Abstract: Prophylactic transfusion of donor lymphocytes (pDLT) is an attractive form of maintenance therapy after allogeneic stem cell transplantation in patients with high risk of relapse. However, clinical experience is limited, and disease response is often achieved at the expense of severe graft-versus-host disease (GvHD). We here report our data on pDLT in high-risk AML and MDS. Cells were given within a prospective protocol that contained a sequence of chemotherapy, reduced intensity conditioning for allogeneic transplantation, and pDLT (FLAMSA-regimen). For pDLT, patients had to be in CR at least 120 days from transplantation, off immunosuppression for 30 days, and free of GvHD. 22/86 patients alive at day +120 fulfilled the criteria for pDLT. They had been transplanted for refractory or relapsed leukemia (n=9 each) or in CR1 because of unfavorable cytogenetics (n=4). 14 patients had an unfavorable karyotype, 8 with complex aberrations. Reasons for withholding pDLT in 64 patients included cGvHD or prolonged immunosuppression (n=38), refractory or relapsed leukemia (n=15), refusal of patient or donor (n=4 each), a history of grade IV acute GvHD (n=2), and chronic infections (n=3). The median time from transplant to first pDLT was 167 days (range 120–297). Median follow up of transfused patients is 696 days (range 209–1341). Ten patients received 1, 6 patients received 2, and 6 patients received 3 transfusions in escalating doses, containing a median of 1x106, 5x106 and 1x107 CD3+ cells/kg at pDLT 1, 2 and 3, respectively. Reasons for giving less than 3 transfusions were GvHD, relapse or refusal of the patient. Induction of GvHD was the main complication; grade III acute GvHD developed in 1, and chronic GvHD in 7 patients. So far, 5 patients have relapsed despite pDLT. One died of refractory leukemia, whereas 2 achieved secondary CR following adoptive immunotherapy. Two patients are currently under treatment. At present, 18/22 patients are alive and in CR at a median of 423 days post DLT. The current leukemia free survival at two years from first pDLT is 79%. Nineteen patients were complete chimeras at time of pDLT. pDLT converted mixed into complete bone marrow chimerism in 1, but failed in 2 cases. In our experience, pDLT is safe after allogeneic transplantation for high risk AML, when given at low doses and to a selected group of patients. Results are encouraging, and long term survival can be achieved. However, further studies need to define more precisely the contribution of pDLT to the therapeutic effect of the entire procedure.

Abstract: To evaluate the role of a second allogeneic hematopoietic stem-cell transplantation (HSCT2) given for relapsed acute leukemia (AL) after related or unrelated first hematopoietic stem-cell transplantation (HSCT1) and to analyze the role of donor change for HSCT2 in both settings. Patients and Methods We performed a retrospective registry study on 179 HSCT2s given for relapse after HSCT1 from matched related donors (n = 75) or unrelated donors (n = 104), using identical or alternative donors for HSCT2. Separate analyses were performed according to donor at HSCT1. Results Independent of donor, 74% of patients achieved complete remission after HSCT2, and half of these patients experienced relapse again. Overall survival (OS) at 2 years was 25% ± 4% (39% ± 7% after related HSCT2; 19% ± 4% after unrelated HSCT2). Long-term survivors were observed even after two unrelated HSCT2s. Multivariate analysis for OS from HSCT2 confirmed established risk factors (remission duration after HSCT1: hazard ratio [HR], 2.37; 95% CI, 1.61 to 3.46; P 〈 .001; stage at HSCT2: HR, 0.53; 95% CI, 0.34 to 0.83; P = .006). Outcome of HSCT2 was better after related HSCT1 than after unrelated HSCT1 (2-year OS: 37% ± 6% v 16% ± 4%, respectively; HR, 0.68; 95% CI, 0.47 to 0.98; P = .042, multivariate Cox regression). After both related and unrelated HSCT1, selecting a new donor for HSCT2 did not result in a relevant improvement in OS compared with HSCT2 from the original donor; however, donor change was not detrimental either. Conclusion After relapse from allogeneic HSCT1, HSCT2 can induce 2-year OS in approximately 25% of patients. Unrelated HSCT2 is feasible after related and unrelated HSCT1. Donor change for HSCT2 is a valid option. However, a clear advantage in terms of OS could not be demonstrated.

