To investigate whether restored PGE2 production and signaling by tumor cells will reverse their resistance to TNF-α–induced killing, we knocked in (KI) the human PTGES gene (hPTGES) into the mouse Ptges-KO D6 clone, denoting these cells as mPtges-KO/hPTGES-KI tumor cells. The gene discussed is TNF; the disease is neoplasm.