Gamma-globin Expression Research Articles

NR2F1 : A Novel Candidate for Gamma Globin Activation

The reactivation of human gamma globin holds tremendous promise as a potential treatment for hemoglobinopathies, including sickle cell disease and beta-thalassemia. Despite identifying various repressors of fetal globin genes in adult erythroid cells over the past decade, evidence concerning stage-specific factors that activate human fetal globin prior to the switch to adult beta-globin remains inadequately understood. In our study, we constructed an erythroid-specific gene regulatory network (GCN) by integrating multiple RNA-seq datasets from erythroid cells at different stages of differentiation and development. Our analysis unveiled both known HbF activators, like HIC2, and novel candidates. Among the novel contenders, NR2F1, a member of the steroid/thyroid hormone receptor superfamily, emerged as a prominent candidate. To validate our predictions, we overexpressed NR2F1 in Hudep2 cells and observed more than a four-fold increase (28% vs. 6%) in the proportion of F cells and a three-fold rise in HbF levels as measured by HPLC. In addition, the overexpression of NR2F1 did not appear to impact beta-globin expression or cell differentiation. Intriguingly, we observed a significant reduction in the protein level of BCL11A, a master regulator of HbF, despite no major change in the total RNA level of BCL11A. This observation suggests that NR2F1 plays a role in the post-transcriptional modification of BCL11A. Additionally, NR2F1 overexpression led to an upregulation of Lin28B expression in Hudep2 cells. Lin28B is known to directly bind BCL11A mRNA and prevent its effective translation without disturbing BCL11A transcription. Consequently, the observed upregulation of Lin28B in NR2F1-overexpressing cells implies a potential NR2F1-Lin28B-BCL11A axis involved in controlling human hemoglobin switching. In conclusion, our findings propose NR2F1 as a novel activator of gamma globin, representing an attractive target for gamma globin reactivation. Additional investigation is required to explore the molecular mechanisms through which NR2F1 regulates gamma globin expression and its role in the NR2F1-Lin28B-BCL11A axis.

Targeted Degradation of the Wiz Transcription Factor for Gamma Globin De-Repression

Sickle cell disease (SCD) is a life-threatening genetic condition arising from a point mutation in the β-globin gene that causes hemoglobin polymerization and vaso-occlusive sickling of erythrocytes. Hereditary persistence or pharmacologic induction of gamma-globin (HBG1 or HBG2) expression leads to increases in fetal hemoglobin (HbF) that biophysically oppose hemoglobin polymerization. Indeed, the standard-of-care, hydroxyurea (HU), increases expression of HbF in the erythroblast, and in patients the magnitude of response (9-24% HbF) correlates with a reduction in pain crises and acute complications. However, the use of HU is limited by variable response, myelosuppression, GI side effects and carcinogenicity risk. New targeted therapeutic approaches to induce HbF are therefore being intently pursued, leveraging the increasingly detailed functional characterization of the globin locus. The recent discovery of BCL11A as a repressor of HBG has prompted the widespread innovation of genetically engineered hematopoietic stem cells that suppress BCL11A expression or function. While a major advance in SCD therapeutics, the complexity and clinical implementation of stem cell transplantation may limit access and impact, especially in developing countries where SCD burden is greatest. We therefore undertook to discover a small-molecule HbF inducer, focusing on transcription factors that repress gamma-globin expression. Although transcription factors as a target class have historically been considered "undruggable," recent mechanistic characterization of phthalimide medicines as serendipitous, cereblon (CRBN)-dependent degraders of IKZF1 and IKZF3 by our organization and others, suggested the plausible degradation of new zinc-finger containing transcription factors by this emerging class of molecular glues. Therefore, we elaborated a large library of CRBN-biased ligands for study in target-directed and phenotypic drug discovery campaigns. Here we report for the first time the phenotypic discovery and structure-based optimization of two molecular glue degraders of the transcription factor, WIZ, which lead to pronounced de-repression of HbF. Using a chemical biology approach, the first molecule, dWIZ-1, was identified by phenotypic screening of a CRBN-biased chemical library for compounds that induce HbF without deleterious effect on erythroid cell proliferation and differentiation. Subsequent target deconvolution by global proteomics revealed WIZ as the target. WIZ knockout using two independent sgRNA elevated the proportion of γ-globin mRNA, HbF protein levels and HbF + cells (Figure 1) in vitro in primary human erythroblasts, validating WIZ as a previously unrecognized repressor of HbF. Optimization of dWIZ-1 led to a second tool compound, dWIZ-2, which was suitable to assess WIZ degradation and HbF induction in vivo due to its superior pharmacokinetic properties. dWIZ-2 treatment increased the proportion of γ-globin mRNA, HbF + cells and HbF protein levels in vitro in sickle cell disease patient-derived erythroblasts (Figure 2). Because many IMiDs lack activity in rodents, we used a humanized mouse model to measure the impact of dWIZ-2 on WIZ degradation and HbF expression in human erythroblasts in vivo. NBSGW mice humanized with CD34 + hematopoietic stem and progenitor cells from healthy human donors were orally dosed once daily with dWIZ-2 for 21 days. dWIZ-2 treatment resulted in robust dose-dependent WIZ degradation and an increase in total HbF and the proportion of HbF + human erythroblasts in the bone marrow. To further study the kinetics of HbF induction in the peripheral blood, and assess the effects of dWIZ-2 on steady-state hematopoiesis, we orally dosed naïve healthy cynomolgus monkeys with vehicle or 30 mg/kg dWIZ-2, once daily for 28 days. We detected elevated levels of γ-globin mRNA in the blood on day 28, reaching up to 37% of β-like globins. Additionally, on day 28, we observed up to 95% HbF + reticulocytes.dWIZ-2 was well-tolerated based on the absence of notable clinical observations during the study and consistent body weight for all animals. There were no dWIZ-2-related changes in hematology, coagulation or clinical chemistry measurements, specifically including reticulocytes, hematocrit and neutrophil counts. These findings support the development of an oral WIZ degrader as a globally accessible therapeutic approach for SCD.

The BACH1 inhibitor ASP8731 inhibits inflammation and vaso-occlusion and induces fetal hemoglobin in sickle cell disease.

