In a mouse model of anti-PD1 resistance, TILs were found to overexpress IDO1, and IDO inhibition was effective in reducing both tumour growth and lung metastasis.53 Certainly in melanoma, adding an IDO pathway inhibitor to a checkpoint inhibitor seems to be a promising strategy.54 Other strategies for further investigation include (1) optimisation of antigen presentation using antibody conjugates such as sacitizimab govitecan (IMMU-132)55,56 and STING or TLR agonists,57 and (2) use of agents which activate effector T cells such as OX40 agonists58 and 4-1BB agonists.59 The gene discussed is IDO1; the disease is melanoma.