Esophageal squamous cell carcinoma （ESCC） is a malignant tumor caused by both environmental and genetic factors. Epidemiology studies have identified smoking as a major environmental risk factor. In recent years， the advancement of genomics research has led to the recognition of the influence of genetic variation in ESCC. We reviewed the research progress in smoking， genetic polymorphism and their interaction on susceptibility to ESCC. Reducing exposure time to tobacco was found to be the most effective way to reduce the risk. At the genetic level， mutations in DNA repair genes， regulation genes of carcinogen-metabolizing enzymes， cell cycle regulation genes， folate metabolism related genes， and alcohol metabolism related genes were found to significantly increase the risk of ESCC. However， studies on the interaction between smoking and genetic polymorphisms in ESCC risk are still limited， more studies are needed for better screening of the high-risk populations and the prevention.

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.