In sickle cell disease (SCD), heme released during intravascular hemolysis promotes oxidative stress, inflammation, and vaso-occlusion. Conversely, free heme can also activate expression of antioxidant and globin genes. Heme binds to the transcription factor BACH1, which represses NRF2-mediated gene transcription. ASP8731, is a selective small molecule inhibitor of BACH1. We investigated the ability of ASP8731 to modulate pathways involved in SCD pathophysiology. In HepG2 liver cells, ASP8731 increased HMOX1 and FTH1 mRNA. In pulmonary endothelial cells, ASP8731 decreased VCAM1 mRNA in response to TNF-α and blocked a decrease in glutathione in response to hemin. Townes-SS mice were gavaged once per day for 4 weeks with ASP8731, hydroxyurea (HU) or vehicle. Both ASP8731 and HU inhibited heme-mediated microvascular stasis and in combination, ASP8731 significantly reduced microvascular stasis compared to HU alone. In Townes-SS mice, ASP8731 and HU markedly increased heme oxygenase-1 and decreased hepatic ICAM-1, NF-kB phospho-p65 protein expression in the liver, and white blood cell counts. In addition, ASP8731 increased gamma-globin expression and HbF+ cells (F-cells) as compared to vehicle-treated mice. In human erythroid differentiated CD34+ cells, ASP8731 increased HGB mRNA and increased the percentage of F-cells 2-fold in manner similar to HU. ASP8731 and HU when given together induced more HbF+ cells compared to either drug alone. In CD34+ cells from one donor that was non-responsive to HU, ASP8731 induced HbF+ cells ~2-fold. ASP8731 and HU also increased HBG and HBA, but not HBB mRNA in erythroid differentiated CD34+ cells derived from SCD patients. These data indicate that BACH1 may offer a new therapeutic target to treat SCD.

Potential Cytoprotective and Regulatory Effects of Ergothioneine on Gene Expression of Proteins Involved in Erythroid Adaptation Mechanisms and Redox Pathways in K562 Cells

This study aimed to establish the importance of ergothioneine (ERT) in the erythroid adaptation mechanisms by appraising the expression levels of redox-related genes associated with the PI3K/AKT/FoxO3 and Nrf2-ARE pathways using K562 cells induced to erythroid differentiation and H2O2-oxidative stress. Cell viability and gene expression were evaluated. Two concentrations of ERT were assessed, 1 nM (C1) and 100 µM (C2), with and without stress induction (100 µM H2O2). Assessments were made in three periods of the cellular differentiation process (D0, D2, and D4). The C1 treatment promoted the induction of FOXO3 (D0 and 2), PSMB5, and 6 expressions (D4); C1 + H2O2 treatment showed the highest levels of NRF2 transcripts, KEAP1 (D0), YWHAQ (D2 and 4), PSMB5 (D2) and PSMB6 (D4); and C2 + H2O2 (D2) an increase in FOXO3 and MST1 expression, with a decrease of YWHAQ and NRF2 was observed. in C2 + H2O2 (D2) an increase in FOXO3 and MST1, with a decrease in YWHAQ and NRF2 was observed All ERT treatments increased gamma-globin expression. Statistical multivariate analyzes highlighted that the Nrf2-ARE pathway presented a greater contribution in the production of PRDX1, SOD1, CAT, and PSBM5 mRNAs, whereas the PI3K/AKT/FoxO3 pathway was associated with the PRDX2 and TRX transcripts. In conclusion, ERT presented a cytoprotective action through Nrf2 and FoxO3, with the latter seeming to contribute to erythroid proliferation/differentiation.

Identification of novel HPFH-like mutations by CRISPR base editing that elevate the expression of fetal hemoglobin.

Naturally occurring point mutations in the HBG promoter switch hemoglobin synthesis from defective adult beta-globin to fetal gamma-globin in sickle cell patients with hereditary persistence of fetal hemoglobin (HPFH) and ameliorate the clinical severity. Inspired by this natural phenomenon, we tiled the highly homologous HBG proximal promoters using adenine and cytosine base editors that avoid the generation of large deletions and identified novel regulatory regions including a cluster at the -123 region. Base editing at -123 and -124 bp of HBG promoter induced fetal hemoglobin (HbF) to a higher level than disruption of well-known BCL11A binding site in erythroblasts derived from human CD34+ hematopoietic stem and progenitor cells (HSPC). We further demonstrated in vitro that the introduction of -123T > C and -124T > C HPFH-like mutations drives gamma-globin expression by creating a de novo binding site for KLF1. Overall, our findings shed light on so far unknown regulatory elements within the HBG promoter and identified additional targets for therapeutic upregulation of fetal hemoglobin.

Preclinical Development of EDIT301, an Autologous Cell Therapy Comprising AsCas12a-RNP Modified Mobilized Peripheral Blood-CD34 + Cells for the Potential Treatment of Transfusion Dependent Beta Thalassemia

Beta thalassemia is one of the most common recessive hematological disorders in the world with more than 200 mutations identified to date. These mutations reduce or completely abrogate beta globin expression. As beta globin pairs with alpha globin to form adult hemoglobin (HbA, α2β2), reduced or absent beta globin results in excessive alpha globin chains, which form toxic aggregates. These aggregates cause maturation blockade and premature death of erythroid precursors, and hemolysis of red blood cells (RBC), leading to varying degrees of anemia. Patients with the most severe form of beta thalassemia, namely beta thalassemia major, are transfusion-dependent, i.e., requiring life-long RBC transfusions accompanied by the burden of iron chelation therapy.EDIT-301 is an experimental autologous cell therapy in which CD34 + cells are genetically modified to promote gamma globin expression. EDIT-301 is currently in clinical development for sickle cell disease, and IND enabling stage for transfusion-dependent beta thalassemia (TDT). Gamma globin decreases the alpha to beta globin chain imbalance in beta thalassemia by pairing with the over-abundant alpha globin chains to form fetal hemoglobin (HbF, α2γ2). Gamma globin induction, and consequently HbF induction, for EDIT-301 is achieved through AsCas12a ribonucleoprotein (RNP)-mediated editing of the distal CCAAT box region of the HBG1 and HBG2 promoters, where naturally occurring hereditary persistence of fetal hemoglobin (HFPH) mutations exist. We chose this target over BCL11A based on previous preclinical data demonstrating that BCL11A editing reduces erythroid output in NBSGW mice. An engineered AsCas12a RNP edits the HBG1 and HBG2 promoter distal CCAAT box with high efficiency and specificity. We have previously shown that on-target editing of >80% was achieved in mobilized peripheral blood (mPB) CD34 + cells from normal donors with no detectable off-target editing both at research scale and at clinical manufacturing scale. Edited normal donor CD34 + cells led to long-term, polyclonal, multilineage engraftment without lineage skewing in immunocompromised mice and sustained robust HbF production in their erythroid progeny.To test whether EDIT-301 may be an efficacious therapy for TDT, mPB CD34 + cells from individuals with TDT were electroporated with the engineered AsCas12a RNP targeting the HBG1 and HBG2 promoters. AsCas12a RNP edited mPB CD34 + cells from individuals with TDT as efficiently as CD34 + cells from normal donors. Importantly, EDIT-301 has the potential to address the underlying pathophysiology of TDT, i.e., the maturation blockade and premature death of erythroid precursors. Erythroid differentiation of edited beta thalassemia CD34 + cells showed significant improvement in erythroid maturation and health. Specifically, ~70% edited erythroblasts reached late erythroblast stage compared to ~53% unedited erythroblasts; ~56% edited erythroid cells underwent terminal maturation and enucleated compared to ~28% of unedited erythroid cells; and non-viable erythroblasts decreased from ~33% to ~22% after editing. The improved erythropoiesis was accompanied by significantly increased total hemoglobin content per cell. These data strongly support that editing of the HBG1 and HBG2 promoter CCAAT box using engineered AsCas12a RNP can reverse the dyserythropoiesis associated with beta thalassemia and increase the hemoglobin production.In summary, we have provided strong preclinical data supporting the development of EDIT-301 for the treatment of TDT. Edited mPB CD34 + cells retained their ability to engraft without lineage skewing, resulted in robust HbF induction long-term, improved erythropoiesis, and increased hemoglobin content in TDT erythroid cells. These data support that a single administration of EDIT-301 may have the potential to safely and effectively reverse dyserythropoiesis and ameliorate anemia in individuals with TDT long-term. Clinical studies to demonstrate the safety and efficacy of EDIT-301 in the treatment of TDT are currently being planned. DisclosuresSousa: Editas Medicine: Current Employment, Current equity holder in publicly-traded company. Janoudi: Editas Medicine: Current Employment, Current equity holder in publicly-traded company. deDreuzy: Editas Medicine: Current Employment, Current equity holder in publicly-traded company. Shearman: Editas Medicine: Current Employment, Current equity holder in publicly-traded company. Zhang: Editas Medicine: Current Employment, Current equity holder in publicly-traded company. Chang: Editas Medicine: Current Employment, Current equity holder in publicly-traded company.

