(A) The membrane from HEK293T cells engineered to express PD-1 is used to form nanovesicles, which are then loaded with 1-methyl-tryptophan (1-MT), an indoleamine 2,3-dioxygenase-1 inhibitor. (B) Therapeutic treatment of tumor-bearing mice with the genetically engineered nanovesicles carrying 1-MT (G7) suppresses tumor growth and improves survival compared to controls of saline (G1), wild-type nanovesicles (G2), free 1-MT (G3), empty engineered nanovesicles (G4), free 1-MT inhibitor with wild-type nanovesicles (G5), and free 1-MT with anti-PD-L1 (G6). (C) Treatment with the engineered nanovesicles carrying 1-MT generates a high intratumoral percentage of CD8+ T cells. Adapted with permission [60]. Copyright 2018, Wiley-VCH.