Acute myeloid leukemia (AML) is a subset of leukemia that is characterized by the clonal expansion of cytogenetically and molecularly abnormal myeloid blasts. These blasts are highly proliferative accumulating in bone marrow and blood which leads to severe infections, anemia, and bone marrow failure. The poor prognosis of AML patients caused by the low tolerance to intensive chemotherapy has encouraged the pursuit of alternative therapeutic approaches. Differentiation therapy which involves the use of agents that can release the differentiation block in these leukemic blasts has emerged as a promising therapeutic approach. The use of All-trans retinoic acid (ATRA) represents a successful example of such an approach, nonetheless its efficacy is restricted to one subtype of AML. Efforts have been focused on finding differentiation agents which are effective for the other more common AML subtypes. Anti-CD44 targeted antibodies that activate the CD44 cell surface antigen are a promising candidate. Previous studies have shown that anti-CD44 treatment has been able to release the differentiation block in AML1 through AML5 subtypes. The exact mechanism by which anti-CD44 treatment is able to induce its effects has not been fully elucidated. Recent studies highlight the role that epigenetic mechanisms play during haematopoiesis and leukemogenesis and therefore, in this work we investigated the epigenetic mechanisms associated with anti-CD44 induced differentiation. Using AML cell lines from different subtypes, we demonstrated that anti-CD44-induced differentiation results in an extensive change of histone modification levels. We found that inhibiting enzymes responsible for the H3K9ac, H3K4me, H3K9me, and H3K27me modifications, attenuated the anti-proliferative and differentiation promoting effects of antic-CD44 treatment. Taken together, these data highlight the promising potential of using anti-CD44 as a therapeutic agent across multiple subtypes in AML

Newer biological treatment strategies have been developed in the last decade with some promising outcomes. Their safety, however, has been questioned lately with multiple reports of increased risk for malignancies and infectious complications. These reports render their use suboptimal. We report a 44-year-old woman receiving adalimumab (Humira®) for advanced juvenile rheumatoid arthritis who then developed acute myelogenic leukemia.

Acute myeloid leukemia (AML) is characterized by a blockage in the differentiation of myeloid cells at different stages. CD44-ligation using anti-CD44 monoclonal antibodies (mAbs) has been shown to reverse the blockage of differentiation and to inhibit the proliferation of blasts in most AML-subtypes. However, the molecular mechanisms underlying this property have not been fully elucidated. Here, we sought to I) analyze the effects of anti-CD44 mAbs on downstream signaling pathways, including the ERK1/2 (extracellular signal-regulated kinase 1 and 2) and mTOR (mammalian target of rapamycin) pathways and II) use state-of-the-art Nuclear Magnetic Resonance (NMR) technology to determine the global metabolic changes during differentiation induction of AML cells using anti-CD44 mAbs and other two previously reported differentiation agents. In the first objective (Chapter 4), our studies provide evidence that CD44-ligation with specific mAbs in AML cells induced an increase in ERK1/2 phosphorylation. The use of the MEK inhibitor (U0126) significantly inhibited the CD44-induced differentiation of HL60 cells, suggesting that ERK1/2 is critical for the CD44-triggered differentiation in AML. In addition, this was accompanied by a marked decrease in the phosphorylation of the mTORC1 and mTORC2 complexes, which are strongly correlated with the inhibition of the PI3K/Akt pathway. In the second objective (Chapter 5), 1H NMR experiments demonstrated that considerable changes in the metabolic profiles of HL60 cells were induced in response to each differentiation agent. These most notable metabolites that significantly changed upon CD44 ligation were involved in the tricarboxylic acid (TCA) cycle and glycolysis such as, succinate, fumarate and lactate. Therefore, we sought to analyze the mechanisms underlying their alterations. Our results revealed that anti-CD44 mAbs treatment induced upregulation in fumarate hydratase (FH) expression and its activity which was accompanied by a decrease in succinate dehydrogenase (SDH) activity. Interestingly, our results indicated that FH induced by anti-CD44 mAb is regulated through the activation of the ERK1/2 pathway. Therefore, our findings highlight new elements in support for the use of anti-CD44 mAbs in AML therapies and open new perspectives to use metabolic profiling as a tool to support the potential possibilities for the development of CD44-targeted therapy of AML.

