Mechanism of adenosine pathway in tumor microenvironment. Adenosine is
autonomously produced from ATP through ADP via CD39 and CD73 expressed mainly on
the surface of cancer cells, B cells or Tregs. The work of extracellular
adenosine is mainly divided into two directions. For immune cells, adenosine has
a potent immunosuppressive ability through A2AR and A2BR. For cancer cells,
adenosine stimulates tumor growth and metastasis through A2BR. Abbreviations:
CTL, cytotoxic lymphocyte; DC, dendritic cell; NK, natural killer; M2, M2
macrophage; MDSC, myeloid derived suppressor cell; Th1, T helper 1; Th17, T
helper 17; Treg, regulatory T cell.