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In acute myeloid leukemia (AML), leukemia-initiating cells exist within the CD34+/CD38- cell compartment. They are assumed to be more resistant to chemotherapy, enriched in minimal residual disease cell populations, and responsible for relapse. Here we evaluated clinical and biological associations and the prognostic impact of a high diagnostic CD34+/CD38- cell burden in 169 AML patients receiving an allogeneic stem cell transplantation in complete remission. Here, the therapeutic approach is mainly based on immunological graft-versus-leukemia effects. Percentage of bone marrow CD34+/CD38- cell burden at diagnosis was measured using flow cytometry and was highly variable (median 0.5%, range 0%-89% of all mononuclear cells). A high CD34+/CD38- cell burden at diagnosis associated with worse genetic risk and secondary AML. Patients with a high CD34+/CD38- cell burden had shorter relapse-free and overall survival which may be mediated by residual leukemia-initiating cells in the CD34+/CD38- cell population, escaping the graft-versus-leukemia effect after allogeneic transplantation. Evaluating the CD34+/CD38- cell burden at diagnosis may help to identify patients at high risk of relapse after allogeneic transplantation. Further studies to understand leukemia-initiating cell biology and develop targeting therapies to improve outcomes of AML patients are needed.

7042 Background: Surface antigen expression evaluation is part of the standard work-up at acute myeloid leukemia (AML) diagnosis. The biological & prognostic implications of surface antigen expression patterns in normal karyotype (NK) AML patients (pts) remain unknown. Methods: The diagnostic antigen expression patterns of mononuclear cells in bone marrow (BM) of 111 NK-AML pts were assessed using a standard flow cytometric panel. At diagnosis common AML gene mutations (mut) & expression levels were analyzed. Pts received stem cell transplantation (SCT, 98% allogeneic, 2% autologous; median age 63 years [y, range 26-74y]) after induction therapy at our institution. Median follow up was 3.3y. With R’s gplot package unsupervised hierarchical clustering of surface antigens was performed & revealed 4 distinct clusters. Results: Pts in cluster 1 (n = 36) had higher expression of immature, in cluster 2 (n = 31) of thrombocytic/T-cell/erythroid, in cluster 3 (n = 24) of monocytic & in cluster 4 (n = 20) of myeloid surface antigens. All 4 clusters associated with distinct clinical & molecular features. At diagnosis, compared to all others, pts in cluster 1 had a higher CD34+/CD38- cell burden ( P< .001), higher blood blasts ( P< .03) & BM blasts ( P< .06) by trend. They had less NPM1 mut ( P< .001) & DNMT3A mut ( P= .02), were more likely to be EVI1 positive ( P= .03) & had higher EZH2 ( P= .02), RUNX1 ( P= .009), BAALC ( P< .001), ERG ( P= .02) & MN1 ( P< .001) expression. Compared to all others, pts in cluster 1 had a higher cumulative incidence of relapse (CIR, P= .002, at 1y 41% vs 15%) & shorter event-free survival (EFS, P= .02, at 1y 50% vs 69%). In multivariate analysis, cluster 1 pts had a significantly higher CIR (Hazard Ratio [HR] 5.4, P= .01) after adjustment for FLT3-ITD & shorter EFS (HR 2.1, P= .02) after adjustment for FLT3-ITD, age & disease status at SCT. Conclusions: Pts in cluster 1 had high expression of immature surface antigens (eg CD34, CD117, CD13), genes involved in stem cell renewal & worse outcome. Our data indicate a relationship between easily accessible surface antigen expression patterns at diagnosis, molecular disease features & aggressiveness of the NK-AML phenotype.

