Durvalumab

Because cancer cells express antigens that are recognized and taken up by antigen-presenting cells (APCs), the immune responses prime and activate cytotoxic T cells, and allow them to travel to the site of the tumour to destroy cancer cells. However, tumours often evade T cell-mediated immune responses to enhance their survival. Inflammatory mediators, such as IFN-gamma, induce the expression of programmed cell death ligand-1 (PD-L1), which is a type 1 transmembrane protein expressed on tumour cells and tumour-associated immune cells in the tumour microenvironment. PD-L1 acts as an immune checkpoint to regulate immune responses. PD-L1 is a ligand to PD-1, which is a cell surface receptor expressed on activated T cells in peripheral tissues following antigen exposure. Both PD-L1 and PD-1 are co-inhibitory molecules involved in blocking T cell-mediated immune responses. PD-L1 also interacts with CD-80, which is a receptor constitutively expressed by T cells and is upregulated early after T cell activation.

The expression of PD-L1 is an adaptive immune response by tumour cells, resulting in the over-expression of the molecule in some cancers. PD-L1 interacts with PD-1 and CD80, which leads to blocked cytotoxic T cell activation, T cell proliferation, and cytokine production. By binding to PD-L1 and preventing its association with PD-1 and CD80, durvalumab activates the immune responses mediated by cytotoxic T cells that attack tumour cells. Durvalumab displays selective and high affinity toward PD-L1 but not PD-L2, which is a regulatory ligand expressed in tumour cells to a lesser extent and involved in regulating inflammation and differentiation of T cells.