Abstract: Background: HBI-8000 is an orally bioavailable member of the benzamide class of histone deacetylase inhibitors (HDACi), that inhibits cancer-associated HDAC enzymes (Class I and IIb). HBI-8000 has anti-tumor activity through various mechanisms of action, including epigenetic reprogramming and immunomodulation. It was recently approved by the Chinese FDA under the name chidamide (Epidaza) for relapsed or refractory (R/R) peripheral T-cell lymphoma (PTCL) with a recommended dose of 30 mg twice weekly (BIW). HBI-8000 is also being manufactured in the USA for clinical development outside of China. The preliminary results of a phase I trial of HBI-8000 to confirm the safety and maximum tolerated dose (MTD) in Japanese patients (pts) with advanced NHL are presented (NCT02697552). Methods: This is a multicenter, prospective phase I trial in Japan. Inclusion criteria: patients are eligible if they have histologically or cytologically proven NHL and no other standard therapy is available. The primary endpoint is the MTD based on the frequency of dose-limiting toxicities (DLTs) observed within 28 days of the first dose. Secondary endpoints include pharmacokinetic (PK) profile and anti-tumor activity. At the time of this abstract submission, the trial is still ongoing. Results: Thirteen out of 14 pts were eligible for the 1st cycle DLT assessment (6 pts in the 30 mg, 7 pts in the 40 mg cohort). Median age was 68 years, gender well balanced, and the majority of pts had ≥ 2 prior treatment regimens. Five pts had the diagnosis of adult T-cell leukemia-lymphoma (ATL), 2 pts presented with PTCL, 3 with diffuse large B-cell lymphoma (DLBLC), 2 with follicular lymphoma (FL), 1 with cutaneous T-cell lymphoma (CTCL), and 1 with marginal zone lymphoma. Overall, the treatment was well tolerated, and adverse drug reactions (ADRs) were predominantly hematologic, consistent with the previous experiences. There were 7 pts in the 40 mg dose cohort because one of the first 3 pts had to be replaced for incomplete dosing due to grade 3 hypertriglyceridemia which was not regarded as DLT by the Data Monitoring Safety Committee (DMC/SMC). In the 40 mg cohort, 2 pts were considered as DLTs by definition in the protocol: grade 4 neutropenia and grade 3 alanine transaminase (ALT) increase. Both pts were asymptomatic. The grade 4 neutropenia promptly resolved with the administration of G-CSF and the grade 3 ALT elevation resolved with dose interruption. The 30 mg dose cohort completed with no DLT after the 1st cycle in 6 pts. The following hematologic grade 3/4 toxicities were noted in the 40 mg dose cohort (N=7): leukopenia (2 pts, 29%), neutropenia (3 pts, 43%), and thrombocytopenia (3 pts, 43%). Non-hematologic ADRs included fatigue, nausea, diarrhea, decreased appetite, erythema and pyrexia. The preliminary pharmacokinetic (PK) results from the 3 patients in the 30 mg cohort, and 7 patients in the 40 mg dose cohort show inter-patient variability as expected of an oral agent. Mean half-life (t ½ ) was between16.5 and 20 hours (h) with a Tmax between 2.5 and 3.5h and consistent with previous findings. Mean Cmax and AUC increased with dose (30 mg: 210 ng/mL; 3660 h*ng/mL and 40 mg: 590 ng/mL; 7200 h*ng/mL). The patient with neutropenia as DLT presented with the highest exposure. Cardiovascular assessments including serial ECGs and troponin assessments did not reveal clinically relevant findings. Best overall response was noted in 40 mg BIW cohort (N=7): 1 CR (10%), 5 PR (30%), 1 SD (20%). Four of the partial responders were ATL patients. In the 30 mg BIW dose cohort, 4/6 patients had stable disease after the 1st cycle. Summary: In this phase l trial evaluating the safety of twice weekly 30 mg and 40 mg doses, HBI-8000 was well tolerated with expected toxicities that could be managed with dose interruptions/reductions. Tumor response results in pts who completed at least one cycle of treatment indicate some clinical benefit especially in pts who started with the 40 mg dose level. The DMC/SMC has provided an opinion that the 2 observed DLTs with HBI-8000 in the phase I trial were clinically manageable and that 40 mg BIW would be recommended as the dosage for subsequent phase II studies. Registration enabling phase II trials to evaluate efficacy and safety in R/R ATL pts (Japan) and R/R PTCL pts (Japan and Korea) are being initiated. Disclosures Ando: SymBio Pharmaceuticals: Research Funding. Yoshimitsu:HUYA Bioscience International: Research Funding. Ishida:Kyowa Hakko Kirin, Co., Ltd.: Honoraria, Research Funding; Celgene KK: Research Funding; Bayer Pharma AG: Research Funding. Hidaka:Chugai-pharm: Research Funding. Nagashima:HUYA Bioscience International: Employment. Miyazato:HUYA Bioscience International: Employment. Schupp:HUYA Bioscience International: Employment. Rolland:HUYA Bioscience International: Employment. Gillings:HUYA Bioscience International: Employment. Lee:HUYA Bioscience International: Employment. Tobinai:Eisai: Honoraria, Research Funding; GlaxoSmithKline: Research Funding; HUYA Bioscience: Honoraria; Janssen Pharmaceuticals: Honoraria, Research Funding; Kyowa Hakko Kirin: Research Funding; Mundipharma: Honoraria, Research Funding; Ono Pharmaceuticals: Research Funding; Servier: Research Funding; Takeda: Honoraria, Research Funding; Zenyaku Kogyo: Honoraria; Chugai Pharma: Research Funding; Celgene: Research Funding; Abbvie: Research Funding.