Despite high remission rate in acute myeloid leukaemia (AML) after chemotherapy, relapse of the underlying disease remains a major challenge and one of the most frequent causes of treatment failure. In this study, the presence of leukaemiaassociated phenotypes (LAPs) was first studied retrospectively using our standard diagnostic protocol with 3-colour flow cytometry. LAPs were present in 54 (64%) of 84 AML patients analysed between 2002 to 2004. The presence of LAPs was correlated with failure to respond to induction chemotherapy (p <0.05) in univariate analysis. Presence of LAPs was shown to be an independent predictor for failure to respond to induction chemotherapy with a relative risk ratio of 1.6 (p < 0.05, 95% CI, 1.0-2.6) in multivariate analysis. Subsequently, in a prospective study, we used 5-colour multiparametric flow cytometry (MFC) for detection of LAPs to determine if LAPs could be detected in a greater proportion of leukaemic patients and minimal residual disease (MRD) detection could therefore be applied in more patients. In 54 consecutive, newly diagnosed AML patients from 2005 to 2007, LAPs were identified in 51 (94%). Thus, MRD studies were potentially applicable to virtually all patients. The sensitivity and specificity of MFC technique was improved by analysing 10 normal and 5 regenerating bone marrows (BM) for the presence of these LAPs and by determining maximum log difference (LD). CD7, CD19, CD2, CD11b and CD56 were the most sensitive and reliable markers for MRD studies. LAPs were rarely detected in either normal or regenerating BMs. Through dilutional experiments from 50% LAPs to 0.001%, it was determined that 1 leukaemic in 104 and 105 normal cells could be detected using the improved techniques. Of the 54 patients, 31 received chemotherapy, with 27 achieving complete remission (CR). Two were LAP negative and thus 25 were evaluable for MRD post induction and 22-post consolidation chemotherapy. Detection of MRD >0.15% was able to distinguish between two groups of patients according to relapse status. Although, the number of patients was small, detection of MRD post induction > 0.15% was shown to be an independent predictor of adverse prognosis for both relapse free survival (RFS) and overall survival (OS) in a multivariate analysis [p = 0.037 and 0.026, 95% CI (1.1-20.5 and 1.2-22.2), hazard ratio 4.7 and 5.2 respectively]. Post consolidation, there was a trend for patients with higher MRD values to show shorter RFS (p = 0.06). MFC using 5-colour allows us to detect LAPs in virtually all AML patients and our preliminary results suggest the technique is a suitable approach for MRD analysis. However, 5-colour MFC is technically challenging, resource intensive, and may not be feasible in a routine diagnostic laboratory. This led us to assess whether we could identify other potential markers for LAPs. Interleukin-3 alpha receptor- chain IL-3_ (CD123) has been suggested to be a marker of leukaemic stem cells (LSC). These cells are thought to be responsible for initiating and maintaining leukaemic cell growth post chemotherapy and hence to give rise to relapse of the disease. Therefore, we analysed 34 AML patients for expression of CD123 in the blast population and defined a population containing leukaemic stem cells using the immunophenotypic markers CD123+/CD34+/CD38-. Thirty-two (94%) of AML patients expressed CD123. We then used a molecular marker to determine whether CD123 expression was confined to the LSC. Thirtynine patients were screened for the presence of FMS-like tyrosine kinase 3 - internal tandem duplication (FLT3/ITD) as the most common molecular abnormality in AML patients. Of those, 12 (31%) were FLT3/ITD positive. In seven of them, CD34+/CD38-/CD123+ and CD34+/CD38-/CD123- populations were sorted to homogeneity by Fluorescence Activated Cell Sorting (BD FACSAriaTM Cell Sorter) and tested for FLT3/ITD. In six of seven patients with FLT3/ITD positive AML, we could not detect the mutation in the CD34+/CD38-/CD123- fraction, but the mutation was detected in the CD34+/CD38-/CD123+ fraction in all seven patients. This novel finding demonstrates that, the oncogenic event occurs in CD123 positive cells, thus supporting the concept that CD123 is a marker of the LSC in CD123 positive AML. This observation suggests novel treatment approaches employing surface marker CD123-targeting antibodies may be of use in the treatment of AML. In conclusion, we demonstrate that using five-colour MFC improves LAP detection in AML and enables MRD studies using immunophenotyping to be applied to virtually all AML patients. Additionally, it increases the sensitivity of the technique for detecting LAP populations. Moreover, evaluation of MRD post induction chemotherapy is the most sensitive time point for detection of MRD, with MRD levels >0.15% predicting relapse and worse prognosis. As an alternative to using individualised LAPs specific to each patient, CD34+/CD38-/CD123+ cells may in the future serve as a better marker for MRD studies. This marker identifies the putative LSC, which is responsible for regrowth of leukaemia and relapse of the disease. Thus, instead of looking at whole “blast” population which results in huge data analysis and interpretation for the different LAPs which may have different underlying biology, it may be more informative to look at the frequency of LSC after achieving CR using CD34+/CD38-/CD123+ as the single LAP for MRD studies. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1317088 / Thesis (Ph.D.) -- University of Adelaide, School of Medicine, 2008

