ALBERT

Description: BACKGROUND: There is need for an artificial oxygen (O2) carrier for use when: stored blood is unavailable or undesirable. To date, efforts to develop hemoglobin (Hb) based oxygen carriers (HBOCs) have failed, because of design flaws which do not preserve physiologic interactions of Hb with: O2 (they capture O2 in lungs, but do not release O2 effectively to tissue) and nitric oxide (NO) (they trap NO, causing vasoconstriction). EM design surmounts these weaknesses by: encapsulating Hb, controlling O2 capture/release with a novel 2,3-DPG shuttle and attenuating NO uptake through shell properties. METHODS: The EM prototype and its lyophilized form were analyzed: (1) structurally (dynamic light scattering (DLS), transmission electron microscopy (TEM) and atomic force microscopy (AFM)), as well as for: (2) payload retention (Drabkin), (3) biocompatibility (ex vivo complement activation), (4) O2 affinity (p50, Hill n, Adair), (5) rheology (cone and plate viscometer in rabbit plasma), (6) NO consumption (chemiluminescence), (7) pharmacokinetic (PK) profile (tracking 99mTc-labeled EM in rats), and (8) in vivo O2 delivery (two rodent models: hemorrhagic shock [rats, instrumented for tissue pO2] and hemodilution [bioluminescent HIF-1α reporter mice]). RESULTS: EM was structurally stable (size: 175±10 nm; polydispersity: 0.26±0.0 by DLS, confirmed by TEM and AFM; zeta potential: 12±2 mV). After 3 months storage, we observed nominal change (0.96); which is likely to translate to a t1/2 in humans of ~ 3h. EM NO sequestration varied as a function of shell crosslinking and was below the rate observed for RBCs. In our hemorrhagic shock model in fully instrumented SD Rats (400g), 40% blood volume was removed; animals were then resuscitated with an equal volume of EM (N=6) or normal saline (N=6). EM was suspended at 40 wt/vol%, [Hb]=4mM. EM infusion rapidly stabilized hemodynamics. During the 1st hour, we observed resolution of both lactic acidosis (3.2±1.5 v 8.2±2.1 mM) [for EM and NS, respectively, throughout] and elevated AV O2 difference (24±11 v 67±23%) as well as improved brain pO2 (30.5±1.4 v 17.2±1.3 Torr); p

Description: Introduction and Objectives: Patients with Thalassemia Major (TM) develop various complications related to iron overload and transfusion associated infections. It is unknown as yet if the specific genotype leading to TM has further impact on the development of liver fibrosis. Therefore, we planned to assess the impact of genotypes in patients with TM on the risk of liver fibrosis. Methods: We included 88 patients with TM with available genotyping data in this study. These patients were followed and transfused in a single tertiary academic center. All those patients had their liver fibrosis assessed by ultrasound elastography (FibroScan device) with a cut off value of 7.8 kPa. The genotyping was done using Amplification Refractory Mutation System (ARMS)-hot start-polymerase chain reaction (PCR) technique. Iron overload was assessed using the average serum ferritin in the 5 years prior to the liver fibrosis assessment. Association was assessed using Chi-squared test and adjustment using multivariable logistic regression. Results: A total of 88 patients were included with a median age of 27 years (Interquartile range [IQR]: 23-31). Females constituted 54% of patients and 34% of patients were splenectomised. The median alanine transaminase, aspartate transaminase, albumin and total bilirubin were 31 U/L (IQR: 20-58), 30 U/L (IQR: 18-46), 46 g/L (IQR: 43-48) and 23 µmol/L (IQR: 15-34) respectively. The median ferritin and liver iron concentration assessed by MRI T2* were 1472 µg/L (IQR: 741-2760) and 7.0 mg/gdw (IQR: 3.5-15.9) respectively. Thirty seven percent of patients had positive serology for HCV while 1% of patients had positive serology for HBV. The genotypes seen in this study included homozygous IVS-I, 5 (G-C) in 39 patients, homozygous codon 44 (-C) in 19 patients, double heterozygous IVS-I, 5 (G-C)/25 bp deletion in 5 patients and others (≤ 3 patients each) in 25 patients. The proportion of patients with fibrosis was 55%. The proportion of patients with fibrosis in the homozygous IVS-I, 5 (G-C) group was 58% compared to 52% in all other genotypes and the difference was not statistically significant (odds ratio of 1.3 with a p value of 0.6652). The impact of the genotype remained non-significant after adjustment of iron overload in the multivariable logistic regression model. The only statistically significant factor was the iron overload (p values: iron overload 0.006, genotype 0.966). Conclusion: The risk of liver fibrosis is associated with the iron overload in patients with TM. There is no additional independent impact of the genotype. Further studies with larger sample size to study the impact of various genotypes are required to confirm these results. Disclosures No relevant conflicts of interest to declare.

