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Although CD31 expression on human thymocytes has been reported, a detailed analysis of CD31 expression at various stages of T cell development in the human thymus is missing. In this study, we provide a global picture of the evolution of CD31 expression from the CD34(+) hematopoietic precursor to the CD45RA(+) mature CD4(+) and CD8(+) single-positive (SP) T cells. Using nine-color flow cytometry, we show that CD31 is highly expressed on CD34(+) progenitors and stays high until the early double-positive stage (CD3(-)CD4(+)CD8α(+)β(-)). After β-selection, CD31 expression levels become low to undetectable. CD31 expression then increases and peaks on CD3(high)CD4(+)CD8(+) double-positive thymocytes. However, following positive selection, CD31 expression differs dramatically between CD4(+) and CD8(+) lineages: homogeneously high on CD8 SP but lower or negative on CD4 SP cells, including a subset of CD45RA(+)CD31(-) mature CD4(+) thymocytes. CD31 expression on TCRγδ thymocytes is very similar to that of CD4 SP cells. Remarkably, there is a substantial subset of semimature (CD45RA(-)) CD4 SP thymocytes that lack CD31 expression. Moreover, FOXP3(+) and ICOS(+) cells are overrepresented in this CD31(-) subpopulation. Despite this CD31(-)CD45RA(-) subpopulation, most egress-capable mature CD45RA(+) CD4 SP thymocytes express CD31. The variations in CD31 expression appear to coincide with three major selection processes occurring during thymopoiesis: β-selection, positive selection, and negative selection. Considering the ability of CD31 to modulate the TCR's activation threshold via the recruitment of tyrosine phosphatases, our results suggest a significant role for CD31 during T cell development.

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), an endocrine disrupting chemical (EDC), can cause carcinogenesis, immunosuppression, and teratogenesis, through a ligand-activated transcription factor, the aryl hydrocarbon receptor (AhR). Despite remarkable recent advances in stem cell biology, the influence of TCDD on hematopoietic stem cells (HSCs), which possess the ability to reconstitute long-term multilineage hematopoiesis, has not been well investigated. In this study we examined the influence of TCDD on HSCs enriched for CD34(-), c-kit(+), Sca-1(+), lineage negative (CD34-KSL) cells. The number of the CD34-KSL cells was found to be increased about four-fold upon a single oral administration of TCDD (40 micro g/kg body weight). Surprisingly, we found that these TCDD-treated cells almost lost long-term reconstitution activity. This defect was not present in AhR(-/-) mice. These findings suggest that modulation of AhR/ARNT system activity may have an effect on HSC function or survival.

Many neuropsychiatric disorders are thought to result from subtle changes in neural circuit formation. We used human embryonic stem cells and induced pluripotent stem cells (hiPSCs) to model mature, post-mitotic excitatory neurons and examine effects of fibroblast growth factor 2 (FGF2). FGF2 gene expression is known to be altered in brain regions of major depressive disorder (MDD) patients and FGF2 has anti-depressive effects in animal models of depression. We generated stable inducible neurons (siNeurons) conditionally expressing human neurogenin-2 (NEUROG2) to generate a homogenous population of post-mitotic excitatory neurons and study the functional as well as the transcriptional effects of FGF2. Upon induction of NEUROG2 with doxycycline, the vast majority of cells are post-mitotic, and the gene expression profile recapitulates that of excitatory neurons within 6 days. Using hES cell lines that inducibly express NEUROG2 as well as GCaMP6f, we were able to characterize spontaneous calcium activity in these neurons and show that calcium transients increase in the presence of FGF2. The FGF2-responsive genes were determined by RNA-Seq. FGF2-regulated genes previously identified in non-neuronal cell types were up-regulated (EGR1, ETV4, SPRY4, and DUSP6) as a result of chronic FGF2 treatment of siNeurons. Novel neuron-specific genes were also identified that may mediate FGF2-dependent increases in synaptic efficacy including NRXN3, SYT2, and GALR1. Since several of these genes have been implicated in MDD previously, these results will provide the basis for more mechanistic studies of the role of FGF2 in MDD.

