AUNP-12 TFA (NP-12 TFA) is a peptide antagonist of the PD-1 signaling pathway, displays equipotent antagonism toward PD-L1 and PD-L2 in rescue of lymphocyte proliferation and effector functions. AUNP-12 TFA exhibits immune activation, excellent antitumor activity, and potential for better management of immune-related adverse events (irAEs).