NPM1-mutated Patients Research Articles

FOXM1 Binds Nucleophosmin in AML and Confers Resistance to Chemotherapy

Background: The nucleo-cytoplasmic shuttle protein nucleophosmin (NPM1) is mutated in 50% of cytogenetically normal AML cases (CN-AML) resulting in the nuclear export of this protein and a favorable prognosis. The mechanism by which mutated NPM1 (NPM1mut) confers this advantage in CN-AML is unclear. We have previously demonstrated that FOXM1, an oncogenic transcription factor, co-localizes with NPM1 in cancer cells and NPM-binding is required for sustaining the level of FOXM1. In the NPM1mut AML cell line OCI-AML3, as detected by immunofluorescence, NPM1 and FOXM1 co-localize in the cytoplasm where FOXM1 is transcriptionally inactive. We hypothesize that improved outcomes in the subset of NPM1mut AML is partly attributable to the cytoplasmic relocalization and functional inactivation of FOXM1.Methods: Patient samples were identified retrospectively using the University of Illinois Cancer Center Registry (IRB #: 2013-1245). Clinical, laboratory and molecular data were collected by chart review. Formalin fixed paraffin embedded bone marrow biopsies were retrieved to prepare slides. Patients with favorable or unfavorable karyotypes were excluded and only biopsies with >70% blasts were included. We performed a 2-target staining protocol with fluorescent antibodies to visualize NPM1 and FOXM1 in the same cells using the Vectra multispectral tissue imaging system. This system combines machine learning capability (inForm® software) with acquisition of spectral data from each pixel in the image, so that multiple targets can be quantified in the same image. Leukemia cell lines with stable knockdown of FOXM1 were generated using lentiviral transduction of HL60 cells (NPM1wt) transduced with PLKO.1-shFOXM1 or PLKO.1-empty vector. In parallel, OCI-AML3 cells (NPM1mut) were transduced with pBabe control or pBabe-FOXM1 expressing retrovirus to induce overexpression of FOXM1.Results: FOXM1 is a well-characterized oncogenic transcription factor. In this study we examined its role in AML. In a series of AML cell lines, cellular fractionation followed by immunoblotting revealed strong nuclear expression of FOXM1 in HL-60 and KG1, both of which express the wild-type NPM1 gene. In comparison the OCI-AML3 cell line, carrying the mutated NPM1 gene, showed predominantly cytoplasmic expression of FOXM1 where it is inactive. To better understand the role of FOXM1 in mediating chemoresistance in AML, we inhibited FOXM1 expression in the HL60 leukemia cell line. Stable knockdown of FOXM1 in this cell line resulted in increased sensitivity to the chemotherapeutic agent cytarabine compared to empty vector transduced cells. This was demonstrated by increased caspase-3 cleavage as detected by immunoblotting and decreased cell viability by Trypan blue exclusion after 24 hour exposure to the drug. We then proceeded to validate our observations of the FOXM1-NPM interaction in primary AML samples. Using quantitative data generated from the Vectra imaging of 20 AML pre-treatment bone marrow biopsies we show a strong correlation between the nuclear: cytoplasmic ratios of FOXM1 and NPM, Pearson correlation co-efficient r=0.87, which is indicative of cellular co-localization. When the patients are stratified in 2 groups based on NPM1 mutation status, mean cytoplasmic expression of FOXM1 is 2-fold higher in NPM1mut patients (36% versus 18%).Conclusion: We demonstrate that FOXM1, an oncogenic transcription factor is predominantly cytoplasmic and thereby inactive when NPM1 is mutated in AML. We show the functional significance of FOXM1 in mediating chemoresistance in this disease using AML cell lines. Using a novel quantitative imaging modality we establish for the first time the cellular co-localization of FOXM1 and NPM1 in AML primary blast cells. Studies are ongoing to manipulate FOXM1 expression in additional leukemia cell lines and xenograft models of AML to confirm our findings that FOXM1 inhibition in AML leads to increased sensitivity to chemotherapy. DisclosuresNo relevant conflicts of interest to declare.

Allogeneic stem-cell transplantation in patients with NPM1-mutated acute myeloid leukemia: results from a prospective donor versus no-donor analysis of patients after upfront HLA typing within the SAL-AML 2003 trial.

The presence of a mutated nucleophosmin-1 gene (NPM1(mut)) in acute myeloid leukemia (AML) is associated with a favorable prognosis. To assess the predictive value with regard to allogeneic stem-cell transplantation (SCT), we compared the clinical course of patients with NPM1(mut) AML eligible for allogeneic SCT in a donor versus no-donor analysis. Of 1,179 patients with AML (age 18 to 60 years) treated in the Study Alliance Leukemia AML 2003 trial, we identified all NPM1(mut) patients with an intermediate-risk karyotype. According to the trial protocol, patients were intended to receive an allogeneic SCT if an HLA-identical sibling donor was available. Patients with no available donor received consolidation or autologous SCT. We compared relapse-free survival (RFS) and overall survival (OS) depending on the availability of a suitable donor. Of 304 eligible patients, 77 patients had a sibling donor and 227 had no available matched family donor. The 3-year RFS rates in the donor and no-donor groups were 71% and 47%, respectively (P = .005); OS rates were 70% and 60%, respectively (P = .114). In patients with normal karyotype and no FLT3 internal tandem duplication (n = 148), the 3-year RFS rates in the donor and no-donor groups were 83% and 53%, respectively (P = .004); and the 3-year OS rates were 81% and 75%, respectively (P = .300). Allogeneic SCT led to a significantly prolonged RFS in patients with NPM1(mut) AML. The absence of a statistically significant difference in OS is most likely a result of the fact that NPM1(mut) patients who experienced relapse responded well to salvage treatment. Allogeneic SCT in first remission has potent antileukemic efficacy and is a valuable treatment option in patients with NPM1(mut) AML with a sibling donor.

The LincRNA HOTAIRM1, Located in the HOXA genomic Region, impacts Prognosis in Acute Myeloid Leukemia and Is Associated with a Distinctive microRNA Signature

