Myeloablative Busulfan Research Articles

Resolution of Sickle Cell Disease Manifestations in Patients Treated with Lentiglobin Gene Therapy: Updated Results from the Phase 1/2 Hgb-206 Group C Study

Background β-globin gene transfer into hematopoietic stem cells (HSCs) could reduce or eliminate sickle cell disease (SCD)-related manifestations. LentiGlobin for SCD gene therapy contains autologous CD34+ cells transduced with the BB305 lentiviral vector (LVV), encoding a human β-globin gene with the anti-sickling T87Q mutation (βA-T87Q). The safety and efficacy of LentiGlobin for SCD is being evaluated in the ongoing Phase 1/2 HGB-206 Study (NCT02140554). The initial 7 patients (Group A) were treated with LentiGlobin made from bone marrow harvested HSCs. The protocol was modified to improve HbAT87Q production by including pre-harvest red blood cell (RBC) transfusions, increasing the total busulfan exposure, and using a refined LentiGlobin manufacturing process (Group B, n=2). An additional modification was made for Group C patients where HSC collection by plerixafor mobilization followed by apheresis was instituted. Data from these Group C patients are discussed here. Results from patients in Groups A and B are reported separately. Methods Patients (≥ 18 years) with severe SCD (including those with recurrent vaso-occlusive crisis [VOC] and acute chest syndrome [ACS]) were screened for eligibility. Patients received 240 µg/kg of plerixafor 4-6 hours prior to HSC collection via apheresis. CD34+ cells were transduced with BB305 LVV. Patients underwent myeloablative busulfan conditioning and subsequent LentiGlobin drug product (DP) infusion. Patients were monitored for adverse events (AEs), engraftment, vector copy number (VCN), total hemoglobin (Hb) and HbAT87Q expression, hemolysis markers, and SCD clinical manifestations. Data are presented as median (min-max). Results: As of 7 March 2019, 19 Group C patients, aged 26 (18-36) years, had initiated mobilization/apheresis and 13 patients were treated with LentiGlobin for SCD gene therapy. Median DP VCN, % transduced cells, and CD34+ cell dose in the 13 treated patients were: 3.8 (2.8-5.6) copies/diploid genome (c/dg), 80 (71-88) %, and 4.5 (3.0-8.0) x 106 CD34+ cells/kg, respectively. The median follow-up was 9.0 (1.0-15.2) months. Twelve patients achieved neutrophil and platelet engraftments at a median of 19 (15-24) days and 28 (19-136) days, respectively. As of the data cut-off, engraftment was not yet evaluable in 1 patient at 1-month post-infusion. All patients stopped red blood cell (RBC) transfusions within about 3 months post-LentiGlobin gene therapy. Median total hemoglobin (Hb) and Hb fractions in patients at various time points are shown in Figure 1. Median HbS levels were at or below 50% in all patients with at least 6 months follow-up. The median total Hb at last visit in 8 patients with at least 6 months of follow-up, was 11.5 (10.2-15.0) g/dL, with a corresponding HbAT87Q median contribution of 5.3 (4.5-8.8) g/dL and a median HbS 5.7 (4.8-8.0) g/dL. Of these 8 patients, 6 had a history of VOCs or ACS. The median annualized VOC+ACS rate in these patients was 5.3 (3-14) pre-treatment and decreased to 0 (0-2) post-treatment. One Grade 2 VOC was observed 3.5 months post-treatment. No ACS or serious VOCs were observed in Group C patients' post- treatment. Lactate dehydrogenase, reticulocyte count, and total bilirubin at last visit post-LentiGlobin infusion were 225.0 (130.0-337.0) U/L, 150.0 (42.1-283.0) 109/L, 22.2 (3.42-39.3) µmol/L, respectively, trending towards normalization. The most common non-hematologic Grade ≥ 3 AEs were febrile neutropenia (n=10) and stomatitis (n=7) post-DP infusion. Serious AEs were reported in 6 patients post-LentiGlobin treatment, most common being nausea and vomiting. To date, there have been no DP-related AEs or graft failure, vector-mediated replication competent lentivirus detected, or clonal dominance reported. Longer follow-up and additional patient data will be presented. Summary The safety profile of LentiGlobin gene therapy for SCD remains consistent with single-agent busulfan conditioning and underlying disease. Patients in HGB-206 Group C experienced high-level, sustained expression of gene-therapy derived hemoglobin, with median HbS levels reduced to ~50% and median total Hb levels of 11.5 g/dL at 6 months. The cessation of clinical complications (no ACS or serious VOCs) and decreased hemolysis suggest a strong therapeutic effect after LentiGlobin gene therapy in patients with SCD. Disclosures Kanter: Peerview: Honoraria; NHLBI: Membership on an entity's Board of Directors or advisory committees; Rockpointe: Honoraria; SCDAA: Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria; Imara: Consultancy; Jeffries: Consultancy; Modus: Consultancy; Guidepoint Global: Consultancy; GLG: Consultancy; Cowen: Consultancy; bluebird bio, Inc: Consultancy; Medscape: Honoraria; Sangamo: Consultancy. Kwiatkowski:Terumo: Research Funding; Novartis: Research Funding; Apopharma: Research Funding; Imara: Consultancy; Celgene: Consultancy; bluebird bio, Inc.: Consultancy, Research Funding; Agios: Consultancy. Schmidt:German Cancer Research Center, Heidelberg, Germany: Employment; GeneWerk GmbH, Heidelberg, Gemrany: Equity Ownership. Miller:bluebird bio, Inc.: Employment, Equity Ownership. Pierciey:bluebird bio, Inc.: Employment, Equity Ownership. Huang:bluebird bio, Inc.: Employment, Equity Ownership. Ribeil:bluebird bio, Inc.: Employment, Equity Ownership. Thompson:Baxalta: Research Funding; Novartis: Consultancy, Research Funding; Celgene: Consultancy, Research Funding; bluebird bio, Inc.: Consultancy, Research Funding. Walters:AllCells, Inc: Consultancy; TruCode: Consultancy; Editas Medicine: Consultancy.

Busulfan Combined with Immunosuppression Allows Efficient Engraftment of Gene-Modified Cells in a Rhesus Macaque Model.

Busulfan conditioning is utilized for hematopoietic stem cell (HSC) depletion in the context of HSC gene-therapy conditioning but may result in insufficient immunosuppression. In this study, we evaluated whether additional immunosuppression is required for efficient engraftment of gene-modified cells using a rhesus HSC lentiviral gene-therapy model. We transduced half of rhesus CD34+ cells with an enhanced green fluorescent protein (GFP)-encoding vector (immunogenic) and the other half with a γ-globin-encoding vector (no predicted immunogenicity). After autologous transplantation of both transduced cell populations following myeloablative busulfan conditioning (5.5mg/kg/day for 4days), we observed immunological rejection of GFP-transduced cells up to 3months post-transplant and stable engraftment of γ-globin-transduced cells in two animals, demonstrating that ablative busulfan conditioning is sufficient for engraftment of gene-modified cells producing non-immunogenic proteins but insufficient to permit engraftment of immunogenic proteins. We then added immunosuppression with abatacept and sirolimus to busulfan conditioning and observed engraftment of both GFP- and γ-globin-transduced cells in two animals, demonstrating that additional immunosuppression allows for engraftment of gene-modified cells expressing immunogenic proteins. In conclusion, myeloablative busulfan conditioning should permit engraftment of gene-modified cells producing non-immunogenic proteins, while additional immunosuppression is required to prevent immunological rejection of a neoantigen.

