Embryonic stem cells

ESCs are pluripotent stem cells isolated from blastomeres that can differentiate into all types of cells, making them highly valuable in regenerative medicine [30, 31]. Since 1998, when hESCs were first cultured and differentiated, many studies of drug-based therapies using ESCs have examined their use for treatment of spinal cord injury, macular degeneration, type 1 diabetes, heart failure, and other conditions [32]. ESCs also have potential for treatment of lung diseases, and studies have demonstrated that hESCs and mouse ESCs can differentiate into type II alveolar epithelial cells (ATIICs) using controlled culture conditions [33, 34]. Previous studies have used established transfection and culture procedures in a laboratory setting to develop genetically screened and highly purified hESC-ATIICs that have characteristics typical of ATIICs, including formation of lamellipodia, expression of surfactant protein, and the ability to proliferate and differentiate into type I alveolar epithelial cells (ATICs) [35]. Previous research demonstrated that ATIICs derived from hESCs can be engrafted into the lungs of mice with acute lung injury, and that this treatment inhibited or reversed fibrotic changes induced by bleomycin [36]. Although hESC-ATIICs have potential as a cellular source for treatments of distal lung diseases, there are many concerns regarding the safety of cell transplantation from differentiated ESCs. Methods such as the formation of embryoid bodies or coculture of these cells with lung mesenchyme have only produced small numbers of ATIICs [33, 34, 37, 38]. Another important concern is that the presence of pluripotent cells within a mixed population of ESC-derived cells may lead to formation of a teratoma, making this approach unsuitable for transplantation into the lungs. There are also serious ethical concerns, because the acquisition of hESCs necessitates the destruction of embryos.

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