Effects of chidamide combined with PD-1 inhibitor on anti-tumor function of CD8+ T cells in mouse model of colorectal cancer
Objective To investigate the efficacy of histone deacetylase(HDAC)inhibitor chidamide combined with the PD-1 inhibitor on CD8+ T cells anti-cancer function in OVA-expressing MC38(MC38-OVA)colorectal-bearing mice.Methods Animal experiments:C57BL/6 tumor models were constructed by subcutaneously injecting MC38-OVA colorectal cancer cells into the back of mice.We randomized mice into control group,chidamide group,anti-PD-1 group and chidamide+anti-PD-1 group(20 each group).We monitored the tumor growth and animal survival rate of each group;we employed a flow-based method to detect the number and ratio of tumor-infiltrating CD8+ T cells,CD8+IFN-γ+ T cells,OVA antigen-specific CD8+ T cells,and the expression changes of regulatory T cells(Treg),myeloid-derived suppressor cells(MDSC),and tumor-associated macrophages(TAM).Cell experiments:We used a flow-based method to detect the apoptosis of CD8+ T cells and MC38-OVA tumor cells after 0,10,25,50,100,or 200 nmol/L chidamide treatment.The proliferation of CD8+ T cells and MC38-OVA tumor cells treated with 0 and 100 nmol/L chidamide was detected by Ki-67 antibody labeling and cell counting.To evaluate CD8+ T cell killing ability,we treated CD8+ T cells with various conditions(control group,chidamide group,anti-PD-1 group and chidamide+anti-PD-1 group)followed by co-culture with MC38-OVA tumor cells,using the flow-based method.In the condition that CD8+ T cells treated with 0 and 100 nmol/L chidamide co-cultured with the same number of MC38-OVA tumor cells,the expression of CD107a was detected by flow cytometry.Results Compared with control group,the tumor growth was inhibited(P<0.05)while the survival rate was improved(P<0.01)in chidamide+anti-PD-1 group.The number of tumor-infiltrating CD8+ T cells was significantly higher in chidamide group,anti-PD-1 group and chidamide+anti-PD-1 group than that in control group(P<0.05).Nonetheless,the ratio and levels of CD8+IFN-γ+ and OVA antigen-specific CD8+ T cells were significantly higher in chidamide+anti-PD-1 group than those in other groups(P<0.05).The in vitro experiment results showed that chidamide could enhance the killing ability of CD8+ T cells and the expression of CD107a.Conclusion Chidamide combined with PD-1 inhibitor significantly enhanced the number and function of tumor-infiltrating CD8+ T cells and increased antigen-specific CD8+ T cells,which will provide a theoretical and experimental basis for the combination of chidamide in clinical solid tumor immunotherapy.
T lymphocyteimmune checkpoint inhibitorsprogrammed death receptor-1chidamide
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