatment of primary CD4+ T-cells from healthy donors with IL-15 (100ng/ml) for 48 hours increases protein expression of BRD4 (Figure 1A). To evaluate the occupancy of BRD4 in regulatory regions of IL-15 receptor genes, we performed ChIP-sequencing for BRD4 binding in CD4+ T-cells from a healthy donor, fresh CTCL cells, and JQ1-treated CTCL cells. At the gene locus for IL-15Rα (Chromosome 10p14-p15), we observed increased BRD4 binding at the transcription start site. This occupancy is reversed upon treatment with JQ1, to a level comparable to that of healthy donor CD4+ T-cells. This pattern is recapitulated in regulatory regions for IL-15Rβ and IL-15Rγ loci. To determine if decreased BRD4 occupancy following JQ1 treatment results in decreased IL-15 receptors gene expression, immunoblotting was performed for each receptor subunit. Treatment of the CTCL cell line HuT78 cells, with JQ1 results in significant reduction in the expression of all three IL-15 receptor subunits compared to vehicle. IL-15Rα expression decreased 2.3-fold, IL-15Rβ by 17-fold, and IL-15Rγ by 122-fold (Figure 1A). To determine the efficacy of JQ1 as an anti-tumor agent, CTCL-derived cell lines were treated with increasing doses of JQ1 for 72 hours. Cell viability and cell cycle analysis was performed and IC50 values were calculated for each cell line. At 10µM dose, there were significant decreases in % cell viability for all 5 cell lines (MyLa 66±2.56; HuT102 37±1.39; HuT78 30±1.86; HH 19±2.15; SeAx 36±0.79; p<0.0001 for all of the above). IC50 for MyLa is 21µM, HuT102 0.445µM, SeAx 4.45µM, HuT78 0.167µM, and HH 0.461µM. Treatment of these cell lines with JQ1 also resulted in a dose-dependent increase of cells in sub-G0 phase of the cell cycle, corresponding with increased Annexin V staining. IL-15 transgenic mice universally develop CTCL by 3-4 weeks of age. We treated these mice with 50mg/kg JQ1 (n=8) or a vehicle control (n=5) beginning at 4 weeks of age for 4 weeks. Scoring of the morphology, and severity of skin lesions histologically (Figure 1B) demonstrated a significant difference between JQ1 treated animals and controls (Figure 1C,p=0.0041), with JQ1-treated animals having milder disease. We conclude that BRD4 binding at regulatory regions enhances IL-15 receptor expression in CTCL. Increased receptor expression may augment IL-15 signaling, a known oncogenic mechanism in this malignancy. Furthermore, JQ1 reverses the effects of BRD4 on IL-15 receptor expression, results in significant cytotoxicity in cell lines, and prevents development of severe disease in a mouse model of CTCL. BRD4 therefore represents a promising therapeutic target in CTCL. Disclosures Porcu: Innate Pharma: Other: Investigator in a clinical trial; celgene: Other: Investigator in a clinical trial; miRagen: Other: Investigator in a clinical trial; Millenium: Other: investigator in a clinical trial.

Chronic lymphocytic leukemia (CLL) is the most prevalent adult leukemia in Western countries and is spelled by substantial genetic and clinical heterogeneity. During CLL transformation, loss or gain of genetic material appears to be a key determinant of disease phenotype and clinical outcome, with major chromosome aberrations observed in up to 80% of patients. Alternatively, balanced translocations, specifically those resulting in constitutive over-expression of various proto-oncogenes under the immunoglobulin heavy chain locus (IGH; 14q32), occur far less frequently. Despite their infrequence, molecular profiling of these rare rearrangements have revealed broad importance of un-recognized genes critical to the pathogenesis of CLL. Employing this strategy, we identified a young CLL patient with a previously undescribed t(X;14)(q28;q32) translocation, co-localization of the mature T cell proliferation 1 (MTCP1; Xq28) coding region with the IGH locus, triggering overexpression of MTCP1 in the CLL cells. Translocations involving MTCP1 are a driving factor in T-prolymphocytic leukemia; however, a role for MTCP1 in CLL has not been described. Inspired by this observation, we screened &gt;1700 suspected CLL cases and evaluated gene expression data for further evidence of MCTP1 aberrations. This query identified seven additional Xq28 rearrangements, revealed MTCP1 mRNA was globally over-expressed in CLL cells compared to normal B-cells, and increased MTCP1 mRNA expression portends a poor response to chemoimmunotherapy. To establish a role for MTCP1 as an oncogene in B cell malignancies, we generated a mouse model with B cell-specific MTCP1 overexpression (Eµ-MTCP1). Longitudinal evaluation revealed a majority of Eµ-MTCP1 mice developed a lethal hematologic malignancy between 5-12 months of age, highlighted by the progressive emergence of clonally related CLL-like B lymphocytes (CD19+/CD5+ B cells) in the blood and accumulating in the spleen and lymph nodes. To support the use of the newly generated Eµ-MTCP1 mouse as a tool for pre-clinical evaluation of CLL therapeutics, we demonstrate that continuous ibrutinib administration in Eµ-MTCP1 mice was sufficient to delay the onset of the CLL-like disease and significantly prolonged survival. In summary, we report Xq28 translocations as rare genetic abnormalities in CLL, yet being one mechanism by which CLL cells amplify expression of MTCP1 compared to normal B cell subsets. Further, the Eµ-MTCP1 mouse model should be considered as an alternative tool for both biologic assessment of co-expressed genes and pre-clinical evaluation of novel CLL therapeutics. Lastly, relevant to all cancer types, successful application of a strategy pursuing the functional consequence of genes involved in rare translocations contributed to the understanding of this disease and identified a novel target for future therapeutic consideration. Citation Format: Janek S. Walker, Zachary A. Hing, Steven Sher, James Cronin, Katie Williams, Bonnie Harrington, Jordan N. Skinner, Casey B. Cempre, Charles T. Gregory, Max Yano, Larry P. Beaver, Brandi R. Walker, Jadwiga M. Labanowska, Nyla A. Heerema, Krzysztof Mrozek, Jennifer A. Woyach, Amy S. Ruppert, Amy Lehman, Hatice Gulcin Ozer, Vincenzo Coppola, John C. Byrd, James S. Blachly, Rosa Lapalombella. Evaluating a rare t(X;14)(q28;q32) translocation reveals MTCP1 as a driving factor in chronic lymphocytic leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2260.