Fig. 1

Treatment of outer membrane vesicles (OMVs) induces complete regression of tumors. a Transmission electron micrograph image of E. coli W3110 wild type-derived OMVs (WT OMVs) and E. coli W3110 msbB mutant-derived OMVs (∆msbB OMVs). Scale bars, 100 nm. b Size distribution of E. coli W3110 WT and ∆msbB OMVs measured by dynamic light scattering analysis (n = 5). c Production yield of E. coli W3110 WT and ∆msbB OMVs from 1 × 10⁹ CFUs bacteria in terms of total protein amount (n = 5, three independent experiments). d Tumor volume of mice bearing CT26 murine colon adenocarcinoma measured after E. coli ∆msbB OMV treatments with various amounts (total n = 14 mice per group, two independent experiments). E. coli ∆msbB OMVs were injected intravenously four times from day 6 with 3 days intervals. e Picture of tumor and tumor tissue histology 48 h after single PBS or ∆msbB OMV (5 μg in total protein amount) injection. Scale bars, 50 μm. f Picture of mice bearing tumor after PBS or ∆msbB OMV (5 μg in total protein amount) treatments. Yellow box indicates tumor sites. g Mice treated with OMV (5 μg in total protein amount) with complete tumor regression were re-challenged with tumors on the opposite flank of the mice 4 weeks after the final injection. Then, these mice were re-challenged with tumor on the middle of the two flanks of the mice 3 weeks after the secondary tumor injection (total n = 14 mice per group, two independent experiments). Data are presented as the mean ± SD from a representative experiments. ***P < 0.001 analysed by unpaired Student’s t-test c or two-way ANOVA with Bonferroni post test to compare each treated group with PBS group d, g