Scheme 1.

Illustration of the preparation of HA/ZIF-8@Gem/D-1-MT NPs and the mechanisms of the synergistic OS chemo-immunotherapy. 2-MI, 2-Methylimidazole; D-1-MT, D-1-Methyltryptophan; Gem, Gemcitabine; IDO, indoleamine-2,3-dioxygenase; Trp, tryptophan; Kyn, kynurenine; MDSC, myeloid-derived suppressor cell; CTLs, cytotoxic T lymphocyte; DCs, dendritic cells