Abstract: Abstract 2258 Poster Board II-235 The long-term outcome of donor lymphocyte infusions (DLI) as first line treatment of relapse of chronic myeloid leukemia (CML) after allogeneic stem cell transplantation was studied and compared to other treatment modalities. Forty five patients were treated with DLI and 36 without DLI. Patients given DLI first did not differ significantly from those given other treatments in gender, age, donor, gender and histocompatibility of the donor, source of stem cells (blood vs marrow), depletion of T cells, stage of the disease, time from diagnosis and year at the time of transplant, acute and chronic graft-versus-host disease (GVHD) and remission duration. The survival of the DLI group was 66.4 percent at 10 and 15 years after transplantation, it was 42.2 and 23.8 percent respectively in the non-DLI group (p=0.019, log rank). Excluding patients with early relapse in the first 6 months the survival of the DLI group was 78 percent at 15 and 20 years, 70 and 26 percent respectively of the non-DLI group (p=0.009). Recurrent leukemia was the predominant cause of death in both groups (11 of 14 patients of the DLI-, 21 of 23 patients of the non-DLI group). Three patients in the DLI group died of recurrent infections, bronchiolitis obliterans (BO) and heart failure respectively, and 2 patients of BO in the non-DLI group. The proportion of surviving patients with positive PCR for bcr/abl was not different in both groups (2 of 13 patients of the non-DLI and 7 of 30 patients in the DLI group). The better survival of the DLI group indicates a better control of residual leukemia by a persistent immune effect. The response to DLI was improved by simultaneous treatment with low doses of interferon-a and GM-CSF. The combination of these cytokines without DLI and transplantation remains to be defined in patients that do not tolerate or respond incompletely to Imatinib. The role of immunotherapy for induction and maintenance of remission is well established in transplant patients. Disclosures: No relevant conflicts of interest to declare.

Abstract: Introduction. Allogeneic hematopoietic cell transplant (HCT) is an established treatment modality that is potentially curative for many patients with acute myeloid leukemia (AML). The development of reduced intensity conditioning (RIC) allows performing HCT in elderly and/or in heavily pretreated patients and in those with comorbidities precluding the use of standard myeloablative conditioning. Post-transplant relapse remains a challenge after RIC, particularly in patients with adverse prognosis factors.The so-called "sequential" transplant approach (e.g. FLAMSA regimen combining both intensive chemotherapy and RIC HCT within the same procedure) initially developed in patients with refractory AML, could be a promising strategy to improve disease control and decrease the risk of relapse in high-risk AML patients in complete remission (CR). Patients and methods. In the current study we analyzed transplantation outcomes in a cohort of 411 adults AML patients in CR at time of transplant, treated between 2002 and 2013. Patients received a "sequential" conditioning regimen based on Fludarabine 30 mg/m2/d, high-dose aracytine 1-2 g/m2/d, amsacrine 100 mg/m2/d for 5 days and after a 3 days rest, total body irradiation (TBI) 4Gy, cyclophosphamide 50-120 mg/kg, and antithymocyte globulin (ATG) for 2 to 3 days (TBI group, n=269 [65%]). In 142 (35%) patients, TBI was substituted by IV Busulfan 3.2 mg/kg/d for 2 days, or orally equivalent dose (Bu group). 