The present disclosure provides compositions and methods and kits relating to anti-CTLA4 antibodies. More specifically, fully human antibodies that bind CTLA4, CTLA4-antibody binding fragments and derivatives of such antibodies, and CTLA4-binding polypeptides comprising such fragments are provided. Further still, there is disclosed nucleic acids encoding such antibodies, antibody fragments and derivatives and polypeptides, cells comprising such polynucleotides, methods of making such antibodies, antibody fragments and derivatives and polypeptides, and methods of using such antibodies, antibody fragments and derivatives and polypeptides, including methods of treating a disease requiring either stimulation of immune responses or suppression. In one aspect, the present disclosure provides an isolated fully human anti-CTLA4 antibody of an IgG class that binds to a CTLA4 epitope with a binding affinity of at least 10?-6 M.