Abstract: We have recently shown that stimulation of glycoprotein (gp) 130, the membrane-anchored signal transducing receptor component of IL-6, by a complex of human soluble interleukin-6 receptor (sIL-6R) and IL-6 (sIL-6R/IL-6), potently stimulates the ex vivo expansion as well as erythropoiesis of human stem/progenitor cells in the presence of stem cell factor (SCF). Here we show that sIL-6R dose-dependently enhanced the generation of megakaryocytes (Mks) (IIbIIIa-positive cells) from human CD34+ cells in serum-free suspension culture supplemented with IL-6 and SCF. The sIL-6R/IL-6 complex also synergistically acted with IL-3 and thrombopoietin (TPO) on the generation of Mks from CD34+ cells, whereas the synergy of IL-6 alone with TPO was barely detectable. Accordingly, the addition of sIL-6R to the combination of SCF + IL-6 also supported a substantial number of Mk colonies from CD34+ cells in serum-free methylcellulose culture, whereas SCF + IL-6 in the absence of sIL-6R rarely induced Mk colonies. The addition of monoclonal antibodies against gp130 to the suspension and clonal cultures completely abrogated the megakaryopoiesis induced by sIL-6R/IL-6 in the presence of SCF, whereas an anti-TPO antibody did not, indicating that the observed megakaryopoiesis by sIL-6R/IL-6 is a response to gp130 signaling and independent of TPO. Furthermore, human CD34+ cells were subfractionated into two populations of IL-6R–negative (CD34+ IL-6R−) and IL-6R–positive (CD34+ IL-6R+) cells by fluorescence-activated cell sorting. The CD34+IL-6R− cells produced a number of Mks as well as Mk colonies in cultures supplemented with sIL-6R/IL-6 or TPO in the presence of SCF. In contrast, CD34+ IL-6R+cells generated much less Mks and lacked Mk colony forming activity under the same conditions. Collectively, the present results indicate that most of the human Mk progenitors do not express IL-6R, and that sIL-6R confers the responsiveness of human Mk progenitors to IL-6. Together with the presence of functional sIL-6R in human serum and relative unresponsiveness of human Mk progenitors to IL-6 in vitro, current results suggest that the role of IL-6 may be mainly mediated by sIL-6R, and that the gp130 signaling initiated by the sIL-6R/ IL-6 complex is involved in human megakaryopoiesis in vivo.

Abstract: Background Copy-number alterations (CNAs) and gene mutations are hallmarks of cancer genomes, and they are implicated in the development of myeloid neoplasm. However, their relationships have not been fully examined. To address this issue, we have recently developed a novel, next-generation sequencing-based platform for copy-number analysis, which enabled us to detect mutations and CNAs simultaneously. We applied this platform to around 2,000 cases with myeloid neoplasms. Aims We aimed at delineating the landscape of CNAs and their relationships with gene mutations in myeloid neoplasms. Methods We examined 2,101 cases with myeloid neoplasms by whole-exome sequencing (WES) or targeted deep sequencing. Excluding 116 samples showing low qualities of copy-number signals, we performed subsequent analysis on the remaining 1,985 cases with myelodysplastic syndromes (MDS, n = 1,102), myelodysplastic/myeloproliferative neoplasms (MDS/MPN, n = 140), de novo acute myeloid leukemia (de novo AML, n = 448), and secondary AML (sAML, n = 295). In copy-number analysis, total copy numbers and allele-specific copy numbers (ASCNs) were quantified based on sequencing depths and allelic ratios on genome-wide probes. Copy-number signals were corrected for multiple biases (e.g. GC content, ASCN, and fragment length). We also validated the performance of this platform through comparison with SNP-array karyotyping data in 115 de novo AML cases. CNAs longer than 5 Mb were regarded as arm-level CNAs, and those shorter than 5 Mb were regarded as focal CNAs. Results In