Abstract: Background Cytomegalovirus (CMV) establishes lifelong latency after primary infection under the control of the immune system because of the numerous virus evasion strategies that interfere with the host immune response at many levels. Human leukocyte antigen (HLA)-restricted cytotoxic T lymphocytes (CTLs) are involved in the early immune response and are an important defense mechanism in CMV infections, reactivation, and related diseases. Furthermore, an assessment of the clonal diversity of T cell responses against CMV infection provides important insight into the molecular basis of T cell immunodominance. In this single-center study, we tried to demonstrate a specific correlation between the donor HLA genotype and cumulative incidence of CMV reactivation and disease. Patients and methods We retrospectively analyzed 613 donors and recipients diagnosed with acute myeloid leukemia (AML) who received allogeneic hematopoietic stem cell transplantation (allo-HSCT) from matched siblings (n=260), matched unrelated donors (n=167), or haploidentical family donors (n=186) from 2012 to 2017. The CMV-related disease was diagnosed with aggressive procedures in suspicious tissues such as the eyes, gastrointestinal tract, or respiratory tract. The cumulative incidence of overall CMV-related diseases was 12.3% (n=71; range, 9.8 - 15.2), and in each matched sibling, matched unrelated, and haploidentical family donor allo-HSCT group were 6.1% (range, 3.6-9.6), 14.4% (9.2-20.7), and 19.4% (14.0-25.5), respectively. Except for seven patients, all 64 patients developed CMV disease in the CMV reactivation state. We determined the genotypes of the HLA-A, B, C, and DRB1 alleles in 613 donors and recipients by sequencing method and further selected 560 (91.4%) CMV IgG seropositive donors to identify the genetic influence of donor HLA according to CMV infection. Results We first analyzed the relationship between entire donor HLA allotypes and the cumulative incidence of CMV-related disease, then subdivided the donor groups by CMV IgG seropositivity. In the CMV IgG seropositive donor group, we conducted subgroup analysis to identify any difference in CMV-related disease incidence according to types of allo-HSCT. As a result, an entire donor CMV serostatus, three genotype alleles, HLA A*3004 (OR 2.8; p-value 0.044), B*5101 (OR 2.3; p-value 0.003), and DRB1*0901 (OR 2.3; p-value 0.004), demonstrated a statistically significant odds ratio (OR) value with the proper number of patients. However, in the donor CMV IgG seropositive subgroup, two allotypes, HLA B*5101 (OR 2.0; p-value 0.003) and DRB1*0901 (OR 2.7; p-value 0.002), remained. Interestingly, the HLA DRB1*0901 allele showed a concrete association (OR 6.0; p-value 〈 0.001, and p(c)-value 0.002) between CMV IgG seropositive donor HLA and the CMV-related disease incidence of the recipient, especially in the haploidentical allo-HSCT setting. The HLA-B*5101 allele showed a statistically significant association in the IgG seropositive donor subgroup with the matched unrelated allo-HSCT recipient and in the IgG seronegative donor subgroup. HLA-DRB1*1302 showed a promising value as the protective marker (OR 0.2; p-value 0.041) only in the IgG seropositive donor subgroup with the matched unrelated allo-HSCT recipient category. HLA-A*2402 (OR 3.6; p-value 0.048) was only significant in the IgG seropositive donor subgroup with the matched sibling and haploidentical allo-HSCT recipient category. HLA-DR*1501 (OR 2.6; p-value 0.039) was only significant in the IgG seropositive donor subgroup with the matched sibling allo-HSCT recipient category. Conclusion This study demonstrated that certain donor alleles, donor CMV IgG serostatus, and types of allo-HSCT, especially the seropositive donor HLA-DR*0901 allele in the haploidentical allo-HSCT setting, significantly correlated with high CMV-related disease incidence and might be considered risk markers for suitable donor selection. Additionally, the specific donor HLA allele showed either protective or aggravated CMV-related disease incidence in a different allo-HSCT setting. For patients receiving various types of allo-HSCT, a strategic approach to donor selection with careful consideration of donor HLA allotype is important and intensive CMV reactivation monitoring may be required, especially in acute GVHD under active steroid pulse treatment. Disclosures Kim: BMS: Research Funding; Novartis: Research Funding; Pfizer: Research Funding; Ilyang: Research Funding. Lee:Alexion Pharmaceuticals, Inc.: Consultancy, Honoraria, Research Funding.

