Reprogramming leukemia-associated macrophages by means of TLR Agonists

Macrophages within the tumor microenvironment exhibit a dual role, either promoting anti-tumor immunity or supporting tumor progression. Similarly to other tumors, we have demonstrated that M2-like macrophages, characterized by their pro-tumorigenic properties, are enriched in the bone marrow (BM) of B-Acute Lymphoblastic Leukemia (B-ALL) patients. Toll-like receptors (TLR) agonists are able to reprogramme M2 macrophages to tumoricidal M1-like macrophages; however, only few have been approved for clinical use. In this work, we evaluate the efficacy of two newly developed synthetic TLR agonists in promoting M2-to-M1 macrophage repolarization and explore their potential therapeutic application in the context of B-ALL. Consistent with previous observations in patients, we demonstrated that B-ALL cells are capable of inducing M2 polarization in monocyte-derived macrophages co-cultured in vitro. Notably, M2-polarized macrophages were efficiently repolarized toward an M1 phenotype by both TLR agonists, as evidenced by a decrease in CD206 expression and a concomitant increase in CD86 levels. This repolarization effect was sustained over time, with treated macrophages maintaining viability comparable to that of classically activated M1 macrophages. M2 macrophages repolarized by TLR agonists also increased the release of the pro-inflammatory cytokines TNFα and IL6 and showed a glycolytic switch in their metabolism. Importantly, repolarized macrophages enhanced their ability to kill and phagocytose co-cultured B-ALL cells, thereby acquiring potential anti-leukemic effector functions. Overall, our results support further investigation into the clinical application of these new TLR agonists as a novel approach to reshape the immune infiltrate within the BM niche of B-ALL.