Cutting edge: The transcription factor eomesodermin enables CD8+ T cells to compete for the memory cell niche.

CD8(+) T cells responding to intracellular infection give rise to cellular progeny that become terminally differentiated effector cells and self-renewing memory cells. T-bet and eomesodermin (Eomes) are key transcription factors of cytotoxic lymphocyte lineages. We show in this study that CD8(+) T cells lacking Eomes compete poorly in contributing to the pool of Ag-specific central memory cells. Eomes-deficient CD8(+) T cells undergo primary clonal expansion but are defective in long-term survival, populating the bone marrow niche and re-expanding postrechallenge. The phenotype of Eomes-deficient CD8(+) T cells supports the hypothesis that T-bet and Eomes can act redundantly to induce effector functions, but can also act to reciprocally promote terminal differentiation versus self-renewal of Ag-specific memory cells.