The Effects Of Blockade Of B7-H1 On Tumor-infiltrating Dendritic Cell-mediated T-cell Function

Objective:To explore the expression of B7-1,B7-2 and B7-H1 on tumor-infiltrating dendritic cells(TiDC) and on splenic dendritic cells(SDC) and to investigate TiDC-mediated and SDC-mediated T-cell function after blocking the B7-H1 on dendritic cells.Methods:To establish the tumor-bearing mice model,the C57BL/6 mice were injected Lewis lung cancer cells in the lateral abdominal wall subcutaneously.The TiDCs and SDCs were isolated using anti-mouse CD11c magnetic beads.The expression of B7-1,B7-2 and B7-H1 on TiDC and SDC was analysed using FACScan flow cytometer.T cells from the Balb/c mice were isolated using anti-mouse CD90 magnetic beads.These T cells were co-cultured with TiDCs or SDCs for the mixed lymphocyte reaction(MLR).In order to compare TiDC-mediated T-cell function with SDC-mediated T-cell function,T-cell proliferation was assessed using XTT method and IL-10 and IFN-γwere detected using ELISA.Monoclonal antibodies to B7-H1 or the isotype control antibodies were added to the MLR cultures in order to investigate the DC-mediated T-cell function after blocking the B7-H1 on TiDCs and SDCs.Results:The number of TiDCs isolated was(2.37±0.33)×10~6 per gram tumor tissue,which accounted for(3.064±0.38)%of all the cells in the tumor tissues.The number of SDC isolated was(6.29±0.89)×10~6 per gram splenic tissue,which accounted for(2.26±0.32)%of all the cells in the spleen.The B7-1 and B7-2 positive cells were significantly less on TiDCs than on SDCs(P＜0.05).B7-H1 was moderately expressed on both TiDCs and SDCs(P＞0.05).The T-cell proliferation stimulated by TiDCs was poorer than stimulated by SDCs and IL-10 produced by T cells was more when stimulated with TiDCs than with SDCs.IFN-γproduction by T cells was below detection levels whether stimulated with TiDCs or SDCs.After blocking B7-H1 on DCs,TiDCs had a stronger stimulating ability comparing with using control antibodies,while SDCs did not have significant changes.Conclusion:TiDCs and SDCs could be isolated from tumor and spleen of the tumor-bearing mice and TiDCs had a weaker T-cell stimulating ability compared with SDCs.B7-1,B7-2 expression level were lower on TiDCs than on SDCs,but B7-H1 was moderately expressed on both TiDCs and SDCs.Blocking B7-H1 on TiDCs would significantly enhanced their ability to activate T cells,while blocking B7-H1 on SDCs would not have significant impact on activating T cells.Blocade of B7-H1 on TiDC may dissolve TiDC-mediated tumor immunosuppression.