The present invention provides antibodies that bind to the T-
cell co-inhibitor
programmed death-1 (PD-1)
protein, and methods of use. In various embodiments of the invention, the antibodies are fully human antibodies that bind to PD-1. In certain embodiments, the present invention provides multi-specific
antigen-binding molecules comprising a first binding specificity that binds to PD-1 and a second binding specificity that binds to an autoimmune tissue
antigen, another T-
cell co-inhibitor, an
Fc receptor, or a T-
cell receptor. In some embodiments, the antibodies of the invention are useful for inhibiting or neutralizing PD-1 activity, thus providing a means of treating a
disease or disorder such as
cancer or a chronic
viral infection. In other embodiments, the antibodies are useful for enhancing or stimulating PD-1 activity, thus providing a means of treating, for example, an
autoimmune disease or disorder.