Antagonistic TNFR superfamily polypeptides, such as antibodies and antigen-binding fragments thereof, and the use of these polypeptides to inhibit the proliferation of regulatory T cells (T-regs). For example, antibodies of the invention include antagonistic TNFR2 antibodies and antigen-binding fragments thereof, and can be used to suppress the T-reg-mediated deactivation of tumor reactive T-lymphocytes, as well as to treat a wide variety of cancers and infectious diseases.
