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Hematopoiesis in patients with cancer is characterized by reduced production of red blood cells and an increase in myelopoiesis, which contributes to the immunosuppressive environment in cancer. Some tumors produce growth factors that directly stimulate myelopoiesis such as G-CSF or GM-CSF. However, for a majority of tumors that do not directly secrete hematopoietic growth factors, the mechanisms involved in the activation of myelopoiesis are poorly characterized. In this study, we document in different murine tumor models activated hematopoiesis with increased proliferation of long-term and short-term hematopoietic stem cells and myeloid progenitor cells. As a consequence, the frequency of myeloid-derived suppressor cells and its ratio to CD8+ T cells increased in tumor-bearing mice. Activation of hematopoiesis and myeloid differentiation in tumor-bearing mice was induced by TNFα, which was mainly secreted by activated CD4+ T cells. Therefore, the activated adaptive immune system in cancer induces emergency myelopoiesis and immunosuppression.Significance:These findings characterize a regulatory circuit linking activated T cells to suppression of tumor-specific immune responses, providing a conceptual advance in the understanding of emergency-hematopoiesis in cancer and opening new targets for therapeutic approaches.

Table S1: suppl. cell cycle analysis to Fig 3; Table S2: suppl. BrDU and AnnexinV analysis to Fig 3; Table S3: suppl. analysis of the compositions of HSPC compartments to Fig 4; Figure S1: suppl. to Fig 1; Figure S2: suppl. to Fig 4; Figure S3: suppl. to Fig 6; Figure S4: suppl. to Fig 7

The effect of cancer immunotherapy on the endogenous immune response against tumors is largely unknown. Therefore, we studied immune responses against murine tumors expressing the glycoprotein (GP) and/or nucleoprotein of lymphocytic choriomeningitis virus (LCMV) with or without adoptive T-cell therapy. In nontreated animals, CTLs specific for different epitopes as well as LCMV-GP–specific antibodies contributed to tumor surveillance. Adoptive immunotherapy with monoclonal CTLs specific for LCMV-gp33 impaired the endogenous tumor-specific antibody and CTL response by targeting antigen cross-presenting cells. As a consequence and in contrast to expectations, immunotherapy enhanced tumor growth. Thus, for certain immunogenic tumors, a reduction of tumor-specific B- and T-cell responses and enhanced tumor growth may be an unwanted consequence of adoptive immunotherapy. [Cancer Res 2007;67(15):7467–76]

Supplementary Legends 1-2 from Decreased Tumor Surveillance after Adoptive T-Cell Therapy

Supplementary Figure 1 from Decreased Tumor Surveillance after Adoptive T-Cell Therapy

PDF file - 488K, Supplementary Figure 1. Growth of large tumor fragments, anti-tumoral CTL responses and tumor RNA immune gene profile in BL/6 and CD27-/- mice. Supplementary Figure 2. Intratumoral T cell subsets, endogenous CD25+ Tregs and effector T cell apoptosis. Supplementary Figure 3. CD27-/- and BL/6 Tregs equally inhibit the proliferation of CD8+ T cells

Supplementary Figure 2 from Decreased Tumor Surveillance after Adoptive T-Cell Therapy

Malignant pleural mesothelioma (MPM) is a lethal malignancy etiologically caused by asbestos exposure, for which there are few effective treatment options. Although asbestos carcinogenesis is associated with reactive oxygen species (ROS), the bona fide oncogenic signaling pathways that regulate ROS homeostasis and bypass ROS-evoked apoptosis in MPM are poorly understood. In this study, we demonstrate that the mitogen-activated protein kinase (MAPK) pathway RAS-RAF-MEK-ERK is hyperactive and a molecular driver of MPM, independent of histological subtypes and genetic heterogeneity. Suppression of MAPK signaling by clinically approved MEK inhibitors (MEKi) elicits PARP1 to protect MPM cells from the cytotoxic effects of MAPK pathway blockage. Mechanistically, MEKi induces impairment of homologous recombination (HR) repair proficiency and mitochondrial metabolic activity, which is counterbalanced by pleiotropic PARP1. Consequently, the combination of MEK with PARP inhibitors enhances apoptotic cell death in vitro and in vivo that occurs through coordinated upregulation of cytotoxic ROS in MPM cells, suggesting a mechanism-based, readily translatable strategy to treat this daunting disease. Collectively, our studies uncover a previously unrecognized scenario that hyperactivation of the MAPK pathway is an essential feature of MPM and provide unprecedented evidence that MAPK signaling cooperates with PARP1 to homeostatically maintain ROS levels and escape ROS-mediated apoptosis.

While inhibitory Siglec receptors are known to regulate myeloid cells, less is known about their expression and function in lymphocytes subsets. Here we identified Siglec-7 as a glyco-immune checkpoint expressed on non-exhausted effector memory CD8+ T cells that exhibit high functional and metabolic capacities. Seahorse analysis revealed higher basal respiration and glycolysis levels of Siglec-7

The production of blood cells during steady-state and increased demand depends on the regulation of hematopoietic stem cell (HSC) self-renewal and differentiation. Similarly, the balance between self-renewal and differentiation of leukemia stem cells (LSCs) is crucial in the pathogenesis of leukemia. Here, we document that the TNF receptor superfamily member lymphotoxin-β receptor (LTβR) and its ligand LIGHT regulate quiescence and self-renewal of murine and human HSCs and LSCs. Cell-autonomous LIGHT/LTβR signaling on HSCs reduces cell cycling, promotes symmetric cell division and prevents primitive HSCs from exhaustion in serial re-transplantation experiments and genotoxic stress. LTβR deficiency reduces the numbers of LSCs and prolongs survival in a murine chronic myeloid leukemia (CML) model. Similarly, LIGHT/LTβR signaling in human G-CSF mobilized HSCs and human LSCs results in increased colony forming capacity in vitro. Thus, our results define LIGHT/LTβR signaling as an important pathway in the regulation of the self-renewal of HSCs and LSCs., Regulation of self-renewal is critical during steady state and stress in haematpoietic stem cells (HSCs), and underlies leukaemia pathology. Here, the authors show that LIGHT and its receptor LTβR promote quiescence and self-renewal of HSCs and that LTβR deficiency promotes survival in a mouse leukaemia model.

Purpose: To explore a prognostic or predictive role of MRI and O-(2–18F-fluoroethyl)-L-tyrosine (18FET) PET parameters for outcome in the randomized multicenter trial ARTE that compared bevacizumab plus radiotherapy with radiotherpay alone in elderly patients with glioblastoma. Patients and Methods: Patients with isocitrate dehydrogenase wild-type glioblastoma ages 65 years or older were included in this post hoc analysis. Tumor volumetric and apparent diffusion coefficient (ADC) analyses of serial MRI scans from 67 patients and serial 18FET-PET tumor-to-brain intensity ratios (TBRs) from 31 patients were analyzed blinded for treatment arm and outcome. Multivariate Cox regression analysis was done to account for established prognostic factors and treatment arm. Results: Overall survival benefit from bevacizumab plus radiotherapy compared with radiotherapy alone was observed for larger pretreatment MRI contrast-enhancing tumor [HR per cm3 0.94; 95% confidence interval (CI), 0.89–0.99] and for higher ADC (HR 0.18; CI, 0.05–0.66). Higher 18FET-TBR on pretreatment PET scans was associated with inferior overall survival in both arms. Response assessed by standard MRI-based Response Assessment in Neuro-Oncology criteria was associated with overall survival in the bevacizumab plus radiotherapy arm by trend only (P = 0.09). High 18FET-TBR of noncontrast-enhancing tumor portions during bevacizumab therapy was associated with inferior overall survival on multivariate analysis (HR 5.97; CI, 1.16–30.8). Conclusions: Large pretreatment contrast-enhancing tumor mass and higher ADCs identify patients who may experience a survival benefit from bevacizumab plus radiotherapy. Persistent 18FET-PET signal of no longer contrast-enhancing tumor after concomitant bevacizumab plus radiotherapy suggests pseudoresponse and predicts poor outcome.

Background Over the past few years, immune checkpoint inhibitors have changed the therapeutic landscape of non-small-cell lung cancer (NSCLC). Response to immune checkpoint inhibitors correlates with a pre-existing anti-tumoral immune response. Checkpoint inhibitors have been introduced as second-line therapy and are only very recently used as monotherapy or in combination with chemotherapy as first-line treatment of NSCLC. However, the effect of conventional first-line platinum-based chemotherapy on the immune infiltrate in the tumor is largely unknown. Methods We measured the gene expression of a custom set of 201 cancer- and immune-related genes in 100 NSCLC tumor biopsies collected before chemotherapy and 33 re-biopsies after platinum-based chemotherapy at the time point of progression. For 29 patients matched pre- and post-chemotherapy samples could be evaluated. Results We identified a cluster of 47 co-expressed immune genes, including PDCD1 (PD1) and CD274 (PD-L1), along with three other co-expression clusters. Chemotherapy decreased the average gene expression of the immune cluster while no effect was observed on the other three cluster. Within this immune cluster, CTLA4, LAG3, TNFRSF18, CD80 and FOXP3 were found to be significantly decreased in patient-matched samples after chemotherapy. Conclusion Our results suggest that conventional platinum-based chemotherapy negatively impacts the immune microenvironment at the time point of secondary progression.

Long noncoding RNAs (lncRNAs) are widely dysregulated in cancer, yet their functional roles in cellular disease hallmarks remain unclear. Here we employ pooled CRISPR deletion to perturb all 831 lncRNAs in KRAS-mutant non-small cell lung cancer (NSCLC), and measure their contribution to proliferation, chemoresistance and migration across two cell backgrounds. Integrative analysis of this data outperforms conventional “dropout” screens in identifying cancer genes, while prioritising disease-relevant lncRNAs with pleiotropic and background-independent roles. Altogether 60 high-confidence oncogenic lncRNAs are active in NSCLC, the majority identified here for the first time, and which tend to be amplified and overexpressed in tumours. A follow-up antisense oligonucleotide (ASO) screen shortlisted two candidates, Cancer Hallmarks in Lung LncRNA (CHiLL 1&2), whose knockdown consistently suppressed cancer hallmarks in a variety of 2D and 3D tumour models. Molecular phenotyping reveals that CHiLL 1&2 control cellular-level phenotypes via distinct transcriptional networks converging on common oncogenic pathways. In summary, this work reveals a multi-dimensional functional lncRNA landscape underlying NSCLC that contains potential therapeutic vulnerabilities.