Description: Introduction: Induction with 3+7 has been standard practice in acute myeloid leukemia (AML) for over 40 years. Addition of a 3rd agent or use of high dose Ara-C has been reported to show better CR rates, but this has not demonstrated a consistent improvement in overall survival. We have consistently used induction with idarubicin, cytarabine 100mg/m2 /day for 7 days and etoposide at 100mg/m2 in young patients, omitting etoposide for suspected secondary AML or AML with myelodysplasia related features, or in those in whom excess toxicity is suspected. Methods: All patients wholly treated for newly diagnosed AML were identified from the prospective institutional AML database. Patients were treated with either ICE (Idarubicin 12mg/m2 day 1-3, Ara-C 100mg/m2 day 1-7, Etoposide 100mg/m2 d1-3) or the same doses of idarubicin and Ara-C without etoposide (3+7). The latter was given in patients with dysplastic features or secondary AML or where there were concerns of toxicity. Results: We Identified 116 patients who received one of the 2 induction regimen between 2005 and 2013. 90 patients received ICE and 26 patients received 3+7. Median ages in the groups were 29y (14-56) and 37y (15-58), respectively. Cytogenetics by ELN classification were similarly distributed between the ICE and 3+7 groups, with favourable/intermediate/adverse cytogenetics comprising 22%/46%/26% and 23% / 38% / 26%, respectively. 21/90 (23%) in the ICE group had 〉5% blasts in a day 14 bone marrow vs 7/26 (27%) in the 3+7 cohort. There was no significant difference in the CR/CRi rate between ICE (82%) and 3 + 7 (77%) groups. The death in aplasia rate was similar at 3.3% and 3.8%, respectively. 65/90 (72%) and 14/26 (54%) of patients received a transplant in CR1 or beyond in the ICE and 3+7 groups, respectively. Leukemia free survival was 40% (SE 10%) and 40% (SE 5%) in both cohorts (Fig.1). Overall survival at 5 years for ICE and 3+7 were 57% (SE 6%) and 49 % (SE 13%), p=0.69 (Fig.2). Conclusion: Our experience in young adults, albeit retrospective, confirms findings of larger studies that demonstrate that addition of etoposide to induction does not appear to improve remission rates significantly or improve survival. In order to improve remission rates in younger adults, FLAG-Ida or other regimens consisting of high dose Ara-C and/or novel agents may provide more tangible improvements in remission rates, although strategies that translate these into better overall survival remain elusive and this should be the target of further prospective trials. Disclosures No relevant conflicts of interest to declare.

