Leukemic Bone Marrow Cells Research Articles

Absence of the Shb gene in mixed-lineage leukemia MLL-AF9 cells increases latency in mice despite higher proliferation rates in vitro

Mixed lineage leukemia (MLL) arises from several KMT2A-gene chromosomal translocations. Shb gene deficiency has been found to exhibit pleiotropic effects in different models of leukemia, and consequently, this study aimed to investigate MLL-AF9-induced leukemia in Shb deficiency. Bone marrow cells from wild type and Shb knockout (KO) mice were transduced with the MLL-AF9 gene. Shb KO MLL-AF9 cells proliferated at an increased rate, exhibited altered expression of certain cytokine genes (Kitl, Csf3, IL6, IL1b) and higher expression of cell cycle genes (Ccnd2, Ccne1). Mice receiving Shb KO MLL-AF9 cells showed longer latency without displaying any difference in rates of leukemic cell proliferation, indicating a dichotomy between the in vitro and in vivo phenotypes. The mice with Shb deficient MLL-AF9 cells had a lower content of leukemic bone marrow cells allowing elevated normal hematopoiesis, explaining the longer latency. Finally, Shb knockout GFP-positive bone marrow cells showed a higher percentage of cells expressing myeloid markers. The result suggests a role of Shb in the progression of leukemia and that the relevance of the Shb gene is context-dependent as inferred from the differences between the in vivo and in vitro responses. These findings help to obtain an increased understanding of human MLL-AF9 leukemia.

Interim Results of a Multicenter, Single-Arm Study to Assess Blinatumomab in Adult Patients (pts) with Minimal Residual Disease (MRD) of B-Precursor (BCP) Acute Lymphoblastic Leukemia (GMALL-MOLACT1-BLINA)

Interim Results of a Multicenter, Single-Arm Study to Assess Blinatumomab in Adult Patients (pts) with Minimal Residual Disease (MRD) of B-Precursor (BCP) Acute Lymphoblastic Leukemia (GMALL-MOLACT1-BLINA)

Overcoming NOTCH1-Driven Chemoresistance in T-Cell Acute Lymphoblastic Leukemia Via Metabolic Intervention with Oxphos Inhibitor

Overcoming NOTCH1-Driven Chemoresistance in T-Cell Acute Lymphoblastic Leukemia Via Metabolic Intervention with Oxphos Inhibitor

Clonal Hematopoiesis Drives Therapy-Related Myeloid Neoplasms Following Autologous Stem Cell Transplantation and Propagates during Disease Evolution

Introduction: Clonal hematopoiesis (CH) denotes somatic mutations in genes related to myeloid neoplasms present at any variant allele frequency (VAF). Clonal hematopoiesis increases the risk of cardiovascular disease, de novo myeloid neoplasms and therapy-related myeloid neoplasms (tMN). It is well established that CH can be detected years before disease onset. Furthermore, the impact of specific mutations with regards to progression from CH to tMN is currently being unraveled. When exposed to cytoreductive therapy, a proliferative advantage of stem cells with CH over normal hematopoietic stem cells (HSCs) has been demonstrated. However, it remains unclear whether CH is to be considered a mere tMN risk factor, or if the mutations directly impact or even drive the development of tMN. We hypothesized that CH contributes to the development of tMN, and pursued this by investigating the evolution of CH, present in patients with lymphoma and multiple myeloma, prior to autologous stem cell transplantation (ASCT) and at time of tMN diagnosis. Methods: Patients included were treated with ASCT at the Department of Hematology, Aarhus University Hospital, Denmark, between 1989 and 2016. Inclusion criteria were (i) treatment with ASCT on the indication of a non-myeloid primary disease; (ii) subsequent development of tMN, and (iii) available mononuclear cells (MNCs) at pre-ASCT and time of tMN. All tMN diagnoses were reviewed by an experienced pathologist. Data from time of ASCT of this cohort has previously been reported (Soerensen et al., 2020, PMID: 32150606). Twelve patients with available MNCs at both time points were identified out of 36 tMN patients. Samples (either leukapheresis products or bone marrow MNCs) were subjected to targeted next-generation sequencing, utilizing a 30-gene panel (Myeloid Tumor Solution, SOPHiA Genetics, Saint Sulpice, Switzerland). Variant exclusion criteria were (1) read depth < 3000; (2) VAF < 0.003; (3) variant location outside ±25 nucleotides of coding region; (4) indel present in homopolymeric stretch, and (5) potential germline variants at pre-ASCT with VAF > 0.95 or between 0.45 and 0.55, representing homo- and heterozygosity, and reported in the Exome Aggregation Consortium (ExAC) database. Results: The cohort included 12 patients with a median age at ASCT of 63 years (range 37-69) and male predominance (75%). Median time to tMN following ASCT was 3.9 years (range 0.7-15.3), with 7 patients developing therapy-related myelodysplastic syndrome and 5 therapy-related acute myeloid leukemia. A total of 36 and 38 mutations were detected at ASCT and tMN, respectively. Prior to ASCT, DNMT3A (39%) and TET2 (19%) were the most frequently mutated genes, whereas the mutational landscape at tMN proved to be more heterogenous, with TP53 (21%), DNMT3A (18%), RUNX1 (13%) and ASXL1 (13%) comprising the majority of mutated genes. Nine patients (75%) had one or more mutations that could be detected at pre-ASCT as well as at tMN. Seven patients (58%) had CH at pre-ASCT that were present at higher VAF (>0.15 VAF) in bone marrow samples at tMN. Of these, 6 patients had CH at VAF < 0.02 at baseline. We found a total of 14 mutations that were detected at both prior to ASCT and tMN diagnosis, distributed among TP53, SRSF2, DNMT3A, ASXL1, TET2, NRAS and EZH2. Importantly, all clones harboring mutations in non-DNMT3A genes expanded until diagnosis of tMN to VAF > 0.30, with the exception of TET2, which displayed only a modest increase in VAF from 0.01 to 0.15. Conclusion: In this cohort of patients treated with ASCT and who subsequently developed tMN, we found the majority of patients to harbor CH in HSCs pre-ASCT that, at time of tMN, completely dominated the malignant clone. Our data suggests both a persistency of CH identified in HSCs in peripheral blood prior to ASCT to the leukemic stem cells in bone marrow at tMN diagnosis, as well as an expansion of the clones over time. These findings provide evidence to support the emerging theories that tMNs are instigated by subsets of hematopoietic cells that gain malignant somatic mutations and drive the pathogenesis years before onset disease. Figure Disclosures No relevant conflicts of interest to declare.

