CD274 and breast cancer: We tested whether mtp53 reactivating compound APR-246 can regulate the expression of inhibitory immune checkpoints, involving PD-L1 (CD274), B7-H3 (CD276), PVR (CD155), PVRL2 (CD112), and HVEM. We found that the expression of at least three different checkpoint molecules was suppressed upon APR-246 treatment in breast cancer cell lines SKBR-3, MDAMB-231 and MDAMB-468 (Fig. 5a), while at least one checkpoint molecule was repressed in four other cancer cell lines (Fig. S4a).