CD274 and neoplasm: After intravenous injection, PMI nanogels exhibited self‐degradation in TME due to the ROS generated by iron‐mediated catalytic reactions, and subsequently reverted the immunosuppressive TME to the anti‐tumor state by following aspects: 1) promoting DCs maturation, 2) repolarizing M2‐like TAMs, and 3) downregulating PD‐L1 expression.