BackgroundImmunodysregulation polyendocrinopathy enteropathy x-linked(IPEX) syndromeis a monogenic autoimmune disease caused by FOXP3 mutations. Because it is a rare disease, the natural history and response to treatments, including allogeneic hematopoietic stem cell transplantation (HSCT) and immunosuppression (IS), have not been thoroughly examined.ObjectiveThis analysis sought to evaluate disease onset, progression, and long-term outcome of the 2 main treatments in long-term IPEX survivors.MethodsClinical histories of 96 patients with a genetically proven IPEX syndrome were collected from 38 institutions worldwide and retrospectively analyzed. To investigate possible factors suitable to predict the outcome, an organ involvement (OI) scoring system was developed.ResultsWe confirm neonatal onset with enteropathy, type 1 diabetes, and eczema. In addition, we found less common manifestations in delayed onset patients or during disease evolution. There is no correlation between the site of mutation and the disease course or outcome, and the same genotype can present with variable phenotypes. HSCT patients (n = 58) had a median follow-up of 2.7 years (range, 1 week-15 years). Patients receiving chronic IS (n = 34) had a median follow-up of 4 years (range, 2 months-25 years). The overall survival after HSCT was 73.2% (95% CI, 59.4-83.0) and after IS was 65.1% (95% CI, 62.8-95.8). The pretreatment OI score was the only significant predictor of overall survival after transplant (P = .035) but not under IS.ConclusionsPatients receiving chronic IS were hampered by disease recurrence or complications, impacting long-term disease-free survival. When performed in patients with a low OI score, HSCT resulted in disease resolution with better quality of life, independent of age, donor source, or conditioning regimen.

Sickle cell disease (SCD) is caused by a single amino acid change in the adult hemoglobin (Hb) β chain that causes Hb polymerization and red blood cell (RBC) sickling. The co-inheritance of mutations causing fetal γ-globin production in adult life hereditary persistence of fetal Hb (HPFH) reduces the clinical severity of SCD. HPFH mutations in the HBG γ-globin promoters disrupt binding sites for the repressors BCL11A and LRF. We used CRISPR-Cas9 to mimic HPFH mutations in the HBG promoters by generating insertions and deletions, leading to disruption of known and putative repressor binding sites. Editing of the LRF-binding site in patient-derived hematopoietic stem/progenitor cells (HSPCs) resulted in γ-globin derepression and correction of the sickling phenotype. Xenotransplantation of HSPCs treated with gRNAs targeting the LRF-binding site showed a high editing efficiency in repopulating HSPCs. This study identifies the LRF-binding site as a potent target for genome-editing treatment of SCD.