total, we identified 4,141 CNAs (52.9 % of cases with at least one CNA), and 3,863 mutations (73.9 % of cases with at least one mutation). Most frequent alterations included -7/del(7q) (13.2 %), del(5q) (11.4 %), trisomy 8 (7.2 %), and del(20q) (5.2 %), and mutations of TET2 (12 .3 %), TP53 (11.3 %), ASXL1 (10.1%), and DNMT3A (9.9 %). To evaluate the difference of copy-number landscapes between de novo AML and myelodysplasia (MDS, MDS/MPN, and sAML), we compared the frequencies of CNAs between them. Uni-parental disomy (UPD) of 13q (FLT3) and 11p (WT1), and amplifications of 11q, 13q, and 21q (ERG) were more enriched in de novo AML, while der(1;7), UPD of 11q (CBL), and del(20q) were enriched in myelodysplasia, suggesting differential involvements of CNAs. We next analyzed the correlations between CNA profiles and prognosis in cases with myelodysplasia. Since TP53 status implies a large impact on both patients' prognosis and CNA profiles, we separately analyzed TP53-positive (n = 53) and negative (n = 686) cases with available survival data. In TP53-negative cases, -7/7qLOH (Hazard ratio(HR): 2.28, q 〈 0.001), and UPD of 11q (CBL) (HR: 2.60, q = 0.0034) significantly correlated with shorter overall survivals (OS), while, in TP53-positive cases, amp(11q), +19, and amp(21q) were marginally associated with shorter OS. To delineate the relationships between CNAs and mutations, we interrogated correlations between both lesions among MDS cases without TP53 alterations (n = 937). A number of significant correlations were detected, such as those between trisomy 8 and del(20q) with U2AF1 mutations (q 〈 0.05, for each), and monosomy 7 and amp(21q) with mutations of RUNX1 and NRAS (q 〈 0.01, for each). These correlations were also revealed in clustering analysis based on CNA and mutation profiles, which identified 5 unique clusters: Cluster 1 (n = 171) with trisomy 8, del(20q), and mutations of U2AF1 and ETV6, Cluster 2 (n = 43) with monosomy 7, amp(21q), and mutations of NRAS, SETBP1, and RUNX1, Cluster 3 (n = 19) with amp(1q) and amp(3q), Cluster 4 (n = 127) with those of SF3B1, TET2, and DNMT3A, and Cluster 5 (n = 50) with those of SRSF2, STAG2, ASXL1, and RUNX1. The remaining 527 cases were not assigned into any cluster due to lack of significantly correlated alterations. Finally, the temporal relationships of coexisting alterations were estimated based on their cell fractions; monosomy 7 had significantly greater cell fractions (P = 0.031) and is predicted to precede NRAS mutations, while the cell fractions of U2AF1 mutations tended to be greater than those of trisomy 8 (P = 0.063), suggesting their implications in different stages of disease progression. Conclusion An integrated analysis of CNAs and mutations in 〉 2,000 cases revealed the impacts of CNAs on disease characteristics and provided novel insight into the interplay between CNAs and mutations in the pathogenesis of MDS. Figure Disclosures Atsuta: CHUGAI PHARMACEUTICAL CO., LTD.: Honoraria; Kyowa Kirin Co., Ltd: Honoraria. Kanda:Celgene: Consultancy, Research Funding; Novartis: Research Funding; Shionogi: Consultancy, Honoraria, Research Funding; Nippon-Shinyaku: Research Funding; Taiho: Research Funding; Asahi-Kasei: Research Funding; Bristol-Myers Squibb: Consultancy, Honoraria; Takeda: Consultancy, Honoraria, Research Funding; Eisai: Consultancy, Honoraria, Research Funding; Eisai: Consultancy, Honoraria, Research Funding; Dainippon Sumitomo: Consultancy, Honoraria, Research Funding; Otsuka: Research Funding; Kyowa-Hakko Kirin: Consultancy, Honoraria, Research Funding; Ono: Consultancy, Honoraria, Research Funding; MSD: Research Funding; Chugai: Consultancy, Honoraria, Research Funding; CSL Behring: Research Funding; Taisho-Toyama: Research Funding; Tanabe Mitsubishi: Research Funding; Dainippon Sumitomo: Consultancy, Honoraria, Research Funding; Takeda: Consultancy, Honoraria, Research Funding; Kyowa-Hakko Kirin: Consultancy, Honoraria, Research Funding; Bristol-Myers Squibb: Consultancy, Honoraria; Astellas: Consultancy, Honoraria, Research Funding; Takara-bio: Consultancy, Honoraria; Novartis: Research Funding; Astellas: Consultancy, Honoraria, Research Funding; Sanofi: Research Funding; Pfizer: Research Funding; Asahi-Kasei: Research Funding; Alexion: Consultancy, Honoraria; CSL Behring: Research Funding; Takara-bio: Consultancy, Honoraria; Mochida: Consultancy, Honoraria; Taiho: Research Funding; Celgene: Consultancy, Research Funding; Tanabe Mitsubishi: Research Funding; Taisho-Toyama: Research Funding; Pfizer: Research Funding; Sanofi: Research Funding; Mochida: Consultancy, Honoraria; Alexion: Consultancy, Honoraria; Otsuka: Research Funding. Sekeres:Celgene: Membership on an entity's Board of Directors or advisory committees; Millenium: Membership on an entity's Board of Directors or advisory committees; Syros: Membership on an entity's Board of Directors or advisory committees. Saunthararajah:EpiDestiny: Consultancy, Equity Ownership, Patents & Royalties; Novo Nordisk: Consultancy. Miyazaki:Chugai: Research Funding; Otsuka: Honoraria; Novartis: Honoraria; Nippon-Shinyaku: Honoraria; Dainippon-Sumitomo: Honoraria; Kyowa-Kirin: Honoraria. Usuki:Boehringer-Ingelheim Japan: Other: Received Research ; Daiichi Sankyo: Other: Received Research ; SymBio Pharmaceuticals Limited.,: Other: Received Research ; Novartis: Speakers Bureau; Ono Pharmaceutical: Speakers Bureau; Takeda Pharmaceutica: Speakers Bureau; Chugai Pharmaceutical: Speakers Bureau; Nippon Shinyaku: Speakers Bureau; Mochida Pharmaceutical: Speakers Bureau; MSD K.K.: Speakers Bureau; Celgene Corporation: Other: Received Research , Speakers Bureau; Sumitomo Dainippon Pharma: Other: Received Research , Speakers Bureau; Pfizer Japan: Other: Received Research ; Stellas Pharma: Other: Received Research ; Otsuka: Other: Received Research ; Kyowa Kirin: Other: Received Research ; GlaxoSmithKline K.K.: Other: Received Research ; Sanofi K.K.: Other: Received Research ; Shire Japan: Other: Received Research ; Janssen Pharmaceutical K.K: Other: Received Research . Imada:Bristol-Meyer Squibb K.K.: Honoraria; Celgene K.K.: Honoraria; Chugai Pharmaceutical Co., Ltd.: Honoraria; Kyowa Hakko Kirin Co., Ltd.: Honoraria; Ono Pharmaceutical Co., Ltd.: Honoraria; Otsuka Pharmaceutical Co., Ltd.: Honoraria; Astellas Pharma Inc.: Honoraria; Novartis Pharma K.K.: Honoraria; Takeda Pharmaceutical Co.,LTD.: Honoraria; Nippon Shinyaku Co.,Ltd.: Honoraria. Takaori-Kondo:Kyowa Kirin: Research Funding; Pfizer: Honoraria; Janssen: Honoraria; Chugai: Research Funding; Takeda: Research Funding; Ono: Research Funding; Bristol-Myers Squibb: Honoraria, Research Funding; Novartis: Honoraria; Celgene: Honoraria, Research Funding. Kiguchi:Celltrion, Inc.: Research Funding; Astellas Pharmaceutical Co., Ltd.: Research Funding; Nippon Shinyaku Co., Ltd.: Research Funding; Otsuka Pharmaceutical Co., Ltd.: Research Funding; Kyowa Hakko Kirin Co., Ltd.: Research Funding; MSD CO., Ltd.: Research Funding; Novartis Pharmaceutical Co., Ltd.: Research Funding; Sumitomo Dainippon Pharmaceutical Co., Ltd.: Research Funding; Bristol-Myeres Squibb Co., Ltd.: Research Funding; Janssen Pharmaceutical Co., Ltd.: Research Funding; Celgene Co., Ltd.: Research Funding; SymBio Pharmaceutical Co., Ltd.: Research Funding; Taiho Pharmaceutical Co., Ltd.: Research Funding; Tejin Co., Ltd.: Research Funding; Sanofi K.K., Ltd.: Research Funding. Maciejewski:Alexion: Consultancy; Novartis: Consultancy. Ogawa:Asahi Genomics: Equity Ownership; Qiagen Corporation: Patents & Royalties; Dainippon-Sumitomo Pharmaceutical, Inc.: Research Funding; RegCell Corporation: Equity Ownership; ChordiaTherapeutics, Inc.: Consultancy, Equity Ownership; Kan Research Laboratory, Inc.: Consultancy.

