[Therapy-refractory thrombocytopenia in a 28-year-old patient]. / Therapierefraktäre Thrombozytopenie bei einem 28-jährigen Patienten.

We report a case of a patient with thrombocytopenia. A sporadic MYH9-associated disease, May Hegglin anomaly, was identified by giant platelets, leucocyte inclusion bodies and the typical distribution of NMMHC-IIA in granulocytes in the absence of impaired renal function, cataract and hearing loss. MYH9-associated diseases are an underestimated differential diagnosis of idiopathic thrombocytopenia. The correct diagnosis is important to prevent unnecessary treatment of a patient with thrombocytopenia and to provide sufficient patient information and genetic counseling. Therefore, careful examination of the blood smear has to be the first diagnostic step in a case of unexplained thrombocytopenia.

[Severe microcytic anemia with megaloblastic changes in the bone marrow. A hematological paradoxon?]. / Schwere mikrozytäre Anämie bei megaloblastären Veränderungen im Knochenmark : Ein hämatologisches Paradoxon?

We discuss the case of a 32 year-old male with severe microcytic anemia (hemoglobin 2,9 g/dl) and megaloblastic changes in the bone marrow. The patient reported of substantial dietary weight loss. The family history was positive for beta-thalassemia. Previous blood work showed iron deficiency with mild anemia. Further work-up verified beta-thalassemia minor and revealed severely decreased vitamin B12 levels with positive anti intrinsic-factor antibodies, pathognomonic for autoimmune pernicious anemia. The paradoxon therefore dissolved as a pernicious anemia with megaloblastic changes with microcytic erythrocytes due to beta-thalassemia.

Coexpression profile of leukemic stem cell markers for combinatorial targeted therapy in AML.

Targeted immunotherapy in acute myeloid leukemia (AML) is challenged by the lack of AML-specific target antigens and clonal heterogeneity, leading to unwanted on-target off-leukemia toxicity and risk of relapse from minor clones. We hypothesize that combinatorial targeting of AML cells can enhance therapeutic efficacy without increasing toxicity. To identify target antigen combinations specific for AML and leukemic stem cells, we generated a detailed protein expression profile based on flow cytometry of primary AML (n = 356) and normal bone marrow samples (n = 34), and a recently reported integrated normal tissue proteomic data set. We analyzed antigen expression levels of CD33, CD123, CLL1, TIM3, CD244 and CD7 on AML bulk and leukemic stem cells at initial diagnosis (n = 302) and relapse (n = 54). CD33, CD123, CLL1, TIM3 and CD244 were ubiquitously expressed on AML bulk cells at initial diagnosis and relapse, irrespective of genetic characteristics. For each analyzed target, we found additional expression in different populations of normal hematopoiesis. Analyzing the coexpression of our six targets in all dual combinations (n = 15), we found CD33/TIM3 and CLL1/TIM3 to be highly positive in AML compared with normal hematopoiesis and non-hematopoietic tissues. Our findings indicate that combinatorial targeting of CD33/TIM3 or CLL1/TIM3 may enhance therapeutic efficacy without aggravating toxicity in immunotherapy of AML.

BH3 mimetic ABT-737 neutralizes resistance to FLT3 inhibitor treatment mediated by FLT3-independent expression of BCL2 in primary AML blasts.

FLT3 defines a promising target for the treatment of acute myeloid leukemia (AML). In contrast to their efficacy in cell lines, FLT3-specific inhibitors as single agents have only modest clinical activity in patients with AML. As demonstrated here, overexpression of anti-apoptotic proteins of the BCL2 family leads to resistance against FLT3 inhibitors in a hematopoietic cell line model with activating FLT3 mutations. The susceptibility to FLT3 inhibition could be restored by treatment with the novel BH3 mimetic ABT-737. Primary AML samples tested in our study showed a high expression of BCL2 protein, but not of BCL-xL or MCL1. BCL2 protein levels were not reduced after dephosphorylation of FLT3 and its downstream target STAT5 in patient samples with FLT3 internal tandem duplications. Interestingly, treatment with ABT-737 caused apoptotic cell death in all primary AML samples at submicromolar level and synergized efficiently with FLT3 inhibition in AML samples with activating FLT3 mutations. In contrast to AML cell lines, BCR-ABL transformed human cells showed resistance to ABT-737, which might be due to the induction of MCL1 by BCR-ABL. Inhibition of BCL2 family members might define a novel highly efficient and specific strategy in the combined or monotreatment of AML.

