Hypoxic tumor conditions, immunosuppressive immune cells such as regulatory T cells (Tregs), tumor-associated macrophages (TAMs), and myeloid-derived suppressor cells (MDSCs), immunosuppressive soluble factors, such as TGF-β, IL-4, and IDO, and expression of inhibitory receptors and ligands by tumor and/or stromal cells, such as PD1/PDL1, CTLA-4, LAG-3, could also impair CAR-T cell function during the CAR-T therapy in vivo. The gene discussed is IDO1; the disease is neoplasm.