Reduced Toxicity Conditioning Research Articles

Excellent Outcomes of the Second Allogeneic Hematopoietic Stem Cell Transplantation in Hematological Malignancies with Reduced Toxicity Conditioning and Donor Change

Introduction: High relapse rate and transplant-related mortality (TRM) are the major obstacles for the second allogeneic hematopoietic stem cell transplantation (allo-HSCT). Reduced-toxicity conditioning (RTC) can decrease TRM and healthier donor may provide stronger anti-leukemia and anti-infection effects.Objective:In current clinical study, the safety and efficacy of the second allo-HSCT with RTC and donor change were examined.Methods: Between April 2018 and June 2021, total 48 patients with hematological malignancies (B-ALL 26, T-ALL/LBL 4,AML16,MDS 2) who failed to the first allo-HSCT(relapsed 47, secondary rejection 1) and underwent the second allo-HSCT in our hospital were enrolled. The median age was 25(5-55) years old. Male to female was 25:23. Before the second allo-HSCT, 35 (72.9%) patients were in complete remission (CR) (minimal residual disease (MRD) negative in 28, MRD positive in 7), and 13 (27.1%) cases (B-ALL7,T-ALL/LBL2,AML3,MDS1) in non-remission(NR). The median interval between twoallo-HSCTs was 19.5 (8-77) months. For better donor selection, the functions of hematopoiesis and immune (subsets of lymphocyte, immune globulin,and granzyme and perforin of NK cell) as well as hematological and immunological hereditary predisposition gene variants for potential donors were tested. The types of the first allo-HSCT included haploidentical (n=33), unrelated (n=8), identical sibling (n=5), and unrelated cord blood (n=2). All donors were changed for the second allo-HSCT(haploidentical 35, unrelated 13)except one recipient no other donor available. RTC regimens were mainly total body irradiation(TBI)/fludarabine (FLU)-based(n=39) or busulfan (BU)/FLU-based (n=7).Two patients were with total marrow irradiation (TMI)/FLU-basedregimen. For TBI/FLU regimen, fractionated TBI (8Gy in 32, 10Gy in 7), cytarabine 1-2g/m 2 for 3 days,FLU 30mg/m 2 for 5 days, Me-CCNU 250mg/m 2 for 1 day, and ATG were used. For BU/FLU regimen, BU 0.8mg/kg q6h for 3 days, cytarabine 1-2g/m 2 for 3 days,FLU 30mg/m 2 for 5 days, Me-CCNU 250mg/m 2 for 1 day, and ATG were used. For TMI/FLU regimen, the same conditioning as TBI/FLU was used except fractionated TMI 10-12Gy instead of TBI. Decitabine (20mg/m 2, 3 days) or etoposide (200mg/m 2, 2 days) were administrated in some patients in NR or MRD positive. Cyclosporine, mycophenolate mofetil and short-term methotrexate were employed for graft-versus-host disease (GVHD) prophylaxis. Some patients received maintenance therapy post-transplant with targeted medicine based on their fusion genes or gene mutations.Results: ALL patients became full donor chimerism. The median time for neutrophil and platelet recovery was 15 (11-22) days and 16 (10-240) days. The incidences of grade II-IV acute GVHD (aGVHD) and chronic GVHD(cGVHD) were 18.8%, 47.5% (limited 25%, extensive 22.5%), respectively. The incidences of CMV and EBV reactivation were 31.3% and 6.3%. No severe hemorrhagic cystitis occurred. The median follow-up was 13(1-38) months. One-year disease-free survival (DFS) and overall survival (OS) of all patients were 68.7% (95% CI:0.511;0.811) and 78.9% (95% CI:0.62;0.889) . Nine patients died(relapse 7,GVHD and infection 2).The relapse rate was 22.9%.TRM was only 4.2%. NR before transplant and TP53 mutation were high risk for disease recurrence post-HSCT. Relapse rates were 53.8% vs. 11.4% in NR and CR patients, and 50% vs. 17.5% in the patients with or without TP53 mutation. Disease status before transplant was key impact factor for survival after the second allo-HSCT. One-year OS in CR and NR settings were81.4 % and 70%, respectively, p=0.13. One-year DFS in CR and NR settingswere79.6%, and 41.9%, respectively, p=0.005. No significant difference of DFS was seen in haploidentical and unrelated transplants(68.1% vs.71.8%, p=0.627).Conclusions: With our strategy of RTC regimens and donor change, excellent outcomes of the second allo-HSCT in hematological malignancies have been achieved. One-year DFS and OS are 68.7% and 78.9%. Both TRM and relapse rate are low (4.2%, 22.9%). The most important factor on prognosis of the second allo-HSCT is disease status before transplant but not donor type. TP53 mutation also has negative impact on DFS after the second allo-HSCT. DisclosuresNo relevant conflicts of interest to declare.

Long-Term Follow-up of Allogeneic Hematopoietic Stem Cell Transplantation after Chimeric Antigen Receptor T-Cell Therapy in Relapsed/Refractory B-Cell Acute Lymphoblastic Leukemia

