title: Cancer exosomes express CD39 and CD73, which suppress T cells through adenosine production.
abstract: Extracellular adenosine is elevated in cancer tissue, and it negatively regulates local immune responses. Adenosine production from extracellular ATP has attracted attention as a mechanism of regulatory T cell-mediated immune regulation. In this study, we examined whether small vesicles secreted by cancer cells, called exosomes, contribute to extracellular adenosine production and hence modulate immune effector cells indirectly. We found exosomes from diverse cancer cell types exhibit potent ATP- and 5'AMP-phosphohydrolytic activity, partly attributed to exosomally expressed CD39 and CD73, respectively. Comparable levels of activity were seen with exosomes from pleural effusions of mesothelioma patients. In such fluids, exosomes accounted for 20% of the total ATP-hydrolytic activity. Exosomes can perform both hydrolytic steps sequentially to form adenosine from ATP. This exosome-generated adenosine can trigger a cAMP response in adenosine A(2A) receptor-positive but not A(2A) receptor-negative cells. Similarly, significantly elevated cAMP was also triggered in Jurkat cells by adding exosomes with ATP but not by adding exosomes or ATP alone. A proportion of healthy donor T cells constitutively express CD39 and/or CD73. Activation of T cells by CD3/CD28 cross-linking could be inhibited by exogenously added 5'AMP in a CD73-dependent manner. However, 5'AMP converted to adenosine by exosomes inhibits T cell activation independently of T cell CD73 expression. This T cell inhibition was mediated through the adenosine A(2A) receptor. In summary, the data highlight exosome enzymic activity in the production of extracellular adenosine, and this may play a contributory role in negative modulation of T cells in the tumor environment.
authors.affiliation: Department of Pharmacology, Radiology and Oncology, School of Medicine, Cardiff University, Velindre Cancer Centre, Whitchurch, Cardiff CF14 2TL, United Kingdom. aled.clayton@wales.nhs.uk
authors.forename: Aled
authors.initials: A
authors.lastname: Clayton
authors.forename: Saly
authors.initials: S
authors.lastname: Al-Taei
authors.forename: Jason
authors.initials: J
authors.lastname: Webber
authors.forename: Malcolm D
authors.initials: MD
authors.lastname: Mason
authors.forename: Zsuzsanna
authors.initials: Z
authors.lastname: Tabi
mesh_terms: D015720:5'-Nucleotidase / Q000096:biosynthesis* / Q000502:physiology; D000241:Adenosine / Q000096:biosynthesis* / Q000502:physiology; D000249:Adenosine Monophosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D015703:Antigens, CD / Q000096:biosynthesis* / Q000502:physiology; D001081:Apyrase / Q000096:biosynthesis* / Q000502:physiology; D018938:Caco-2 Cells; D045744:Cell Line, Tumor; D015536:Down-Regulation / Q000276:immunology*; D055354:Exosomes / Q000276:immunology* / Q000378:metabolism* / Q000473:pathology; D058851:GPI-Linked Proteins / Q000096:biosynthesis / Q000502:physiology; D006801:Humans; D006868:Hydrolysis; D019169:Jurkat Cells; D008654:Mesothelioma / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D010766:Phosphorylation / Q000276:immunology; D010997:Pleural Neoplasms / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D050378:T-Lymphocytes, Regulatory / Q000276:immunology* / Q000378:metabolism* / Q000473:pathology
chemical_list: D015703:Antigens, CD; D058851:GPI-Linked Proteins; D000249:Adenosine Monophosphate; D000255:Adenosine Triphosphate; D015720:5'-Nucleotidase; C548241:NT5E protein, human; D001081:Apyrase; C067869:CD39 antigen; D000241:Adenosine