Magnetic Resonance Characteristics of CNS Changes Resulting from Targeted Human Embryonic Stem Cell Administration
Regenerative medicine through the use of human embryonic stem cells (hESC) represents an emerging therapeutic approach with great promise for treating a wide range of diseases. Perhaps one of the most exciting applications is toward the regeneration of central nervous system (CNS) tissue in the hope of reversing damage due to trauma or degenerative disease. The impact of such a therapy upon the practice of neurology and upon society in general would be enormous, since, currently, such CNS trauma and degenerative disease is often irreversible or partially reversible. Such possibilities have fueled tremendous excitement and optimism among patient groups, and, now, a popular vote in California has called for intensive research to bring these therapies to the bedside as soon as is safely possible. A pressing need, however, for the advancement of hESC therapy for CNS diseases is the ability to examine, in a rapid, efficient, and, eventually, noninvasive manner, the effects of hESCs upon the CNS. It is critical to develop such techniques 1) to track the effects of hESC administration to determine that the cells are, indeed, reaching and having an effect upon the target of interest and 2) to detect and characterize any dangerous effects that hESCs may have upon surrounding tissue, such as inflammation, scarring, or tumor formation. Recent developments in high field magnetic resonance (MR) imaging have shown an ability to detect subtle changes in CNS tissue that, previously, could only be detected using the microscope. These "high-definition" MR imaging techniques, also known as MR microscopy, may provide the tools needed to follow the effects of hESCs over time in the living organism, thus providing the safety and efficacy information needed to proceed with human studies. This proposal will examine central nervous system (CNS) effects of hESC administration in rats and mice with spinal cord injuries using MR microscopy. We will examine the tissue for signal changes corresponding to clinically relevant effects, including intended effects such as growth of connections between cells, but also for unintended and dangerous effects such as tissue rejection, scarring, and tumor formation. We will examine these new MR imaging techniques with the goal of providing a tool for use in human clinical trials. Therefore, in addition to imaging tissue that has been taken out of animals that have died, we will examine living animals undergoing hESC therapy for CNS injury. Our findings with MR microscopy will be directly compared to findings under the microscope to validate the technique. In addition, we will test whether or not these techniques can easily be adapted for use in clinical MR scanners already present at most hospitals. Therefore, our research aims to define the MR techniques that will be most useful to doctors and their patients undergoing hESC therapy. Federal funding of this project is not allowed, so we are applying to CIRM.
Statement of Benefit to California:
The proposed research aims to speed the availability of human embryonic stem cell (hESC) therapies to generations of Californians who will, unfortunately, experience the deeply troubling afflictions of central nervous system (CNS) trauma and degenerative illness, including paralysis due to spinal cord injury, stroke, multiple sclerosis, amyotrophic lateral sclerosis, Parkinson's disease and a host of other CNS afflictions not mentioned here. The researchers, if funded, will work toward providing a diagnostic tool that, first, can be used by other researchers to evaluate safety and efficacy of various hESC therapies under development, and, second, can be used by doctors to safely and effectively monitor patients undergoing clinical trials in hESC therapy. In addition to the above potential for relief of physical suffering, if successful, this research may lead to an invention that could generate significant revenue for the State of California under the revenue sharing requirements of the CIRM.
SYNOPSIS: This proposal seeks to evaluate the changes related to human embryonic stem cell (hESC) transplantation into the CNS using high resolution magnetic resonance imaging. The applicant will use high resolution imaging along with histologic correlates to detail the CNS responses to hESC transplantation. In Specific Aim 1, they will use a 7T magnet to define the baseline data on the spinal cords and brains of control and damaged rodents. In Specific Aim 2, they will quantitate the parameters defined in Specific Aim 1 in control and damaged CNS into which hESCs had been transplanted. The tissue from these animals will then be examined histologically to compare with the MR images. In Specific Aim 3, they will use a 3T MRI to evaluate the results of hESC transplant in live animals imaged longitudinally. SIGNIFICANCE AND INNOVATION: The proposal is designed to provide important information on the response of the CNS to stem cell transplantation. The techniques they describe to carry this out, though not novel, are appropriate. Thus, the proposal is reasonably innovative, but the significance of the work is difficult to ascertain since it seems like a fishing expedition with a hypothesis that axon growth, gliosis, cell damage, ischemia, tumorigenesis and inflammation will each have a characteristic MR signature that can be used to optimize in-vivo detection. STRENGTHS: The major strength of this proposal lies with the group of investigators and the facilities at UCSD. The questions to be asked are important, and MR microscopy can be very useful in ascertaining damage reversal from CNS trauma or degenerative disease. MRI at the 3T and 7T field strengths makes translation to bedside easier. WEAKNESSES: The overarching problem with the proposal is in the choice of transplanting undifferentiated hESCs. While the applicant acknowledges that tumors may form, reviewers question the relevance of this approach and the data it will generate given that it is extremely unlikely that undifferentiated hESCs will be transplanted into the human CNS. Moreover, it is not clear how viability imaging will be performed with MRI. In the specific aims section, Aim 1 states that MR microscopy will be used with diffusion tensor imaging (DTI) to quantitate T1, T2, T2* and ADC. This is incorrectly stated, as evident in the detailed experimental plan. DTI is not needed to quantify the aforementioned parameters, and in the case of several of these parameters, not able to do so. Specific Aim 2 appropriately applies DTI. DISCUSSION: This proposal aims to study hESCs after transplantation using MRI, where the PI will collect baseline data following sham injections. The investigators are clearly leaders in the field; however, the major weakness of this proposal is the choice to transplant undifferentiated stem cells. One reviewer recommends that the applicant differentiate hESC to hNSC prior to the transplantation and imaging studies. Another reviewer views the proposal as a "fishing expedition" and considers this to be a problem. With a 50 micron resolution, unless there is gross damage and repair it would be hard to imagine that spectroscopy would be useful, or that MRI will give characteristic patterns for the states in question. Reviewers expect that there will be lots of partial volume effects, and that this work probably would not translate into small animal or clinical work. Nevertheless, it would be interesting to see the MR images especially for the reversal of damage, and DTI will be good for looking at axonal regrowth. The fixed versus washed comparison could also be interesting.