Figure 6.

Abrogation of Ig subclass response and antitumor activity by the depletion of immune cell subsets. (A) Sera obtained from mice immunized with XVEGF-p were tested against mouse VEGF or Xenopus VEGF by ELISA. Immunization with XVEGF-p showed an apparent elevation of IgG1 (striped bar) and IgG2b (dotted bar), which can crossreact with mouse VEGF, and a slight increase in Ig2a (solid bar) without an increase in IgM (open bar) or IgA (hatched bar). Treatment with anti-CD4 can abrogate the elevation of IgG1 and IgG2b. In contrast, treatment with anti-CD8, anti-NK, or isotype controls (IgG2a and IgG2b) has no effect. Immunization with MVEGF-p, c-p, or saline alone showed no effect on the Ig subclass response to VEGF. The data are expressed as means ± SD. (B) Abrogation of antitumor activity by the depletion of immune cell subsets. Mice were immunized and then challenged with H22 hepatoma cells as described in Fig. 1. Depletion of immune cell subsets was described in Materials and Methods. Depletion of CD4⁺ T lymphocytes showed complete abrogation of the antitumor activity of the XVEGF-p vaccine. The results are expressed as means ± SEM. Data represent day 25 after tumor cell injection. Similar results can be found at other time points.