323 patients (79%) had de-novo AML and 88 (21%) had a secondary AML (with prior myelodysplastic syndrome). At time of transplant, 300 (73%) patients were in CR1 and 111 (27%) in CR2. Cytogenetic study in de novo AML was favorable in 19 patients (6%), intermediate in 102 (32%) and poor in 41 (13%). Cytogenetic data were missing in 161 (50%). 104 (25%) patients received matched related donors (MRD) and 307 (75%) unrelated donor (URD) HCT. Majority of patients (94%) received mobilized peripheral blood stem cells graft. Results. Median follow-up of surviving patients was 28 months and median age at transplant was 54 years (18-76). ANC 〉 500/μL was achieved at a median of 17 (range, 9-74) days after HCT. Sixteen patients (4%) failed to engraft. Two year cumulative incidence of relapse (RI) and non-relapse mortality (NRM) were 22% (95%CI, 18-26%) and 22% (95%CI, 18-27%), respectively. The Kaplan-Meier estimate of overall (OS) and leukemia-free survival (LFS) at 2 years were 59% (95%CI, 54-65%) and 56% (95%CI, 50-61%), respectively. Acute GVHD (grade II-IV) occurred in 109 (28%) patients. The 2-year cumulative incidence of chronic GVHD was 31% (95%CI, 26-36), extensive in 17% (95%CI, 12-21). Two years RI, NRM, LFS and OS in TBI vs. Bu patients were 21.8% vs 21.7% (p=0.69), 29.4% vs 18.3% (p=0.008), 48.8% vs 59.6% (p=0.045) and 51.2% vs 64.0% (p=0.013), respectively. In multivariate analysis adjusted for variable with different distribution between Bu and TBI groups, the type of conditioning (TBI vs Bu) has no impact on RI, NRM, LFS and OS. Age over 55 at transplant was an independent adverse prognostic factor in multivariate analysis for NRM (hazard ratio (HR: 1.61, 95% CI: 1.00-2.61, p=0.05)), LFS (HR: 1.39, 95% CI: 1.00-1.92, p=0.05) and OS (HR: 1.55, 95% CI: 1.11-2.18, p=0.01). Being treated in an experienced center (defined as having including 10 or more transplants in the study) was associated with a significant lower RI (HR: 0.84, 95% CI: 0.75-0.93, p=0.001) and better LFS (HR: 0.91, 95% CI: 0.84-0.98, p=0.01) and OS (HR: 0.91, 95% CI: 0.84-0.98, p=0.02). Finally, transplantation from an URD was associated with a significant increase in NRM (HR: 2.11, 95% CI: 1.14-3.91, p=0.02). Of note, CR1 vs. CR2 and de novo vs. secondary AML had no impact on patients' outcome. Conclusions. These results in a rather large cohort of patients with AML suggest that a FLAMSA "sequential" regimen provided an efficient disease control in high-risk AML patients including in CR2 and secondary AML. Furthermore Busulfan and TBI based FLAMSA "sequential" regimens provide a similar outcome. These results should be confirmed in a multicenter well design randomized study. Disclosures Off Label Use: off-label drug use: antithymocyte globulin (ATG) for allo-SCT conditioning. Tischer:Sanofi-Aventis: Other: advisory board. Schmid:Neovii: Consultancy; Janssen Cilag: Other: Travel grand. Mayer:Janssen: Research Funding. Hallek:Pharmacyclics: Honoraria, Other: Speakers Bureau and/or Advisory Boards, Research Funding; Janssen: Honoraria, Other: Speakers Bureau and/or Advisory Boards, Research Funding; Boehringher Ingelheim: Honoraria, Other: Speakers Bureau and/or Advisory Boards; Mundipharma: Honoraria, Other: Speakers Bureau and/or Advisory Boards, Research Funding; Celgene: Honoraria, Other: Speakers Bureau and/or Advisory Boards, Research Funding; Gilead: Honoraria, Other: Speakers Bureau and/or Advisory Boards, Research Funding; Roche: Honoraria, Other: Speakers Bureau and/or Advisory Boards, Research Funding; AbbVie: Honoraria, Other: Speakers Bureau and/or Advisory Boards, Research Funding.