Studies validating the prognostic accuracy of the tumor-node-metastases (TNM) classification in patients with lung cancer treated by neoadjuvant therapy are scarce. Tumor regression, particularly major pathological response (MPR), is an acknowledged prognostic factor in this setting. We aimed to validate a novel combined prognostic score. This retrospective single-center study was conducted on 117 consecutive patients with non-small cell lung cancer resected after neoadjuvant treatment at a Swiss University Cancer Center between 2000 and 2016. All cases were clinicopathologically re-evaluated. We assessed the prognostic performance of a novel prognostic score (PRSC) combining T-category, lymph node status, and MPR, in comparison with the eighth edition of the TNM classification (TNM8), the size adapted TNM8 as proposed by the International Association for the Study of Lung Cancer (IASLC) and MPR alone. The isolated ypT-category and the combined TNM8 stages accurately differentiated overall survival (OS, stage p = 0.004) and disease-free survival (DFS, stage p = 0.018). Tumor regression had a prognostic impact. Optimal cut-offs for MPR emerged as 65% for adenocarcinoma and 10% for non-adenocarcinoma and were statistically significant for survival (OS p = 0.006, DFS p < 0.001). The PRSC differentiated between three prognostic groups (OS and DFS p < 0.001), and was superior compared to the stratification using MPR alone or the TNM8 systems, visualized by lower Akaike (AIC) and Bayesian information criterion (BIC) values. In the multivariate analyses, stage III tumors (HR 4.956, p = 0.003), tumors without MPR (HR 2.432, p = 0.015), and PRSC high-risk tumors (HR 5.692, p < 0.001) had significantly increased risks of occurring death. In conclusion, we support 65% as the optimal cut-off for MPR in adenocarcinomas. TNM8 and MPR were comparable regarding their prognostic significance. The novel prognostic score performed distinctly better regarding OS and DFS.

Leukemia stem cells (LSCs) promote the disease and seem resistant to therapy and immune control. Why LSCs are selectively resistant against elimination by cytotoxic CD8+ T cells (CTLs) is still unknown. In this study, we demonstrate that LSCs in chronic myeloid leukemia (CML) can be recognized and killed by CD8+ CTLs in vitro. However, Tregs, which preferentially localized close to CD8+ CTLs in CML bone marrow (BM), protected LSCs from MHC-class I dependent CD8+ CTL-mediated elimination in vivo. BM Tregs in CML were characterized by the selective expression of tumor necrosis factor receptor 4 (Tnfrsf4). Stimulation of Tnfrsf4-signaling did not deplete Tregs but reduced the capacity of Tregs to protect LSCs from CD8+ CTL-mediated killing. In the BM of newly diagnosed CML patients, TNFRSF4 mRNA levels were significantly increased and correlated with the expression of the Treg-restricted transcription factor FOXP3. Overall, these results identify Tregs as key regulator of immune escape of LSCs and TNFRSF4 as a potential target to reduce the function of Tregs and boost anti-leukemic immunity in CML.

BackgroundImmune-checkpoint (IC) inhibitors have revolutionized the treatment of multiple solid tumors and defined lymphomas, but they are largely ineffective in acute myeloid leukemia (AML). The reason why especially PD1/PD-L1 blocking agents are not efficacious is not well-understood but it may be due to the contribution of different IC ligand/receptor interactions that determine the function of T cells in AML.MethodsTo analyze the interactions of IC ligands and receptors in AML, we performed a comprehensive transcriptomic analysis of FACS-purified leukemia stem/progenitor cells and paired bone marrow (BM)-infiltrating CD4+ and CD8+ T cells from 30 patients with AML. The gene expression profiles of activating and inhibiting IC ligands and receptors were correlated with the clinical data. Epigenetic mechanisms were studied by inhibiting the histone deacetylase with valproic acid or by gene silencing of PAC1.ResultsWe observed that IC ligands and receptors were mainly upregulated in leukemia stem cells. The gene expression of activating IC ligands and receptors correlated with improved prognosis and vice versa. In contrast, the majority of IC receptor genes were downregulated in BM-infiltrating CD8+ T cells and partially in CD4+ T cells, due to pathological chromatin remodeling via histone deacetylation. Therefore, treatment with histone deacetylase inhibitor (HDACi) or silencing of PAC1, as a T cell-specific epigenetic modulator, significantly increased the expression of IC receptors and defined effector molecules in CD8+ T cells.ConclusionsOur results suggest that CD8+ T cells in AML are dysfunctional mainly due to pathological epigenetic silencing of activating IC receptors rather than due to signaling by immune inhibitory IC receptors, which may explain the limited efficacy of antibodies that block immune-inhibitory ICs in AML.

Background: For patients with resectable stage IIIA(N2) non-small cell lung cancer (NSCLC) neoadjuvant chemotherapy with three cycles of cisplatin and docetaxel followed by surgery has been shown to yield a 1-year event-free survival (EFS) rate of 48% and is an accepted standard of care. Neoadjuvant PD-(L)1 inhibitors can result in high response rates in resectable NSCLC. Methods: Neoadjuvant treatment consisted of three cycles of cisplatin 100 mg/m 2 and docetaxel 85 mg/m 2 q3w followed by two cycles of durvalumab 750 mg q2w. Adjuvant durvalumab was continued for 1 year after surgery. The primary endpoint was 1-year EFS. The hypothesis for statistical considerations was an improvement of 1-year EFS from 48% to 65%. This trial is registered with ClinicialTrials.gov, NCT02572843. Findings: Sixty-eight patients were enrolled, 67 were included in the full analysis set. Radiographic response rate was 43·3% (95%CI: 31·2-56·0) after neoadjuvant chemotherapy (complete remission (CR): 2·9%, partial remission (PR): 40·3%, stable disease (SD): 44·8%) and 58·1% (95%CI: 44·8-70·5) after additional neoadjuvant immunotherapy (CR: 6·5%, PR: 51·6%, SD: 25·8%). Fifty-five patients were resected, of which 34 (61·8%) achieved a major pathological response (MPR; ≤10% viable tumour cells), and 10 (18·2%) amongst them a complete pathological response. Postoperative nodal down-staging (ypN0-1) was observed in 37 patients (67·3%). Fifty-one (92·7%) patients had an R0 resection. There was no significant effect of pre-treatment PD-L1 expression on MPR or nodal down-staging. In the entire study population, the 1-year EFS rate was 73·4% (90%CI: 62·7-81·5). Median EFS and overall survival were not reached after 28 months of median follow-up. Fifty-nine (88·1%) patients had an adverse event (AE) grade ≥3 including two fatal AEs that were not assessed to be treatment-related. Interpretation: This is thus far the largest report on perioperative PD-(L)1 inhibition in patients with resectable stage IIIA(N2) NSCLC. The addition of perioperative durvalumab to neoadjuvant chemotherapy is safe and exceeds historical data of chemotherapy alone with a high MPR and an encouraging 1-year EFS rate of 73·4%. Trial Registration: This trial is registered with ClinicialTrials.gov, NCT02572843. Funding Statement: The study was supported by research agreements with the following institutions: Swiss State Secretary for Education, Research and Innovation (SERI), Swiss Cancer Research Foundation (SCS) and Swiss Cancer League (SCL). Research funding for translational research projects was granted by Gateway for Cancer Research and Rising Tide Foundation. AstraZeneca provided drug and financial support. Declaration of Interests: SIR: Honoraria for advisory boards and consulting (all paid to the institution) from Astra-Zeneca, BMS, Boehringer-Ingelheim, Eisai, Eli Lilly, Merck Serono, MSD, Novartis, Pfizer, Roche, Takeda. Research funding from AbbVie, Astra-Zeneca, BMS, Boehringer-Ingelheim, Merck. Support for travel and accommodations from Amgen, AstraZeneca, BMS, Boehringer-Ingelheim, MSD, Roche, Takeda. Member of the Federal Drug Commission of the Federal Office of Public Health. AZ: Honoraria for advisory boards and consulting (all paid to the institution) from Bristol-Myers Squibb, Merck Sharp & Dohme, Hoffmann–La Roche, NBE Therapeutics, Secarna, ACM Pharma and Hookipa. Non-commercial research agreements with Hoffmann–La Roche, NBE Therapeutics, Secarna, ACM Pharma, Hookipa, and BeyondSpring. EIE: None SSP: Honoraria for advisory boards and consulting from Astra-Zeneca, BMS, Boehringer-Ingelheim, MSD, Novartis, Pfizer and Roche. DB: None AB: None MF: Research grants from Bristol-Myers-Squibb and Astra Zeneca (paid to the institution). Honoraria for advisory boards from Bristol-Myers Squibb, AstraZeneca, Takeda, Roche, Boehringer-Ingelheim and MSD. MJ: Research grants from Bristol-Myers Squibb, Roche and Merck. DL: None HG: None LAM: Honoraria for advisory boards from AstraZeneca, Bristol-Myers-Squibb, Takeda, Roche and MSD. Support for travel and accommodations from AstraZeneca and Roche. CB: Honoraria for advisory boards from AstraZeneca, Pfizer, Roche, Takeda, Janssen-Cilag and Boehringer-Ingelheim. Support for travel and accommodations from AstraZeneca and Takeda. WW: Honoraria for advisory boards and consulting from Astra Zeneca SP: Personal fees from Abbvie, grants and personal fees from Amgen, grants and personal fees from AstraZeneca, personal fees from Bayer, personal fees from Biocartis, grants and personal fees from Boehringer-Ingelheim, grants and personal fees from Bristol-Myers Squibb, grants and personal fees from Clovis, personal fees from Daiichi Sankyo, personal fees from Debiopharm, personal fees from Eli Lilly, grants and personal fees from F. Hoffman - La Roche, personal fees from Foundations Medicine, grants and personal fees from Illumina, personal fees from Janssen, grants and personal fees from Novartis, personal fees from Pharma Mar, grants and personal fees from Pfizer, personal fees from Regeneron, personal fees from Sanofi, personal fees from Seattle Genetics, personal fees from Takeda, grants and personal fees from Merck Sharp and Dohme, personal fees from Merck Serono, personal fees from Merrimack. MM: Honoraria for advisory boards from AstraZeneca, Bristol-Myers-Squibb, MSD, Roche and Takeda. Research grant (to the institution) from AstraZeneca. RC: Honoraria for advisory boards (all paid to the institution) from AstraZeneca, Astellas, MSD, Bristol-Myers-Squibb, Janssen-Cilag, Roche, Pfizer, Merck Serono, Ipsen and Bayer. AFO: None WDJ: None CW: None NM: None PF: Honoraria for advisory from Pfizer, Roche, Takeda, Boehringer-Ingelheim and BristolMyers Squibb. MB: None PB: None GG: None CR: None MG: Honoraria for advisory boards and consulting (all paid to the institution) from Astra-Zeneca. MP: Honoraria for advisory boards from AbbVie, AstraZeneca, Boehringer-Ingelheim, BristolMyers-Squibb, Eisai, MSD, Novartis, Pfizer, Roche, Takeda and Merck. Speakers fee from Janssen-Cilag. Support for travel and accommodations from AstraZeneca, BoehringerIngelheim, Bristol-Myers-Squibb and Vifor. Ethics Approval Statement: The trial was done in accordance with the principles of the Declaration of Helsinki. The protocol was approved by the ethics committee of each participating site. Written informed consent was obtained from all patients.

