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Introduction: Allogeneic hematopoietic cell transplantation is an only potentially curative option for patients with higher-risk myelodysplastic syndrome (MDS). Owing to the advances in treatment strategies including reduced intensity conditioning, graft-versus-host disease (GVHD) prevention and supportive care, more elderly patients or those with comorbidities can proceed to allogeneic HCT. However, the long-term survival rate following allogeneic HCT is reported to be less than 50%, and non-relapse mortality (NRM) rate is still high reaching upto 30%. In this study, we aimed to evaluate the feasibility of using post-transplantation cyclophosphamide (PTCy) as a GVHD prophylaxis in allogeneic HCT for higher-risk MDS patients. We also compared the post-transplantation outcomes of PTCy group and those of historical control who received HCT using anti-thymocyte globulin (ATG). Methods: Patients with higher-risk MDS or MDS/myeloproliferative neoplasm (MPN) with bone marrow blast ≥ 5% were included in this study. Higher-risk MDS was defined by MDS with International Prognostic Scoring System >1.0 or bone marrow blast ≥ 5% at any time points before HCT. Conditioning regimen consists of busulfan (4-days for patients aged Results: Ninety-two and 144 patients received allogeneic HCT using PTCy and ATG, respectively. The median overall survival were 47.9 and 44.0 months, respectively (P=.383). Cumulative incidence of total and grade II-IV acute GVHD in PTCy and ATG group were 19.6% vs. 37.5% (P=.002), and 2.6% vs. 21.7% (P Conclusion: Allogeneic HCT using PTCy as GVHD prophylaxis in higher-risk MDS seems feasible in terms of low rate of acute GVHD and relapse incidence. Disclosures Choi: Ingenium Therapeutics, Daejeon, Korea: Consultancy, Current holder of individual stocks in a privately-held company. Lee: Ingenium Therapeutics, Daejeon, Korea: Consultancy, Current holder of individual stocks in a privately-held company. Lee: Korean Society of Hematology: Membership on an entity's Board of Directors or advisory committees; Astellas Pharma, Inc.: Consultancy, Honoraria, Other: Advisory board; AbbVie: Honoraria, Other: Advisory board.

Background Idiopathic cytopenia of undetermined significance (ICUS) is characterized by a persistent and clinically significant cytopenias which does not meet the diagnostic criteria for myelodysplastic syndrome (MDS). In some patients with ICUS, disease evolution to MDS or acute myeloid leukemia after variable periods of time was observed in several studies. However, the incidence and predictive factors of progression as well as management guidelines for ICUS patients are not well established. We aimed to identify the clinical and genetic characteristics of ICUS in comparison with lower-risk MDS for understanding the pathophysiologic features and providing guidance for treating physicians. Methods We performed targeted deep sequencing including 61 myeloid neoplasm-related genes with a MiSeqDx sequencer (Illumina) using bone marrow (BM) samples obtained from the patients with ICUS (n=139) and MDS (n=226) between May 2009 and December 2019. The cut-off level of variant allele frequency (VAF) was set to 2.0% of mutant allele reads. Cloncal cytopenia of undetermined significance (CCUS) was defined as ICUS with ≥ 2% VAF of mutations and lower-risk MDS was defined as MDS with revised international prognostic scoring system ≤3.5. Results When we compared the overall survival (OS) of the patients according to the disease subtypes, OS of CCUS (77.0% at 5-year) was significantly better than that of higher-risk MDS (41.0%, P Conclusion In our study, CCUS and lower-risk MDS showed similar OS which was significantly better than higher-risk MDS and worse than non-clonal ICUS. The clinical and mutational characteristics were also similar except for the degree of anemia and the SF3B1 and STAT3 mutation. Our findings suggest that the patients with CCUS may be regarded and treated as the lower-risk MDS despite a lack of significant dysplasia or MDS-associated definitive chromosomal abnormality. Disclosures Choi: Ingenium Therapeutics, Daejeon, Korea: Consultancy, Current holder of individual stocks in a privately-held company. Lee: Ingenium Therapeutics, Daejeon, Korea: Consultancy, Current holder of individual stocks in a privately-held company. Lee: Korean Society of Hematology: Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria, Other: Advisory board; Astellas Pharma, Inc.: Consultancy, Honoraria, Other: Advisory board.

