Programmed Death-Ligand 1 (PD-L1) is an immune checkpoint molecule expressed on antigen-presenting cells and various cancer cells, critically involved in modulating T-cell-mediated immune responses. Its interaction with programmed cell death protein 1 (PD-1) on activated T cells delivers inhibitory signals that suppress cytotoxic activity and promote immune tolerance-a mechanism exploited by malignancies to evade immune surveillance. Elevated PD-L1 expression has been documented across multiple tumor types including non-small cell lung carcinoma, melanoma, and gastrointestinal cancers, correlating with advanced disease progression and poorer prognostic outcomes.
CD47 molecule, also referred to IAP (Integrin associated protein), OA3 or MER6, is a 35 kDa transmembrane glycoprotein of 323 amino acids and belongs to the immunoglobulin (Ig) superfamily. In humans, this ubiquitously expressed cell surface protein is encoded by the gene mapping at the chromosome 3q13.12. CD47 plays a pivotal role in self-recognition and regulates the innate immunity by acting as an inhibitory signal for phagocytosis through macrophages, neutrophils, and dendritic cells. One critical mechanism under CD47-mediated immune evasion is that it can interact with SIRPα (Signal regulatory protein-alpha) expressed on myeloid cells, ultimately delivering an anti-phagocytic signal. Various solid and hematologic carcinomas exploit CD47 expression so as to escape immunological eradication. And its overexpression is clinically associated with poor prognoses.