CD274 and cancer: When an immune response is no longer needed, PD-1/PD-L1 binding suppresses the immune system, serving as an immune checkpoint and maintaining immune homeostasis.40 In cancer, these cells, as well as cancer cells themselves, are known to increase expression of PD-1/PD-L1 inhibiting T-cell receptor (TCR) dependent activation of T-cells, thus helping to escape the anti-tumourigenic immune response.41