PDCD1 and neoplasm: The ex vivo tumor tissues exhibited significantly decreased sizes and weight only with aPD-1@PMPN treatment (Fig. S5), which is consistent with the trend of tumor growth inhibition in Fig. 5D. Immune cell analysis revealed that aPD-1@PMPNs reduced the level of accessible PD-1 in CD8+ T cells, suggesting their effective engagement and occupation of PD-1 receptors (Fig. 6B) [35].