Acute myeloid leukemia (AML) is driven by leukemia stem cells (LSCs) that resist conventional chemotherapy and are the major cause of relapse1,2. Hypomethylating agents (HMAs) are the standard of care in the treatment of older or unfit patients with AML, but responses are modest and not durable3-5. Here we demonstrate that LSCs upregulate the tumor necrosis factor family ligand CD70 in response to HMA treatment resulting in increased CD70/CD27 signaling. Blocking CD70/CD27 signaling and targeting CD70-expressing LSCs with cusatuzumab, a human αCD70 monoclonal antibody with enhanced antibody-dependent cellular cytotoxicity activity, eliminated LSCs in vitro and in xenotransplantation experiments. Based on these preclinical results, we performed a phase 1/2 trial in previously untreated older patients with AML with a single dose of cusatuzumab monotherapy followed by a combination therapy with the HMA azacitidine (NCT03030612). We report results from the phase 1 dose escalation part of the clinical trial. Hematological responses in the 12 patients enrolled included 8 complete remission, 2 complete remission with incomplete blood count recovery and 2 partial remission with 4 patients achieving minimal residual disease negativity by flow cytometry at

Cell lines are essential tools to standardize and compare experimental findings in basic and translational cancer research. The current dogma states that cancer stem cells feature an increased tumor initiation capacity and are also chemoresistant. Here, we identified and comprehensively characterized three morphologically distinct cellular subtypes in the non–small cell lung cancer cell line A549 and challenge the current cancer stem cell dogma. Subtype-specific cellular morphology is maintained during short-term culturing, resulting in the formation of holoclonal, meroclonal, and paraclonal colonies. A549 holoclone cells were characterized by an epithelial and stem-like phenotype, paraclone cells featured a mesenchymal phenotype, whereas meroclone cells were phenotypically intermediate. Cell-surface marker expression of subpopulations changed over time, indicating an active epithelial-to-mesenchymal transition (EMT), in vitro and in vivo. EMT has been associated with the overexpression of the immunomodulators PD-L1 and PD-L2, which were 37- and 235-fold overexpressed in para- versus holoclone cells, respectively. We found that DNA methylation is involved in epigenetic regulation of marker expression. Holoclone cells were extremely sensitive to cisplatin and radiotherapy in vitro, whereas paraclone cells were highly resistant. However, inhibition of the receptor tyrosine kinase AXL, whose expression is associated with an EMT, specifically targeted the otherwise highly resistant paraclone cells. Xenograft tumor formation capacity was 24- and 269-fold higher in holo- than mero- and paraclone cells, respectively. Our results show that A549 subpopulations might serve as a unique system to explore the network of stemness, cellular plasticity, tumor initiation capacity, invasive and metastatic potential, and chemo/radiotherapy resistance.

Follicular lymphomas (FL) are slow-growing, indolent tumors containing extensive follicular dendritic cell (FDC) networks and recurrent EZH2 gain-of-function mutations. Paradoxically, FLs originate from highly proliferative germinal center (GC) B cells with proliferation strictly dependent on interactions with T follicular helper cells. Herein, we show that EZH2 mutations initiate FL by attenuating GC B cell requirement for T cell help and driving slow expansion of GC centrocytes that become enmeshed with and dependent on FDCs. By impairing T cell help, mutant EZH2 prevents induction of proliferative MYC programs. Thus, EZH2 mutation fosters malignant transformation by epigenetically reprograming B cells to form an aberrant immunological niche that reflects characteristic features of human FLs, explaining how indolent tumors arise from GC B cells.

Summary Self-renewal is a key characteristic of leukemia stem cells (LSCs) responsible for the development and maintenance of leukemia. In this study, we identify CD93 as an important regulator of self-renewal and proliferation of murine and human LSCs, but not hematopoietic stem cells (HSCs). The intracellular domain of CD93 promotes gene transcription via the transcriptional regulator SCY1-like pseudokinase 1 independently of ligation of the extracellular domain. In a drug library screen, we identify the anti-emetic agent metoclopramide as an efficient blocker of CD93 signaling. Metoclopramide treatment reduces murine and human LSCs in vitro and prolongs survival of chronic myeloid leukemia (CML) mice through downregulation of pathways related to stemness and proliferation in LSCs. Overall, these results identify CD93 signaling as an LSC-specific regulator of self-renewal and proliferation and a targetable pathway to eliminate LSCs in CML.

Co-stimulatory signals, cytokines and transcription factors regulate the balance between effector and memory cell differentiation during T cell activation. Here, we analyse the role of the TRAF2-/NCK-interacting kinase (TNIK), a signaling molecule downstream of the tumor necrosis factor superfamily receptors such as CD27, in the regulation of CD8+ T cell fate during acute infection with lymphocytic choriomeningitis virus. Priming of CD8+ T cells induces a TNIK-dependent nuclear translocation of β-catenin with consecutive Wnt pathway activation. TNIK-deficiency during T cell activation results in enhanced differentiation towards effector cells, glycolysis and apoptosis. TNIK signaling enriches for memory precursors by favouring symmetric over asymmetric cell division. This enlarges the pool of memory CD8+ T cells and increases their capacity to expand after re-infection in serial re-transplantation experiments. These findings reveal that TNIK is an important regulator of effector and memory T cell differentiation and induces a population of stem cell-like memory T cells.

Background The addition of bevacizumab to temozolomide-based chemoradiotherapy (TMZ/RT → TMZ) did not prolong overall survival (OS) in patients with newly diagnosed glioblastoma in phase III trials. Elderly and frail patients are underrepresented in clinical trials, but early reports suggested preferential benefit in this population. Patients and methods ARTE was a 2 : 1 randomized, multi-center, open-label, non-comparative phase II trial of hypofractionated RT (40 Gy in 15 fractions) with bevacizumab (10 mg/kg×14 days) (arm A, N = 50) or without bevacizumab (arm B, N = 25) in patients with newly diagnosed glioblastoma aged ≥65 years. The primary objective was to obtain evidence for prolongation of median OS by the addition of bevacizumab to RT. Response was assessed by RANO criteria. Quality of life (QoL) was monitored by the EORTC QLQ-C30/BN20 modules. Exploratory studies included molecular subtyping by 450k whole methylome and gene expression analyses. Results Median PFS was longer in arm A than in arm B (7.6 and 4.8 months, P = 0.003), but OS was similar (12.1 and 12.2 months, P = 0.77). Clinical deterioration was delayed and more patients came off steroids in arm A. Prolonged PFS in arm A was confined to tumors with the receptor tyrosine kinase (RTK) I methylation subtype (HR 0.25, P = 0.014) and proneural gene expression (HR 0.29, P = 0.025). In a Cox model of OS controlling for established prognostic factors, associations with more favorable outcome were identified for age

