Genome editing in the mouse brain with minimally immunogenic Cas9 RNPs.

Transient delivery of CRISPR-Cas9 ribonucleoproteins (RNPs) into the central nervous system (CNS) for therapeutic genome editing could avoid limitations of viral vector-based delivery including cargo capacity, immunogenicity, and cost. Here, we tested the ability of cell-penetrant Cas9 RNPs to edit the mouse striatum when introduced using a convection-enhanced delivery system. These transient Cas9 RNPs showed comparable editing of neurons and reduced adaptive immune responses relative to one formulation of Cas9 delivered using AAV serotype 9. The production of ultra-low endotoxin Cas9 protein manufactured at scale further improved innate immunity. We conclude that injection-based delivery of minimally immunogenic CRISPR genome editing RNPs into the CNS provides a valuable alternative to virus-mediated genome editing.

Stem cell-based multi-tissue platforms to model human autoimmune diabetes.

BACKGROUND: Type 1 diabetes (T1D) is an autoimmune disease in which pancreatic insulin-producing ß cells are specifically destroyed by the immune system. Understanding the initiation and progression of human T1D has been hampered by the lack of appropriate models that can reproduce the complexity and heterogeneity of the disease. The development of platforms combining multiple human pluripotent stem cell (hPSC) derived tissues to model distinct aspects of T1D has the potential to provide critical novel insights into the etiology and pathogenesis of the human disease. SCOPE OF REVIEW: In this review, we summarize the state of hPSC differentiation approaches to generate cell types and tissues relevant to T1D, with a particular focus on pancreatic islet cells, T cells, and thymic epithelium. We present current applications as well as limitations of using these hPSC-derived cells for disease modeling and discuss efforts to optimize platforms combining multiple cell types to model human T1D. Finally, we outline remaining challenges and emphasize future improvements needed to accelerate progress in this emerging field of research. MAJOR CONCLUSIONS: Recent advances in reprogramming approaches to create patient-specific induced pluripotent stem cell lines (iPSCs), genome engineering technologies to efficiently modify DNA of hPSCs, and protocols to direct their differentiation into mature cell types have empowered the use of stem cell derivatives to accurately model human disease. While challenges remain before complex interactions occurring in human T1D can be modeled with these derivatives, experiments combining hPSC-derived ß cells and immune cells are already providing exciting insight into how these cells interact in the context of T1D, supporting the viability of this approach.

Lin28 paralogs regulate lung branching morphogenesis.

The molecular mechanisms that govern the choreographed timing of organ development remain poorly understood. Our investigation of the role of the Lin28a and Lin28b paralogs during the developmental process of branching morphogenesis establishes that dysregulation of Lin28a/b leads to abnormal branching morphogenesis in the lung and other tissues. Additionally, we find that the Lin28 paralogs, which regulate post-transcriptional processing of both mRNAs and microRNAs (miRNAs), predominantly control mRNAs during the initial phases of lung organogenesis. Target mRNAs include Sox2, Sox9, and Etv5, which coordinate lung development and differentiation. Moreover, we find that functional interactions between Lin28a and Sox9 are capable of bypassing branching defects in Lin28a/b mutant lungs. Here, we identify Lin28a and Lin28b as regulators of early embryonic lung development, highlighting the importance of the timing of post-transcriptional regulation of both miRNAs and mRNAs at distinct stages of organogenesis.

Constrained chromatin accessibility in PU.1-mutated agammaglobulinemia patients.

The pioneer transcription factor (TF) PU.1 controls hematopoietic cell fate by decompacting stem cell heterochromatin and allowing nonpioneer TFs to enter otherwise inaccessible genomic sites. PU.1 deficiency fatally arrests lymphopoiesis and myelopoiesis in mice, but human congenital PU.1 disorders have not previously been described. We studied six unrelated agammaglobulinemic patients, each harboring a heterozygous mutation (four de novo, two unphased) of SPI1, the gene encoding PU.1. Affected patients lacked circulating B cells and possessed few conventional dendritic cells. Introducing disease-similar SPI1 mutations into human hematopoietic stem and progenitor cells impaired early in vitro B cell and myeloid cell differentiation. Patient SPI1 mutations encoded destabilized PU.1 proteins unable to nuclear localize or bind target DNA. In PU.1-haploinsufficient pro-B cell lines, euchromatin was less accessible to nonpioneer TFs critical for B cell development, and gene expression patterns associated with the pro- to pre-B cell transition were undermined. Our findings molecularly describe a novel form of agammaglobulinemia and underscore PU.1's critical, dose-dependent role as a hematopoietic euchromatin gatekeeper.

Calmodulin inhibitors improve erythropoiesis in Diamond-Blackfan anemia.