Expression levels of miR-29 family members (i.e. miR-29a, miR-29b, & miR-29c) are deregulated in various neoplastic diseases, including acute myeloid leukemia (AML), known to affect DNA-methylation profiles by targeting epigenetic modifiers, & have been shown to be important for normal hematopoietic stem cell function. Mir-29 is organized in two distinctively regulated bi-cistronic clusters: the miR-29a/b-1 cluster & the miR-29b-2/c cluster. Here we evaluated the biological associations & clinical impact of the differential expression of pre-miR-29a/b-1 & pre-miR-29b-2/c clusters in AML. We analysed121 AML patients (pts) (median age 63 years [y], range 37-75 y) who have been consolidated with hematopoietic stem cell transplantation following non-myeloablative conditioning (nma-HCT; Fludarabin 30 mg/m2 on day -4 till -2 & 2 Gy total body irradiation) between 2000 & 2014 with pretreatment bone marrow material (BM) available. Disease status at nma-HCT was first (CR1 62%) or second complete remission (CR2 18%) or CR with incomplete peripheral recovery (CRi 20%). The mutation status (mut) of the ASXL1, CEBPA, DNMT3A IDH1, IDH2, NPM1, & TP53 gene & the FLT3-ITD & EVI1 expressionstatusas well as common surface marker expressions were assessed at diagnosis. European LeukemiaNet (ELN) classification was favorable (25%), intermediate-I (23%), intermediate-II (21%), adverse (27%) or unknown (4%). Pretreatment pre-miR-29a/b-1 & pre-miR-29b-2/c clusters expressionin bone marrow (BM)was measured by quantitative reverse transcription polymerase chain reaction & normalized to 18S. The median normalized gene expression defined high & low pre-miR-29a/b-1 & pre-miR-29b-2/c clusterexpressers. Median follow-up was 4.4y for pts alive. At diagnosis a high pre-miR-29a/b-1 expression did not associate with clinical characteristics. High pre-miR-29a/b-1 expressers were less likely to be TP53 mut (p=.01). Pts with high pre-miR-29b-2/c expression at diagnosis had higher BM blast counts (p=.01), were more likely to have a normal cytogenetics (CN, p=.03) & were less likely to be TP53 (p=.004) or ASXL1 mutated (p=.03). When we combined the expression status information of the two miR-29 clusters we found that AML blasts of pts with high expression of both clusters were less likely to be CD34 (p=.05) or CD117 (p=.04) positive & more likely to be CD11b positive (p=.05). These pts more often had CN-AML (p=.04) & better ELN genetic risk (p=.03). High expressers of both miR-29 clusters were also more likely to be DNMT3A mut (p=.01) & less likely to be EVI1 positive (p=.007). Noteworthy, none of the pts with high expression of both clusters had a TP53 (p=.16) or ASXL1 mutation (p=.08). Pts with a high expression of both miR-29 clustershad a significant longer relapse free survival (RFS, p=.01, Figure 1a) & overall survival (OS, p=.03) compared to pts with low expression of one or both miR-29 clusters. In conclusion, high expression of pre-miR-29a/b-1 & pre-miR-29b-2/c associated with different clinical & genetic characteristic at AML diagnosis. High expressers of both clusters were more often DNMT3A mutated, a gene targeted by miR-29. Furthermore, none of these patients harbored TP53 mutations, a gene known to be indirectly activated by miR-29 family members. These findings provide new insights into the miR-29 associated AML biology, which may contribute to the observed impact on AML pts outcomes. While we observed a trend for better survival for each miR-29 cluster, pts with high expression of the pre-miR-29a/b-1 & the pre-miR-29b-2/c clusterhad significantly longer RFS & OS. Figure 1 Figure 1. Disclosures Poenisch: Mundipharma: Research Funding.

Introduction: The transcription factor ZBTB7A regulates early differentiation of hematopoietic progenitors & has been associated with oncogenic as well as oncosuppressive functions. While it was shown that ectopic overexpression of Zbtb7a in immature lymphocytes leads to the development of an aggressive T-cell lymphoblastic leukemia, high ZBTB7A expression in cytogenetically normal acute myeloid leukemia (CN-AML) is associated with improved outcomes. Furthermore, recently a leukemogenic cooperation between RUNX1/RUNX1T1 & ZBTB7A mutations in t(8;21)-associated AML was suggested. Here, we further evaluated the complex role of ZBTB7A expression in hematopoietic malignancies by assessing its potential prognostic impact in AML pts undergoing hematopoietic stem cell transplantation (HSCT) after non-myeloablative conditioning (NMA). Methods: We analyzed bone marrow (BM) at diagnosis of 140 pts (median age 63 years [y], range 37-75y) treated at our institution between 2000 & 2015. All pts received NMA conditioning (3x30mg/m2 Fludarabine on days -4 to -1 & 2Gy total body irradiation) followed by HSCT in complete remission with (CR; n=111; 79.3%) or without peripheral hematological recovery (CRi; n=29; 20.7%). Median follow-up for pts alive was 3.5y. Our cohort included pts with CN-AML (n=62, 44.3%), complex karyotype (n=17; P=12.1%) & other cytogenetic abnormalities (n=61; 43.6%). At diagnosis mutations in the genes CEBPA, DNMT3A, IDH1, IDH2, NPM1 & the presence of FLT3-ITD were determined. In diagnostic BM cytogenetics were analyzed using standard techniques for banding & fluorescence in-situ hybridization & the expression of common surface markers was analyzed using flow cytometry. The expression of ZBTB7A was assessed using quantitative RT-PCR & normalized to ABL1 as internal control. As a cut-off the third quartile of normalized gene expression was identified to group high & low ZBTB7A expressers. Results: At diagnosis pts with a high ZBTB7A expression more