Highlights d Longitudinal scRNA-seq of tumor-specific TCF-1 + CD8 + T cells in KP lung adenocarcinoma d Identified a proliferative Slamf6 + TCF-1 + T cell subset and a non-cycling SlamF6 À subset d The lymph node contains a recruitable reservoir of functional TCF-1 + CD8 + T cells d Flt3L+CD40 boosts cDC1, increases TCF-1 + CD8 + T cell frequencies, decreases tumor burden

Highlights d Single-cell profiling of CD4 T cells along tumor development in a mouse model d T reg diversity shifts to a Klrg1 + Areg + (KA) effector phenotype in advanced tumors d Il1rl1 (encoding ST2) + T regs have higher expression of KA effector T reg genes d T reg -specific ST2 loss enhances CD8 + T cell infiltration and decreases tumor burden

No abstract

Regulatory T cells (T regs ) can impair anti-tumor immune responses and are associated with poor prognosis in multiple cancer types. T regs in human tumors span diverse transcriptional states distinct from those of peripheral T regs , but their contribution to tumor development remains unknown. Here, we used single cell RNA-Seq to longitudinally profile conventional CD4 + T cells (T conv ) and T regs in a genetic mouse model of lung adenocarcinoma. Tissue-infiltrating and peripheral CD4 + T cells differed, highlighting divergent pathways of activation during tumorigenesis. Longitudinal shifts in T reg heterogeneity suggested increased terminal differentiation and stabilization of an effector phenotype over time. In particular, effector T regs had enhanced expression of the interleukin 33 receptor ST2. T reg -specific deletion of ST2 reduced effector T regs , increased infiltration of CD8 + T cells into tumors, and decreased tumor burden. Our study shows that ST2 plays a critical role in T reg -mediated immunosuppression in cancer, highlighting new potential paths for therapeutic intervention.