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Lung cancer tumors recruit macrophages and granulocytes, which then secrete serine proteases like elastase and proteinase 3. These enzymes are then internalized by the tumor cells, which causes a cascade of events. The proteases both contain a peptide sequence, PR1, that was presented on the lung cancer cell surface HLA-A2 and recognized by antitumor cytotoxic T cells (CTLs). These proteases also induced production of a unique set of endogenous peptides by the tumor cells. CTLs specific for these novel antigens were enriched in lung cancer patients. Read more in the research article by Peters and colleagues on page 319, in this issue of Cancer Immunology Research. The confocal micrograph portrays a corona of PR1 peptide–HLA-A2 (yellow) on the surface of lung H2023 cancer cells and nuclei stained blue with DAPI. Micrograph from the laboratory of Dr. J.J. Molldrem. Artwork by Lewis Long.