Haoran Zha

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.

Anti-PD-1/PD-L1 therapy has achieved great success in the clinic; however, only a small fraction of cancer patient benefit from PD-1/PD-L1 blockade therapy, and overcoming resistance to PD-1/PD-L1 blockade has thus become a primary priority. In this study, we demonstrated that administration of PD-1/PD-L1 antibodies resulted in the activation of the complement system and massive generation of C5a. Generation of C5a did not change the accumulation of MDSCs in either the tumor or spleen but enhanced their inhibitory potential. In addition, blockade of C5a-C5aR signaling in combination with PD-1/PD-L1 antibodies greatly enhanced the anti-tumor efficacy of PD-1/PD-L1 antibodies. Overall, these data indicate an immunosuppressive role of C5a in the context of PD-1/PD-L1 blockade therapy and provide a strong incentive to clinically explore combination therapies using a C5a antagonist.

In immune system, B cells are classically positive modulators that regulate inflammation and immune responses. Regulatory B cells (Bregs) are a subset of B cells which play crucial roles in various conditions, including infection, allergies, autoimmune diseases, transplantation, and tumors. Until now, unequivocal surface markers for Bregs still lack consensus, although numerous Breg subsets have been identified. Generally, Bregs exert their immunoregulatory functions mainly through cytokine secretion and intercellular contact. In the tumor microenvironment, Bregs suppress effector T cells, induce regulatory T cells and target other tumor-infiltrating immune cells, such as myeloid-derived suppressor cells, natural killer cells and macrophages, to hamper anti-tumor immunity. Meanwhile, the cross-regulations between Bregs and tumor cells often result in tumor escape from immunosurveillance. In addition, accumulating evidence suggests that Bregs are closely associated with many clinicopathological factors of cancer patients and might be potential biomarkers for accessing patient survival. Thus, Bregs are potential therapeutic targets for future immunotherapy in cancer patients. In this review, we will discuss the phenotypes, functions, and clinical relevance of Bregs in cancer.

BACKGROUND: Mounting evidence suggests that complement components promote tumor progression via modulating immune suppression, angiogenesis, or tumor cell proliferation. However, the role of C3a-C3aR signaling in regulating lung metastasis of breast cancer remains unknown. METHODS: We performed various ex-vivo and in-vivo assays. Genetic and pharmacological C3aR blockade models were applied to investigate the role of C3a-C3aR in metastasis of breast cancer. RESULTS: C3a-C3aR signaling in CAFs facilitates the metastasis of breast cancer. Mechanically, C3a-C3aR signaling augments pro-metastatic cytokine secretion and extracellular matrix components expression of CAFs via the activation of PI3K-AKT signaling. Genetic or pharmacological blockade of C3aR signaling effectively inhibited lung metastasis of breast cancer in mouse models. CONCLUSIONS: C3a-C3aR signaling in CAFs facilitates the metastasis of breast cancer. Targeting C3aR signaling is a potential anti-metastasis strategy for breast cancer therapy.

Fibrinogen-like protein 2 (Fgl2), a member of the fibrinogen super family, is a pleiotropic cytokine that impacts diverse cellular functions. Previous studies have shown that tumor cell-derived Fgl2 promotes tumorigenesis and metastasis in immune-deficient mice, and it also functions as an immune-suppressive modulator in glioblastoma multiform (GMB). This study aimed to evaluate whether and how tumor stroma-derived Fgl2 affects tumorigenesis and tumor progression. We established the syngeneic transplantable Lewis lung carcinoma (LLC) model in Fgl2-knock-out (Fgl2-KO) mice and we found that deficiency of host Fgl2 is associated with reduced growth of syngeneic LLC tumors. Furthermore, we confirmed that host Fgl2 deficiency significantly decreased the accumulation of myeloid-derived suppressor cells (MDSCs) through down-regulation of chemokine (C-X-C motif) ligand 12 (CXCL12) expression. More importantly, we demonstrated that Fgl2 induced an activated and pro-tumorigenic phenotype of cancer-associated fibroblasts (CAFs) which are the principal source of CXCL12 in the tumor microenvironment (TME). Our results present a novel role of stroma-derived Fgl2 in CAF activation and function, suggesting that Fgl2 is an effective therapeutic target for treating lung cancer.