Not to be wearing a tin-foil hat or anything here, but:
Knowing the direction mankind often tends to take, especially with the paranoia of global (or at least local) overpopulation and government control (as well as their backers) over what gets released and etc. under such pretense, the ability and practicality of their use (especially when mastered and mass-produced) relatively will become that much more difficult to release, as well as a reason not to get released as a civilian-level treatment and be mocked as snake oil from all angles from the upper class (while at the same time, they partake in said "snake oil" themselves under a different name) if it does somehow get past the shitstorm of red tape in it's path (call me pessimistic, but the odds of success is extremely low). Even if it does get mastered and can also easily be mass-produced, and cuts through all the red tape, we have other problems with it's release once it's out.
Naturally, and probably most predictably, we can always foresee that most-all minorities and those of "other interests" will naturally be denied the treatment, even if it were legally provided (under strict monitoring of government regulations). And just in case they get hostile about it, chances would be likely a grand majority of those that are given the treatment as form of good will will most likely get a placebo, or something much worse, but subtle, as to not draw attention from good people that can make a difference.
Why are the elite and government(s) so easy to paint in a negative light? It's like a paint-by-numbers thing. Anyway, that's my conspiracy-level thought about this. Even if it does come out, it likely won't be for everyone if it does it; and even if they do get it somehow, they won't be getting the real "it".
EDIT:
As for the source of the stem cells; that's a big part of my motivation as to why I would never accept this as a vaccine for any ailment. If millions had to unwillingly sacrifice their lives in order for this to come into light (yes, I'm a bit of a pro-lifer here; and yes, I see this as similar to the Philosopher's Stone in FMA), then I cannot in good conscience take this. Just as well, I'd rather die like a normal human being, and wait for my immune system to crap-out.