CD274 and osteosarcoma: To assess potential systemic adverse effects resulting from PD-L1–mediated excessive activation of CPR/CART, we treated mice with established 143B osteosarcoma xenografts using two intraperitoneal injections of 10 × 106 CARζ/CPR41BB (n = 7) or CAR41BBζ (n = 5) cells on day +5 and day +13 after tumor inoculation (Supplementary Fig. S10D).