Whereas Treg cells from 4-week-old Gimap5sph/sph mice showed a slight but significant reduction in their ability to suppress wild-type CD8+ T cell proliferation in vitro, Treg cells from older (6-week-old) Gimap5sph/sph mice were incapable of suppressing wild-type CD8+ T cell proliferation, suggesting a critical loss of Treg function and survival to be responsible for colitis development in these mice (Figure 2). Here, CD8A is linked to colitis.