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Allogeneic hematopoietic stem cell transplantation (HSCT) is the gold standard curative therapy for infants and children with many inborn errors of immunity (IEI), but adolescents and adults with IEI are rarely referred for transplant. Lack of published HSCT outcome data outside small, single-center studies and perceived high risk of transplant-related mortality have delayed the adoption of HSCT for IEI patients presenting or developing significant organ damage later in life. This large retrospective, multicenter HSCT outcome study reports on 329 IEI patients (age range, 15-62.5 years at HSCT). Patients underwent first HSCT between 2000 and 2019. Primary endpoints were overall survival (OS) and event-free survival (EFS). We also evaluated the influence of IEI-subgroup and IEI-specific risk factors at HSCT, including infections, bronchiectasis, colitis, malignancy, inflammatory lung disease, splenectomy, hepatic dysfunction, and systemic immunosuppression. At a median follow-up of 44.3 months, the estimated OS at 1 and 5 years post-HSCT for all patients was 78% and 71%, and EFS was 65% and 62%, respectively, with low rates of severe acute (8%) or extensive chronic (7%) graft-versus-host disease. On univariate analysis, OS and EFS were inferior in patients with primary antibody deficiency, bronchiectasis, prior splenectomy, hepatic comorbidity, and higher hematopoietic cell transplant comorbidity index scores. On multivariable analysis, EFS was inferior in those with a higher number of IEI-associated complications. Neither age nor donor had a significant effect on OS or EFS. We have identified age-independent risk factors for adverse outcome, providing much needed evidence to identify which patients are most likely to benefit from HSCT. ispartof: BLOOD vol:140 issue:14 pages:1635-1649 ispartof: location:United States status: published

Dedicator of cytokinesis (DOCK) proteins play a central role in actin cytoskeleton regulation. This is highlighted by the DOCK2 and DOCK8 deficiencies leading to actinopathies and immune deficiencies. DOCK8 and DOCK11 activate CDC42, a RHO-GTPase involved in actin cytoskeleton dynamics, among many cellular functions. The role of DOCK11 in human immune disease has been long suspected but has never been described so far. We studied eight male patients, from seven unrelated families, with hemizygous DOCK11 missense variants leading to reduced DOCK11 expression. The patients were presenting with early-onset autoimmunity, including cytopenia, systemic lupus erythematosus, skin, and digestive manifestations. Patients' platelets exhibited abnormal ultrastructural morphology and spreading as well as impaired CDC42 activity. In vitro activated T cells and B lymphoblastoid cell lines (B-LCL) of patients exhibited aberrant protrusions and abnormal migration speed in confined channels concomitant with altered actin polymerization during migration. A DOCK11 knock-down recapitulated these abnormal cellular phenotypes in monocytes-derived dendritic cells (MDDC) and primary activated T cells from healthy controls. Lastly, in line with the patients' autoimmune manifestations, we also observed abnormal regulatory T cells (Tregs) phenotype with profoundly reduced FOXP3 and IKZF2 expression. Moreover, we found a reduced T cell proliferation and an impaired STAT5B phosphorylation upon IL2 stimulation of the patients' lymphocytes. In conclusion, DOCK11 deficiency is a new X-linked immune-related actinopathy leading to impaired CDC42 activity and STAT5 activation, and associated with abnormal actin cytoskeleton remodeling as well as Tregs phenotype culminating in immune dysregulation and severe early-onset autoimmunity.

In these two short reports, the authors approach the issue of whether hydroxyurea (HU) use in young males has major irreversible effects on sperm production. Joseph et al analyzed and compared sperm parameters in male patients with sickle cell disease (SCD) who were exposed or not exposed to HU before puberty. They report semen abnormalities in all patients but no differences between groups. Independently, Gille et al provide evidence for the lack of in vivo HU-related decreases in the spermatogonial pool in biopsy specimens from young males with SCD but evidence for a negative effect of SCD itself. Together, these reports suggest that the use of HU in young males does not adversely affect fertility.

Introduction Pediatric-onset Evans syndrome (pES) is defined by the association between immune thrombocytopenic purpura (ITP) and autoimmune hemolytic anemia (AIHA) before the age of 18 years and may be associated to various immunopathological manifestations (IMs). No comprehensive study of this rare disease exists, and its long-term outcomes are poorly described. Methods Patients from the nationwide French prospective OBS'CEREVANCE cohort with pES and more than 5 years of follow-up were included (excepted pES secondary to bone marrow transplantation or primary immunodeficiencies known at the inclusion). All patients, including those with less than 5 years of follow-up, were included in survival analyses. Multivariate Cox proportional hazards model was used to analyze factors associated with time-dependent variables. Results Of the 216 patients with pES in the cohort, 151 (88 males and 63 females) were included with a median (min-max) follow-up time after first cytopenia diagnosis of 11.3 (5.1-38) years. Median age at final follow-up was 18.5 (6.8-50.0) years. The proportion of patients achieving a sustained complete response (i.e. persisting until final follow-up) increased after cytopenia onset (Fig. 1A). ITP and AIHA were in complete remission in 40.5% and 54.5%, 74.1% and 62.3%, and 78.4% and 86% of patients at 5, 10, and 15 years, respectively. Clinical IMs (cIMs) developed in 100/151 patients (66%), before the first diagnosis of cytopenia in 21/100 cases. The number of cIMs increased over time (Fig. 1B). The proportions of patients with one and more than one cIM were 50% and 14%, 57% and 19%, and 81% and 44% at 5, 10, and 15 years after the first cytopenia diagnosis, respectively. A broad spectrum of cIMs were present, lymphoproliferation (n = 71), dermatological (n = 26), gastrointestinal/hepatic (n = 23), and pneumological manifestations (n = 16) being the most common. Three patients had a hematological malignancy. Biological IMs (bIMs) were diagnosed in 101/151 patients (67%) and also increased over time, with hypogammaglobulinemia (n = 54) being the most common. Autoimmune neutropenia developed in 43 patients (28.5%) and was independently associated with the number of cIMs (hazard ratio [HR], 2.4; 95% confidence interval [CI], 1.5-3.8; p = 0.0002). Severe or recurrent infections were present in 53 patients (35%). The number of second-line treatments received (i.e. other than steroids and immunoglobulins) increased over time without reaching a plateau (Fig. 1C). Half of the patients had received at least one, two, and three different treatments at 2.7, 10.5, and 14.7 years after the first cytopenia diagnosis, respectively. The number of cIMs was independently associated with the number of second-line treatments received (HR, 1.3; 95% CI, 1.08-1.6; p = 0.006). Systemic lupus erythematosus (SLE) was diagnosed in 11/151 patients (7.3%, 1/88 males and 10/63 females) and autoimmune lymphoproliferative syndrome (ALPS) in six (4.0%). Sixteen of the 151 patients followed for more than 5 years (10.6%) died, and seven died before the fifth year of follow-up (23 deaths in total). Survival at 5, 10, and 15 years after the first cytopenia was 97%, 92%, and 84%, respectively (Fig. 1D). Deaths occurred regularly throughout the follow-up period, at a median age of 18.0 (1.7-31.5) years. The most frequent cause of death was infections (n = 12, 52%). Four patients (18%) died of hemorrhage, all were less than 13 years old. The numbers of second-line treatments (HR, 1.3; 95% CI, 1.1-1.6; p = 0.004) and severe or recurrent infections (HR, 3.4; 95% CI, 1.2-9.7; p = 0.02) were independently associated with mortality after 5 years of follow-up. Overall, 20-year-old compared to 10-year-old patients more frequently showed a sustained complete response for AIHA (72% vs. 30%) and ITP (50% vs. 26%), but more frequently had cIMs (74% vs. 37%), bIMs (75% vs. 39%), and ongoing second-line treatments (88% vs. 47%; p < 0.001 for all comparisons). Conclusions Long-term outcomes of pES were associated to IMs and second-line treatment burden, not active cytopenia. The significant mortality rates, mostly among adolescents and young adults, were linked to drug-induced and/or constitutive immunodeficiencies. Few cases were associated with SLE or ALPS, which is consistent with a heterogeneous genetic background. These results highlight the importance of multidisciplinary care during the transition from childhood to adulthood. Figure 1 Disclosures No relevant conflicts of interest to declare.

Subcutaneous panniculitis-like T-cell lymphoma (SPTCL) is a distinct subset of cutaneous lymphomas in which neoplastic cytotoxic α/β CD8+ T cells infiltrate subcutaneous adipose tissue.1-3 SPTCL may affect both children and adults.4 Systemic symptoms such as fever, asthenia, and weight loss, associated with cytopenias and liver dysfunction, are common. In addition, hemophagocytic lymphohistiocytosis (HLH) is observed in 20% of cases,3 which is associated with poor prognosis and may be the leading cause of death.3 There is no standardized therapy for SPTCL alone or in association with HLH. Chemotherapy with cyclophosphamide, doxorubicin, vincristine, and prednisolone is frequently used, with an overall remission rate of 50%.1 Immunosuppressive regimens, particularly cyclosporine A (CsA), may be also effective.5 In some severe cases, stem cell transplantation has been attempted.1 Recently, germline mutations causing loss of function of T-cell immunoglobulin mucin 3 (TIM-3) were identified in 60% to 85% of SPTCL patients.6,7 In these patients, TIM-3 deficiency was shown to promote T-lymphocyte and -macrophage activation and the production of proinflammatory cytokines, challenging the malignant nature of skin T-lymphocyte infiltration.6 Ruxolitinib is a selective JAK1/JAK2 inhibitor licensed for treatment of myelofibrosis and polycythemia vera in adults.8,9 Studies in animal models of HLH support the efficacy of this drug to prevent and treat HLH in these models.10,11 Anecdotal experiences of successful use of ruxolitinib to control refractory primary HLH or secondary HLH are also reported in humans.12-19 JAK1/JAK2 inhibitors are also increasingly used in inflammatory diseases. We herein report the use and efficacy of ruxolitinib in a patient with recurrence of SPTCL and HLH and in whom TIM-3 deficiency was recently identified.6