Introduction: Chimeric antigen receptor T-cell (CART) Therapy has induced high complete remission (CR) in the patients with relapsed/refractory (r/r) B-cell acute lymphoblastic leukemia (B-ALL), but the median event-free survival is only 6.1 months (Park JH. et al. NEJM 2018). To achieve durable leukemia-free survival (LFS), it may helpful to receive allogeneic hematopoietic stem cell transplantation (allo-HSCT) after CR with CART therapy.Objective: In current study, safety and long-term outcomes of allo-HSCT after CART therapy in r/r B-ALL were assessed and risk factors for overall survival (OS) and LFS were analyzed.Methods: Between June 2017 to June 2020, 137 patients with r/r B-ALL who achieved CR with CD19 or CD22 CART then bridge to allo-HSCT in our hospital were evaluated. The median age was 9.7 years (1.8-56). Bone marrow (BM) samples were collected to detect somatic gene mutations of leukemic cells. Blood samples from patients, parents, and potential related donors were collected to analyze germline mutations of hematological and immunological hereditary predisposition genes. The disease status before transplant was minimal residual disease (MRD) negative in 114 (83.2%) patients and MRD positive in 23 (16.8%) patients. The median time from CART infusion to allo-HSCT was 51 days (29-94). The types of transplant were haploidentical (105, 76.6%), unrelated (26, 19.0%), and identical siblings (6, 4.4%). Myeloablative reduced-toxicity conditioning (RTC) with either total body irradiation (TBI)/fludarabine-based (84, 61.3%) or busulfan (BU) /fludarabine-based (53, 38.7%) were applied. Cyclosporine, mycophenolate mofetil and short-term methotrexate were employed for graft-versus-host disease (GVHD) prophylaxis.Results: Full donor engraftment was achieved in all patients. The median time for neutrophil and platelet engraftment was 15 days (9-21) and 13 days (5-33). With a median follow-up of 653 days (481-783), two-year OS was 74.1% (64.4-81.5) and two-year LFS was 64.4% (54.6-72.6). The incidences of grade Ⅱ to Ⅳ and severe acute GVHD (aGVHD) were 27%, 14.5%, respectively. Twenty-five (18.2%) cases developed chronic GVHD (cGVHD) (limited 18, extensive 7). The incidences of CMV and EBV viremia were 20.1%, 12.5%. Hemorrhagic cystitis was found in 32 (22.2%) cases. Thirty-six (26.3%) cases relapsed after transplant, 28/114 (24.6%) in MRD negative cohort and 8/23 (43.5%) in MRD positive cohort. Thirty (21.9%) patients died (relapsed 22, infection 5, multiple organ failure 2, thrombotic microangiopathy 1). Transplant-related mortality was only 5.8%. Total 137 patients with 99 kinds of somatic mutations, the most frequent 15 mutations were TP53, CYP2C19, KRAS, NRAS, PTPN11, CREBBP, KMT2D, KIT, NR3C1, STK11, FLT3, NF1, NUDT15, ABL1, ADAMTS13. LFS was significantly reduced in patients with TP53, KIT, NF1 mutation (P < 0.0001; P < 0.025; P < 0.003). Total 114 evaluable patients with 93 kinds of hematological and immunological hereditary predisposition gene mutations, the most frequent 15 mutations were BLTA, SERPINE1, CYP2C19, F7, TP53, DPYD, MLH1, TNFAIP3, YARS2, HIFIA, ATM, EP300, KIT, ADAMTS13, BRCA2. LFS was significantly reduced in patients with germline EP300 mutation (P < 0.00027). Univariate analysis showed that BU-based regimen (P=0.0194), somatic TP53 mutation (P= 0.002), fungal infection (P= 0.0217), viral infection (P=0.0187) and MRD positive before transplant (P= 0.0227) were adverse factors of OS. The negative factors of LFS were BU-based regimen (P=0.0139), germline EP300 mutation (P<0.001) and fungal infection (P =0.0002). Multivariate analysis showed that TBI-based regimen (P=0.019) and aGVHD (P=0.047) increased LFS remarkably, but fungal infection (P=0.002), somatic TP53 mutation (P<0.001) and germline EP300 mutation (P<0.001) decreased LFS significantly.Conclusions: Our large series and long-term outcomes have demonstrated that LFS and OS have been improved remarkably in r/r B-ALL who achieved CR with CART then quick bridge to RTC allo-HSCT. Our study has shown the somatic and germline mutation profiles in r/r/ B-ALL and found that somatic TP53 mutation and germline EP300 mutation are negative factors for LFS. TBI-based regimen , MRD negative before transplant and aGVHD have positive impact on LFS, and fungal infection, somatic TP53 and germline EP300 have negative impact on LFS. DisclosuresNo relevant conflicts of interest to declare.

Safety of Anti-NKG2A Blocking Antibody Monalizumab As Maintenance Therapy after Allogeneic Hematopoietic Stem Cell Transplantation: A Phase I Study

BackgroundFollowing allogeneic hematopoietic stem cell transplantation (Allo-HSCT), the phenotype and function of circulating NK Cells are altered; notably NK cells display an immature (CD56-bright/KIR -/CD57 -/NKG2A +) phenotype and a low cytotoxic activity. Since NK cells have demonstrated anti-leukemic activity in the context of Allo-HCT while less prone to induce GVHD than T cells, we hypothesized that NKG2A inhibition using the checkpoint inhibitor monalizumab (humanized IgG4 blocking monoclonal antibody) could improve NK cell mediated graft-versus-tumor effect, without triggering graft-versus-host disease. We thus performed the first clinical trial evaluating the safety of monalizumab as a prophylactic treatment after Allo-HSCT (NCT02921685).MethodThe objective was to determine the maximal tolerated dose (MTD) of a single infusion of monalizumab administered on day+75 or thereafter following Allo-HSCT. Inclusion criteria were: 1) adult patients who underwent first Allo-HSCT for hematological malignancy; 2) no prior history of GVHD, 3) reduced toxicity conditioning regimen, 4) ATG or PT-Cy based GVHD prophylaxis, and 5) GVHD prophylaxis with cyclosporine A ongoing at the time of monalizumab infusion.Four dose levels were investigated in this dose escalation study (0.04, 0.1, 0.3, and 1.0 mg/kg). Dose limiting toxicities (DLT) were defined by the occurrence of any grade 3 to 4 monalizumab-related adverse event within 28 days after infusion, including grade 3 to 4 acute GVHD and moderate to severe chronic GVHD. In case of DLT, a Bayesian continuous reassessment model (CRM) was used to predict the maximal tolerated dose (MTD) after each series of 3 patients treated at a given dose level. It was planned to treat 18 patients. Beyond clinical safety, blood samples were collected for NK and T cell immunomonitoring and receptor saturation assay.ResultsFifteen patients received monalizumab at a median time of 83 days (range: 75-103) after Allo-HSCT (3 at 0.04 mg/kg, 3 at 0.1 mg/kg, 3 at 0.3 mg/kg, and 6 at 1 mg/kg). Patients were transplanted for hematological diseases (9 AML, 3 MDS, 1 lymphoma, 1 CLL and 1 myelofibrosis), from a matched sibling (n=8), matched unrelated (n=6) or haploidentical donor (n=1).No DLT was observed during the dose escalation process or among the 6 patients treated at the highest dose level, justifying study early termination after 15 patients. Two patients developed transient low grade GVHD that spontaneously resolved without treatment (1 grade I acute GVHD on day+8 and 1 mild chronic GVHD on day+118). Systemic steroid requiring GVHD occurred in 3 patients (20%): 1 severe overlap GVHD (day+42, CR after treatment), 1 severe chronic GVHD (day+80, death from GVHD) and 1 late severe chronic GVHD after cyclosporine tapering for mixed chimerism (day+149, complete remission [CR] after treatment). No disease recurrence was observed, except for one patient with myelofibrosis who relapsed 3 years after monalizumab infusion. At a median follow up of 22 months (3-48) after monalizumab infusion, 13 out of 15 patients are in CR from their underlining malignancy without GVHD and immunosuppressive treatment at last contact.At the dose of 1 mg/kg, receptor saturation assays (RSA) showed persistent binding of monalizumab on peripheral blood NK cells. Indeed, more than 90% of NKG2A-positive NK cells were positive for monalizumab detection (Anti-IgG4-PE) until at least 14 weeks post treatment.ConclusionsMonalizumab can be safely administered after Allo-HSCT, with prolonged persistence on circulating NK cells. In the absence of DLT, MTD was not reached. Future trials will aim at measuring the clinical efficacy of monalizumab in this context, alone or in combination therapy. Disclosuresboyer Chammard: Innate Pharma: Current Employment. Chabannon: Sanofi SA: Other: Travel Support, Research Funding, Speakers Bureau; Bellicum Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees, Other: Travel Support, Speakers Bureau; Novartis: Speakers Bureau; BMS/Celgene: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Janssen Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Terumo BCT: Speakers Bureau; Miltenyi Biotech: Research Funding; Fresenius Kabi: Research Funding; EBMT: Membership on an entity's Board of Directors or advisory committees. Vey: Amgen: Honoraria; BMS: Honoraria; BIOKINESIS: Consultancy, Research Funding; NOVARTIS: Consultancy, Honoraria, Research Funding; SERVIER: Consultancy; JAZZ PHARMACEUTICALS: Honoraria; JANSSEN: Consultancy. Olive: ImCheck Therapeutics: Current holder of individual stocks in a privately-held company, Membership on an entity's Board of Directors or advisory committees; Alderaan Biotechnology: Current holder of individual stocks in a privately-held company, Membership on an entity's Board of Directors or advisory committees; Emergence Therapeutics: Current holder of individual stocks in a privately-held company, Membership on an entity's Board of Directors or advisory committees. Blaise: Jazz Pharmaceuticals: Honoraria.

