The prodrug nanoparticles facilitated the recruitment and activation of DCs and CD8+ T cells, decreased myeloid‐derived suppressor cells (MDSCs), and achieved more potent antitumor immunity compared to either treatment alone in xenograft tumor models of C57BL/6 mice.[91b] These results highlight the synergistic potential of co‐delivering STING agonists and IDO inhibitors, providing a rational basis for designing combination regimens that coordinate STING activation with IDO blockade to maximize therapeutic efficacy and safety. The gene discussed is IDO1; the disease is neoplasm.