Abstract: Background A rapid enumeration of CD34+ cells is expected to facilitate a safe and efficient PBSC collection for a successful transplantation. We previously reported a novel enumeration method of hematopoietic progenitor cells (designated as HPC) using an automated hematology analyzer, XN-series model (Sysmex Corporation, Japan), which does not require monoclonal antibody. This method seemed very promising in a pilot study in a single institute (ASH meeting #1922, 2011). Hence, we conducted a multicenter study to confirm the results in a larger number of subjects in various situations. In this study, we used an up-graded analyzer which had been installed with a revised analytical program. This new program employs an automatically-adjusted gating to fit the individual variety, whereas the former used a fixed gating for detecting HPC. We planned to divide the study into 2 parts; the first is to confirm the outcome of the previous single-institute study and to develop a model to predict CD34+ cell counts from HPC, and the second is to validate the model. Here we show the results of the first part of the study. Patients and Method PB or PBSC samples were taken from G-CSF- and/or chemo-mobilized subjects (25 patients undergoing PBSCT and 25 healthy donors) in 5 institutes. Samples were divided into 2 tubes; one is for in-house assay in which HPC and CD34+ cells were counted in each institute within a few hours without any manipulation, and another was shipped to the central laboratory (SRL, Inc., Japan) where CD34+ cell count was examined. HPC and central labo-assayed CD34+ cell counts were compared with each other and used in a correlation analysis. HPC and in-house CD34+ cells were used in the analysis of kinetics. This study was approved by IRB, and an informed consent was obtained from each participant before apheresis. Results Five PBSC samples (2.3%) were estimated to be invalid for HPC assay because of difficulty in identifying HPC, and were excluded from the analysis. There were good correlations between HPC and CD34+ cell counts in all samples (n=211; R2 0.9576, slope 1.0678, Fig.1), in PB (n=87; R2 0.7631, slope 0.8878) and PBSC (n=124; R2 0.9501, slope 1.0689), in autologous PBSCT patients (n=116; R2 0.9759, slope 1.0596) and donors (n=95; R2 0.7914, slope 1.1381). However, HPC and CD34+ cell counts differ more than 3 times around the critical concentrations for making decision in some samples. Concerning their kinetics in PB during mobilization, which was observed in 2 donors and 9 patients, HPC showed a very similar trend as CD34+ cells, and the timing of appearance and increase in PB was almost concordant in most cases (Fig. 2). Conclusions In this multicenter study, we confirmed not only there was a good correlation between HPC and CD34+ cell counts, but also both HPC and CD34+ cell counts in PB showed a very similar trend during mobilization, as was observed in our previous single-institute study. However, a few samples were estimated as invalid for HPC assay, and there were a few more samples in which HPC and CD34+ cell counts differ significantly. Therefore, it remains to be elucidated how much HPC could be helpful in the clinical setting for determining the optimal timing of collection, for predicting the number of CD34+ cells in the apheresis product, and for determining the optimal blood volume to be apheresed. We are currently underway of the later validation part of this study to evaluate these issues. Disclosures: Tanosaki: Sysmex Corporation: Automated hematology instruments were provided on loan and the cost for CD34+ cell counts were owed to Sysmex Corporation, Kobe, Japan in this study. Other.

Abstract: While germline predisposition to myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) has long been recognized mainly through rare familial and pediatric cases, it has been drawing an increasing attention, on the basis of the recent discovery of novel risk alleles for MDS/AML through studies relying on revolutionized sequencing technologies; according to these studies, it suggest that more numbers of MDS/AML cases than expected might have germline predisposition. Moreover, it is suggested that germline variations may also confer predisposition to age-related clonal hematopoiesis or "CHIP", which has been implicated in the development of MDS/AML. In this study, we explored germline predisposition to MDS and CHIP through intensive sequencing of blood samples from large cohorts of AML/MDS patients and 'hematologically' healthy individuals (HHIs), in which germline variants in 21 genes implicated in sporadic or familial MDS/AML or CHIP were interrogated among patients with MDS/AML from the Japan Marrow Donor Program (n=797) and HHIs aged 〉 60 years from Biobank Japan (n=10,852). Germline variants were referred to NCBI dbSNP Build 151 database, excluding the entries in COSMIC ver.7 and in-house database, followed by manual curations. Somatic mutations and CHIP in the 21 genes were also analyzed for MDS/AML and HHIs, respectively. In total, 30,286 germline variants, including both synonymous and non-synonymous changes, were detected in 21 genes in the entire cohort. By comparing their frequencies between in MDS/AML and HHIs, we identified 6 germline variants in showing a significant enrichment in MDS/AML. Among these most frequently observed was variants in DDX41, for which a total of 3,721 variants were detected in 3,688 HHIs. Among these, 3 variants were significantly enriched in MDS/AML, including p.A500fs (OR=13.1 [6.6-25.9] (95%CI) (n=15), p.S363del (OR=41.0, [4.3-349.5] ) (n=3), and p.Y259C (OR=34.2, [6.6-176.8]) (n=5). Of interest, 14 of 23 MDS patients with one of these alleles carried somatic DDX41 mutations, typically p.R525H, which were not found in any of HHIs, further supporting the relevance of these DDX41 risk alleles. Also