Sequential Fludarabine, Ara-C, Etoposide (FLAV) Followed By Fludarabine/ Busulfan Reduced Toxicity Conditioning Is Safe and Effective Salvage for Adult Patients with Refractory Acute Myeloid Leukemia and High Risk Myelodysplasia

BackgroundA significant proportion of patients with acute myeloid leukemia (AML) will either be refractory to initial chemotherapy or will suffer refractory relapse. The role of allogeneic transplantation (SCT) in active disease is contentious. There is a growing body of literature that sequential chemotherapy, pioneered by the German FLAMSA regimen, followed by RIC SCT is a safe and efficacious modality in these patients, and there have been numerous modifications of this regimen, especially as amsacrineis not widely available. Fludarabine, cytarabineand and etoposide (VP16) (FLAV) have been reported as an effective salvage regimen. Here we report on single center outcomes of a variation of the FLAMSA regimen, substituting amsacrine for etoposide with mainly myeloablative conditioning.MethodsPatients were offered this regimen if fit for allogenic HSCT and had AML which is refractory to two cycles of chemotherapy or refractory to one cycle and considered at high risk for complication with second cycles. Patients with MDS received this regimens if eligible for transplant with high or very high risk cytogenetics. All patients received cytoreductive chemotherapy consisted of fludarabine 30mg/m2/day x 4 days, Cytarabine 2g/m2/day x 4 days, etoposide 100mg/m2/day x 3days, commenced simultaneously. After 3 days of rest, conditioning chemotherapy consisted of fludarabine 30mg/m2 x 2 days and and IV busulfan 0.8mg/m2 q 6 hours; the number of busulfan doses varied between 8 - 12, depending on patient comorbidity. All patients received 2 doses of ATG at 2.5mg/m2/day on day -3 and -2. All patients received GCSF mobilized peripheral blood hematopoietic cells. Post-transplant GVHD prophylaxis consist of CsA and MMF. CsA was tapered from day+60 and stopped at day +90 in the absence of GVHD. MMF was discontinued between day +30 and day +40. Donor lymphocyte infusions were collected for planned prophylactic DLI.ResultsTwenty six patients received FLAV-SCT between March 2014 and July 2019. The median age was 38 (14-60); 16 (62%) female. Overall 12 (46%) pts had de novo AML, 10 (39%) pts had secondary or therapy related AML and 4 (15%) pts had MDS. Fourteen (54%) pts had adverse risk cytogenetics include 8 (31%) pts had complex or monosomal karyotype. Patients' characteristics are summarized in Table 1.All patients had active disease prior to FLAV-SCT. The median time for ANC and platelet engraftment was 14 (10 - 42) days and 17 (10 - 52) days respectively. Day 30 assessment shows CR in 16 (61%) pts and CR/CRi in 17 (65%) pts. Outcomes are summarized in Table 2. Three patients (12%) developed veno-occlusive disease. Acute GVHD grade II-IV and III-IV occurred in 9 (35%) pts and 2 (8%) pts respectively. Three (12%) patients developed chronic GVHD. Cumulative incidence of NRM at 100 days and 2 years was 8% and 12% respectively. The median OS for all pts was 5.2 months with 2 years rate of 32% (15 - 50). Among responders, the median OS and RFS were 19.2 months and 8.7 months, 2y-OS and RFS were 47% and 25%, respectively (Figure 1).ConclusionOur result demonstrates that transplant is an effective therapeutic modality in this very high risk refractory AML/MDS patients. Sequential chemotherapy (FLAV) followed by SCT with busulfan at myeloablative dose is tolerable with an acceptable toxicities and encouraging results. [Display omitted] DisclosuresChaudhri: Novartis: Honoraria; Abbvie: Honoraria; Astra Zeneca: Honoraria. Alzahrani: King Faisal Specialist Hospital and Research Centre: Current Employment; Novartis: Consultancy, Honoraria; Bayer: Consultancy, Honoraria, Speakers Bureau; Sobi: Consultancy, Honoraria, Speakers Bureau; Pfizer: Consultancy, Honoraria, Speakers Bureau.

Haploidentical Versus Cord Blood Stem Cell Transplantation As the Second Transplant for Relapsed Acute Myeloid Leukemia Patients after the First Stem Cell Transplantation

Haploidentical Versus Cord Blood Stem Cell Transplantation As the Second Transplant for Relapsed Acute Myeloid Leukemia Patients after the First Stem Cell Transplantation

Combination of treosulfan, fludarabine and cytarabine as conditioning in patients with acute myeloid leukemia, myelodysplastic syndrome and myeloproliferative neoplasms

PurposeTreosulfan and fludarabine (Treo/Flu) were successfully introduced into toxicity-reduced conditioning for SCT. However, the risk of post-SCT relapse remains a matter of concern. We report the results of a novel individual treatment approach with Treo/Flu and cytarabine (Treo/Flu/AraC) conditioning prior to allogeneic SCT in patients with acute myeloid leukemia (AML), myelodysplastic syndrome (MDS), or myeloproliferative neoplasms (MPN).Methods Seventy-seven patients (median age 54 years) at high risk of disease relapse due to unfavorable cytogenetics or failure to achieve complete remission prior to SCT were included. Median follow-up was 3.2 years.ResultsThe 1-, 2- and 3-year RFS rates were 49.4%, 41.7%, and 37.6% and OS rates were 59.3%, 49.3%, and 45.4%, respectively. Cumulative incidence of NRM was 10% at 100 days, 18.8% at 1 year and 20.1% at 2 years. The cumulative incidence of relapse increased from 31% at 1 year to 38.5% after 3 years. The cumulative incidences of engraftment, chimerism, graft-versus-host disease (GvHD) and toxicities were acceptable and comparable with similar patients conditioned with Treo/Flu or FLAMSA-RIC.Conclusion In conclusion, Treo/Flu/AraC provides tolerable, feasible, and effective conditioning for patients with AML, MDS or MPN, even in advanced disease states. The incidence of NRM and relapse is acceptable in this heavily pre-treated population with high-risk disease. Future research will aim to confirm these initial findings and include a larger number of participants in a prospective trial.

Reduced-Intensity/Reduced-Toxicity Conditioning Approaches Are Tolerated in XIAP Deficiency but Patients Fare Poorly with Acute GVHD.