β-globin gene transfer into hematopoietic stem cells (HSCs) has the potential to reduce or eliminate the symptoms and long-term complications of severe sickle cell disease (SCD). LentiGlobin Drug Product (DP) is a gene therapy product containing autologous CD34+ cells transduced with the BB305 lentiviral vector. BB305 encodes a human β-globin gene containing a single point mutation (AT87Q) designed to confer anti-sickling properties similar to those observed in fetal hemoglobin (γ-globin). In two ongoing studies, subjects with transfusion-dependent β-thalassemia (Studies HGB-204 and HGB-205) or SCD (Study HGB-205) receiving LentiGlobin DP have demonstrated sustained expression of 3-9 g/dL therapeutic hemoglobin (HbAT87Q) and have shown marked improvements in clinical symptoms 1 year post-treatment. Study HGB-206 is a multi-center, Phase 1/2 safety and efficacy study of LentiGlobin DP in adults with severe SCD. We previously (ASH 2015) presented results from 2 subjects, who had 3 and 6 months of follow-up after LentiGlobin treatment. We now present data from 7 treated subjects, 4 of whom have ≥6 months of follow-up data. Subjects (≥18 years of age) with severe SCD (history of recurrent vaso-occlusive crisis [VOC], acute chest syndrome, stroke, or tricuspid regurgitant jet velocity of >2.5 m/s) were screened for eligibility. Following bone marrow harvest (BMH), CD34+ cells were transduced with the BB305 vector. Subjects underwent myeloablative conditioning with busulfan prior to infusion of the transduced cells. Safety assessments include adverse events (AEs), integration site analysis (ISA) and surveillance for replication competent lentivirus (RCL). After infusion, subjects are monitored for hematologic engraftment, vector copy number (VCN), HbAT87Q expression, and other laboratory and clinical parameters. As of July 2016, 7 subjects with severe SCD (median age: 26 years, range 18-42 years) have received LentiGlobin DP in this study. All subjects successfully underwent BMH, with a median of 2 harvests required (range 1-4). Fifteen Grade 3 AEs in 5 subjects were attributed to BMH: pain (n=10), anemia (n=3) and VOC (n=2); all resolved with standard measures. Table 1 summarizes cell harvest, DP characteristics, and lab results. The median LentiGlobin DP cell dose was 2.1x10e6 CD34+ cells/kg (range 1.6-5.1) and DP VCN was 0.6 (0.3-1.3) copies/diploid genome. Median post-infusion follow-up as of July 2016 is 7.1 months (3.7-12.7 months). All subjects successfully engrafted after receiving LentiGlobin DP, with a median time to neutrophil engraftment of 22 days (17-29 days). The toxicity profile observed from start of conditioning to latest follow-up was consistent with myeloablative conditioning with single-agent busulfan. To date, there have been no DP-related ≥Grade 3 AEs or serious AEs, and no evidence of clonal dominance or RCL. The BB305 vector remains detectable at low levels in the peripheral blood of all subjects infused, with median VCN 0.08 (0.05-0.13, n=7) at last measurement. All subjects express HbAT87Q, with a median of 0.4g/dL (0.1-1.0 g/dL, n=7) at 3 months; most subjects demonstrated modest increases over time, and the 2 subjects with the longest follow-up expressed 0.31 and 1.2 g/dL HbAT87Q at 9 months. All 4 subjects with ≥6 months of follow-up experienced multiple VOCs in the 2 years prior to study entry (2-27.5 VOCs annually). Since LentiGlobin DP infusion, 3 of these 4 subjects have had fewer VOCs, although this trend may be confounded by the short follow-up, the effects of transplant conditioning, and/or post-transplant RBC transfusions. The decrease in VCN between DP and peripheral cells contrasts with previous reports of successful LentiGlobin gene therapy in ongoing studies HGB-204 and HGB-205. The relatively low in vivo VCN in this study appears to result in the lower HbAT87Q expression seen to date. We are exploring multiple hypotheses as to the etiology of the VCN drop between DP and peripheral blood, including the adverse impact of sickle marrow pathology on HSCs, the adequacy of myeloablation, and the magnitude of the transduced cell dose. We will provide an update on study data and ongoing efforts to increase in vivo VCN in patients with SCD, such as increasing the transduced cell dose through alternate HSC procurement methods or enhancing the DP VCN through manufacturing improvements. Disclosures Kanter: Novartis: Consultancy. Walters:Bayer HealthCare: Honoraria; AllCells, Inc./LeukoLab: Other: Medical Director ; ViaCord Processing Laboratory: Other: Medical Director ; Leerink Partners, LLC: Consultancy; Kiadis Pharma: Honoraria; bluebirdBio, Inc: Honoraria. Kwiatkowski:Ionis pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Shire Pharmaceuticals: Consultancy; Sideris Pharmaceuticals: Consultancy; Apopharma: Research Funding; Luitpold Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees. von Kalle:bluebird bio: Consultancy; GeneWerk: Equity Ownership. Kuypers:Children's Hospital Oakland Research Institute: Employment; bluebird bio: Consultancy. Leboulch:bluebird bio: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Research Funding. Joseney-Antoine:bluebird bio: Employment, Equity Ownership. Asmal:bluebird bio: Employment, Equity Ownership. Thompson:bluebird bio: Consultancy, Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Research Funding; Amgen: Research Funding; Baxalta (now part of Shire): Research Funding; ApoPharma: Consultancy, Membership on an entity's Board of Directors or advisory committees; Mast: Research Funding; Eli Lily: Research Funding.

