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Allogeneic hematopoietic stem cell transplantation (alloHSCT) is a curative treatment for hematologic malignancies. Acute and chronic graft-versus-host disease (GvHD) are the major immune-mediated complications after alloHSCT. However, there is controversy whether neurologic complications after alloHSCT might represent manifestations of GvHD. We report three patients who acquired distinct, severe immune-mediated peripheral or central nervous system diseases after alloHSCT without other, concomitant GvHD manifestations. One patient had been diagnosed with B-cell chronic lymphocytic leukemia and two patients with high risk myelodysplastic syndrome. Patient #1 presented as LGI1- and GAD-IgG positive immune-mediated encephalitis, patient #2 was diagnosed with MOG-IgG positive encephalomyelitis, and patient #3 had chronic inflammatory polyneuropathy associated with SSA(Ro)-IgG positive Sjögren’s syndrome. 100% donor chimerism was detectable in the peripheral blood in all three. The specific antibodies were undetectable in donors’ and patients’ blood before alloHSCT suggesting that the antibodies had arisen from the transplanted donor immune system. Early intensive immunotherapy led to improvement of clinical symptoms and stability of the neurological disease, however, at the cost of losing the graft-versus-malignancy effect in one patient. In conclusion, we provide evidence of isolated, severe allo-immune diseases of the peripheral and central nervous system as complications of alloHSCT (“neuro-GvHD”). Interdisciplinary surveillance and thorough diagnostic work-up are needed for early diagnosis and treatment of neuro-immunologic complications after alloHSCT to improve the otherwise poor outcome.

Monitoring of measurable residual disease (MRD) provides prognostic information in patients with Nucleophosmin1-mutated (NPM1mut) acute myeloid leukemia (AML) and represents a powerful tool to evaluate treatment effects within clinical trials. We determined NPM1mut transcript levels (TLs) by quantitative reverse-transcription polymerase chain reaction and evaluated the prognostic impact of NPM1mut MRD and the effect of gemtuzumab ozogamicin (GO) on NPM1mut TLs and the cumulative incidence of relapse (CIR) in patients with NPM1mut AML enrolled in the randomized phase 3 AMLSG 09-09 trial. A total of 3733 bone marrow (BM) samples and 3793 peripheral blood (PB) samples from 469 patients were analyzed. NPM1mut TL log10 reduction ≥ 3 and achievement of MRD negativity in BM and PB were significantly associated with a lower CIR rate, after 2 treatment cycles and at end of treatment (EOT). In multivariate analyses, MRD positivity was consistently revealed to be a poor prognostic factor in BM and PB. With regard to treatment effect, the median NPM1mut TLs were significantly lower in the GO-Arm across all treatment cycles, resulting in a significantly greater proportion of patients achieving MRD negativity at EOT (56% vs 41%; P = .01). The better reduction in NPM1mut TLs after 2 treatment cycles in MRD positive patients by the addition of GO led to a significantly lower CIR rate (4-year CIR, 29.3% vs 45.7%, P = .009). In conclusion, the addition of GO to intensive chemotherapy in NPM1mut AML resulted in a significantly better reduction in NPM1mut TLs across all treatment cycles, leading to a significantly lower relapse rate.

Introduction: Myeloid neoplasia, including acute myeloid leukemia and myelodysplastic syndrome are heterogeneous hematopoietic stem cell disorders which are marked by the acquisition of somatic alterations and clonal evolution 1. Patients with myeloid neoplasia are classified due to the WHO classification systems and besides clinical and hematological criteria, cytogenetic and molecular genetic alterations highly impact treatment stratification 2. In routine diagnostics, a combination of methods is used to decipher different types of genetic variants, i.e. single nucleotide variants (SNVs), insertions/deletions (indels), structural variants (SVs) and copy number variations (CNVs) which may not be detected using one single method. Methods: We used a bioinformatic approach to analyze clonal evolution and genetic architecture in patients with myeloid neoplasia using single nucleotide variants (SNVs), insertions/deletions (indels), structural variants (SVs) and copy number variations (CNVs). Six patients were comprehensively analyzed using karyotyping, fluorescence in situ hybridization (FISH), array-CGH and a custom NGS panel with 148 genes/ gene regions that are recurrently affected in patients with hematologic neoplasia. At the initial time point or during disease course all patients showed many genomic variants: Two patients (#1, #2) were analyzed at one time point (initial), two patients (#3, #4) were analyzed at two time points (initial and progression), one patient (#5) was analyzed at four time points (initial, progression, remission, relapse), and one patient (#6) was analyzed at five time points (initial, remission, relapse, progression, remission). Results and Conclusions: Clonal evolution was reconstructed manually, integrating all mutational information on SNVs, indels, SVs and CNVs 3. Cancer cell fractions (CCFs) for SNVs and indels were estimated based on VAFs, assuming heterozygous variants (2*VAF=CCF). CCFs for SVs and CNVs were estimated based on cell counts reported for karyotyping and FISH analyses. For SVs as well as CNVs, which were only detected by array-CGH, CCF was estimated based on logRatio. In case of a CNV overlapping the position of an SNV or indel, calculation of CCF is less straightforward. Altogether, we differentiate between three cases: 1) The CNV occurred prior to the SNV/indel, but in the same cells. 2) The SNV/indel occurred prior to the CNV, but in the same cells. 3) SNV/indel and CNV exist in parallel, independent of each other. The bioinformatic approach reconstructed clonal evolution (linear and/or branching) for all patients and the results were visualized by fishplots. We identified alterations, which play a role in the pathogenesis of the disease (driver) and alterations, which occur during disease development (passenger). On two samples, we showed that reconstruction of clonal evolution is possible even with data from one time point only. For other samples, providing data on more than one time point, the effect of therapy was estimated. This bioinformatic approach offers the possibility of analyzing clonal evolution and genetic architecture at one or more time points of analysis. The visualization of the results in fishplots contributes to a better understanding of genetic architecture and helps to identify possible targets for the disease (personalized therapy). Furthermore, this model can be used to identify markers in order to assess minimal residual disease (MRD). Figure 1 Reconstruction of clonal evolution (time point of analysis: black triangle) for patient #4 (diagnosis: secondary acute myeloid leukemia). References: 1. Doulatov S, Papapetrou EP. Studying clonal evolution of myeloid malignancies using induced pluripotent stem cells. Curr Opin Hematol. 2021;28(1):50-56. 2. Edited by Swerdlow SH CE, Harris NL, Jaffe ES, Pileri SA, Stein H, Thiele J. WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues. International Agency for Research on Cancer. 2017;Revised 4th edition. 3. Reutter K, Sandmann S, Rohde J, et al. Reconstructing clonal evolution in relapsed and non-relapsed Burkitt lymphoma. Leukemia. 2021;35(2):639-643. Figure 1 Figure 1. Disclosures Thol: Jazz: Honoraria; BMS/Celgene: Honoraria, Research Funding; Abbvie: Honoraria; Astellas: Honoraria; Novartis: Honoraria; Pfizer: Honoraria. Heuser: Daiichi Sankyo: Membership on an entity's Board of Directors or advisory committees, Research Funding; Bayer Pharma AG: Research Funding; Roche: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS/Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Karyopharm: Research Funding; Tolremo: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Honoraria; Jazz: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Astellas: Research Funding; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding; BergenBio: Research Funding.

Introduction: MLN-eo associated with gene rearrangements of PDGFRA, PDGFRB, FGFR1, or PCM1-JAK2 are rare haematological neoplasms primarily affecting adults. Eosinophilia commonly occurs but may also be absent. The heterogeneous clinical picture and the rarity of the disease, especially in children, may delay an early diagnosis. MLN-eo are characterized by constitutive tyrosine kinase activity due to gene fusions. It is thus of prognostic importance to obtain a prompt genetic diagnosis to start a specific therapy. Here we report two female paediatric cases of MLN-eo (6 months and 13 years old at initial diagnosis). Methods: In both cases, bone marrow morphology, karyotyping, fluorescence in-situ hybridization analysis (FISH) via break apart probes (PDGFRB (5q32), FGFR1 (8p12), JAK2 (9p24), FIP1L1/CHIC2/PDGFRA (4q12)), targeted RNA sequencing and in one case array CGH were performed. Results: The 6 months old girl was admitted to hospital with a 3-month history of rash and leukocytosis with eosinophilia. The skin showed multiple purpuric lesions (Fig 1 A/B). Mild splenomegaly was noted. White blood count (WBC) was 48000/µl with 38% eosinophils. Bone marrow trephine showed hypercellular marrow with mild fibrosis and eosinophilia without increase in blasts. Biopsy of a skin nodule displayed a histological pattern of interface dermatitis with eosinophilic infiltrate. (Fig 1 C/D). Fluorescence R-banding showed a normal karyotype (46,XX) (Fig. 2 A). However, FISH and array CGH detected an interstitial deletion of 5` PDGFRB (5q32) in 61 % of interphase nuclei (Fig. 2 B-D). Targeted RNA sequencing (RNA-seq) confirmed, as the array CGH suggested, the suspected TNIP1/PDGFRB fusion. According to the WHO criteria, diagnosis of a myeloid neoplasia with PDGFRB rearrangement due to an interstitial deletion in 5q was made. Because of the PDGFRB rearrangement, imatinib (250 mg/m²/d) therapy was started. Leukocyte and eosinophil counts normalized within 4 days without signs of tumour lysis. Skin lesions disappeared within 2 weeks. After 4 weeks, the dose was reduced to 100 mg/m² 3 x/week. Now at 14 months of age, peripheral counts continue to be normal and the fusion transcript is not detectable in the peripheral blood. The 13 years old girl was admitted with severe tachypnoea due to pleural effusions, hepatosplenomegaly and lymphadenopathy. Echocardiography showed endocarditis, left ventricular fibrosis and mitral insufficiency. WBC was 112170 /µL with 39% eosinophils. Bone marrow aspirate and trephine showed a feature of myeloproliferative neoplasia (MPN) with eosinophilia. The karyotype was normal. A rearrangement involving the FGFR1 locus was detected by FISH (Fig. 3 B/C). Splitting of the probe signals indicated an inversion on chromosome 8. Targeted RNA sequencing revealed a PCM1-FGFR1 fusion transcript. Diagnosis of a MLN-eo with FGFR1 rearrangement and evidence of a PCM1-FGFR1 fusion, most likely caused by an inversion on chromosome 8, was made. The girl stabilized after therapy with prednisone, vincristine, hydroxycarbamide and anti-IL-5 antibody. Peripheral blood counts normalized within 2 weeks. Eight weeks after initial diagnosis she presented with signs of a transient ischemic attack, respiratory distress and arterial hypotension. At that time WBC was 139000/µl with 53% myeloid blasts and 5% eosinophils. Trisomy 8 was detected in all metaphases and 88% of cells in FISH (Fig.3 A-C). Diagnosis of a progression to a myeloid blast phase was made. Induction chemotherapy (cytarabine, idarubicin, etoposidphosphate) was administered. On day +22 bone marrow aspirates showed the persisting picture of MPN. Preparations for hematopoietic stem cell transplantation (HSCT) and ponatinib therapy were begun, but cardiac and respiratory insufficiency that developed during chemotherapy were fatal. Conclusion: As these two cases have shown, standard cytogenetic and molecular methods may not be sufficient to diagnose MLN-eo due to cytogenetically cryptic aberrations. Thus, genetic diagnosis must be precise and quick (e.g. break apart FISH, targeted RNA-seq) in order to initiate adequate therapies with tyrosine kinase inhibitors or HSCT. Patients with rearrangements of PDGFRA or PDGFRB usually respond well to imatinib, whereas patients with FGFR1 and JAK2 gene fusions exhibit more aggressive diseases with variable sensitivity to tyrosine kinase inhibitors and have an early indication for HSCT. Figure 1 Figure 1. Disclosures Reiter: Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel expenses, Research Funding; Blueprint Medicines: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel expenses; Incyte: Membership on an entity's Board of Directors or advisory committees, Other: Travel expenses; AOP Orphan Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel support; Deciphera: Membership on an entity's Board of Directors or advisory committees, Other: Travel expenses; Abbvie: Membership on an entity's Board of Directors or advisory committees; Celgene/BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel support.

