CD39+ CD4+ conventional T cells with exhaustion traits and cytotoxic potential infiltrate tumors and expand upon CTLA4 blockade

CD4+ conventional T (Tconv) lymphocytes display an important role in tumor immunity; however, their contribution to tumor elimination remains poorly understood. Here we describe a subset of tumor-infiltrating Tconv cells characterized by the expression of CD39. In mouse cancer models CD39+ Tconv cells accumulate with tumor growth but are absent in lymphoid organs. Compared to tumor CD39- Tconv cells, CD39+ cells exhibit a cytotoxic and exhausted signature at the transcriptomic level, confirmed by high protein expression of co-inhibitory receptors and transcription factors related to exhaustion. Additionally, CD39+ Tconv cells show an increased production of INFg, Granzyme B, Perforin and CD107a, but a reduced production of TNF upon in vitro stimulation. In vivo, CTLA-4 blockage induces the expansion of CD39+ Tconv cells in the tumor, while maintaining their features of cytotoxicity and exhaustion. In breast cancer patients, CD39+ Tconv cells are found in tumors, and at lower frequency in the adjacent non-tumoral mammary tissue. CD39+ Tconv cells are also present in metastatic but not detected in non-metastatic lymph nodes and blood. Human tumor CD39+ Tconv cells constitute a heterogeneous cell population with features of exhaustion, impaired TNF production, and high expression of co-inhibitory receptors and CD107a. High gene expression of CD4 and ENTPD1 (CD39) in human tumor tissues correlates with higher overall survival rate in breast cancer patients. Our results identify CD39 as a biomarker of CD4+ T cells with characteristics of both exhaustion and cytotoxic potential and put forward CD39+ Tconv cells as pivotal players of the immune response against tumors. Overall design: B16F10-OVA tumors from 9 FOXP3-GFP tumor-bearing mice were processed for RNA sequencing. Tumors were shaped into 3 pools and purified CD4+ T cells were obtained by positive selection (CD39neg, CD39pos and Tregs)