Purification of cell populations from human fetal brain using flow cytometric techniques

Isolation and Enrichment of Defined Neural Cell Populations from Heterogeneous Neural Stem Cell Progeny

The renewable source of neural stem cells (NSCs) with multi-lineage differentiation capability toward neurons, astrocytes, and oligodendrocytes represents an ideal supply for cell therapy of central nervous system (CNS) diseases. In spite of this, the clinical use of NSCs is hampered by heterogeneity, poor neuronal cell yield, predominant astrocytic differentiation of NSC progeny, and possible uncontrolled proliferation and tumor formation upon transplantation. The ability to generate highly enriched and defined neural cell populations from the renewable source of NSCs might overcome many of these impediments and pave the way toward their successful clinical applications.Here, we describe a simple method for NSC differentiation and subsequent purification of neuronal progenitor cells, taking advantage of size and granularity differences between neuronal cells and other NSC progeny. This highly enriched neuronal cell population provides an invaluable source of cells for both in vitro and in vivo studies.

The importance of detailed epigenomic profiling of different cell types within organs

The human body consists of hundreds of kinds of cells specified from a single genome overlaid with cell type-specific epigenetic information. Comprehensively profiling the body's distinct epigenetic landscapes will allow researchers to verify cell types used in regenerative medicine and to determine the epigenetic effects of disease, environmental exposures and genetic variation. Key marks/factors that should be investigated include regions of nucleosome-free DNA accessible to regulatory factors, histone marks defining active enhancers and promoters, DNA methylation levels, regulatory RNAs, and factors controlling the three-dimensional conformation of the genome. Here we use the lung to illustrate the importance of investigating an organ's purified cell epigenomes, and outline the challenges and promise of realizing a comprehensive catalog of primary cell epigenomes.

Isolation and enrichment of defined neural cell populations from heterogeneous neural stem cell progeny

The renewable source of neural stem cells (NSCs) with multi-lineage differentiation capability towards neurons, astrocytes, and oligodendrocytes represent an ideal supply for cell therapy of central nervous system (CNS) diseases. In spite of this, the clinical use of NSCs is hampered by heterogeneity, poor neuronal cell yield, predominant astrocytic differentiation of NSC progeny and possible uncontrolled proliferation, and tumor formation upon transplantation. The ability to generate highly enriched and defined neural cell populations from the renewable source of NSCs might overcome many of these impediments and pave the way towards their successful clinical applications. Here, we describe a simple method for NSC differentiation and subsequent purification of neuronal progenitor cells, taking advantage of size and granularity differences between neuronal cells and other NSC progeny. This highly enriched neuronal cell population provides an invaluable source of cells for both in vitro and in vivo studies.

Purification of immature neuronal cells from neural stem cell progeny

Large-scale proliferation and multi-lineage differentiation capabilities make neural stem cells (NSCs) a promising renewable source of cells for therapeutic applications. However, the practical application for neuronal cell replacement is limited by heterogeneity of NSC progeny, relatively low yield of neurons, predominance of astrocytes, poor survival of donor cells following transplantation and the potential for uncontrolled proliferation of precursor cells. To address these impediments, we have developed a method for the generation of highly enriched immature neurons from murine NSC progeny. Adaptation of the standard differentiation procedure in concert with flow cytometry selection, using scattered light and positive fluorescent light selection based on cell surface antibody binding, provided a near pure (97%) immature neuron population. Using the purified neurons, we screened a panel of growth factors and found that bone morphogenetic protein-4 (BMP-4) demonstrated a strong survival effect on the cells in vitro, and enhanced their functional maturity. This effect was maintained following transplantation into the adult mouse striatum where we observed a 2-fold increase in the survival of the implanted cells and a 3-fold increase in NeuN expression. Additionally, based on the neural-colony forming cell assay (N-CFCA), we noted a 64 fold reduction of the bona fide NSC frequency in neuronal cell population and that implanted donor cells showed no signs of excessive or uncontrolled proliferation. The ability to provide defined neural cell populations from renewable sources such as NSC may find application for cell replacement therapies in the central nervous system.

Human central nervous system tissue culture: a historical review and examination of recent advances

Tissue culture has been and continues to be widely used in medical research. Since the beginning of central nervous system (CNS) tissue culture nearly 100 years ago, the scientific community has contributed innumerable protocols and materials leading to the current wide variety of culture systems. While nonhuman cultures have traditionally been more widely used, interest in human CNS tissue culture techniques has accelerated since the middle of the last century. This has been fueled largely by the desire to model human physiology and disease in vitro with human cells. We review the history of human CNS tissue culture summarizing advances that have led to the current breadth of options available. The review addresses tissue sources, culture initiation, formats, culture ware, media, supplements and substrates, and maintenance. All of these variables have been influential in the development of culturing options and the optimization of culture survival and propagation.