In Vivo HSC Transduction and Selection Results in Long-Term, High-Level Expression of Human Gamma Globin in Peripheral Blood Erythrocytes of Mice

Current protocols for HSC gene therapy, involving the transplantation of ex vivo lentivirus vector-transduced HSCs into myeloablated recipients, are complex and not without risk for the patient. We have developed a new approach for in vivo gene delivery into HSCs that does not require myeloablation and HSC transplantation. It involves injections of G-CSF/AMD3100 to mobilize HSCs from the bone marrow into the peripheral blood stream and the intravenous injection of an integrating, helper-dependent adenovirus (HDAd5/35++) vector system. Transgene integration is achieved (in a random pattern) using a hyperactive Sleeping Beauty transposase (SB100x). We demonstrated in adequate mouse models, using GFP as a transgene, that primitive HSCs transduced in the periphery home back to the bone marrow where they persist and stably express GFP long-term (Blood 128:2206 (2016). To achieve high level transgene marking in differentiated peripheral blood cells, we combined our in vivo HSC transduction approach with in vivo selection of transduced HSCs using the mgtmP140K mutant and low dose O6BG/BCNU treatment. Here were tested the potential of this approach for the therapy of hemoglobinopathies. Our HDAd5/35++ vector contained the human-gamma globin gene under the control of a 6kb version of the beta-globin LCR (containing HS1 to HS4 and the beta globin promoter) and the mgmtP140K gene under the control of the PGK promoter. Mobilized immunocompetent hCD46 transgenic mice were injected IV with the integrating vector system and subjected to three rounds of treatment with low-dose O6BG/BCNU followed by immunosuppression to avoid immune responses against the human transgene product. The procedure was safe and resulted in stable human gamma globin expression in >95% of erythrocytes in the peripheral blood of in vivo transduced cells mice. Human gamma globin levels were 100% of endogenous mouse beta globin levels in erythrocytes measured by HPLC. Analysis of bone marrow at week 16 after in vivo transduction showed that >60% of bone marrow LSK cells contained the integrated transgene cassette and that the beta globin LCR efficiently restricted gamma globin expression to erythroid cells. After transplantation of unsorted, lineage-depleted bone marrow cells into lethally irradiated recipients, long-term gamma-globin expression at levels seen in the primary in vivo treated mice was demonstrated. The efficacy of our approach achieved in this study indicates that it would be curative in thalassemia models or patients. Our new approach avoids the collection of HSCs, their transduction ex vivo, and subsequent transplantation into myeloablated recipients. It therefore could greatly simplify HSC gene therapy of common diseases. DisclosuresKiem:Rocket Pharmaceuticals: Consultancy, Equity Ownership, Patents & Royalties, Research Funding.

Screening Fetal Hemoglobin Inducing Compounds in Human Umbilical Cord Blood-Derived Erythroid Progenitor Cells

Background: Human Umbilical Cord Blood-Derived Erythroid Progenitor Cells-2 (HUDEP-2) cells are an immortalized human CD34+ hematopoietic stem and progenitor cell (HSPC)-derived erythroid precursor cell line that expresses BCL11A and β-globin. HUDEP-1 cells are an immortalized human CD34+ HSPC-derived erythroid precursor cell line that does not express BCL11A, predominantly expresses γ-globin, and exhibits an increase in γ-globin after differentiation. High baseline γ-globin and difficulty in distinguishing between true γ-globin induction and changes in HUDEP-1 differentiation, which increases g-globin, combined with the lack of β-globin expression, make HUDEP-1 cells a suboptimal system in which to study hemoglobin switching. HUDEP-2 cells have been used successfully to demonstrate HbF induction in several gene editing experiments involving deletion of BCL11A enhancer regions and substitution mutations in the γ-globin locus. HUDEP-2 also express very low levels of γ-globin; this has led to the hope that potential HbF inducing compounds can be screened in HUDEP-2 cells, causing them to express significant amounts of γ-globin, and potentially a reduction in β-globin expression, demonstrating hemoglobin switching.Objectives: Determine if HUDEP-2 cell lines are suitable systems in which to examine pharmacologic hemoglobin switching. We will determine if γ-globin induction can be achieved in HUDEP-2 cells from hydroxyurea, metformin, piceatannol, decitabine, or pomalidomide at doses that induce HbF in human HSPCs and raise γ-globin expression in HUDEP-1 cells.Methods: We performed drug treatment on differentiated HUDEP-1 andHUDEP-2 cells as well as hematopoietic stem and progenitor cells (HSPCs) from SCD patients with hydroxyurea, metformin, piceatannol, decitabine and pomalidomide at different doses. The effect of the drugs on HUDEP-1 differentiation was determined by measurement of Band3 by quantitative western blot. After 7 days of drug treatment, HbF was measured by western blot and HPLC in HSPCs, and by RT-qPCR (gamma globin expression) and western blot in HUDEP-1 and HUDEP-2.Results: Hydroxyurea, metformin, piceatannol, decitabine and pomalidomide all significantly increased γ-globin expression in HUDEP-1 cells, and HbF in HSPCs derived from patients with SCD. However, metformin was shown to increase HUDEP-1 differentiation, as measured by a rise in Band 3, which could explain the rise in γ-globin expression. HPLC analysis of the culture of HSPCs derived from patients with SCD showed that drug treatment with 30 µM hydroxyurea, 100 µM Metformin, 25 µM piceatannol or 200 nM decitabine produced a 2.3 fold, 2.1 fold, 3.1 fold, and 2.9 fold increase in HbF respectively. No change was observed in γ-globin expression or HbF in HUDEP-2 cells with any of the 5 drugs tested.Conclusions: γ-globin is not inducible in HUDEP-2 cells using hydroxyurea, metformin, piceatannol, decitabine and pomalidomide, known HbF inducing drugs that are believed to act through different pathways and mechanisms. It is therefore unlikely that HUDEP-2 cells will be effective in screening drug compounds for HbF induction activity. HUDEP-1 cells do show increased γ -globin levels in response to these agents, but care must be taken to show that the rise in γ-globin is not due to further differentiation of HUDEP-1 cells. DisclosuresNo relevant conflicts of interest to declare.

