HMOX1 and cervical cancer: In a co-culture of an HO-1 positive cervical cancer cell (CCC) line and NK cells, pretreatment with various HO-1 inhibitors, tin II protoporphyrin IX (SnPPIX) and ZnPPIX, restores the expression of NKG2D, NKp30, and NKp46, markers of NK activation, and increases the production of IFN-ɣ and TNF-α, enhancing NK killing activity towards cancer cells [139].