The BCR‐ABL negative myeloproliferative neoplasms are subjected to unknown phenotypic modifiers. GATA‐1 is upregulated in ET patients, regardless of treatment regimen or mutational status. Myelofibrosis (MF) megakaryocytes displayed decreased GATA‐1 staining. GATA‐1 may have utility as a diagnostic marker in ET and in its differential diagnosis from MF. Abstract BackgroundThe BCR‐ABL‐negative myeloproliferative neoplasms, i.e., polycythemia vera, essential thrombocythemia (ET), and myelofibrosis (MF), are characterized by mutations in JAK2, CALR, or MPL. However, an as yet unknown factor drives the precise disease phenotype. The hematopoietic transcription factor GATA‐1 and its downstream targets NFE2 and FLI1 are responsible for determining erythroid and megakaryocyte lineages during hematopoietic stem cell differentiation. Previous studies have demonstrated a low level of GATA‐1 expression in megakaryocytes from patients with MF. Objectives and methodsThe expression of GATA‐1, NFE2 and FLI1 was studied for changes in the peripheral blood (PB) of ET patients. Peripheral blood samples were obtained from 36 ET patients, 14 MF patients, and seven healthy control donors. Total RNA from PB mononuclear cells (PBMCs) was extracted, and quantitative polymerase chain reaction was used to determine relative changes in gene expression. Protein levels of GATA‐1 were also determined in bone marrow sections from ET and MF patients. ResultsGATA‐1 mRNA was upregulated in ET patients, regardless of treatment regimen or mutational status. FLI1 expression was significantly downregulated, whereas NFE2 expression was unaffected by changes in GATA‐1 mRNA levels. Megakaryocytes from ET patients showed increased protein levels of GATA‐1 as compared with those from MF patients. ConclusionsOur results confirmed, in PB, our previous data demonstrating elevated levels of GATA‐1 mRNA in total bone marrow of ET patients. GATA‐1 mRNA levels are independent of cytoreductive therapies, and may have utility as a diagnostic marker in ET and in its differential diagnosis from MF.

Myelodysplastic neoplasms (MPN) and myelodysplastic syndrome (MDS) are myeloid malignancies characterized by either overproduction of mature blood cells or hyperplastic bone marrow and peripheral cytopenia, but both with a tendency to evolve into acute myeloid leukaemia. In solid tumours, calreticulin (CALR) overexpression produces a pro-phagocytic signal and is counteracted by concomitant expression of anti-phagocytic CD47, reflecting an apoptosis vs survival mechanism. Increases of both CALR and CD47 on the cell membrane have been observed in response to chemotherapy, however their role in myeloid malignancies is poorly understood. Aims: Investigate the expression and cellular localisation of CALR and CD47 in untreated and treated patients with essential thrombocythemia (ET), polycythemia vera (PV) myelofibrosis (MF), and in MDS patients in comparison with healthy controls. Methods: Mononuclear cells were collected by Ficoll separation, from peripheral blood of 27 MPN (8 PV, 16 ET, 3 MF); 14 MPN patients received cyto-reductive therapies (Hydroxyurea, Anagrelide or Ruxolitinib); 10 MDS patients and 4 controls. Cells were fractionised into 4 compartments: membrane, cytoplasm, cytosol and nucleus. Proteins were extracted using TRIzol, with CALR and CD47 protein expression analysed by western blotting. Results: Total CALR and CD47 protein expression increased in MPN samples compared with controls (CALR- 7.9 vs 5.1; CD47- 2.7 vs 2.2 fold, respectively). CD47 showed higher expression of its overall protein on MPN cell membranes when compared with CALR (22% vs 13.9%). We observed a significant reduction of CALR expression in all MPN subtypes when patients were treated with cyto-reductive agents (ET- untreated 43.3% vs treated 2%, PV- 3.6% vs 2.2%, ET- 21% vs 11%). Interestingly we have observed a significant increase in CD47 cell membrane expression after treatment in MF and PV (CD47 in MF- untreated 11.8% vs treated 34.3%, PV-11.4% vs 35.9%), suggesting an anti-phagocytic effect being induced by cytotoxic drugs in MF and PV cells. In ET cell membranes however, CD47 expression is reduced after cyto-reductive treatment (22% vs 16.6%), suggesting instead a prophagocytic effect. Similarly, in MDS cells CD47 is overexpressed compared with controls (CD47- 11.31 vs 2.2 fold, respectively) and it mainly located to the membrane. Interestingly the degree of CD47 expression correlated to patients IPSS-R, increasing from low risk to high risk (low - 15.7%, intermediate 1 - 41.3%, intermediate 2 - 53.9% and high - 67.6%). CALR expression is also reduced in MDS cells comparing with controls when split by IPSS-R risk score (low - 9%, intermediate 1 - 16.9%, intermediate 2 - 17%, high - 17.9% Vs control - 29.1%). Summary/Conclusion: CD47, but not CALR, is overexpressed on the membrane of patients with MPN and MDS. In MDS, we observed a progressive increase in CD47 expression as the MDS evolve in accordance to the IPSS-R risk score. This opposes previous studies in solid tumours, which showed significant increases of both CALR and CD47 as disease progresses, suggesting a role for CD47 as a strong antiphagocytic signal responsible for immune survival in MPN and MDS. All MPN patients showed decreased CALR expression during cyto-reduction therapy, but we observed a significant difference in CD47 expression across different MPN subtypes. In fact, treating MF and PV patients with cyto-reductive agents, increases CD47 expression leading to a stronger anti-phagocytic signal, while in ET we observed a reduction, suggesting a more pro-phagocytic reaction to cytotoxic drugs in ET. A larger cohort of patients is required to confirm our findings and allow a further stratification based of type of cyto-toxic drugs. The use of anti-CD47 antibodies could represent a new strategy to enhance the pro-phagocytic signal via increasing the CALR expression, and in combination with standard cyto-reduction therapy, might represent a new therapeutical strategy in both MPN and MDS. Disclosures No relevant conflicts of interest to declare.