Abstract: Background: Relapse is the most frequent cause of failure after alloSCT for acute leukemia (AL). Unlike in CML, infusion of donor lymphocytes (DLI) is of limited efficacy in overt hematological relapse. Hence, it may be preferable to give DLI in complete hematological remission (CHR) after alloSCT, to exploit the allogeneic graft-versus-leukemia (GvL) effect either as maintenance in high risk patients (prophylactic DLI, proDLI), or as early intervention to prevent hematological recurrence in case of decreasing donor chimerism or minimal residual disease (preemptive DLI, preDLI). However, no systematic analysis of this strategy is available so far, neither concerning the optimal way of application, nor with respect to safety and clinical efficacy. Here, the Acute Leukemia Working Party of the EBMT presents results from a registry-based survey on 343 patients with AML (n=266) or ALL (n=77), who received DLI in CHR after alloSCT. Patients: Median age was 48y, 64% of patients had received alloSCT from a matched sibling, 36% from an 8/8 matched unrelated donor. Disease status at time of alloSCT was CR1/CR2/advanced in 68%/14%/17% of cases, respectively. Patients had received standard/reduced intensity conditioning in 53%/47% of cases. Before alloSCT, 55% had received in vivo T-cell depletion (TCD), 16% ex vivo TCD, 10% in vivo plus ex vivo, and 19% no TCD. Reasons for preDLI were persisting mixed or decreasing donor cells chimerism (n=167, 49%) and persisting or recurrent minimal residual disease (MRD; n=32, 9%). ProDLI without any sign of leukemia was given to 144 patients (42%) with high risk disease Results: Median follow up from DLI1 was 6.5 years (range, 1.1-14.5). Median interval from alloSCT to first DLI (DLI1) was 180 days (range, 15-1178). Patients received a median of 2 infusions with the median CD3+ cell dose at DLI1 being 1x106/kg (range, 0.1-163). Reasons to discontinue DLI were: number of planned infusions reached (56%), GvHD (17%), disease progression (13%), and documented improvement of donor chimerism (6%). At 5y from DLI1, cumulative incidence of leukemia relapse was 43% and 28% in patients receiving preDLI for MRD and mixed chimerism, and 28% among recipients of proDLI given for maintenance in high risk disease. The corresponding 5y OS rates were 55%, 66% and 64%, 5y-LFS rates were 52%, 57% and 58%. Efficacy of preDLI could be directly demonstrated by decreasing MRD in 71% (15/21) and by improvement of donor chimerism in 68% (110/163) of informative patients. Furthermore, hematologic improvement was observed in 13 patients following proDLI. Cumulative incidences of acute GvHD grade II-IV and chronic GvHD after DLI were 13% and 32%, respectively. A multivariate model identified a history of aGvHD ≥grade II after alloSCT (p=0.009, HR 2.1, 95% CI 1.2-3.7), an interval from alloSCT to DLI 〈 6 months (p=0.003, HR 0.997, 95% CI 0.006-0.999), and a CD3+ cell count 〉 1 x 106/kg at DLI1 (p=0.024, HR 1.011, 95% CI 1.001-1.021) as risk factors for induction of GvHD after DLI in CHR. One hundred and thirty three patients (39%) had died at last follow-up, with relapse still being the most frequent cause of death (n=87). Sixteen patients (5% of the entire cohort) died from DLI-induced GvHD, and 29 patients died from other courses. In summary, in this large cohort of patients receiving DLI for AL in CHR after alloSCT, efficacy of preemptive DLI cells could be demonstrated in 69% of patients. About half of patients with MRD, and 〉 70% of patients with mixed chimerism did not experience hematological relapse during a follow up period of 〉 5 years, suggesting a clinically meaningful effect of preDLI in AL. GvHD was the most devastating complication, leading to death in 5% of patients. The identification of risk factors for GvHD may influence the selection of candidates for prophylactic and preemptive DLI in general, and may help to refine the use of DLI in this context with respect to cell dose and timing. Disclosures Schmid: Neovii: Consultancy; Janssen Cilag: Other: Travel grand. Bug:Celgene, Novartis: Research Funding; NordMedica, Boehringer Ingelheim, Gilead: Membership on an entity's Board of Directors or advisory committees; TEVA Oncology, Astellas: Other: Travel Grant. Tischer:Sanofi-Aventis: Other: advisory board. Esteve:Celgene: Consultancy, Honoraria; Janssen: Consultancy, Honoraria.

