Indeed, use of a GFP-tolerized strain (e.g., Cx3cr1-GFP, BALB/c mice) completely eliminated the CD8+ T cell–driven immune response against GFP, allowed unabated primary tumor progression of GFP-expressing 4T1 mammary tumor cells, and permitted outgrowth of GFP+ metastasis within this immune-competent setting (4). The gene discussed is CD8A; the disease is neoplasm.