CTLA4, also known as cytotoxic T-lymphocyte protein 4 isoform CTLA4-TM, is a type I transmembrane T cell inhibitory molecule that is a member of the Ig superfamily. The affinity of CTLA4 for its natural B7 family ligands, CD80 and CD86, is considerably stronger than the affinity of their cognate stimulatory coreceptor CD28. Recombinant human CTLA4, fused to hIgG His-tag at C-terminus, was expressed in insect cell and purified by using conventional chromatography techniques.