An efficient method for the culturing and generation of neurons and astrocytes from second trimester human central nervous system tissue

The isolation, culturing and expansion of human neural progenitors cells has important potential clinical applications in cellular transplantation strategies as well as in developmental studies involving the central nervous system (CNS). This study describes an efficient method to culture neurons and astrocytes as primary cultures, as well as from proliferative progenitor cells derived from second trimester fetal CNS tissue. Second trimester fetal human tissue was mechanically dissociated and subjected to trypsin-dissociation and trituration. The resulting suspension was passed over a Percoll density gradient. The middle (second) fraction of cells was centrifuged to yield a homogenous population of cells with 80%-90% viability. These cells were either cultured directly on laminin coated dishes with defined medium supplemented with fetal bovine serum or in defined medium supplemented with growth factors including epidermal growth factor, basic fibroblast growth factor and leukemia inhibitory factor. The primary cell cultures yielded neurons and astrocytes after 3-5 days in vitro verified by immunostaining with MAP2ab and GFAP. Cells exposed to growth factor supplemented medium formed free-floating spheres within one week. Upon growth factor removal and plating on laminin-coated dishes, brain derived spheres gave rise to neurons, astrocytes and oligodendrocytes; spinal cord derived spheres generated only astrocytes. This protocol describes an efficient method to generate and culture neurons and astrocytes from second trimester human CNS tissue that may be useful in transplantation and developmental studies.

Interleukin-1 is a key regulator of matrix metalloproteinase-9 expression in human neurons in culture and following mouse brain trauma in vivo

An acute trauma to the CNS rapidly results in the upregulation of inflammatory cytokines that include interleukin-1 (IL-1). We report here that the levels of several matrix metalloproteinases (MMPs) are also elevated following a corticectomy trauma injury to the mouse CNS. The delayed upregulation of MMPs compared to that for IL-1 suggests the possibility that inflammatory cytokines regulate MMP production in CNS trauma. To resolve this, we developed a method to isolate and maintain highly enriched human fetal neurons or astrocytes in culture and examined the regulation by cytokines of the activity of a subgroup of MMPs, the gelatinases (MMP-2 and -9). While both neuronal and astrocytic cultures displayed comparable MMP-2 activity, as evidenced by gelatin zymography, levels of MMP-9 were proportionately higher in neurons compared to astrocytes. Of a variety of cytokines and growth factors tested in vitro, only IL-1beta was effective in increasing the neuronal expression of MMP-9. Finally, an IL-1 receptor antagonist attenuated the increase of neuronal MMP-9 in culture and abolished the injury-induced increase of MMP-9 in the mouse brain. These results implicate IL-1beta as a key regulator of neuronal MMP-9 in culture and of the elevation of MMP-9 that occurs following mouse CNS trauma.

Gap junctions: the "kiss of death" and the "kiss of life"

Cells expressing herpes simplex-thymidine kinase (HSV-tk) can be killed "in vitro" within 5 days of treatment with 20 microM ganciclovir (GCV) and transmit this toxicity to adjacent cells lacking HSV-tk; this phenomenon was termed "bystander effect" or "kiss of death". On testing a large number of cell lines in vitro, a wide range of sensitivity to GCV-mediated bystander killing has been reported. Although intercellular transfer of GCV metabolites through gap junction channels seems to be a likely mechanism for the "kiss of death", some studies suggest that other pathways may contribute to induced apoptosis of neighboring cells. To further investigate the mechanism underlying cell death mediated by HSV-tk and to evaluate the efficacy of gap junction channels formed by different connexins in this process, we have stably transfected a virtually uncoupled mouse neuroblastoma cell line (N2A cells) with different connexin-types expressed by neural cells (Cx32, Cx37, Cx40, Cx43) and co-cultured these cells with N2A cells stably transfected with Cx37 and HSV-tk. Here, we confirm our previous studies and those of others that the extent of cell death and sensitivity to GCV depend on the degree of connexin expression in transfectants. Further, we show that the bystander effect also depends on which connexin is expressed; reported disparities regarding the extent of GCV-mediated cellular apoptosis are likely due both to the degree of functional coupling and the type of connexin expressed. These results support the notion that gap junction hemichannels formed of certain connexins are more likely than others to pair functionally with Cx37, and suggest co-transfection strategies that might prove effective in sensitizing tumor cell populations to GCV. In addition, potential applications are discussed for use of the "good Samaritan effect", a mechanism by which bystander cells have been suggested to prevent cytotoxicity.

Fetal human cortical neurons grown in culture: morphological differentiation, biochemical correlates and development of electrical activity

Cultured fetal human cortical neurons derived from second trimester human fetal cortex were analyzed with regard to their morphological differentiation and expression of cell-specific markers. The culture method was adapted from standardized protocols originally developed for the isolation and culture of rodent oligodendrocytes and astrocytes. This technique takes advantage of the different adhesive properties and stratification of central nervous system cells in vitro. Under these culture conditions fetal human cortical neurons underwent morphological differentiation, expressed neuron-specific markers and voltage- and ligand-gated ion channels. Highly enriched cultures of microglia and astrocytes generated from the same starting material also expressed cell-type specific markers. These cultures serve as a valuable tool for the establishment of normative data and as experimental models for neurodevelopmental and neurodegenerative studies.