AML is driven by leukemic stem cells (LSC) that resist conventional chemotherapies and remain unaffected in their niche, continually replenishing circulating blast cells. We postulated that an avidity-engineered CD3 engaging DARPin ® (Designed Ankyrin Repeat Protein) able to simultaneously target LSC-specific CD70 as well as CD123 and CD33 could allow highly efficient and specific T cell-mediated killing of AML LSCs and circulating blast cells while preserving a therapeutic window towards healthy cells. Moreover, this simultaneous targeting of three different tumor associated antigens (TAAs) has the potential to address tumor heterogeneity, allowing targeting of AML cells with different co-expression patterns and/or expression levels of each single TAA. To achieve this ambitious goal we used our DARPin ® platform to build a novel class of triple targeting CD3 engaging molecules. Our DARPin ® libraries contain trillions of molecules allowing the generation of highly diverse binders against target proteins that can be easily combined into multi-specific DARPins ® to elicit desired biological effects. We leveraged this proprietary platform to screen multi-specific CD3 engaging DARPin ® molecules, including serum albumin binding DARPins ® for systemic half-life extension, and identify the optimal target affinity and molecular architecture to ensure potent avidity-driven T cell-mediated killing of AML cells while sparing healthy cells. This approach allowed the generation of CD3 engaging DARPins ® able to target simultaneously CD33, CD123, and CD70. Such DARPins ® demonstrated, in both allogenic and autologous setting, single digit pM potency against AML cell lines and primary cells expressing any combination of at least 2 of the 3 targeted TAAs, while showing low activity against single TAA-expressing cells, the latter representing cells of the healthy compartment. Higher expression of the selected TAAs on LSCs vs normal hematopoietic stem cells (HSC) can further enhance the selectivity of such an avidity driven molecule, leading to the preferential killing of LSC over HSC. Moreover, our multi-specific T cell engager (TCE) format resulted in a significant decrease in cytokine release in a whole blood test system for cytokine release syndrome (CRS) when compared to other mono-targeting TCE therapies, confirming its specificity and the potential for an improved safety profile within the normal hematopoietic system. Additionally, while showing similar anti-tumor efficacy in a mouse xenograft model using Molm-13 cell line and human PBMCs, CRS measured in serum 4 h after the initial injection of our multi-specific DARPin ® molecule was drastically reduced compared to a reference CD33 TCE, further strengthening the evidence that our multi targeting DARPins might also exhibit a good safety profile in humans. In conclusion, we were able to generate multi-specific CD3 engaging DARPin ® molecules with tailored affinities towards different TAAs showing exceptional efficacy and with the potential for superior safety over mono-specific TCE approaches, including systemic half-life extension to avoid a continuous intravenous infusion-based therapy. Disclosures Bianchi: Molecular Partners AG (MAG): Current holder of stock options in a privately-held company. Reschke: Molecular Partners AG (MAG): Current holder of stock options in a privately-held company. Reichen: Molecular Partners AG (MAG): Current holder of stock options in a privately-held company. Fischer: Molecular Partners AG (MAG): Other: Owns stock options and/or shares of the company. Grübler: Molecular Partners AG (MAG): Other: Owns stock options and/or shares of the company. Eggenschwiler: Molecular Partners AG (MAG): Other: Owns stock options and/or shares of the company. Krieg: Molecular Partners AG (MAG): Other: Owns stock options and/or shares of the company. Ioannou: Molecular Partners AG (MAG): Other: Owns stock options and/or shares of the company. Ragusa: Molecular Partners AG (MAG): Other: Owns stock options and/or shares of the company. Looser: Molecular Partners AG (MAG): Other: Owns stock options and/or shares of the company. Spitzli: Molecular Partners AG (MAG): Other: Owns stock options and/or shares of the company. Herzog: Molecular Partners AG (MAG): Other: Owns stock options and/or shares of the company. Villemagne: Molecular Partners AG (MAG): Other: Owns stock options and/or shares of the company. Kaufmann: Molecular Partners AG (MAG): Other: Owns stock options and/or shares of the company. Matzner: Molecular Partners AG (MAG): Other: Owns stock options and/or shares of the company. Auge: Molecular Partners AG (MAG): Other: Owns stock options and/or shares of the company. Hänggi: Molecular Partners AG (MAG): Other: Owns stock options and/or shares of the company. Ali: Molecular Partners AG (MAG): Other: Owns stock options and/or shares of the company. Franchini: Molecular Partners AG (MAG): Other: Owns stock options and/or shares of the company. Kirkin: Molecular Partners AG (MAG): Other: Owns stock options and/or shares of the company. Schlereth: Molecular Partners AG (MAG): Other: Owns stock options and/or shares of the company. Luethi: Molecular Partners AG (MAG): Other: Owns stock options and/or shares of the company. Ochsenbein: Molecular Partners AG (MAG): Other: Owns stock options and/or shares of the company. Riether: Molecular Partners AG (MAG): Other: Owns stock options and/or shares of the company. Steiner: Molecular Partners AG (MAG): Other: Owns stock options and/or shares of the company. Goubier: Molecular Partners AG (MAG): Other: Owns stock options and/or shares of the company.

BACKGROUND In recent years, several treatment modalities have proved to be effective in the treatment of neuroendocrine tumours (NETs). However, there is currently no consensus on the sequence in which these options are best used. METHODS In this observational study, we analysed the treatment modalities and sequences of all patients included in the Swiss NeuroEndocrine Tumour registry (SwissNET). SwissNET is a national registry, which has prospectively included patients with a NET from all regions of Switzerland since 2008. RESULTS The registry includes 1366 patients; 1063 had documented therapies after the main diagnosis and were included in the analysis. The median follow-up time was 1.86 years. The most common primary site was the small intestine (291 patients, 27%) followed by pancreas (254 patients, 24%), lung (172 patients, 16%) and appendix (163 patients, 15%). A total of 167 different therapy sequences were observed. In 708 (67%) patients, surgery was the only treatment. The sequence of surgery followed by chemotherapy was most frequently documented in poorly (G3) differentiated (24 patients, 60%) and pancreatic (15 patients, 34%) NETs. Tumours treated with surgery followed by biotherapy or followed by peptide receptor radionuclide therapy (PRRT) were predominantly well-differentiated G1 NETs of the small intestine. In patients who were treated with either PRRT or systemic therapy (chemotherapy or molecular therapy) or both, PRRT was used more frequently than systemic therapy in patients with a small intestinal NET (35 patients, 62% vs 30, 54%), whereas the opposite held true in pancreatic (44 patients, 59% vs 56, 70%) and lung NETs (6 patients, 14% vs 40, 97%). If both chemotherapy and molecular therapy were used, chemotherapy was applied prior to molecular therapy in 13 of 19 (68%) patients with a pancreatic NET. CONCLUSION Surgery represents the treatment of choice in most patients with a NET irrespective of tumour stage. In patients receiving additional treatment, an impressive variety of treatment sequences were documented. In small intestinal NETs, patients received PRRT more often than chemotherapy, whereas the opposite holds true for patients with pancreatic and lung NETs.

CD8+ T cell immunosurveillance is crucial in solid tumors and T cell dysfunction leads to tumor progression. In contrast, the role of CD8+ T cells in the control of leukemia is less clear. We characterized the molecular signature of leukemia stem/progenitor cells (LSPCs) and paired CD8+ T cells in patients with acute myeloid leukemia (AML). Epigenetic alterations via histone deacetylation reduced the expression of immune-related genes in bone marrow (BM)-infiltrating CD8+ T cells. Surprisingly, a silenced gene expression pattern in CD8+ T cells significantly correlated with an improved prognosis. To define interactions between CD8+ T cells and LSPCs, we performed comprehensive correlative network modeling. This analysis indicated that CD8+ T cells contribute to the maintenance/expansion of LSPCs, particularly in favorable risk AML. Functionally, CD8+ T cells in favorable AML induced the expansion of LSPCs by stimulating the autocrine production of important hematopoietic cytokines such as interleukin (IL)-3. In contrast, LSPCs in aggressive AML were characterized by a higher activation of stemness/proliferation-related pathways and develop independent of BM CD8+ T cells. Overall, our study indicates that CD8+ T cells support and expand LSPCs in favorable risk AML whereas intermediate and adverse risk AML possess the intrinsic molecular abnormalities to develop independently.

Co-stimulatory signals, cytokines and transcription factors regulate the balance between effector and memory cell differentiation during T cell activation. Here, we analyse the role of the TRAF2-/NCK-interacting kinase (TNIK), a signaling molecule downstream of the tumor necrosis factor superfamily receptors such as CD27, in the regulation of CD8+ T cell fate during acute infection with lymphocytic choriomeningitis virus. Priming of CD8+ T cells induces a TNIK-dependent nuclear translocation of β-catenin with consecutive Wnt pathway activation. TNIK-deficiency during T cell activation results in enhanced differentiation towards effector cells, glycolysis and apoptosis. TNIK signaling enriches for memory precursors by favouring symmetric over asymmetric cell division. This enlarges the pool of memory CD8+ T cells and increases their capacity to expand after re-infection in serial re-transplantation experiments. These findings reveal that TNIK is an important regulator of effector and memory T cell differentiation and induces a population of stem cell-like memory T cells., Coordinate expression of multiple factors play critical roles in the regulation between effector and memory CD8+ T cell differentiation. Here the authors show upon acute viral infection TNIK is critically required as a regulator of effector and memory T cell differentiation.

Glioblastoma multiforme (GBM) is the most prevalent primary malignant brain tumor, which has an aggressive phenotype and mostly fatal recurrence after standard therapy. MET, the hepatocyte growth factor (HGF) receptor is a relevant target for GBM treatment as it is expressed in up to 50% of cases and its expression, which may be induced by radiation therapy (RT), can potentially contribute to RT-resistance of GBM stem cells, and tumor recurrence. MET-based chimeric antigen (CAR) T cell therapy is currently being evaluated in several solid tumor working settings. A combination of T cell-based therapies with RT may improve the efficacy of the CAR T cell therapy through by the RT-induced immune activation via release of cytokines and induction of antigen expression, similarly as has been observed when combining RT with immune checkpoint inhibitors. Here we investigated the combination of MET-targeting CAR T cells with RT for GBM treatment, hypothesizing enhanced anti-tumor effects. The current study used a panel of MET-proficient and MET-deficient human GBM and GBM stem-like cell lines. Cells have been irradiated with a single dose of 0, 2, 5, or 10 Gy and RT impact on MET expression has been assessed at various time points after RT administration. Results show MET increase after RT in some cell lines. To test MET-targeting CAR T effect on the GBM cell lines, CAR constructs that are based on HGF-MET binding elements have been introduced into virus-producing cells and used for human T cells transduction to generate MET-targeting CAR T cells. CAR T cells co-cultured with GBM cell lines in vitro have specifically and significantly decreased viability of MET-positive cancer cells. Data resulting from combination of RT and CAR T cells treatment suggest that radiation exhibits an enhancement of CAR T cells anti-tumor killing activity, indicating a synergism between the two modalities. In conclusion, our data are the first to indicate the efficacy of a MET-based CAR T immunotherapy approach in GBM cell lines. The results also demonstrate a basis for the combination of a MET CAR T modality together with RT. The mechanisms for understanding the interaction between RT and the MET CAR T cells are under investigation. Citation Format: Lusine Hovhannisyan, Daniel M. Aebersold, John Maher, Adrian F. Ochsenbein, Carsten Riether, Michaela Medova, Yitzhak Zimmer. Radiation therapy enhances anti-tumor activity of a MET CAR T-based immunotherapy approach for glioblastoma multiforme [abstract]. In: Proceedings of the AACR Virtual Special Conference on Radiation Science and Medicine; 2021 Mar 2-3. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(8_Suppl):Abstract nr PO-039.