Background Allogeneic hematopoietic cell transplantation (HCT) has been more widely applicable to the patients with hematologic malignancies owing to the increased donor availability, advances in conditioning regimen, prevention of transplantation-related toxicities, and general supportive care. However, there is no comprehensive and uniform approach for decision making which incorporates transplantation-related factors including patients and donor selection, conditioning intensity, or prevention of graft-versus-host disease (GVHD). In this regard, we aimed to establish and validate a machine learning-based predictive model for survival after allogeneic HCT in hematologic malignancies. Method Data from 2,011 patients with hematologic malignancies (1,464 acute leukemia, 296 myelodysplastic syndrome, 100 chronic myeloid leukemia, 45 myeloproliferative neoplasm, 85 lymphoma, and 21 multiple myeloma) who received allogeneic HCT between December 1993 and December 2019 at the Asan Medical Center were retrospectively analyzed. Results The median overall and event-free survival of total patients were 4.2 year (95% confidence interval [CI], 2.9-5.4) and 1.5 year (95% CI, 1.1-1.8), respectively. To predict post-transplantation survival, the patients were classified into "survived more than 5 years" and "died before 5 years". Among four major machine learning models (random forest [RF], support vector machine, logistic regression, and feed forward neural network), we selected RF method according to the predictive power of each algorithm. Using the RF machine learning algorithm, we developed a post-transplantation survival predicting model with the training cohort of 1,408 patients (70%) and tested it with the validation cohort of 603 patients (30%). Of >200 variables, 33 were selected using recursive feature elimination, and the estimated area under the receiver operator characteristic curve and accuracy of the model was 0.812 and 0.73, respectively. We then evaluated the robustness of predictive power of the model using 10-fold cross-validation in validation cohort. In addition, risk scores were calculated from each patient in the validation cohort, and there was an agreement between the estimated predicted risk and observed risk. Conclusion In conclusion, the machine learning-based prediction model seems feasible assuming post-transplantation survival outcomes in hematologic malignancies. Our findings could be helpful for clinicians to select more appropriate donor in terms of age or type of human leukocyte antigen mismatch, conditioning regimen, and GVHD prophylaxis. Disclosures Lee: Astellas: Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees. Lee:Hanmi: Research Funding.

Background Following the advances in genetic tests, including next-generation sequencing, there have been new insights into hereditary hematopoietic malignancies. The germline mutation in DDX41 was included in a new category, myeloid neoplasms with germline predisposition, of the updated 2016 WHO classification. Based on the reported data to date, there seem to be racial differences in the mutation variants of DDX41 gene, which were found in patients with myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML). Idiopathic cytopenia of undetermined significance (ICUS) is known to be a precursor lesion of MDS, but the DDX41 mutations have not been evaluated in patients with ICUS. In this study, we aimed to reveal the incidence, genetic characteristics, and clinical features of the DDX41 mutations in patients with ICUS, MDS, and AML. Methods We performed targeted deep sequencing of 141 genes with a MiSeqDx sequencer (Illumina) using bone marrow (BM) samples obtained from the patients with ICUS (n=77), MDS (n=175), and AML (n=148) between May 2009 and June 2019. ICUS was defined by the proposed criteria of 2007 Consensus Group. The cut-off level of variant allele frequency (VAF) was set to 2.0% of mutant allele reads. We divided ICUS into clonal cytopenia of undetermined significance (CCUS), which was defined as ICUS with ≥ 2% VAF of somatic mutations of myeloid malignancy-associated genes and non-CCUS. Results Overall, DDX41 mutations