Abstract
In the 1980s, it was demonstrated that human tumors had tumor antigens, and immune responses against human tumor antigens were induced. These days, various new immunotherapies are attempted to enhance immune responses against tumors and prevent tumor growth and progression. Nonetheless, it is difficult to reject tumors by only immune responses. One of the reasons is an immunosuppressive state in tumor-bearing hosts. It is considered that an immunosuppressive state is induced by various factors from the tumor side or host side, but the precise mechanism is not clear. When we consider the effective immune responses against tumors, we need to make clear and improve the immunosuppressive state in the tumor-bearing hosts.
