An agonistic humanized monoclonal antibody that recognizes inducible T-cell co-stimulator (ICOS; CD278), with potential antineoplastic activity. Upon administration, anti-ICOS agonist monoclonal antibody JTX-2011 targets and binds to ICOS expressed on certain T-cells. This stimulates ICOS-mediated signaling, induces proliferation of ICOS-positive T-cells, enhances cytotoxic T-lymphocyte (CTL) survival and augments the CTL-mediated immune response against tumor cells. ICOS, a T-cell specific, CD28-superfamily co-stimulatory molecule and immune checkpoint protein, is normally expressed on certain activated T-cells and plays a key role in the proliferation and activation of T-cells.