Human stem and progenitor cells have emerged as potentially useful substrates for cardiovascular repair through neovascularization and myocardial regeneration. However, efficacy is limited by impedance to stem cell retention, homing and differentiation in hostile microenvironments, as occur in infarcted myocardium. The objective of the current study was to regulate gene function for tailored therapy in post infarct myocardium. Here we show that hypoxic and inflammatory stimuli of the infarct microenvironment regulate a proportional response in gene expression in human endothelial progenitor (EPC) and mesenchymal stem cells (MSC). Highly efficient lentiviral vectors incorporating hypoxia (HRE) and nuclear factor kappa B (NFkB) responsive elements are used to drive transgenes for survival, autologous stem cell homing and cardiogenic differentiation. Utilizing an internal cytomegalovirus promoter deleted lentiviral transfer vector, an HRE-NFkB bicistronic promoter-reporter vector was constructed with a modified internal ribosome entry sequence between green fluorescent protein and luciferase or therapeutic genes. Either hypoxia or inflammation resulted in a seven to ten-fold response of transgene expression assessed by luciferase activity in EPC (hypoxia, 7608±954; inflammation 11492±1384, P<0.01 and P<0.001 vs control 1049±139 respectively, N=6), while combined hypoxic-inflammatory stimuli resulted in a sixty-fold increase of transgene expression (hypoxic-inflammation, 62364±6609, P<0.001 vs control 1049±139, N=6). These results were recapitulated in MSC and with a series of therapeutic genes as determined by transcript, protein expression and activity. Our results demonstrate that regulated vectors provide a proportional response to hostile post-infarct myocardium. Translating cardiovascular regenerative medicine using stem cells requires managing stem cell survival, function and differentiation. Utilizing site-specific pathophysiological cues to auto-regulate reparative and regenerative gene expression, this study is a starting point for sophisticated platforms for patient tailored cell-based cardiogenic therapy.
Armed therapeutic viruses: Strategies and challenges to arming oncolytic viruses with therapeutic genes
