CD28 and infection: To evaluate the function of the memory T cells from Cd28−/− or Ox40−/− CD8+ T cells expressing c-Myc or CA-IKKβ, at day 35 post-infection of VV-OVA, splenocytes were stimulated with OVA peptide for intracellular IFN-γ staining, gating on Thy1.2+ cells.