DNA doesn't vary by cell, and the method of introduction is chemical, I imagine this creates a chained effect, otherwise how would cells pass on activated chains through the body when your DNA naturally changes.
The DNA of a body does not naturally change (in any organized way). Cells pass on changed DNA only to their progeny. Only genetic changes to gametes will be passed on genetically to children.
However, the regulation of DNA can be transmitted. One can turn genes on and off throughout the body by exposing the cells to particular signals such as hormones. But those don't change the DNA, they just change the interpretation and usage of the DNA that's already present.
Radiation. Mutagenic chemicals. Transcription errors. Even viruses.
Not anything natural to the human body e.g. it does not change without external influences.
