Cross-priming of CD8⁺ T-cell responses to RBC surface antigens. In this highly schematized model, a tranfused RBC expressing a polymorphic variant of a cell-surface protein is taken up by a recipient antigen presenting cell. Peptides derived from RBC proteins are loaded onto class I MHC molecules, then shuttled to the cell surface, where they can stimulate responses in recipient cognate CD8⁺ T cells.