The first Tang Prize for Biopharmaceutical Science has been awarded to Prof. James P. Allison and Prof. Tasuku Honjo for their contributions leading to an entirely new way to treat cancer by blocking the molecules cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) and programmed cell death protein 1 (PD-1) that turn off immune response. The treatment, called "immune checkpoint blockade therapy," has opened a new therapeutic era. Here the discoveries of the immune checkpoints and how they contribute to the maintenance of self-tolerance, as well as how to protect tissues from the excess immune responses causing damage are reviewed. The efforts made by Prof. Allison and Prof. Honjo for developing the most promising approaches to activate therapeutic antitumor immunity are also summarized. Since these certain immune checkpoint pathways appear to be one of the major mechanisms resulting in immune escape of tumors, the presence of anti-CTLA-4 and/or anti-PD-1 should contribute to removal of the inhibition signals for T cell activation. Subsequently, it will enhance specific T cell activation and, therefore, strengthen antitumor immunity.