Description: Protein arginine methyltransferase-5 (PRMT5), a major type II arginine methyltransferase, is an important epigenetic modifier with oncogene-like properties due to its transcriptional repressive activity. When over-expressed, PRMT5 has been shown to target and silence the expression of multiple regulatory and tumor suppressor genes. Global symmetric dimethylation of arginine residues within the N-terminal of histones (H2A(Me2)R3, H3(Me2)R8, H4(Me2)R3) plays a critical role in B cell transformation, correlates with increased tumor cell proliferation and survival. PRMT5 expression is enhanced in aggressive B-cell non-Hodgkin's lymphomas, including mantle cell lymphoma (MCL) and supports constitutive CYCLIN D1/CDK4/6 activity leading to inactivation of the RBL2/E2F tumor suppressor pathway. Other work has identified PRMT5 as a vital contributor to MYC-driven oncogenesis. While PRMT5 has been characterized as a transcriptional repressor, few micro-RNAs (miRs) have been identified as direct targets. Here we utilize next generation sequencing and whole genome mapping to identify miRs targeted by PRMT5 in mantle cell lymphomas. ChIP-seq analysis revealed genome-wide recruitment of the PRMT5-specific epigenetic mark H3(Me2)R8 in B-cell lymphoma cell lines (Jeko, Pfeiffer, SUDHL2) with minimal enrichment on chromatin from normal B cells. PRMT5 was found to target as many as 8593 genes in each lymphoma cell line examined with 4662 genes that are common targets between three different lymphoma cell lines. Comparing Chip-Seq to RNA-Seq data of each lymphoma cell line treated with PRMT5 shRNA identified miR-33b, miR-96 and miR-503 as direct targets. Predicted 3' untranslated region (UTR) targets of these miRs included CYCLIN D1 (miR-33b, miR-96, miR-503), MYC (miR-33b) and PRMT5 (miR-96), three gene products that have been shown to be highly relevant to the malignant phenotype of aggressive MCL. Validation studies with ChIP-real-time polymerase chain reaction (RT-PCR) and quantitative-RT-PCR demonstrated that CRISPR-CAS9-mediated PRMT5 deletion led to transcriptional derepression of miR-33b, miR-96 and miR-503 in MCL lines (CC-MCL, Jeko, and SP53) and in primary MCL patient samples. Inhibition of PRMT5 led to loss of recruitment of an epigenetic repressor complex at the miR-96 promoter containing PRMT5 and HDAC3, gain of p65 and enrichment of hyperacetylated lysine epigenetic marks H4K8, H3K14 and H2BK12, changes consistent with restored transcriptional activity of miR96. Promoter regions of miR33b and miR503 showed loss of recruitment of a repressive complex consisting of SP1, HDAC2 and gain of p300, CBP and hyperacetylated lysine epigenetic marks H3K9 and H3K14 following PRMT5 inhibition. Restored expression of miR-33b led to simultaneous down-modulation of CYCLIN D1 and c-MYC, whereas miR-96 re-expression led to loss of CYCLIN D1 and PRMT5. Re-expression of miR-503 on the contrary only impacted CYCLIN D1 expression. Furthermore, luciferase reporter assays with wild-type and mutant 3' UTRs showed that binding sites of miR-33b, miR-96 and miR-503 were critical for translational regulation of CYCLIN D1 and C-MYC. Inducible re-expression of miR-33b, miR-96 and miR-503 inhibited proliferation of MCL cells as determined by MTS assay and promoted cellular apoptosis as measured by staining with Annexin V/PI staining and flow cytometry. In vivo studies with the MCL cell line CC-MCL1 designed to conditionally express miR-96 and or miR-33b are currently underway. These results link dysregulated PRMT5 expression to transcriptional silencing of tumor suppressor miRs capable of regulating critical drivers of aggressive histologic subtypes of MCL and indicate that multiple mechanisms are involved in the regulation of CYCLIN D1 expression in MCL. Furthermore, this data supports PRMT5 overexpression as a critical factor involved with maintenance of the malignant phenotype of MCL, and supports strategies to selectively inhibit this promising therapeutic target in this disease. Disclosures Baiocchi: Essanex: Research Funding.