Diamond-Blackfan anemia (DBA) is a rare hematopoietic disease characterized by a block in red cell differentiation. Most DBA cases are caused by mutations in ribosomal proteins and characterized by higher than normal activity of the tumor suppressor p53. Higher p53 activity is thought to contribute to DBA phenotypes by inducing apoptosis during red blood cell differentiation. Currently, there are few therapies available for patients with DBA. We performed a chemical screen using zebrafish ribosomal small subunit protein 29 (rps29) mutant embryos that have a p53-dependent anemia and identified calmodulin inhibitors that rescued the phenotype. Our studies demonstrated that calmodulin inhibitors attenuated p53 protein amount and activity. Treatment with calmodulin inhibitors led to decreased p53 translation and accumulation but does not affect p53 stability. A U.S. Food and Drug Administration-approved calmodulin inhibitor, trifluoperazine, rescued hematopoietic phenotypes of DBA models in vivo in zebrafish and mouse models. In addition, trifluoperazine rescued these phenotypes in human CD34+ hematopoietic stem and progenitor cells. Erythroid differentiation was also improved in CD34+ cells isolated from a patient with DBA. This work uncovers a potential avenue of therapeutic development for patients with DBA.

Transcriptome Dynamics of Hematopoietic Stem Cell Formation Revealed Using a Combinatorial Runx1 and Ly6a Reporter System.

Studies of hematopoietic stem cell (HSC) development from pre-HSC-producing hemogenic endothelial cells (HECs) are hampered by the rarity of these cells and the presence of other cell types with overlapping marker expression profiles. We generated a Tg(Runx1-mKO2; Ly6a-GFP) dual reporter mouse to visualize hematopoietic commitment and study pre-HSC emergence and maturation. Runx1-mKO2 marked all intra-arterial HECs and hematopoietic cluster cells (HCCs), including pre-HSCs, myeloid- and lymphoid progenitors, and HSCs themselves. However, HSC and lymphoid potential were almost exclusively found in reporter double-positive (DP) cells. Robust HSC activity was first detected in DP cells of the placenta, reflecting the importance of this niche for (pre-)HSC maturation and expansion before the fetal liver stage. A time course analysis by single-cell RNA sequencing revealed that as pre-HSCs mature into fetal liver stage HSCs, they show signs of interferon exposure, exhibit signatures of multi-lineage differentiation gene expression, and develop a prolonged cell cycle reminiscent of quiescent adult HSCs.

Treg cell-based therapies: challenges and perspectives.

Cellular therapies using regulatory T (Treg) cells are currently undergoing clinical trials for the treatment of autoimmune diseases, transplant rejection and graft-versus-host disease. In this Review, we discuss the biology of Treg cells and describe new efforts in Treg cell engineering to enhance specificity, stability, functional activity and delivery. Finally, we envision that the success of Treg cell therapy in autoimmunity and transplantation will encourage the clinical use of adoptive Treg cell therapy for non-immune diseases, such as neurological disorders and tissue repair.

Polymer-stabilized Cas9 nanoparticles and modified repair templates increase genome editing efficiency.

Versatile and precise genome modifications are needed to create a wider range of adoptive cellular therapies1-5. Here we report two improvements that increase the efficiency of CRISPR-Cas9-based genome editing in clinically relevant primary cell types. Truncated Cas9 target sequences (tCTSs) added at the ends of the homology-directed repair (HDR) template interact with Cas9 ribonucleoproteins (RNPs) to shuttle the template to the nucleus, enhancing HDR efficiency approximately two- to fourfold. Furthermore, stabilizing Cas9 RNPs into nanoparticles with polyglutamic acid further improves editing efficiency by approximately twofold, reduces toxicity, and enables lyophilized storage without loss of activity. Combining the two improvements increases gene targeting efficiency even at reduced HDR template doses, yielding approximately two to six times as many viable edited cells across multiple genomic loci in diverse cell types, such as bulk (CD3+) T cells, CD8+ T cells, CD4+ T cells, regulatory T cells (Tregs), γδ T cells, B cells, natural killer cells, and primary and induced pluripotent stem cell-derived6 hematopoietic stem progenitor cells (HSPCs).

A systems biology pipeline identifies regulatory networks for stem cell engineering.

A major challenge for stem cell engineering is achieving a holistic understanding of the molecular networks and biological processes governing cell differentiation. To address this challenge, we describe a computational approach that combines gene expression analysis, previous knowledge from proteomic pathway informatics and cell signaling models to delineate key transitional states of differentiating cells at high resolution. Our network models connect sparse gene signatures with corresponding, yet disparate, biological processes to uncover molecular mechanisms governing cell fate transitions. This approach builds on our earlier CellNet and recent trajectory-defining algorithms, as illustrated by our analysis of hematopoietic specification along the erythroid lineage, which reveals a role for the EGF receptor family member, ErbB4, as an important mediator of blood development. We experimentally validate this prediction and perturb the pathway to improve erythroid maturation from human pluripotent stem cells. These results exploit an integrative systems perspective to identify new regulatory processes and nodes useful in cell engineering.

