PD-1 antagonists are disclosed that can be used to reduce the expression or activityof PD-1 in a subject. An immune response specific to an infectious agent or to tumorcells can be enhanced using these PD- 1 antagonists in conjunction with an antigenfrom the infectious agent or tumor. Thus, subjects with infections, such as persistentinfections can be treated using PD-1 antagonists. In addition, subjects withtumors can be treated using the PD-1 antagonists. In several examples, subjectscan be treated by transplanting a therapeutically effective amount of activatedT cells that recognize an antigen of interest and by administering a therapeuticallyeffective amount of a PD-1 antagonist.
