The purified 3C8 was obtained by two step column purification,including Protein G affinity purification and DEAE anion exchange purification.The purity of purified 3C8 was about 93％ when analyzed by reverse column.SDS-PAGE showed that the purity of 3C8 was increased greatly by two step purification.By flowcytometry we found that 3C8 specifically binded with B7-H4/293T cells and did not bind with Mock/293T cells,moreover 3C8 did not bind with other B7 family members transgene cells.In confocal experiment 3C8 could specifically stained B7-H4/293T cells.In Western blot only B7-H4/293T cells showed positive band while Mock/293T cells showed negative result.The result of immunohistochemistry showed that B7-H4 was highly expressed in prostate cancer and renal cell carcinoma,while para-cancer tissues did not express B7-H4.The T cell proliferation experiment showed that B7-H4-Ig could bind to activate T cells and inhibit T cell proliferation,while 3C8 could block the binding of B7-H4-Ig and reverse the T cell proliferation inhibition effect of B7-H4-Ig by CFSE and CCK8 assay.The cytokine IFN-γ and IL-2 secreted by activating T cells was decreased by B7-H4-Ig and 3C8 could reverse the effect of B7-H4-Ig.