Myelodysplastic syndromes (MDS) are characterized by ineffective hematopoiesis with potential for progression to acute myeloid leukemia (AML). We compared natural killer (NK) cytolytic function in 48 MDS patients with 37 healthy donors and found reduced activity in the patient population (K562 cytolysis, 19% ؎ 21% SD versus 40% ؎ 17%) (P < .001). NK cytotoxicity in MDS patients was reduced against 3 disparate tumor targets with differential activating receptor requirement, suggesting global defects in NK function. Reduced NK function in MDS was significantly associated with higher International Prognostic Score (P ‫؍‬ .01), abnormal karyotype (P ‫؍‬ .05), the presence of excess blasts (P ‫؍‬ .01), and ageadjusted bone marrow hypercellularity (P ‫؍‬ .04). MDS patients had a display of the activating receptor NKp30, and NKG2D down-regulation closely correlated with impaired NK function (P ‫؍‬ . IntroductionThe myelodysplastic syndromes (MDS) are stem cell malignancies that display hematologic heterogeneity but share features of ineffective hematopoiesis and a potential for progression to acute myeloid leukemia (AML). 1,2 Multiple factors have been implicated in the pathogenesis of MDS, including cytogenetic and molecular abnormalities and disturbance in cellular immunity. Abnormal natural killer (NK) function, including reduced antibody-dependent cell cytotoxicity (ADCC) and diminished direct NK cell cytolytic function, have been previously described; however, the biologic mechanisms underlying these changes have not be defined. [3][4][5][6][7] Normal NK cells, ␥␦ T cells, and some ␣␤ T cells mediate their biologic action through 3 families of NK receptors: killer cell immunoglobulin-like receptors (KIRs), C lectin-like (NKG2) family receptors, and natural cytotoxicity receptors ([NCRs] eg, NKp30, NKp44, and NKp46). 8 Regulation of innate immunity occurs through balanced signaling by these families of NK receptors with activating and inhibitory function. [9][10][11] Constitutively expressed activating receptors such as NKp46 and NKp30 along with NKG2D mediate most non-major histocompatibility complex (non-MHC)-induced tumor-specific cytotoxicity by NK cells, and the activation-restricted NCR (NKp44) increases NK cytotoxicity after cytokine activation. 12 Although many NK receptors with both activating and inhibitory function have been identified and details of their downstream signaling pathways have been elucidated, a void exists in the identification of activatory NK ligands and the pathologic situations in which they are induced in tumor and virally infected cells. The best-characterized NK receptor ligands are the stress-inducible MHC class I-related chain A (MICA), MICB, and UL16-binding proteins (ULBPs), which constitute the major cellular ligands for human NKG2D. [13][14][15][16][17] In addition to viralinduced expression, NKG2D ligands are often expressed by tumor cells. 18,19 Ligands for NKp30, NKp44, and NKp46 have not yet been delineated.In MDS, the pathogenesis and clinical implications of reduced NK ...

Key Points• GM-CSF-dependent STAT5 hypersensitivity is detected in 90% of CMML samples and is enhanced by signaling mutations.• Treatment with a GM-CSF-neutralizing antibody and JAK2 inhibitors reveals therapeutic potential.Granulocyte-macrophage-colony-stimulating factor (GM-CSF) hypersensitivity is a hallmark of juvenile myelomonocytic leukemia (JMML) but has not been systematically shown in the related human disease chronic myelomonocytic leukemia (CMML). We find that primary CMML samples demonstrate GM-CSF-dependent hypersensitivity by hematopoietic colony formation assays and phospho-STAT5 (pSTAT5) flow cytometry compared with healthy donors. Among CMML patients, the pSTAT5 hypersensitive response positively correlated with high-risk disease, peripheral leukocytes, monocytes, and signalingassociated mutations. When compared with IL-3 and G-CSF, GM-CSF hypersensitivity was cytokine specific and thus a possible target for intervention in CMML. To explore this possibility, we treated primary CMML cells with KB003, a novel monoclonal anti-GM-CSF antibody, and JAK2 inhibitors. We found that an elevated proportion of immature GM-CSF receptor-a(R) subunit-expressing cells were present in the bone marrow myeloid compartment of CMML. In survival assays, we found that myeloid and monocytic progenitors were sensitive to GM-CSF signal inhibition. Our data indicate that a committed myeloid precursor expressing CD38 may represent the progenitor population with enhanced GM-CSF dependence in CMML, consistent with results in JMML. These preclinical data indicate that GM-CSF signaling inhibitors merit further investigation in CMML and that GM-CSFR expression on myeloid progenitors may be a biomarker for this therapy. (Blood. 2013;121(25):5068-5077)

Selected patients with Myelodysplastic Syndromes (MDS) are responsive to immunosuppressive therapy, suggesting that hematopoietic suppressive T cells have a pathogenic role in ineffective hematopoiesis. We assessed T-cell receptor (TCR) clonality through combined flow cytometry and molecular analysis of the complementarity determining region (CDR)-3 of the T-cell receptor-Vb gene. We identified clonal T cells in 50% of MDS patients (n ¼ 52) compared to 5% of age-matched normal controls (n ¼ 20). The presence of T-cell clones was not associated with features linked previously to immunosuppression response, including WHO diagnostic category, karyotype, marrow cellularity, IPSS category, sex or age p60. Using flow cytometry to identify expanded Vb-families, we found that T cells showed greater expansion in the bone marrow compared with peripheral blood, and were characterized as CD8 þ /CD57 þ /CD28 À effector T cells. Expanded effector T cell were CD62L negative and expressed the natural killer C-lectinfamily receptor NKG2D and CD244 (2B4). We conclude that clonal T-cell expansion is common among all MDS prognostic subgroups.

No abstract