Because transfusions don't have the desired outcome per tests so far. They are not capturing whatever the desired mechanism might be, or factors relevant to the

Because transfusions don't have the desired outcome per tests so far. They are not capturing whatever the desired mechanism might be, or factors relevant to the effects are short-lived, or some such. I'm not expecting that trial to do any better based on mouse results to date: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4215333/ http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4215333/