Disclosed is a method for enhancing the function of a T cell, which is characterized by inhibiting the expression of programmed death-1 ligand 1 (PD-L1) and/or programmed death-1 ligand 2 (PD-L2) in the T cell. Also disclosed is a function-enhanced T cell which is produced by the function enhancement method. Further disclosed is a therapeutic agent comprising the function-enhanced T cell. The T cell can enhance an immune response to cancer, and is useful in an immunotherapy effective for cancer and the treatment or prevention of infectious diseases and autoimmune diseases.