Figure 3.

Effect of immunization on vSP therapy. A) Cytotoxicity of vSP in five murine cancer cell lines. Cells were treated with different doses of vSP for 72 hours, and cell viability was determined using the sulforhodamine B assay. Cells treated with PBS were used as the control, and their viability was set at 100%. Each data point represents the means ± standard deviations of three independent experiments. B) Serum neutralization antibody against vSP. Serum was obtained 4 weeks after the initial immunization with vSP or PBS. The neutralization antibody titer was determined as described in Materials and Methods. Values represent the means ± standard deviations of 3 animals per group. C) Tumor growth over time. CT26 murine colorectal adenocarcinoma cells were inoculated subcutaneously in BALB/c mice immunized with PBS or vSP and then treated with PBS or vSP, respectively. Tumor volume was monitored over time. Values are means ± standard errors of 5-7 animals per group. The difference in overall tumor growth rate growth was significant between the vSP // vSP group and each of the other three groups (P < 0.05 for each comparison).