The immune checkpoint molecule TIM-3 is expressed in activated human T cells, NK cells, and monocytes.100 High TIM-3 expression in several syngeneic models has been associated with acquired resistance toward PD-1 blockade.109–111 For example, Koyama et al. correlated acquired resistance after anti-PD-1 therapy with TIM-3 upregulation in a lung adenocarcinoma murine model.110 The same TIM-3 upregulation was observed in lung cancer patients who had PD following PD-1 blockade. Here, PDCD1 is linked to lung cancer.