Studies about indoleamine 2,3‐dioxygenase (IDO) have been widely reported, and it is an immunosuppressive molecule overexpressed by tumor and dendritic cells (IDO+DCs) to limit the proliferation and function of effector T cells.[94] Therefore, with a small molecule inhibitor of IDO, 1‐methyl‐tryptophan (1‐MT) encapsulated into the PD‐1 Bio‐MVs could simultaneously block the PD‐1/PD‐L1 axis and overcome the inhibitory effects of IDO on effector T cells within the tumor microenvironment. The gene discussed is IDO2; the disease is neoplasm.