were detected in 6 (7.8%) of 77 ICUS, 19 (10.9%) of 175 MDS, and 8 (5.4%) of 148 AML patients. Thirty-eight (49.4%) of 77 ICUS patients had CCUS. Of 6 DDX41 mutated patients with CCUS, 5 showed biallelic mutations with the median VAF of 44.7% (range, 29.3−50.0) and 10.2% (range, 3.3−25.4), indicating that one germline and one somatic mutation exists. Of 175 MDS patients, 78 were categorized into lower-risk MDS (revised international prognostic scoring system [IPSS-R] < 3.5) and 97 into higher-risk MDS (IPSS-R ≥ 3.5), and DDX41 mutations were identified in 6 (7.7%) of 78 lower-risk MDS and 13 (13.4%) of 97 higher-risk MDS patients. Interestingly, biallelic mutations were found in 16 of 18 DDX41-mutated MDS patients with the median VAF of 47.75% (range, 43.4−55.6) and 13.8% (range, 2.7−35.8). In contrast, only one of 8 DDX41-mutated AML patients had biallelic mutation. Patients with DDX41 mutations typically showed hypocellular marrow (median BM cellularity, 30%; range, 5−95) with significant neutropenia (median neutrophil counts, 607/μL; range, 142−1675), male predominance (29/33, 87.9%), and relatively older age (median age, 64 years; range, 41−79) at diagnosis. In addition, we found novel mutation locations, which were different between presumed germline and somatic variants: V152G in germline, and T227M in somatic (Table 2). During a median follow-up duration of 2.9 years, 1 of 6 ICUS patients progressed to MDS-EB-1 after 17.3 months and 1 to non-severe aplastic anemia after 51.3 months. Conclusion Our data show that a significant proportion of ICUS, MDS, and AML patients had DDX41 mutations, many of which are presumably germline. These findings suggest that careful consideration of the predisposing germline mutation is important when selecting a familial donor for allogeneic HCT. We also found novel mutation locations of DDX41 gene which were different between somatic and germline variants. Further studies are warranted to define the clinical and molecular characteristics of DDX41 mutations and therapeutic implications in myeloid neoplasms. Disclosures No relevant conflicts of interest to declare.

Background: Unexplained cytopenia comprises a spectrum of hematological diseases from idiopathic cytopenia of undetermined significance (ICUS) to myelodysplastic syndrome (MDS). Revised International Prognostic Scoring System (IPSS-R) is the standard tool to assess risk in MDS. Here, we investigated the occurrence, characteristics, and changing pattern of mutations in patients with ICUS and MDS stratified by IPSS-R score. Methods: A total of 211 patients were enrolled: 73 with ICUS and 138 with MDS. We analyzed the sequencing data of a targeted gene panel assay covering 141 genes using the MiSeqDx platform (Illumina). The lower limit of variant allele frequency (VAF) was set to 2.0% of mutant allele reads. Bone marrow components were assessed for the revised diagnosis according to the 2016 WHO classification. Lower-risk (LR) MDS was defined as those cases with very low- or low-risk MDS according to the IPSS-R. Higher-risk (HR) MDS was defined as those cases with high- or very high-risk MDS according to the IPSS-R. Results: Patients with ICUS were classified as very low-risk (39.7%), low-risk (54.8%), and intermediate-risk (5.5%) according to the IPSS-R. Patients with MDS were classified as LR (35.5%), intermediate-risk (30.4%), and HR (34.1%). In the ICUS, 28 (38.4%) patients carried at least one mutation in the recurrently mutated genes in MDS (MDS mutation). The most commonly mutated genes were DNMT3A (11.0%), followed by TET2 (9.6%), BCOR (4.1%), and U2AF1, SRSF2, IDH1 and ETV6 (2.7% for each). IPSS-R classification was not associated with mutational VAF and the number of mutations in ICUS. In the 49 LR MDS, 28 (57.1%) patients carried at least one MDS mutation. The most commonly mutated genes were SF3B1 (20.4%), followed by TET2 (12.2%), U2AF1 (10.2%), DNMT3A (10.2%), ASXL1 (10.2%), and BCOR (6.1%). Higher VAF and number of mutations were observed in LR MDS compared to ICUS patients. In the 42 intermediate-risk MDS, 27 (64.3%) patients carried at least one MDS mutation. The most commonly mutated genes were