Spoiler alert - this will give away some of the ending.
This book has (at least) two fatal flaws:
1. Why do the donors die after four donations? The author does not even attempt to provide a rationale for this to occur. A little more depth as to what is being collected would give this book some credibility.
2. Why do the characters never figure out what is going on, or try to change things? Even with full access to 'society' they all seem to lack any intellectual curiosity about their existence or fate.
I found this book failed to answer some fundamental questions that might have made its premise plausible. Without considering more about the science of what is going on, or allowing the characters to question their own existence, they became more like sheep and less like people.