AUTHOR=Vaupel Peter , Multhoff Gabriele TITLE=Commentary: A Metabolic Immune Checkpoint: Adenosine in Tumor Microenvironment JOURNAL=Frontiers in Immunology VOLUME=7 YEAR=2016 URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2016.00332 DOI=10.3389/fimmu.2016.00332 ISSN=1664-3224