S1632 SAFETY AND EFFICACY OF LENTIGLOBIN GENE THERAPY IN PATIENTS WITH TRANSFUSION‐DEPENDENT B‐THALASSAEMIA AND NON‐B0/B0 GENOTYPES IN THE PHASE 3 NORTHSTAR‐2 STUDY

Background:Transfusion‐dependent β‐thalassaemia (TDT) is a severe genetic disease typically treated by regular, lifelong red blood cell (RBC) transfusions that may result in serious complications and organ damage. Most patients with TDT are not candidates for allogeneic haematopoietic stem cell (HSC) transplantation. LentiGlobin gene therapy is being investigated in patients with TDT and contains autologous CD34+ HSCs transduced ex vivo with the BB305 lentiviral vector (LVV) encoding β‐globin with a T87Q amino acid substitution.Aims:To evaluate LentiGlobin gene therapy in paediatric, adolescent, and adult patients with TDT (≥100 mL/kg/yr of red blood cells [RBCs] or ≥8 RBC transfusions/yr) and non‐β0/β0 genotypes in the ongoing, international, single‐arm, phase 3 Northstar‐2 study (HGB‐207; NCT02906202).Methods:HSCs are mobilised with G‐CSF and plerixafor, collected by aphaeresis, and CD34+ cells are transduced with the BB305 LVV. Patients receive single‐agent, pharmacokinetic‐adjusted, myeloablative busulfan before the transduced cells are infused. The primary endpoint is transfusion independence (TI, weighted average haemoglobin [Hb] ≥9 g/dL without RBC transfusions for ≥12 months). Patients are followed for 2 yrs and offered participation in a long‐term follow‐up study.Results:Sixteen patients have been treated in Northstar‐2 as of 14 September 2018. The median age was 19 (min‐max: 8–34) yrs; 2 patients <12 yrs of age have been treated. Median time to neutrophil and platelet engraftment was 19 (min‐max: 13–32) days and 44.5 (min‐max: 20–84) days, respectively. As of the most recent data analysis, 1 patient (1‐month follow‐up) and 4 patients (≤2 months follow‐up) had not achieved neutrophil and platelet engraftment, respectively.Non‐haematologic grade ≥3 adverse events in ≥3 patients included stomatitis, febrile neutropenia, epistaxis, pyrexia, and liver veno‐occlusive disease (VOD). One event of grade 3 thrombocytopenia was considered possibly related to LentiGlobin. There have been no graft failures, deaths, detection of vector‐mediated replication competent lentivirus, or insertional mutagenesis.Of the 3 patients evaluable for TI, 2 have satisfied the primary endpoint of TI. Ten of 11 patients with ≥3 months follow‐up have stopped RBC transfusions. At last study visit, these 10 patients had total Hb levels of 11.1–13.3 g/dL comprised of 7.7–10.6 g/dL gene therapy‐derived Hb, HbAT87Q. Hb levels remained stable with median Hb of 11.9 g/dL (n = 9), 12.2 g/dL (n = 7), and 12.3 g/dL (n = 5) at 6, 9, and 12 months after LentiGlobin infusion, respectively.To assess correction of dyserythropoiesis, bone marrow samples from 6 patients with ≥12 months follow‐up were assessed for cellularity and myeloid:erythroid (M:E) ratios. All 5 patients who stopped RBC transfusions showed improved M:E ratios at month 12 (min‐max: 0.77–1.1) compared to baseline (min‐max: 0.18–0.45). Four of these 5 patients had soluble transferrin receptor levels available at month 12 and showed a decrease at month 12 (median 45.3; min‐max: 37.7–69.4 nmol/L) compared to baseline (median 173.5; min‐max: 90.6–235.3 nmol/L; reference range: 22.4–51.8 nmol/L).Summary/Conclusion:The safety profile of LentiGlobin gene therapy in Northstar‐2 is generally consistent with previous experience with busulfan conditioning. Delayed platelet engraftment was observed in some patients. Ten of 11 of patients with ≥3 months follow‐up stopped chronic RBC transfusions following treatment with LentiGlobin. Total Hb is stable at near‐normal levels and bone marrow morphology indicates improvements in erythropoiesis.

S141 CLINICAL OUTCOMES OF LENTIGLOBIN GENE THERAPY FOR TRANSFUSION‐DEPENDENT β‐THALASSAEMIA (TDT) FOLLOWING COMPLETION OF THE NORTHSTAR (HGB‐204) STUDY

Background:While regular red blood cell (RBC) transfusions extend the lifespan of patients with transfusion‐dependent β‐thalassaemia (TDT), iron overload and end‐organ damage can result. The curative alternate, allogeneic haematopoietic stem cell (HSC) transplantation, is limited by donor availability and transplant‐related risks. LentiGlobin gene therapy in TDT is under investigation as a treatment option that may overcome some of these limitations. LentiGlobin gene therapy contains autologous CD34+ cells transduced ex vivo with the BB305 lentiviral vector (LVV) encoding β‐globin with a T87Q substitution.Aims:To evaluate the safety and efficacy of LentiGlobin gene therapy in adolescents and adults with TDT (≥ 100 mL/kg/yr of RBCs or ≥ 8 RBC transfusions/yr) in the phase 1/2 Northstar study (NCT01745120).Methods:HSCs were mobilised with G‐CSF and plerixafor and enriched CD34+ cells were transduced with the BB305 LVV. Patients received myeloablative busulfan, after which transduced HSCs were infused. Primary efficacy endpoints were sustained production of ≥ 2 g/dL of gene therapy‐derived haemoglobin (Hb), HbAT87Q, between months 18–24 and transfusion independence (TI; weighted average Hb ≥ 9 g/dL without RBC transfusions for ≥ 12 months). Patients were monitored for 2 years and offered participation in the long‐term follow‐up study, LTF‐303.Results:Eighteen patients with TDT (median age 20 [min‐max: 12–35] years) were treated in Northstar. As of 14 September 2018, median follow‐up was 38.9 (29.3–48.1) months. Median time to neutrophil and platelet engraftment was 18.5 (14–30) and 39.5 (19–191) days, respectively. There was no graft failure. Grade ≥ 3 non‐haematologic adverse events (AEs) in ≥ 25% of patients were stomatitis, febrile neutropenia, and pharyngeal inflammation. Serious AEs reported in ≥ 2 patients were thrombosis (n = 2) and liver veno‐occlusive disease (n = 2), all of which resolved. The vector integration site profile in all patients remains polyclonal.Sixteen of 18 (89%) patients met the primary endpoint of sustained production of ≥ 2 g/dL of HbAT87Q from months 18–24. Eight of 10 (80%) patients with non‐β0/β0 genotypes achieved transfusion independence with a median weighted average Hb during TI of 10.2 (min‐max: 9.3–13.2 g/dL). TI has been maintained for a median of 38 (min‐max: 21‐ 44) months. The median time to last RBC transfusion after LentiGlobin infusion was 2.0 (min‐max: 0.3–5.8) months. In the 8 patients who achieved TI, median (min‐max) total Hb, RBC counts, and mean corpuscular volume (MCV) were 10.8 (9.7–14.1) g/dL, 4.1 (2.8–5.8) x1012/L, and 83.0 (74.2–108.6) fL at last study visit.Of 8 patients with β0/β0 genotypes, 3 (38%) achieved TI for 16–21 months during any interval post‐infusion. Median time to last RBC transfusion was 19.4 (min‐max: 1.8–19.8) months. At last study visit, median (min‐max) total Hb, RBC counts, and MCV in these 3 patients were 10.3 (9.1–10.9) g/dL, 4.2 (3.4–4.4) x1012/L, and 82.8 (78.3–83.8) fL.Liver iron concentration as measured by magnetic resonance imaging in patients who achieved TI is shown in Figure 1. Patients re‐initiated iron chelation therapy at a median of 13 (min‐max: 2–16) months after infusion.Summary/Conclusion:With up to 4 years of follow‐up, we observed durable transfusion independence in 8/10 and 3/8 patients with non‐β0/β0 genotypes and β0/β0 genotypes, respectively, and a safety profile that is consistent with myeloablative conditioning. Two ongoing Phase 3 studies, Northstar‐2 and Northstar‐3, are evaluating refined manufacturing of LentiGlobin with the goal to improve patient outcomes.image

T-cell mitochondrial dysfunction and lymphopenia in DOCK2-deficient patients

This study delineates the mitochondrial defects in DOCK2-deficient T cells contributing to the T cell lymphopenia characteristic of this primary immunodeficiency.

