... Why are you bringing aliens into this?
We have never even seen non-Earth-based microbial life, let alone intelligent life. And even if it existed, it's almost certainly nowhere near us and would have little impact on us beyond the philosophical. I highly doubt we'd even be able to communicate with them, let alone figure out what technologies they know and don't know.
Anyway, brain is special because it's unique among the animals (don't give me the whole "Ravens and octopods and dolphins, oh my!" They're smart, but not technology-using, so we're still unique) and, more importantly (because any immortality technology would HAVE to be, as a moral and ethical concern, a deeply personal choice therefore it is the person who matters in this question and not the species), the brain is the center of our personality. It is all that matters to our personality, it's not like you suddenly turn into another person if you lose a limb or something. Whereas our DNA mutates all the time and has little-to-no affect on us personally, outside of cancer, and a) that's not exactly a good thing, and b) only brain-tumors are likely to affect the personality and identity.
DNA just... doesn't matter, outside of reproduction, for the singular human. The brain does.
Edit: What does that mean? "Not human", okay, we can agree on that, it's not literally human, but what does that -mean-? It's sentient, sapient, has feelings. Does it not being human mean that it doesn't deserve "human" rights, even if it shares all the things that makes humans human? Or does it not being human not enter into that, in which case why even bother with the whole "Is it human or isn't it?" outside the academic?