Balb/c mice were injected with 1x106 CT26 cells in the shoulder. Starting on day 7 post-inoculation when the tumors have an average tumor diameter of about 3–4 mm, mice were injected i.p. with 12.5 mg/kg of either anti-CD137 antibody (clone 3H3; BioXCell) or anti-PD-L1 (clone 10F.9G2; BioXCell) every other day for four treatments. On day 15 post-tumor inoculation, mice were injected with 89Zr-radiolabeled malDFO-169 cDb for immuno-PET imaging and biodistribution the following day (22 h post-injection). Average tumor diameter was calculated using calipers on days 7, 11 and 15 post-tumor inoculation.