Complete donor chimerism is strongly associated with complete remission after allogeneic stem cell transplantation (allo-SCT) in patients with hematologic malignancies. Donor-derived allo-immune responses eliminate the residual host hematopoiesis and thereby mediate the conversion to complete donor chimerism. Recently, cytomegalovirus (CMV) reactivation was described to enhance overall T cell reconstitution, to increase graft-versus-host disease incidence, and to reduce the leukemia relapse risk. However, the link between CMV and allo-immune responses is still unclear. Here, we studied the relationship between CMV-specific immunity, overall T cell reconstitution, and residual host chimerism in 106 CMV-seropositive patients transplanted after reduced-intensity conditioning including antithymocyte globulin. In accordance with previous reports, the recovery of CMV-specific cytotoxic T cells (CMV-CTLs) was more frequent in CMV-seropositive recipients (R) transplanted from CMV-seropositive than from seronegative donors (D). However, once CMV-CTLs were detectable, the reconstitution of CMV-specific CTLs was comparable in CMV R+/D– and R+/D+ patients. CD3+ and CD8+ T cell reconstitution was significantly faster in patients with CMV-CTLs than in patients without CMV-CTLs both in the CMV R+/D– and R+/D+ setting. Moreover, CMV-CTL numbers correlated with CD3+ and CD8+ T cell numbers in both settings. Finally, presence of CMV-CTLs was associated with low host chimerism levels 3 months after allo-SCT. In conclusion, our data provide a first indication that CMV-CTLs in CMV-seropositive patients might trigger the reconstitution of T cells and allo-immune responses reflected by the conversion to complete donor chimerism.

Hypomorphic germline variants in TERT, the gene encoding the reverse transcriptase component of the human telomerase complex, occur with a frequency of 3-5% in acute myeloid leukemia. We analyzed the clinical and prognostic impact of the most common TERT A1062T variant in younger patients with acute myeloid leukemia intensively treated within two prospective multicenter trials. Four hundred and twenty patients (age 17-60 years) were analyzed for the TERT A1062T variant by direct sequencing. Fifteen patients (3.6%) carried the TERT A1062T variant. Patients with the TERT A1062T variant had a trend towards less favorable and more intermediate 2/adverse karyotypes/genotypes according to the European Leukemia Net classification. In univariate and multivariate analysis, patients with the TERT A1062T variant had a significantly inferior overall survival compared to wild-type patients (6-year overall survival 20 vs. 41%, p = 0.005). Patients with the TERT A1062T variant showed a high rate of treatment-related mortality: 5/15 (33%) died during induction therapy or in complete remission as compared to 62/405 (15%) of the wild-type patients. In patients with the TERT variant, 14/15 (93%) suffered from non-hematological/non-infectious grade 3/4 adverse events (mostly hepatic and/or mucosal) as compared to 216/405 (53%) wild-type patients (p = 0.006). In multivariate analysis, the TERT A1062T variant was an independent risk factor predicting for adverse events during induction chemotherapy. In conclusion, the TERT A1062T variant is an independent negative prognostic factor in younger patients with acute myeloid leukemia and seems to predispose those patients to treatment-related toxicity.

Introduction: Clonal hematopoiesis initiated by acquired somatic mutations in hematopoietic cells has been identified as an independent driver of increased all-cause mortality, risk of coronary artery disease and heart failure. Oncogenic mutations in isocitrate dehydrogenases 1 and 2 (IDH1 and IDH2) lead to conversion of αKG to R-2-hydroxyglutarate (R-2HG), which is a competitive inhibitor of TET2 and a known oncometabolite. Oncometabolite R-2HG (produced by IDH mutant cells) has been implicated in pathological cardiac remodeling and dysfunction in preclinical studies. Whether IDH mutant leukemic cells in patients with established AML are also associated with the development of cardiovascular diseases or exacerbate cardiotoxicity during anthracycline containing chemotherapy is still unknown. Methods: In this observational study, a propensity score-based analysis was performed in 363 adult AML patients being stratified by mutation status in the IDH gene. To analyze whether the IDH mutation status in AML patients was associated with increased cardiotoxicity, we analyzed echocardiographic left ventricular ejection fraction (LVEF) in the control group (AML patients without IDH mutation) and the exposed group (AML patients with IDH mutation) at baseline and at different time points during AML therapy. Results: IDH 1 and IDH2 mutations occurred in 26 (7.2%) and 39 adult AML patients (10.7%), respectively. The median age of the total population was 60 years. The estimated 2-year relapse-free survival and overall survival rates in the overall study cohort were 49.4% (5-year RFS 38.9%) and 59.2% (5-year OS 43.1%) during a median follow-up of 7.6 years. IDH1 mutant AML patients exhibited a significantly higher prevalence of coronary artery disease (26.1% vs. 6.4%, p=0.002). A propensity score analysis by inverse probability-weighting was performed based on the 295 patients who received intensive cytarabine and anthracycline-containing chemotherapy. This analysis revealed an increased risk for a declining cardiac function during AML treatment in IDH1/2 mutated compared to IDH1/2 wild type patients [LVEF pretreatment compared to 10 months after diagnosis: 59.2% to 41.9% (P Conclusion: The presence of an IDH mutation in adult AML was associated with a higher prevalence of coronary artery disease and an exacerbated cardiotoxicity during anthracycline treatment, which was at least in part mediated by the oncometabolite R-2HG. Disclosures Thol: Daiichi Sankyo: Membership on an entity's Board of Directors or advisory committees; Astellas: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees. Ganser:Novartis: Consultancy; Celgene: Consultancy. Heuser:BerGenBio ASA: Research Funding; Roche: Research Funding; Astellas: Research Funding; Janssen: Consultancy; Abbvie: Consultancy; Pfizer: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Amgen: Research Funding; PriME Oncology: Honoraria; Daiichi Sankyo: Consultancy, Research Funding; Stemline Therapeutics: Consultancy; Bayer: Consultancy, Research Funding; Karyopharm: Research Funding.

Background GATA2 deficiency is an inherited immunodeficiency and predisposition syndrome with a high risk of developing myelodysplastic syndrome (MDS) early in life. Allogeneic hematopoietic stem cell transplantation (HSCT) is presently the only curative therapy for affected patients (pts), but to date there has been no larger study examining in detail outcomes after HSCT for GATA2-related pediatric MDS. Here we report the results of an analysis of pts with a germline GATA2 mutation undergoing HSCT for a diagnosis of MDS enrolled in the registry of the European Working Group of MDS in Childhood (EWOG-MDS). Patients and transplantation procedure Of the 87 pts with GATA2 deficiency registered before the age of 18 years, 66 underwent HSCT between 01/1997 and 11/2018. One pt had to be excluded from the analysis due to lack of data. The 65 remaining pts (34 males/31 females) were transplanted at a median age of 13.5 (4.6-19.9) years. Twenty-seven pts were transplanted for refractory cytopenia of childhood (RCC), while 38 pts had advanced disease. The highest bone marrow (BM) blast percentage prior to HSCT was 5-19% (n=23), 20-29% (n= 9) or >30% blasts (n=5); in one pt with myelofibrotic MDS a blast count was not attainable. Karyotypes included monosomy 7 (n=44), der (1;7) (n=4), trisomy 8 (n=4), random aberration (n=1) or a normal karyotype (n=12). Five of the 38 pts with an increased blast percentage had received intensive AML-type therapy prior to HSCT. Pts were grafted from a matched sibling donor (MSD; n=17), unrelated donor (UD; n=40) or a mismatched family donor (MMFD; n=8). The stem cell source was BM (n=37), peripheral blood (n=27) or cord blood (n=1). Pts were prepared with a busulfan-based (n=35), treosulfan-based (n=21), total body irradiation-based (n=5) or an alternative conditioning regimen (n=4). Results At 5 years the probability of overall survival (pOS) and disease-free survival (DFS) was 0.74 [0.62-0.86] and 0.69 [0.57-0.81], respectively, non-relapse mortality was 0.15 [0.08-0.27] and the cumulative incidence of relapse was 0.16 [0.09-0.29]. All pts engrafted initially. The cumulative incidence of acute graft versus host disease (GVHD) grade II-IV and III-IV was 0.34 [0.24-0.48] and 0.12 [0.06-0.24], respectively, and of overall and extensive chronic GVHD 0.25 [0.16-0.39] and 0.08 [0.03-0.20]. The most common post-transplant infections were viral (39 of the 43 pts with infections) with one pt each with EBV-related post-transplant lymphoproliferative disease and primary CMV disease. There were no mycobacterial infections. The most common non-infectious complications were hepatobiliary (13 pts, including 3 with veno-occlusive disease) and pulmonary (10 pts, 5 of whom had been prepared with a busulfan-based conditioning regimen). Pts with >20% BM blasts showed a trend towards a poorer DFS (0.52 [0.24-0.80]) compared to pts with 5-19% blasts (0.72 [0.53-0.91]) or pts with RCC (0.80 [0.64-0.96]; p=0.15). Examining the influence of karyotype in pts with RCC, there were a total of 2 relapses and 3 deaths (1 after relapse) among the 12 pts with monosomy 7, while there was one event among the 15 RCC pts with a normal karyotype (n=10, 1 death), trisomy 8 (n=3), der (1;7) (n=1) or random aberration (n=1). Limiting the analysis to 9/10 or 10/10 HLA matched-donors, DFS was comparable for pts transplanted from an UD (0.73 [0.55-0.91]) versus a MSD (0.82 [0.64-1.00]). Of the 8 pts transplanted from a MMFD, one patient died after secondary graft failure. No major difference in outcome was seen according to age at HSCT, gender, time from diagnosis to HSCT or stem cell source. Of the five pts who had received AML-type therapy prior to HSCT, three died of a transplant-related cause or relapse. Conclusions and perspectives In summary, HSCT resulted in a pOS of 0.74 in this cohort of children and adolescents with GATA2 deficiency and MDS. Pts with increased blasts had a tendency towards poorer outcomes. The high risk of developing advanced MDS and the better outcome in early stages of the disease indicates that HSCT should be performed early in the clinical course of children diagnosed with GATA2 deficiency and MDS. Of note, there was no indication of excessive toxicity, disease-associated comorbidities or an increased risk of GVHD. The HSCT outcomes of children and adolescents with MDS and GATA2 deficiency are similar to what has been previously published for pts transplanted for MDS in the absence of GATA2 germline disease. Disclosures Bader: Amgen (Brasil), Novartis: Consultancy, Speakers Bureau; Celgene: Consultancy; Medac: Patents & Royalties, Research Funding; Riemser, Neovii: Research Funding. Locatelli:Miltenyi: Honoraria; bluebird bio: Consultancy; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bellicum: Consultancy, Membership on an entity's Board of Directors or advisory committees. Niemeyer:Celgene: Consultancy.