After Treatment Decrease of Bone Marrow Tregs and Outcome in Younger Patients with Newly Diagnosed Acute Myeloid Leukemia.

An emerging body of evidence demonstrates that defects in antileukemic effector cells in patients with acute myeloid leukemia (AML) can contribute to the development and/or persistence of the disease. In particular, immune suppressive regulatory T cells (Tregs) may contribute to this defective antileukemic immune response, being recruited by bone marrow leukemic cells to evade immune surveillance. We evaluated Tregs (CD4+/CD45RA-/CD25high/CD127low), performing multiparametric flow cytometry on freshly collected bone marrow aspirate (BMA), in addition to the usual molecular and cytogenetic work-up in newly diagnosed AML patients to look for any correlation between Tregs and the overall response rate (ORR). We studied 39 AML younger patients (<65 years), all treated with standard induction chemotherapy. ORR (complete remission (CR)+CR with incomplete hematologic recovery (CRi)) was documented in 21 out of 39 patients (54%); two partial responder patients were also recorded. Apart from the expected impact of the molecular-cytogenetic group (p = 0.03) and the NPM mutation (p = 0.05), diagnostic BMA Tregs did not show any correlation with ORR. However, although BMA Tregs did not differ in the study population after treatment, their counts significantly decreased in responder patients (p = 0.039), while no difference was documented in nonresponder ones. This suggested that the removal of Treg cells is able to evoke and enhance anti-AML immune response. However, the role of BMA Tregs in mediating immune system-AML interactions in the diagnostic and posttreatment phase should be confirmed in a greater number of patients.

Functional expression cloning of molecules inducing CD34 expression in bone marrow-derived stromal myofibroblasts

We have previously shown a fraction of stromal fibroblasts/myofibroblasts (Fibs) from leukemic bone marrow cells expresses leukemia-specific transcripts along with hematopoietic and Fib-related markers. Normal bone marrow-derived Fibs (nFibs) do not express CD34 or CD45; however, nFibs may express hematopoietic markers with some specific stimulations. CD34 expression was detected in nFib cultures following the addition of a culture supernatant of blood mononuclear cells stimulated with phytohemagglutinin (PHA)-P. To identify the molecules responsible for inducing CD34 expression in nFibs, cDNA clones were isolated using functional expression cloning with a library constructed from PHA-P-stimulated human blood mononuclear cells. Positive clones inducing CD34 transcription in nFibs were selected. We confirmed that an isolated positive cDNA clone encoded human interleukin (IL)-1 beta (β). CD34 expression was observed in the nFib cultures with recombinant human (rh) IL-1β protein. And CD34 transcription was suppressed when a rhIL-1β neutralizing antibody was added to the IL-1β-stimulated nFib cultures. nFibs expressed gp130 and IL-6 receptors, and CD45 expression was detected in nFibs cultured with rhIL-1β and rhIL-6. Chronic myelogenous leukemia (CML) cells reportedly respond well to IL-1β. When CML-derived Fibs were cultured with rhIL-1β and rhIL-6, CD45-positive cells increased in number. Cell fate may be influenced by an external specific stimulation without gene introduction.

Gamma-Delta CAR-T Cells Show CAR-Directed and Independent Activity Against Leukemia.

Autologous T cells engineered to express a chimeric antigen receptor (CAR) against the CD19 antigen are in the frontline of contemporary hemato-oncology therapies, leading to high remission rates in B-cell malignancies. Although effective, major obstacles involve the complex and costly individualized manufacturing process, and CD19 target antigen loss or modulation leading to resistant and relapse following CAR therapy. A potential solution for these limitations is the use of donor-derived γδT cells as a CAR backbone. γδT cells lack allogenecity and are safely used in haploidentical transplants. Moreover, γδT cells are known to mediate natural anti-tumor responses. Here, we describe a 14-day production process initiated from peripheral-blood mononuclear cells, leading to a median 185-fold expansion of γδ T cells with high purity (>98% CD3+ and >99% γδTCR+). CAR transduction efficacy of γδ T cells was equally high when compared to standard CAR-T cells (60.5 ± 13.2 and 65.3 ± 18.3%, respectively). CD19-directed γδCAR-T cells were effective against CD19+ cell lines in vitro and in vivo, showing cytokine production, direct target killing, and clearance of bone marrow leukemic cells in an NSG model. Multiple injections of γδCAR-T cells and priming of mice with zoledronate lead to enhanced tumor reduction in vivo. Unlike standard CD19 CAR-T cells, γδCAR-T cells were able to target CD19 antigen negative leukemia cells, an effect that was enhanced after priming the cells with zoledronate. In conclusion, γδCAR-T cell production is feasible and leads to highly pure and efficient effector cells. γδCAR-T cell may provide a promising platform in the allogeneic setting, and may target leukemic cells also after antigen loss.

