Cell Transplantation

Human stem cells, progenitor cells, and cell lines have been derived from embryonic, fetal, and adult sources in the search for graft tissue suitable for the treatment of CNS disorders. An increasing number of experimental studies have shown that grafts from several sources survive, differentiate into distinct cell types, and exert positive functional effects in experimental animal models, but little attention has been given to developing cells under conditions of good manufacturing practice (GMP) that can be scaled up for mass treatment. The capacity for continued division of stem cells in culture offers the opportunity to expand their production to meet the widespread clinical demands posed by neurodegenerative diseases. However, maintaining stem cell division in culture long term, while ensuring differentiation after transplantation, requires genetic and/or oncogenetic manipulations, which may affect the genetic stability and in vivo survival of cells. This review outlines the stages, selection criteria, problems, and ultimately the successes arising in the development of conditionally immortal clinical grade stem cell lines, which divide in vitro, differentiate in vivo, and exert positive functional effects. These processes are specifically exemplified by the murine MHP36 cell line, conditionally immortalized by a temperature-sensitive mutant of the SV40 large T antigen, and cell lines transfected with the c-myc protein fused with a mutated estrogen receptor (c-mycERTAM), regulated by a tamoxifen metabolite, but the issues raised are common to all routes for the development of effective clinical grade cells.

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the selective degeneration of dopaminergic (DA) neurons in the substantia nigra of the midbrain. Pharmacological treatment of PD has been a prevailing strategy. However, it has some limitations because its effectiveness gradually decreases and side effects develop. As an alternative, cell transplantation therapy has been tried. Although transplantation of fetal ventral mesencephalic cells looks promising for the treatment of PD in some cases, ethical and technical problems in obtaining large numbers of human fetal brain tissues also lead to difficulty in its clinical application. Our recent studies showed that a high yield of DA neurons could be derived from embryonic stem (ES) cells and they efficiently induced behavioral recovery in a PD animal model. Here we summarize methods for generation of functional DA neurons from ES cells for application to PD models.

Over the last decade, molecular biology has progressively developed, leading to new technology with subsequent clinical application for various cerebral diseases including Parkinson's disease (PD), one of the most investigated neurodegenerative disorders. The therapy for PD is mainly composed of medication, including drug replacement therapy, surgical treatment, and cell transplantation. Cell therapy for PD has been explored by using fetal nigral cells as an allo- or xenograft, autologous sympathetic ganglion, adrenal medulla, and carotid body in clinical settings. In addition, neurotrophic factors, including glial cell line-derived neurotrophic factor (GDNF), have a strong potency to rescue degenerating dopaminergic cells. Protein and/or gene therapy also might be a therapeutic option for PD. In this review, genetically engineered cell transplantation for animal models of PD, including catecholamine/neurotrophic factor-secreting cell transplantation with or without encapsulation, as performed in our laboratories, and their potential future as clinical applications are described with recent clinical studies in this field.

Neural stem cells (NSCs) have been proposed as a promising cellular source for the treatment of diseases in nervous systems. NSCs can self-renew and generate major cell types of the mammalian central nervous system throughout adulthood. NSCs exist not only in the embryo, but also in the adult brain neurogenic region: the subventricular zone (SVZ) of the lateral ventricle. Embryonic stem (ES) cells acquire NSC identity with a default mechanism. Under the regulations of leukemia inhibitory factor (LIF) and fibroblast growth factors, the NSCs then become neural progenitors. Neurotrophic and differentiation factors that regulate gene expression for controlling neural cell fate and function determine the differentiation of neural progenitors in the developing mammalian brain. For clinical application of NSCs in neurodegenerative disorders and damaged neurons, there are several critical problems that remain to be resolved: 1) how to obtain enough NSCs from reliable sources for autologous transplantation; 2) how to regulate neural plasticity of different adult stem cells; 3) how to control differentiation of NSCs in the adult nervous system. In order to understand the mechanisms that control NSC differentiation and behavior, we review the ontogeny of NSCs and other stem cell plasticity of neuronal differentiation. The role of NSCs and their regulation by neurotrophic factors in CNS development are also reviewed.

