Hello everyone, please help.

[JoeSilver]

Hello everyone who reads this, sorry to intrude but unfortunately all I want is to know the name of a book I remember very little about. It was read to me in 8th grade (4 years ago) by my language arts teacher, here it goes:


From what I can remember, it was about a boy as the main character who has a sister that he finds out is dying of some sort of disease. I believe it is post apocalyptic (from what I imagined and I believe it looked that way on the cover) or it may have been science-fiction/futuristic. Anyways so he swears to his sister that he will find a cure and he ventures off out of the place he lived in, to find out that the world is a very harsh place to go exploring. Along the way looking for a cure or someone who can help he has some good run ins - some bad run ins with people/things in this seemingly wasteland type/ broken-down city. So eventually he meets some ppl and travels with them on this journey and notices a beautiful, very clean being that seems as if she's glowing. Someone he was travelling with calls it a "Pure" or something along those lines from (the books name).

I think it was called something like Eutopia, or Eden. But this is where i'm having my problem, I can not remember the name of the place where the Pures (not sure if that's what they were called) lived therefore I cannot remember the name of the book. But it was a place of great interest, I pictured large fields of plantlife trees and gardens. Where everything was like a paradise, these beings lived there and did not let any of the outside population in. So anyways if I remember, I think the boy takes his sister to this place with the help of the beautiful female being he enountered