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Induced stem cells from healthy adults

Problem

Stem cells are cells that have the potential to develop into many different cell types, meaning that they are almost universally useful in the internal physiological healing process. Stem cells differentiate into the specialized cells that they replace, including muscle cells, red blood cells, and neurons. It is possible for them to differentiate into cells of all three germ layers, a condition referred to as “pluripotency.” However, stem cell transplants in patients are often rejected by the immune system or induce cancerous growths. Further, there are ethical issues involved in harvesting human embryonic stem cells.
Shinya Yamanaka shared in the Nobel Prize award for converting mature epithelial cells harvested from adult mice into stem cells, referred to as induced Stem Cells (iSC’s). Yamanaka began by isolating 10 candidate factors that could potentially induce pluripotency in somatic cells. A pluripotent state is indicated by resistance to the antibiotic G418 in the cells. Yamanaka examined the formation of induced stem cell colonies after placing the cells in an embryonic environment and removing an individual factor from each colony. Results are shown below.
Figure 1: The effect of removing individual factors on the number of G418 resistant cell colonies produced.
Further, iSC’s were transplanted into the respective healthy adult mice from which the cells were harvested. This grafting procedure resulted in tumors composed of various tissues from the mesoderm, ectoderm, and endoderm. See Figure 2 for details.
Figure 2: Staining of different tissue from the mice. Anti-G418 antibodies were stained brown, and normal cells were counter-stained blue.
Which of the following is evidence that iSC’s are as effective as regular stem cells?
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