CAR-Macrophages and CAR-T Cells Synergistically Kill Tumor Cells In Vitro

Chimeric antigen receptor (CAR)-expressing macrophages (CAR-M) have a great potential to improve cancer therapy, as shown from several recent preclinical studies. However, unlike CAR-T cell therapy, which has been widely studied, the efficacy and limitations of CAR-M cells remain to be established. To address this issue, in the present study, we compared three intracellular signaling domains (derived from common γ subunit of Fc receptors (FcRγ), multiple EGF-like-domains protein 10 (Megf10), and the CD19 cytoplasmic domain that recruits the p85 subunit of phosphoinositide-3 kinase (PI3K), respectively) for their ability to promote primary CAR-M functions, and investigated the potential synergistic effect between CAR-M and CAR-T cells in their ability to kill tumor cells. We found that CAR-M^FcRγ exerted more potent phagocytic and tumor-killing capacity than CAR-M^Megf10 and CAR-M^PI3K. CAR-M and CAR-T demonstrated synergistic cytotoxicity against tumor cells in vitro. Mechanistically, the inflammatory factors secreted by CAR-T increased the expression of costimulatory ligands (CD86 and CD80) on CAR-M and augmented the cytotoxicity of CAR-M by inducing macrophage M1 polarization. The upregulated costimulatory ligands may promote the fitness and activation of CAR-T cells in turn, achieving significantly enhanced cytotoxicity. Taken together, our study demonstrated for the first time that CAR-M could synergize with CAR-T cells to kill tumor cells, which provides proof-of-concept for a novel combinational immunotherapy.