We studied acute myeloid leukemia (AML) patients with lympho-myeloid clonal hematopoiesis (LM-CH), defined by the presence of DNA methyltransferase 3A (DNMT3A) mutations in both the myeloid and lymphoid T-cell compartment. Diagnostic, complete remission (CR) and relapse samples were sequenced for 34 leukemia-related genes in 171 DNMT3A mutated adult AML patients. AML with LM-CH was found in 40 patients (23%) and was associated with clonal hematopoiesis of indeterminate potential years before AML, older age, secondary AML and more frequent MDS-type co-mutations (TET2, RUNX1 and EZH2). In 82% of AML patients with LM-CH, the preleukemic clone was refractory to chemotherapy and was the founding clone for relapse. Both LM-CH and non-LM-CH MRD-positive AML patients who achieved CR had a high risk of relapse after 10 years (75% and 75%, respectively) compared with patients without clonal hematopoiesis in CR with negative MRD (27% relapse rate). Long-term survival of patients with LM-CH was only seen after allogeneic hematopoietic stem cell transplantation (HSCT). We define AML patients with LM-CH as a distinct high-risk group of AML patients that can be identified at diagnosis through mutation analysis in T cells and should be considered for HSCT.

Myelodysplastic syndromes (MDS) are difficult to culture long-term showing the need of a model to study the fate of cells with MDS-abnormalities associated with chromosomal instability (CIN). This approach to establish a xenograft model transplanting human hematopoietic stem cells (HSC) with different independent lentivirally-mediated MDS-related modifications into immunodeficient mice is a long-lasting and tedious experiment with many parameters and every positive as well as non-functioning intermediate step will help the research community. As the establishment of appropriate xenograft models is increasing worldwide we aim to share our experiences to contribute toward minimizing loss of mice and following the "right" approach. Here, modified HSCs were intrafemorally transplanted into NSG and/or NSGS mice: (1) RPS14-haploinsufficiency, (2) TP53-deficiency, (3) TP53 hotspot mutations (R248W, R175H, R273H, R249S). Engraftment was achieved and cytogenetic analyses showed human cells with normal karyotypes. However, in all experiments with NSG mice, mainly control cells or GFP-negative cells were engrafted, not allowing observation of modified HSCs. In NSGS mice, engraftment rate was higher, but mice developed graft-versus-host disease. In summary, engraftment of HSCs is promising and could be used to analyze the induction of CIN. However, the analysis of modified HSCs is limited and further experiments are required to improve this model.

Erythropoiesis is arranged in erythroblastic islands (Ery-Is),[1][1] the specialized niche known for more than 50 years[2][2] in which erythroid precursors proliferate and differentiate. However, the significance of erythropoiesis in anemia, the leading symptom of myelodysplastic syndromes (MDS)

Chronic mucocutaneous candidiasis (CMC) is a disease that is characterized by susceptibility to chronic or recurrent infections with Candida spp. due to mutations affecting mainly the IL-17 signaling of T-Cells. The most common etiologies of CMC are gain-of-function (GOF) mutations in the STAT1 gene. In this paper we report the generation of a hiPSC line from a patient suffering from CMC due to a heterozygous GOF STAT1 p.R274Q mutation which can be used for disease modeling purposes.

Molecular measurable residual disease (MRD) assessment is not established in approximately 60% of acute myeloid leukemia (AML) patients because of the lack of suitable markers for quantitative real-time polymerase chain reaction. To overcome this limitation, we established an error-corrected next-generation sequencing (NGS) MRD approach that can be applied to any somatic gene mutation. The clinical significance of this approach was evaluated in 116 AML patients undergoing allogeneic hematopoietic cell transplantation (alloHCT) in complete morphologic remission (CR). Targeted resequencing at the time of diagnosis identified a suitable mutation in 93% of the patients, covering 24 different genes. MRD was measured in CR samples from peripheral blood or bone marrow before alloHCT and identified 12 patients with persistence of an ancestral clone (variant allele frequency [VAF] >5%). The remaining 96 patients formed the final cohort of which 45% were MRD+ (median VAF, 0.33%; range, 0.016%-4.91%). In competing risk analysis, cumulative incidence of relapse (CIR) was higher in MRD+ than in MRD− patients (hazard ratio [HR], 5.58; P < .001; 5-year CIR, 66% vs 17%), whereas nonrelapse mortality was not significantly different (HR, 0.60; P = .47). In multivariate analysis, MRD positivity was an independent negative predictor of CIR (HR, 5.68; P < .001), in addition to FLT3-ITD and NPM1 mutation status at the time of diagnosis, and of overall survival (HR, 3.0; P = .004), in addition to conditioning regimen and TP53 and KRAS mutation status. In conclusion, NGS-based MRD is widely applicable to AML patients, is highly predictive of relapse and survival, and may help refine transplantation and posttransplantation management in AML patients.

We integrated molecular data with available prognostic factors in patients undergoing allogeneic hematopoietic cell transplantation (alloHCT) for myelodysplastic syndrome (MDS) or secondary acute myeloid leukemia (sAML) from MDS to evaluate their impact on prognosis. Three hundred four patients were sequenced for mutations in 54 genes. We used a Cox multivariate model and competing risk analysis with internal and cross validation to identify factors prognostic of overall survival (OS), cumulative incidence of relapse (CIR), and non-relapse mortality (NRM). In multivariate analysis, mutated NRAS, U2AF1, IDH2, and TP53 and/or a complex karyotype were significant prognostic markers for OS besides age above 60 years, remission status, IPSS-R cytogenetic risk, HCT-CI > 2 and female donor sex. Mutated NRAS, IDH1, EZH2, and TP53 and/or a complex karyotype were genetic aberrations with prognostic impact on CIR. No molecular markers were associated with the risk of NRM. The inclusion of molecular information results in better risk prediction models for OS and CIR when assessed by the Akaike information criterion. Internal cross validation confirmed the robustness of our comprehensive risk model. In summary, we propose to combine molecular, cytogenetic, and patient- and transplantation-associated risk factors into a comprehensive risk model to provide personalized predictions of outcome after alloHCT.

Typical features of dyskeratosis congenita (DC) resulting from excessive telomere shortening include bone marrow failure (BMF), mucosal fragility, and pulmonary or liver fibrosis. In more severe cases, immune deficiency and recurring infections can add to disease severity. RTEL1 deficiency has recently been described as a major genetic etiology, but the molecular basis and clinical consequences of RTEL1-associated DC are incompletely characterized. We report our observations in a cohort of six patients: five with novel biallelic RTEL1 mutations p.Trp456Cys, p.Ile425Thr, p.Cys1244ProfsX17, p.Pro884_Gln885ins53X13, and one with novel heterozygous mutation p.Val796AlafsX4. The most unifying features were hypocellular BMF in 6/6 and B-/NK-cell lymphopenia in 5/6 patients. In addition, three patients with homozygous mutations p.Trp456Cys or p.Ile425Thr also suffered from immunodeficiency, cerebellar hypoplasia, and enteropathy, consistent with Hoyeraal-Hreidarsson syndrome. Chromosomal breakage resembling a homologous recombination defect was detected in patient-derived fibroblasts but not in hematopoietic compartment. Notably, in both cellular compartments, differential expression of 1243aa and 1219/1300aa RTEL1 isoforms was observed. In fibroblasts, response to ionizing irradiation and non-homologous end joining were not impaired. Telomeric circles did not accumulate in patient-derived primary cells and lymphoblastoid cell lines, implying alternative pathomechanisms for telomeric loss. Overall, RTEL1-deficient cells exhibited a phenotype of replicative exhaustion, spontaneous apoptosis and senescence. Specifically, CD34+ cells failed to expand in vitro, B-cell development was compromised, and T-cells did not proliferate in long-term culture. Finally, we report on the natural history and outcome of our patients. While two patients died from infections, hematopoietic stem cell transplantation (HSCT) resulted in sustained engraftment in two patients. Whether chemotherapy negatively impacts on the course and onset of other DC-related symptoms remains open at present. Early-onset lung disease occurred in one of our patients after HSCT. In conclusion, RTEL deficiency can show a heterogeneous clinical picture ranging from mild hypocellular BMF with B/NK cell lymphopenia to early-onset, very severe, and rapidly progressing cellular deficiency.