A Phase I Study of Haploidentical Bone Marrow Transplantation with Post-Transplant Cyclophosphamide and/or Bendamustine

Background The nearly universal donor accessibility afforded by haploidentical bone marrow transplantation (haplo-BMT) is salient for our program, as half of the patients undergoing hematopoietic cell transplantation (HCT) are ethnic or racial minorities. This highlights the need for effective haplo-BMT regimens and improvements in graft-versus-host disease (GvHD) prophylaxis. Balancing GvHD prevention with the maintenance of graft-versus-leukemia (GvL) is an ongoing challenge in the field of HCT. We have previously shown in mice that bendamustine (BEN) can safely replace cyclophosphamide (CY) as post-transplant (PT) GvHD prophylaxis following haplo-BMT, with comparable protection from GvHD and superior GvL effects. Based on our preclinical data, we have initiated a Phase I/II study to replace PT-CY (given on days +3 and +4) with PT-BEN following haplo-BMT. Methods Phase I is a standard 3 + 3 dose escalation design with six dose level cohorts. The first three cohorts (1-3) consist of a combination of sequentially reduced doses of CY and increased doses of BEN on day +4 post-BMT with the dose of CY on day +3 remaining unchanged. The next three cohorts (4-6) will involve progressive substitution of CY with BEN on day +3. We are enrolling patients ages 8-60 years with a diagnosis of acute leukemia, chronic myeloid leukemia, myelodysplastic syndrome, Hodgkin's or non-Hodgkin's lymphoma who do not have a readily available HLA-matched (10/10) donor. Myeloablative busulfan, fludarabine, and melphalan or TBI and fludarabine are used as conditioning regimens. Engraftment, immune reconstitution, T-cell receptor β (TRB) diversity, GvHD, infections, relapse, non-relapse mortality (NRM), event-free survival (EFS) and overall survival (OS) are monitored. Patients undergoing haplo-BMT (using the same conditioning regimens) who do not wish to receive PT-BEN are consented as PT-CY controls for the clinical endpoints and immune reconstitution studies. Results We have enrolled through Cohort 2 with no dose-limiting toxicities. Cohort 2 of PT-BEN had significantly earlier neutrophil engraftment than PT-CY controls (median day +13 compared to +17), with >5-fold higher neutrophil to lymphocyte ratios through day +100. PT-BEN patients displayed higher CD4 to CD8 ratio and demonstrated significantly greater TRB diversity than PT-CY only patients through 1 year following transplant. Patients receiving PT-BEN had a trend toward a lower incidence of CMV reactivation, 33% compared to 100% in PT-CY controls. No PT-BEN patient has developed grade III-IV acute GvHD or chronic GvHD. Conclusions PT-BEN has been well-tolerated, with patients demonstrating early engraftment. Preliminary data with PT-BEN indicate potential differences in immune reconstitution and TRB diversity. This may be advantageous in viral control, as well as in GvHD and GvL responses.

Lentiglobin Gene Therapy for Transfusion-Dependent β-Thalassemia: Outcomes from the Phase 1/2 Northstar and Phase 3 Northstar-2 Studies

Introduction Transfusion-dependent β-thalassemia (TDT) is a severe genetic disease characterized by anemia, iron overload and serious comorbidities for which gene therapy may be an effective treatment option. LentiGlobin gene therapy contains autologous CD34+ hematopoietic stem cells (HSCs) transduced ex vivo with the BB305 lentiviral vector (LVV) encoding β-globin with a T87Q substitution. Objective Evaluate the efficacy and safety of LentiGlobin in patients with TDT in the phase 1/2 Northstar (HGB-204; NCT01745120) and phase 3 Northstar-2 (HGB-207; NCT02906202) studies. Methods Patients with TDT (≥100 mL/kg/yr of red blood cells [RBCs] or ≥8 RBC transfusions/yr) received G-CSF and plerixafor for mobilization and HSCs were transduced with the BB305 LVV. Patients underwent single agent busulfan myeloablative conditioning, were infused with transduced cells, and were followed for engraftment, safety, and efficacy. Statistics are presented as median (min – max). Results As of March 7, 2018, 18 patients (12 – 35 yrs) were treated in Northstar (follow-up 32.1 [23.1 – 41.9] months) and as of May 15, 2018, 11 patients (12 – 24 yrs) were treated in Northstar-2 (follow-up 8.5 [0.3 – 16.2] months). Patients received a median cell dose of 8.0 (5.0 – 19.4) CD34+ cells × 106/kg in both studies. The median time to neutrophil and platelet engraftment in both studies was 19 (14 – 30) days and 44 (19 – 191) days, respectively; 1 patient in Northstar-2 (0.3 months follow-up) had not engrafted at time of analysis. Of 6 patients with platelet engraftment ≥ Day 60, 4 had non-serious bleeding events prior to engraftment. All 6 had intact spleens and 3/6 received G-CSF between Days 0 – 21. Both factors appeared associated with time to platelet engraftment. In Northstar, 8/10 patients with non-β0/β0 genotypes and 2/8 patients with β0/β0 genotypes achieved transfusion independence (TI; weighted average hemoglobin [Hb] ≥ 9 g/dL without RBC transfusions for ≥ 12 months). Median Hb during TI was 10.0 (9.3 – 13.1) g/dL. In Northstar-2, 7/8 patients with non-β0/β0 genotypes and ≥ 6 months follow-up stopped RBC transfusions with Hb of 11.1 – 13.3 g/dL at last visit; the first patient treated achieved TI. Non-hematologic grade ≥ 3 adverse events post-infusion in ≥ 5/29 (15%) patients were stomatitis, febrile neutropenia, and pharyngeal inflammation. Veno-occlusive liver disease attributed to busulfan occurred in 4/29 patients (Table 1). There was no transplant-related mortality, vector-mediated replication competent lentivirus, or clonal dominance. Conclusion In Northstar, 80% of patients with non-β0/β0 genotypes achieved TI and early Northstar-2 data suggest that patients can achieve near-normal Hb without transfusions. The safety profile of LentiGlobin is consistent with myeloablative busulfan conditioning. Longer time to platelet engraftment was observed in few patients, but no graft failure or deaths were reported.

