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. 2021 May 10;10(5):1152. doi: 10.3390/cells10051152

Figure 1.

Figure 1

Programmed Death-1 Signaling Axis The PD-1/PD-L1/PD-L2 checkpoint pathway renders tumor cells resistant to T-cell immune attack. Ligation of T-cell PD-1 by PD-L1 or PD-L2 which are present on tumor cells or antigen presenting cell. PD-1 ligation dephosphorylates multiple members of the TCR signaling pathway attenuating TCR and CD28 signaling and promoting T-cell anergy and functional exhaustion. PD-1, programmed death-1; PD-L1, PD ligand-1; PD-L2, PD ligand-2; MHC, major histocompatibility complex; TCR, T-cell receptor.