A Severe Mouse Model of Alpha-Thalassemia to Study Abnormal Iron Metabolism and Erythropoiesis, Hematopoietic Stem Cell Behavior and Development of a Gene Therapy Approach for Its Treatment

Abstract Alpha thalassemia (α-thal) is caused by insufficient production of the α-globin protein because of either deletional or non-deletional inactivation of endogenous α-globin genes. Clinical presentation of deletional α-thal varies from an asymptomatic condition (one inactivated α-globin gene) to a complete knockout (Hb Bart's Hydrops Fetalis). In patients with severe α-thal, a blood transfusion independent state is achievable through allogeneic bone marrow transplantation. The aims of this study are to develop a novel adult mouse model of α-thal and a gene therapy approach for this disease. We generated adult animals that do not produce α-globin chains (α-KO) through transplantation of homozygous B6.129S7-Hbatm1Paz/J fetal liver cells (FLC; isolated at E14.5) into WT recipient mice. These animals demonstrate a worsening phenotype, paradoxically showing elevated hematocrit, high reticulocyte count and a high number of red blood cells (RBC) which expressed only β-globin chains (HbH). RBC show aberrant morphology and aggregation of α- globin tetramers on RBC membranes. Due to severe inability of these RBC to deliver oxygen, the mice eventually succumb to anemia, showing splenomegaly and other organ pathologies, including vaso-occlusive events. These animals show iron deposition in the liver and kidney, in agreement with very low levels of hepcidin expression in the liver, and elevated erythropoietin (EPO) in the kidney. Interestingly, α-KO embryos show lower numbers of FLC compared to WT embryos, lower frequency of engraftable hematopoietic stem cells (HSC; Lin-Sca-1+c-kit+CD48-), decreased clonogenic potential (fewer class 4 CFUs) and elevated erythroferrone. Lethally irradiated mice transplanted with FLC-KO require 5-6x as many cells as those transplanted with FLC-WT for recovery, further suggesting some level of engraftment impairment. Our current hypothesis is that excessive hypoxia in the embryos impairs HSC function and stem cell fitness. Additional assays are in progress to assess the nature of this impairment. To generate a gene therapy tool to rescue these animals and eventually cure severe human α-thal patients, we screened multiple lentiviral vectors to identify the variant capable of producing the highest human α-globin protein per copy. The selection was conducted in murine erythroleukemia cells and human umbilical cord derived erythroid progenitor (HUDEP) cells, modified by knocking out all the human α-globin genes. We identified ALS20α, a vector where α-globin is under control of the β-globin promoter and its locus control region, as the most efficient vector. One copy of ALS20α produces exogenous α-globin at a level comparable to that produced by one endogenous α-globin gene. These results suggest that a relatively low VCN could result in dramatic therapeutic benefits. Transplantation of ALS20α transduced murine BM-KO results in correction of the disease phenotype in a dose-dependent manner. At VCN<1 we observe a delay in death proportional to the VCN value, while at VCN>1 we observe phenotypic normalization, including Hb, hepcidin and EPO levels. We tested ALS20α in CD34 cells isolated from four patients with both deletional and non- deletional HbH disease. We measured the change of β/α-globin mRNA ratio (β/αR) and protein level by HPLC in erythroblasts derived from these cultures. For the specimen with mutational HbH, the initial β/αR matches that of healthy controls, as the mutations do not eliminate the ability for the gene to produce aberrant mRNA transcripts, and decreased with increasing VCN. Erythroblasts with deletional HbH have a β/αR approximately 3x higher than normal cells, decreasing in a dose dependent manner with increasing VCN. HPLC detection of HbH (β4), a hallmark of HbH disease, is observed in hemolysis products from all non-transduced α−thal erythroblasts. A ~50% reduction of HbH is detected in the very same specimens upon integration of ALS20α (VCN between 1 and 2). In conclusion, we generated an adult mouse model of lethal α-thal and, in preliminary experiments, we rescue it with ALS20α. Furthermore, ALS20α successfully improves α-globin levels in patient cells. Further experiments are in progress to establish the consistency of our vector's expression in vivo, as well as to demonstrate its ability to transduce bona fide long-term HSCs. Disclosures Kattamis: Agios Pharmaceuticals: Consultancy; IONIS: Consultancy; VIFOR: Consultancy; CRISPR/Vertex: Consultancy, Honoraria; BMS/Celgene: Consultancy, Honoraria, Research Funding; Chiesi: Honoraria; Novartis: Consultancy, Honoraria, Research Funding; Amgen: Consultancy. Rivella: Celgene Corporation: Consultancy; Keros Therapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees; Disc Medicine: Consultancy, Membership on an entity's Board of Directors or advisory committees; MeiraGTx: Consultancy, Membership on an entity's Board of Directors or advisory committees; Forma Theraputics: Consultancy; Incyte: Consultancy; Ionis Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees.

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Inducible SBDS Deficiency Impairs Bone Marrow Niche Function to Engraft Donor Hematopoietic Stem Cell after Transplantation

Blood ◽

10.1182/blood-2019-121763 ◽

2019 ◽

Vol 134 (Supplement_1) ◽

pp. 3199-3199

Author(s):

Ji Zha ◽

Lori Kunselman ◽

Hongbo Michael Xie ◽

Brian Ennis ◽

Jian-Meng Fan ◽

...