Author Correction: A systems biology pipeline identifies regulatory networks for stem cell engineering.

In the version of this article initially published, the second NIH grant "R24-DK49216" to author George Q. Daley contained an error. The grant number should have read U54DK110805. The error has been corrected in the HTML and PDF versions of the article.

A CLK3-HMGA2 Alternative Splicing Axis Impacts Human Hematopoietic Stem Cell Molecular Identity throughout Development.

While gene expression dynamics have been extensively cataloged during hematopoietic differentiation in the adult, less is known about transcriptome diversity of human hematopoietic stem cells (HSCs) during development. To characterize transcriptional and post-transcriptional changes in HSCs during development, we leveraged high-throughput genomic approaches to profile miRNAs, lincRNAs, and mRNAs. Our findings indicate that HSCs manifest distinct alternative splicing patterns in key hematopoietic regulators. Detailed analysis of the splicing dynamics and function of one such regulator, HMGA2, identified an alternative isoform that escapes miRNA-mediated targeting. We further identified the splicing kinase CLK3 that, by regulating HMGA2 splicing, preserves HMGA2 function in the setting of an increase in let-7 miRNA levels, delineating how CLK3 and HMGA2 form a functional axis that influences HSC properties during development. Collectively, our study highlights molecular mechanisms by which alternative splicing and miRNA-mediated post-transcriptional regulation impact the molecular identity and stage-specific developmental features of human HSCs.

Regulation of embryonic haematopoietic multipotency by EZH1.

All haematopoietic cell lineages that circulate in the blood of adult mammals derive from multipotent haematopoietic stem cells (HSCs). By contrast, in the blood of mammalian embryos, lineage-restricted progenitors arise first, independently of HSCs, which only emerge later in gestation. As best defined in the mouse, 'primitive' progenitors first appear in the yolk sac at 7.5 days post-coitum. Subsequently, erythroid-myeloid progenitors that express fetal haemoglobin, as well as fetal lymphoid progenitors, develop in the yolk sac and the embryo proper, but these cells lack HSC potential. Ultimately, 'definitive' HSCs with long-term, multilineage potential and the ability to engraft irradiated adults emerge at 10.5 days post-coitum from arterial endothelium in the aorta-gonad-mesonephros and other haemogenic vasculature. The molecular mechanisms of this reverse progression of haematopoietic ontogeny remain unexplained. We hypothesized that the definitive haematopoietic program might be actively repressed in early embryogenesis through epigenetic silencing, and that alleviating this repression would elicit multipotency in otherwise lineage-restricted haematopoietic progenitors. Here we show that reduced expression of the Polycomb group protein EZH1 enhances multi-lymphoid output from human pluripotent stem cells. In addition, Ezh1 deficiency in mouse embryos results in precocious emergence of functional definitive HSCs in vivo. Thus, we identify EZH1 as a repressor of haematopoietic multipotency in the early mammalian embryo.

Drug discovery for Diamond-Blackfan anemia using reprogrammed hematopoietic progenitors.

Diamond-Blackfan anemia (DBA) is a congenital disorder characterized by the failure of erythroid progenitor differentiation, severely curtailing red blood cell production. Because many DBA patients fail to respond to corticosteroid therapy, there is considerable need for therapeutics for this disorder. Identifying therapeutics for DBA requires circumventing the paucity of primary patient blood stem and progenitor cells. To this end, we adopted a reprogramming strategy to generate expandable hematopoietic progenitor cells from induced pluripotent stem cells (iPSCs) from DBA patients. Reprogrammed DBA progenitors recapitulate defects in erythroid differentiation, which were rescued by gene complementation. Unbiased chemical screens identified SMER28, a small-molecule inducer of autophagy, which enhanced erythropoiesis in a range of in vitro and in vivo models of DBA. SMER28 acted through autophagy factor ATG5 to stimulate erythropoiesis and up-regulate expression of globin genes. These findings present an unbiased drug screen for hematological disease using iPSCs and identify autophagy as a therapeutic pathway in DBA.

Developmental Vitamin D Availability Impacts Hematopoietic Stem Cell Production.

