ALBERT

Description: Introduction: Hematopoietic stem cell transplantation (HSCT) is a potentially curative or consolidative therapy for a large number of hematological diseases. Sexual dysfunction (SD) and abnormal level of the sexual hormone are common in patients after HSCT, which are usually caused by intensive myeloablative conditioning. The change of sexual hormone level and SD resulted in the poor quality of life in this population after transplantation. The current aims of this study were to determine: (i) the incidence rate of SD and the association with androgen post both autologous (auto) and allogeneic (allo) HSCT; (ii) multi-factors analysis between SD and clinical characteristics, primary diease, donor type, cGVHD, etc; (iii) the association of androgen with cGVHD and glucocorticoid (GC) therapy. Methods: From April 2010 to February 2019, a total of 126 (74 males and 52 females) patients with hematological diseases undergoing HSCT were enrolled in our study. The reason for the small sample of patients was that only 126 patients completed our Sexual Function Questionnaire. Controls were 108 healthy, age and gender matched persons came from Medical Examiniation Center of our hospital. Assessment indexes included clinical characteristics, donor type, GVHD incidence, sex hormone levels, and Sexual Functioning Questionnaire (SFQ). The SFQ was implemented by the team members of our research group through a telephone interview, email, paper letter, and WeChat. All of the information and privacy of each patient was strictly conserved. Results: 1. Clinical characteristics of the 126 patients who underwent HSCT were shown in Table 1. The median age of the patients was 38 years old (range 16-66) and the follow up after HSCT was from 6 months to 7 years. The predominant disease spectra were multiple myeloma (MM) and acute leukemia in auto- and allo-HSCT group, respectively. Our results showed a significant difference in gender (P

Description: Introduction - Multiple Myeloma (MM) is a hematologic malignancy characterized by clonal growth of differentiated plasma cells (PCs). Despite improvement in MM therapy, the disease remains mostly incurable and is characterized by recurrent relapses with development of resistant clones that eventually lead to patient death. The pathways that lead to resistant and aggressive MM are not fully understood highlighting the need to improve our understanding of MM biology to identify potential new pathways and therapeutical targets. PHD Finger Protein 19 (PHF19) is a regulator of Polycomb Repressive Complex 2 (PRC2), the sole methyltransferase complex capable of catalyzing H3K27me3 to induce and enforce gene repression. PRC2 employs enhancer of zeste homolog 1 and 2 (EZH1/EZH2) as enzymatic subunits to hypermethylate H3K27. While overexpression and gain of function mutations of EZH1/2 have been observed in many cancers the role of this particular pathway in MM remains poorly understood. In the present study, we report on PHF19 as a new candidate gene to play a potential crucial role in MM oncogenesis. Methods- Gene expression profiling (GEP; Affymetrix U133 Plus 2.0) was performed on 739 MM patients (from total therapy trials [TT] 3-5; low risk MM n=636, high risk MM n=103), 42 patients with monoclonal gammopathy of undetermined significance (MGUS), 73 smoldering MM patients, 42 patients with primary plasma cell leukemia and 34 healthy donors. Myeloma risk was determined by the GEP 70 signature as previously defined. To test the implications of functional PHF19 knock down (KD) we used TRIPZ inducible PHF19 shRNA vs. scrambled control (Dharmacon) in two MM cell lines (JJN3 and ARP1). Real time PCR as well as western blotting was used to confirm PHF19 KD as well as to elucidate the effect on H3K27me3 (Cell