Enhanced STAT5a activation rewires exhausted CD8 T cells during chronic stimulation to acquire a hybrid durable effector like state

Rewiring exhausted CD8 T cells (T EX ) towards more functional states is a major goal of cancer immunotherapy but has proven challenging due to the epigenetic stability of T EX . Indeed, T EX are epigenetically programmed by the transcription factor Tox. However, epigenetic changes continue to occur as T EX transition from progenitor (T EX prog ), to intermediate (T EX int ) and terminal (T EX term ) subsets, suggesting potential developmental flexibility in mature T EX subsets. By examining the transition of T EX prog into T EX int cells, we discovered a reciprocally antagonistic circuit between Stat5a and Tox in T EX cells. Stat5-activity controlled T EX int development, antagonized Tox, and instigated partial effector biology. Stat5 was also essential for T EX reinvigoration by PD-1 blockade. Indeed, temporal induction of Stat5-activity in T EX using an orthogonal IL-2/IL2Rβ-pair fostered T EX int cell accumulation and synergized with PD-L1 blockade. Constitutive Stat5a activity (STAT5CA) antagonized Tox-dependent T EX epigenetic programming to generate a durable hybrid effector/NK-like population with enhanced tumor control. Finally, enforcing Stat5-signals in established T EX prog partially rewired the T EX epigenetic landscape towards the effector/memory lineage. Together, these data highlight therapeutic opportunities of manipulating Stat5 to rewire T EX towards a durably protective hybrid program.