Intracellular Activation of Complement C3 Leads to PD-L1 Antibody Treatment Resistance by Modulating Tumor-Associated Macrophages

Abstract Complement aids in the construction of an immunosuppressive tumor microenvironment. Tumor cell–derived C3 has been previously reported, but whether and how it acts on antitumor immunity remains to be elucidated. Here, we describe a mechanism for tumor cell–derived C3 in suppressing antitumor immunity. Tumor cell–derived C3 was activated intracellularly, which results in generation of C3a. C3a modulated tumor-associated macrophages via C3a-C3aR-PI3Kγ signaling, thereby repressing antitumor immunity. Deletion of C3 in tumor cells that had high C3 expression enhanced efficacy of anti–PD-L1 treatment. Collectively, our results suggest tumor cell–derived C3 may be a useful target for cancer immunotherapy and that targeting C3 in tumor cells may enhance antitumor immunity.