Keyword(s):

Bone Marrow ◽

Stem Cell ◽

Mouse Model ◽

Board Of Directors ◽

Hematopoietic Stem Cell ◽

Graft Failure ◽

Advisory Committees ◽

Hematopoietic Stem ◽

Bm Niche ◽

Deficient Mice

Hematopoietic stem cell (HSC) transplantation (HSCT) is required for curative therapy for patients with high-risk hematologic malignancies, and a number of non-malignant disorders including inherited bone marrow failure syndromes (iBMFS). Strategies to enhance bone marrow (BM) niche capacity to engraft donor HSC have the potential to improve HSCT outcome by decreasing graft failure rates and enabling reduction in conditioning intensity and regimen-associated complications. Several studies in animal models of iBMFS have demonstrated that BM niche dysfunction contributes to both the pathogenesis of iBMFS, as well as impaired graft function after HSCT. We hypothesize that such iBMFS mouse models are useful tools for discovering targetable niche elements critical for donor engraftment after HSCT. Here, we report the development of a novel mouse model of Shwachman-Diamond Syndrome (SDS) driven by conditional Sbds deletion, which demonstrates profound impairment of healthy donor hematopoietic engraftment after HSCT due to pathway-specific dysfunctional signaling within SBDS-deficient recipient niches. We first attempted to delete Sbds specifically in mature osteoblasts by crossing Sbdsfl/flmice with Col1a1Cre+mice. However, the Col1a1CreSbdsExc progenies are embryonic lethal at E12-E15 stage due to developmental musculoskeletal abnormalities. Alternatively, we generated an inducible SDS mouse model by crossing Sbdsfl/flmice with Mx1Cre+ mice, and inducing Sbds deletion in Mx1-inducible BM hematopoietic and osteolineage niche cells by polyinosinic-polycytidilic acid (pIpC) administration. Compared with Sbdsfl/flcontrols, Mx1CreSbdsExc mice develop significantly decreased platelet counts, an inverted peripheral blood myeloid/lymphoid cell ratio, and reduced long-term HSC within BM, consistent with stress hematopoiesis seen in BMF and myelodysplastic syndromes. To assess whether inducible SBDS deficiency impacts niche function to engraft donor HSC, we transplanted GFP+ wildtype donor BM into pIpC-treated Mx1CreSbdsExc mice and Sbdsfl/flcontrols after 1100 cGy of total body irradiation (TBI). Following transplantation, Mx1CreSbdsExc recipient mice exhibit significantly higher mortality than controls (Figure 1). The decreased survival was related to primary graft failure, as Mx1CreSbdsExc mice exhibit persistent BM aplasia after HSCT and decreased GFP+ reconstitution in competitive secondary transplantation assays. We next sought to identify the molecular and cellular defects within BM niche cells that contribute to the engraftment deficits in SBDS-deficient mice. We performed RNA-seq analysis on the BM stromal cells from irradiated Mx1CreSbdsExc mice versus controls, and the results revealed that SBDS deficiency in BM niche cells caused disrupted gene expression within osteoclast differentiation, FcγR-mediated phagocytosis, and VEGF signaling pathways. Multiplex ELISA assays showed that the BM niche of irradiated Mx1CreSbdsExc mice expresses lower levels of CXCL12, P-selectin and IGF-1, along with higher levels of G-CSF, CCL3, osteopontin and CCL9 than controls. Together, these results suggest that poor donor HSC engraftment in SBDS-deficient mice is likely caused by alterations in niche-mediated donor HSC homing/retention, bone metabolism, host monocyte survival, signaling within IGF-1 and VEGF pathways, and an increased inflammatory state within BM niches. Moreover, flow cytometry analysis showed that compared to controls, the BM niche of irradiated Mx1CreSbdsExc mice contained far fewer megakaryocytes, a hematopoietic cell component of BM niches that we previously demonstrated to be critical in promoting osteoblastic niche expansion and donor HSC engraftment. Taken together, our data demonstrated that SBDS deficiency in BM niches results in reduced capacity to engraft donor HSC. We have identified multiple molecular and cellular defects in the SBDS-deficient niche contributing to this phenotype. Such niche signaling pathway-specific deficits implicate these pathways as critical for donor engraftment during HSCT, and suggest their potential role as targets of therapeutic approaches to enhance donor engraftment and improve HSCT outcome in any condition for which HSCT is required for cure. Disclosures Olson: Merck: Membership on an entity's Board of Directors or advisory committees; Bluebird Bio: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Miltenyi: Honoraria.

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CML-CP Mouse Model of Genomic Instability.

Blood ◽

10.1182/blood.v116.21.1210.1210 ◽

2010 ◽

Vol 116 (21) ◽

pp. 1210-1210

Author(s):

Elisabeth Bolton ◽

Linda Kamp ◽

Hardik Modi ◽

Ravi Bhatia ◽

Steffen Koschmieder ◽

...