Background: Non-coding RNAs (ncRNAs) have recently emerged as key regulators of diverse cellular processes, including leukemia. ncRNAs are classified according to their size as short (eg, microRNAs) or long ncRNAs. lincRNAs are long ncRNAs located in intergenic regions and have multiple regulatory functions, including gene expression regulation. Interestingly, active crosstalk between microRNAs and lincRNAs has been observed. lincRNAs are known to be deregulated in some cancers but their importance in acute myeloid leukemia (AML) is so far unknown. HOX genes play an important role in hematopoiesis and are deregulated in AML. lincRNAs are especially abundant in the clusters of HOX genes. HOTAIRM1, a myeloid lineage-specific lincRNA, is located at the 3’end of the HOXA cluster and seems to play a regulatory role in myelopoiesis. However, to date the potential prognostic role of HOTAIRM1 expression in AML has not been examined.Aims: To investigate first whether the expression of the lincRNA HOTAIRM1 is associated with the clinical, cytogenetic and molecular characteristics and microRNA expression in AML patients. Secondly, since intermediate risk (IR) AML patients have a highly diverse prognosis, we analyzed the potential prognostic value of HOTAIRM1 expression in IR-AML patients.Methods: To explore the expression level of HOTAIRM1 among different AML subtypes, we analyzed samples from 244 AML patients including CBF-rearranged AML (n=5), APL (n=4), MLL-rearranged AML (n=3), EVI1-rearranged AML (n=3), t(6;9) AML (n=9), AML with monosomal karyotype (n=3), and a large cohort of IR-AML (described below). For the analysis of prognostic value of HOTAIRM1, we analyzed specifically the outcome of 217 IR-AML patients (median age, 52; 51% males) sequentially included in CETLAM trials during the period 1995-2009. Molecular genotyping of this group identified NPM1 mutation (NPM1mut), FLT3-ITD, and biallelic CEBPA mutation (CEBPA mut) in 99 (45%), 79 (36%) and 17 (11%), respectively. The expression of HOTAIRM1 was analyzed using TaqMan® Gene Expression Assays (Applied Biosystems). microRNA and mRNA expression data were obtained in previous studies (Díaz-Beyá, Leukemia 2013). Statistical analyses were performed with BRB Array Tools, SPSS v20 and R v3.0. MaxStat package from R software was used to determine the optimal cutoff point of HOTAIRM1 expression.Results: Among all 244 patients, HOTAIRM1 expression was significantly different among the 7 included genetic subgroups (ANOVA p=0.0024), with the lowest levels observed in APL-AML patients and the highest in the t(6;9)AML patients. Within the IR-AML group, HOTAIRM1 overexpression was observed in NPM1mut patients (p<0.001).The prognostic study showed that high HOTAIRM1 expression was associated with shorter 5-year overall survival (OS) (27+11% vs.47+8%; p=0.009) shorter 5-year disease-free survival (LFS) (22+12% vs. 53+9%; p<0.001), and a higher cumulative incidence of relapse (CIR) at 5 years (55+15% vs. 34+8%; p=0.004). The effect on outcome was maintained within the subgroup with favorable molecular features (i.e., NPM1mut and CEBPAmut without FLT3-ITD) (OS: 75+11% vs. 39+29%; p=0.026). In the multivariate analysis including age, sex, WBC, NPM1mut, FLT3-ITD and number of treatment cycles for CR achievement as covariates, HOTAIRM1 expression emerged as an independent prognostic marker in OS (HR=2.44; 95% CI: 1.51-3.93; p<0.0001), LFS (HR=2.07; 95% CI: 1.31-3.24; p=0.002) and CIR (HR=2.05; 95% CI: 1.18-3.55; p=0.01).Supervised analysis by means of t-test based on multiple permutations revealed a distinctive 33-microRNA signature which correlated with HOTAIRM1 expression including miR-196b (p<0.001) located in the HOXA genomic region. Moreover, we correlated the expression of HOX genes and HOTAIRM1 and observed a positive correlation with HOXA4 gene expression (R2= 0.6; p=0.001).Conclusion: The expression level of the lincRNA HOTAIRM1 varied among different molecularly-defined AML. Interestingly, HOTAIRM1 expression level showed independent prognostic value within the IR-AML group. Moreover, HOTAIRM1 expression strongly correlates with its neighboring HOXA4 gene and harbors a distinctive microRNA signature. Our findings can pave the way for further studies of HOX-related lincRNAs and microRNAs regulatory networks and their influence on clinical outcome.Acknowledgments: ISCIII RH13/00205, SEHH, FIS13/00999 DisclosuresNo relevant conflicts of interest to declare.

Analysis Of Leukemic Stem Cell Population Comparing NPM1wt and NPM1mut AML Patients and Potential Therapeutic Targets

Treatment of acute myeloid leukemia (AML) patients became more effective, yet the relapse rate is still high and cure rate still low. Different therapeutic approaches, based on molecular targeting are offering new treatment strategies using markers like FLT3, NPM1, cKIT and DNMT3A. Many others are currently under investigation. Leukemic stem cells (LSC) might be the source for leukemic disease self-renewal and account for disease relapse after treatment. Therefore LSC represent a critical target for further therapeutic options. AML with mutated nucleophosmin (NPM1) gained attention because of its distinctive molecular, clinical, and prognostic features. NPM1 mutation is also an interesting target for specific immunotherapy (Greiner et al., Blood 2012), however LSC of this new entity have not been completely characterized. Differentially expressed genes might influence molecular and immunological relevant pathways which could have an impact on the better overall survival of the mutated patients.In this study, we were interested in expression differences of the LSC enriched cell fraction descendent of NPM1wt and NPM1mut primary AML patients. We suggest that expression differences between the patients groups could be a factor for the better overall survival of NPM1mut patients. In addition we aimed to study new targets on NPM1mut LSC for new therapeutical purposes.We enriched the CD34+CD38- fraction of primary AML peripheral blood mononuclear cells (PBMC), by Fluorescence-activated cell sorting (FACS) and Magnetic-activated cell sorting (MACS), comparing both methods in efficiency and feasibility. We chose FACS for further enrichment assays, as it resulted in a mean purity of 92% vs 88% using MACS, and a higher cell number after sorting (9% more) in the first pilot trials. We sorted 21 AML patient samples; 12 NPM1wt and 9 NPM1mut. We also enriched healthy donor samples for HSC purification using FACS, in order to compare expression levels. We showed that enriched CD34+CD38- cells in NPM1mut AML samples harbor cytoplasmic NPM1 via immunocytochemical staining, indicating that these cells belong to the leukemic clone. The cell number and RNA quality was sufficient for further Microarray studies in which we analysed the CD34+CD38- enriched compartments descendent from NPM1mut and NPM1wt patients. Those showed significant differences in gene expression patterns which noticeably are immunologically coined, for example: immunoglobulin superfamily, member 10 (p = 0.0003405; fold change: 6.22) and the interleukin 12 receptor, beta 1 (p = 0.000834, fold change: 1.87). This impression was confirmed by pathway analysis indicating deregulation of pathways like the NO2-dependent IL 12 Pathway in NK cells and the Th1/Th2 Differentiation and the Platelet Amyloid Precursor Protein Pathway.Functional assays, confirming the biological importance of these factors have been performed for example an assay to test the effect of IL12 on AML cellines.Furthermore we screened our data for new potential therapeutic target structures, specifically on enriched CD34+CD38- cells of NPM1mut patients, comparing the expression level of target genes to NPM1wt CD34+CD38- cells, and the expression level on HSC. Amongst others, our most promising candidates are SERPINA1 (p = 0.0062344, fold change: 14.32), OSCAR (p = 6.11E-05, fold change: 9.03) and several further interesting genes. These genes could be used in order to target CD34+CD38- cells of NPM1mut patients in a therapeutic manner.Taken together, we successfully enriched the CD34+CD38- fraction of NPM1mut and NPM1wt AML patients and performed Microarray analysis, unraveling gene expression differences between the two patients groups, which seem to be of an immunological nature. This could be a factor, amongst others, for the better overall survival of the NPM1mut patient group. Furthermore we described new potential targets structures on CD34+CD38- cells for NPM1mut patient's treatment. Disclosures:No relevant conflicts of interest to declare.

