The Effects Of Regulatory Gemcitabine Chemotherapy On The Breast Tumor Immune Microenvironment

Chemotherapy is a major cancer treatment modality,but the efficacy is very limited.In addition,traditional chemotherapy usually has serious side-toxicities due to the usage of maximum tolerant dose.Thus,researchers are trying to use chemotherapeutic drug in a lower dose with a higher frequency,which was named as metronomic chemotherapy.In this thesis work,we treated EO771 and 4T1 breast tumors with different doses and frequencies of metronomic gemcitabine(Met-GEM)chemotherapy,and then characterized their effects on tumor-infiltrating immune cells and tumor vessels.In EO771 breast tumor,although Met-GEM did not affect tumor growth,it altered the tumor immune microenvironment.Met-GEM therapy decreased overall myeloid-derived suppressor cells(MDSCs)and monocytic myeloid-derived suppressor cells(M-MDSCs)in EO771 breast tumors,while the treatment did not reduce granulocytic myeloid-derived suppressor cells(G-MDSCs),and even increased G-MDSCs under 4 mg/kg daily and 6 mg/kg daily treatments.In addition,Met-GEM therapy significantly reduced CD4~+and CD8a~+T cells.Among subsets of T cells,Met-GEM treatments preferentially decreased immune inhibitory T cell populations,including CD4~+CD25~+in all treated groups,as well as CD4~+CD279~+and CD8~+CD279~+under 5 mg/kg daily and 6 mg/kg daily treatments.Meanwhile,Met-GEM treatments increased the proportions of activated T cell subtypes,i.e.CD8~+CD69~+and CD4~+CD69~+.In addition,6 mg/kg daily Met-GEM therapy significantly reduced tumor vessel density.Taken together,these data suggest that Met-GEM(i.e.6 mg/kg daily)reconditions the tumor immune microenvironment to reduce the immunosuppression in EO771 breast tumor.In 4T1 breast tumor model,1 mg/kg daily and 3 mg/kg 3days Met-GEM treatments inhibited tumor growth.2 mg/kg 3 days and 3 mg/kg 3 days Met-GEM treatments not only significantly reduced G-MDSCs,elevated CD8~+and CD4~+T cells,but also increased the proportion of M1-TAMs while reduced that of M2-TAMs.Met-GEM therapy did not influent tumor vessels in 4T1 breast tumor.Together,the data suggest that Met-GEM(3 mg/kg 3 days)therapy modulates the tumor immune microenvironment to reduce immunosuppression in 4T1 breast tumor.The above data showed that Met-GEM therapy could significantly alter the tumor immune microenvironment,but the effects varied in different tumor models.Firstly,Met-GEM decreased MDSCs in both breast tumor models,but the changes in subsets of MDSC were opposite.Secondly,Met-GEM reduced T cells in EO771 breast tumors,especially immunosuppressive subsets,such as CD4~+CD25~+,CD4~+CD279~+and CD8~+CD279~+.Conversely,Met-GEM therapy increased CD4~+and CD8~+T cells in 4T1breast tumors.Thirdly,Met-GEM therapy polarized part of TAMs from M2 to M1phenotype in 4T1,but not EO771,breast tumors.Finally,Met-GEM therapy reduced tumor vessel density in EO771,but not 4T1,breast tumors.Taken together,our study suggests that Met-GEM therapy can be optimized to recondition the tumor immune microenvironment to reduce the immunosuppression.The establishment of regulatory chemotherapy may provide a novel strategy to develop more effective combinational cancer immunotherapy.