TESPA1 (Thymocyte-expressed positive selection-associated protein 1) is required for the development and maturation of T-cells, its function being essential for the late stages of thymocyte development. It plays a role in T-cell antigen receptor (TCR)-mediated activation of the ERK and NFAT signaling pathways, possibly by serving as a scaffolding protein that promotes the assembly of the LAT signalosome in thymocytes.