Differential co-expression of inhibitory receptors by CD8+ T cells depending on priming. In brief, epitope-specific T cells from immunized mice were highly purified and analyzed without additional stimulation. Gene expression patterns were defined using hierarchical clustering; CD8+ T cells from naïve mice were used as a reference control. The bottom half of the figure summarizes the results pertaining to expression of inhibitory receptors such as PD-1, as average fold change of gene expression relative to control. There was coordinated up-regulation of gene expression corresponding to membrane receptors with inhibitory activity (yellow shaded section: Lag3, CTLA-4 and PD-1) in CD8+ T cells primed by peptide without adjuvant, but not DNA vaccine (summary of results in ref. ).