Signaling). Functional in vitro studies included proliferation (Promega), clonogenic assays (StemCell), cell cycle and apoptosis assays (both Invitrogen). In vivo studies were performed using SCID mice that were subjected to tail vain injection with PHF19 KD JJN3 cells (n=10) or scrambled shRNA control (n=10). Weekly ELISA (Bethyl) and in vivo imaging (Xenogen) were performed and survival was recorded. Results- GEP of the previously mentioned patient populations and healthy controls identified PHF19 (chr9q33.2) as a candidate gene that was consistently dysregulated in MM patients. Mean expression levels at different MM stages correlated with disease aggressiveness (ANOVA, p10.46) at diagnosis correlated significantly with adverse clinical parameters, including ISS III, anemia and elevated LDH, as well as worse overall survival (5 yr OS = 29% for patients with high PHF19 expression vs 77% for patients with low PHF19 expression [log275% reduction in both cell lines, p

Description: Introduction: Although recent studies have refined the classification of B-progenitor and T-lineage acute lymphoblastic leukemia into gene-expression based subgroups, a comprehensive integration of significantly mutated genes and pathways for each subgroup is needed to understand disease etiology. Methods: We studied 2789 children, adolescents and young adults (AYA) with newly diagnosed B-ALL (n=2,322 cases) or T-ALL (n=467) treated on Children's Oncology Group (n=1,872) and St. Jude Children's Research Hospital trials (n=917). The cohort comprised childhood NCI standard-risk (41.8%; age range 1-9.99 yrs, WBC ≤ 50,000/ml), childhood NCI high-risk (44.5%; age range ≥10 to 15.99 yrs) and AYA (9.9%; age range 16-30.7 yrs). Genomic analysis was performed on tumor and matched-remission samples using whole transcriptome sequencing (RNA-seq; tumor only; n=1,922), whole exome sequencing (n=1,659), whole genome sequencing (n=757), and single nucleotide polymorphism array (n=1,909). Results: For B-ALL, 2104 cases (90.6%) were classified into 26 subgroups based on RNA-seq gene expression data and aneuploidy or other gross chromosomal abnormalities (iAMP21, Down syndrome, dicentric), deregulation of known transcription factors by rearrangement or mutation (PAX5 P80R, IKZF1 N159Y), or activation of kinase alterations (Ph+, Ph-like). For T-ALL, cases were classified into 9 previously described subtypes based on dysregulation of transcription factor genes and gene expression. In 1,659 cases subject to exome sequencing (1259 B-ALL, 405 T-ALL) we identified 18,954 nonsynonymous single nucleotide variants (SNV) and 2,329 insertion-deletion mutations (indels) in 8,985 genes. Overall, 161 potential driver genes were identified by the mutation-significance detection tool MutSigCV or by presence of pathogenic variants in known cancer genes. Integration of sequence mutations and DNA copy number alteration data in B-ALL identified 7 recurrently mutated pathways: transcriptional regulation (40.6%), cell cycle and tumor suppression (38.0%), B-cell development (34.5%), epigenetic regulation (24.7%), Ras signaling (33.0%), JAK-STAT signaling (12.0%) and protein modification (ubiquitination or SUMOylation, 5.0%). The top 10 genes altered by deletion or mutation in B-ALL were CDKN2A/B (30.1%), ETV6 (27.0%), PAX5 (24.6%), CDKN1B (20.3%), IKZF1 (17.6%), KRAS (16.5%), NRAS (14.6%), BTG1 (7.5%) histone genes on chromosome 6 (6.9%) and FLT3 (6.1%), and for T-ALL, CDKN2A/B (74.7%), NOTCH1 (68.2%), FBXW7 (21.3%), PTEN (20.5%) and PHF6 (18.2%) (Figure 1A). We identified 17 putative novel driver genes involved in ubiquitination (UBE2D3, UBE2A, UHRF1, and USP1), SUMOylation (SAE1, UBE2I), transcriptional regulation (ZMYM2, HMGB1), immune function (B2M), migration (CXCR4), epigenetic regulation (DOT1L) and mitochondrial