Myeloid-derived suppressor cells as immunosuppressive regulators and therapeutic targets in cancer

Myeloid-derived suppressor cells(MDSCs)are a heterogenic population of immature myeloid cells with immunosuppressive effects,which undergo massive expansion during tumor progression.These cells not only support immune escape directly but also promote tumor invasion via various non-immunological activities.Besides,this group of cells are proved to impair the efficiency of current antitumor strategies such as chemotherapy,radiotherapy,and immunotherapy.Therefore,MDSCs are considered as potential therapeutic targets for cancer therapy.Treatment strategies targeting MDSCs have shown promising outcomes in both preclinical studies and clinical trials when administrated alone,or in combination with other anticancer therapies.In this review,we shed new light on recent advances in the biological characteristics and immunosuppressive functions of MDSCs.We also hope to propose an overview of current MDSCs-targeting therapies so as to provide new ideas for cancer treatment.

CXCL13 expression in mouse 4T1 breast cancer microenvironment elicits antitumor immune response by regulating immune cell infiltration

Breast cancer is the most commonly diagnosed cancer type and the leading cause of cancer-related deaths among women worldwide.Previous studies have reported contradictory performance of chemokine CXC motif ligand 13(CXCL13)in breast cancer.In this study,The Cancer Genome Atlas database analysis revealed that CXCL13 was overexpressed in various human cancers including breast carcinoma,and associated with good clinical prognosis in breast cancer.Flow cytometry detection also found upregulated intracellular CXCL13 expression in human breast cancer cell lines.To explore the possible role of CXCL13 in the breast cancer microenvironment,mouse triple negative breast cancer(TNBC)was lentivirally transfected to stably overexpress mouse CXCL13(4T1-CXCL13).Both parental 4T1 and 4T1-CXCL13 strains showed no in vitro or in vivo endogenous cell surface CXCR5 expression.In immune-competent BALB/c mice,the in vivo tumor growth of 4T1-CXCL13 was significantly inhibited and even completely eradicated,accompanied with increased infiltrations of CD4^(+),CD8^(+)T lymphocytes and CD11b^(+)CD11c^(+)DCs.Further investigations showed that CXCL13 expression in the 4T1 tumor microenvironment elicited long-term antitumor immune memory,and rejection of distal parental tumor.The antitumor activity of CXCL13 was remarkedly impaired in BALB/cA-nu nude mice,or in BALB/c mice with CD8^(+)T lymphocyte or NK cell depletion.Our investigation indicated that CXCL13 expression in TNBC triggered effective antitumor immunity by chemoattracting immune cell infiltrations and could be considered as a novel prognostic marker for TNBC.

A PD-L1-targeting chimeric switch receptor enhances efficacy of CAR-T cell for pleural and peritoneal metastasis

Pleural and peritoneal metastasis accompanied by malignant pleural effusion(MPE)or malignant ascites(MA)is frequent in patients with advanced solid tumors that originate from the lung,breast,gastrointestinal tract and ovary.Regional delivery of CAR-T cells represents a new strategy to control tumor dissemination in serous cavities.However,malignant effusions constitute an immune-suppressive environment that potentially induces CAR-T cell dysfunction.Here,we demonstrated that the anti-tumor cytotoxicity of conventional 2nd-generation CAR-T cells was significantly inhibited by both the cellular and non-cellular components of MPE/MA,which was primarily attributed to impaired CAR-T cell proliferation and cytokine production in MPE/MA environment.Interestingly,we found that PD-L1 was widely expressed on freshly-isolated MPE/MA cells.Based on this feature,a novel PD-L1-targeting chimeric switch receptor(PD-L1.BB CSR)was designed,which can bind to PD-L1,switching the inhibitory signal into an additional 4-1BB signal.When co-expressed with a 2nd-generation CAR,PD-L1.BB CSR-modified CAR-T cells displayed superior fitness and enhanced functions in both culture medium and MPE/MA environment,causing rapid and durable eradication of pleural and peritoneal metastatic tumors in xenograft models.Further investigations revealed elevated expressions of T-cell activation,proliferation,and cytotoxicity-related genes,and we confirmed that PD-L1 scFv and 4-1BB intracellular domain,the two important components of PD-L1.BB CSR,were both necessary for the functional improvements of CAR-T cells.Overall,our study shed light on the clinical application of PD-L1.BB CSR-modified dual-targeting CAR-T cells.Based on this study,a phase I clinical trial was initiated in patients with pleural or peritoneal metastasis(NCT04684459).