When mRNA (from a vaccine) enters a cell and the transcription process gets underway, the host cell effectively becomes an antigen factory. How does the antigen leave the cell so that it can trigger the intended immune response, and what is the fate of the host cell? As I understand it, one mRNA molecule can produce many antigen particles before it decays; does this continue until the host cell ruptures? After antigen production has shut down, does the host cell "get back to its normal life"?
I'm not a biologist, and it's difficult to find a straightforward explanation, but it sounds like the cells present the spike protein on their surface, and are then recognized as infected and killed by T-cells.
Some of the spike proteins form spikes that migrate to the surface of the cell and stick out their tips. The vaccinated cells also break up some of the proteins into fragments, which they present on their surface. These protruding spikes and spike protein fragments can then be recognized by the immune system
The antigen-presenting cells can also activate another type of immune cell called a killer T cell to seek out and destroy any coronavirus-infected cells that display the spike protein fragments on their surfaces.
In an article about N protein vaccines:
Tiny fragments of N protein are then displayed on the surface of infected cells. T cells recognise these fragments, identify cells as infected, then kill the cell and consequently any virus.
Presumably vaccinated cells present the spike protein on the surface the same way as infected cells, and are killed in the same way, but neither of these articles explicitly say so, and I can't find any that do.