including an additional 2 nonsense/splicing variants, 5 DDX41 alleles found in 25 MDS/AML patients were thought to represent germline predisposition to MDS/AML. Similarly, RUNX1 p.H85N (OR=9.10, [1.52-54.52] ) (n=2), CBL p.P782L (OR=4.27, [1.56-11.70]) (n=5), and GNAS p.H69N (OR = 2.90, [1.28-6.59] ) (n=7) showed a significant enrichment in MDS/AML. Combined, these putative risk alleles accounted for 4.6% (37/797) of sporadic MDS and sAML. None of these alleles were observed in the Caucasian population of Exome Aggregation Consortium dataset, suggesting Asian origins of these variants. We next evaluated the effects of germline variants on CHIP. CHIP mutations were detected in 929 HHIs, where DNMT3A mutations (n=290) were most prevalent, followed by TET2 (n=124) and ASXL1 (n=68) mutations. By comparing allele frequency of each of 1,276 germline variants between healthy donors with and without CHIP, we identified two haplotypes at the JAK2 and TET2 loci, defined by T/A at c.C489T/c.G2490A (JAK2) and G/G/T at c.G652A/c.G3117A/c.T4140C (TET2), which were significantly enriched in the cases carrying CHIP with the JAK2 (p.V617F) and TET2 mutations, respectively (T/A vs. C/G; OR=3.36, [1.41-8.01] for JAK2 and G/G/T vs. A/A/C; OR=1.85, [1.19-2.86] for TET2). Intriguingly, the JAK2 risk haplotype (C/G) were also enriched in MDS cases with JAK2 p.V617F mutations (T/A vs. C/G; OR=3.06, [1.26-7.60]). Similarly, the TET2 risk haplotype (G/G/T) tended to be enriched in MDS cases with TET2 mutations, although not statistically significant. Finally, variant allele frequency of JAK2 p.V617F mutations in CHIP exceeded 0.5 in 4 out of 26 JAK2 CHIP-positive patients (15%), suggesting the presence of loss of heterozygosity (LOH) in chromosome 9p. In conclusion, through a large-scale detection of germline variants in 21 common drivers of MDS/AML as well as CHIP, we identified multiple novel germline variants or haplotypes that showed a significant predisposition to the development of adult-onset MDS or CHIP, respectively. Our findings provide novel insights into the genetic basis of myeloid leukemogenesis and the development of CHIP. Disclosures Nakagawa: Sumitomo Dainippon Pharma Co., Ltd.: Research Funding. Kanda:Otsuka: Research Funding; Dainippon-Sumitomo: Consultancy, Honoraria, Research Funding; Eisai: Consultancy, Honoraria, Research Funding; Chugai: Consultancy, Honoraria, Research Funding; Nippon-Shinyaku: Research Funding; Astellas: Consultancy, Honoraria, Research Funding; Kyowa-Hakko Kirin: Consultancy, Honoraria, Research Funding; Taiho: Research Funding; Pfizer: Research Funding; MSD: Research Funding; Takeda: Consultancy, Honoraria, Research Funding; Asahi-Kasei: Research Funding; Ono: Consultancy, Honoraria, Research Funding; Sanofi: Research Funding; Novartis: Research Funding; Shionogi: Consultancy, Honoraria, Research Funding; Taisho-Toyama: Research Funding; CSL Behring: Research Funding; Tanabe-Mitsubishi: Research Funding; Bristol-Myers Squibb: Consultancy, Honoraria; Celgene: Consultancy, Honoraria; Mochida: Consultancy, Honoraria; Alexion: Consultancy, Honoraria; Takara-bio: Consultancy, Honoraria.

Abstract: Frequent pathway mutation involving multiple components of the RNA splicing machinery is a cardinal feature of myeloid neoplasms showing myeloid dysplasia, in which the major mutational targets include U2AF35, ZRSR2, SRSF2 and SF3B1. Among these, SF3B1 mutations were strongly associated with MDS subtypes characterized by increased ring sideroblasts, such as refractory anemia and refractory cytopenia with multiple lineage dysplasia with ring sideroblasts, suggesting the critical role of SF3B1 mutations in these MDS subtypes. However, currently, the molecular mechanism of SF3B1mutation leading to the ring sideroblasts formation and MDS remains unknown. The SF3B1 is a core component of the U2-small nuclear ribonucleoprotein (U2 snRNP), which recognizes the 3′ splice site at intron–exon junctions. It was demonstrated that Sf3b1 null mice were shown to be embryonic lethal, while Sf3b1 +/- mice exhibited various skeletal alterations that could be attributed to deregulation of Hox gene expression due to haploinsufficiency of Sf3b1. However, no detailed analysis of the functional role of Sf3b1 in hematopoietic system in these mice has been performed. So, to clarify the role of SF3B1 in hematopoiesis, we investigated the hematological phenotype of Sf3b1 +/- mice. There was no significant difference in peripheral blood counts, peripheral blood lineage distribution, bone marrow total cellularity or bone marrow lineage composition between Sf3b1 +/+ and Sf3b1 +/- mice. Morphologic abnormalities of bone marrow and increased ring sideroblasts were not observed. However, quantitative analysis of bone marrow cells from Sf3b1 +/- mice revealed a reduction of the number of hematopoietic stem cells (CD34 neg/low, cKit positive, Sca-1 positive, lineage-marker negative: CD34-KSL cells) measured by flow cytometry analysis, compared to Sf3b1 +/+ mice. Whereas examination of hematopoietic progenitor cells revealed a small decrease in KSL cell populations and megakaryocyte - erythroid progenitors (MEP) in Sf3b1 +/- mice, and common myeloid progenitors (CMP), granulocyte - monocyte progenitors (GMP) and common lymphoid progenitors (CLP) remained unchanged between Sf3b1 +/+ and Sf3b1 +/- mice. In accordance with the reduced number of hematopoietic stem cells in Sf3b1 +/- mice, the total number of colony-forming unit generated from equal number of whole bone marrow cells showed lower colony number in Sf3b1 +/- mice in vitro. Competitive whole bone marrow transplantation assay, which irradiated recipient mice were transplanted with donor whole bone marrow cells from Sf3b1 +/+ or Sf3b1 +/- mice with an equal number of competitor bone marrow cells, revealed impaired competitive whole bone marrow