Tyrosine kinase inhibition increases the cell surface localization of FLT3-ITD and enhances FLT3-directed immunotherapy of acute myeloid leukemia.

The fms-related tyrosine kinase 3 (FLT3) receptor has been extensively studied over the past two decades with regard to oncogenic alterations that do not only serve as prognostic markers but also as therapeutic targets in acute myeloid leukemia (AML). Internal tandem duplications (ITDs) became of special interest in this setting as they are associated with unfavorable prognosis. Because of sequence-dependent protein conformational changes FLT3-ITD tends to autophosphorylate and displays a constitutive intracellular localization. Here, we analyzed the effect of tyrosine kinase inhibitors (TKIs) on the localization of the FLT3 receptor and its mutants. TKI treatment increased the surface expression through upregulation of FLT3 and glycosylation of FLT3-ITD and FLT3-D835Y mutants. In T cell-mediated cytotoxicity (TCMC) assays, using a bispecific FLT3 × CD3 antibody construct, the combination with TKI treatment increased TCMC in the FLT3-ITD-positive AML cell lines MOLM-13 and MV4-11, patient-derived xenograft cells and primary patient samples. Our findings provide the basis for rational combination of TKI and FLT3-directed immunotherapy with potential benefit for FLT3-ITD-positive AML patients.

[Nonsymptomatic leukocytosis]. / Leukozytose ohne weitere Symptome. Im Zweifelsfall ein Differenzialblutbild.

Leukocytosis is a condition often met with in the clinical and ambulatory setting. Although it is usually caused by an increase in the numbers of neutrophilic granulocytes, an increase in other leukocytes populations may also account for leukocytosis. Etiologically, both primary pathological conditions affecting the white blood cells, such as various forms of leukemia and lymphomas, and also rare genetic disorders must be considered. Decidedly more common, however, are reactive changes caused by infections, cigarette smoking, chronic inflammation, necrotic tissue or certain drugs. Although moderate leukocytosis in the absence of a clinical correlate and/or an apparent trigger, requires no diagnostic clarification, it should be kept under observation. If the etiology is uncertain, or a treatment-requiring disorder is suspected, the differential blood count is at the focus of the further diagnostic work-up. Depending upon the findings, this is supplemented by additional laboratory parameters, bone marrow examination, microbiological investigations and imaging procedures. Leukostasis resulting from vasoocclusion in the presence of very high numbers of leukocytes represents an emergency situation, and is an indication for leukapheresis.

[Elevated Hemoglobin--polyglobulia or polycythemia?]. / Zu viele Erythrozyten. Wie Sie eine Polyglobulie von der Polyzythämie abgrenzen.

An increase in Hb levels, haematocrit or the absolute number of red blood cells may be evidence of polycythemia rubra vera. Much more commonly, however, erythrocytosis is due to an underlying non-hematological disease. To establish the diagnosis of polycythemia, a secondary polyglobulia must first be excluded. If no evidence of polyglobulia is found, or if EPO levels are decreased, or splenomegaly not accountable for by portal hypertension is present, a specific diagnostic work-up must be performed by a hematologist/oncologist. This includes a bone marrow aspiration, cytological examination and molecular genetic testing.

[Fortuitous finding: thrombocytopenia and thrombocytosis]. / Zufallsbefunde Thrombozytopenie und Thrombozytose. Wann müssen Sie aktiv werden?