Riether et al. show that CD70/CD27 signaling activates stem cell gene expression programs in acute myeloid leukemia (AML). Blocking the CD70/CD27 interaction inhibits self-renewal and induces differentiation of AML blasts and stem/progenitor cells., Aberrant proliferation, symmetric self-renewal, increased survival, and defective differentiation of malignant blasts are key oncogenic drivers in acute myeloid leukemia (AML). Stem cell gene signatures predict poor prognosis in AML patients; however, with few exceptions, these deregulated molecular pathways cannot be targeted therapeutically. In this study, we demonstrate that the TNF superfamily ligand–receptor pair CD70/CD27 is expressed on AML blasts and AML stem/progenitor cells. CD70/CD27 signaling in AML cells activates stem cell gene expression programs, including the Wnt pathway, and promotes symmetric cell divisions and proliferation. Soluble CD27, reflecting the extent of CD70/CD27 interactions in vivo, was significantly elevated in the sera of newly diagnosed AML patients and is a strong independent negative prognostic biomarker for overall survival. Blocking the CD70/CD27 interaction by mAb induced asymmetric cell divisions and differentiation in AML blasts and AML stem/progenitor cells, inhibited cell growth and colony formation, and significantly prolonged survival in murine AML xenografts. Importantly, hematopoietic stem/progenitor cells from healthy BM donors express neither CD70 nor CD27 and were unaffected by blocking mAb treatment. Therefore, targeting CD70/CD27 signaling represents a promising therapeutic strategy for AML.

9016 Background: For patients (pts) with resectable stage IIIA(N2) non-small cell lung cancer (NSCLC) neoadjuvant chemotherapy (chemo) with 3 cycles cisplatin (cis)/docetaxel (doc) followed by surgery is an accepted standard of care leading to a 1-year (yr) event-free survival (EFS) of 48% and a 5-yr overall survival (OS) of 37%. PD-1/PD-L1 inhibitors have recently shown to lead to high response rates in resectable NSCLC. Methods: SAKK 16/14 is an open-label single-arm phase II study including 68 pts with resectable NSCLC stage IIIA(N2) (T1-3 N2 M0), irrespective of histological subtype, genomic aberrations or PD-L1 expression status. Neoadjuvant treatment consisted of 3 cycles of cis 100 mg/m2 and doc 85 mg/m2 q3w followed by 2 cycles of durvalumab 750 mg q2w. Durvalumab was continued after surgery q2w for 1 yr. The primary endpoint is EFS at 1 yr. The statistical hypothesis is to improve EFS at 1 yr from 48% based on the SAKK 16/00 study to 65%. Here, we report the primary endpoint and response data from 67 evaluable pts included in the study. Results: 68 pts were included from 06/16 to 01/19 and 67 pts (35 males, 32 females) were evaluable. Median age was 61 yrs (range, 41-74). 52 pts (77.6%) had a WHO PS of 0. 95.5% were current or former smokers. The majority of tumors were adenocarcinoma (55.2%) followed by squamous cell histology (32.8%). Clinical stage T1, T2 and T3 were present at diagnosis in 22.4%, 49.3% and 28.4%, respectively. 81.1% of pts underwent resection. The main reason for not undergoing surgery was disease progression (33.3%). Pneumonectomy was performed in 5 pts (9.1%), 43 pts underwent lobectomy and 7 pts bilobectomy. 30-day postoperative mortality was observed in one patient (1.8%). One patient died due to a bleeding complication after surgery most likely not related to neoadjuvant therapy. Radiographic response was 44.8% (95%CI: 32.6-57.4) after neoadjuvant chemo and 59.7% (95%CI: 46.4-71.9) after additional neoadjuvant immunotherapy. 1-yr EFS was 73.3% (90%CI: 62.5-81.4). Results for pathologic remission rate as well as correlation with PD-L1 status will be presented during the meeting. Conclusions: We report on treatment outcomes of the largest cohort of pts with resectable stage IIIA(N2) NSCLC receiving perioperative immune checkpoint inhibitor therapy. The addition of perioperative durvalumab to standard of care cis/doc is safe and leads to a high response rate and a very encouraging 1-yr EFS rate that appears substantially higher than with chemo alone. Clinical trial information: NCT 02572843.

2520 Background: Bevacizumab failed to demonstrate overall survival benefit despite markedly prolonged progression-free survival in glioblastoma patients. Reasons for this divergence may include suboptimal patient selection and delayed diagnosis of progression on MRI scans under bevacizumab. Imaging analyses of retrospective and uncontrolled clinical trial cohorts suggest MRI diffusion mapping as a predictor of benefit from bevacizumab. Moreover, amino acid PET has been proposed by the RANO working group for the differentiation of tumor versus edema or gliosis based on proof-of-principle studies demonstrating earlier detection of progression with PET compared to MRI. Methods: ARTE (NCT01443676) was a 2:1 randomized, multi-center, open-label trial of hypofractionated radiotherapy in combination with intravenous bevacizumab every 2 weeks (BEV/RT) versus RT alone in patients with newly diagnosed glioblastoma aged 65 years or older. Patients with histologically and molecularly confirmed IDH wildtype glioblastoma aged 65 years or older were analyzed. MRI was available from 67 and serial 18FET PET from 30 patients in this post hoc analysis. 18FET PET intensity ratios and herein reported MRI parameters including tumor volumetric analyses and ADC were analyzed blinded for outcome and study arm. Results: Demographic, clinical and molecular parameters were balanced between treatment arms. Overall survival benefit from bevacizumab was observed for larger contrast-enhancing tumor volumes (hazard ratio [HR] per cm3 0.94, 95% CI 0.89-0.99, p = 0.032) and higher ADC (HR 0.18, 95% CI 0.05-0.66, p = 0.025) on pre-treatment MRI. Response in the BEV/RT arm by the standard MRI-based RANO criteria was associated with overall survival by trend (HR 0.56, 95% CI 0.30-1.10, time-dependent p = 0.094). In a multivariate model controlling for established risk factors, 18FET tumor-to-brain uptake ratios (TBR) of non-contrast-enhancing tumor portions predicted inferior overall survival specifically in the BEV/RT arm (HR [per 0.1 18FET TBR] 1.50, 95% CI 1.05-2.13, time-dependent p = 0.025). Controlling for 18FET TBR at first follow-up identified benefit from BEV/RT by trend (HR 0.41, 95% CI 0.16-1.07, p = 0.069). Conclusions: Large contrast-enhancing tumor mass and high ADC identify patients with overall survival benefit from bevacizumab. Under bevacizumab, non-contrast enhancing tumor portions can be adequately monitored by amino acid PET.

Introduction: Long-term data on outcomes of operable stage III NSCLC are scarce. Methods: Individual patient data from 368 patients enrolled in one phase III and two phase II trials were pooled and outcomes after applying the eighth (denoted with an asterisk [*]) versus the sixth TNM staging edition were compared. Patients were treated with either preoperative radiotherapy following 3 cycles of induction chemotherapy (trimodal) or neoadjuvant chemotherapy alone (bimodal). Results: With the sixth version, the 5- and 10-year survival rates were 38% and 28% for stage IIIA, respectively, and 36% and 24% for stage IIIB, respectively. Factors associated with improved 5-year overall survival were younger age, R0 resection, and pathologic complete remission (pCR) (p = 0.043, p < 0.001 and p = 0.009). With the eighth TNM staging version, 162 patients were moved from stage IIIA to IIIB*. The 5- and 10-year survival rates were 41% and 29% for stage IIIA*, respectively, and 35% and 27% for stage IIIB* patients, respectively. There was no difference in the bi- versus trimodal group with regard to median overall survival (28 months [95% confidence interval (CI): 21-39 months] and 37 months [95% CI: 24-51 months], p = 0.9) and event-free survival (12 months [95% CI: 9-15 months] versus 13 months [95% CI: 10-22 months], p = 0.71). Conclusions: We showed favorable 10-year survival rates of 29% and 27% in stage IIIA* and IIIB*, respectively. Younger age, R0 resection, and pathologic complete response were associated with improved long-term survival. Outcomes using the sixth versus eighth edition of the TNM classification were similar in operable stage III NSCLC.

An understanding of natural killer (NK) cell physiology in acute myeloid leukemia (AML) has led to the use of NK cell transfer in patients, demonstrating promising clinical results. However, AML is still characterized by a high relapse rate and poor overall survival. In addition to conventional NKs that can be considered the innate counterparts of CD8 T cells, another family of innate lymphocytes has been recently described with phenotypes and functions mirroring those of helper CD4 T cells. Here, in blood and tissues, we identified a CD56(+) innate cell population harboring mixed transcriptional and phenotypic attributes of conventional helper innate lymphoid cells (ILCs) and lytic NK cells. These CD56(+) ILC1-like cells possess strong cytotoxic capacities that are impaired in AML patients at diagnosis but are restored upon remission. Their cytotoxicity is KIR independent and relies on the expression of TRAIL, NKp30, NKp80, and NKG2A. However, the presence of leukemic blasts, HLA-E–positive cells, and/or transforming growth factor-β1 (TGF-β1) strongly affect their cytotoxic potential, at least partially by reducing the expression of cytotoxic-related molecules. Notably, CD56(+) ILC1-like cells are also present in the NK cell preparations used in NK transfer–based clinical trials. Overall, we identified an NK cell–related CD56(+) ILC population involved in tumor immunosurveillance in humans, and we propose that restoring their functions with anti-NKG2A antibodies and/or small molecules inhibiting TGF-β1 might represent a novel strategy for improving current immunotherapies.