Improved Clinical Outcomes in Adults with Sickle Cell Disease and Diabetes Treated with Metformin

▪BackgroundComplications of sickle cell disease (SCD) include pain episodes, chronic anemia, cardiopulmonary disease, and long-term end-organ damage. Hydroxyurea is efficacious in preventing these complications by increasing fetal hemoglobin levels (HbF); however, adherence is limited. Metformin, a Food and Drug Administration-approved drug used for type-2 diabetes mellitus (DM), was recently found to induce HbF through upregulation of FOXO3 and gamma-globin expression. However, the relation of metformin utilization to clinical outcomes and healthcare utilization in adults with SCD and DM has not been studied.ObjectivesOur specific aims were to 1) estimate the prevalence of DM in a cohort of adult patients with SCD and 2) assess the association of metformin with clinical outcomes and healthcare utilization in this population. We hypothesized that adults with SCD and DM on metformin have less frequent SCD-related complication and lower utilization of hospital care for those complications.MethodsWe analyzed subjects with SCD and DM ≥18 years of age from the Truven Health MarketScan® Multi-State Medicaid Database from 2009-2015 with continuous enrollment of ≥365 days. Subjects with SCD and DM were identified through the presence of ≥1 inpatient or ≥2 outpatient disease-specific billing codes or ≥1 outpatient DM code and ≥1 DM-related drug claim. Subjects with drug claims for insulin, hydroxyurea, or iron chelation were excluded. Metformin use was defined as having ≥1 metformin-related drug claim in the study period. Outcomes included annual rates of all-cause inpatient hospitalizations, SCD-related hospitalizations, all-cause emergency department (ED) visits, SCD-related ED visits, vaso-occlusive episodes (VOE), strokes, acute chest syndrome (ACS) episodes, avascular necrosis (AVN) events, and gallstone events. Outcomes were identified based on claims records after the subject's first DM diagnosis record in the dataset. Clinical events among metformin users and non-users were compared using chi square tests. Rate ratios (RR) comparing annual rates of clinical events among metformin users to non-users were estimated using negative binomial regression, controlling for age, sex, and claims-data-defined Charlson Comorbidity Index (CCI) score.ResultsWe identified 7,617 subjects with SCD and 1,296 (17%) of them also had a diagnosis of DM. Our final cohort included a total of 375 subjects who met all our pre-defined criteria; of them, 126 (34%) were treated with metformin. Subjects were 72% female and 82% Black, and had a median age of 44 years (interquartile range (IQR) 33-52) and CCI score of 2 (IQR 0-4). All clinical events were less frequent in metformin users when compared to non-users, summarized in Table 1a, and subjects in both groups were similar in age, sex, race and CCI score. Using negative binomial regression, adjusted for age, sex and CCI score, metformin users had significantly lower all-cause inpatient stays (rate ratio (RR) 0.55; 95% confidence interval (CI) 0.42-0.72), SCD-related inpatient stays (RR 0.36; 95% CI 0.24-0.54), all-cause ED visits (RR 0.65; 95% CI 0.50-0.86), SCD-related ED visits (RR 0.43; 95% CI 0.27-0.68), VOE (RR 0.15; 95% CI 0.08-0.27), ACS (RR 0.14; 95% CI 0.03-0.59) and AVN (RR 0.29; 95% CI 0.09-0.91), compared to metformin non-users (Table 1b). Similar trends were also seen when patients were stratified by age as young adults (<40 years) vs. adults (≥40 years), as shown in Table 1b.ConclusionsThis study is the first to examine clinical associations of metformin use with SDC-related complications in adults with SCD and DM. These findings strongly suggest that metformin has important protective effects on all-cause and SCD-related hospital-treated clinical events. Among adults with SCD and DM, metformin users had 45% fewer SCD-related inpatient stays and roughly 85% fewer VOE or ACS episodes after controlling for confounding variables. These benefits are consistent with the effects of metformin on HbF induction observed in earlier laboratory data. An analysis of the effects of adherence to metformin on clinical outcomes and healthcare utilization in our cohort is ongoing. Given our findings and the known safety profile of metformin, future prospective studies are warranted to evaluate its efficacy and cost-effectiveness in relation to clinical outcomes, quality of life, mortality and healthcare utilization in adults with SCD. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

9-(2-Phosphonyl-methoxyethyl)-adenine promotes erythrocytic differentiation and disrupts cell replication in chronic myelogenous leukemia K562 cells

Disruption during cellular differentiation can cause hematopoietic stem cells to proliferate uncontrollably, resulting in the development of cancer. Differentiation therapies are being investigated as a type of cancer treatment which involve inducing agents that promote the differentiation of cancer cells into those with similar properties to normal blood cells. These cells can then undergo apoptosis at an accelerated and controlled rate compared to cancer cells, making this a potential therapeutic technique. In this study, the ability of human chronic myelogenous leukemia K562 cells to undergo cellular differentiation in response to the inducing agent 9-(2-Phosphonyl-methoxy ethyl)-adenine (PMEA) is investigated. PMEA has previously been shown to disrupt cell replication, and promote erythrocytic differentiation in K562 cells. In order to further test the effectiveness of this inducer, cell proliferation was measured with a cell growth curve, hemoglobin presence was measured with benzidine staining, and gamma-globin expression (a protein subunit of fetal hemoglobin) was measured in both induced and uninduced K562 cell cultures via RT-qPCR and western blotting. The results indicate that PMEA slows cell replication, and promotes hemoglobin (and subsequently gamma-globin) expression in treated cells. In summary, the findings support the conclusion that PMEA is able to promote erythrocytic differentiation in K562 cells, and provides information that supports differentiation therapies as a method for cancer treatment.

