Kinetically distinct processing pathways diversify the CD8 + T cell response to a single viral epitope.

The source proteins from which CD8 ⁺ T cell-activating peptides are derived remain enigmatic. Glycoproteins are particularly challenging in this regard owing to several potential trafficking routes within the cell. By engineering a glycoprotein-derived epitope to contain an N-linked glycosylation site, we determined that optimal CD8 ⁺ T cell expansion and function were induced by the peptides that are rapidly produced from the exceedingly minor fraction of protein mislocalized to the cytosol. In contrast, peptides derived from the much larger fraction that undergoes translocation and quality control are produced with delayed kinetics and induce suboptimal CD8 ⁺ T cell responses. This dual system of peptide generation enhances CD8 ⁺ T cell participation in diversifying both antigenicity and the kinetics of peptide display.