Preclinical assessment of stem cell therapies for neurological diseases

Bio-distribution and toxicity potential of human umbilical cord mesenchymal stem cells in cynomolgus monkeys

Mesenchymal stem cells (MSCs) have demonstrated promising advantages in the therapies of many diseases, while its multi-directional differentiation potential and immunotoxicity are the major concerns hindered their clinical translation. In this study, human umbilical Mesenchymal stem cell (hUC-MSCs) were labeled with a near-infrared fluorescent dye DiR before infused into cynomolgus monkeys, and the amount of hUC-MSCs in the peripheral blood were dynamically estimated from 5 min to 28 days post a single administration at 3 × 106 cells/kg and 2 × 107 cells/kg intravenously. As results, some hUC-MSCs distributed to the whole body within 5 min, while most of the cells accumulate in the lungs along with the systemic blood circulation, and subsequently released into the blood. The toxicity potentials of hUC-MSCs were investigated in another 30 cynomolgus monkeys, and the cells were repeatedly administrated at doses of 3 × 106 cells/kg and 2 × 107 cells/kg for 5 times on a weekly basis, with a recovery period of 1 months. hUC-MSCs showed no obvious toxic effects in cynomolgus monkeys, except xenogeneic immune rejection to human stem cells. Low levels of the hUC-MSC gene were detected in the peripheral blood of a few animals administered 2 × 107 cells/kg at 30 min subsequent to the first and last administration, and there was no significant difference in the copy number of the hUC-MSC gene in the blood samples compared with the first and last administration, indicating that the hUC-MSC was not significantly amplified in vivo, and it its safe in non-human primates. Our study for the first time verified the safety of long-term use of hUC-MSCs in primates. We have pioneered a technology for the real-time detection of hUC-MSCs in peripheral blood and provide dynamicand rapid monitoring of the distribution characteristics of hUC-MSCs in vivo. Here, we provide data supporting the application of such products for clinical treatment and the application of stem cells in major refractory diseases and regenerative medicine.

Highly specific, quantitative polymerase chain reaction probe for the quantification of human cells in cynomolgus monkeys

Quantification of human cells may be performed using quantitative polymerase chain reaction (qPCR). In preclinical studies, the human Alu sequence is widely used as biomarker for human DNA. However, because the Alu gene is shared by primates, its use is limited to non-primate studies. The biodistribution of human cells in primates is also necessary for translational studies. Therefore, we aimed to design a novel, human-specific primer/probe that enables the quantification of human cells in primates and other animal models. A novel primer/probe set was successfully designed based on highly repetitive LINE1 sequences. qPCR efficiency (94.95-99.21%) and linearity of calibration curves (r² = 0.996-0.999) were confirmed in tissue homogenates of cynomolgus monkey. The lower limit of detection was 10 cells per 15-mg tissue sample, a sensitivity that is equivalent to existing Alu primers/probes. The set was also effective in other animal models such as mice, rabbits, pigs, and common marmosets. To our knowledge, this is the first study describing the successful design of a human-specific qPCR primer/probe for human cell quantification in various animals, including non-human primates, using LINE1 sequence. The excellent selectivity, sensitivity, and versatility of the LINE1 primers/probes make it a promising quantification tool in preclinical biodistribution studies.

Advancing research in regeneration and repair of the motor circuitry: non-human primate models and imaging scales as the missing links for successfully translating injectable therapeutics to the clinic

Regeneration and repair is the ultimate goal of therapeutics in trauma of the central nervous system (CNS). Stroke and spinal cord injury (SCI) are two highly prevalent CNS disorders that remain incurable, despite numerous research studies and the clinical need for effective treatments. Neural engineering is a diverse biomedical field, that addresses these diseases using new approaches. Research in the field involves principally rodent models and biologically active, biodegradable hydrogels. Promising results have been reported in preclinical studies of CNS repair, demonstrating the great potential for the development of new treatments for the brain, spinal cord and peripheral nerve injury. Several obstacles stand in the way of clinical translation of neuroregeneration research. There seems to be a key gap in the translation of research from rodent models to human applications, namely non-human primate models, which constitute a critical bridging step. Applying injectable therapeutics and multimodal neuroimaging in stroke lesions using experimental rhesus monkey models is an avenue that a few research groups have begun to embark on. Understanding and assessing the changes that the injured brain or spinal cord undergoes after an intervention with biodegradable hydrogels in non-human primates seem to represent critical preclinical research steps. Existing innovative models in non-human primates allow us to evaluate the potential of neural engineering and injectable hydrogels. The results of these preliminary studies will pave the way for translating this research into much needed clinical therapeutic approaches. Cutting edge imaging technology using Connectome scanners represents a tremendous advancement, enabling the in vivo, detailed, high-resolution evaluation of these therapeutic interventions in experimental animals. Most importantly, they also allow quantifiable and clinically meaningful correlations with humans, increasing the translatability of these innovations to the bedside.

The transcriptomes of novel marmoset monkey embryonic stem cell lines reflect distinct genomic features

Embryonic stem cells (ESCs) are useful for the study of embryonic development. However, since research on naturally conceived human embryos is limited, non-human primate (NHP) embryos and NHP ESCs represent an excellent alternative to the corresponding human entities. Though, ESC lines derived from naturally conceived NHP embryos are still very rare. Here, we report the generation and characterization of four novel ESC lines derived from natural preimplantation embryos of the common marmoset monkey (Callithrix jacchus). For the first time we document derivation of NHP ESCs derived from morula stages. We show that quantitative chromosome-wise transcriptome analyses precisely reflect trisomies present in both morula-derived ESC lines. We also demonstrate that the female ESC lines exhibit different states of X-inactivation which is impressively reflected by the abundance of the lncRNA X inactive-specific transcript (XIST). The novel marmoset ESC lines will promote basic primate embryo and ESC studies as well as preclinical testing of ESC-based regenerative approaches in NHP.

Polyglutamine (PolyQ) diseases: genetics to treatments

The polyglutamine (polyQ) diseases are a group of neurodegenerative disorders caused by expanded cytosine-adenine-guanine (CAG) repeats encoding a long polyQ tract in the respective proteins. To date, a total of nine polyQ disorders have been described: six spinocerebellar ataxias (SCA) types 1, 2, 6, 7, 17; Machado-Joseph disease (MJD/SCA3); Huntington's disease (HD); dentatorubral pallidoluysian atrophy (DRPLA); and spinal and bulbar muscular atrophy, X-linked 1 (SMAX1/SBMA). PolyQ diseases are characterized by the pathological expansion of CAG trinucleotide repeat in the translated region of unrelated genes. The translated polyQ is aggregated in the degenerated neurons leading to the dysfunction and degeneration of specific neuronal subpopulations. Although animal models of polyQ disease for understanding human pathology and accessing disease-modifying therapies in neurodegenerative diseases are available, there is neither a cure nor prevention for these diseases, and only symptomatic treatments for polyQ diseases currently exist. Long-term pharmacological treatment is so far disappointing, probably due to unwanted complications and decreasing drug efficacy. Cellular transplantation of stem cells may provide promising therapeutic avenues for restoration of the functions of degenerative and/or damaged neurons in polyQ diseases.

Endometrial stem cell transplantation in MPTP- exposed primates: an alternative cell source for treatment of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease caused by the loss of dopaminergic neurons in the substantia nigra. Cell-replacement therapies have emerged as a promising strategy to slow down or replace neuronal loss. Compared to other stem cell types, endometrium-derived stem cells (EDSCs) are an attractive source of stem cells for cellular therapies because of their ease of collection and vast differentiation potential. Here we demonstrate that endometrium-derived stem cells may be transplanted into an MPTP exposed monkey model of PD. After injection into the striatum, endometrium-derived stem cells engrafted, exhibited neuron-like morphology, expressed tyrosine hydroxylase (TH) and increased the numbers of TH positive cells on the transplanted side and dopamine metabolite concentrations in vivo. Our results suggest that endometrium-derived stem cells may provide a therapeutic benefit in the primate model of PD and may be used in stem cell based therapies.

Intravenous transplantation of bone marrow mesenchymal stem cells promotes neural regeneration after traumatic brain injury

To investigate the supplement of lost nerve cells in rats with traumatic brain injury by intravenous administration of allogenic bone marrow mesenchymal stem cells, this study established a Wistar rat model of traumatic brain injury by weight drop impact acceleration method and administered 3 × 10⁶ rat bone marrow mesenchymal stem cells via the lateral tail vein. At 14 days after cell transplantation, bone marrow mesenchymal stem cells differentiated into neurons and astrocytes in injured rat cerebral cortex and rat neurological function was improved significantly. These findings suggest that intravenously administered bone marrow mesenchymal stem cells can promote nerve cell regeneration in injured cerebral cortex, which supplement the lost nerve cells.

Patient-specific induced pluripotent stem cells in neurological disease modeling: the importance of nonhuman primate models

The development of the technology for derivation of induced pluripotent stem (iPS) cells from human patients and animal models has opened up new pathways to the better understanding of many human diseases, and has created new opportunities for therapeutic approaches. Here, we consider one important neurological disease, Parkinson's, the development of relevant neural cell lines for studying this disease, and the animal models that are available for testing the survival and function of the cells, following transplantation into the central nervous system. Rapid progress has been made recently in the application of protocols for neuroectoderm differentiation and neural patterning of pluripotent stem cells. These developments have resulted in the ability to produce large numbers of dopaminergic neurons with midbrain characteristics for further study. These cells have been shown to be functional in both rodent and nonhuman primate (NHP) models of Parkinson's disease. Patient-specific iPS cells and derived dopaminergic neurons have been developed, in particular from patients with genetic causes of Parkinson's disease. For complete modeling of the disease, it is proposed that the introduction of genetic changes into NHP iPS cells, followed by studying the phenotype of the genetic change in cells transplanted into the NHP as host animal, will yield new insights into disease processes not possible with rodent models alone.

Large animal models for stem cell therapy

The field of regenerative medicine is approaching translation to clinical practice, and significant safety concerns and knowledge gaps have become clear as clinical practitioners are considering the potential risks and benefits of cell-based therapy. It is necessary to understand the full spectrum of stem cell actions and preclinical evidence for safety and therapeutic efficacy. The role of animal models for gaining this information has increased substantially. There is an urgent need for novel animal models to expand the range of current studies, most of which have been conducted in rodents. Extant models are providing important information but have limitations for a variety of disease categories and can have different size and physiology relative to humans. These differences can preclude the ability to reproduce the results of animal-based preclinical studies in human trials. Larger animal species, such as rabbits, dogs, pigs, sheep, goats, and non-human primates, are better predictors of responses in humans than are rodents, but in each case it will be necessary to choose the best model for a specific application. There is a wide spectrum of potential stem cell-based products that can be used for regenerative medicine, including embryonic and induced pluripotent stem cells, somatic stem cells, and differentiated cellular progeny. The state of knowledge and availability of these cells from large animals vary among species. In most cases, significant effort is required for establishing and characterizing cell lines, comparing behavior to human analogs, and testing potential applications. Stem cell-based therapies present significant safety challenges, which cannot be addressed by traditional procedures and require the development of new protocols and test systems, for which the rigorous use of larger animal species more closely resembling human behavior will be required. In this article, we discuss the current status and challenges of and several major directions for the future development of large animal models to facilitate advances in stem cell-based regenerative medicine.

Unrestricted somatic stem cells as vehicle for nerve growth factor gene transfer

OBJECTIVE

Nerve growth factor (NGF), a member of the neurotrophic factor family, plays a critical role in the maintenance and regeneration of different types of neurons. To overcome drastic challenges in the peripheral delivery of NGF, transplantation of NGF secreting stem cells to the target site of an injury may be an effective procedure. Unrestricted somatic stem cells (USSCs), a subtype of umbilical cord blood (UCB) stem cells, have shown promise for gene therapy purposes, and proper results have been observed from transplantation experiments in neurodegenerative disorders. Based on the considerable potential of USSCs for gene delivery applications, the goal of the current study was to establish a betaNGF gene containing USSCs, which is able to secrete functional recombinant betaNGF protein.

METHODS

Unrestricted somatic stem cells were isolated from UCB and were cultured in a DMEM medium. The betaNGF gene was cloned in the EFalpha-promoting lentiviral vector, and virus production was performed as a third generation lentivirus packaging system. Enzyme-linked immunosorbent assay, real-time PCR, co-culture, MTT, and immunocytochemistry assays were performed to evaluate the genetically engineered USSCs.