Abstract: Given that there are only a few prospective studies with conflicting results, we investigated the prognostic value of multiparameter geriatric assessment (GA) domains on tolerance and outcomes after intensive chemotherapy in older adults with acute myeloid leukemia (AML). In all, 105 newly diagnosed patients with AML who were older than age 60 years and who received intensive chemotherapy consisting of cytarabine and idarubicin were enrolled prospectively. Pretreatment GA included evaluations for social and nutritional support, cognition, depression, distress, and physical function. The median age was 64 years (range, 60-75 years), and 93% had an Eastern Cooperative Oncology Group performance score & lt;2. Between 32.4% and 69.5% of patients met the criteria for impairment for each domain of GA. Physical impairment by the Short Physical Performance Battery (SPPB) and cognitive dysfunction by the Mini-Mental State Examination in the Korean version of the Consortium to Establish a Registry for Alzheimer’s Disease (CERAD) Assessment Packet (MMSE-KC) were significantly associated with nonfatal toxicities, including grade 3 to 4 infections (SPPB, P = .024; MMSE-KC, P = .044), acute renal failure (SPPB, P = .013), and/or prolonged hospitalization (≥40 days) during induction chemotherapy (MMSE-KC, P = .005). Reduced physical function by SPPB and depressive symptoms by the Korean version of the short form of geriatric depression scales (SGDS-K) were significantly associated with inferior survival (SPPB, P = .027; SGDS-K, P = .048). Gait speed and sit-and-stand speed were the most powerful measurements for predicting survival outcomes. Notably, the addition of SPPB and SGDS-K, gait speed and SGDS-K, or sit-and-stand speed and SGDS-K significantly improved the power of existing survival prediction models. In conclusion, GA improved risk stratification for treatment decisions and may inform interventions to improve outcomes for older adults with AML. This study was registered at the Clinical Research Information Service as #KCT0002172.

Abstract: Donor lymphocyte infusion (DLI) is one of the effective options for post-transplant disease control of myelodysplastic syndrome (MDS). Its success or failure depends on the induction of antitumor immune reactions, durability of clinical responses, and severity of unwanted toxicities mainly from graft- versus-host disease (GVHD). Methods: By analyzing 61 patients receiving DLI for post-transplant MDS relapse, we assessed treatment outcomes and affecting factors, especially focusing on the level of relapse (hematological, molecular, and imminent relapse). Results: The response rate (42.1%, 36.4%, 72.7%), and overall survival (OS) at 2 years (27.8%, 45.5%, 70.1%) were different for each relapse level with imminent relapse group showing the most promising results. For OS, response to DLI or pre-DLI chemotherapy, and time to relapse were independent prognostic factors. Meanwhile, post-DLI GVHD and time to relapse were independently predictive for DLI response; post-DLI GVHD was predictive for DLI response, but not for OS, suggesting a potential detrimental impact of GVHD on survival. The incidence of GVHD and GVHD-related deaths were 37.7% and 10.0%, respectively, and CD3 + cell doses triggering GVHD tended to be lower in cases with haploidentical donor or imminent relapse. Conclusion: Despite being limited by small number of cases and its retrospective nature, this study again demonstrated the therapeutic effects of DLI in relapsed MDS, and that earlier detection and intervention at lower level relapse might possibly be associated with better results. Furthermore, we propose that tailored cell dosing schedule based on relapse level and donor source may be helpful in minimizing fatal GVHD.

