Objective:To detect the expression of PD-1 on allo-recipients’ PBMCs and T cells administrated with immunosuppressant and investigate the significance of positive cooperativity of PD-1 mAb combined with CsA on T cells. Methods:Double and single labeled FCM was used to detect the expression of PD-1 on PBMCs and T cells of patients. The mixed lymphocytes assay(MLA) was used to establish a model of the transplant rejection in vitro. MTT was used to detect the cooperativity of PD-1 mAb and CsA. Results:Compared with normal person,PD-1 was highly expressed on T cells in allo-recipients who administrated with immunosuppressant. In mixed lymphocytes assay,the expression of PD-1 seemed to be induced by CSA,and PD-1 mAb plus CsA displayed a positive cooperativity,which would owe to the low intensity of costimulatory signal. Conclusion:PD-1 might be used as a new target of immune interference of allograft survival.