CTLA4, also known as cytotoxic T-lymphocyte protein 4 isoform 1, is a type 1 membrane protein and a member of the immunoglobulin-superfamily. Besides, this protein contains an extra cellular domain, a transmembrane domain and a cytoplasmic tail. It is generally expressed with highest levels in lymphoid tissues. Also, it is similar to T-cell costimulatory protein CD28 since both of the molecules bind to CD80 and CD86 on antigen-presenting cells. CTLA4 and CD28 effectively regulate to T cell responses as opposing signals transmitted through two related cell-surface receptors. Recombinant mouse CTLA4, fused to hIgG-His-tag at C-terminus, was expressed in insect cell and purified by using conventional chromatography techniques.