Induced pluripotent stem cell (iPSC) vs Embryonic stem cell (ESC)
 Induced pluripotent stem cells (iPSCs)
Induced pluripotent stem cells use a number of techniques to revert a differentiated cells back into a cells that appear to have similarities to undifferentiated cells, like ESCs. These cells can then be directed to differentiate into the desired cell types. This step is also limited by the technique involved.
iPSCs have almost no ethical issues in their use, as they involve generating an ESC-like cell from a person's somatic cells (like fat cells) and do not require the destruction of an embryo.
iPSCs may have issues in their ability to differentiate, and their undifferentiated state can be viewed as "incomplete" according to their epigenetic landscape.
 Embryonic stem cells (ESCs)
ESCs require the destruction of an embryo (though they have attempted to extract ESCs without killing the embryo on mice, no one has tried it on an actual human embryo) and subsequently the harvesting of the ESCs.
ESCs have ethical issues because they involve the destruction of an embryo.
ESCs are truly pluripotent stem cells, and can differentiate into all kinds of cells.
 Challenges for iPSCs in the context of ESCs
Advantages: iPSCs allow having the advantages of reprogramming mature (somatic) cells into undifferentiated (ESC-like) state, skipping the cloning techniques of somatic nuclear transfer. (1) This eliminates the difficulties of cloning, having high efficiency; (2) no eggs are required; (3) no embryos are involved.
Challenges: (1) iPSCs are not like true ESCs, as they contain “old memories” due to epigenetic profiling/modification of the chromosome; (2) c-myc (one of the factors used to de-differentiate mature cells) is an oncogene, and up-regulation of this gene is associated with types of cancers (the genes are linked to constitutive promoters, keeping them on all the time) (3) iPSCs have foreign genetic material (4) the foreign genetic material is introduced through viral infection and thus random insertion into the genome, disrupting the genome integrity.