Figure 1.

Increased immunogenicity of B16.F1 melanoma tumors following intraperitonial treatment with Salmonella typhimurium strain BRD509E. Decreased tumor weights (A) in Salmonella-treated mice correlates with increased percentage (B) and absolute counts (C) of tumor-infiltrating leukocytes (TIL) as elucidated by CD45 expression and analyzed by multi-color FACS analysis of total tumor cells. Increased cellular infiltration into tumor tissue is observed for CD11b⁺ myeloid cells (D,E), CD8⁺ T cells (F,G), and CD4⁺ T cells (H,I). The increase in cellular infiltration is observed in terms of the percentage of indicated cells in the whole tumor (D,F,H) and in terms of absolute cell counts per gram of tumor tissue (E,G,I). Salmonella treatment also enhanced infiltration and maturation of tumor-associated macrophages (TAMs) (J–N) and monocytic myeloid-derived suppressor cells (MDSCs) (O–S). Percentage of CD11b⁺F4/80⁺Ly6G⁻Ly6C⁻ TAMs (J) and CD11b⁺Ly6G⁻Ly6C⁺ M-MDSCs (O) among total tumor cells. The proportion of both myeloid cell types was significantly higher in Salmonella-treated tumors than non-treated tumors. Percentage of Sca-1-positive and Sca-1 expression level shown as mean fluorescent intensity among TAMs (K,L) and MDSCs (P,Q). Percentage of MHC class II-positive and MHC class II expression level among TAMs (M,N) and MDSCs (R,S). (T–U) Representative FACS plots of the data highlighting the gating strategy for untreated (T) and Salmonella-treated tumors (U). The gated CD11b⁺ cells are out of selected CD45⁺ cells. The analysis was carried out on day 12 post Salmonella administration. Asterisks indicate significant differences, *p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001.