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Human pluripotent stem cells (hPSCs) provide a valuable model for the study of human development and a means to generate a scalable source of cells for therapeutic applications. This protocol specifies cell fate efficiently into cardiac and endothelial lineages from hPSCs. The protocol takes 2 weeks to complete and requires experience in hPSC culture and differentiation techniques. Building on lessons taken from early development,this monolayer-directed differentiation protocol uses different concentrations of activin A and bone morphogenetic protein 4 (BMP4) to polarize cells into mesodermal subtypes that reflect mid-primitive-streak cardiogenic mesoderm and posterior-primitive-streak hemogenic mesoderm. This differentiation platform provides a basis for generating distinct cardiovascular progenitor populations that enable the derivation of cardiomyocytes and functionally distinct endothelial cell (EC) subtypes from cardiogenic versus hemogenic mesoderm with high efficiency without cell sorting. ECs derived from cardiogenic and hemogenic mesoderm can be matured into textgreater90% CD31(+)/VE-cadherin(+) definitive ECs. To test the functionality of ECs at different stages of differentiation,we provide methods for assaying the blood-forming potential and de novo lumen-forming activity of ECs. To our knowledge,this is the first protocol that provides a common platform for directed differentiation of cardiomyocytes and endothelial subtypes from hPSCs. This protocol yields endothelial differentiation efficiencies exceeding those of previously published protocols. Derivation of these cell types is a critical step toward understanding the basis of disease and generating cells with therapeutic potential. View Publication

To develop a purification strategy for isolating the most primitive hematopoietic stem cells present in normal human marrow we have combined cell separation techniques with an assay for cells that initiate sustained hematopoiesis in vitro in the presence of irradiated human marrow adherent cells. These feeders" were established by subculturing 2- to 6-week-old primary long-term marrow culture adherent layers at a density of 3 x 10(4) irradiated cells per square centimeter. Test "long-term culture (LTC)-initiating cells" were plated on top of the feeders and the cocultures then maintained as standard long-term marrow cultures with half-media changes and removal of half of the nonadherent cells each week. The total number of myeloid� View Publication

Human embryonic stem cells (hESCs) are used as platforms for disease study,drug screening and cell-based therapy. To facilitate these applications,it is frequently necessary to genetically manipulate the hESC genome. Gene editing with engineered nucleases enables site-specific genetic modification of the human genome through homology-directed repair (HDR). However,the frequency of HDR remains low in hESCs. We combined efficient expression of engineered nucleases and integration-defective lentiviral vector (IDLV) transduction for donor template delivery to mediate HDR in hESC line WA09. This strategy led to highly efficient HDR with more than 80% of the selected WA09 clones harboring the transgene inserted at the targeted genomic locus. However,certain portions of the HDR clones contained the concatemeric IDLV genomic structure at the target site,probably resulted from recombination of the IDLV genomic input before HDR with the target. We found that the integrase protein of IDLV mediated the highly efficient HDR through the recruitment of a cellular protein,LEDGF/p75. This study demonstrates that IDLV-mediated HDR is a powerful and broadly applicable technology to carry out site-specific gene modification in hESCs. View Publication

The host responds to virus infection by activating type I interferon (IFN) signaling leading to expression of IFN-stimulated genes (ISGs). Dysregulation of the IFN response results in inflammatory diseases and chronic infections. In this study,we demonstrate that IFN regulatory factor 2 (IRF2),an ISG and a negative regulator of IFN signaling,influences alphavirus neuroinvasion and pathogenesis. A Sindbis virus strain that in wild-type (WT) mice only causes disease when injected into the brain leads to lethal encephalitis in Irf2(-/-) mice after peripheral inoculation. Irf2(-/-) mice fail to control virus replication and recruit immune infiltrates into the brain. Reduced B cells and virus-specific IgG are observed in the Irf2(-/-) mouse brains despite the presence of peripheral neutralizing antibodies,suggesting a defect in B cell trafficking to the central nervous system (CNS). B cell-deficient μMT mice are significantly more susceptible to viral infection,yet WT B cells and serum are unable to rescue the Irf2(-/-) mice. Collectively,our data demonstrate that proper localization of B cells and local production of antibodies in the CNS are required for protection. The work advances our understanding of host mechanisms that affect viral neuroinvasion and their contribution to immunity against CNS infections. View Publication