This review article summarizes the clinical outcomes and genotoxicity issues of gene therapy for hemoglobinopathies based on lentiviral vectors carrying a β-globin–like gene or genome editing to correct the erythropoietic defect.

In gene therapy with human hematopoietic stem and progenitor cells (HSPCs), each gene-corrected cell and its progeny are marked in a unique way by the integrating vector. This feature enables lineages to be tracked by sampling blood cells and using DNA sequencing to identify the vector integration sites. Here, we studied 5 cell lineages (granulocytes, monocytes, T cells, B cells, and natural killer cells) in patients having undergone HSPC gene therapy for Wiskott-Aldrich syndrome or β hemoglobinopathies. We found that the estimated minimum number of active, repopulating HSPCs (which ranged from 2000 to 50 000) was correlated with the number of HSPCs per kilogram infused. We sought to quantify the lineage output and dynamics of gene-modified clones; this is usually challenging because of sparse sampling of the various cell types during the analytical procedure, contamination during cell isolation, and different levels of vector marking in the various lineages. We therefore measured the residual contamination and corrected our statistical models accordingly to provide a rigorous analysis of the HSPC lineage output. A cluster analysis of the HSPC lineage output highlighted the existence of several stable, distinct differentiation programs, including myeloid-dominant, lymphoid-dominant, and balanced cell subsets. Our study evidenced the heterogeneous nature of the cell lineage output from HSPCs and provided methods for analyzing these complex data.

Background: CD40 ligand (CD40L) deficiency, an X-linked primary immunodeficiency, causes recurrent sinopulmonary, Pneumocystis and Cryptosporidium species infections. Long-term survival with supportive therapy is poor. Currently, the only curative treatment is hematopoietic stem cell transplantation (HSCT). Objective: We performed an international collaborative study to improve patients' management, aiming to individualize risk factors and determine optimal HSCT characteristics. Methods: We retrospectively collected data on 130 patients who underwent HSCT for CD40L deficiency between 1993-2015. We analyzed outcome and variables' relevance with respect to survival and cure. Results: Overall survival (OS), event-free survival (EFS), and disease-free survival (DFS) were 78.2%, 58.1%, and 72.3% 5 years after HSCT. Results were better in transplantations performed in 2000 or later and in children less than 10 years old at the time of HSCT. Pre-existing organ damage negatively influenced outcome. Sclerosing cholangitis was the most important risk factor. After 2000, superior OS was achieved with matched donors. Use of myeloablative regimens and HSCT at 2 years or less from diagnosis associated with higher OS and DFS. EFS was best with matched sibling donors, myeloablative conditioning (MAC), and bone marrow-derived stem cells. Most rejections occurred after reduced-intensity or nonmyeloablative conditioning, which associated with poor donor cell engraftment. Mortality occurred mainly early after HSCT, predominantly from infections. Among survivors who ceased immunoglobulin replacement, T-lymphocyte chimerism was 50% or greater donor in 85.2%. Conclusion: HSCT is curative in patients with CD40L deficiency, with improved outcome if performed before organ damage development. MAC is associated with better OS, EFS, and DFS. Prospective studies are required to compare the risks of HSCT with those of lifelong supportive therapy.

Gene therapy using patient's own stem cells is rapidly becoming an alternative to allogeneic stem cell transplantation, especially when suitably compatible donors cannot be found. The advent of efficient virus-based methods for delivering therapeutic genes has enabled the development of genetic medicines for inherited disorders of the immune system, hemoglobinopathies, and a number of devastating metabolic diseases. Here, we briefly review the state of the art in the field, including gene editing approaches. A growing number of pediatric diseases can be successfully cured by hematopoietic stem-cell-based gene therapy.

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