Abstract: No standard treatment is available for relapse of acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) after allogeneic stem cell transplantation (alloSCT). Efficacy of donor lymphocyte transfusion (DLT) was limited, at least in part, by the rapid pace of the disease, overwhelming any allogeneic immune response. However, induction chemotherapy before DLT was complicated by severe toxicity. Based on a pilot trial conducted in Munich, a prospective, multicenter phase II trial for relapsed AML and MDS after alloSCT was initiated in 2000 by the German transplant cooperative group. The study evaluated the sequence of low-dose(ld)AraC for leukemic control (intensive chemotherapy for progressive disease only), transfusion of donor PBSC without immunosuppression as adoptive immunotherapy, and systemic application of GM-CSF. GM-CSF was included, since in combination with other cytokines, it has been able to improve the antigene presentation capacity of myeloid blasts in vitro. Between 2000 and 2006, 41 patients with hematological relapse of AML or MDS & gt;3 months after alloSCT were included. Median age was 47y, 50% had an unrelated donor. Median remission after SCT was 223d (93–1614), median percentage of BM blasts at relapse was 40%. Median follow up was 28 months. Control of leukemic proliferation by ldAraC was achieved in 61%, allowing outpatient care in the majority of these patients. 39% required intensive chemotherapy. Three patients died from infections before donor cell transfusion (DCT), one patient was not transfused due to progressive leukemia. Median time from relapse to DCT was 52 days. 25/34 evaluable patients were found to be free of blasts in BM at d35 after PBSC and were considered initial responders. In an intent-to-treat analysis, overall survival (OS) of the entire cohort at 1 and 2 years from relapse was 41% and 32%. Among initial responders, 1y- and 2y-OS was 68% and 49%. A remission & gt;6months after alloSCT, and control of leukemia by ldAraC prior to DCT were associated with better outcome. At last follow up, 8 patiens were in continous CR, 2 were alive with second relapse, 18 had died from leukemia, and 13 had died in remission or aplasia. In conclusion, ldAraC seems to be effective for initial control of leukemic proliferation in relapsed AML and MDS after alloSCT. A longer duration of post-transplant remission and response to ldAraC may identify patients who will benefit from adoptive immunotherapy. On an intend-to-treat-basis, the overall results of our trial compare favorably to other published strategies; nevertheless, outcome is still unsatisfying and warrants further investigation.

Abstract: Allogeneic hematopoietic cell transplantation (HCT) offers the highest chance for cure in patients with adverse-risk acute myeloid leukemia (AML) when performed in first remission (CR1). In contrast, patients in CR1 with favorable risk do not seem to benefit from allogeneic HCT due to the inherent risk of transplant-related mortality. Donor vs. no donor comparisons as well as prospective matched-pair analyses have suggested that allogeneic HCT performed in intermediate-risk AML may provide a higher probability of overall survival or relapse-free survival in patients ≤ 60 years of age with an acceptable risk for transplant-related mortality. On the other hand, many intermediate-risk patients relapsing after conventional chemotherapy may be successfully salvaged by allogeneic HCT. The role of allogeneic HCT in cytogenetically defined intermediate-risk AML patients in CR1 was addressed by a prospective randomized trial performed in 16 centers in Germany. Key inclusion criteria were: AML with intermediate-risk cytogenetics, first CR or CRi after conventional induction therapy, age of 18-60 years, and availability of an HLA-matched sibling or unrelated donor. For unrelated donors, a 9 out of 10 HLA allelic match was