Neutrophils as key regulators of tumor immunity that restrict immune checkpoint blockade in liver cancer

Objective:Liver cancer is a deadly malignancy associated with high mortality and morbidity.Less than 20%of patients with advanced liver cancer respond to a single anti-PD-1 treatment.The high heterogeneity of neutrophils in the tumor immune microenvironment in liver cancer may contribute to resistance to immune checkpoint blockade(ICB).However,the underlying mechanism remains largely unknown.Methods:We established an orthotopic liver cancer model by using transposable elements to integrate the oncogenes Myc and KrasG12Dinto the genome in liver cells from conditional Trp53 null/null mice(pTMK/Trp53^(-/-)).Flow cytometry and immunohistochemistry were used to assess the changes in immune cells in the tumor microenvironment.An ex vivo coculture assay was performed to test the inhibitory effects of tumor-associated neutrophils(TANs)on CD8^(+)T cells.The roles of neutrophils,T cells,and NK cells were validated through antibody-mediated depletion.The efficacy of the combination of neutrophil depletion and ICB was evaluated.Results:Orthotropic pTMK/Trp53^(-/-)mouse liver tumors displayed a moderate response to anti-Ly6G treatment but not PD-1 blockade.Depletion of neutrophils increased the infiltration of CD8^(+)T cells and decreased the number of exhausted T cells in the tumor microenvironment.Furthermore,depletion of either CD8^(+)T or NK cells abrogated the antitumor efficacy of anti-Ly6G treatment.Moreover,the combination of anti-Ly6G with anti-PD-L1 enhanced the infiltration of cytotoxic CD8^(+)T cells and thereafter resulted in a significantly greater decrease in tumor burden.Conclusions:Our data suggest that TANs may contribute to the resistance of liver cancer to ICB,and combining TAN depletion with T cell immunotherapy synergistically increases antitumor efficacy.