Despite high remission rate in acute myeloid leukaemia (AML) after chemotherapy, relapse of the underlying disease remains a major challenge and one of the most frequent causes of treatment failure. In this study, the presence of leukaemiaassociated phenotypes (LAPs) was first studied retrospectively using our standard diagnostic protocol with 3-colour flow cytometry. LAPs were present in 54 (64%) of 84 AML patients analysed between 2002 to 2004. The presence of LAPs was correlated with failure to respond to induction chemotherapy (p <0.05) in univariate analysis. Presence of LAPs was shown to be an independent predictor for failure to respond to induction chemotherapy with a relative risk ratio of 1.6 (p < 0.05, 95% CI, 1.0-2.6) in multivariate analysis. Subsequently, in a prospective study, we used 5-colour multiparametric flow cytometry (MFC) for detection of LAPs to determine if LAPs could be detected in a greater proportion of leukaemic patients and minimal residual disease (MRD) detection could therefore be applied in more patients. In 54 consecutive, newly diagnosed AML patients from 2005 to 2007, LAPs were identified in 51 (94%). Thus, MRD studies were potentially applicable to virtually all patients. The sensitivity and specificity of MFC technique was improved by analysing 10 normal and 5 regenerating bone marrows (BM) for the presence of these LAPs and by determining maximum log difference (LD). CD7, CD19, CD2, CD11b and CD56 were the most sensitive and reliable markers for MRD studies. LAPs were rarely detected in either normal or regenerating BMs. Through dilutional experiments from 50% LAPs to 0.001%, it was determined that 1 leukaemic in 104 and 105 normal cells could be detected using the improved techniques. Of the 54 patients, 31 received chemotherapy, with 27 achieving complete remission (CR). Two were LAP negative and thus 25 were evaluable for MRD post induction and 22-post consolidation chemotherapy. Detection of MRD >0.15% was able to distinguish between two groups of patients according to relapse status. Although, the number of patients was small, detection of MRD post induction > 0.15% was shown to be an independent predictor of adverse prognosis for both relapse free survival (RFS) and overall survival (OS) in a multivariate analysis [p = 0.037 and 0.026, 95% CI (1.1-20.5 and 1.2-22.2), hazard ratio 4.7 and 5.2 respectively]. Post consolidation, there was a trend for patients with higher MRD values to show shorter RFS (p = 0.06). MFC using 5-colour allows us to detect LAPs in virtually all AML patients and our preliminary results suggest the technique is a suitable approach for MRD analysis. However, 5-colour MFC is technically challenging, resource intensive, and may not be feasible in a routine diagnostic laboratory. This led us to assess whether we could identify other potential markers for LAPs. Interleukin-3 alpha receptor- chain IL-3_ (CD123) has been suggested to be a marker of leukaemic stem cells (LSC). These cells are thought to be responsible for initiating and maintaining leukaemic cell growth post chemotherapy and hence to give rise to relapse of the disease. Therefore, we analysed 34 AML patients for expression of CD123 in the blast population and defined a population containing leukaemic stem cells using the immunophenotypic markers CD123+/CD34+/CD38-. Thirty-two (94%) of AML patients expressed CD123. We then used a molecular marker to determine whether CD123 expression was confined to the LSC. Thirtynine patients were screened for the presence of FMS-like tyrosine kinase 3 - internal tandem duplication (FLT3/ITD) as the most common molecular abnormality in AML patients. Of those, 12 (31%) were FLT3/ITD positive. In seven of them, CD34+/CD38-/CD123+ and CD34+/CD38-/CD123- populations were sorted to homogeneity by Fluorescence Activated Cell Sorting (BD FACSAriaTM Cell Sorter) and tested for FLT3/ITD. In six of seven patients with FLT3/ITD positive AML, we could not detect the mutation in the CD34+/CD38-/CD123- fraction, but the mutation was detected in the CD34+/CD38-/CD123+ fraction in all seven patients. This novel finding demonstrates that, the oncogenic event occurs in CD123 positive cells, thus supporting the concept that CD123 is a marker of the LSC in CD123 positive AML. This observation suggests novel treatment approaches employing surface marker CD123-targeting antibodies may be of use in the treatment of AML. In conclusion, we demonstrate that using five-colour MFC improves LAP detection in AML