CEBPA gene mutation analysis in acute myeloid leukemia

To investigate the incidence, molecular features and clinical significance of CCAAT/enhancer binding protein alpha (CEBPA) gene mutation in patients with acute myeloid leukemia (AML). Mutation analysis of the entire coding region of CEBPA gene in 206 de novo AML patients was performed by using polymerase chain reaction (PCR) followed by sequence analysis and fragment length analysis. Of 206 AML patients, 31 (15%) had CEBPA gene mutations, including 23 with double mutations (duCEBPA) and 8 with single mutation (siCEBPA). CEBPA gene mutations presented mainly in M2 subtype or intermediate risk patients. As compared with those with wild type CEBPA gene, patients with mutated CEBPA gene were of higher white blood cell counts [20.92(0.86-351.43)× 10(9)//L vs 8.17(0.47-295.2) × 10(9)/L, P=0.003], higher hemoglobin levels [97.5(51-128) g/L vs 80.5(13-153) g/L, P=0.015] and lower platelet counts [27.5(5-81)× 10(9)//L vs 44(3-548)× 10(9)/L, P=0.004]. Patients with CEBPA gene mutation had higher complete remission (CR) rate than those with wild type (P=0.009). While co-existing of NPM1 and siCEBPA mutations was observed in M5 subtype (2/8, 25%), NPM1 gene mutation was not present in any patients with duCEBPA mutation (0/23, 0%). Dynamic tracking analysis showed that CEBPA mutations disappeared at CR, and the same mutations re-appeared at relapse. When compared to sequence analysis, the coincidence rate of CEBPA mutations detected by fragment length analysis was 100% (54/54). CEBPA gene mutation is a recurring genetic change in AML patients and has a certain correlation with clinical and laboratory features. It could be reliably used as a potential marker for minimal residual disease follow up. The prognostic significance of co-existing of siCEBPA with NPM1 mutations in patients with AML-M5 subtype needs further investigation.

Effect of NPM1 and FLT3 Mutations on the Outcomes of Elderly Patients With Acute Myeloid Leukemia Receiving Standard Chemotherapy

The effect of prognostically important gene mutations (MUTs), nucleophosmin (nucleolar phosphoprotein B23, numatrin) (NPM1) and fms-related tyrosine kinase 3 (FLT3), in elderly patients with acute myeloid leukemia (AML) is not well defined. We analyzed 557 patients, 65 years of age or older with newly diagnosed AML, treated at our institution between 2000 and 2010 with cytotoxic chemotherapy. NPM1 and FLT3 analysis were available in 146 patients (26%) and 388 patients (70%), respectively. NPM1 and FLT3 MUTs occurred in 16% and 12% of patients, respectively. No difference in median overall survival was observed between FLT3-MUT and NPM1-MUT patients who received cytotoxic chemotherapy. Outcome was significantly better among patients with NPM1-MUT/FLT3-wild type (WT) genotype (n= 14) compared with patients carrying FLT3/NPM1 genotypes other than NPM1-MUT/FLT3-WT (n= 125). The complete remission rates were 71% and 49%, respectively (P= .11). The median survival was 21.5 months vs. 9.0 months and estimated 2-year survival rates were 51% vs. 38%, respectively (P= .003). NPM1 and FLT3 MUTs appear to occur less frequently in elderly AML patients. The prognostic effect of isolated NPM1- or isolated FLT3-MUT is minimal. Elderly AML patients with NPM1-MUT/FLT3-WT genotype have significantly improved outcomes compared with patients with other NPM1/FLT3 genotypes when treated with cytotoxic chemotherapy.

Favorable outcome of patients with acute myeloid leukemia harboring a low-allelic burden FLT3-ITD mutation and concomitant NPM1 mutation: relevance to post-remission therapy

AbstractRisk associated to FLT3 internal tandem duplication (FLT3-ITD) in patients with acute myeloid leukemia (AML) may depend on mutational burden and its interaction with other mutations. We analyzed the effect of FLT3-ITD/FLT3 wild-type (FLT3wt) ratio depending on NPM1 mutation (NPM1mut) in 303 patients with intermediate-risk cytogenetics AML treated with intensive chemotherapy. Among NPM1mut patients, FLT3wt and low ratio (<0.5) subgroups showed similar overall survival, relapse risk, and leukemia-free survival, whereas high ratio (≥0.5) patients had a worse outcome. In NPM1wt AML, FLT3-ITD subgroups showed a comparable outcome, with higher risk of relapse and shortened overall survival than FLT3wt patients. Allogeneic stem cell transplantation in CR1 was associated with a reduced relapse risk in all molecular subgroups with the exception of NPM1mut AML with absent or low ratio FLT3-ITD. In conclusion, effect of FLT3 burden is modulated by NPM1 mutation, especially in patients with a low ratio.

CD34 expression on bone marrow blasts is a novel predictor of poor prognosis independent of FlT3-ITD in acute myeloid leukemia with the NPM1-mutation

To explore the prognostic value of CD34 expression in NPM1-mutated acute myeloid leukemia (NPM1m+AML), seventy-one NPM1m+AML patients were retrospectively analyzed. The patients with >7% CD34 expression (according to the ROC analysis) had a lower complete remission (CR) rate after 1 course of induction, disease-free survival (DFS), and overall survival (OS) compared to those with ≤7% CD34 expression (p=0.0038; p=0.001; p<0.0001). A multivariate analysis revealed that CD34 expression is a prognostic factor that is independent of FlT3-ITD for relapse, DFS and OS. We established a novel prognostic model based on the CD34 and FLT3 status at diagnosis, which could facilitate the segregation of patients into three prognostically different subgroups. We demonstrate that CD34 expression on blasts is a novel, poor predictor independent of FlT3-ITD in NPM1-mutated patients and established a new prognostic model based on the CD34 and FLT3 status at diagnosis, which may facilitate immediate clinical utility for prognostic stratification and risk-adapted therapeutic choices.

