I'm adding a spoiler warning to the title of this thread, so every post doesn't need to be invisible.
Jenova cells didn't bring Vincent back to life. He was only shot once, and we don't know where exactly, or whether or not it was a fatal wound or not. Furthermore, I doubt that he had any Jenova injected into him, because he was not drawn toward the Northern Cave during Reunion. If Cloud & co. had not disturbed his rest, he probably never would have awoken.