Thrombocytopenia is present when the number of platelets drops to below 150 G/l. Leaving aside pseudothrombocytopenia, such a situation may be triggered by pregnancy or a range of different drugs, or may signify the presence of idiopathic thrombocytopenic purpura (ITP). Thrombocytosis is present when the platelet count exceeds 500 G/l. This condition includes a large variety of forms of reactive thrombocytosis, a clonal increase in thrombocytes in hematological diseases, and the rare condition of familial thrombocytosis.

Persistence of pre-leukemic clones during first remission and risk of relapse in acute myeloid leukemia.

Some patients with acute myeloid leukemia (AML) who are in complete remission after induction chemotherapy harbor persisting pre-leukemic clones, carrying a subset of leukemia-associated somatic mutations. There is conflicting evidence on the prognostic relevance of these clones for AML relapse. Here, we characterized paired pre-treatment and remission samples from 126 AML patients for mutations in 68 leukemia-associated genes. Fifty patients (40%) retained ⩾1 mutation during remission at a variant allele frequency of ⩾2%. Mutation persistence was most frequent in DNMT3A (65% of patients with mutations at diagnosis), SRSF2 (64%), TET2 (55%), and ASXL1 (46%), and significantly associated with older age (P<0.0001) and, in multivariate analyses adjusting for age, genetic risk, and allogeneic transplantation, with inferior relapse-free survival (hazard ratio, 2.34; P=0039) and overall survival (hazard ratio, 2.14; P=036). Patients with persisting mutations had a higher cumulative incidence of relapse before, but not after allogeneic stem cell transplantation. Our work underlines the relevance of mutation persistence during first remission as a novel risk factor in AML. Persistence of pre-leukemic clones may contribute to the inferior outcome of elderly AML patients. Allogeneic transplantation abrogated the increased relapse risk associated with persisting pre-leukemic clones, suggesting that mutation persistence may guide postremission treatment.Leukemia accepted article preview online, 18 December 2017. doi:10.1038/leu.2017.350.

Assessment of imatinib as first-line treatment of chronic myeloid leukemia: 10-year survival results of the randomized CML study IV and impact of non-CML determinants.

Chronic myeloid leukemia (CML)-study IV was designed to explore whether treatment with imatinib (IM) at 400 mg/day (n=400) could be optimized by doubling the dose (n=420), adding interferon (IFN) (n=430) or cytarabine (n=158) or using IM after IFN-failure (n=128). From July 2002 to March 2012, 1551 newly diagnosed patients in chronic phase were randomized into a 5-arm study. The study was powered to detect a survival difference of 5% at 5 years. After a median observation time of 9.5 years, 10-year overall survival was 82%, 10-year progression-free survival was 80% and 10-year relative survival was 92%. Survival between IM400 mg and any experimental arm was not different. In a multivariate analysis, risk group, major-route chromosomal aberrations, comorbidities, smoking and treatment center (academic vs other) influenced survival significantly, but not any form of treatment optimization. Patients reaching the molecular response milestones at 3, 6 and 12 months had a significant survival advantage. For responders, monotherapy with IM400 mg provides a close to normal life expectancy independent of the time to response. Survival is more determined by patients' and disease factors than by initial treatment selection. Although improvements are also needed for refractory disease, more life-time can currently be gained by carefully addressing non-CML determinants of survival.

Silencing of GATA3 defines a novel stem cell-like subgroup of ETP-ALL.