ASXL1 (23.8%), followed by TET2 (21.4%), RUNX1 (16.7%), U2AF1 (14.3%), DNMT3A (14.3%), SF3B1 (9.5%), and SRSF2, BCOR, STAG2 and CBL (7.1% for each). In the 47 HR MDS, 36 (76.6%) patients carried at least one MDS mutation. The most commonly mutated genes were TET2 (25.5%), followed by DNMT3A (14.9%), TP53 (14.9%), RUNX1 (12.8%), U2AF1 (10.6%), ASXL1 (10.6%), and SRSF2 and KRAS (6.4% for each). As the disease progressed, VAF and number of the MDS mutations gradually increased, and mutations involving RNA splicing, histone modification, transcription factor or p53 pathway had a trend for increasing frequency. Specifically, ASXL1, TP53, and RUNX1 mutations were the most striking features in patients with advanced stage of the disease. Cohesin mutations were not detected in ICUS, whereas these mutations were detected at a relatively high frequency in HR MDS. Our data were summarized in Table 1. Conclusions: We demonstrate that on disease progression, MDS mutations are increased in number as well as are expanded in size. Furthermore, a subset of mutations tends to be enriched for intermediate- to HR MDS. The results of this study can aid both diagnostic and prognostic stratification in patients with unexpected cytopenia. In particular, characterization of MDS mutations can be useful in refining bone marrow diagnosis in challenging situations such as distinguishing LR MDS from ICUS. Disclosures No relevant conflicts of interest to declare.

Background Improvement of cytopenia is one of the primary treatment purposes for patients with the lower-risk myelodysplastic syndrome (MDS). Androgens have been used for the treatment of aplastic anemia, immune thrombocytopenia, and telomere diseases. In this retrospective study, we aimed to evaluate the efficacy of androgen therapy in lower-risk MDS. Methods We analyzed the data of 139 patients who received androgens (danazol or oxymetholone) for treatment of cytopenia between February 1997 and May 2018. All patients had the international prognostic scoring system low or intermediate-1 risk at the time of androgen therapy. The assessment of hematologic improvement (HI) was based on the international working group response criteria for MDS. Results Androgens (oxymetholone for 83 patients and danazol for 56) were given as first (n=108, 77.7%) or over second (n=31, 22.3%)-line treatment for MDS (Table 1). The time interval between diagnosis and androgen treatment was median 1.3 months (range, 0-240.6), and 75 patients (54.0%) were red blood cell (RBC) transfusion-dependent before treatment. The dose intensity of oxymetholone and danazol was 79 and 385 mg/day respectively, and the median treatment duration was 5.8 months (range, 0.9-92.2). Seventy-nine patients (56.8%) achieved HI at any lineage: 29.0% for erythroid (HI-E), 51.9% for platelet (HI-P), and 60.5% for neutrophil (HI-N). The median time to HI following androgen therapy was 4.1 months (range, 0.6-124.5) for HI-E, 1.7 (range, 0.4-40.4) for HI-P, and 1.8 (range, 0.2-8.4) for HI-N. In univariate analysis, presence of RBC transfusion-dependence (46.7% vs. 68.8%, P=.009), pre-treatment low hemoglobin (45.2% vs. 74.5%, P=.001), high platelet count (46.5% vs. 73.6%, P=.002), and high neutrophil count (4.94% vs. 67.2%, P=.036) were associated with lower HI rate (Table 2). In multivariate analysis, pre-treatment low hemoglobin, high platelet count, and high neutrophil count remained as significant factors for lower HI rate (Table 2). During the median follow-up duration of survivors of 40.8 months (95% confidence interval [CI], 38.0-67.5), the estimated 5-year overall survival (OS) and acute myeloid leukemia-free survival was 68.8% and 67.7%, respectively. Achievement of HI was associated with longer OS (hazard ratio, 0.346; 95% CI, 0.174-0.688). There were no significant differences in HI and OS rates between danazol and oxymetholone. Conclusion Our data suggest that androgen can be a reasonable treatment option for lower-risk MDS patients with significant cytopenia. Prospective studies are warranted to investigate the efficacy of androgen therapy in lower-risk MDS. Disclosures No relevant conflicts of interest to declare.

