In multicellular organisms, specific stem cell types with distinct developmental potentials occur during development. Transient pluripotent stem cells, which can differentiate into derivatives of all three germ layers (endoderm, ectoderm and mesoderm), are generated during blastocyst development. Adult stem cells, developing at later stages, are more restricted in their potential, since they can differentiate into progenitors and mature effector cell types of only one stem cell system. Adult stem cells have been identified in a variety of tissues in the adult organism and are important for lifelong tissue homeostasis and repair.
Stem cells are functionally defined by two unique attributes: their high self-renewal capacity and their multilineage differentiation potential. The presence of both characteristics in one cell is rare and sets these highly specialized cells aside from the majority of the somatic cell populations. These unique properties make stem cells ideal targets for stem cell engineering to generate cells with wanted properties.
The laboratory studies pluripotent stem cells (ES cells and iPS cells) and adult stem cells (hematopoietic stem cells and mesenchymal stem cells). Patient and disease specific iPS cells are obtained from somatic cells by reprogramming. Hematopoietic stem cells are differentiated into dendritic cells. Genome editing with CRISPR/Cas is used for precision genome engineering.
Maintenance of all hematopoietic cells in our organism is achieved by the continuous growth and differentiation of a population of multipotent hematopoietic stem cells. We employ transcriptional profiling with DNA microarrays and RNA-Seq to determine the gene expression repertoire of stem/progenitor cells and their differentiated progeny (Hacker et al., 2003; Hieronymus et al., 2005; Zenke and Hieronymus, 2006; Felker et al., 2010; Lin et al., 2015). Epigenetic signatures of cells are investigated by ChIP-Seq, ATAC-Seq and HiChIP-Seq to elucidate how chromatin architecture determines stemness, differentiation potential and cell identity (Chauvistré et al., 2014; Lin et al., 2015) (see also Epigenetic and Transcriptional Architecture of Dendritic Cell Development).
Induced pluripotent stem cells (iPS cells) represent engineered stem cells, which are obtained by reprogramming of somatic cells with specific sets of transcription factors, such as Oct4, Sox2, Klf4 and c-Myc. We found that Ezh2, a core subunit of Polycomb repressive complex 2 (PRC2), is critical for efficient iPS cell generation (Ding et al., 2014). Ezh2 acts during reprogramming at least in part through repressing the Ink4a/Arf locus, which represents a major roadblock for iPS cell generation.
iPS cells provide unique opportunities for disease modeling, drug development and cell therapy. However, frequently their differentiation potential is rather poor. We used cell fusion of iPS cells with hematopoietic stem cells to increase the propensity and differentiation potential of pluripotent stem cells towards hematopoietic cells and other mesendodermal lineages, such as cardiomyocytes, hepatocytes and endothelial cells (Qin et al., 2014).
Immunogenicity of iPS cells and iPS cell-derived cells remains controversial. Sertoli cells constitute the structural framework in testis and provide an immune-privileged environment for germ cells. We found that early-passage Sertoli cell-derived iPS cells retain some somatic memory of Sertoli cells that confers reduced immunogenicity of iPS cells and iPS cell-derived cells in vivo and in vitro (Wang et al., 2014). Our data suggest that immune-privileged Sertoli cells represent a preferred source for iPS cell generation if it comes to the use of iPS cell-derived cells for transplantation.
Human IRF8-/- iPS cells and IRF8-/- ES cells are obtained by CRISPR/Cas9 genome editing and differentiated into hematopoietic progenitors and their progeny (cDC1 and cDC2, classical dendritic cells type 1 and 2, respectively; pDC, plasmacytoid dendritic cells).
iPS cells and precision genome engineering with CRISPR/Cas are particularly well suited for cell engineering. We used CRISPR/Cas to generated human iPS cells deficient in IRF8 (interferon regulatory factor 8). IRF8 is a lineage determining transcription factor in hematopoiesis and IRF8-/- iPS cell-derived hematopoietic cells are deficient in development of specific DC subsets and in DC function (Sontag et al., 2017a, 2017b). IRF8-/- iPS cells now allow studying human immune deficiency in vitro, including the pathophysiology of IRF8 deficient DC.
(A) Human IRF8-/- and IRF8+/+ iPS cells (left) are induced to differentiate into hematopoietic progenitors and their differentiated progeny (right).
(B) Gene expression in IRF8-/- and IRF8+/+ hematopoietic cells depicted in heat map format (red, high and blue, low gene expression)
Patient specific iPS cells allow modeling aspects of human diseases in vitro. We have generated a panel of patient specific iPS cells with disease specific point mutations, which are being used for disease modeling (leukaemia, pain) and compound screening (Meents, Bressan, Sontag and Foerster et al. 2019). This work is being done in collaboration with colleagues at RWTH Aachen University Hospital, Aachen, Germany and international colleagues.
To meet the need of obtaining large numbers of iPS cells for disease modeling and drug development, a consortium of experts in engineering sciences and stem cell biology develops an automatic production system for iPS cells, referred to as StemCellFactory (www.stemcellfactory.net, www.stemcellfactory.org).
The institute operates a Stem Cell Engineering Unit as a member of the German Stem Cell Cores (German Stem Cell Cores).
RWTH Aachen University and RWTH Aachen University Hospital are members of the Stem Cell Network.NRW.
StemCellFactory III: Dieses Vorhaben wurde aus Mitteln des Europäischen Fonds für regionale Entwicklung (EFRE) gefördert.
The role of Nav1.7 in human nociceptors: insights from human iPS cell-derived sensory neurons of erythromelalgia patients.
Differentiation of human induced pluripotent stem cells (iPS cells) and embryonic stem cells (ES cells) into dendritic cell (DC) subsets.
Modelling IRF8 deficient human hematopoiesis and dendritic cell development with engineered induced pluripotent stem cells.
Reduced immunogenicity of induced pluripotent stem cells derived from Sertoli cells.
Cell fusion enhances mesendodermal differentiation of human induced pluripotent stem cells.
The polycomb protein Ezh2 impacts on induced pluripotent stem cell generation.
Polycomb group protein Bmi1 promotes hematopoietic cell development from ES cells.
Human adult germline stem cells in question.
Pluripotent stem cells induced from adult neural stem cells by reprogramming with two factors.
Pluripotency associated genes are reactivated by chromatin modifying agents in neurosphere cells.