Apoptotic breast cancer cells after chemotherapy induce pro-tumour extracellular vesicles via LAP-competent macrophages.

Chemotherapy is important in the systemic therapy for breast cancer. However, after chemotherapy, the left living tumour cells are more progressive. There is an urgent need to study the underlying mechanism which is still unclear to further improve the therapeutic efficacy of chemotherapy in breast cancer. Here we find a pro-tumour effect of the apoptotic cells induced by the chemotherapy, which is mediated by a new subset of macrophages undergoing LC3-associated phagocytosis (LAP). By transferring exosomal S100A11 into the living tumour cells after chemotherapy, the macrophage exhibits a more pro-tumour phenotype than classic M2-type macrophages. Moreover, S100A11 binds to IFITM3, inducing Akt phosphorylation of living tumour cells after chemotherapy, which promotes tumour progression. Of note, Akt inhibitor can enhance the therapeutic effcicay of chemotherapy in breast cancer. This study provides a novel mechanistic link between tumour-associated macrophages and breast cancer, uncovering Akt as a potential therapeutic target to improve chemotherapy efficacy.