Intracerebral transplantation and successful integration of astrocytes following genetic modification with a high-capacity adenoviral vector

Neural Precursor Cells as Carriers for a Gene Therapeutical Approach in Tumor Therapy

Conventional therapeutical approaches such as surgery, radiotherapy, or chemotherapy have been shown to be rather unsuccessful in the treatment of infiltrative growing tumors such as the malignant glioblastoma multiforme. Thus, new therapeutical strategies have to be developed that are suitable for inducing cell death also in migrating tumor cells. These new therapeutical stategies include cell and/or gene therapeutical approaches. We demonstrate that glial-restricted progenitor cells as well as embryonic stem cell-derived neural stem cells belong to cell populations applicable to such therapeutical concepts. Both cell types can be efficiently transduced using a third-generation high-capacity “gutless” adenoviral vector, and show a tropism for the F98 glioma cells by migrating towards a spheroid of F98 glioma cells with a tendency to form a barrier around the tumor spheroid in an in vitro tumor confrontation model. Moreover, in a migration assay, secretion products of glial-restricted precursor cells have shown a potency to inhibit the migratory activity of glioma cells in vitro. In vivo, F98 glioma cell-derived tumor formation in the right striatum resulted in migration of glial as well as neural precursor cells towards the tumor area when cotransplanted in the corpus callosum of the contralateral hemisphere. After arrival, both cell types surround the tumor mass and even invade the experimentally induced tumor. These data indicate that glial-restricted as well as embryonic stem cell-derived neural precursor cells are good candidates as carriers for an ex vivo gene therapeutical approach in tumor therapy.

Microglia and neuroprotection: from in vitro studies to therapeutic applications

Microglia are the main immune cells in the brain, playing a role in both physiological and pathological conditions. Microglial involvement in neurodegenerative diseases is well-established, being microglial activation and neuroinflammation common features of these neuropathologies. Microglial activation has been considered harmful for neurons, but inflammatory state is not only associated with neurotoxic consequences, but also with neuroprotective effects, such as phagocytosis of dead neurons and clearance of debris. This brought to the idea of protective autoimmunity in the brain and to devise immunomodulatory therapies, aimed to specifically increase neuroprotective aspects of microglia. During the last years, several data supported the intrinsic neuroprotective function of microglia through the release of neuroprotective molecules. These data led to change the traditional view of microglia in neurodegenerative diseases: from the idea that these cells play an detrimental role for neurons due to a gain of their inflammatory function, to the proposal of a loss of microglial neuroprotective function as a causing factor in neuropathologies. This "microglial dysfunction hypothesis" points at the importance of understanding the mechanisms of microglial-mediated neuroprotection to develop new therapies for neurodegenerative diseases. In vitro models are very important to clarify the basic mechanisms of microglial-mediated neuroprotection, mainly for the identification of potentially effective neuroprotective molecules, and to design new approaches in a gene therapy set-up. Microglia could act as both a target and a vehicle for CNS gene delivery of neuroprotective factors, endogenously produced by microglia in physiological conditions, thus strengthening the microglial neuroprotective phenotype, even in a pathological situation.

Transplanted astrocytes internalize deposited beta-amyloid peptides in a transgenic mouse model of Alzheimer's disease

Alzheimer's disease (AD) is one of the most devastating neurodegenerative disorders. The neuropathological hallmarks include extracellular senile plaques consisting of deposited beta-amyloid (Abeta) peptides and intraneuronal neurofibrillary tangles. Neuroinflammation and activation of astrocytes are also well-established features of AD neuropathology; however, the relationships between astrocytes and Abeta deposition remain unclear. Previous studies have shown that adult mouse astrocytes internalize and degrade Abeta deposits in brain sections prepared from human amyloid precursor protein (APP) transgenic mice. In the present study, we demonstrate that cultured adult, but not neonatal mouse astrocytes, respond morphologically and degrade Abeta deposits present in human AD brain. We also transplanted astrocytes isolated from enhanced green fluorescent protein expressing adult and neonatal mice into the hippocampi of human Abeta plaque-bearing transgenic APPSwe+PS1dE9 (APdE9) mice and their wild-type littermates and followed the migration and localization of these astrocytes by confocal microscopy upto 7 days after transplantation. Posttransplantation the astrocytes localized as aggregates or thin strings of many cells within the hippocampi of APdE9 and wild-type mice and showed limited migration from the injection site. Interestingly, most of the transplanted astrocytes were found near Abeta deposits in the hippocampi of APdE9 mice. In contrast to findings in ex vivo degradation assay, confocal microscopy revealed that both adult and neonatal transplanted astrocytes internalized human Abeta immunoreactive material in vivo. These results support the role of astrocytes as active Abeta clearing cells in the CNS that may have important implications for future development of therapeutic strategies for AD.

