To test whether guadecitabine could effectively prime tumors for response to immunotherapy, we allowed MMTV-neu tumors in syngeneic hosts to reach slightly larger average tumor volumes (200–300 mm3), prior to beginning guadecitabine therapy as before, administered daily for 3 days, followed by intraperitoneal injection of anti-PD-L1 antibody twice weekly for 2 weeks or IgG control. The gene discussed is CD274; the disease is neoplasm.