Inhibition of Tumor Development in CCR5−/− Mice
The effect of CCR5 in tumor development was investigated using CCR5+/+ and CCR5−/− mice. B16-F0 melanoma cells were inoculated subcutaneously into CCR5+/+ and CCR5−/− mice (n = 20). Tumor growth was monitored for 31 days. Tumor growth in the CCR5−/− mice was significantly lower than that in the CCR5+/+ mice. The tumor growth in the CCR5−/− mice was reduced to 19.1%, whereas the tumor growth in the CCR5+/+ mice was only reduced to 24.3%, in both tumor weight (Figure 1A and 1B) and tumor volume, respectively (Figure 1A and 1C). These results correlated with mice survival rates. There was a significant difference in survival rates between CCR5−/− mice (75% of starting time) and CCR5+/+ mice (15%) at the end of the experiment (Figure 1D). There was a significant difference in survival rates between CCR5−/− mice and CCR5+/+ mice. At the end of the experiment, 75% of the CCR5−/− mice survived while only 15% of the CCR5+/+ mice survived. Subcutaneous tumors were harvested from the sacrificed mice 31 days after inoculation. The immunohistochemical analysis of tumor sections, stained with H&E and for proliferation antigen PCNA, revealed greater inhibition of tumor cell growth in CCR5−/− mice. The histologic findings after H&E staining indicated that the tumor tissues of the CCR5−/− mice, but not those of the CCR5+/+ mice, contained large areas of necrosis. PCNA reactive cells were significantly reduced in the CCR5−/− mice (Figure 1E).
10.1371/journal.pone.0033747.g001 Figure 1  Inhibition of tumor development in CCR5−/− mice.
A–C, Tumor images, volumes, and weights. B16 melanoma cells (5×105 cells/mouse) were inoculated s.c. into CCR5+/+ mice and CCR5−/− mice (n = 20). Tumor volumes were measured every day and tumor weights were measured at study termination (Day 31). The CCR5−/− mice had a significant reduction in tumor growth and volume as compared to CCR5+/+ mice. The results are expressed as mean ± SD. * indicates significant difference from CCR5+/+ mice (P<0.05). D, The CCR5−/− mice demonstrated significantly higher survival rates compared to CCR5+/+ mice (by Log-rank Test). E. Tumor sections were analyzed by H&E stain and expression of proliferating cell nuclear antigen (PCNA) by immunohistochemistry. Data are means ± S.D. of four experimental animals. * indicates significant difference from CCR5+/+ mice (P<0.05). Scale bar indicates 50 m.