Disparate host response and donor survival after the transplantation of mesenchymal or neuroectodermal cells to the intact rodent brain

BACKGROUND

To circumvent ethical and legal complications associated with embryonic cell sources, investigators have proposed the use of nonneural donor sources for use in neural transplantation strategies. Leading candidate sources include autologous marrow stromal cells (MSCs) and fibroblasts, which are mesodermal derivatives. However, we recently reported that MSCs transplanted to the adult brain are rapidly rejected by an inflammatory response. Whether extrinsic variables or intrinsic mesenchymal traits stimulated inflammation and rejection is unknown. To determine the future utility of these cells in neural transplantation, we have now performed a systematic analysis of MSC transplantation to the brain.

METHODS

To examine the effects of extrinsic variables on transplantation, green fluorescent protein (GFP)-expressing rat MSCs, cultured under distinct conditions, were transplanted stereotactically to the normal adult rat striatum, and donor survival and the host response was compared. To examine whether intrinsic donor traits promoted rejection, 50,000 GFP-expressing rat MSCs, fibroblasts, or astrocytes were transplanted stereotactically to the adult rat striatum and graft survival and the host response was compared.

RESULTS

Irrespective of preoperative culture conditions, MSCs elicited an inflammatory response and were rejected by 14 days, indicating acute rejection was not mediated by culture conditions. Comparison of MSC, fibroblast, or astrocyte grafts revealed that mesenchymal derivatives, MSCs and fibroblasts, elicited an inflammatory response and were rapidly rejected, whereas neuroectodermal astrocytes demonstrated robust survival in the absence of inflammation.

CONCLUSIONS

Our findings suggest that intrinsic characteristics of mesenchymal cells may stimulate host inflammation, and thus may not represent an ideal donor source for transplantation to the adult brain.

Human bone marrow stroma cells display certain neural characteristics and integrate in the subventricular compartment after injection into the liquor system

Because the neural differentiation capacity of bone marrow stromal cells (BMSCs) is still a matter of controversial debate, we performed a thorough investigation into the differentiation capacity of human BMSCs and examined their therapeutic potency. BMSCs were isolated from the femur and kept in cell cultures with various cultivation protocols being applied. In standard culture conditions using a fetal calf serum-enriched medium, while not exhibiting a neural phenotype, the majority of cells expressed a variety of neuronal marker proteins as well as the astrocyte marker GFAP. Only a minority of stem cells expressed nestin, a marker for neural precursor cells. Cultivation in serum-free medium supplemented with specific growth factors resulted in a markedly higher percentage of nestin-positive cells. To establish the therapeutic potency of bone marrow-derived cells, the synthesis of neurotrophic factors such as NGF, BDNF and GDNF was analyzed under non-stimulating standard culture conditions as well as after a neural selection procedure. The therapeutic potency of BMSCs was further examined with regard to their migratory potential in vitro and after transplantation in vivo. After stereotactic engraftment into the lateral ventricle of adult rats, mesenchymal stem cells were seen to adhere to the ependymocytes and cells of the choroids plexus. Afterwards grafted cells passed through the ependymal barrier, locating in the subventricular space. Their BMSCs took up a close host graft interaction without any degenerative influence on the host cells. Furthermore, there was morphological as well as immunohistochemical evidence for a transdifferentiation within the host tissue. In addition, BMSCs could be efficiently transduced using a third-generation adenoviral vector, indicating their potential feasibility for a gene-therapeutic option.