Adipose tissue is an abundantly available source of proliferative and multipotent mesenchymal stem cells with promising potential for regenerative therapeutics. We previously demonstrated that both human and mouse adipose-derived stem cells (ASCs) can be reprogrammed into induced pluripotent stem cells (iPSCs) with efficiencies higher than those that have been reported for other cell types. The ASC-derived iPSCs can be generated in a feeder-independent manner, representing a unique model to study reprogramming and an important step toward establishing a safe, clinical grade of cells for therapeutic use. In this study, we provide a detailed protocol for isolation, preparation and transformation of ASCs from fat tissue into mouse iPSCs in feeder-free conditions and human iPSCs using feeder-dependent or feeder/xenobiotic-free processes. This protocol also describes how ASCs can be used as feeder cells for maintenance of other pluripotent stem cells. ASC derivation is rapid and can be completed in textless1 week, with mouse and human iPS reprogramming times averaging 1.5 and 2.5 weeks, respectively.

Achievements in tissue engineering using mesenchymal stem cells (MSC) demand a clinically acceptable off-the-shelf" cell therapy product. Efficacy of cryopreservation of human bone marrow-derived MSC in clinically safe animal product-free medium containing 2% 5% and 10% dimethyl sulfoxide (DMSO) was evaluated by measuring cell recovery viability apoptosis proliferation rate expression of a broad panel of MSC markers and osteogenic differentiation. Rate-controlled freezing in CryoStor media was performed in a programmable cell freezer. About 95% of frozen cells were recovered as live cells after freezing in CryoStor solutions with 5% and 10% DMSO followed by storage in liquid nitrogen for 1 month. Cell recovery after 5 months storage was 72% and 80% for 5% and 10% DMSO respectively. Measurements of caspase 3 activity demonstrated that 15.5% and 12.8% of cells after 1 month and 18.3% and 12.9% of cells after 5 months storage in 5% and 10% DMSO respectively were apoptotic. Proliferation of MSC recovered after cryopreservation was measured during 2 weeks post-plating. Proliferation rate was not compromised and was even enhanced. Cryopreservation did not alter expression of MSC markers. Quantitative analysis of alkaline phosphatase (ALP) activity ALP surface expression and Ca deposition in previously cryopreserved MSC and then differentiated for 3 weeks in osteogenic medium demonstrated the same degree of osteogenic differentiation as in unfrozen parallel cultures. Cell viability and functional parameters were analyzed in MSC after short-term storage at 4°C in HypoThermosol-FRS solution also free of animal products. Hypothermic storage for 2 and 4 days resulted in about 100% and 85% cell recovery respectively less than 10% of apoptotic cells and normal proliferation marker expression and osteogenic potential. Overall our results demonstrate that human MSC could be successfully cryopreserved for banking and clinical applications and delivered to the bedside in clinically safe protective reagents.

Induced pluripotent stem cells (iPSC) are important tools for drug discovery assays and toxicology screens. In this manuscript, we design high efficiency TALEN and ZFN to target two safe harbor sites on chromosome 13 and 19 in a widely available and well-characterized integration-free iPSC line. We show that these sites can be targeted in multiple iPSC lines to generate reporter systems while retaining pluripotent characteristics. We extend this concept to making lineage reporters using a C-terminal targeting strategy to endogenous genes that express in a lineage-specific fashion. Furthermore, we demonstrate that we can develop a master cell line strategy and then use a Cre-recombinase induced cassette exchange strategy to rapidly exchange reporter cassettes to develop new reporter lines in the same isogenic background at high efficiency. Equally important we show that this recombination strategy allows targeting at progenitor cell stages, further increasing the utility of the platform system. The results in concert provide a novel platform for rapidly developing custom single or dual reporter systems for screening assays. View Publication