X-linked inhibitor of apoptosis (XIAP) deficiency is an inherited primary immunodeficiency characterized by chronic inflammasome overactivity and associated with hemophagocytic lymphohistiocytosis (HLH) and inflammatory bowel disease (IBD). Allogeneic hematopoietic cell transplantation (HCT) with fully myeloablative conditioning may be curative but has been associated with poor outcomes. Reports of reduced-intensity conditioning (RIC) and reduced-toxicity conditioning (RTC) regimens suggest these approaches are well tolerated, but outcomes are not well established. Retrospective data were collected from an international cohort of 40 patients with XIAP deficiency who underwent HCT with RIC or RTC. Thirty-three (83%) patients had a history of HLH, and thirteen (33%) patients had IBD. Median age at HCT was 6.5 years. Grafts were from HLA-matched (n = 30, 75%) and HLA-mismatched (n = 10, 25%) donors. There were no cases of primary graft failure. Two (5%) patients experienced secondary graft failure, and three (8%) patients ultimately received a second HCT. Nine (23%) patients developed grade II–IV acute GVHD, and 3 (8%) developed extensive chronic GVHD. The estimated 2-year overall and event-free survival rates were 74% (CI 55–86%) and 64% (CI 46–77%), respectively. Recipient and donor HLA mismatch and grade II–IV acute GVHD were negatively associated with survival on multivariate analysis with hazard ratios of 5.8 (CI 1.5–23.3, p = 0.01) and 8.2 (CI 2.1–32.7, p < 0.01), respectively. These data suggest that XIAP patients tolerate RIC and RTC with survival rates similar to HCT of other genetic HLH disorders. Every effort should be made to prevent acute GVHD in XIAP-deficient patients who undergo allogeneic HCT.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10875-021-01103-6.

Feasibility and Efficacy of a Pharmacokinetics-Guided Busulfan Conditioning Regimen for Allogeneic Stem Cell Transplantation with Post-Transplantation Cyclophosphamide as Graft-versus-Host Disease Prophylaxis in Adult Patients with Hematologic Malignancies

Busulfan (Bu) is an alkylating agent routinely used for conditioning regimens before allogeneic stem cell transplantation (allo-SCT). Bu shows wide pharmacokinetic (PK) variability among patients. Patients can have a higher systemic exposure (expressed as area under the curve [AUC]) with an increased risk of toxicity or a lower AUC with a higher probability of graft rejection and/or disease relapse. After i.v. administration, an optimal Bu therapeutic window (AUC target of 16,000 to 24,000 μM·minute) has been identified. The use of PK-guided Bu dosing leads to improved overall survival (OS) and progression-free survival (PFS) compared with fixed-dose administration in a variety of hematologic diseases. The aim of this study was to evaluate the outcomes and feasibility of a reduced-toxicity conditioning (RTC) regimen comprising thiotepa, Bu, and fludarabine (TBF) with therapeutic drug monitoring of Bu in patients with hematologic disorders. We report on 41 adult patients with myeloid or lymphoid malignancies who underwent an allo-SCT with a PK-guided Bu-based RTC regimen between January 2019 and October 2020. Patients received a total Bu dose to achieve a target AUC of 16,000 μM·minute in combination with Flu and thiotepa. The median time to absolute neutrophil count recovery and transfusion-independent platelet count recovery was 23 days (range, 15 to 42 days) and 29 days (range, 14 to 97 days), respectively. The cumulative incidence (CI) of nonrelapse mortality was 7% at 100 days and 13% at 1 year. Grade 3 liver toxicity was observed in 6 patients. One patient developed sinusoidal obstruction syndrome at day +27. Grade 3 mucositis occurred in 18 patients. Looking at grade ≥3 infections, the CI was 29% at 30 days, 34% at 60 days, 44% at 100 days, and 56% at 1 year. The 180-day CI of grade II-IV acute graft-versus-host disease (GVHD) was 15%, and the 1-year CI of overall chronic GVHD was 20%. With a median follow-up of alive patients of 14.4 months (range, 3.2 to 24 months), the CI of relapse at 1 year was 6%. The 1-year PFS was 81%, and 1-year OS was 84%. In conclusion, these data support the efficacy of PK-guided Bu dose in the context of a TBF conditioning regimen and the feasibility of therapeutic dosage monitoring of i.v. Bu for patients with hematologic diseases. © 2021 American Society for Transplantation and Cellular Therapy. Published by Elsevier Inc.

Promising Results at 1 Year Follow-up Following Familial Haploidentical (FHI) T-Cell Depleted (TCD) with CD34 Enrichment and T-Cell (CD3) Addback Allogeneic Stem Cell Transplantation in Patients with High-Risk Sickle Cell Disease (SCD) (IND 14359)

AlloSCT from HLA-matched MSD has been successful for high-risk SCD, and is the only known curative therapy (Talano/Cairo et al EJH, 2014). We have recently demonstrated 100% EFS and absence of sickle cell symptoms following reduced toxicity conditioning in HLA matched sibling donor (MSD) or cord blood AlloSCT (Bhatia/Cairo et al BMT, 2014). However, 5 out of 6 children lack an HLA MSD without SCD. Only 19% of recipients of African descent will identify a well-matched unrelated donor (MUD) and results after unrelated UCBT are poor (Radhakrishnan/Cairo et al BBMT, 2013). Recent results utilizing matched unrelated donors in a multi-center trial showed unacceptable rates of cGVHD at 62% (95% CI 41-77) (Shenoy et al Blood, 2016). We demonstrated CD34+ selection followed by T-cell addback from MUD in pediatric recipients led to 100% engraftment with minimal aGVHD (Geyer/Cairo et al BJH, 2011). Limitations in the past of various T-cell depletion methods have included a higher incidence of graft failure, delayed immune reconstitution, opportunistic fungal infection and higher incidence of cGVHD. FHI TCD AlloSCT utilizing the approach of CD34+ enrichment and T-cell addback could expand the donor pool and improve outcomes for patients with high risk SCD and have similar outcomes to AlloSCT from HLA MSD.This SCD consortium trial (www.sicklecelltransplantconsortium.org) (NCT01461837) is investigating the safety, feasibility, EFS, donor chimerism, graft failure, aGVHD and cGVHD after FHI TCD AlloSCT in high-risk SCD patients.High risk included: ≥1 CVA, ≥2 ACS, ≥3 VOC in past 2 years, or 2 abnormal TCDs. Patients (2-<21 yrs) who have ≥1 high-risk SCD features were eligible. Patients received hydroxyurea and azathioprine, day -59 - day -11, fludarabine (150mg/m2), busulfan (12.8mg/kg) (targeted trough Css of 600-900), thiotepa (10 mg/kg), cyclophosphamide (200mg/kg), R-ATG (8mg/kg), and TLI (500cGy) followed by FHI T-cell depleted AlloSCT. AGVHD prophylaxis: tacrolimus. We utilized the CliniMACS to enrich for peripheral blood HPC's; target dose of 10 x 106 CD34+ cells/kg with a fixed dose of 2 x 105 CD3+ T cells/kg. The Child Health Rating Inventories (CHRIs) was used to serially collect parent proxy-rated health-related quality of life (HRQL).Twenty-one patients have been enrolled. Nineteen patients have received AlloSCT to date. Fifteen patients utilized maternal donors and 4 patients utilized paternal donors. Two donors encountered thrombocytopenia that resolved spontaneously. The mean ± SD CD34+ enrichment prior to cryopreservation was 12.66 ± 3.3 x 106/kg and log T-cell depletion was 4.8 ± 0.58. Evaluable pts had early neutrophil engraftment (median day +9), and ≥95% whole blood and RBC (CD71) donor chimerism at 1yr. Probability of aGVHD n=17, 7.1% (CI95: 0-70.0); cGVHD n=17, 20% (CI95: 0.7-59.6) (Figure 1A and 1B). Probability of 1-Year Overall Survival (OS) n=17; 88.2% (CI95: 60.6-96.9) (Figure 1C). Immune reconstitution was robust with 1 yr NK, CD3, CD4 and CD8 204±37 cells/μL, 795±168 cells/μL, 408±102 cells/μL and 375±90 cells/μL, respectively. Two-yr PFT results were also robust with % predicted FVC, FEV1, TLC and DLCO of 89%, 84%, 82%, and 68%, respectively. All survivors are free of SCD symptoms and without signs of progression of multi-organ toxicity. One patient developed late hepatic SOS and died at day +59; one patient died at day +390 due to complications of CGVHD, and one patient died at day +141 of steroid refractory aGVHD, the remainder are alive and free of SCD symptoms with a median follow-up of +711 days (range, +231 to +1684 days). Most importantly, mean + SD HRQL score (0-100) reported at 1 yr for emotional, physical functioning, role, and global scores were 82.9±9.7 points, 82.8±15.8 points, 89.6±13.3 points, and 86±8.2 points, respectively.Early results indicate promising results in 1 yr OS, stable donor chimerism, and low incidence of acute and/or cGVHD after FHI HCT utilizing CD34 enrichment and CD3/MNC addback in high-risk SCD patients who lack a MSD or URD. A longer term follow-up is needed to assess long-term safety and outcomes. This research was supported by RO1FD004090-01A1. [Display omitted] DisclosuresWalters:AllCells, Inc: Other: Medical Director; bluebird bio: Research Funding; Sangamo Therapeutics: Consultancy; ViaCord Processing Lab: Other: Medical Director. Cairo:Jazz Pharmaceuticals: Speakers Bureau.