Demographic and pattern of childhood acute leukemia in Duhok, Kurdistan region of Iraq, 2009-2018

Background and objectives: Leukemia is a common childhood cancer, constituting more than 25% in many pop- ulations. The most frequent type of childhood leukemia is acute lymphoblastic leukemia. The aim of this study is to describe the annual incidence, rate and demographics of acute childhood leukemia and their patterns in Duhok, Kurdistan - Iraq, in the period from 2009 to 2018. Methods:It is a retrospective study that was conducted at Heevi Pediatric Teaching Hospital in Duhok. A total of 198 patients, who were diagnosed as new cases of acute leukemia and were less than 15 years of age in the past ten years (from 2009 to 2018), were included in this study. Demographic data and the presenting hematological values of acute leukemia, based on cytomorphologic characteristics of bone marrow leukemic blast cells, were studies. Results: Childhood acute leukemia represented about 40 % of the total percentage of cancers among children in Duhok. It was more predominant in boys (53.5%) than in girls (46.5%). The cases peaked at 2-10 years cohort (69.2%). The number of cases ranged from 17 cases in 2009 to 15 cases in 2018 and reached a peak of 31 cases in 2016. The most prevalent type of leukemia was Acute Lymphoblastic Leukemia (ALL) (161 cases, 81.6%), followed by Acute Myeloid Leukemia (37 cases, 18.4%). The overall annual incidence rate was 2.0 cases /100,000 per year. The yearly incidence rates of leukemia were 1.3 – 2.4 cases /100,000. The highest incidence rate was in Duhok center (2.4 cases /100,000) and Zakho (2.3 cases /100,000); however, the least incidence rate was in Amedi (1.3 cases /100,000). The incidence of ALL appears to be nearly fourfold higher than the incidence of Acute Myeloid Leukemia in different areas of Duhok. Conclusions:It was found that childhood acute leukemia had lower prevalence in Duhok, and the clinical hematological features were similar to that of other studies.

Night Transplantation and Catecholamine Exposure Accelerates In Vivo Leukemia Development By Enhancing Bone Marrow Homing Capacity in Leukemic Cells

Xenografts in immune suppressed mice are routinely used for in vivostudies on human acute myeloid leukemia (AML). However, a significant proportion of primary AML samples (»50-60% of cases) were engrafting in mice with particularly latency. Here, we report that changing the transplantation time-point from day (5:00 pm) to night (4:00 am) accelerates the engraftment of human AML cells in NOD/SCID/IL2Rgnull(NSG) mice. Equal numbers of freshly thawed AML cells from the same donor (n=5 patients) were transplanted into sublethally irradiated gender-matched 6 to 8 weeks old mice at day or at night (n=3-5 mice per condition and patient). Transplanted mice were monitored for leukemic engraftment in peripheral blood (PB), bone marrow (BM) and other hematopoietic organs using flow cytometry and immunohistochemistry. Enhanced leukemic engraftment was observed in night vs. day transplanted mice for each AML case (Fig. A). Interestingly, in 2/5 samples, engraftment was exclusively detected with the night transplant condition. Limiting dilutions showed that night transplantation allows leukemia (Fig. B) induction from lower cell numbers. Results were confirmed in a syngeneic MLL-PTD/FLT3-ITD mouse leukemia model (Fig. C): mice analyzed at the same time-point after night versus day transplantation showed enhanced splenomegaly (401.2 mg vs. 234.5 mg, p&amp;lt;0.05, Fig. D) and abnormal blood counts (white blood cells numbers 55.41x109vs. 18.63x109, p&amp;lt;0.01). To explore underlying mechanisms, homing assays were performed with fluorescently labelled human AML cells injected via tail vein and analyzed 12 hours later. Significantly higher BM colonization was found with cells injected at night versus day times (0.31±0.09 vs. 0.13±0.18, p&amp;lt;0.001, n=7 AML patients, Fig. E). Intriguingly, mice transplanted at night showed stress-related behavioral abnormalities. We thus hypothesized that night transplantation induced catecholamine release may affect homing and leukemogenesis. ELISAs indeed revealed enhanced epinephrine levels in PB (318.00±12.96 vs. 122.20±47.11 ng/mL, p&amp;lt;0.001) and BM (21.08±1.04 vs. 13.50±3.57 ng/ml, p&amp;lt;0.05) of night vs. day transplanted animals. Adrenergic receptors have been previously described to express in BM cells, and to regulate hematopoietic stem and progenitor cells (HSPCs) mobilization, Here, we show that these pathways are also important during leukemogenesis. Blocking adrenergic signaling with the b1/2-blocker propranolol prior to night transplantation (10mg/kg, intraperitoneal (i.p.) injection, 1h pre-transplant) reduced homing (0.22±0.17 vs. 0.39±0.22% leukemic cells, p=0.09) and long-term engraftment (23±7.42 vs. 80.2±11.1% leukemic blasts in BM, p&amp;lt;0.0001), and enhanced survival (Fig. F) in NSG mice transplanted with human AML cells and in syngeneic murine leukemia models. Consistently, treatment of mice with epinephrine prior to transplantation (2mg/kg, i.p., 1h pre-transplant) enhanced homing (0.38±0.09 vs. 0.16±0.04%, p&amp;lt;0.0001) and accelerated long-term leukemia induction (12.49±5.23 vs. 4.43±3.6%, p&amp;lt;0.01).. Surprisingly, even though all our AML samples express the homing molecule CXCR4, blocking CXCR4 (anti-CXCR4 antibody, 50mM) prior to transplantation could not counteract epinephrine-driven homing (0.032±0.017 vs. 0.038±0.025% leukemic cells in BM, p=0.53), indicating that the stimulating effect of adrenergic signaling on homing was independent of the SDF1-CXCR4 axis. Notably, transplantations of healthy human cord-blood CD34+ HSPCs or of mouse BM Lin- cells revealed no difference in the hematopoietic reconstitution in night vs. day transplantations (Fig. G). This indicates that the observed mechanisms are leukemia specific. To explore further potential mechanisms, RNAseq was performed on MS-5 cells, a mouse stromal cell line, treated with either epinephrine or vehicle control. Preliminary analyses indicate upregulated vitamin D receptor (VDR) expression (log2FC=1.18, p=1.32x1012) as potentially involved in catecholamine-induced homing of leukemic cells. We conclude that enhanced catecholamine levels (e.g. induced by night transplantation) accelerate leukemia development from AML cells, by enhancing the homing of leukemic cells to BM niches via SDF1-CXCRR4 independent, leukemic specific mechanisms. Figure Disclosures No relevant conflicts of interest to declare.

