Glycogen synthase kinase-3 is essential for Treg development and function

T_regs are critical regulators of the immune response, but the cellular and metabolic signaling pathways that control their development and homeostasis remain to be determined. We found that glycogen synthase kinase-3 (GSK3), a kinase that integrates signals from Akt and mTOR, was essential for T_reg development, restraining fatal autoimmunity. Loss of Gsk3 led to metabolic rewiring in T_regs, with disordered nucleotide metabolism and activation of OxPhos. Acute deletion of Gsk3 did not affect T_reg frequency or numbers but induced an effector gene expression program and led to the formation of populations with pro-inflammatory signatures. The acute loss of Gsk3 in T_regs profoundly enhanced anti-tumoral immune responses and suppressed tumor growth. Overall, we demonstrate that GSK3 critically regulates T_reg homeostasis and anti-tumor immune responses.