function (LETM1). We also observed variation in the frequency of genes and pathways altered across B-ALL subtypes (Figure 1B). Interestingly, alteration of SAE1 and UBA2, novel genes that form a heterodimeric complex important for SUMOylation, and UHRF1 were enriched in ETV6-RUNX1 cases. Deletions of LETM1, ZMYM2 and CHD4 were associated with near haploid and low hypodiploid cases. Deletion of histone genes on chromosome 6 and alterations of HDAC7 were enriched in Ph+ and Ph-like ALL. Mutations in the RNA-binding protein ZFP36L2 were observed in PAX5alt, DUX4 and MEF2D subgroups. Genomic subtypes were prognostic. ETV6-RUNX1, hyperdiploid, DUX4 and ZNF384 ALL were associated with good outcome (5-yr EFS 91.1%, 87.2%, 91.9% and 85.7%, respectively), ETV6-RUNX1-like, iAMP21, low hyperdiploid, PAX5 P80R and PAX5alt were associated with intermediate outcome (5-yr EFS 68.6%, 72.2%, 70.8%, 77.0% and 70.9%, respectively), whilst KMT2A, MEF2D, Ph-like CRLF2 and Ph-like other conferred a poor prognosis (55.5%, 67.1%, 51.5% and 62.1%, respectively). TCF3-HLF and near haploid had the worst outcome with 5-yr EFS rates of 27.3% and 47.2%, respectively. Conclusions: These findings provide a comprehensive landscape of genomic alterations in childhood ALL. The associations of mutations with ALL subtypes highlights the need for specific patterns of cooperating mutations in the development of leukemia, which may help identify vulnerabilities for therapy intervention. Disclosures Gastier-Foster: Bristol Myers Squibb (BMS): Other: Commercial Research; Incyte Corporation: Other: Commercial Research. Willman:to come: Patents & Royalties; to come: Membership on an entity's Board of Directors or advisory committees; to come: Research Funding. Raetz:Pfizer: Research Funding. Borowitz:Beckman Coulter: Honoraria. Zweidler-McKay:ImmunoGen: Employment. Angiolillo:Servier Pharmaceuticals: Consultancy. Relling:Servier Pharmaceuticals: Research Funding. Hunger:Jazz: Honoraria; Amgen: Consultancy, Equity Ownership; Bristol Myers Squibb: Consultancy; Novartis: Consultancy. Loh:Medisix Therapeutics, Inc.: Membership on an entity's Board of Directors or advisory committees. Mullighan:Amgen: Honoraria, Other: speaker, sponsored travel; Loxo Oncology: Research Funding; AbbVie: Research Funding; Pfizer: Honoraria, Other: speaker, sponsored travel, Research Funding; Illumina: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: sponsored travel.

Description: Background: Relapse remains the main cause of treatment failure post transplantation. Relapse prevention is an important strategy for acute myeloid leukemia (AML) patients. M ethods: We retrospectively analyzed the results of21 high risk AML patients who received a median number of 3 courses (range, 2 - 8) of decitabine (DAC) maintenance treatment (20mg/m2/d ×5d every 3 months for 1 year). Meanwhile, another 63 high risk AML patients without any prophylactic treatment after transplantation were included as a control group for 1:3 pair matched study. Results: With median follow-up of 23 months, 20 out of 21 (95.2%) patients maintained complete molecular remission (CMR) in DAC group, while 35 out of 63 (55.6%) patients maintained CMR in control group. Comparing with control group, the patients of DAC group had higher 3-year overall survival (OS) rates and 3-year leukemia free survival (LFS) rates (92.9% vs 51.8%, P =0.003; 94.1% vs 54.7%, P=0.002 respectively). Moreover, DAC maintenance was well tolerated in all patients and grade 3/4 or 4/4 hematological toxicities were observed in 11 of 21 (52.4%) patients. Conclusion: Our results suggested that DAC maintenance therapy was an effective and safe treatment option to prevent relapse after transplantation for high risk AML patients. Disclosures No relevant conflicts of interest to declare.

