Pancreatic tumor-bearing immunocompetent C57BL/6 mice were treated with isotype Ab, DON (0.5 mg/kg/ 3 days a week), anti-PD1 Ab (100 μg/3 times), and DON (0.5 mg/kg/ 3 days a week)+anti-PD1 Ab (100 μg/3 times). Treatment with DON as well as with DON+anti-PD1 Ab showed significant decrease in tumor volume (A) as well as in tumor weight (B). Combination treatment also increased survival of tumor-bearing animals (C). DON decreased PDL1 expression, as seen by immunohistochemistry image (D). Treatment with DON decreased HA and collagen in the syngeneic tumors; however, the decrease of these ECM components in the combination group was marginal (E). The histological images for PDL1, HA, and collagen were acquired at 10× magnification. n = 10 mice for each group. Result are represented as mean ± SEM. One-way ANOVA was used for statistical analysis.