The present invention relates to antagonistic antigen binding proteins, a nucleic acid encoding the antagonistic binding protein, a recombinant expression vector comprising the nucleic acid molecule, a host cell comprising the vector, a method of making the antagonistic antigen binding protein, an antagonistic binding protein produced by the method and a pharmaceutical composition comprising the antagonistic binding protein, the nucleic acid or the vector. The present invention further relates to a kit comprising the pharmaceutical composition and use of the antagonistic binding protein in the treatment of cancer and/or chronic infectious diseases.