and enables MRD studies using immunophenotyping to be applied to virtually all AML patients. Additionally, it increases the sensitivity of the technique for detecting LAP populations. Moreover, evaluation of MRD post induction chemotherapy is the most sensitive time point for detection of MRD, with MRD levels >0.15% predicting relapse and worse prognosis. As an alternative to using individualised LAPs specific to each patient, CD34+/CD38-/CD123+ cells may in the future serve as a better marker for MRD studies. This marker identifies the putative LSC, which is responsible for regrowth of leukaemia and relapse of the disease. Thus, instead of looking at whole “blast” population which results in huge data analysis and interpretation for the different LAPs which may have different underlying biology, it may be more informative to look at the frequency of LSC after achieving CR using CD34+/CD38-/CD123+ as the single LAP for MRD studies. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1317088 / Thesis (Ph.D.) -- University of Adelaide, School of Medicine, 2008

Indiana University-Purdue University Indianapolis (IUPUI) / Acute Myeloid Leukemia (AML) is the most common hematologic malignancy. Malglycemia is a disorder of glucose metabolism and includes hyperglycemia, hypoglycemia and the combination of hyperglycemia and hypoglycemia. Malglycemia has been shown to occur frequently during hospitalization among critical care patients and has been associated with increased risk of sepsis and mortality. Little is known, however, about the prevalence and role of malglycemia on the health outcomes of AML patients hospitalized for initial induction therapy. Malglycemia may be of particular importance to the patient with AML because, researchers have found that malglycemia may promote cellular changes which facilitate the progression of cancer, alter treatment response, and attenuate immune response. The purpose of this study was to determine the prevalence of malglycemia (hyperglycemia, hypoglycemia or the combination) and to examine its role on a comprehensive set of health outcomes (neutropenic days, infection, and septicemia, and sepsis, induction hospital length of stay, complete remission and mortality) in AML patients hospitalized for initial induction therapy. A retrospective cohort study design was used. Records of 103 AML patients, hospitalized for initial induction chemotherapy were reviewed. Results of the study showed that 98% of the AML patients had at least one episode of hyperglycemia, with a prevalence rate of 33% over the entire induction inpatient hospitalization for this population. All patients noted with hyperglycemia also had hypoglycemia and thus, the prevalence rate of hypoglycemia alone could not be determined. Prevalence of the combination of hyperglycemia and hypoglycemia was 1.4 %. Although not statistically significant, a trend was noted for AML patients with hyperglycemia to experience more days with neutropenia, greater numbers of infection, sepsis, septicemia and death (mortality) than patients without hyperglycemia during induction treatment. Patients with the combination of hyperglycemia and hypoglycemia also experienced an increased risk of developing septicemia (p = .025) and sepsis (p =.057). Future studies with larger sample sizes are needed to confirm these findings.

Tumour initiation and progression occur due to oncogenic mutations that also contribute to therapeutic resistance in many human tumours. Mutations activating the "PI3K/AKT" signalling pathway and inactivating the "TP53" tumour suppressor gene are common mechanisms that cancer cells require to proliferate and escape pre-programmed cell death. p53 mutant (p53mut) tumours not only fail to respond to DNA damaging therapy, but are also described to promote therapeutic resistance by dominant negative suppression of p53 dependent promoter activity. Our work identifies the crucial interaction between the PI3K/AKT pathway and p53 mutations that regulate treatment sensitivity in tumours. Using a combination of in vitro and in vivo techniques we demonstrate that AKT inhibition promotes reduced cellular levels of p53mut via a novel Nucleophosmin 1 (NPM) mediated regulation of the tumour suppressor p14ARF and promotes re-engagement of cell cycle arrest, senescence and increased sensitivity to ionising radiation in both in vivo and in vitro systems. We show that the PI3K/AKT pathway plays an important role in the regulation of p53mut and inhibitors of this pathway can re-sensitise treatment resistant tumours. This has helped us to simultaneously highlight the cohort of patients where the greatest efficacy may be achieved in clinical practise. We further show that the AKT mediated regulation of NPM that we describe in solid tumours is relevant in Acute Myeloid Leukaemia (AML) with mutated NPM, albeit showing physiologically different effects. This further highlights the necessity for rational treatment planning with the newer targeted agents that inhibit specific signalling pathways in AML patients.