Abstract: Despite recent emergence of novel target agents, allogeneic stem cell transplantation is still the favored option for disease control in relapsed patients with acute myeloid leukemia (AML). Allotransplant from alternative donors such as haploidentical donor or cord blood can be done when fully HLA matched donor is not available. As for patients relapsed after the first stem cell transplantation (SCT1), these alternative stem cell sources often become only available options for the second transplantation. However, there has been no report comparing haploidentical stem cell (HIT) and cord blood transplantation (CBT), especially for the second transplantation. We performed a retrospective cohort study on AML patients who relapsed after SCT1 and underwent second allogeneic SCT from either alternative donor at our institution. We identified a total of 50 corresponding patients between January 2008 and February 2021 where 31 HIT and 19 CBT were included, and analyzed SCT outcomes including overall survival (OS), disease free survival (DFS), cumulative incidence of relapse (CIR), non-relapse mortality (NRM) and the incidence of SCT complications with comparing between the 2 groups. Conditioning regimens for HIT and for CBT were as follows: Fludarabine (30mg/m2/day intravenous (IV) for 5 days), busulfan (3.2mg/kg/day IV for 2 days), fractionated total body irradiation (fTBI, 4-8Gy total) and rabbit antithymoglobulin at a dose of 1.25mg/kg/day for four days for in vivo T cell depletion from D-5 to D-2 was given for HIT. G-CSF-mobilized peripheral blood stem cell was used as allograft. Graft-versus-host disease (GVHD) prophylaxis was done with tacrolimus and methotrexate. For CBT, fludarabine (30mg/m2/day IV for 5 days), cytarabine (1.5g/m2 twice daily for 3 days) with fTBI (12Gy). All CBT patients received double cord blood units. GVHD prophylaxis was done with tacrolimus and mycophenolate mofetil. The median follow-up period for survivors was 64.6 months (range 5.3-154.1). The type of SCT1 differed between the two groups; more patients of HIT were the recipient of prior autologous transplantation (41.9%), and 63.2% of CBT had underwent prior HIT (p & lt;0.001). However, age, sex, disease status pre-transplant, HCT-CI, time from SCT1 to relapse, time from post-transplant relapse to SCT2, FLT3-ITD mutation status and cytogenetic risk distribution did not differ between each group. Overall respective outcomes of HIT and CBT were as follows; 41% and 29% for 2-year OS (p=0.017), 41% and 16% for 2-year DFS (p=0.016), 36% and 36% for 2-year CIR (p=0.91) and 23% and 48% for 2-year NRM (p=0.021). Early NRM within 100 days of SCT2 was more frequent in CBT than HIT although not statistically significant (26.3% vs 9.7%, p=0.23). Median days to neutrophil and platelet engraftment were 12 (range 11-23) and 13 (range 9-38) in HIT, and 29 (range 16-48), 51 (range 27-167) for CBT, respectively (p & lt;0.001 for both). Cumulative incidence of acute and chronic GVHD were analyzed as follows; 39% and 42% for 1-year acute GVHD (p=0.82) and 43% and 11% for 2-year chronic GVHD (p=0.037) in HIT and CBT. In multivariate analysis, acute GVHD ≥ grade 2 after SCT1 (HR for OS 2.68, p=0.023; HR for DFS 2.49, p=0.036) and cytogenetic risk at diagnosis (HR for OS 2.07, p=0.018; HR for DFS 2.02, p=0.019) were significantly associated with worse outcomes. Hemorrhagic cystitis occurred more frequently in HIT patients than CBT group (32.3% vs 5.3%, p=0.035), while there were no significant differences between incidences of CMV DNAemia, CMV disease, thrombotic microangiopathy and sinusoidal obstructive syndrome. In subgroup analysis for patients relapsed after first allogeneic SCT1 only (18 patients in HIT and CBT group each), trend towards better outcomes in HIT than CBT were present, similar to those of all patients; 38% and 25% for 2-year OS (p=0.095), 39% and 10% for 2-year DFS (p=0.10), 22% and 51% for 2-year NRM (p=0.11) and 40% and 39% for 2-year CIR (p=0.90). This is the first report, to the best of our knowledge, to compare outcomes of the second transplantation from alternative donors for relapsed AML patients after SCT1. Our unique T-cell replete HIT using a reduced-toxicity conditioning regimen seems to provide better survival than CBT. Figure 1 Figure 1. Disclosures Lee: Alexion, AstraZeneca Rare Disease: Honoraria, Membership on an entity's Board of Directors or advisory committees. Kim: AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; AIMS Biosciense: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; AML-Hub: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Astellas: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; BL & H: Research Funding; BMS & Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Boryung Pharm Co.: Consultancy; Daiichi Sankyo: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Handok: Consultancy, Honoraria; LG Chem: Consultancy, Honoraria; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Honoraria; Pintherapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees; Sanofi Genzyme: Honoraria, Speakers Bureau; SL VaxiGen: Consultancy, Honoraria; VigenCell: Consultancy, Honoraria.