BACKGROUND: GATA3 is pivotal for the development of T lymphocytes. While its effects in later stages of T cell differentiation are well recognized, the role of GATA3 in the generation of early T cell precursors (ETP) has only recently been explored. As aberrant GATA3 mRNA expression has been linked to cancerogenesis, we investigated the role of GATA3 in early T cell precursor acute lymphoblastic leukemia (ETP-ALL). METHODS: We analyzed GATA3 mRNA expression by RT-PCR (n = 182) in adult patients with T-ALL. Of these, we identified 70 of 182 patients with ETP-ALL by immunophenotyping. DNA methylation was assessed genome wide (Illumina Infinium® HumanMethylation450 BeadChip platform) in 12 patients and GATA3-specifically by pyrosequencing in 70 patients with ETP-ALL. The mutational landscape of ETP-ALL with respect to GATA3 expression was investigated in 18 patients and validated by Sanger sequencing in 65 patients with ETP-ALL. Gene expression profiles (Affymetrix Human genome U133 Plus 2.0) of an independent cohort of adult T-ALL (n = 83) were used to identify ETP-ALL and investigate GATA3low and GATA3high expressing T-ALL patients. In addition, the ETP-ALL cell line PER-117 was investigated for cytotoxicity, apoptosis, GATA3 mRNA expression, DNA methylation, and global gene expression before and after treatment with decitabine. RESULTS: In our cohort of 70 ETP-ALL patients, 33 % (23/70) lacked GATA3 expression and were thus defined as GATA3low. DNA methylation analysis revealed a high degree of GATA3 CpG island methylation in GATA3low compared with GATA3high ETP-ALL patients (mean 46 vs. 21 %, p < 0.0001). Genome-wide expression profiling of GATA3low ETP-ALL exhibited enrichment of myeloid/lymphoid progenitor (MLP) and granulocyte/monocyte progenitor (GMP) genes, while T cell-specific signatures were downregulated compared to GATA3high ETP-ALL. Among others, FLT3 expression was upregulated and mutational analyses demonstrated a high rate (79 %) of FLT3 mutations. Hypomethylating agents induced reversal of GATA3 silencing, and gene expression profiling revealed downregulation of hematopoietic stem cell genes and upregulation of T cell differentiation. CONCLUSIONS: We propose GATA3low ETP-ALL as a novel stem cell-like leukemia with implications for the use of myeloid-derived therapies.

Blockade of the PD-1/PD-L1 axis augments lysis of AML cells by the CD33/CD3 BiTE antibody construct AMG 330: reversing a T-cell-induced immune escape mechanism.

Bispecific T-cell engagers (BiTEs) are very effective in recruiting and activating T cells. We tested the cytotoxicity of the CD33/CD3 BiTE antibody construct AMG 330 on primary acute myeloid leukemia (AML) cells ex vivo and characterized parameters contributing to antileukemic cytolytic activity. The E:T ratio and the CD33 expression level significantly influenced lysis kinetics in long-term cultures of primary AML cells (n=38). AMG 330 induced T-cell-mediated proinflammatory conditions, favoring the upregulation of immune checkpoints on target and effector cells. Although not constitutively expressed at the time of primary diagnosis (n=123), PD-L1 was strongly upregulated on primary AML cells upon AMG 330 addition to ex vivo cultures (n=27, P<0.0001). This phenomenon was cytokine-driven as the sole addition of interferon (IFN)-γ and tumor necrosis factor-α also induced expression. Through blockade of the PD-1/PD-L1 interaction, AMG 330-mediated lysis (n=9, P=0.03), T-cell proliferation (n=9, P=0.01) and IFN-γ secretion (n=8, P=0.008) were significantly enhanced. The combinatorial approach was most beneficial in settings of protracted AML cell lysis. Taken together, we have characterized a critical resistance mechanism employed by primary AML cells under AMG 330-mediated proinflammatory conditions. Our results support the evaluation of checkpoint molecules in upcoming clinical trials with AMG 330 to enhance BiTE antibody construct-mediated cytotoxicity.

The target cell of transformation is distinct from the leukemia stem cell in murine CALM/AF10 leukemia models.

