To improve the efficacy of targeted immunotherapy and reduce off-target adverse effects, drug or cell delivery systems precisely delivering therapeutic agents to the tumor microenvironment have been widely applied. The advantages of using drug delivery systems are obvious and manifold: delivery of multiple agents simultaneously, enabling synergistic effects, 159 enhancing pharmacokinetics by improving the stability and half-life, highly specific targeting achieved via functionalization with targeting ligands that recognize specific biomarkers on cancer cells or immune cells. Frequently used delivery systems include nanoparticles, cell-based and exosome-based delivery systems, biomaterial-based implants, and injectable hydrogels and scaffolds. With attractive tunable size and surface properties, nanocarriers can increase the delivered drug's overall therapeutic index that are either encapsulated or conjugated to the surfaces of nanoparticles. Materials such as lipids, metals, polymers, and others have been applied (Fig. ). Clinical research has demonstrated that a significant proportion of cancer patients exhibit insensitivity to immunotherapy, mostly because of the immunomodulatory exchanges between tumor cells and the immunosuppressive tumor microenvironment, managing the immune tolerance of tumors. Significant efforts have been concentrated on introducing nano-sized carriers to cancer medicine. Targeted remodeling of the immunosuppressive tumor microenvironment using appropriately engineered nanoparticles provides a favorable strategy for enhancing the effectiveness of tumor immunotherapy and help to overcome immune tolerance of tumors. 163