Inhibition of cytokine production and cytotoxic activity of human antimelanoma specific CD8+ and CD4+ T lymphocytes by adenosine-protein kinase A type I signaling.

The goal of this study was to investigate the effects of adenosine and its stable analogue 2-chloroadenosine (CADO) on the cytotoxic activity and cytokine production by human antimelanoma specific CD8+ and CD4+ T-helper type 1 (Th1) clones. The cytotoxic activity of CD8+ T cells was inhibited by adenosine and CADO. Using Lab MAP multiplex technology, we found that adenosine inhibits production of various cytokines and chemokines by CD8+ and CD4+ T cells. Studies with CGS21680, a specific agonist of adenosine A2A receptor (AdoRA2A), and ZM241385, an AdoRA2-selective antagonist, indicate that the inhibitory effects of adenosine are mediated via cyclic AMP (cAMP)-elevating AdoRA2A, leading to protein kinase A (PKA) activation. Using cAMP analogues with different affinities for the A and B sites of the regulatory subunits of PKAI and PKAII, we found that activation of PKAI, but not of PKAII, mimicked the inhibitory effects of adenosine on T-cell cytotoxic activity and cytokine production. Inhibitors of the PKA catalytic subunits (H89 and PKA inhibitor peptide 14-22) failed to abrogate the inhibitory effects of CADO. In contrast, Rp-8-Br-cAMPS that antagonizes binding of cAMP to the regulatory I subunit and PKA activation was efficient in blocking the inhibitory effect of adenosine on the functional activity of T cells. Our findings on the ability of adenosine to inhibit the effector function of antimelanoma specific T cells suggest that intratumor-produced adenosine could impair the function of tumor-infiltrating T lymphocytes. Thus, blocking the inhibitory activity of tumor-produced adenosine might represent a new strategy for improvement of cancer immunotherapy.