Is Reliable In Vivo Detection of Stem Cell Viability Possible in a Large Animal Model of Myocardial Injury?

In vivo cellular and molecular imaging of the stem cells has been developed to characterize the biological processes at the most fundamental level in an intact, living organism. With the emergence of cell-based therapy in a failing heart, the capability to evaluate engraftment and survival of the transplanted stem cells in vivo represents a critical measure of therapeutic efficacy. The stem cells at the very least must survive to restore the injured myocardium.1,2 Cell viability signal holds physiological relevance because it may correlate with the resultant myocardial restoration. There are 2 primary considerations for in vivo imaging of stem cell viability in the heart: (1) amplification of molecular and cellular signals and (2) high spatial and temporal resolution imaging of the myocardium. It is widely acknowledged that there is no single imaging modality that will fulfill all needs of in vivo stem cell imaging. However, an imaging modality that optimizes the technical objectives may extract meaningful information on cellular and molecular events of the transplanted cells. The predominant imaging modalities to assess stem cell survival in vivo in preclinical models consist of radionuclide imaging, optical imaging, and MRI. These modalities are commonly used in small animal models. Direct transfer of in vivo cellular and molecular imaging techniques from small to large animal models, however, has not been straightforward.Article see p 430The report by Templin et al3 in this issue of Circulation addresses the critical issue of in vivo imaging of stem cell viability in a porcine myocardial injury model. The study evaluated sodium iodide symporter (NIS) transgene to follow in vivo survival of human induced pluripotent stem cells (hiPSCs) and their derivatives. A stable transgenic hiPSC line expressing a fluorescent reporter and NIS (NISpos-hiPSCs) was used. Longitudinal dual isotope single-photon emission computed …