The present invention provides monoclonal antibodies that specifically bind to human PD-1 with high affinity. Nucleic acid molecules encoding the antibodies of the invention, expression vectors, host cells and methods for expressing the antibodies of the invention are also provided. The PD-1 antibodies of the present invention inhibit the binding of PD-L1 to PD-1, thereby modulating immune responses in general, and those mediated by TcR and CD28, in particular. The invention also provides methods for treating various diseases, including infectious diseases and cancer using the PD-1 antibodies of the present invention.
