CD8A and neoplasm: PD-1 is a surface transmembrane glycoprotein that belongs to the CD28 receptor family and is expressed on activated T cells (CD4 and CD8+ T cells), while programmed death ligand 1 (PD-L1) belongs to the B7 superfamily and is expressed constitutively at low levels ion antigen-presenting cells (APCs), with increased expression on tumor cells [20,21].