A bispecific antibody that simultaneously binds to two different and as of yet undisclosed antigens co-expressed specifically on tumor-infiltrating regulatory T-cells (Tregs), with potential immunomodulating and antineoplastic activities. Upon administration, AGEN1223 targets and binds to the two antigens co-expressed specifically on tumor-infiltrating Tregs. This leads to the selective depletion of immunosuppressive Tregs in the tumor microenvironment (TME), while sparing peripheral Tregs and effector T-cells, enhancing the overall antitumor response. AGEN1223 may also co-stimulate antigen-specific effector T-cells, resulting in tumor cell death.