MPPE1 and neoplasm: COX-2/PGE2 can also inhibit the secretion of CCL5 and XCL1 by natural killer (NK) cells and the expression of CCR5 and XCR1 in conventional type 1 dendritic cells (cDC1), which can impair the function of NK cells and the accumulation of cDC1 in the TME, which are responsible for tumor immunity (24).