An agonist of human glucocorticoid-induced tumor necrosis factor receptor (tumor necrosis factor superfamily, member 18; TNFRSF18; GITR), with potential immunomodulating and antineoplastic activities. Upon administration, GITR agonist MEDI1873 binds to GITR found on multiple types of T-cells, thereby inducing both the activation and proliferation of tumor antigen-specific T effector cells. This abrogates the suppression of T effector cells which is induced by inappropriately activated T regulatory cells (Tregs), and activates the immune system to help eradicate tumor cells. GITR, a member of the TNF receptor superfamily, is expressed on the surface of multiple types of immune cells, including regulatory T cells, effector T cells, B cells, dendritic cells (DCs) and natural killer (NK) cells.