IDO Believe in Immunotherapy

Indoleamine 2,3-dioxygenase 1 is central to immune downregulation. A recent phase I/II study tested the indoleamine 2,3-dioxygenase 1 inhibitor linrodostat with nivolumab ± ipilimumab in patients with advanced solid tumors. Although efficacy was not augmented, correlative analyses identified tryptophan 2,3 dioxygenase as a resistance mechanism; dual targeting may be necessary to realize improved response to PD-1 inhibition. See related article by Luke et al., p. 2134.