CD14+ monocytes repress gamma globin expression at early stages of erythropoiesis

In β-hemoglobinopathies, reactivation of gamma- at the expense of beta-globin is a prominent therapeutic option. Expression of the globin genes is not strictly intrinsically regulated during erythropoiesis, supported by the observation that fetal erythroid cells switch to adult hemoglobin expression when injected in mice. We show cultured erythroblasts are a mix of HbA restrictive and HbA/HbF expressing cells and that the proportion of cells in the latter population depends on the starting material. Cultures started from CD34+ cells contain more HbA/HbF expressing cells compared to erythroblasts cultured from total peripheral blood mononuclear cells (PBMC). Depletion of CD14+ cells from PBMC resulted in higher HbF/HbA percentages. Conversely, CD34+ co-culture with CD14+ cells reduced the HbF/HbA population through cell–cell proximity, indicating that CD14+ actively repressed HbF expression in adult erythroid cultures. RNA-sequencing showed that HbA and HbA/HbF populations contain a limited number of differentially expressed genes, aside from HBG1/2. Co-culture of CD14+ cells with sorted uncommitted hematopoietic progenitors and CD34-CD36+ erythroblasts showed that hematopoietic progenitors prior to the hemoglobinized erythroid stages are more readily influenced by CD14+ cells to downregulate expression of HBG1/2, suggesting temporal regulation of these genes. This possibly provides a novel therapeutic avenue to develop β-hemoglobinopathies treatments.

Establishing a Link between Zinc Homeostasis and Globin Gene Expression

Sickle cell disease (SCD) affects millions of people around the world and is the most common inherited disease in the United States, affecting 1 of 1800 births and 1 of 400 African-American births. Patients with SCD have an improved clinical course when fetal hemoglobin (HbF) levels are increased, and this is the basis for treatment with hydroxyurea as a disease modifying therapy. Hydroxyurea has been shown to decrease the frequency of pain episodes and decrease the incidence of stroke in patients who are at risk based on transcranial doppler velocities. Hydroxyurea is one of two FDA approved treatments for SCD patients, so there is need for new therapies, including the identification of druggable transcriptional activators that specifically up-regulate the gamma-globin genes (HbF). Understanding the mechanisms underlying control of globin gene expression, particularly those involved in activation of gamma-globin gene expression, is important for developing new treatments for SCD. Metal-responsive transcription factor-1 (MTF-1) is a key regulator of zinc metabolism in higher eukaryotes that controls the metal-inducible expression of metallothioneins and a number of other genes directly involved in the intracellular sequestration and efflux transport of zinc. Bao et al published that adults with SCD showed increased red blood cells (RBCs), hemoglobin (Hb) and hematocrit levels after 3 months of zinc supplementation compared to the placebo group. Furthermore, previous studies demonstrated that MTF-1 plays an essential role in liver development and that MTF-1-deficient mice display an anemic phenotype, suggesting a role for MTF-1 in hematopoiesis. In our study, we observed a 2.4-fold increase in gamma-globin expression in K562 cells at 4 hours. We also demonstrated increased gamma-globin expression in adult blood from MTF-1 overexpression, human beta-globin locus yeast artificial chromosome (beta-YAC) bi-transgenic (bigenic) mouse lines at the mRNA level by quantitative real-time RT-PCR (qPCR) and at the protein level by FACS analysis. Lastly, gamma-globin gene expression was induced 12-fold in bone marrow cells (BMCs) derived from these bigenic mice compared to BMCs derived from beta-YAC-only mice, and 3-fold after 6 hours of zinc treatment in beta-YAC-only BMCs. Co-immunoprecipitation (Co-IP) analysis showed that GATA-2 associated with MTF-1 in MTF-1 overexpression, beta-YAC BMCs, but not in beta-YAC-only BMCs, suggesting that reactivation of gamma-globin expression by MTF-1 might be mediated by a MTF-1-GATA-2 protein complex. Chromatin immunoprecipitation (ChIP) experiments indicated that MTF-1 and GATA-2 co-occupy the same sites in the gamma-globin promoter. Our data suggest that activation of gamma globin by MTF-1 is mediated by protein-protein interaction with GATA-2 and that this multi-protein complex is targeted to GATA sites located in the gamma-globin gene-promoters via binding of the GATA-2 protein. Based on our data, we hypothesize that zinc supplementation will increase plasma HbF by inducing MTF-1 thus activating gamma-globin gene expression. This protein represents a potential new target in strategies to reactivate gamma-globin in hemoglobinopathies where higher levels of HbF would have beneficial effects. More clinical and basic science studies are needed to further characterize the role of zinc in globin gene expression and hemoglobin F levels in the clinical setting. Disclosures No relevant conflicts of interest to declare.

Codanin-1 Mutations Engineered in Human Erythroid Cells Allow Investigation of Mechanisms Underlying Congenital Dyserythropoietic Anemia

The generation of a functional erythrocyte from a committed progenitor requires significant changes in gene expression during a time of hemoglobin accumulation, rapid cell division, and nuclear condensation. Disruption of this process is associated with myelodysplastic syndromes and congenital anemias. Congenital Dyserythropoietic Anemia type I (CDA-I), is an autosomal recessive disease that presents with severe macrocytic anemia early in infancy or early childhood. Patients with CDA-I have erythroid hyperplasia in the bone marrow. The erythroblasts in CDA-I are frequently binucleate, have chromatin bridging, and defective chromatin condensation (Renella 2011). CDA-I is most commonly caused by mutations in the protein codanin 1 (CDAN1). The function of CDAN1 is poorly understood, but it is thought to regulate histone incorporation into nascent DNA during cellular replication (Ask 2012). The study of CDA-1 has been limited by lack of in vitro models that recapitulate key features of the disease, and to date, the majority of studies on CDAN1 function have been done in non-erythroid cells. To model CDA-I we introduced a point mutation (PM) commonly observed in CDA-1 patients (R1042W) into HUDEP2 cells. In addition, we generated two HUDEP2 cell lines with heterozygous deletion of CDAN1 (del-R1042). All CDAN1 mutant cell lines had decreased viability in during both expansion and terminal maturation compared to control lines. Chromatin bridges and multinucleate cells were observed in all three mutant CDAN1 lines but were most prominent in the PM line. Intriguingly, global gene analysis demonstrated that all mutated lines had significantly elevated gamma-globin expression compared to controls, consistent with reports of elevated fetal globin expression in CDA-1 patients. Interestingly, the PM cell line had faster cell divisions than the del-R1042 or control lines, characterized by decreased doubling time and verified by quantifying dilution of a fluorescent dye. In contrast, the del-R1042 lines had slower cell doubling times than both the controls and the PM line. The PM line also had an increased median intensity of BrdU compared to controls and del-R1042 lines, suggesting an accelerated S-phase. KI67 staining of the PM line showed an increase percentage of mitotic cells. These data are consistent with the finding that multinucleate cells and chromatin bridges are more common in the PM line. Furthermore, electron microscopy suggests the PM cell line may have defects in heterochromatin formation. Together, these data imply a specific functional role for residue R1042, and suggest that within the context of R1042W, loss of the arginine residue and replacement thereof with a tryptophan may have different mechanistic consequences. Collectively, our preliminary data suggests that CDAN1 is important in the regulation of DNA replication and organization in maturing erythroblasts. Specific mutations may confer a change of function which results in dysplastic erythroid cells that are sensitive to dysregulated cell cycle mechanics due to the high rate of cell division. We hypothesize R1042W substitution may accelerate cell division at the expense of appropriate checkpoints and result in dysplastic erythroid cells and mimic the clinical presentation of increased multinuclearity, decreased cell viability, and increased gamma globin expression. Most importantly, generation of models with specific patient mutations will provide further mechanistic insight into CDA-I pathology. Disclosures No relevant conflicts of interest to declare.

