3044 Background: PD-1/B7-H1 (PD-L1) axis blockade can reinvigorate T cells, and overcome tumor immune evasion of multiple tumor types. AMP-224 is the first recombinant B7-DC-Fc fusion protein tested in patients that binds to and modulates the PD-1 axis through a unique MOA. The MoA hypothesis for AMP-224 is depletion of PD-1high expressing T-cells representing exhausted effector cells. Subsequent replenishment of the T-cell pool with functional T-cells may restore immune function. Methods: Patients with advanced solid tumors received low dose CTX on Day 0, followed by AMP-224 (IV infusion) on Days 1 and 15 of each 28-day cycle in doses ranging from 0.3 to 30 mg/kg. Blood samples were assessed serially for changes in lymphocyte subsets, PD-1HIT cells and T cell effector function. IHC staining of paired biopsies for B7-H1, CD8, PD-1, CD4 and FoxP3 was performed to assess immunological status of the tumor at baseline and following treatment and then relative to peripheral readouts. Results: 42 patients (83% ...