Zhou, Maggie H.

Abstract Sensing of extracellular metabolites controls CD8+ T cell function. Their accumulation can occur through export by specialized molecules, such as the release channel Pannexin-1 (Panx1). Here, we report that T cell-specific Panx1 is needed for efficient CD8+ T cell responses to viral infection and cancer. Panx1 favors both the expansion of effector CD8+ T cells and the survival of memory CD8+ T cells. Our data suggests that, while memory CD8+ T cells require Panx1 for mitochondrial function, Panx1 promotes the glycolytic pathway in effector CD8+ T cells. Panx1 promotes memory CD8+ T cell survival together with the eATP sensor P2RX7. However, Panx1 induces effector CD8+ T cells independently of eATP. Rather, we found an unexpected link between Panx1, lactate export and the activation of effector CD8+ T cells. Therefore, Panx1 regulates effector and memory CD8+ T cells through export of distinct metabolites and by engaging different intracellular pathways.

Abstract The tumor microenvironment (TME) is characterized by high levels of extracellular ATP (eATP) and adenosine, which are sensed by purinergic receptors. CD8+ T cells express two important receptors that bind these ligands: the extracellular receptor P2RX7 binds eATP and is generally immunostimulatory, while the adenosine receptor A2AR promotes immunosuppression. However, the role of the TME itself in the T cell expression of purinergic receptors is not clear. We used in vitro co-cultures of tumor cells and CD8+ T cells, and specifically found that A2AR is significantly upregulated after activation, in a tumor cell number-correlated manner. These tumor-induced changes in A2AR expression are independent of TCR:MHC contact, which was evidenced by co-cultures using transwells to physically separate tumor cells and T cells, as well as distinct combination of transgenic T cells and tumors. In vivo murine solid tumor models confirmed that tumor-infiltrating CD8+ T cells upregulate A2AR. As previously found by our group, P2RX7 expression is limited to a small percentage of tumor-infiltrating CD8+ T cells. Interestingly, we identified that these few P2RX7-expressing tumor-infiltrating CD8+ T cells are enriched for high A2AR expression – suggesting that co-expression of these two receptors is favored in T cells exposed to tumors. Overall, our findings suggest that TME exposure – likely through TCR-independent factors – directly promote the expression of A2AR in CD8+ T cells. We are currently investigating the nature of the tumor-derived factor(s) promoting this upregulation, as well as the possible role of A2AR/P2RX7 co-expressing tumor-infiltrating CD8+ T cells as effector antitumor cells with longer intratumoral lifespan. Supported by grants from NIH (R00 AI139381, NIAID).

Abstract Expression of the purinergic receptor P2RX7 by CD8+ T cells promotes the generation of memory populations following acute infections. However, data suggest that P2RX7 may limit the efficacy of antitumor responses. Herein, we show that P2RX7 is beneficial for optimal melanoma control in a mouse CD8+ T-cell adoptive transfer model. Tumor-specific P2rx7–/– CD8+ T cells exhibited impaired mitochondrial maintenance and function but did not display signs of overt exhaustion early in the antitumor response. However, as the tumor burden increased, the relative frequency of P2RX7-deficient CD8+ T cells declined within the tumor; this correlated with reduced proliferation, increased apoptosis, and mitochondrial dysfunction. Extending these studies, we found that the transient in vitro stimulation of P2RX7 using the ATP analogue BzATP led to enhanced B16 melanoma control by CD8+ T cells. These findings are in keeping with the concept that extracellular ATP (eATP) sensing by P2RX7 on CD8+ T cells is required for their ability to efficiently eliminate tumors by promoting mitochondrial fitness and underscore the potential for P2RX7 stimulation as a novel therapeutic treatment to enhance tumor immunotherapy.