CD8

Summary Background Postoperative hemithoracic radiotherapy has been used to treat malignant pleural mesothelioma, but it has not been assessed in a randomised trial. We assessed high-dose hemithoracic radiotherapy after neoadjuvant chemotherapy and extrapleural pneumonectomy in patients with malignant pleural mesothelioma. Methods We did this phase 2 trial in two parts at 14 hospitals in Switzerland, Belgium, and Germany. We enrolled patients with pathologically confirmed malignant pleural mesothelioma; resectable TNM stages T1–3 N0–2, M0; WHO performance status 0–1; age 18–70 years. In part 1, patients were given three cycles of neoadjuvant chemotherapy (cisplatin 75 mg/m 2 and pemetrexed 500 mg/m 2 on day 1 given every 3 weeks) and extrapleural pneumonectomy; the primary endpoint was complete macroscopic resection (R0–1). In part 2, participants with complete macroscopic resection were randomly assigned (1:1) to receive high-dose radiotherapy or not. The target volume for radiotherapy encompassed the entire hemithorax, the thoracotomy channel, and mediastinal nodal stations if affected by the disease or violated surgically. A boost was given to areas at high risk for locoregional relapse. The allocation was stratified by centre, histology (sarcomatoid vs epithelioid or mixed), mediastinal lymph node involvement (N0–1 vs N2), and T stage (T1–2 vs T3). The primary endpoint of part 1 was the proportion of patients achieving complete macroscopic resection (R0 and R1). The primary endpoint in part 2 was locoregional relapse-free survival, analysed by intention to treat. The trial is registered with ClinicalTrials.gov, number NCT00334594. Findings We enrolled patients between Dec 7, 2005, and Oct 17, 2012. Overall, we analysed 151 patients receiving neoadjuvant chemotherapy, of whom 113 (75%) had extrapleural pneumonectomy. Median follow-up was 54·2 months (IQR 32–66). 52 (34%) of 151 patients achieved an objective response. The most common grade 3 or 4 toxic effects were neutropenia (21 [14%] of 151 patients), anaemia (11 [7%]), and nausea or vomiting (eight [5%]). 113 patients had extrapleural pneumonectomy, with complete macroscopic resection achieved in 96 (64%) of 151 patients. We enrolled 54 patients in part 2; 27 in each group. The main reasons for exclusion were patient refusal (n=20) and ineligibility (n=10). 25 of 27 patients completed radiotherapy. Median total radiotherapy dose was 55·9 Gy (IQR 46·8–56·0). Median locoregional relapse-free survival from surgery, was 7·6 months (95% CI 4·5–10·7) in the no radiotherapy group and 9·4 months (6·5–11·9) in the radiotherapy group. The most common grade 3 or higher toxic effects related to radiotherapy were nausea or vomiting (three [11%] of 27 patients), oesophagitis (two [7%]), and pneumonitis (two [7%]). One patient died of pneumonitis. We recorded no toxic effects data for the control group. Interpretation Our findings do not support the routine use of hemithoracic radiotherapy for malignant pleural mesothelioma after neoadjuvant chemotherapy and extrapleural pneumonectomy. Funding Swiss Group for Clinical Cancer Research, Swiss State Secretariat for Education, Research and Innovation, Eli Lilly.

Background Most guidelines recommend at least 2-cm excision margin for melanomas thicker than 2 mm. Objective We evaluated whether 1- or 2-cm excision margins for melanoma (>2 mm) result in different outcomes. Methods This is a retrospective cohort study on patients with melanomas (>2 mm) who underwent tumor excision with 1-cm (228 patients) or 2-cm (97 patients) margins to investigate presence of local recurrences, locoregional and distant metastases, and disease-free and overall survival. Results In all, 325 patients with mean age of 61.84 years and Breslow thickness of 4.36 mm were considered for the study with a median follow-up of 1852 days (1995-2012). There was no significant difference in the frequency of locoregional and distant metastasis between the 2 groups ( P = .311 and .571). The survival analysis showed no differences for disease-free ( P = .800; hazard ratio 0.948; 95% confidence interval 0.627-1.433) and overall ( P = .951; hazard ratio 1.018; 95% confidence interval 0.575-1.803) survival. Limitations The study was not prospectively randomized. Conclusions Our study did not show any significant differences in important outcome parameters such as local or distant metastases and overall survival. A prospective study testing 1- versus 2-cm excision margin is warranted.

Hematopoiesis in patients with cancer is characterized by reduced production of red blood cells and an increase in myelopoiesis, which contributes to the immunosuppressive environment in cancer. Some tumors produce growth factors that directly stimulate myelopoiesis such as G-CSF or GM-CSF. However, for a majority of tumors that do not directly secrete hematopoietic growth factors, the mechanisms involved in the activation of myelopoiesis are poorly characterized. In this study, we document in different murine tumor models activated hematopoiesis with increased proliferation of long-term and short-term hematopoietic stem cells and myeloid progenitor cells. As a consequence, the frequency of myeloid-derived suppressor cells and its ratio to CD8+ T cells increased in tumor-bearing mice. Activation of hematopoiesis and myeloid differentiation in tumor-bearing mice was induced by TNFα, which was mainly secreted by activated CD4+ T cells. Therefore, the activated adaptive immune system in cancer induces emergency myelopoiesis and immunosuppression. Significance: These findings characterize a regulatory circuit linking activated T cells to suppression of tumor-specific immune responses, providing a conceptual advance in the understanding of emergency-hematopoiesis in cancer and opening new targets for therapeutic approaches.

Oncogenic KRAS mutations comprise the largest subset of lung cancer defined by genetic alterations, but in the clinic no targeted therapies are available that effectively control mutational KRAS activation. Consequently, patients with KRAS-driven tumors are routinely treated with cytotoxic chemotherapy, which is often transiently effective owing to development of drug resistance. In this study, we show that hyperactivated mammalian target of rapamycin (mTOR) pathway is a characteristic hallmark of KRAS-mutant lung adenocarcinoma after chemotherapy treatment, and that KRAS-mutant lung cancer cells rely on persistent mTOR signaling to resist chemotherapeutic drugs. Coherently, mTOR inhibition circumvents the refractory phenotype and restores sensitivity of resistant KRAS-mutant lung cancer cells to chemotherapy. Importantly, drug combinations of clinically approved mTOR inhibitors and chemotherapy drugs synergize in inhibiting cell proliferation of KRAS-mutant cancer cells in vitro and in vivo, and the efficacy of this combination treatment correlates with the magnitude of mTOR activity induced by chemotherapy alone. These results pinpoint mTOR as a mechanism of resistance to chemotherapy in KRAS-mutant lung cancer and validate a rational and readily translatable strategy that combines mTOR inhibitors with standard chemotherapy to treat KRAS-mutant adenocarcinoma, the most common and deadliest lung cancer subset.

Innate lymphoid cells (ILCs), defined as lineage negative (Lin−) CD127+ cells, have emerged as novel important immune effector cells, playing a critical role also in tumor immunosurveillance.1–5 Recently, it was shown that the number of ILCs in acute myeloid leukemia (AML) patients is significantly reduced after chemotherapy/radiotherapy as compared to healthy donors.6 However, so far, no data on ILC frequency, subset distribution and function in AML treatment naive patients are available. Therefore, we analyzed the frequency, subset distribution and function of ILCs in AML patients before any treatment, a parameter that is of paramount importance to understand the role of ILCs during leukemogenesis and to assess the impact of current treatments on these cells. ILCs are a novel family of lineage negative CD127+ innate immune cells belonging to the lymphoid lineage, yet not expressing rearranged antigen specific receptors. Instead, they are activated and regulated mainly by cytokine mediated signals. To date, three distinct subsets of ILCs have been described, based on their transcriptional regulation and cytokine profiles that mirror those of T-helper subsets: ILC1, expressing T-bet and producing IFN-γ and TNF-α, ILC2, expressing GATA-3 and secreting IL-4, -5, -13 and ILC3, expressing Rorγt and secreting IL-17A and/or IL-22.7,8 Although a population of ILCs CD127dim/− has recently been described,9 here we focused on circulating ILC populations that are CD127+ in peripheral blood (PB). We identified ILCs within the PB lymphocyte region by multicolor flow cytometry, on the basis of their forward (FSC) and side scatter (SSC) profiles (FSC low and SSC low) and by excluding from the analysis doublets (FSC H/FSC W dot plot, followed by SSC A/SSC W dot plot) and dead cells [positive for ViViD LIVE/DEAD fixable dead cell stain kit (LifeTechnologies)]. Total ILCs were gated as Lin−CD127+ cells. Subsequently, ILC1 were identified as CRTH2−cKit−CD56− cells, ILC2 as CRTH2+cKit+/− cells, ILC3 NCR+ as CRTH2−cKit+NKp46+ cells and ILC3 NCR− as CRTH2−cKit+NKp46− cells, as described by Spits et al.7 A minimum of 106 MNCs was acquired on a Gallios flow cytometer (Beckman Coulter). Data were analyzed using FlowJo™ software (TreeStar). Statistical analysis was performed using t-tests or ANOVAs. We compared the frequency of total ILCs in PB samples from 38 age- and sex-matched healthy subjects and 38 newly diagnosed AML patients [(median age 61, range 21–79; sex ratio (M:F) 21:17; primary AML 38 of 38 (100%); hyperleukocytosis 21 of 38 (55.3%); cytogenetic risk group: low 6 of 38 (15.8%), intermediate 22 of 38 (57.9%), high 10 of 38 (26.3%)]. All patients provided written informed consent (EMATC-2013-01 or approval by the local ethical committee of the Canton of Bern, Switzerland), and the research was conducted in accordance with the Declaration of Helsinki. Remarkably, we measured a highly significant reduction of circulating ILCs in patients at disease onset compared to controls both in percentage and absolute number (Figure 1A–C). Moreover, we found a positive correlation between the number of circulating ILCs and the percentage of circulating leukemic blasts (R2=0.3477, P=0.0031) (Figure 1D). Then, we analyzed the relative frequency of the different ILC subsets, characterized by the combination of surface marker expression detailed above and of specific transcription factors: T-bet for ILC1, GATA-3 for ILC2 and Rorγt for ILC3 (Figure 1E). Strikingly, we found a significant enrichment of ILC1 in AML patients and a concomitant profound reduction of ILC3 NCR+ cells. No differences were detectable in the levels of ILC2 and ILC3 NCR− cells (Figure 1F). No difference was observed either in the frequency of total circulating ILCs and in the distribution of the ILC subsets among the three cytogenetic risk groups (data not shown). In addition, since AML is a malignancy originating in the bone marrow (BM), we compared the frequencies of ILCs between paired BM and PB samples from 17 patients. We did not find any difference either in percentage of total ILCs (data not shown), or in the relative proportions of the different ILC subsets (Figure 1G), suggesting a similar composition of ILCs in BM and PB in AML patients at disease onset. To test the functionality of ILCs in terms of their capacity to produce type 1 (IFN-γ and TNF-α), type 2 (IL-5 plus IL-13) and type 3 (IL-17A and IL-22) cytokines, we stimulated MNCs with 1 μg/mL PMA plus 0.5 μg/mL Ionomycin, in the presence of BrefeldinA (Sigma-Aldrich), for 3 h and stained them for intracellular cytokine production. Following this direct ex vivo short-term activation, ILCs of AML patients were dramatically impaired in their production of IFN-γ, TNF-α as well as type 2 cytokines (e.g. IL-5/IL-13) as compared to ILCs of healthy subjects, while we found no difference in type 3 cytokines (e.g. IL-17A and IL-22) (Figure 2A and B). Moreover, in order to assess the role the ILCs might have in vivo, we used fresh PB of 4 newly diagnosed AML patients and, by adapting a method recently described,11 we isolated AML blasts from MNCs using a monoclonal antibody cocktail against CD14 and CD33 (Miltenyi). Then, we depleted the CD14−CD33− MNCs’ flow through fraction from CD4+ and CD8+ cells so as to obtain MNCs that are both depleted of leukemic cells, and enriched in ILCs. It was seen that ILC-enriched MNCs, of both healthy donors and leukemic patients, incubated with target cells (i.e. blasts) are able to produce cytokines in response to respectively allogeneic or autologous blasts (Figure 2C and D). Figure 1. Innate lymphoid cells frequency and subtypes in AML patients at diagnosis. Total circulating ILCs were identified as Lineage [(FITC-conjugated anti-CD3, anti-CD4, anti-CD14, anti-CD16, anti-CD19 (Beckman Coulter), anti-CD8, anti-CD15 (AbD Serotech), anti-CD20, ... Figure 2. Cytokine production by ILCs in AML patients at diagnosis. (A and B) MNCs were stimulated ex vivo for 3 h, then the intracellular staining was performed using PE-conjugated anti-IL-17A, PerCP-conjugated anti-IL-22, PE-Cy7-conjugated anti-IFN-γ, ... Even if we cannot exclude the involvement of alloreactivity in the recognition of leukemic blasts by ILCs from healthy donors, our data suggest that ILCs from AML patients could be impaired in the production of IFN-γ or type 2 cytokines in comparison to ILCs from healthy donors. Of note, the capacity of ILCs from AML patients to produce TNF-α in response to autologous blasts suggest that ILCs might be able to control, through the TNF-α/TNF-R1 pathway, the leukemic cell growth/survival.12 Finally, we compared the percentage of total circulating ILCs in AML patients (n=9) responding to standard chemotherapy (2 cycles of daunorubicin/cytarabine) with that of patients at diagnosis and of healthy donors [F (2, 82)=56.26; P

