The study investigates the role of programmed cell death protein 1 (PD-1) expression on tumor-associated macrophages (TAMs) in tumor immunity. PD-1 is an immune checkpoint receptor that, when upregulated on activated T cells, induces immune tolerance. The authors found that both mouse and human TAMs express PD-1, with expression increasing over time in mouse models and with disease progression in primary human cancers. PD-1 expression on TAMs negatively correlates with their phagocytic ability against tumor cells. In vivo studies showed that blocking the PD-1/PD-L1 pathway increased TAM phagocytosis, reduced tumor growth, and improved survival in mouse models of cancer. The results suggest that PD-1/PD-L1 therapies may also affect TAM function, providing new insights into the mechanisms of anti-tumor immunity and potential treatment combinations.The study investigates the role of programmed cell death protein 1 (PD-1) expression on tumor-associated macrophages (TAMs) in tumor immunity. PD-1 is an immune checkpoint receptor that, when upregulated on activated T cells, induces immune tolerance. The authors found that both mouse and human TAMs express PD-1, with expression increasing over time in mouse models and with disease progression in primary human cancers. PD-1 expression on TAMs negatively correlates with their phagocytic ability against tumor cells. In vivo studies showed that blocking the PD-1/PD-L1 pathway increased TAM phagocytosis, reduced tumor growth, and improved survival in mouse models of cancer. The results suggest that PD-1/PD-L1 therapies may also affect TAM function, providing new insights into the mechanisms of anti-tumor immunity and potential treatment combinations.