TRAF1 is a signaling adaptor known for its role in tumor necrosis factor receptor-induced cell survival. Here we show that monocytes from healthy human subjects with a rheumatoid arthritis-associated single-nucleotide polymorphism (SNP) in the TRAF1 gene express less TRAF1 protein but greater amounts of inflammatory cytokines in response to lipopolysaccharide (LPS). The TRAF1 MATH domain binds directly to three components of the linear ubiquitination (LUBAC) complex,SHARPIN,HOIP and HOIL-1,to interfere with the recruitment and linear ubiquitination of NEMO. This results in decreased NF-κB activation and cytokine production,independently of tumor necrosis factor. Consistent with this,Traf1(-/-) mice show increased susceptibility to LPS-induced septic shock. These findings reveal an unexpected role for TRAF1 in negatively regulating Toll-like receptor signaling,providing a mechanistic explanation for the increased inflammation seen with a disease-associated TRAF1 SNP. View Publication

Human NK cell deficiencies are rare yet result in severe and often fatal disease,particularly as a result of viral susceptibility. NK cells develop from hematopoietic stem cells,and few monogenic errors that specifically interrupt NK cell development have been reported. Here we have described biallelic mutations in IRF8,which encodes an interferon regulatory factor,as a cause of familial NK cell deficiency that results in fatal and severe viral disease. Compound heterozygous or homozygous mutations in IRF8 in 3 unrelated families resulted in a paucity of mature CD56dim NK cells and an increase in the frequency of the immature CD56bright NK cells,and this impairment in terminal maturation was also observed in Irf8-/-,but not Irf8+/-,mice. We then determined that impaired maturation was NK cell intrinsic,and gene expression analysis of human NK cell developmental subsets showed that multiple genes were dysregulated by IRF8 mutation. The phenotype was accompanied by deficient NK cell function and was stable over time. Together,these data indicate that human NK cells require IRF8 for development and functional maturation and that dysregulation of this function results in severe human disease,thereby emphasizing a critical role for NK cells in human antiviral defense. View Publication

Human embryonic stem cells can replicate indefinitely while maintaining their undifferentiated state and,therefore,are immortal in culture. This capacity may demand avoidance of any imbalance in protein homeostasis (proteostasis) that would otherwise compromise stem cell identity. Here we show that human pluripotent stem cells exhibit enhanced assembly of the TRiC/CCT complex,a chaperonin that facilitates the folding of 10% of the proteome. We find that ectopic expression of a single subunit (CCT8) is sufficient to increase TRiC/CCT assembly. Moreover,increased TRiC/CCT complex is required to avoid aggregation of mutant Huntingtin protein. We further show that increased expression of CCT8 in somatic tissues extends Caenorhabditis elegans lifespan in a TRiC/CCT-dependent manner. Ectopic expression of CCT8 also ameliorates the age-associated demise of proteostasis and corrects proteostatic deficiencies in worm models of Huntington's disease. Our results suggest proteostasis is a common principle that links organismal longevity with hESC immortality. View Publication

Autoantigen-specific regulatory immunity emerges in the spleen of mice recovering from experimental autoimmune uveitis (EAU),a murine model for human autoimmune uveoretinitis. This regulatory immunity provides induced tolerance to ocular autoantigen,and requires melanocortin 5 receptor (MC5r) expression on antigen presenting cells with adenosine 2 A receptor (A2Ar) expression on T cells. During EAU it is not well understood what roles MC5r and A2Ar have on promoting regulatory immunity. Cytokine profile analysis during EAU revealed MC5r and A2Ar each mediate distinct T cell responses,and are responsible for a functional regulatory immune response in the spleen. A2Ar stimulation at EAU onset did not augment this regulatory response,nor bypass the MC5r requirement to induce regulatory immunity. The importance of this pathway in human autoimmune uveitis was assayed. PBMC from uveitis patients were assayed for MC5r expression on monocytes and A2Ar on T cells,and comparison between uveitis patients and healthy controls had no significant difference. The importance for MC5r and A2Ar expression in EAU to promote the induction of protective regulatory immunity,and the expression of MC5r and A2Ar on human immune cells,suggests that it may be possible to utilize the melanocortin-adenosinergic pathways to induce protective immunity in uveitic patients. View Publication