Low-Toxicity/High-Efficacy HLA Haploidentical Transplantation for Elderly/Unfit Patients with Acute Leukemia

Allogeneic hematopoietic transplantation is the most powerful therapy for patients with acute leukemia at high risk of relapse. For HLA haploidentical transplantation, we recently applied a protocol consisting of a high-intensity TBI-based conditioning regimen and a peripheral blood CD34+ hematopoietic stem cell graft combined with the adoptive transfer of naturally occurring regulatory T cells (Tregs) and conventional T cells (Tcons). No post-transplant pharmacologic immune suppressive GvHD prophylaxis was given. Such a protocol was associated with remarkably low GvHD and relapse rates (Martelli MF et al., Blood. 124:638-644, 2014; reviewed in Mancusi A et al., Blood 128:2616-2623, 2016).However, patients who are unfit (because of multiple chemotherapy cycles, previous transplants, infections, or co-morbidities) or elderly are not expected to withstand high-intensity conditioning regimens. For these patients, we developed a reduced-toxicity version based on total marrow and total lymphoid irradiation (TMI/TLI) (Rosenthal J et al., Blood. 2011;117:309-315). TMI/TLI (13.5 Gy and 11.5 Gy respectively) were administered by means of Helical Tomotherapy HI-ART (in 9 fractions delivered two times a day in 4 and a half days). Target volumes were defined as the skeletal bone and major lymph node chains and spleen. In patients with ALL the brain was added as target volume. TMI/TLI was followed by chemotherapy with Thiotepa (2,5mg/kg/day for 2 days), Fludarabine (30 mg/m2/day for 5 days) and Cyclophosphamide (15 mg/kg/day for 2 days). As per our high-intensity protocol, the hematopoietic stem cell graft was foregone by an infusion of 2x10e6/Kg freshly isolated CD4/CD25/FOXP3-positive Tregs and a subsequent infusion of 1x10e6 Tcons. No post-transplant pharmacologic immune suppressive GvHD prophylaxis was given. To date 19 patients with high-risk acute leukemia in remission were enrolled (16 AML, 3 ALL). Median age was 57 years (range: 22-68). All patients engrafted. Four patients developed aGvHD grade ≥ 2. Transplant-related mortality was 21% (2 patients died of infections, 1 of VOD and 1 of aGvHD). Remarkably, no relapse or cGvHD were observed. With a median follow up of 12 months (range: 1-24), 15 of the 19 patients are alive. Thus, leukemia/cGvHD-free survival is 79%. Of course, these data need to be confirmed in a larger cohort of patients and with longer follow up.In conclusion, the present transplantation protocol was designed to make HLA haploidentical transplantation feasible and effective for unfit or elderly patients with high-risk leukemia. It combines a reduced-toxicity conditioning regimen with safe cellular immunotherapy of leukemia. To date, the clinical results are excellent and extremely encouraging. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Lineage-Specific Chimerism and Outcome After Hematopoietic Stem Cell Transplantation for DOCK8 Deficiency

Bi-allelic variants in the dedicator of cytokinesis 8 (DOCK8) gene cause a combined immunodeficiency, characterized by recurrent sinopulmonary and skin infections, food allergies, eczema, eosinophilia, and elevated IgE. Long-term outcome is poor given susceptibility to infections, malignancy, and vascular complications. Allogeneic hematopoietic stem cell transplantation is currently the only curative treatment option and has shown promising outcome. The impact of mixed chimerism on long-term outcome is unclear. We reasoned that reversal of disease phenotype would depend on cell lineage-specific chimerism. DOCK8 variants were confirmed by Sanger and/or exome sequencing and immunoblot and/or intracellular flow cytometry. Donor chimerism was analyzed by XY-fluorescence in situ hybridization or quantitative short tandem repeat PCR. Outcome was assessed by laboratory tests, lymphocyte subsets, intracellular DOCK8 protein flow cytometry, T-cell proliferation analysis, and multiparameter immunoblot allergy screening. We report on nine patients, four of whom with mixed chimerism, with a median follow-up of 78 months after transplantation. Overall, we report successful transplantation with improvement of susceptibility to infections and allergies, and resolution of eczema in all patients. Immunological outcome in patients with mixed chimerism suggests a selective advantage for wild-type donor T-cells but lower donor B-cell chimerism possibly results in a tendency to hypogammaglobulinemia. No increased infectious and allergic complications were associated with mixed chimerism. Aware of the relatively small cohort size, we could not demonstrate a consistent detrimental effect of mixed chimerism on clinical outcomes. We nevertheless advocate aiming for complete donor chimerism in treating DOCK8 deficiency, but recommend reduced toxicity conditioning.

Pretransplant myeloid and immune suppression, reduced toxicity conditioning with posttransplant cyclophosphamide: Initial outcomes of novel approach for matched unrelated donor hematopoietic stem cell transplant for hemoglobinopathies.

