Abstract During specific immune responses, naive T cells give rise to terminally differentiated effector T cells and pluripotent, self-renewing central memory T cells. We recently provided evidence that, after approximately 3 cell divisions, TCF1, a key transcription factor of memory CD8+ T cells, is unequally expressed by sibling T cells undergoing cytokinesis. We now show that repression of TCF1 by one sibling is cell cycle-dependent and subsequently irreversible. Using pharmacological inhibitors, we found that cells which fail to progress through cell cycle are incapable of silencing TCF1. Using a transcriptional reporter of TCF1, we found that cells that extinguish TCF1 expression do not revert to TCF1-expressing cells. Although inhibition of PI3K/mTOR signaling blocks initiation of TCF1 repression, the same blockade fails to alleviate established silencing of TCF1. T cell progeny that maintain TCF1 expression undergo self-renewal and appear to remain pluripotent, while progeny that lose TCF1 expression appear destined to become functional, but short-lived, effector cells. TCF1-expressing cells generated in initial cell divisions, prior to irreversible TCF1 loss, appear to become quiescent, memory-like cells, whereas those cells that retain TCF1 expression when their sibling cells undergo irreversible TCF1 loss have more effector-like characteristics. The unidirectional quality of TCF1 silencing is compatible with a model wherein central memory cells represent cellular progeny that have yet to repress TCF1, rather than descendants of effector cells that lost TCF1-expression. Asymmetric, intra-divisional differentiation may explain the regenerative quality of lymphocyte clones during immunity.