Description: Introduction: Emerging data collected from whole genome and epigenomic studies in solid and blood cancers has pointed toward dysregulation of chromatin remodelers as a unique class of cancer drivers. Next generation sequencing of lymphoma has identified several mutations affecting enzymes that regulate epigenetic control of gene expression. The epigenetic modifier protein arginine methyltransferase 5 (PRMT5) that has been shown to be essential for Epstein-Barr virus-driven B-cell transformation, is overexpressed in several histologic subtypes of B-cell non-Hodgkin's lymphomas (NHL) and is required for the driver activity of oncogenes such as MYC and NOTCH. While these findings suggest that PRMT5 may act as a driver of lymphomagenesis, definitive experiments to address its driver activity have yet to be performed. To address this question, we developed a transgenic mouse model by immunoglobulin m heavy chain enhancer/promoter (Em)-driven PRMT5 over expression in the lymphoid compartment of FVB/N mice. Methods: Eµ-hPRMT5 transgenic mice were created by injecting a vector containing floxed human PRMT5 under the control of the Eµ enhancer/promoter into FVB/N pronuclei that were implanted into pseudo-pregnant FVB/N mice. We obtained 5 founder lines demonstrating the presence of transgene construct by genotype PCR analysis of tail snip DNA. Founder mice were crossed with wild type FVB/N mice to obtain a F1 generation. Mice were followed clinically in standard pathogen-free housing until exhibiting phenotypic features at which time necropsy was performed. Immunophenotypic analysis was performed by flow cytometry, clonality by T cell receptor (TCR) Vb PCR, and pathology by hematoxylin-eosin staining and tissue micro-arrays developed for immunohistochemical staining (IHCS). Statistical significance was determined using a two-tail t-test and survival analysis conducted using Kaplan Meier curves. Results: F1 generation Eµ-hPRMT5 mice significantly overexpressed PRMT5 mRNA in unpurified splenocytes or bone marrow relative to non-transgenic mice (p-value 〈 0.001). Sorting B (CD19), NK (NK1.1) and T-cell (CD3) mononuclear subsets from splenocytes collected from Eµ-hPRMT5 mice (n=3/group) revealed PRMT5 mRNA to be overexpressed 37-fold (p-value

Description: Introduction : Hemorrhagic cystitis (HC) is one of common complications after allogeneic hematopoietic SCT (HSCT) with reported incidence varying from 7 to 70%. Several reports have shown that BK is strongly associated with HC (BK-HC) following HSCT. We conducted an institutional retrospective study to analyze the incidence and clinical factors associated with BK-HC following HSCT. Methods : A total of 517 consecutive patients above the age of 14 years receiving HSCT from 2009 and June 2015 were included in this retrospective analysis and evaluated for HC and urinary BK. HC was defined as documented hematuria of any grade and BK viruria was defined as positive at any level by BKV quantitative PCR testing in urine. Patients were stratified, based on hematuria and urinary BK virus, into the following groups (a) BK virus positive hemorrhagic cystitis (BK+HC), (b) BK virus negative hemorrhagic cystitis (BK-HC) and (c) Non-hemorrhagic cystitis (HC-). Screening for microscopic hematuria was performed only for patients with any kind of urinary symptoms. Results: 479 patients (92.6%) were matched related donor and 308 (60%) were male with a median age of 24 (range 14 to 66). Diagnoses were AML for 195 (38%), ALL for 183 (35%) and bone marrow failure for 44 (8.5%). Conditioning regimen was cyclophosphamide based in 427 (82.6%) patients (97%) versus others in 90 (17.4%) patients. GVHD prophylaxis was CSA/MTX for 456 (88.4%) however, T cell depletion was used in 13%. Peripheral blood stem cells were used for 56% of patients. With a median follow-up of 60 months for survivors (range 2 to 116.5 months), 43 (8%) patients showed BK+HC, 264 (51%) BK- HC while 209 (41%) did not have any hematuria (HC- group). Median time from transplantation to BK+ HC was 67 days (range 7 to 1261 days). Univariate analysis for risk factors of BK+ HC showed male, use of T-cell depletion and AML diagnosis were statistically significant factors. Other factors like age, conditioning regimen, GVHD prophylaxis, stem cell source, mismatched and remission status were not statistically significant. BK+ HC group was associated with higher incidence of other infections like CMV viremia (p=0.01) and fungal infection (p

