This disclosure relates to binding agents with specificity for programmed cell death 1 (PD-1) and to methods for using the same to treat, prevent and / or ameliorate an infectious disease (e.g., human immunodeficiency virus (HIV)), cancer and / or autoimmunity. In addition, this disclosure identifies a novel binding patch ("P2") on PD-1 that is linked with a previously unidentified functional activity of PD-1 that is distinct from the interaction site involved with either the PD-L1 or PD-L2 ligands. Furthermore, we demonstrate that antibodies that interact with this region of PD-1 are able to act as antagonists of PD-1 and that this antagonism is further enhanced with the addition of antibodies that act through the blockade of the PD-1 / PD-L1/L2 interaction.