Background Patients with FLT3-ITD mutated acute myeloid leukemia (AML) have generally poor survival. Recent update of ECOG trial comparing standard- vs. high-dose daunorubicin showed that daunorubicin dose intensification improved survival in AML with FLT3-ITD mutants (Blood 2016;127:1551). In subgroup analysis of our previous randomized trial, high-dose daunorubicin seemed to be more effective than idarubicin in AML patients with FLT3-ITD mutants (ASH abstract No. 2535, 2015). In this retrospective investigation, we aimed to evaluate the role of daunorubicin dose intensification for induction therapy in AML patients with FLT3-ITD mutants who were treated at a single institute. Methods We analyzed data from 120 patients of newly diagnosed FLT3-ITD mutated AML patients who received induction chemotherapy between January 2002 and March 2016. The regimens consisted of high-dose daunorubicin (HD-DN, 90 mg/m2/d x 3d, n=39), standard-dose daunorubicin (SD-DN, 45 mg/m2/d x 3d, n=48), or idarubicin (IDA, 12 mg/m2/d x 3d, n=33) in combination with cytarabine (200 mg/m2/d x 7d). Patients with acute promyelocytic leukemia were not included. Results After the first round of induction chemotherapy, 53 patients had persistent leukemia; 50 received the second round of induction chemotherapy consisting of daunorubicin (45 mg/m2/d x 2d) or idarubicin (8 mg/ m2/d x 2d) in addition to cytarabine (200 mg/m2/d x 5d) and 3 received other regimens. A total of 81 patients achieved CR, and the CR rates were 76.9%, 58.3%, and 69.7% in HD-DN, SD-DN, and IDA, respectively (P=0.175). The 4-year cumulative incidence of relapse (CIR) of these 81 patients was 48.8%. With the median follow-up duration of survivors of 59.9 months (range, 4.6-170.7), 4-year overall survival (OS) and event-free survival (EFS) were 57.1%/27.7%/35.7% (P=0.025) and 45.2%/23.9%/36.0% (P=0.042) in HD-DN, SD-DN, and IDA, respectively. HD-DN showed statistically higher OS (hazard ration [HR], 0.424; P=0.005) and EFS (HR, 0.497; P=0.01), and lower CIR (P=0.036) than SD-DN, while OS and EFS differences between HD-DN and IDA were not statistically significant. Conclusion Daunorubicin dose intensification for induction therapy seemed to be effective in AML patients with FLT3-ITD mutants. Further studies are needed to investigate whether HD-DN is superior to IDA in this population. Considering high relapse rate, combination strategies of daunorubicin dose intensification and targeted agents such as FLT3 inhibitors should be developed. Disclosures No relevant conflicts of interest to declare.

Background: Allogeneic hematopoietic cell transplantation (HCT) has been increasingly used for the treatment of lymphoma. The outcomes of HCT in lymphoma depend on baseline patient characteristics including chemosensitivity and International Prognostic Index (IPI). Several studies have shown that post-transplant occurrence of acute or chronic graft-versus-host disease (GVHD) and immune recovery might be associated with the outcomes. In this retrospective study, we investigated baseline and post-transplant prognostic factors in lymphoma patients receiving allogeneic HCT. Patients and methods: Between May 1998 and December 2015, a total of 61 patients underwent allogeneic HCT for lymphoma and the median age was 39 years (range, 16-62 years). Thirty four patients (55.7%) had chemo-sensitive disease and 24 patients had received autologous HCT. Fifty-six of 61 patients received reduced-intensity conditioning regimens. We evaluated tumor response, overall survival (OS), progression-free survival (PFS), non-relapse mortality (NRM), and event-free survival (EFS) after allogeneic HCT along with potential prognostic factors including GVHD and immune reconstitution. Results: Objective tumor response after HCT was observed in 41 (67.2%; complete 30 and partial 11). The 5-year probabilities of OS, NRM, PFS, and EFS were 30.7%, 23.5%, 41.3%, and 24.0%, respectively. Among the baseline characteristics, chemosensitivity had a significant impact on OS, NRM, and EFS. Persistent disease status at allogeneic HCT had an adverse effect on OS and low IPI risk category at HCT was associated with longer OS and EFS. HCT co-morbidity index ≥1 was an independent prognostic factor for higher NRM. Grade III-IV acute GVHD was associated with lower OS and higher NRM. Severe chronic GVHD had higher OS (60.0% vs. 19.8%, P=0.002), PFS (68.8% vs.35.9%, P Conclusion: Chemosensitivity was the most important prognostic factor in allogeneic HCT for lymphoma. Acute GVHD had unfavorable impact, whereas, chronic GVHD had favorable impact on post allogeneic HCT outcomes. Early immune recovery could predict allogeneic HCT outcomes. Disclosures No relevant conflicts of interest to declare.