Common Myeloid Progenitors As Biomarkers of Hbf Response to Hydroxyurea in Sickle Cell Disease

Background Hydroxyurea (HU) is used to treat sickle cell disease (SCD) in part because of its ability to increase hemoglobin F (HbF) concentration, but the mechanism by which HU induces HbF, and the low or lack of HbF response in a fraction of the patient remains unclear. HU causes myelo-suppression and induces stress hematopoiesis, which is associated with increase production of HbF. Earlier research has shown that HbF levels in SCD patients are inversely correlated with reticulocytes, which can be secondary to: 1) HbF-induced decreased hemolysis with less needs for red blood cell (RBC) production, and 2) Myelo-suppression. It has also been shown that the number of CD34+ cells is generally lower in HU treated patients, but the overall response of the hematopoietic system in relationship to HbF has not been characterized. Here, we prospectively isolated hematopoietic stem and progenitor cells (HSPCs) from HU-treated SCD patients and characterize their hematopoietic and HbF responses. Methods Peripheral blood (PB) was collected from 19 HbSS who had been HU for &gt;3 years and from 12 healthy controls. Frozen mono-nuclear cells were analyzed by flow cytometry using CD49f, 90 45Ra, 123, 235a, 38, 34, 33 and lineage antibodies. The number of 49f+ long-term Hematopoietic Stem Cells (LT-HSC), Multipotent Progenitors (MPPs), Common Myeloid Progenitors (CMPs), Megakaryocyte-Erythroid Progenitors (MEPs), and Granulocyte-Monocyte Progenitors (GMPs) per uL of blood or per CD34+ cells was then quantified. Results The percentages of reticulocytes per uL of blood were found to correlate positively with the concentration per uL of blood of all stem and progenitor cell populations tested (CD34 (R2 = 0.6583), LT-HSC (R2 = 0.3532), MPP (R2 = 0.2603), CMP (R2 = 0.5889), MEP (R2 = 0.2411), and GMP (R2 = 0.6911)). Statistically significant (p&lt;0.05) inverse correlations were also observed between HbF levels and the number of CD34+/uL ( R2 = 0.2931), and the number of CMP/uL (R2 = 0.3732). Normalization of the data to the number of circulating CD34+ cells revealed that there was a strong inverse correlation between HbF levels and the percentage of circulating CMPs (R2 = 0.5424), and importantly, that this correlation was specific to the CMP population since Hb F did not correlates with any of the other HSPC populations analyzed . Analysis of the PB of 12 healthy individuals revealed that, as in SCD patients, the percentage of CMPs varied between &lt; 10% and &gt;60% of the total circulating CD34+ cells. Further analysis revealed that the CMP percentages in both SCD and healthy controls appeared characteristics of each individual tested since the measurements were remarkably correlated (R2 &gt;0.7) when they were repeated on blood samples collected at intervals of two-weeks or one-year. Discussion The positive correlation between the reticulocyte and HSPC populations that we observed was previously unreported and suggests that, in first approximation, the reticulocytes could serve as a proxy for the levels of circulating HSPCs which could help assess the degree of bone marrow suppression in compliant non-responding HU-treated patients. We identified an inverse correlation between percentages of HbF and circulating CMPs in HU-treated SCD patients that is specific to these progenitors. The specificity of the correlation suggests that the major mechanism for the correlation is unlikely to be differential mobilization of CMPs to the PB since inducing mobilization generally affect all HSPCs. A depletion of the CMPs in the bone marrow of high Hb F responders is therefore a more likely mechanism. A possible mechanism for the correlation is that HU acts directly on CMPs by accelerating their differentiation leading to the relative depletion of these progenitors in high F individuals, and initiating the reprogramming of gene expression that ultimately results in high level of gamma-globin expression. Alternatively, the similar range of variability in the percentage of CMPs in HU-treated SCD patients and in healthy individuals never exposed to HU, and the observation that the percentage of circulating CMP seem to be an intrinsic characteristic of each individual suggest that the percentage of circulating CMPs might be a genetically determined marker associated with the ability to produce HbF in response to HU therapy, rather than being a consequence of the treatment. Figure Disclosures Minniti: Doris Duke Foundation: Research Funding. Manwani:Novartis: Consultancy; Pfizer: Consultancy; GBT: Consultancy, Research Funding.

Insulin-like Growth Factor Binding Protein-3 (IGFBP3) Induces Fetal Hemoglobin in Hematopoietic Stem and Progenitor Cells from Patients with Sickle Cell Anemia