Abstract: Introduction Geriatric assessment (GA) typically refers to a multidimensional evaluation designed to evaluate an older person's functional ability, physical health, cognition, psychological health, nutritional status, and social support. The purpose of GA is to develop time-efficient and straightforward tools to evaluate multiple patient characteristics, which may be predictive of treatment outcomes of elderly acute myeloid leukemia (eAML) patients treated with intensive chemotherapy. Given that there have been few prospective studies with conflicting results, we performed a single-center prospective observational cohort study (#KCT0002172) investigating the prognostic value of multiparameter GA domains for eAML patients' tolerance and survival outcomes after intensive chemotherapy. Patients and methods Newly diagnosed eAML patients aged over 60 years who received intensive chemotherapy (n=105) were prospectively enrolled between November 2016 and December 2019. The median age was 64 years (range, 60-75), and they were all considered fit for intensive chemotherapy, with adequate performance and organ function. All the enrolled patients were administered various questionnaires for pretreatment GA and functional evaluation, which included evaluation for social and nutritional support, cognition, depression, distress, and physical function. Results Of the 105 enrolled patients, 93% had an Eastern Cooperative Oncology Group performance score of 1 and received intensive chemotherapy. Among them, between 32.4% and 69.5% of patients met the criteria for impairment on each GA domain. Physical impairment measured by the Short Physical Performance Battery (SPPB) was significantly associated with non-fatal toxicities of Grade III-IV severe infection (odds ratio (OR) 3.000, 95% confidence interval (CI), 1.159-7.788, p=0.024) and acute renal failure (OR 3.891, 95% CI, 1.329-11.39, p=0.013). Cognitive dysfunction measured by the Mini-Mental Status Examination- Korean version of CERAD Assessment Packet was significantly associated with a higher risk of Grade III-IV infection (OR 2.667, 95% CI, 1.025-6.939, p=0.044) and prolonged hospitalization (OR 4.208, 95% CI, 1.485-4.229, p=0.005). Reduced physical function measured by the SPPB and depressive symptoms measured by the Korean version of Short form Geriatric Depressive Scale (SGDS-K) were predictive of worse overall survival (OS; hazard ratio (HR) 1.917, 95% CI, 1.074-3.420, p=0.027 and HR 1.902, 95% CI, 1.005-3.602, p=0.048). SPPB impairment was also significantly related to higher treatment-related mortality (TRM; HR 2.023, 95% CI, 11.057-3.874, p=0.033). Furthermore, gait or sit-and-stand speed, a component of SPPB, was the single most powerful tool to predict survival outcomes of both OS (HR 2.766, 95% CI, 1.471-5.200, p=0.002 and HR 3.615, 95% CI, 1.868-6.999, p & lt;0.001) and TRM (HR 2.461, 95% CI, 1.233-4.913, p=0.011 and HR 3.814, 95% CI, 1.766-8.237, p & lt;0.001). We reconfirmed the prognostic value of preexisting survival prediction models, Wheatley index scores, and web-based AML scores, contrasting to the lack of significance of Ferrara criteria. The addition of SPPB/SGDS-K or gait (or sit-and-stand) speed/SGDS-K improved the predictability of the Wheatley index and web-based AML scores with 69% and 90% relative increases in predictive power for survival, respectively. Conclusions We prospectively demonstrated the prognostic value of physical and psychological assessment by GA for survival outcomes in intensively treated eAML patients. Gait or sit-and-stand speed was the single most powerful tool to identify frailty and predict survival outcomes. The prognostic value of preexisting survival prediction models, Wheatley index scores, and AML scores was reconfirmed.. The addition of measures for physical function and depression improved the predictability of those prediction models for survival. Cognitive and physical impairment were able to identify non-fatal toxicities during intensive chemotherapy in eAML patients. Our data will facilitate the incorporation of GA measures into validated survival prediction models to determine initial treatment for eAML patients in routine clinical care and clinical trials. Further studies are warranted to determine the best ways to adjust the care provided for frail patients to improve treatment tolerance and outcomes. Disclosures Kim: Novartis: Research Funding; BMS: Research Funding; Pfizer: Research Funding; ILYANG: Research Funding; Takeda: Research Funding. Lee: Alexion, AstraZeneca Rare Disease: Honoraria, Membership on an entity's Board of Directors or advisory committees. Kim: AbbVie: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; AIMS Biosciense: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; AML-Hub: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Astellas: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; BL & H: Research Funding; BMS & Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Boryung Pharm Co.: Consultancy; Daiichi Sankyo: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Handok: Consultancy, Honoraria; LG Chem: Consultancy, Honoraria; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Honoraria; Pintherapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees; Sanofi Genzyme: Honoraria, Speakers Bureau; SL VaxiGen: Consultancy, Honoraria; VigenCell: Consultancy, Honoraria.

