Figure 1.

Toxoplasma gondii ΔGRA17 strain significantly reduces the growth of melanoma in mice. (A) Schematic representation of the treatment regimen and timeline for mice inoculated with B16-F10 cells in the right flank. Once the B16-F10 tumor size has reached 5 mm at ~9 day, the tumor was injected with 100 µL of phosphate buffered saline (PBS) (control) or 5×10⁴ ΔGRA17 tachyzoites and then again at days 11 and 13 after implantation of B16-F10 cells. Using a vernier caliper, the tumor size was measured, starting from day 9 and every other day until 19 days after B16-F10 cells’ implantation. When the tumor size has reached ~15 mm, mice were humanely euthanized. (B) ΔGRA17 administration significantly reduced the tumor size compared with control mice treated with PBS only. (C) The size and location of the tumors detected in mice euthanized on day 19. (D) The tumors dissected from mice shown in (C), showing a significant reduction in the tumor size of ΔGRA17-injected mice compared with control mice. (E) Immunohistochemical analysis and the corresponding Immunoreactivity Score (IRS) of mouse melanoma markers CD63, S100β, and Ki67. (F) Survival curve of B16-F10-bearing mice shows a significant improvement in the survival of ΔGRA17-inoculated mice compared with control mice. (G) Tumor-free mice were reinoculated in the left flank with 1×10⁶ to 3×10⁶ B16-F10 cells at 30 days and their survival was monitored for 60 days (ie, 90 days after tumor implantation). The survival of tumor-bearing mice was presented as Kaplan-Meier plots and tested for significance using log-rank tests. Data are mean±SD (n=6 mice/group) of three independent experiments; unpaired Student’s t-test, *p<0.05, **p<0.01, ***p<0.001, n/s, not significant, compared with the indicated control.