Abstract The effect of tumor-targeting Salmonella typhimurium A1-R on CD8+ cell infiltration was determined on Pan02 murine pancreatic adenocarcinoma cells implanted orthotopically on the pancreatic tail of C57BL/6 mice. Three weeks after orthotopic implantation, mice were randomized into G1: untreated control group (n = 8); and G2: Salmonella typhimurium A1-R treatment group (n = 8, 1 × 107 CFU/body, iv, weekly, 3 weeks). On the 22nd day from initial treatment, all mice were sacrificed and tumors were harvested. The tumor volume ratio was defined as ratio of tumor volume at the 1st day to the 22nd day. H&E staining was performed to evaluate tumor destruction which was classified into 4 categories according to the Evans grading system: Grade I; 0-9% destruction, Grade IIA; 10-50% destruction, Grade IIB; 51-90% destruction, Grade III; few (<10%) viable cancer cells. Immunohistochemical staining using anti-mouse CD8+ antibody was performed to count tumor infiltrating CD8+ cells. The tumor volume ratio was significantly lower in G2 (3.0 ± 2.8) than G1 (39.9 ± 30.7, p < 0.01). Six mice in G1 had peritoneal dissemination whereas no mice showed peritoneal dissemination in G2 (p < 0.01). Significant tumor destruction was observed in G2 (Grade I: 0, Grade IIA: 1, Grade IIB: 6, Grade III: 1) compared to G1 (Grade I: 5, Grade IIA: 3, Grade IIB: 0, Grade III: 0, p < 0.01). Tumor infiltrating CD8+ cells per high-magnification field were significantly higher in G2 (133.5 ± 32.2) than G1 (45.1 ± 19.4, p < 0.001). Strong tumor destruction correlated with higher numbers of tumor-infiltrating CD8+ cells per high-magnification field (Grade I: 35.5 ± 18.3, Grade IIA: 77.3 ± 32.8 Grade IIB and III: 134.7 ± 34.8). The present study demonstrates that Salmonella typhimurium A1-R promotes CD8+ T cell infiltration in a syngeneic pancreatic cancer mouse model. Citation Format: Takashi Murakami, Yukihiko Hiroshima, Yong Zhang, Ming Zhao, Tasuku Kiyuna, Ryusei Matsuyama, Takashi Chishima, Kuniya Tanaka, Michael Bouvet, Itaru Endo, Robert M. Hoffman. Tumor-targeting Salmonella typhimurium A1-R promotes CD8+ T cell infiltration in pancreatic cancer in an orthotopic syngeneic mouse model. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1408.