Description: Introduction and Objectives: Iron overload in patients with Thalassemia Major (TM) leads to various complications including liver fibrosis. The independent impact of gender on this risk has been previously investigated but not yet confirmed. We, therefore, planned to assess the independent impact of gender in patients with TM on the risk of liver fibrosis. Methods: We included 96 patients with TM followed and transfused in one academic tertiary hospital. Patients underwent assessment of liver fibrosis using ultrasound elastography (FibroScan device) with a cut off value of 7.8 kPa. The mean ferritin in the 5 years prior to elastography assessment was used to represent iron overload. Association was tested using Chi-squared and the independent impact of gender was confirmed in the multivariable logistic regression with a model that included mean ferritin and gender. Results: The median age of the 96 included patients was 26 years (Interquartile range [IQR]: 22-30). Males constituted 45% of patients and 33% of patients were splenectomised. The median alanine transaminase, aspartate transaminase, albumin and total bilirubin were 30 U/L (IQR: 18-64), 30 U/L (IQR: 18-46), 46 g/L (IQR: 44-48) and 21 µmol/L (IQR: 14-32) respectively. The median ferritin and liver iron concentration assessed by MRI T2* were 1293 µg/L (IQR: 753-2715) and 6.7 mg/gdw (IQR: 3.5-16.1) respectively. Thirty seven percent of patients had positive serology for HCV while 1% of patients had positive serology for HBV. The proportion of patients with fibrosis as assessed by elastography was 59%. The proportion of male patients with fibrosis was 70% compared to 51% in female patients with a trend towards statistical significance (odds ratio [OR] of 2.2 with a p value of 0.094). In the multivariable logistic regression model, both gender (OR of 3.0, P value of 0.0188) and ferritin (OR of 1.0004, p value of 0.0036) were statistically significant independent predictors of liver fibrosis. Conclusion: Male gender increases the risk of liver fibrosis independent from iron overload. Our study confirms the previously suspected but unproven association. Follow up and therapy may be tailored to include gender as a decision factor. Larger studies are needed to further confirm these results. Disclosures No relevant conflicts of interest to declare.

Description: Chromosomal translocation t(8;21) (q22;q22) leading to generation of oncogenic RUNX1-RUNX1T1 fusion is a cytogenetic abnormality observed in about 10% of acute myelogenous leukemia (AML). Studies in animal models and recent next generation sequencing approaches have suggested cooperativity of secondary genetic lesions with t(8;21) in inducing leukemogenesis. In this study, we used targeted and whole exome sequencing of 93 cases (including 30 with matched relapse samples) to profile the mutational landscape of t(8;21) AML at initial diagnosis and post-therapy relapse. We identified recurrent mutations of KIT, TET2, MGA, FLT3, NRAS, DHX15, ASXL1 and KMT2Dgenes in this subtype of AML. In addition, high frequency of truncating alterations in ASXL2 gene (19%) also occurred in our cohort. ASXL2 is a member of mammalian ASXL family involved in epigenetic regulation through recruitment of polycomb or trithorax complexes. Unlike its closely related homolog ASXL1, which is mutated in several hematological malignancies including AML, MDS, MPN and others; mutations of ASXL2 occur specifically in t(8;21) AML. We observed that lentiviral shRNA-mediated silencing of ASXL2 impaired in vitro differentiation of t(8;21) AML cell line, Kasumi-1, and enhanced its colony forming ability. Gene expression analysis uncovered dysregulated expression of several key hematopoiesis genes such as IKZF2, JAG1, TAL1 and ARID5B in ASXL2 knockdown Kasumi-1 cells. Further, to investigate implications of loss of ASXL2 in vivo, we examined hematopoiesis in Asxl2 deficient mice. We observed an age-dependent increase in white blood cell count in the peripheral blood of Asxl2 KO mice. Myeloid progenitors from Asxl2 deficient mice possessed higher re-plating ability and displayed altered