Abstract
Precisely how macrophages regulate response to immunotherapy remains unclear. In this issue of Cancer Cell, Chow et al. demonstrate a tumor-promoting role of TIM-4(+) cavity macrophages which affects the response of metastatic malignancies to immunotherapy. Specifically, TIM-4(+) macrophages engage with phosphatidylserine-expressing cytotoxic T lymphocytes, inhibiting their activity even during PD-1 blockade.