Lentiglobin Gene Therapy in Patients with Sickle Cell Disease: Updated Interim Results from Hgb-206

Introduction β-globin gene transfer may reduce or eliminate complications in patients with sickle cell disease (SCD). LentiGlobin gene therapy (GT) comprises drug product (DP) made from autologous hematopoietic stem cells (HSCs) transduced with the BB305 lentiviral vector (LVV) encoding β-globin with an anti-sickling T87Q substitution (HbAT87Q). The safety and efficacy of LentiGlobin GT in adults with SCD is being evaluated in a phase 1 study, HGB-206 (NCT02140554). Patients were initially treated with DP made from bone marrow harvested (BMH) HSCs (Group [Grp] A, fully enrolled), then from DP made from BMH HSCs but using a refined manufacturing process (Grp B, fully enrolled), and subsequently from plerixafor mobilized HSCs (Grp C, currently enrolling). Objective Assess safety and feasibility of plerixafor mobilization in patients with SCD and describe outcomes of LentiGlobin GT in the HGB-206 study. Methods Adults with severe SCD (history of recurrent vaso-occlusive crisis, acute chest syndrome, stroke, or tricuspid regurgitant jet velocity of >2.5 m/s) were enrolled. Autologous CD34+ cells, collected by BMH or apheresis following mobilization with 240 µg/kg plerixafor, were transduced with BB305 LVV. After myeloablative busulfan conditioning (area under the curve goal of 5000 [range 4400—5400] µM*min daily), patients were infused with the transduced cells and monitored for safety and efficacy. Summary statistics are median (min-max). Results As of May 15, 2018, 22 patients had HSCs collected, 18 patients had DP made and 15 patients were treated. BMH was performed in 11 patients (9 in Grp A, 2 in Grp B) and mobilization/apheresis in 12 patients (1 in Grp B [also had BMH], 11 in Grp C). Median of 4.3 (0.1—10.8) × 106 and 10.4 (3.8—21.6) × 106 CD34+ cells/kg were collected per BMH (N=26) and per mobilization cycle (N=17), respectively. Eighteen grade 3 adverse events (AEs) in 6 patients were attributed to BMH and 5 grade 3 AEs in 3 patients to mobilization/apheresis. DP and treatment characteristics are shown in Table 1. DP characteristics were improved in Grp B and Grp C vs Grp A. The safety profile post-DP infusion was consistent with myeloablative conditioning and underlying SCD; most common non-hematologic grade ≥3 AEs were stomatitis, febrile neutropenia, and vaso-occlusive pain. At last visit (Table 1), HbAT87Q levels were higher in Grp B (3.2—7.2 g/dL) vs Grp A (0.5—1.2 g/dL). In 4 Grp C patients at the 3-month visit, HbAT87Q (4.1 [3.2—6.0] g/dL) levels were equal to or exceeded HbS levels (3.3 [2.8—3.8] g/dL). In 1 Grp C patient at the 6-month visit, HbAT87Q was 8.8 g/dL and total Hb was 14.2 g/dL. Conclusion These data support the safety and feasibility of plerixafor-mediated HSC collection in patients with SCD. HGB-206 protocol changes have improved LentiGlobin DP characteristics yielding higher HbAT87Q levels. Additional data will determine the clinical effect of increased HbAT87Q/HbS ratios.

Reduced Toxicity Conditioning Is Better Tolerated but Has Higher Graft Failure Compared to Myeloablative Conditioning in Children with Inherited Metabolic Disorders

Background: Hematopoietic stem cell transplantation (HCT) is a primary treatment option for various inherited metabolic diseases (IMDs). Successful engraftment is crucial for favorable survival and functional outcomes and correlates with optimal conditioning in these patients with an intact immune system. Traditional regimens have used myeloablative Busulfan and Cyclophosphamide (BuCy) which is associated with significant potential morbidity. Alternate reduced toxicity regimens, like Busulfan and Fludarabine (BuFlu), are often utilized to reduce treatment related toxicities.Objective: To compare outcomes and complications with BuCy and BuFlu based conditioning regimens in patients with IMDs.Methods: This is the largest single institution retrospective analysis of University of Minnesota's transplant database for patients with IMDs who underwent HCT using BuCy + campath or BuFlu + ATG based preparative regimen from March 2008 to September 2017. Incidence of neutrophil and platelet recovery were determined using standard definitions. Complications such as graft failure, sinusoidal obstruction syndrome, hemorrhagic cystitis and respiratory failure were compared. Graft failure includes primary aplastic graft failure, primary graft failure with autologous recovery, secondary aplastic failure and secondary graft failure with autologous recovery. Incidence of viral infections post-transplant comparing two regimens were also determined.Results: Total of 99 patients were studied who underwent HCT for IMDs during the study period. Sixty-four received BuCy conditioning and 35 received BuFlu. Hurler syndrome (46%) and adrenoleukodystrophy (43%) were most common IMDs transplanted and umbilical cord blood was the most common donor source (74%). One-year overall survival was similar in both groups (81.2% in BuCy vs. 85.5% in BuFlu; p=0.8) with a similar incidence of grade 3-4 acute GVHD (9% in BuCy vs. 6% in BuFlu; p=0.5) and chronic GVHD (9% in BuCy vs. 7% in BuFlu; p=0.67) in the two groups. Neutrophil and platelet recovery were similar in both groups with significantly shorter duration of hospital stay noted in BuFlu group (median 21 d vs. 34 d, p = 0.002). The cumulative incidence of graft failure was higher with BuFlu conditioning (29% vs 14%, p= 0.08, Figure 1a). Significantly higher rates of second HCT was noted following BuFlu conditioning (27% vs. 3%, p= 0.001; Figure 1b). The incidence of adenoviral infection (14% vs. 0%, p=0.02) and hemorrhagic cystitis (23% vs. 3%, p=0.01) were notably higher in the BuCy group. Though donor myeloid engraftment was similar in both groups, donor T-cell engraftment occurred sooner with BuCy conditioning until 1-year post transplant (Figure 2).Conclusions: Reduced toxicity conditioning leads to lower rates of infections and other transplant related complications, but is associated with a high rate of graft failure in patients with IMD. Alternate immune suppressive agents should be considered to reduce graft failure and minimize toxicities. Alternate donor options, including expanded UCB, should also be considered to improve engraftment in patients with IMDs. [Display omitted] DisclosuresShanley:Magenta Therapeutics: Research Funding. Miller:Sangamo Therapeutics: Employment. Orchard:Magenta Therapeutics: Research Funding.

Addition of Melphalan to Fludarabine/Busulfan (FLU/BU4/MEL) Provides Survival Benefit for Patients with Myeloid Malignancy Following Allogeneic Bone Marrow Transplantation/Peripheral Blood Stem Cell Transplantation

