NLG919 potently blocks IDO-induced T-cell suppression and restored robust T-cell responses with ED50 of 80 nM. Similarly, using IDO-expressing mouse DCs from tumor-draining lymph nodes, NLG919 abrogated IDO-induced suppression of antigen-specific T cells (OT-I) in vitro, with ED50 of 120 nM. NLG919 increases the cytotoxic activity of paclitaxel toward B16-F10 cells in the presence of pretreatment with interferon (IFN)-γ in vitro.