Current studies into programmed cell death receptor-1 (PD-1)- or programmed cell death ligand-1 (PD-L1)-mediated immunity have indicated that PD-L1 expression in MPE tumour cells is significantly correlated with PD-L1 expression in macrophages, suggesting interaction between tumour cells and MPE macrophages [5]. The gene discussed is PDCD1; the disease is neoplasm.