Our work is focused on the analysis of recent thymic emigrants (the youngest peripheral T cells) from mice carrying a transgene for green fluorescent protein driven by the RAG2 promoter. Our work has shown that T cells complete both functional and phenotypic maturation in the lymphoid periphery, a process driven by factors other than those that control T cell homeostasis and survival. Our work suggests the purpose of post-thymic T cell maturation is to expose young T cells to antigens expressed only outside the thymus, during a tolerance-prone transitional phase of development. Current work is centered on interrogating the environmental cues (such as the inflammatory milieu) that tune this tolerance process and to develop a model to test the involvement of recent thymic emigrants (including neonatal T cells) in tumor rejection.