Identification of Two Novel NPM1 Mutations in Patients with Acute Myeloid Leukemia

BackgroundGenetic abnormalities in adult AML are caused most frequently by somatic mutations in exon 12 of the NPM1 gene, which is observed in approximately 35% of AML patients and up to 60% of patients with cytogenetically normal AML (CN-AML).MethodsWe performed mutational analysis, including fragment analysis and direct sequencing of exon 12 of the NPM1 gene, on 83 AML patients to characterize the NPM1 mutations completely.ResultsIn this study, NPM1 mutations were identified in 19 (22.9%) of the 83 AML patients and in 12 (42.9%) of the 28 CN-AML patients. Among the 19 patients with NPM1 mutations, type A NPM1 mutations were identified in 16 (84.2%) patients, whereas non-A type NPM1 mutations were observed in 3 (15.8%) patients. Two of the 3 non-A type NPM1 mutations were novel: c.867_868insAAAC and c.869_873indelCTTTAGCCC. These 2 novel mutant proteins display a nuclear export signal motif (L-xxx-L-xx-V-x-L) less frequently and exhibit a mutation at tryptophan 290 that disrupts the nucleolar localization signal.ConclusionsThis study suggests that novel NPM1 mutations may be non-rare and that supplementary sequence analysis is needed along with conventional targeted mutational analysis to detect non-A types of NPM1 mutations.

NPM1, IDH1/2 and DNAH11 Gene Mutations Can Improve a Prognostic Stratification of Acute Myeloid Leukemia Patients with Normal Karyotype but Not Harboring FLT3/ITD Mutation.

AbstractAbstract 2534▪▪This icon denotes a clinically relevant abstract Background:Acute myeloid leukemia with normal karyotype (AML-NK) is known to be heterogeneous in the molecular level. Accordingly, it has become more critical to dissect this group of patients according to their prognosis using a molecular genetic technology. We attempted to analyze the incidence and prognostic implication of genetic abnormalities on survival in 426 adult patients with AML-NK. Methods:A total of 67 AML-NK patients achieved complete remission (CR), candidate mutations in 21 genes were identified by whole exome sequencing which has 41–89× coverage and by single-nucleotide polymorphism array analysis using marrow mononuclear cells at diagnosis of AML-NK. Subsequently, mutation analysis of 11 genes (i.e. FLT3/ITD, NPM1, DNMT3a, IDH1, IDH2, TET2, NRAS, WT1, DNAH11, SF3B1, and PHF6) which are known to be involved in the pathogenesis of hematologic diseases, were performed using Sanger sequencing in another subset of 359 AML-NK patients as a validation cohort. Results:Of 426 patients in total (median age: 51, ranges: 15–85), FLT3/ITD, NPM1, and DNMT3a mutations were associated with higher leukocytes counts at presentation of AML-NK. In 284 patients who received standard remission induction (RI) chemotherapy (excluding 119 patients with conservative treatment and 22 early death/1 follow-up loss after RI chemotherapy), those with FLT3/ITD mutation were significantly associated with a higher risk of relapse (p=0.02), a shorter leukemic-free survival duration (LFS)(p<0.01) or overall survival (OS) (p=0.01). Accordingly, we divided the patients into FLT3/ITD+ and FLT3/ITD− population, and analyzed their treatment outcomes according to the other mutations. In the FLT3/ITD− group (n=200), those with NPM1 mutation showed a higher CR rates after one or two cycles of RI chemotherapy (p<0.01) and a longer OS duration (p<0.01), hazard ratio (HR) 0.43, 95% confidence interval (CI) 0.25–0.73, adjusted by other clinical variables including age, leukocyte counts at diagnosis, and transplantation (Figure 1). In the FLT3/ITD+ patients (n=84), NPM1 mutation was found to be a favorable prognostic factor showing a lower relapse rate (p=0.00), a longer LFS duration (p<0.01, HR 0.35, 95% CI 0.18–0.70), and OS duration (p=0.04, HR 0.55, 95% CI 0.31–0.98) in NPM1 mutated patients. In addition, OS was significantly different in favor of those with IDH2, especially R140Q IDH2 mutation, (p=0.04, HR 0.30, 95% CI 0.09–0.99), whereas DNAH11 mutation was associated with inferior OS (p<0.01, HR 5.78, 95% CI 1.65–20.25). Accordingly, we stratified the FLT3/ITD+ patients into three subgroups according to the NPM1, IDH1/2 and DNAH11 mutation status, Group 1: NPM1 mutation and IDH1 or 2 mutations (n=16), Group 2: isolated DNAH11 mutation (n=4) and Group 3: all mutations were negative (n=64). The group 1 showed significantly better OS than group 2 (p<0.01, HR 16.90, 95% CI 3.48–82.15) or group 3 (p<0.01, HR 3.40, 95% CI 1.20–9.55) (Figure 2). In a subgroup analysis of younger patients less than 60 years of age, similar outcomes were also observed in favor of group 1 in terms of OS (data not shown). Conclusion:Our study confirmed that NPM1 mutation is an independent prognostic factor in adult patients with AML-NK not harboring FLT3/ITD mutation. In addition, several other genetic markers were identified as prognostic including IDH1/2 or DNAH11 mutations as well as NPM1 mutation in a subgroup of AML-NK patients with FLT3/ITD mutation. [Display omitted] [Display omitted] Disclosures:No relevant conflicts of interest to declare.

Mutated Nucleophosmin 1 (NPM1) Is an Immunogenic Target and Patients with NPM1mut Acute Myeloid Leukemia (AML) Showed High Expression of Different Leukemia-Associated Antigens (LAAs)

Abstract 3592Nucleophosmin gene 1 mutations (NPM1mut) are one of the most frequent molecular alterations in AML and distinct immune responses might contribute to the favorable prognosis of AML patients with NPM1mut. Recently, we showed specific T cell responses of CD4+ and CD8+ T cells against epitopes derived from mutated regions of NPM1 (Greiner et al., Blood. 2012 May 16, Epub). In the present study, we investigated clinical parameters and the clinical outcome of NPM1mut AML patients in accordance to their immune responses against different NPM1 epitopes. Moreover, we examined the quantitative expression of different leukemia-associated antigens (LAAs) in NPM1mutAML patients.In ELISpot analysis of 33 healthy volunteers and 27 AML patients, we detected T cell responses of CD4+ and CD8+ T cells against epitopes derived from the mutated region of NPM1. We performed further tetramer assays against the most interesting epitopes and chromium release assays to show the cytotoxicity of peptide-specific T cells. Microarray analysis was performed to analyze the expression of different LAAs in NPM1mut and NPM1wtAML patients.Two epitopes (peptide #1 and #3) derived from NPM1mut induced CD8+ T cell responses. 33% of the NPM1mut AML patients showed immune responses against peptide #1 and 44% against peptide #3. NPM1mut AML patients showed a significantly higher frequency of T cell responses against peptide #3 in contrast to HVs (p=0.046), whereas for peptide #1 the frequency of T cell responses of AML NPM1mut patients and HVs was not significantly different. Specific lysis of pulsed T2 cells but also NPM1mut leukemic blasts was detected in chromium release assays. Therefore, overlapping peptides (OL) were analyzed in ELISpot assays and the peptide called OL8 showed favorable results to activate both CD8+ and CD4+ T cells.We performed survival analysis for these 33 NPM1mut patients analyzed by ELISpot comparing cases with or without specific T cell responses. Our data suggest a trend to a better overall survival (OS) for patients with specific T cell responses against peptide #1 or #3. However, the patient numbers are small and the data have to be interpreted carefully. Analyses with material from larger controlled clinical trials with a high number of patients with NPM1mut AML have to be performed. Our microarray analysis of 30 AML patients showed a high expression of different LAAs like RHAMM, WT-1 and BCL-2 in all subtypes of cells of NPM1mutAML patients, also in leukemic progenitor cells. This demonstrates that NPM1 is an AML subtype suitable for poly-targeted immunotherapeutic trials.Taken together, NPM1mut might constitute an interesting target structure for individualized immunotherapeutic approaches in NPM1mut AML patients. We hypothesize that immune responses to NPM1 mutation may contribute to the favorable prognosis. Disclosures:No relevant conflicts of interest to declare.

