CD8A and influenza: The role of GITR stimulation for the expansion of CD8+ cells is further and definitely demonstrated by Snell et al. who use GITR−/− OT-I transgenic mice in an in vivo model of severe influenza infection in which purified CD8+ GITR−/− OT-I cells are transferred into recipient mice successively infected with influenza A/HK-X31-OVA [59].