Anti-idiotype antibody response was not required for the vaccine-induced tumor protection. (A-B) Serum samples obtained from mice vaccinated as in Figure 1 were examined for anti-idiotype antibodies by enzyme-linked immunoabsorbent assay with the use of plates coated with recombinant A20 idiotype protein (gift from D. Gold, Favrille Biotech).²⁵  Bound antibodies were detected by HRP-conjugated anti–mouse IgG1. Anti-idiotype antibodies were primarily observed after the first boost dose, peaking after the second boost, and persisting after tumor challenge. (C) Ten wild-type BALB/c (WT) or antibody-deficient J_h mice per group were vaccinated with MCP3-sFv DNA plus cardiotoxin as shown in Figure 1 or with saline and then challenged with tumor and followed for survival. (D) Tumor-free J_h and WT mice from vaccinated groups as in panel C were rechallenged with tumor and followed for survival (J_h, n = 8; WT, n = 7).