O gene humano lysine methyltransferase 2E (KMT2E) pertence ao grupo Trithorax (TrxG) e age como proteína modificadora de histonas envolvida no controle transcricional de genes relacionados a hematopoiese. Foi previamente identificado como supressor tumoral, atuando sobre a diferenciação, proliferação e ciclo celular. DAMM et al. (2011) e LUCENA-ARAÚJO et al. (2014) descreveram a associação entre baixos níveis de expressão do gene KMT2E e desfechos desfavoráveis do tratamento de pacientes com leucemia mielóide aguda (LMA) e leucemia promielocítica aguda (LPA), respectivamente. O objetivo desse trabalho foi estudar os efeitos do aumento da expressão do gene KMT2E na leucemia mielóide aguda (LMA). Foi utilizada a linhagem celular U937, reconhecida como modelo de LMA, e o aumento da expressão do gene de interesse foi obtido por meio da transfecção das células com um vetor lentiviral contendo o cDNA codificante para a isoforma longa do gene (pCDH-MSCV-MCS-EF1-GFP+Puro, aqui chamado pMEG). As partículas lentivirais foram geradas por co-transfecção em células da linhagem HEK 293T, e posteriormente, titulados com a linhagem celular HT 1080. A expressão do gene e a presença da proteína foram confirmadas por qPCR e western blotting, respectivamente. Foram realizados ensaios funcionais de ciclo celular, proliferação, viabilidade, apoptose espontânea e induzida por trióxido de arsênico e luz ultravioleta e diferenciação celular induzida por 12-miristato 13-acetato de forbol (TPA), com as amostras U937 wild type (WT), U937 pMEG (U937 transduzidas com o vetor vazio) e U937 pMEG-KMT2E. Também foram realizadas mensurações da massa tumoral das células inoculadas em camundongos NSG. A expressão relativa do gene KMT2E na célula U937 pMEG-KMT2E foi 1000 vezes mais alta que na célula U937 sem a modificação genética. Os ensaios de diferenciação celular demonstraram que as células U937 pMEG-KMT2E apresentaram maior diferenciação em monócitos/macrófagos que as células controles, quando levada em consideração a marcação para o antígeno CD11c. A expressão induzida de KMT2E em células U937 não alterou a proliferação, viabilidade, ciclo celular, apoptose, ix espontânea ou induzida e o aspecto clonogênico in vitro, porém, foi associado a um maior crescimento tumoral em modelo animal. Nossa hipótese para justificar as diferenças entre os achados in vitro e in vivo é que o aumento da expressão de KMT2E, talvez por meio do aumento de CD11c, facilitou a interação entre as células e o microambiente, estimulando assim o crescimento tumoral in vivo. / The human lysine methyltransferase 2E (KMT2E) gene belongs to the Trithorax (TrxG) group and acts as a histone modifying protein participating in the transcriptional regulation of hematopoiesis-related genes. KMT2E has been previously described as a tumor suppressor, involved in cellular differentiation, proliferation and cell cycle progression. DAMM et al. (2011) and LUCENA-ARAÚJO et al. (2014) described the association between low levels of KMT2E gene expression and poor treatment outcomes in patients with acute myeloid leukemia (AML) and acute promyelocytic leukemia (APL), respectively. The aim of this project was to study the effects of high levels of KMT2E expression in acute myeloid leukemia (AML). For this purpose, the U937 AML cell line was used and an high expression of the gene was obtained by transfecting the cells with a lentiviral vector containing the cDNA encoding the long isoform of the gene (pCDH-MSCV-MCS-EF1- GFP + Pure, here called pMEG). The lentiviral particles were transfected into HEK 293T cells and the viral concentration was determined by titration using HT 1080 cells. The gene expression and the protein presence were confirmed by qPCR and western blotting, respectively. All experiments to determine the biological function of overexpressed KMT2E were conducted with U937 wild type, U937 pMEG (U937 transduced with the empty vector) and U937 pMEG-KMT2E cells. In-vitro the impact of overexpressed KMT2E was studied on cell cycle progression, proliferation and cell viability, spontaneous and induced apoptosis by arsenic trioxide and ultraviolet light and cell differentiation induced by 12-myristate 13-phorbol acetate (TPA). In vivo, the effect of overexpressed KMT2E was detected by comparing the tumor mass growth in NSG mice when inoculating U937 pMEG and pMEG-KMT2E cells in each flank of the same mouse. The relative expression level of the KMT2E gene in pMEG-KMT2E U937 cells was 1000 higher than in the wild type U937 strain. The cell differentiation assay revealed that U937 pMEG-KMT2E cells presented an increased monocyte/macrophage differentiation, when analyzing the CD11c antigen. Induced xi overexpression of KMT2E in U937 cells did not alter cell proliferation, cell viability, cell cycle progression, spontaneous or induced apoptosis or clonogenic appearance in vitro. However, the overexpression of KMT2E resulted in an increased tumor mass formation in vivo. Taking our discrepant in vitro and in vivo results into account, we could hypothesize that the increased expression of KMT2E, possibly caused by the enhanced expression of CD11c, favored the interaction between U937 pMEGKMT2E cells and their microenvironment, thereby stimulating tumor growth in vivo.

