Mno<i>_x</i> Nanoenzyme Armed CAR‐NK Cells Enhance Solid Tumor Immunotherapy by Alleviating the Immunosuppressive Microenvironment

Adoptively transferred cells usually suffer from exhaustion, limited expansion, and poor infiltration, partially attributing to the complicated immunosuppressive microenvironment of solid tumors. Therefore, it is necessary to explore more effective strategies to improve the poor tumor microenvironment (TME) to efficaciously deliver and support extrinsic effector cells in vivo. Herein, an intelligent biodegradable hollow manganese dioxide nanoparticle (MnO_X) that possesses peroxidase activity to catalyze excess H₂O₂ in the TME to produce oxygen and relieve the hypoxia of solid tumors is developed. MnO_X nanoenzymes modified with CD56 antibody could specifically bind CAR-NK (chimeric antigen receptor modified natural killer) cells. It is demonstrated that CAR-NK cells incorporated with MnO_X nanoenzymes effectively infiltrate into tumor tissues with an improved TME, which results in superior antitumor activity in solid tumor-bearing mice. The antibody connection between MnO_X nanoenzymes and CAR-NK endows the lowest efficient dosage of MnO_X. This study features a smart synergistic immunotherapy approach for solid tumors using MnO_X nanoenzyme-armed CAR-NK cells, which would provide a valuable tool for immunocyte therapy in solid tumors.