Inoculation of mice with a recombinant vaccinia virus expressing the full-length mouse wild-type p53 protein (Vp53-wt) was shown to induce partial protection against peripheral challenge with a mouse glioblastoma cell line, termed GL261, expressing high levels of nuclear, endogenous wild-type p53.In vivo experiments with knockout (KO) mice and mice treated with depleting doses of antibodies specific to lymphocyte subsets revealed that vaccine efficacy depended on CD4 and CD8 T cells as well as on natural killer (NK) cells. Vp53-wt virus-vaccinated mice that failed to develop tumours upon challenge with a minimal tumourigenic dose of GL261 cells remained completely resistant to further challenge with increased doses of GL261 cells. The efficacy of the Vp53-wt vaccine was improved by adding recombinant mouse interleukin-12 (rIL-12) as an adjuvant at the time of tumour challenge. The induction of T cells to p53 in Vp53-wt virus-immune mice was also demonstrated at the tumour site by immunochemistry and was further confirmed by a delayed-type hypersensitivity response to the p53 protein, although in vitro experiments using splenocytes from vaccinated mice failed to demonstrate CD4 or CD8 T-cell activity to p53.