Keyword(s):

Stem Cells ◽

Dna Damage ◽

Stem Cell ◽

Mouse Model ◽

Board Of Directors ◽

Genomic Instability ◽

Oxidative Dna Damage ◽

Advisory Committees ◽

Hematopoietic Stem ◽

Dependent Effect

Abstract Abstract 1210 Background: BCR-ABL1 transforms hematopoietic stem cells to induce chronic myeloid leukemia in chronic phase (CML-CP). Although CML is stem cell-derived, it is a progenitor cell-driven disease. In CML-CP, leukemia stem cells (LSCs) are characterized by elevated BCR-ABL1 expression in comparison to leukemia progenitor cells (LPCs). Increased expression of BCR-ABL1 kinase is also associated with progression from CML-CP to CML-blast phase. Previously we showed that BCR-ABL1 kinase stimulates reactive oxygen species (ROS)-dependent DNA damage resulting in genomic instability in vitro, which was responsible for acquired imatinib-resistance and accumulation of chromosomal aberrations (Nowicki et al., Blood, 2005; Koptyra et al., Blood, 2006; Koptyra et al., Leukemia, 2008). Result: To examine the effects of BCR-ABL1 expression on genomic instability during in vivo leukemogenesis we employed an inducible transgenic mouse model of CML-CP with targeted expression of p210BCR-ABL1 in hematopoietic stem and progenitor cells (Koschmieder et al., Blood, 2005). Mice exhibiting CML-CP-like disease resulting from BCR-ABL1 induction demonstrated splenomegaly, leukocytosis, and Gr1+/CD11b+ myeloid expansion in bone marrow, spleen and peripheral blood, as detected by FACS analysis. BCR-ABL1 mRNA expression was higher in Lin-c-Kit+Sca1+ stem-enriched cells than in Lin-c-Kit+Sca1- progenitor-enriched cells, thus reminiscent of CML-CP (LSCs>LPCs). BCR-ABL1 increased levels of ROS (hydrogen peroxide, hydroxyl radical) and oxidative DNA lesions (8-oxoG) in LSC-enriched Lin-c-Kit+Sca1+ cells. Preliminary data also suggested that quiescent (CFSEmax) Lin-c-Kit+Sca1+ cells from BCR-ABL1-induced mice exhibited greater ROS (superoxide) production than non-induced counter parts. Moreover, higher levels of ROS were detected in BCR-ABL1-positive Lin-c-Kit+Sca1+ stem-enriched population in comparison to BCR-ABL1-positive Lin-c-Kit+Sca1- progenitor population, suggesting a dosage-dependent effect of BCR-ABL1. To confirm that BCR-ABL1 exerts a dosage-dependent effect on ROS-induced oxidative DNA damage, we showed that the levels of ROS, 8-oxoG and DNA double-strand breaks were proportional to BCR-ABL1 kinase expression in murine 32Dc13 and human CD34+ cells. Conclusion: In summary, this mouse model recapitulates the BCR-ABL1 expression profile attributed to stem and progenitor populations in human CML-CP. It also shows that the BCR-ABL1-positive, stem cell-enriched Lin-c-Kit+Sca1+ population displays elevated levels of ROS and oxidative DNA damage in comparison to normal counterparts, which makes it suitable to study the mechanisms of genomic instability in LSCs. Single nucleotide polymorphism (SNP) arrays will shed more light on the genomic instability of this BCR-ABL1-induced transgenic model of CML-CP. Disclosures: Koschmieder: Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS: Membership on an entity's Board of Directors or advisory committees.

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Activation of ULK1 Kinase Mediates Clearance of Free Alpha-Globin in Human Beta-Thalassemic Erythroblasts

Blood ◽

10.1182/blood-2018-99-113901 ◽

2018 ◽

Vol 132 (Supplement 1) ◽

pp. 411-411

Author(s):

Christophe Lechauve ◽

Julia Keith ◽

Eugene Khandros ◽

Stephanie Fowler ◽

Kalin Mayberry ◽

...

Keyword(s):

