CD27 sustains survival of CTLs in virus-infected nonlymphoid tissue in mice by inducing autocrine IL-2 production

Immunity to infections relies on clonal expansion of CD8(+) T cells, their maintenance as effector CTLs, and their selection into a memory population. These processes rely on delivery of survival signals to activated CD8(+) T cells. We here reveal the mechanism by which costimulatory CD27-CD70 interactions sustain survival of CD8(+) effector T cells in infected tissue. By unbiased genome-wide gene expression analysis, we identified the Il2 gene as the most prominent CD27 target gene in murine CD8(+) T cells. In vitro, CD27 directed IL-2 expression and promoted clonal expansion of primed CD8+ T cells exclusively by IL-2-dependent survival signaling. In mice intranasally infected with influenza virus, Cd27(-/-) CD8(+) effector T cells displayed reduced IL-2 production, accompanied by impaired accumulation in lymphoid organs and in the lungs, which constitute the tissue effector site. Reconstitution of Cd27(-/-) CD8(+) T cells with the IL2 gene restored their accumulation to wild-type levels in the lungs, but it did not rescue their accumulation in lymphoid organs. Competition experiments showed that the IL-2 produced under the control of CD27 supported effector CD8(+) T cell survival in the lungs in an autocrine manner. We conclude that CD27 signaling directs the IL-2 production that is reportedly essential to sustain survival of virus-specific CTLs in nonlymphoid tissue.