The total number of CD8+ T cells, virus-specific Tet-GP33+ CD8+ T cell expansion (Supplementary Fig. 3a), and intracellular cytokine (IFN-γ and TNF) production (Supplementary Fig. 3b) was limited in Ceacam1–/– mice 8 days after infection. The gene discussed is CEACAM1; the disease is infection.