Introduction: The IPSS has been widely used for risk stratification in myelodysplastic syndromes (MDS), and patients with IPSS low and intermediate-1 scores are designated as having lower-risk (LR) MDS. Despite its utility, the outcomes of patients with LR disease defined by IPSS are variable and a subset of patients experience inferior than expected outcomes. Treatment with hypomethylating agents is the standard of care in higher-risk MDS, but there have been little data for hypomethylating therapy in LR MDS. We retrospectively collected and analyzed the data related to hypomethylating therapy in IPSS LR MDS from 12 Korean institutes. Patients and Methods: A total of 610 patients, who were treated with azacitidine or decitabine for IPSS LR MDS, were included in this retrospective case series study. All patients received azacitidine (7-day) or decitabine (5-day). Both regimens were repeated every 4 weeks. The overall response rate (ORR) included rates for complete response (CR), partial response (PR), marrow CR (mCR), and stable disease (SD) with hematologic improvements (HI). For 139 patients who underwent allogeneic hematopoietic cell transplantation (HCT), all survival data were censored at the time of HCT. Results: Median age was 63 (19-84) years. IPSS category was low in 44 and intermediate-1 in 566. The patients were reclassified with other scoring systems including revised IPSS (R-IPSS), WPSS, and LR-PSS, and between 21.8% and 37.7% of patients were identified as having high or very high risk features by the other prognostic indices. Patients received azacitidine (n=436) or decitabine (n=174) for a median of 5 (1-46) courses. ORR was 51.3% (CR 78, PR 12, mCR with HI 27, mCR without HI 20, and SD with HI 176). 294 patients (48.2%) showed any HI. Median OS was 2.35 years and patients with HI had significantly longer OS than those without HI (P=0.001). Our case series patients were well stratified in terms of OS by R-IPSS (P=0.001), WPSS (P Conclusion: IPSS LR MDS included a broad range of prognostic implications. Hypomethylating therapy brought varying degrees of response in about half of the patients with IPSS LR MDS. The patients who had high risk features with other prognostic indices showed poor OS and allogeneic HCT should be considered during the course of hypomethylating therapy in these patients. Disclosures No relevant conflicts of interest to declare.