Megakaryocytopoiesis gives rise to platelets by proliferation and differentiation of lineage-specific progenitors, identified in vitro as Colony Forming Unit-Megakaryocytes (CFU-Mk). The aim of this study was to refine and optimize the in vitro Standard Operating Procedure (SOP) of the CFU-Mk assay for detecting drug-induced thrombocytopenia and to prevalidate a model for predicting the acute exposure levels that cause maximum tolerated decreases in the platelets count, based on the correlation with the maximal plasma concentrations (C max) in vivo. The assay was linear under the SOP conditions, and the in vitro endpoints (percentage of colonies growing) were reproducible within and across laboratories. The protocol performance phase was carried out testing 10 drugs (selected on the base of their recognised or potential in vivo haematotoxicity, according to the literature). Results showed that a relationship can be established between the maximal concentration in plasma (C max) and the in vitro concentrations that inhibited the 10-50-90 percent of colonies growth (ICs). When C max is lower than IC10, it is possible to predict that the chemicals have no direct toxicity effect on CFU-Mk and could not induce thrombocytopenia due to bone marrow damage. When the C max is higher than IC90 and/or IC50, thrombocytopenia can occur due to direct toxicity of chemicals on CFU-Mk progenitors.

Embryoid bodies (EBs) can be generated by culturing human pluripotent stem cells in ultra-low attachment culture vessels, under conditions that are adverse to pluripotency and proliferation. EBs generated in suspension cultures are capable of differentiating into cells of the ectoderm, mesoderm, and endoderm. In this chapter, we describe techniques for generation of EBs from human pluripotent stem cells. Once formed, the EBs can then be dissociated using specific enzymes to acquire a single cell population that has the potential to differentiate into cells of all three germ layers. This population can then be cultured in specialized conditions to obtain progenitor cells of specific lineages. Pure populations of progenitor cells generated on a large scale basis can be used for research, drug discovery/development, and cellular transplantation therapy.

Glioblastoma (GBM) is distinguished by a high degree of intratumoral heterogeneity, which extends to the pattern of expression and amplification of receptor tyrosine kinases (RTKs). Although most GBMs harbor RTK amplifications, clinical trials of small-molecule inhibitors targeting individual RTKs have been disappointing to date. Activation of multiple RTKs within individual GBMs provides a theoretical mechanism of resistance; however, the spectrum of functional RTK dependence among tumor cell subpopulations in actual tumors is unknown. We investigated the pattern of heterogeneity of RTK amplification and functional RTK dependence in GBM tumor cell subpopulations. Analysis of The Cancer Genome Atlas GBM dataset identified 34 of 463 cases showing independent focal amplification of two or more RTKs, most commonly platelet-derived growth factor receptor α (PDGFRA) and epidermal growth factor receptor (EGFR). Dual-color fluorescence in situ hybridization was performed on eight samples with EGFR and PDGFRA amplification, revealing distinct tumor cell subpopulations amplified for only one RTK; in all cases these predominated over cells amplified for both. Cell lines derived from coamplified tumors exhibited genotype selection under RTK-targeted ligand stimulation or pharmacologic inhibition in vitro. Simultaneous inhibition of both EGFR and PDGFR was necessary for abrogation of PI3 kinase pathway activity in the mixed population. DNA sequencing of isolated subpopulations establishes a common clonal origin consistent with late or ongoing divergence of RTK genotype. This phenomenon is especially common among tumors with PDGFRA amplification: overall, 43% of PDGFRA-amplified GBM were found to have amplification of EGFR or the hepatocyte growth factor receptor gene (MET) as well.