reconstitution capacity of Sf3b1 +/- mice in vivo. These data demonstrated Sf3b1 was required for hematopoietic stem cells maintenance. To further examine the function of hematopoietic stem cells in Sf3b1 +/- mice, we performed competitive transplantation of purified hematopoietic stem cells from Sf3b1 +/+ or Sf3b1 +/- mice into lethally irradiated mice together with competitor bone marrow cells. Sf3b1 +/- progenitors showed reduced hematopoietic stem cells reconstitution capacity compared to those from Sf3b1 +/+ mice. In serial transplantation experiments, progenitors from Sf3b1 +/- mice showed reduced repopulation ability in the primary bone marrow transplantation, which was even more pronounced after the second bone marrow transplantation. Taken together, these data demonstrate that Sf3b1 plays an important role in normal hematopoiesis by maintaining hematopoietic stem cell pool size and regulating hematopoietic stem cell function. To determine the molecular mechanism underlying the observed defect in hematopoietic stem cells of Sf3b1 +/- mice, we performed RNA-seq analysis. We will present the results of our biological assay and discuss the relation of Sf3b1 and hematopoiesis. Disclosures: No relevant conflicts of interest to declare.

Abstract: Abstract 782 Recent genetic studies have revealed a number of novel gene mutations in myeloid malignancies, unmasking an unexpected role of deregulated histone modification and DNA methylation in both acute and chronic myeloid neoplasms. However, our knowledge about the spectrum of gene mutations in myeloid neoplasms is still incomplete. In the previous study, we analyzed 29 paired tumor-normal samples with chronic myeloid neoplasms with myelodysplastic features using whole exome sequencing (Yoshida et al., Nature 2011). Although the major discovery was frequent spliceosome mutations tightly associated with myelodysplasia phenotypes, hundreds of unreported gene mutations were also identified, among which we identified recurrent mutations involving STAG2, a core cohesin component, and also two other cohesin components, including STAG1 and PDS5B. Cohesin is a multimeric protein complex conserved across species and is composed of four core subunits, i.e., SMC1, SMC3, RAD21 and STAG proteins, together with several regulatory proteins. Forming a ring-like structure, cohesin is engaged in cohesion of sister chromatids in mitosis, post-replicative DNA repair and regulation of gene expression. To investigate a possible role of cohesin mutations in myeloid leukemogenesis, an additional 534 primary specimens of various myeloid neoplasms was examined for mutations in a total of 9 components of the cohesin and related complexes, using high-throughput sequencing. Copy number alterations in cohesin loci were also interrogated by SNP arrays. In total, 58 mutations and 19 deletions were confirmed by Sanger sequencing in 73 out of 563 primary myeloid neoplasms (13%). Mutations/deletions were found in a variety of myeloid neoplasms, including AML (22/131), CMML (15/86), MDS (26/205) and CML (8/65), with much lower mutation frequencies in MPN (2/76), largely in a mutually exclusive manner. In MDS, mutations were more frequent in RCMD and RAEB (19.5%) but rare in RA, RARS, RCMD-RS and 5q- syndrome (3.4%). Cohesin mutations were significantly associated with poor prognosis in CMML, but not in MDS cases. Cohesin mutations frequently coexisted with other common mutations in myeloid neoplasms, significantly associated with spliceosome mutations. Deep sequencing of these mutant alleles was performed in 19 cases with cohesin mutations. Majority of the cohesin mutations (16/19) existed in the major tumor populations, indicating their early origin during leukemogenesis. Next, we investigated a possible impact of mutations on cohesin functions, where 17 myeloid leukemia cell lines with or without cohesin mutations were examined for expression of each cohesin component and their chromatin-bound fractions. Interestingly, the chromatin-bound fraction of one or more components of cohesin was substantially reduced in cell lines having mutated or defective cohesin components, suggesting substantial loss of cohesin-bound sites on chromatin. Finally, we examined the effect of forced expression of wild-type cohesin on cell proliferation of cohesin-defective cells. Introduction of the wild-type RAD21 and STAG2 suppressed the cell growth of RAD21- (Kasumi-1 and MOLM13) and STAG2-defective (MOLM13) cell lines, respectively, supporting a leukemogenic role of compromised cohesin functions. Less frequent mutations of cohesin components have been described in other cancers, where impaired cohesion and consequent aneuploidy were implicated in oncogenic action. However, 23 cohesin-mutated cases of our cohort had completely normal karyotypes, suggesting that cohesin-mutated cells were not clonally selected because of aneuploidy. Alternatively, a growing body of evidence suggests that cohesin regulate gene expression, arguing for the possibility that cohesin mutations might participate in leukemogenesis through deregulated gene expression. Of additional note, the number of non-silent mutations determined by our whole exome analysis was significantly higher in 6 cohesin-mutated cases compared to non-mutated cases. Since cohesin also participates in post-replicative DNA repair, this may suggest that compromised cohesin function could induce DNA hypermutability and contribute to leukemogenesis. In conclusion, we report a new class of common genetic targets in myeloid malignancies, the cohesin complex. Our findings highlight a possible role of compromised cohesin functions in myeloid leukemogenesis. Disclosures: Haferlach: MLL Munich Leukemia Laboratory: Equity Ownership. Alpermann:MLL Munich Leukemia Laboratory: Employment. Haferlach:MLL Munich Leukemia Laboratory: Equity Ownership.