First Line Treatment with Venetoclax and Ibrutinib Induction Followed By Obinutuzumab Intensification Exclusively in CLL/SLL Patients Not in Complete Remission and/or with Detectable Bone Marrow Minimal Residual Disease (NEXT STEP trial)

First Line Treatment with Venetoclax and Ibrutinib Induction Followed By Obinutuzumab Intensification Exclusively in CLL/SLL Patients Not in Complete Remission and/or with Detectable Bone Marrow Minimal Residual Disease (NEXT STEP trial)

A Case of Acute Lymphocytic Leukaemia with t(3;13) and Central Nervous System Leukemia after Allogenic Cord Blood Transplantation

Background: Acute lymphoblastic leukemia (ALL) is a neoplastic cancer characterized by clonal expansion of leukemic cells in lymph organs and bone marrow. Lots of kinds of different chromosomal translocation can be found in those leukemic cells. However, the role of the abnormal chromosomals and genes in leukemogenesis is not yet fully understood. Identifying new chromosomal translocation can facilitate a better understanding of pathogenesis of this disease. Case presentation: We report a rare case of acute lymphocytic leukaemia with t(3;13)(q29,q21). The patient was diagnosed pre-B-ALL with no abnormal chromosomal or gene fusion and achieved complete remission (CR) after induction chemotherapy. Ten months later, she relapsed in the consolidation with cytogenetics test showing 46,XX,t(3;13)(q29,q21). Given no CR after 2 chemotherapy regimens, she received salvage cord blood transplantation. Regular intrathecal methotrexate was applied to prevent central nervous system leukemia. Good graft-versus-leukemia (GVL) effect was induced by daily injection of low dose of IL-2 two months post transplantation. Minimal residual disease (MRD) negativity was maintained until central nervous system leukemia was found 8 months after transplantation. A whole exome sequencing was performed. Nine driver mutation genes and seven tumor genes were found. Conclusions: We highly suspect that the relapse in central nervous system after transplantation is associated with the rare chromosomal translocation. Disclosures No relevant conflicts of interest to declare.

Role of HDAC8 Upregulation in Resistance of FLT3-ITD AML Stem Cells to FLT3 Inhibitors

