Thus, we prepared two subcutaneous tumor models by syngeneic subcutaneous transplantation of CT26 into normal BALB/c mice or BALB/c nude mice, and compared CTLA-4 and T cell marker expression in the CT26 tumor tissues from the tumor-bearing BALB/c mice with those from the tumor-bearing BALB/c nude mice by RT-PCR analysis (Fig. 2). This evidence concerns the gene CTLA4 and neoplasm.