A combination regimen of fludarabine and myeloablative busulfan (FLU/BU4) has been widely used as a myeloablative conditioning regimen with reduced intensity for myeloid malignancies. However, FLU/BU4 has two major disadvantages. A disadvantage is the insufficient anti-leukemic effect in advanced cases. Although the overall survival (OS) after FLU/BU4 treatment is approximately 50-80% for myeloid malignancies in the 1st complete remission (CR), the regimen could result in unsatisfactory outcomes with 19-32% OS in patients with advanced disease (Shimoni 2010; Alatrash 2011). Another disadvantage is the slow achievement of complete donor-type chimerism, especially T-cell chimerism (Rambaldi 2015), which also affects the outcome of allogeneic hematopoietic stem cell transplantation (allo-HCT), particularly relapse (Peterlin 2015).To overcome these issues, we designed a combination regimen with FLU, intravenous (IV) BU, and melphalan (FLU/BU4/MEL) and conducted retrospective analyses in this study. The FLU/BU4/MEL regimen consisted of 30 mg/m2 FLU for 5 days (150 mg/m2), 3.2 mg/kg BU for 4 days (12.8 mg/kg), and 50 mg/m2 MEL for 2 days (100 mg/m2) administered by IV infusion. A total body irradiation of 3 Gy was given in cases of unrelated transplantation, and 5 mg/kg anti-thymocyte globulin (Thymoglobuline®) was given for human leukocyte antigen-mismatched transplantation.Between January 2009 and March 2016, 42 patients, including 33 with acute myeloid leukemia and 9 with myelodysplastic syndromes, received allogeneic bone marrow transplantation or peripheral blood stem cell transplantation (allo-BMT/PBSCT) with the FLU/BU4/MEL regimen in our institute. The median patient age at transplantation was 46.5 years (range: 20-63 years), and the median follow-up time was 1513.5 days (214-2975 days). At transplantation, 29 (69%) patients were in hematological CR, and 13 (31%) patients were not in CR. Most of the patients received standard prophylaxis for graft-versus-host disease (GVHD) with IV tacrolimus or cyclosporin A and methotrexate. The rate of neutrophil and platelet engraftment was 100% and 95.2% (95% CI: 81.6-98.8%), respectively, and the median time for their engraftment was 19 days (13-30 days) and 25 days (14-108 days), respectively. Among the patients who were examined for chimerism in the whole blood or T-cell fraction at day 28 after transplantation (n=32 in whole blood; n=16 in T-cell fraction), complete donor chimerism was achieved. Febrile neutropenia and severe (≧grade 3) oral/pharyngeal mucositis occurred in more than 80% of the patients. Although sinusoidal obstruction syndrome did not occur, thrombotic microangiopathy (TMA) occurred in 4 (10%) patients. The cumulative incidence of grade II-IVacute GVHD at day +100 was 42.2% (25.0-55.6%), and the cumulative incidence of moderate-to-severe chronic GVHD was 33.0% (14.4-53.0%).At the last follow-up, 28 of 42 patients were alive, and 14 patients died because of infection (n=9; bacterial: 8, viral: 1), relapse (n=2), interstitial pneumonia (n=2), and TMA (n=1). The 1-year OS, disease-free survival (DFS), non-relapse mortality (NRM), and relapse rate (RR) of all patients were 73.7% (57.5-84.5%), 66.7% (50.3-78.7%), 19.0% (8.8-32.2%), and 14.3% (5.7-26.7%), respectively, and the 4-year OS, DFS, NRM, and RR were 66.0% (49.4-78.3%), 59.5% (43.2-72.6%), 19.0% (10.2-32.1%), and 21.4% (10.5-34.9%), respectively. Among patients who were not in CR at allo-HCT, the 4-year OS and DFS were 49.4% (19.7-73.6%) and 38.5% (14.1-62.8%), respectively. These results indicated an improvement in the OS of patients with uncontrolled disease after the addition of MEL to FLU/BU4. In contrast, although the RR among patients who were in CR at allo-HCT was exceedingly low (1-year: 0.0% (0.0-0.0%); 4-year: 3.4% (0.2-15.4%)), the NRM after HCT in this group was relatively high (day +100: 13.8% (4.2-28.9%); 1-year: 24.1% (10.4-40.9%); 4-year: 27.6% (12.8-44.6%)). The most frequent cause of NRM in this group was bacterial infection, which was closely related to the high incidence of mucositis. Given the extremely low RR, the FLU/BU4/MEL regimen can be modified to reduce NRM in such cases.In conclusion, FLU/BU4/MEL had curative potential even for patients with advanced myeloid malignancies, accompanied by the rapid complete chimerism achievement after allo-BMT/PBSCT. The NRM should be minimized to further improve the outcomes. DisclosuresYokota:Bristol-Myers Squibb: Research Funding; Pfizer Inc.: Research Funding; MSD K.K.: Research Funding; CHUGAI PHARMACEUTICAL CO., LTD.: Research Funding; Celgene: Research Funding. Shibayama:Bristol-Meyer Squibb K.K: Honoraria, Research Funding; Novartis Pharma K.K.: Honoraria, Research Funding; Fujimoto Pharmaceutical: Honoraria, Research Funding; Ono Pharmaceutical Co.,LTD: Honoraria, Research Funding; Jansen Pharmaceutical K.K: Honoraria; Mundipharma K.K.: Honoraria, Research Funding; Takeda Pharmaceutical Co.,LTD.: Honoraria, Research Funding; Celgene K.K.: Honoraria, Research Funding. Tomiyama:Sysmex Corporation: Consultancy; Chugai Pharmaceutical Co., Ltd.: Honoraria; Novartis Pharma Co., Ltd.: Honoraria, Membership on an entity's Board of Directors or advisory committees; Kyowa Hakko Kirin Co., Ltd.: Honoraria. Kanakura:Alexion Pharmaceuticals, Inc.: Consultancy, Honoraria, Research Funding.

Outcomes for Initial Patient Cohorts with up to 33 Months of Follow-up in the Hgb-206 Phase 1 Trial

Outcomes for Initial Patient Cohorts with up to 33 Months of Follow-up in the Hgb-206 Phase 1 Trial

Flipping the Switch: Initial Results of Genetic Targeting of the Fetal to Adult Globin Switch in Sickle Cell Patients

▪Autologous gene therapy (GT) for beta-hemoglobinopathies has demonstrated encouraging early safety and efficacy using addition of a sickling-resistant globin gene to stem cells. Another therapeutic strategy for sickle cell disease (SCD) is erythroid-specific inactivation of BCL11A, which is a validated repressor of gamma globin expression (Sankaran et al. Science 2011). This approach has the distinct advantage of simultaneously inducing fetal hemoglobin (HbF) while coordinately decreasing sickle hemoglobin (HbS). Since hemoglobin (Hb) polymerization in sickle red cells is highly dependent on the intracellular concentration of HbS and is strongly inhibited by HbF, effective BCL11A repression should prevent the sickling phenotype within red cells. We have shown that erythroid-specific expression of microRNA-adapted shRNAs (shRNAmiR) targeting BCL11A effectively induces HbF in human erythroid cells derived from transduced HSCs, largely attenuating the hematologic effects of SCD in a murine model while avoiding negative effects in HSCs and B lymphocytes (Brendel et al. JCI 2016). Here we report the initial results of a pilot clinical study utilizing a shRNAmiR lentiviral vector (LVV) targeting BCL11A for autologous GT in SCD patients.Transduction of hematopoietic cells with GMP lentiviral vector (BCH_BB-LCRshRNA(miR)) expressing the shRNAmiR for BCL11A in an erythroid-specific fashion showed no toxicity in engraftment and genotoxicity assays, efficient transduction rates of 80-95% of CD34+-derived erythroid colony forming cells from healthy donors and SCD patients, and >95% of transduced erythroid colonies demonstrating HbF levels of 50-95% of total Hb. Transduction at clinical scale with plerixafor mobilized CD34+ cells from three SCD donors yielded vector copies of 3.7 - 5.2/cell.Patients with severe SCD were screened for eligibility according to an IND enabled, IRB-approved investigator-initiated protocol. The first cohort included patients ≥ 18 years old. After at least 3 months of protocol-required transfusions, autologous CD34+ cells were collected by plerixafor mobilization and apheresis, and then transduced under GMP conditions with the BCH_BB-LCRshRNA(miR) vector. As of July 28, 2018, 3 patients representing the adult cohort had undergone a total of 3 (n=2) or 4 (n=1) days of mobilization. Mean single-day apheresis yields were 3.2 (range 1.5 - 6.8) x 106 CD34+ cells/kg. No Grade 3 or 4 AEs were attributed to mobilization and collection, although one subject developed an incidentally-discovered line-associated atrial clot and pulmonary embolism. Transduced cell products for these 3 patients have cell doses of 3.3 - 6.7 x 106 CD34+ cells/kg, VCN of 3.3 - 5.1 copies per cell and >95% vector-positive CD34+-derived colonies. One subject (BCL002), who had been regularly transfused for 17 years, has undergone infusion of gene-modified cells after myeloablative busulfan conditioning and achieved neutrophil engraftment after 22 days. Post-infusion follow-up is 78 days. At the time of the last analysis 76 days after GT and 64 days after last RBC transfusion (Table 1) subject BCL002 had a sustained Hb of >10 g/dL and, compared to pre-GT, there was a notable absence of irreversibly sickled cells on peripheral smear and a persistently low absolute reticulocyte count consistent with markedly reduced hemolysis. Hb electrophoresis showed 23.3% HbF, 51.8% HbS and 22.3% HbA (from residual transfused cells) with a HbF/(HbF+HbS) ratio of 29.7%. At day 76, the number of F cells had risen to 59.7% with 12pg HbF/F cell. In flow-sorted immature erythroid cells γ-globin mRNA was >80% of total β-like globins in the graft-derived population and BCL11A protein was reduced by ~90%. Adverse events observed from the start of conditioning until latest follow-up were consistent with myeloablative conditioning, and there have been no product-related adverse events and no SCD-related complications.These early results show: (1) feasibility of enrollment, cell procurement, and GMP manufacturing of gene modified CD34+ cells in 3 adult SCD patients; (2) the first proof of principle demonstrating shRNAmiR-based gene knockdown in humans, and (3) successful rapid induction of HbF in the first patient infused, with marked attenuation of hemolysis in the early phase of autologous reconstitution. Based on the trajectory of increasing HbF/(HbF+HbS), near full suppression of the SCD phenotype is expected. [Display omitted] DisclosuresEsrick:Bluebird Bio: Honoraria. Negre:bluebird bio: Other: Spouse employed by bluebird Bio. Dansereau:Bluebird Bio: Consultancy. Braunewell:Bluebird Bio: Employment, Equity Ownership. Christiansen:Bluebird Bio: Employment, Equity Ownership, Other: Salary. Nikiforow:Kite Pharma: Consultancy. Achebe:Luitpold Pharmaceutical: Consultancy; AMAG Pharmaceuticals, Inc.: Membership on an entity's Board of Directors or advisory committees; Syros pharmaceuticals: Consultancy. Negre:Bluebird Bio: Employment, Equity Ownership, Other: Salary. Heeney:Sancilio Pharmaceuticals: Consultancy, Research Funding; Ironwood: Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees; Vertex/Crisper: Other: Data Monitoring Committee; Pfizer: Research Funding; Astra Zeneca: Consultancy, Research Funding. Williams:Bluebird Bio: Research Funding.