differentiation potential in vitro. Flow cytometric analysis of 〉1 year old mice revealed increased proportion of Lin-Sca1+Kit+ (LSK) cells in the bone marrow of Asxl2 deficient mice, while the overall bone marrow cellularity was significantly reduced. In vivo 5-bromo-2'-deoxyuridine incorporation assay showed increased cycling of LSK cells in mice lacking Asxl2. Asxl2 deficiency also led to perturbed maturation of myeloid and erythroid precursors in the bone marrow, which resulted in altered proportions of mature myeloid populations in spleen and peripheral blood. Further, splenomegaly was observed in old ASXL2 KO mice and histological and flow cytometric examination of ASXL2 deficient spleens demonstrated increased extramedullary hematopoiesis and myeloproliferation compared with the wild-type controls. Surprisingly, loss of ASXL2 also led to impaired T cell development as indicated by severe block in maturation of CD4-CD8- double negative (DN) population in mice 〉1 year old. These findings established a critical role of Asxl2 in maintaining steady state hematopoiesis. To gain mechanistic insights into its role during hematopoietic differentiation, we investigated changes in histone marks and gene expression affected by loss of Asxl2. Whole transcriptome sequencing of LSK population revealed dysregulated expression of key myeloid-specific genes including Mpo, Ltf, Ngp Ctsg, Camp and Csf1rin cells lacking Asxl2 compared to wild-type control. Asxl2 deficiency also caused changes in histone modifications, specifically H3K27 trimethylation levels were decreased and H2AK119 ubiquitination levels were increased in Asxl2 KO bone marrow cells. Global changes in histone marks in control and Asxl2 deficient mice are being investigated using ChIP-Sequencing. Finally, to examine cooperativity between the loss of Asxl2 and RUNX1-RUNX1T1 in leukemogenesis, KO and wild-type fetal liver cells were transduced with retrovirus expressing AML1-ETO 9a oncogene and transplanted into irradiated recipient mice, the results of this ongoing study will be discussed. Overall, our sequencing studies have identified ASXL2 as a gene frequently altered in t(8;21) AML. Functional studies in mouse model reveal that loss of ASXL2 causes defects in hematopoietic differentiation and leads to myeloproliferation, suggesting an essential role of ASXL2 in normal and malignant hematopoiesis. *LH and NH contributed equally Disclosures Ogawa: Takeda Pharmaceuticals: Consultancy, Research Funding; Sumitomo Dainippon Pharma: Research Funding; Kan research institute: Consultancy, Research Funding.

Description: Background HLH is an under-estimated and under-reported syndrome with diverse etiologies but can cause life threatening cytopenia (s) and organ failure with very high mortality in critically ill patients. Early diagnosis and management are of paramount importance for better survival. The current HLH 2004 diagnostic criteria are not optimal to achieve such a goal. Monocytopenia is not included in the diagnostic criteria although HLH is associated with activation, mobilization of and shift of monocytes to tissues where phagocytosis occurs. Hypothesis and Goal We hypothesized that monocytopenia is expected to occur patho-physiologically in HLH and accompany other cytopenias and treatment should be associated with reversal of monocytopenia in adults with HLH associated with different diseases. Methods and subjects: This is a retrospective analysis of 20 consecutive adult patients (〉/= 16 years) with complete records diagnosed on in ICU or in-patient hematology consult service at our institution who presented with fever and cytopenia(s) between Dec. 1st and June 30th, 2016. All patients fulfilled at least 5 out of 8 HLH2004-diagnostic criteria and/or had a genetic mutation of Familial HLH. Results: A total of 20 patients (3 females) with a median age 27 y (range 16-69) with diverse diagnoses (Table 1): 10 patients had malignancies; the most common (7; 70%) were lymphomas (3 HD, 1 DLBCL, 1 Plasmablastic NHL, 1 T cell NHL and PTLPD). 