Tumor immune cell targeting chimeras reprogram tumor-associated macrophages

Abstract

Immune cells in the tumor microenvironment are not only powerful regulators of immunosuppression and tumorigenesis but also a dominant cell population, with tumor-associated macrophages (TAMs) comprising up to 50% solid tumor mass. Immunotherapies such as immune checkpoint inhibitors derive efficacy from this cancer–immune interface; however, immune-related adverse events from systemic blockade remain a major challenge. To address this need for potent, tumor-specific immunotherapies, we developed tumor immune cell targeting chimeras (TICTACs) that selectively deplete immune checkpoint receptors such as SIRPα from TAM surfaces. These chimeras consist of a synthetic ligand targeting CD206, a TAM marker, conjugated to a nonblocking antibody that binds to the checkpoint receptor without inhibiting it. By engaging CD206, which constitutively recycles between the plasma membrane and early endosomes, TICTACs drive robust checkpoint degradation in CD206high macrophages, with no effect on CD206low cells. This decoupling of antibody selectivity from blocking function presents a new paradigm for tumor-specific immunotherapies. Tumor-associated macrophages (TAMs) predominantly adopt an M2-like pro-tumor phenotype, promoting anti-inflammatory signaling and cancer cell metastasis. Now, tumor immune cell targeting chimeras enable targeted degradation of immune checkpoint receptor SIRPα on TAMs to reprogram TAMs.