Blocking programmed cell death 1 in combination with adoptive cytotoxic T-cell transfer eradicates chronic myelogenous leukemia stem cells

The addition of bevacizumab to temozolomide-based chemoradiotherapy (TMZ/RT→TMZ) prolonged progression-free survival (PFS), but not overall survival (OS) in patients with newly diagnosed glioblastoma in two double-blind phase III trials. Elderly and frail patients are underrepresented in most clinical trials, but early reports of bevacizumab in glioblastoma suggested preferential benefit in this population. ARTE was a 2:1 randomized, multi-center, open-label trial of hypofractionated RT (40 Gy in 15 fractions) in combination with bevacizumab (10 mg/kg x 14 days) (arm A, N=50) versus RT alone (arm B, N=25) in patients with newly diagnosed glioblastoma aged >65 years. The primary endpoint was median OS. Quality of life (QoL) was monitored by the EORTC QLQ-C30/BN20 modules. Response was assessed by RANO criteria. Exploratory studies included 18F-fluoro-ethyltyrosine positron emission tomography (FET-PET, N=34), as well as whole methylome (N=57) and nanostring gene expression (N=54) analyses. Median PFS was longer in arm A versus arm B (7.6 vs. 4.8 months, p=0.003), but OS was similar (12.1 vs 12.2 months, p=0.8). Clinical deterioration was delayed and more patients came off steroids in arm A versus arm B. Longer PFS in arm A versus arm B was confined to the receptor tyrosine kinase (RTK) I methylation subtype and to the proneural gene expression subtype, but was not observed for patients with RTK II, classical or mesenchymal subtype glioblastoma. Applying a Cox model to OS that controlled for established prognostic factors, we detected an association with age and KPS. Exploration of imaging predictors of OS in this model identified the presence of non-enhancing tumor detected by FET-PET (HR 0.31, p=0.02) as an important prognostic factor. Efficacy outcomes and exploratory analyses of ARTE do not support the notion that bevacizumab generally prolongs survival in elderly glioblastoma patients. However, novel molecular and imaging biomarkers may identify patients with preferential benefit from bevacizumab.

The interaction of the tumor necrosis factor receptor (TNFR) CD27 with its ligand CD70 is an emerging target to treat cancer. CD27 signaling provides costimulatory signals to cytotoxic T cells but also increases the frequency of regulatory T cells. Similar to other TNFR ligands, CD70 has been shown to initiate intracellular signaling pathways (CD70 reverse signaling). CD27 is expressed on a majority of B-cell non-Hodgkin lymphoma, but its role in the immune control of lymphoma and leukemia is unknown. We therefore generated a cytoplasmic deletion mutant of CD27 (CD27-trunc) to study the role of CD70 reverse signaling in the immunosurveillance of B-cell malignancies in vivo. Expression of CD27-trunc on malignant cells increased the number of tumor-infiltrating interferon γ-producing natural killer (NK) cells. In contrast, the antitumoral T-cell response remained largely unchanged. CD70 reverse signaling in NK cells was mediated via the AKT signaling pathway and increased NK cell survival and effector function. The improved immune control by activated NK cells prolonged survival of CD27-trunc-expressing lymphoma-bearing mice. Finally, CD70 reverse signaling enhanced survival and effector function of human NK cells in a B-cell acute lymphoblastic leukemia xenotransplants model. Therefore, CD70 reverse signaling in NK cells contributes to the immune control of CD27-expressing B-cell lymphoma and leukemia.

Objectives Molecular subclassification of non small-cell lung cancer (NSCLC) is essential to improve clinical outcome. This study assessed the prognostic and predictive value of circulating micro-RNA (miRNA) in patients with non-squamous NSCLC enrolled in the phase II SAKK (Swiss Group for Clinical Cancer Research) trial 19/05, receiving uniform treatment with first-line bevacizumab and erlotinib followed by platinum-based chemotherapy at progression. Materials and methods Fifty patients with baseline and 24h blood samples were included from SAKK 19/05. The primary study endpoint was to identify prognostic (overall survival, OS) miRNA's. Patient samples were analyzed with Agilent human miRNA 8x60K microarrays, each glass slide formatted with eight high-definition 60K arrays. Each array contained 40 probes targeting each of the 1347 miRNA. Data preprocessing included quantile normalization using robust multi-array average (RMA) algorithm. Prognostic and predictive miRNA expression profiles were identified by Spearman's rank correlation test (percentage tumor shrinkage) or log-rank testing (for time-to-event endpoints). Results Data preprocessing kept 49 patients and 424 miRNA for further analysis. Ten miRNA's were significantly associated with OS, with hsa-miR-29a being the strongest prognostic marker (HR=6.44, 95%-CI 2.39–17.33). Patients with high has-miR-29a expression had a significantly lower survival at 10 months compared to patients with a low expression (54% versus 83%). Six out of the 10 miRNA's (hsa-miRN-29a, hsa-miR-542-5p, hsa-miR-502-3p, hsa-miR-376a, hsa-miR-500a, hsa-miR-424) were insensitive to perturbations according to jackknife cross-validation on their HR for OS. The respective principal component analysis (PCA) defined a meta-miRNA signature including the same 6 miRNA's, resulting in a HR of 0.66 (95%-CI 0.53–0.82). Conclusion Cell-free circulating miRNA-profiling successfully identified a highly prognostic 6-gene signature in patients with advanced non-squamous NSCLC. Circulating miRNA profiling should further be validated in external cohorts for the selection and monitoring of systemic treatment in patients with advanced NSCLC.

SummaryCytotoxic CD8+ T cells (CTLs) play a major role in host defense against intracellular pathogens, but a complete clearance of pathogens and return to homeostasis requires the regulated interplay of the innate and acquired immune systems. Here, we show that interferon γ (IFNγ) secreted by effector CTLs stimulates hematopoiesis at the level of early multipotent hematopoietic progenitor cells and induces myeloid differentiation. IFNγ did not primarily affect hematopoietic stem or progenitor cells directly. Instead, it promoted the release of hematopoietic cytokines, including interleukin 6 from bone marrow mesenchymal stromal cells (MSCs) in the hematopoietic stem cell niche, which in turn reduced the expression of the transcription factors Runx-1 and Cebpα in early hematopoietic progenitor cells and increased myeloid differentiation. Therefore, our study indicates that, during an acute viral infection, CTLs indirectly modulate early multipotent hematopoietic progenitors via MSCs in order to trigger the temporary activation of emergency myelopoiesis and promote clearance of the infection.