Board Of Directors ◽

Protein Quality ◽

Therapeutic Potential ◽

Dependent Manner ◽

Ineffective Erythropoiesis ◽

Advisory Committees ◽

Mtor Inhibition ◽

Hematopoietic Stem ◽

Rapamycin Treatment ◽

Α Chain

Abstract β-Thalassemia is a common, frequently debilitating, inherited anemia caused by HBB gene mutations that reduce or eliminate the expression of the β-globin subunit of adult hemoglobin (HbA, α2β2). Consequently, excess free α-globin forms toxic precipitates in red blood cells (RBCs) and their precursors, leading to ineffective erythropoiesis and hemolytic anemia. Previously, we showed that free α-globin is eliminated by protein quality-control pathways, including the ubiquitin-proteasome system and autophagy (Khandros et al., Blood 2012;119:5265). In β-thalassemic mice, disruption of the Unc-51-like autophagy activating kinase gene (Ulk1) increased α-globin precipitates and worsened the pathologies of β-thalassemia. Treatment of β-thalassemic mice with rapamycin to inhibit mTOR (an ULK1 inhibitor) reduced α-globin precipitates, lessened ineffective erythropoiesis, and increased the lifespan of circulating RBCs in an Ulk1-dependent fashion. To investigate the therapeutic potential of rapamycin in human β-thalassemia, we treated erythroid precursors generated by in vitro differentiation of patient-derived CD34+ hematopoietic stem and progenitor cells. Reverse-phase high-performance liquid chromatography (HPLC) analysis of hemoglobinized erythroblasts generated from transfusion-dependent (TD, n = 5) or non-transfusion-dependent (NTD, n = 5) β-thalassemia patients revealed α-chain excesses (α-chain/β-like [β + γ + δ] chain) of approximately 40% and 15%, respectively (compared to 7 normal donors; P < 0.001). Rapamycin (10µM or 20µM) or the proteasome inhibitor MG132 (2.5µM) was added to day 13 cultures, which contained mid- to late-stage erythroblasts, and α-globin accumulation was determined by HPLC 2 days later. As expected, proteasome inhibition by MG132 raised free α-globin levels in thalassemic erythroblasts (P < 0.01) and induced cell death (P < 0.01). In contrast, rapamycin reduced free α-globin in a dose-dependent manner by 40% and 85% in TD (P < 0.0001) and NTD β-thalassemia (P < 0.001), respectively, but had no effect on erythroblasts derived from normal CD34+ cells (figure). We also observed decreases in the accumulation of autophagic markers, such as SQSTM1/p62 protein, by Western blotting. We observed no negative effects of rapamycin on the survival of patient-derived erythroblasts. Also of note, under our experimental conditions, rapamycin treatment of erythroblasts did not induce fetal hemoglobin production, as has been previously reported, thereby excluding this potential mechanism for reducing globin chain imbalances. Overall, rapamycin treatment significantly reduced the accumulation of free α-globin in TD β-thalassemia and almost fully corrected the imbalance in NTD β-thalassemia cells. Our findings identify a new drug-regulatable pathway for ameliorating β-thalassemia. Rapamycin is approved and well studied, and it has a generally manageable toxicity profile. Moreover, there are additional pharmacologic approaches to activating ULK via mTOR inhibition or other pathways. These approaches may lead to effective drug therapies for β-thalassemia, particularly NTD or intermittently TD forms of the disease. Disclosures Cappellini: Celgene Corporation: Membership on an entity's Board of Directors or advisory committees; Vifor: Membership on an entity's Board of Directors or advisory committees; Sanofi/Genzyme: Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria.

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Interim Results from a Phase 1/2 Clinical Study of Lentiglobin Gene Therapy for Severe Sickle Cell Disease

Blood ◽

10.1182/blood.v128.22.1176.1176 ◽

2016 ◽

Vol 128 (22) ◽

pp. 1176-1176 ◽

Cited By ~ 19

Author(s):

Julie Kanter ◽

Mark C. Walters ◽

Matthew M. Hsieh ◽

Lakshmanan Krishnamurti ◽

Janet Kwiatkowski ◽

...

Keyword(s):

Gene Therapy ◽

Board Of Directors ◽

Research Funding ◽

Phase 1 ◽

Globin Gene ◽

Advisory Committees ◽

Cell Dose ◽

Cd34 Cells ◽

Equity Ownership

Abstract 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.

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Loss of Alpha Globin Genes in Human Subjects Is Associated with Improved Nitric Oxide-Mediated Vascular Perfusion

Blood ◽

10.1182/blood-2020-136745 ◽

2020 ◽

Vol 136 (Supplement 1) ◽

pp. 6-7

Author(s):

Christopher C Denton ◽

Payal Shah ◽

Silvie Suriany ◽

Honglei Liu ◽

Wanwara Thuptimdang ◽

...

Keyword(s):