Hematopoietic stem cell transplant (HSCT) is currently the only curative option for thalassemia major (TM) and sickle cell disease (SCD). We report our experience of using pretransplant immune suppression (PTIS), augmented Johns Hopkins conditioning, and posttransplant cyclophosphamide (PTCy) as graft-versus-host disease (GvHD) prophylaxis for matched unrelated donor (MUD) transplant in TM/SCD. At a median follow-up of 307.5days (range 251-395), all patients (three TM, one SCD) are alive and disease free. MUD HSCT with PTIS, augmented Johns Hopkins conditioning, and PTCy as GvHD prophylaxis is a promising way of treating patients with hemoglobinopathies with low regimen-related toxicity (RRT), no risk of graft failure (GF) and minimal GvHD rates.

Multicenter Outcome of Hematopoietic Stem Cell Transplantation for Primary Immune Deficiency Disorders in India.

BackgroundHematopoietic stem cell transplantation (HSCT) is the curative option for many primary immune deficiency disorders (PID). In the last 5 years, increased awareness, availability of diagnostics based on flow cytometry, genetic testing, improved supportive care, use of reduced toxicity conditioning, and success of haploidentical donor HSCT have improved access to HSCT for children with PID in India. We present results on children with PID who underwent HSCT across India and the factors that influenced outcome.Patients and MethodsWe collected retrospective data on the outcome of HSCT for PID from seven centers. We analyzed the impact of the type of PID, conditioning regimen, time period of HSCT- before or after January 2016, graft versus host disease prophylaxis, cause of mortality and overall survival.ResultsA total of 228 children underwent HSCT for PID at a median age of 12 months (range, 1 to 220 months) with a median follow up of 14.4 months. Infants accounted for 51.3% of the cohort and the male female ratio was 3:1. SCID (25%) and HLH (25%) were the more frequent diagnoses. Matched family donor was available in 36.4% and 44.3% children had a haploidentical HSCT. Reduced and myeloablative conditioning regimens were used with 64% children receiving a treosulfan based conditioning regimen. Peripheral blood stem cells were the predominant graft source at 69.3%. The survival in infants (60.2%) was inferior to children aged over 1 year (75.7% p value = 0.01). Children with Wiskott Aldrich syndrome (74.3%) and chronic granulomatous disease (82.6%) had the best outcomes. The survival was superior in children receiving HSCT from a matched sibling (78%) versus an alternate donor HSCT (61% p value = 0.04). In the cohort transplanted after January 2016 survival improved from 26.8% to 77.5% (p value = 0.00). Infection remains the main cause of mortality at in over 50% children. The 5-year overall survival rate was 68%.ConclusionSurvival of children with PID undergoing HSCT in India has improved dramatically in last 5 years. Alternate donor HSCT is now feasible and has made a therapeutic option accessible to all children with PID.

Treosulfan-based conditioning for inborn errors of immunity.

Inborn errors of immunity (IEI) are inherited disorders that lead to defects in the development and/or function of the immune system. The number of disorders that can be treated by haematopoietic stem-cell transplantation (HSCT) has increased rapidly with the advent of next-generation sequencing. The methods used to transplant children with IEI have improved dramatically over the last 20 years. The introduction of reduced-toxicity conditioning is an important factor in the improved outcome of HSCT. Treosulfan has myeloablative and immunosuppressive properties, enabling engraftment with less toxicity than traditionally used doses of busulfan. It is firmly incorporated into the conditioning guidelines of the Inborn Errors Working Party of the European Society for Blood and Marrow Transplantation. Unlike busulfan, pharmacokinetically guided dosing of treosulfan is not part of routine practice, but data are emerging which indicate that further improvements in outcome may be possible, particularly in infants who have a decreased clearance of treosulfan. It is likely that individualized dosing, not just of treosulfan, but of all agents used in conditioning regimens, will be developed and implemented in the future. This will lead to a reduction in unwanted variability in drug exposure, leading to more predictable and adjustable exposure, and improved outcome of HSCT, with fewer late adverse effects and improved quality of life. Such conditioning regimens can be used as the basis to study the need for additional agents in certain disorders which are difficult to engraft or require high levels of donor chimerism, the dosing of individual cellular components within grafts, and effects of adjuvant cellular or immunotherapy post-transplant. This review documents the establishment of treosulfan worldwide, as a safe and effective agent for conditioning children with IEI prior to HSCT.

Investigation of the Influences on Decision-Making Algorithms in Allogeneic Stem Cell Transplantation in Different Groups of Pediatric Nonmalignant Diseases

Background: Haematopoietic stem cell transplantation (HSCT) represents the definitive treatment for many non-malignant diseases. Treosulfan is considered a safe and effective conditioning drug compared to other conventional myeloablative conditioning (MAC) regimens, especially in patients with comorbidities. Aim of the work: To evaluate the safety and efficacy of Fludarabine-Treosulfan-Thiotepa reduced toxicity conditioning in different paediatric nonmalignant disease. Patients and methods: 54 patients (55 transplants) were reviewed retrospectively, they had metabolic, immunodeficiency, BM failure, hemoglobinopathy and other nonmalignant diseases. All had the same conditioning. 96% received serotherapy (Alemtuzumab/ATG). post-transplant Graft-versus-Host disease (GVHD) prophylaxis was given in all patients, based mostly on ciclosporin. 90% of the patients were fully HLA-matched. Results: Median age at transplant was six years. No primary graft failure, 4%(n=2) had secondary graft failure. Overall survival at a median follow-up of 15months was 90.9%. Neutrophil engraftment occurred at a median of 12 days, Platelet engraftment occurred at a median of 19 days. immune reconstitution was achieved at a median time of nine Chimerism was full donor in 64%(n=35), high donor in 18%(n=10), and mixed donor in 6%(n=3). 60%(n=33) developed GVHD but only 4%(n=2) had acute severe GVHD, another 4%(n=2) had severe chronic GVHD. One patient had severe VOD. Conclusion: This study demonstrates that Fludarabine-Treosulfan-Thiotepa regimen is a safe and effective conditioning that can achieve engraftment, with very low rates of graft failure, transplant-related mortality and morbidity, even if it is used twice in the same patient.

Citrulline Trajectory during Allogeneic Hematopoietic Stem Cell Transplantation Is Correlated to Conditioning Intensity and Non-Relapse Mortality