Description: Leukemia is the most common malignant tumor in children under 15 years old, which is divided into several subtypes, including acute lymphoblastic leukemia (ALL), acute myeloid leukemia (AML), chronic lymphoblastic leukemia (CLL) and chronic myeloid leukemia (CML), based on the disease phases and effected cells. Each subtype has its specific molecular feature and key regulation factors. In our previous studies, we reported that β-arrestin1 (ARRB1), the pivotal scaffold protein to transduce various cellular signals, could bind with EZH2 to increase Bcr/Abl H4 acetylation level and thus promote CML progression (Brit J Cancer 2014, 111(3): 568-76). ARRB1 could enhance DNMT1 activity and PTEN methylation, decrease PTEN expression and promote self-renew of B-ALL leukemia initiating cells (LICs) (Cancer Lett 2015, 357(1): 170-8.). ARRB1 could increase P300 to bind with SP1 to hTERT promoter, and thus increase hTERT transcription/expression, telomerase activity, telomere length and cell senescence in B-ALL LICs (Cell Death Diff 2017, 8(4): e2756.). However, little is known in the T-ALL, which about 70% have the mutations of NOTCH1 gene. Here, we unveil ARRB1 could curb the progression of T-ALL cells in vitro and in vivo, while the expression of ARRB1 was suppressed by the aberrant increased miR-223. Mechanistically, ARRB1 could recruit DTX1, the E3 ubiquitin ligase, to promote the ubiquitination and degradation of NOTCH1 protein in T-ALL. Furthermore, Overexpression of ARRB1-derived miR-223 sponge BUTR was incompatible with cell proliferation and induces apoptosis in T-ALL cells. Collectively, our results for the first time revealed that ARRB1 acted as a tumor suppressor by promoting NOTCH1 degradation in T-ALL cells where miR-223 effectively antagonized ARRB1 functions. This provides that miR-223 may serve as a valid drug target for developing novel and efficacious T-ALL therapeutics. Disclosures No relevant conflicts of interest to declare.

Description: Introduction. Acute erythroid leukemia (AEL) is a high-risk leukemia subtype of poorly understood genetic basis. In integrated comparative genomic analysis of 159 AEL and 1509 non AEL myeloid tumors, we identified 5 age-related AEL subtypes with distinct genomic features and outcome: adult AEL with bi-allelic alterations in TP53 (31%), frequently co-occurring with alterations in DNMT3A,BCOR, EZH2, RB1, or NFIX; NPM1-mutated (12%); KMT2A-mutated/rearranged (11%), mostly co-mutated with STAG2; pediatric, NUP98-rearranged (5%) and adult, DDX41-mutated (3%). Thirty-eight percent of cases lacked an identifiable exclusive recurrent founding alteration but were enriched in mutations in ASXL1, TET2 and splicing factors. Methods. To explore the roles and cooperativity of the identified alterations in leukemogenesis we used CRISPR-Cas9 genome editing to induce combinations of loss-of-function mutations in 9 recurrently mutated genes in AEL (Tp53, Tet2, Dnmt3a, Asxl1, Ezh2, Stag2, Bcor, Ppm1d, Rb1 and Nfix). Based on patterns of mutation association, we generated 6 pools of lentiviral vectors (Table 1) with different combinations of single guide RNA (sgRNA) to induce multiplex genome editing in Cas9-eGFP-mouse lineage-negative hematopoietic stem cells (HSCs). Transduced cells were transplanted into lethally irradiated congenic mice. Tumors were characterized by morphology, immunophenotyping, and genomic analysis (sequencing of sites of editing, and exome, methylation and transcriptome sequencing). Ex vivo drug screening was performed to test sensitivity to 192 therapeutic agents, including conventional chemotherapeutic agents, and compounds targeting epigenetic regulators, protein kinases and cell cycle checkpoints. Results. In contrast to the uniform representation of guide RNAs observed in HSCs pre-transplant, tumors exhibited enrichment of specific sgRNAs with tumors of specific phenotype. We frequently observed bi-allelic