Abstract: Background Transplantation-associated thrombotic microangiopathy (TA-TMA) is a significant complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT) and may affect 20% of recipients on average. A few groups have proposed risk or prognostic factors for TA-TMA, including a recent prospective study in a cohort that included both children and young adults (Jodele et al. Blood 2014), yet there has been no reproduced or validated data for consensus. Furthermore, with rapid advances in transplantation technology such as an increased variety of donors, conditioning regimens, and graft-versus-host disease (GVHD) prophylaxis, currently used diagnostic criteria and risk factors for TA-TMA must be re-evaluated using recent large cohorts. Patients and method The purpose of this study is to investigate risk and prognostic factors for TA-TMA in adult patients with acute myeloid leukemia (AML). TA-TMA was primarily diagnosed with previously published diagnostic criteria proposed by our group (Cho et al. Transplantation 2010). Then, we analyzed TA-TMA incidence, risk, and prognostic factors in two independent cohorts for training (n = 382, 2012-2015, retrospective) and validation (n = 231, 2016-2017, prospective). In particular, predictive factors for TA-TMA in a prospective cohort, including children and young adults as recently suggested by Jodele et al., were evaluated in our adult AML patients. Results In the entire cohort (n = 613), the median TA-TMA onset was 66 (range, 5-511) days from allo-HSCT. Among TA-TMA patients, 33.6% and 32.6% of them suffered from proteinuria and AKI, respectively. Also, 33.2% suffered from preceding or concurrent hemorrhagic cystitis (any grade), and 12.7% suffered from VOD/SOS at the time of TA-TMA diagnosis. Regarding the treatment of TA-TMA, 87.3% of patients discontinued or reduced the calcineurin inhibitor with supportive care, while 12.7%, 5.6%, and 4.2% were treated with total plasma exchange, t-PA, and defibrotide addition to calcineurin inhibitor dose modification, respectively. Thirty percent of patients achieved complete remission, and TA-TMA was related to poor three-year OS. There were no significant clinical characteristic differences between the training and validation cohorts with the exception of more haploidentical allo-HSCT in the validation cohort (training vs. validation; 26.7% vs. 36.4%, p = 0.012), and the cumulative incidence of TA-TMA was significantly (p 〈 0.001) higher among the validation cohort (18.8%) than the training cohort (8.9%). For the risk factors of TA-TMA, univariate and multivariate analyses revealed that LDH 〉 1.5 x upper normal limit (training p = 0.042 and validation p = 0.0042), proteinuria ≥30 mg/dL (training p = 0.0019 and validation p = 0.0012), and ≥Grade I hemorrhagic cystitis (training p = 0.0460 and validation p = 0.0049) were significantly associated with an increased risk of TA-TMA in both the training and validation cohorts. Among patients with TA-TMA, concurrent hemorrhagic cystitis upon diagnosis of TA-TMA was a significant factor for inferior overall survival in the entire cohort (32.3% vs. 5.9%, p = 0.031). Conclusions This study validates the feasibility of diagnostic criteria for TA-TMA proposed by our group with a recent large cohort consisting of training and validation cohorts and points out the role of preceding hemorrhagic cystitis as a risk and prognostic factor for TA-TMA in AML. Of note, proteinuria and elevated LDH prior to the appearance of MAHA proposed by Jodele et al. with a younger population were proven to be useful for predicting the occurrence of TA-TMA among adult populations with AML. Disclosures Kim: Celgene: Consultancy, Honoraria; Astellas: Consultancy, Honoraria; Hanmi: Consultancy, Honoraria; AGP: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; SL VaxiGen: Consultancy, Honoraria; Novartis: Consultancy; Amgen: Honoraria; Chugai: Honoraria; Yuhan: Honoraria; Sanofi-Genzyme: Honoraria, Research Funding; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees; Handok: Honoraria; Janssen: Honoraria; Daiichi Sankyo: Honoraria, Membership on an entity's Board of Directors or advisory committees; Otsuka: Honoraria; BL & H: Research Funding. Kim:BMS: Research Funding; Pfizer: Research Funding; Takeda: Research Funding; Il-Yang co.: Research Funding; Novartis: Research Funding. Lee:Achillion: Research Funding; Alexion: Consultancy, Honoraria, Research Funding.

