The A2A adenosine receptor (A2AR) has been shown to be a critical and nonredundant negative regulator of immune cells in protecting normal tissues from inflammatory damage. We hypothesized that A2AR also protects cancerous tissues by inhibiting incoming antitumor T lymphocytes. Here autoimmunity ͉ cancer ͉ therapy ͉ hypoxia ͉ inflammation T he coexistence of tumors and antitumor immune cells is currently explained by the inhibition of immune cells in a poorly understood ''hostile'' tumor microenvironment (1-3). This unidentified immunosuppressive mechanism limits promising cancer therapies using antitumor T cells (4-14). We hypothesized that cancerous tissues are protected from antitumor T cells because of immunosuppressive signaling via T cell A2A adenosine receptor (A2AR) (15-17) activated by extracellular adenosine produced from hypoxic tumor (Fig. 1a). Indeed, hypoxic cancerous tissues may be protected by the same hypoxia3adenosine3A2AR pathway that was recently shown to be critical and nonredundant in preventing excessive damage of normal tissues by overactive immune cells in vivo (18). It is well established that some areas of solid tumors often have transient or chronic hypoxia (19,20), which is conducive to extracellular adenosine accumulation (21). Hypoxia has been implicated in mechanisms of tumor protection against ionizing radiation and some chemotherapeutic agents (19) and is associated with poor prognosis (20).T cells, including antitumor T cells, do predominantly express cAMP-elevating Gs protein-coupled high-affinity A2AR and͞or low-affinity A2B adenosine receptors (A2BR) (16,17,(22)(23)(24); the number of A2AR per T cell may determine the intensity of maximal T cell response to adenosine (25, 26). Whereas we focused on A2AR, others have discounted A2 receptors and suggested the A3 adenosine receptors as responsible for inhibition of antitumor killer T cells (27,28). Here we report that genetic deletion of A2AR accomplishes the complete rejection of immunogenic tumors by antitumor CD8 ϩ T cells in the majority (Ϸ60%) of mice, whereas the antagonists of A2 receptors facilitate CD8 ϩ T cell-mediated retardation of tumor growth. Results The Gradient of T Cell-Inhibiting Extracellular Adenosine in Tumors.It was important to confirm the presence of elevated extracellular adenosine levels in cancerous tissues using a reliable method (29). The HPLC analysis and the use of equilibrium dialysis probes demonstrated higher levels of extracellular adenosine (Fig. 1b), increased adenosine metabolism, and the concomitant increase in cAMP (29) in a solid tumor microenvironment (Fig. 7, which is published as supporting information on the PNAS web site). We also confirmed that antitumor CD8 ϩ T cells used in this study do express the cAMP-elevating functional A2AR and A2BR (Fig. 1c). To directly test whether A2AR inhibit antitumor T cells in vivo, we studied the effects of A2AR gene deletion or competitive antagonists on tumor growth in mice using different CD8 ϩ T celldependent cancer immunosurveillance and ad...

Antitumor T cells either avoid or are inhibited in hypoxic and extracellular adenosine-rich tumor microenvironments (TMEs) by A2A adenosine receptors. This may limit further advances in cancer immunotherapy. There is a need for readily available and safe treatments that weaken the hypoxia–A2-adenosinergic immunosuppression in the TME. Recently, we reported that respiratory hyperoxia decreases intratumoral hypoxia and concentrations of extracellular adenosine. We show that it also reverses the hypoxia-adenosinergic immunosuppression in the TME. This, in turn, stimulates (i) enhanced intratumoral infiltration and reduced inhibition of endogenously developed or adoptively transfered tumor-reactive CD8 T cells, (ii) increased proinflammatory cytokines and decreased immunosuppressive molecules, such as transforming growth factor–β (TGF-β), (iii) weakened immunosuppression by regulatory T cells, and (iv) improved lung tumor regression and long-term survival in mice. Respiratory hyperoxia also promoted the regression of spontaneous metastasis from orthotopically grown breast tumors. These effects are entirely T cell– and natural killer cell–dependent, thereby justifying the testing of supplemental oxygen as an immunological coadjuvant to combine with existing immunotherapies for cancer.

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Gender has an important influence on blood pressure, with premenopausal women having a lower arterial blood pressure than age-matched men. Compared with premenopausal women, postmenopausal women have higher blood pressures, suggesting that ovarian hormones may modulate blood pressure. However, whether sex hormones are responsible for the observed gender-associated differences in arterial blood pressure and whether ovarian hormones account for differences in blood pressure in premenopausal versus postmenopausal women remains unclear. In this review, we provide a discussion of the potential blood pressure regulating effects of female and male sex hormones, as well as the cellular, biochemical and molecular mechanisms by which sex hormones may modify the effects of hypertension on the cardiovascular system.

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