Mesenchymal stem cells (MSCs) are fibroblast-like multipotent stem cells that can differentiate into cell types of mesenchymal origin. Because of their immune properties and differentiation, potential MSCs are discussed for the use in tissue regeneration and tolerance induction in transplant medicine. This cell type can easily be obtained from the umbilical cord tissue (UCMSC) without medical intervention. Standard culture conditions include fetal bovine serum (FBS) which may not be approved for clinical settings. Here, we analyzed the phenotypic and functional properties of UCMSC under xeno-free (XF, containing GMP-certified human serum) and serum-free (SF) culture conditions in comparison with standard UCMSC cultures. Phenotypically, UCMSC showed no differences in the expression of mesenchymal markers or differentiation capacity. Functionally, XF and SF-cultured UCMSC have comparable adipogenic, osteogenic, and endothelial differentiation potential. Interestingly, the UCMSC-mediated suppression of T cell proliferation in an allogeneic mixed lymphocyte reaction (MLR) is more effective in XF and SF media than in standard FBS-containing cultures. Regarding the mechanism of action of MLR suppression, transwell experiments revealed that in neither UCMSC culture a direct cell-cell contact is necessary for inhibiting T cell proliferation, and that the major effector molecule is prostaglandin E₂ (PGE₂). Taken together, GMP-compliant growth media qualify for long-term cultures of UCMSC which is important for a future clinical study design in regenerative and transplant medicine.

Mesenchymal stem or stromal cells (MSCs) have many potential therapeutic applications including therapies for cancers and tissue damages caused by cancers or radical cancer treatments. However, tissue-derived MSCs such as bone marrow MSCs (BM-MSCs) may promote cancer progression and have considerable donor variations and limited expandability. These issues hinder the potential applications of MSCs, especially those in cancer patients. To circumvent these issues, we derived MSCs from transgene-free human induced pluripotent stem cells (iPSCs) efficiently with a modified protocol that eliminated the need of flow cytometric sorting. Our iPSC-derived MSCs were readily expandable, but still underwent senescence after prolonged culture and did not form teratomas. These iPSC-derived MSCs homed to cancers with efficiencies similar to BM-MSCs but were much less prone than BM-MSCs to promote the epithelial-mesenchymal transition, invasion, stemness, and growth of cancer cells. The observations were probably explained by the much lower expression of receptors for interleukin-1 and TGFβ, downstream protumor factors, and hyaluronan and its cofactor TSG6, which all contribute to the protumor effects of BM-MSCs. The data suggest that iPSC-derived MSCs prepared with the modified protocol are a safer and better alternative to BM-MSCs for therapeutic applications in cancer patients. The protocol is scalable and can be used to prepare the large number of cells required for off-the-shelf" therapies and bioengineering applications." View Publication

Genetic manipulation of human embryonic stem cells (hESC) has been limited by their general resistance to common methods used to introduce exogenous DNA or RNA. Efficient and high throughput transfection of nucleic acids into hESC would be a valuable experimental tool to manipulate these cells for research and clinical applications. We investigated the ability of two commercially available electroporation systems, the Nucleofection® 96-well Shuttle® System from Lonza and the Neon™ Transfection System from Invitrogen to efficiently transfect hESC. Transfection efficiency was measured by flow cytometry for the expression of the green fluorescent protein and the viability of the transfected cells was determined by an ATP catalyzed luciferase reaction. The transfected cells were also analyzed by flow cytometry for common markers of pluripotency. Both systems are capable of transfecting hESC at high efficiencies with little loss of cell viability. However, the reproducibility and the ease of scaling for high throughput applications led us to perform more comprehensive tests on the Nucleofection® 96-well Shuttle® System. We demonstrate that this method yields a large fraction of transiently transfected cells with minimal loss of cell viability and pluripotency, producing protein expression from plasmid vectors in several different hESC lines. The method scales to a 96-well plate with similar transfection efficiencies at the start and end of the plate. We also investigated the efficiency with which stable transfectants can be generated and recovered under antibiotic selection. Finally, we found that this method is effective in the delivery of short synthetic RNA oligonucleotides (siRNA) into hESC for knockdown of translation activity via RNA interference. Our results indicate that these electroporation methods provide a reliable, efficient, and high-throughput approach to the genetic manipulation of hESC.