My understanding is that normal viral infections cause proteins to be expressed by cells in the same way — in fact, uninfected cells also continually display a "status report" of protein fragments. Your immune system monitors this to detect cells that have gone haywire, whether by mutation or infection.

https://en.wikipedia.org/wiki/MHC_class_I#Effect_of_viruses

I don't honestly understand how the immune system decides which protein fragments are okay to develop a response to, but the point is that that is already part of the normal immune response pathway that learns new antigens every day; after the protein fragment shows up on the cell surface, the rest of the process is similar to the response to an attenuated-virus vaccine or a natural infection.