Lentiglobin Gene Therapy for Patients with Transfusion-Dependent β-Thalassemia (TDT): Results from the Phase 3 Northstar-2 and Northstar-3 Studies

Lentiglobin Gene Therapy for Patients with Transfusion-Dependent β-Thalassemia (TDT): Results from the Phase 3 Northstar-2 and Northstar-3 Studies

HLA Class I Alloimmunization and Platelet Transfusion Support in HLA-Identical Bone Marrow Transplant for Sickle Cell Disease: A Sickle Transplant Alliance for Research Study

Introduction: HLA alloimmunziation has been described in patients, including pediatric patients with sickle cell disease (SCD), who received only leukocyte-reduced red blood cell (RBC) transfusions. While HLA alloimmunization has significant implications in bone marrow transplant (BMT) with an HLA-disparate donor (donor-specific HLA antibodies increase the risk of graft rejection), the clinical significance of this alloimmunization in HLA-identical BMT is unclear. In particular, it is unknown whether HLA class I alloimmunization affects platelet transfusion support during BMT. Platelet transfusions are especially important in BMT for SCD because of the historic high incidence of intracranial bleeding and the subsequent adoption of a relatively high platelet transfusion threshold.Methods: We tested for HLA class I alloimmunization using pre-BMT serum or plasma from 32 pediatric patients with SCD undergoing BMT with an HLA-identical sibling donor. HLA class I alloimmunization was evaluated using the FlowPRA® (panel reactive antibody) screening test which detects IgG antibodies to the majority of HLA class I antigens. Pre-BMT, patients had received leukocyte-reduced RBC transfusions. All patients undergoing BMT received leukocyte-reduced, irradiated, apheresis platelet transfusions to maintain a platelet count greater than 50 x 109/L. The number of platelet transfusions received in the first 45 days post-BMT was compared between those with a positive PRA versus those with a negative PRA using a two-sample t-test.Results: Among the 32 patients studied, the mean age at BMT was 9.4 years (range 1-21 years). Pre-BMT, 40% had received greater than 10 RBC transfusions and 32% of the entire cohort was receiving chronic RBC transfusions. BMT conditioning regimens included: traditional myeloablative busulfan, cyclophosphamide, antithymocyte globulin (BU-CY-ATG) (n=10); dose-reduced BU-CY-ATG + fludarabine (flu) (n=16); reduced intensity conditioning (RIC) alemtuzumab, flu, melphalan +/- thiotepa (n=5); and RIC BU-flu-ATG (n=1). All patients received HLA-identical sibling donor bone marrow, with 3 patients receiving a combined bone marrow and cord blood graft. All patients engrafted with 100% survival at day +45. Six patients developed acute graft-versus-host disease (GVHD): 1 grade I, 3 grade II, 1 grade 3, 1 grade 4. No patient had an intracranial bleed or other serious bleeding.From testing of the pre-BMT sample, 11/32 (34%) of patients had a positive HLA class I antibody screen. HLA class I alloimmunized patients received significantly more platelet transfusions than non-alloimmunized patients: mean 19.2 (SD 13.9) vs. 11.2 (SD 8.0) transfusions, p=0.049 (Figure). On univariate analysis, age, sex, conditioning regimen, and GVHD were each not significantly associated with the number of platelet transfusions (p>0.1). Only two patients developed hepatic sinusoidal obstruction syndrome (one HLA alloimmunized patient, one non-alloimmunized patient). Mean day of platelet engraftment was not significantly different between alloimmunized compared to non-alloimmunized patients: day +34.6 (SD 10.6) vs. day +30.2 (SD 11.3), p=0.28. Among HLA class I alloimmunized patients, the mean positive PRA was 19.7% (range 4-55%); there was no association with this PRA value and the number of platelet transfusions (r2=0.0064, p=0.81).Conclusion: In pediatric HLA-identical sibling BMT for SCD, pre-BMT HLA class I alloimmunization (but not the absolute PRA value) appears to be associated with more platelet transfusions. It is unclear if this increased platelet transfusion requirement is due directly to HLA antibody immune-mediated clearance of transfused platelets or other inherent differences of HLA class I alloimmunized patients. [Display omitted] DisclosuresQayed:Novartis: Consultancy.

Reduced Intensity Vs. Myeloablative Conditioning Followed By Allogeneic Stem Cell Transplantation for Patients with Myelodysplastic Syndrome: Long Term Follow-up of a Prospective Randomized EBMT Phase III Study (RICMAC-Trial)