Abstract: Antihuman T-lymphocyte immune globulin (ATG) was shown to lower the incidence of chronic graft-versus-host disease (cGVHD) after allogeneic hematopoietic stem cell transplantation (allo-HSCT) from an unrelated donor. The type, dose, and duration of ATG treatment is a matter of ongoing controversy in allo-HSCT. Furthermore, there has been no phase 3 study to explore the role of ATG-thymoglobulin for the prevention of cGVHD in allo-HSCT from matched siblings, whereas results from a recent randomized trial of ATG-Fresenius was reported (NEJM 2016). We performed a prospective, single-center, open-label, randomized trial of ATG-thymoglobulin as a part of the conditioning regimen. The primary endpoint was the cumulative incidence (CI) of cGVHD at a 2-year evaluation. A total of 126 patients with acute leukemia were planned to be enrolled and assigned randomly at a 1:1 ratio to receive ATG-thymoglobulin (1.25 mg/kg at three and two days before allo-HSCT) or receive no ATG-thymoglobulin stratified according to the refined Disease Risk Index and conditioning intensity. Both groups were well balanced for NCCN risk, disease type, disease status, and MRD status at HSCT. The current study finally enrolled 120 patients with a median of 560 days of follow-up (range 52 - 1257). The CI of cGVHD in the ATG group (n=60) and non-ATG (n=60) group at 2 years after allo-HSCT was 37.2% and 82.7%, respectively (p & lt;0.001). Moderate-to-severe cGVHD occurred in 11.7% of the ATG group and 47.2% of the non-ATG group (p & lt;0.001). In multivariate analysis, non-AGT group, NCCN favorable to intermediate risk, and reduced intensity conditioning remained significant risk factors for the CI of chronic GVHD. There were no significant between-group differences in the CI of infectious complications, acute GVHD, or other allo-HSCT-related adverse events. In contrast, the ATG group had a significantly increased CI of relapse (CIR) compared with the non-ATG-group (28.8% vs 11.7%, p=0.010), which remained significant in the multivariate analysis. Disease-free survival, overall survival, and GVHD and relapse free survival were similar between the ATG and non-ATG groups. In conclusion, the current study revealed that the use of ATG-thymoglobulin, even at a relatively low dose (2.5 mg/kg), decreases the occurrence of cGVHD at a cost of an increased risk for relapse in the setting of allo-HSCT from matched sibling donors for acute leukemia. The optimal dose, timing, and duration of ATG-thymoglobulin should be investigated further. Disclosures Kim: BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Sun Pharma.: Research Funding; ILYANG: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding, Speakers Bureau; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Takeda: Research Funding. Lee:Alexion Pharmaceuticals Inc.: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Kim:Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; AML Global Portal: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Hanmi: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; BL & H: Research Funding; Astellas: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Chugai: Consultancy, Honoraria; Amgen Inc.: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Yuhan: Consultancy, Honoraria; SL VaxiGen: Consultancy, Honoraria; AbbVie: Honoraria; Sanofi-Genzyme: Honoraria; Daiichi Sankyo: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees.