Inhibitory Nerve Cell Precursors: Dosing, Safety and Efficacy
Many neurological disorders are characterized by an imbalance between excitation and inhibition. Our ultimate goal: to develop a cell-based therapy to modulate aberrant brain activity in the treatment of these disorders. Our initial focus is on epilepsy. In 20-30% of these patients, seizures are unresponsive to drugs, requiring invasive surgical resection of brain regions with aberrant activity. The candidate cells we propose to develop can inhibit hyperactive neural circuits after implantation into the damaged brain. As such, these cells could provide an effective treatment not just for epilepsy, but also for a variety of other neurological conditions like Parkinson's, traumatic brain injury, and spasticity after spinal cord injury. We propose to bring a development candidate, a neuronal cell therapy, to the point of preclinical development. The neurons that normally inhibit brain circuits originate from a region of the developing brain called the medial ganglionic eminence (MGE). When MGE cells are grafted into the postnatal or adult brain, they disperse seamlessly and form inhibitory neurons that modulate local circuits. This property of MGE cells has not been shown for any other type of neural precursor. Our recent studies demonstrate that MGE cells grafted into an animal model of epilepsy can significantly decrease the number and severity of seizures. Other "proof-of-principle" studies suggest that these progenitor cells can be effective treatments in Parkinson's. In a separate effort, we are developing methods to differentiate large numbers of human MGE (H-MGE) cells from embryonic stem (ES) cells. To translate this therapy to humans, we need to determine how many MGE cells are required to increase inhibition after grafting and establish that this transplantation does not have unwanted side-effects. In addition, we need simple assays and reagents to test preparations of H-MGE cells to determine that they have the desired migratory properties and differentiate into nerve cells with the expected inhibitory properties. At present, these issues hinder development of this cell-based therapy in California and worldwide. We propose: (1) to perform "dose-response" experiments using different graft sizes of MGE cells and determine the minimal amount needed to increase inhibition; (2) to test whether MGE transplantation affects the survival of host neurons or has unexpected side-effects on the behavior of the grafted animals; (3) to develop simple in vitro assays (and identify reagents) to test H-MGE cells before transplantation. Our application takes advantage of an established multi-lab collaboration between basic scientists and clinicians. We also have the advice of neurosurgeons, epilepsy neurologists and a laboratory with expertise in animal behavior. If a safe cell-based therapy to replace lost inhibitory interneurons can be developed and validated, then clinical trials in patients destined for invasive neurosurgical resections could proceed.
This proposal is designed to accelerate progress toward development of a novel cell-based therapy with potentially broad benefit for the treatment of multiple neurological diseases. The potential to translate our basic science findings into a treatment that could benefit patients is our primary focus and our initial target disease is epilepsy. This work will provide benefits to the State of California in the following areas:
* California epilepsy patients and patients with other neurological diseases will benefit from improved therapies. The number of patients refractory to available medications is significant: a recent report from the Center for Disease Control and Prevention [www.cdc.gov/epilepsy/] estimates that 1 out of 100 adults have epilepsy and up to one-third of these patients are not receiving adequate treatment. In California, it is one of the most common disabling neurological conditions. In most states, including California, epileptic patients whose seizures aren't well-controlled cannot obtain a driver's license or work certain jobs -- truck driving, air traffic control, firefighting, law enforcement, and piloting. The annual cost estimates to treat epilepsy range from $12 to $16 billion in the U.S. Current therapies curb seizures through pharmacological management but are not designed to modify brain circuits that are damaged or dysfunctional. The goals of our research program is to develop a novel cell-based therapy with the potential to eliminate seizures and improve the quality of life for this patient population, as well as decrease the financial burden to the patients' families, private insurers, and state agencies. Since MGE cells can mediate inhibition in other neurological and psychiatric diseases, the neural based therapy we are proposing is likely to have a therapeutic and financial impact that is much broader.
* Technology transfer in California. Historically, California institutions have developed and implemented a steady flow of technology transfer. Based on these precedents and the translational potential of our research goals, both to provide bioassays and potentially useful markers to follow the differentiation of MGE cells, this program is likely to result in licensing of further technology to the corporate sector. This will have an impact on the overall competitiveness of our state's technology sector and the resulting potential for creation of new jobs.
* Stem cell scientists training and recruitment in California. As part of this proposal we will train a student, technicians, and associated postdocs in MGE progenitor derivation, transplantation, and cell-based therapy for brain repair. Moreover, the translational nature of the disease-oriented proposal will result in new technology which we expect to be transferable to industry partners for facilitate development into new clinical alternatives.
