What about the diet of the donor mother. What if she was a smoker or a drinker. I'm sure I've read about trace elements of these toxins in breastmilk. I don't smoke, didn't drink and I made sure I ate the best diet when I was BF so my babies would have the most benefit.
If I couldn't BF I'd consider using a milk bank but there is a lot to consider isn't there, and not just about AIDS.