Incidence and prognostic impact of ASXL2 mutations in adult acute myeloid leukemia patients with t(8;21)(q22;q22): a study of the German-Austrian AML Study Group

Prognostic effect of calreticulin mutations in patients with myelofibrosis after allogeneic hematopoietic stem cell transplantation

ABL-class fusions other than BCR-ABL1 (or Ph+) are found in 2-3% of precursor B-cell acute lymphoblastic leukemia (pB-ALL) in children and adolescents. Occasional reports suggest that this rare ALL subtype has a poor prognosis and patients can benefit from treatment with tyrosine kinase inhibitors (TKIs). Aim of this retrospective study is to investigate the presenting features, treatment response and outcome in ABL-class fusion positive cases identified within large cohorts of patients treated in AIEOP-BFM ALL trials. This retrospective survey of ABL-class fusion positive pB-ALL other than Ph+ ALL was performed in patients aged 1-17 years at the diagnosis, treated from October 2000 to August 2018 according to the AIEOP-BFM (Associazione-Italiana- di- Ematologia-Oncologia Pediatrica-Berlin-Frankfurt-Münster) ALL 2000 and 2009 protocols in Austria, Australia, Czech Republic, Germany, Israel, Italy and Switzerland. While ABL-class fusions screening was not required by protocols, it was performed in some patients, according to centers' policies, usually after poor early treatment response. Overall, 46 ABL-class fusion positive cases with ABL1 fusions (N=15), ABL2 fusions (N=5), CSF1R fusions (N=3) and PDGFRB rearrangements (N=23) were identified. Compared with other pB-ALL children and adolescents, the ABL-class fusion positive cases presented with higher proportions of patients aged 10 years or older (52.2 vs. 22.2, P< .0001), hyperleukocytosis (WBC ≥100x109/l, 41.3 vs. 6.3, P< .0001), or poor minimal residual disease (MRD) response (>5x10-4 levels were observed in 65.2% vs. 18%, P< .0001 of patients after induction treatment phase IA and in 45.7% vs. 4.8%, P< .0001 after consolidation phase IB). For the entire cohort of 46 cases, the 5-year probability of event-free survival (EFS) was 49.1+8.9% and that of overall survival (OS) 69.6+7.8%; the cumulative incidence of relapse (CI) was 25.6+8.2% and treatment-related mortality 20.8+6.8%. Although not prescribed by the protocols, 13 patients received a TKI during different phases of treatment (TKI group), by choice of treating physicians, generally due to poor early treatment response. Eight TKI patients with high MRD levels at the end of induction phase IA received the TKI during consolidation phase IB, and six of them achieved either a low positive or negative MRD level at the end of consolidation phase IB. Nine of the 13 patients treated with TKIs underwent hematopoietic stem cell transplantation (HSCT) and only 1/9 (TKI+HSCT) relapsed. Thirty-three cases did not receive any TKI (no-TKI group) and eight of them relapsed; 6/17 patients treated with chemotherapy only, versus only 2/16 who underwent HSCT. Overall, 25 patients underwent HSCT, and of them 3 relapsed and 6 died of treatment-related complications. In patients with a WBC higher or lower than 100x109/L, the 5-year EFS was 36.8+12.7% vs. 59.9+11.6%, respectively (P= .21), and the 5-year OS was significantly lower in patients with a high WBC (48.8+12.9% vs. 87.4+6.8%, P= .036). This difference was more pronounced in the no-TKI group with a 5-year EFS 27.8+13.6% vs 61.8+12.7%, (P= .07), and an OS of 36.7+14.6% vs 94.4+5.4%, respectively (P= .0015). Presenting features, treatment response and outcome in this cohort of ABL-class fusion positive patients are markedly similar to those of patients with Ph+ ALL included in the EsPhALL studies. Our results suggest that TKIs and HSCT may be beneficial in reducing the risk of relapse. Thus there is an urgent need for large international cooperative controlled studies to investigate the impact of TKI, in combination with an appropriate chemotherapy backbone and the role of HSCT. To this purpose, an early identification of patients with ABL-class fusion positive acute lymphoblastic leukemia will be necessary. Disclosures Izraeli: sightdx: Consultancy; novartis: Honoraria; prime oncology: Speakers Bureau. Locatelli:Miltenyi: Honoraria; bluebird bio: Consultancy; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bellicum: Consultancy, Membership on an entity's Board of Directors or advisory committees. White:BMS: Honoraria, Research Funding; AMGEN: Honoraria, Speakers Bureau. Schrappe:Together with study group from SHIRE, JazzPharma, Servier, SigmaTau, Amgen, and Novartis.: Research Funding; SHIRE, Servier, and JazzPharma: Honoraria.

Introduction: The combination treatment of venetoclax (VEN) with both low-dose cytarabine (LDAC) and hypomethylating agents (HMA) in untreated primarily elderly AML patients yielded promising response rates leading to its approval for newly diagnosed AML patients who are 75 years or older, or who have comorbidities that preclude use of intensive induction chemotherapy. Prolonged cytopenias are of potential concern in venetoclax treated patients, especially in patients who underwent allogeneic hematopoietic cell transplantation (alloHCT) prior venetoclax treatment. Objective: To compare hematologic recovery in patients treated with VEN in combination with intensive and non-intensive chemotherapy regimens for the treatment of relapsed or refractory (R/R) acute myeloid leukemia (AML) depending on the pretreatment status for alloHCT. Methods: In this retrospective controlled study (www.clinicaltrials.gov NCT03662724), we included patients aged 18 years or older with R/R acute leukemia previously treated with VEN (days 1-7) combined with intensive salvage chemotherapy (fludarabine, cytarabine, idarubicin - FLAVIDA) or VEN combined with non-intensive regimens, namely HMA or LDAC. Eighty-one patients who were treated with FLA-IDA for R/R AML served as control for the intensively treated patients included in this analysis. Responses were evaluated per revised International Working Group criteria for AML. Main outcome measure was the rate of objective response (complete remission [CR] + CR with incomplete blood count recovery [CRi] + partial remission [PR] + morphologic leukemia-free state (MLFS; defined as less than 5% blasts in an aspirate sample). Safety and efficacy analyses included all patients who received at least one cycle of VEN combination treatment. This study was approved by the local Ethics Review Committee in accordance with the Declaration of Helsinki. Results: Between January 2017 and May 2019 49 patients with a median age of 59 years (range 18-80) received VEN with either FLA-IDA (n=14), HMA (n=31) or LDAC (n=4) and had safety and efficacy outcomes reported. The patient cohort was a high-risk cohort of relapsed (n=24) and refractory (n=25) patients. The analysis included 24 patients (49%) with secondary AML and two patients with biphenotypic acute leukemia (BAL). Twenty-two patients (45%) had received prior alloHCT and 7 (14%) had relapsed For intensively treated patients the ORR was 79% (n=11) with 9 CR/CRis (64%), one MLFS, and one PR compared to an ORR of 47% in the FLA-IDA control cohort. Median time to neutrophil (≥1.0x109/L) and platelet recovery (≥100x109/L) in intensively treated responding patients were 34 and 36 days compared to 39 and 41 days in the control cohort. Median recovery times in patients with and without prior alloHCT were similar (FLAVIDA: 34 vs. 33 days for neutrophil recovery; 36 vs. 36 days for platelet recovery, Fig. 1 C-D; FLA-IDA control: 41 vs. 38 days for neutrophil recovery; 70 vs. 38 days for platelet recovery, Fig. 1 E-F). After a median follow-up of 10.5 months the median overall survival (OS) was 8 months in non-intensively treated patients. After a median follow-up of 9.9 months the median OS was not reached in intensively treated patients. Median event-free survival was 5.8 months in non-intensively treated patients and was not reached in intensively treated patients. Conclusions: Venetoclax in combination with intensive chemotherapy as well as non-intensive regimens showed promising response rates for treatment of relapsed or refractory AML with good tolerability and acceptable duration of cytopenias with no differences in recovery times in patients with and without prior alloHCT. Disclosures Koenecke: Novartis: Other: none. Heuser:Bayer Pharma AG, Berlin: Research Funding; Synimmune: Research Funding.

Few studies have evaluated granulocyte colony-stimulating factor (G-CSF) priming in elderly patients with intensively treated acute myeloid leukemia (AML), and no data are available for genetically defined AML subgroups. We provide long-term results (median follow-up 7.6 years) of a randomized trial in which 183 patients (median age 67 years) received G-CSF prior to (G-CSF priming) or after two cycles of induction chemotherapy. CR rates with G-CSF priming and G-CSF post-chemotherapy were comparable (57 vs. 67 %, p = 0.153), with overall survival (OS) probabilities of 14 vs. 17 % at 10 years. Induction mortality was significantly higher with G-CSF priming (23 vs. 10 %, p = 0.015), primarily in normal karyotype (NK) AML. In this subgroup, a trend for better relapse-free survival (RFS) was observed with G-CSF priming (44 vs. 22 % at 10 years, p = 0.074) but did not translate into an OS benefit. G-CSF priming had no impact on AML with FLT3-ITD and NPM mutations and did not improve outcome in patients with adverse cytogenetics. In a landmark analysis, late consolidation with autologous stem cell transplantation or a second consolidation cycle significantly improved RFS compared with one consolidation cycle (21.0 vs. 12.8 months, p = 0.046). Future studies on G-CSF priming should be restricted to NK AML and used only in post-remission therapy.

Deregulation of the hematopoietic stem cell (HSC) compartment represents a hallmark of acute myeloid leukemia (AML). Recently, in vivo screening for genes that are involved in the regulation of HSCs has led to the discovery of Musashi-2 (MSI2) as a key regulator of HSCs and as a suppressor of NUMB. In order to analyze the prognostic importance of MSI2 and NUMB expression in AML, MSI2 and NUMB transcript levels from 454 AML patients treated in multicenter trials AML SHG 0199 (ClinicalTrials Identifier NCT00209833) and 0295, and 38 healthy volunteers were analyzed by reverse transcriptase PCR in the context of other molecular markers (NPM1, FLT3, CEBPA, IDH1/IDH2, DNMT3A, NRAS, WT1, KIT, MN1, BAALC, ERG, and WT1). In AML, patients with high MSI2 expression were more likely to be FLT3-ITD positive (P

CMV reactivation is a major complication after allogeneic stem cell transplantation (SCT). Immune reconstitution of CMV-specific CTLs (CMV-CTLs) is essential for virus control. During CMV-CTL monitoring using mutated HLA/CMV tetramers selectively detecting high-avidity T cells, we observed coappearance of CMV-CTLs with low (CMV tetlow CTLs) and high tetramer binding (CMV tethigh CTLs) in 53/115 CMV IgG+ patients stem cell transplanted from CMV IgG+ donors. However, the relevance of these coappearing differentially tetramer binding (“dual”) CMV-CTLs was unclear. In this study, we investigated the kinetics, properties, and clinical impact of coappearing CMV tetlow and tethigh CTLs after allogeneic SCT. Patients with dual CMV-CTLs had more CMV tethigh than tetlow CTLs. Chimerism analysis of isolated CMV tetlow and tethigh CTLs revealed their exclusive donor origin. CMV tetlow and tethigh CTLs had an identical effector memory CD45RA−CCR7− and CD45RA+CCR7− T cell distribution, equal differentiation, senescence, and exhaustion marker expression and were negative for regulatory CD8+ T cell markers. Isolated CMV tetlow and tethigh CTLs were equally sensitive to CMV peptides in IFN-γ release and cytotoxicity assays. However, CMV tethigh CTLs proliferated more in response to low CMV peptide concentrations than tetlow CTLs. TCR repertoire analysis revealed that CMV tetlow and tethigh CTLs use different TCRs. Finally, dual CMV-CTLs were not associated with CMV antigenemia. In conclusion, these data show for the first time, to our knowledge, that both CMV tetlow and tethigh CTLs are functional effector T cells differing by proliferation, numbers in peripheral blood, and probably by their precursors without increasing the CMV reactivation risk after allogeneic SCT.