Introduction Acute myeloid leukemia (AML) is a very heterogeneous hematological malignancy characterized by the accumulation of myeloid blasts. Treatment options for unfit AML patients greater than 65 year of age are still limited and outcomes are dismal. The current standard of care for older AML patients are hypomethylating agents (HMA) or low dose Ara-C. However, even though inducing hematological remissions in up to 30 percent of the patients, responses are not durable and survival of these patients is only marginally prolonged. The poor durability is due to insufficient action on leukemia stem cells (LSC) which drive and maintain the disease and are resistance to therapy (Craddock et al, 2013 and DiNardo et al, 2019). We described how aberrant CD70/CD27 signaling drives stemness of AML LSCs and identified CD70 as potential new target for the treatment of AML patients (Riether et al, 2017). In a recent Phase 1 clinical trial, treatment of older and unfit AML patients with the ADCC-enhanced humanized monoclonal anti CD70 antibody (mAb) cusatuzumab in combination with HMA demonstrated promising clinical activity and a favorable tolerability profile. The BCL-2 antagonist, venetoclax, targets and eliminates LSCs by suppression of oxidative phosphorylation and demonstrated very promising activity in older AML patients in clinical phase I and II studies in combination with standard of care (Pollyea et al, 2018). However, even with novel agents such as venetoclax, there are still patients that become refractory or relapse. We hypothesized that combining venetoclax and cusatuzumab with distinct but complementary mechanisms of action could successfully eliminate LSCs. Experimental design To test this hypothesis, we performed a drug-combination study according to the Chou-Talalay method (Chou 2010) in CD70-expressing AML cell lines such as MOLM-13, MV4-11, and NOMO-1 cells in vitro. In addition, we tested the effect of the cusatuzumab/venetoclax and the cusatuzumab/venetoclax/HMA combination on colony formation and re-plating capacity of primary CD34+CD38- LSCs from newly diagnosed AML patients. Results We first treated MOLM-13, MV4-11, and NOMO-1 AML cells with vehicle, cusatuzumab alone or in combination with venetoclax or decitabine in a constant ratio in the presence of CFSE-labeled NK cells (ratio 1:1). AML cell numbers were assessed 72 hours later. Cusatuzumab in combination with venetoclax or decitabine and NK cells synergistically eliminated CD70-expressing AML cells in a broad dose range (Figure 1). To assess the effect of the cusatuzumab/venetoclax combination on primary human AML LSCs, we treated CD34+ CD38- LSCs with cusatuzumab or venetoclax monotherapy or in combination in the presence of NK cells and assessed colony formation. Cusatuzumab/venetoclax co-treatment was more efficacious than each monotherapy alone and strongly reduced LSCs and leukemia progenitors (Figure 2). To analyze the effect of the cusatuzumab/venetoclax treatment on LSC function in a more stringent way, we performed serial re-plating experiments in vitro. The impaired colony formation after combination treatment observed after the first plating was maintained during subsequent the re-plating, even though cusatuzumab and venetoclax were not present in the re-plating, indicating an effective reduction of LSCs. Mechanistically, we could show that treatment with venetoclax results in up-regulation of CD70 on LSCs, suggesting that venetoclax renders LSCs more susceptible to cytolytic killing with cusatuzumab. In older AML patients, cusatuzumab and venetoclax each have demonstrated promising clinical activity in combination with HMA. We determined whether addition of HMA to the cusatuzumab/venetoclax co-treatment could more effectively eliminate LSCs. The triplet combination cusatuzumab/venetoclax/decitabine did not further reduce growth of AML cell lines in vitro (Figure 1) nor colony and re-plating capacity of human LSCs compared to the cusatuzumab/venetoclax co-treatment. Conclusions Overall, these results indicate that a combination of cusatuzumab with venetoclax eliminates LSCs synergistically and more efficiently than as a monotherapy. Tolerability and efficacy will be tested in mouse models using both primary AML and cell line xenografts. The results suggest that targeting LSCs by combining venetoclax and cusatuzumab treatments is a promising novel treatment strategy in AML. Disclosures Johnson: Janssen R&D: Employment. Drenberg:Janssen R&D: Employment. Syed:Janssen R&D: Employment. Moshir:Argenx: Employment, Equity Ownership. Hultberg:Argenx: Employment. Leupin:Argenx: Employment, Equity Ownership, Patents & Royalties. De Haard:Argenx: Employment, Equity Ownership, Patents & Royalties.

Background: The introduction of BCR/ABL-specific tyrosine kinase inhibitors (TKIs) more than two decades ago revolutionized chronic myelogenous leukemia (CML) therapy. The majority of CML patients treated with TKIs obtain durable cytogenetic and molecular responses. However, only a subgroup of these patients can successfully discontinue TKI therapy and maintain a treatment-free remission (Laneuville et al. 2011). TKI-resistant leukemia stem cells (LSCs) persist in the majority of patients at low levels over a prolonged period. These quiescent, self-renewing LSCs in the BM are the major cause of relapse after drug discontinuation (Holyoake et al, 2017). The selective elimination of LSCs requires the definition of unique signaling pathways that promote self-renewal of LSCs but not of normal HSCs. Based on the documented expression of CD93 on LSCs (Kinstrie et al, 2015), the aim of the present study was to investigate the role of the cell surface receptor CD93 in the regulation of self-renewal of human and murine CML LSCs and its contribution to disease development and progression. Methods and Results: We found CD93 expression on LSCs and leukemia progenitor cells but not on more differentiated leukemia granulocytes in a murine retroviral lineage-negative Sca-1+ c-kit+ (LSK) transduction/transplantation CML model. Next-generation sequencing analysis revealed that Cd93-/- LSCs have a silenced gene expression signature particularly in genes involved in the regulation of gene expression, stem cell maintenance and proliferation. Out of the 1120 genes differentially expressed between BL/6 and Cd93-/- LSCs, 1108 genes were down-regulated. In contrast, naïve BL/6 and Cd93-/- hematopoietic stem cells (HSCs) did not display a dysregulation in these pathways. Functionally, CD93-deficiency in LSCs resulted in impaired self-renewal, reduced LSC frequencies in vitro (at least by a factor of 100, P To study whether CD93-signaling in LSCs relies on ligand-binding to the extracellular domain of CD93, we generated an extracellular domain deletion mutant of CD93 (mCd93intra). Comparable to transduction with full-length mCd93, the expression of Cd93intra restored colony formation of Cd93-/- LSCs in vitro, suggesting that the maintenance of LSC self-renewal is independent of ligand-binding to the extracellular domain of CD93. Furthermore, analysis of the sub-cellular localization of CD93 in CML cells using a lentiviral expression vector encoding for AcGFP1-N1-Cd93 demonstrated nuclear localization of the CD93 intracellular domain (ICD). SCY1 like pseudokinase 1 (SCYL1), a regulator of gene transcription, directly interacts with the highly charged juxta membrane domain of the cytoplasmic tail of CD93 (Bohlson et al, 2005). Silencing of Scyl1 significantly reduced colony formation of BL/6 but not Cd93-/- LSCs in vitro suggesting that the ICD of CD93 regulates gene transcription via Scyl1 in CML LSCs. To discover compounds that affect LSC function similarly as genetic CD93 blockade, we performed a compound screen using the FDA approved drug library V2. The antiemetic agent metoclopramide, which is widely used in clinical routine to reduce nausea in cancer patients, was one very promising candidate identified in the screen. Metoclopramide treatment reduced clonogenic potential of CD93-competent LSCs to comparable levels as CD93-deficient LSCs in vitro without further affecting colony formation of CD93-deficient LSCs. Analysis of LSCs from newly diagnosed CML patients similarly demonstrated that CD93-signaling induces the expression of genes associated with proliferation and stemness, resulting in an increased clonogenic potential in vitro. In addition, colony formation and re-plating capacity in semisolid cultures of human CD34+CD38- LSCs was significantly impaired by metoclopramide at a pharmacological concentration of 0.1mM compared to control treatment. Conclusions: Overall, these results indicate that CD93-siganling is an important regulator of stemness and proliferation of human and murine CML LSCs. Furthermore, this study identifies expression of CD93 by LSCs as promising novel target for the treatment of CML. Disclosures Baerlocher: Novartis: Research Funding.

Chronic myeloid leukemia (CML) is a typical stem-cell driven malignancy, driven by leukemia stem cells (LSCs). LSCs are resistant to conventional therapies. This resistance is mediated by cell-intrinsic mechanisms and interactions with the microenvironment. LSCs depend on signals from a specialized microenvironment, a so called niche, to maintain their stem cell characteristics. In CML the bone marrow (BM) as a niche is well-investigated and several therapeutic targets, which aim at LSCs by interrupting their interaction with the BM-niche are under investigation. However, even though splenomegaly is a hallmark of CML the contribution of the splenic microenvironment to CML development has not been studied so far. This project aims to investigate the role of the splenic microenvironment as an independent secondary LSC niche and its contribution to disease development. To induce a CML-like disease in mice we retrovirally transduced FACS-sorted Lineage- Sca-1+ cKit+ BM cells with pMSCV-p210BCR/ABL-IRES-GFP and injected the transduced cells into non-irradiated mice. To find out if the spleen contributes to disease development we induced CML in splenectomized and sham operated mice. Splenectomized mice survived significantly longer compared to sham operated controls (median survival 31 vs. 22 days; p=0.0006) with 20% of the splenectomized mice surviving longer than 90 days. Moreover, the number of LSCs in the BM of splenectomized mice was reduced 3.7-fold (p=0.002). Flowcytometric analysis of the spleen and BM compartments of CML bearing mice revealed that the majority of the leukemic stem and progenitor cells (LSPCs) were located in the spleen (19-fold more LSCs in the spleen; p =0.007). Moreover we found the leukemic compartment in the spleen to be enriched for LSPCs compared to the BM (20 % spleen vs. 10 % BM; % LSPCs of total leukemic cells; p=0.01). To confirm this phenotypic observation functionally we performed a limiting dilution transplantation of leukemic cells from spleen and BM. In line with the phenotypic observation we found a higher frequency of LSCs in the spleen compared to the BM (1/41'703 vs. 1/432'594; p=0.02). We next analyzed the gene expression of LSPCs from spleen and BM. We found that the gene expression profile of splenic LSPCs showed higher expression of stemness-related genes and reduced expression of myeloid differentiation genes compared to BM LSPCs, indicating that the spleen is more supportive of primitive LSPCs. Knowing that the spleen contributes to disease development by providing an alternate niche for LSCs we next analyzed the spleens using confocal microscopy. We found that the LSCs resided exclusively in the red pulp. Previous studies have shown that HSCs reside in direct contact with red pulp macrophages (RPMs) during extramedullary hematopoiesis (Dutta et al., JEM, 2015). In addition we found that in spleens from human CML patients CD34+ leukemia cells localized together with macrophages (p=0.001). Furthermore we could show that RPMs are capable of producing both SCF and G-CSF. To test the role of RPMs as a potential niche component in vitro we co-incubated LSCs and RPMs overnight before plating the LSCs in a colony formation assay. We found that the co-incubation with RPMs improved the colony formation capacity of LSCs (CFUs 166 vs. 138; p=0.0356). To test the role of RPMs in vivo we depleted macrophages in CML mice using clodronate liposomes. This resulted in significantly reduced splenomegaly (867mg vs. 249mg; p In summary, we found that the spleen provides an alternate niche for LSCs, thereby contributing to CML development. Compared to the BM niche the splenic niche is more supportive of primitive LSPCs, as shown by the higher frequency of LSCSs found in the spleen and the higher expression of stemness related genes in splenic LSCs compared to BM LSCs. Moreover we identified CD24low RPMs as a unique and central component of the splenic LSC niche. Even though we could show that RPMs are capable of producing SCF and G-CSF the exact mechanisms by which RPMs support LSCs remains to be investigated. Disclosures No relevant conflicts of interest to declare.