Maybe this is a naive question, but your immune system works by identifying foreign proteins and killing those cells. Is there no way for your immune system to target cells contaminated with prions?
The fundamental issue with prions is that they are *not* foreign. Prions are legitimate proteins made by your own body but folded wrong. A misfolded protein acts like a catalyst to cause more misfolding. Prions are *not* alive, they have no ability to reproduce other than through misfolding existing proteins. It's basically a form of crystallization.
Antibodies are shape-sensitive though, so there could be antibodies targeting the mis-folded protein. In fact, maybe many people exposed to them where able to develop an immune response and we just don't know about it because these people never had any symptoms (think about the survivor bias, but in reverse, or from the point of view of the prion).