Background: Fetal hemoglobin (HbF, α2g2) induction is known to reduce the clinical complications of sickle cell anemia (SCA). Progress in identifying novel HbF inducing strategies has been slowed by an incomplete understanding of gamma-globin regulation. We have used natural genetic variation to identify novel genes and pathways associated with HbF levels in patients with SCA, beginning with whole exome sequencing (WES). This approach identified FOXO3, a transcription factor important for insulin signaling and erythroid maturation, among other functions, as a positive regulator of HbF. We then confirmed the role of FOXO3 in HbF regulation with functional studies in erythroid culture (Zhang, Blood 2018). To overcome the limitations of WES, namely the absence of regulatory and promotor sequencing data, we performed whole genome sequencing (WGS) on 658 pediatric SCA patients, and analyzed the data for common variants predictive of HbF levels.Methods: WGS was performed on a cohort of 658 pediatric patients with HbSS and HbSβ0 with IRB approval from Texas Children's Hospital, and from St Jude Children's Research Hospital, as part of the Sickle Cell Clinical Research and Intervention Program (Hankins et al 2018). Baseline HbF levels, not on hydroxyurea therapy, was measured by HPLC. Subjects were between 6 months and 21 years of age from both institutions; 52% were male. We used mixed linear regression models to screen for variants associated with transformed HbF values, and performed ridge regression with 10-fold cross-validation to confirm associations after adjustment for HBG and BCL11A-associated variants, age, sex, and race (determined by principal components analysis).Hematopoietic stem and progenitor cells (HSPCs) from 3 patients (all HbSS) were treated with recombinant human IGFBP3 (1µg/ml) beginning on day 7 of two-phase culture. Effects of IGFBP3 on gamma-globin expression were evaluated by RT-qPCR, and on HbF levels by HPLC, on days 14 and 21 of culture. The effects of IGFBP3 on known modifiers of HbF and the FOXO3 pathway were assessed by RT-qPCR and western blot on day 21 of culture. Erythroid maturation was assessed by flow cytometry using anti-CD71, GPA, and Band3 on day 21 of culture.Results: Our whole genome sequencing data identified a strong association between all 11 variants 200 kb upstream of IGFBP3 and baseline HbF levels (p<1x10-9). The association of IGFBP3 variants with HbF remained after correcting for HBG and BCL11A variants in addition to patient age, sex, and race (p<0.001). Eleven SNPs were tested, and corrected for multiple testing. Mean HbF levels for patients heterozygous for an IGFBP3 variant predicted to alter IGFBP3 levels as determined by NESDA conditional eQTL catalog (Jenson et al, 2017) were 43% higher compared to patients without a variant (t-test p<0.0002).In erythroblasts treated with IGFBP3, gamma globin expression doubled compared to untreated (p=0.01). %HbF in IGFBP3 treated cells at day 21 of culture was the same as on day 14, while the HbF of untreated cells declined (Figure 1). IGFBP3 did not alter expression of known gamma globin regulators BCL11A, KLF1, and MYB, nor did it alter erythroid maturation as measured by flow cytometry with anti-CD71, GPA, and Band3, and morphologic examination.Conclusions: WGS analysis identified variants in the regulatory region of IGFBP3 as associated with higher levels of HbF. Addition of exogenous human recombinant IGFBP3 to HSPCs prevented the physiologic decline of HbF, resulting in higher %HbF levels in erythroblasts, functionally confirming the association. Exogenous IGFBP3 did not arrest maturation, supporting our hypothesis that IGFBP3 affects HbF production directly via gamma globin induction, rather than through manipulation of maturation. IGFBP3 did not alter expression of known regulators of HbF (BCL11A, KLF1, and MYB). These findings are compatible with our prior data identifying FOXO3 as a positive regulator of gamma globin, and our use of metformin as a HbF inducer in an ongoing clinical trial. Metformin increases IGFBP3 levels, and it has been shown that increases in IGFBP3 lead to activation of FOXO3 through the insulin signaling pathway. We therefore conclude that the insulin signaling pathway plays a significant role in gamma-globin regulation and is an important therapeutic target for HbF induction in patients with SCA. DisclosuresHankins:Global Blood Therapeutics: Research Funding; bluebird bio: Consultancy; Novartis: Research Funding; NCQA: Consultancy. Estepp:Global Blood Therapeutics: Consultancy, Research Funding; NHLBI: Research Funding; Daiichi Sankyo: Consultancy; ASH Scholar: Research Funding.

The Role of Adenosine Monophosphate Activated Protein Kinase Alpha 1 (AMPK) in Gamma-Globin Regulation

Background: Fetal hemoglobin (HbF, α2g2) induction has long been an area of investigation, as it is known to reduce the clinical complications of sickle cell disease (SCD) and beta thalassemia. Progress in identifying novel HbF inducing strategies has been stymied by an incomplete understanding of gamma-globin regulation. We used natural genetic variation to identify novel genes and pathways associated with HbF levels in patients with SCD. Our whole exome sequencing analysis of 1290 samples from patients with SCD identified the insulin signaling pathway to be related to HbF regulation. Functional studies performed in hematopoietic stem and progenitor cells (HSPCs) from patients with SCD established that FOXO3 is a positive regulator of HbF, and that metformin, a FOXO3 and AMPK activator, can induce HbF (Zhang et al, Blood 2018). We hypothesized that other proteins in the insulin signaling pathway, particularly AMPK, a direct activator of FOXO3, may contribute to HbF regulation and be a potential target for pharmacologic induction of HbF.Objectives: We now seek to determine the role of AMPK and AMPK activators such as piceatannol in HbF regulation through functional studies in HSPCs from patients with SCD.Methods: HSPCs from 3 unique patients with SCD were transduced with AMPK shRNA on day 5 of two phase primary erythroid culture. AMPK, FOXO3, gamma and beta globin gene expression were measured by RT-qPCR and HbF by HPLC respectively on day 14 of culture. HSPCs from 3 unique patients with SCD were treated with AICAR, piceatannol at 12.5µM and metformin at 100 µM on day 7 of erythroid culture. Cell lysate was collected on day 14, and AMPK, FOXO3, gamma and beta globin gene expression and protein levels measured by RT-qPCR and western blot respectively. Levels of pAMPK, at Thr172, were quantified by western blot. 1 µM Compound C was added with piceatannol and with metformin in separate erythroid cultures on day 7, and the effect on gamma globin and phosphorylation of AMPK at Thr172 was measured on day 14 by RT-qPCR and western blot respectively.Results: 70% knockdown of AMPK resulted in a 50% decrease in HbF (p<0.01) and a three-fold reduction in gamma-globin expression (p<0.001). HSPCs treated with metformin or piceatannol exhibited a 2-3 fold rise in AMPK, FOXO3 and gamma globin gene expression (p<0.001). HSPCs treated with piceatannol and metformin showed an increase in pAMPK at Thr172, the activated form of AMPK. In the presence of a specific AMPK inhibitor, Compound C, metformin and piceatannol, no induction of gamma globin was observed (Figure 1), and pAMPK was reduced to untreated levels.Conclusions: Knockdown of AMPK in HSPCs reduces gamma globin expression and %HbF, supporting the role of AMPK in gamma globin regulation. Drugs known to activate AMPK, metformin and piceatannol, increase gamma globin in SCD patient derived HSPCs. Pharmacologic blockage of AMPK activity with Compound C results in reduction of HbF induction, and reduces the gamma globin induction of metformin and piceatannol to untreated levels. We therefore conclude that AMPK is a positive regulator of HbF, and that pharmacologic induction of HbF with metformin and piceatannol requires AMPK activity. Further work is needed to establish if FOXO3 and AMPK alone are instrumental in HbF regulation, or if other proteins in the insulin signaling pathway may play a role in HbF regulation. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

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

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

The effect of DNA hydroxymethylase Tet2 on γ globin activation in the treatment of β-thalassemia