Background: The JL1 antigen is a novel epitope of CD43, a cell surface glycoprotein of mucin family. JL1 is a differentiation antigen expressed on stage II double positive (CD4+CD8+) human cortical thymocytes. The antigen is not expressed on mature peripheral blood cells or other normal tissues. The anti-JL1 monoclonal antibody binds to human leukemia MOLT-4 cells with 5,100-9,600 binding sites per cell. Preclinical studies have shown the cytotoxic effects of anti-JL1-based immunotoxin against JL1-positive leukemic cells, sparing most normal tissues other than thymocytes and some bone marrow mononuclear cells. Phase I clinical trial of new anti-leukemic agent with an anti-JL1 antibody (Leukotuximab; DiNonA, Korea) is now underway. In this study, we prospectively investigated the JL1 expression in patients with acute leukemia and myelodysplastic syndrome (MDS). Patients & methods: Flow cytometric analysis for the JL1 expression on leukemic blasts was performed using a FACSCanto II (Becton-Dickinson, Sunnyvale, CA, USA). The percent expression of JL1 antigen among leukemic blasts was recorded. Positive JL1 expression was defined if 20% or more leukemic blasts expressed the antigen. Association of JL1 expression with clinical, pathologic, and genetic characteristics was analyzed. Influence of JL1 expression on clinical outcomes of patients was also explored. Results: Between March 2014 and June 2015, a total of 245 adult patients with acute myeloid leukemia (AML, n=170), acute lymphoblastic leukemia (ALL, n=52), and MDS (n=23) were enrolled in this study. Positive JL1 expression was observed in 96 (57.1%) patients with AML, 28 (51.9%) with ALL, and 5 (21.7%) with MDS (P =0.006), while three normal controls showed negative JL1 antigen expression. Interestingly, JL1 expression was positive in all 14 patients with AML M3 with a median expression of 94.3% (range, 60.3-97.8%). In contrast, only 13 (39.4%) of 33 patients with AML with myelodysplasia-related changes (MRC) had positive JL1 expression. In AML patients, positive JL1 expression was significantly associated with CD34- (P =0.003), HLA-DR- (P =0.019), PML-RARA + (P =0.001), FLT3-ITD + (P =0.026), mutated NPM1 (P =0.003), and complex karyotype (3 or more clonal chromosomal abnormalities) (P =0.020). Cytarabine plus anthracycline based chemotherapy was given to 117 patients with AML, and the complete remission (CR) rate was significantly different between 63 JL1 expression positive patients and 54 negative patients (84.1% vs. 59.3%, P =0.003). Positivity of JL1 expression was not significantly associated with overall survival in all patients with AML (median survival, JL1 positive vs. negative, 20.6 vs. 18.2 months, P =0.489). In ALL patients, positive JL1 expression was significantly associated with CD13- (P =0.032) and the CR rate was not significantly different by JL1 expression. JL1 expression was measured twice or more in 85 patients during their clinical courses and positivity of JL1 expression was not changed in 61 (71.8%) (P =0.307). Five MDS patients progressed to AML and JL1 expression was changed in only one patient (JL1 positive to JL1 negative). Conclusion: JL1 was expressed in around 50% of patients with AML or ALL while less frequent expression of JL1 was observed in MDS and AML with MRC. JL1 expression was significantly associated with some immunophenotypic and genetic features, especially PML-RARA +. JL1 expression was significantly associated with the CR rate of AML patients. Expression of JL1 seems to be stable during clinical courses. Our data suggest that immunotherapeutic approach targeting JL1 antigen may be feasible in significant proportion of patients with acute leukemia and MDS. Disclosures Kim: Dinona Institute, Dinona Inc.: Employment. Yoon:Dinona Institute, Dinona Inc.: Employment. Jung:Dinona Institute, Dinona Inc.: Employment.