The FLT3-ITD mutation occurs in 25-30% of acute myeloid leukemia (AML) incidence, and is associated with higher relapse rate and inferior survival. FLT3 inhibitors have shown potent antileukemic effect, but the responses are not sustained in most FLT3-ITD AML patients. Histone deacetylases (HDACs) are crucial for cancer stem cell maintenance through epigenetically regulating gene expression, modulating the function of non-histone proteins via post-translational modification, and maintaining genome stability. Here we investigated the potential role of HDACs in FLT3 inhibitors resistance and FLT3-ITD AML stem cells maintenance. We firstly evaluated mRNA expression alterations of 11 HDACs in FLT3-ITD+ MV4-11 and MOLM-13 AML cells upon FLT3 inhibitor AC220 (Quizartinib) treatment, and found that HDAC8 was the most significantly upregulated gene. Inhibition of FLT3 signaling via siRNA-mediated knockdown of FLT3 also resulted in increased expression of HDAC8. Treatment of primary FLT3-ITD+ CD34+ AML cells with AC220 confirmed HDAC8 upregulation. Targeting HDAC8 using specific HDAC8 inhibitor 22d or knockdown of HDAC8 readily resulted in significant apoptosis of cell lines and primary AML samples, and inhibited colony growth and replating activity in primary FLT3-ITD+ CD34+ AML cells. Moreover, these antileukemic effects were even more pronounced upon 22d and AC220 combination. To explore the mechanism of HDAC8 mediated FLT3 inhibitor resistance, we investigated transcriptomic change of MV4-11 cells upon 22d treatment by RNA-seq. KEGG pathway analysis revealed that the p53 signaling pathway was significantly upregulated. Upstream regulator prediction by Ingenuity pathway analysis also showed p53 as the key activated upstream transcription factor. Western blot analysis on acetylated p53 (Lys382) demonstrated that targeting FLT3 signaling had little effect on the p53 acetylation, while suppression of HDAC8 markedly increased p53 acetylation, and this effect was even more significant when both FLT3 and HDAC8 were inhibited simultaneously. Knockdown of p53 could partially rescued FLT3-ITD AML cells from 22d and/or AC220 induced apoptosis, and offset the inhibitory effect on growth and colony formation. We next studied the mechanism of HDAC8 upregulation upon FLT3 signally inhibition. We found FOXO1 and FOXO3 (FOXOs) binding motifs in HDAC8 promoter. FLT3 signaling inhibition promoted the binding of FOXOs to HDAC8 promoter. Knockdown both FOXOs abrogated HDAC8 upregulation upon AC220 treatment, and caused growth inhibition and apoptosis of FLT3-ITD AML cells. Finally, to translate our experimental results into clinical usage, we tested the in vivo effect of 22d, AC220, and the combination of both on patient-derived xenograft (PDX) model engrafted with four primary FLT3-ITD AML samples. 22d or AC220 treatment reduced the percentage and total number of human CD45+ leukemic cells in murine bone marrow, and prolonged the survival of leukemic mice. The combination of 22d and AC220 significantly reduced AML cell engraftment compared with either 22d or AC220 alone, and further elongated the survival period. Human CD34+ cells in BM were markedly reduced in mice treated with 22d or AC220 alone, with further reduction seen in combination. Secondary transplantation of BM cells from mice receiving combination treatment resulted in significantly reduced engraftment compared with AC220 treatment alone, indicating reduced LSC capacity of residual cells. These results show that combination of 22d and AC220 enhances targeting of primitive AML stem cells in vivo. In conclusion, upon FLT3 inhibitor treatment, FLT3-ITD AML cells may upregulate the expression of HDAC8 through FOXOs activation, which in turn inhibit the function of tumor suppressor gene p53, and promote the maintenance of FLT3-ITD AML stem cells and drug resistance. Targeting FLT3 and HDAC8 simultaneously may be promising approach to eliminating FLT3-ITD AML stem cells, and to cure this subset of leukemia. Disclosures No relevant conflicts of interest to declare.

Heme Oxygenase-1 in Leukemia Cells Promotes Cancer Associated Fibroblasts Mediating Progression of Acute Lymphoblastic Leukemia

Backgroud and objective: Recurrence and resistance is still the biggest challenges for Acute lymphoblastic leukemia (ALL). In recent years, a new concept has been proposed that the interaction between bone marrow microenvironment and leukemia cells could reduce the sensitivity of leukemia cells to chemotherapy. As an important matric element of the bone marrow microenvironment, Cancerassociated fibroblasts (CAFs) can mediate changes in bone marrow microenvironment to promote tumor proliferation and infiltration, but its role in ALL has not been described. Heme Oxygenase-1 (HO-1) is a rate-limiting enzyme in the process of heme catabolism, which is highly expressed in leukemia cells and can promote chemo-resistance by regulating the preservation of hematopoietic stem progenitor cells in the bone marrow microenvironment according to the recent research. In this article, we explored that HO-1 may be a key factor for promoting cancer associated fibroblasts to mediated chemo-resistance of ALL in the bone marrow microenvironment. M ethods : For clinical sample analysis, Bone marrow nucleated cells of 16 ALL patients with complete remission (ALL-CR), 12 ALL with relapse/refractory (ALL-R/R) and 10 normal controls were btained from bone marrow puncture. The expression of HO-1 and CAFs markers which includes α-SMA, FAP and FSP-1 was examined by quantitative reverse transcription-PCR (RT-PCR) and Western blot. In vitro cell experiments, CAFs was obtained from transfusion of bone marrow-derived mesenchymal stem cells (BM-MSCs) with recombinant human TGF-β1 (rhTGF-β1) stimulating. We used ALL primary cells and ALL cell lines (Nalm-6/Super-B15) to culture alone or co-culture with CAFs to detect proliferation, apoptosis and cell cycle of leukemia cells. In addition, we transfected ALL cell lines by constructing siHO-1 lentiviral vector, and co-cultured with CAFs or cultured separately to detect the above index changes in leukemia cells. R esults : The expressions of α-SMA, FAP, FSP-1 and HO-1 were significantly higher in ALL-R/R patients than in ALL-CR group and normal control group (P&lt;0.05), which suggested that CAFs and HO-1 are closely related to recurrence and resistance of ALL. In vitro tests, after rhTGF-β1 stimulated BM-MSCs for 48h, the mRNA and protein expression levels of α-SMA, FAP and FSP-1 were significantly higher than those in BM-MSCs alone (P&lt;0.05), This step was used to obtain CAFs. Then proceed to CAFs and Nalm-6/Super-B15 cell lines or ALL primary cells co-cultured tests. Results showed that CAFs can enhanced the leukemia cells proliferation and decreased apoptosis, and leukemia cells arrested in the G0/G1 phase was increased. Interestingly, this effect could be decreased by silencing HO-1 expression in Nalm-6/Super-B15 cell lines, which suggested that HO-1 may be a key factor mediating the interaction between leukemia cells and CAFs in bone marrow microenvironment. Conclusion:As an important component of the bone marrow microenvironment, CAFs are closely related to the recurrence and resistance of ALL. HO-1 may be a key component mediating the interaction between CAFs and leukemia cells of ALL. This results may provide a new entry point for deepening the mechanism of ALL progression and finding more effective targeted therapies. But further in vitro and in vivo experiments are still needed for verification. Disclosures No relevant conflicts of interest to declare.

