Protective effects of DKK1-DNA vaccines against myeloma. Results shown are measurements of tumor burdens (A) and survival (B) of mice receiving different treatments. Balb/c mice (10 per group) were IM vaccinated thrice with either PBS, vector control, DKK1 DNA, or DKK1 DNA plus CpG, followed by challenge with MOPC-21 myeloma cells. Tumor burdens were measured twice every week. Mice were euthanized when subcutaneous tumors reached 225 mm² or when mice became moribund. Tumor burdens of tumor-free surviving mice (5 per group) previously treated with DKK1-DNA vaccine (C,E) or vaccine plus CpG (D,F) after rechallenge with the same myeloma cells on days 90 (C-D) and 180 (E-F) since the first tumor injection. Representative results of one of 3 to 4 independent experiments performed are shown. *P < .05; **P < .01, compared with PBS or vector controls.