Allogeneic hematopoietic cell transplantation (HCT) from HLA-matched sibling (MS) or unrelated donors (MU) is a well-established treatment for patients with intermediate/high-risk acute myelogenous leukemia (AML) in remission. When HLA-matched donors are not available, however, use of haploidentical family (HF) donors for HCT remains controversial. Therefore, we performed a prospective study, where patients with AML in complete remission (CR) underwent allogeneic HCT according to the donor priority of MS, MU, or HF donors. Conditioning regimen for MS-HCT was busulfan (3.2 mg/kg • 4 days)-cyclophosphamide (60 mg/kg • 2 days) or, for patients >55 years or with co-morbidity, busulfan (3.2 mg/kg • 2 days)-fludarabine (30 mg/m2 • 6 days)-Thymoglobulin (1.5 mg/kg • 3 days). Patients undergoing MU- or HF-HCT received busulfan (3.2 mg/kg • 2 days)-fludarabine (30 mg/m2 • 6 days)-Thymoglobulin (3 mg/kg • 3 days) (Lee K-H et al; Blood 2011;118:2609-2617; Am J Hematol 2011;86:399-405). Ex-vivo T cell depletion was not performed. GVHD prophylaxis included cyclosporine plus a short course of methotrexate. Between January 2010 and December 2014, 244 patients enrolled. Of those, 16 patients were excluded from the analysis (12 patients relapsed before HCT; 3 with major protocol violation; and 1 with incomplete data). Of remaining 228 patients, 81 underwent HCT from MS donors, 90 from MU donors, and 57 from HF donors. The donors for MU-HCT were younger and more male-dominant than those for MS- or HF-HCT. The characteristics of patients and their donors were summarized in Table 1. Table 1. MS-HCT (n=81) UD-HCT (n=90) HF-HCT (n=57) P* Median age, yr (range) 48 (19-66) 43 (16-66) 46 (17-69) Sex, male/female 37/44 44/46 29/28 0.824 CR1/CR2 76/5 82/8 47/10 0.098 Chromosome risk,low**/intermediate/high/high-monosomal 6/57/10/5 4/65/16/3 2/40/7/5 0.751 Donor median age, yr (range) 45 (18-63) 28 (20-45) 29 (15-58) Donor age, yrup to 2526-45over 45 44136 29610 19326 0.000 Donor sex, male/female 46/35 76/14 36/21 0.000 Donor relation, parents/sibling/offspring 7/24/26 HLA allele mismatch/8 (GVH direction), 0/1/2/3/4 81/0/0/0 51/26/10/2/1 0/0/5/22/30 0.000 Graft, bone marrow/peripheral blood 28/53 0/90 0/57 0.000 Median nucleated cell count, •108/kg (range) 8.0 (0.9-19.0) 10.8 (4.1-31.4) 10.8 (5.1-19.3) Median CD34+ count, •106/kg (range) 4.9 (0.8-18.0) 8.0 (1.4-26.2) 6.4 (2.4-25.7) *by Chi-square test; **Twelve patients with AML of low-risk chromosomal abnormality included 6 patients in CR2, 3 with c-kit mutation, and 3 with persistent aml1-eto or cbf beta-myh11 after induction chemotherapy. The median follow-up duration of 164 survivors in the study was 34.7 months (range, 3.7-63.6) after HCT. The donor-group effect on the HCT outcomes was described in Table 2. Patients who underwent MS-HCT showed slightly slower neutrophil engraftment and higher incidence of chronic GVHD. Otherwise, in terms of disease recurrence, NRM, graft failure, EFS, and OS, there was no significant difference according to the donor-type. For AML recurrence, cytogenetic risk was an independent prognostic factors (P =0.003; hazard ratio of low-risk to; intermediate-risk, 1.42; high-risk, 2.53; high-risk with monosomal karyotype, 5.47). Table 1. MS-HCT (n=81) UD-HCT (n=90) HF-HCT (n=57) P Cumulative incidence ( 95% confidence interval)* AML recurrence 29% (19-40%) 26% (17-36%) 35% (20-51%) 0.785 Non-relapse mortality (NRM) 8% (3-16%) 7% (2%-16%) 11% (4-21%) 0.435 Graft failure 1% (0.1-6%) 6% (2-12%) 5% (1-13%) 0.293 ANC>500/uL median days (range) 100% 13 (9-20) 99%12 (10-45) 98% 12 (6-22) 0.049 Platelet>20,000/uL median days (range) 99% (86-100%) 14 (0-83) 97% (88-99%) 13 (0-77) 96% (83-99%) 14 (0-106) 0.352 Grades 2-4 acute graft-versus-host disease (GVHD) 12% (6-21%) 13% (7-21%) 23% (13-34%) 0.176 Moderate to severe chronic GVHD 39% (28-50%) 22% (13-30%) 23% (13-35%) 0.0452 4-year survival** Event-free (EFS) 63% 69% 54% 0.381 Overall (OS) 62% 74% 64% 0.077 *compared by Gray's method; **compared by log-rank test Our study showed that, despite heterogeneity of baseline donor characteristics (age and sex), conditioning regimen, and graft source (bone marrow vs. peripheral blood), overall post-transplant outcomes were similar among recipients from MS-, MU-, and HF-donors. Therefore, for patients with AML in CR but without an HLA-matched donor available, HCT from a haploidentical family member may be considered. Disclosures No relevant conflicts of interest to declare.