Evidence for distinct human cancer stem cells (CSCs) remains contentious and the degree to which differentcancer cells contribute to propagating malignancies in patients remains unexplored. In low- to intermediate-risk myelodysplastic syndromes (MDS), we establish the existence of rare multipotent MDS stem cells (MDS-SCs), and their hierarchical relationship to lineage-restricted MDS progenitors. All identified somatically acquired genetic lesions were backtracked to distinct MDS-SCs, establishing their distinct MDS-propagating function invivo. In isolated del(5q)-MDS, acquisition of del(5q) preceded diverse recurrent driver mutations. Sequential analysis in del(5q)-MDS revealed genetic evolution in MDS-SCs and MDS-progenitors prior to leukemic transformation. These findings provide definitive evidence for rare human MDS-SCs invivo, with extensive implications for the targeting of the cells required and sufficient for MDS-propagation. © 2014 Elsevier Inc.

Background Myb-like, SWIRM, and MPN domains 1 (MYSM1) is a transcriptional regulator mediating histone deubiquitination. Its role in human immunity and hematopoiesis is poorly understood. Objectives We sought to investigate the clinical, cellular, and molecular features in 2 siblings presenting with progressive bone marrow failure (BMF), immunodeficiency, and developmental aberrations. Methods We performed genome-wide homozygosity mapping, whole-exome and Sanger sequencing, immunophenotyping studies, and analysis of genotoxic stress responses. p38 activation, reactive oxygen species levels, rate of apoptosis and clonogenic survival, and growth in immune and nonimmune cells were assessed. The outcome of allogeneic hematopoietic stem cell transplantation (HSCT) was monitored. Results We report 2 patients with progressive BMF associated with myelodysplastic features, immunodeficiency affecting B cells and neutrophil granulocytes, and complex developmental aberrations, including mild skeletal anomalies, neurocognitive developmental delay, and cataracts. Whole-exome sequencing revealed a homozygous premature stop codon mutation in the gene encoding MYSM1. MYSM1-deficient cells are characterized by increased sensitivity to genotoxic stress associated with sustained induction of phosphorylated p38 protein, increased reactive oxygen species production, and decreased survival following UV light–induced DNA damage. Both patients were successfully treated with allogeneic HSCT with sustained reconstitution of hematopoietic defects. Conclusions Here we show that MYSM1 deficiency is associated with developmental aberrations, progressive BMF with myelodysplastic features, and increased susceptibility to genotoxic stress. HSCT represents a curative therapy for patients with MYSM1 deficiency.

Maintenance of hematopoietic stem cells and their potential to give rise to progenitors of differentiated lymphoid and myeloid cells are accomplished by a network of regulatory processes. As a part of this network, the heteromeric transcription factor GA-binding protein (GABP) plays a crucial role in self-renewal of murine hematopoietic and leukemic stem cells. Here, we report the consequences of functional impairment of GABP in human hematopoietic and in leukemic stem/progenitor cells. Ectopic overexpression of a dominant-negative acting GABP mutant led to impaired myeloid differentiation of CD34+ hematopoietic stem/progenitor cells obtained from healthy donors. Moreover, drastically reduced clonogenic capacity of leukemic stem/progenitor cells isolated from bone marrow aspirates of chronic myeloid leukemia (CML) patients underlines the importance of GABP on stem/progenitor cell maintenance and confirms the relevance of GABP for human myelopoiesis in healthy and diseased states.

Germline GATA2 mutations cause cellular deficiencies with high propensity for myeloid disease. We investigated 426 children and adolescents with primary myelodysplastic syndrome (MDS) and 82 cases with secondary MDS enrolled in two consecutive prospective studies of the European Working Group of MDS in Childhood (EWOG-MDS) conducted in Germany over a period of 15 years. Germline GATA2 mutations accounted for 15% of advanced and 7% of all primary MDS cases, but were absent in children with MDS secondary to therapy or acquired aplastic anemia. Mutation carriers were older at diagnosis and more likely to present with monosomy 7 and advanced disease as compared to wildtype cases. For stratified analysis according to karyotype 108 additional primary MDS patients registered with EWOG-MDS were studied. Overall, we identified 57 MDS patients with germline GATA2 mutations. GATA2 mutations were highly prevalent among patients with monosomy 7 (37%, all ages) reaching its peak in adolescence (72% of adolescents with monosomy 7). Unexpectedly, monocytosis was more frequent in GATA2-mutated patients. However, when adjusted for the selection bias from monosomy 7, mutational status had no effect on the hematological phenotype. Finally, overall survival and outcome of hematopoietic stem cell transplantation (HSCT) were not influenced by mutational status. This study identifies GATA2 mutations as the most common germline defect predisposing to pediatric MDS with a very high prevalence in adolescents with monosomy 7. GATA2 mutations do not confer poor prognosis in childhood MDS. However, the high risk for progression to advanced disease must guide decision-making towards timely HSCT.

The European LeukemiaNet classification combines a heterogeneous group of aberrations as adverse-risk abnormalities. Our goal was to investigate the outcomes associated with distinct high-risk chromosomal abnormalities in acute myeloid leukemia (AML) after allogeneic hematopoietic stem cell transplantation (HSCT). We performed a retrospective cohort analysis in patients with high-risk AML who received first, HLA-compatible, allogeneic HSCT between January 2005 and December 2008. Data from 236 patients with a median age of 55 years were included. Because complex karyotype (CK), −5/5q−, and abnl(17p) are overlapping categories, a hierarchical classification system based on the presence or absence of abnl(17p) and −5/5q− was developed. Patients with abnl(17p) had a 2-year event-free survival (EFS) of 11% (95% confidence interval [CI], 0%-25%), patients with −5/5q− but no abnl(17p) a 2-year EFS of 29% (95% CI, 14%-44%), and patients with adverse-risk AML but neither of the 2 marker lesions a 2-year EFS of 49% (95% CI, 39%-59%). Notably, complex and monosomal karyotypes lost their prognostic value when these marker lesions were excluded. In conclusion, hierarchical classification of adverse-risk karyotypes by 2 marker lesions, abnl(17p) and −5/5q−, is effective in prognostication of the outcome of allogeneic HSCT in AML.

We aimed to determine the prognostic impact of monosomal karyotype (MK) in acute myeloid leukemia (AML) in the context of the current World Health Organization (WHO) classification and to evaluate the outcome of MK+ patients after allogeneic HSCT. Of 1058 patients with abnormal cytogenetics, 319 (30%) were MK MK+. MK+ patients were significantly older (P = .0001), had lower white blood counts (P = .0006), and lower percentages of BM blasts (P = .0004); MK was associated with the presence of −5/5q−, −7, 7q−, abnl(12p), abnl(17p), −18/18q−, −20/20q−, inv(3)/t(3;3), complex karyotype (CK), and myelodysplasia (MDS)–related cytogenetic abnormalities (P < .0001, each); and NPM1 mutations (P < .0001), FLT3 internal tandem duplications (P < .0001), and tyrosine kinase domain mutations (P = .02) were less frequent in MK+. Response to induction therapy and overall survival in MK+ patients were dismal with a complete remission rate of 32.5% and a 4-year survival of 9%. MK retained its prognostic impact in AML with CK, AML with MDS-related cytogenetic abnormalities, and in a revised definition (MK-R) excluding cases with recurrent genetic abnormalities according to WHO classification and those with derivative chromosomes not leading to true monosomies. In younger patients, allogeneic HSCT from matched related and unrelated donors resulted in a limited improvement of overall survival.

The prognostic relevance of additional cytogenetic findings at diagnosis of chronic myeloid leukemia (CML) is unclear. The impact of additional cytogenetic findings at diagnosis on time to complete cytogenetic (CCR) and major molecular remission (MMR) and progression-free (PFS) and overall survival (OS) was analyzed using data from 1151 Philadelphia chromosome–positive (Ph+) CML patients randomized to the German CML Study IV. At diagnosis, 1003 of 1151 patients (87%) had standard t(9;22)(q34;q11) only, 69 patients (6.0%) had variant t(v;22), and 79 (6.9%) additional cytogenetic aberrations (ACAs). Of these, 38 patients (3.3%) lacked the Y chromosome (−Y) and 41 patients (3.6%) had ACAs except −Y; 16 of these (1.4%) were major route (second Philadelphia [Ph] chromosome, trisomy 8, isochromosome 17q, or trisomy 19) and 25 minor route (all other) ACAs. After a median observation time of 5.3 years for patients with t(9;22), t(v;22), −Y, minor- and major-route ACAs, the 5-year PFS was 90%, 81%, 88%, 96%, and 50%, and the 5-year OS was 92%, 87%, 91%, 96%, and 53%, respectively. In patients with major-route ACAs, the times to CCR and MMR were longer and PFS and OS were shorter (P < .001) than in patients with standard t(9;22). We conclude that major-route ACAs at diagnosis are associated with a negative impact on survival and signify progression to the accelerated phase and blast crisis.

SF3B1 mutations in myelodysplastic syndromes: clinical associations and prognostic implications

Purpose To evaluate the prognostic value of minimal residual disease (MRD) in patients with acute myeloid leukemia (AML) with NPM1 mutation (NPM1mut). Patients and Method RNA-based real-time quantitative polymerase chain reaction (RQ-PCR) specific for the detection of six different NPM1mut types was applied to 1,682 samples (bone marrow, n = 1,272; blood, n = 410) serially obtained from 245 intensively treated younger adult patients who were 16 to 60 years old. Results NPM1mut transcript levels as a continuous variable were significantly associated with prognosis after each treatment cycle. Achievement of RQ-PCR negativity after double induction therapy identified patients with a low cumulative incidence of relapse (CIR; 6.5% after 4 years) compared with RQ-PCR–positive patients (53.0%; P < .001); this translated into significant differences in overall survival (90% v 51%, respectively; P = .001). After completion of therapy, CIR was 15.7% in RQ-PCR–negative patients compared with 66.5% in RQ-PCR–positive patients (P < .001). Multivariable analyses after double induction and after completion of consolidation therapy revealed higher NPM1mut transcript levels as a significant factor for a higher risk of relapse and death. Serial post-treatment assessment of MRD allowed early detection of relapse in patients exceeding more than 200 NPM1mut/104 ABL copies. Conclusion We defined clinically relevant time points for NPM1mut MRD assessment that allow for the identification of patients with AML who are at high risk of relapse. Monitoring of NPM1mut transcript levels should be incorporated in future clinical trials to guide therapeutic decisions.

