Compositions for cancer or infection treatment via immunopotentiation caused by inhibition of the immunosuppressive signal induced by PD-1, PD-L1, or PD-L2 and therapies using them, immunopotentiative substrates included as the active ingredient, screening methods of the substrates for cancer or infection treatment, cell lines used for the screening methods, evaluation methods that select the substrates for cancer treatment, and carcinoma cell transplanted mammals used for the evaluation methods. The compositions of the present invention that inhibit the function of PD-1, PD-L1, or PD-L2 are useful for treatment of cancer or infection.