The binding of Programmed Cell Death Protein 1 (PD-1), a receptor expressed on activated T-cells, to its ligands, PD-L1 and PD-L2, negatively regulates immune positive responses. The PD-1 ligands are found on most cancers, and PD-1:PD-L1/2 interaction inhibits T cell activity and allows cancer cells to escape immune surveillance.
Cell cycle control system acts like a timer, or a clock, which sets a fixed amount of time for the cell to spend in each phase of the cell cycle. The four major phases of the mammalian cell cycle are G1, S, G2 and M phases of the cycle. Cell-cycle arrest means the cell enters quiescent stage, where the cell becomes a permanent cell and is no longer active in the process of cell division.