Stable and reproducible engraftment of primary adult and pediatric acute myeloid leukemia in NSG mice

Bcr-abl-negative myeloproliferative neoplasms (MPN), comprising polycythaemia vera (PV), primary myelofibrosis (PMF) and essential thrombocythaemia (ET), usually follow a biphasic course. From a phase which is characterized by excess production of mature haematopoietic cells of one or more lineages, many, but not all MPN, progress to haematopoietic insufficiency with cytopenia affecting two or three lineages. The latter may be the result of either fibrosis, blastic transformation or both. An intermediate stage of variable duration is called acceleration. Unlike bcr-abl-positive chronic myeloid leukaemia (CML), acceleration in MPN is not homogeneously defined. Long-lasting PV may progress to a PMF-like myelofibrosis, labelled spent phase. Less frequently, PV develops into a myelodysplastic/myeloproliferative neoplasm (MDS/MPN) resembling either atypical CML or chronic myelomonocytic leukaemia. Progression in PMF and ET leads either to advanced osteomyelofibrosis or to MDS/MPN with fibrosis. CML and bcr-abl-negative MPN share the same definition for transformation with ≥20% blasts in the blood or bone marrow. Transformation to blast crisis can occur at any stage in MPN and is more likely in PMF and PV than ET. There are different molecular pathways to progression. In a subset of MPN, transformation is accompanied by the occurrence of a complex karyotype.

Purpose To assess the prognostic importance of mixed lineage leukemia 5 (MLL5) expression in acute myeloid leukemia (AML). Patients and Methods MLL5 transcript levels from 509 patients with AML who were treated in multicenter trials AML SHG 0199 and AML SHG 0295 and 48 healthy volunteers were analyzed by real-time reverse-transcription polymerase chain reaction in the context of other molecular markers (NPM1, FLT3, CEBPA, IDH1/IDH2, NRAS, KIT, MN1, BAALC, ERG, and WT1). Results Patients with high (n = 127) compared with low (n = 382) MLL5 expression had a higher complete response rate in multivariate analysis (odds ratio, 1.87; 95% CI, 1.08 to 3.24; P = .026). In multivariate analysis, high MLL5 expression was a favorable prognostic marker for overall survival (OS; hazard ratio [HR], 0.66; 95% CI, 0.49 to 0.89; P = .007) and relapse-free survival (RFS; HR, 0.72; 95% CI, 0.52 to 1.01; P = .057). Patient characteristics, cytogenetic aberrations, and gene mutations were similarly distributed between patients with high and low MLL5 expression except for a higher platelet count in those with high MLL5 expression. MLL5 expression independently predicted prognosis in cytogenetically normal AML patients (n = 268; OS: HR, 0.53; 95% CI, 0.33 to 086; P = .011; RFS: HR, 0.61; 95% CI, 0.38 to 0.99; P = .05) and in patients with core-binding factor leukemias (n = 81; OS: HR, 0.12; 95% CI, 0.02 to 0.91; P = .04; RFS: HR, 0.18; 95% CI, 0.04 to 0.77; P = .02). The prognostic importance of high MLL5 expression was independently validated in 167 patients treated in the AMLSG 07/04 trial (OS: HR, 0.5; 95% CI, 0.27 to 0.92; P = .023; RFS: HR, 0.49; 95% CI, 0.25 to 0.96; P = .033). Conclusion High MLL5 expression levels are associated with a favorable outcome and may improve risk and treatment stratification in AML.

Dyskeratosis congenita (DC) belongs to the group of inherited bone marrow failure syndromes (IBMFS) and is characterized by premature telomere shortening caused by mutations in components of the telomerase or the shelterin complexes. The main cause of death in affected patients is hematopoietic failure, but there is also a 10-15% risk of malignant transformation into secondary myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). Critically short telomeres activate a DNA damage response with p53-mediated cell cycle inhibition, senescence and/or apoptosis, the latter mediated primarily by PUMA, a BCL-2 family member belonging to the group of pro-apoptotic BH3-only proteins and transcriptionally regulated by p53. Activation of p53 and expression of its target genes are critical for the exhaustion of hematopoietic stem cells (HSCs) in DC patients. Inactivation of the DNA damage checkpoint could possibly mitigate hematopoietic failure but poses a significant risk of genomic instability and leukemia. Based on our earlier mouse model of secondary leukemia (Genes Dev, 24(15):1602-7), we hypothesized that selective inhibition of p53-mediated apoptosis - while all other p53-checkpoint-induced pathways remain active - could both delay hematopoietic failure and prevent malignant transformation. We established a DC mouse model by serial transplantation of hematopoietic stem and progenitor cells (HSPCs) derived from generation 3 mTerc-/- (G3 mTerc-/-) mice lacking the RNA telomerase component. While 8-12 week old donor mice and primary recipients had only a mild hematopoietic phenotype, secondary recipients demonstrated severe lymphopenia. 41% of secondary recipients died within 50 days after transplantation, and flow cytometric and histological analysis revealed pancytopenia and bone marrow aplasia. The surviving secondary recipients were analyzed 16 weeks after transplantation and displayed severely reduced HSPC viability ex vivo. Aiming to inhibit HSPC apoptosis in vivo, we deleted Puma in G3 mTerc-/- mice. PUMA deficiency significantly rescued bone marrow numbers, HSPC viability ex vivo (72% vs. 50% viable HSPCs, p=0.01) and hematopoietic output on a G3 mTerc-/-background. Most importantly, death of secondary recipients was fully prevented in the absence of PUMA. This rescue is associated with significantly longer telomeres and reduced levels of γH2AX foci in G3 mTerc-/-Puma-/- donor and recipient HSPCs when compared to their PUMA proficient counterparts. Notably, no signs of myelodysplasia or leukemia were found in mice receiving serial transplantations of G3 mTerc-/-Puma-/- bone marrow. Our data indicate that specific inhibition of the intrinsic apoptosis pathway is sufficient to restrain the death of HSPCs with critically short telomeres and ensure blood formation. The resulting reduction of proliferative pressure within the HSPC compartment preserves functional and genetic integrity of HSCs and leads to generally longer telomeres in the HSPC pool. We anticipate that prevention of bone marrow failure is sufficient to prevent outgrowth of (pre)malignant clones and transformation to secondary MDS and AML. Disclosures Niemeyer: Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees.

Background: PPM1D is a serine/threonine phosphatase that inactivates p53 tumor suppressor pathway. Recently, PPM1D mutations have been described in clonal hematopoiesis and are more frequently found in therapy-related MDS than in primary MDS (15% vs. 3%). Del(5q), is the most prevalent cytogenetic abnormality in MDS. A high proportion of MDS del(5q) patients respond to lenalidomide, but almost 40% of them progress to AML. Scharenberg et al. identified recurrent mutations in a limited number of genes i.e. TP53, RUNX1, and TET2 in a longitudinal cohort of 35 MDS del(5q) patients that progressed to AML. The clinical impact and occurrence of PPM1D mutations in MDS del(5q) patients remains unknown. Aim: To determine the clinical impact of PPM1D mutations in MDS del (5q) patients on lenalidomide resistance and AML progression. Methods: We studied a cohort of 243 patients with MDS or AML following MDS and 5q deletion diagnosed according to the 2008 WHO classification. Patients were cytogenetically characterized by chromosome banding analysis and followed for disease progression, treatment and survival. From 22 del(5q) patients treated with lenalidomide, follow-up (FU) material was available before and after treatment. Molecular analysis for mutations in all 6 exons of PPM1D was performed by Sanger and/or a next-generation sequencing panel covering mutations in 46 genes frequently mutated in MDS, including TP53 and CSNK1A1. Results: At the time of diagnosis 14 PPM1D mutations were detected in 13 of 243 (5.3%) MDS patients with del(5q), 12 of which were found in the previously described hotspot region of PPM1D between amino acids 427 and 542. Six patients had nonsense mutations, 3 patients had frameshift mutations (one patient with 2 frameshift mutations), and 4 patients had missense mutations. TP53 mutations were found in 34 of 243 (14%) MDS patients with del(5q). Three TP53 mutated patients, two with complex karyotype, carried an additional PPM1D mutation. Co-occurrence of PPM1D and CSNK1A1 mutations was not observed in any patient. In total, 71 of 243 patients were treated with lenalidomide and had available information about treatment response. Eleven patients (15.5%) did not respond to lenalidomide and 17 patients (24%) progressed to AML. Nine of 71 (12.6%) patients were TP53 (n=5, 7%) or PPM1D mutated (n=4, 5.6%). For 22 of 71 patients who either achieved a complete remission (n=5), developed resistance to lenalidomide followed by MDS progression (n=7) or AML transformation (n=10), FU samples were available before and after lenalidomide treatment. Of the 5 patients with complete remission 4 patients displayed no mutations, while 1 patient was PPM1D- and ASXL1-mutated with a variant allele frequency (VAF) of 27.6% and 12.1%, respectively, prior to lenalidomide treatment. After 76 months on lenalidomide, both mutations had disappeared. Of the 17 patients with lenalidomide resistance/AML progression, 5 patients (29.4%) carried mutations either in PPM1D (n=2) or in TP53 (n=3) prior to lenalidomide treatment, with a mean VAF of 15.3% and 13.5%, respectively. The 2 PPM1D-mutated patients progressed to AML 59.4 and 79.6 months after diagnosis. None of the 3 initially TP53-mutated patients progressed to AML. All 3 TP53-mutated patients co-expressed SF3B1 mutations. At the time of lenalidomide resistance/AML progression, we observed 2 known and 1 novel PPM1D mutation in a patient previously wildtype for PPM1D and TP53, 3 known and 6 novel TP53 mutations in 5 patients previously wildtype for PPM1D and TP53, and 1 novel TP53 mutation in a patient who was previously found mutated in PPM1D. Thus, at the time of lenalidomide resistance or AML progression 10 of 17 patients (58.8%) were mutated for PPM1D (n=3, 18%) and/or TP53 (n=9, 53%; 2 of 9 co-expressed PPM1D mutations). At the time of lenalidomide resistance/AML progression, VAF increased from 10.2% to 23.3% for PPM1D and from 4% to 16.9% for TP53 mutations, indicating expansion of the mutated clone under the selective pressure of lenalidomide. Conclusion: PPM1D mutations are recurrently found in MDS del(5q) patients at a frequency of 5.3% and may be coexpressed with TP53 mutations in 5q- MDS/AML cells. Frequency at resistance/AML progression was 18% for PPM1D and 53% for TP53 mutated patients, respectively. Our findings indicate an association of PPM1D mutations in addition to the previously described TP53 mutations with lenalidomide resistance and AML progression. Disclosures Meggendorfer: MLL Munich Leukemia Laboratory: Employment. Krönke:Celgene: Honoraria. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Thiede:Novartis: Honoraria, Research Funding; AgenDix: Other: Ownership. Germing:Janssen: Honoraria; Novartis: Honoraria, Research Funding; Celgene: Honoraria, Research Funding. Kobbe:Amgen: Honoraria, Research Funding; Roche: Honoraria, Research Funding; Celgene: Honoraria, Other: Travel Support, Research Funding. Koenecke:Amgen: Consultancy; Roche: Consultancy; abbvie: Consultancy; BMS: Consultancy. Sperr:Novartis: Honoraria; Pfizer: Honoraria; Daiichi Sankyo: Honoraria. Valent:Novartis: Honoraria; Pfizer: Honoraria; Incyte: Honoraria. Ganser:Novartis: Membership on an entity's Board of Directors or advisory committees. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Platzbecker:Celgene: Research Funding. Heuser:BergenBio: Research Funding; StemLine Therapeutics: Consultancy; Astellas: Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Bayer Pharma AG: Consultancy, Research Funding; Pfizer: Consultancy, Honoraria, Research Funding; Janssen: Consultancy; Karyopharm: Research Funding; Daiichi Sankyo: Research Funding; Sunesis: Research Funding; Tetralogic: Research Funding.

