The safety of induced pluripotent stem cells (iPSCs) haws been debated in several studies and publications. Original studies of the genetic differences between the cellular sources of iPSCs and the iPSCs derived from them tended to show a whole gaggle of new mutations that seemed to not appear in the original cells. Therefore, several commentators warned about the “dark side of pluripotency.”. However, other studies that utilized higher-resolution techniques showers that many of these mutations that occurred in iPSCs did exist in the original cells before their reprogramming, but that these mutations occurred at low frequencies, but became amplified during the culturing of reprogrammed cells.
One feature that has received less attention in these discussions of the safety of iPSC derivation is that the method by which iPSCs are made has distinct consequences for the stem cells that are made. Typically, methods that utilize gene vectors that do not integrate into the genomes of the host cells are inherently safer than those vectors that do integrate. PiggyBac transposon vectors integrate, but self-excise soon after their integration, and, therefore, do not leave a trace or their previous integration. Minicircles also do not integrate and tend to produce safer iPSCs. For this reason, this present paper is of interest to us.
Franklin West and his colleagues at the University of Georgia have made chicken iPSCs using minicircles to reprogram adult cells. West was interested in using iPSCs to make recombinant chickens, since chickens are a rather primary food source and major component of economic development in several countries. Making transgenic or recombinant chickens by means of stem cell technology makes it possible to make animals with improved meat and egg production or disease resistance.
To this end, West and his group made chicken (c) iPSCs from skin fibroblast cells by means of a nonviral minicircle reprogramming method. This resulted in ciPSCs that showed excellent stem cell appearance and expressed key stem cell marker genes (alkaline phosphatase, POU5F1, SOX2, NANOG, and SSEA-1). These cells also showed very rapid growth in culture and expressed high levels of the enzyme telomerase, which is an enzyme that is vital for the maintenance of chromosomes.
When West and his research group transplanted late-passage ciPSCs into stage X chicken embryos, the cIPSCs successfully integrated into the growing embryo and contributed to tissues derived from all three primary germ layers (ectoderm, mesoderm, and endoderm). These ciPSCs also contributed to the gonads, which means that the ciPSCs could make gametes that could contribute to the production of a new generation of chicken.
These ciPSCs provide an exciting new tool to create transgenic chickens and has broad and exciting implications for agricultural and transgenic animal fields at large. However, it also demonstrates that iPSCs can be safely produced and used for agricultural purposes. This means that if non-integration-based or non-viral-based techniques are used to make iPSCs it should be possible to make them safely for therapeutic purposes also.