IntroductionRetrospective studies in MDS/sAML suggest that reducing the intensity of the conditioning regimen prior to allogeneic stem cell transplantation reduces the risk of non-relapse mortality but is associated with a higher risk of relapse. A higher risk of relapse after RIC was confirmed in a prospective BMT CTN study but the prospective randomized studies from the EBMT for MDS and sAML did not show a difference in outcome after 2 years (J Clin Oncol. 2017 Jul 1;35(19):2157-2164). Here we present a long term follow-up of the study after a median follow-up of 75 months (range 4-150 months).MethodsWithin the European Society of Blood and Marrow Transplantation (EBMT) we conducted a prospective, multicenter, open label, randomized phase III trial comparing comparing a busulfan based (Busulfan 8mg/kg orally or equivalent dosis intravenously (iv) plus fludarabin 180mg/m²) reduced intensity conditioning regimen (RIC) and a standard myeloablative busulfan (Busulfan 16mg/kg orally or equivalent dosis iv plus cyclophosphamide 120mg/kg) based regimen (MAC) in patients with MDS or sAML (<20 % blasts). Between May 2004 and December 2012, a total of 129 patients were enrolled from 18 centers. Patients were randomly assigned in a 1 : 1 ratio and stratified according to donor, age and blast count.ResultsIn the first report (JCO 2017) the CI of NRM after 1 year was 17% (95% CI 8-26%) after RIC and 25% (95% CI 15-36%) after MAC (p = 0.29). The CI of relapse at 2 years was 17% (95% CI 8-26%) after RIC and 15% (95% CI 6-24%) after MAC (p = 0.6), resulting in a 2 year relapse-free and overall survival of 62% (95% CI 50-74%) and 76% (95% CI 66-87%) after RIC and 58% (95% CI 46-71%) and 63% (95% CI 51-75%) after MAC (p = 0.58 and p = 0.08, respectively). In the current follow-up study, all cases but one who were alive at last report could be updated. The median follow-up is now 75 months in the MAC and 72 months in the RIC arm. Since last follow-up =18 death occurred in both arm (MAC n=8, RIC n=10) 8 relapses (MAC n=4; RIC n=4) and 6 NRM (MAC n=2; RIC n=4). Second allogeneic stem cell transplantation was performed in 18 patients (n=10 in RIC and n=8 in MAC) due to graft failure (n=4) relapse (n=11) and others (n=3). The CI of chronic GvHD at 5 years was 65% (95% CI: 53-78) after RIC and 68% after MAC ((95% CI: 55-81; p = 0.70). At 5 years there was no difference in CI of NRM (22%, 95%CI: 12-32 vs 30% , 95%CI : 19-42, p=0.5) in CI of Relapse (22% , 95% CI: 12-32 vs18%, 95% CI: 8-28, p= 0.7), Relapse free- (57%, 95% CI: 44-69 vs51%, 95% CI: 39-64, p=0.8) and Overall survival (69%, 95% CI: 58-80 vs 53%, 95% CI: 40-65, p=0.15) between RIC and MAC, respectively.ConclusionThis long term follow-up of the prospective randomized EBMT trial confirmed early results that RIC resulted in at least similar long term relapse-free and overall survival as MAC in patients with MDS or sAML. The trial was registered under ClinicalTrials.gov Identifier: NCT01203228. DisclosuresNiederwieser:Miltenyi: Speakers Bureau; Novartis: Research Funding. Platzbecker:Celgene: Research Funding. Scheid:Celgene: Honoraria; Janssen: Honoraria; Novartis: Honoraria, Research Funding; Takeda: Honoraria, Research Funding; BMS: Honoraria; Amgen: Honoraria. Stelljes:MSD: Consultancy; Amgen: Honoraria; JAZZ: Honoraria; Pfizer: Consultancy, Honoraria, Research Funding; Novartis: Honoraria. Heim:Novartis: Research Funding. Bethge:Miltenyi Biotec GmbH: Consultancy, Honoraria, Research Funding; Neovii GmbH: Honoraria, Research Funding. Kobbe:Roche: Honoraria, Research Funding; Amgen: Honoraria, Research Funding; Celgene: Honoraria, Other: Travel Support, Research Funding.

Fludarabine with a higher versus lower dose of myeloablative timed-sequential busulfan in older patients and patients with comorbidities: an open-label, non-stratified, randomised phase 2 trial

Haemopoietic stem-cell transplantation (HCT) conditioning regimens that can reduce risk of relapse without increasing non-relapse mortality are needed. We aimed to test the safety of timed-sequential delivery of low-dose versus high-dose myeloablative busulfan in older patients and patients with comorbidities. This non-stratified, open-label, randomised phase 2 trial was done at The University of Texas MD Anderson Cancer Center (Houston, TX, USA). Patients with haematological cancers aged between 5 and 75 years were eligible to participate in the study. Patients who had HIV or uncontrollable infections were excluded. Eligible patients were randomly assigned (1:1 by a computer-generated programme in block sizes of four) to receive a total intravenous busulfan dose to achieve an area under the curve of 16 000 μmol/min (16K group) or 20 000 μmol/min (20K group) on the basis of pharmacokinetic analysis, plus intravenous fludarabine 40 mg/m2 for 4 days. The investigators and the research nurses were masked to the block size to conceal allocation. The primary outcome was day 100 non-relapse mortality. All analyses were by modified intention to treat, including only patients who received at least one dose of the study drug. No interim analyses were planned and accrual is complete. This study is registered with ClinicalTrials.gov, number NCT01572662. Between April 18, 2012, and Dec 9, 2015, 98 patients were enrolled. 49 patients were randomly assigned to the 16K group and 49 to the 20K group, one of which was removed from the study before starting the intervention. Median age was 60 years (IQR 54-67). 50 (52%) patients had an HCT-specific comorbidity index score of 3 or more, and 41 (42%) had a high or very high Disease Risk Index score. Day 100 non-relapse mortality was 4% (95% CI 0-10) in the 16K group and 6% (0-13) in the 20K group (p=0·65). Infection was the most common grade 3-5 toxicity in both the 20K group (25 [52%] of 48 patients) and the 16K group (24 [49%] of 49 participants). Mucositis (nine [19%] of 48 patients vs three [6%] of 49 patients), idiopathic pneumonia syndrome (nine [19%] of 48 patients vs two [4%] of 49 patients), and culture-negative neutropenic fever (16 [33%] of 48 patients vs eight [16%] of 49 patients) were more common in the 20K group than in the 16K group. Myeloablative doses of busulfan administered in a timed-sequential manner with fludarabine is associated with low non-relapse mortality in older patients and patients with comorbidities. Additional studies are required to show whether this approach can reduce the risk of relapse. Cancer Center Support Grant (US National Cancer Institute, National Institutes of Health).

Evaluation of a Test Dose Strategy for Pharmacokinetically-Guided Busulfan Dosing for Hematopoietic Stem Cell Transplantation

Targeted busulfan dosing helps limit chemotherapy-related toxicity and optimize disease outcomes in hematopoietic stem cell transplantation (HCT). The objective of this study was to evaluate busulfan exposure from a pharmacokinetic (PK)-guided dosing strategy using a test dose. This retrospective evaluation included adult patients who underwent HCT at our institution with busulfan-based myeloablative (>9 mg/kg) conditioning between January 2014 and October 2015. A weight-based test dose of 0.8 mg/kg was used with PK assessments to predict area under the curve (AUCpred) achieved with weight-based dosing, with a target AUC of 4800 µM*minute (AUCtarget). PK from the test dose was then used to calculate a PK-guided first myeloablative busulfan dose. PK assessments were also done after the first dose to assess if the goal area under the curve (AUC) had been achieved (AUCfirst). A PK-guided first dose resulted in achievement of target AUC with target ranges of ±10% in 50% of patients, ±15% in 75%, and ±20% in 94%. This was an improved rate of target achievement compared with the 33%, 44%, and 63% of patients who achieved the desired AUC for these respective target ranges when using weight-based dosing (P = .12, .004, and <.001, respectively). The PK-guided strategy also decreased the variability of AUC from 3.6-fold in AUCpred from the weight-based test doses (2700.8 to 9631 µM*minute; SD, 1211.6 µM*minute) to 1.8-fold in AUCfirst from the PK-guided first doses (3672.1 to 6609.8 µM*minute; SD, 574.7 µM*minute). This reflects a 2-fold improvement in AUC variability with a PK-guided dosing strategy. This is also improved from the 3-fold variability in AUC reported in other studies. Weight and body surface area were significantly associated with the likelihood of AUCfirst being within the ±10% target range (P = .04 for both associations). There was no significant association between AUCfirst and death, relapse, or a composite of the two. These results demonstrate a significant improvement in target AUC attainment and less interpatient variability with PK-guided dosing using a test dose strategy compared with weight-based dosing.

Gene Therapy in Patients with Transfusion-Dependent β-Thalassemia

BackgroundDonor availability and transplantation-related risks limit the broad use of allogeneic hematopoietic-cell transplantation in patients with transfusion-dependent β-thalassemia. After previously establishing that lentiviral transfer of a marked β-globin (βA-T87Q) gene could substitute for long-term red-cell transfusions in a patient with β-thalassemia, we wanted to evaluate the safety and efficacy of such gene therapy in patients with transfusion-dependent β-thalassemia.MethodsIn two phase 1–2 studies, we obtained mobilized autologous CD34+ cells from 22 patients (12 to 35 years of age) with transfusion-dependent β-thalassemia and transduced the cells ex vivo with LentiGlobin BB305 vector, which encodes adult hemoglobin (HbA) with a T87Q amino acid substitution (HbAT87Q). The cells were then reinfused after the patients had undergone myeloablative busulfan conditioning. We subsequently monitored adverse events, vector integration, and levels of replication-competent lentivirus. Efficacy assessments included levels of total hemoglobin and HbAT87Q, transfusion requirements, and average vector copy number.ResultsAt a median of 26 months (range, 15 to 42) after infusion of the gene-modified cells, all but 1 of the 13 patients who had a non–β0/β0 genotype had stopped receiving red-cell transfusions; the levels of HbAT87Q ranged from 3.4 to 10.0 g per deciliter, and the levels of total hemoglobin ranged from 8.2 to 13.7 g per deciliter. Correction of biologic markers of dyserythropoiesis was achieved in evaluated patients with hemoglobin levels near normal ranges. In 9 patients with a β0/β0 genotype or two copies of the IVS1-110 mutation, the median annualized transfusion volume was decreased by 73%, and red-cell transfusions were discontinued in 3 patients. Treatment-related adverse events were typical of those associated with autologous stem-cell transplantation. No clonal dominance related to vector integration was observed.ConclusionsGene therapy with autologous CD34+ cells transduced with the BB305 vector reduced or eliminated the need for long-term red-cell transfusions in 22 patients with severe β-thalassemia without serious adverse events related to the drug product. (Funded by Bluebird Bio and others; HGB-204 and HGB-205 ClinicalTrials.gov numbers, NCT01745120 and NCT02151526.)

439 - Similar Survival but Increased Toxicity with a Sequential Versus Concurrent FluBu4 Regimen

Abstract Combined in vitro treatment with fludarabine and busulfan has been shown to lead to synergistic cytotoxicity. Maximal synergy is achieved when fludarabine is administered immediately prior to busulfan. However, fludarabine and myeloablative busulfan (FluBu4) has been administered in both a concurrent and a sequential, non-overlapping fashion. Because timed sequential regimens are becoming increasingly popular, we sought to compare survival and relapse outcomes as well as toxicity between patients receiving allogeneic stem cell transplant (SCT) with a concurrent 5-day versus a sequential 9-day FluBu4 regimen. We analyzed 102 consecutive patients who received FluBu4 prior to allogeneic SCT between 2003 and 2016. Thirty-seven (36%) patients received the 5-day regimen, which consisted of fludarabine 40 mg/m2 and intravenous busulfan (target AUC 4800 mmol-min per dose) administered daily from Day -5 to Day -2. In 65 (64%) patients, the 9-day regimen was administered, utilizing equivalent doses of fludarabine on day -9 to day -6 and busulfan on day -5 to day -2. All patients received graft-versus-host disease (GVHD) prophylaxis with tacrolimus and methotrexate. Patients undergoing a matched unrelated donor transplant received anti-thymocyte globulin. Baseline characteristics including gender, race, median time to transplant, median lines of prior treatment, disease risk index, hematopoietic cell transplantation-comorbidity index (HCT-CI), donor type, stem cell source, and mean CD34 count were similar between the two groups. Patients in the 9-day group were younger compared to the 5-day group (median age 45 versus 51 years, p=0.003). The majority of patients in both groups were diagnosed with acute myeloid leukemia, myelodysplastic syndrome, or acute lymphoblastic leukemia. The median time to neutrophil and platelet engraftment was not different between the two groups. More patients receiving the 9-day regimen experienced Grade 4 mucositis (53 versus 6 patients, p Median one-year GVHD-free, relapse-free survival (GRFS) was significantly worse for patients receiving a 9-day FluBu4 regimen (68.4 versus 144 days, p=0.032). In a multivariate analysis adjusted for HCT-CI, a trend towards significance was observed with the 5-day regimen predicting for longer GRFS compared to the 9-day regimen (p=0.07). Notably, we observed no differences in overall survival, progression-free survival, or relapse rates between the 5- and 9-day regimen. This is the first study to compare outcomes between a concurrent 5-day and sequential 9-day FluBu4 regimen. We demonstrate similar survival and relapse rates, suggesting that concurrent administration of fludarabine and busulfan may not be necessary for synergistic cytotoxicity. At the same time, we observed increased early toxicity, less MTX administration, and higher aGVHD rates in patients receiving sequential 9-day FluBu4. Contrary to what has been observed with timed sequential regimens, our data suggests that a prolonged administration schedule of conditioning chemotherapy leads to greater toxicity resulting in higher GVHD rates. Disclosures Patel: Celgene: Consultancy, Honoraria.

Reduced-Intensity Conditioning with Busulfan, Fludarabine, and Antithymocyte Globulin for Hematopoietic Cell Transplantation from Unrelated or Haploidentical Family Donors in Patients with Acute Myeloid Leukemia in Remission

To investigate the role of antithymocyte globulin (ATG)-containing reduced-intensity conditioning (RIC) in hematopoietic cell transplantation (HCT) from unrelated (UD) or haploidentical family donors (HFD), we conducted a phase 2 trial of 237 patients (age range, 16 to 69 years) with acute myeloid leukemia (AML) in remission. Patients undergoing UD-HCT (n = 93) or HFD-HCT (n = 59) received RIC comprising busulfan, fludarabine, and ATG, 9 mg/kg, whereas those undergoing HCT from matched sibling donors (MSD, n = 85) received myeloablative busulfan and cyclophosphamide conditioning or aforementioned RIC with ATG, 4.5 mg/kg. For graft-versus-host disease (GVHD) prophylaxis, cyclosporine and methotrexate were administered. The median follow-up period was 44.7 months after HCT for 161 survivors. For UD-HCT versus HFD-HCT, there were no significant differences in leukemia recurrence, nonrelapse mortality, relapse-free survival, grades 2 to 4 acute GVHD, and moderate-to-severe chronic GVHD. Furthermore, when the outcomes of UD-HCT and HFD-HCT were combined and compared with those of MSD-HCT, there were no significant differences in leukemia recurrence (3-year cumulative incidence, 30% versus 29%), nonrelapse mortality (3-year cumulative incidence, 7% versus 8%), relapse-free survival (3-year estimate, 63% versus 63%), and grades 2 to 4 acute GVHD (120-day cumulative incidence, 16% versus 13%). Moderate-to-severe chronic GVHD, however, occurred less frequently in UD/HFD-HCT (2-year cumulative incidence, 22% versus 40%; P = .006). The addition of ATG to conditioning regimen was a significant predictor for less chronic GVHD (subdistribution hazard ratio, .59). In AML in remission, UD/HFD-HCT after ATG-containing RIC achieved leukemia control equivalent to that of MSD-HCT. Despite HLA disparity in UD/HFD-HCT, chronic GVHD occurred less frequently after ATG-containing RIC, suggesting a strong GVHD-modulating effect of ATG.