IDO1 and cancer: B7-H3 is expressed in a series of cancers, and higher expression is associated with worse prognosis.227–236 Moreover, B7-H3 is co-expressed with other immunosuppressive molecules such as PD-L1, B7-H4, and IDO1 on cancer cells.237 B7-H3 is also upregulated on APCs in the TME, suppressing T cell immunity.238 Anti-B7-H3 mAb induced CD8+ T and/or NK cell dependent anti-tumor immunity.227,239,240 However, due to the yet elusive immunobiology of B7-H3, the therapeutic approach using it as a TAA to develop CAR-T cells, ADCs, or bsAbs is more common.