The creation of a humanized chimeric mouse nervous system permits the study of human neural development and disease pathogenesis using human cells in vivo. Humanized glial chimeric mice with the brain and spinal cord being colonized by human glial cells have been successfully generated. However,generation of humanized chimeric mouse brains repopulated by human neurons to possess a high degree of chimerism have not been well studied. Here we created humanized neuronal chimeric mouse brains by neonatally engrafting the distinct and highly neurogenic human induced pluripotent stem cell (hiPSC)-derived rosette-type primitive neural progenitors. These neural progenitors predominantly differentiate to neurons,which disperse widely throughout the mouse brain with infiltration of the cerebral cortex and hippocampus at 6 and 13 months after transplantation. Building upon the hiPSC technology,we propose that this potentially unique humanized neuronal chimeric mouse model will provide profound opportunities to define the structure,function,and plasticity of neural networks containing human neurons derived from a broad variety of neurological disorders. View Publication

Affinity- and stability-engineered variants of CTLA4-Ig fusion molecules with enhanced pharmacokinetic profiles could yield improved therapies with the potential of higher efficacy and greater convenience to patients. In this study,to our knowledge,we have,for the first time,used in vitro evolution to simultaneously optimize CTLA4 affinity and stability. We selected for improved binding to both ligands,CD80 and CD86,and screened as dimeric Fc fusions directly in functional assays to identify variants with stronger suppression of in vitro T cell activation. The majority of CTLA4 molecules showing the largest potency gains in primary in vitro and ex vivo human cell assays,using PBMCs from type 1 diabetes patients,had significant improvements in CD80,but only modest gains in CD86 binding. We furthermore observed different potency rankings between our lead molecule MEDI5265,abatacept,and belatacept,depending on which type of APC was used,with MEDI5265 consistently being the most potent. We then created fusions of both stability- and potency-optimized CTLA4 moieties with human Fc variants conferring extended plasma t1/2 In a cynomolgus model of T cell-dependent Ab response,the CTLA4-Ig variant MEDI5265 could be formulated at textgreater100 mg/ml for s.c. administration and showed superior efficacy and significantly prolonged serum t1/2 The combination of higher stability and potency with prolonged pharmacokinetics could be compatible with very infrequent,s.c. dosing while maintaining a similar level of immune suppression to more frequently and i.v. administered licensed therapies. View Publication

The regulatory properties of B cells have been studied in autoimmune diseases; however,their role in allergic diseases is poorly understood. We demonstrate that Semaphorin 4C (Sema4C),an axonal guidance molecule,plays a crucial role in B cell regulatory function. Mice deficient in Sema4C exhibited increased airway inflammation after allergen exposure,with massive eosinophilic lung infiltrates and increased Th2 cytokines. This phenotype was reproduced by mixed bone marrow chimeric mice with Sema4C deficient only in B cells,indicating that B lymphocytes were the key cells affected by the absence of Sema4C expression in allergic inflammation. We determined that Sema4C-deficient CD19(+)CD138(+) cells exhibited decreased IL-10 and increased IL-4 expression in vivo and in vitro. Adoptive transfer of Sema4c(-/-) CD19(+)CD138(+) cells induced marked pulmonary inflammation,eosinophilia,and increased bronchoalveolar lavage fluid IL-4 and IL-5,whereas adoptive transfer of wild-type CD19(+)CD138(+)IL-10(+) cells dramatically decreased allergic airway inflammation in wild-type and Sema4c(-/-) mice. This study identifies a novel pathway by which Th2-mediated immune responses are regulated. It highlights the importance of plasma cells as regulatory cells in allergic inflammation and suggests that CD138(+) B cells contribute to cytokine balance and are important for maintenance of immune homeostasis in allergic airways disease. Furthermore,we demonstrate that Sema4C is critical for optimal regulatory cytokine production in CD138(+) B cells. View Publication

The aryl hydrocarbon receptor (AhR),a transcription factor known for mediating xenobiotic toxicity,is expressed in B cells,which are known targets for environmental pollutants. However,it is unclear what the physiological functions of AhR in B cells are. We show here that expression of Ahr in B cells is up-regulated upon B-cell receptor (BCR) engagement and IL-4 treatment. Addition of a natural ligand of AhR,FICZ,induces AhR translocation to the nucleus and transcription of the AhR target gene Cyp1a1,showing that the AhR pathway is functional in B cells. AhR-deficient (Ahr(-/-)) B cells proliferate less than AhR-sufficient (Ahr(+/+)) cells following in vitro BCR stimulation and in vivo adoptive transfer models confirmed that Ahr(-/-) B cells are outcompeted by Ahr(+/+) cells. Transcriptome comparison of AhR-deficient and AhR-sufficient B cells identified cyclin O (Ccno),a direct target of AhR,as a top candidate affected by AhR deficiency. View Publication