CD28 and neoplasm: Mesoporous silica microparticles were embedded within this matrix, loaded with the STING agonist c‐di‐GMP, and functionalized to display the immunostimulatory signals, including anti‐CD3, anti‐CD28, and anti‐CD137 antibodies for T cells.[107] When implanted into a surgical cavity, the scaffold enabled substantial T cell expansion and migration to the tumor resection site and tumor‐draining lymph nodes, effectively eliminating residual tumor cells and reducing the risk of relapse.