Hereditary predisposition has been ever since implicated in the etiology of childhood myelodysplastic syndromes (MDS). Until recently, GATA2 deficiency prevailed as a major germline cause in pediatric primary MDS. In the past 2 years, we and others identified germline mutations in paralogue genes SAMD9 and SAMD9L residing on chromosome 7q21.2 as new systemic diseases with high propensity for MDS with monosomy 7. Although initially, mutations in SAMD9 and SAMD9L genes were associated with MIRAGE and Ataxia-Pancytopenia syndromes, respectively, with recent reports the phenotypes are becoming more intertwined. Nevertheless, the predisposition to MDS with monosomy 7 (-7) remains a common clinical denominator. Both genes are categorized as negative regulators of cellular proliferation and mutations were shown to be activating. Because of their high evolutionary divergence, classical in silico prediction is erratic, thereby establishing in vitro testing as the current gold standard for pathogenicity evaluation. The objectives of this study were to define the prevalence of SAMD9/9L germline mutations in primary pediatric MDS, and to describe the clinical phenotype and outcome. In addition, we aimed to characterize the somatic mutational architecture and develop a functional scoring system. Within the cohort of 548 children and adolescents with primary MDS diagnosed between 1998 and 2016 in Germany, 43 patients (8%) carried SAMD9/9L mutations that were mutually exclusive with GATA2 deficiency and known constitutional bone marrow (BM) failure. MDS type refractory cytopenia of childhood was diagnosed in 91% (39/43), and MDS with excess blasts in 9% (4/43) of mutated cases. Karyotype at diagnosis was normal in 58%, and -7 was detected in 37% of SAMD9/9L cohort. Within MDS subgroup with -7 (n=74), SAMD9/9L mutations accounted for 22% of patients. Notably, the demographics, familial disease, diagnostic blood and BM findings, overall survival (OS) and the outcome after HSCT were not influenced by mutational status in our study cohort (n=548). At the last follow up, 88% (38/43) of SAMD9/9L MDS patients were alive; 35/43 had been transplanted with a 5-year-OS of 85%. Next, we added 26 additional cases with SAMD9/9L mutations diagnosed in Europe within EWOG-MDS studies. In the total cohort of 69 germline mutated patients we found a total of 75 SAMD9/9L mutations, of which 67 were novel. Of those we tested 47 using a HEK293 cell in vitro system and 45/47 mutants inhibited proliferation. While 53/69 patients carried only single germline mutations (missense in 50/53 and truncating in 3/53), in the remaining 16 patients, 11 additional truncating and 7 missense mutations were found. We did not observe an association between germline mutation and phenotype. Immunological issues (e.g. recurring infections, low Ig) were described in 32%/50% of SAMD9/9L-mutated patients, while physical anomalies were very heterogeneous and reported in ~50% of patients in both mutational groups. Intriguingly, genital phenotypes occurred in 40% of SAMD9L, while neurological problems were present in 30% of SAMD9 - mutational subgroups. To elucidate the somatic mutational landscape, we performed whole exome and deep sequencing of 58 SAMD9/9L patients and identified recurrent somatic mutations in known oncogenes that were earlier associated with pediatric MDS: SETBP1 (10%), RUNX1 (7%), ASXL1 (5%), EZH2 (5%), CBL (3%). The identified somatic mutations occurred in association with monosomy 7 background (18/20). Finally, we utilized the results from functional testing of the 47 SAMD9/9L variants as our test cohort to develop combinatorial in silico scoring. The rationale was to decrease the dependency on functional validation. Based on the results of 20 in silico tools we could concatenate a matrix of 5 algorithms to resolve the pathogenicity of >80% of variants. Using this model, all variants predicted as pathogenic showed also growth-restrictive effect in vitro. In summary, pathogenic SAMD9/9L germline mutations account for 8% of primary pediatric MDS and 22% of MDS/-7. The mutations identified are heterogeneous and their effect can be predicted using a combinatorial in silico - in vitro approach. Finally, the clinical outcome and somatic mutational landscape are not influenced by the mutational status. Disclosures Locatelli: Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees; Bellicum: Consultancy, Membership on an entity's Board of Directors or advisory committees; bluebird bio: Consultancy; Miltenyi: Honoraria; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees. Niemeyer:Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees.

Background: Measurable residual disease (MRD), as determined by quantitation of Nucleophosmin 1-mutated (NPM1mut) transcript levels (TL), provides significant prognostic information independent of other risk factors in patients (pts) with acute myeloid leukemia (AML). This is also addressed by the 2017 European LeukemiaNet (ELN) risk stratification system, which recommends taking into account results from MRD monitoring when selecting the appropriate post-remission therapy. Furthermore, MRD monitoring provides a powerful tool to evaluate treatment effects within clinical trials investigating novel therapies. Aims: To determine the impact of the anti-CD33 immunotoxin Gemtuzumab-Ozogamicin (GO) on kinetics of NPM1mut TL in pts with newly diagnosed NPM1mut AML [18 to 82 years (yrs), median age 58 yrs] enrolled in our randomized Phase III AMLSG 09-09 study (NCT00893399). In this study GO was randomized (1:1) to standard chemotherapy plus ATRA. Patients and Methods: In total, 588 evaluable pts were enrolled in the clinical AMLSG 09-09 study. Standard treatment comprised two cycles of induction therapy with A-ICE (ATRA, idarubicin, cytarabine, etoposide; arm A) followed by three consolidation cycles of high-dose cytarabine (n=371, 63%) or allogeneic hematopoietic cell transplantation (n=42, 8%). In the investigational arm (arm B), GO (3 mg/m²) was given at d1 of each induction and in the first consolidation cycle. 296 pts were randomized to arm A and 292 pts to arm B. For this correlative study, outcome analysis was restricted to the clinical endpoint cumulative incidence of relapse (CIR) due to study protocol requirements allowing overall survival analysis to be performed only two years after the last pt had been enrolled. MRD monitoring was performed in a total 503 pts for whom at least one bone marrow (BM) sample was available using RQ-PCR technique; the median follow-up (FU) of the 503 pts was 2.8 yrs. NPM1mut TL (ratio of NPM1mut/ABL1 transcripts x 104) were determined by RQ-PCR (sensitivity 10-5 to 10-6). Results: In total, 3711 BM samples were analyzed (at diagnosis, n=415; during treatment, n=1765; during FU, n=1531). Both study arms were well balanced with regard to pts characteristics and pretreatment NPM1mut TL. First, we evaluated the impact of GO on kinetics of NPM1mut TL during treatment. After the first induction cycle, median NPM1mut TL were significantly lower in the investigational arm (p=.001) and this was true for all subsequent treatment cycles [after induction II (p=.008), consolidation I (p Conclusion: In our randomized Phase III AMLSG 09-09 study, the addition of GO to intensive chemotherapy plus ATRA was associated with a significantly better reduction of NPM1mut TL after each treatment cycle. This better clearance translated into a significantly lower CIR in the investigational arm with GO. Disclosures Paschka: Otsuka: Membership on an entity's Board of Directors or advisory committees; Bristol-Meyers Squibb: Other: Travel support, Speakers Bureau; Jazz: Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Other: Travel support, Speakers Bureau; Pfizer: Membership on an entity's Board of Directors or advisory committees; Sunesis: Membership on an entity's Board of Directors or advisory committees; Amgen: Other: Travel support; Janssen: Other: Travel support; Celgene: Membership on an entity's Board of Directors or advisory committees, Other: Travel support, Speakers Bureau; Astex: Membership on an entity's Board of Directors or advisory committees; Agios: Membership on an entity's Board of Directors or advisory committees; Astellas: Membership on an entity's Board of Directors or advisory committees, Travel support; Takeda: Other: Travel support. Krönke:Celgene: Honoraria. Fiedler:Amgen: Other: support for meetíng attendance; GSO: Other: support for meeting attendance; Teva: Other: support for meeting attendance; Gilead: Other: support for meeting attendance; JAZZ Pharmaceuticals: Other: support for meeting attendance; ARIAD/Incyte: Membership on an entity's Board of Directors or advisory committees, support for meeting attendance; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Amgen: Research Funding; Pfizer: Research Funding; Amgen: Patents & Royalties; Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding; Daiichi Sankyo: Other: support for meeting attendance. Schroeder:Celgene: Consultancy, Honoraria, Research Funding. Lübbert:Janssen: Honoraria, Research Funding; TEVA: Other: Study drug; Cheplapharm: Other: Study drug; Celgene: Other: Travel Support. Götze:JAZZ Pharmaceuticals: Honoraria; Novartis: Honoraria; Takeda: Honoraria, Other: Travel aid ASH 2017; Celgene: Honoraria, Research Funding. Schleicher:Novartis: Membership on an entity's Board of Directors or advisory committees, Other: Investigator; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Ipsen: Membership on an entity's Board of Directors or advisory committees; Eissai: Other: Investigator; Astra Zeneca: Other: Investigator; Pfizer: Speakers Bureau; Janssen: Speakers Bureau; Celgene: Speakers Bureau. Schlenk:Pfizer: Research Funding, Speakers Bureau. Ganser:Novartis: Membership on an entity's Board of Directors or advisory committees. Döhner:Amgen: Consultancy, Honoraria; Astex Pharmaceuticals: Consultancy, Honoraria; Novartis: Consultancy, Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Pfizer: Research Funding; Agios: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria; Jazz: Consultancy, Honoraria; Celator: Consultancy, Honoraria; AROG Pharmaceuticals: Research Funding; Seattle Genetics: Consultancy, Honoraria; Astellas: Consultancy, Honoraria; AROG Pharmaceuticals: Research Funding; Bristol Myers Squibb: Research Funding; Bristol Myers Squibb: Research Funding; Astex Pharmaceuticals: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria; Astellas: Consultancy, Honoraria; Pfizer: Research Funding; Seattle Genetics: Consultancy, Honoraria; Jazz: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Celator: Consultancy, Honoraria; Sunesis: Consultancy, Honoraria, Research Funding; Agios: Consultancy, Honoraria; Novartis: Consultancy, Honoraria, Research Funding; Sunesis: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Research Funding.

