CD8A and cancer: Our view on antigen processing was significantly extended by analysis of cancer patient-derived CD8+ T cells revealing that by proteasome-catalyzed peptide splicing (PCPS) proteasomes can also fuse excised peptide fragments in a reverse proteolysis reaction, thereby generating new immune reactive spliced epitopes (splicetopes) with an amino acid sequence that differs from that of the substrate protein (Hanada et al., 2004; Vigneron et al., 2004).