Nitric Oxide ◽

Beneficial Effect ◽

Board Of Directors ◽

Globin Gene ◽

Globin Genes ◽

Vascular Perfusion ◽

Advisory Committees ◽

Alpha Thalassemia ◽

Alpha Globin ◽

Thalassemia Trait

Introduction Absence of alpha globin genes has long been known to influence the physiology of sickle cell disease (SCD). Individuals with SCD who are missing one or two alpha globin genes have decreased rates of cerebral vasculopathy, stroke, acute chest syndrome, and leg ulcers (Bernaudin, Blood 2008; Flanagan, Blood 2011; Nolan, Br J Haematol 2006). Although there is laboratory evidence of decreased hemolytic rate in these patients (Higgs, N Engl J Med 1982), the mechanism for their improved clinical outcomes has not been identified. Recently, the alpha globin protein has been shown to be present in the endothelial wall of human arterioles, where it modulates nitric oxide (NO) scavenging during vasoconstriction (Straub, Nature 2012). In mice, pharmacological inhibition of alpha globin leads to increased endothelial NO activity, independently of NO production, and results in increased blood perfusion, reduced systemic hypertension, and increased pulmonary artery vasodilation (Keller, Hypertension 2016; Alvarez, Am J Respir Cell Mol Biol 2017). The relationship between absence of alpha globin and arterial vasodilation, and the role of alpha globin in NO-mediated vascular signaling are potential mechanisms that could explain the beneficial effect of missing alpha globin genes in SCD. Using alpha thalassemia as a naturally occurring human model of alpha globin gene knockout, we hypothesized that loss of alpha globin genes leads to improvement in microvascular blood flow in thalassemia trait subjects without hemolysis. Methods Alpha thalassemia trait subjects missing one or two alpha globin genes, and healthy controls were recruited to the study, which was approved by the Children's Hospital Los Angeles Institutional Review Board. Blood samples were obtained from all subjects to test for hemoglobin, mean corpuscular volume (MCV), reticulocyte count, plasma hemoglobin, lactate dehydrogenase, and alpha globin genotype. We assessed flow-mediated dilation (FMD) of the brachial artery following distal forearm occlusion (Detterich, Blood 2015) simultaneously with laser Doppler flowmetry (LDF) and photoplethysmography (PPG) in the fingertip. We also measured the increase in microvascular perfusion with a thermal stimulus. The maximal change in vascular perfusion after provocation indicates vasodilatory capacity. Statistical analysis was performed in JMP® version 14 (SAS Institute Inc., USA). Results Twenty-seven subjects were enrolled, including 12 controls (4 alpha globin genes), 10 patients with 3 alpha globin genes and 5 with 2. The mean MCV was lower in subjects missing alpha globin genes than in controls (p=0.0099). Importantly, hemoglobin levels and markers of hemolysis were normal in both groups. There was no detectable difference in FMD between individuals missing one and two alpha globin genes; thus, these groups were combined and labeled as alpha trait for further analyses. FMD was significantly higher in alpha trait subjects after adjusting for age (Figure 1, p=0.0357). Missing alpha globin genes had no effect on microvascular flow by LDF or PPG (data not shown). Discussion FMD is an established and specific predictor of NO bioavailability (Thijssen, Am J Physiol Heart Circ Physiol 2011), and, in addition to shear-mediated NO circulation in conduit vessels, it reflects the sum of flow in multiple arteriolar networks downstream of the conduit artery. Using this method, a difference in endothelial function between control and alpha thalassemia trait was easily detected (Figure 1). Because endothelial alpha globin is present in arterioles rather than conduit vessels (Butcher, Free Radic Biol Med 2014), we measured microvascular flow in a 1-mm3 volume in the skin using a laser Doppler sensor, and in the fingertip by PPG, but were unable to detect an effect of alpha trait. As none of the subjects had anemia or evidence of hemolysis, the significantly increased FMD associated with loss of alpha globin genes is most likely due to increased NO as a result of decreased scavenging by alpha globin. The finding reported here that lower alpha globin gene number is associated with increased NO-related perfusion in humans may explain the beneficial effect of alpha thalassemia trait in SCD and suggests that the presence of alpha thalassemia trait may also play a role in other types of vascular disease. Disclosures Wood: BiomedInformatics: Consultancy; Imago Biosciences: Consultancy; BluebirdBio: Consultancy; Celgene: Consultancy; WorldcareClinical: Consultancy; Philips Medical Systems: Research Funding. Coates:apo pharma (Chiesi Pharma): Consultancy, Honoraria; Sangamo: Honoraria, Membership on an entity's Board of Directors or advisory committees; Agios pharma: Consultancy, Honoraria; Vifor Pharma: Consultancy, Honoraria; Celgene, BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Bluebird Pharma: Honoraria, Membership on an entity's Board of Directors or advisory committees.

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AVID200, a Potent Trap for TGF-β Ligands Inhibits TGF-β1 Signaling in Human Myelofibrosis

Blood ◽

10.1182/blood-2018-99-116474 ◽

2018 ◽

Vol 132 (Supplement 1) ◽

pp. 1791-1791 ◽

Cited By ~ 7

Author(s):

Lilian Varricchio ◽

John Mascarenhas ◽

Anna Rita Migliaccio ◽

Maureen O'Connor-McCourt ◽

Gilles Tremblay ◽

...

Keyword(s):