often had a complex karyotype (P=.02) & were less likely to have core-binding factor AML by trend (P=.18). Additionally, high ZBTB7A levels associated with significantly fewer blasts in peripheral blood (P=.008) & BM (P=.02). The BM mononuclear cells in high ZBTB7A expressers were to a smaller extent positive for myeloid markers (CD38 P=.03; CD33 P=.11; CD13 P=.13) & exhibited a higher percentage of erythroid (Glycophorin A P=.03) as well as monocytic (CD11b P=.04; CD14 P=.01) surface markers. We did not find any statistical associations between ZBTB7A levels & the mutation status of NPM1, CEBPA, IDH1, DNMT3A or the presence of FLT3-ITD. Yet, there was a trend for more IDH2 mutations in the group of high ZBTB7A expressers (P=.18). At diagnosis a high expression of ZBTB7A associated with a significantly higher cumulative incidence of relapse (CIR; P=.002, Figure 1A). This finding also translated into a significantly shorter overall survival (OS; P=.01; Figure 1B) for AML pts with high ZBTB7A levels at diagnosis. When we restricted our analyses to CN-AML, high ZBTB7A expression remained a negative prognostic factor by trend (CIR P=.16; OS P=.11). Conclusion: Expression of ZBTB7A associated with distinct biological features & surface marker pattern in AML. This underlines the results of recent studies which identified ZBTB7A as a novel player in leukemogenesis. However, our findings are in contrast with the previously shown favorable prognostic impact of high ZBTB7A levels in a CN-AML cohort mainly treated with chemotherapy. In contract all pts included in our studies were consolidated with NMA-HSCT. Since this treatment regimen is mainly based on the graft versus leukemia effect a high ZBTB7A expression could potentially interfere with the immunological recognition of the AML blasts resulting in a reduced response to NMA-HSCT. Consequently, future functional studies & clinical trials should aim at further characterize the complex role of ZBTB7A in AML. Figure Figure. Disclosures Poenisch: Mundipharma: Research Funding.

Introduction: Outcomes of most acute myeloid leukemia (AML) patients (pts) remain poor. Enhanced risk-stratification and individualized treatment approaches are urgently needed. The Hedgehog (Hh) signaling pathway is important in embryonic development & stem cell biology & converges into activation of the transcription factor GLI1. In mice, loss of Gli1 increased the number of quiescent long-term hematopoietic stem cells with enhanced engraftment capacities & impaired myeloid development. Nevertheless, the biological role & prognostic impact of GLI1 expression in human AML remains to be fully elucidated. Non-myeloablative conditioning regimens (NMA) are increasingly used in AML pts undergoing hematopoietic stem cell transplantation (HCT) ineligible for conventional conditioning. In NMA-HCT the therapeutic approach is mainly based on an immunological graft-versus-leukemia (GvL) effect. Here, we tested whether the expression of GLI1 is associated with outcome in AML pts undergoing NMA-HCT. Patients & Methods: We analyzed 135 pts with diagnostic bone marrow (BM) available who were treated at our institution between January 2000 & June 2012. Median age at diagnosis was 64 years (y; range 38-75y). We included pts with de novo (n=84; 62.2%), secondary (n=37; 27.4%) or therapy-related (n=14; 10.4%) AML. All pts received NMA-HCT consisting of fludarabine (30mg/m² at days -4 to -2) & 2Gy total body irradiation (day 0). All pts received granulocyte colony stimulating factor (G-CSF)-mobilized peripheral blood stem cells on day 0. Donors were HLA-matched related (n=22; 16.3%) or HLA-matched (n=80; 59.3%) or mismatched (≥1 antigen; n=33; 24.4%) unrelated. Median follow-up was 4.3 y for pts alive. At diagnosis, cytogenetics were determined using standard techniques for banding & fluorescence in-situ hybridization in BM of all pts. The presence of FLT3 -ITD, FLT3 -TKD & expression status of EVI1, BAALC, ERG, MN1, mir-9 & mir-181a as well as the mutation status of the NPM1, CEBPA, IDH1, IDH2 & DNMT3A genes were determined. All mononuclear cells in pts' BM were assessed for presence of CD7, CD14, CD34, CD38, CD34+/CD38-, CD45, CD56, CD117, CD56 & glycophorin A. GLI1 expression was measured by a Taqman-probe based quantitative reverse transcription polymerase chain reaction & normalized to 18S as internal control. The third quartile of the normalized gene expression was used to define high & low GLI1 expressers. Results: At diagnosis, pts with high GLI1 expression had increased % of blasts in BM (p High GLI1 expressers also had a significantly longer overall survival (OS; p Conclusion: High GLI1 expression associated with distinct clinical and biological characteristics. The observation that elevated GLI1 expression was linked to IDH2 mutations suggests that - similar to glioblastoma - IDH mutations may be associated with an activated hedgehog signaling pathway in AML. Moreover, we found that high GLI1 expression was an independent prognostic factor for longer OS in AML pts receiving NMA-HCT. An effect that may be mediated by a decreased number of quiescent long-term AML stem cells in high GLI1 expressers, which may be especially beneficial in NMA-HCT treated AML pts. Further mechanistic studies are needed to explore the observed results biologically & clinical validation studies are necessary to confirm our finding of an improved outcome of high GLI1 expressers in AML receiving NMA-HCT. Figure 1. Figure 1. Disclosures Franke: Novartis: Other: Travel Costs; MSD: Other: Travel Costs; BMS: Honoraria. Niederwieser:Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau.