Severe Combined Immunodeficiencies (SCID) are defined by a complete absence of T lymphocytes in the blood and lymphoid organs, with variable defects in other WBC subsets depending on the gene defect. From a clinical perspective SCIDs are characterized by early development of life-threatening infections accounting for early death if untreated. The treatment of choice is allogeneic HSCT with very high success rates if a HLA identical sibling (MRD) or unrelated donor (MUD) is used. However, due to the scarcity of matched-related donors, SCID can benefit from haploidentical HSCT. In contrast to the continuous improvement of HLA compatible donor transplantations, no significant improvements have been obtained over the last twenty years for haploidentical HSCT. The profound immunodeficiency during the first months following haploidentical HSCT exposes patients to opportunistic viral, bacterial and fungal infections, which account for approximately 30-40% of the transplant related mortality (TRM). The rapid restoration of the T-cell compartment is the main aim of stem cell therapy in this setting. To this end we have recently set up a phase I/II clinical trial (ClinicalTrials.gov Identifier: NCT03879876) aiming to accelerate the immune reconstitution by injection of ex vivo generated Human T lymphoid progenitors (ProTcell TM) following haploidentical HSCT. T cell progenitors in this trial are generated in vitro within 7 days from mobilized peripheral blood (mPB) CD34 + hematopoietic stem and precursor cells (HSPCs) using our Notch ligand Delta-like 4 GMP culture platform so called SMART Immune's SMART101 product. This open-label, non-randomized study evaluates safety and efficacy of the SMART101 injection following CD34 + selected, haploidentical HSCT in SCID patients and is designed as a dose-escalation study comprising 6 doses of the SMART101 product obtained from the patient's haploidentical stem cell graft. The aim of this protocol is to define the highest efficacy dose without any toxicity. The conditioning regimen is based on Busulfan and Fludarabine according to IE-WP/EBMT guidelines with upfront administration of ATG to prevent graft rejection. Tight monitoring of ATG serum levels is applied in order to assure injection of SMART101 when ATG is below the lymphotoxicity threshold. Here we report the results of the first two SCID patients. P1 presented a homozygous Artemis deficiency. At diagnosis he had an ALC of 341/µl, with complete absence of T cells (CD3 + < 4/µl, CD4 + < 1/µl, CD8 + < 2/µl) and B cells (CD19 + 0/µl). NK cells were present in the normal range for age (CD16 +CD56 + 331/µl). In the absence of an HLA compatible donor, the patient`s father was chosen as haploidentical stem cell donor. P1 received upfront ATG (5 mg /kg total dose), Busulfan (AUC of 16058 microM.min) and Fludarabine (160 mg/m²). He received Defibrotide prophylaxis from D0 until D+21, as well as Ursodeoxycholic acid until D+80. The CD34 + immunoselected graft contained 1.04 x 10 8 nucleated cells/kg with 24.15 x10 6 CD34 + cells/kg and 4000 CD3 + cells/kg on D0. After ATG monitoring 0.12x10 6 Smart101 cells were administered at D+14 post- HSCT. In the follow-up P1 didn't develop any acute or chronic SAEs, no acute or chronic GVHD, and no infection. He was discharged at D+121 post HSCT. The day +100 post transplantation CD4 + cell count/microliter exceeded 10 times the CD4 + count of our historical cohort of RAG1/2 or Artemis deficient patients transplanted with haploidentical HSCT alone following the same conditioning regimen. At 6 months post HSCT this difference remains important (851 versus 300 CD4 + cells/µl); Ig replacement therapy could be stopped as early as 9 months post transplantation and vaccinations have been started. At last follow up; almost 14 months post HSCT P1 is alive and well. P2 had an undefined molecular SCID diagnosis. She has been treated with the same conditioning regimen and received the second dose of 0.2x10 6 CD7 + cells, but unfortunately died from severe VOD emphasizing the need to replace chemotherapy with less toxic myeloablative agents. The preliminary results obtained after injection of Human T lymphoid progenitors in P1 are encouraging. While deserving confirmation in larger numbers of patients they could represent an important step forward in improving the outcome of haploidentical HSCT for SCID. Disclosures Cavazzana: Smart Immune: Other: co-founder.

ARPC1B is a key factor for the assembly and maintenance of the ARP2/3 complex that is involved in actin branching from an existing filament. Germline biallelic mutations in ARPC1B have been recently described in 6 patients with clinical features of combined immunodeficiency (CID), whose neutrophils and platelets but not T lymphocytes were studied. We hypothesized that ARPC1B deficiency may also lead to cytoskeleton and functional defects in T cells. We have identified biallelic mutations in ARPC1B in 6 unrelated patients with early onset disease characterized by severe infections, autoimmune manifestations, and thrombocytopenia. Immunological features included T-cell lymphopenia, low numbers of naïve T cells, and hyper–immunoglobulin E. Alteration in ARPC1B protein structure led to absent/low expression by flow cytometry and confocal microscopy. This molecular defect was associated with the inability of patient-derived T cells to extend an actin-rich lamellipodia upon T-cell receptor (TCR) stimulation and to assemble an immunological synapse. ARPC1B-deficient T cells additionally displayed impaired TCR-mediated proliferation and SDF1-α−directed migration. Gene transfer of ARPC1B in patients’ T cells using a lentiviral vector restored both ARPC1B expression and T-cell proliferation in vitro. In 2 of the patients, in vivo somatic reversion restored ARPC1B expression in a fraction of lymphocytes and was associated with a skewed TCR repertoire. In 1 revertant patient, memory CD8+ T cells expressing normal levels of ARPC1B displayed improved T-cell migration. Inherited ARPC1B deficiency therefore alters T-cell cytoskeletal dynamics and functions, contributing to the clinical features of CID.

To the editor: In juvenile myelomonocytic leukemia (JMML), activating RAS mutations are responsible for a hyperactive RAS/ERK signaling.[1][1] Somatic codons 12-13-61 RAS mutations are described in cases of RAS -associated lymphoproliferative disease (RALD),[2][2][⇓][3]-[4][4] believed to be a

Background Hemophagocytic lymphohistiocytosis (HLH) is an inflammatory condition caused by uncontrolled proliferation of activated lymphocytes and macrophages secreting an excess of inflammatory cytokines. When untreated, primary HLH is invariably fatal. Treatment requires the achievement of remission of HLH prior to allogeneic hematopoietic stem cell transplantation. Despite significant treatment progress, pre-HSCT mortality remains a challenge. In the Etoposide-based HLH-94 and HLH-2004 studies pre-HSCT mortality was 27% and 19%, respectively. A better understanding of the pathophysiology of primary HLH has opened new avenues for targeted immunotherapy. Based on our previous observation concerning the use of Antithymoglobulin in HLH, we propose a new therapeutic strategy with Alemtuzumab in association with steroids and cyclosporine A (CSA) as first line treatment in primary HLH. In contrast to ATG, Alemtuzumab does not activate T lymphocytes while killing them. Therefore, we expect a better tolerance and efficacy of Alemtuzumab. This may have a positive impact not only on survival until HSCT, but also on overall survival and quality of life, especially with regard to long-term neurological sequelae. Methods 24 consecutive treatment naïve patients with genetically confirmed primary HLH had received first line Alemtuzumab in association to steroids and CSA from 01/2009 to 06/2015 in the Unit for Pediatric Immunology in Necker Hospital Paris, as well as two additional patients in 10/2016 and 10/2018 respectively, who could not be included in the prospective trial. From 06/2015 to 06/2019, 29 patients have been enrolled in a multicenter, open, phase I/II, non-comparative, non randomized study (NCT02472054). Patients with lymphohistiocytic activation syndrome who had not received any specific treatment prior to enrollment except steroids and CSA were included. Treatment consisted in intravenous administration of Alemtuzumab in association to Methylprednisolone and CSA. The primary outcome measures is the number of surviving patients until HSCT, secondary outcome measures the number of complete remissions following treatment at Day (D)14, D21, D28. To assess the efficacy of the Alemtuzumab, the time of delay between the first administration of Alemtuzumab and complete remission will be determined. Alemtuzumab Pharmacokinetics will be done. All adverse events are reported. Results Retrospective analysis of 26 patients (pilot study): The median age of patients was 1.9 months (birth - 7 years), 6 patients were neonates. When Alemtuzumab was started, out of 26 patients 12 (46.1%) required intensive care, 8 (30.7%) mechanical ventilation, 13 (50%) had neurological involvement, 9 (34.6%) hepatocellular insufficiency. One 2-month-old Munc13-4 patient died at H+48 after two administrations of Alemtuzumab (total dose 1.5mg/kg) for hepatic failure and acute renal failure. A second patient with Perforin deficiency did not respond neither to three courses of Alemtuzumab (cumulative dose 6.5mg/kg) nor repeated Etoposid, 40mg/kg ATG, or Ruxulotinib. He died at D+65. The 24 remaining patients survived until HSCT (survival 92.3%). As shown in the figure, two patients required additional treatment. Overall 22 patients achieved CR, 2 PR at the time of HSCT. The prospective study enrolled 29 patients from 06/2015 to 06/2019. Median age at onset of HLH was 0.5 years (range 0.02 to 17.2 years), one patient withdrawed consent. 12 patients received one course, 13 two, 2 three and one patient 4 courses of Alemtuzumab. 24 patients with a genetic confirmed HLH predisposition reached the primary endpoint with 22 surviving until HSCT (91,6%). One patient is still awaiting HSCT. The three remaining patients are one CA-EBV patient and a newborn with secondary HLH due to fulminant HSV hepatitis, who both died, as well as a patient with predominant neurological HLH without genetic diagnosis who is in sustained remission without any specific treatment. Detailed results from the completed study will be presented. Conclusions This is the first report on Alemtuzumab as first line approach in the treatment of primary HLH. Our results in more than 50 pediatric patients treated in a pilot study and prospective trial indicate that Alemtuzumab allows controlling HLH activity with a favorable safety and tolerability profile in a very fragile population. 92.3% and 91.6% of patients respectively survived to HSCT. Figure Disclosures No relevant conflicts of interest to declare. Off Label Disclosure: Alemtuzumab (Campath) has been used in a prospective trial to evaluate its efficacy as first line treatment in Familial Lymphohistiocytosis.

The presence of cerebral macrovasculopathy as detected by transcranial Doppler (TCD) exposes children with sickle cell anemia (SCA) to a high risk of stroke, preventable by chronic transfusion or stem cell transplantation (SCT). However, long-term outcomes of stenosis have not been well described. The Drepagreffe trial (NCT01340404) was a prospective trial comparing cerebral vasculopathy outcome after SCT vs standard-care in children with abnormal TCD with or without stroke history. Results from the whole population have recently been reported (Bernaudin et al, JAMA 2019). The decrease in velocities was significantly higher after SCT than standard-care (p Sixty-seven SCA-children on chronic transfusion for abnormal-TCD history were enrolled (Dec-2010/June-2013) in this prospective trial with two treatment groups defined by the random-availability of having a matched-sibling donor (MSD). Thirty-two with MSD were transplanted while 35 without MSD were maintained on chronic transfusion for at least one-year and eventually switched to hydroxyurea thereafter if no stenosis and normalized velocities. Cerebral and cervical magnetic-resonance angiography (MRA) was systematically performed at enrollment, and 1- and 3-year post-enrollment. Stenosis was defined as a narrowing ≥25%. The MRA stenosis-score, was calculated as the weighted sum of the scores in the 8 assessed cerebral arteries (right and left middle cerebral (MCA), anterior (ACA), internal carotid (ICA) and extracranial internal carotid arteries (eICA)), with 0 = stenosis, 1 = mild stenosis (25-49%), 2 = moderate stenosis (50-74%), 3 = severe stenosis (75-99%), and 4 = occlusion. All 67 patients were alive at 3-year, and the 32 transplanted patients successfully engrafted. No stroke or recurrence occurred during the follow-up. No chronic-GVHD was observed. Among the 7 patients with stroke-history, all had stenosis at enrollment and the stenosis score increased in the 4 transplanted patients, but always in the arteries with previous stenosis and those feeding ischemic territories, while stenosis score remained mostly stable in the 3 patients maintained on chronic transfusion,. However, the difference between treatment groups was not significant (p=0.057). Among the 60 stroke-free patients at enrollment, 28 with MSD were transplanted while 32 without MSD were maintained on chronic transfusion. At enrollment, 28 patients (14 patients in each treatment group) had stenosis. At 1-year, 9 patients in the SCT group had stenosis, whereas in the transfusion/standard-care group, 10 had stenosis. At 3-year, 5 patients in the SCT group had stenosis, while 10 still had stenosis in the standard-care group. Moreover, 2 patients, who had no stenosis at enrollment, developed one stenosis between 1 and 3-year, despite chronic transfusion in one case and after switch to hydroxyurea in the other. In another patient, stenosis had disappeared on chronic transfusion at 1-year, although it reappeared at 3-year after a switch to hydroxyurea. In the SCT group, no worsening of stenosis was observed, and stenosis improved in 13/14 and was stable in one; in contrast, worsening of stenosis score was observed in the standard-care group in 6 patients on chronic transfusion (p=0.035), The stenosis-score between enrollment and 3-year improved more significantly in the SCT group (mean (SD): -1.39 (2.47)) than in the standard care group (-0.06 (1.18)); (p=0.012). Conclusions: This prospective trial reporting the outcome of stenosis in stroke and stroke-free SCA-patients with a history of abnormal-TCD shows a trend to worsening of the stenosis-score after SCT in stroke-patients, but no stroke recurrence; in contrast, in stroke-free patients, stenosis outcome was significantly better after SCT and with better prevention of stenosis occurrence than on standard care. These results support early recommendation of SCT in children with a history of abnormal-TCD and an MSD. Figure Disclosures Verlhac: Addmedica, Paris: Other: Financial Support; Bluebird Bio: Consultancy. Brousse:bluebird bio: Consultancy; Add medica: Consultancy. De Montalembert:Addmedica: Consultancy, Honoraria; Novartis: Consultancy, Honoraria; Bluebird Bio: Membership on an entity's Board of Directors or advisory committees. Thuret:BlueBird bio: Other: investigators for clinical trials, participation on scientific/medical advisory board; Celgene: Other: investigators for clinical trials, participation on scientific/medical advisory board; Novartis: Other: investigators for clinical trials, participation on scientific/medical advisory board; Apopharma: Consultancy. Bernaudin:GBT: Membership on an entity's Board of Directors or advisory committees; AddMedica: Honoraria, Other: Help for travel to meeting; BlueBirdBio: Consultancy.

Background LentiGlobin gene therapy contains autologous CD34+ hematopoietic stem cells (HSCs) transduced with the BB305 lentiviral vector (LVV), encoding human β-globin with a T87Q substitution. This substitution confers anti-sickling properties to the gene therapy-derived hemoglobin (HbAT87Q) and allows for its quantification in transduced HSCs. The proof of concept for LentiGlobin gene therapy in patients with transfusion-dependent β-thalassemia (TDT) and sickle cell disease (SCD) was established in the recently completed HGB-205 study (NCT02151526). Herein, we provide the safety and efficacy outcomes and long-term follow-up data for all 7 treated patients, 4 with TDT and 3 with SCD. Methods Patients 5−35 years old with TDT (≥ 100 mL/kg of packed red blood cells [pRBCs]/year) or severe SCD (e.g., ≥ 2 acute chest syndromes [ACS] or ≥ 2 vaso-occlusive crises in the preceding year or the year before regular transfusions) were enrolled. CD34+ HSCs were obtained by mobilization and apheresis in patients with TDT or by bone marrow harvest in patients with SCD. Following collection, cells were transduced with the BB305 LVV. Patients underwent busulfan myeloablative conditioning and were infused with transduced cells. Patients were monitored for engraftment, adverse events (AEs), HbAT87Q levels, and other hematologic and clinical parameters. After 2 years in HGB-205, patients transitioned into the long-term follow-up study, LTF-303 (NCT02633943). Summary statistics are shown as median (min-max). Results As of June 2019, patients with TDT (n=4) and SCD (n=3) had a median follow-up of 49.6 (40.5-60.6) and 28.5 (25.5-52.5) months, respectively. Table 1 shows patient and drug product characteristics and several key efficacy outcomes. All patients achieved HSC engraftment. LentiGlobin safety profile was consistent with busulfan myeloablative conditioning and, in case of SCD, with the underlying disease state. The most common non-hematologic Grade ≥ 3 AEs post-LentiGlobin gene therapy (≥ 2 patients) for patients with TDT were stomatitis (n=4) and increased aspartate aminotransferase (n=2), and for patients with SCD were ACS (n=2) and vaso-occlusive pain (n=2). In all 4 patients with TDT, total Hb and HbAT87Q levels remained generally stable up to 5 years post-LentiGlobin infusion. Three of 4 patients achieved transfusion independence (TI; defined as weighted average Hb ≥ 9g/dL without pRBC transfusions for ≥ 12 months), for an ongoing duration of 56.3 (38.2-57.6) months. Weighted average total Hb during TI was 11.4 (10.5-13.0) g/dL. One patient has been off transfusions for 37.5 months and had total Hb of 7.7 g/dL, which was below the ≥ 9 g/dL requirement to meet the protocol definition of TI. At last visit, HbAT87Q levels in these 4 patients ranged from 6.2-11.2 g/dL, which contributed 73.8-86.8% of the total Hb. The first patient treated with LentiGlobin for SCD experienced one vaso-occlusive pain episode, which developed at 30 months after LentiGlobin gene therapy following a case of acute gastroenteritis with fever and dehydration. The second SCD patient had 2 serious AEs (SAEs) of ACS approximately 6 and 8 months after LentiGlobin gene therapy. The patient resumed chronic pRBC transfusions and hydroxyurea treatment and subsequently experienced 2 SAEs of vaso-occlusive pain; no additional SAEs of vaso-occlusive pain or ACS were reported during the last 16 months of follow-up after LentiGlobin infusion. The third SCD patient had no episodes of vaso-occlusive pain or ACS during 25.5 months of follow-up post-LentiGlobin gene therapy as of the data cut-off. Two patients with SCD who have been off chronic pRBC transfusions, showed improvement in hemolysis markers post-LentiGlobin treatment and stabilization of HbAT87Q expression at approximately 6 months post-LentiGlobin infusion. Total Hb levels for patients with SCD at last visit were 13.0 g/dL (patient 1), 9.4 g/dL (patient 2), and 9.8 g/dL (patient 3), with corresponding HbAT87Q contributions of 47.9%, 7.9%, and 25.8%, respectively. Summary With up to 5 years of follow-up, treatment with LentiGlobin gene therapy was well tolerated and resulted in improvement in hematologic parameters and disease-related symptoms. Further results from the completed study will be presented. Disclosures Hermine: Celgene: Research Funding; Novartis: Research Funding; AB science: Consultancy, Equity Ownership, Honoraria, Research Funding. Brousse:bluebird bio, Inc: Consultancy; AddMedica: Consultancy. El Nemer:Hemanext: Other: Other. Bartolucci:Novartis: Membership on an entity's Board of Directors or advisory committees; AddMedica: Honoraria, Membership on an entity's Board of Directors or advisory committees; Global Blood Therapeutics: Membership on an entity's Board of Directors or advisory committees; Agios: Membership on an entity's Board of Directors or advisory committees; Roche: Membership on an entity's Board of Directors or advisory committees; HEMANEXT: Membership on an entity's Board of Directors or advisory committees. Asmal:bluebird bio, Inc: Employment, Equity Ownership. Whitney:bluebird bio, Inc: Employment, Equity Ownership. Gayron:bluebird bio, Inc: Employment, Equity Ownership. Huang:bluebird bio, Inc.: Employment, Equity Ownership. de Montalembert:AddMedica: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; bluebird bio, Inc: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Ribeil:bluebird bio, Inc: Employment, Equity Ownership. Cavazzana:SmartImmune: Other: Founder.

Severe combined immunodeficiencies (SCID) are a heterogeneous group of inherited disorders characterized by a profound reduction or alteration of T lymphocyte function. They arise from a variety of molecular defects which affect T lymphocytes development and function. The number of infections prior hematopietic stem cells tansplantaton (HSCT), genotype, and the type of donor are described as prognostic factors for stem cell transplants. In this retrospective study, we included 30 pediatric patients suffering from SCID who underwent to CD34+-selected grafts between January 2008 to December 2017 in our center. Diagnosis of reticular dysgenesis, ADA deficiency, or leaky SCIDs and intra thymic deficiency were excluded. A mechanistic mathematical model of all available data was performed and provided a dynamic appreciation of immune reconstitution, while removing bias. T-cell populations were maintained through proliferation and loss model and thymic output have been integrated to the production function. This joint modeling approach aimed to predict rate and extent of T cell immune reconstitution over time (mainly CD3+ T cells, CD3+CD4+ helper T cells, and the CD3+CD4+ CD45RA+ cells). With a median follow-up time of 97.28 months [range 0.85; 131.54], there were 345 points of T cell phenotyping concentrations in total with a median of 12 samples per patient (range, 0 -35 samples) taken post-transplantation. In this data-set, 13 % of the patients (n= 4) died from infections. Time to reach half of the maximal T cell concentrations was estimated to 3.4 months, 95%CI [2.5 - 4.6]. In covariate analysis, genetic diagnosis (p= 0.0047) and conditioning regimen (p= 0.01) were found to be significant pre transplant covariates which impacted the trajectory of T cell concentration with time. This modeling approach appeared to be the best method to learn about the dynamic T cell reconstitution after transplant in patients suffering from SCID. In the context of new cell therapy approach for T cell depletion and in vitro thymic maturation, this mechanistic joint model can be used for the design and analysis of incoming clinical trials. Figure Disclosures Cavazzana: Smartimmune: Other: Founder of Smartimmune.

Lentivector mediated gene transfer into hematopoietic stem/progenitor cells and T cells has resulted in long-term stable integration of transgenes and significant clinical benefits in many diseases. We previously reported (De Ravin et al Sci Transl Med. 2016) early outcome data for 5 patients with X-linked severe combined immunodeficiency (X-SCID) enrolled in a first-in-human lentivector gene therapy clinical trial (NCT03315078) as salvage therapy for older children and young adults who had received prior haplo-identical hematopoietic stem cell transplantation (HSCT) as infants without chemotherapy-based conditioning. Lymphocyte-depleted haplo-identical stem cell transplant in X-SCID infants without conditioning generally results in only a T-cell engraftment that may also decline over time which, combined with B- and NK-cell dysfunction, may result in the progression of multi-system clinical problems (bronchiectasis, infections, gastrointestinal malabsorption, failure to grow, immune dysregulation). By 2016 three additional patients were treated and the cohort of 8 patients have now been followed for 3 to 7 years (Cohort A), where we observed gradual clinical benefit in the clearance of chronic norovirus and associated improved abdominal complaints, malabsorption, and growth and IgG production. Four patients were able to cease immunoglobulin replacement therapy. Despite these encouraging results, the relatively inefficient transduction of hematopoietic stem/progenitor cells (HSPCs) required large quantities of vector, and resulted in relatively low vector copy number in myeloid cells in some patients, with delayed immune cell recovery and persistent clinical disease especially in the last patient treated, P8. To address this, we developed a refined enhanced transduction (ET) procedure consisting of a single overnight transduction after 48hours pre-stimulation in cytokines (Stem cell factor, Thrombopoietin, Flt3-ligand; 100ng/mL) and incorporated transduction enhancers LentiBoost 1:100 and dimethyl prostaglandin 2 (dmPGE2; 1mM) and recently treat 6 patients, including re-treatment of P8 (Cohort B). Here we compared the early outcomes from Cohort B patients who received autologous CD34+ HSPCs processed with the enhanced transduction (ET) procedure. These patients (aged 12 to 36 yo) had significant problems with donor T cell infiltration of liver, bone marrow and kidneys, and near absent B and NK cells. Cryopreserved G-CSF/plerixafor mobilized peripheral blood CD34+ HSPCs (5x106/kg to 28x106/kg) were transduced by the ET process at 5% vector concentration, compared to previous method without transduction enhancers of two daily transductions at 20-30% final vector concentration, representing a 10-12 fold reduction in vector used. Colony forming unit assays showed 78%-92% versus 17%-58% vector-positive clones in Cohort B compared with Cohort A, with VCN of 1.5-12 copies (Cohort B), compared with 0.06 to 0.5 copies in Cohort A. At one month following infusion of gene corrected cell product, we isolated peripheral blood CD14+ myeloid cells as indication of early marrow output from engrafted HSPCs, and observed VCN of 1 to 4 copies (P9-12 and re-treat P8), a ≥10x increase from Cohort A (0.04 to 0.23) at same early time point after infusion (Fig 1). In addition to earlier clinical improvement (abdominal complaints, appetite, growth), there was also an early appearance of B and NK cells (Fig. 2) at much higher levels in Cohort B than previously observed even at years after treatment in Cohort A. In conclusion, we observed significantly improved measures of early clinical outcomes from lentivector gene therapy of older children and young adults with X-SCID using enhanced transduction procedure with addition of LentiBoost and dmPGE2, that achieves much greater transduction efficiencies with >10 fold less vector, and results in faster immune reconstitution and more significant clinical benefit by 3 months. The patients are monitored closely for potential risks from higher VCNs that may be balanced by reduced selection pressure due to the greater numbers of gene corrected clones. Figure Disclosures Puck: NIAID: Research Funding; Pfeizer: Other: spouse serves on Rare Disease Advisory Board; Invitae: Other: spouse employment. Cowan:bluebird bio: Consultancy; Homology Medicine: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; UpToDate: Honoraria; California Institute Of Regenerative Medicine: Research Funding; NIH NIAD: Research Funding; Rocket Pharma: Consultancy; Leadiant: Consultancy. Mamcarz:ASSISI Foundation of Memphis: Research Funding; MBIO: Other: St. Jude Children's Research Hospital has an existing exclusive license and ongoing partnership with Mustang Bio for the further clinical development and commercialization of this XSCID gene therapy; California Institute of Regenerative Medicine: Research Funding; NHLBI: Research Funding; UpToDate: Honoraria; American Lebanese Syrian Associated Charities: Research Funding. Gottschalk:Patents and patent applications in the fields of T-cell & Gene therapy for cancer: Patents & Royalties; California Institute for Regenerative Medicine: Research Funding; NHLBI: Research Funding; America Lebanese Syrian Associated Charities: Research Funding; TESSA Therapeutics: Other: Research Collaboration; ViraCyte: Consultancy; MBIO: Other: St. Jude Children's Research Hospital has an existing exclusive license and ongoing partnership with Mustang Bio for the further clinical development and commercialization of this XSCID gene therapy; Sanofi: Honoraria; Tidal: Membership on an entity's Board of Directors or advisory committees; Merck: Consultancy; EMD Serono: Honoraria; ASSISI fundation of Memphis: Research Funding; Inmatics: Membership on an entity's Board of Directors or advisory committees. Meagher:MBIO: Other: St. Jude Children's Research Hospital has an existing exclusive license and ongoing partnership with Mustang Bio for the further clinical development and commercialization of this XSCID gene therapy.

Seventeen patients transplanted with hematopoietic cells to correct severe T lymphocyte immunodeficiency resulting from complete DiGeorge anomaly were identified worldwide, and retrospective data were obtained using a questionnaire-based survey. Patients were treated at a median age of 5 months (range, 2-53 months) between 1995 and 2006. Bone marrow was used in 11 procedures in 9 cases: 6 from matched unrelated donors, 4 from human leukocyte antigen (HLA)-identical siblings, and one haploidentical parent with T-cell depletion. Unmobilized peripheral blood was used in 8 cases: 5 from HLA-identical siblings, one from a matched unrelated donor, one from an HLA-identical parent, and one unrelated matched cord blood. Conditioning was used in 5 patients and graft-versus-host disease prophylaxis in 11 patients. Significant graft-versus-host disease occurred in 9 patients, becoming chronic in 3. Median length of follow-up was 13 months, with transplantation from HLA-matched sibling showing the best results. Median survival among deceased patients (10 patients) was 7 months after transplantation (range, 2-18 months). The overall survival rate was 41%, with a median follow-up of 5.8 years (range, 4-11.5 years). Among survivors, median CD3 and CD4 counts were 806 (range, 644-1224) and 348 (range, 225-782) cells/mm3, respectively, CD4+/CD45RA+ cells remained very low, whereas mitogen responses were normalized.

Three patients with Chediak-Higashi syndrome underwent allogeneic bone marrow transplantation between the ages of 2 years 9 months and 7 years. The outcome was uneventful, with sustained mixed chimerism. No subsequent recurrent infections or hemophagocytic syndrome were observed. At the age of 22 to 24 years, these 3 patients developed a neurologic deficit combining difficulty walking, loss of balance, and tremor. Neurologic evaluation demonstrated cerebellar ataxia and signs of peripheral neuropathy. Moderate axon loss and rarefaction of large myelinated fibers were observed on semithin sections of peripheral nerve. Cerebellar atrophy was detected by cerebral magnetic resonance imaging in 2 patients. We also reviewed the very long-term outcome of the other 11 patients with Chediak-Higashi syndrome who had received bone marrow transplants at our center since 1981. All displayed neurologic deficits or low cognitive abilities.

Introduction: β-globin gene transfer into hematopoietic stem cells (HSCs) has the potential to reduce or eliminate the symptoms of severe sickle cell disease (SCD) and reduce or eliminate transfusion requirements in transfusion-dependent β-thalassemia (TDT). LentiGlobin Drug Product (DP) contains autologous CD34+ cells transduced with the BB305 lentiviral vector, which encodes a human β-globin gene containing a single point mutation (AT87Q) designed to confer anti-sickling properties similar to those observed with γ-globin. We previously reported proof of concept for LentiGlobin DP treatment in severe SCD and early data from 4 treated patients with TDT. We now report 18 months of follow-up for the patient with SCD and between 9 and 30 months of follow-up for the 4 patients with TDT. Patients (5-35 years of age) with severe SCD (e.g. ≥2 acute chest syndrome episodes or ≥2 vaso-occlusive crises [VOC] in preceding year/in year prior to regular transfusions) or TDT (≥100mL/kg of packed red blood cells [RBCs] per year) were enrolled. Following mobilization and apheresis (for TDT) or bone marrow harvest (for SCD), autologous CD34+ cells were transduced with the BB305 lentiviral vector. Patients underwent myeloablative conditioning with busulfan prior to infusion of the transduced cells. After infusion, patients were monitored for hematologic engraftment, vector copy number (VCN), and HbAT87Q expression. Disease-specific assessments included transfusion requirements for TDT, or VOCs and hospitalizations for SCD. Safety assessments included adverse events (AEs) and integration site analysis. Results: As of July 2016, 1 patient with severe SCD (male; 13 years old) and 4 patients with TDT (2 male, 2 female; 16-19 years old) have received LentiGlobin DP in Study HGB-205. The median LentiGlobin DP cell dose was 8.9 (range 5.6-13.6) x 106 CD34+ cells/kg with a DP VCN of 1.2 (range: 0.8-2.0) vector copies/diploid genome. Median post-infusion follow-up as of July 6, 2016 is 20.8 months (range 9.5-31.3). All subjects successfully engrafted after receiving LentiGlobin DP, with a median time to neutrophil engraftment of 17 days (range 14-38 days). VCN in peripheral blood has remained generally consistent from Month 3 in all patients with a range of 0.2 to 3.4 at last measurement. The toxicity profile observed from start of conditioning to latest follow-up remains consistent with myeloablative conditioning with single-agent busulfan, with no DP-related ≥Grade 3 AEs or serious AEs and no evidence of clonal dominance reported to date. Three patients with TDT have β0/βE genotypes and 1 is homozygous for the severe β+ mutation IVS1 nt 110 G>A. The 2 patients who have completed the 2-year primary follow-up period (both β0/βE) have not required RBC transfusions for 31 and 28 months, with total Hb of 10.9 and 13.5 g/dL, and HbAT87Q expression of 7.7 and 10.1 g/dL, respectively, at most recent study visit. Iron chelation has been discontinued and phlebotomy initiated for 1 of the patients. The remaining patient with β0/βE genotype has 9 months of follow-up and has not required transfusions since 4 days post-LentiGlobin DP infusion, achieving a total Hb of 11.3 g/dL at last study visit. The patient with the severe IVS1 genotype has 12 months of follow-up and has been free of transfusions for 9 months, with a total Hb of 8.3 g/dL at last study visit. The patient with severe SCD, who prior to study enrollment received regular RBC transfusions, has experienced no clinical symptoms or complications of SCD in the 18 months since treatment, despite discontinuing transfusions 3 months after LentiGlobin DP infusion. Total Hb in this patient was 12.5 g/dL, with 6.6 g/dL HbAT87Q (53%) and 5.7 g/dL HbS (45%) at last study visit. Compared with values at screening, unconjugated bilirubin had dropped 78% (50 to 11 μmol/L), lactate dehydrogenase had dropped 54% (626 to 287 U/L), and reticulocyte count had dropped 45% (238x109/L to 132x109/L) by Month 18. Conclusions: Data from this ongoing Phase 1/2 clinical study suggest that treatment with LentiGlobin DP can result in sustained production of therapeutic HbAT87Q, which ameliorates the clinical and biochemical effects of severe SCD and TDT, with an acceptable safety profile. Gene therapy presents a potentially promising therapy for patients with severe hemoglobinopathies. Further follow-up and additional data from patients are needed to confirm the encouraging results seen to date in this study. Disclosures Ribeil: Bluebirdbio: Consultancy; Addmedica: Research Funding. Payen:bluebird bio: Patents & Royalties. Hermine:Alexion: Research Funding; Celgene: Research Funding; Novartis: Research Funding; AB science: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding, Speakers Bureau. Asmal:bluebird bio: Employment, Equity Ownership. Joseney-Antoine:bluebird bio: Employment, Equity Ownership. De Montalembert:Addmedica: Research Funding; Novartis: Research Funding, Speakers Bureau. Leboulch:bluebird bio, Inc: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding.

Non-malignant diseases (NMD) include a wide spectrum of either congenital or acquired disorders occurring in early and later childhood. The primary goal of conditioning in NMD is either the replacement of missing cells as in severe aplastic anaemia (SAA) or severe combined immunodeficiencies (SCID) or the exchange of a deficient blood cell compartment as in hemoglobinopathies, hemophagocytic syndromes or metabolic disorders. The right choice of a conditioning regimen before allogeneic hematopoietic stem cell transplantation (HSCT) is crucial for the outcome of patients with NMD, many of whom are often critically ill due to infections, organ dysfunctions, vascular complications or metabolic problems. As a consequence of a highly activated immune-system and no pre-treatment with chemotherapy, graft rejection is a known severe complication in these patients. To get up-to-date information on the most commonly used conditioning regimen for children with NMD, we performed an EBMT- registry-based analysis: 2187 patients from 39 countries with a congenital or acquired NMD below the age of 18 years who underwent first allogeneic HSCT between January 2010 and December 2014 registered in the EBMT database were included. 51% of children were transplanted before 4 years of age, 489 patients were less than 12 months old, and 61.5% were male. Majority of patients (32,2%) underwent HSCT for hemoglobinopathies (463 thalassemia major, 127 sickle cell disease), the second most common disease type was SCID with 17.4%, followed by other primary immunodeficiencies, chronic granulomatous disease and bone marrow failure syndromes (excluding Fanconi anaemia): 13.2%, 11% and 10.4%, respectively. The given conditioning regimen was under discretion of the treating physician. The most common conditioning regimen consisted of a combination of busulfan (bu)/fludarabine (flu) in 1063 patients, of treosulfan (treo)/flu in 422 patients; 473 patients received a combination of treo/flu/thiotepa (tt) and 229 patients received bu/flu/tt. The median total dose of the respective conditioning drugs was comparable (treo: 41 g/m2 or 42g/m2; bu: 160 mg/m2; tt: 201 and 205 mg/m2). In univariate analysis, overall survival (OS) was significantly different between the conditioning groups (p = 0.0032): 2y-OS 87.7% [84.3%-91.2%] for treo/flu/tt vs. 82.4% [78.5%-86.5%], 81.8% [77.8%-86.0%] for treo/flu, 80.8% [78.1%-83.5%] and 78.2% [75.2%-81.3%] for bu/flu and 81.3% [75.9%-87.0%] and 80.4% [74.9%-86.4%] for bu/flu/tt, respectively. Transplant-related mortality (TRM) was significantly different between the conditioning groups (p = 0.0015): day-100 TRM was lowest after treo/flu/tt: 4.8% [2.8%-6.7%] compared to 9.2% [6.3%-12.0%] after treo/flu, 7.9% [6.2%-9.5%] after bu/flu and 9.9% [5.9%-13.8%] after bu/flu/tt. TRM at 1 year post-transplant: 8.3% [5.5%-11.0%] for treo/flu/tt, 16.2% [12.2%-20.0%] after treo/flu, 16.9% [14.2%-19.4%] after bu/flu and 14.9% [9.7%-19.8%] after blu/flu/tt, respectively. In multivariate analysis, the HR was adjusted on age groups at HSCT, underlying disease, year of HSCT, stem cell source and donor types. 1-y OS was significantly better after treo/flu/tt (89.5 [86.5 - 92.6], CI 95%, p 0.0032) than with treo/flu, bu/flu or bu/flu, respectively. Day 100- and 1-year TRM was lower after treo/flu/tt compared to the other three conditioning combinations. A pairwise testing of the different treatment groups revealed no statistical significant difference in OS, TRM, disease-free survival (DFS) for bu/flu vs. treo/flu, bu/flu vs. bu/flu/tt and bu/flu/tt vs. treo/flu; a significant better OS, DFS and less TRM for treo/flu/tt vs. bu/flu, treo/flu/tt vs. treo/flu and a better DFS for treo/flu/tt vs. bu/flu/tt with a trend for better OS and less TRM for treo/flu/tt vs. bu/flu/tt. No statistically significant differences were found among the 4 conditioning regimens for acute or chronic GVHD. Conclusion: For children with NMD, a variety of conditioning regimen are in use to facilitate engraftment, prevent rejection, and enable sufficient cell function. Beside treo and bu, flu and tt are established drugs to eradicate lymphocytes. In this analysis, the combination of treo/flu/tt shows promising outcome results and should be further evaluated in diseases specific prospective trials. Disclosures Peters: Pfizer: Consultancy; Amgen: Consultancy; Jazz: Speakers Bureau; Novartis: Consultancy; Medac: Consultancy. Slatter:Medac: Other: Travel grants. Bader:Medac: Consultancy, Research Funding; Riemser: Research Funding; Neovii Biotech: Research Funding; Servier: Consultancy, Honoraria; Novartis: Consultancy, Honoraria.

Background: In patients with hemoglobinopathies, hematopoietic stem cell (HSC) gene therapy has the potential to induce production of functional β-globin in the red blood cell lineage with the aim of reducing or eliminating the symptoms of disease. Previous results from 1 subject with severe sickle cell disease (SCD; 6 months follow-up) and 2 subjects with β0/βE-thalassemia major (up to 15 months follow-up) treated in clinical study HGB-205 suggested that transplantation with autologous CD34+ cells transduced with the LentiGlobin BB305 lentiviral vector containing an engineered βA-T87Q-globin gene (LentiGlobin BB305 Drug Product) resulted in near-normal levels of total hemoglobin (Hb) and rapid clinical improvement. Here we provide data on a new subject enrolled and additional follow-up data on the 3 subjects previously presented in Study HGB-205. Subjects and Methods: Subjects with severe SCD underwent HSC collection via bone marrow harvest, while subjects with β-thalassemia major underwent HSC collection via peripheral blood apheresis following mobilization. CD34+ cells were selected and transduced with LentiGlobin BB305 lentiviral vector to produce the drug product. Subjects underwent myeloablation with intravenous busulfan, followed by infusion of drug product. Subjects were monitored for hematological engraftment, vector copy number, βA-T87Q-globin expression, adverse events and transfusion requirements. Integration site analysis (ISA) and replication-competent lentivirus (RCL) assays were performed. Prophylactic RBC transfusions were continued in subjects with SCD who were on chronic transfusion pre-transplant to maintain HbS Results: As of 31 July 2015, 1 subject with severe SCD (Subject 1204, βS/βS with multiple vaso-occlusive crises, silent infarct, acute chest syndrome, and on prophylactic transfusions) and 3 subjects withβ-thalassemia major (Subjects 1201, 1202 and 1203) have been infused with the LentiGlobin BB305 Drug Product. The outcome of these subjects to date is shown in Table 1. No subject has experienced a drug product-related adverse event, and ISA analyses demonstrate highly polyclonal reconstitution without clonal dominance. The subject with severe SCD is producing approximately 51.5% of anti-sickling hemoglobin (48% HbAT87Q, 1.8% HbF, 1.7% HbA2) at 9 months post-infusion. This subject has not had a post-infusion hospitalization for a SCD-related event despite stopping chronic transfusions at Day +88. Both subjects with β0/βE-thalassemia major have remained transfusion-free for at least 15 months post-infusion, with a consistent expression of βA-T87Q-globin; the subject with β0/β0-thalassemia major has only had 1 month follow-up post-drug product infusion to date. Conclusion: The subject with severe SCD is producing approximately 51.5% anti-sickling globins with HbS of 48.5% and remains free of SCD-related events despite stopping chronic transfusion therapy. Two subjects with β0/βE-thalassemia major remain transfusion-free for at least 15 months post infusion of LentiGlobin BB305 Drug Product. Gene therapy using autologous HSC transduced with LentiGlobin BB305 lentiviral vector is a promising approach for the treatment of patients with hemoglobinopathies. Table 1. Demographics and Transplantation Outcomes Subject Age (years)/ Sex (M/F) Genotype BB305 Drug Product Day of Neutrophil Engraftment Drug Product- related Adverse Events Day of Last pRBC Transfusion Last Study Visit (Months) Hb at Last Visit (g/dL) VCNa CD34+ cell dose (x106 per kg) Subject with severe sickle cell disease HbAT87Q/HbF/ HbS/Total Hb 1204 13/ M βS/βS 1.2 / 1.0 5.6 Day +37 None Day +88 9M 5.5/0.2/5.5/11.4 Subjects with β-thalassemia major Hb AT87Q/ Total Hb 1201 18/ F β0/βE 1.5 8.9 Day +13 None Day +10 18M 7.8/10.7 1202 16/ M β0/βE 2.1 13.6 Day +15 None Day +12 15M 9.7/12.8 1203 19/ M β0/β0 0.8 8.8 Day +28 None Day +15 1M Pending/9.2 As of 31 July 2015 aVCN, vector copy number; F=female; M= Male for gender, and months for day of last follow-up Disclosures Payen: bluebrid bio: Consultancy. Beuzard:bluebird bio Inc: Consultancy, Equity Ownership. von Kalle:bluebird bio, Inc.: Consultancy. Sandler:bluebird bio, Inc.: Employment, Equity Ownership. Soni:bluebird bio, Inc.: Employment, Equity Ownership. De Montalembert:Novartis: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Leboulch:bluebird bio: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding.

Introduction: Busulfan (Bu) is recognized worldwide as the cornerstone for HSCT conditioning regimens (CR). It has a narrow therapeutic window (TW), and graft rejection or toxicity are related to Bu exposure. In very young children, Bu exhibits large pharmacokinetic (PK) variability, and its metabolic clearance is non-linearly related to body weight (BW). In this setting, Bu dosage is stratified according to BW and commonly monitored once after the 1st of 16 total 2-hr infusions and finally, 96-hr exposure to this major alkylating agent. Given the narrow TW of Bu in relation to clinical outcomes and to better understand its PK/PD relationship, it is important to attempt to optimize both the duration and the intensity of exposure to Bu in children undergoing HSCT, whatever their BW and pathologies. Study objective: To optimize Bu duration/intensity exposure in children undergoing HSCT, we studied the possible contribution of double TDM of IV Bu dosing in children receiving Bu-based CR for HSCT, by comparing the expected targeted values of exposure after performing 1 PK (1st dose, PK1) and finally 2 PK (1st dose, PK1, and 9th dose, PK2). Patients and methods: In this single-centre* prospective observational study (05/2012-07/2015), the PK of Bu was performed using the NONMEM® software; a one-compartment PK model suitably fitted the concentrations vs. time data. The PK of Bu was assessed on 6 plasma samples (3 samples/PK) using a validated LC-MS/MS method, with area under the concentration-time curve (AUC) calculation from the 1st and 9th doses. AUC calculated after the 1st dose and extrapolated to the 16th one were compared intraindividually by the non-parametric Wilcoxon signed-rank test to the sum of AUC1-6 with TDM1 applied from the 7th dose with or without TDM2 applied from the 13th or 14th dose; p≤0.025 was considered statistically significant. 63 patients (Pts) undergoing HSCT were included with median follow up of 14 months [1-39]. Median age was 17 months [1-193] and BW 11 kg [3-59]. Most Pts had non-malignant diseases, received allogenic HSCT and Bu-based CR in combination with Flu (morphometric, disease and CR details will be provided). *one of the 14 French Pediatric BMT units, involved in the therapeutic monitoring of IV Bu dosing in children undergoing HSCT. Results: 63 Pts (37 males (59%) and 26 females (41%)) were included. According to the EBMT-ESID recommendations, a median Bu posology of 1 mg/kg 4x/day for 4 days [0.6-1.3 mg/kg] was given. We demonstrate that: (a) estimated total AUC obtained from 2 PK differ significantly from those calculated after none (p=8.6455 E-7) or PK1 alone (p=7.2157 E-8), (b) double TDM allows achieving no difference between the expected AUC [20,706-23,180 mmol/min] desired by the medical staff in view of diseases vs. estimated AUC (p=0.5285). In 2/63 (3.2%) Pts, PK analysis did not lead to change Bu dosage. In 11/63 (18%) and 15/63(24%) Pts, dosage was modified after PK1 (TDM1 Group) or PK2 alone, respectively. In 35/63 (56%) Pts, changes were required twice, after the 2 PK (Double-TDM Group). The mean total dose of Bu were as follows: (a) a theoretical value of 220.80 mg (20.11 mg/kg) would have been given through 16 consecutive infusions without any TDM, (b) 199.35 mg (18.08 mg/kg) were administered in the TDM1 Group (16 doses), (c) 246.00 mg (19.46 mg/kg) were administered in the Double-TDM Group, avoiding the infusion of 24.00 mg of Bu vs. PK1 alone in these Pts. In 16/63 (25%) Pts, a decision of discontinuation of Bu exposure was taken. Indeed, the value that was desired by the medical staff was achieved after 13 (6 Pts) or 14 (10 Pts) doses; the mean total amounts of Bu were 273.22 mg (14.96 mg/kg) and 225.88 mg (16.16 mg/kg), respectively, vs. 336.27 mg (18.45 mg/kg) and 262.56 mg (18.60 mg/kg) theoretically after TDM1 alone. Conclusion: In this large paediatric cohort, the double TDM of Bu is a relevant and feasible option to better control Bu exposure and to potentially minimize the risk of overexposure. Correlations with toxicities (VOD, aGVH), CR, OS are under analysis. Based on these data, the double-TDM procedure is routinely applied in our centre. Disclosures Petain: Laboratoires Pierre Fabre: Employment. Nguyen:Laboratoires Pierre Fabre: Employment.

Introduction: Hematopoietic stem cell transplantation (HSCT) is, to date, the only curative therapy for sickle cell disease (SCD). However, HSCT is offered to relatively few patients with SCD for a number of reasons including lack of a suitable HLA-matched donor, lack of consensus on indications for HSCT, the potential for trading one chronic condition (i.e., SCD) for another, such as chronic graft-versus-host disease (GVHD), and the mortality associated with the procedure. To-date, most HSCTs for SCD have utilized matched siblings as donors and are performed in children and adolescents. We report outcomes after HLA-matched sibling HSCT of patients reported to the Eurocord-Monacord/European Group for Blood and Marrow Transplantation (EBMT) and Center for International Blood and Marrow Transplant Research (CIBMTR). Material and methods: One thousandpatients with SCD received HLA identical sibling HSCT between 1991 and 2013; n=439 from CIBMTR and n=561 from EBMT centers. HSCTs were performed in 90 centers in 23 countries. Results: Median age at HSCT was 9 years (range 1-54y); 85% of patients were aged The cumulative incidence (CI) of neutrophil engraftment at day+60 was 98% (96.6% for CB, 98.3% for BM and 95.2% for PB) with a median time to recovery of 19 days, while that for platelet engraftment was 98 % (96±2% for CB, 99±1% for BM and 98±9% for PBSC) with a median time to recovery of 25 days. Twenty-six patients experienced primary and 47 patients secondary graft failure; 67 patients died mainly due to GVH or infection. The 3-year probabilities of overall (OS) and event-free survival (EFS, alive with engraftment) were 94% (95% CI 92-95) and 90% (95% CI 68-82), respectively. According to stem cell source, 3-year OS was 99% after CB, 94% after BM and 80% after PBS (p Conclusion: This large registry based international study shows that HLA identical sibling transplant is successful more than 90% of the patients with severe SCD with limited transplant related complications (rejection, GVHD). Strategies aimed at lowering graft failure and GVHD are desirable to further optimize the observed 3-year event-free survival. Importantly, these data should increase awareness to early referral to HSCT of patients with severe SCD. Disclosures Walters: ViaCord and AllCells, Inc: Other: Medical director. Bertrand:ERYTECH Pharma: Consultancy. Peters:Medac: Research Funding; Fresenius: Research Funding; Amgen: Research Funding; Jazz: Research Funding; Novartis: Research Funding; Pfizer: Research Funding; Sanovi: Research Funding; Pierre-Fabre: Research Funding.

Background. Wiskott Aldrich Syndrome (WAS) is a rare primary immunodeficiency associated with thrombocytopenia, eczema, severe infectious and autoimmune complications, and lymphomas. Mismatched allogeneic hematopoietic stem cell transplantation (HSCT) is an alternative for patient lacking an HLA-matched donor but is associated with an increased frequency of complications. Moreover low lymphoid and myeloid chimerism is related to a higher rate of autoimmunity and thrombocytopenia. Recent gene therapy (GT) trials showed that gene-corrected autologous CD34+ cells infusion could be an appropriate therapeutic approach for these patients. It has been recently shown that B cell homeostasis is altered in WAS. As the B cell reconstitution participates to the restoration of immunological competence, a comprehensive study of this compartment after GT and the comparison with mismatched allogeneic HSCT is crucial. Objective. To perform a longitudinal study of B cell reconstitution in WAS patients after lentiviral vector-mediated GT, compared to mismatched allogeneic HSCT. Methods. Five patients (age 0.8-15.5 years) underwent GT at our center since 2011(follow-up 1.5-4.2 years) after near-myeloablative and immunosuppressive conditioning regimen with (n=3) or without (n=2) anti-CD20 administration. Patient 2 (P2) died 7 months after GT from a pre-existing infectious complication. Eleven patients undergoing mismatched allogeneic HSCT (age 0.6-10.9 years) at the same center were studied (follow-up 5.1-14.7 years). Longitudinal B cell assessment included B cell count before and after treatment, and the following subsets: switched memory (SM, CD19+ CD27+ IgD-), marginal zone (MZ, CD19+ CD27+ IgD+), naives (CD19+ CD27- IgD+), transitional (CD19+ CD27- IgD+ CD24high CD38high), circulating plasma cells (CD19+ CD27+ IgD- CD27high CD38high) and CD21low B cells (CD19+ CD21low CD38-), a subset abnormally expanded in WAS. Quantification of the B cell replication history was assessed through k-deleting recombination excision circles (KRECs). Analyses were compared to age-matched controls. WAS protein (WASP) expression and vector copy number (VCN) were measured in sorted B cells. Results. All alive GT patients show stable engraftment of functionally corrected lymphoid cells, without adverse events. Transduced B cells number and WASP expression increased progressively after GT. Absolute B cell count attained normal values in all the patients, and correlates with WASP expression and VCN in B cells. IgM levels are below normal ranges in four patients. P3 and P4 attained a B-cell phenotype within normal ranges; P3 discontinued intravenous immunoglobulin (IvIg) replacement. No expansion of CD21low B cells was observed. P1 and P5 (follow-up 18 months) present a variable defect in SM, naives and/or MZ B cells. P1 recently developed autoimmune manifestations; no significant changes were observed concomitantly. A defect in B cell lymphopoiesis was observed before GT as measured by KRECs analysis, normalizing after GT (P1, P3 and P4). Several complications were recorded in patients undergoing mismatched allogeneic HSCT, including dysimmunity, arthritis, developmental deficit and infections. Total B cell count normalized in eight patients, IgM levels were low in three. Among patients with available information, four still remain under IvIg replacement. Four patients developed a mixed lymphoid and myeloid chimerism, variably associated with low B cell count, low IgM and IvIg replacement. A complete B cell assessment for these patients is ongoing. Conclusions. B cell transgene expression is obtained after lentiviral vector-mediated GT in WAS patients and is associated with improved B cell lymphopoiesis. A correct B cell phenotype is observed in two patients who did not receive rituximab prior GT. The question whether this is related to the treatment will need a longer follow-up to be answered. Patients undergoing mismatched allogeneic HSCT present a higher frequency of complications. Although a higher proportion of these patients discontinued IvIg replacement, B cell reconstitution is not optimal. Analysis of patients in particular with mixed chimerism will provide important information in the setting of GT. The analysis of B cell reconstitution after GT and mismatched allogeneic HSCT deserves particular attention in the assessment of immunological reconstitution. Disclosures No relevant conflicts of interest to declare.

Background: "Drepagreffe" is a French national prospective trial involving 67 sickle cell anemia (SCA)-children with a history of abnormal cerebral arterial velocities by TCD, and comparing for the first time the outcome of cerebral vasculopathy following transfusion program (TP) or transplantation (HSCT). Inclusion criteria at enrollment were children with SCA (SS/Sb0), younger than 15 years, with a history of abnormal cerebral arterial velocities (TAMMX ≥ 200 cm/sec) and placed on long-term TP, with at least one non-SCA sibling, and with parents accepting HLA-typing and HSCT if a genoidentical donor was available. The 2 arms (TP/HSCT) were defined by the random-availability of a genoidentical donor. Seven of the 67 patients had a history of stroke. Transplanted patients (n=32) received a conditioning regimen of Busilvex-CY 200 mg/kg and 20 mg/kg rabbit Thymoglobulin, with CSA and a short course of MTX or MMF for GvHD prophylaxis. In the TP arm (n=35), HbS% was maintained at < 30%, with an Hb at 9-11g/dL. At enrollment and 12 months post-enrollment, blood screening, Doppler, and cerebral MRI/MRA were performed along with cognitive performance testing, the latter being done in parallel in the non-SCA siblings. Preliminary findings on cerebral velocities as the primary endpoint were reported at the last ASH meeting (abstract 67237), and demonstrated that all patients were alive at one year and that the 32 transplanted patients had no chronic GVHD and the same hemoglobin profile as their donor. Velocities were significantly lower post-HSCT than under TP (p Patients and Methods: We report here the cerebral imaging (MRI/MRA) and cognitive performance data performed at enrollment and after 12 months. The scoring applied for MRI was: 3 = territorial, 2 = borderzone (cortical and subcortical), 1 = white matter or basal ganglia infarcts, 0 to 3 = atrophia, and for MRA: 1 = mild stenosis (25-49%), 2 = moderate stenosis (50-74%), 3 = severe stenosis (75-99%), 4 = occlusion for each artery and 0 to 2 for Moya presence. Cognitive testing using the WPPSI-3 (3-6 yr), WISC-4 (7-16 yr) or WAIS-3 (>16 yr) scales, depending on the age, was performed in patients and in siblings when possible. Results: MRI/MRA data were available in 66/67 patients. At enrollment (M0), ischemic lesions and stenoses were present in 25 and 35/66 patients, respectively. Cognitive testing was obtained in 64 patients and 56 siblings. Paired analysis with siblings (Table 1) showed significant differences in Verbal Comprehension Index (VCI) with a mean difference of 7.6±14.5(p =0.0004), Processing Speed Index (PSI) 6.3±20.5 (p =0.04), and Full Scale IQ (FSIQ) 7.3±15.0 (p =0.01). After exclusion of the 7 patients with stroke history, significant differences were still observed in VCI (p =0.013) and FSIQ (p =0.019). Patient cognitive performance indexes were correlated negatively and significantly with the MRI and MRA scores (Table 2). At post-enrollment (M12),ischemic lesions and stenoses were present in 26/66 patients. The mean variation in MRI and MRA scores between M12 and M0 was not significantly different between the 2 arms (Table 3). The cognitive tests were performed at M12 in 60 patients (Table 4) and the performance indexes were improved in the TP compared to the HSCT arm, but only significantly for FSIQ. Conclusion This first prospective trial initially showed that HSCT reduces more significantly the cerebral velocities at M12 and in a higher proportion of patients than TP. Here, we show that patients with a history of abnormal cerebral velocities had significantly lower cognitive performances than their siblings, even in the absence of stroke history; however, there was no significant difference between the 2 arms for the outcomes of ischemic lesions and stenosis at M0 and M12. The fact that cognitive performances were improved in the TP compared to the HSCT arm might be explained by the stress of the HSCT procedure and the lack of schooling during this period. Despite the higher ability of HSCT to decrease velocities at M12 compared to TP, a longer follow-up will be required to demonstrate its effect on stenosis and cognitive performances; therefore, patients will be reassessed at 3 years post-HSCT. Disclosures Bernaudin: Novartis: Research Funding.

Background : Evidence-based practices have shown that transfusion program (TP) is beneficial to SCA-patients with abnormally high velocities by Doppler; however, TP cannot be stopped safely, except following HSCT. No prospective trial has to date compared the extent of cerebral vasculopathy following TP or HSCT. The premise of the French National Trial “Drepagreffe” is that cerebral velocities will be reduced to a greater extent after HSCT than under TP. Patients and Methods : We present here preliminary results from this prospective trial with 2 arms (TP/HSCT), defined by the random-availability of a genoidentical donor. Inclusion criteria were SCA (SS/Sb0) children younger than 15 years with a history of abnormal cerebral arterial velocities (TAMMX ≥ 200 cm/sec), placed on long-term transfusion programs, with at least one non-SCA sibling and parents accepting HLA-typing and HSCT if a genoidentical donor was available. Transplanted patients received as conditioning regimen Busilvex-CY 200 mg/kg and 20 mg/kg rabbit Thymoglobulin with CSA and short MTX or MMF for GVHD prophylaxis. In the TP arm, HbS% was maintained at < 30% with Hb 9-11g/dL. At enrollment and 12 months post-enrollment, blood screening, Doppler, cerebral MRI/MRA were performed along with cognitive performance testing, the latter done in parallel in the control sibling. Primary endpoint was the significantly greater reduction of velocities in the HSCT than in the TP arm. Among the various secondary endpoints, Doppler normalization defined by velocities < 170 cm/s in all arteries was to occur more often after HSCT than on TP. Results: SCA-children (n=67; 36F-31M) from 10 French SCA-centers were enrolled between 12/2010 and 6/2013 at the mean (SD) age of 7.6 (3.1) years. History of stroke was present in 6 patients (4 in HSCT and 2 in TP) and 1 TIA in HSCT arm. At TP initiation, velocities≥200/cm/sec were found in middle (n=50), anterior (n=11) and internal carotid arteries (n=30) as abnormal velocities were observed in more than one artery in several patients. Mean (SD) maximum velocities were 219 (26) cm/s (range: 200-333). At enrollment all patients were on TP and paired analysis showed that mean(SD) maximum velocities had significantly decreased (p Conclusions: This prospective national trial comparing TP vs. HSCT in SCA-patients with a history of abnormal velocities shows for the first time that HSCT repeatedly and significantly results in a greater decrease in velocities than TP, and has very little toxicity. These preliminary results are encouraging and suggest that suppression of host SCA-erythropoiesis by HSCT is the treatment of choice for SCA-children with abnormal-TCD and genoidentical donor. Figure 1 Figure 1. Figure 2 Figure 2. Disclosures Bernaudin: Novartis: Research Funding.

Background : In patients with β-thalassemia major, hematopoietic stem cell (HSC) gene therapy has the potential to induce production of β-globin, γ-globin or modified β-globin in the red blood cell lineage and reduce or stop the need for blood transfusions. We have previously presented early results for 2 subjects with β/βE -thalassemia major that suggested that transplantation with autologous CD34+ cells transduced with a replication-defective, self-inactivating LentiGlobin BB305 lentiviral vector containing an engineered β-globin gene (βA-T87Q) resulted in near-normal levels of total hemoglobin (Hb) early after HSC infusion. Herein, we provide additional follow-up data on these two subjects. Subjects and Methods : After obtaining informed consent, subjects with β-thalassemia major underwent HSC collection via peripheral blood apheresis and CD34+ cells were selected. Estimation of the mean ex- vivo vector copy number (VCN) was obtained by quantitative PCR performed on pooled colony-forming progenitors. Subjects underwent myeloablation with intravenous busulfan, followed by infusion of transduced CD34+ cells. Subjects were monitored for hematological engraftment, βA-T87Q-globin expression (by high performance liquid chromatography) and transfusion requirements. Integration site analysis (ISA, by linear amplification-mediated PCR and high-throughput sequencing on nucleated cells) and replication-competent lentivirus (RCL) assays were performed. Results: As of 31 July 2014, two subjects with β0/βE thalassemia major (Subjects 1201 and 1202) have undergone infusion with drug product. The outcome of these two subjects to date is shown in Table 1. The initial safety profile is consistent with myeloablation, without serious adverse events or drug product-related adverse events. Both subjects remain transfusion independent. ISA analyses in both the subjects at 3 months shows polyclonal reconstitution. An additional 2 subjects have been enrolled in this study but have not yet undergone drug product infusion. Conclusion: In the first two subjects, early transfusion independence was achieved and has been maintained as of 31 July 2014. Further follow up data on these two subjects and additional data on subjects who have undergone drug product infusion in this study will be presented. Gene therapy using autologous HSC transduced with LentiGlobin BB305 lentiviral vector is a promising approach for the treatment of patients with β-thalassemia major. | Subject | Age (years) and gender | Genotype | BB305 Drug Product | Day of Neutrophil Engraftment | Drug Product-related Adverse Events | Day of last pRBC transfusion | Day of last follow up | βA-T87Q-Hb at last follow-up visit /Total Hb (g/dL) | | ------- | ----------------------------- | -------- | ------------------ | ----------------------------- | ----------------------------------- | ---------------------------- | --------------------- | --------------------------------------------------- | -------- | | VCNa | CD34+ cell dose (x106 per kg) | | 1201 | 19 F | β/βE | 1.5 | 8.9 | Day +13 | None | Day +10 | Day +180 | 7.2/10.2 | | 1202 | 16 M | β/βE | 2.1 | 13.6 | Day +15 | None | Day +12 | Day +90 | 6.8/11.0 | Abstract 4797. Table 1. Preliminary Results of Dosing Parameters and Transplantation Outcomes As of 31 July 2014 a VCN, mean vector copy number Disclosures Payen: bluebird bio, Inc: Consultancy. Beuzard: bluebird bio, Inc: Consultancy, Equity Ownership. Sandler: bluebird bio, Inc: Employment, Equity Ownership. Soni: bluebird bio, Inc.: Employment, Equity Ownership. De Montalembert: Novartis : Speakers Bureau. Leboulch: bluebird bio: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding.

Abstract 664 Severe combined immune deficiency (SCID) diseases, as well as other severe T-cell deficiencies like Omenn syndrome, are considered pediatric emergencies. To date, hematopoietic stem cell transplantation (HSCT) is the only curative therapy for these children. Considering the urgency of these transplants, for patients lacking an identical sibling donor, the use of mismatched related donors (MMRD) and unrelated umbilical cord blood (UCB) are important alternatives. In a retrospective study, we compared the outcomes of 175 children with severe T-cell deficiencies (SCID=152, Omenn syndrome=23) receiving MMRD transplants and 74 (SCID=52, Omenn syndrome=15) receiving UCB transplants, reported to the SCETIDE and Eurocord databases, from 1995 to 2005. MMRD transplants were performed in 12 different centers and UCB transplants were distributed among 30 different centers. Only 5 centers performed the two techniques. The median age at transplant was 6.4 months for the UCB group and 6.5 months for the MMRD group (p=0,87). Median time elapsed between diagnosis and transplant was 47 days for MMRD (range 4-485) and 55 days (range 17-526) for UCB transplants (p=0.06). There were no statistically significant differences between the two groups regarding gender and incidence of failure to thrive, chronic diarrhea or respiratory impairment before transplant. Patients receiving UCB had more often B-negative phenotype (61% UCB vs. 41% MMRD; p=0.009), while patients receiving MMRD had a greater incidence of viral infections prior to transplant (59% MMRD vs. 36% UCB; p=0.004). The year of transplantation also differed between the two groups, as more patients receiving UCB were transplanted between 2000-2005 (65%) compared to MMRD (50%) (p=0.014). Regarding HLA (considering HLA-A,B-low resolution and DRB1-high resolution), in the UCB group, 67% of patients had 0 or 1 disparities while 33% had 2 or 3 disparities. In the MMRD group, 10% had 1 disparity and 90% had 2 or 3 disparities. Seven patients receiving UCB (16%) transplants and 30 patients receiving MMRD (17%) did not receive any preparative regimen prior to graft infusion. Conditioning regimen was non-myeloablative in 45% of MMRD transplants and 30% of UCB transplants. The remaining received myeloablative regimens. Graft-versus-host disease (GVHD) prophylaxis was cyclosporine A-based in the majority of the UCB transplants (n=71). T-cell depletion was used in all transplants with MMRD and 52 patients received immunosuppressants, mostly cyclosporine A. The median follow-up time was 84 months for patients given a MMRD and 59 months for UCB transplants recipients. Sixty-one patients receiving UCB transplants engrafted (82%), all with full donor chimerism in CD3+ cells. On the CD3- compartment 75% had full donor, 5% mixed and 20% had recipient chimerism. In MMRD group, 130 patients engrafted (74%), 98% with full donor chimerism in CD3+ cells. On CD3- cells, 33% had full donor chimerism, 48% were mixed and 19% recipient chimerism. Forty-six patients in the MMRD group and 7 patients in the UCB group needed to receive second transplants. The cumulative incidence of acute GVHD had no statistically significant difference between groups (33% UCB vs. 23% MMRD; p=0.13). However, patients receiving UCB transplants had more chronic GVHD (22% UCB vs. 11% MMRD; p=0.04). In a univariate analysis, 5-year overall survival was 62 ± 4% for MMRD and 58% ± 6% for UCB transplants (p=0.83). In a multivariate analysis adjusting for differences between the two groups, 5-year overall survival was not statistically different (p=0.54). Regarding T-cell reconstitution, we analyzed the total lymphocyte, CD3+ and CD4+ cell numbers and there were no statistically significant differences between the two groups comparing absolute numbers at 6, 12 and 24 months after transplantation. In conclusion, both unrelated cord blood and mismatched related donors are choices for transplants in severe T-cell deficiencies lacking an HLA-identical sibling donor. The choice of donor type will depend on centre's strategy regarding the possibility of efficiently deplete MMRD grafts of T-cells, or find a rapidly available UCB unit. Disclosures: No relevant conflicts of interest to declare.

Introduction: Hepatic veno-occlusive disease (VOD) is one of the most significant regimen-related toxicities of stem cell transplantation (SCT), which when complicated by multi-organ failure (MOF) has a case fatality rate >90%. Defibrotide (DF) is a polydisperse oligonucleotide, with anti-thrombotic, anti-ischemic and thrombolytic properties, especially on microvasculature. Results in earlier studies of DF therapy for VOD/MOF have consistently shown manageable toxicity with promising complete response (CR) rates and D+100 survival post SCT. We report the results of the largest compassionate use program (CUP) performed to date. Methods: Physicians in Europe requesting DF for the treatment of pts with VOD obtained the drug on a named patient basis and were requested to collect data by a standardized CRF. Patients (pts) were reviewed to identify the nature and frequency of Suspected Adverse Drug Reactions (SADR). CR and D+100 survival post-SCT were assessed with CR defined as bilirubin Conclusions: In this largest study of pts treated with DF to date, no unexpected toxicities were reported and side effects were generally manageable. CR was obtained in 52% with D+100 survival in 46%, including 34% in those pts with severe disease. This is consistent with prior studies and suggests that DF offers a relatively safe and effective treatment for hepatic VOD post SCT.

Hepatic Sinusoidal Obstruction Syndrome (SOS) following high dose cytotoxic therapy remains a serious complication after heamatopoietic stem cell transplantation (HSCT). Genetic polymorphisms that interfere with metabolism of drugs used in conditioning regimens have been associated with SOS after HSCT. In order to study this association in children given a HSCT for inherited diseases of the heamatopoietic system we have analyzed candidate genes in 99 children: 35 who developed SOS and in 64 children who did not develop SOS; both groups were transplanted in the same center and matched for year of transplant (from 1998 to 2004). Four families of candidate genes were analyzed: P450 cytochrome [CYP2B6*2(C64T), *3(C777A), *4(A785G), *5(C1459T), *6(G516T)], Glutathione-S-Transferases [GSTM1 (null), GSTT1 (null), GSTP1 (A313G)], Methylenetetrahydrofolate reductase [MTHFR (C677T)] and Vitamin D receptor [VDR (ApaI, TaqI and BsmI)]. The most frequent diagnosis was severe combined immunodeficiency. The two groups had no statistical differences for gender, diagnosis, type of transplant and source of stem cells. Conditioning regimen consisted in busulfan and cyclophosphamide in 91% of SOS patients and 87% of non-SOS patients (p=ns). There was no statistical difference on the frequency of all gene polymorphisms studied in both groups of patients, except for the gene CYP2B6*2 (C64T). In fact, the mutant allele T (genotypes CT or TT) was present in 31% of SOS patients and 9% of remainders (p=0.01). CYP2B6 is known to play an important role in the metabolism of chemotherapeutic agents such as cyclophosphamide (CY). In conclusion, we found that the polymorphism in CYP2B6*2 allele of the P450 cytochrome family is more frequent in children with inherited diseases who have developed SOS after HSCT than in those who did not develop SOS. This finding may define better surveillance and prophylaxis of SOS for children with the mutant allele of CYP2B6*2 given a HSCT.

Background: In children busulfan (Bu) is often included in conditioning regimens prior to allogeneic (allo-) haematopoietic stem cell transplantation (HSCT). The IV Bu formulation represents a substantial improvement over the oral Bu form for the control of Bu-systemic drug exposure (AUCs) and for successful targeting, but the age-based dosing (3–4 years cut-off) is not likely to be the optimal strategy (L Nguyen et BMT 2004). We tested IVBu fixed dose body-weight (BW) based calculation combined with cyclophosphamide (Cy) as conditioning regimen prior to allo-HSCT. Aims: To validate and confirm the PK relevance of this new dosing strategy which allows to target AUC (900–1500 μM.min) in children, To investigate the safety especially the early non-relapse mortality (NRM), to evaluate the consequences of such IVBu administration modalities upon children clinical outcomes. Methods: Thirty-six children (21 male/15 female) with a median age and weight of 7.5 y (range 0.3 to 17.2 y) and 27 kg (range 5.0 to 62.0) were enrolled. Indications for HSCT were: AML (n = 17: 14 CR1, 2 CR2, 1 PR), CML (n = 3), ALL (n = 1), MDS (n = 1), SAA (n = 1); hemoglobinopathy (n = 8), and immunodeficiency (n = 5). IVBu (Busilvex®) was given over 2 h q6h × 16 doses at: 1.0 mg/kg, 1.2 mg/kg, 1.1 mg/kg, 0.95 mg/kg, and 0.8 mg/kg for pts with 23–34 kg, and >34 kg BW, respectively. Cy was given at 50 mg/kg qd×4. Donors were HLA-matched related (28/36) or unrelated (5/36). Pharmacokinetics (PK) of Bu at dose 1, 9, and 13, and regimen-related toxicity (RRT) were determined. Cumulative incidence (Ci) of relapse / NRM, and Kaplan-Meier EFS/OS were estimated. Results: PK results are available in 28/36 pts. Although Bu clearance was highly variable (CV= 45%), the average AUCs after 1st and subsequent doses were similar whatever age and BW. In 75 % of pts AUC was within the target AUC. Mean AUC at dose 1 was 1205 ± 187 μM.min (range 963–1619 μM.min). All pts engrafted at 19 days (range 9–47) for neutrophils ≥ 0.5 ×109/L, and 30 days (range 16–111) for platelets ≥ 50 ×109/L. Donor cells (DC) were documented in all recipients: 31/36 achieved complete chimerism (> 99% DC), and 5/36 were mixed chimeras (> 85% DC). IVBu was well tolerated: one grade (G) IV toxicity (pulmonary), G III (mainly stomatitis) occurred in 14 pts. VOD occurred in 8% (95% CI: 1.8–22.5%) but none was severe. Grades II–IV a-GVHD rate was 42%. There was one death (3%) at day+100, and Ci of NRM was 6% ±8% (hemorrhage =1, c-GVHD =1). After a median follow-up of 36.7 months (range 3.9–49.1) the Ci of relapse, EFS and OS rates were: 12% ±11%, 82% ±13%, and 85% ±12%, respectively. For pts with malignancies (mainly AML) the results are excellent: neither VOD nor NRM, and EFS and OS rates were 82% ±16%, and 86% ±14%, respectively. Conclusions: The new IVBu dosing optimises Bu treatment, confirming that IVBuCy is an efficacious, reduced-toxicity, myeloablative conditioning regimen for children undergoing standard HSCT.