Sustained macrophage reprogramming is required for CD8 T cell-dependent long-term tumor resolution

Tumor-associated macrophages (TAMs) exhibit a dual role in tumor progression and antitumor immunity. However, understanding the functional states and molecular mechanisms of antitumor TAMs remains a challenge. Here, we show that combined TLR3 and CD40 agonists (myeloid cell treatment, MCT) reprogram TAMs to adopt a protective antitumor phenotype in an orthotopic mouse breast cancer model, leading to tumor regression. Single-cell RNA sequencing of TAMs from different tumor stages and post-MCT treatment revealed a transient antitumor TAM phenotype, present at 12h post-MCT, characterized by markers such as iNOS and CD38, which was replaced by TAMs co-expressing tumor-limiting and promoting features by 72h post-MCT. Maintenance of antitumor TAMs required repeated MCT administrations, and reactive oxygen species and TNF-α were pivotal molecular mechanisms in TAM-mediated tumor control. Importantly, repeated MCT promoted the activation of CD8 T cells and long-term tumor eradication. Our findings uncover the vulnerability of transient TAM reprogramming which can be overcome by repeated MCT administrations to sustain efficient immune responses.