AIM:To investigate the expression of B7-H1 in human colorectal carcinoma (CRC) to define its regulating effects on T cells in tumor microenvironment.METHODS:One hundred and two paraffin blocks and 33 fresh samples of CRC tissues were subject to this study.Immunohistochemistry was performed for B7-H1 and CD3 staining in CRC tissues.Ficoll-Hypaque density gradient centrifugation was used to isolate peripheral blood mononuclear cells of fresh CRC tissues;flow cytometry and immunofluorescence staining were used for detection of regulatory T cells.Data was analyzed with statistical software.RESULTS:Costimulatory molecule B7-H1 was found strongly expressed in CRC tissues,localized in tumor cell membrane and cytoplasm,while weak or none expression of B7-H1 was detected in pared normal colorectal tissues.Meanwhile,CD3 positive T cells were found congregated in CRC tumor nest and stroma.Statistic analysis showed that B7-H1 expression level was negatively correlated to the total T cell density in tumor nest (P<0.0001) and tumor stroma (P=0.0200) of 102 cases of CRC tissues.Among the total T cells,a variable amount of regulatory T cells with a clear Foxp3+ (forkhead box P3) staining could be detected in CRC tissues and patients’ blood.Interestingly,in the 33 samples (15 cases of B7-H1 high CRC tissues and 18 cases of B7H1 low CRC tissues) of freshly isolated mononuclear cells from CRC tissues,the percentages of CD4+ Foxp3+ and CD8+ Foxp3+ regulatory T cells were found remarkably higher in B7-H1 high CRC tissues than in B7-H1 low CRC tissues (P=0.0024,P=0.0182),indicating that B7-H1 expression was involved in proliferation of regulatory T cell.No significant difference was found in CRC peripheral blood (P=0.0863,P=0.0678).PD-1 is the specific ligand for B7-H1 pathway transferring inhibitory signal to T cell,which is expressed by activated T cell.Our further analysis of PD-1 expression on T cells in CRC tissues showed that conventional T cells (CD4+ Foxp3/CD8+ Foxp3),which was thought to contribute to the anti-tumor immune response,highly expressed PD-1;while regulatory T cells (CD4+ Foxp3+/CD8+ Foxp3) almost failed to express PD-1.The average percentage of PD-1 expression on regulatory T cells was significantly higher than the percentage of PD-1 on conventional T cells (CD4+ Foxp3 T cell,P<0.0001;CD8+ Foxp3 T cell,P<0.0001).The diverse expression of PD-1 might lead to different fate of T cell subsets in B7-H1 over-expression CRC tumor microenvironment.CONCLUSION:B7-H1 expression in tumor cells can in hibit the conventional T cell proliferation in tumor micro environment through the PD-1 expression on conventiona T cells. AIM: To investigate the expression of B7-H1 in human colorectal carcinoma (CRC) to define its regulating effects on T cells in tumor microenvironment. METHODS: One hundred and two paraffin blocks and 33 fresh samples of CRC tissues were subject to this study. Immunohistochemistry was performed for B7-H1 and CD3 staining in CRC tissues. Ficoll-Hypaque density gradient centrifugation was used to isolate peripheral blood mononuclear cells of fresh CRC tissues; flow cytometry and immunofluorescence staining were used for detection of regulatory T cells. Data was analyzed with statistical software .RESULTS: Costimulatory molecule B7-H1 was found strongly expressed in CRC tissues, localized in tumor cell membrane and cytoplasm, while weak or none expression of B7-H1 was detected in pared normal colorectal tissues. Meanwhile, CD3 positive T cells were found congregated in CRC tumor and stroma. Statistical analysis showed that B7-H1 expression level was negatively correlated to the total T cell density i Of the 102 cases of CRC tissues. Patients who received T cells in a variable amount of regulatory T cells with a clear Foxp3 + (forkhead box P3) staining could be detected in (P <0.0001) CRC tissues and patients’ blood.Interestingly, in the 33 samples (15 cases of B7-H1 high CRC tissues and 18 cases of B7H1 low CRC tissues) of freshly isolated mononuclear cells from CRC tissues, the percent of CD4 + Foxp3 + and CD8 + Foxp3 + regulatory T cells were remarkably higher in B7-H1 high CRC tissues than in B7-H1 low CRC tissues (P = 0.0024, P = 0.0182), indicating that B7-H1 expression was involved in proliferation of regulatory T cell. No significant difference was PD-1 expression was found in CRC peripheral blood (P = 0.0863, P = 0.0678). PD-1 is the specific ligand for B7-H1 pathway carry inhibitory signal to T cell, which is expressed by activated T cell. on T cells in CRC tissues showed that conventional T cells (CD4 + Foxp3 / CD8 + Foxp3), which was thought to contribute to the anti-tumor immune response, highly expressed PD-1; while regulatory T cells (CD4 + Foxp3 + / CD8 + Foxp3) higher than the percentage of PD-1 on conventional T cells. The diverse expression of PD-1 might lead to different fates of T cell subsets in B7 (P <0.05; CD8 + Foxp3 T cell, -H1 over-expression CRC tumor microenvironment. CONCLUSION: B7-H1 expression in tumor cells can in hibit the conventional T cell proliferation in tumor micro environment through the PD-1 expression on conventions T cells.