Purification of human fetal hippocampal neurons by flow cytometry for transplantation

We have established primary cultures, highly enriched in neurons, from the hippocampus of human fetal brains at 20-23 gestational weeks. More than 80% of cells were viable when seeded. Neurons were isolated from primary cultures by flow cytometry to a high degree of purity, as demonstrated by immunocytochemical staining. FACS scanning analysis using a DNA-staining dye showed that hippocampal neurons did not divide in culture. To demonstrate that FACS-sorted neurons can be transplanted and integrated into the host brain, neuron-enriched primary culture from human fetal striatum was infected with a viral-mediated vector containing a reporter gene, beta-galactosidase. Striatal neurons were subsequently purified by flow cytometry and transplanted into the striatum of rats. Following transplantation, the rat brains were processed for beta-galactosidase histochemistry and electron microscopy. Beta-galactosidase expression indicates that transplanted human neurons survived in the host and were metabolically active. The transplanted neurons received synaptic inputs, as judged from the presence of presynaptic terminals on their surface. Our study demonstrates connectivity between transplanted human fetal primary neurons and host tissue at the ultrastructural level. Our results support the feasibility of ultimately transplanting neurons into humans as a possible treatment for recovery of the nervous system (e.g., neurodegenerative diseases).

Severe Combined Immunodeficiency Mice Engrafted With Human T Cells, B Cells, and Myeloid Cells After Transplantation With Human Fetal Bone Marrow or Liver Cells and Implanted With Human Fetal Thymus: A Model for Studying Human Gene Therapy

To develop an in vivo model wherein human hematopoiesis occurs, we transplanted severe combined immunodeficiency (SCID) mice with either human fetal bone marrow (HFBM) or human fetal liver (HFL). After transplantation of SCID mice with cultured HFBM (BM-SCID-hu mice) or HFL cells (Liv-SCID-hu mice), significant engraftment of the mouse bone marrow (BM) and population of the peripheral blood with human leukocytes was detected. Human colony-forming unit–granulocyte macrophage and burst forming unit-erythroid were detected in the BM of the BM-SCID-hu and Liv-SCID-hu mice up to 8 months after transplantation. When the HFBM or HFL cells were transduced with a retroviral vector before transplantation, integrated retroviral sequences were detected in human precursor cells present in the SCID mouse BM and in leukocytes circulating in the peripheral blood (PB) up to 7 months after transplantation. The PB of the BM-SCID-hu mice also became populated with human T cells after implantation with human thymic tissue, which provided a human microenvironment wherein human pre-T cells from the BM could mature. When the HFBM was retrovirally transduced before transplantation, integrated retrovirus was detected in sorted CD4+CD8+ double positive and CD4+ single positive cells from the thymic implant and CD4+ cells from the PB. Taken together, these data indicated that the BM of our BM-SCID-hu and Liv-SCID-hu mice became engrafted with retrovirally transduced human hematopoietic precursors that undergo the normal human hematopoietic program and populate the mouse PB with human cells containing integrated retroviral sequences. In addition to being a model for studying in vivo human hematopoiesis, these mice should also prove to be a useful model for investigating in vivo gene therapy using human stem/precursor cells.

Severe Combined Immunodeficiency Mice Engrafted With Human T Cells, B Cells, and Myeloid Cells After Transplantation With Human Fetal Bone Marrow or Liver Cells and Implanted With Human Fetal Thymus: A Model for Studying Human Gene Therapy

To develop an in vivo model wherein human hematopoiesis occurs, we transplanted severe combined immunodeficiency (SCID) mice with either human fetal bone marrow (HFBM) or human fetal liver (HFL). After transplantation of SCID mice with cultured HFBM (BM-SCID-hu mice) or HFL cells (Liv-SCID-hu mice), significant engraftment of the mouse bone marrow (BM) and population of the peripheral blood with human leukocytes was detected. Human colony-forming unit–granulocyte macrophage and burst forming unit-erythroid were detected in the BM of the BM-SCID-hu and Liv-SCID-hu mice up to 8 months after transplantation. When the HFBM or HFL cells were transduced with a retroviral vector before transplantation, integrated retroviral sequences were detected in human precursor cells present in the SCID mouse BM and in leukocytes circulating in the peripheral blood (PB) up to 7 months after transplantation. The PB of the BM-SCID-hu mice also became populated with human T cells after implantation with human thymic tissue, which provided a human microenvironment wherein human pre-T cells from the BM could mature. When the HFBM was retrovirally transduced before transplantation, integrated retrovirus was detected in sorted CD4+CD8+ double positive and CD4+ single positive cells from the thymic implant and CD4+ cells from the PB. Taken together, these data indicated that the BM of our BM-SCID-hu and Liv-SCID-hu mice became engrafted with retrovirally transduced human hematopoietic precursors that undergo the normal human hematopoietic program and populate the mouse PB with human cells containing integrated retroviral sequences. In addition to being a model for studying in vivo human hematopoiesis, these mice should also prove to be a useful model for investigating in vivo gene therapy using human stem/precursor cells.