Vitamin D insufficiency is a worldwide epidemic affecting billions of individuals, including pregnant women and children. Despite its high incidence, the impact of active vitamin D3 (1,25(OH)D3) on embryonic development beyond osteo-regulation remains largely undefined. Here, we demonstrate that 1,25(OH)D3 availability modulates zebrafish hematopoietic stem and progenitor cell (HSPC) production. Loss of Cyp27b1-mediated biosynthesis or vitamin D receptor (VDR) function by gene knockdown resulted in significantly reduced runx1 expression and Flk1+cMyb+ HSPC numbers. Selective modulation in vivo and in vitro in zebrafish indicated that vitamin D3 acts directly on HSPCs, independent of calcium regulation, to increase proliferation. Notably, ex vivo treatment of human HSPCs with 1,25(OH)D3 also enhanced hematopoietic colony numbers, illustrating conservation across species. Finally, gene expression and epistasis analysis indicated that CXCL8(IL-8) was a functional target of vitamin D3-mediated HSPC regulation. Together, these findings highlight the relevance of developmental 1,25(OH)D3 availability for definitive hematopoiesis and suggest potential therapeutic utility in HSPC expansion.

De novo generation of HSCs from somatic and pluripotent stem cell sources.

Generating human hematopoietic stem cells (HSCs) from autologous tissues, when coupled with genome editing technologies, is a promising approach for cellular transplantation therapy and for in vitro disease modeling, drug discovery, and toxicology studies. Human pluripotent stem cells (hPSCs) represent a potentially inexhaustible supply of autologous tissue; however, to date, directed differentiation from hPSCs has yielded hematopoietic cells that lack robust and sustained multilineage potential. Cellular reprogramming technologies represent an alternative platform for the de novo generation of HSCs via direct conversion from heterologous cell types. In this review, we discuss the latest advancements in HSC generation by directed differentiation from hPSCs or direct conversion from somatic cells, and highlight their applications in research and prospects for therapy.

The importance of leadership in Soldiers' nutritional behaviors: results from the Soldier Fueling Initiative program evaluation.

INTRODUCTION: Improving Soldiers' nutritional habits continues to be a concern of the US Army, especially amidst increasing obesity and high injury rates. This study examines leadership influence on nutritional behaviors within the context of the Soldier Fueling Initiative, a program providing nutrition education and improved dining facility menus to Soldiers in Basic Combat Training (BCT) and Advanced Individual Training (AIT). METHODS: A mixed methods design using surveys (N=486) and focus groups (N=112) was used to collect data at Fort Jackson, SC, and Fort Eustis, VA, in 2011. RESULTS: Survey results showed 75% of Soldiers in BCT believed their drill sergeant was helpful in making performance-enhancing food choices, and 86% agreed their drill sergeant believed it is important to eat for performance. Soldiers in AIT perceived their cadre as less helpful than their BCT drill sergeants and agreed less frequently that the AIT cadre believed it was important to eat for performance (P<.05). These measures of leader influence were significantly associated with nutritional attitudes and behaviors in both BCT and AIT. Focus groups revealed 5 key themes related to cadre influence and nutrition behavior (listed in order of most to least frequent): (1) cadre influence food choices through consequences related to selection, (2) cadre teach Soldiers how to eat, (3) cadre rush Soldiers to eat quickly to return to training, (4) cadre influence choice through example but often do not make healthy choices, and (5) cadre have no influence on food choices. COMMENT: Leaders influence most Soldiers' nutrition practices within the training environment, particularly within BCT. Given that leader influence can impact Soldiers' attitudes and behaviors, it is critical that military leaders become knowledgeable about optimal nutrition practices to disseminate appropriate information to their Soldiers, avoid reprimand associated with trainees' food choices, reinforce key messages associated with nutrition programming, and lead by example in their own food choices.

Induction of multipotential hematopoietic progenitors from human pluripotent stem cells via respecification of lineage-restricted precursors.

Human pluripotent stem cells (hPSCs) represent a promising source of patient-specific cells for disease modeling, drug screens, and cellular therapies. However, the inability to derive engraftable human hematopoietic stem and progenitor cells (HSPCs) has limited their characterization to in vitro assays. We report a strategy to respecify lineage-restricted CD34(+)CD45(+) myeloid precursors derived from hPSCs into multilineage progenitors that can be expanded in vitro and engrafted in vivo. HOXA9, ERG, and RORA conferred self-renewal and multilineage potential in vitro and maintained primitive CD34(+)CD38(-) cells. Screening cells via transplantation revealed that two additional factors, SOX4 and MYB, conferred engraftment. Progenitors specified with all five factors gave rise to reproducible short-term engraftment with myeloid and erythroid lineages. Erythroid precursors underwent hemoglobin switching in vivo, silencing embryonic and activating adult globin expression. Our combinatorial screening approach establishes a strategy for obtaining transcription-factor-mediated engraftment of blood progenitors from human pluripotent cells.