Minimal Residual Disease Assessed by WT1 Expression and NPM1 Mutations Specific RQ-PCR Assays Identifies Patients with Distinct Outcomes in the ALFA 0701 Trial and Is Decreased by Treatment with Gemtuzumab Ozogamicin

AbstractAbstract ▪659▪This icon denotes a clinically relevant abstract Background:NPM1 mutations and WT1 expression are frequently identified in acute myeloid leukemia (AML). Both markers have been reported as suitable molecular target for minimal residual disease (MRD) monitoring. Recently, Gemtuzumab Ozogamicin (GO) has been shown to improve event free survival and overall survival in adult AML. Aims:To follow MRD in AML patients with NPM1 mutations (NPM1mut) and/or WT1 expression (WT1+) and treated in the randomized ALFA 0701 GO trial conducted by the Acute Leukemia French Association (Castaigne et al, Lancet 2012), in order to validate their prognostic significance and to evaluate the effect of GO on MRD response. Methods:The ALFA 0701 trial included 278 patients aged 50–70 years with newly-diagnosed de novo AML, randomized to receive or not five doses of 3 mg/m2 GO, on day 1, 4 and 7 of standard induction chemotherapy and on day 1 of two consolidation chemotherapy courses, respectively. A total of 77 NPM1mut (35 in control arm, 42 in GO arm) and 178 WT1+ (87 in control arm, 91 in GO arm) AML patients were studied. WT1 + at diagnosis was defined as a ratio WT1/ABL transcript above 25% in bone marrow (BM) or 5% in peripheral blood (PB) samples. PB and BM samples were collected at diagnosis, after induction and after each consolidation course. MRD levels were assessed using cDNA-based real-time quantitative PCR (RQ-PCR) and reported as the ratio NPM1mut or WT1 transcript/100 ABL transcript. Occurrence of a MRD level below the threshold (NPM1mut <0.1% and WT1 transcript < 0.5% in PB) was defined here as a good MRD response. The prognostic value of MRD was assessed by comparing the outcome of good versus poor MRD responders after induction in terms of cumulative incidence of relapse (CIR) at 18 months. Effect of GO was then evaluated by comparing MRD response in both treatment arms. Results:178 patients (favorable cytogenetics: 4%, intermediate: 69%, unfavorable: 27%) were WT1+. WT1 transcript levels at diagnosis had no prognostic impact on complete remission (CR) rate or CIR. In the 104 patients who achieved CR, post-induction WT1 MRD level was predictive of relapse: 18-month CIR was 70% (95%CI: [49% - 84%]) in poor responders (n=31) versus 38% [26% - 50%] in good responders (n=73) (p=0.0001). When adjusted on cytogenetics, randomization arm and FLT3-ITD status, WT1 MRD remained independently associated with relapse (HR: 2.43, [1.25 – 4.75], p=0.009).Similarly, NPM1mut transcript levels at diagnosis had no prognostic impact on CR rate or CIR. Among the 67 NPM1mut patients who achieved CR, post-induction NPM1mut MRD level was predictive of relapse: 18-month CIR was 64% [45% – 70%] in poor responders (n=50) versus 25% [10% – 42%] in good responders (n=17) (p=0.0007). When adjusted on randomization arm and FLT3-ITD status, NPM1 MRD remained independently associated with relapse (HR: 4.2, [1.2 – 14.3], p=0.02).We were able to evaluate both MRD markers in 53 patients after induction (NPM1+/WT1+ n=16, NPM1+/WT1- n=24, NPM1-/WT1- n= 13). 18-month CIR was significantly different in the 3 groups (respectively 69% [38% - 87%], 40% [19% - 60%] and 25% [5% - 51%], p=0.008). In patients with poor MRD response assessed by NPM1mut, the presence of a positive WT1 MRD level was associated with a higher CIR.NPM1 MRD good response was more frequently observed in GO arm as compared to control arm (OR: 4.38 [2.12 – 9.03], p<0.0001). The rate of good NPM1 MRD response was 41% versus 7% after induction, 76% versus 35% and 93% versus 62% after first and second consolidation in GO and control arms respectively. WT1 MRD good response was more frequently observed in GO arm, although not reaching statistical significance (OR: 1.84 [0.89 – 3.77] p=0.098). The rate of good WT1 MRD response was 76% versus 65% after induction, 87% versus 66% and 87% versus 80% after first and second consolidation, respectively in GO and in control arms (figure 1). Conclusion:Our study confirms the predictive value of MRD based on NPM1 mutations and WT1 expression in patients treated in the ALFA 0701 randomized trial. In multivariate analysis, WT1 and NPM1 MRD levels remained independent prognostic factors for relapse. We showed that treatment with GO significantly improved MRD response in adult AML. [Display omitted] Disclosures:Castaigne:Wyeth: Consultancy.

FLT3-ITD-associated gene-expression signatures in NPM1-mutated cytogenetically normal acute myeloid leukemia

Concomitance of the FLT3-ITD mutation is associated with poor prognosis in NPM1-mutated cytogenetically normal acute myeloid leukemia (CN-AML) patients, and precise studies on its role in leukemogenesis are needed; these may be elucidated at the molecular level by gene express profiling. In the present study, we built a gene-expression-based classifier using prediction analysis of microarray to characterize the FLT3-ITD signature in NPM1-mutated CN-AML patients, which comprised 10 annotated genes, and demonstrated an overall accuracy of 83.8 % in cross-validation. To characterize the signature in another way, differential expression was revealed for 34 genes by class comparison, and the up-regulation of LAPTM4B and MIR155HG was validated by quantitative RT-PCR in our small cohort of NPM1-mutated CN-AML samples, which appeared to be associated with this specific subtype. The 10-gene classifier and differentially expressed genes identified in this study indicate a potential utility for risk-assessed treatment stratification, and suggest new therapeutic targets for these high-risk AML patients.