editing of Tp53, Bcor, Tet2, Dnmt3a, Rb1 and Nfix in agreement with the presence of bi-allelic loss in patients. Concomitant editing and inactivation of Tp53/Bcor/Dnmt3a, or Tp53/Bcor/Rb1/Nfix promoted the development of acute erythroid leukemia (GATA1+/RUNX1+/GlyA+/-Ter119+/- and B220/CD19/PAX5/CD3/Mac1/Gr1-). Concomitant editing of Tp53/Bcor/Tet2 promoted the development of B-lineage ALL, and editing of Dnmt3a and Tet2 without Tp53 promoted T-cell ALL. Leukemic clones from primary tumors were serially transplantable across multiple different genetic backgrounds, with the same dominant clone present in all transplanted mice. Notably, mice that did not develop leukemia showed enrichment of different combinations of sgRNAs for Tet2, Dnmt3a and/or Asxl1, genes commonly mutated in clonal hematopoiesis of indeterminate potential, confirming that these mutations are alone not sufficient to induce leukemogenesis. Additional somatic mutations were acquired during clonal expansion of leukemic cells such as alterations of Notch1 and Ikzf1 in T-ALL; Setd2 at the serial passaging of T-ALL; Ptpn11, Kit (D816V), Kras (Q61L) and Lmo7 in the AEL models; and Sf3b3 in the B-ALL model (Fig 1A). Tumors with mutated Tp53 acquired aneuploidy whereas Tet2-mutated cells were genomically stable (Fig. 1B). Unsupervised hierarchical clustering of gene expression profiling identified 3 subgroups (Fig. 1C) associated with distinct genotypes and methylation profiles (Fig. 1D). Tet2-mutated tumors showed increase of hypermethylated sites and co-mutated Bcor/Dnmt3a leukemic cells showed loss of methylation. Eleven tumors representative of key AEL genotypes from the established models were selected to explore drug sensitivity. Response to individual drugs was associated with genotype with co-mutated Tet2/Dnmt3a T-ALL cells sensitive to bromodomain and histone methyltransferase inhibitors; co-mutated Bcor/Tp53/Dnmt3a or Bcor/Rb1 AEL cells to CDK9 inhibitor (LY2857785); Tp53 mutations alone were exclusively sensitive only to PARP inhibition (Talazoparib). In vivo mouse studies are ongoing to confirm ex vivo results. Conclusions: We successfully generated genetically defined models of AEL, demonstrated the role of Tp53 and Bcor mutations in driving the erythroid phenotype, and showed that sensitivity to different classes of compounds is genotype-dependent. These results provide the rational for testing new targeted agents in AEL. Disclosures Mullighan: Abbvie: Research Funding; Amgen: Honoraria, Speakers Bureau; Loxo Oncology: Research Funding; Cancer Prevention and Research Institute of Texas: Consultancy; Pfizer: Honoraria, Research Funding, Speakers Bureau.

Description: Background: According to the 2016 revised World Health Organization (WHO) Classification of Lymphoid Tumors, high grade B-cell lymphoma (HGBL) has been delimited as a new category with two subgroups: HGBL with rearrangements of MYC and BCL2 and/or BCL6 (so-called "double/triple hit lymphoma), and HGBL-NOS (HGBLs with features intermediate between DLBCL and Burkitt lymphoma). Retrospective data indicated many patients with HGBL diagnosed at an advanced stage and often have extremely poor outcome even if they received intensive chemotherapy. The accurate genetic and pathological mechanism of this high-risk lymphoma remains uncertain. For HGBL, traditional scoring may not be systematic enough and has limited reference value, more accurate prognostic grouping indicators are needed. The aim of this study was to evaluate the clinicopathological significances in newly diagnosed HGBL and DLBCL. Several clinical and hematological indexes in concert with Fluorescence in situ hybridization (FISH) rearrangement and Immunohistochemistry (IHC) expression profiles of biomarkers between HGBL and DLBCL will also be analyzed. Methods: We reviewed 52 patients diagnosed as HGBL or DLBCL in our hospital from 2017 to 2018 retrospectively. The clinical and