Finally, the presence of cognate antigen within the VacV-infected skin microenvironment significantly enhanced the subsequent formation of CD69+CD103+ TRM CD8+ T cells (Fig. 1p–r), demonstrating that local antigen is required for IFNγ expression by effector CD8+ T cells during infection, as well as the subsequent formation of TRM CD8+ T cells following viral clearance. This evidence concerns the gene IFNG and infection.