The Mutated Region of Cytoplasmatic Nucleophosmine 1 (NPM1) Elicits Both CD4+ and CD8+ T Cell Responses

Abstract 2569 IntroductionIn AML, mutations in the nucleophosmin (NPM1) gene are one of the most frequent molecular alterations and predominantly occur in AML with normal cytogenetics. Patients with NPM1 mutation without FLT3-ITD mutation show a favourable prognosis of their disease. The functional role of mutated NPM1 for the improved clinical outcome is under evaluation. Immune responses might be involved in the clinical outcome of the disease. In this work, we demonstrate both CD4+ and CD8+ T cell responses against the mutated region of NPM1. MethodsThe entire amino acid sequences of the NPM1 wild type protein as well as of the mutated cytoplasmic NPM1 types A, B, C and D were screened for HLA-A*0201 binding T cell epitopes using the algorithms of the SYFPEITHI, the Rankpep and the HLA-Bind software programs. Ten peptides with most favourable characteristics were subjected to ELISpot analysis for interferon-γ and granzyme B in 22 healthy volunteers and 27 AML patients to test specific T cell responses of CD8+ T cells. Tetramer assays against the two most interesting epitopes have been performed and chromium release assays have been used to show the cytotoxicity of peptide-specific T cells to lyse T2 cells and leukemic blasts. Moreover, HLA-DR binding epitopes were screened in algorithmic analysis and HLA-DR*0701 binding peptides were exploited to stimulate CD4+ T cells. In the presence of overlapping peptide stimulated CD4+ T cells, NPM1-A specific CD8+ T cells revealed augmented interferon-γ and granzyme B secretion and up-regulation of intracellular interferon-γ. CD4+, CD4-CD8+, CD4-CD8- cell fractions were separated from PBMCs of HLA-A2+DR*0701+ healthy volunteers using a combination of CD4 and CD8 MicroBeads. ResultsTwo epitopes (P3 and P9) derived from the NPM1-mutated protein showed specific T cell responses in healthy volunteers and AML patients. In NPM1-mutated AML patients 33% showed immune responses of CD8+ T cells against peptide P3 and 42% against peptide P9. Specific lysis was detected in chromium release assays NPM1 peptide-primed effector T cells generated from NPM1-mutated AML patients. Tetramer assays showed peptide-specific T cells. To obtain a robust and effective immune response against tumor cells, the activation of CD4 + helper T cells is crucial. Thus NPM1-peptide-A overlapping MHC class II epitopes were searched by primary structure analysis program. Based on plenary search, eight favourable overlapping peptides OL 1–8 were synthesized and exploited for CD4+ T cell stimulation. In granzyme B ELISPOT assay, OL8 co-pulsed NPM1-A CD8+ T cells indicated notable S.I., in contrast other OL1-7 disabled to increase granzyme B secretion. To ensure that Th1 cytokine secretion, under the condition of CD8+ and CD4+ T cells mixed culture, was resulted from NPM1-A CD8+ T cells but not HLA-DR epitope stimulated CD4+ T cells activation, HLA-A2 blocking effect was confirmed in ELISPOT assay. NPM1-A CD8+ T cells co-pulsed with OL6, 7 and 8 showed lesser interferon-γ secretion after HLA-A2 blocking antibody exposure as 73, 35 and 57%. Of note, 83–94% of granzyme B secretion levels were reduced by HLA-A2 blockade administration, and by which NPM1-A CD8+ T cells seemed to be the most probable IFN-gamma and granzyme B producers and CD4+ T cells to interfere with CD8+ T cells. ConclusionTaken together, mutated NPM1 is a promising target structure for specific immunotherapies in AML patients. Disclosures:No relevant conflicts of interest to declare.

DNMT3A mutations Predict for Inferior Outcome in NPM1-Wildtype and Molecular Unfavorable Cytogenetically-Normal Acute Myeloid Leukemia: A Study of the German-Austrian AMLSG

Abstract 415▪▪This icon denotes a clinically relevant abstract Background:Alteration of DNA methylation, a hallmark of epigenetic modification, is currently discussed as one important pathomechanism in leukemogenesis. Using a next-generation sequencing approach, a frameshift mutation of the gene encoding the DNA methyltransferase (DNMT3A) in an acute myeloid leukemia (AML) case was identified. DNMT3A catalyses the addition of a methyl group to the cytosine residue of CpG dinucleotides, thereby affecting promoter methylation status and gene expression. Subsequent sequencing analysis in an independent cohort of 288 AML patients (pts) revealed DNMT3A mutations (DNMT3Amut) in 22% of the pts; mutations were associated with intermediate-risk cytogenetics and poor outcome. Aims:To evaluate frequency and clinical impact of DNMT3Amut in pts with AML aged 18 to 61 years who were treated within AMLSG treatment trials AML HD98A (Schlenk et al., J Clin Oncol 2010;28:4642–8) and AMLSG 07–04 (NCT00151242). Methods:DNMT3A mutation analysis was performed in 1218 AML (HD98A, n=685; AMLSG 07–04, n=533; de novo AML, n=1102; s-AML, n=45; t-AML, n=69) using a DNA-based PCR assay for all coding exons (1 to 23) followed by direct sequencing. The median follow-up was 5.06 years. Results:DNMT3Amut were found with an overall frequency of 19.6% (239/1218); 189 mutations were located in the MTase domain clustering at amino acid R882 (79%). All but one mutation were heterozygous; only 4 cases had two mutations. DNMT3A sequence alterations included 17 frameshift, 4 nonsense, and 222 missense mutations.DNMT3Amut pts were significantly older (P=.01), more frequently females (P=.001), had higher white blood cell and platelet counts (both P<.0001), and higher bone marrow blasts percentage (P=.001). DNMT3Amut were associated with cytogenetically-normal AML (CN-AML, P<.0001), while DNMT3Amut were rare in favorable and adverse-risk karyotypes (P<.0001). Correlations with other molecular markers (NPM1, CEBPA, FLT3, IDH1/2, TET2, ASXL1) revealed a significant association with NPM1 (P<.0001), FLT3-ITD (P<.0001), and IDH1/2 (IDH1R132, P<.0001; IDH2R140, P=.0003; IDH2R172, P=.03) mutations, while co-occurrence of CEBPA (P=.02) and ASXL1 (P=.02) mutations was less frequent.DNMT3A mutational status did not impact complete remission (CR) rate, event-free (EFS) and relapse-free survival (RFS), neither in the whole cohort (P=.09, P=.98, P=.11; respectively) nor in the subgroup of CN-AML (P=.39, P=.79, P=.19, respectively). DNMT3Amut had a negative impact on overall survival (OS) in trend in the whole cohort (P=.07) and significantly in CN-AML (P=.02). In multivariable analyses, DNMT3Amut were in trend associated with a negative prognostic impact on OS (hazard ratio, 1.24; P=.06). In addition, we performed subgroup analyses according to (1) the NPM1 mutational status, and (2) the molecular risk groups of CN-AML (as defined by the European LeukemiaNet classification). DNMT3Amut did not impact OS in NPM1-mutated patients in the whole cohort as well as in CN-AML (P=.34; P=.22; respectively), while in NPM1-wildtype patients DNMT3Amut were associated with inferior OS in both, the whole cohort and in CN-AML (P=.001; P=.005; respectively). In molecular unfavorable CN-AML (NPM1-wildtype with or without FLT3-ITD, NPM1-mutated with FLT3-ITD, CEBPA-wildtype), DNMT3Amut were significantly associated with worse OS (P=.002) compared with DNMT3A-wildtype pts, even outweighing FLT3-ITD as an unfavorable prognostic marker. There was no effect of DNMT3Amut in molecular favorable-risk CN-AML. Conclusions:DNMT3A mutations are confirmed as frequent genetic aberrations in AML, associated with normal karyotype, NPM1, FLT3-ITD, and IDH1/2 mutations. DNMT3Amut predicts for inferior outcome in molecularly-defined subsets of AML, that is, NPM1-wildtype AML and molecular unfavorable CN-AML. As a single marker, DNMT3Amut only had a moderate effect on outcome. Disclosures:No relevant conflicts of interest to declare.