hematological characteristics of the patients including age, gender, Ann-Arbor stage, B symptoms, serum LDH levels, β2-microglobulin (β2-MG), peripheral EBV-DNA copies, white blood cell (WBC), absolute neutrophil count (ANC), absolute lymphocyte count (ALC), and IPI score were collected. FISH detection was done in each patient to identify whether the patient had MYC, BCL2, and BCL6 rearrangement. The expressions of the above three indexes were done by IHC as well. NLR (neutrophil to lymphocyte ratio) was definited as ANC/ALC ratio. Results: A total of 52 newly diagnosed patients were included in this study, including 34 (65.4%) males and 18 (34.6%) females. The median age at diagnosis was 54.1 years old (range, 15-88 years), and 22 (42.3%) of them were more than 60 years old. Six patients were classified into the HGBL category and 2 of them were HGBL-NOS subgroup. Twenty-five patients were MYC, BCL2, or BCL6 rearrangement single-positive. Among them, MYC, BCL2, and BCL6 rearrangement were detected in 13.5%, 7.7%, and 30.8% of 52 patients respectively.MYC (cut-off value 〉40%), BCL2 (cut-off value 〉50%), and BCL6 expression was found in 48.1%, 50%, and 65.4% of 52 patients, respectively. Among all of the patients, 32.7% (17/52) CD5 positive and 73.1% (38/52) MUM1 positive. 30.8% (16/52) of them were at stage Ⅰ/Ⅱ and 69.2% (36/52) of them were at stage Ⅲ/Ⅳ. 53.8% (28/52) of the patients had a high blood LDH level, 26.9% (14/52) showed an elevation of β2-MG level (〉3mg/L) and 38.5% (20/52) presented high IPI score (IPI〉2). The baseline clinical, hematological, and pathological characteristics are described in Table 1, 2. 3. With Pearson's Chi-square Tests analysis, the IPI score was significantly higher in patients older than 60 years old (P

Description: Objective: To investigate and analyze the incidence, risk factors, prophylaxis and treatment of thromboembolism associated with lenalidomide-based regimens for multiple myeloma (MM) patients. Methods: 22 newly diagnosed / relapsed MM patients received lenalidomide-based regimes from May 2013 to May 2015 in our department. All diagnosis of thromboembolism were based on objective clinical symptoms, and confirmed by imaging (lower extremity vascular ultrasound, chest CT angiography (CTA), and two-dimensional echocardiography). Investigatethe incidence of thethromboembolism, and analyze the prophylaxis and treatment for the thromboembolism according to risk factors such as patients' characteristics, disease status, and therapy regimes. Results: Aspirin was used as thromboprophylaxis in 16 patients, low molecular weight heparin (LMWH) in 2 patients, and warfarin in 1 patient, while 3 patients received no thromboprophylaxis. There were 4 cases were diagnosedas thromboembolism with the incident of 18.2%. Threeof them were deep vein thrombosis (DVT), while 1 patient was combined withpulmonary embolism (PE), andthe rest one was found thromboembolism in the left atria. The chemotherapy regimes were lenalidomide plus dexamethasone (≤40mg qw). Other risk factors include: old age, male, immobility, central venous catheter (CVC), surgical history, hypertension, cardiovascularevent, IgG/IgA and light chain type, newly diagnosis, and erythropoietin (EPO). The management of thromboembolism included LMWH, warfarin, venous filter placement, adjustment of chemotherapy regimes and maintenance therapy of antithromboembolism. All the 4 patients were well managedat the last follow-up. Conclusion: Thromboembolism was one of the most common non-hematologic adverse events of lenalidomide-based therapy. Aspirin was an effective option for thromboprophylaxis. More cases will be observed for longer time to optimize further evaluations forantithromboticprophylaxes, which include risk stratification-based prophylacticstrategies, new predictors and specific assessment of all thromboprophylaxis options. Disclosures No relevant conflicts of interest to declare.

