In order to protect us from pathogen reexposure, memory lymphocytes must undergo homeostatic self-renewal and remain poised to respond to subsequent infection. In the case of CD8+ T cells, several antagonistic pairs of transcription factors appear to regulate the initial decision to become a terminally differentiated effector cell or a self- renewing memory cell. However, it remains unclear how these transcription factors are themselves coordinately regulated, and further which genetic circuits are responsible for subsequent memory cell self-renewal. Given that memory lymphocytes exhibit many of the functional attributes typically associated with stem cells, we hypothesized that memory lymphocytes have reactivated a portion of the hematopoietic stem cell genetic program. In support of this idea, we published a common transcriptional signature shared between memory B cells, memory CD8+ T cells and hematopoietic stem cells. We further identified a transcription factor, Pou6f1, that is selectively upregulated in memory B and CD8+ T cells relative to shorter-lived cells. Pou6f1 is a member of the Pou-domain family of transcription factors and is a paralog of the embryonic stem cell self-renewal regulator Pou5f1 (aka Oct4). We believe Pou6f1 functions in memory CD8+ T cells in a manner similar to Oct4 in embryonic stem cells. The central hypothesis of this proposal is that Pou6f1 directs memory CD8+ T cell self-renewal by establishing and maintaining a self-reinforcing genetic circuit that coordinates the expression of multiple transcription factors and signaling pathways. In order to test this hypothesis in vivo, we have generated mice expressing two different floxed alleles of Pou6f1 that will allow us to test Pou6f1's functional relevance and identify Pou6f1's transcriptional targets in memory CD8+ T cells. By elucidating the core genetic circuitry responsible for memory CD8+ T cell generation, function and maintenance, this proposal will provide key insights into the mechanisms controlling adaptive immune memory. PUBLIC HEALTH RELEVANCE: Memory lymphocytes are responsible for long-lived immunity, driving immune responses that can be either life-saving (as in the case of vaccines) or life-threatening (as in the case of autoimmune diseases). Despite the importance of memory cells, there are no memory-specific therapies currently available. In the fullness of time, we anticipate that identification of the genetic circuitry of CD8+ T cell memory, its targets, and the upstream signaling network that drives it will provide potential therapeutic candidates that might be used to aid in the design of more efficacious therapeutic cancer vaccines.