Plays a critical role in induction and maintenance of immune tolerance to self.; As a ligand for the inhibitory receptor PDCD1/PD-1, modulates the activation threshold of T-cells and limits T-cell effector response.; Through a yet unknown activating receptor, may costimulate T-cell subsets that predominantly produce interleukin-10 (IL10); The PDCD1-mediated inhibitory pathway is exploited by tumors to attenuate anti-tumor immunity and escape destruction by the immune system, thereby facilitating tumor survival.; The interaction with PDCD1/PD-1 inhibits cytotoxic T lymphocytes (CTLs) effector function.; The blockage of the PDCD1-mediated pathway results in the reversal of the exhausted T-cell phenotype and the normalization of the anti-tumor response, providing a rationale for cancer immunotherapy.

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