Objective: To study the function of ten-eleven translocation 2 (Tet2) in γ globin gene expression in patients with β- thalassemia. Methods: Gamma globin expression was induced by 5-azacytidine and Tet2 gene expression was knocked down by short hairpin RNA (shRNA) in a human immortalized myelogenous leukemia K562 cell line. The global 5-hydroxymethylcytosine (5hmC) level was measured by an ELISA kit. 5hmC level of γ globin gene was quantified by sulfite sequencing. The mRNA level of Tet2, γ globin, and related transcription factors Nfe4 and Klf1 were quantified by real-time PCR. Results: Tet2 knockdown resulted in a decreased global 5hmC level from 0.14% to 0.03% as of the control group in K562 cells. The expression of γ globin was enhanced after 5-azacytidine treatment in vitro. However, γ globin mRNA level in Tet2 knockdown cells was only 55% as that in control group. The CG sites on γ globin gene were unmethylated. As Tet2 was down-regulated, the expression levels of Nfe4 and Klf1 decreased by about 80% and increased to 3.5 folds, respectively. Conclusions: Tet2 appears to maintain 5hmC level and facilitates γ globin gene activation. Moreover, Tet2 more likely regulates γ globin expression via affecting transcription factors rather than the gene itself. Thus, Tet2 could be a potential therapeutic target for β thalassemias.

Tough decoy targeting of predominant let-7 miRNA species in adult human hematopoietic cells

BackgroundIn humans, the heterochronic cascade composed of the RNA-binding protein LIN28 and its major target, the let-7 family of microRNAs (miRNAs), is highly regulated during human erythroid ontogeny. Additionally, down-regulation of the let-7 miRNAs in cultured adult CD34(+) cells or the over-expression of LIN28 in cultured erythrocytes from pediatric patients with HbSS genotype causes increased levels of fetal hemoglobin (HbF) in the range of 19–40% of the total. Therefore, we hypothesized that focused targeting of individual let-7 miRNA family members would exhibit regulatory effect on HbF expression in human adult erythroblasts.MethodsThe expression levels of mature let-7 family members were measured by RT-qPCR in purified cell populations sorted from peripheral blood. To study the effects of let-7 miRNAs upon globin expression, a lentiviral construct that incorporated the tough decoy (TuD) design to target let-7a or let-7b was compared with empty vector controls. Transductions were performed in CD34(+) cells from adult healthy volunteers cultivated ex vivo in erythropoietin-supplemented serum-free media for 21 days. Downstream analyses included RT-qPCR, Western blot and HPLC for the characterization of adult and fetal hemoglobins.ResultsThe expression of individual let-7 miRNA family members in adult peripheral blood cell populations demonstrated that let-7a and let-7b miRNAs are expressed at much higher levels than the other let-7 family members in purified adult human blood cell subsets with expression being predominantly in reticulocytes. Therefore, we focused this study upon the targeted inhibition of let-7a and let-7b with the TuD design to explore its effects upon developmentally-timed erythroid genes. Let-7a-TuD transductions significantly increased gamma-globin mRNA expression and HbF to an average of 38%. Let-7a-TuD also significantly decreased the mRNA expression of some ontogeny-regulated erythroid genes, namely CA1 and GCNT2. In addition, the erythroid-related transcription factors BCL11A and HMGA2 were down- and up-regulated, respectively, by let-7a-TuD, while ZBTB7A, KLF1 and SOX6 remained unchanged.ConclusionsOverall, our data demonstrate that let-7 miRNAs are differentially expressed in human hematopoietic cells, and that targeted inhibition of the highly-expressed species of this family is sufficient for developmentally-specific changes in gamma-globin expression and HbF levels.

IGF2BP3 Moderately Increases Fetal Hemoglobin Levels in Human Adult Erythroblasts

Recent studies demonstrated that IGF2BP1 over-expression (IGF2BP1-OE) in adult erythroblasts has robust effects on fetal hemoglobin (HbF; >65% of the total globin levels), accompanied by reversal of the beta-like globin expression patterns to a fetal-like phenotype. Here we investigated if another member of the insulin-like growth factor 2 mRNA-binding protein family, IGF2BP3, also has potential for HbF regulation that may be useful for therapeutic application among patients with beta-hemoglobin disorders.The developmental pattern and expression levels for IGF2BP3 were initially determined in cord blood versus adult blood CD34(+) samples cultivated ex vivo in erythropoietin-supplemented serum-free media for 21 days. RNA samples were collected at culture day 14 and expression levels were measured by qRT-PCR. IGF2BP3 showed a developmentally regulated expression pattern similar to IGF2BP1 (IGF2BP1: cord blood: 1.3.E+03 ± 4.3.E+02 and adult blood: below detection limits; IGF2BP3: cord blood: 5.8.E+02 ± 2.4.E+02 and adult blood: below detection limits). These results were confirmed in vivo by comparing human fetal liver to adult bone marrow samples (IGF2BP1: fetal liver: 3.5.E+02 ± 5.7.E+01, adult bone marrow: below detection limits and IGF2BP3: fetal liver: 2.0.E+01 ± 2.7.E+00, adult bone marrow: below detection limits). To investigate the effects of IGF2BP3 upon erythropoiesis and globin expression, a lentiviral construct was designed for expression of IGF2BP3 driven by the erythroid-specific gene promoter region of the human SPTA1 gene (IGF2BP3-OE), with a matched empty vector control. Transductions were performed in CD34(+) cells from four adult healthy volunteers cultivated ex vivo in erythropoietin-supplemented serum-free media for 21 days. Over-expression of IGF2BP3 was confirmedby qRT-PCR and Western blot analyses at culture day 14. IGF2BP3-OE cells maintained their ability to differentiate and enucleate ex vivo compared to donor-matched controls. The expression levels of globin genes were evaluated at culture day 14 by qRT-PCR and showed that IGF2BP3-OE caused significantly increased gamma-globin expression levels compared to control transductions (control: 7.7.E+05 ± 1.7.E+05; IGF2BP3-OE: 8.4.E+06 ± 3.2.E+06; p=0.018). Consistent with increased gamma-globin, HbF rose to moderately high levels upon IGF2BP3-OE (control: 4.0 ± 2.1%; IGF2BP3-OE: 18.6 ± 1.0%; p=0.0021). In addition, the expression pattern of the erythroid transcription factor BCL11A was investigated by qRT-PCR at culture day 14 and no significant changes were observed (control: 5.6.E+02 ± 2.7.E+02; IGF2BP3-OE: 6.7.E+02 ± 3.5.E+02; p=0.694). However, minor decreases in BCL11A protein levels were detected by Western analysis.These results demonstrate that IGF2BP3 is developmentally regulated in human erythroid tissues with silencing during the fetal-to-adult transition. However, the effects of IGF2BP3-OE on HbF levels were less robust when compared to IGF2BP1-OE in cultured adult erythroblasts. DisclosuresNo relevant conflicts of interest to declare.