No abstract

Myelodysplastic syndrome and myeloproliferative neoplasms are clonal myeloid disorders arising from haematopoietic stem cells that have the tendency to progress into acute myeloid leukaemia. Multiple prognostic scoring systems have been proposed and utilised in clinical practice to predict disease evolution, however none of them can predict treatment response. In solid tumours, the relationship between the pro-phagocytic calreticulin and the anti-phagocytic CD47 is repeatedly investigated. Overexpression of calreticulin has been documented to produce a pro-phagocytic signal in solid tumour and it is often counteracted by a concomitant expression of the antiphagocytic CD47 as they act in response to one another, reflecting an apoptosis vs survival mechanism in response to chemotherapy. The role of both calreticulin and CD47 are currently poorly understood in myeloid malignancies including myelodysplastic syndrome and myeloproliferative neoplasms. The aim of this review is to elaborate on the current understanding round the roles and implications of calreticulin and CD47 signalling with in solid and haematological cancers, discuss potential roles for calreticulin and CD47 expression in transformation of myeloid cells in patients with MDS or MPN into AML and how these advances are starting to be used to design new therapeutic strategies to determine disease progression and treatment response in both solid cancer and myeloid malignancies.

Myeloproliferative neoplasms (MPN) are chronic myeloid cancers characterized by the overproduction of mature blood cells, and the tendency to evolve into acute leukaemia. In solid tumours, calreticulin (CALR) overexpression on the cell surface, produces a pro-phagocytic signal and is counteracted by concomitant expression of anti- phagocytic CD47, reflecting an apoptosis vs survival mechanism. In this study, we investigated the expression of CALR and CD47 in patients with MPN and potential changes induced by treatment. CALR and CD47 gene and protein expression were measured by Real Time PCR and western blotting, in K562 and in mononuclear cells obtained by FICOLL separation, from peripheral blood of 13 MPN patients [4 Polycythaemia Vera, 8 Essential Thrombocythemia, and 1 myelofibrosis; 7 treated (IFN or Hydroxyurea) and 6 untreated] and compared with 4 healthy controls. Cells were also fractionised into 4 compartments: membrane, cytoplasm, cytosol and nucleus and protein fractions analysed. We found a significant increase in CD47 protein expression into the membrane of MPN patients comparing with controls (91.9 % vs 19.7%). Interestingly in treated MPN the CD47 expression increases even further in comparison with untreated (92.6% vs 91.9%). No significant differences were found in total CALR expression comparing with controls (3.23, vs 2.95-fold), however in treated patients we observed a reduction in the expression in the membrane comparing with untreated (26.4 % vs 39.5 %) and an increase into cytoplasm (69.4 % vs 54.6 %). These findings suggest CD47 exposure as a mechanism of defence in MPN cells during treatment. To better understand the potential effects of therapy on CALR and CD47 expression, we incubated K562 with 0.05μM/ml of Ruxolitinib (RUXO), re-dosed at 24 hours and harvested at 48 hours. RUXO induced CALR internalization, reducing its expression into the membrane (RUXO 8.2% vs Untreated: 13.3%), but increasing its expression in cytosol (RUXO 51% vs Untreated 48.4%) and in the cytoplasm (RUXO 13.5% vs Untreated 2.9%). In contrast, CD47 expression remains relatively unmodified, with only slight increases on the membrane (RUXO 43.1% vs Untreated 40.4%) and in the cytoplasm (RUXO 34.5% vs UT 32.5%). In this study we demonstrated that CD47 but not CALR, is overexpressed on the membrane of patients with MPN. This opposes previous studies in solid tumours, which show significant increases of both CALR and CD47. This suggests a role for CD47 as a strong anti-phagocytic signal responsible for immune survival in MPN. We have also shown a potential mechanism adopted by MPN cells in response to therapy, with the internalization of CALR and the enhanced membrane expression of CD47 which remains strongly expressed on cell surface. The addition of Anti-CD47 compounds in combination with conventional therapies might represent a future therapeutically strategy to counteract MPN cells immune-escape mechanism. Disclosures No relevant conflicts of interest to declare.