DNMT3A with Leukemia-Associated Mutations Directs Sensitivity to DNA Damage at Replication Forks

Mutations in the DNA methyltransferase 3A (DNMT3A) gene are recurrent in de novoacute myeloid leukemia (AML) and are associated with poor prognosis. Although studies demonstrated survival benefit of induction chemotherapy dose intensification, outcomes remain unsatisfactory in most patients due to advanced age, comorbidities, and hence inability to tolerate treatment. Clinical trials of low-intensity regimens combining cytarabine and cladribine, nucleoside analog chain terminators that stall DNA replication, appear to be safe and effective, and tend to particularly benefit patients with DNMT3Amutations. Consistently, we observe increased sensitivity to cytarabine, fludarabine, and cladribine in multiple cellular systems harboring mutant DNMT3Ain vitro (Figure 1A, B). Differential sensitivity to cytarabine was confirmed in normal and leukemic primary bone marrow cells derived from mice with and without Dnmt3a mutations ex vivo (Figure 1C). Dynamic chromatin organization plays a pivotal role in DNA-associated cellular processes including DNA replication and damage repair. We previously found altered chromatin remodeling in cells expressing mutant DNMT3A after genotoxic stress. Gene expression studies by us and others demonstrated negative enrichment of cell cycle related signatures including G2/M checkpoint adaptation, in cells with DNMT3A mutations. These signatures are implicated in DNA damage response and replication fork integrity and suggest sensitivity to replication stress. To investigate the mechanism of differential sensitivity to cytarabine-induced DNA damage, we overexpressed wildtype (WT) or R882 mutant (MUT) forms of DNMT3A in U2OS cells, a well-established model for DNA damage studies. Analysis of the DNA damage signaling proficiency in response to cytarabine revealed persistent intra-S phase checkpoint activation (phospho-CHK1), accompanied by accumulation of DNA damage visualized by γH2A.X foci and by Comet assay in the DNMT3A(mut) overexpression cells (Figure 1D). This damage was only partially resolved after drug had been removed and cells were allowed to repair the DNA (Figure 1E), and was carried through mitosis, resulting in increased rate of micronucleation.At the same time, DNMT3A mutant cells remained proficient in initiating homology-directed repair (HDR) and non-homologous end joining (NHEJ) pathways, evidenced by RAD51 and 53BP-1 foci formation, respectively. These data demonstrate enhanced sensitivity to cytarabine in cells expressing mutant DNMT3A is due to increased susceptibility to DNA damage during replication, rather than defects in double-strand DNA break repair. In support of this, cells with mutant DNMT3Awere characterized by accentuated replication stress as evidenced by high levels of phospho-RPA, which persisted after drug wash-out (Figure 1F). Consistently, DNMT3A-mutant cells treated with cytarabine were characterized by a higher number and a larger area of PCNA foci. Pulse-chase double-labeling experiments with EdU and BrdU after cytarabine wash-out demonstrated that while the overall kinetics of replication restart remained unchanged, cells with DNMT3A(mut) showed higher rate of fork collapse and increased reliance on latent replication origins (Figure 1G). Gene expression profiling by RNA-seq identified dysregulation of pathways associated with cell cycle progression, specifically G1/S phase transition, DNA replication, DNA integrity checkpoint, and chromatin. Our studies show cells with DNMT3A mutations have a defect in recovery from replication fork arrest and subsequent accumulation of unresolved DNA damage, which may have therapeutic tractability. These results demonstrate, in addition to its role in epigenetic control, DNMT3A contributes to preserving genome integrity during DNA replication and suggest that cytarabine-induced replication fork stalling may further synergize with other agents aimed at DNA damage and replication. Figure 1 Disclosures No relevant conflicts of interest to declare.