Characterisation of antigen expression patterns is part of the standard diagnostic work-up in acute myeloid leukemia (AML). But the biological & clinical implication of such antigen expression patterns have not been studied extensively & remain unclear in AML patients (pts) undergoing allogeneic stem cell transplantation (SCT). We analyzed the diagnostic antigen expression patterns of 162 AML pts (median age 64.7 years [y, range 46.6-76.2y]) with available data who received allogeneic peripheral blood SCT after non-myeloablative conditioning (NMA-SCT) between 2001 & 2013 at our institution. Conditioning regimen was fludarabine 3x30mg/m2 & 2Gy total body irradiation. Donors were human leukocyte antigen (HLA) matched related (12%) or HLA matched (59%) or mismatched unrelated (29%). Mutation (mut) status of the NPM1, CEBPA, IDH1, IDH2 & DNMT3A gene, presence of FLT3 -ITD & FLT3-TKD & the expression status of BAALC, ERG, MN1, EVI1, miR-9 & miR-181a at diagnosis were accessed. Pts were grouped according to the European LeukemiaNet (ELN) genetic classification in 22% favorable (fav), 24% intermediate-I (int-I), 21% intermediate-II (int-II) & 32% adverse (adv). Median follow up was 3.2y. To assess antigen expression patterns at diagnosis for all pts, flow cytometric analysis utilizing a standard panel (CD2, CD7, CD11b, CD13, CD14, CD15, CD33, CD34, CD38, CD45, CD56, CD61, CD64, CD65, CD117 & Glycophorin A) of mononuclear cells in bone marrow (BM) was performed. Using R's gplot package we performed unsupervised hierarchical clustering of the antigen expression which revealed 4 subgroups with distinct antigen expression patterns (Figure 1). At diagnosis, pts grouped in cluster 1 (n=19) had higher white blood count (WBC, P=.004) & lower peripheral blood (PB) blast count (P =.03) & were more likely to have de novo AML (P =.05). They were also less likely to have trisomy 8 (P=.08) by trend & more likely to have normal karyotype (KT, P=.05), to have ELN fav risk (P =.04), to be NPM1 mut (P =.002) & to be DNMT3A mut by trend (P=.08) & had lower miR-181a (P=.04), lower BAALC (P Pts grouped in cluster 2 (n=35) had higher WBC (P Pts grouped in cluster 3 (n=59) had lower WBC (P Pts grouped in cluster 4 (n=49) had lower WBC (P=.03), higher PB blasts (P=.007) & BM blasts (P For the entire set of pts, belonging to one of the antigen expression clusters did not impact on outcome. However, when the ELN groups were regarded separately, within the ELN fav group, cluster 1 pts had a significantly shorter event free survival (EFS, P=.04, Figure 2A) & within the ELN int-I group, cluster 3 pts had a trend for better (P=.096) & cluster 4 pts for worse EFS (P=.087). In conclusion, the antigen expression patterns at diagnosis obtained by unsupervised cluster analysis associated with distinct biological & clinical features (Figure 2B): NPM1 mut were enriched in clusters 1 & 2. Cluster 1 was characterized by ELN fav risk, normal KT, de novo disease & lower BAALC, ERG, MN1 & miR-181a expression. Cluster 2 was characterized by a high incidence of FLT3-ITD. We found more pts with ELN adv risk, monosomal KT, secondary AML & low miR-9 expression in cluster 3 & higher miR-9 as well as lower BAALC, ERG & MN1 expression levels in cluster 4. Even though we did not observe a prognostic impact of the antigen expression patterns in the entire cohort, the patterns may help to refine the ELN risk classification for AML pts undergoing SCT. Assessing the diagnostic antigen expression patterns provides information on disease biology, clinical parameters and potentially disease aggressiveness in AML. Figure 1. Figure 1. Figure 2. Figure 2. Disclosures Franke: BMS: Honoraria; MSD: Other: Travel Costs; Novartis: Other: Travel Costs. Niederwieser:Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau.