Immune checkpoint blockade involves the targeted antagonism of immunosuppressive interactions between antigen-presenting cells and/or tumor cells and effector T cells. Blockade of B7-H1, also known as programmed death-ligand 1 (PD-L1), prevents the ligation of inhibitory PD-L1 molecules to programmed cell death receptor 1 (PD-1) on T cells, engendering a potentiated response of tumor-specific T cells against tumor cells. In a Cancer Research article, Hirano and colleagues showed that T-cell-mediated tumor immunity becomes impaired when tumor cells interact with T cells via PD-L1 in the mouse tumor microenvironment. They showed that targeting PD-L1 or PD-1 with mAbs increased tumor cell lysis by T cells and suggested that tumor PD-L1 forms a "shield" preventing tumor cell lysis. Alongside other original mouse and human studies, this work generated scientific rationales for a new generation of cancer treatment focused on targeting the inhibitory PD-1/PD-L1 signaling pathway in the tumor microenvironment.See related article by Hirano and colleagues, Cancer Res 2005;65: 1089-96.
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