Description: Introduction: The myelodysplastic syndromes (MDS) are a group of clonal diseases derived from hematopoietic stem cells (HSC). Colony-forming unit cell (CFU-C) assay is an effective method to study the number and the function of HSC in vitro. In this study, we focus on the characteristics and the prognostic value of CFU-C in patients with MDS. Patients and Method: CFU-C assays were performed according to the protocol of MethoCultTM H4435 Enriched (STEMCELL Technologies). A colony was defined as an aggregate of 〉40 cells. Clusters consisted of 4 to 40 cells. 560 consecutive newly-diagnosed, untreated subjects with MDS diagnosed from March, 2001 to April, 2013 were studied. All subjects were reclassified according to the 2008 WHO criteria. 535 subjects with evaluable cytogenetics were classified using the International Prognostic Scoring System (IPSS) and the revised International Prognostic Scoring System (IPSS-R) criteria. Follow-up data were available for 470£¨84%£©subjects. Median follow-up of survivors was 26 months (range, 1-170) months. Subjects receiving an allotransplants were censored in survival analyses. Erythroid and myeloid colonies were isolated from each subject with one cytogenetic abnormality such as del(5/5q-) or +8. Cytogenetic abnormalities of each colony were analyzed by fluorescence in situ hybridization (FISH). SPSS 17.0 software was used to make statistical analysis. Results: Frequencies of burst-forming units-erythroid (BFU-E), colony forming unit-erythroid (CFU-E) and colony forming unit-granulocytes/macrophages (CFU-G/M) were significantly lower than normals (P 60%. Figure 1. Overall survival in subjects with cluster- to CFU-G/M ratios ¡Ü or 〉 60%. Disclosures No relevant conflicts of interest to declare.

Description: TET family proteins (TET1, TET2 and TET3) have recently emerged as important epigenetic modifiers by catalyzing the conversion of 5-methylcytosine (5mc) to 5-hydroxymethylcytosine (5hmc). Although they have been documented to play important roles in a variety of biological processes, their function in erythroid differentiation has yet to be defined. In the present study, we show that of the three TET family members, TET2 and TET3 but not TET1 are expressed in erythroid cells and that TET3 is more abundantly expressed than TET2. Using shRNA-mediated knockdown approach we explored the role of TET proteins in erythroid differentiation of CD34+ human cells. We first showed that consistent with their role in the production of 5hmc, knockdown of either TET2 or TET3 led to a decrease in global 5hmc levels as assessed by mass spectrometric analysis. However, knockdown of TET2 or TET3 resulted in distinctly different phenotypic changes during erythropoiesis. Knockdown of TET3 in human CD34+ cells resulted in impaired cell growth which is accompanied by increased apoptosis of late stage erythroblasts. Knockdown of TET3 also led to generation of bi/multinucleated polychromatic/orthochromatic erythroblasts which is accompanied by impaired enucleation. To explore the molecular mechanisms for the observed phenotypic changes, we performed RNA-seq analysis on control and TET3 knockdown erythroblasts at same stages of development. Bioinformatics analysis revealed that the expression levels of several apoptosis-promoting genes such as FOXO1, TNFRSF10B, TGFB1 and BTG1 are increased and that of a mitosis/cytokinesis associated gene KLHDC8B is decreased in polychromatic and orthochromatic erythroblasts following TET3 knockdown. Measurement of 5hmc and 5mc at promoter region of KLHDC8B locus revealed decreased 5hmc level concurrent with increased 5mc level. Importantly, knockdown of KLHDC8B in CD34+ cells as with knockdown on TET3 led to generation of increased numbers of bi/multinucleated polychromatic/orthochromatic erythroblasts and impaired enucleation implying a role for this protein in cytokinesis of late stage but not early stage erythroblasts. These findings demonstrate that TET3 regulates erythropoiesis in a stage-specific manner by targeting different set of genes. Importantly, knockdown of TET2 led to phenotypic changes that were very different from that seen following knockdown of TET3 but the observed changes are similar to the erythroid development defects noted in myelodysplastic syndromes (MDS). These include hyper-proliferation of early stage erythroid cells; delayed terminal erythroid differentiation and increased apoptosis of late stage erythroblasts. Together with the fact that TET2 gene mutation is one of the most common mutations in MDS and dyserythropoiesis is a hallmark of this disorder, our findings suggest that TET2 gene mutations can directly account for dyserythropoiesis of MDS. Our findings demonstrate distinct and important roles for TET2 and TET3 in regulating erythropoiesis and provide significant new and novel insights into epigenetic regulation of erythropoiesis at distinct development stages. The findings are likely to be very useful for furthering our understanding of epigenetic regulation of normal and disordered human erythropoiesis. Disclosures No relevant conflicts of interest to declare.