Regulatable genetic modifications of HESC for in vivo imaging and safety monitoring of implanted HESC: applications to neurodegeneration models
Human embryonic stem cells (HESC) can be differentiated into any cell of the body. This will allow HESC to be used to replace diseased or damaged cells. The brain is made up of mostly non-dividing cells; thus, upon brain cell death, there are no new cells that can take up the role of the diseased or damaged cells. HESC are thus of great importance for the future replacement of brain cells damaged in neurodegenerative disorders such as Parkinson’s Disease (PD), Alzheimer’s Disease (AD), Amyotrophic Lateral Sclerosis (ALS), or multiple sclerosis. When sufficient brain cells have been killed by the disease process and no functional capabilities can be sustained, disease symptoms ensue. If cells in the substantia nigra die, patients develop PD; if cells from the basal forebrain and cerebral cortex die, they will develop AD, and if motor neurons from the anterior horn die, they will develop ALS. Fortunately, HESC can be differentiated into dopaminergic neurons (like those of the substantia nigra), cholinergic neurons and cortical neurons (such as those dying in AD), and into motor neurons (affected by ALS). Implantation of neurons of the right type into the diseased region of the brain could potentially overcome the severe symptoms of these diseases.
There are two challenges when HESC are implanted into diseased brains. One is to be able to track the implanted cells; i.e. are they staying within the implanted region, or are they moving away? Secondly, will HESC remain as differentiated cells, or will they form a tumor or teratoma. To address these issues we will develop two viral vectors, one derived from HIV and called a lentivirus (LV), and one derived from adenovirus, called a high-capacity adenovirus (HC-Ad). Both vectors have been engineered to remove their toxic and pathogenic genes, and are safe for use in animals and humans. The system will work in the following manner: LV will express genes in both non-dividing and dividing cells, while HC-Ad will sustain expression in non-dividing cells, but will be lost from dividing cells. HESC will be differentiated before implantation; to be of therapeutic use they should remain differentiated, and thus, non dividing. If they do, we will detect this as imaging signals originating from both vectors. However, it will be crucial to monitor in humans whether suddenly these cells start growing into a stem cell tumor, also known as teratoma. Should this happen, we will detect an increasing signal from the LV, but will lose the signal from the HC-Ad. Importantly the engineered HESC will have a gene encoded within their genome which will allow us to kill them should they become cancerous. In summary, we propose to develop a novel tool to track the location of implanted HESC in the brain, and their growth patterns. The system will be engineered to allow imaging in experimental animals and humans, thus, being a valuable translational tool as HESC move from the bench to therapies.
The promise of harnessing human embryonic stem cells for the treatment of human disease is being stimulated in great measure by the California Initiative in Regenerative Medicine. The graying of California’s population is given by the fact that this is the most populous state in the Union, and thus, subjected to the progressive ageing of our population, as seen throughout the USA. In addition, due to its very favorable climate, California is increasingly attracting retirees to its midst. As a consequence it is highly likely that due to these demographic factors, California will experience a continued increase in the incidence of serious chronic neurodegenerative disorders.
Many of the diseases of old age sadly affect the structure and function of the brain. HESC’s promise is to develop cells that will replace cells affected by these chronic, progressive diseases. Although sometimes diseases like Parkinson’s, Alzheimer’s or Lou Gehrig disease can affect patients in their late thirties or early forties, most of the patients affected by these diseases are 60 years of age or older. California’s population is expected to increase by 172% by 2040, with the greatest growth being among those aged 85 and older. Their numbers are expected to grow by 200% by 2040. Thus, it is expected that by 2040 the ratio of the elderly to adults under age 65 will have increased by 80%! It is expected that by 2010 there will be close to 500,000 Californians with Alzheimer’s alone, and could rise to 1,000,000 by 2040. Added to other chronic neurodegenerative diseases with increased incidence in the aged, new therapies are urgently needed.
The proposed application will develop unique novel tools and technologies to track the location and fate of implanted therapeutic HESC in the brains of affected patients. In addition, the novel tools will have safety elements that will allow to monitor whether implanted HESC become tumoral, and if so, to eliminate them. In summary, work proposed in this application will provide a strong platform for the development of effective and safe HESC-based therapies for devastating chronic brain diseases. Further, the HESC and the novel viral vectors to be used in this proposal have already been generated by our team in the State of California, thus, taking advantage of the intellectual and technological know-how developed in our State.