Introduction Citrulline, a non-essential amino acid produced exclusively by enterocytes in the small intestine and involved in the synthesis of L-arginine, is not metabolized by the liver. Therefore citrulline serum concentration is highly correlated with functional enterocyte mass, and decreases with digestive toxicity induced by conditioning therapy (radiotherapy and/or chemotherapy) for hematopoietic stem cell transplantation (HSCT) . Acute Graft-versus-host disease (GvHD), one of the major complications of HSCT, is correlated to conditioning-induced gut barrier damage and may be predicted by pre-transplant serum citrulline level (Rashidi, BBMT 2018). It could be interesting to know whether citrulline kinetics could also represent a biomarker for conditioning toxicity, non-relapse mortality (NRM), and GvHD. The aim of this study is thus to define group-based trajectory modeling, to identify clusters of individual serum citrulline kinetics in the early phase of allogeneic HCST, and to test whether these unsupervised trajectories were correlated with these early complications. Materials and Methods Serum citrulline was quantified by liquid chromatography in blood samples collected from consecutive patients who received an allogeneic HSCT in our institution between July 2014 and November 2019. These samples were drawn at different time-points: pre-transplant (D-7, D-3); day of transplant (D0), and post-transplant (D7, D15, D21). Distinct trajectories were identified for serum citrulline by using the semiparametric mixture model described by Nagin (Nagin, Stat Methods Med Res 2018). Results Among 161 patients (pts) included in the study, with a median age of 53 years (17-72), 98 pts (60.9%) received a reduced-intensity conditioning (RIC), 36 pts (22.4%) reduced-toxicity conditioning (RTC), 18 pts (11.1 %) sequential conditioning, and 9 pts (5.6%) myeloablative conditioning (MAC). Donor were identical sibling (22%), matched unrelated donor (52%) and haploidentical sibling (25%). Graft source was peripheral blood mononuclear cells in 144 pts (89.4%) and bone marrow in 17 pts (10.6%) respectively. HCT-CI score was low, intermediate and high-risk in 38%, 32%, and 30% of pts respectively. Disease-Risk Index (DRI) was low/intermediate in 111 pts (69%) and high/very-high in 50 pts (31%). With a median follow up of 29.1 month, 3-year overall survival (OS), disease-free survival (DFS), and NRM rates were 64.5%, 58.3%, and 18.9%, respectively. The median number of citrulline samples per patient was 7 [3-16]. Median citrulline concentrations before conditioning and at D-3, D0, D7 and D15 were statistically different during RIC, RTC, MAC, and sequential conditioning (p&amp;lt;0,001 respectively) but was not different at D21 (p=0.296). In the whole cohort, 3 citrulline trajectories were determined in an unsupervised method. Patients belonging to these 3 trajectories were different according to intensity of conditioning received with lower citrulline trajectories during MAC and sequential conditioning (p&amp;lt;0.001). In the uper citrulline trajectorie, pts were significantly older (p=0.005). However, citrulline trajectories were not correlated to OS (p = 0.1), NRM (p=0.24), cumulative incidence of acute GvHD (p=0.39) or chronic GvHD (p=0.2). After restricting the analysis to pts who received RIC conditioning (n=98), higher pre-HSCT citrulline concentrations were associated with a lower NRM (p=0.042). Unsupervised analysis in this setting individualized 4 clusters of individual trajectories (figure 1), that did neither distinguish age (p=0.28), DRI (p=0.87), HCT-CI score (p=0.81) nor the incidence of acute (p=0.6) or chronic (p=0.4) GvHD. However, the lowest citrulline trajectory contained significantly more haploidentical transplantations (p=0.004) and less pts who received antithymocyte globulin for GvHD prophylaxis (p=0.005). Interestingly in this RIC cohort, cumulative incidence of NRM at 12 months was 23%, 21%, 8%, and 0% respectively according to the 4 citrulline trajectories (figure 2). Conclusion In patients receiving allogeneic HSCT, the variation of serum citrulline concentrations depends on the intensity of the conditioning regimen. In patients who received RIC conditioning, lower plasma citrulline trajectories are associated with higher NRM. In this setting, citrulline may be an attractive biomarker for predicting conditioning toxicity and NRM. Disclosures Hunault: Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Diachi: Membership on an entity's Board of Directors or advisory committees; Jansen: Honoraria; Servier: Honoraria, Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees. Thepot:astellas: Honoraria; novartis: Honoraria; sanofi: Honoraria; celgene: Honoraria.

Reduced Intensity Vs. Non-Myeloablative Conditioning Regimens for Haploidentical Transplantation in Complete Remission Acute Myeloid Leukemia: A Study from the ALWP of the EBMT

Background: In the context of a haploidentical stem cell transplantation (Haplo-SCT) platform with post transplantation cyclophosphamide (PT-Cy) for acute myeloid leukemia (AML) patients, the optimal conditioning regimen remains unknown. A non-myeloablative conditioning (NMAC) regimen (cyclophosphamide + fludarabine + 2Gy TBI [CyFluTBI]) was initially reported by the Johns Hopkins group as a safe approach in this setting, notably to treat patients of advanced age and/or with comorbid conditions. However, relapse incidence after NMAC Haplo-SCT remains high in AML where it can reach 45%. Alternatively, a reduced intensity conditioning (RIC) regimen containing an antileukemic drug combination like thiotepa and reduced-dose busulfan in addition to fludarabine (TBF) may decrease AML relapse. However, this anticipated benefit may be counterbalanced by a higher incidence of toxicity, graft-versus-host disease (GVHD) and non-relapse mortality (NRM). To date, no study comparing TBF vs. CyFluTBI has been published in complete remission (CR) AML. We performed this retrospective comparison on behalf of the Acute Leukemia Working Party (ALWP) of the European Society for Blood and Marrow Transplantation (EBMT). Methods: We retrospectively analyzed 398 patients from the EBMT registry database with the following inclusion criteria: 1) adult patient in CR1 or CR2 AML; 2) T-replete Haplo-SCT with PT-Cy; 3) no in vivo depletion using antithymocyte globulin or alemtuzumab; and 4) receiving either TBF RIC (equivalent of 2-day iv busulfan dose) or CyFluTBI NMAC regimen. We compared separately TBF vs. CyFluTBI in patients younger (n=170, 82 TBF vs. 88 CyFluTBI) and older (n=228, 141 TBF vs. 87 CyFluTBI) than 60 years. Results: In patients younger than 60 years, the 2-year cumulative incidence of relapse (CIR) was significantly lower in the TBF group compared with the CyFluTBI group (TBF vs. CyFluTBI: 14% vs. 43%, p&amp;lt;0.01). No significant increase in 2-year NRM was observed (TBF vs. CyFluTBI: 22% vs. 16%, p=0.15). This led to a significantly higher 2-year leukemia-free survival (LFS) probability in the TBF group (64% vs. 41%, p=0.03). After adjustment in multivariate analysis, CyFluTBI was associated with a higher risk of relapse (hazard ratio [HR] 3.4, 95%CI [1.4-6.9], p&amp;lt;0.01), lower LFS (HR 1.8, 95%CI 1.1-3.0, p=0.03) and lower overall survival (OS) (HR 1.8, 95%CI 1.1-3.1, p=0.02), without significant impact of conditioning regimen on incidence of GVHD and NRM. In patients older than 60 years, univariate analysis did not show any significant difference in outcome according to the type of conditioning regimen (2-year NRM: TBF vs. CyFluTBI: 33% vs. 25%, p=0.23; 2-year CIR: TBF vs. CyFluTBI: 23% vs. 28%, p=0.20; 2-year LFS: TBF vs. CyFluTBI: 44% vs. 47%, p=0.96). Multivariate analysis showed a significant reduction in the risk of NRM after CyFluTBI (HR 0.5, 95%CI [0.2-0.9], p=0.04), while a non-significant increase in the risk of relapse was observed (HR 1.9, 95%CI [0.8-4.2], p=0.13). Finally, there was no significant difference in LFS (HR 0.9, 95%CI [0.5-1.5], p=0.67) and OS (HR 0.9, 95%CI [0.5-1.5], p=0.67). Conclusion: Our study suggests that in CR AML patients aged younger than 60 years, the use of TBF RIC provides better outcomes than NMAC CyFluTBI due to lower incidence of relapse, without significant increase in the risk of NRM. Conversely, it seems that older patients do not benefit from such conditioning intensification, due to a significantly higher risk of NRM after TBF RIC. Thus, in CR AML patients who will not receive a truly myeloablative regimen prior to PT-Cy Haplo-SCT, age could be used for determining the conditioning intensity from the wide variety of reduced toxicity conditioning regimens. Beyond the patient age, further prospective trials should assess patient-based parameters that may be useful for a fine tuning of conditioning intensity in a more individualized approach. Disclosures Labopin: Jazz Pharmaceuticals: Honoraria. Blaise:Jazz Pharmaceuticals: Honoraria. Bug:Sanofi: Other: Travel; Neovii: Other: Travel; Jazz: Honoraria; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: Travel; Hexal: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Membership on an entity's Board of Directors or advisory committees; Eurocept: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees, Other: Travel. Mohty:Amgen: Consultancy, Honoraria, Research Funding, Speakers Bureau; BMS: Consultancy, Honoraria, Research Funding, Speakers Bureau; Novartis: Consultancy, Honoraria, Research Funding, Speakers Bureau; GSK: Consultancy, Honoraria, Research Funding, Speakers Bureau; Janssen: Consultancy, Honoraria, Research Funding, Speakers Bureau; Takeda: Consultancy, Honoraria, Research Funding, Speakers Bureau; Sanofi: Consultancy, Honoraria, Research Funding, Speakers Bureau; Jazz Pharmaceuticals: Consultancy, Honoraria, Research Funding, Speakers Bureau; Celgene: Consultancy, Honoraria, Research Funding, Speakers Bureau; Stemline: Consultancy, Honoraria, Research Funding, Speakers Bureau.