The CALM/AF10 fusion gene is found in various hematological malignancies including acute myeloid leukemia (AML), T-cell acute lymphoblastic leukemia and malignant lymphoma. We have previously identified the leukemia stem cell (LSC) in a CALM/AF10-driven murine bone marrow transplant AML model as B220+ lymphoid cells with B-cell characteristics. To identify the target cell for leukemic transformation or 'cell of origin of leukemia' (COL) in non-disturbed steady-state hematopoiesis, we inserted the CALM/AF10 fusion gene preceded by a loxP-flanked transcriptional stop cassette into the Rosa26 locus. Vav-Cre-induced panhematopoietic expression of the CALM/AF10 fusion gene led to acute leukemia with a median latency of 12 months. Mice expressing CALM/AF10 in the B-lymphoid compartment using Mb1-Cre or CD19-Cre inducer lines did not develop leukemia. Leukemias had a predominantly myeloid phenotype but showed coexpression of the B-cell marker B220, and had clonal B-cell receptor rearrangements. Using whole-exome sequencing, we identified an average of two to three additional mutations per leukemia, including activating mutations in known oncogenes such as FLT3 and PTPN11. Our results show that the COL for CALM/AF10 leukemia is a stem or early progenitor cell and not a cell of B-cell lineage with a phenotype similar to that of the LSC in CALM/AF10+ leukemia.

Long-term outcome of patients with newly diagnosed chronic myeloid leukemia: a randomized comparison of stem cell transplantation with drug treatment.

Tyrosine kinase inhibitors represent today's treatment of choice in chronic myeloid leukemia (CML). Allogeneic hematopoietic stem cell transplantation (HSCT) is regarded as salvage therapy. This prospective randomized CML-study IIIA recruited 669 patients with newly diagnosed CML between July 1997 and January 2004 from 143 centers. Of these, 427 patients were considered eligible for HSCT and were randomized by availability of a matched family donor between primary HSCT (group A; N=166 patients) and best available drug treatment (group B; N=261). Primary end point was long-term survival. Survival probabilities were not different between groups A and B (10-year survival: 0.76 (95% confidence interval (CI): 0.69-0.82) vs 0.69 (95% CI: 0.61-0.76)), but influenced by disease and transplant risk. Patients with a low transplant risk showed superior survival compared with patients with high- (P<0.001) and non-high-risk disease (P=0.047) in group B; after entering blast crisis, survival was not different with or without HSCT. Significantly more patients in group A were in molecular remission (56% vs 39%; P=0.005) and free of drug treatment (56% vs 6%; P<0.001). Differences in symptoms and Karnofsky score were not significant. In the era of tyrosine kinase inhibitors, HSCT remains a valid option when both disease and transplant risk are considered.

Increasing intensity of therapies assigned at diagnosis does not improve survival of adults with acute myeloid leukemia.

We randomized 3375 adults with newly diagnosed acute myeloid leukemia (AML) or high-risk myelodysplastic syndrome to test whether increasingly intensive chemotherapies assigned at study-entry and analyzed on an intent-to-treat basis improved outcomes. In total, 1529 subjects <60 years were randomized to receive: (1) a first course of induction therapy with high-dose cytarabine and mitoxantrone (HAM) or with standard-dose cytarabine, daunorubicin and 6-thioguanine (TAD) followed by a second course of HAM; (2) granulocyte-colony stimulating factor (G-CSF) or no G-CSF before induction and consolidation courses; and (3) high-dose therapy and an autotransplant or maintenance chemotherapy. In total, 1846 subjects ⩾60 years were randomized to receive: (1) a first induction course of HAM or TAD and second induction course of HAM (if they had bone marrow blasts ⩾5% after the first course); and (2) G-CSF or no G-CSF as above. Median follow-up was 7.4 years (range, 1 day to 14.7 years). Five-year event-free survivals (EFSs) for subjects receiving a first induction course of HAM vs TAD were 17% (95% confidence interval, 15, 18%) vs 16% (95% confidence interval 14, 18%; P=0.719). Five-year EFSs for subjects randomized to receive or not receive G-CSF were 19% (95% confidence interval 16, 21%) vs 16% (95% confidence interval 14, 19%; P=0.266). Five-year relapse-free survivals (RFSs) for subjects <60 years receiving an autotransplant vs maintenance therapy were 43% (95% confidence interval 40, 47%) vs 40 (95% confidence interval 35, 44%; P=0.535). Many subjects never achieved pre-specified landmarks and consequently did not receive their assigned therapies. These data indicate the limited impact of more intensive therapies on outcomes of adults with AML. Moreover, none of the more intensive therapies we tested improved 5-year EFS, RFS or any other outcomes.