Both Arid1b and Arid2 Are Tumor Suppressors in MLL-AF9 Leukemogenesis

ATP-dependent chromatin remodeling complexes, including BAF (BRG1 associated factor) and PBAF (Polybromo-associated BRG1 associated factor), play major roles in development and disease. These complexes contain multiple subunits and utilize ATP to remodel nucleosomes and, as a result, affect downstream processes. Subunits of the BAF and PBAF complexes are frequently mutated in various cancers, including in acute myeloid leukemia. However, the role of distinct members of these complexes in leukemogenesis is poorly understood. BAF and PBAF complexes are distinguished from each other by unique AT-rich interacting domain (ARID) subunits, ARID1A/B and ARID2, respectively. Recently, Arid2 was suggested to have tumor suppressive functions in MLL-AF9 leukemogenesis, however the role of Arid1b is unknown. In this study, we further evaluated the tumor suppressor roles of Arid2 and Arid1b in MLL-AF9 leukemogenesis. To study the effect of the loss of Arid2 and Arid1b on MLL-AF9 leukemia in vitro, hematopoietic stem and progenitor cells from Arid1bfl/fl, Arid2fl/fl and wild type (control) mice were transformed by retroviral expression of MLL-AF9. Arid1b or Arid2 was then deleted by retroviral delivery of Cre-recombinase and cellular phenotypes were characterized by flow cytometry. In vitro characterization revealed Arid1b-/-and Arid2-/-MLL-AF9 cells have similar growth rates to control cells and no changes in cell cycle status and apoptosis. To study leukemogenesis in vivo, two hematopoietic specific conditional knockout mouse models, Vav1Cre, a constitutively active Cre-recombinase, and Mx1Cre, an inducible Cre-recombinase, were used. Primary and secondary transplant recipient mice were assessed for survival, disease burden, and leukemia stem cell frequency. In primary transplantation, leukemic initiation was not altered by the loss of the Arid2. Overall survival of primary recipients and disease burden in moribund mice (percentage of GFP positive MLL-AF9 cells in bone marrow/spleen and spleen weight) were similar to control counterparts. However, in limiting dilution secondary transplantation of Arid2fl/flVav1Cre (Arid2-/-) and wild type Vav1Cre (control) MLL-AF9, median survival of the Arid2-/- cohort decreased 1 to 2 weeks in comparison to the control cohort and there was a two-fold increase in leukemia initiating cell frequency upon deletion of Arid2. Together these results support the previous indication that Arid2 is a tumor suppressor in MLL-AF9 leukemic initiation. To gain insight into the function of Arid1b in MLL-AF9 leukemogenesis, we performed primary transplantation of Arid1bfl/flcells transduced with MLL-AF9. Our data showed that loss of Arid1b enhanced leukemic initiation in the MLL-AF9 leukemia model. One-month post induction with pIpC, Arid1bfl/fl Mx1Cre MLL-AF9 cells accumulated faster in the peripheral blood and primary recipients exhibited decreased median survival compared with wild type Mx1Cre controls. Percentage of GFP+ leukemia cells was higher in the spleen of moribund mice in the Arid1bfl/fl Mx1Cre cohort, compared with the control cohort. Taken together, our data suggests Arid1b, in addition to Arid2, acts as a potential novel tumor suppressor in MLL-AF9 leukemogenesis. To study the mechanism of Arid1b and Arid2's function in MLL-AF9 leukemogenesis, RNA-sequencing of leukemic bone marrow cells was conducted. Consistent with the previous study, Arid2 null leukemia cells had increased Gata2 expression and decreased p57 expression. Gene Set Enrichment Analysis of Arid1b null cells showed enrichment of oncogenic signatures including ATM, Cyclin D and macrophage development as potentially contributing to the underlying tumor suppressive mechanism of Arid1b. In summary, our study uncovered Arid1b, in addition to Arid2, as a potential novel tumor suppressor in MLL-AF9 leukemia. Our study, together with published studies on the requirement of other subunits (SMARCA4, SMARCD2 and DPF2) of the BAF and PBAF complexes in MLL-AF9 leukemia, reveal opposing roles of the components of the BAF and PBAF complexes in leukemogenesis, the mechanism of which require further investigation. Disclosures No relevant conflicts of interest to declare.

Immunoliposomes in Acute Myeloid Leukaemia Therapy: An Overview of Possible Targets and Obstacles.

Acute Myeloid Leukaemia (AML) is the neoplastic transformation of Hematopoietic Stem Cells (HSC) and relapsed disease is a major challenge in the treatment. Despite technological advances in the field of medicine and our heightened knowledge regarding the pathogenesis of AML, the initial therapy of "7+3" Cytarabine and Daunorubicin has remained mainly unchanged since 1973. AML is a disease of the elderly, and increased morbidity in this patient group does not allow the full use of the treatment and drug-resistant relapse is common. Nanocarriers are drug-delivery systems that can be used to transport drugs to the bone marrow and target Leukemic Stem Cells (LSC), conferring less side-effects compared to the free-drug alternative. Nanocarriers also can be used to favour the transport of drugs that otherwise would not have been used clinically due to toxicity and poor efficacy. Liposomes are a type of nanocarrier that can be used as a dedicated drug delivery system, which can also have active ligands on the surface in order to interact with antigens on the target cells or tissues. In addition to using small molecules, it is possible to attach antibodies to the liposome surface, generating so-called immunoliposomes. By using immunoliposomes as a drug-delivery system, it is possible to minimize the toxic side effects caused by the chemotherapeutic drug on healthy organs, and at the same time direct the drugs towards the remaining AML blasts and stem cells. This article aims to explore the possibilities of using immunoliposomes as a drug carrier in AML therapy. Emphasis will be on possible target molecules on the AML cells, leukaemic stem cells, as well as bone marrow constituents relevant to AML therapy. Further, some conditions and precautions that must be met for immunoliposomes to be used in AML therapy will be discussed.

Stromal cells downregulate miR-23a-5p to activate protective autophagy in acute myeloid leukemia

Complex molecular cross talk between stromal cells and the leukemic cells in bone marrow is known to contribute significantly towards drug-resistance. Here, we have identified the molecular events that lead to stromal cells mediated therapy-resistance in acute myeloid leukemia (AML). Our work demonstrates that stromal cells downregulate miR-23a-5p levels in leukemic cells to protect them from the chemotherapy induced apoptosis. Downregulation of miR-23a-5p in leukemic cells leads to upregulation of protective autophagy by targeting TLR2 expression. Further, autophagy inhibitors when used as adjuvants along with conventional drugs can improve drug sensitivity in vitro as well in vivo in a mouse model of leukemia. Our work also demonstrates that this mechanism of bone marrow stromal cell mediated regulation of miR-23a-5p levels and subsequent molecular events are relevant predominantly in myeloid leukemia. Our results illustrate the critical and dynamic role of the bone marrow microenvironment in modulating miRNA expression in leukemic cells which could contribute significantly to drug resistance and subsequent relapse, possibly through persistence of minimal residual disease in this environment.

Flow Cytometric Analysis of Mitochondrial Reactive Oxygen Species in Murine Hematopoietic Stem and Progenitor Cells and MLL-AF9 Driven Leukemia.

