Human CSPG4-targeting CAR-macrophages inhibit melanoma growth

Approximately half of melanoma patients relapse or fail to respond to current standards of care, highlighting the need for new treatment options. Engineering T-cells with chimeric antigen receptors (CARs) has revolutionized the treatment of hematological malignancies but has been clinically less effective in solid tumors. We therefore sought to engineer alternative immune cell types to inhibit melanoma progression. Engineering macrophages with CARs has emerged as a promising approach to overcome some of the challenges faced by CAR-T cells; however, whether these engineered macrophages can effectively inhibit melanoma growth is unknown. To determine whether CAR-macrophages (CAR-Ms) specifically target and kill melanoma cells, we engineered CAR-Ms targeting chondroitin sulfate proteoglycan 4 (CSPG4), an antigen expressed in melanoma. CSPG4-targeting CAR-Ms exhibited specific phagocytosis of CSPG4-expressing melanoma cells. We developed 3D approaches to show that CSPG4-targeting CAR-Ms efficiently infiltrated melanoma spheroids. Furthermore, combining CSPG4-targeting CAR-Ms with strategies inhibiting CD47/SIRPα "don't eat me" signaling synergistically enhanced CAR-M-mediated phagocytosis and robustly inhibited melanoma spheroid growth in 3D. Importantly, CSPG4-targeting CAR-Ms inhibited melanoma tumor growth in mouse models. These results suggest engineering macrophages against melanoma antigens is a promising solid tumor immunotherapy approach for treating melanoma.