A Fc-engineered human fusion protein composed of two trimers of tumor necrosis factor (ligand) superfamily, member 18 (TNFSF18; GlTRL) linked to an immunoglobulin Fc domain (GITRL-Fc), with potential immunostimulatory and antineoplastic activities. Upon administration, trimeric GITRL-Fc OMP-336B11 targets, binds to and activates its co-stimulatory surface receptor (glucocorticoid-induced tumor necrosis factor receptor (GITR; TNFRSF18) expressed on T-lymphocytes and certain tumor cell types. This activates T-lymphocytes, causes T-lymphocyte proliferation and suppresses the activity of regulatory T-cells (Treg). This promotes cytotoxic T-lymphocyte (CTL)-mediated killing of tumor cells. GITRL, a member of the tumor necrosis factor (TNF) family of ligands, functions to activate the co-stimulatory receptor GITR to enhance T-cell modulated immune responses.