Strauss et al generated a mouse model in which PD-1 was selectively deleted in myeloid cells.15 The authors employed these mice to dissect the relative contribution of myeloid versus T cell PD-1 signaling in colon cancer.11 Interestingly, myeloid-specific PD-1 deletion was as effective at limiting tumor growth as global PD-1 deletion, and more effective than selective ablation of PD-1 in T cells.15 One caveat to these studies is that genetic approaches to interrupt PD-1/PDL-1 signaling may not accurately model therapeutic antagonist therapies. The gene discussed is PDCD1; the disease is colonic neoplasm.