This is a very interesting idea! But, is it known that macrophages are able to break down prions? My understanding of the problem is that part of it is that they're just quite hardy.
Disagree. Every single antibody alzheimer's drug that has targeted the amyloid plaques and none of them have succeeded.
You're just as likely to elicit an immune response to the prion plaques, stabilize them, and recruit inflammation to the point of deposit, making matters worse.