3 patients had myeloid malignancies (1 MDS, 1 active AML and one after FA salvage for AML), 3 were post allo-HSCT in CR (2 cGVHD; one on Cyclosporine), 1 post-Autologous HSCT for AML in CR, 1 HLH with RAB27 mutation, 1 ITP and AIHA (Evan's) presented with portal and superior mesenteric vein thrombosis, 1 Kostman Syndrome, 1 HIV on HAART therapy, 1 MethylMalonic Acidemia (MMA) and one with Adult Onset MAS -SJIA. The triggering or Co-triggering factors were considered to be due to H1N1 in 10 (50%) patients (5 with active malignancy) as it is an epidemic in Saudi Arabia since 2009; one with CMV reactivation post Allo-HSCT, EBV in 2 (10%) (1 with PTLPD after renal transplant on CSA and 1 with HLH-RAB27 mutation), , 1 chemotherapy (Fludarabine+ AraC) triggered during extended neutropenia and sepsis, 3 patients (DLBCL, T Cell NHL, HD) presented with malignancies with HLH without known triggering factor except malignancy (Malignancy-triggered HLH). 4 patients had no known triggering factors (T cell -NHL, DLBCL and t- MDS in CR 5 years after 2-CDA therapy for HCL. All patients fulfilled at least 5 criteria out of 8 according to HLH-94/HLH 2004 guidelines' criteria as shown in table-1 including a patient with HLH with RAB27 mutation 19 (95%) patients developed monocytopenia

Description: Introduction: The use of a Myeloablative (MA) regimen followed bypost-transplantation high dose Cyclophosphamide (PT-CY) has been adopted to overcome the increased relapse risk following nonmyeloablative conditioning regimen and unmanipulated Haploidentical Bone Marrow Transplantation, in patients with high-risk hematological malignancies, with acceptable TRM and risk of GVHD. We added ATG to our Myeloablative regimen with PT-CY after noticing significant incidence of grade II-IV aGVHD with the first few cases. Here we compare the outcomes of the 12 patients who received ATG to the outcomes of the first 11 patients who were transplanted without ATG. Patients and Methods: our haploidentical program was started in 2013 as a phase I/II prospective clinical trial. After reviewing the first 11 cases enrolled on the trial (MA regimen with PT-CY, without ATG), we noticed significant incidence of high grade aGVHD (54.55%). We amended our protocol in early 2015. Rabbit ATG was added at a dose of 3 mg/kg (1.5 mg/kg day -3 and day -2) to our conditioning regimen [thiotepa (5mg/kg/day on day -8 and -7), busulfan (3.2mg/kg/day IV day-6, -5 and -4), fludarabine (50mg/m2/day on day -6, -5 and -4 )] or [TBI 1000 cGy (200cGy twice a day on days -10, -9 and one dose on day -8), fludarabine (30mg/m2/day on Days -7, -6, -5 and -4)]. Graft-versus-host disease (GVHD) prophylaxis consisted of PT-CY (50mg/kg/day) on days +3 and +5, cyclosporine (starting day +4), and mycophenolate mofetil (starting day +1). Table 1 summarizes the disease-type and disease-status at transplant. Patient characteristics were comparable at baseline between the 2 groups. Results (Table 2): We enrolled patients with high risk hematologic malignancies in need for SCT but have no matched donor (MSD, MUD). Despite the small sample size, our results showed a statistically significant difference in the rate of acute GVHD between the 2 groups (p= 0.0161) in favor of the ATG group, chronic GVHD was more frequent in the non-ATG group however the difference did not reach statistical significance probably due to the small sample size. There was no statistically-significant difference in the risk of relapse, CMV reactivation or Hemorrhagic cystitis between the 2 groups. However, there was a trend of higher relapse rate (33.3% vs 18.18%), a higher rate of Hemorrhagic cystitis (50% vs 18.18%) and a higher rate of CMV reactivation (100% vs 81.82%) in the ATG group. The cumulative incidence of TRM at day 100 was in favor of the ATG group (figure 1), with a trend toward a better DFS in these patients 6 months post-transplant (figure 2). To be noted the follow up period was shorter for the ATG group because ATG was added later on. Figure 3 shows the survival for ATG vs non ATG group. Conclusion: The use of ATG with myeloablative Haplo conditioning can significantly reduce the risk of acute GVHD and early TRM. We have seen more relapses, higher rate of CMV reactivation, and hemorrhagic cystitis with the addition of ATG but these did not reach statistical significance probably due to the small sample size. A lower dose of ATG might be the way to go to strike a careful balance and improve the outcomes of myeloablative haploidentical transplant. Disclosures No relevant conflicts of interest to declare.