Advances in stem cell research and regenerative medicine have led to the potential use of stem cell therapies for neurodegenerative, developmental and acquired brain disease. The Alvarez-Buylla lab at UCSF is part of a collaboration that is pioneering the investigation of therapeutic interneuron replacement for the correction of neurological disorders arising from defects in neural excitation/inhibition. Our preliminary data suggests that grafting interneuron precursors into the postnatal rodent brain allows for up to a 35% increase in the number of cortical interneurons. Interneuron replacement has been used in animal models to modify plasticity, prevent spontaneous epileptic seizures, ameliorate hemiparkinsonian motor symptoms, and prevent PCP-induced cognitive deficits. Transplantation of interneuron precursors therefore holds therapeutic potential for treatment of human neurological diseases involving an imbalance in circuit inhibition/excitation.
The goal of the research in progress here is to ultimately prepare human interneuron precursors for clinical trials. Towards the therapeutic development of inhibitory neuron precursor transplantation for human neurological disorders, we have made significant progress in the differentiation of these cells from human ESCs and will complete optimization of this protocol. We will continue our investigation of rodent-derived interneuron transplantation to obtain relevant preclinical data for dose response, safety and efficacy in animal models. These dosing and safety data will then serve as the baseline for comparison with human interneuron precursors and inform design of preclinical studies of these cells in immunosuppressed mice. Together, these data will provide essential information for developing a plan for clinical trials using human interneuron precursors.
During this first year, we have made considerable headway in the optimization of the human interneuron precursor differentiation protocol, verified functional engraftment of these cells in mice, and begun to collect dose, safety and efficacy data for rodent-derived interneuron transplantation. Importantly, we have achieved the development of a protocol that robustly generates interneuron-like progenitor cells from human ES cells and demonstrated that these progenitors mature in vitro and in vivo into GABAergic inhibitory interneurons with functional potential. We have also compared the behavior of primary fetal cells to these human interneuron precursor-like cells both in vivo and in vitro. As we continue to optimize our ES cell differentiation protocol, these primary interneuron precursors will enable initial human cell dose response and behavior experiments and, along with rodent-derived cells, will provide important baseline measures.
In sum, this work will provide essential knowledge for the therapeutic development of inhibitory neuron transplantation. The experiments underway will yield insights that will be critical to the development of a clinical trial using human interneuron precursors.
During the reporting period, we have developed methods to enable the optimization of inhibitory nerve precursor cell, or MGE cell, derivation from human pluripotent stem cells (hPSCs). Optimization encompassed increasing MGE cell motility, enhancing MGE cell maturation into inhibitory nerve subtypes, and elimination of tumors post-transplantation into the rodent brain. Furthermore, we demonstrated that the injected hPSC-MGE cells functionally matured into inhibitory nerves with advanced physiological properties that integrated into the rodent brain. In addition, we determined an optimum dose of injected mouse MGE cells in rodent. Moreover, following injection of either the optimum dose or a 10-fold higher dose of mouse MGE cells, we found no detectable behavioral side effects from MGE cell transplantation.
In this reporting period, we continued to improve the acquisition of migratory medial ganglionic eminence (MGE)-type interneurons from human embryonic stem cells (hESC). We compared alternative procedures by testing MGE marker expression, and we developed additional tests to measure cell division and migration of MGE cell made from hESCs. We also extended our methods to clinical-grade hESC lines. With these optimized procedures, both research and clinical grade lines were transplanted into the rodent brain. In addition, we completed an evaluation of human fetal MGE transplants after-injection into the rodent brain. Finally, we report safety, survival, and neuronal differentiation of both hESC-MGE and human Fetal-MGE grafts at three months post-injection into the brain of the non-human primate rhesus macaque. A manuscript is in preparation concerning this work. Our work has continued to show the viability of using a cell therapy technique in the potential treatment of brain-related disease.
- Cell Stem Cell (2013) Functional Maturation of hPSC-Derived Forebrain Interneurons Requires an Extended Timeline and Mimics Human Neural Development. (PubMed: 23642366)
- Nat Neurosci (2013) GABA progenitors grafted into the adult epileptic brain control seizures and abnormal behavior. (PubMed: 23644485)
- Nature (2012) Intrinsically determined cell death of developing cortical interneurons. (PubMed: 23041929)