Towards a pathogenesis-oriented therapy of acute myeloid leukemia.

Genetic and molecular techniques have provided increasing insights into the biology of acute myeloid leukemia (AML). These investigations showed that AML is not a homogeneous disease but a heterogeneous group of biologically different subentities. These subentities are currently primarily defined by cytogenetics by which three main subgroups can be discriminated: AML with balanced translocations, AML with unbalanced aberrations and AML without cytogenetically detectable aberrations. Within the latter group molecular alterations are identified in more than half of cases such as NPM mutations, FLT3 mutations, MLL duplications and mutations of CEBP-alpha. The clinical meaning of these findings is illustrated by substantial differences in response to therapy and long-term outcome. As demonstrated by the recent multicenter trial of the German AML Cooperative Group (AMLCG) and other studies intensification of induction therapy may improve the results in distinct subtypes but fails to do so in others. Therefore, new strategies need to be explored which incorporate the knowledge about the biology of AML to develop biology adapted treatment strategies. This process has just begun and is predominantly determined by the availability of new agents and their evaluation in clinical phase I and II studies. A variety of targets are currently explored and some trials have yielded promising results already. The step towards a biology adapted treatment of AML is long and requires the combined efforts of researchers, clinicians and the pharmaceutical industry. The first steps towards this goal have been taken and give rise to the hope for more effective and more specific therapies of AML.

Functional features of neutrophils induced by G-CSF and GM-CSF treatment: differential effects and clinical implications.

G-CSF and GM-CSF are hematopoietic growth factors required for proliferation and differentiation of hematopoietic precursors. G-CSF is now widely used to overcome neutropenias of various origins. Beside the absolute number, the functional capacity of neutrophils at sites of inflammation is of major importance in host defense. This review summarizes major functional and phenotypical features of neutrophils induced by G-CSF treatment in patients with acquired and congenital neutropenias. Furthermore, we focus on the differential effect of G-CSF and GM-CSF on neutrophil function in vitro and in vivo. Some of the altered abilities of cytokine-induced neutrophils are important to understand side-effects of G-CSF therapy.

Expression of granulocyte colony-stimulating factor- and granulocyte-macrophage colony-stimulating factor-associated signal transduction proteins of the JAK/STAT pathway in normal granulopoiesis and in blast cells of acute myelogenous leukemia.

Acute myelogenous leukemia (AML) is characterized by the malignant transformation of hematopoietic stem cells leading to dysregulated growth and differentiation of myeloid cells. Normally, proliferation and differentiation of myeloid cells are regulated by cytokines such as granulocyte colony-stimulating factor (G-CSF) or granulocyte-macrophage colony-stimulating factor (GM-CSF). Abnormal signaling of the signal transduction pathway from the cytokine receptors via Janus kinases (JAKs) and signal transducers and activators of transcription (STATs) might be involved in the pathogenesis of AML. We examined whether an abnormal expression of one of the four JAKs, STAT1, STAT3, STAT5, or the tyrosine phosphatase SHP-1, a negative regulator of this pathway, is associated with malignant transformation in AML. Analysis of the expression of proteins of the JAK/STAT pathway in normal myeloid cells at three stages of maturation revealed a strong expression of all proteins in CD34+ cells, whereas the level of the proteins was significantly lower in granulocytic precursors and mature neutrophils. Furthermore, during maturation the relation of the isoforms of STAT1 and STAT3 changed from predominantly alpha to predominantly beta. Leukemic blast cells from 25 patients and 12 cell lines showed a high level of STAT proteins and SHP-1, whereas a deficiency of at least one of the four JAKs was found in 10 of 25 patients. In primary AML blast cells a deficiency of three JAKs was more common in patients with an abnormal karyotype. In addition, a lack of JAK2 and Tyk2 protein was strongly associated with the FAB M2 phenotype. The proliferation rate in response to GM-CSF available in a small number of patients appears to be related to the JAK2 expression. Our data suggest that the degree of expression of G-CSF/GM-CSF receptor-associated proteins of the JAK/STAT pathway in normal myeloid cells is related with their clonogenic potential. STAT3 appears to be involved in early differentiation. Similar to CD34+ cells, it is likely that the high levels of STATs and SHP-1 found in leukemic cells reflects their proliferative activity, whereas a lack of members of the JAK family might lead to an inability to proliferate in response to G-CSF/GM-CSF described in a considerable percentage of AML blasts.

