Spikes are produced inside a cell. These will be presented on MHC class I to dendritic cells and cytotoxic t cells. Any spikes that if spilled, for example, by the action of the T cells will be picked up by the local dendritic cells and macrophages. These cells will present this antigen on MHC class II complexes to naive T cells. This presentation in turn will start the process of B cell and cytotoxic t cell activation. Any antigen still left over might bind to the ACE2 receptors. But, that amount will be very low, almost negligible. An example to understand why this is not a concern is the use of ACE Inhibitor drugs. One has to continue to take these drugs because the cells continue to make new enzyme, and the previous enzyme complexes are removed. Finally, actual virus continues to produce not only the spikes, but the whole viruses in a large number. It then causes a disease not just because of the spike protein but because of the viral antigens produced in cells stimulating the immune system, and by the destruction of the cells which it infects. A vaccine based spike protein cannot offer more antigens that are part of the whole virus, neither can these replicate and infect other cells.