Umbilical cord blood (UCB) banking has become a new obstetrical trend. It offers expectant parents a biological insurance policy that can be used in the event of a child or family member's life-threatening illness and puts patients in a position of control over their own treatment options. However, its graduation to conventional therapy in the clinical realm relies on breakthrough research that will prove its efficacy for a range of ailments. Expanding the multipotent cells found within the mononuclear fraction of UCB so that adequate dosing can be achieved, effectively expanding desired cells ex vivo, establishing its safety and limitations in HLA-mismatched recipients, defining its mechanisms of action, and proving its utility in a wide variety of both rare and common illnesses and diseases are a few of the challenges left to tackle. Nevertheless, the field is moving fast and new UCB-based therapies are on the horizon.

Stroke remains a major cause of death in the US and around the world. Over the last decade, stem cell therapy has been introduced as an experimental treatment for stroke. Transplantation of stem cells or progenitors into the injured site to replace the nonfunctional cells, and enhancement of proliferation or differentiation of endogenous stem or progenitor cells stand as the two major cell-based strategies. Potential sources of stem/progenitor cells for stroke include fetal neural stem cells, embryonic stem cells, neuroteratocarcinoma cells, umbilical cord blood-derived nonhematopoietic stem cells, and bone marrow-derived stem cells. The goal of this article is to provide an update on the preclinical use of bone marrow-derived stem cells with major emphasis on mesenchymal stem cells (MSCs) and multipotent adult progenitor cells (MAPCs) because they are currently most widely applied in experimental stroke studies and are now being phased into early clinical trials. The phenotypic features of MSCs and MAPCs, as well as their application in stroke, are described.

Stroke remains a leading cause of death and disability worldwide. An increasing number of animal studies and preclinical trials have, however, provided evidence that regenerative cell-based therapies can lead to functional recovery in stroke patients. Stem cells can differentiate into neural lineages to replace lost neurons. Moreover, they provide trophic support to tissue at risk in the penumbra surrounding the infarct area, enhance vasculogenesis, and help promote survival, migration, and differentiation of the endogenous precursor cells after stroke. Stem cells are highly migratory and seem to be attracted to areas of brain pathology such as ischemic regions. The pathotropism may follow the paradigm of stem cell homing to bone marrow and leukocytes migrating to inflammatory tissue. The molecular signaling therefore may involve various chemokines, cytokines, and integrins. Among these, stromal cell-derived factor-1 (SDF-1)/CXC chemokine receptor-4 (CXCR4) signaling is required for the interaction of stem cells and ischemia-damaged host tissues. SDF-1 is secreted primarily by bone marrow fibroblasts and is required for BMSC homing to bone marrow. Overexpression of SDF-1 in ischemic tissues has been found to enhance stem cell recruitment from peripheral blood and to induce neoangiogenesis. Furthermore, SDF-1 expression in the lesioned area peaked within 7 days postischemia, in concordance with the time window of G-CSF therapy for stroke. Recent data have shown that SDF-1 expression is directly proportional to reduced tissue oxygen tension. SDF-1 gene expression is regulated by hypoxic-inducible factor-1 (HIF-1), a hypoxia-dependent stabilization transcription factor. Thus, ischemic tissue may recruit circulating progenitors regulated by hypoxia through differential expression of HIF-1α and SDF-1. In addition to SDF-1, β2-integrins also play a role in the homing of hematopoietic progenitor cells to sites of ischemia and are critical for their neovascularization capacity. In our recent report, increased expression of β1-integrins apparently contributed to the local neovasculization of the ischemic brain as well as its functional recovery. Identification of the molecular pathways involved in stem cell homing into the ischemic areas could pave the way for the development of new treatment regimens, perhaps using small molecules, designed to enhance endogeneous mobilization of stem cells in various disease states, including chronic stroke and other neurodegenerative diseases. For maximal functional recovery, however, regenerative therapy may need to follow combinatorial approaches, which may include cell replacement, trophic support, protection from oxidative stress, and the neutralization of the growth-inhibitory components for endogenous neuronal stem cells.