Identification of the antigen recognized by the monoclonal antibody 31D8.

The monoclonal antibody (mAb) 31D8 has previously been described to bind more avidly to functionally active neutrophils and proved to be useful as a differentiation marker of neutrophils. However, attempts to further characterize the antigen recognized by 31D8 have not been successful. Studying the altered Fcgamma-receptor expression of human neutrophils induced by granulocyte colony-stimulating factor (G-CSF) in vivo, we could demonstrate a parallel decrease in the expression of 31D8 and the CD16 antigen. Furthermore, 31D8 showed a binding pattern on leukocyte subsets similar to that of clustered CD16 antibodies, exhibiting identical cells in double-staining experiments. Preincubation of neutrophils with 31D8 resulted in a dose-dependent inhibition of the binding of immune complexes. A decreased expression of the 31D8 antigen was found on the same cell clones to the same extent as found for the 3G8 antigen on neutrophils from patient with paroxysmal nocturnal hemoglobinuria (PNH). Treatment of polymorphonuclear leukocytes (PMN) with PIPLC resulted in a dose-dependent decrease of mAb 31D8 binding, showing that the 31D8 antigen is phosphatidylinositolglycan (PIG)-anchored. Moreover, 31D8 competed with the binding of antibodies (such as mAb 3G8) directed against the binding site of FcgammaRIII for the Fc-part of IgG. However, this mAb did not influence the binding of a CD16 antibody (mAb B73.1) which recognizes an epitope elsewhere on the CD16 antigen. We conclude from our experiments that the mAb 31D8 binds with high avidity to fcgammaRIII (CD16 antigen). Furthermore, our data indicate that its binding site is most probably located at the binding site for the Fc-part of IgG.

Dual PI3K/mTOR inhibition shows antileukemic activity in MLL-rearranged acute myeloid leukemia.

In acute myeloid leukemia (AML), several signaling pathways such as the phosphatidylinositol-3-kinase/AKT and the mammalian target of rapamycin (PI3K/AKT/mTOR) pathway are deregulated and constitutively activated as a consequence of genetic and cytogenetic abnormalities. We tested the effectiveness of PI3K/AKT/mTOR-targeting therapies and tried to identify alterations that associate with treatment sensitivity. By analyzing primary samples and cell lines, we observed a wide range of cytotoxic activity for inhibition of AKT (MK-2206), mTORC1 (rapamycin) and PI3K/mTORC1/2 (BEZ-235) with a high sensitivity of cells carrying an MLL rearrangement. In vivo PI3K/mTOR inhibition delayed tumor progression, reduced tumor load and prolonged survival in an MLL-AF9(+)/FLT3-ITD(+) xenograft mouse model. By performing targeted amplicon sequencing in 38 MLL-AF9(+) and 125 cytogenetically normal AML patient samples, we found a high additional mutation rate for genes involved in growth factor signaling in 79% of all MLL-AF9(+) samples, which could lead to a possible benefit of this cohort. PI3K/mTOR inhibition for 24 h led to the cross-activation of the ERK pathway. Further in vitro studies combining PI3K/mTOR and ERK pathway inhibition revealed highly synergistic effects in apoptosis assays. Our data implicate a possible therapeutic benefit of PI3K/mTOR inhibition in the MLL-mutated subgroup. Inhibiting rescue pathways could improve the therapeutic efficacy of PI3K-targeted therapies in AML.