Receptor desensitization and blockade of the suppressive effects of prostaglandin E-2 and adenosine on the cytotoxic activity of human melanoma-infiltrating T lymphocytes

Previous studies document that PGE(2) and adenosine suppress production of inflammatory cytokines. The present study demonstrates for the first time that (1) PGE(2) and 2-chloroadenosine (CADO; a stable analog of adenosine) directly inhibit the cytolytic function of human tumor-infiltrating lymphocytes (TILs); (2) the combination PGE(2) and CADO have additive suppressive effects; and (3) the cooperative immunosuppressive actions of PGE(2) and CADO are mediated via EP2 receptors (EP2Rs) and A(2A) receptors (A(2A)Rs) and are due to amplification of cAMP production, activation of protein kinase A (PKA) and T cell receptor (TCR) inhibitor Csk leading to inhibition of Lck, ZAP-70 and Akt phosphorylation. (4) During ex vivo expansion, TILs undergo three stages of differentiation converting from TILs with high cytotoxic activity and relative resistance to combined EP2R/A(2A)R suppression (stage I) to TILs retaining high cytotoxicity and gaining sensitivity to combined suppression (stage II) and then to TILS that are less cytotoxic and very sensitive to combined suppression (stage III). (5) Finally, we find that pretreatment of TILs with non-inhibitory concentrations of EP2R agonists (such as PGE(2) or butaprost) or A(2A)R agonists (such as CADO or CGS21680) increases their cytotoxic activity and induces resistance to EP2R and A(2A)R inhibitory signaling (cross-resistance) due to homologous and heterologous desensitization and internalization of EP2Rs and A(2A)Rs, thus preventing their inhibitory signaling. We conclude that inducing resistance of TILs to the suppressive effects of PGE(2) and adenosine in the tumor microenvironment could represent a novel strategy for improving the efficacy of adoptive immunotherapy.