Magnetic resonance imaging (MRI) has emerged as one of the predominant modalities to evaluate the effects of stem cells in restoring the injured heart. However, MRI does not enable assessment of a fundamental issue in cell therapy, survival of the transplanted cells. The transplanted human embryonic cells (hESCs) must at the very least survive to restore the injured heart. In order to address this issue, this research has conducted the fundamental work to develop a reporter gene as outlined in the proposal and developed a reliable system to evaluate the survival of the transplanted hESCs.
First, using a commercially available genetic construct, the reporter gene was designed to generate specific cell surface tags as a signal of cell survival. Molecular assays demonstrated proper characteristics of the reporter gene and the construct has been inserted into human embryonic kidney cells to demonstrate proof of concept. MRI signal was generated from these cells and this result has been validated by flow cytometry confirming the expression of cell surface tags by the reporter gene. Second, the metabolic effects of the contrast agent, iron-oxide, used to magnetically activate the antibodies have been evaluated. The results demonstrated that the iron-oxide has no toxic effects to the cell metabolism. Finally, preliminary MRI of the iron-oxide labeled hESC injected directly into the mouse heart was obtained.
Based on above results, the molecular signal was further refined to generate optical signal of cell survival as an additional validation tool. Robust molecular signal of hESC survival was generated following transplantation of the reporter gene transduced hESC into the mouse myocardium. During the no cost extenstion period, correlation between hESC survival and functional restoration of the injured heart will be assessed. Using MRI, cell survival and functional restoration of the heart will be imaged non-invasively in order to obtain longitudinal information regarding survival of transplanted hESC and restoration of heart function.