The cGAS-STING pathway is a crucial signaling pathway of the innate immune system. The STING signaling mechanisms in myeloid cells are well studied. However, STING expression in healthy and diseased tissue and STING signaling activities in other cell types are much less understood. In the previous funding period, we generated the StingS365A mouse, which allowed us to uncover many IFN-independent activities of STING in T cells and their physiological significance in diseases. In this renewal application, we created a Sting reporter mouse and discovered interesting dynamics of STING expression in T cells from development to maturity. We have also created additional transgenic mice that allow us to modulate STING expression and signaling in specific tissues or cell types. Our main hypothesis is that dynamic regulation of STING expression and signaling is essential for maintaining T cell development, homeostasis, and functionality in response to cancer. Aim 1 will define the regulatory mechanism of STING expression in T cells. Aim 2 will determine how STING signaling regulates T cell development and function. Aim 3 will define the role of STING in thymopoiesis and T cell immunity in cancer. Through these studies, we hope to uncover a new facet of STING biology that uniquely connects innate and adaptive immunity. The potential influence of STING signaling on thymopoiesis also has immediate clinical implications for the successful development of STING agonists as cancer immunotherapy.