RESULTS

Overexpression of betaNGF gene in human USSCs created a USSC line that is able to secrete high amounts of functional betaNGF protein. betaNGF-secreting USSCs showed a high rate of viability along with acceptable immunological and morphological properties for transplantation into the nervous system.

DISCUSSION

Long-term expression of functional betaNGF, high viability of betaNGF producing USSCs, and expression of primary neuronal markers suggest that USSCs may be useful to deliver betaNGF into targeted sites of the nervous system in neurodegenerative disorders.

Comparative phenotypic and molecular characterization of porcine mesenchymal stem cells from different sources for translational studies in a large animal model

Mesenchymal stem cells have demonstrated their potentiality for therapeutic use in treating diseases or repairing damaged tissues. However, in some cases, the results of clinical trials have been disappointing or have not worked out as well as hoped. These disappointing results can be attributed to an inadequate or insufficient preclinical study. For medical and surgical purposes, the similarities between the anatomy of pig and human make this animal an attractive preclinical model. In this sense, for mesenchymal stem cell-based therapy, it is strongly necessary to have well characterized animal-derived mesenchymal stem cell lines to validate preclinical effectiveness of these cells. In this work, porcine mesenchymal stem cells (pMSCs) were isolated from bone marrow, adipose tissue and peripheral blood and compared in terms of differentiation potential, cell surface markers and gene expression. Our results demonstrated that the isolation and in vitro expansion protocols were feasible and effective. The data presented in this work are relevant because they provide an extensive phenotypic characterization; genetic study and differentiation behavior of the most commonly used stem cell lines for clinical practices. These pMSCs are widely available to scientists and could be a valuable tool to evaluate the safety and efficacy of adoptively transferred cells.

Modeling HIV-associated neurocognitive disorders in mice: new approaches in the changing face of HIV neuropathogenesis

It is well established that infection with the human immunodeficiency virus (HIV) leads to immune suppression. Less well known is the fact that long-term, progressive HIV disease is associated with the development of cognitive deficits. Since the introduction of combined antiretroviral therapy (cART), the clinical presentation of HIV infection has evolved into a chronic illness with very low levels of viral replication and chronic immune activation, with compliant affected individuals surviving for decades with a high quality of life. Despite these advances, many HIV-infected individuals develop some degree of neurodegeneration and cognitive impairment. The underlying pathophysiological mechanisms are not well understood, and there are no effective treatments. Thus, there is an unmet need for animal models that enable the study of HIV-associated neurocognitive disorders (HAND) and the testing of new therapeutic approaches to combat them. Here, we review the pros and cons of existing mouse models of HIV infection for addressing these aims and propose a detailed strategy for developing a new mouse model of HIV infection.

Cell transplantation and gene therapy in Parkinson's disease

Parkinson's disease is a progressive neurodegenerative disorder affecting, in part, dopaminergic motor neurons of the ventral midbrain and their terminal projections that course to the striatum. Symptomatic strategies focused on dopamine replacement have proven effective at remediating some motor symptoms during the course of disease but ultimately fail to deliver long-term disease modification and lose effectiveness due to the emergence of side effects. Several strategies have been experimentally tested as alternatives for Parkinson's disease, including direct cell replacement and gene transfer through viral vectors. Cellular transplantation of dopamine-secreting cells was hypothesized as a substitute for pharmacotherapy to directly provide dopamine, whereas gene therapy has primarily focused on restoration of dopamine synthesis or neuroprotection and restoration of spared host dopaminergic circuitry through trophic factors as a means to enhance sustained controlled dopamine transmission. This seems now to have been verified in numerous studies in rodents and nonhuman primates, which have shown that grafts of fetal dopamine neurons or gene transfer through viral vector delivery can lead to improvements in biochemical and behavioral indices of dopamine deficiency. However, in clinical studies, the improvements in parkinsonism have been rather modest and variable and have been plagued by graft-induced dyskinesias. New developments in stem-cell transplantation and induced patient-derived cells have opened the doors for the advancement of cell-based therapeutics. In addition, viral-vector-derived therapies have been developed preclinically with excellent safety and efficacy profiles, showing promise in clinical trials thus far. Further progress and optimization of these therapies will be necessary to ensure safety and efficacy before widespread clinical use is deemed appropriate.