acceptable except for patients with an NPM1 mutation, for whom full 10/10 allele matching was required. Randomization was stratified according to age ( & lt; 40 vs. 40-60), NPM1/FLT3, and CEBP-alpha mutational status and unrelated vs. related donor availability. Endpoints included overall-survival as primary outcome and relapse-free survival (RFS), cumulative incidence of relapse, treatment-related mortality, and quality of life measured according to the short form (36) health status. From 2010 - 2018, 143 patients in CR1 were randomized into Arm A (n=76, allogeneic HCT) and Arm B (n=67, conventional consolidation and allo-HCT only in case of relapse). In July 2018, the trial was stopped prematurely due to slow accrual (143 out of 356 pts. randomized). Median age of the trial cohort was 51 years (range, 19-60), with 42% exhibiting an NPM1 and 25% a FLT3 mutation. A normal karyotype was reported in 84% of the included patients. All mentioned characteristics did not differ between both treatment arms. Sibling donors were available for 44 (31% of patients), matched unrelated donors for 99 (69%) patients. According to the intent-to-treat analysis, the probability of survival at 2 years was 71% (95% CI 60-81%) and 84% (95% CI 73-92%) in Arm A (Transplant) and Arm B (conventional consolidation), respectively (p=0.120, Figure 1A). RFS after allogeneic HCT was 69% (95% CI 57-80%) compared to 41% (95% CI 29-54%) after conventional consolidation (p=0.001, Figure 1B). Primary allogeneic HCT reduced the cumulative incidence of relapse at 2 years from 57% [95%-CI 46-71%] after conventional consolidation to 20% [95%-CI 13-31%] after HCT (p & lt;0.001). Non-relapse mortality at 2 years after primary allogeneic HCT was 9% [95%-CI 5-19%] compared to 2% [95%-CI 0-11%] after consolidation (p=0.017).Most importantly, all 38 patients relapsing in arm B (33 hematologic, 4 molecular and 1 extramedullary) proceeded to allogeneic HCT as salvage therapy. Multivariable Cox regression analysis revealed a status of CRi compared to CR before randomization to be associated with a significantly higher risk of death (HR 3.3, p=0.009). SF (36) scoring suggested a trend towards a lower physical functioning throughout the first 3 months after randomization in the primary HCT arm. No significant differences in vitality, mental health, social and emotional functioning could be documented between both treatment arms. In summary, the results of this first prospective randomized trial did not show that allogeneic HCT performed immediately after achievement of CR1 in patients with cytogenetically defined intermediate-risk AML ≤ 60 years of age conveys an overall survival advantage. However, allogeneic HCT in CR1 significantly reduced the relapse risk and was not associated with relevant impairments in quality of life. Although the limited statistical power of the trial does not allow definitive conclusions, delayed allogeneic transplantation seems to be a potential treatment algorithm in CR1 intermediate-risk AML with an available donor. Figure 1 Figure 1. Disclosures Schliemann: Jazz Pharmaceuticals: Consultancy, Research Funding; Roche: Consultancy; Philogen S.p.A.: Consultancy, Honoraria, Research Funding; Pfizer: Consultancy; AstraZeneca: Consultancy; Boehringer-Ingelheim: Research Funding; Novartis: Consultancy; Abbvie: Consultancy, Other: travel grants; Astellas: Consultancy; BMS: Consultancy, Other: travel grants. Schetelig: Roche: Honoraria, Other: lecture fees; Novartis: Honoraria, Other: lecture fees; BMS: Honoraria, Other: lecture fees; Abbvie: Honoraria, Other: lecture fees; AstraZeneca: Honoraria, Other: lecture fees; Gilead: Honoraria, Other: lecture fees; Janssen: Honoraria, Other: lecture fees . Glass: Riemser: Research Funding; Roche: Consultancy, Research Funding, Speakers Bureau; Kite: Consultancy; BMS: Consultancy; Novartis: Consultancy; Helios Klinik Berlin-Buch: Current Employment. Platzbecker: Janssen: Honoraria; Celgene/BMS: Honoraria; Novartis: Honoraria; Takeda: Honoraria; Geron: Honoraria; AbbVie: Honoraria. Burchert: Novartis: Honoraria, Research Funding; AOP Orphan: Honoraria, Research Funding; Pfizer: Honoraria; Incyte: Honoraria; Gilead: Honoraria; BMS: Honoraria. Haenel: Jazz: Consultancy, Honoraria; GSK: Consultancy; Bayer Vital: Honoraria; Takeda: Consultancy, Honoraria; Roche: Consultancy, Honoraria; Novartis: Consultancy, Honoraria; Amgen: Consultancy; Celgene: Consultancy, Honoraria. Mueller: Amgen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Other: Travel Support; CTI: Membership on an entity's Board of Directors or advisory committees; Gentium: Other: Travel Support; Gilead: Other: Travel Support; Janssen: Other: Travel Support; Novartis: Other: Travel Support; Pfizer: Other: Travel Support; Sanofi: Other: Travel Support. Berdel: Philogen S.p.A.: Consultancy, Current equity holder in publicly-traded company, Honoraria, Membership on an entity's Board of Directors or advisory committees. Stelljes: Novartis: Consultancy, Speakers Bureau; MSD: Consultancy, Speakers Bureau; Pfizer: Consultancy, Research Funding, Speakers Bureau; Kite/Gilead: Consultancy, Speakers Bureau; Celgene/BMS: Consultancy, Speakers Bureau; Medac: Speakers Bureau; Amgen: Consultancy, Speakers Bureau.

Abstract: Background: Relapse of acute leukemia (AL) after allogeneic hematopoietic stem cell transplantation (allo-HSCT) is frequently treated with 2nd allo-HSCT. Donor change has not yielded a significantly different outcome over choosing the original HLA-identical donor (Christopeit et al., JCO 2013). Using a haploidentical donor at second allo-HSCT might represent a feasible option (Tischer et al., BMT 2014) Study design and population: To define the role for second haploidentical allo-HSCT for AL relapsing after 1st allo-HSCT, a retrospective analysis was conducted 63 consecutive patients (female n=30, male n=33; AML n=51, ALL n=12) from 9 German centers were included. Median age was 40 years (range, 16-65). Grafts at 1st allo-HSCT were from matched related (32%), matched unrelated (33%), mismatch unrelated (18%), haploidentical donors (6%), and other donors, including cord blood (8%). Median duration of complete remission (CR) after 1st allo-HSCT was 414 days (range, 18-1633). Relapse was initially treated by cytoreductive chemotherapy in all cases; stage at start of conditioning for haploidentical second allo-HSCT was CR in 27%, active disease in 66% and not evaluated in 8%. Conditioning for second HSCT was myeloablative/reduced in 14%/86% To overcome the HLA barrier, 23 patients (36%) received ex vivo T-cell depletion (TCD), following either CD3/CD19 negative or CD34 positive selection. 4 patients received in vivo TCD only, two received no TCD at all, and 35 patients (55%) received high-dose cyclophosphamide post-transplant according to the Baltimore protocol. Results: Neutrophil engraftment was achieved after a median of 12 days (range, 8-26). 50 patients (78%) achieved CR after 2nd haploidentical allo-HSCT, out of which 23 (46%) relapsed again. After a median follow-up of 425 days, 47 patents had died, 22 from leukemia, and 25 from treatment-related causes. Kaplan-Meier estimated overall survival at one and two years from haploidentical second HSCT was 41+/-6% and 19+/-6%. Conclusions: Haploidentical second allo-HSCT is a promising approach to the treatment of AL relapse after first allogeneic transplant. OS rates at least comparable to alternative treatments were observed. Different strategies to overcome the HLA barrier seem feasible. This retrospective study was registered as NCT01997918 at clinicaltrials.gov. Maximilian Christopeit and Johanna Tischer as well as Wolfgang Bethge and Christoph Schmid contributed equally to this work. Disclosures No relevant conflicts of interest to declare.