CD59 and cancer: Complement‐mediated cytotoxicity is an effective mechanism for killing cancer cells, in part through induction of MAC activity,[3, 4] and over‐expression of CD59 in cancer cells contributes to immunotherapy resistance (Figure 1b).[5, 6] CD59 is also co‐opted by opportunistic bacterial effectors, which use the receptor to target and lyse human cells (Figure 1c).[7] Therefore, developing therapeutics that can regulate CD59 activity has the potential to impact both immunotherapy resistance mechanisms and bacterial pathogenesis (Figure 1b,d).