Research in the last 5ish years has shown that "any" cell can be induced to change into a stem cell by changing its environment and adding specific growth factors.
Edit:
I spent an hour looking for the research I was referring to. I found the papers and dissertation of the author who's talk I went to where the topic was discussed. Unfortunately, with a quick read I didn't find where the author talked about it, leading me to believe it was a discussion had at the end of their defense.
Although I couldn't find the research, [email protected] found what I was talking about (induced pluripotent stem cells)
Edit 2: As [email protected] points out the techniques are not currently at the level where induced stem cells can replace native stem cells.