Histone Deacetylase Inhibitors Induce Cell Growth Inhibition and Apoptosis in NPM1-Mutated AML Cells: A Possible Role for Epigenetic Therapies in AML Carrying NPM1 Gene Mutations

Abstract 2621Acute myeloid leukemia (AML) carrying nucleophosmin (NPM1) gene mutations account for about one-third of adult AML, show distinctive biological and clinical features and have been included as a provisional entity in the 2008 World Health Organization (WHO) classification of myeloid neoplasms. In spite of the relatively good prognosis of NPM1-mutated AML, there are still cases that show poorer outcome, especially those associated with FLT3-ITD mutation and elderly patient population. Therefore new therapeutic strategies need to be explored. As for other types of cancer, evidence is emerging that, besides the genomic DNA alterations, epigenetic dysregulation may play a role in AML pathogenesis. We investigated the effects of sodium butyrate, a short-chain fatty acid which has long been known to be a histone deacetylase inhibitor (HDACi) able to induce maturation in normal and tumor cells, in cellular models of NPM1-mutated AML in vitro: i) the OCI/AML3 cell line, previously identified as a human AML cell line carrying cytoplasmic mutated NPM1 in the absence of FLT3-ITD; ii) primary AML cells originated from a patient with NPM1-mutated AML bearing FLT3-ITD mutation (MONT1) and propagated as cell line in NOD/SCID mice; and iii) primary AML cells from NPM1-mutated AML patients at diagnosis. In either cell lines or patients’ primary AML cells carrying NPM1 mutation, but not in the U937 or OCI/AML2 cell lines (not harboring NPM1 gene mutation) used as control, growth arrest, cell cycle arrest (G0-G1 phase) and pro-apoptotic effects were evident after 24 hrs and marked after 48 hrs of treatment with doses of drug of 0.5–1 mM. No signs of differentiation were evident at morphological and flow cytometric examinations of treated cells. Western blot analysis with specific antibodies showed that levels of either NPM1 mutant or wild-type protein did not appear significantly affected by treatment with sodium butyrate. Interestingly, induction of apoptosis was associated with marked activation of caspase-8, suggesting involvement of the death cell receptors pathway. Indeed, flow cytometric analysis showed 2-fold increased expression of TRAIL-receptor DR5 upon drug treatment at 48 hrs. Moreover, concomitant treatment with a specific caspase-8 inhibitor prevented sodium butyrate induced-cell growth arrest and markedly reduced apoptosis in OCI/AML3 cell line. Derivatives of butyrate, which are capable of acting as HDAC inhibitors, are currently being investigated in clinical trials; preliminary results suggest their potential applicability in cancer treatment. Here we investigated the effect of panobinostat (LBH589), a pan HDACi, in human AML cells lines and show results similar to those observed upon sodium butyrate treatment in OCI/AML3 cells. In particular, we show that panobinostat induces dose-dependent cell growth arrest, with G0-G1 block, associated with p21 protein induction, and apoptosis, associated with TRAIL-receptor DR5 upregulation and activation of caspase 8, in AML cells harboring NPM1 gene mutation. However, unlike what was observed with sodium butyrate, panobinostat induced also dowregulation of NPM1 mutant (and to a lesser extent, wild type) protein. Mechanisms underlying this phenomenon are under investigation. In particular, the possible role of acetylation of the heat shock protein Hsp90 (as a consequence of panobinostat-mediated HDAC6 inhibition) with disruption of its chaperone functions followed by instability of its client proteins, including cytoplasmic NPM1, is explored. Disclosures:Falini:Xenomics: Patents & Royalties.

Performance and Clinical Evaluation of a Sensitive Multiplex Assay for the Rapid Detection of Common NPM1 Mutations

Determination of NPM1 mutation status has become essential for the molecular classification of acute myeloid leukemias (AML). Methods with high clinical sensitivity and specificity adapted to the molecular laboratory workflow are required for the diagnosis, prognosis, and monitoring of AML with normal karyotype. We report here the development and evaluation of a novel, streamlined, RNA-based assay for the rapid multiplex detection of common NPM1 mutations in a 96-well assay format. Using synthetic transcripts and total RNA from leukemic cell lines, we show that the assay can specifically detect NPM1 wild-type and mutants A, B, D, or J transcripts in the same reaction. Dilution experiments indicate an assay dynamic range >4 log units with an analytical sensitivity of approximately 0.01%. Evaluation of 69 clinical specimens at initial diagnosis resulted in 100% agreement with reference methods. Of patients with AML with normal karyotype, 53% carried one of four different mutations. The assay was also combined with other laboratory-developed tests to simultaneously detect NPM1 mutant transcripts and fusion transcripts resulting from t(8;21) or inv(16) in a single reaction well. Overall, these results show that the assay is a versatile and specific tool for the screening of NPM1 mutations in patients with AML. Its high analytical sensitivity further suggests potential utility for the monitoring of residual disease in AML with normal karyotype.

Incidence and significance of FLT3-ITD and NPM1 mutations in patients with normal karyotype acute myeloid leukaemia

Acute myeloid leukaemia (AML) is a heterogeneous clonal disorder of haematopoietic progenitor cells. Approximately half of all adult AML patients have a normal karyotype (NK-AML) and an intermediate risk prognosis. To determine the incidence and prognostic significance of NPM1 and FLT3-ITD mutations in a population of patients with NK-AML. FLT3-ITD and NPM1 mutation status was retrospectively sought in presentation samples from 44 NK-AML patients. FLT3-ITD and NPM1 mutations were detected in 45.5 and 54.5% of patients, respectively, allowing stratification according to genotype. FLT3-ITD and NPM1 mutation status can be defined in NK-AML. Prospective screening for these mutations is advocated in all NK-AML patients, as the genotype is of clinical importance when considering treatment options including stem cell transplantation.