Abstract: Chemotherapy with Rituximab is widely used to treat patients with various B-cell lymphomas and auto-transplantation with Rituximab is promising strategy due to the potential for in vivo purging. However, the possibility of late onset neutropenia and immunoglobulin suppression after auto-transplantation with Rituximab has been indicated. We studied the frequency and degree of these phenomena. We performed a retrospective analysis on 26 consecutive patients at three centers during the period of January 1998 to March 2005. Thirteen patients (Follicular 8, Marzinal zone B cell lymphoma 2, Diffuse large B 3) received auto-transplantation without Rituximab (R-) compared with 13 patients (Follicular 8, MZBCL 2, DLB 3) received auto-transplantation with Rituximab (R+). In R+ patients pripheral blood stem cells were harvested after High dose AraC followed by three times of Rituximab (375mg/m2 day -2 of AraC, day7, 14). Conditioning regimen consisted of MCEC (MCNU, CBDCA, ETOP, Cy) or TBI+Cy followed by three times of Rituximab (375mg/m2 day 0, 7, 14). Mean immunoglobulin concentration one month after transplantation was 890 mg/dl for R- vs. 470 mg/dl for R+ (P=0.04). Lowest neutrophil numbers over 4 weeks after transplantation was 1.24X109/L for R- vs. 0.36X109/L for R+ (p=0.02). Late onset neutropenia ( & lt;0.5X109/L) were seen in three cases of R+ group, but no case in R- group. Therapy related death was seen one case in R+ group. This case showed low immunoglobulin level after transplantation and died of Pneumocystis Carinii. These data, although preliminary, indicates that the addition of Rituximab to auto-transplantation leads to decrease in immmunoglobulin and neutrophil levels after transplantation.

Abstract: Abstract 4580 Many reports were seen about reactivation of human herpes virus 6 (HHV6) after stem cell transplantation (SCT) in adult patients, and this reactivation sometimes induce severe condition of patients. However, few reports were seen about pediatric patients. Therefore, we examined HHV 6 reactivation after stem cell transplantation in patients with children, retrospectively. The cases were 80 patients, 48 male, 32 female, and the median age was 6 years old (range 0–20 years old). Transplantations were 23 related bone marrow transplantations (BMT) or peripheral blood stem cell transplantations (PBSCT), 18 unrelated BMT, one related cord blood transplantation (CBT), 31 unrelated CBT, and seven autologous BMT or PBSCT. We analyzed HHV6 DNA samples of serum with these patients before SCT, 20 days and 40 days after SCT using PCR method. In addition, we analyzed relationship between HHV6 reactivation and syndrome of inappropriate antidiuretic hormone secretion (SIADH). In samples of 20 days after SCT, 35.0% of samples were positive for HHV6 DNA. On the other hand, 2.5% and 5.0% were positive before SCT and 40 days after SCT, respectively. From 24 out of 28 samples, over 10E3 of HHV6 DNA were detected in positive samples. Factors associated with HHV6 reactivation were CBT, unrelated donor, malignant diseases, use of total body irradiation as conditioning, cyclosporine and methyl prednisolone as GVHD prophylaxis, acute GVHD ( 〉 grade 2), chronic GVHD and use of steroid using univariate analysis. Moreover, CBT was an only risk factor of HHV6 reactivation using multivariate analysis. In 14 patients with SIADH, 78.6% of patients had HHV6 reactivation. On the other hand, 25.8% of patients had HHV6 reactivation in 66 patients without SIADH. This result was statistically significant (p 〈 0.001). From this analysis, we can understand HHV6 reactivation was seen in many patients with children. In addition, we thought about the possibility of SIADH is one symptom of the encephalopathy by the HHV6 reactivation. Disclosures: No relevant conflicts of interest to declare.