We present a flow cytometric approach for analyzing mitochondrial ROS in various live bone marrow (BM)-derived stem and progenitor cell populations from healthy mice as well as mice with AML driven by MLL-AF9. Specifically, we describe a two-step cell staining process, whereby healthy or leukemia BM cells are first stained with a fluorogenic dye that detects mitochondrial superoxides, followed by staining with fluorochrome-linked monoclonal antibodies that are used to distinguish various healthy and malignant hematopoietic progenitor populations. We also provide a strategy for acquiring and analyzing the samples by flow cytometry. The entire protocol can be carried out in a timeframe as short as 3-4 h. We also highlight the key variables to consider as well as the advantages and limitations of monitoring ROS production in the mitochondrial compartment of live hematopoietic and leukemia stem and progenitor subpopulations using fluorogenic dyes by flow cytometry. Furthermore, we present data that mitochondrial ROS abundance varies among distinct healthy HSPC sub-populations and leukemia progenitors and discuss the possible applications of this technique in hematologic research.

PB1659 WHOLE EXOME SEQUENCING IN ADULT PATIENT WITH PHILADELPHIA / BCR‐ABL1 POSITIVE ACUTE LYMPHOBLASTIC LEUKEMIA

Background:BCR‐ABL1 gene fusion is detected at approximately 20% of adult acute lymphoblastic leukemia (ALL). Patients with Philadephia (Ph) / BCR‐ABL1 positive are a high risk group that associated with poor prognosis and short duration remission. Patients showed markedly improved with introduction of tyrosine kinase inhibitor combined with chemotherapy regimen but a small fraction of these patients remain refractory and poor response to treatment.Aims:The aim of this study was to determine the somatic mutations profile using whole exome sequencing of patient with Ph‐positive ALL.Methods:DNA from matched tumour‐normal samples for four patients with Ph‐positive ALL was extracted from peripheral blood or bone marrow leukemia cells by QIAamp DNA Mini kit. The exome library was enriched using the Nextera Rapid Capture Expended Enrichement kit (Illumina, San Diego, CA) according to the manufacturer's protocol and were subsequently sequenced on Illumina HiSeq 2500 system. Somatic mutations were separated from germline variants using Genome Analaysis Toolkits (GATK) best practices filtering strategy.Results:We identified a total of 14,804 intragenic somatic mutations (range from 2,948 to 4,165 in each). Of these 760 variants were passed through the variant caller. Among them 462 were single nucleotide variants (SNVs) and 298 were insertion/deletions (InDels). Total of 48 common variants were observed but failed Mutect caller. Among SNVs, 110 variants were nonsynonymous, 46 synonymous, 6 stopgain, 3 unknown and majority 297 (64.3%) null variants. A total of 53 nonsynonymous SNVs and 14 InDeLs (8 were frameshift deletion, 5 frameshift insertion and one stopgain) were identified as possible pathogeneic variants. The identified mutation genes in this study mostly also found in other malignancies disease and two alteration genes MCM7 and STAT5 were found in disease progression of CML.Summary/Conclusion:We have sequenced the whole coding sequence of four Ph / BCR‐ABL1 positive ALLs and corresponding normal samples that allows us to overview of candidate gene in the coding regions that driving Ph‐positive ALL development and as well as enhanced our understanding of the candidate genes in diagnosis testing and prognostic prediction of adult ALLs patient.

PF156 SINGLE-CELL TRANSCRIPTIONAL HETEROGENEITY SUGGESTS NOVEL FINGERPRINT OF RELAPSE IN ACUTE MYELOID LEUKEMIA

Background: Some rare subgroups of leukemia cells harboring relapse-inducing genes were selected after chemotherapy. Tounravel intra-tumoral heterogeneity and selective drug-resistance, single-cell RNA sequencing (scRNA-seq) was already performed on many solid tumors and blood cancer to achieve the high-resolutiontranscriptome profiling on individual cells from a larger heterogeneous population. However,the comprehensive investigation on cancer heterogeneityduring cancer development at single-cell resolution is still rare. Aims: To identify diverse subsets and molecular characteristics of acute myeloid leukemia (AML) relapse Methods: Since single-cell suspension was obtainedfrom bone marrow of acute myeloid leukemia samples, we used the 10x GenomicsChromium platform to capture transcriptomes of singlecells on barcoded mRNA capture beadsfor massively parallel scRNA-seq. Data processing followed by the Cell Ranger software pipelineto demultiplex cellularbarcodes, and map reads to the genome and transcriptome hg38 using the STAR aligner. Uniquemolecular identifier (UMI) count matrix and quality control were performed using Seurat. The t-SNE map was calculated using Rtsne package Results: We analyzed transcriptome data from near 50K single leukemia bone marrow cells across 3 patients during newly diagnosed, complete remission and relapse stages. To define the landscape of cellular heterogeneity and its association with outcome in an unbiased manner, we performed unsupervised machine learning algorithm on near 50K single cells from leukemia bone marrow and identify one robust 14-cluster solution (from 0 to 13, Figure 1A) and the hallmark genes within each clusters (Figure 1B). The pattern exhibits distinct distribution on different stages (Figures 1C), indicating intra-tumoral heterogeneity during leukemia progression. Within cluster 0, the subgroups expressing such as LILRB2, TNFAIP2 or PTAFR were chemotherapy sensitive (Figure 2A). While the subgroups expressing such as APOC1, CDKN2A, KLF1 or GATA1 were chemotherapy resistant (Figure 2B). These chemotherapy resistant subgroups may play some key roles in leukemia relapse.Summary/Conclusion: We identify novel relapse subgroups in highly heterogeneous leukemia, which could not be found using traditional bulk RNA-seq.