Stem Cell ◽

Board Of Directors ◽

Research Funding ◽

Type I Collagen ◽

Normal Donor ◽

Type I ◽

Cell Transplant ◽

Dependent Manner ◽

Advisory Committees ◽

Hematopoietic Stem

Abstract Myelofibrosis (MF) is caused by driver mutations which upregulate JAK/STAT signaling. The only curative treatment for MF is hematopoietic stem cell transplant. Ruxolitinib alleviates many of the symptoms in MF but does not significantly alter survival. There is, therefore, an urgent need for additional rational therapies for MF. Bone marrow fibrosis and collagen deposition are hallmarks of MF which have been attributed to megakaryocyte (MK) derived TGFβ, which also plays a role in myelo-proliferation. There are three isoforms of TGFβ (TGFβ1, β2, and β3). AVID200, which was constructed by fusing TGFβR ectodomains to IgG Fc regions, is a potent TGFβ trap with pM potency against two of the three TGFβ ligands, TGFβ1 and β3 (IC50 values of ~ 3 pM ). AVID200's IC50 for TGFβ2 is ~4,000-fold higher indicating that it has minimal activity against TGFβ2, which is desirable since TGFβ2 is a positive regulator of hematopoiesis. We explored the therapeutic potential of AVID200 by culturing MF or normal donor (ND) mononuclear cells (MNCs) first in the presence of stem cell factor and thrombopoietin (TPO) and then TPO alone in order to generate MK-enriched populations. Although the percentage of mature MKs from ND and MF MNCs was similar, the absolute number of CD41+/CD42+ MKs generated from MF MNCs was two-fold greater than ND MNCs. To determine the levels of TGFβ secreted by the MKs we screened MF and ND MNC conditioned media (CM). We observed significantly higher levels of TGFβ1 but not TGFβ2 and TGFβ3 in MF MK CM. The effects of AVID200 on MKs were then evaluated by measuring the levels of phosphorylated SMAD2. Treatment with 0.001 - 0.1 nM AVID200 decreased phosphorylation of SMAD2, suggesting that AVID200 blocks autocrine MK TGFβ signaling. The increased levels of TGFβ in MF patients promote the proliferation and deposition of collagen by mesenchymal stem cells (MSCs). Cellular proliferation of MSCs was evaluated following treatment with either recombinant TGFβ1 or ND/MF CM in the presence or absence of AVID200. In the absence of AVID200, both recombinant TGFβ1 and MK-derived CM increased the proliferation of MSCs by 1.4- and 1.6-fold respectively, which returned to basal levels with the addition of increasing concentrations of AVID200. These data indicate that AVID200 directly blocks the effect of TGFβ1 on MSCs. MF stroma is characterized by an increase in Type I collagen. We therefore examined if treatment with AVID200 interferes with the ability of TGFβ1 to induce collagen expression by MSCs. MSCs were cultured in presence of recombinant TGFβ1 alone or in combination with varying concentrations of AVID200 for 72 hours. Recombinant TGFβ1 alone induced an increase in COL1A1 mRNA expression as compared to untreated controls (p<0.01). Addition of AVID200 eliminated the TGFβ-mediated increase in COL1A1 expression in a dose dependent manner. ND and MF MK-derived CM also increased COL1A1 expression by MSCs as compared to un-treated controls (p<0.01) and that effect was eliminated by AVID200 treatment (p<0.01). We next demonstrated that TGFβ1 activated pSMAD2 in MSCs without affecting total SMAD2/3 expression and that SMAD2 phosphorylation was reduced by adding AVID200. Furthermore, AVID200 treatment decreased pSTAT3 which is associated with the ability of TGFβ to induce fibrosis. We next investigated the effect of AVID200 on MF hematopoiesis. Briefly, MNCs (which produce TGFβ) from two JAK2V617F+ MF patients were incubated with or without 50 nM of AVID200 and plated in semi-solid media. Treatment with AVID200 did not affect the overall number of colonies generated, but reduced the numbers of JAKV617F+ colonies while increasing the numbers of WT colonies: for PT1, there were 32% JAKV617F+ CFUs in untreated cultures (11 JAKV617F+/34 total colonies) versus 16% JAKV617F+ CFUs (7 JAKV617F+/42 total CFUs) in AVID200 treated cultures; for PT2 there were 100% JAKV617F+ CFUs in untreated cultures (37 JAKV617F+/37 total CFUs) versus 94% JAKV617F+ CFUs (49 JAK2V617F+/52 total CFUs) in AVID200 treated cultures. The in vivo effects of AVID200 on the development of MF in GATA1 low mice will be presented at the meeting. These data indicate that AVID200 selectively suppresses TGFβ1 signaling associated with the proliferation of MSCs and type I collagen synthesis, and depletes MF MNCs of JAK2V617F+progenitor cells. We conclude that AVID200 is a promising agent for treating MF patients which will be evaluated in a phase 1 clinical trial. Disclosures Mascarenhas: Novartis: Research Funding; CTI Biopharma: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees; Roche: Research Funding; Janssen: Research Funding; Promedior: Research Funding; Merck: Research Funding; Incyte: Membership on an entity's Board of Directors or advisory committees, Research Funding. Iancu-Rubin:Incyte: Research Funding; Merck: Research Funding; Summer Road, LLC: Research Funding; Formation Biologics: Research Funding. Hoffman:Incyte: Research Funding; Summer Road: Research Funding; Merus: Research Funding; Janssen: Research Funding; Formation Biologics: Research Funding.

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Correction of β-thalassemia by CRISPR/Cas9 editing of the α-globin locus in human hematopoietic stem cells

Blood Advances ◽

10.1182/bloodadvances.2020001996 ◽

2021 ◽

Vol 5 (5) ◽

pp. 1137-1153 ◽

Cited By ~ 1

Author(s):

Giulia Pavani ◽

Anna Fabiano ◽

Marine Laurent ◽

Fatima Amor ◽

Erika Cantelli ◽

...

Keyword(s):

Oxygen Carrier ◽

Globin Gene ◽

Globin Genes ◽

Blood Disorders ◽

Erythroid Progenitor ◽

Gene Deletions ◽

Hematopoietic Stem ◽

Globin Chains ◽

Novel Strategy ◽

Novel Therapeutic Strategies

Abstract β-thalassemias (β-thal) are a group of blood disorders caused by mutations in the β-globin gene (HBB) cluster. β-globin associates with α-globin to form adult hemoglobin (HbA, α2β2), the main oxygen-carrier in erythrocytes. When β-globin chains are absent or limiting, free α-globins precipitate and damage cell membranes, causing hemolysis and ineffective erythropoiesis. Clinical data show that severity of β-thal correlates with the number of inherited α-globin genes (HBA1 and HBA2), with α-globin gene deletions having a beneficial effect for patients. Here, we describe a novel strategy to treat β-thal based on genome editing of the α-globin locus in human hematopoietic stem/progenitor cells (HSPCs). Using CRISPR/Cas9, we combined 2 therapeutic approaches: (1) α-globin downregulation, by deleting the HBA2 gene to recreate an α-thalassemia trait, and (2) β-globin expression, by targeted integration of a β-globin transgene downstream the HBA2 promoter. First, we optimized the CRISPR/Cas9 strategy and corrected the pathological phenotype in a cellular model of β-thalassemia (human erythroid progenitor cell [HUDEP-2] β0). Then, we edited healthy donor HSPCs and demonstrated that they maintained long-term repopulation capacity and multipotency in xenotransplanted mice. To assess the clinical potential of this approach, we next edited β-thal HSPCs and achieved correction of α/β globin imbalance in HSPC-derived erythroblasts. As a safer option for clinical translation, we performed editing in HSPCs using Cas9 nickase showing precise editing with no InDels. Overall, we described an innovative CRISPR/Cas9 approach to improve α/β globin imbalance in thalassemic HSPCs, paving the way for novel therapeutic strategies for β-thal.