Childhood myelodysplastic syndromes (MDS) account for less than 5% of pediatric hematologic malignancies and differ from their adult counterpart in terms of biology, genetics, and cure rates. Complete (-7) or partial loss (del7q) of chromosome 7 constitutes the most common cytogenetic abnormality and is associated with more advanced disease typically requiring timely hematopoietic stem cell transplantation (HSCT). Previously, we and others established a link between -7 and germline GATA2 mutations in pediatric MDS (37% of MDS/-7 cases are GATA2-deficient) as well as constitutional SAMD9/9L disorders where -7 is utilized as an escape mechanism from the growth-restrictive effect of SAMD9/9L mutations. To date, comprehensive sequencing studies have been performed in 96 children with primary MDS, as reported by Pastor et al, Leukemia 2017 and Schwartz et al, Nature Comm 2017. This work established mutations in SETBP1, ASXL1, PTPN11, RUNX1 and RAS pathway genes as common somatic drivers. However, little is known about the clonal development of -7 and the role of additional somatic mutations. The knowledge about clonal hierarchies is essential for the understanding of disease progression on molecular level and for mapping potential drug targets. The rationale for the current study was to i) define the most common somatic drivers in a large cohort of patients with childhood MDS, ii) identify clonal/subclonal mutations, iii) infer clonal architecture of monosomy 7 and track the changes over time. We studied a cohort of 576 children and adolescents with primary MDS diagnosed between 1998 and 2016 in Germany, consisting of 482 (83%) patients with refractory cytopenia of childhood (RCC) and 94 (17%) MDS with excess blasts (EB). All patients underwent deep sequencing for 30 genes relevant to pediatric MDS and additional WES was performed in 150/576 patients. Using 20 computational predictors (including CADD and REVEL), population databases and germline testing, we identified the most likely pathogenic mutations. First, we excluded germline predisposing mutations in GATA2, SAMD9/SAMD9L and RUNX1 detected in 7% (38/576), 8% (43 of 548 evaluable) and 0.7% (4/576) of patients, respectively. Then we focused on the exploration of somatic aberrations. Most common karyotype abnormalities were monosomy 7 (13%, 77/576) and trisomy 8 (3%, 17/576). A total of 104 patients carried somatic mutations, expectedly more prevalent in the MDS-EB group as compared to RCC (56%, 53/94 vs 10.6%, 51/482; pSETBP1>ASXL1; -7>SETBP1>ASXL1>PTPN11; -7>SETBP1>ASXL1>CBL, -7>EZH2>PTPN11). Finally, we tracked clonal evolution over time in 12 cases with 2-12 available serial samples using deep sequencing complemented by serial CFC-analysis. This confirmed that SETBP1 clones are rapidly expanding, while ASXL1 subclones exhibit an unstable pattern with clonal sweeping, while additional minor clones are acquired as late events. In 2 of 11 transplanted patients who experienced relapse, the original clonal architecture reappeared after HSCT. In summary, the hierarchy of clonal evolution in pediatric MDS with -7 follows a defined pattern with -7 aberrations arising as ancestral event followed by the acquisition of somatic hits. SETBP1 mutations are the dominant driver while co-dominant ASXL1 mutations are unstable. The functional interdependence and potential pharmacologic targetability of such somatic lesions warrants further studies. Disclosures Niemeyer: Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees.

FLT3-ITD (internal tandem duplication) is a late event in the pathogenesis of acute myeloid leukemia (AML). Identification of early cooperating events for FLT3 mutations may improve our understanding of the pathogenesis of AML and lead to a more efficient treatment and improved outcome for AML patients. p53 alteration can be found in up to 70% of AML patients with complex karyotypes, while studies from our group and others show a relatively low incidence of p53 mutation (generally around 10%) in other AML patients. Dysfunction of p53 pathway resulting from overexpressed MDM2/MDM4 is more often found than p53 mutations in patients with de novo AML. An early mouse study identified the FLT3 gene to be preferentially mutated by insertional mutagenesis in p53 knock-out but not in p53 wild-type tumors. Importantly, p53 mutation appears to be an early event in the pathogenesis of AML. In this study, we investigated whether p53 haploinsufficiency or loss cooperates with FLT3-ITD in the induction of AML. To this end, we crossed FLT3-ITD knock-in mice with p53 knockout mice to generate mice harboring both ITD/ITD and p53 knockout mutations. ITD/ITD; p53+/- (FLT3-ITD homozygous and p53 heterozygous) mice became moribund much faster than mice with ITD/ITD alone or p53+/- alone. The median survival of ITD/ITD;p53+/- mice (n=69) was 313 days, which was significantly shorter than that of ITD/ITD mice (littermates of ITD/ITD; p53+/- mice, 583 days, n=16), p53+/- mice (521 days, n=30), and WT mice (862 days, n=10) (p50% ITD/ITD; p53-/- mice and ITD/ITD; p53+/- mice with acute leukemia demonstrated a bi-clone disease, with co-existence of AML and ALL. Unexpectedly, all analyzed murine AMLs with complete or heterozygous loss of p53 (n=9) showed normal karyotypes. p53 haploinsufficiency or loss did not increase self-renewal of hematopoietic stem/progenitor cells as defined by serial replanting assays in vitro and limiting dilution transplantation of leukemic cells in vivo. However, animals with only AML in the ITD/ITD; p53+/- group showed a significant increase of CMPs in comparison with ITD/ITD mice with CMML, P53+/- and WT mice, e.g. a 66-fold increase of CMPs in #1376 mouse compared with WT mice. This suggests that the block of differentiation from CMPs to GMPs may have contributed to the development of AML. P53 haploinsufficiency or loss reduced the sensitivity of murine FLT3-ITD leukemia to crenolanib in vitro (IC50: 313.3nM, 461.4nM, and 185.8nM for ITD/ITD;p53+/-, ITD/ITD;p53-/-, and ITD/ITD leukemia, respectively), but not their sensitivity to midostaurin (IC50: 117.3nM, 110.2nM, and 201.3nM). To develop an efficient therapy for p53-mutated AML, we firstly tried to combine FLT3 inhibitors and MDM2 antagonist idasanutlin, FLT3 inhibitor and Bcl2 inhibitor venetoclax. Unfortunately, these did not enhance induction of apoptosis in leukemic cells from ITD/ITD;p53+/- mice. However, exposure to the proteasome inhibitor carfilzomib had a strong cytotoxic effect against ITD/ITD; p53+/- and ITD/ITD;p53-/-, leukemic cells (IC50: 5.2nM and 17.1nM vs. 6.8nM for ITD/ITD leukemia). In addition, the combination of carfilzomib with midostaurin showed an additive cytotoxicity in murine ITD/ITD; p53+/- leukemia as well as in primary leukemic cells from most patients with AML (n=10). Taken together, our data indicate a strong cooperating effect of FLT3-ITD and p53 haploinsufficiency or loss in the induction of AML and ALL. Our data emphasize more careful analysis of p53 deregulation in AML. Targeting FLT3 in combination with drugs working independently of p53 status, such as proteasome inhibitor carfilzomib, might improve outcomes of AML patients. Disclosures Ganser: Novartis: Membership on an entity's Board of Directors or advisory committees.

The microRNA/miR deregulation in BCR-ABL-negative myelodysplastic-myeloproliferative neoplasms (MDS/MPN) is not known. Myelopoiesis-associated miR-10a, miR-17-5p, miR-155, miR-223 and miR-424 were analysed by real-time polymerase chain reaction (PCR) in bone marrow cells of atypical chronic myeloid leukaemia (aCML, n = 7) and chronic myelomonocytic leukaemia (CMML, n = 8) and were compared to BCR-ABL-positive chronic myelogenous leukaemia (CML, n = 10) and non-neoplastic haematopoiesis (n = 10). Down-regulation of miR-10a was found in CMML but also in CML (each p

Gene-modified autologous hematopoietic stem cells (HSC) can provide ample clinical benefits to subjects suffering from X-linked chronic granulomatous disease (X-CGD), a rare inherited immunodeficiency characterized by recurrent, often life-threatening bacterial and fungal infections. Here we report on the molecular and cellular events observed in two young adults with X-CGD treated by gene therapy in 2004. After the initial resolution of bacterial and fungal infections, both subjects showed silencing of transgene expression due to methylation of the viral promoter, and myelodysplasia with monosomy 7 as a result of insertional activation of ecotropic viral integration site 1 (EVI1). One subject died from overwhelming sepsis 27 months after gene therapy, whereas a second subject underwent an allogeneic HSC transplantation. Our data show that forced overexpression of EVI1 in human cells disrupts normal centrosome duplication, linking EVI1 activation to the development of genomic instability, monosomy 7 and clonal progression toward myelodysplasia.

Neurotrophins (NTs) and their receptors play a key role in neurogenesis and survival. The TRK (tropomyosin-related kinase) receptor protein tyrosine kinases (TRKA, TRKB, TRKC) are high-affinity NT receptors that are expressed in a variety of human tissues. Their role in normal and malignant hematopoiesis is poorly understood. In a prospective study involving 94 adult patients we demonstrate for the first time cell-surface expression of the 3 TRKs and constitutive activation in blasts from patients with de novo or secondary acute leukemia. At least one TRK was expressed in 55% of the analyzed cases. We establish a clear correlation between the TRK expression pattern and FAB classification. Although only few point mutations were found in TRK sequences by reverse-transcriptase–polymerase chain reaction (RT-PCR), we observed coexpression of BDNF (ligand for TRKB) in more than 50% of TRKB+ cases (16/30). Activation of TRKA or TRKB by NGF and BDNF, respectively, efficiently rescued murine myeloid cells from irradiation-induced apoptosis. Coexpression of TRKB/BDNF or TRKA/NGF in murine hematopoietic cells induced leukemia. Moreover, activation of TRKs was important for survival of both human and murine leukemic cells. Our findings suggest that TRKs play an important role in leukemogenesis and may serve as a new drug target.