Augmented immunosuppression and PTCY-based haploidentical hematopoietic stem cell transplantation for thalassemia major.

Alternate donor HSCT for thalassemia major from a matched unrelated donor or haploidentical family donor is a feasible therapeutic option in children with no matched family donor. Aggressive pretransplant immunosuppression, reduced toxicity conditioning, and PTCY result in excellent thalassemia-free survival. We describe here our experience in this cohort. We performed a retrospective analysis of the data on children who underwent a haploidentical HSCT for thalassemia major with PTCY at our center from August 2017 to August 2019. All children received pretransplant immune suppression for 6weeks with fludarabine and dexamethasone, hypertransfusion and chelation with intravenous desferrioxamine. Conditioning included thiotepa, fludarabine, rabbit ATG, and cyclophosphamide, and GvHD prophylaxis included PTCY with tacrolimus. Twenty children were included and nineteen children engrafted. Acute hypertension occurred in five children, bacterial infection in eight children and viral respiratory infection in three children. Three children suffered from graft rejection. Reactivation of viruses namely CMV, adenovirus, and BK virus was seen in 60% of children. Grades 1-2 acute GvHD of the skin in four children (20%) and limited chronic GvHD of the skin in four children (20%). Immune cytopenia was documented in three children (15%). Haploidentical HSCT offers a therapeutic option for children with thalassemia major with no suitably matched family or unrelated donors. Our reduced toxicity regimen with PTCY offers a DFS of 75% and OS of 95% with low transplant-related mortality of 5%.

Experience with a Reduced Toxicity Allogeneic Transplant Regimen for Non-CGD Primary Immune Deficiencies Requiring Myeloablation.

A need exists for reduced toxicity conditioning regimens that offer less toxicity while maintaining myeloablation, especially for primary immune deficiencies where myeloablation or high donor myeloid chimerism is required to achieve cure. We adapted a busulfan and fludarabine regimen by Gungor et al. for children and young adults undergoing allogeneic HCT for non-CGD primary immune deficiencies requiring myeloablation or high donor myeloid chimerism, and herein report our experience. We retrospectively reviewed records of 41 consecutive patients who underwent allogeneic HCT for Wiskott-Aldrich syndrome (n = 12), primary HLH/XLP (n = 10), CD40L deficiency (n = 7), or other (n = 12) primary immune deficiencies with a conditioning regimen containing pharmacokinetic-guided busulfan dosing which achieved a cumulative AUC between 57 and 74mg/L × h (65-80% of conventional myeloablative exposure), along with fludarabine and alemtuzumab or anti-thymocyte globulin at 3 transplant centers between 2014 and 2019. Forty-one patients underwent a first (n = 33) or second (n = 8) allogeneic HCT. Median age was 2.3years (range, 0.3years-19.8years). All but one patient (97.5%) achieved neutrophil recovery at a median of 14days (range, 11-34days). One patient developed sinusoidal obstruction syndrome and two patients developed diffuse alveolar hemorrhage. Four patients developed grades II-IV acute GVHD. Three patients developed chronic GVHD. One-year overall survival was 90% (95% confidence interval [CI] 81-99%) and event-free survival was 83% (95% CI 71-94%). Our experience suggests that a reduced toxicity busulfan-fludarabine regimen offers low toxicity, low incidence of grades 2-4 GVHD, durable myeloid engraftment, and excellent survival, and may be considered for a variety of primary immune deficiencies where myeloablative HCT is desired.

Total body irradiation + fludarabine compared to busulfan + fludarabine as "reduced-toxicity conditioning" for patients with acute myeloid leukemia treated with allogeneic hematopoietic cell transplantation in first complete remission: a study by the Acute Leukemia Working Party of the EBMT.

The optimal conditioning for patients with acute myeloid leukemia in first complete remission treated with allogeneic hematopoietic cell transplantation (allo-HCT) has not been defined so far. In this retrospective study, we compared two "reduced-toxicity" regimens: intravenous busulfan at a total dose of 9.6 mg/kg (3 days) + fludarabine (Bu3/Flu) and total body irradiation at a dose of 8 Gy + fludarabine (TBI8Gy/Flu). In the entire study cohort (n = 518), the probabilities of overall survival (OS), leukemia-free survival (LFS), relapse and non-relapse mortality (NRM) at 2 years for Bu3/Flu and TBI8Gy/Flu were 62% vs. 72.5% (p = 0.051), 59.5% vs. 65% (p = 0.15), 30% vs. 20% (p = 0.01), and 10% vs. 14% (p = 0.18), respectively. In multivariate model for patients <50 years old, TBI8Gy/Flu was associated with improved LFS (hazard ratio (HR) = 0.5, p = 0.04), OS (HR = 0.31, p = 0.004), and survival free from both graft-versus-host disease and relapse (HR = 0.55, p = 0.03), as well as tendency to reduced risk of relapse (HR = 0.53, p = 0.08). Among patients aged 50 years or older the use of TBI8Gy/Flu was associated with increased incidence of NRM (HR = 3.9, p = 0.0009), with no significant impact on other outcome measures. We conclude that the use of TBI8Gy/Flu as "reduced-toxicity" regimen may be advised in younger patients with AML referred for allo-HCT.