Dissecting the Hierarchical Level of Hematopoietic Progenitors' Involvement in AML with NPM1 Gene Mutation and Their Engraftment Potential in Immunocompromised Mice.

Abstract 480Acute myeloid leukemia with mutated NPM1 gene and cytoplasmic nucleophosmin (NPMc+ AML) [Falini B et al, NEJM 2005;352:254-266] is a new entity of WHO classification that shows distinctive biological and clinical features [Falini B et al, Blood 2007;109:874-885] which include negativity for CD34 antigen expression at both immunohistochemistry and gene expression profiling. Flow cytometric analysis shows that, in most NPM1-mutated AML, percentages of CD34+ cells are in the low range (< 5-10%). Detection of NPM1 mutations by molecular techniques and/or immunohistochemistry and Western Blot analysis with specific antibodies provides an important tool for tracking the genetic lesion in leukemic cells at different hierarchical stage. We previously reported involvement by NPM1 gene mutation of the CD34+ cell fraction isolated from patients with NPM1-mutated AML, and, in one case, the involvement, in particular, of the early progenitor CD34+/CD38- [Martelli MP et al, Blood (ASH Annual Meeting Abstracts) 2008;112:307]. Here we expand and confirm our previous observation in 5 cases of CD34-negative NPM1-mutated AML. CD34+/CD38- cells were isolated by either FACS (3 cases, purity >98%) or MACS-sorting (2 cases, purity >92%) and analyzed by molecular analysis and Western Blot with a specific anti-NPM1 mutant antibody, respectively. The presence of either NPM1 gene mutation or mutant protein was demonstrated in all samples analyzed proving the CD34+/CD38- cells belong to the leukemic clone. This cell subpopulation displayed also immunophenotypic features classically associated to leukemic stem cells (LSCs) (CD123+/CD33+/CD90-) in all (16/16) samples analyzed, suggesting they might actually represent the LSCs in NPM1-mutated AML. Indeed, CD34+ cell fraction isolated from NPM1-mutated AML was able to generate leukemia in immunocompromised mice resembling the original patient's disease. However, there is experimental evidence that, at least in some CD34-negative AML, also the CD34- population may contain LSCs. Whether the CD34- cell compartment in NPM1-mutated AML is also able to engraft and outgrow into leukemia in mice remains to be clarified. For this purpose, we assessed the engraftment ability of CD34- cells from 5 NPM1-mutated AML patients. No engraftment was observed in one case. Interestingly, in three patients with myelomonocytic (M4, 2 cases) and myelocytic (M2, 1 case) AML, the CD34- fraction resulted into marrow engraftment by human CD45+/CD33+ myeloid cells that, at morphological and immunohistological grounds, consisted of a mixed population of macrophage cells expressing the CD68 (PG-M1) antigen and mature looking myeloperoxidase (MPO)-positive cells. This pattern possibly reflects short-term engraftment by leukemic cells devoid of self-renewal potential that differentiated into mature elements. However, the neoplastic nature of engrafted cells could be established with certainty only in one case by western blotting detection of NPM1 mutant protein. Immunohistochemistry could not help in these cases to establish the leukemic nature of human cells since terminally differentiated leukemic cells in NPM1-mutated AML show nucleus-restricted NPM1 positivity. In contrast, the pure CD34+ fraction (availabel for comparison in one of these three cases) engrafted as AML with clear blastic morphology and cytoplasmic dislocation of nucleophosmin. In a fourth patient, the highly purified CD34- fraction from relapsed NPM1-mutated AML engrafted in mice with a typical AML picture. These preliminary findings suggest that in general the CD34- fraction from NPM1-mutated AML may have more limited engraftment potential than the CD34+ fraction. Further studies are ongoing to address this issue. Disclosures:Falini:Xenomics: Patents & Royalties.

Acute Myeloid Leukemia with Mutated NPM1 Presenting with Life-Threatening, Either Arterial or Venous, Thromboembolism: a Report of 4 Cases.

Abstract 4135Acute myeloid leukemia (AML) expressing mutated NPM1 gene and cytoplasmic nucleophosmin (NPMc+ AML) [Falini B et al, NEJM 2005;352:254-266] is a new entity of WHO classification that shows distinctive biological and clinical features. AML with mutated NPM1 usually presents with a high white blood cell count; the bone marrow biopsy is usually markedly hypercellular and leukemic cells frequently show myelomonocytic or monocytic features, with dysplasia and involvement of two or more cell lineages in about 25% of cases. Lack, or low expression, of CD34 in over 90% of cases is the most distinctive immunophenotypic feature of NPM1-mutated AML and is independent of leukemic cell maturation. NPM1 gene mutation without concomitant FLT3-ITD identify a subgroup of AML patients with a favorable prognosis and has been associated with an approximately 50-60% probability of survival at 5 years in younger patients. Here we report 4 out of 41 (10%) patients, admitted at our Hospital in the last year, with new-diagnosed AML with mutated NPM1 presenting with life-threatening thromboembolic (either arterial or venous) events. The main characteristics of these patients are summarized in Table 1. The patients had neither personal nor family history concerning thromboembolism. Hyperleukocytosis was a common feature of the vast majority of NPM1-mutated AML patients at diagnosis. Immunophenotypic analysis did not show a peculiar phenotype in these patients.Table 1Characteristics of patients with NPM1-mutated AML and thrombosis.Case report noAgeSex (M/F)FAB subtypeWBC/mmcType of thrombosisSite of thrombosis141FM114970arterialAnterior interventricular branch of left coronary artery256MM493990arterialexternal iliac and femoral (right limb)363MM2113000deep venousgreat saphenous veins (bilateral)473FM4190000deep venousiliac and femoralIn two patients (cases 1 and 2), the arterial thromboembolic event (acute myocardial infarction and acute ischemia of right lower limb, respectively) presented about one month before diagnosis of leukemia. In the other 2 patients (cases 3 and 4), deep venous thromboembolism was concomitant with the diagnosis of leukemia. One patient (case 4), who could not initiate chemotherapy for severe concomitant renal failure, died few days after diagnosis. The other patients recovered from the acute event and upon diagnosis of leukemia were promptly treated with standard polychemotherapy which allowed to obtain complete hematological remission associated with complete resolution of the thromboembolic event. The clinical course after chemotherapeutic treatment of the patients outlines the importance and life saving role of early chemotherapy even under adverse circumstances. The pathogenesis of thromboembolic disease in hematological malignancies is complex and multifactorial: tumor cell-derived procoagulant, fibrinolytic or proteolytic factors and inflammatory cytokines affect clotting activation. Other important factors include infectious complications and hyperleukocytosis. However, large vessel thrombosis is a very rare clinical presentation. Our report of severe thromboembolic events at presentation in AML with mutated NPM1 suggests some still unidentified biological features of this leukemia which we are currently investigating. Disclosures:No relevant conflicts of interest to declare.