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Genetic Engineering in Hematopoietic Stem Cells for Gene Therapy of Hemoglobinopathies

Blood ◽

10.1182/blood-2019-121119 ◽

2019 ◽

Vol 134 (Supplement_1) ◽

pp. SCI-23-SCI-23

Author(s):

Giuliana Ferrari

Keyword(s):

Stem Cells ◽

Gene Therapy ◽

Hematopoietic Stem Cells ◽

Conflicts Of Interest ◽

Globin Gene ◽

Genetically Modify ◽

Fetal Hemoglobin ◽

Beta Thalassemia ◽

Globin Genes ◽

Hematopoietic Stem

Beta-thalassemia and sickle cell disease (SCD) are congenital anemias caused by mutations in the beta-globin gene, resulting in either reduced/absent production of globin chains or abnormal hemoglobin structure. At present, the definitive cure is represented by allogeneic hematopoietic stem cell transplantation, with a probability to find a well-matched donor of <25%. Experimental gene therapy for hemoglobinopathies is based on transplantation of autologous hematopoietic stem cells genetically modified to express therapeutic hemoglobin levels. Approaches to genetically modify HSCs for treatment of hemoglobinopathies include: 1) the addition of globin genes by lentiviral vectors and 2) gene editing by nucleases to reactivate fetal hemoglobin either through inhibition of repressors or by reproducing mutations associated with high fetal hemoglobin levels. The outcomes of early clinical trials are showing the safety and potential efficacy, as well as the hurdles still limiting a general application.Current challenges and improved strategies will be presented and discussed. Disclosures No relevant conflicts of interest to declare. OffLabel Disclosure: Plerixafor

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Disturbed NK Cell Compartment In Human CML and Bcr-Abl Positive Mice.

Blood ◽

10.1182/blood.v116.21.1207.1207 ◽

2010 ◽

Vol 116 (21) ◽

pp. 1207-1207

Author(s):

Christiane I-U Chen ◽

Steffen Koschmieder ◽

Linda Kamp ◽

Bianca Altvater ◽

Sibylle Pscherer ◽

...

Keyword(s):

Mouse Model ◽

Nk Cells ◽

Board Of Directors ◽

Nk Cell ◽

Chronic Phase ◽

Target Cells ◽

Imatinib Treatment ◽

Cell Compartment ◽

Advisory Committees ◽

Hematopoietic Stem

Abstract Abstract 1207 Targeted pharmacologic therapy with tyrosine kinase inhibitors (TKIs) has become the first-line treatment for patients with CML. However, BCR-ABL+ stem cells resist elimination by continuous TKI treatment in most patients. By contrast, graft-versus-leukemia effects during allogeneic hematopoietic stem cell transplantation can eradicate the disease, suggesting an important role of the immune system in this disease. Besides cytotoxic T cells, natural killer (NK) cells may be involved in immune control of CML. Here, we explored numbers and functionality of NK cells in CML patients and in a transgenic inducible BCR-ABL mouse model. In 18 patients with newly diagnosed chronic-phase CML, the relative proportions of peripheral blood CD56+CD3- NK cells within the lymphocyte gate were significantly reduced compared to age-matched healthy controls (7.0 ± 5.8% versus 13.1 ± 5.1, p=0.005) and did not recover to normal levels during imatinib-induced remission (9.2 ± 5.9%, p=0.024, follow-up 10–59 months). Functional experiments showed reduced in vitro expansion of CML NK cells at diagnosis in response to stimulation with 4-1BBL/mbIL-15 transduced K562 cells (23.5 ± 14.46 fold vs 41.2 ± 7.2 fold, p=0.013) and under imatinib treatment (31.5 ± 10.5 fold, p=0.03), and a reduced degranulation response to K562 target cells by CD107 upregulation (2.8 ± 2.7% at diagnosis and 9.0 ± 13.2% under treatment, vs. 19.1 ± 8.0% in controls, p=0.003 and p=0.045, respectively). To investigate, whether the defective NK-cell compartment in CML is a consequence of the characteristic BCR-ABL-induced myeloproliferation, we addressed the quantity and functionality of NK cells in a double transgenic mouse model of human CML. Consistent with the results in human CML, the relative proportions of NK1.1+ NK cells among total splenic lymphocytes were significantly reduced in BCR-ABL induced mice (6.4 ± 3.5% vs. 14.7 ± 1.8%, p=0.005). Moreover, compared to NK cells isolated and expanded from BCR-ABL-non-induced control mice, the degranulation response of splenic NK cells from BCR-ABL+ mice to YAC-1/NIH-3T3 cells was significantly decreased (25.7 ± 1.6% vs 42.4 ± 5.6%, p=0.002), and analogous results were obtained with NK cells expanded from bone marrow of these mice (7.7 ± 4.9% vs. 25.0 ± 7.1%, p=0.033). These results suggest both quantitative and qualitative defects within the NK cell compartment in CML. Further work will aim at identifying the underlying mechanisms of the NK cell deficiency in CML, and the development of strategies to utilize NK cells for immunotherapy of CML. Disclosures: Koschmieder: Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS: Membership on an entity's Board of Directors or advisory committees.