In Western Europe and North America, acute myeloid leukaemia (AML) is predominantly a disease of the elderly, with a median age at the time of presentation in excess of 60 years. However, many clinical trials in AML fail to recruit elderly adults due to a combination of strict entry criteria, or physician or patient bias. Thus, clinical outcome data from many trials may not be readily applicable to older patients with the disease. Furthermore, because the clinical outcome for many older patients with AML is frequently poor, elderly patients who receive intensive chemotherapy with curative intent are frequently selected for treatment on clinical criteria rather than on objective prognostic criteria that may define clinical outcome. The karyotype at the time of presentation may be considered one of the most important prognostic factors in adult AML. Therefore, the aim of this thesis were firstly to analyse the clinical outcome data from a cohort of elderly patients managed at a single centre in order to document the cytogenetic features of AML in an elderly population, to define the prognostic importance of presentation karyotype in the elderly, and to identify other prognostic factors. Retrospective analysis clearly demonstrated improved clinical outcome for older patients with AML over time, primarily as a consequence of improved supportive care and the delivery of more intensive chemotherapy. In addition, 'unfavourable' presentation karyotype, increasing age and raised serum LDH were found to correlate with poor clinical outcome Molecular cytogenetic techniques based upon fluorescence in-situ hybridisation technology offer the chance to detect and analyse cytogenetic aberrations at a higher resolution than can be achieved with conventional techniques. The cytogenetic data provided by comparative genomic hybridisation and mulitplex fluorescence in-situ hybridisation when used in the analysis of elderly patients with AML were found to correlate well with results obtained by conventional methods. Importantly, additive cytogenetic data were more likely to be provided if multiplex-fluorescence in-situ hybridisation was used in the analysis of cases with marker chromosomes or in cases with complex karyotype, although the technique was limited by an inability to reliably detect telomeric translocations. In addition, although both techniques can be used to complement conventional G-banding analysis, conventional FISH methods are often required to confirm the results.

The tumour microenvironment consists of an immunosuppressive niche created by the complex interactions between cancer cells and surrounding stromal cells. A critical component of this environment are myeloid-derived suppressor cells (MDSCs), a heterogeneous group of immature myeloid cells arrested at different stages of differentiation and expanded in response to a variety of tumour factors. MDSCs exert diverse effects in modulating the interactions between immune effector cells and malignant cells. An increased presence of MDSCs is associated with tumour progression, poorer outcomes, and decreased effectiveness of immunotherapeutic strategies. In this project, we sought to quantify and characterise MDSC populations in patients with Acute Myeloid Leukaemia (AML) and delineate the mechanisms underlying their expansion. We have demonstrated that immune suppressive MDSCs are expanded in the peripheral blood and bone marrow of patients with AML. Furthermore, AML cells secrete extra-cellular vesicles (EVs) that skew the tumour microenvironment from antigen-presentation to a tumour tolerogenic environment, through the expansion of MDSCs. We then demonstrated that MDSC expansion is dependent on tumour and EV expression of the oncoproteins MUC1 and c-Myc. Furthermore, we determined that MUC1 signalling promotes c-MYC expression in a microRNA (miRNA) dependent mechanism. This observation lead us to elucidate the critical role of MUC1 in suppressing microRNA-genesis in AML, via the down-regulation of the DICER protein, a key component of miRNA processing machinery. Finally, exploiting this critical pathway, we showed that MDSCs can be targeted by MUC1 inhibition or by the use of a novel hypomethylating agent SGI-110.