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Eltrombopag Creates a Transient Chemical Phenocopy of TET2 Loss of Function That Contributes to Hematopoietic Precursor Expansion

Blood ◽

10.1182/blood-2019-131525 ◽

2019 ◽

Vol 134 (Supplement_1) ◽

pp. 453-453

Author(s):

Yihong Guan ◽

Bhumika J. Patel ◽

Metis Hasipek ◽

Dale Grabowski ◽

Hassan Awada ◽

...

Keyword(s):

Board Of Directors ◽

In Silico ◽

Structural Model ◽

Data Monitoring Committee ◽

Dependent Manner ◽

Loss Of Function ◽

Advisory Committees ◽

Hematopoietic Stem ◽

Free System ◽

Dose Dependent

Eltrombopag (Epag) is FDA approved for immune thrombocytopenic purpura (ITP) and aplastic anemia (AA), in which it induces tri-lineage responses in primary and refractory settings. These biologic effects suggest that Epag helps to regenerate not only committed megakaryocytic progenitors, but also hematopoietic stem and progenitor cells (HSPCs). Epag is a small molecule thrombopoietin receptor (TpoR) agonist that activates the JAK-STAT pathway to increase platelet counts similar to the polypeptide based TpoR agonist Nplate. In addition, some of Epag's activity may, unlike that of Nplate, be independent of TpoR. Epag increases HSC self-renewal in mice despite the lack of binding to murine TpoR and showed efficacy in a TpoR-deficient strain. Here we show that Epag binds and inhibits TET2 in an iron-chelation independent manner, to in this way increase precursor expansion. Since iron is a key prosthetic component of the TET2 enzyme, we determined if Epag sequestration of iron in HSPCs inhibits TET2 function. In silico modeling indicated that Epag can form a tripartate complex with Fe2+, αKG and TET2 (Fig.A). Epag interacted with TET2 via N1387 and H1984 forming a two-way H-bond and also coordinating Fe2+ sandwiched between N-Oxalylglycine a surrogate for aKG and H1381 residues of TET2 (Fig.A). To experimentally confirm the computational structural model and study the effect of Epag on TET2, we used an ELISA-based TET2 activity assay in a cell-free system. We found that Epag inhibits TET2 in a dose-dependent manner with an IC50 of 1.6±0.1 µM in the presence of 25 µM each of aKG and Fe2+ (Fig.B). Interestingly, this observed IC50 of Epag for TET2 inhibition is 10-fold lower than the plasma Cmax of Epag that is produced in humans at standard clinical doses. Therefore, we performed a dose dependent TET2 rescue experiment by increasing aKG and Fe2+. There was no proportional effect on the TET2 inhibitory IC50 of Epag upon increasing either Fe2+ or αKG suggesting the inhibition of TET2 is independent of both these co-factors (Fig.B). This was consistent with in silico structural model data indicating that Epag specifically binds and traps TET2 in an inactive state, explaining why increasing concentration of Fe2+ or Fe3+ failed to rescue TET2 activity (Fig.C). Also consistent with this model of how Epag inhibits TET2, we did not experimentally observe any significant effect of ascorbic acid (100 µM), known to activate TET2 through maintenance of Fe3+↔Fe2+ homeostasis during TET2 catalysis. Underscoring likely relevance of TpoR independent actions of Epag, Epag treatment of K562 cells displaying undetectable levels of TpoR mRNA as well as protein, significantly reduced levels of 5hmC, while Tpo had no effects on 5hmC (Fig.D). We are currently measuring, after written informed consent on an IRB approved protocol, 5hmc levels serially in patients who are receiving Epag. In summary, we demonstrate TpoR-independent actions of Epag, its direct inhibition of TET2 activity, most likely by locking TET2 in an inactive configuration. Given the fundamental role of TET2 in promoting differentiation, this mechanism-of-action of Epag could be one pathway by which it expands HSPCs, independent of TpoR. In short, Epag creates a transient chemical phenocopy of TET2 loss of function, simultaneously having the capacity to activate JAK-STAT signaling via TpoR. These actions together can explain the clinical potency of Epag. Figure Disclosures Nazha: Abbvie: Consultancy; Tolero, Karyopharma: Honoraria; Daiichi Sankyo: Consultancy; Incyte: Speakers Bureau; MEI: Other: Data monitoring Committee; Novartis: Speakers Bureau; Jazz Pharmacutical: Research Funding. Saunthararajah:Novo Nordisk: Consultancy; EpiDestiny: Consultancy, Equity Ownership, Patents & Royalties. Sekeres:Celgene: Membership on an entity's Board of Directors or advisory committees; Millenium: Membership on an entity's Board of Directors or advisory committees; Syros: Membership on an entity's Board of Directors or advisory committees. Maciejewski:Novartis: Consultancy; Alexion: Consultancy.

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